Modified Auto-Combustion Synthesis of Mesoporous TiO₂-NiO Nanosheets for Selective Adsorption and Photodegradation of Alizarin Yellow Dye under Direct Sunlight and Reaction Kinetic Study

Abstract

The application of a photocatalyst with effective adsorption capacity and higher photocatalytic activity under direct sunlight for the treatment of industrial effluent contaminated with dyes has received increased attention. In this work, mesoporous TiO2-NiO nanosheets were synthesized by a modified auto-combustion technique followed by thermal post-treatment at 400°C. The XRD pattern for modified auto-combusted resulting TiO2 (sc) and TiO2-NiO (sc) [5wt%NiO] nanosheets comprised of mixed-phase anatase and rutile for TiO2 and cubic for NiO. The result of SEM demonstrated that the morphology of TiO2 is a sheet and TiO2-NiO is a rod-like structure. UV-vis spectroscopy results imply that the bandgap of TiO2 and TiO2-NiO mixed phase is 3.1eV and 2.7eV. N2 sorption (BET) showed a mesoporous structure and interpret specific surface areas of 19.528m2/g and 63.215 m²/g. Adsorption of the dye on the solid catalyst is inexpensive and efficient but disposing of the adsorbed dye is challenging. Among various dye removal techniques, photocatalytic degradation under direct sunlight is significant, cost-effective, and sustainable. Photocatalytic experiments using alizarin yellow as a model pollutant showed that the degradation percentage of AY was 93.54% in 120min for 100mg of TiO2(sc) and 97% in 90min for 60mg of TiO2-NiO(sc). Degradation of AY using TiO2(sc) and TiO2-NiO(sc) follows a pseudo-first-order reaction, whereas adsorption of AY on TiO2-NiO(sc) follows the second-order kinetics, fits well in the Freundlich Isotherm model. Therefore, nanosized mesoporous TiO2-NiO(sc) nanosheets with a p-n junction are considered efficient photocatalysts under direct sunlight due to narrowing down in bandgap, larger surface, and mixed-phase.