Photocatalytic oxidation of 2,4,6-trinitrotoluene in the presence of ozone under irradiation with UV and visible light

Abstract

Under irradiation in the presence of ozone the photocatalytic mineralization of 2,4,6-trinitrotoluene, proceeded at a significantly higher rates, compared to those in the presence of O 2 only and they depend on the UV light source energy. ► The effectiveness of the 2,4,6-trinitrotoluene (TNT) degradation, catalysed by nanosized Au/WO 3 /TiO 2 photocatalysts was accelerated upon adding O 3 to the oxygen. ► In the presence of O 3 the rate constants of TNT destruction increased from 6 to 21 times. ► Doping of the semiconductor materials with gold nanoparticles increases 1.4–2.2 times the rate constants of TNT mineralization. The photooxidation of 2,4,6-trinitrotoluene (TNT), catalysed by nanosized photocatalysts: TiO 2 , WO 3 /TiO 2 , Au/TiO 2 and Au/WO 3 /TiO 2 was studied under irradiation with UV or visible light in the presence of O 2 or O 2 –O 3 mixture. The photocatalysts were characterized by the BET, XPS, TEM methods and adsorption of the model pollutant. The effectiveness of the processes of under UV-A, UV-C and visible light irradiation destruction in the presence of O 3 , photocatalysed by the WO 3 /TiO 2 , Au/TiO 2 and Au/WO 3 /TiO 2 samples is considerably higher than that registered in process, occurring with pure TiO 2 . Thus in the presence of O 3 the rate constants of 2,4,6-trinitrotoluene photooxidation under UV-A, UV-C and visible light irradiation catalysed by Au/WO 3 /TiO 2 are respectively 2.1, 1.4 and 6.2 times higher than that registered with pure TiO 2 . On the other side the ozone rate constants of 2,4,6-trinitrotoluene photooxidation under UV or visible light irradiation are also much higher than those, registered in the presence of O 2 only. Thus under UV light irradiation the O 3 rate constants of 2,4,6-trinitrotoluene photooxidation, catalysed by Au/WO 3 /TiO 2 are 6 times higher, while under visible light they are 11 times higher than those with oxygen only. Under irradiation with UV-A, UV-C and visible light in the presence of ozone a synergistic effect has been registered, expressed most strongly in the case of TNT destruction, photocatalysed by Au/WO 3 /TiO 2 . Doping of the semiconductor materials with gold nanoparticles increases 1.4–2.2 times the rate constants of 2,4,6-trinitrotoluene mineralization, compared to the undoped samples, which is due to more efficient separation of the electron–hole charges generated upon irradiation.