Preparation Of TiO₂Nanoparticles Modified By Copper Or Stannum And Its Applications In Acifluorfen Photocatalitic Degradation

The anatase crystalline form of TiO₂has been the best photocatalyst of choice.It has been found to have the best overall properties in terms of photo-stability,toxicity, cost, availability and redox efficiency. However, the efficiency ofphotocatalytic reactions is limited by the high recombination rate of photoinducedelectron-hole pairs formed in photocatalytic processes and by the absorptioncapability for visible light of photocatalysts. The aim of this research is to solvethese key problems using Cu or Sn elements to modifiy TiO₂photocatalyst.The effects of copper ions have been studied on the photodegradation oforganic pollutant, but many aspects with regard to the role of copper species withmultivalent states in the photocatalytic reaction remain unclear. In this research, aseries of Cu-TiO₂catalysts have been synthesized by sol-gel method. The obtainedsamples were characterized in detail via TG, XRD, DRS, SPS and XPS methods.The photocatalytic activity of Cu-TiO₂was studied by degrading the RhodamineBextra solution （RhB）. Meanwhile, the effects of different metal content，calcination temperature，and calcination time on the photocatalytic activity ofsamples were investigated. The modified mechanism of the Cu doping TiO₂wasinvestigated via DRS, SPS and XPS technologies: when the Cu concentration isfeasible, oxygen vacancies and Cu species could trap the photoinduced electronsand effectively inhibit the recombination of the photoinduced charges consequentlyin the photocatalytic process, in addition, the content of surface hydroxyl on thesurface of the0.06mol%Cu-TiO₂was increased remarkably in contrast to that ofpure TiO₂, these factors were favor to the increase of the photocatalytic activity forsamples. When copper dopant content exceeds0.06mol%, however, excessiveoxygen vacancies and Cu species could be the recombination centers of thephotoinduced electrons and holes. Meanwhile, at heavy Cu doping concentration,excessive P-type Cu2O can cover the surface of TiO₂, which leads to decrease in thephotocatalytic activity of photocatalyst.The thermal hydrogen （H2） treatment of TiO₂was also found to be capable toaccelerate the e-h separation and improved photocatalytic activity of the TiO₂catalyst. However, there were many insufficiencies in the process of the thermalhydrogen （H2） treatment of TiO₂, such as, there were the factors of inflammable and explosive, the technologies route was complicated, furthermore, this method wastoo time-consuming and expensive. These factors limited its practical application.To overcome these difficulties and disadvantages, in this thesis, a rapid andsimple method, the so-called stannous chemical reducing method was developed toprepare the nanocrystalline Sn-TiO₂-X. The mechanism of the Sn modified TiO₂wasinvestigated via DRS, SPS, XPS and EIS methods. Firstly, that is deu to theexistence of Ti3+ions, which can elevate the Femi energy level and increase thenumber of the the active oxygen species. Secondly, the amount of oxygen vacanciesis increased, which can effectively trap photoinduced carriers and inhibit therecombination of the photoinduced electrons and holes. Thirdly, Sn species areformed as SnO2on the surface of TiO₂, the Fermi levels of SnO2is lower than thatof TiO₂, which leads to the photoinduced electrons transfer from the conductiveband of TiO₂to that of SnO2on the surface of TiO₂, not to the bulk of TiO₂, whichcan also trap photoinduced electrons and inhibit the recombination of thephotoinduced electrons and holes. At last, Sn-modified TiO₂introduce the doppingenergy level of Ti3+and Sn species, which can result in the sub-band gap transitionof catalysts, the doped energy level participate in the photochemistry process, thelight whose energy is less than the Eg can be absorbed by catalysts, so, theabsorption range of photocatalyst could beexpanded to visible region. Thephotocatalyst prepared by the stannous chemical reducing method have efficacies ofboth the thermal hydrogen （H2） treatment and Sn4+doping modification.Acifluorfen is a diphenyl ether herbicide contained chlorine used inpostemergence for the selective control of most broadleaf weeds in soybeans andrice. The half-life of Acifluorfen is sufficiently long that it may be washed awaytoward surface waters （rivers and lakes） and had caused great damage to theenvironment.In present work, the experiments of the photocatalytic degradation ofAcifluorfen were carried out using Cu-TiO₂and Sn-TiO₂-Xas photocatalysts. Ourobjective was to explore the effects of the irradiation intensity, the catalyst dosage,pH values, the type and the amount of anions and cations often used in agriculture,and the initial concentration on the degradation of Acifluorfen. The experimentalresults indicate that:The smaller activities found at acidic and basic pH are explained byconsidering the ionisation state of Acifluorfen and the charge density of TiO₂; Effect of the anions addition on the degradation of Acifluorfen is remarkable for thereaction system using Cu-TiO₂as photocatalyst, but there is less effect forSn-TiO₂-X; The influence of metal ions like K+and Ca2+on the photocatalyticefficiency of TiO₂in the elimination of Acifluorfen is unnoticeable, but adetrimental effect of the presence of Cu2+is observed.In addition, the roles of the active species generated in TiO₂systems areidentified using i-PrOH and dissolved oxygen as·OH and photoinduced electronsscavenging reactant, and the role of the main active species in the photodegradationof Acifluorfen is determined. The experimental results indicate that·OH is the mainactive specie for Cu-TiO₂, and the amount of the active oxygen species in thereaction system using Sn-TiO₂-Xas photocatalyst are more than that of Cu-TiO₂.Finally, the removal kinetics of Acifluorfen, and established the primaryintermediate products and degradation pathways of Acifluorfen have been studied.The results of photocatalytic experiment reveal that the decline of Acifluorfenconcentration in the solution followed a zero-order kinetics.