Shape Effect of Zinc-Tin Oxide Nanostructures on Photodegradation of Methylene Blue and Rhodamine B under UV and Visible Light

Water pollutants are currently a major concern, demanding for simple processes for water treatment, photocatalysis being one of the most efficient and promising processes. Metal oxide materials are being widely studied for this application, due to their wide band gaps, with nanostructures being particularly interesting because of their high surface-to-volume ratio. In this context, zinc-tin oxide (ZTO) nanostructures are quite appealing owing to the multiplicity of structures and morphologies possible to achieve with low-cost solution-based synthesis and to the lack of critical elements in favor of abundant and nontoxic ones. In this work, three different ZTO nanostructures, namely, ZnSnO3 nanowires, Zn2SnO4 nanoparticles, and Zn2SnO4 polyhedrons, were studied for the photodegradation of methylene blue and rhodamine B under both UV and visible light irradiation. The nanostructures were synthesized by a low-cost seed-layer-free hydrothermal method at only 200 °C, compatible with direct growth on flexible substrates. ZnSnO3 nanowires in the powder form, reported as photocatalytic agents for the first time, showed enhanced photocatalytic activity, especially under UV light, degrading both dyes in only 90 min and outperforming Zn2SnO4 nanoparticles and polyhedrons. Photocatalysis under visible light is also demonstrated, with a degradation of >40% of rhodamine B in 12 h. This work shows the feasibility of a simple, low-cost fabrication method and sustainable, nontoxic materials to achieve structures with efficient photocatalytic activity.