Investigation of performance of bimodal/functionalized mesoprorous silica nanoparticles on the adsorption of methylene blue from aqueous solution

In this study, bimodal mesoporous silica, i.e. UVM-7, was synthesized and functionalized with sulfonic acid and characterized using XRD, nitrogen physisorption, SEM, TEM and acid/base titration. The results displayed that bimodal mesopore structure was firmly formed and acidic functional groups were grafted on the surface of the UVM-7. The concentration of the acidic functional groups was determined via titration by the standard NaOH solution. At the second step, the adsorption of methylene blue from aqueous solutions onto UVM-7 and UVM-7/ SO3H was investigated. The effect of PH, temperature, dye concentration, salt concentration and contact time on the adsorption of methylene blue was studied. The adsorption equilibrium isotherms were well fitted to Langmuir rather than Freundlich model. Methylene blue adsorption on UVM-7 increases with increasing the temperature and PH, which indicates that the process is endothermic. Maximum adsorption capacity of methylene blue by UVM-7 and UVM-7/SO3H were 107.5 mg/g and 129.9 mg/g, respectively. The adsorption kinetics of methylene blue for both UVM-7 and UVM-SO3H were pseudo-second order and well fitted to Langmuir model.