Synergistic Catalysis Of Photochemistry,Electrochemistry And Enzyme For Degradation Of PPCPs In The Environment

Photoelectrocatalysis?PEC?and electroenzymatic catalysis?EEC?are two important techniques for degradation of refractory organic compounds.However,previous research mainly focused on oxidation or reduction process on one electrode,and another electrode in the system is barely studied or utilized.Therefore,it is of great value to explore the PEC-EEC coupled system,which can make full use of the anodic and cathodic reactions to realize the effective utilization of photogenerated electrons and holes and then increase the active species of the reaction system,thereby improving the degradation effect.PEC plays a major role in the coupled system,and the selection and preparation of semiconductor materials directly affect the PEC process.In this thesis,different semiconductors were prepared by liquid phase deposition,electrodeposition,dropping coating and layer-by-layer adsorption,and then they were characterized and analyzed by various techniques for construction of PEC system.At the same time,the EEC system was constructed by hemin-graphene hybrids,where hemin was served as mimic enzyme.Based on these two systems,PEC-EEC coupled system was established.Finally,the decolorization of dyes and degradation of drugs were explored in three different systems,and the pathways were elucidated after the intermediate products were separated and analyzed by liquid chromatography-mass spectrometry?LC-MS?.The main research work is as follows:?1?A p-n heterojunction film of Cu₂O/?-Fe₂O₃ was constructed by electrodepositing p-type Cu₂O microcubes on liquid phase deposited film of n-type?-Fe₂O₃.The surface morphology,the crystal phase and composition of Cu₂O/?-Fe₂O₃ heterojunction film were characterized by scanning electron microscopy?SEM?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?.The enhanced absorption in the visible light region was observed in UV-visible diffuse reflectance spectra?DRS?.Meanwhile,an efficiently improved separation and faster transfer of photogenerated electrons and holes were revealed by photoluminescence spectra and electrochemical impedance spectra?EIS?.The Cu₂O/?-Fe₂O₃ p-n heterojunction was applied to photoelectrocatalytic degradation of oxytetracycline at a bias potential of+0.5 V under visible light illumination.After 60-min photoelectrocatalytic treatment,73.3%of oxytetracycline was removed and the degradation rate constant reached 2.14?10^-2 min^-1.Moreover,the crystal phases and compositions for the used and fresh Cu₂O/?-Fe₂O₃ films were studied,and a possible photoelectrocatalytic mechanism was proposed.?2?Based on the peroxidase-like activity of hemin and unique physicochemical property of graphene,a novel electroenzymatic system was developed for degradation of diclofenac.The prepared graphene-hemin hybrid materials were characterized by Fourier transform infrared?FT-IR?spectroscopy and SEM,and then they were immobilized on the surface of graphite electrode and studied by EIS.In the electroenzymatic process,H₂O₂ was generated from the electroreduction of oxygen through aeration to the electrolytic solution,which could oxidize and degrade orga nic compounds under the catalysis of hemin.Under the optimal bias potential of-0.4 V,the decoloration of dyes demonstrated that graphene can effectively promote the efficiency of such an electroenzymatic process.Using the graphene-hemin integrated electroenzymatic system,more than 96%of diclofenac could be removed after 11-h treatment.According to LC-MS analysis,the pathway for electroenzymatic degradation of diclofenac was proposed.?3?By combing PEC and EEC?PEC-EEC?,a novel system for efficient removal of chloramphenicol?CAP?driven by visible light was developed.This coupling system was constructed by a CdS/WO₃/FTO photoanode and a hemin-graphene immobilized cathode.The photoanode was fabricated by layer-by-layer assembly of CdS quantum dots on WO₃/FTO to provide high visible light catalytic activity.In order to achieve the EEC process,graphite cathode was modified with hemin-graphene composite,in which hemin served as the mimic enzyme.When CdS/WO₃/FTO anode was irradiated under visible light,photogenerated holes participated in the formation of hydroxyl radicals while photogenerated electrons were driven to the cathode by bias potential for the reduction of oxygen into H₂O₂.Thus,organic pollutant could be degraded by the oxidation reactions with either the hydroxyl radicals or the H₂O₂ under the catalysis of hemin.The visible light-driven PEC-EEC system was applied to the removal of CAP under visible light illumination at a bias potential of+1.0 V,degradation percentage reached 98.7%after10-h treatment.The intermediates formed during the degradation process were analyzed by LC-MS,and a degradation pathway for CAP in such a PEC-EEC system was proposed.?4?When PEC was coupled with EEC,H₂O₂,which was produced by effective utilization of electrons during PEC process,played an important role in the enzymatic catalysis.As the yield of H₂O₂ depended on the cathode material,a dual-cathode PEC-EEC system for pollutant removal was designed.In this system,BiVO₄ photoanode was prepared by electrodeposition for visible light-driven PEC process while carbon cloth was used as the first cathode for electrogeneration of H₂O₂ and hemin/Cu prepared by electrophoretic deposition acted as the second cathode for enzymatic catalysis.The performances of the constructed dual-cathode PEC-EEC system were evaluated by decoloring Rhodamine B?RhB?under visible light illumination at a bias potential of+0.8 V,which showed high decoloration percentage with acceptable stability and reusability.Further,the system was applied to degradation of tetracycline?TC?and about93.6%of TC was removed after 2-h treatment.A degradation pathway for TC in such a dual-cathode PEC-EEC system was proposed based on the intermediates determined by LC-ESI-MS/MS.