Novel chemically reduced cobalt-doped g-C3N4 (CoCN-x) as a highly heterogeneous catalyst for the super-degradation of organic dyes via peroxymonosulfate activation

Abstract

This work presents a novel approach for the design and the stabilization of cobalt oxide nanoparticles supported on g-C₃N₄ (CoCN-x) catalyst to efficiently degrade various organic pollutants through peroxymonosulfate (PMS) activation. The catalyst support synthesis process involved a two-step thermal treatment of urea, resulting in high-purity g-C₃N₄ material, confirmed by XPS, ¹³C NMR, and TGA analyses. Two cobalt oxide NP-based catalysts, CoO and α-Co(OH)₂, were then prepared by depositing the cobalt nanoparticles on the g-C₃N₄ support using gas-phase reduction by H₂ (CoCN–H₂) and liquid-phase reduction by NaBH₄ (CoCN–NaBH₄), respectively. The prepared CoCN-x materials were characterized using several techniques, such as FTIR spectroscopy, XRD, TEM, and SEM-EDS, which evidenced that the cobalt oxides were successfully introduced into g-C₃N₄. The effectiveness of the prepared catalysts in degrading organic contaminants was evaluated by activating PMS to generate reactive oxygen species (ROSs), ¹O₂, SO₄˙⁻, O₂˙⁻, and HO˙, as confirmed through quenching experiments and electron paramagnetic resonance (EPR) analysis. These ROSs were responsible for the oxidation of the target contaminants, thereby promoting their mineralization. The results showed that both catalysts, CoCN–NaBH₄ and CoCN–H₂, exhibited high catalytic activity throughout a wide pH spectrum, achieving hence complete degradation yields for various organic dyes, including OG, MO, BM, and RhB.