Photocatalytic degradation of DNT wastewater by composite catalyst and its degradation mechanism

To explore the catalytic activity and degradation mechanism of the photocatalytic degradation of explosive wastewater by supported polyoxometalate composite catalysts, three kinds of supported polyoxometalate composite catalysts, H₃PW₁₂O₄₀/TiO₂, H₃PW₁₂O₄₀/TiO₂ (P123) and SO₄^2--H₃PW₁₂O₄₀/TiO₂ (P123), were prepared by the sol-gel-solvothermal route. Taking the typical organic pollutant-dinitrotoluene (DNT) in explosive wastewater as traget compound, the photocatalytic activities of the prepared catalysts in the photocatalytic degradation of DNT wastewater were investigated. The reasonable explanation for the photocatalytic activity difference between different catalysts was performed. The relationship between structure and photocatalytic properties of the catalysts was analyzed. The species of reactants and products in wastewater were identified and analyzed by gas chromatography-mass spectrometry (GC-MS) instruments. The photocatalytic degradation mechanism and mineralization degree of DNT wastewaters were studied by photocatalytic oxidation method. The results show that the degradation rate of DNT in wastewater after 4 h irradiation is 98.73% when SO₄^2--H₃PW₁₂O₄₀/TiO₂ (P123) is used as catalyst. The reaction of methyl oxidation, nitro removal and decarboxylation occurs in the process of photocatalytic degradation of DNT wastewater. Intermediate products of degradation mainly include p-nitrobenzoic acid, m-nitrobenzoic acid, 1,3-dinitrobenzene, 2,4-di-tert-butylphenol and 2,4-dinitrobenzaldehyde. After 4 h degradation, the nitrobenzene compounds were degraded completely, except for a small amount of 3,4-DNT.