Ordered cubic mesoporous silica KIT-5 functionalized with carboxylic acid groups for dye removal

Abstract

Cubic cage-type KIT-5 mesoporous silica functionalized with carboxylic acid (–COOH) groups, ranging from 0 to 45 mol% based on silica, were synthesized via co-condensation of tetraethyl orthosilicate (TEOS) and carboxyethylsilanetriol sodium salt (CES) in the presence of Pluronic F127 in acidic media. The materials thus obtained were characterized by powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, FTIR, thermogravimetric analysis, acid–base titration, and solid-state NMR measurements. The –COOH functionalized KIT-5 was used to adsorb different types of dyes such as phenosafranine (PF), methylene blue (MB), orange II (OII) and rhodamine B (RhB). The –COOH functionalized KIT-5 materials exhibited excellent adsorption capacities for cationic PF and MB, and amphoteric RhB in comparison to pure silica KIT-5, but the opposite for anionic OII. The adsorption was highly dependent on the electrostatic interaction between the adsorbent and the dye molecules. External mass transfer and intra-particle diffusion collectively control the adsorption process.