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 SiO 2 , Fe 2 O 3 , and Al 2 O 3 . 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 BS 400 , BS 600 , and BS 300 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 BS 400 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 BS 400 catalyst.