Electrochemical Removal of Se(IV) from Wastewater Using RuO₂-Based Catalysts

The removal of selenite (SeO₃^2-) from water is challenging due to the risk of secondary pollutants. To address this, we developed RuO₂-based nanocatalysts on the titanium plate (RuO₂/TP) for direct electrochemical reduction of Se(IV) to elemental selenium [Se(0)]. Optimizing Sn doping in RuO₂ nanoparticles to induce charge redistribution enabled the Ru_0.9Sn_0.1O/TP catalyst to achieve ∼90% Se(IV) removal across concentrations of 0.1, 1, and 10 mM at -2 mA cm^-2 over 8 h, outperforming undoped RuO₂/TP. Furthermore, Ru_0.9Sn_0.1O/TP also maintained ∼90% removal efficiency in 1 mM of Se(IV) solutions containing competitive anions (0.5 M Cl^-, 0.1 M SO₄^2-, 0.01 M NO₃^-, and their mixtures), demonstrating suitability for complex wastewater treatment. Importantly, the catalysts were recyclable, with no observable contamination introduced into the solution. Density functional theory (DFT) calculations suggest that Sn doping effectively reduces the energy barrier for the reduction of Se(IV) to Se(0).