Toxic crystal violet dye removal by novel, eco-friendly seablite biochar–ferrite composite: adsorption isotherm, kinetics, and artificial neural network

Abstract

Rising water demand has intensified pollution and created an urgent need for efficient treatment methods. Adsorption is a green and low-cost approach, yet conventional adsorbents often face sustainability and regeneration challenges. In this study, a novel adsorbent was developed by pyrolyzing Suaeda monoica leaf powder (LP) into biochar (BC300), followed by base treatment and coprecipitation with NiCuZnFe₂O₄ spinel to form a ferrite–biochar composite (FCOB). FCOB effectively removed Crystal Violet (CV) dye from aqueous solution. FE-SEM images revealed a layered morphology, while FTIR analysis confirmed multiple adsorption mechanisms, including hydrogen bonding, electrostatic attraction, surface complexation, and pore filling for CV adsorption. Optimization studies showed maximum CV removal at pH 8 with a 30 mg FCOB dose, maintaining >95% removal up to 200 mg L⁻¹ dye concentration. For higher concentrations, 150, 250 mg L⁻¹, the equilibrium time was 120 min. The Langmuir model indicated monolayer adsorption with a maximum capacity (q_max) of 325.5 mg g⁻¹ at 30 °C, whereas the Dubinin–Radushkevich (D–R) model (E < 8 kJ mol⁻¹) suggested physical adsorption. Kinetic analysis revealed that the pseudo-second-order (PSO) model best described the process, indicating the chemical nature of CV adsorption onto FCOB, while the Elovich model provided a better fit at higher concentrations, reflecting surface heterogeneity. Thermodynamic parameters confirmed that CV adsorption was spontaneous and endothermic (ΔH° = 49.03 kJ mol⁻¹). FCOB retained >275 mg g⁻¹ capacity after five regeneration cycles, demonstrating good reusability. Artificial neural network (ANN) modeling reliably predicted adsorption performance (R² > 0.99) using pH, dye concentration, dose, time, and temperature as inputs. These findings highlight FCOB as an economical, eco-friendly, and scalable adsorbent for dye removal from wastewater.