Gold-modified N-doped TiO2 and N-doped WO3/TiO2 semiconductors as photocatalysts for UV–visible light destruction of aqueous 2,4,6-trinitrotoluene solution

•Au/N-doped WO3/TiO2 were synthesized as photocatalyst.•Efficient photodegradation of 2,4,6-trinitrotoluene is achieved by using UV-A and visible light irradiation.•The enhancement of activity is explained in terms of a more efficient charge carrier separation.

The photocatalytic performance of TiO2, WO3/TiO2, Au/TiO2, and Au/WO3/TiO2 and their corresponding nitrogen-doped metal oxide samples in the photooxidation of aqueous 2,4,6-trinitrotoluene (TNT) solution was investigated. Oxidation was carried out using both visible and UV irradiation. The average particle size of the synthesized TiO2 and N-doped TiO2 photocatalysts was ≈20 nm, while particles size of WO3/TiO2 and N-doped WO3/TiO2 was ≈17 nm. The average size of the Au nanoparticles supported on the catalysts was ≈5 nm. XPS and UV–vis diffuse reflectance spectroscopy measurements confirm the replacement of oxygen atoms by nitrogen atoms in the crystal lattice of TiO2 and WO3. Calculated rate constant values for 2,4,6-trinitrotoluene photooxidation by visible light on the different catalysts had the following order: kAu/N-(WO3/TiO2)>kAu/WO3/TiO2>kN-(WO3/TiO2)≈kAu/N-TiO2>kWO3/TiO2>kN-TiO2≫kAu/TiO2≈kTiO2kAu/N-(WO3/TiO2)>kAu/WO3/TiO2>kN-(WO3/TiO2)≈kAu/N-TiO2>kWO3/TiO2>kN-TiO2≫kAu/TiO2≈kTiO2. The rate constants of 2,4,6-trinitrotoluene photocatalytic degradation under visible light irradiation were lower by an order of magnitude compared to the rate constants under UV irradiation. In 2,4,6-trinitrotoluene photooxidation under UV light irradiation the rate constant kAu/N-(WO3/TiO2)kAu/N-(WO3/TiO2) was about 4 times larger than kN-doped TiO2,kN-doped TiO2, while for photooxidation under visible light irradiation the former was 8 times larger than the latter.

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