Adsorption of hazardous Acid Violet 17 on Vachellia nilotica biochar: experimental and statistical physics modelling

Inadequate management of chemical industrial effluents necessitates the development of high-capacity, sustainable wastewater treatment technologies. This study investigates the adsorptive removal of hazardous Acid Violet 17 (AV17) dye using a novel biochar derived from Vachellia nilotica stems (VNBB). Characterization via HRTEM and BET analysis revealed a mesoporous, sponge-like architecture with a surface area of 50.92 m 2 g − 1 and an average pore diameter of 8.02 nm. Batch experiments demonstrated that VNBB is highly effective, achieving a maximum removal efficiency of 97.94% at pH 6. Equilibrium data were best described by the Langmuir isotherm, yielding a superior maximum adsorption capacity ( Q max ) of 333.33 mgg − 1 . Adsorption kinetics followed the pseudo-second order model, (R² = 0.995), implying strong correlation with the experimental results. From thermodynamic and statistical physics study, it was found that the adsorption mechanism followed mainly physical interaction. To provide deeper mechanistic insights, advanced statistical physics modeling was applied. A double-layer model with five parameters successfully described the adsorption isotherms. The steric parameter n ranged from 0.39 to 0.42, indicating a multi-docking mechanism where AV17 molecules maintain a horizontal orientation on the VNBB surface. Thermodynamic analysis confirmed the process is endothermic and spontaneous, with adsorption energies ( E 1 ) between 22.16 and 24.48 kJmol − 1 , signifying a physical component to the binding. Furthermore, the biochar exhibited excellent stability, maintaining high performance across five regeneration cycles with less than a 2% loss in capacity. These findings position VNBB as a high-performance, cost-effective, and reusable adsorbent for the remediation of dye-contaminated industrial wastewater.