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

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 <i>Suaeda monoica</i> 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 (<i>q</i> _max) of 325.5 mg g^-1 at 30 °C, whereas the Dubinin-Radushkevich (D-R) model (<i>E</i> < 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 (Δ<i>H</i>° = 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 (<i>R</i> ² > 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.