A Molten-Salt Pyrolysis Synthesis Strategy toward Sulfur-Functionalized Carbon for Elemental Mercury Removal from Coal-Combustion Flue Gas

: The emission of mercury from coal combustion has caused consequential hazards to the ecosystem. The key challenge to abating the mercury emission is to explore highly efﬁcient adsorbents. Herein, sulfur-functionalized carbon (S-C) was synthesized by using a molten-salt pyrolysis strategy and employed for the removal of elemental mercury from coal-combustion ﬂue gas. An ideal pore structure, which was favorable for the internal diffusion of the Hg 0 molecule in carbon, was obtained by using a SiO 2 hard template and adjusting the HF etching time. The as-prepared S-C with an HF etching time of 10 h possessed a saturation Hg 0 adsorption capacity of 89.90 mg · g − 1 , far exceeding that of the commercial sulfur-loaded activated carbons (S/C). The S-C can be applied at a wide temperature range of 25–125 ◦ C, far exceeding that of commercial S/C. The inﬂuence of ﬂue gas components, such as SO 2 , NO, and H 2 O, on the Hg 0 adsorption performance of S-C was insigniﬁcant, indicating a good applicability in real-world applications. The mechanism of the Hg 0 removal by S-C was proposed, i.e., the reduced components, including sulfur thiophene, sulfoxide, and C-S, displayed a high afﬁnity toward Hg 0 , which could guarantee the stable immobilization of Hg 0 as HgS in the adsorbent. Thus, the molten-salt pyrolysis strategy has a broad prospect in the application of one-pot carbonization and functionalization sulfur-containing organic precursors as efﬁcient adsorbents for Hg 0 .


Introduction
The excessive emission of mercury from industrial activities has caused consequential hazards to the ecosystem and human health [1][2][3]. Coal combustion is one of the largest industrial sources of mercury emission. The mercury emitted from typical coal-combustion flue gas generally existed in three forms, i.e., elemental mercury (Hg 0 ), oxidized mercury (Hg 2+ ), and particulate bound mercury (Hg p ) [4][5][6][7][8]. The Hg p can be captured by using particulate matter control devices, while the Hg 2+ can be removed by using wet flue-gas scrubbers due to Hg 2+ 's water solubility [9][10][11][12]. However, Hg 0 is difficult to remove owing to its water insolubility and high volatility [13][14][15]. As a consequence, Hg 0 is the primary species of mercury discharged into the atmosphere from coal-combustion flue gases. The highly efficient removal of Hg 0 is a key challenge to reducing mercury pollution from coal-fired power plants.

Sample Preparation
S-C was prepared by using a molten-salt pyrolysis strategy [38]. Two grams of 2,2bithiophene and 2.0 g of SiO 2 were added into 150 mL of tetrahydrofuran and stirred at room temperature for 6 h. The mixture was then dried and then ground to a powder. After that, the powder was placed into a rail boat and covered with 5.0 g of Co(NO 3 ) 2 ·6H 2 O, which was heated at 800 • C for 2 h. Then, the SiO 2 was removed by using 10% HF solution.
To obtain different porosity of S-C, the sample was etched by using HF for different times (0, 24, 48 and 56 h). After drying at 105 • C for 10 h, the S-C was finally obtained.

Sample Characterization
The morphology of the sample was studied by using a scanning electronic microscope (SEM, FEI F50, New York, NY, USA). Transmission electron microscope (TEM, EOL JEM 2100F, microscope Tokyo, Japan) and high-resolution TEM (HRTEM) were used to study the morphology and structure of sample. The valence states of samples were characterized by using X-ray photoelectron spectroscopy (XPS, Thermo ESCALAB 250Xi, New York, NY, USA).

Hg 0 Adsorption Activity Tests
The Hg 0 adsorption activity test was measured on a fixed-bed reactor [42,43]. The adsorbent was placed in a quartz reactor, reaction temperature of which was controlled by using a tube furnace. The flue gas was composed of N 2 , O 2 , SO 2 , NO, and H 2 O, with the total flow rate of 1 L·min −1 . Hg 0 was provided by a mercury permeation tube placed in a constant temperature water bath, delivering Hg 0 by using N 2 to ensure a stable concentration of 65 µg·m −3 . The concentration of Hg 0 was monitored by using an online mercury analyzer (RA-915M, Lumex, Tianjin, China). The Hg 0 adsorption capability was calculated by using the following equations: where C in (µg·m −3 ) and C out (µg·m −3 ) represent the inlet and outlet concentrations of Hg 0 , Q (µg·g −1 ) is the Hg 0 adsorption capacity, m (g) is the sample amount, f (m 3 ·h −1 ) is the gas flow rate, and t (h) is the reaction time.

Pseudo-First-Order Model
This model is described as follows [44]: Based on the initial conditions, i.e., t = 0 q t = 0, Equation (2) is revised as: where q t and q e represent the adsorbed mercury amount at any time t and equilibrium time (µg·g −1 ). k 1 represents the rate constant (min −1 ).

Pseudo-Second-Order Model
This model is described as follows [45]: On the basis of initial conditions, i.e., t = 0 and q t = 0, Equation (4) is modified as: where k 2 represents the rate constant (µg/(cm 3 ·min)).

Elovich Model
This model is described as follows [46]: where α represents the initial rate and β is related to surface coverage and activation energy. If t is much larger than t 0 , this equation is modified as follows:

Intra-Particle Diffusion Model
This model is described by the following formula [47]: where k id represents the diffusion rate constant within the particle and C is a constant, which is related to the boundary layer.

Preparation and Characterization of Samples
The S-C was prepared by using the molten Co(NO 3 ) 2 ·6H 2 O-assisted carbonization of sulfur-containing small organic molecule precursors. SiO 2 nanoparticles were adopted as hard templates, followed by an HF etching step to remove the SiO 2 template. The porosity of S-C was adjusted by using the HF etching time (shown in Figure 1). As listed in Table 1, the HF etching step will generate mesopores on the S-C. The S-C with HF etching for 10 h possessed the largest BET surface area of 318.5 m 2 ·g −1 , with an average pore size of 7.31 nm and total pore volume of 0.58 cm 3 ·g −1 . Pore size affects the internal mass transfer process of Hg 0 on adsorbents, thus affecting the removal rate of Hg 0 . As shown in Figure 2a, the N 2 absorption-desorption isotherms for S-C belonged to a typical II isotherm, indicating that the porosity of S-C was very limited. The S-C after the HF etching step presented a typical IV isotherm with a negligible absorption at lower pressures but significant absorption at higher pressures (p/p 0 = 0.2-1.0). This indicates that S-C is composed of mesopores or macropores rather than micropores. The pore distribution curves shown in Figure 2b demonstrate that the pore size of the S-C was in the range of 2-10 nm. The mesoporous structure in the range of 2-50 nm is beneficial for Hg 0 's diffusion to the inner surface of an adsorbent [48]. Thus, the pore structure of S-C is favorable for Hg 0 adsorption.   sizes of individual particles are in the range of 100-200 mesh. As shown, the morphology of S-C was significant dependent on the HF etching time. The S-C without HF etching displayed a dense surface, and there were negligible pores observed on the S-C surface. After etching with HF, abundant pores were generated on the S-C surface, and more pores were generated with the extension of the HF etching time from 5 to 10 h. Thus, the SiO 2 was embedded in the carbon structure as a template, which could be removed by using the HF solution to induce the formation of a porous structure. However, upon reaching a higher HF etching time, the resultant carbon framework collapsed, which might have affected the internal diffusion of mercury. Therefore, a SiO 2 template was used to achieve the adjustable preparation of porous carbons.    Figure 3 shows the morphologies of S-Cs with different HF etching times. These images display the high-solution local microscopies of individual particles, in which the sizes of individual particles are in the range of 100-200 mesh. As shown, the morphology of S-C was significant dependent on the HF etching time. The S-C without HF etching displayed a dense surface, and there were negligible pores observed on the S-C surface. After etching with HF, abundant pores were generated on the S-C surface, and more pores were generated with the extension of the HF etching time from 5 to 10 h. Thus, the SiO2 was embedded in the carbon structure as a template, which could be removed by using the HF The surface-functional groups of S-C were studied by using FTIR. As shown in Figure 4, there were four main peaks on the FTIR spectra, which could be assigned to the C-OH (3392 and 615 cm −1 ) and aromatic C = C (1626 and 1100 cm −1 ) [49]. Figure 5 shows the XPS spectra for S-C. As shown in Figure 5a, the spectra for high-solution C 1s spectra could be divided into three peaks at 284.8, 286.0, and 288.8 eV, assigned to the characteristic peaks of C = C, C-O, and C = O [30]. Figure 5b shows the O 1s spectra for C-S, in which the peaks at 531.5, 532.3, and 533.3 eV are regarded as C-OH, C-O, and O-H [31]. Figure 5c shows the S spectra for S-C. The sulfur on the S-C existed in four forms. The two peaks at 164.2 and 165.3 eV corresponded to S 2p3/2 and S 2p1/2 for thiophenic sulfur (i.e., -C-S x -C-, x = 1-2), the small peak at 169.1 eV could be assigned to sulfoxide [50], the peak at 166.2 eV could be assigned to C-S, while the peaks at 167.2 and 170.3 eV could be assigned to sulfate [51,52]. solution to induce the formation of a porous structure. However, upon reaching a higher HF etching time, the resultant carbon framework collapsed, which might have affected the internal diffusion of mercury. Therefore, a SiO2 template was used to achieve the adjustable preparation of porous carbons. The surface-functional groups of S-C were studied by using FTIR. As shown in Figure  4, there were four main peaks on the FTIR spectra, which could be assigned to the C-OH (3392 and 615 cm −1 ) and aromatic C = C (1626 and 1100 cm −1 ) [49]. Figure 5 shows the XPS spectra for S-C. As shown in Figure 5a, the spectra for high-solution C 1s spectra could be divided into three peaks at 284.8, 286.0, and 288.8 eV, assigned to the characteristic peaks of C = C, C-O, and C = O [30]. Figure 5b shows the O 1s spectra for C-S, in which the peaks at 531.5, 532.3, and 533.3 eV are regarded as C-OH, C-O, and O-H [31]. Figure 5c shows the S spectra for S-C. The sulfur on the S-C existed in four forms. The two peaks at 164.2 and 165.3 eV corresponded to S 2p3/2 and S 2p1/2 for thiophenic sulfur (i.e., -C-Sx-C-, x = 1-2), the small peak at 169.1 eV could be assigned to sulfoxide [50], the peak at 166.2 eV could be assigned to C-S, while the peaks at 167.2 and 170.3 eV could be assigned to sulfate [51,52].      Figure 6 shows the Hg 0 adsorption performances of S-Cs with various HF etching times. As shown, the normalized-outlet Hg 0 concentration of S-C without etching climbed dramatically to above 0.90. Thus, the S-C without etching has a poor Hg 0 adsorption performance, and the removal rate of Hg 0 is only below 10%. However, after the HF etching, the S-C displayed far superior Hg 0 removal performances. The HF etching times played significant roles in the Hg 0 adsorption of S-C. After etching for 5 h, the concentration of Hg 0 at the normalized outlet remained below 0.2. With the extension of the etching time to 10 h, the Hg 0 adsorption performance of S-C can be further improved. However, a too-long etching time resulted in a decrease in Hg 0 adsorption performance. This is attributed to the fact that HF etching can remove the SiO 2 template to generate abundant pores on S-C, which allows for accessible mercury molecule transportation. As a result, the sulfur in S-C can be accessible sufficiently for binding mercury. However, the excessive etching will result in the collapse of the framework of carbons, hence the weakening of the Hg 0 adsorption on S-C. to 10 h, the Hg 0 adsorption performance of S-C can be further improved. However, a toolong etching time resulted in a decrease in Hg 0 adsorption performance. This is attributed to the fact that HF etching can remove the SiO2 template to generate abundant pores on S-C, which allows for accessible mercury molecule transportation. As a result, the sulfur in S-C can be accessible sufficiently for binding mercury. However, the excessive etching will result in the collapse of the framework of carbons, hence the weakening of the Hg 0 adsorption on S-C. The saturated adsorption capacity of an adsorbent is an important index to use to evaluate the adsorption performances of materials, so it is necessary to study the change in S-C adsorption capacity with time. The curve of Hg 0 adsorption capacity changing over time is shown in Figure 7. When the reaction duration was 1200 min, the adsorption capacity of Hg 0 exceeded 50% and reached 45.39 mg·g −1 . In addition, it can be seen from the figure that the adsorption rate increases first and then decreases with time, and the slope is zero when the adsorption is saturated. Adsorption kinetic models can be adopted to investigate the process of Hg 0 adsorption and the dominant controlling factors. The pseudo-first-order-based kinetic model is the most common adsorption kinetic model. Ln(qe-qt) is used to plot t, and the adsorption mechanism conforms to the pseudo-firstorder model if a straight line can be obtained. The pseudo-second-order model is based on the assumption that the adsorption rate is controlled by the chemisorption mechanism. Elovich describes a series of reaction mechanism processes, which are suitable for processes with large activation energy changes in reactions and for complex heterogeneous diffusion processes. The intra-particle diffusion model is commonly used to analyze the control steps in the reaction. Generally, the material adsorption process is divided into two processes: adsorbent surface adsorption and slow pore diffusion. If the fitting result fails to reach the origin, it indicates that the internal diffusion of the material is not the only step to controlling the adsorption process. As shown in Figure 8, the pseudo-first- The saturated adsorption capacity of an adsorbent is an important index to use to evaluate the adsorption performances of materials, so it is necessary to study the change in S-C adsorption capacity with time. The curve of Hg 0 adsorption capacity changing over time is shown in Figure 7. When the reaction duration was 1200 min, the adsorption capacity of Hg 0 exceeded 50% and reached 45.39 mg·g −1 . In addition, it can be seen from the figure that the adsorption rate increases first and then decreases with time, and the slope is zero when the adsorption is saturated. Adsorption kinetic models can be adopted to investigate the process of Hg 0 adsorption and the dominant controlling factors. The pseudo-first-order-based kinetic model is the most common adsorption kinetic model. Ln(q e -q t ) is used to plot t, and the adsorption mechanism conforms to the pseudo-firstorder model if a straight line can be obtained. The pseudo-second-order model is based on the assumption that the adsorption rate is controlled by the chemisorption mechanism. Elovich describes a series of reaction mechanism processes, which are suitable for processes with large activation energy changes in reactions and for complex heterogeneous diffusion processes. The intra-particle diffusion model is commonly used to analyze the control steps in the reaction. Generally, the material adsorption process is divided into two processes: adsorbent surface adsorption and slow pore diffusion. If the fitting result fails to reach the origin, it indicates that the internal diffusion of the material is not the only step to controlling the adsorption process. As shown in Figure 8, the pseudo-first-order model was closest to the adsorption process of Hg 0 on S-C, with an extremely high correlation coefficient (R 2 = 0.9982). The saturation adsorption capacity of S-C was simulated as 89.90 mg·g −1 . When the molar ratio of Hg:S is 1:1, it is equivalent to 55% of the sulfur accessibility in Hg 0 adsorption. For comparison, the Hg 0 saturation adsorption capacity of a sulfur-loaded commercial activated carbon (S/C) was also investigated. It should be noted that the S/C possessed a higher sulfur content and surface area compared with S-C. However, the saturation adsorption capacity of S/C was less than 1 mg·g −1 , which was much lower compared with its theoretical adsorption capacity of 352.1 mg·g −1 . Thus, most of the sulfur in S/C was not adopted sufficiently for binding mercury, although it possessed a higher surface area. It fully shows that the key to Hg 0 adsorption improvements lies in the high dispersion of active sulfur species [53]. Thus, the molten-salt pyrolysis synthesis strategy toward sulfur-functionalized carbon would be more superior compared with other traditional methods, such as impregnation when significantly dispersing the active components (i.e., sulfur). which was much lower compared with its theoretical adsorption capacity of 352.1 mg·g −1 . Thus, most of the sulfur in S/C was not adopted sufficiently for binding mercury, although it possessed a higher surface area. It fully shows that the key to Hg 0 adsorption improvements lies in the high dispersion of active sulfur species [53]. Thus, the molten-salt pyrolysis synthesis strategy toward sulfur-functionalized carbon would be more superior compared with other traditional methods, such as impregnation when significantly dispersing the active components (i.e., sulfur). with S-C. However, the saturation adsorption capacity of S/C was less than 1 mg·g −1 , which was much lower compared with its theoretical adsorption capacity of 352.1 mg·g −1 . Thus, most of the sulfur in S/C was not adopted sufficiently for binding mercury, although it possessed a higher surface area. It fully shows that the key to Hg 0 adsorption improvements lies in the high dispersion of active sulfur species [53]. Thus, the molten-salt pyrolysis synthesis strategy toward sulfur-functionalized carbon would be more superior compared with other traditional methods, such as impregnation when significantly dispersing the active components (i.e., sulfur).

Impact of Operation Conditions on Hg 0 Adsorption Capacity
An excellent adsorbent should have a good stability at various conditions. Figure 9 shows the influence of temperature on the Hg 0 adsorption capacities of S-C and S/C. The normalized-outlet Hg 0 concentration when passing through the S-C was maintained be-

Impact of Operation Conditions on Hg 0 Adsorption Capacity
An excellent adsorbent should have a good stability at various conditions. Figure 9 shows the influence of temperature on the Hg 0 adsorption capacities of S-C and S/C. The normalized-outlet Hg 0 concentration when passing through the S-C was maintained below 0.05 in a wide reaction temperature range of 25-125 • C. This suggests that an above 95% Hg 0 adsorption efficiency was obtained; even the sorbent dosage was as low as 5 mg. This wide temperature range proves that the S-C can be applied flexibly at different scenes for Hg 0 removal. In contrast, the S/C exhibited significantly different Hg 0 adsorption capacities under various temperatures, in which relatively limited Hg 0 adsorption capacities were obtained at low temperatures. Even at the optimum reaction temperature and the same amount of adsorbent, the concentration of Hg 0 at the normalized outlet is still higher than 0.15, much higher than S-C. Depending on the preferred temperature range, setting the S/C upstream of the ESP is the ideal application in which the Hg 0 adsorption capacity of S-C might be affected by various flue gas components, such as high concentrations of fly ash, SO 2 , and NO 2 .

Impact of Operation Conditions on Hg 0 Adsorption Capacity
An excellent adsorbent should have a good stability at various conditions. Figure 9 shows the influence of temperature on the Hg 0 adsorption capacities of S-C and S/C. The normalized-outlet Hg 0 concentration when passing through the S-C was maintained below 0.05 in a wide reaction temperature range of 25-125 °C. This suggests that an above 95% Hg 0 adsorption efficiency was obtained; even the sorbent dosage was as low as 5 mg. This wide temperature range proves that the S-C can be applied flexibly at different scenes for Hg 0 removal. In contrast, the S/C exhibited significantly different Hg 0 adsorption capacities under various temperatures, in which relatively limited Hg 0 adsorption capacities were obtained at low temperatures. Even at the optimum reaction temperature and the same amount of adsorbent, the concentration of Hg 0 at the normalized outlet is still higher than 0.15, much higher than S-C. Depending on the preferred temperature range, setting the S/C upstream of the ESP is the ideal application in which the Hg 0 adsorption capacity of S-C might be affected by various flue gas components, such as high concentrations of fly ash, SO2, and NO2.  According to previous studies, SO 2 and H 2 O generally compete with Hg 0 for adsorption sites, hence exhibiting inhibitive effects on the Hg 0 removal over carbonaceous sorbents [54,55]. However, the S-C exhibited an excellent resistance to these detrimental flue gas components. Figure 10a-c show that, in the presence of SO 2 , H 2 O, as well as NO, the Hg 0 removal performance was very similar to that under a pure N 2 atmosphere. Even adding 1200 ppm of SO 2 , 12% H 2 O, or 400 ppm of NO, the normalized-outlet Hg 0 concentration was kept at less than 0.05. As a direct comparison, the adsorption performance of S/C for Hg 0 was investigated. As shown in Figure 10d, the SO 2 , H 2 O, and NO significantly weakened the adsorption capacity of S/C. These results could fully demonstrate the excellent resistance of S-C to the detrimental impacts of flue gas impurities compared with commercial activated carbon, which would facilitate the real-world applications.
the Hg 0 removal performance was very similar to that under a pure N2 atmosphere. Even adding 1200 ppm of SO2, 12% H2O, or 400 ppm of NO, the normalized-outlet Hg 0 concentration was kept at less than 0.05. As a direct comparison, the adsorption performance of S/C for Hg 0 was investigated. As shown in Figure 10d, the SO2, H2O, and NO significantly weakened the adsorption capacity of S/C. These results could fully demonstrate the excellent resistance of S-C to the detrimental impacts of flue gas impurities compared with commercial activated carbon, which would facilitate the real-world applications.

Reaction Mechanism
To study the mechanism of a Hg 0 removal on S-C, the valence states of elements on spent S-C after adsorbing mercury were investigated by using XPS. Figure 11a shows that there is no significant change in the spectral binding energy of C 1s for the spent adsorbent, indicating that C did not participate in the Hg 0 adsorption [56]. Figure 11b shows the O 1s spectra for the spent adsorbent. The spectra of O 1s can be divided into four separate corresponding peaks: C = O, C-O-C, COOH, and H2O at 531.3, 532.5, 533.8, and 536.1 eV, respectively [57]. After the Hg 0 adsorption, part of the C-O groups changed to C

Reaction Mechanism
To study the mechanism of a Hg 0 removal on S-C, the valence states of elements on spent S-C after adsorbing mercury were investigated by using XPS. Figure 11a shows that there is no significant change in the spectral binding energy of C 1s for the spent adsorbent, indicating that C did not participate in the Hg 0 adsorption [56]. Figure 11b shows the O 1s spectra for the spent adsorbent. The spectra of O 1s can be divided into four separate corresponding peaks: C = O, C-O-C, COOH, and H 2 O at 531.3, 532.5, 533.8, and 536.1 eV, respectively [57]. After the Hg 0 adsorption, part of the C-O groups changed to C = O, and H 2 O was generated on the adsorbent surface, which may have been caused by a charge imbalance after binding Hg 0 . Figure 11c shows the S 2p for the spent adsorbent, including only two peaks: C-S at 163.94 eV and thiophene at 165.22 eV [58]. The transformations of sulfur species on the spent adsorbent indicate that sulfur played a crucial role in the Hg 0 removal. The absolute content of thiophene and C-S decreased after adsorbing Hg 0 , especially the peaks for sulfoxide, which disappeared compared with the fresh adsorbent. This variation indicates that thiophene (i.e., -C-S x -C-, x = 1-2), sulfoxide, and C-S were beneficial to improving the Hg 0 removal capacity. This is in line with a previous study [59], i.e., findings that the sulfur in sulfide existing in a low state as well as the reducing sulfur (such as thiosulfone) had a high affinity with the Hg 0 atom. Electrons around the sulfur atom were easy to combine with Hg 0 , which was conducive to the removal of mercury. Figure 11d shows that the two peaks of Hg 4f corresponded to the peaks of 103 and 107 eV of HgS [60], further demonstrating that the sulfur in the adsorbent was active for binding Hg 0 .
in the Hg 0 removal. The absolute content of thiophene and C-S decreased after adsorbing Hg 0 , especially the peaks for sulfoxide, which disappeared compared with the fresh adsorbent. This variation indicates that thiophene (i.e., -C-Sx-C-, x = 1-2), sulfoxide, and C-S were beneficial to improving the Hg 0 removal capacity. This is in line with a previous study [59], i.e., findings that the sulfur in sulfide existing in a low state as well as the reducing sulfur (such as thiosulfone) had a high affinity with the Hg 0 atom. Electrons around the sulfur atom were easy to combine with Hg 0 , which was conducive to the removal of mercury. Figure 11d shows that the two peaks of Hg 4f corresponded to the peaks of 103 and 107 eV of HgS [60], further demonstrating that the sulfur in the adsorbent was active for binding Hg 0 .

Conclusions
Sulfur-functionalized carbon (S-C) derived from a molten-salt pyrolysis strategy was employed for a Hg 0 removal. Abundant pores could be generated by using a SiO2 hard

Conclusions
Sulfur-functionalized carbon (S-C) derived from a molten-salt pyrolysis strategy was employed for a Hg 0 removal. Abundant pores could be generated by using a SiO 2 hard template and a subsequent HF etching step. The HF etching time significantly affected the Hg 0 removal performances of S-Cs. With an HF etching time of 10 h, the S-C presented the best Hg 0 removal performance, the saturation Hg 0 -adoption capacity of which reached 89.90 mg·g −1 . This value far exceeded that of the commercial sulfur-loaded activated carbon (S/C), which was specialized for Hg 0 removals. The S-C displayed a good applicability at 25-125 • C, while the S/C could be adopted around only 125 • C since the Hg 0 adsorption performances decreased when deviating from this temperature. The SO 2 , NO, and H 2 O had negligible adverse effects on Hg 0 adsorption over S-C. The good Hg 0 removal performance of S-C was ascribed to the existence of reduced sulfurs, such as thiophene, sulfoxide, and C-S, which have high affinities toward Hg 0 , and the fact that gaseous Hg 0 was converted into HgS after the adsorption. These results indicate that molten-salt pyrolysis