Effects Of Manganese Oxides On The Photocatalytic Properties Of TiO₂-based Photocatalysts

Photocatalytic oxidation technology is an important technique with potential applicationin water treatment, and has received much attention in recent decades. However, photocatalystdeactivation is a common phenomenon in practical application, and need to be solvedurgently. Therefore, the study of excellent photocatalytic material is necessary. TiO₂is awidely used photocatalys. In recent years, many efforts have been made on the modificationof TiO₂to improve its photocatalytic activity and stability. However, the effect of solidparticles in water on the doped TiO₂is seldom studied. Therefore, it is necessary to study theinfluence of manganese oxides on the doped-TiO₂and find the excellent photocatalyticmaterials. The following are the main research contents and results of this dissertation.（1） Using Naphthol blue-black as a model pollutants, the influence of three kinds ofmanganese oxide on the photocatalytic activity of TiO₂and ZnO has been investigated bydynamics methods. The result showed that the particles significangly inactivatiedsubmicrosized anatase TiO₂and nanosized mixed crystal TiO₂, but has little effect tosubmicrosized wurtzite ZnO and nanosized ZnO. The UV-Vis DRS and PL spectra provedthat manganese oxides significantly increased the bandgap of TiO₂, and promoted therecombination of photo-generated electron and hole as deep level impurities, thus leading tothe deactivation of TiO₂photocatalyst.（2） A series of metal-doped TiO₂were synthsized by Sol-gel methods, and theirphotocatalytic properties for the degradation of Naphthol blue-black were investigated. Theresults showed that Cd, Bi, Fe and Zn doped TiO₂had good thermal stability and theirphotocatalytic activity was improved with the increase of temperature, while Co, Ni and Sndoped TiO₂had poor thermal stability and their photocatalytic activity was high at lowtemperature. The Ce doped TiO₂have the best thermal stability and its activity was improvedwhen it was treated at high temperature. The thermal stability and photocatalytic activity ofthe doped TiO₂are dependent on the kind of doped ion.（3） The influences of different crystalline manganese oxides on the photocatalyticactivity of metal doped TiO₂were studied by dynamics methods. The result showed that the three crystalline manganese oxides could obviously inhibit the photocatalytic activity of Cd,Bi, Fe and Ni doped TiO₂, and the poisoning effect was in the order of δ-MnO₂>α-MnO₂>γ-MnOOH. In the system of Co-doped TiO₂, δ-MnO₂and γ-MnOOH have significantinfluence, and α-MnO₂has no influence. The three crystalline manganese oxides promoted thedegradation in the early stage and had weak inhibitory effect in the last stage. Thephotocatalytic activity of metal doped TiO₂was associated with the intensity of their PLspectrum.（4） A series of nonmetal doped TiO₂were prepared by sol-gel methods, and theirphotocatalytic activities were studied by dynamics methods. The result showed that thephotocatalytic activity of Cl, F and B doped TiO₂treated at500℃exhibited the best activities,whereas temperature had no effect on the photocatalytic activity of S doped TiO₂.（5） The influences of different crystalline manganese oxides on the photocatalytic activityof nonmetal doped TiO₂were studied by dynamics methods. The result showed that the threecrystal types of manganese oxides could markedly inhibit the photocatalytic activity of Cl, Fand B doped TiO₂, and the poisoning effect was in the order of δ-MnO₂>α-MnO₂>γ-MnOOH.α-MnO₂could slightly inhibit the photocatalytic activity of S doped TiO₂. However, δ-MnO₂had no influence. Manganese oxide could decreased the spectrum peak intensity of nonmetaldoped TiO₂.