Preparation of a Heterogeneous Catalyst CuO-Fe 2 O 3 /CTS-ATP and Degradation of Methylene Blue and Ciproﬂoxacin

: A heterogeneous particle catalyst (CuO-Fe 2 O 3 /CTS-ATP) was synthesized via injection molding and ultrasonic immersion method, which is fast and effective. The particle catalyst applied attapulgite (ATP) wrapped by chitosan (CTS) as support, which was loaded dual metal oxides CuO and Fe 2 O 3 as active components. After a series of characterizations of catalysts, it was found that CuO and Fe 2 O 3 were successfully and evenly loaded on the surface of the CTS-ATP support. The catalyst was used to degrade methylene blue (MB) and ciproﬂoxacin (CIP), and the experimental results showed that the degradation ratios of MB and CIP can reach 99.29% and 86.2%, respectively, in the optimal conditions. The degradation mechanism of as-prepared catalyst was analyzed according to its synthesis process and · OH production, and the double-cycle catalytic mechanism was proposed. The intermediate products of MB and CIP degradation were also identiﬁed by HPLC-MS, and the possible degradation pathways were put forward.


Introduction
Refractory organics (ROS), such as dyes, antibiotics, pesticides, etc., always threaten the survival and health of animals and human beings [1][2][3][4]. Methylene blue (MB) is a common dye in the printing and dyeing industry, and it is also used as a chemical indicator and biological dye [5]. Ciprofloxacin (CIP), as one of the third generation of antibacterial medicines, is widely used for fighting against various organ infections due to its broadspectrum antibacterial activity. Due to a high percentage (60%-90%) of CIP discharge into the natural environment, nowadays CIP is considered to be one of the most important emerging pollutants due to their inhibition of bacterial activities [6][7][8][9][10]. Ciprofloxacin is generally difficult to biodegrade and enters the environment in the form of prototypes or metabolites [11,12], which poses a serious threat to the health of humans and aquatic organisms.
As the most promising methods, advanced oxidation processes, such as Fenton reactions, photocatalysis, electrocatalysis, ozone oxidation, etc., are often used to deal with refractory organic compounds in water which can produce a lot of hydroxyl radicals with strong oxidizing activity [13][14][15][16][17][18]. Fenton reactions, including all kinds of Fenton-like reactions, have become a research hotspot in the field of water treatment due to its high degradation efficiency, mild reaction conditions, low energy consumption, and simple operation [19][20][21][22]. In particular, the heterogeneous Fenton method has the advantages of wide pH range, low H 2 O 2 and catalysts consumption, easy separation, and no secondary pollution with high removal ratios [23][24][25][26].
Attapulgite clay is a crystalline hydrated magnesium aluminium silicate mineral with unique layer-chain structure. It is made up of two layers of silicon-oxygen tetrahedrons that are sandwiched with a layer of magnesium (aluminium) oxygen octahedron. Attapulgite

Degradation Experiments of MB and CIP by the Catalysts
In addition, 1 g/L methylene blue and 250 mg/L ciprofloxacin stock solutions were prepared for later use. An appropriate amount of MB or CIP stock solutions and a certain amount of deionized water were added into a 250 mL flask to obtain MB or CIP solutions with different concentrations. Add catalyst and 30% w/w hydrogen peroxide into the flask, stirring it at a certain temperature. Take water samples every 10 min, and measure the absorbance of the solution by UV-1900 UV-visible spectrophotometer (Aoyi Instrument Co., Ltd., Shanghai, China). In order to reduce experimental error, one blank and three same samples were tested at the same conditions in each experiment group. The removal ratios of MB or CIP solutions under different conditions can be calculated by Equation (1): Removal ratio (%) = (C 0 − C t )/C 0 × 100% (1) C 0 is the initial concentration of MB or CIP solutions before treatment, and C t is the concentration at reaction time t.

OH Measurement and Intermediate Product Determination
·OH can react with salicylic acid and produce a chemical substance called 2, 3dihydroxybenzoic acid with maximum absorption peak at the wavelength of 510 nm. Thus, the ·OH concentration produced by CuO-Fe 2 O 3 /CTS-ATP/H 2 O 2 system can be measured by a UV1900 type ultraviolet-visible spectrophotometer with ·OH spectrophotometry at λ of 510 nm.
The intermediate products of MB and CIP degraded by CuO-Fe 2 O 3 /CTS-ATP/H 2 O 2 system were determined by high performance liquid chromatography-mass spectrometry (HPLC-MS). Chromatography and mass spectrometry were performed by Agilent 1200 high performance liquid chromatography (Agilent, Santa Clara, CA, USA) and a 6130 quadruple mass spectrometer (Agilent, Santa Clara, CA, USA), respectively. The separation column is ZORBAX Eclipse Plus C18 (Analytical 4.6 mm × 150 mm 5-Micron). The operating conditions for the analysis of MB and CIP intermediate products were as follows: the mobile phase A was 0.2% formic acid high pure water, mobile phase B was acetonitrile, the temperature of separation column was 30 • C, the injection volume was 10 µL, the Electron Spray Ionization (ESI) in negative ion mode was adopted as the mass spectrometer detector, the capillary current was 5 nA, the flow rate of dry gas was 10 L/min, and the dry gas temperature was 350 • C.

Characterization of Samples
To investigate the crystalline structure and stability of ATP, Fe 2 O 3 /CTS-ATP and CuO-Fe 2 O 3 /CTS-ATP composites and powder X-ray diffraction patterns were recorded by an X-ray diffractometer. It can be seen from Figure 1a [41,42]. These indicate that the metal oxides are successfully loaded on the surface of CTS-ATP. The infrared spectrums of the samples were shown in Figure 1b  quadruple mass spectrometer (Agilent, Santa Clara, CA, USA), respectively. The separation column is ZORBAX Eclipse Plus C18 (Analytical 4.6 mm × 150 mm 5-Micron). The operating conditions for the analysis of MB and CIP intermediate products were as follows: the mobile phase A was 0.2% formic acid high pure water, mobile phase B was acetonitrile, the temperature of separation column was 30 °C, the injection volume was 10 μL, the Electron Spray Ionization (ESI) in negative ion mode was adopted as the mass spectrometer detector, the capillary current was 5 nA, the flow rate of dry gas was 10 L/min, and the dry gas temperature was 350 °C.

Characterization of Samples
To investigate the crystalline structure and stability of ATP, Fe2O3/CTS-ATP and CuO-Fe2O3/CTS-ATP composites and powder X-ray diffraction patterns were recorded by an X-ray diffractometer. It can be seen from Figure 1a that all samples showed diffraction peaks at 2θ of 8.5°, 19.5°, 27.8°, 34.7°, and 35.4°, corresponding to the diffraction peaks of attapulgite crystal structure, indicating that ATP's crystal structure was not damaged when CTS and metal oxides were introduced into ATP while the disorder degree of ATP crystal increased due to the changes of basal peaks. The diffraction peaks at 2θ of 24.2°, 33.2°, 40.9°, 49.6°, and 54.2° belong to Fe2O3 [41], and the diffraction peaks of 35.6°, 38.7°, 49.1°, 53.5°, 58.3°, and 65.9° are characteristic peaks of CuO [41,42]. These indicate that the metal oxides are successfully loaded on the surface of CTS-ATP. The infrared spectrums of the samples were shown in Figure 1b  To compare the structure and morphology characteristics of ATP, CTS-ATP, Fe2O3/CTS-ATP, and CuO-Fe2O3/CTS-ATP, scanning electron microscopy (SEM), Mapping, and EDS were used to observe and analyze the element content and distribution on the sample surface. The results are shown in Figure 2. Figure 2a-d are SEM images of the samples, which showed that ATP has rod crystal structure (a), and ATP was wrapped by CTS when ATP mixed with CTS (b), and further loading Fe2O3 or Fe2O3/CuO and calcined to form active sites and holes (c,d). The purpose of introducing CTS into ATP is to regulate the surface morphology of the catalyst and make the loaded active materials more uniform on support, which can be proved by the Mapping results of Figure 2e,f, showing that  showing that the loaded Fe or Fe/Cu on the surfaces of the catalysts are relatively uniform. Figure 2g-i are DES results of the samples, and, from Figure 2h,i, it is also clearly shown that Fe or Fe/Cu were successfully loaded on the catalysts.   Table 1 shows the specific surface area, pore volume, and pore size of ATP, Fe2O3/CTS-ATP and CuO-Fe2O3/CTS-ATP. The BET specific surface area and pore volume of Fe2O3/CTS-ATP (21.977 m 2 /g and 0.061 cm 3 /g) and CuO-Fe2O3/CTS-ATP (23.23 m 2 /g and 0.095 cm 3 /g) decreased dramatically compared to those of ATP (93.620 m 2 /g and 21.509 cm 3 /g) due to the wrapping of CTS on ATP, while the pore size of Fe2O3/CTS-ATP (11.013 nm) and CuO-Fe2O3/CTS-ATP (14.271 nm) increased greatly compared to that of ATP (0.227 nm), which meant that mesopores are formed on the surface of the catalyst during the roasting process [43].  Figure 3 is nitrogen adsorption and desorption (A-D) curves as well as pore size distribution diagrams of Fe2O3/CTS-ATP and CuO-Fe2O3/CTS-ATP. The A-D curves of the two samples belong to type III isotherms and H3 magnetic loop according to IUPAC classification, representing their mesoporous structure, which is in accordance with the characteristic result of SEM images. The attached pore size distribution diagrams showed that the two samples had the same pore size distribution, while CuO-Fe2O3/CTS-ATP had more pores with the size ranging from 50-100 nm, and the pore structure belongs to the slit pore.  Table 1 shows the specific surface area, pore volume, and pore size of ATP, Fe 2 O 3 /CTS-ATP and CuO-Fe 2 O 3 /CTS-ATP. The BET specific surface area and pore volume of Fe 2 O 3 /CTS-ATP (21.977 m 2 /g and 0.061 cm 3 /g) and CuO-Fe 2 O 3 /CTS-ATP (23.23 m 2 /g and 0.095 cm 3 /g) decreased dramatically compared to those of ATP (93.620 m 2 /g and 21.509 cm 3 /g) due to the wrapping of CTS on ATP, while the pore size of Fe 2 O 3 /CTS-ATP (11.013 nm) and CuO-Fe 2 O 3 /CTS-ATP (14.271 nm) increased greatly compared to that of ATP (0.227 nm), which meant that mesopores are formed on the surface of the catalyst during the roasting process [43].  Figure 3 is nitrogen adsorption and desorption (A-D) curves as well as pore size distribution diagrams of Fe 2 O 3 /CTS-ATP and CuO-Fe 2 O 3 /CTS-ATP. The A-D curves of the two samples belong to type III isotherms and H3 magnetic loop according to IUPAC classification, representing their mesoporous structure, which is in accordance with the characteristic result of SEM images. The attached pore size distribution diagrams showed that the two samples had the same pore size distribution, while CuO-Fe 2 O 3 /CTS-ATP had more pores with the size ranging from 50-100 nm, and the pore structure belongs to the slit pore.
In order to analyze the chemical state of various elements of the samples, XPS tests of the catalysts were performed. The total spectra and characteristic spectra of the elements are shown in Figure 4. The survey spectra of the samples confirmed that Fe and Cu were present in these two samples besides C, O, and Si, while the peaks of Fe and Cu were very weak due to the low loading deposition level (Figure 4a). In Figure 4b, the peaks at 284.8, 286.2, and 286.6 eV of the samples were C1s bonded to H, N, and O, which might be formed during the roasting of the samples. In Figure 4c, the peaks at 531 eV of the samples were relevant to O1s bonded to Fe, Cu, and Si, whereas the peaks at higher binding energy of 532.2 eV were ascribed to the presence of OH − group [44,45] on the catalysts' surface. High resolution XPS spectrum of Fe2p in Figure 4d   In order to analyze the chemical state of various elements of the samples, XPS tests of the catalysts were performed. The total spectra and characteristic spectra of the elements are shown in Figure 4. The survey spectra of the samples confirmed that Fe and Cu were present in these two samples besides C, O, and Si, while the peaks of Fe and Cu were very weak due to the low loading deposition level (Figure 4a). In Figure 4b, the peaks at 284.8, 286.2, and 286.6 eV of the samples were C1s bonded to H, N, and O, which might be formed during the roasting of the samples. In Figure 4c, the peaks at 531 eV of the samples were relevant to O1s bonded to Fe, Cu, and Si, whereas the peaks at higher binding energy of 532.2 eV were ascribed to the presence of OH − group [44,45] on the catalysts' surface. High resolution XPS spectrum of Fe2p in Figure 4d    In order to analyze the chemical state of various elements of the samples, XPS tests of the catalysts were performed. The total spectra and characteristic spectra of the elements are shown in Figure 4. The survey spectra of the samples confirmed that Fe and Cu were present in these two samples besides C, O, and Si, while the peaks of Fe and Cu were very weak due to the low loading deposition level (Figure 4a). In Figure 4b, the peaks at 284.8, 286.2, and 286.6 eV of the samples were C1s bonded to H, N, and O, which might be formed during the roasting of the samples. In Figure 4c, the peaks at 531 eV of the samples were relevant to O1s bonded to Fe, Cu, and Si, whereas the peaks at higher binding energy of 532.2 eV were ascribed to the presence of OH − group [44,45] on the catalysts' surface. High resolution XPS spectrum of Fe2p in Figure 4d Figure 5 shows the effects on the MB and CIP removal ratios in five different systems (only H2O2 existing, only Fe2O3/CTS-ATP or CuO-Fe2O3/CTS-ATP existing, Fe2O3/CTS-ATP/H2O2 system or CuO-Fe2O3/CTS-ATP/H2O2 system), respectively. From Figure 5a,b, it can be seen that MB can obtain higher removal ratios than CIP at the same conditions. This means that oxidation of MB is easier than that of CIP, and the structure of CIP is more stable than that of MB. When only hydrogen peroxide exists, MB and CIP can obtain about 40% removal ratios after 60 min reaction because H2O2 has a certain oxidation ability but not too much (Figure 5a,b). When only Fe2O3/CTS-ATP or CuO-Fe2O3/CTS-ATP exists in the system, MB and CIP removal ratios were 60% or 50% separately due to the adsorption of catalysts and O2 oxidation (Figure 5a,b). In the Fe2O3/CTS-ATP/H2O2 system, MB and CIP can obtain over 95% and 80% removal ratios after 60 min reaction because Fe2O3 catalyzed H2O2 to decompose ·OH, which had higher oxidation ability than O2 and H2O2, whether in acidic or alkaline conditions, as can be seen in Figure 5c. In the CuO-Fe2O3/CTS-ATP/H2O2 system, MB and CIP can obtain over 99% and 90% removal ratios after 60 min reaction, which were higher and faster than those in the Fe2O3/CTS-ATP/H2O2 system, which also can be seen from the catalytic reaction rate constant k (Figure 5a,b). The above results can be explained by Figure 5d. In the Fe2O3/CTS-ATP/H2O2 catalytic system, Fe(III) and Fe(II) formed a cycle during the process of catalyzing H2O2 to generate ·OH, while, in the CuO-Fe2O3/CTS-ATP/H2O2 catalytic system, Fe(III) and Fe(II), and Cu(I)   Figure 5a,b, it can be seen that MB can obtain higher removal ratios than CIP at the same conditions. This means that oxidation of MB is easier than that of CIP, and the structure of CIP is more stable than that of MB. When only hydrogen peroxide exists, MB and CIP can obtain about 40% removal ratios after 60 min reaction because H 2 O 2 has a certain oxidation ability but not too much (Figure 5a,b). When only Fe 2 O 3 /CTS-ATP or CuO-Fe 2 O 3 /CTS-ATP exists in the system, MB and CIP removal ratios were 60% or 50% separately due to the adsorption of catalysts and O 2 oxidation (Figure 5a,b). In the Fe 2 O 3 /CTS-ATP/H 2 O 2 system, MB and CIP can obtain over 95% and 80% removal ratios after 60 min reaction because Fe 2 O 3 catalyzed H 2 O 2 to decompose ·OH, which had higher oxidation ability than O 2 and H 2 O 2 , whether in acidic or alkaline conditions, as can be seen in Figure 5c. In the CuO-Fe 2 O 3 /CTS-ATP/H 2 O 2 system, MB and CIP can obtain over 99% and 90% removal ratios after 60 min reaction, which were higher and faster than those in the Fe 2 O 3 /CTS-ATP/H 2 O 2 system, which also can be seen from the catalytic reaction rate constant k (Figure 5a Figure S3, MB, and CIP, can obtain high removal ratios, and, with the temperature increasing, their removal ratios were increasing due to the boosting of ·OH radicals at a higher temperature and a faster catalysis to decompose H 2 O 2 . As can be seen from Figure S4, MB and CIP obtained the highest removal ratios at pH values of 2 attributed to a high redox potential of ·OH in an acidic condition. In addition, they all reached over 60% removal ratios under all experimental pH values. Figures S5 and S6 indicated that degradation ratios of MB and CIP ascended with increasing catalyst dosage and H 2 O 2 concentration, suggesting that the more catalysts and H 2 O 2 there are, the more active sites OH radicals there are, resulting in high removal efficiencies. However, too many catalysts and H 2 O 2 will lead to high costs, and too many H 2 O 2 will react with ·OH radicals and release oxygen. Recycle degradation experiments of MB and CIP by CuO-Fe 2 O 3 /CTS-ATP catalysts were performed five times to test their durability ( Figure S7). The catalyst was only washed by distilled water after every run, and the reaction conditions maintained the same in every run. After five runs, MB and CIP also can obtain 98% and 86% degradation ratios, separately. and Cu(II), formed a dual catalytic cycle to catalyze more H2O2 and generate more ·OH, which led to higher degradation ratios and faster degradation rates.  Figures S3-S7). From 40 to 80 °C, as shown in Figure S3, MB, and CIP, can obtain high removal ratios, and, with the temperature increasing, their removal ratios were increasing due to the boosting of ·OH radicals at a higher temperature and a faster catalysis to decompose H2O2.As can be seen from Figure S4, MB and CIP obtained the highest removal ratios at pH values of 2 attributed to a high redox potential of ·OH in an acidic condition. In addition, they all reached over 60% removal ratios under all experimental pH values. Figures S5 and S6 indicated that degradation ratios of MB and CIP ascended with increasing catalyst dosage and H2O2 concentration, suggesting that the more catalysts and H2O2 there are, the more active sites OH radicals there are, resulting in high removal efficiencies. However, too many catalysts and H2O2 will lead to high costs, and too many H2O2 will react with ·OH radicals and release oxygen. Recycle degradation experiments of MB and CIP by CuO-Fe2O3/CTS-ATP catalysts were performed five times to test their durability ( Figure S7). The catalyst was only washed by distilled water after every run, and the reaction conditions maintained the same in every run. After five runs, MB and CIP also can obtain 98% and 86% degradation ratios, separately.

OH Concentrations Measurement
·OH concentrations in two catalytic systems were also detected, and the results were shown in Figure 6. It can be seen that the concentration of ·OH in CuO-Fe 2 O 3 /CTS-ATP/H 2 O 2 system was more than that in the Fe 2 O 3 /CTS-ATP/H 2 O 2 system, and the production rate of ·OH in former system was also higher than that in the latter. The results confirmed that these two systems could produce enough ·OH to degrade ROS, and CuO could be a good assistant catalytic component to enhance the ·OH production rate dramatically, which was coincident with the degradation mechanisms in Figure 5d.
·OH concentrations in two catalytic systems were also detected, and the results were shown in Figure 6. It can be seen that the concentration of ·OH in CuO-Fe2O3/CTS-ATP/H2O2 system was more than that in the Fe2O3/CTS-ATP/H2O2 system, and the production rate of ·OH in former system was also higher than that in the latter. The results confirmed that these two systems could produce enough ·OH to degrade ROS, and CuO could be a good assistant catalytic component to enhance the ·OH production rate dramatically, which was coincident with the degradation mechanisms in Figure 5d.

The Pathways of MB and CIP Degradation by CuO-Fe2O3/CTS-ATP
As can be seen in Scheme 1a, attapulgite and chitosan combined via hydrogen bond; thus, a core-shell structure with attapulgite as the core and chitosan as the shell was formed. After calcination, chitosan was carbonized and formed a net structure to wrap attapulgite. When loading active components, iron oxide and copper oxide first formed an alloy [47][48][49] and then combined with the carrier (CTS-ATP) in the form of a covalent bond, in order to obtain an efficient surface catalytic system.
In order to explore the intermediate products of MB and CIP in CuO-Fe2O3/CTS-ATP/H2O2, HPLC-MS was used to analyze the degradation products of MB and CIP at reaction times of 30 and 60 min, respectively. The treated-water samples were filtered and then sent into the separation column through the autosampler. When MB solution was catalyzed for 30 min, the signal peak of MB (m/z = 284.19) at 14.6 min disappeared, and many small mass fragments appeared. The possible degradation path of MB molecule is shown in Scheme 1b, where the substance with m/z = 242.82 is the product after MB demethylation under the attacking of ·OH [50]; then, the -S-bond and -N= were broken, and MB was broken into two pieces. After a series of degradations, the main identified products were benzoquinone (m/z = 107, RT = 3.161 min), hydroquinone (m/z = 109, RT = 3.098 min), catechol (m/z = 109, RT = 3.308 min), and resorcinol (m/z = 109, RT 5.098 min).
The characteristic signal peak of the CIP was m/z = 332.20 at 2.9 min, and it disappeared completely after the 30 min degradation of CIP. According to the identity results of CIP intermediate products by HPLC-MS, the possible degradation path is shown in Scheme 1c. Under the attacking of ·OH, CIP lost its carboxyl (-COOH) firstly, and the piperazine ring in CIP molecule underwent oxidation and ring opening; then, it was totally removed. After losing -C3H5N [51], another nitrogen-containing heterocycle of CIP was also opened. The oxidation process continued, and the carbon chain containing

The Pathways of MB and CIP Degradation by CuO-Fe 2 O 3 /CTS-ATP
As can be seen in Scheme 1a, attapulgite and chitosan combined via hydrogen bond; thus, a core-shell structure with attapulgite as the core and chitosan as the shell was formed. After calcination, chitosan was carbonized and formed a net structure to wrap attapulgite. When loading active components, iron oxide and copper oxide first formed an alloy [47][48][49] and then combined with the carrier (CTS-ATP) in the form of a covalent bond, in order to obtain an efficient surface catalytic system.
In order to explore the intermediate products of MB and CIP in CuO-Fe 2 O 3 /CTS-ATP/H 2 O 2 , HPLC-MS was used to analyze the degradation products of MB and CIP at reaction times of 30 and 60 min, respectively. The treated-water samples were filtered and then sent into the separation column through the autosampler. When MB solution was catalyzed for 30 min, the signal peak of MB (m/z = 284.19) at 14.6 min disappeared, and many small mass fragments appeared. The possible degradation path of MB molecule is shown in Scheme 1b, where the substance with m/z = 242.82 is the product after MB demethylation under the attacking of ·OH [50]; then, the -S-bond and -N= were broken, and MB was broken into two pieces. After a series of degradations, the main identified products were benzoquinone (m/z = 107, RT = 3.161 min), hydroquinone (m/z = 109, RT = 3.098 min), catechol (m/z = 109, RT = 3.308 min), and resorcinol (m/z = 109, RT 5.098 min).
The characteristic signal peak of the CIP was m/z = 332.20 at 2.9 min, and it disappeared completely after the 30 min degradation of CIP. According to the identity results of CIP intermediate products by HPLC-MS, the possible degradation path is shown in Scheme 1c. Under the attacking of ·OH, CIP lost its carboxyl (-COOH) firstly, and the piperazine ring in CIP molecule underwent oxidation and ring opening; then, it was totally removed. After losing -C 3 H 5 N [51], another nitrogen-containing heterocycle of CIP was also opened. The oxidation process continued, and the carbon chain containing aldehyde and carboxylic acid on the benzene ring was broken to form fluorophenol. Finally, the benzene ring was opened. aldehyde and carboxylic acid on the benzene ring was broken to form fluorophenol. Finally, the benzene ring was opened.
Scheme 1. Formation of catalytic system (a) and possible degradation pathways of MB (b) and CIP (c) molecules by the CuO-Fe2O3/CTS-ATP/H2O2 system.

Conclusions
In this study, a heterogeneous catalyst with dual support components (CTS-ATP) and dual active components (Fe2O3-CuO) was prepared for the degradation of MB and CIP. The catalysts were characterized by XRD, FI-IR, SEM, BET, and XPS, which showed that both Fe2O3 and CuO were successfully loaded on the surface of the carrier, and CTS as a functional material wrapped ATP would make the loaded active components more uniform, which greatly improves the catalytic degradation performance of CuO-Fe2O3/CTS-ATP. The preparation conditions and degradation conditions were optimized. Under the optimal preparation and reaction conditions, the degradation ratios of MB and CIP can reach 99.29% and 86.20%, respectively. The new degradation mechanisms and possible pathways of MB and CIP were proposed. The authors believed that Fe2O3 and CuO first formed an alloy and then combined with the carrier (CTS-ATP) in the form of covalent bonds, in order to obtain an efficient surface catalytic system. Fe(III) and Fe(II) and Cu(I) and Cu(II) formed a dual catalytic cycle to catalyze more H2O2 and generate more ·OH, which led to higher degradation ratios and faster degradation rates.

Supplementary Materials: Page: 11
The following supporting information can be downloaded at: www.mdpi.com/xxx/s1, Figure S1: Influences of precursor concentration (during catalyst preparation) on MB (a) and CIP (b) removal.; Figure S2: Influences of ultrasonic impregnation time (during catalyst preparation) on MB (a) and CIP (b) removal.; Figure S3: Influences of reaction temperature on MB (a) and CIP (b) removal.;

Conclusions
In this study, a heterogeneous catalyst with dual support components (CTS-ATP) and dual active components (Fe 2 O 3 -CuO) was prepared for the degradation of MB and CIP. The catalysts were characterized by XRD, FI-IR, SEM, BET, and XPS, which showed that both Fe 2 O 3 and CuO were successfully loaded on the surface of the carrier, and CTS as a functional material wrapped ATP would make the loaded active components more uniform, which greatly improves the catalytic degradation performance of CuO-Fe 2 O 3 /CTS-ATP. The preparation conditions and degradation conditions were optimized. Under the optimal preparation and reaction conditions, the degradation ratios of MB and CIP can reach 99.29% and 86.20%, respectively. The new degradation mechanisms and possible pathways of MB and CIP were proposed. The authors believed that Fe 2 O 3 and CuO first formed an alloy and then combined with the carrier (CTS-ATP) in the form of covalent bonds, in order to obtain an efficient surface catalytic system. Fe(III) and Fe(II) and Cu(I) and Cu(II) formed a dual catalytic cycle to catalyze more H 2 O 2 and generate more ·OH, which led to higher degradation ratios and faster degradation rates.
Supplementary Materials: The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/coatings12050559/s1, Figure S1: Influences of precursor concentration (during catalyst preparation) on MB (a) and CIP (b) removal.; Figure S2: Influences of ultrasonic impregnation time (during catalyst preparation) on MB (a) and CIP (b) removal.; Figure  S3: Influences of reaction temperature on MB (a) and CIP (b) removal.; Figure S4

Conflicts of Interest:
The authors declare no conflict of interest.

Abbreviations
ATP attapulgite CTS chitosan ROS refractory organics MB methylene blue CIP ciprofloxacin