Abstract Coal fly ash, a major industrial waste from coal combustion, remains largely underutilized despite its high content of reactive amorphous silica. Therefore, this study explored its valorization for the synthesis of mesoporous silica nanoparticles and evaluated their performance in the adsorption of methylene blue from water. Coal fly ash was pretreated through calcination at 600 °C and subjected to sequential acid–alkaline leaching. This was followed by a cetyltrimethylammonium bromide-templated sol–gel process to produce high-purity amorphous silica particles. The silica particles were characterized using X-ray Diffraction, Thermogravimetric analysis, Brunauer–Emmett–Teller analysis, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy techniques. Surface area analysis revealed a high surface area of 788.54 m 2 /g and an average pore diameter of 3.35 nm, confirming the formation of a mesoporous structure. Batch adsorption experiments showed rapid dye removal, with efficiencies ranging from 81.84 to 100%. Optimum conditions were 10 mg/L methylene blue, 5 mg adsorbent, 60 min, pH 9, and 25 °C, yielding the best performance. Adsorption kinetics were well described by pseudo-first-order (R 2 = 0.996) and pseudo-second-order (R 2 = 0.997) models, indicating a surface-controlled process with multiple adsorption mechanisms. Isotherm analysis followed the Langmuir model (R 2 = 0.990), with a maximum adsorption capacity (q max ) of 215.66 mg/g, indicating predominantly monolayer adsorption. Furthermore, the silica particles exhibited 98.6–99.9% removal over four cycles, demonstrating good reusability. Overall, this study highlights a practical, low-cost route for converting coal fly ash into high-performance adsorbents for the treatment of dye-contaminated water.
Tenza et al. (Thu,) studied this question.