Adsorption behavior of cationic dye on mesoporous silica SBA-15 carried by calcium alginate beads: Experimental and molecular dynamics study

Abstract

This paper describes the fabrication of composites beads based on functionalized SBA-15 materials encapsulated in calcium alginate (ALG) which are employed for removing methylene blue (MB). The prepared composites beads were characterized by various techniques such as XRD, FTIR, SEM, zeta potential measurements and TGA. As results, the SBA-15 material was well immobilized in the alginate matrix. The best adsorbent beads were determined by evaluating the kinetics of MB adsorption from aqueous solutions. It has also been established that the hydrogel beads with a pure SBA-15 have a negative surface and therefore a greater capacity for adsorption of cationic dye compared to the adsorbents beads containing amine-functionalized SBA-15. The combination of two matrices (Pure SBA-15 and alginate) containing negatively charged surfaces generates excellent properties through the removal of the MB dye. The maximum adsorption capacity of the ALG-SBA-15 composite was 333.33 mg.g−1. The adsorption well followed the pseudo-second-order kinetics and Langmuir isotherm, and was spontaneous endothermic process. The adsorption of MB dye on the ALG-SBA-15 beads could be easily realized through electrostatic interactions and hydrogen bonding. Furthermore, molecular dynamic (MD) simulations were performed on pure SBA-15 structure models with different pore diameters to get a glimpse on the dynamic behavior of MB molecules upon adsorption on the mesoporous material.