Comparative evaluation of phosphate-activated carbons for malachite green removal: Adsorption performance and process optimization

This study investigates the preparation and performance of activated carbons derived from agricultural biomass using different phosphate activating agents for the removal of malachite green (MG) dye from aqueous solutions. Three activating agents (H₃PO₄, Na₃PO₄, and Na₅P₃O₁₀) were comparatively evaluated by producing porous carbons with distinct surface characteristics to determine their influence on adsorption performance. The materials were characterized using BET, SEM, XRD, and zeta potential analysis. Batch adsorption experiments were conducted to evaluate the effects of pH, contact time, and initial dye concentration. Response surface methodology (RSM) based on central composite design was applied to optimize the adsorption process. Among the prepared samples, the carbon activated with H₃PO₄ (PAC1) exhibited the highest adsorption capacity, reaching 81.3 mg/g under optimal conditions, demonstrating the potential of the prepared adsorbents for practical wastewater treatment applications. Adsorption kinetics followed a pseudo-second-order model, while equilibrium data were best described by the Langmuir isotherm, indicating monolayer adsorption. Thermodynamic analysis confirmed that the adsorption process is spontaneous and primarily physical in nature. The findings demonstrate that the choice of phosphate activating agent significantly influences the surface properties and adsorption performance of activated carbons. The study provides practical insights into the design of cost-effective adsorbents for dye-contaminated wastewater treatment.