Effect of Functionalization Synthesis Type of Amino-MCM-41 Mesoporous Silica Nanoparticles on Its RB5 Adsorption Capacity and Kinetics

This study was undertaken to evaluate the adsorption of Reactive Black 5 dye (RB5), in aqueous solution, onto MCM-41 mesoporous silica nanoparticles (MSNs) functionalized with 3-aminopropyltriethoxysilane (APTES) by two methods: co-condensation and post-synthesis. The morphological and surface properties of both functionalized materials were compared by SEM, SAXS, N2 sorption and XPS characterization techniques. Sorption experiments were performed in order to determine the effect of pH, contact period and initial concentration of aqueous RB5 on the adsorption properties of bare- and both types of amino-MSNs. The results show that there exist morphological changes in the nanoparticles according to the type of functionalization synthesis, i.e. loss of hexagonal structure in co-condensation method and more density of amino groups on the surface of post-synthesis functionalized materials. The adsorption of RB5 on both type of materials is independent of the pH since they present adsorptions close to 100% in the evaluated pH range. The best fit of the data from adsorption kinetic studies is a pseudo-second-order model, being the material functionalized by the co-condensation method, which presents a higher adsorption rate because of its greater pore volume. The adsorption isotherms fitted well to the Langmuir model, with the amino-MSNs functionalized via the post-synthesis method presenting a higher capacity of adsorption, due to a greater density of amino groups on its surface, thereby facilitating their interaction with the RB5 molecules. Altogether, the results indicate that the type of functionalization synthesis affects the morphological characteristics of the nanoparticles and these, in turn, modify their adsorption properties.