Ionic liquid assisted hydrothermal syntheses of Au doped TiO2 NPs for efficient visible-light photocatalytic hydrogen production from water, electrochemical detection and photochemical detoxification of hexavalent chromium (Cr6+)

Abstract

Au/TiO₂ NPs have been successfully prepared at 130 °C in one day using an ionic liquid assisted hydrothermal method using methoxyethyl methyl imidazolium methanesulfonate as the ionic liquid, titanium(IV) isopropoxide and tetrachloroaurate(III) trihydrate as precursors. Physico-chemical properties of the obtained photocatalysts were investigated via thorough characterizations. The framework substitution of Au in TiO₂ NPs was established by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDS) techniques. X-ray diffraction (XRD) and transmission electron microscopy (TEM) image results confirmed the anatase phase and nanocrystalline nature of Au/TiO₂. The optical properties revealed an extended tailing of the absorption edge toward the visible region upon Au doping. The concentration of Au in the TiO₂ matrix has been fine-tuned to improve the hydrogen production, electrochemical detection and photochemical detoxification of hexavalent chromium (Cr⁶⁺). But there are no reports utilizing a single material for all three applications such as photocatalytic hydrogen production from water and photochemical as well as electrochemical reduction of Cr⁶⁺ to Cr³⁺. The synergy between the Au and TiO₂ has an optimum for concentration of 0.5 wt% Au doped TiO₂. The optimized product has produced promising hydrogen evolution of 3344 μmol g⁻¹ under illumination with a visible light source in a water/ethanol system. The optimized product has shown promising electrocatalytic reduction and the photocatalytic detoxification ability of the material towards Cr⁶⁺ was explored. Amperometric studies showed a linear range from 0.1 to 2.7 mM, and limits of detection and quantification of 0.01 mM and 0.023 mM, respectively. The Au/TiO₂ nanoparticle modified glassy carbon has been used for electrochemical monitoring of Cr⁶⁺ in natural water samples. The material also showed better photochemical reduction of Cr⁶⁺ in sunlight compared to UV light.