All that Glitters Is Not Gold: A Probe into Photocatalytic Nitrate Reduction Mechanism over Noble Metal Doped and Undoped TiO₂

Photocatalytic reduction of aqueous nitrate has been thoroughly studied over noble metals doped and pristine TiO₂ synthesized by a customized single step microwave assisted hydrothermal method. The synthesized catalysts are systematically characterized using XRD, Raman spectroscopy, FE-SEM, HR-TEM, XPS, diffuse reflectance spectroscopy, and PL measurements. The characterization reveals the successful synthesis of highly crystalline doped and undoped nano-TiO₂. The photocatalytic rate of aqueous nitrate reduction over undoped TiO₂ is found to be higher than that of noble metal doped TiO₂. Mechanistic studies of the photocatalytic reduction are carried out with the help of different hole (oxalic acid, and methanol) and electron (sodium persulfate) scavengers, which reveal that the photogenerated electrons are the primary agents toward efficient nitrate photoreduction. Detailed studies have revealed that the noble metal doping in TiO₂ helps in efficient photogeneration of H₂ compared to the undoped analogue, however, the <i>in situ</i> produced H₂ is found to be inefficient in reducing NO₃^–. The conduction band position from first principle calculations with respect to the nitrate and hydrogen reduction potentials derived from cyclic voltammetry provide insights to the electron transfer process in determining the reaction pathway