Engineering the photo-induced charge generation between TiO2 and FeS2 heterojunction for enhanced photocatalytic wastewater purification

Abstract

Wastewater treatment using photocatalytic processes is an eco-friendly approach to tackle the scarcity of drinkable water. In this study, a heterojunction of TiO2 and FeS2 nanostructures was synthesized via a one-pot polyol method, and their activity was investigated in eliminating crystal violet as a dye pollutant. The difference in the thermodynamic stability of iron and titanium oxides in polyol solution containing thiourea led to the formation of TiO2 nanorods and sulfurization of iron in the form of FeS2 nanospheres. Incorporating TiO2 nanorods with FeS2 chalcogenide nanostructures narrowed the band gap energy (from 3.05 to 2.6 eV) and enhanced the photo-induced charge carriers’ separation by forming an internal electric field. Compared to TiO2 nanorods, the synthesized heterojunction photocatalyst using 0.5 ml TBOT (FST-0.5) exhibited the best activity and increased crystal violet degradation from 55% to 89%. The optimization and modeling of the interaction between operating parameters were performed by response surface methodology based on central composite design. The statistically significant quadratic polynomial model was best for fitting the experimental data. Regarding this model, adjusting the catalyst weight, pollutant concentration, and solution pH at an optimum amount of 0.015 g, 4 ppm, and 9 causes the highest photocatalytic degradation, around 94%. The kinetics studies also revealed that photocatalytic degradation follows first-order kinetics with an apparent rate constant of 0.0184 min−1. The contribution of active species was determined by free-radical capture experiment. Herein, photo-holes had the main contribution (38.3%), and the rest accounted for hydroxide radicals (26.6%), superoxide anions (11.7%), and electrons (23.4%).