Study On Preparation And Photocatalytic Activity Of Metal Co-doped TiO₂

Environmental pollution is one of the most serious problems facing mankind today, and it brings moreand more serious danger, especially water pollution. Compared with the traditional water treatment such asbiological, chemical and physical treatment process, the photocatalytic oxidation method, which is a newlydeveloped method in recent years, has the advantages of high ability of oxidation treatment，low-energyconsumption，no secondary pollution and so on. It has a promising future and will become effective methodof sewage treatment. Titanium dioxide is an ideal photocatalyst with chemical stability, low-cost, innocuous,indissolvable, high photocatalytic efficiency and so on. However, the actual application in photoctalysiswere limited because of its wide direct band gap and low quantum efficiency of photocatalyst. On the onehand metal doping could change the forbidden band width of the TiO₂; On the other hand metal dopingcould introduce crystal cavities into TiO₂or make the change in crystallization, which effectively restrainthe complex of photoelectron and holes and prolong the life-span of current carriers. Therefore, thephotocatalytic activity of TiO₂could improve by doping metal.In this thesis, Bi-La co-doped TiO₂, Bi-Co co-doped TiO₂, Bi-Cu co-doped TiO₂, Bi-Fe co-doped TiO₂were prepared by sol-gel method. The structures and status of modified samples were characterized by thetechniques of TG-DSC, XRD and so on. This thesis investigated the main influence factors and the kineticsof photocatalytic reaction by degrading reactive black KN-B and obtained the optimum technologicalcondition of photocatalytic degradation.The results show that: all the metal co-doped TiO₂calcinated at500℃were anatase, the particle sizesof metal co-doped TiO₂were in the range of10.0¹4.0nm. Metal co-doped could enhance the thermalstability, increase the crystal transition temperature, inhibit the crystallite size and the crystallite phasetransition, and improve photocatalytic activity of TiO₂.The influence of variant doping amount of metal, calcination temperature, dosage of catalysts, initialconcentration and pH value of solution were discussed. The research finds the optimal calcinationtemperature of metal co-doped TiO₂was500℃. The amount of metal doped in TiO₂has great impact on thefinal photocatalytic performance and the different metal has different optimal doping concentration. The optimal doping of Bi was_0.5%and La was0.2%in the Bi-La co-doped TiO₂, the optimal dopingconcentration of Bi and Co was_0.5%and0.05%respectively in the Bi-Co co-doped TiO₂, as for doping Biand Cu, the optimal doping concentration was_0.5%and0.01%respectively, the optimal doping of Bi was_0.5%and Fe was0.1%in the Bi-Fe co-doped TiO₂, too much or too little doping concentration reduced thephotocatalytic activity of catalyst. The degradation rate of metal co-doped TiO₂increased first anddecreased later with increasing of catalyst dosage, the optimal dosage of the Bi_0.5Fe0.1/TiO₂, Bi_0.5La0.2/TiO₂and Bi_0.5Co0.05/TiO₂was2.0g/L, the optimal dosage of the Bi_0.5Cu0.01/TiO₂was4.0g/L. The degradationrate of metal co-doped TiO₂decreased with increasing of initial concentration of reactive black KN-Bsolution, the catalyst could give full play to catalytic performance when initial concentration of reactiveblack KN-B solution was40mg/L. The influence of initial pH of the solution was great, the degradationrate in acid medium was faster than that in alkaline medium, the best initial pH of Bi_0.5La0.2/TiO₂,Bi_0.5Co0.05/TiO₂, Bi_0.5Cu0.01/TiO₂and Bi_0.5Fe0.1/TiO₂was2.20,3.30,2.01and2.20, respectively. Thephotocatalytic activity of metal co-doped TiO₂was better than that of the pure TiO₂and Bi single-dopedTiO₂, however, the catalysts of doping different metal show different catalytic activity, under the optimalcondition the degradation rate of reactive black KN-B reached up99%after30min reaction for the Bi-Laand Bi-Cu co-doped TiO₂, while the Bi-Co and Bi-Fe co-doped TiO₂need50min. The reaction of reactiveblack KN-B follows first order reaction kinetics. Many dyes were degraded efficiently by metal co-dopedTiO₂prepared by Sol-Gel process.The possible mechanism of photocatalytic activity improved by metal co-doped TiO₂was discussed,the main influence factors and the catalytic activity of metal co-doped TiO₂were investigated. This researchof metal co-doped TiO₂enriches the basic theory of photocatalytic oxidation technology and semiconductorphotocatalyst, and provides theory support for its practical application.