Chemically activated walnut shell-derived biochar for enhanced adsorption of dibutyl phthalate

Dibutyl phthalate (DBP) is a crucial component in microplastics, posing a serious threat to human health. Biochar (BC) can be obtained from agricultural by-products and wastes, which has attracted great attention as a promising candidate for DBP removal. Herein, walnut shell-derived biochar is prepared using pyrolysis method, followed by pretreatment with water, hydrochloric acid (HCl), and sodium hydroxide (NaOH), respectively. According to the characterization of morphology, component, and porous structure, HCl pretreated biochar shows the highest specific surface area of 205.61 m² g^-1, which is expected to promote the physical adsorption process of DBP. Based on adsorption kinetics and isotherms experiments, NaOH pretreated biochar exhibits the largest adsorption capacity (7.08 mg g^-1), and the removal rate only decreased by 8.2% after six cycles. In addition, thermodynamic analysis indicating that NaOH pretreated biochar shows the minimized Gibbs free energy of - 3.559 kJ mol^-1 K^-1, owing to the joint effect of physical adsorption and chemical adsorption. This work helps to further research the application of biochar-based materials in DBP removal.