Hierarchical nano-porous biochar prepared by a MgO template method for high performance of PNP adsorption

Abstract

Hierarchical nano-porous biochar (HNBC) was prepared by one-pot pyrolysis of Enteromorpha prolifera (EP) powder after impregnation with magnesium acetate solution, which was utilized to investigate the adsorption properties for p-nitrophenol (PNP). Herein, the prepared samples were characterized by N₂ adsorption and desorption, X-ray photoelectron spectroscopy and scanning electron microscopy. BET data manifest that the specific surface area of HNBC-3 among the prepared samples is the largest with a value of 1500.2 m² g⁻¹. In addition, HNBC-3 exhibited a high adsorption capacity at 298 K for PNP (365.6 mg g⁻¹). The surface and nano-porous channels provide abundant adsorption sites, which make the adsorption performance of HNBC-3 more outstanding. Further research shows that HNBC-3 is more in line with the Freundlich isotherm and the pseudo-second-order kinetic equation. The adsorption of PNP in aqueous solution is an exothermic and spontaneous process. In addition, the recovery and reuse of the template agent using the acetic acid washing method can effectively cut down the cost of porous biochar preparation, and the pore structure of the porous biochar prepared using the recovered magnesium acetate is almost similar to that of the porous biochar prepared with magnesium acetate under the same conditions. The reusability experiment found that HNBC-3 showed no evident loss of adsorption capacity for PNP after four cycles of regeneration. This paper emphasizes that utilizing renewable biomass as a carbon source to prepare porous biochar using a MgO template method is a green, feasible and promising approach.