Preparation of a Novel N-Doped Biochar from Agricultural Waste for Cu(Ⅱ) Removal: Insights into the Kinetic, Equilibrium, Adsorption Mechanisms and Economic Feasibility

Abstract In this study, a novel nitrogen (N)-doped biochar was successfully synthesized from rice husk through urea-assisted co-pyrolysis and utilized as an efficient adsorbent for Cu(Ⅱ) removal from aqueous solutions. A systematic investigation of pyrolysis temperature (600 ℃ vs 800 ℃) revealed their critical role in modulating the properties of the biochar. The N-doped biochar produced at 800 ℃ (NBC-800) demonstrated a maximum adsorption capacity of 53.8 mg·g −1 under optimal conditions (pH 5, adsorbent dose 2 g·L −1 , initial concentration 100 mg·L −1 , contact time 24 h), representing approximately a tenfold enhancement compared to the non-doped biochar (BC). Kinetics and isotherm studies indicated that the adsorption process adhered to the pseudo-second-order and Langmuir models, suggesting a chemisorption-dominated mechanism. Comprehensive characterization revealed that the enhanced performance was due to the synergistic effects of an increased specific surface area, a developed porous structure, and the introduction of N-containing functional groups (e.g., pyridinic-N, pyrrolic-N, graphitic N), which facilitated electrostatic attraction and surface complexation with Cu(Ⅱ). Furthermore, an economic analysis demonstrated that the cost of Cu(Ⅱ) removal using the synthesized N-doped biochar was significantly lower than that of commercial activated carbon, underscoring its economic feasibility for practical applications. Thus, this study not only presents a high-performance adsorbent derived from agricultural waste but also offers valuable mechanistic insights and economic justification for its potential application in the treatment of heavy metal-contaminated water.