Tailoring Novel SnO₂/α-MnO₂ Composites for Photocatalytic Performance Under Visible-Light

Efficient removal of industrial effluents from wastewater is critical for a clean and sustainable water supply. In this study, novel nanosized SnO₂/MnO₂ photocatalysts with crystallite size between 34–40 nm were synthesized and evaluated for methylene blue (MB) degradation under visible light. The optimal percentage of MnO₂ nanowires was explored for superior photocatalytic efficiency by varying its amount in the composites. The findings suggested that the SnO₂/MnO₂ composites exhibited enhanced photocatalytic performance compared to their individual components, which was attributed to the synergistic interaction between SnO₂ and MnO₂. Preliminary analysis by X-ray diffraction, Raman spectra, and EDX confirmed the crystalline structure and chemical composition of SnO₂, MnO₂ and their composites. Additionally, the morphology of MnO₂ was observed to be of nanowires; while SnO₂ was found to be comprised of agglomerated particles. Notably, the photocatalysts demonstrated a systematic reduction in the bandgap of the composites with increasing MnO₂ content, leading to improved visible light utilization. Among all the prepared photocatalysts, the optimized SnO₂/MnO₂ composite with 75 wt. % MnO₂ (denote as SM-3) revealed exceptional photocatalytic activity by degrading 93% of MB in 150 min of light exposure. Moreover, the catalytic process followed pseudo-first-order kinetics, highlighting the efficiency of the composites. The scavenger studies suggested that holes, hydroxyl and superoxide radicals are primarily responsible for the MB degradation. The composite SM-3 also exhibited impressive stability and reusability. This study demonstrates the potential of SnO₂/MnO₂ composites as effective photocatalysts for wastewater treatment under visible light.