Photocatalytic degradation of benzothiophene and dibenzothiophene using supported gold nanoparticle

Photocatalytic oxidation of benzothiophene (BT) and dibenzothiophene (DBT) was studied over Au nanoparticles (NPs) incorporated titania (Au/TiO2) catalyst under UV radiation using H2O2 as oxidant. The reaction parameters such as, catalyst weight, Au loading, calcination of Au/TiO2 catalysts and [H2O2]:[DBT] mole ratio are studied. The Au/TiO2 catalyst was synthesised by deposition-precipitation method. The catalysts were characterized by ICPAES, XRD and TEM analysis. ICP-AES analysis demonstrate that with a nominal amount of 1, 1.5, 2, 2.5 and 3 at.% of Au in a solution at pH 7, the amount of gold deposited on the TiO2 was 0.78, 1.42, 1.92, 2.45 and 2.87 at.% respectively. The average particle size of Au in the 2 at.% Au/TiO2 sample after drying was 3 nm and in the sample after calcination at 573 K was 5 nm. The XPS spectra of Au/TiO2 sample demonstrate that the sample dried at 373 K contains Au0 and Au3+ and the sample after calcination at 573 K contains Au0 and negligible amount of Au3+. The photocatalysis studies show that the Au nanoparticles (NPs) incorporated titania showed higher activity for the removal of DBT compared to pure titania. The optimum Au loading in Au/TiO2 for the photocatalytic removal of DBT was found to be 1.5 at.% Au. The Au NPs act as electron sink to enhance e/h+ charge separation and produce number of oxidizing species, thereby increase the reaction rate. The calcined catalyst sample showed higher activity toward DBT removal compared to the uncalcined sample. This is due to the presence of metallic gold in the calcined sample, which can effectively involve in the charge separation. The optimum catalyst weight for DBT removal was found to be 0.3 g of Au/TiO2 for 200 ml of DBT in isooctane (200 ppm S). The optimum [H2O2]:[DBT] molar ratio was found to be 3. Comparison of photocatalytic removal of DBT and BT showed that the removal of DBT is faster than the BT.