Fabrication Of TiO₂ Photocatalytic Membranes With Multifunction And Their Performance For Water Treatment

Membrane separation technology has been attractively employed for water and wastewater treatment.However,the drawbacks of membrane single function as well as its fouling have been the main obstacles for extended application.On the other hand,TiO₂ photocatalysis is regarded as an efficient and environmental benign technology,and has been widely used for photodegradation of various pollutants and inactivation of diverse bacteria in aquatic environments.Over the past decades,intensive investigations have been devoted to developing and improving the photocatalytic activity of TiO₂-based photocatalysts.However, the issue concerning on its recycle and reuse is an inherent and significant drawback. TiO₂-based photocatalytic membranes are proposed to provide a possible and beneficial solution to these problems because it provides unique multifunction of membrane separation and photocatalytic degradation concurrently.A sol-gel method followed by dip-coating and calcination was used to fabricated two types of TiO₂ based photocatalytic membrane,Si-doped TiO₂/Al₂O₃ tubular composite membrane for ultrafiltration(UF) and Ag-TiO₂/HAP(hydroxyapatite,Ca₁₀(PO₄)₆(OH)₂)/Al₂O₃ flat composite membrane for microfiltration(MF) in the application of water treatment.Si-doped TiO₂/Al₂O₃ composite membrane,with Si-doped TiO₂ top layer and controllable thickness,possesses nanoporous membrane structure for separation,pure anatase TiO₂ phase with large membrane surface area and small crystalline size(8.0 nm) for photocatalytic degradation,and super-hydrophilicity for improving membrane flux.The controllable preparation could be realized by repeated-coating procedure.The evaluation of effectiveness of membrane separation concurrent photocatalysis was obsearved by the treatment of dye solution Reactive Red ED-2B.A significantly synergetic effect under UV irradiation was observed at pH 7.0 by membrane separation concurrent photocatalytic degradation.The permeate flux of concurrent process was evidently higher than that of membrane separation alone,which suggested the anti-fouling ability of as-prepared membrane.At pH 2.4,the removal efficiency of this multifunctional membrane for reactive dye solution was approximately 77.3%under UV irradiation,while the removal efficiency of single membrane separation was only 27.5%.The treatment of E.coli suspension showed that approximately 4 log units of E.coli strain was removed by membrane separation concurrent photocatalytic degradation,which was 1 log unit over membrane separation alone.The attempt of this concurrent system coupling other advanced oxidation processes(AOPs) was carried out by removal of Reactive Red 141.As the amount of hydrogen peroxide was 1.25 mM,both the effectiveness and the permeat flux of concurrent system were improved evidently.Ag-TiO₂/HAP/Al₂O₃ flat composite membrane,fabricated Ag-TiO₂/HAP composite layer with a thickness of 10μm overlaid on Al₂O₃ support,with microporous structure and a superior ability of promoted interfacial charge-transfer reactions realized the enhancement of photocatalytic activity and improvement of permeate flux.In this membrane system,HAP acted as a high efficient bio-adsorbent and effective rejection on macromolecules,and Ag-TiO₂ provided powerful decomposition on organic pollutants and destruction on pathogenic agents.Under UV irradiation,the removal efficiencies for TOC of the humic acid (HA) solution and E.coli suspension were approximately 3.4 times and 3 Log units improvement than that of membrane separation alone,respectively.Meanwhile,the flat composite membrane also showed anti-fouling ability during the processes of water treatment for both HA solution and E.coli suspension.The characteristics and behavior of membrane fouling during the treatment of HA solution were analyzed.Anti-fouling ability of membrane by filtration concurrent photocatalysis is mainly due to photocatalytic degradation of foulants by UV irradiation.Compared with in dark,the transition in fouling mode from initial pore blocking to cake filtration occurs much slower by UV irradiation on membrane surface. Enhanced anti-fouling property in certain extent could be obtained by increase the UV light intensity or decrease TMP.Oure results also showed that the fouling rate is obviously greater in membrane filtration as the leading process than photocatalysis in concurrent processes.According to these results,TiO₂ photocatalytic membranes,being proven of ingenious architecture,as well as multifunction of photocatalysis and separation,are believed as promising membrane products for water purification in the future.