Construction Of Functionalized Titanium Dioxide Membranes And Their Application In Visible Light Photocatalysis

Photocatalytic membranes(PMs)are advanced materials capable of photocatalysis and membrane separation,which have been widely used in environment remediation due to advantages of easy separation,non-pollution,and sustainability.Titanium dioxide(TiO₂)has become one of the best candidates for constructing PMs due to its non-toxic,cheap,environmentally friendly and outstanding photocatalytic ability.However,there are still challenges that limit the practical application of TiO₂-based PMs:1)low light utilization rate and unsatisfactory photocatalytic activity under visible light;2)Poor ability in anti-fouling and self-cleaning makes it hardly be used in complex practical environment.The functionalization of TiO₂-based PMs is one of the effective methods to tackle above challenges.The key point of this dissertation is the functionalization of TiO₂-based PMs and the design of hierarchical porous structure.The functionalization of TiO₂-based PMs is dedicated to improving the range and intensity of visible light response,endowing TiO₂ with vis-responsive photocatalytic activity.Membranes with hierarchical porous structure possess the advantages of high utilization and more active sites,showing greater potential for self-cleaning than those films with flat and smooth surface.Hence,based on the combination of electrospinning membrane and other approaches like sol-gel method,hydrothermal process,in situ polymerization and so on,a series of functionalized TiO₂-based PMs was constructed and employed to remove tetracycline(TC)and achieve self-cleaning property under visible light.The research content of this dissertation includes the following five parts:1.Construction of carbon-doped TiO₂ nanotube membrane and its application research in visible light photocatalysisBased on the electrospinning technology,an in situ strategy was proposed for the construction of carbon doped TiO₂ nanotube membrane(C-TiO₂)using surface-sulfonated polystyrene(SSPS)fibers/titania composite as the precursors of TiO₂ and carbon source via a facile route of calcination.This technique involves the preparation of morphology well controlled PS fibers,sulfonation of PS fibers,sol-gel synthetic process of TiO₂ and the pyrolysis of SSPS fibers.All results confirmed the carbon doping in the as-prepared C-TiO₂.As a result of the enhanced ability in visible light absorption and charge separation,this composite achieved complete degradation of TC within 150 min UV irradiation with kinetic constant(k)of 0.02410 min-1,which was 2.64 times than that of pure TiO₂.The as-prepared membrane was also capable of degrading 93.1%of TC within 210 min visible light with k of 0.01247 min-1,indicating great potential for dealing with organics.2.Construction of seaweed-like porous g-C3N4/m-TiO₂ heterojunction membrane and its application research in visible light photocatalysisBased on the electrospinning technology,a vapor-assisted in situ polymerization strategy was proposed for the controllable loading of porous g-C3N4(PCN)on mesoporous TiO₂ nanofibrous membrane(m-TiO₂).Morphology and structure analysis confirmed the uniform loading of seaweed-like PCN on m-TiO₂,improving porous property and the ability of visible light absorption and charge separation.After optimizing PCN loading content,the as-prepared membrane exhibited highly enhanced vis-responsive activity,which achieved complete degradation of TC within 150 min visible light(k=0.02126 min-1).In dynamic and complex photocatalysis-separation system,the efficient removal of TC was also realized(k=0.01388 min-1).The self-cleaning ability indicated the promising potential in practical application.3.Construction of 2D/2D covalent triazine framework@TiO₂ heterojunction membrane and its application research in visible light photocatalysis and anti-foulingBased on the electrospinning technology,an initiator vapor-induced in situ polymerization was proposed to realize the controllable loading of covalent triazine frameworks(CTFs)by using TiO₂ nanosheet membrane as a confined environment.Morphology and structure characterization showed that the homogeneous loading of CTFs on TiO₂ nanosheets enhanced specific surface area and pore volume.After optimizing the loading content of CTFs,the as-prepared membrane exhibited highly enhanced ability in visible light absorption and charge transfer due to unique 2D/2D face-to-face heterojunction.The complete degradation of TC was achieved with 90 min irradiation of visible light(k=0.03420 min-1).This heterojunction membrane was also capable of removing TC in dynamic and complex pollutant system(k=0.01840 min-1).Due to the unique hierarchical porous structure and hydrophilic characteristics,the as-constructed membrane showed excellent performance in anti-fouling and self-cleaning,reflecting promising future in practical application.4.Construction of Ti3+-doped TiO₂ phase junction membrane and its application research in visible light photocatalysis and emulsion separationBased on the electrospinning technology,a F--mediated hydrothermal process and low-temperature vacuum activation was designed to construct anatase/rutile TiO₂ phase junction membrane with stable Ti3+ and oxygen vacancy active sites.Morphology and structure characterization confirmed that TiO₂ nanorods with a diameter of about 150 nm grew uniformly on the fiber trunk,forming a dense and interweaved tree-like structure.XPS and EPR results indicated that active sites of Ti3+and oxygen vacancy were located in the hollow mesopores existed in the bulk of nanorods.This unique structure prevented Ti3+from oxidation and loss of activity.In the optimized state,the as-constructed membrane possessed enhanced ability in visible light absorption and charge transfer.95.9%of TC was degraded with 100 min irradiation of visible light(k=0.02917 min-1),and the membrane could still maintain high removal efficiency in dynamic and complex system(k=0.01971 min-1).Due to the dense and interweaved tree-like structure and super-hydrophilicity,this membrane was also capable of efficient emulsion separation,showing strong capacity in treating oily organic wastewater.5.Construction of ?-cyclodextrin/Ag-doped TiO₂ membrane and its research application in visible light photocatalysis and dynamic adsorptionBased on the electrospinning technology,a UV-assisted electrospinning process and low-temperature hydrothermal reaction was rationally designed to construct?-cyclodextrin/Ag-doped TiO₂ membrane(?-CD/Ag-TiO₂).Morphology and structure characterizations confirmed that TiO₂ nanoparticles as the outer shell were uniformly coated on ?-CD/Ag/PAN nanofibers as the inner core,forming core-shell structure.Combined with a detachable filter head,the as-constructed membrane could be applied to the dynamic adsorption of TC.The adsorption behavior fitted well with Langmuir model and the dynamic adsorption capacity was mainly derived from the introduction of ?-CD and the loading of mesoporous TiO₂ nanoparticles.Due to the synergistic effect of ?-CD and Ag doping,this membrane also possessed highly enhanced vis-responsive photoactivity,which could complete degrade TC with 60 min of visible light(k=0.05910 min-1),and still maintained high removal efficiency in the dynamic and complex system(k=0.02228 min-1).The strong self-cleaning ability also indicated the promising potential in practical application.