Experimental and theoretical insights into metal-free catalytic reduction of nitrophenols over porous nitrogen-doped reduced graphene oxide

Herein, a series of metal-free porous nitrogen-doped reduced graphene oxides (PNrGOs) are obtained and employed as metal-free catalysts for the reduction of aromatic nitrophenols. Owing to the developed holey structure, unique two-dimensional structure, higher nitrogen content and excellent electron transfer ability, the PNrGOs show outstanding catalytic activity for nitrophenol reduction. Among the PNrGOs, 2-PNrGO has the largest specific surface area (778 m2·g−1) and suitable nitrogen content (5.67 at.%), displaying the highest reaction rate of 1.563 min−1 and maximal turnover frequency for 4-nitrophenol of 8.75 × 10−5 mol·mg−1·min−1, which is comparable even superior to the reported noble metal-based catalyst. The catalytic reaction kinetic model, surface active sites, electron transfer pathway and the role of pore and nitrogen dopant were investigated by experimental and theoretical calculations thoroughly. The results demonstrated that the strongly active sites can merely be created by the synergistic effect between the nitrogen-doping and holey structure.