Preparation Of Functional Titanium Dioxide Based Photocatalytic Composite Membranes And Performance Study Of Photocatalytic Degradation Of Tetracycline

Tetracycline（TC）,a broad-spectrum antibiotic typically used to treat bacterial infectious diseases,has been commonly used in medical,livestock and poultryand,aquaculture industries,but overuse into the environment will lead to the production of drug-resistant bacteria and drug-resistant genes,seriously endangering human health and the balance of water ecosystems.Semiconductor photocatalysis has been successfully applied to the treatment of organic pollutants in wastewater as an efficient,safe and environmentally friendly water purification technology.However,the difficulty of recycling traditional powder-based semiconductor photocatalysts has limited its further development.Photocatalytic composite membranes are the result of exploration and innovation in wastewater treatment technology,which combines membrane separation technology and photocatalysis technology to achieve photocatalytic degradation of organic pollutants in wastewater,while solving the problems of difficult recovery of photocatalysts and easy contamination of membranes.Phase inversion technique is the most common method for preparing photocatalytic composite membranes,which is simple and convenient,but also has its drawbacks,such as the photocatalytic active component is easily embedded during the blending process with the casting solution,thus reducing the photocatalytic performance.Therefore,the traditional phase inversion technique needs to be improved to increase the effective photocatalytic active sites and improve the utilization of light energy.In this paper,TiO₂ photocatalysts were modified with Bi₃O₄Cl,Fe₃O₄ and ZnCdS/rGO to address the shortcomings of TiO₂ wide bandgap and photogenerated carriers that tend to compound.Polyvinylidene fluoride（PVDF）was used as the membrane matrix,in addition to the traditional phase inversion method,with the help of magnetic field induced force and the construction of freezing penetration type macroporous structure photocatalytic membrane to solve the above-mentioned defects.The crystal structure,chemical composition and morphological characteristics of the photocatalysts and composite membranes were analysed by modern analytical and testing techniques.The photocatalytic activity,membrane flux and fouling resistance of various membranes were tested,and the photocatalytic mechanism of degrading TC was further explored.The main research contents are as follows:1.TiO₂/Bi₃O₄Cl/PVDF（TB/PVDF）photocatalytic composite membranes were successfully prepared by a simple phase inversion method.Among them,the Z-scheme2D/2D TiO₂/Bi₃O₄Cl heterojunction synthesized by the solid-phase calcination method improves the separation efficiency of photogenerated charges and has good photocatalytic activity under visible light irradiation.When the doping amount of TiO₂/Bi₃O₄Cl was 1.5%,the photocatalytic degradation efficiency of the TB/PVDF membrane for TC was as high as 83.02%.Compared to pure PVDF membranes,TB/PVDF photocatalytic composite membranes have higher porosity（85.19%）,pure water flux(283.01 L m^-2 h^-1 bar^-1)and eccellent anti-fouling properties.In addition,the TB/PVDF membranes showed good stability after five cycles.2.Magnetic Fe₃O₄@TiO₂/PVDF（FTM（Y））photocatalytic composite membranes were successfully prepared by magnetically induced phase inversion method.Among them,Fe³⁺acts as an electron capture centre to improve the charge separation,and the impurity energy level formed broadens the photoresponse range.Compared with the pure PVDF membrane and the non-magnetically induced FTM（N）photocatalytic composite membrane,the degradation efficiency of FTM（Y）for TC was as high as79.63%.In particular,after magnetic induction,FTM（Y）forms porous and macroporous structures and exhibits excellent fouling resistance.FTM（Y）has the higher retention（80.44%）and lower static adsorption（6.24%）of BSA,and the water contact angle of FTM（Y）was reduced from 111.0°to 93.3°,and the pure water flux was significantly increased to 2255.03 L m^-2 h^-1 bar^-1.3.Z-scheme TiO₂/rGO/ZnCd S/PVDF photocatalytic composite membranes（T-rGO-ZCSM）were successfully prepared by the freezing phase inversion method.Among them,the composite of ZnCd S/rGO and TiO₂ was constructed into a Z-scheme heterojunction to improve the visible light utilization and the separation efficiency of photogenerated charges.Compared with the unfreezing nf-PVDF and nf-T-rGO-ZCSM,the T-rGO-ZCSM exhibited a micron-scale ordered penetration macroporous structure with an average pore size of 0.9099μm,which largely improved the pure water flux of T-rGO-ZCSM(19000-25000 L m^-2 h^-1 bar^-1).Meanwhile,this structure promotes the absorption of visible light and increases the effective contact of the active site with the contaminant.T-rGO-ZCSM showed superior photocatalytic activity for the removal of tetracycline（TC）,levofloxacin（LEV）and ciprofloxacin（CIP）under visible light.After four cycles of experiments,T-rGO-ZCSM showed good stability and reusability.The highest TC degradation efficiency of 87.46%was achieved by T-rGO-ZCSM under continuous 6.0 h of solar irradiation.Besides,T-rGO-ZCSM has a good anti-fouling ability against BSA.