Unveiling the enhanced rhodamine B degradation in water by Sn3O4@Au: Insight into degradation pathway and by-products toxicity evaluation

Abstract

The present study investigated the catalytic degradation of Rhodamine B (RhB) by using Sn₃O₄@Au nanocomposites (NCs) synthesized via a green approach by utilizing Polyscias balfouriana ‘Marginata’ extract. Sn₃O₄@Au-10 % in the presence of Cu²⁺ ions achieved the highest RhB degradation efficiency which was 99.14 % in one min. The study showed the enhanced catalytic degradation of RhB by the synergetic effect of Au, Cu²⁺ and Sn₃O₄. Maximum degradation occurred at pH 6, catalyst dosage of 10 mg/L and RhB concentration of 15 mg/L, and the degradation efficiency declined at higher acidic and alkaline conditions. Cu²⁺ ions played a dominant role in enhancing degradation through the electron transfer, while ions such as Al³⁺, Ca²⁺, HCO₃⁻, and SO₄²⁻ exhibited inhibitory effects. Kinetic analysis revealed that catalysis process follows pseudo-first-order reaction. Structural characterization revealed that Au incorporation increased the surface area from 10.7 m²/g (pristine Sn₃O₄) to 13.4 m²/g (Sn₃O₄@Au). The catalyst demonstrated excellent reusability, maintaining 99 % efficiency after six consecutive cycles, and the structural stability was confirmed by XPS and XRD analyses. The degradation pathway was elucidated based on GC–MS analysis and the degradation process involves hydroxylation, deethylation, and aromatic ring cleavage, ultimately leading to mineralization. ECOSAR toxicity predictions indicated progressively reduced toxicity of intermediates compared to the parent compound. The study establishes Au-deposited Sn₃O₄ as an efficient, stable, and eco-friendly catalyst for wastewater treatment. These results paves a way for manufacturing innovation in near future.