Enhanced nonradical catalytic oxidation by encapsulating cobalt into nitrogen doped graphene: highlight on interfacial interactions

Abstract

Supported metal catalysts are widely used for heterogeneous catalytic processes (e.g., Fenton-like reaction), but the mechanisms of interfacial processes are still ambiguous. Herein, unique nanocarbon based catalysts with Co nanoparticles encapsulated in nitrogen (N)-doped graphene (Co@NG) were prepared by calcination of Co based metal–organic frameworks (MOFs), which showed excellent catalytic performance for peroxymonosulfate (PMS) activation. Comprehensive characterization revealed that there were strong interfacial interactions between Co and the NG layer due to the presence of special nitrogen species, especially graphitic-N. Density functional theory calculations suggested that the strong interfacial interactions provided optimal active sites with low adsorption energy (−1.99 eV) for PMS accumulation, which enabled the generation of highly oxidizing NG–PMS* intermediates as evidenced by in situ Raman microscopy. Electrochemical analyses revealed that the interfacial interactions facilitated surface-to-surface electronic communication across atomic interface-bonding (N–Co). Consequently, phenol was quickly degraded by the NG–PMS* via direct oxidation by an anodic-like nonradical process, and reasonable graphitic-N (G-N) content and pore size are important for this process. Phenol at 1 mM was completely removed within only 12 min by Co@NG-900 (which was prepared at 900 °C), with an apparent rate constant 20 times higher than that of pure NG-900. This work sheds new insights on the critical role of interfacial interactions in nonradical PMS activation.