Minimization of electrical energy consumption in the photocatalytic reduction of Cr(vi) by using immobilized Mg, Ag co-impregnated TiO2 nanoparticles

Abstract

Magnesium and silver co-impregnated TiO₂ nanoparticles were immobilized on a glass plate and used as a fixed-bed system for photocatalytic reduction of Cr(VI) to the less harmful Cr(III). Response surface methodology as a statistical technique was employed for optimizing the preparation conditions of Mg–Ag/TiO₂, focusing on minimization of electrical energy consumption as the most important factor in selecting a wastewater treatment technology. Results showed that maximum photocatalytic reduction (84.44%), with minimum electrical energy consumption (30.31 kW h per m³ per order) were achieved at the optimized preparation conditions: Mg content of 0.82 wt%, Ag content of 2.6 wt%, and calcination temperature of 495 °C, whereas at the same conditions, using pure TiO₂, Mg/TiO₂, and Ag/TiO₂ samples lead to 21.17%, 32.59%, and 63.61% photocatalytic reduction rates, and 232.1, 152.03, and 71.42 kW h per m³ per order electrical energy consumptions, respectively. The optimized Mg, Ag co-impregnated TiO₂ nanoparticles were characterized by using XRD, SEM, TEM, DRS, EDX, and PL techniques. The considerable PL quenching in the co-impregnated TiO₂ with optimized metals content suggests that the co-impregnation of Mg and Ag onto TiO₂ could effectively inhibit the recombination probability of photogenerated electrons–holes pairs. Co-impregnation of Mg and Ag metals, and optimization of preparation conditions provides a synergistic effect in enhancement of the TiO₂ activity and effective minimization of the electrical energy consumption and treatment cost.