Synthesis And Application Of Copper Based Catalysts For Degradation Of Sulfadiazine Via Hydrogen Peroxide Activation

Sulfadiazine（SDZ）is frequently used as a typical sulfonamide antibiotic drug.Currently,SDZ residues have been detected widely in water environmental samples worldwide.Due to the biotoxicity and bioenrichment of SDZ,it is easy to cause the emergence of drug-resistant bacteria and the spread of drug-resistant genes.Therefore,the potential risks of SDZ to human health and ecological environment security have attracted high attention.Traditional water treatment process cannot effectively degrade SDZ,but the emerging Fenton oxidation technology based on copper catalyst has a better degradation effect on antibiotic drugs.Compared with traditional iron-based catalyst,copper-based catalyst has a higher Fenton reaction activity,wider p H adaptation range,and does not produce metal sludge.Therefore,the development of novel copper-based catalysts has become the focus of Fenton oxidation technology.However,copper-based catalysts are still faced with problems such as difficult regeneration of low-cost copper,low activation efficiency of hydrogen peroxide（H₂O₂）and large amount of metal dissolution.Aiming at the above problems,in order to further improve the performance of copper-based catalysts,three new copper-based catalysts,Cu₂ZnSnS₄（CZTS）,Fe₃O₄@CuS and Cu₂S@MoS₂,were prepared by adopting various strategies including crystal type control,bimetal co-catalysis and defect control.These three new catalysts were used to degrade SDZ in water via H₂O₂ activation.The physicochemical properties of the catalyst were characterized by a variety of characterization methods,and the efficiency of SDZ degradation was studied and the related catalytic mechanisms were proposed.Firstly,according to the crystal modulation strategy,two kinds of Cu-based catalysts with different crystal types were synthesized by hydrothermal method using ultra-pure water and ethylene glycol（EG）as solvent to obtain wurtzite crystal Cu₂ZnSnS₄（CZTS-W）and kesterite crystal Cu₂ZnSnS₄（CZTS-EG）,respectively.Scanning electron microscopy（SEM）and high resolution transmission electron microscopy（HRTEM）showed that CZTS-W presented spherical shape,while CZTS-EG presented the morphology of staggered distribution of nanorods and nanosheets.The N₂ adsorption-desorption（BET）proved that CZTS-W and CZTS-EG were mesoporous structures with specific surface areas of 104.37 and 172.53 m²/g,respectively.The tests of SDZ degradation showed that the degradation rates were up to 0.032min^-1（CZTS-W）and 0.030 min^-1（CZTS-EG）,respectively,which was better than that of Cu₂S prepared by hydrothermal method(0.004 min^-1).This was due to the high oxidation states of metal elements Zn（Ⅱ）and Sn（Ⅳ）in CZTS,which provided adsorption sites for·OOH and·OH.The results of regeneration cycle tests and X-ray diffractometry（XRD）suggested that CZTS-W had better reusability and stability.Quenching tests and electron paramagnetic resonance spectroscopy（ESR）proved that the active oxidizing species（ROS）,·OH,·O₂^-and ¹O₂,were produced in CZTS/H₂O₂ system,and·OH was dominant ROS.X-ray photoelectron spectroscopy（XPS）and catalytic mechanism analysis indicated that the low-valent sulfur in CZTS as electron donor promoted the redox cycle of Cu（Ⅱ）/Cu（Ⅰ）,thus enhanced the activation efficiency of H₂O₂.Secondly,according to a morphological regulation strategy,a magnetic Fe₃O₄@CuS composite catalyst with a typical core-shell structure was successfully synthesized by using ZIF-8 as the precursor template through simple methods of chemical etching and ion exchange.SEM and HRTEM characterization results revealed that Fe₃O₄@CuS retained the ZIF-8rhombic dodecahedron morphology,with Fe₃O₄ as the core and CuS as the shell.BET results demonstrated that Fe₃O₄@CuS had a typical microporous structure,and the specific surface area reached 777.20 m²/g,which is much higher than that of Fe₃O₄（78.67 m²/g）.At the same time,the hysteresis loop test（VSM）revealed that Fe₃O₄@CuS could be rapidly separated from water by magnetic adsorption due to the strong magnetic property.The catalytic degradation tests showed that the degradation rate of SDZ by Fe₃O₄@CuS/H₂O₂ system(0.055 min^-1)was much higher than that of Fe₃O₄/H₂O₂(0.002 min^-1)and（ZIF-8 derived CuS）ZD-CuS/H₂O₂(0.015 min^-1)system.Fe₃O₄@CuS also hold a good removal efficiency of SDZ≥88.2%in a wide p H range（3.0-9.0）and≥90.1%after five cycle tests.Quenching tests and ESR tests showed that three kinds of ROS,·OH,·O₂^-and ¹O₂,were generated in the catalytic system,and·OH was dominant.Mechanism analysis proved that the activation process of H₂O₂ mainly relied on the effect of the sulfur-enhanced Cu-based Fenton reaction center at the shell,sulfur-enhanced Fe-based Fenton reaction center at the core and the Cu-Fe synergy between the core and shell.Finally,using a defect control strategy,a series of Cu₂S@MoS₂-x nanocomposite catalysts with different ratios（x=1,2,3,4）of Cu and Mo were synthesized by a hydrothermal method which used Cu₂O as precursor templates.SEM,HRTEM and XRD characterization showed that Cu₂S@MoS₂ was composed of Cu₂S cubes and surface-staggered MoS₂ sheets.X-ray absorption spectroscopy（XAS）and ESR characterization clarified the formation of sulfur vacancies（Sv）in Cu₂S@MoS₂-2.The catalytic degradation tests of SDZ indicated that Cu₂S@MoS₂-2 with the ratio of Cu to Mo（x=2）had the strongest performance,and the reaction rate constant reached 0.2385 min^-1,which was much higher than that of single component Cu₂S(0.0622 min^-1)and MoS₂(0.0057 min^-1).The Cu²⁺leaching amount of Cu₂S@MoS₂-2 was only0.57 mg/L,which was much lower than that of Cu₂S（2.41 mg/L）and Cu₂O（3.97 mg/L）.Also,the removal efficiency of SDZ decreased by only 11.4 percentage points in Cu₂S@MoS₂-2/H₂O₂ system after five cycles,suggesting the strong stability of Cu₂S@MoS₂-2.Quenching tests and ESR tests showed that·OH and ¹O₂ were the main ROS to degrade SDZ in the system.By comparing the effects of different Sv contents and different dissolved oxygen（DO）concentrations on the removal of SDZ,it was determined that Sv and DO were important factors to affect the production of ¹O₂.Density functional theory（DFT）calculations demonstrated that Sv was the preferred adsorption site for O₂ and can excite O₂ to·O₂^-and ultimately transformed¹O₂.Combined with XPS characterization,the reaction mechanism of the system was proposed:（i）the sulfur-enhanced Cu-based Fenton reaction on the surface of Cu₂S mainly produced OH;（ii）the outer shell of MoS₂ sheets mainly catalyzed the decomposition of H₂O₂ to generate a large amount of O₂;（iii）Sv on the surface of Cu₂S was the primary adsorption site of O₂,and Sv as the defect strengthening center stimulated the conversion of O₂ into·O₂^-,and·O₂^-further generated to ¹O₂.In addition,liquid chromatography-mass spectrometry（LC-MS）was used to identify the degradation products of SDZ in the three catalytic systems,and the main degradation pathways of SDZ were proposed.The ecotoxicity of SDZ and its degradation products was calculated and evaluated by the ecotoxicity assessment software ECOSAR.The results showed that the general ecotoxicity of SDZ and its products could be effectively reduced after the catalytic reaction of the three systems.The biotoxicity of the three catalysts was evaluated by cytotoxicity tests.The results showed that CZTS-W and Fe₃O₄@CuS had good biocompatibility,while Cu₂S@MoS₂-2 needed to control the dosage under 50 mg/L for safety.