Preparation Of New Type TiO₂–based Composite Photocatalyst And Their Catalytic Performance For Organic Wastewater Treatment

In the21st century, water pollution problems have been deeply affected thesurvival and development to human being. It is difficult to solve water pollution withthe traditional wastewater treatment technology for its high cost, slow processingspeed, incomplete purification or secondary pollution. So to exploit and research amore economical and effective new wastewater treatment technology have becomehot research topic in the world. Semiconductor photocatalytic oxidation technology isconsidered one of the most potential technology in the wastewater treatment. Amongvarious photocatalytic materials, TiO₂has been considered as a promising material forapplication because of its high chemical stability, non-toxicity, low cost and corrosionresistant. However, the low quantum efficiency and the high band gap of pure TiO₂（absorbing only the UV light） on TiO₂particles result in a low efficiency ofphotocatalysis. In this thesis, TiO₂was modified to improve the quantum efficiencyand extend light absorption of TiO₂toward the visible light. The TiO₂compositematerials with enhanced photocatalytic activity were prepared. The structure,morphology, surface physicochemical property, and optical absorption property of theTiO₂composites were characterized in detail. We also have researched the pollutiondegradation with the single-or codoped-TiO₂composite photocatalyst systemically.Some new and interesting results are as following:1. A series of ordered mesoporous WO₃-TiO₂composite materials with differentWO₃loadings were developed by a single step nonionic-surfactant-templatingstrategy combined with evaporation-induced self-assembly（EISA）technique. Themesostructure, morphology, porosity, optical absorption property, composition andstructure of as-prepared materials were well characterized by small-angle X-rayscattering（SAXS）, wide-angle X-ray diffraction（WAXD）, transmission electronmicroscopy（TEM）, nitrogen gas porosimetry, UV-Vis diffuse reflectancespectroscopy（DRS）, X-ray photoelectron spectroscopy（XPS） and Raman scatteringspectroscopy. The characterization results confirmed that the ordered compositematerials exhibited2D hexagonal p6mm symmetry and anatase phase structure withlarger BET surface area（152-154m2/g） and more uniform pore size（5.3nm） comparedwith the disordered WO₃-TiO₂composite material as well as narrowed bandgap（3.0eV） with respect to pure TiO₂. Subsequently, the ordered mesoporous compositematerials were successfully applied to the degradation of rhodamine B and 2,4-dichlorophenoxy acetic acid in the liquid phase under λ>400nm visible-lightirradiation. At3.49%WO₃loadings, the WO₃-TiO₂system exhibited the highestvisible-light photocatalytic activity. In addition, the visible-light photocatalyticactivity of the ordered mesoporous WO₃-TiO₂composite material exceeded that ofthe disordered WO₃-TiO₂composite material and pure TiO₂. The reasons of thisenhanced photocatalytic activity were discussed logically.2. Mesoporous graphene-TiO₂composite materials were successfully preparedby one-step sol-gel co-condensation technique combine with hydrothermal treatmentin the presence of nonionic surfactant P123. Compare with pure TiO₂, the materialsexhibited larger BET surface area, more uniform pore size, and narrower bandgapwith3D interconnected mesostructure and anatase/brookite mixed phase. Thephotocatalytic activity of as-prepared materials was evaluated through the degradationof aqueous organic pollutant rhodamine B and aldicarb under Xe lamp irradiation atdifferent wavelength region. Enhanced photocatalytic activity compared with pureTiO₂was obtained for the graphene-TiO₂composite with low graphene loading atboth simulated sunlight and visible light region. Reasons for this enhancedphotocatalytic activity was revealed preliminary.3. Successfully prepared graphene and SiO₂co-doped TiO₂composite materialswith enhanced photocatalytic activity, based on the research of preliminary work. Theordered mesoporous graphene-TiO₂/SiO₂composite materials with two-dimensionalhexagonal p6mm symmetries and anatase phase structures was prepared by a directsol-gel co-condensation technique combined with hydrothermal treatment in thepresence of a triblock copolymer non-ionic surfactant （P123）. The mesostructure,morphology, surface physicochemical property, optical absorption property,composition and structure of the as-prepared composites were characterized in detail.The composites exhibited more uniform pore size distribution, larger pore volume andBET surface area compared with the disordered graphene-TiO₂/SiO₂compositematerial. The composites were then successfully applied in the degradation of anendocrine-disrupting chemical atrazine under simulated sunlight Xe lamp irradiation.At1%graphene and4:1TiO₂:SiO₂molar ratio doping, the graphene-TiO₂/SiO₂composite material exhibited the highest photocatalytic activity; additionally, Thecomposites were found to have enhanced photocatalytic activities compared with pureTiO₂, single-doped TiO₂system （graphene-TiO₂or TiO₂-SiO₂） as well as P123free-graphene-TiO₂/SiO₂codoped system. Reasons for this enhanced photocatalytic activity was revealed and the intermediates of the atrazine were discussed.4. Based on the research of preliminary work, successfully prepared TiO₂composite materials codoped with graphene and tourmaline by one step hydrothermalmethod. The resulting composites exhibited an anatase phase structure, and3Dinterconnected mesostructure. The photocatalytic activity of as-prepared materialswas evaluated through the degradation of rhodamine B under Xe lamp irradiation.The composite materials were also applied to kill algae in eutrophic waters. Thephotocatalytic degradation of RB indicated that the activity of the three-componentsystem exceeded that of single-doped TiO₂system（G-TiO₂or T-TiO₂） and pure TiO₂.The photocatalytic removal of algae indicated that G/T-TiO₂has a very strongcapacity to kill algae. But compare with pure TiO₂, G/T-TiO₂did not show higheractivity which is different from RB. The reasons for this enhanced photocatalyticactivity were revealed. At the same time, the reasons why the photocatalyticdegradation is different between RB and algae with the same materials werediscussed.