Efficient selenate removal from impaired waters with TiO₂-assisted electrocatalysis

Area of Science:

• Environmental Chemistry
• Electrochemistry
• Materials Science

Background:

• Aquatic selenium oxyanions pose significant risks to ecosystems and human health.
• Converting toxic selenate (Se(VI)) to elemental selenium (Se(0)) is crucial for pollution mitigation.
• Kinetic limitations hinder the direct transformation of Se(VI) into Se(0).

Purpose of the Study:

• To investigate the electrocatalytic efficiency of affordable catalysts for Se(VI) transformation.
• To identify optimal conditions for Se(VI) reduction and elemental selenium immobilization.
• To evaluate catalyst stability and environmental impact during the process.

Main Methods:

• Electrocatalytic reduction of Se(VI) using graphite cathodes modified with five catalysts: TiO2, UPD Cu, UPD Cd, Co, and CuFe.
• Cyclic voltammetry and chronoamperometry to assess catalytic activity and Se(VI) removal.
• Electrochemical impedance spectroscopy to optimize catalyst loading and reaction conditions.
• Analysis of metal leaching and product characterization (elemental Se(0)).

Main Results:

• TiO2 demonstrated superior performance, removing over 80% of 1-mM Se(VI) with negligible metal leaching.
• Other catalysts showed <5% Se(VI) removal and significant metal cation leaching.
• Se(VI) reduction to Se(0) occurred via a six-electron pathway at -0.30 V (vs. Ag/AgCl).
• Optimal Se(VI) removal (88.7 ± 2.3%) was achieved at pH 1.0–2.5 with TiO2 loading of 0.55 mg cm⁻², under -0.70 V, and 3.6 kWh kg⁻¹ Se energy input.

Conclusions:

• TiO2-coated graphite cathodes are highly effective and stable for electrocatalytic selenate removal from impaired waters.
• The study establishes a foundation for developing efficient selenium remediation technologies.
• Further research should focus on long-term catalyst performance and reactor design optimization.