Controlling textural, surface and adsorption characteristics of MCM-48 via hydrothermal treatment

Abstract

Excluding the autoclaving step in the synthesis recipe of MCM-48 resulted in the formation of silica lacking the three-dimensional channel system, the cubic microstructure and the surface silanol groups. This sample has poor wettability that limits the diffusion rate in aqueous media. Adsorption of methylene blue, MB, on such solid is pH-independent, dispersion forces-controlled, practically reversible, endothermic, non-spontaneous, and follows the pseudo-first-order kinetics and Freundlich mode of adsorption. The adsorbed molecules, 15 mg/g, lay flat on the surface with the formation of a double layer. The usual MCM-48 formed after autoclaving possessed a high adsorption capacity of 480 mg/g obtained through the specific mode of adsorption that increased with pH and proceeded practically irreversibly, exothermically, spontaneously, following the pseudo-second-order kinetics and favorable according to Langmuir model. In case of both types of obtained silica the adsorption of MB resulted in a general decrease in the entropy function.

Keywords

• MCM-48
• methylene blue
• autoclave
• adsorption
• pore structure