Highly active nitrogen-doped biochar for catalytic reduction of 4-nitro-phenol: Kinetic, thermodynamic and mechanism investigation

Biomass derived metal-free carbon catalysts are urgently needed in wastewater remediation and organic transformation, due to their environmental friendliness, low cost. In this respect, a series of nitrogen-doped hierarchically porous carbons (NHPCs) derived from cheap and abundant eggplant were fabricated via a one-pot strategy under different temperatures from 600 to 900 degrees C, and employed as metal-free catalysts for the reduction of aromatic nitrophenols. Benefiting from the synergistic effects of the hierarchically porous structure, large specific surface area and abundant structural defects, NHPCs obtained from 800 degrees C has the highest reduction rate of 2.072 min- 1 and maximal turnover frequency (TOF) for 4-nitrophenol of 1.23 x 10- 2 mM & sdot;mg- 1 & sdot;min- 1, which is superior to most of the reported metal-free catalysts. In addition, the NHPC-800 also exhibits satisfactory practicality and universality. The kinetic and thermodynamic studies were also conducted, finding that the obtained kinetics data over NHPC-800 fit well to L-H model with a low apparent activation energy (Ea = 18.96 kJ & sdot;mol- 1). Furthermore, the mechanism was also elucidated by experimental investigation and theoretical calculations, which revealed that the pore creation and doping nitrogen can promote the adsorption of 4-NP and NaBH4 onto NHPC. This study make a significant contribution to the advancement of catalytic reduction of 4-NP by N-doped biochar catalysts.