Synthesis, characterization, and comparison of N-modified biochar with different nitrogen sources for bisphenol A adsorption

Nitrogen source–modified biochar was produced from rice straw–derived biochar (RSBC) via pyrolysis carbonization using nitrogen sources such as ammonium chloride, dicyandiamide, melamine, thiourea, and urea. The characteristics of the resulting biochars were compared, including their elemental compositions, surface functional groups, and morphology. The N-modified biochar contained N- and O-based groups (N–H, C–N, C≡N, O–H, and C–O), primarily consisted of mesopores (3.01 ~ 14.42 nm pore diameter), and had a specific surface area ranging from 95.87 to 167.86 m2 g −1 . The N-modified biochar’s BPA adsorption capacity was correlated to the activation temperature (correlation coefficient n  = 0.5), with adsorption capacities varying from 7.43 to 63.09 mg g −1 . Ammonium chloride–modified biochar synthesized at 800 °C had over twice the BPA adsorption capacity of pristine biochar (28.80 mg g −1 ) among various nitrogen sources evaluated. The pseudo-second-order model characterized the adsorption kinetics of BPA, while the Freundlich model faithfully captured its isotherms. This study emphasizes the significance of proper nitrogen source selection and optimal modification temperatures to enhance the BPA adsorption capacity of biochar. Graphical Abstract