Effective adsorption of bisphenol A from aqueous solution using phosphoric acid-assisted hydrochar

Sycamore leaf biochar (PSAC) was prepared by a two-step phosphoric acid-assisted hydrothermal carbonization combined with a short-time activation method. The characterization results showed that the introduction of phosphoric acid molecules and thermal activation resulted in a substantial increase in the specific surface area (994.21 m²/g) and microporous capacity (0.307 cm³/g) of PSAC. The batch adsorption results showed that the adsorption process of PSAC on bisphenol A (BPA) was best described by the pseudo-second-order kinetic model and Sips isothermal model, with a maximum adsorption capacity of 247.42 mg/g. The adsorption of BPA onto PSAC was determined to be a spontaneous endothermic process. The equilibrium adsorption capacity of PSAC exhibited an upward trend with increasing initial BPA concentration and temperature while decreasing with higher adsorbent dosage and pH value. Coexisting cations and humic acids in water have little impact on the adsorption performance of PSAC for BPA. The adsorption mechanism of BPA by PSAC was mainly governed by pore filling and hydrogen bonding interactions, π-π interactions, and intraparticle diffusion. Furthermore, PSAC demonstrated good reusability by its sustained adsorption capacity of BPA, which remained at 82.6% of the initial adsorption capacity even after four adsorption-desorption cycles. These findings highlight the potential of utilizing low-cost sycamore leaf biochar as an effective adsorbent for the removal of the endocrine disruptor BPA.