Effect of the amount and time of addition of a dye template on the adsorption and photocatalytic performance of molecularly imprinted silica

Abstract

A molecularly imprinted (MI) photocatalyst was prepared via an acid-catalyzed sol-gel route using Rhodamine B (RhB) as the template. The aim of this study was to evaluate the effect of the amount and time of addition of RhB on the photocatalytic degradation. The adsorption kinetics of MI silica xerogels were also investigated. Several methods of extraction were employed, and the use of ultrasound (in methanol) exhibited the best results with respect to increasing the surface area, template removal and economy of spent solvent volume. The samples were characterized in terms of their pore diameter, surface area and aggregation of primary particles using small-angle X-ray scattering. For systems containing a fixed mass of template (150mg), the textural evidence suggests that the large pores and large surface areas may explain the improved results that were achieved by systems where the template was added at t=0. In addition, the effect of the added template amount at a fixed time indicated that there is a threshold at which degradation was improved. The results suggest that using a higher template content in the synthesis of the photocatalysts may hinder removal from the silica network and increase the aggregation of molecules, affecting the photocatalytic performance.