Spherical mesoporous silica designed for the removal of methylene blue from water under strong acidic conditions

This work proposes a novel technology for environmental remediation based on mesoporous silica spheres, which were successfully synthesized by the solvothermal method using the cetyltrimethylammonium bromide as a structuring agent. The adsorbent was designed to remove cationic dyes at strong acidic conditions. The surface was modified by a careful thermal treatment aiming at the condensation of silanol to siloxane groups. The adsorbent was characterized by XRD, SEM, FTIR, N₂ adsorption/desorption and the equilibrium technique to determine the pH_pzc. The kinetic of the adsorption followed a pseudo-second-order model and the process was ruled by physical forces. The isotherms were fitted to Freundlich and Temkin models, indicating that the physisorption occurred with multilayer formation, with the interaction adsorbate-adsorbate being relevant to the whole process. The adsorption capacity was approximately 60 mg g^-1 and the adsorbents performance in the fast-contact system showed removal of 65%wt. of a 93 mg L^-1 methylene blue (MB) solution in a single application.