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

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, C-13 NMR, and TGA analyses. Two cobalt oxide NP-based catalysts, CoO and alpha-Co(OH)(2), were then prepared by depositing the cobalt nanoparticles on the g-C3N4 support using gas-phase reduction by H-2 (CoCN-H-2) 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), O-1(2), SO4 center dot-, O-2(center dot)-, and HO center dot, 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-H-2, exhibited high catalytic activity throughout a wide pH spectrum, achieving hence complete degradation yields for various organic dyes, including OG, MO, BM, and RhB.