Nitrogen-mediated engineering cobalt phosphide sites for enhanced peroxymonosulfate activation towards organic wastewater purification

Abstract

Introducing heteroatoms into cobalt phosphide-based materials is expected to enhance their effectiveness in wastewater purification through peroxymonosulfate (PMS) activation by altering the electronic structure and reconfiguring the catalytic sites. In this study, we describe an efficient one-step calcination method for fabricating CoP@NC/NF, wherein simultaneous phosphorization and nitrogen nitridation occur during the calcination process. The CoP@NC/NF/PMS system effectively activates PMS and achieves a tetracycline (TC) removal rate of 92.3 % within 30 min. The calculated rate constant achieves 0.1615 min⁻¹, representing a 1.85-fold increase compared to the CoP@C/NF/PMS system. Furthermore, the CoP@NC/NF/PMS system exhibits remarkable resistance to interference from various inorganic anions and humic acid. Mechanistic examinations reveal that non-radical pathways including ¹O₂ and electron transfer are the dominant mechanisms in the catalytic system. Additionally, potential catalytic sites for TC removal via PMS activation by CoP@NC/NF include Co²⁺, Co-N_x, graphitic N, and C=O. Finally, four potential degradation pathways were identified through the analysis of fourteen intermediates from TC decomposition. Toxicity assessments indicate a marked decrease in the toxicity of the degraded solution. Overall, this catalyst, characterized by multiple active sites and enhanced stability, presents a highly effective oxidation system for eliminating antibiotic pollutants from water.