| With the rapid development of economy and industry,the shortage of fresh water resources and the continuous deterioration of water ecological environment have become a worldwide problem.In order to eliminate the adverse effects of water pollution,various sewage treatment technologies have been developed to improve the performance of water treatment at this stage,such as adsorption,sedimentation,coagulation/flocculation and membrane separation.Among them,ultrafiltration technology plays a vital role in water treatment owing to its excellent interception performance.However,due to the blockage of pollutants in the membrane pores and the continuous deposition on the membrane surface during the filtration process,membrane fouling problem will be caused,and its removal efficiency and service life will also be affected.The problem of membrane fouling seriously hinders the wide promotion of ultrafiltration technology in water treatment.At present,membrane modification technologies have been applied to improve the anti-fouling performance and reduce the negative impact of membrane fouling during the filtration process.Common membrane modification technologies include surface coating,chemical grafting and radiation grafting.However,in these modification methods,the modification materials are usually easy to fall off,and the performance of the modified membranes can not be guaranteed.In contrast,many research works have designed and prepared composite membranes by blending modification materials.The composite membranes can be fabricated by blending the modification materials with membrane material to form the casting solution.The results showed that the composite membranes prepared by blending modification materials could effectively prevent membrane fouling.Photocatalysis technology is one kind of advanced oxidation technologies for efficient removal of pollutants based on the oxidation-reduction ability of photocatalyst under light irradiation in recent years.Compared with other advanced oxidation technologies,photocatalysis technology is more environmentally friendly and the operation process is simpler.Using photocatalyst as membrane modification material can not only endow the membrane with photocatalytic ability,make it produce ROS radicals to oxidize and degrade the pollutants attached and adsorbed in the membrane structure during the process of filtration,the loading of photocatalyst in the membrane structure can also effectively solve the problem of catalyst recovery.At the same time,in the photocatalytic materials system,the functional materials with synergistic photothermal conversion and photocatalytic activity are favored by the majority of researchers.blending the photocatalyst with excellent photothermal response into the membrane and constructing the photocatalytic-photothermal membrane separation system can endow the composite membrane with new functional characteristics on the premise of ensuring the anti pollution performance.In addition,although various photocatalytic membranes have been widely developed,it is necessary to systematically study the photocatalytic antifouling mechanism and self-cleaning effect.At present,most of the work mainly focuses on reducing membrane pollution by considering the size change of membrane and the adhesion between pollutants and membrane.However,during the process of membrane separation,the interaction mechanism between pollutant components affected by photocatalytic effect and filter membrane has not been explored.In order to widely apply photocatalytic technology to membrane separation technology as soon as possible,it is very necessary to explore its anti-fouling mechanism.Therefore,in this work,the synergistic photocatalysis-membrane separation system and photothermal-photocatalysis-membrane separation system are designed to effectively control the occurrence of membrane fouling.At the same time,the mechanism of anti-fouling performance by photocatalysis is deeply explored,as follows:（1）Ag@Bi OBr/PVDF photocatalytic membrane with remarkable anti-fouling property for BSA filtrationThe composite Ag@Bi OBr/PVDF ultrafiltration membrane was successfully prepared,Ag@Bi OBr photocatalyst was prepared by alcoholothermal method and photoreduction method,and Ag@Bi OBr nanoparticles were uniformly dispersed in PVDF casting solution,the casting solution was scraped into the composite membrane by phase conversion method.The Ag@Bi OBr/PVDF composite membrane achieved a larger water flux and higher BSA rejection efficiency than pristine PVDF membrane.The anti-fouling and self-cleaning performances were dominated by·OH radicals,which led to the change of protein structure and molecule,and the adhesive forces between foulants and membranes were also weakened under simulated visible-light irradiation.This work has provided experimental feasibility and theoretical support for enhancing anti-fouling performances of membranes by photocatalysis.（2）Study on Pd Cu-Ti O2/PVDF photothermal-photocatalytic-membrane separation system for enhancing membrane permeability and anti-fouling performanceBy combining the traditional pressure-driven photocatalytic membrane separation with the solar thermal technology based on photothermal membrane,a photocatalytic-photothermal membrane separation system was developed for efficient water treatment.Pd Cu-Ti O2photocatalyst was prepared by hydrothermal method.The loading of Pd Cu alloy nanoparticles achieved excellent photocatalytic and photothermal properties under full band light illumination.The prepared Pd Cu-Ti O2 nanoparticles were evenly dispersed in PVDF membrane casting solution,the surface and pore channel of composite membrane were uniformly loaded with Pd Cu-Ti O2 photocatalyst.Humic acid was selected as the target pollutant solution,Pd Cu-Ti O2/PVDF composite membrane showed excellent membrane separation performance and anti-fouling performance under light irradiation.In addition,Pd Cu-Ti O2 photocatalyst has excellent light capture and photothermal conversion performance.The Pd Cu-Ti O2/PVDF composite membrane with photothermal response can effectively in situ heat the feed filtration solution and improve the water flux.More importantly,during the permeation process,the permeate could be partially vaporized due to the local heating of Pd Cu-Ti O2 photocatalyst,realizing a collaborative system similar to membrane distillation.The vapor-liquid mixed transmission of the composite membrane permeation channel can further improve the overall permeability of the membrane.At the same time,the photothermal effect also promotes the anti-fouling performance and further improves the overall separation efficiency of the composite membrane. |
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