Preparation Of G-C₃N₄/CNTs/Al₂O₃ Photoelectrocatalytic Membrane And Its Performance For Water Treatment Under Visible Light Irradiation

Membrane filtration is widely applied in wastewater treatment fields,because of its low energy cost,no chemical addition and easy operational control.However,membranes usually separate contaminants via size-exclusion,which causes two major obstacles:one is membrane fouling caused by concentration polarization and pore blocking;the other is the contaminants can't be decomposed and easily cause secondary pollution.Coupling membrane filtration with photocatalysis provides a promising way to improve the membrane performance for water treatment.However,the quick recombination of photogenerated electron-holes and poor visible light response in photocatalytic layer limit its practical application.Herein,a g-C₃N₄/CNTs/Al₂O₃ photoelectrocatalytic membrane was prepared through sequentially coating carbon nanotubes?CNTs?layer with good electroconductivity and g-C₃N₄ layer with visible-light response on the Al₂O₃ support.Phenol,natural organic,E.coli and surface water were selected as the target pollutants to investigate the performance of g-C₃N₄/CNTs/Al₂O₃ membrane.The photoelectrocatalytic membrane filtration process?PECM?showed increasing pollutant removal with the increase of the voltage supply.At 1.0 V,the phenol removal of PECM was 2.7 times and 10.1 times higher than that of photocatalytic membrane filtration process and membrane filtration alone,respectively.The PECM process also presented improved antifouling capability during the removal of natural organic matters.The stable permeate flux of PECM was 1.4 and 2.5 times higher than that of PCM and membrane filtration alone,respectively.The PECM process also has good performance on removing E.coli.The E.coil was completely removed after 10 min and the stable flux of membrane was 1.9 times and 1.2 times as much as that of membrane filtration alone and PCM process.Additionally,the PECM process displays better water treatment performance and antifouling capability than that of photocatalytic membrane or membrane filtration process in surface water treatment.For better understanding the high performance of g-C₃N₄/CNTs/Al₂O₃ PECM process induced by the assistance of voltage supply,the mechanism of this integrated process was analyzed.Photogenerated electron-holes generates in the g-C₃N₄ layer under the irradiation of visible light.Once the positive voltage is applied on the electro-conductive CNTs layer,the photogenerated electrons could be drained from the photocatalytic layer to the CNTs layer,and continuously flows to the cathode?titanium mesh?via external circuit.This process effectively separates photogenerated electron-holes and inhibits their recombination.Meanwhile,the holes retained on the photocatalytic layer could directly oxidize the pollutants/foulants into CO2 and H2O,or it may react with water to produce the strong oxidants such as hydroxyl radical?·OH?for pollutants mineralization.Thanks to the effective separation of photogenerated electron-holes,the PECM process is able to take full advantage of the photogenerated holes for pollutants degradation,thus resulting in the enhanced pollutants removal efficiency as well as membrane fouling resistance.