Unleashing the power of cobalt pyroborate: superior performance in sulfate radical advanced oxidation processes†

Abstract

This study presents structurally robust cobalt pyroborate (Co₂B₂O₅) as a heterogeneous catalyst for advanced oxidation processes (AOPs). The Co₂B₂O₅ nanoparticles were systematically characterized and employed to activate peroxymonosulfate (PMS) effectively in the degradation of various organic recalcitrant pollutants. When compared to conventional heterogeneous CoO and Co₃O₄ catalysts in sulfate radical-advanced oxidation processes (SR-AOPs), the Co₂B₂O₅ catalyst exhibited seven-fold and 2.7-fold increases in degradation rate, respectively. The Co₂B₂O₅/PMS system was optimized to enable degradation of a diverse array of persistent organic pollutants, including tetracycline, 4-nitrophenol and sulfamethoxazole, with respective first-order rate constants of 0.136 min⁻¹ and 0.104 min⁻¹, and 0.092 min⁻¹, respectively. Mechanistic insights, supported by selective trapping experiments and electron paramagnetic resonance (EPR) analyses, revealed that surface-bound sulfate radicals serve as the primary reactive oxygen species (ROS) under dark conditions. Singlet oxygen species also contributed to the degradation process via a non-radical pathway. Remarkably, the catalyst maintained its effectiveness in the presence of natural organic matter, highlighting its potential practical applicability for wastewater treatment. This study presents the single-component cobalt pyroborate catalyst with high catalytic activity under varying conditions, thus providing unprecedented benefits for industrial wastewater treatment applications.