Rape seedling peel-derived biochar prepared by low-temperature vacuum pyrolysis method for adsorbing p-nitrophenol

Novel rape seedling peel-derived biochars (BCs) prepared by vacuum pyrolysis were used as cost-saving and sustainable biosorbents for wastewater remediation. The adsorption properties of BCs for p-nitrophenol (PNP) were investigated. The results showed that BC400 prepared at 400°C possessed the highest adsorption capacity of 55.78 mg g−1 towards PNP. Scanning electron microscopy, Energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Zeta potential analysis and Brunauer-Emmett-Teller specific surface area analyses were performed to characterise the physicochemical properties of BC samples. The microporous structure and abundant surface heteroatomic functional groups of BC400 were confirmed. The effects of adsorption conditions (contact time, temperature, initial PNP solution pH, initial PNP concentration) on the adsorption of PNP by BC400 were investigated. Adsorption behaviour was more consistent with the linear Freundlich model and linear pseudo-second-order kinetic model. Thermodynamic study showed that the adsorption of PNP on BC400 was a spontaneous endothermic process, and the disorder degree increased after adsorption. In addition, the adsorption capacities of BC400 for different phenols including hydroquinone, 3-nitrophenol, 1-naphthol (AN) and tert-butyl hydroquinone were compared, and the mechanism was also proposed. BC400 with aromatic and heteroatom-containing functional groups could interact effectively with PNP through various intermolecular interactions including π-π stacking, hydrogen bonding and electrostatic attraction. Reusability assessment indicated BC400 remained high removal rate even after 10 consecutive adsorption-desorption cycles.