The Photocatelytic Research Of Co₃O₄/Bi₂O₃ Composite Catalysts On Toluene

Today condensed state physicists,chemists and material scientistsare paying attention to semiconductor nanoparticles because of itsespecial optical property,catalytic activity, mechanical property,magnetic property and so on. In recent years, application of thesemiconductor nanoparticle to environmental cleanup has been one ofthe most active areas in heterogeneous photocatalysis. This is inspiredby the potential application of semiconductor metal oxides andsulfides photocatalysts to the complite destruction of organiccompounds in polluted air and wastewaters. We can choose excellentphotocatalyst based on specific requirement. Usual photocatalyst,under TiO₂, ZnO, Fe₂O₃, SnO₂,SrTiO₃,Bi₂O₃,CdS,WO₃, ZnS,PbS, etc, are semiconductors, i.e. they have a moderate energyband-gap between their valence and conduction bands. Underillumination by photons of will enegy higher than band-gap energies,the valence band electrons can be excited to the conduction band,creating highly reactive electron-hole pairs. After migration to thesolid surface, these may undergo electron-transfer processes withadsorbates of suitable redox potentials. At moderate conditions (roomtemperature, one atmosphere pressure and with molecular oxygen asthe only oxidant), the above mentioned semiconductors have proved tobe effective photocatalysts for the thermodynamically favoredtransformations of many organics to CO2 and H2O. TiO2 is the mostone to attract people's attention because if has many advantages suchas nonpoisonous, high catalytic activity, high oxidation ability, goodstability, low cost, and so on. However the band-gap of TiO2 is wide(Ebg=3.2eV), and it only absorbs light wave of wave-length≤387nm.Thus, studying and preparing new photocatalyst or improvingphotocatalytic efficiency is the important assignment. One of the mostactive fields of research in heterogeneous photocatalysis usingsemiconductor particles is the development of systems capable ofusing natural sunlight to degrade a large number of organic andinorganic contaminants. It has been reported that the band-gap energyof Bi2O3 semiconductor is 2.8ev and Bi2O3 semiconductor can absorblight longer wave-length. Anthony.H. has applied Bi2O3 semiconductorto photocatalytic degradate organic chlorine pollutant in water.CUI Yu-ming and WANG Jun-Zhen have tried to apply Bi2O3semiconductor to water treatment. Only using Bi2O3 is not very good,so I use Co3O4/Bi2O3 for improving the photocatalytic activity.In this paper, Co3O4/Bi2O3 nanoparticles were prepared by meansof the chemical precipitation and microemulsion chemical method.Co3O4/Bi2O3 particles prepared by means of the two methods bothpresent quantum size. The crystallite dimension of Co3O4/Bi2O3nanoparticles prepared by microemulsion chemical method is smaller,the photocatalytic activity prepared by means of microemulsion chemicalmethod is better than the one prepared by means of chemicalprecipitation method.For C7H8-O2-Bi2O3 system, toluene can be oxidized with CO2and H2O as the final products. In this paper, we have preparedCo3O4/Bi2O3 nanoparticles, and have studied the structure andproperties of Co3O4/Bi2O3 nanoparticles by means of many moderntechniques such as TG-DTA, XRD, XPS and FT-IR spectrum. Thephotocatalytic activity of composite semiconductor nanoparticles ishigher than that of Bi2O3 nanoparticles, which due to different energylevel causing separation of changes and extending extent of excitationwave length. The increasing level of photocatalytic activity is up to thevalues of n(Co):n(Bi) and the best one is 0.02. With the calciningtemperature increasing, the photocatalytic activity is increasing, andthe best calcining temperature is 750℃.Fitting 0.1g Co3O4/Bi2O3 nanoparticles into reactor, using tolueneas object reactant, charging some oxygen, using nitrogen as diluent gas,under the exposure of high-voltage mercury lamp, we research theeffect of initial density of toluene, the density of oxygen, theamount of water and the intensity of illumination on photocatalyticdegradation reaction rate of toluene.