Black sand as a cost-effective catalyst for methylene blue photo-remediation under visible light

Abstract

Methylene blue (MB) is commonly a persistent and perilous pollutant in industrial wastewater effluent. While MB has a massive negative effect on human and ecology safety. The neutralization of such harmful material would save a huge clean water amount. This work proposes the natural and abundant black sand as a catalyst for MB photodegradation. The sand sample was calcined at three temperatures of 300°, 400°, and 600 °C. The properties of samples were analyzed with different micro- as well as spectroscopic techniques. The experimental data revealed the sample's main composition of SiO2, Fe2O3, and Al2O3. XRD and XPS results proved the formation of mixed oxides composites due to calcination, especially at 400 °C. The UV–vis analysis conducted showed that samples can absorb light in the visible range. The photodegradation reached a maximum of 975.3%, 82.7%, and 75.7% for BS400, BS600, and BS300 respectively; by illumination for 2.5 h in the visible range. The observed distinguishable catalytic performance was discussed via the spectroscopic analysis and oxygen availability in the catalyst lattice. When AO, t-BuOH, and BQ are used as scavengers instead of just BQ during the photodegradation of MB dye over BS400 catalyst, the photodegradation rate drops significantly. The degradation % of MB dye diminished to 60%, and 70% by using AO, t-BuOH, and BQ scavengers; respectively. This proved that rather than hydroxyl radicals, superoxide radicals or positive hole production is the main determining step in MB photo-degradation over BS400 catalyst.