Use of the sunscreen for the degradation of a toxic methyl blue dye with hydrogen peroxide

To protect against sunlight, the sunscreen (SC) is widely used, and here we demonstrate their novel application in environmental remediation. SC effectively degraded the toxic dye methyl blue (MBD) from aqueous solution under a household bulb within 18 min, while other common dyes (congo red, methylene blue, methyl orange, crystal violet, malachite green) remained unaffected. The process required hydrogen peroxide (H₂O₂) as a co-catalyst. Titanium dioxide in SC generated hydroxyl radicals in the presence of H₂O₂, enabling MBD degradation. Mechanistic studies with scavengers revealed that both electron and hole pathways were essential, as their inhibition significantly reduced the reaction rate. Fluorescence spectroscopy confirmed the degradation, showing characteristic fluorescent products of MBD breakdown. Comparative studies using SCs from different manufacturers demonstrated that an inexpensive, commercially available, and non-toxic pharmaceutical sunscreen exhibited the highest efficiency. This approach highlights the potential of repurposing consumer products for sustainable wastewater remediation.