Biogenic chitosan cross-linked cherry gum and N-doped biochar beads: An eco-friendly platform for versatile dual-site...

The escalating discharge of synthetic dyes demands eco-friendly solutions, as conventional adsorbents suffer from inadequate regeneration, structural integrity, and the potential risk of harmful secondary pollutants. This study introduces a green strategy to formulate high-performance biodegradable adsorbents by cross-linking chitosan with oxidized dialdehyde cherry gum (CG-CS) and subsequently transforming the hydrogel into nitrogen-doped biochar (N-BC) by low-temperature pyrolysis. The resultant CG-CS hydrogel and N-BC beads were utilized to eliminate anionic Congo Red (CR) and cationic Rhodamine B (RhB) dyes, respectively. The adsorbents exhibited a hierarchically mesoporous architecture and swelling capacity of 385 ± 1.73 % at pH = 3 ± 0.05. Optimal adsorption was observed at pH = 5 ± 0.05 for CR and pH = 8 ± 0.05 for RhB, with maximal capacities of 1477 mg·g^-1 and 2042 mg·g^-1, respectively. Monte Carlo simulations revealed stronger CR binding to CG-CS, yet experimentally, N-BC displayed superior RhB uptake due to its greater porosity and multi-modal interaction routes. Kinetics adhered to a dual-phase mechanism comprising initial electrostatic attraction (PFO model, R² > 0.99) followed by pore-diffusion (Bangham model). The adsorption process was optimally characterized by the Koble-Corrigan isotherm (R² = 0.998 for CR, 0.980 for RhB), indicating monolayer saturation at high-affinity sites, succeeded by multilayer occupancy in heterogeneous regions. Simulation validated robust binding energies and favored interactions via π-π stacking, hydrogen bonding, and charge-assisted electrostatics. Both adsorbents sustained approximately 70-85 % efficiency after 10 reuse cycles. These eco-engineered materials provide a sustainable, and adaptable method for eliminating structurally diverse dyes from intricate aqueous matrices.