Synthesis of mesoporous SiO 2 derived from coal fly ash for methylene blue adsorption

Abstract Porous silica has been widely employed as an adsorbent owing to its high surface area, tunable pore structure, and abundant surface silanol groups. Owing to its abundant silicon content, coal fly ash (CFA) can serve as a low-cost silicon source for the preparation of porous silica materials, while enabling the upcycling of CFA. Therefore, this study proposed a synthesis strategy for a porous silica-rich adsorbent using CFA after a phase separation-acid leaching treatment as the silica source. The experimental results indicate that mesoporous silica synthesized under the optimal conditions (a Si/CTAB/NaOH molar ratio of 1:0.65:0.6, a crystallization temperature of 80°C and a crystallization time of 1.5 h) exhibits a maximum specific surface area of 774.42 m·g − 1 , an average pore size of 7.27 nm, and a pore volume of 1.41 cm·g − 1 . Adsorption tests for methylene blue (MB) further verify that the synthesized mesoporous silica delivers a high MB adsorption capacity of 186.81 mg·g − 1 at pH 11 and 298.15 K, with an initial MB concentration of 200 mg·L − 1 and an adsorbent dosage of 1 g·L − 1 .This study provided a potential pathway for the resource utilization of CFA and carries the typical significance of waste-to-treat-waste strategy.