Trace-level detection of sulfonamide antibiotics using quaternary ammonium polymeric ionic liquid-based effervescence-enhanced dispersive solid-phase extraction followed by LC-DAD analysis in environmental waters

Conventional ionic liquids possess several disadvantages, such as high viscosity, difficult sampling/retrieval, and great loss in aqueous solution, limiting their wide applications in the pretreatment field. To solve these drawbacks, we synthesized a quaternary ammonium polymeric ionic liquid (PIL) and pressed it into an effervescent tablet for developing an effervescence-enhanced dispersive solid-phase extraction method (QAP-EDSE). The pressed effervescent tablet was composed of PIL as an extractant, tartaric acid as an acidic source, NaHCO3 as an alkaline source, and water-soluble starch as a filler, respectively. Under the CO2-driven dispersion, the QAP-EDSE method integrated rapid enrichment, extraction, and dispersion into one synchronous step. Employing the one-factor-at-a-time approach, several important variables were optimized as follows: 200 mg of P[VBTHEA]Cl as sorbent, 400 μL of acetone as elution solvent, 5 min of elution, solution pH 9.0, and 1 : 1.25 molar ratio of alkaline to acidic sources. Combining LC-DAD analysis, this proposed approach offered the limits of detection as low as 0.11–0.31 μg L−1 and satisfactory recoveries of 81.40–102.62% for five sulfonamides (SAs) in environmental waters. The lower relative standard deviations (1.9–6.7%) evidenced the higher intraday and interday experimental precision by this method. Overall, the newly developed method is environmentally benign, time-saving, and easy to operate with low detection limit and high recovery and thus shows excellent prospects in the trace-level detection of SAs in environmental waters.

Introduction
Sulfonamides antibiotics (SAs), belonging to amphoteric antimicrobial compounds, are extensively used as bactericidal and bacteriostatic agents in human medicine and livestock industry. 1 SA metabolism requires long time in the human body, and thus a large amount of drug prototypes are excreted in the feces and urine. 2 They can eventually enter environmental water bodies with runoff from agricultural elds and as effluents from wastewater treatment plants. 3 Among commonly used SAs, ve species are frequently detected at the levels of 10-500 ng L −1 in rivers, lakes, and groundwater, 4 which include sulfamethoxydiazine (SMD), sulfadimethoxine (SDM), sulfathiazole (ST), sulfamethoxazole (SMZ), and sulfadiazine (SD).
Their indiscriminate use or prolonged contact with residues may lead to antibiotic resistance in both veterinary and human applications. On the other hand, they are found to be carcinogenic and have relatively long half-lives. 5 Therefore, the widespread use of SAs risk the contamination of food and their metabolites endanger the health of consumers. Notably, because SAs are oen used in animal feed, their residues are frequently detected in some agricultural products and livestock wastewater. 6,7 For example, Jansomboon's group reported that the highest concentrations of SMD, SD, ST, and SDM spanned the range of 6.23-245.91 ng g −1 in imported Pangasius catsh products in Thailand, which were close to or higher than the European Union (EU) standard. 8 It is well known that large doses of SAs over a short period can cause acute poisoning, and chronic poisoning can be caused by small doses of SAs over a long period, including allergies and hematological, immune, urinary, and neurological disorders, 2 as well as potential carcinogenicity. 9 In addition, many fungi will develop resistance to SAs when they remain in the body for a long time. 10  and ecofriendly methodologies for the determination of SAs in environmental waters.
Currently, various pretreatment methods for SAs detection have been developed, including liquid-phase microextraction (LPME), 11 solid-phase extraction (SPE), 12 and solid-phase microextraction (SPME). 13 Although these approaches have satisfactory extraction efficiencies for SAs, they have many distinct shortcomings, such as the use of toxic solvent, timeconsuming, tedious operation, and high cost. 14 Dispersive solid-phase extraction (d-SPE) is a modication of SPE, in which the target analytes are extracted by adding the sorbent directly to the sample solution. 15 Aer dispersion, the contact surface between the analyte and the sorbent is greatly enhanced, which effectively shortens the time for mass transfer and extraction equilibrium. Therefore, as compared to conventional SPE, d-SPE requires only mg-level sorbent and can complete the entire extraction process in a shorter time.
To realize rapid dispersion, adsorption, and elution of analytes, sorbents with large specic surface area, high adsorption efficiency, and good dispersive ability are required in the d-SPE techniques. Compared to inorganic sorbent materials such as carbon, 16 silica, 17 and metal-organic frameworks (MOFs), 18 organic materials have a wider variety of functional groups, which may improve the extraction efficiency and sorbent selectivity. 19 Among organic materials, ionic liquids (ILs) are deemed as "green" extraction media and have designable structures, which provide multiple interactions with target molecules, including hydrophobic/hydrophilic interactions, hydrogen bonding, p-p conjugation, ion-exchange, and electrostatic attraction or repulsion. 20 However, the applications of ILs in the pretreatment methods still have some distinct limitations due to high viscosity, difficult retrieval, and low utilization efficiency. 21 In comparison, polymeric ionic liquids (PILs) possess the advantages of both ILs and polymers, and thus have good ionic and conductive properties, 22 which expand their applications as the t-for-purpose and functional ILs. PILs have higher thermal stability, better durability, improved mechanical robustness, and longer service life compared to ordinary ILs. Moreover, they possess similar characteristics as that of regular polymers, including processability, plasticity, and spatial controllability, and thus can be used as promising alternatives in several extraction methods. 23 So far, PILs have been extensively employed in gas adsorption and separation, especially in CO 2 adsorption, which solve the bottleneck problem of ILs in high viscosity and low-adsorption selectivity. 24 Although there have been many reports on the utilization of PILs as catalysts and adsorbents, few reports are concerned with their applications as extractants the pretreatment procedures.
The dispersion of sorbents in the d-SPE methods is usually assisted by the introduction of an external energy source, such as sonication, stirring, vortexing, or microwave; 25 thus, it usually requires a long reaction time and specialized equipment. Effervescence-enhanced extraction is based on a simple acid-base reaction to generate CO 2 bubbles to promote the dispersion of extraction solvents or/and adsorbent particles. 26 The generated bubbles enlarge the contact surface area between the extractant and the sample solution and promote mass transfer, thereby enhancing extraction efficiency. In this investigation, effervescent tablets were introduced into the d-SPE procedures, which eliminated the need of physical energy and special equipment to disperse the sorbents, thereby simplifying the operational process and shortening the extraction time. 27 Using the above information, we herein synthesized a quaternary ammonium PIL (P[VBTHEA]Cl) and employed it in an effervescence-enhanced dispersive solid-phase extraction method, hereaer abbreviated as QAP-EDSE. The application of solid P[VBTHEA]Cl not only solves the disadvantages of conventional ILs (high viscosity, difficult retrieval, and great loss in aqueous phase) but also realizes the specic adsorption/ extraction of SAs due to rich amino groups in this PIL. In the QAP-EDSE method, P[VBTHEA]Cl was used as an adsorbent/ extractant in aqueous solution, and its rapid dispersion was achieved with the aid of vigorous CO 2 bubbles from an acidbase effervescent reaction. Consequently, it integrated concentration, extraction, and quick dispersion into one synchronous step. Combined with LC-DAD detection, this proposed method provided satisfactory analytical indicators for trace-level SAs detection in environmental waters, and thus shows excellent prospects in the sample pretreatment eld.

Instrumentation
The morphology of (P[VBTHEA]Cl) was characterized by scanning electron microscopy (SEM, Sigma 300, Germany), and its corresponding FT-IR spectrum was measured with a scanning range of 400-4000 cm −1 by the KBr method in a Bruker Tensor II infrared spectrometer (Brook, Germany). X-ray photoelectron spectroscopy (XPS) was determined using a PHI Quantera Spectrometer with AlKa X-ray (hn ¼ 1486.6 eV) radiation. The thermal stability of P[VBTHEA]Cl was detected by a SDT Q600 thermogravimetric analyzer (PerkinElmer, MA, USA). The Brunauer-Emmett-Teller (BET) surface area was measured by N 2 adsorption-desorption at 77 K using an ASAP 2020 System (Quantachrome, USA). Zeta potential was detected by a zeta potential analyzer (Malvern, UK). The solution pH was measured by a Leici PHB-4 pH meter (Inesa Scientic Corporation, Shanghai, China). Ultrapure water (>18.2 MU) was generated with a Hangzhou Yongjieda purication system (Hangzhou, China). The nylon membrane lter (50 mm Â 0.45 mm) was acquired from Tianjin Jinteng Chemical Corporation (Tianjin, China).

Detection of SAs by LC-DAD
The concentrations of ve SAs were detected by a Shimadzu LC-20AT liquid chromatograph equipped with a diode-array detector (LC-DAD). Chromatographic separation was conducted on a Shim-Pack GIST C 18 column (250 mm Â 4.6 mm, 5 mm), which was operated under the following conditions: mobile phase, acetonitrile-water at 35% : 65% (v/v) for 15 min; ow rate, 0.8 mL min −1 ; and column temperature, 30 C. The detection wavelength was set at 270 nm, and the injection volume was 10 mL.

Identication of SAs by LC-MS/MS
The identication and quantication of the ve SAs in water samples were accomplished on an LC-MS/MS (AB Sciex API 4000, Los Angeles, CA, USA), which was equipped with an electrospray ionization (ESI) ionization probe. A CNW Athena C18-WP analytical column (2.1 mm Â 100 mm, 3 mm particle size) was used for separations. The mobile phase consisted of methanol (v/v) (solvent A) and ultrapure water with 0.1% (v/v) formic acid (solvent B), and the optimized program was as follows: 0-7.0 min ¼ 10-75% A, 7.0-7.2 min ¼ 75-10% A, and 7.2-9.0 min ¼ 10% A. At the same time, the ow rate was set at 0.25 mL min −1 , column temperature was set at 30 C, and the injection volume was 10 mL. To enhance the sensitivity and selectivity for the detection of the target SAs, MS analysis was performed using multiple reaction monitoring (MRM) with positive ESI mode. The mass parameters including ionization mode, parent ion, product ion, collision energy, and cone voltage for each analyte were optimized and are shown in ESI Table 2. † The parameters of the mass spectrometer were as follows: the capillary voltage and temperature were 3500 V and 350 C, respectively, argon was used as the collision gas and the sheath gas and auxiliary gas pressure were 20 MPa and 5 MPa, respectively.

Fabrication of the [VBTHEA]Cl
Firstly, the main reactant 4-VBC was puried by distillation in a vacuum distiller to collect its 80-90 C fractions to remove polymerization inhibitors and other impurities. Then, 4-VBC (7.65 g, 0.05 mol), TEA (7.46 g, 0.05 mol), anhydrous ethanol (20 mL), and DBMP (0.17 g) were introduced into a three-necked round-bottom ask and heated at 50 C under a gentle N 2 ow ( Fig. 1a and ESI 1a †). The reuxing reaction of the mixed solution was kept for 24 h. The solution viscosity increased quickly and became larger. Aer the reaction, a yellow viscous liquid was acquired (ESI Fig. 2a-c †). Subsequently, the resultant liquid was washed with dichloromethane three times to remove the unreacted chemicals and polymerized inhibitors, and dried under vacuum for 24 h (Fig. 1a). The yield of [VBTHEA]Cl was 13.78 g with the yield rate of 91.2%.

P[VBTHEA]
Cl was synthesized based on free radical polymerization using AIBN as an initiator. Briey, [VBTHEA]Cl (5.0 g), AIBN (0.06 g), and anhydrous ethanol (20 mL) were added to a 100 mL three-necked ask and heated at 60 C under N 2 atmosphere. With continuous reaction, we rst observed the formation of yellowish white occulent chemical, which was gradually accumulated into blocks (ESI Fig. 2d-

Preparation of the P[VBTHEA]Cl-based effervescent tablets
Aer optimizing the effervescent precursors, the mixture of NaHCO 3 (2.0 g), tartaric acid (2.5 g), an approximate amount of P[VBTHEA]Cl, and water-soluble starch was carefully ground into a ne, homogeneous powder. An aliquot ($0.80 g) of the homogeneous powder was compressed into an effervescent tablet (8 mm diameter Â 2 mm thickness) using a T5 Single Punch Press (Chaoyi Machinery Factory, Shanghai, China). The as-fabricated tablets were stored in a sealed plastic bag in a desiccator. The detailed preparation process for effervescent tablets is exhibited in Fig. 1b.

Collection and preparation of water samples
Four water samples were collected from the Biyu River, Fuqian River, Shi Lake, and Taying Lake, Suzhou, China. Aliquots (30 mL) of the water samples were centrifuged at 5000 rpm for 10 min, and the supernatant was ltered through a 0.45 mm nylon membrane lter. The puried water samples were subjected to the subsequent effervescent reaction-enhanced microextraction procedures.

Procedures for the QAP-EDSE method
The overall operational procedures for the QAP-EDSE method are shown in Fig. 1b and ESI 3. † Firstly, the pretreated water sample (8.0 mL) was introduced into a 15 mL conical centrifuge tube (ESI Fig. 3a †). An effervescent tablet was placed into the solution, producing a continuous stream of CO 2 bubbles due to an acid-base reaction (ESI Fig. 3b †). Obviously, the effervescent tablet was quickly disintegrated, and the PIL was diffused into the solution with the aid of vigorous dispersion from CO 2 bubbles (ESI Fig. 3c-e †). Aer 2-3 min effervescent reaction, the resultant solution was kept still for 2 min (ESI Fig. 3f †). Subsequently, the supernatant was removed, and the sedimented PIL was eluted with 400 mL acetone, transferred to a 1.5 mL Eppendorf tube by a pipette, dried under gentle N 2 ow, and quantitatively dissolved in 100 mL methanol. Finally, an aliquot (10 mL) of the above sample was collected and subjected to LC-DAD detection.  Fig. 2 displays four SEM images of P[VBTHEA]Cl at 1,000, 2,500, 5,000Â, and 100 00Â magnication. Obviously, this quaternary ammonium-based PIL presents irregular and asymmetric block structure with rough surface and no xed crystal shape. From the overall appearance, P[VBTHEA]Cl is close to the shape of jade and piled up with different sizes of particles, demonstrating the formation of amorphous polymers. 28 Elemental analysis by EDS mapping demonstrated the presence of C, O, Cl, and N in the as-synthesized nanocomposites, and the surface of P[VBTHEA]Cl consisted of 69.32% C (wt%), 17.07% O, 9.40% Cl, and 5.21% N (Fig. 3a), implying that the PIL P[VBTHEA]Cl was successfully polymerized with aid of the initiator AIBN.

Results and discussion
3.1.2. FT-IR and 13 C NMR spectra of P[VBTHEA]Cl. As shown in Fig. 3b, the stretching-vibration peak at 3302.6 cm −1 is attributable to O-H, which indicates intramolecular or intermolecular hydrogen bonds, 29 while the peak at 2921.1 cm −1 belongs to C-H on the methylene-CH 2 , and 1616.4 cm −1 and 1452.0 cm −1 are attributed to the characteristic absorption of the benzene skeleton. Comparatively, the peaks at 1098.5 cm −1 and 1043.4 cm −1 are attributable to C-N and C-O, while those at 915.7 cm −1 and 827.9 cm −1 are ascribed to the C-H bending vibration of benzene skeleton, respectively. In addition, the vibration intensity reected the absorption value of the bond in the FT-IR spectrum, and obviously, the O-H vibration displays the strongest absorption among all the peaks.
The 13 C NMR spectrum of P[VBTHEA]Cl is displayed in Fig. 3c. The peak at 147.19 ppm corresponds to two C atoms (positions 13 and 14) close to the link point between the vinyl group and the benzene ring. In contrast, the peak at 131.51 ppm is attributable to other two C atoms (positions 9 and 10) far from the link point, and that at 125.49 ppm is ascribed to two C atoms at positions 11 and 12. Similarly, the peak at 55.31 ppm corresponds to C (position 7) in the CH 2 -N + chain, and the broad peak at 39.65 ppm is attributed to the C atoms of N + -CH 2 -CH 3 at (positions 1, 2, 3, 4, 5, and 6).
3.1.3. TGA, BET specic surface area (SSA), and pore size of P[VBTHEA]Cl. The TGA curve of P[VBTHEA]Cl was mainly divided into three stages (Fig. 3d). In the rst stage, the weight loss was 10.03% below 200 C, which resulted from the loss of water. For the second stage, additional weight loss of 40.90% occurred from 200 to 380 C, possibly derived from the decomposition of N + -CH 2 -CH 2 -OH chain. In the third stage, $35.40% weight loss appeared, which came from the disintegration of the polymer framework.
According to the N 2 adsorption-desorption curves (Fig. 4a), the BET SSA of P[VBTHEA]Cl was computed to be 22.7 m 2 g −1 , and its average pore size was 24.5 nm within the range of 2-50 nm for mesoporous materials (2-50 nm). 30 In contrast to carbon-based nanomaterials, such as rGO, C 3 N 4 , and nanosheets, with SSAs of 100-600 m 2 g −1 , 30 the smaller SSA of P [VBTHEA]Cl was not favorable to highly-efficient adsorption/ extraction of SAs in the aqueous phase. Consequently, we conjectured that other action forces, such as H-bonding effect and electrical attraction, might play an important role in enhancing SAs adsorption/extraction.
3.1.4. Zeta potential of P[VBTHEA]Cl. Fig. 4b elaborates the changes in the zeta potentials of P[BTQA]Cl at varying solution pH of 2.0-9.0. Evidently, they are positively charged on the surface of P[BTQA]Cl before microextraction. In stark contrast, the zeta potentials dramatically decrease with increasing solution pH aer extraction, and they are positively charged across the pH range of 2.0-8.0 but negatively charged when the solution pH is > 8.0. As for all SA species, they have two dissociation constants (pK a,1 and pK a,2 ), which are in the range of 4.0-7.0. 31 SAs present positive charges under strong acid conditions (pH < 5.0) but negative charges under strong base conditions (Fig. 4c). As a consequence, there is an electrostatic attraction between P [BTQA]Cl and the molecules of SAs under alkaline conditions, whereas a repulsive force under strong acidic conditions.

Optimization of the synthetic conditions for PIL
In the synthetic process, the spiked amount of anhydrous ethanol and initiator AIBN had signicant effects on the physicochemical properties of P[VBTHEA]Cl. When the amount of anhydrous ethanol was too little (<15 mL), the synthesized [VBTHEA]Cl is highly viscous and even sticky (ESI Fig. 2c †), thereby producing too hard PIL and low yield. On the contrary  Fig. 2a †). Similarly, when too little and large amount of AIBN was added, the resulting PIL offered a low yield or very high elasticity to be ground into a powder (ESI Fig. 4 †). As illustrated in ESI Fig. 5, † the synthesized PIL was easy to be ground into a powder for the subsequent preparation of effervescent tablets, when the amount or volume of anhydrous ethanol and AIBN was 20 mL and 60 mg, respectively, in the presence of 5.0 g [VBTHEA]Cl. As such, the highest yield up to 4.48 g was achieved with a yield rate of 89.6%. Consequently, the above proportion for the amounts of reactive precursors was chosen in the synthesis of P[VBTHEA]Cl.

Optimization of the extraction conditions in the QAPI-EDM procedures
The spiked samples containing ve SAs at 20 mg L −1 were prepared by fortifying the stock standard solutions into 200 mL deionized water. A series of important variables were optimized, including the amount of P[VBTHEA]Cl, extraction time, type and amount of elution solvent, solution pH, and elution time, were rigorously investigated to obtain high average extraction recoveries (ERs) for ve SAs in the water samples.

Amount of P[VBTHEA]
Cl. In a constant volume of water sample, a very little amount of PIL will lead to insufficient adsorption and extraction, while a very large amount will produce great loss in the following collection and elution processes, both of which substantially decrease the extraction efficiency. Thus, a series of PIL amount (50-250 mg) was added to 10 mL water sample to investigate the effects on ERs for SAs. As depicted in Fig. 5a, the average ER reached as low as 36.5% at the fortied amount of 50 mg, which resulted from the insuf-cient adsorption due to little PIL. As expected, the ERs for ve SAs increased prominently with the rising PIL amount from 50 to 200 mg. However, they showed a declining trend with further increase from 200 to 250 mg, demonstrating that the adsorption reached a plateau at 200 mg. Consequently, 200 mg P[VBTHEA] Cl was deemed as the optimal amount.
3.3.2. Type and amount of the elution solvent. Elution is a crucial step in the QAPI-EDM procedures for the desorption of all analytes from PILs. 32 Under the conditions of 200 mg PIL, four kinds of elution solvents were investigated in terms of their respective ERs, including methanol, acetonitrile, acetone, and ethyl alcohol. As displayed in Fig. 5b, acetone offered the highest average ER for SAs ($84.2%), followed by ethyl alcohol (80.1%); however, acetonitrile yielded the lowest elution efficiency (58.4%). Varying water-soluble solvents have differential polarities (log Kow values), thereby leading to "high-to-low" extraction efficiencies for SAs based on the "like-dissolves-like" principle. Building upon the above data, we chose acetone as the appropriate elution solvent in the subsequent trials.
As for the volume of the elution solvent, a very small amount is not enough for the complete elution of analytes from the extractant, while a very large amount causes increased cost and solvent pollution. According to the preliminary experiment results, we investigated the effects of varying volumes (200-600 mL) of acetone on ERs (Fig. 5c). Obviously, the increasing acetone volumes (200-400 mL) led to a gradual increase in the average ERs from $48.6% to 72.4%. In contrast, further rise in acetone volumes (400-600 mL) caused slight changes in ERs. Hence, 400 mL was adopted in the subsequent trials.

Effect of elution time.
In the effervescence-enhanced extraction process, SAs should be transferred from the sample solution to the sorbent, which is a time-dependent transfer process. 33 As displayed in Fig. 5d, the elution time was optimized from 1 to 9 min. With the prolongation of elution time from 1 to 5 min, the average ERs for SAs increased monotonically from $32.5% to 56.7%, while they remained nearly constant (78.3%) when the elution time varied from 5 to 9 min, implying the achievement of an extraction equilibrium. Therefore, 5 min was selected as the optimal elution time.

Optimization of solution pH.
Because the solution pH determines the molecular or ionic state of analytes, it can produce signicant inuences on the ERs. 33 In the pH range of 3.0-11.0, the highest average ER (92.5%) for SAs was achieved at pH 9.0 (Fig. 5e). When the solution pH was decreased to 3.0 or 5.0, the extraction efficiency for ve SAs by P[VBTHEA]Cl-based effervescent tablet was signicantly reduced. Relatively, the average ERs showed an increasing trend at pH 7.0. Boreen et al. 34 reported that SAs could undergo the acid-base process and the cationic (SH 2+ ), neutral (SH), and anionic (S − ) forms are attributed to the protonation and deprotonation of the amino and sulfonamide groups. When the solution pH was higher than pK a,1 and pK a,2 , the amino and sulfonamide groups exist predominantly (91%) in the neutral and ionized forms, respectively. 34 The pKa values of the ve SAs in aqueous solution ranged from 5.0 to 7.0, resulting in the SAs to be positively charged under acidic conditions and negatively charged under alkaline conditions (ESI Table 1 †). 35 Under acidic conditions with pH < 3.7, the main forms of SDM in the solution are SDM + (sulfadimethoxine particles with positive nuclei) and part of SDM 0 (sulfadimethoxine particles with neutral electricity), and SDM − (sulfadimethoxine particles with negative nuclei) is almost absent (Fig. 4c). When the pH value varies between 3.7 and 6.2, SDM 0 gradually increases, while SDM + gradually decreases. As the solution is neutral, SDM + almost disappears, and SDM 0 becomes the main particle in the solution. When the solution pH ranges from 6.2 to 8.6, the number of SDM 0 decreases gradually, the number of SDM − increases gradually, and there is almost no SDM + . Under alkaline conditions with pH value > 8.6, SDM − is the main particle in the solution. 36 The predominant forms of SDM were anionic state under alkaline conditions, and the surface of PILs P[VBTHEA]Cl was positively charged. Therefore, the phenomenon of positive-negative charge attraction leads to a strong extraction efficiency for SAs. As a consequence, all the subsequent experiments were conducted at a solution pH of 9.0. 3.4. Ratio of acidic source to alkaline source in an effervescent tablet As two of the most important components in effervescent tablets, the molar ratio of acidic source to alkaline source can signicantly affect the extraction or adsorption efficiency. If the proportion is not appropriate, it will not only lead to insufficient quantication of CO 2 bubbles but also trigger strong acidic or alkaline solution pH aer an effervescent reaction. In the rst case, vigorous dispersion from CO 2 bubbles cannot be achieved, while in the second case, the inappropriate solution pH inuences the percentage of molecular and ionic states of SAs, both of which are not conducive to the highly efficient extraction of analytes. According to our previous report, NaHCO 3 and TTA were selected as acidic and alkaline sources, respectively. When the proportions of acidic and alkaline sources decreased from 1.50 : 1.00 to 1.00 : 1.50, the produced CO 2 amount showed an upward trend rstly from 10.30 to 15.67 mg, but a declining trend from 15.67 to 9.77 mg (ESI Table 3 †). In addition, the longest and shortest disintegration time was observed to be 174 and 111 s, respectively, at the acidic-basic mass ratio of 1.00 : 1.25 and 1.00 : 1.50. Overall, the investigated acidic-basic ratios did not cause in the signicantly differential disintegration time across the range of 2-3 min. Moreover, the solution pH prominently increased with the decreasing acidic-basic ratios from 4.59 to 7.03 under an initial solution of pH 7.0 (ESI Table 3 †). Based on a comprehensive consideration of disintegration time and CO 2 amount produced, we selected the 1.25 : 1.00 acidic-basic mass ratio as the appropriate component of an effervescent tablet.

Reusability of P[VBTHEA]Cl in effervescent tablets
The reusability of PILs is an important indicator for improving the application potential of solidied ILs. 37 We analyzed the reusability of the P[VBTHEA]Cl adsorbent by regenerating with three washing cycles of ethanol and water, and subsequent drying for use in another effervescent-tablet preparation and extraction cycle. As a result, the as-fabricated effervescent tablets could be reused for at least four cycles with average ER losses of < 11.8% (Fig. 5f), conrming that the as-synthesized PIL retains excellent recyclability and stability. Thus, we posit that P[VBTHEA]Cl is endowed with excellent characteristics for long-term use in the monitoring of trace SAs in environmental waters.

Analytical performance of the QAP-EDSE method
Under the optimized conditions (200 mg of sorbent, 400 mL of eluent, and solution pH 9.0 in 8 mL water sample), the analytical performance of the QAP-EDSE method was evaluated based on the following metrics: linear ranges (LRs), coefficient of determination (R 2 ), limits of detection (LODs), limits of quan-tication (LOQs), as well as intraday and interday precision. As generalized in Table 1, the LRs spanned the range of 1.0-500 mg L −1 for ST, SMD, SDM, SMZ, and 0.5-500 mg L −1 for SD, with all R 2 values > 0.9976. Based on the signal to noise of 3 and 10 (S/N ¼ 3, 10), the LODs and LOQs for ve SAs were 0.11-0.31 mg L −1 and 0.36-1.03 mg L −1 , respectively. At three spiking levels (5 mg L −1 (low), 20 mg L −1 (middle), and 50 (high) mg L −1 ), the interday and intraday precision, expressed as relative standard deviations (RSDs), were in the range of 1.9-5.1% and 2.7-6.7%, respectively. Collectively, these performance metrices evidence that the QAP-EDSE method can satisfy the technical requirements for the trace-level detection of SAs in environmental waters.

Analyses of SAs by the QAP-EDSE/LC-DAD method in real-world waters
The chromatographic proles for the standards of SAs are elaborated in Fig. 4d, and the retention times of ST, SD, SMD, SDM, and SME were 3.05, 4.19, 5.00, 7.29, and 9.91 min, respectively. Typical chromatograms for ve SAs are shown in Fig. 6 in the unspiked (blank) and spiked (20 mg L −1 ) samples, including the Taying lake, Shi lake, Fuquan river, and Biyu river waters.
In addition, the total ion chromatograms with very good separation of 5 kinds of SAs in the spiked (20 mg L −1 ) Taying lake sample are shown in ESI Fig. 6 †, and the retention times of SD, ST, SMD, SMZ, and SDM were 3.84, 4.05, 5.02, 5.68, and 6.83 min, respectively. By the present QAP-EDSE/LC-DAD method, SD was detected to be 0.61 and 0.94 mg L −1 , respectively, in the Biyu river and Taying lake, respectively, while SDM was monitored to be 1.50 mg L −1 in Taying lake (Table 2). When three concentrations of SAs (5,20, and 50 mg L −1 ) were fortied in the blank water samples, the relative recoveries for SAs spanned the range of 81.40-102.62%. These data document that the newly developed method is feasible for SAs detection with high accuracy and precision in real-world water samples.

Comparison of the QAP-EDSE/LC-DAD with previous methods
The newly developed method was compared with the previously reported methods in the context of analytical indexes such as ERs, RSDs, LODs, extraction time, and amount of sorbent ( Table 3). The effervescence tablets used in this QAP-EDSE method can be prepared in advance and stored in a desiccator until required without any deterioration, and the analytical operations are very simple. Many approaches have been reported for the assay of SAs, such as SPE, 38 41 and BP@SD-SPE (3.0-49%). 42 The LODs (0.11-0.31 mg L −1 ) offered by the newly developed are substantially lower than SPE (0.19-0.50 mg L −1 ) 39 and SPME (0.30-0.35 mg L −1 ), 39 but higher than MSPE (0.09-0.16 mg L −1 ) 41 combined with MS detector (MIPs-SPE and BP@SD-SPE). 41,42 The RSDs are in the range of 1.9-6.7%, which are comparable with SPE (1.2-6.4%) 38 and MIP-SPE (3.6-7.2%), 41 and much better than that of MSPE (9.8-10.7%) 40 and BP@SD-SPE (15%). 42 The amount of adsorbent (200 mg of PIL) is much lower than SPE (500 mg). 38 But it is worth noting that the sample preparation time (<3 min) by the present method is in general agreement with that by SPE (5 min), 38 and much shorter than most other pretreatment methods, such as 40 min for SPME, 8 min for MSPE, 40 15 min for MIP-SPE, 41 and over 24 h for BP@SD-SPE. 42 Compared to the previous methods mentioned above, this proposed method does not require the use of organic solvents to activate and elute the solid-phase extraction column, which effectively reduces the volume of organic solvents. With the aid of high extraction efficiency of P[VBTHEA]Cl to SAs and excellent dispersion of effervescent reaction, it can quickly complete the extraction of target SAs within 5 min. Therefore, the QAP-EDSE method can quickly and efficiently analyze and detect trace SAs in environmental waters.

Conclusions
Herein, a PIL P[VBTHEA]Cl was synthesized and characterized by a series of spectral techniques. The solid P[VBTHEA]Cl overcame the drawbacks of conventional ILs, such as high viscosity, difficult sampling and retrieval, as well as easy volume loss in aqueous solution, when used in the extraction or microextraction procedures. This PIL was employed as an extraction sorbent and pressed into an effervescent tablet for developing a fast and "green" QAP-EDSE approach. The tablet precursors were composed of P[VBTHEA]Cl, TTA, NaHCO 3 , and water-soluble starch, which could be quickly dispersed by a vigorous effervescent reaction from acidic and alkaline sources. The prominent advantages of the QAP-EDSE method lie in that it realizes the integration of rapid enrichment, extraction, and dispersion into one synchronous step with the aid of vigorous CO 2 bubbles. Based on a series of satisfactory performance metrics for SAs detection, we posit that the QAP-EDSE/ LC-DAD method is a promising pretreatment alternative as it offers good accuracy and reproducibility without use of any special instruments.


Analysis of the Influence of Activated Carbons’ Production Conditions on the Porous Structure Formation on the Basis of Carbon Dioxide Adsorption Isotherms

The results of a study of the impact of activation temperature and the mass ratio of the activator to the carbonised precursor on the porous structure of nitrogen-doped activated carbons obtained from lotus leaves by carbonisation and chemical activation with sodium amide (NaNH2) are presented. The analyses were carried out via the new numerical clustering-based adsorption analysis, the Brunauer–Emmett–Teller, the Dubinin–Raduskevich, and the density functional theory methods applied to carbon dioxide adsorption isotherms. Carbon dioxide adsorption isotherms’ analysis provided much more detailed and reliable information about the pore structure analysed. The analyses showed that the surface area of the analysed activated carbons is strongly heterogeneous, but the analysed activated carbons are characterised by a bimodal pore structure, i.e., peaks are clearly visible, first in the range of pore size from about 0.6 to 2.0 nm and second in the range from about 2.0 to 4.0 nm. This pore structure provides optimal adsorption performance of carbon dioxide molecules in the pore structure both for adsorption at atmospheric pressure, which requires the presence of narrow pores for the highest packing density, as well as for adsorption at higher pressures, which requires the presence of large micropores and small mesopores. However, there are no micropores smaller than 0.5 nm in the analysed activated carbons, which precludes their use for carbon dioxide adsorption for processes conducted at pressures less than 0.01 MPa.

Introduction
The greenhouse effect is a natural process that enables life on Earth by absorbing heat provided by solar radiation, and then releasing it in the form of emission of longwave radiation to the components of the atmosphere and secondary emission towards the Earth's surface [1,2]. It is a natural and desired process through which air near the Earth's surface gains the appropriate temperature [3]. The heat required to live on Earth is held in the atmosphere by a layer of greenhouse gases, such as carbon dioxide, methane, freons, ozone, hydrocarbons, and oxides of nitrogen. However, due to human activity, more radiation builds up in the atmosphere, causing a global problem known as global warming. Climatic models predict that global temperatures will increase by about 6 • C by the year 2100. The spread of global warming is linked to increased greenhouse gas emissions in the atmosphere because of rapid urbanisation and increased energy and industrial consumption [3]. The negative impact of global warming is manifested through melting glaciers, rising ocean temperatures, and increased frequency of extreme weather events, including heat waves [3].
Currently, the best way to reduce the amount of carbon dioxide (CO 2 ) in the atmosphere is through carbon capture and storage. At present, four main methods for sequestering CO 2 are being developed: pre-combustion, post-combustion, oxyfuel, and chemical looping combustion [3]. However, in the case of heavy industrial plants, such as steel mills, cement plants, or power plants, which derive energy from the combustion of fossil fuels, the most used method is the capture of carbon dioxide from the flue gases after the combustion process [4,5].
In large-scale practical applications, the CO 2 sequestration method should be characterised by low energy input necessary for the process, low production cost, easy availability of materials, and their high service life, as well as high efficiency of the CO 2 absorption process and no negative impact on the natural environment. One of the most common ways of capturing carbon dioxide is chemical absorption through aqueous mixtures of organic amines [6]. The downside of this method is the use of highly volatile and corrosive components of the absorbing mixture and the need to supply significant amounts of energy in the amine regeneration process. However, the most promising method for sequestering carbon dioxide, which can be widely applied in practice, is the adsorption method [7][8][9][10][11]. Carbon dioxide sequestration by adsorption is the process of separating CO 2 from the combustion gas by adsorbing it to the surface of the adsorbent. The adsorption process is performed to saturate the adsorbent with CO 2 . After that, at the desorption stage, the adsorbed gas is released under the influence of a specified temperature. The adsorbents used in the CO 2 sequestration method are zeolites, metal oxides, silica gels, ion-exchange resins, and especially activated carbons [12].
The development of advanced adsorption technologies requires activated carbons with very high adsorption capacity as well as suitable mechanical properties. Therefore, new solutions are being sought in the field of activated carbon production technologies by chemical activation [25][26][27]. However, it should be noted that the optimal method of chemical activation should not only develop a porous structure, but also, through appropriate reagents, modify the properties of the adsorbents. The method of doping activated carbons with nitrogen shows great potential, because even with a small amount of nitrogen, activated carbons significantly increases its carbon dioxide adsorption capacity [28]. Nitrogen present in the activated carbon structure changes the surface electrostatic potential of adjacent carbon atoms, increasing its local electron density, which has the effect of enhancing the interaction between the surface of activated carbon and adsorbed CO 2 [28][29][30]. The first attempts to apply nitrogen atoms to the microporous structure of activated carbon were carried out with the use of gaseous ammonia and a pre-prepared activated carbon precursor. The disadvantage of this method was the necessity to conduct the process in two stages and its energy consumption, ammonia toxicity, and low efficiency. As a source of nitrogen and an activator in the production of activated carbons, sodium amide (NaNH 2 ) is used. This compound allows the activation process to be conducted at a lower temperature than the activators used so far and has a lower toxicity than ammonia [31,32].
Despite the widespread use of nitrogen in the analysis of adsorption processes, it is increasingly emphasised that the use of this adsorbate, especially for the analysis of microporous materials, leads to erroneous estimates of structure parameters due to the hysteresis effects observed during nitrogen (N 2 ) adsorption [33,34]. This is due, among other things, to the fact that the value of the so-called sitting area of the nitrogen molecule of 0.162 nm 2 assumes that the nitrogen molecule adsorbs flat on the adsorbent surface. In fact, functional groups interacting with the quadrupole moment of nitrogen have been shown to lead to a change in the orientation of the adsorbed nitrogen molecule. Consequently, the sitting cross-sectional area of a nitrogen molecule can be much smaller than the commonly assumed value, which consequently can lead to a significant error in the estimation of the specific surface area [33,34].
Nitrogen molecules also cannot enter the narrowest micropores, i.e., less than 0.45 nmwide due to kinetic constraints. Carbon dioxide molecules at room temperature do not have this type of limitation due to their smaller kinetic diameter, compared to nitrogen molecules. Consequently, a commonly used complement to porous structure analyses based on isotherms of nitrogen adsorption at temperature is the study based on isotherms of adsorption of carbon dioxide (CO 2 ) at 273 K [35][36][37][38].
Adsorption of CO 2 at atmospheric pressure requires the presence of narrow pores, i.e., less than 1 nm, which are essential for optimal CO 2 adsorption performance at atmospheric pressure [39]. Therefore, the evaluation of the ability of microporous carbon materials in capturing CO 2 at atmospheric pressure, i.e., the total adsorption capacity, is determined by the volume of narrow micropores [39][40][41].

Materials and Methods
The results of a study which yielded nitrogen-doped activated carbons prepared from lotus leaves via carbonisation and chemical activation with NaNH 2 were presented by Kwiatkowski and Hu [42], carried out on the basis of on nitrogen adsorption isotherms. Since the activated carbons obtained from lotus leaves analysed by Kwiatkowski and Hu were characterised by a microporous structure [42], the concept of a significant extension of the conducted studies by a comprehensive analysis was based on carbon dioxide adsorption isotherms obtained at 273 K [43].
The current study can provide more insights on the effect of activation parameters on porous structure formation for carbonaceous adsorbents and hence can help to design more effective materials for removing CO 2 from combustion flue gas. This can reduce significant amounts of CO 2 and be beneficial to Earth's environment and sustainable development.

Discussion of the Obtained Results
The results of the analyses performed are presented collectively in the Table 1, as well as in the Figures 1 and 2. On the basis of the aforementioned results, it can be concluded that the analysed samples of activated carbons obtained from lotus leaves are characterised by relatively low values of the specific surface area determined by means of the BET equation. As can be seen, in the case of the sample obtained at 450 • C, with an increase in the mass ratio of the activator to the char, R from 1 to 2, the value of the specific surface area increased. With a further increase in the mass ratio R = 3, however, a significant decrease in the value of this parameter occurred. On the other hand, for the sample obtained at 500 • C, a slight difference can be observed between the S BET surface values determined for samples obtained at R equal to 1 and 2. Meanwhile, in the case of mass ratio R = 3, a significant decrease in the specific surface value S BET can be observed analogously as before.     The micropore volume values Vmicro DR and Vtotal DFT achieved via the DR and DFT methods also indicate that as the mass ratio value, R, increases, the micropore volume decreases.
Significant information about the analysed structure was obtained using the LBET method; namely, for the analysed activated carbon samples, the average values of the firstlayer adsorbed volume parameter, VhA, were obtained, and for the sample prepared at 450 °C, the values of the parameter VhA decreased with increasing mass ratio, R. On the other hand, for the sample obtained at T = 500 °C, the value of the VhA parameter increased at a mass ratio of R = 2 and then decreased at a mass ratio of R = 3. For the sample prepared at 550 °C, the same situation occurred as for the sample obtained at 500 °C.
The values of energy parameters QAk/RT and BC calculated for the analysed samples indicate preferential conditions for the formation of extended clusters of adsorbate molecules, and the values of heterogeneity parameters, h, indicate that the surface of the studied samples is geometrically and energetically heterogeneous. In turn, the values of geometric parameters α and β indicate that high and forking clusters of carbon dioxide molecules are adsorbed in the pores of the analysed samples.
The values of the dispersion of the fitting error, σe, point to very good fitting of the theoretical isotherms for empirical data, but as can be seen in Table 1, relatively low identification rates were obtained for all the analysed activated carbons, indicating the existence of some significant deviation of the pore structure from the assumptions of the theory underlying the LBET method. The shapes of the adsorption energy distributions on the In the case of the sample obtained at 550 • C, a significant decrease in the value of the specific surface area was observed already at mass ratio, R, equal to 2, in comparison with the value obtained at R = 1, and successively, a further decrease in the value of this parameter at mass ratio R = 3. As can be seen, the values of specific surface area calculated via the BET equation are correlated with the values of total pore volume, V total DFT , determined via the DFT method. The micropore volume values V micro DR and V total DFT achieved via the DR and DFT methods also indicate that as the mass ratio value, R, increases, the micropore volume decreases.
Significant information about the analysed structure was obtained using the LBET method; namely, for the analysed activated carbon samples, the average values of the first-layer adsorbed volume parameter, V hA , were obtained, and for the sample prepared at 450 • C, the values of the parameter V hA decreased with increasing mass ratio, R. On the other hand, for the sample obtained at T = 500 • C, the value of the V hA parameter increased at a mass ratio of R = 2 and then decreased at a mass ratio of R = 3. For the sample prepared at 550 • C, the same situation occurred as for the sample obtained at 500 • C.
The values of energy parameters Q Ak /RT and B C calculated for the analysed samples indicate preferential conditions for the formation of extended clusters of adsorbate molecules, and the values of heterogeneity parameters, h, indicate that the surface of the studied samples is geometrically and energetically heterogeneous. In turn, the values of geometric parameters α and β indicate that high and forking clusters of carbon dioxide molecules are adsorbed in the pores of the analysed samples.
The values of the dispersion of the fitting error, σ e , point to very good fitting of the theoretical isotherms for empirical data, but as can be seen in Table 1, relatively low identification rates were obtained for all the analysed activated carbons, indicating the existence of some significant deviation of the pore structure from the assumptions of the theory underlying the LBET method. The shapes of the adsorption energy distributions on the first layer determined via the LBET method indicate the existence of a wide energy range of primary adsorption sites. In addition, as can be seen with the growth in the value of the mass ratio, R, to a value equal to 2, the width of the adsorption energy distributions on the surface of the tested adsorbents noticeably decreased.
Similar results were achieved via the DFT study, especially in obtaining the shapes of pore size distributions (Figure 2). Based on pore size distributions determined via the DFT method, it has been presented that the analysed activated carbons were characterised by a bimodal pore structure, i.e., peaks were clearly visible, first in the range of pore size from about 0.6 to 2.0 nm and second in the range from about 2.0 to 4.0 nm.
This pore structure provides optimal adsorption performance of carbon dioxide molecules in the pore structure both for adsorption at atmospheric pressure, which requires the presence of narrow pores, preferably below 0.7-0.8 nm for the highest packing density, as well as for adsorption at higher pressures, which requires the presence of large micropores (1 to 2 nm) and small mesopores (pores larger than 2 nm). It is worth noting the absence of the smallest pores, i.e., smaller than 0.5 nm, which excludes the application of the obtained activated carbons for carbon dioxide adsorption for processes carried out at a pressure of 0.01 MPa.

Conclusions
The use of waste biomass to produce carbonaceous adsorbents for application in carbon dioxide capture processes is in keeping with the concept of a circular economy. Activated carbons derived from biomass are not only environmentally friendly materials, thanks to the reduction of waste generation, but they are also relatively inexpensive due to the possibility of easy acquisition of raw material. As demonstrated in the present work, the morphological structure and porous structure of activated carbons prepared from lotus leaves via pyrolysis and chemical activation provide, thanks to the specific bimodal porous structure, good conditions for the carbon dioxide adsorption process both at atmospheric pressure and high pressures. Also noteworthy is the large availability of raw material and the relatively low cost of both the raw material and the chemical activator, which creates prospects for the development of the production of activated carbons by this method on an industrial scale. As the analyses showed, the LBET method allowed obtaining a wider range of information on the porous structure of the analysed activated carbons compared to the BET and DR methods. However, the complete range of information about the analysed pore structure is only provided by the simultaneous use of LBET and DFT methods, which are complementary to each other.

Data Availability Statement:
The data presented in this work can be made available upon request.


Metallation of sensitive fluoroarenes using a potassium TMP-zincate supported by a silyl(bis)amido ligand

Combining a bulky bis(amide) and a reactive one-coordinate TMP (2,2,6,6-tetramethylpiperidide) ligand, a new mixed K/Zn heteroleptic base has been developed for regioselective zincation of fluoroarenes. This special ligand set allows for trapping and structural authentication of the first intermediates of direct Zn–H exchange of fluoroarenes obtained via deprotonative metallation, providing mechanistic insights of the processes involved.

General Methods
All the reactions and manipulation were performed under protective Argon atmosphere; using the standard Schlenk technique or Glovebox MBraun equipped with a gas purification and recirculation unit. Hexane was dried over alumina column of Solvent Purification System (a MBraun MBSPS 5) and stored over activated 4Å molecular sieves collection and under argon atmosphere Tetrahydrofuran were dried over sodium and benzophenone ketyl and purified by distillation under argon atmosphere, after the collection it was stored over activated 4 Å molecular sieves and argon atmosphere. Ph 2 Si(NHAr*) 2 [{Ph 2 Si(NHAr*)(NAr*)K] ∞ were prepared as reported in literature. [1,2] NMR spectra were performed in J. Young's NMR tube, prior oven dried and flushed with argon. NMR spectra were recordered using a Bruker AV 400 spectrometer operating at 400.13 MHz for 1 H and 19 F, 100.62 MHz for 13 C{ 1 H} or a Bruker AV 400 spectrometer operating at 300 MHz for 1 H and 19 F, 75 MHz for 13 C{ 1 H} . 1 H and 13 C{ 1 H} NMR spectra were calibrated against the appropriate solvent signal. All the deuterated solvents for NMR were dried and distilled over NaK 2.8 and stored over activated 4 Å molecular sieves and argon atmosphere.

Synthetic Procedures
Synthesis of ZnTMP 2 2.72 mL of 2,2,6,6-tetramethylpiperidine (16 mmol) were solubilized in 10 mL of THF and then 10 mL of n BuLi solution (1.6 M in hexane) were added drop by drop affording a yellow solution. 1.09 g of ZnCl 2 (8 mmol) were added, instantaneously a white precipitate was formed. The mixture was allowed to stir at room temperature for 1h. All the volatiles were removed under reduced pressure affording a yellow waxy solid. 30 mL of Hexane were added affording a white suspension. The suspension was filtered through celite and the mother liquor was evaporated furnishing Zn(TMP) 2 as white solid (2700 mg 98%). The solid can be further purified via sublimation as reported in the literature. [3]  Synthesis of [{Ph 2 Si(NAr*) 2 Zn(TMP)}¯{K(THF) 6 } + ] (1) 572 mg of freshly prepared [{Ph 2 Si(NHAr*)(NAr*)K] ∞ (I) [2] (1 mmol) and 346 mg of Zn(TMP) 2 (1 mmol) were solubilized in 10 mL of THF and the solution was allowed to stir at reflux overnight. Volatiles (2) 126 mg of KCH 2 SiMe 3 (1mmol), 346 mg of ZnTMP 2 (1mmol) and 10 mL of hexane were added to a flushed Schlenk tube. The white suspension was left stirring for 2 hours until it becomes a fine suspension to which 1 mmol of Ph 2 Si(NHAr*) 2 (530 mg) and 1 mL of THF were added, the yellowish suspension was gently heated and allowed to stir overnight. Volatiles were removed under vacuum and to the white residue 7 mL of hexane and 0.7 mL of THF was added, affording a pale-yellow suspension. The mixture was heated under reflux and let slowly cool down at room temperature depositing a crop of colourless crystals of 2 after 24h at room temperature. (550 mg, yield 76%). The synthesis of this compound can be achieved using a different procedure reported in literature before. [ All the volatiles were removed under reduced pressure. The resulting waxy solid was suspended in 10 mL of hexane and the suspension was filtered through celite. The remaining yellow-white solid was solubilized in 3 mL of hexane and 0.8 mL of THF. Overnight storage in the freezer (-15°C) furnishing yellow crystals of 3h. Any attempt in isolating the pure product was unsuccessful due to the cocrystallization of [K(THF) x Zn(C 6 F 6 ) 3 ] and Ph 2 Si(NHAr*) 2 . The yield determined in NMR scale reaction using hexamethylbenzene as internal standard in 1 H-NMR spectrum was 91%.  to stir at room temperature for 30 minutes. The solution was then left to stir at reflux for 16h. The next day all the volatiles were removed under reduced pressure. The obtained white solid was washed with 6 mL of hexane and solubilized in 2 ml of THF. Layering 1.5 mL of hexane on the yellow solution furnished colourless crystals of 3j (59 mg, 11%). %). The yield determined by 1 H NMR spectroscopy using hexamethylbenzene as an internal standard was 84%.  [5] General Experimental Procedure for the 1

H NMR Monitoring of the Zn-H Exchange Reactions
In a glovebox, a J. Young's NMR tube was filled with 78 mg of 1 (0.1       Adding a three fold excess of pentafluorobenzene 1 exhibits a polybasicity. 3h further reacts through the silyl bis(amido) ligand, generating 4 and Ph 2 Si(NHAr*) 2 (Figure S 7). Notably the reaction did not proceed stepwise and 4 and Ph 2 Si(NHAr*) 2 were generated with almost the same ratio. Pentafluorobenzene is still present in the mixture (Figure S 8   29 -3.098° < θ < 77.579° for 3h. A total of 6512 frames were collected using ω scans, with 0.7 second exposure time (4 s for high-angle reflections), a rotation angle of 0.5° per frame, a crystal-detector distance of 34.0 mm, at T = 100.0(5) K.
Data reduction was performed using the CrysAlisPro program [7] . The intensities were corrected for Lorentz and polarization effects, and an absorption correction based on the multi-scan method using SCALE3 ABSPACK in CrysAlisPro [7] was applied.
The structures were solved by direct methods using SHELXT [8] , which revealed the positions of all nonhydrogen atoms of the title compound. All non-hydrogen atoms were refined anisotropically. H-atoms were assigned in geometrically calculated positions and refined using a riding model where each H-atom was assigned a fixed isotropic displacement parameter with a value equal to 1.2Ueq of its parent atom (1.5Ueq for methyl groups). refinement of the structures was carried out on F 2 using full-matrix least-squares procedures, which minimized the function Σw(F o 2 -F c 2 ) 2 . The weighting scheme was based on counting statistics and included a factor to downweight the intense reflections. All calculations were performed using the SHELXL-2014/7 [9] program in OLEX2.4 [10] The X-ray crystal structure determination service unit of the Department of Chemistry and Biochemistry of the University of Bern is acknowledged for measuring, solving, refining and summarizing the structures of compounds 3b, 3c 3d, 3e, 3h, 3j and 4. The Synergy diffractometer was partially funded by the Swiss National Science Foundation (SNF) within the R'Equip programme (project number 206021_177033).
Selected crystallographic data are presented in Table S1-S4 and full details in cif format can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.uk/data_request/cif


Photo-thermo semi-hydrogenation of acetylene on Pd1/TiO2 single-atom catalyst

Semi-hydrogenation of acetylene in excess ethylene is a key industrial process for ethylene purification. Supported Pd catalysts have attracted most attention due to their superior intrinsic activity but often suffer from low selectivity. Pd single-atom catalysts (SACs) are promising to significantly improve the selectivity, but the activity needs to be improved and the feasible preparation of Pd SACs remains a grand challenge. Here, we report a simple strategy to construct Pd1/TiO2 SACs by selectively encapsulating the co-existed small amount of Pd nanoclusters/nanoparticles based on their different strong metal-support interaction (SMSI) occurrence conditions. In addition, photo-thermo catalysis has been applied to this process where a much-improved catalytic activity was obtained. Detailed characterization combined with DFT calculation suggests that photo-induced electrons transferred from TiO2 to the adjacent Pd atoms facilitate the activation of acetylene. This work offers an opportunity to develop highly stable Pd SACs for efficient catalytic semi-hydrogenation process.

REVIEWER COMMENTS</B>
Reviewer #1 (Remarks to the Author): In the article entitled "Photo-thermo semi-hydrogenation of acetylene on Pd1/TiO2 single-atom catalyst", the authors present convincing experimental and theoretical evidences of semi-hydrogenation of acetylene improved by the combined effect of the presence of Pd Single Atom Catalysts and formation of electron-hole pairs in the oxide support. Clearly it is a significant work, with a methodology that is well founded. It is not entirely original, in the sense that photo-thermal catalysts have been already used for others reactions such as CO2 reduction. The concept of Strong Metal-Support Interaction is thus evoked as the main mechanism to selectively control the amount small NP/large NP of Pd grown on the support. By the way, historical references on this point should be added in the introduction to my opinion. The description of the synthesis procedure as well as the computational details allow for work to be reproduced. I think the present paper could be published after considering the following points: --what is the mechanism of formation of the SAC. It is not clear to me which step of the synthesis is responsible for their presence, and which experimental parameter(s) would be able to control the NP/SAC ratio ? --To be entirely convincing on the nature of the Pd-1 catalytic site could the authors provide information such as XPS data that usually give hints about the charge character on the metal center ?
--In the same spirit, if the authors could provide Density of States (DoS) pictures out of DFT calculations it would certainly help the readers to better understand the electronic structure of those SACs.
--A more technical details on the DFT models. Do the authors have to apply for dipolar correction on the support cell to estimate properly the energy ? It is not obvious that polarization effect upon Pd adsorption can be neglected.
--There are several reports in the literature now, proving experimentally and theoretically that H2 can not dissociate easily on SAC, but rather on metal NPs. I think that fact deserves an additional comment.
--Thermodynamics aspects of the C2H2 and H2 adsorption on Pd1 site are missing in the discussion. Could the authors provide such information ?
--a minor comment on the SI: Table X1 would be more valuable if errors were given instead.
Sincerely yours, Reviewer #2 (Remarks to the Author): In this article, Li, Qiao et al report important results on the selective hydrogenation of acetylene, an important reaction in industry. The authors are based on convincing experimental results, supported by theoretical calculations to demonstrate a photo-thermal effect operating on ultradisperse Pd/TiO2 catalysts. The significance of these results is in line with a publication in Nat. Common. once the following changes have been introduced: 1) The proposed green chemistry approach should be discussed in the perspective of the following article: Room-temperature electrochemical acetylene reduction to ethylene with high conversion and selectivity. Nat Catal 4, 565-574 (2021). https://doi-org.inc.bib.cnrs.fr/10.1038/s41929-021-00640-y 2) the authors use as support a rutile/anatase mixture, which is certainly not innocent (cf. J. Phys. Chem. B 2006, 110, 15, 8019-8024;J. Chem. Phys. 136, 104107 (2012 )). It is not clear in the manuscript whether the PdSAs are localized on the rutile and/or anatase phase. Please use the EELS analyses to try to see more clearly (cf 10.1557/proc-139-327). Please also comment on the binding energies of the PdSAs on these two phases. In order to be able to conclude on the nature of the active phase PdSA/TiO2-a or PdSA/TiO2-r.
Reviewer #3 (Remarks to the Author): In this work, Guo et al. demonstrated semi-hydrogenation of acetylene in excess ethylene on atomically dispersed Pd species on TiO2 supports prepared by two different methods. The authors exploited the strong metal-support interaction (SMSI) to selectively encapsulate Pd nanoparticles and clusters by the SMSI overlayer via high-temperature reduction of the catalysts in H2, leaving single-atom Pd species exposed for catalysis. This treatment resulted in substantial improvement in C2H4 product selectivity in thermocatalysis. The selectivity gradually dropped from 60% to about 40% over 40 hours of reactivity test with stable %100 C2H2 conversion. Next, the authors demonstrated that high energy near UV photons could be utilized to drive the same reaction at milder operating conditions. Supported by their computational and experimental studies, the authors suggest that the origin of the reactivity enhancement in photocatalysis is the photoexcitation of TiO2 and the transfer of charge carriers to Pd sites for chemical bond activation (primary to activate C-C bonds). The combination of the SMSI and light to control catalysis is interesting! However, there are significant concerns on the photocatalysis side and the associated discussion. In particular, an important aspect of the photocatalysis results that the authors seemingly refused to acknowledge is regarding the selectivity of the process. Light can promote the reactivity but also lead to a substantial drop in desired product selectivity in this case (see below). This poses a major concern for using the current photocatalysis approach for driving the semihydrogenation of acetylene on the proposed catalyst system. • Comparison of the results in Figure 4 and S8 (e.g., focusing on their panel (a)) reveals that lightpromoted reactivity comes at the expense of a substantial drop in the C2H4 product selectivity. Looking at the entire 35 min of the experiment, the selectivity decreases from 80% to near 40%. Even with the assumption that some drop in selectivity during the initial light-on cycle is due to measurement under non-steady-state condition (that has its own issue), it is clear that there is an additional 10% drop in the selectivity each time that is light is turned on with a total of near 20% selectivity drop just in two illumination cycles. Regrettably, the authors consider this as a "slight" decrease in selectivity or even "stable" selectivity (during the second cycle)! • The drop in selectivity also implies that additional light-on cycles (if performed) could potentially lead to a further decrease in selectivity. • Furthermore, the light-induced drop in the C2H4 product selectivity is an important result that is deserved to be highlighted in the main text along with the reactivity results in photocatalysis.
• Notably, the authors repeatedly state that there is only one report on heterogeneous photocatalytic semi-hydrogenation of acetylene (ref. 26, Zhou et al., Adv Mater 2019) while oversight the previous original work in this area (Swearer et al., PNAS 2016) using visible light and a plasmonic photocatalyst for semi-hydrogenation of acetylene. Interestingly, unlike the current results, the work by Swearer et al. demonstrated that light could promote both the reactivity and the selectivity for this reaction.
• The authors should also discuss how the use of light in this system leads to worsened C2H4 selectivity. Reportedly, the results of DFT calculations and H2-D2 exchange experiment suggest the primary role of Pd/TiO2 photoexcitation being the C-C bond activation acetylene activation, but the discussion of product selectivity is missing. • Regarding the authors' discussion on the role of light and the underlying mechanism: It is stated that the reactivity enhancement is due to a charge-driven mechanism from photoexcitation of TiO2 and as supported by the authors XPS and DFT results. This statement is broadly true. However, there are important aspects of light-induced catalyst heating that should be considered when discussing the role of light in photocatalytic processes. For instance, despite the authors' statement, the use of a circulating water bath does not necessarily exclude the photothermal heating effect in catalysis. This is due to the potential presence of local nanoscale hot spots, especially with supported metal catalysts. Also, the magnitude of the light-induced heating within the catalyst bed strongly depends on multiple factors, including the optical properties (ensemble photon absorption) and thermal conductivity of the catalyst, incident photon flux, illumination wavelength, etc. Currently, the information regarding the power density of the incident photons in Figure 4 is missing. Also, the use of Al2O3 support in the control experiment and the lack of photocatalytic reactivity does not necessarily exclude the thermal effect on TiO2 since this is a comparison of two different systems with a very different absorption properties and thermal conductivities. • Furthermore, the authors state that "it is suggested that the light can still increase the reactor temperature by 10 oC below 100 oC. Therefore, a 10 oC-correction was used when performing photothermo catalysis." Suggested by who and based on what evidence? Again, the magnitude of lightinduced heating depends on several factors, as discussed above. Also, did the authors apply this "undocumented" correction to the Arrhenius plot of photocatalysis in Figure 4e? • The authors suggested a charge carrier-driven mechanism for bond activation under illumination with charge transfer from TiO2 to Pd sites. They should also provide a scheme to discuss the proposed mechanism further, especially to examine whether there is a net charge transfer process to adsorbate(s) and that the catalyst remains in a neutral state or not. If the process is associated with net charge transfer, it results in a charge build-up and eventually a decrease in photocatalytic reactivity. A longterm stability test in photocatalysis should therefore be provided. • Spectrum of the light source used for illumination is missing. • Intensity-dependent photocatalytic studies should provide more insights regarding light-matter interactions for photocatalysis in this system? • Improper citations! The past decade has witnessed huge progress in light-driven heterogeneous catalysis, especially with supported metal catalysts, using a combination of light and external heating or only light to drive the chemistry (the latter is more ideal). The authors must more appropriately acknowledge the previous efforts in this area rather than citing a few very recent examples as the pioneering work in the field, which is indeed an incorrect remark!!! • The authors consider photogenerated carriers in TiO2 as "hot carriers". This should not be confused from well-known hot carrier generation in plasmonic metal nanostructure. • Words such as "obvious", "clearly", etc. are overused throughout the manuscript. Their use should be minimized as they do not necessarily always reinforce the best scientific scenario.

Respond to Reviewers
We appreciate all the reviewers for their encouraging comments, valuable questions and constructive suggestions which are helpful to improve our manuscript. Specific response/answers to each question/suggestion are listed below.

Response to Reviewer 1
In the article entitled "Photo-thermo semi-hydrogenation of acetylene on Pd1/TiO2 single-atom catalyst", the authors present convincing experimental and theoretical evidences of semi-hydrogenation of acetylene improved by the combined effect of the presence of Pd Single Atom Catalysts and formation of electron-hole pairs in the oxide support. Clearly it is a significant work, with a methodology that is well founded. It is not entirely original, in the sense that photo-thermal catalysts have been already used for others reactions such as CO2 reduction.
The description of the synthesis procedure as well as the computational details allow for work to be reproduced. I think the present paper could be published after considering the following points: 1--The concept of Strong Metal-Support Interaction is thus evoked as the main mechanism to selectively control the amount small NP/large NP of Pd grown on the support. By the way, historical references on this point should be added in the introduction to my opinion.
2--What is the mechanism of formation of the SAC. It is not clear to me which step of the synthesis is responsible for their presence, and which experimental parameter(s) would be able to control the NP/SAC ratio?
Response: In this work, we have used three methods to prepare Pd/TiO2 catalysts, i.e., ball-milling, strong electrostatic adsorption (SEA) and a common impregnation method. The first one is based on the ''precursor-dilution'' mechanism [Nat. Commun. 2019, 10, 3663] while the second mechanism is "promoting attractive interaction between Pd ions and the support" [J Am Chem Soc. 2017, 139, 14150-14165] for SAC preparation. Our original purpose was to prepare "absolute" Pd single-atom catalysts (SACs), i.e., the presence of only isolated single atoms without any clusters/NPs in our catalysts. However, the results showed that even using such effective methods the presence of Pd nanoparticles/clusters is still unavoidable, highlighting the difficulty of preparing absolute Pd single-atom catalysts [Chem. Rev. 2020, 120, 11986-12043]. This is the reason why we'd like to try to encapsulate the co-existed Pd NPs by utilizing the different strong metal-support interaction (SMSI) concurrence conditions of Pd single atoms and Pd NPs. We think this is one of the major values/significances of this work, that is, it provides a simple yet relatively universal strategy to "tune" common supported Pd catalysts into Pd SACs with good reversibility. The impregnation method was designedly used to strengthen the value of this strategy because impregnation method is simple and has been widely used in industrial process, which generally results in the co-existence of single atoms and NPs. The results turn out that Pd catalysts prepared by such a common and simple method can be "tuned" into Pd SACs, highlighting the university and potential application of this strategy.
As to the ratio of Pd single atoms and NPs, we don't think the ratio matters so we didn't try to control; and it's actually hard to control by the methods we adopted.
3--To be entirely convincing on the nature of the Pd-1 catalytic site could the authors provide information such as XPS data that usually give hints about the charge character on the metal center?
Response: Thank you for your good suggestion. In our original manuscript, the charge character of Pd had been characterized by XANES. It suggested that the Pd existed as positively charged state. Considering the fact that under SMSI state Pd NPs often existed as metallic or even negatively charged state [Catal. Today. 2016, 260, 21-31], the positive chemical state is attributed to Pd single atoms [Chem. Rev., 2020, 120(21):11986-12043;Nanoscale, 2017, 9, 6643-6648;J. Am. Chem. Soc. 2018, 140, 954-962]. It is also suggested that the proportion of Pd NPs in the catalyst should be low as their metallic or negatively charged state can be compensated by the positively charged state of Pd single atoms.
According to the review's suggestion, we further performed XPS measurement ( Figure R1 below). The binding energies of Pd 3d can be fitted into two peaks of 335.1 eV and 336.5 eV even after reduction at 600 o C, which are assigned to Pd 0 and Pd δ+ , respectively. This result is consistent with the XANES result and further verifying the high valence of Pd single atoms.
We have added the result and discussion into the revised manuscript and supplementary file      Figure R2 in nearly the same range. However, gaps between the highest states and lowest unoccupied states projected onto C atoms are quite large, which implies impossibility of C≡C bond activation due to electron excitation in this model. Figure R5. Projected density of states of dissociated hydrogen and acetylene co-adsorbed structures. Fermi levels are shifted to 0 eV. Due to there are only two C atoms and one Pd atom in models, to make PDOS of C and Pd can be clearly seen, PDOS of C and Pd are rescaled via normalization (PDOS/max(PDOS)) and multiplied by factor 0.02. In all these three models, C≡C activation due to electronic excitation is possible because gaps between the highest occupied states projected onto Ti or Pd (for example see Figure R8) and the lowest unoccupied states projected onto C (for example see Figure R9) are approximately 4 eV, corresponding to a wavelength about 310 nm.  Figure R5, gaps between the highest occupied states projected onto Pd or Ti (for example, see Figure R10) and the lowest unoccupied states projected onto C (for example, see Figure R11) are 3 eV approximately, corresponding a wavelength 414 nm. Figure R8. The highest occupied state of model a101.Pd-2-ace-2H. Figure R9. The lowest unoccupied states projected onto C atoms in model a101.Pd-2-ace-2H.
A feature of pi* orbital symmetry can be seen clearly.  A feature of pi* orbital symmetry can be seen clearly.    semi-hydrogenation of acetylene into ethylene seems more efficient, and has been extensively applied in industry for decades.
2) The authors use as support a rutile/anatase mixture, which is certainly not innocent (cf. J. Response: This is a very good question. The XRD measurements have shown that our TiO2 support after high-temperature reduction consists of both anatase and rutile. The AC-STEM image analysis also confirmed the mixture of both phases, Figure R12. Therefore, according to the literature reports and our study experience on TiO2 supported metal single atoms, we believe that Pd single atoms can locate at both anatase and rutile phase.
However, it should be noted that the catalysts used in that work are quite different from ours. To further convince the reviewer we have performed additional control experiment. It is generally accepted that anatase (or mixture of anatase and rutile with suitable ratio, such as P25) is more suitable as support to load metal atoms than rutile. Therefore, although it's hard to obtain pure anatase supported catalyst after high-temperature treatment due to the phase transformation from anatase to rutile, we can prepare rutile supported Pd catalyst. If rutile supported Pd SAC shows similar performance, it means that support doesn't have significant influence. We therefore prepared a rutile supported Pd catalyst and reduced at different temperatures and tested their performance. The results show a similar scenario that the ethylene selectivity after reduction at a higher temperature 700 o C is much improved compared with that reduced at 200 o C, Figure R14. A slightly higher reduction temperature of 700 o C was adopted is because rutile is slightly harder to form SMSI than anatase and P25 [Sci. Adv., 2017, 3(10): e1700231; Angew. Chem. Int. Ed., 59, 11824-11829]. We have added the discussion in revised Supplementary file ( Supplementary Fig. 9).

Response to Reviewer 3
In this work, Guo et al. demonstrated semi-hydrogenation of acetylene in excess ethylene on atomically dispersed Pd species on TiO2 supports prepared by two different methods. The authors exploited the strong metal-support interaction (SMSI) to selectively encapsulate Pd nanoparticles and clusters by the SMSI overlayer via high-temperature reduction of the catalysts in H2, leaving single-atom Pd species exposed for catalysis. This treatment resulted in substantial improvement in C2H4 product selectivity in thermocatalysis. The selectivity gradually dropped from 60% to about 40% over 40 hours of reactivity test with stable %100 C2H2 conversion. Next, the authors demonstrated that high energy near UV photons could be utilized to drive the same reaction at milder operating conditions. Supported by their computational and experimental studies, the authors suggest that the origin of the reactivity enhancement in photocatalysis is the photoexcitation of TiO2 and the transfer of charge carriers to Pd sites for chemical bond activation (primary to activate C-C bonds). The combination of the SMSI and light to control catalysis is interesting! However, there are significant concerns on the photocatalysis side and the associated discussion. In particular, an important aspect of the photocatalysis results that the authors seemingly refused to acknowledge is regarding the selectivity of the process. Light can promote the reactivity but also lead to a substantial drop in desired product selectivity in this case (see below). This poses a major concern for using the current photocatalysis approach for driving the semi-hydrogenation of acetylene on the proposed catalyst system. Figure 4 and S8 (e.g., focusing on their panel (a)) reveals that light-promoted reactivity comes at the expense of a substantial drop in the C2H4 product selectivity. Looking at the entire 35 min of the experiment, the selectivity decreases from 80% to near 40%. Even with the assumption that some drop in selectivity during the initial light-on cycle is due to measurement under non-steady-state condition (that has its own issue), it is clear that there is an additional 10% drop in the selectivity each time that is light is turned on with a total of near 20% selectivity drop just in two illumination cycles. Regrettably, the authors consider this as a "slight" decrease in selectivity or even "stable" selectivity (during the second cycle)!

Response:
We sincerely thank the reviewer for the good questions and suggestions mainly regarding to ethylene selectivity.
In fact, the semi-hydrogenation of ethyne in excess ethylene over Pd metal can be regarded as a "preferential" hydrogenation process, similar to the preferential oxidation of CO in excess of H2. The reason we must remove ethyne from excess ethylene (or CO from excess H2) is their adsorption (ethyne or CO) on metal is much stronger than their counterparts (ethylene or H2), thus preferentially covering the catalyst active sites and inhibiting the conversion of alkene (H2), giving rise to the so-called catalyst poison. Therefore, the conversion of alkene (reflected as alkene selectivity) is highly alkyne-coverage-dependent.
With the acetylene conversion increase (coverage decrease), the possibility of ethylene adsorption and activation increase, i.e., increased acetylene conversion will result in a decreased ethylene selectivity (especially at relatively higher conversion). This is a common phenomenon in ethyne semi-hydrogenation reaction in rich ethylene atmosphere [Catal. Rev. 2006, 48, 91-144;Frontiers of Chemical Science and Engineering 2015, 9, 142-153].
Therefore, the selectivity drop might mainly originate from the conversion increase upon photo-thermo condition. At full ethyne conversion, ethylene can adsorb and undergo hydrogenation, leading to a sharp decrease of ethylene selectivity, that's the reason why on Pd NPs the ethylene selectivity can quickly drop from >90% to as low as -500% in our work ( Figure 3b). Theoretically, in our test condition the ethylene selectivity could vary from -800% to 100%, a very large range. Therefore, 20% change is small compared with such a large range (20/900 × 100% = 2.2%). That's the reason we claim a small selectivity change. But according to the reviewer's comments, we have deleted this word to avoid any possible misleading.
As to the claim of "stable" in second cycle, it is based on the experimental data that in first cycle (either light off or light on) both activity and selectivity changed gradually (activity increase while selectivity decrease), suggesting a change of the catalyst under reaction condition. However, in second cycle both activity and selectivity are stable despite the different values in light on and light off conditions, suggesting the catalyst became stable after first cycle. To further convince the reviewer, we have conducted another photo-thermo catalytic experiment with more cycles. As shown Figure R15, the catalyst is quite stable after first cycle. We have added the new data and discussion into our revised Supplementary file ( Supplementary Fig. 12). Figure R15. Catalytic Performance of photo-thermo catalysis over Pd/TiO2-600H with more cycles.
2. The drop in selectivity also implies that additional light-on cycles (if performed) could potentially lead to a further decrease in selectivity.
Response：As mentioned above, we think the selectivity change mainly comes from the ethyne conversion increase. Therefore, in additional light-on cycles the selectivity should not change much if conversion didn't change much. This can be confirmed by the additional cycle experiment results, Figure R15.
3. Furthermore, the light-induced drop in the C2H4 product selectivity is an important result that is deserved to be highlighted in the main text along with the reactivity results in photocatalysis.
Response: Thank you for your suggestion, we have added corresponding discussion in the revised manuscript: It turns out that the introduction of light irradiation can indeed boost the conversion of acetylene in semi-hydrogenation reaction remarkably (from 20% to 80%) with a decreased ethylene selectivity, Fig. 4 and Supplementary Fig. 10, indicating that the photogenerated charges may involve in the reaction process. The decreased selectivity upon irradiation might stem from the increased acetylene conversion as the ethylene selectivity is usually acetylene-conversion-dependent. [Catal. Rev. 2006, 48, 91-144] 4. Notably, the authors repeatedly state that there is only one report on heterogeneous Response: We sincerely thank the reviewer for pointing out this work that we had left out.
We have cited this paper in our revised manuscript in introduction section. Swearer et al.
[ PANS 2016, 113, 8916-8920] used Pd nanoparticles and aluminum nanocrystals (AlNC) to construct a heterometallic antenna-reactor complexes photocatalyst for semi-hydrogenation of acetylene under white-light illumination by controlling the surface plasmon resonance. They found ethylene selectivity shows an increase with increased laser power density but a limited yield differing from traditional thermal catalysis under the same reaction conditions. The reason is mainly that plasmon-induced hot carriers improve the desorption efficiency of H2, limiting the additional hydrogenation of surface ethylene, but also limiting the hydrogenation of acetylene, leading to a low target product yield simultaneously. Their study is based on two preconditions, ethylene desorption and hydrogenation on Pd NPs have similar activation barriers, and the small change of dissociated H2 has big influence on ethylene desorption or over-hydrogenation. But in our work, the catalyst is totally different. As can be seen in our answer to question 7 of reviewer #1, ethyne adsorbed by di-σ bond which has a much higher intensity than H2 adsorption (homolytic dissociation adsorption). Therefore, any changes of C2H2 or H2 adsorption will have strong influence on each other and subsequently the catalytic activity. However, on Pd SACs, ethyne usually adsorbs by π-bond on isolated Pd atoms while H2 adsorbs on Pd atoms and the adjacent support through heterolytic dissociation adsorption, resulting in a noncompetitive adsorption of ethyne and H2 on SACs [Natl. Sci. Rev. 5,[653][654][655][656][657][658][659][660][661][662][663][664][665][666][667][668][669][670][671][672]. Therefore, minimal change of dissociated H2, if any, will not determine the ethylene tendency towards desorption or over-hydrogenation. Besides, our H2-D2 isotope exchange reaction had demonstrated that H2 dissociation ability is almost the same upon light irradiation or not. However, in an ethylene-rich condition, with the increasing of acetylene conversion, the possibility of ethylene to adsorb and activate on active sites is increasing, i.e., increased acetylene conversion will result in decreased ethylene selectivity.
5. The authors should also discuss how the use of light in this system leads to worsened C2H4 selectivity. Reportedly, the results of DFT calculations and H2-D2 exchange experiment suggest the primary role of Pd/TiO2 photoexcitation being the C-C bond activation acetylene activation, but the discussion of product selectivity is missing.
Response: Thank you for this question which is actually very similar or closely related to your question 1 and 2. As can be seen in answers to question 1 and 2, the worsened C2H4 selectivity comes from the increased ethyne conversion as in additional light-on cycles ethylene selectivity didn't decrease further.
6. Regarding the authors' discussion on the role of light and the underlying mechanism: It is stated that the reactivity enhancement is due to a charge-driven mechanism from photoexcitation of TiO2 and as supported by the authors XPS and DFT results. This statement is broadly true. However, there are important aspects of light-induced catalyst heating that should be considered when discussing the role of light in photocatalytic processes. For instance, despite the authors' statement, the use of a circulating water bath does not necessarily exclude the photothermal heating effect in catalysis. This is due to the potential presence of local nanoscale hot spots, especially with supported metal catalysts. Also, the magnitude of the light-induced heating within the catalyst bed strongly depends on multiple factors, including the optical properties (ensemble photon absorption) and thermal conductivity of the catalyst, incident photon flux, illumination wavelength, etc. Currently, the information regarding the power density of the incident photons in Figure 4 is missing. Also, the use of Al2O3 support in the control experiment and the lack of photocatalytic reactivity does not necessarily exclude the thermal effect on TiO2 since this is a comparison of two different systems with a very different absorption properties and thermal conductivities.

Response:
We sincerely thank the reviewer for this critical comment and good suggestion. As we used white TiO2 crystal as support, we believe that the heat effect will not significant.
Second and perhaps of more importance, to avoid any possible heat effect, we have used a differential reactor with a very low catalyst bed (<1 mm) and have also highly diluted the catalyst bed by using dozens of times of diluter (for example, 10 mg catalyst diluted by 400 mg quartz sand). In this case, we think the heat effect, if any, could be minimized.
According to reviewer's suggestion, we have added this discussion into our revised manuscript. We have also supplied the power density information for Fig. 4 and Supplementary Fig. 10 in the revised manuscript.
7. Furthermore, the authors state that "it is suggested that the light can still increase the reactor temperature by 10 o C below 100 o C. Therefore, a 10 o C-correction was used when performing photo-thermo catalysis." Suggested by who and based on what evidence? Again, the magnitude of light-induced heating depends on several factors, as discussed above. Also, did the authors apply this "undocumented" correction to the Arrhenius plot of photocatalysis in Figure 4e?
Response: Thank you for your good questions. We are sorry for not making this clearly in our original manuscript. A more detailed picture of our fixed-bed reactor has been provided in the revised Supplementary Fig. 11. As mentioned above, the 10 o C-correction below 100 o C was obtained based on our oft-repeated experiments. As shown in Figure R16, thermocouple-1 was put inside of the furnace for temperature setting while thermocouple-2 was put into the reactor tube just upon the catalyst thin layer to measure the temperature of catalyst bed.  Figure R16. The fixed-bed reactor (a) and amplification of the furnace part (b) for photo-thermo semi-hydrogenation of acetylene.
8. The authors suggested a charge carrier-driven mechanism for bond activation under illumination with charge transfer from TiO2 to Pd sites. They should also provide a scheme to discuss the proposed mechanism further, especially to examine whether there is a net charge transfer process to adsorbate(s) and that the catalyst remains in a neutral state or not. If the process is associated with net charge transfer, it results in a charge build-up and eventually a decrease in photocatalytic reactivity. A long-term stability test in photocatalysis should therefore be provided.
Response: Thanks for your good suggestion. The possible mechanism for photo-thermo catalysis over the constructed Pd1/TiO2 is proposed in Figure R17 ( Supplementary Fig. 30 in the revised version). The scheme can be described as follows.
1) Irradiation leads to band-gap excitation of TiO2 support, generating electron-hole pairs: TiO 2 +hv→TiO 2 (e -,h + ) 2) Photo-generated electrons transfer to isolated Pd sites, facilitating the activation of According to this mechanism, every electron transfer is accompanied with a hole and the net charge is noncumulative. Therefore, our understanding is that upon reaction condition, the net charge is noncumulative. However, without the presence of reactants, a certain degree of net charge accumulation is not impossible as the Pd atoms accepted some electrons from the support, resulting in a difficulty in electron-hole recombination. To further confirm the result, we tested the stability of a Pd/TiO2-H200 according to the reviewer's suggestion (to avoid any potential effect of light on the SMSI state and then on the catalytic performance). It can be seen that the catalytic performance is quite stable upon light irradiation after an evaluation in the initial few hours in dark condition, as shown in Figure R18. We have added this data into the revised Supplementary file (Supplementary Fig. 31).  9. Spectrum of the light source used for illumination is missing.

Response:
Thanks for reminding us about the missing spectrum, we have added the following spectrum ( Figure R19) to Supplementary Fig. 29 in the revised version.  11. Improper citations! The past decade has witnessed huge progress in light-driven heterogeneous catalysis, especially with supported metal catalysts, using a combination of light and external heating or only light to drive the chemistry (the latter is more ideal). The authors must more appropriately acknowledge the previous efforts in this area rather than citing a few very recent examples as the pioneering work in the field, which is indeed an incorrect remark!!!