Chitosan-functionalized magnetic peanut shell biochar composite for efficient adsorptive removal of Congo red from...

Synthetic dye discharge into aquatic systems has become an escalating environmental concern because these colorants are chemically recalcitrant, toxic, and resistant to biodegradation. In the present study, a Chitosan-functionalized magnetic peanut shell biochar composite (CS-MPSB) was engineered as an economical, biomass-derived, and magnetically retrievable adsorbent for Congo red elimination from aqueous media. Peanut shell biochar (PSB) was first anchored with Fe₃O₄ nanoparticles to produce magnetic biochar (MPSB), followed by CS coating to enrich the surface with additional binding functionalities. The as-prepared materials were subjected to comprehensive physicochemical scrutiny using FTIR, XRD, SEM, TEM, TGA, and BET techniques. CS-MPSB showed a surface area of 248.9 m² g^-1, a pore volume of 0.2083 cm³ g^-1 and a mesoporous structure with an average pore width of 3.76-3.77 nm. Batch adsorption experiments indicated that the pH significantly affected the Congo red removal, with optimum removal at pH 5.0. The adsorption capacities were found to increase with initial dye concentration, respectively, to 259, 282, and 307 mg g^-1 for PSB, MPSB and CS-MPSB. The adsorption kinetics and equilibrium data were interpreted using the pseudo-second-order kinetic model and Langmuir isotherm model, respectively, with CS-MPSB exhibiting the highest Langmuir monolayer capacity of 322.6 mg g^-1. Thermodynamic analysis showed that the adsorption of Congo red was thermodynamically favorable with positive enthalpy and entropy change suggesting that the adsorption was promoted at higher temperatures and increased randomness was present at the interface of the adsorbent and solution. The composite also showed good regeneration ability and salt tolerance, indicating its potential for dye-contaminated wastewater treatment.