Facile Synthesis of High-Performance Nitrogen-Doped Hierarchically Porous Carbon for Catalytic Oxidation
Zhe Yang, Xiaoguang Duan, Jun Wang, Yang Li, Xiaobin Fan, Fengbao Zhang, Guoliang Zhang, Wenchao Peng
Abstract
Carbonaceous materials are emerging metal-free catalysts for advanced water purification without secondary pollution. In this study, nitrogen-doped and hierarchically porous carbons with ultrahigh specific surface areas (SSAs) (>4500 m2 g–1) are fabricated using sodium nitrate (NaNO3) as a template and polyacrylamide as nitrogen and carbon precursors. Highly hierarchical porous structures can be created with uniform-dispersed macropores (50∼200 nm), mesopores (2∼4 nm), and micropores (0.7∼1.2 nm). These materials are then employed as metal-free catalysts for catalytic oxidation of phenol with peroxymonosulfate (PMS). The system demonstrates an outstanding catalytic activity with a rate constant of 0.622 min–1, outperforming many metal-based (Fe2+, Co2+, and Ag+) homogeneous systems. The catalytic mechanism is investigated by electron paramagnetic resonance (EPR) and radical quenching tests. The nonradical pathway contributed to the majority of phenol oxidation and to the minor amounts of SO4•–, •OH, and O2•– are also detected. The ultrahigh catalytic activity of the carbocatalysts results from the large SSA, nitrogen modification, abundance of defective sites, and functional groups. This salt-templating method is facile and generates high quality samples without residual template. The approach has a great potential for the practical production of low-cost, high-performance, and functional carbon materials for wastewater treatment. This work also provides new insights into metal-free catalysis in PMS activation.