Preparation Of TiO₂ Photocatalytic Composite Membranes And Their Performance For Water Treatment Under Assistance Of UV And H₂O₂

As a green,effective,and easy-operated technology,membrane separation technology has been widely employed in various processes including wastewater treatment,desalination and drinking water purification,showing great application prospect.However,the major separation mechanism of conventional membrane separation technology is size exclusion,in which contaminants with size smaller than membrane pore size can not be rejected.Besides,pollutants existing on the membrane surface or in the pores can lead to the membrane fouling,which will cause the flux loss.Membrane regeneration offers a possible solution to alleviate the fouling,but results in the increased cost and process complexity.Coupling membrane separation and photocatalysis provides a prospective way to solve the aforementioned problems.Nevertheless,the photocatalytic membrane still confronts unsatisfied water treatment efficiency due to the negative impact of influent water for light transmittance,insufficient active species,limited retention time of contaminants on the membrane and the recombination of photo-induced electron-hole pairs.To address these problems,multiple processes including adding H2O2 into the photocatalytic membrane system,constructing the heterojunction structure and utilizing the carbon nanomaterials was introduced to the photocatalytic membrane system to enhance the water treatment ability.The main research contents are shown as follows:?1?By adding H₂O₂ to the photocatalytic membrane process,multipaths are involved to produce the active species.What's more,the UV/H₂O₂ process favors for the decrease of influent water influence.In this study,the photocatalytic TiO₂ nanofiber membrane?NFM?with UV response was prepared through vacuum-filtration and dip-coating methods.Profiting from the network structure,the nanofiber membrane bestows the high porosity,large surface area and high pure water flux.The TiO₂ NFM has an average pore size of 392 nm,which is recognized as the microfiltration membrane.Phenol as its size smaller than membrane pore size was selected as target pollution to evaluate the water treatment ability of TiO₂ NFM.Results show that phenol has 3.0%removal efficiency by membrane separation.After adding H₂O₂ of5.3 mM,the phenol removal efficiency of photocatalytic membrane process is up to 89.4%,which is 30.0,2.0 and 1.6 times higher than that of membrane,photocatalytic membrane and ceramic membrane?with no photocatalytic ability?with the UV/H₂O₂ processes,respectively.Meanwhile,almost no flux loss is observed of TiO₂ NFM with UV and H₂O₂ in the presence of nature organic matters?NOM?and its flux is 1.8 and 1.4 times higher than that of membrane and photocatalytic membrane processes,respectively?after running for 60 min?.Results above suggest that photocatalytic TiO₂ NFM possesses enhanced contaminants removal efficiency and antifouling capacity in the presence of H₂O₂.?2?A TiO₂/CNTs hollow fiber membrane?HFM?was prepared.The composite of CNTs and TiO₂ can construct the heterojunction structure to inhibit the recombination of photo-induced electron-hole pairs.Furthermore,the unique adsorption ability of CNTs is able to prolong the retention time of pollutants on the membrane,which is beneficial for improving the water treatment efficiency of photocatalytic membrane with H₂O₂.In this work,a CNTs HFM was prepared through the wet-spinning method and TiO₂ was coated on CNTs HFM through the heterogeneous nucleation process.The attracting pore structure formed by interweaved nanotubes endows the TiO₂/CNTs HFM with high porosity and flux.Under the assistance of UV and H₂O₂,the phenol removal efficiency of TiO₂/CNTs HFM is up to 59.2%.Nevertheless,almost no removal is observed?after running for 120 min?in other processes including membrane,photocatalytic membrane and membrane with H₂O₂.Separation test process shows the flux of TiO₂/CNTs photocatalytic membrane with H₂O₂ is 2.5-fold,1.3-fold and 1.7-fold higher than that of the membrane,photocatalytic membrane and membrane with H₂O₂processes,respectively?after running for 120 min?.All of the results above reveal that in the presence of UV and H₂O₂,the TiO₂/CNTs HFM presents enhanced ability for phenol removal and fouling mitigation.To sum up,the UV/H₂O₂ assisted photocatalytic membrane system has been successfully proposed.The addition of H₂O₂ can remarkably enhance the performance of photocatalytic membrane for separation efficiency and fouling mitigation.Such fascinating results provide a theoretical basis for extending membrane application in water treatment.