Study of Congo Red and Methyl Orange Removal from Aqueous Solutions by Silica-Based Microspheres

Silica-based microspheres were synthesized by modified Stӧber method. The structure characteristic and the adsorption capacity of microspheres calcined and uncalcined for dyes, Congo red and methyl orange, were compared. The uncalcined microspheres showed better adsorption performance for the two dyes and the cause was analyzed. The adsorption process of microspheres for the two dyes accorded with the pseudo-second-order kinetic model. Both Langmuir isotherm and Freundlich isotherm could fit the experimental data well. The maximum adsorption capacity of microspheres for Congo red and methyl orange could reach 416.67 and 285.71 mg/g, respectively, according to the Langmuir isotherm model. It was inferred that the spontaneous adsorption process was endothermic and driven mainly by physical adsorption through thermodynamic parameters calculated.