Oxygen-vacancy enhanced CoO/CeO2 heterojunction for synchronous regulation of sulfur resourcing and selenium adsorption separation from flue gas desulfurization wastewater

Abstract

Wastewater detoxication and sulfate purification of flue gas desulfurization wastewater by the simultaneous catalytic oxidation of SO₃²⁻ and separation of Se is desirable for the circular economy, but still faces many challenges. Here, an oxygen-vacancy-enriched cobalt-ceria (OV-CoO/CeO₂) bimetallic oxide was fabricated that increased the catalytic oxidation rate of SO₃²⁻ to 0.1735 mmol L⁻¹ s⁻¹, 13 times that of the uncatalyzed reaction. The Se adsorption efficiency reached 92% with an adsorption capacity over 120 mg g⁻¹. The homogeneous surface diffusion model predicted the Se adsorption behavior, and the surface diffusion coefficient was 4.17 × 10⁻¹³ cm² s⁻¹. The free energy for Se adsorption on OV-CoO/CeO₂ was 10.09 kJ mol⁻¹, indicating chemisorption. Characterization of the catalyst showed that the ceria dioxide (CeO₂) induced the formation of cobalt oxide (CoO) nanoclusters, which were highly dispersed on the CeO₂ lamella matrix, creating more available Co sites and oxygen vacancies (OVs). The Ce⁴⁺/Ce³⁺ redox pair coupled with the abundant OVs increased the Co²⁺-induced catalytic oxidation of SO₃²⁻ by increasing the yield and transfer of O* by OV-O₂. The contribution of different components to Se adsorption was in the order CeO₂ > CoO > OVs. The surface –OH on Ce⁴⁺/Ce³⁺/Co²⁺ dominated the Se adsorption by forming Me–O–SeO_x²⁻, and the reaction between Me–O* and Se also contributed to Se adsorption. This dual functional material may provide a new method for the simultaneous production of high-quality sulfate and separation of toxic Se from flue gas desulfurization wastewater.