Abstract The adsorption of methylene blue (MB) onto silica synthesized from coal fly ash (CFA) was investigated to evaluate its efficiency, kinetics, and thermodynamics. Adsorption studies revealed nearly 100 % MB removal under optimized conditions (50 ppm MB, pH 7, 3.1 g adsorbent dosage, and 50 min contact time). Equilibrium data fitted best with the Langmuir isotherm model ( R 2 = 0.9881, Q max = 32.76 mg g −1 ), confirming monolayer adsorption and strong adsorbate–adsorbent interactions. Kinetic modeling showed that the pseudo‐second‐order model ( R 2 = 0.99) best described the process, indicating chemisorption as the dominant mechanism. Thermodynamic analysis confirmed that the adsorption was spontaneous and exothermic (Δ G < 0, Δ H = − 22.84 kJ mol −1 ), with a decrease in system entropy, suggesting an energy‐efficient process that favours lower temperatures. Reusability studies demonstrated that the silica adsorbent retained 97.5% ± 0.17 % MB removal efficiency over 12 cycles, highlighting its economic and industrial feasibility. Additionally, ethanol‐based desorption proved to be effective, ensuring sustainable regeneration. These findings establish silica from CFA as a cost‐effective, environment friendly, and highly efficient adsorbent for wastewater treatment applications, particularly in dye‐contaminant removal.
Manyepedza et al. (Tue,) studied this question.