High density (3-aminopropyl) triethoxysilane grafted silica aerogel-based materials for cefixime adsorption: Optimization of preparation and grafting method, experimental design, kinetic and equilibrium study

Abstract

In this study, the effective removal of cefixime antibiotic by pumice derived silica aerogel (PDSA) functionalized with (3-aminopropyl) triethoxysilane (APTES) was investigated. The PDSA with 656 m2/g specific surface areas was obtained at 12 h of aging time. The amorphous phase of PDSA samples were confirmed by X-ray diffraction analysis. Spherical and homogeneous morphology with a mean diameter of <25 nm without any agglomeration was confirmed by field emission scanning electron microscopes. The formation of pearl-necklace-like skeletal structure containing silica particle ranging from 2 to 18 nm in the PDSA backbone was observed by transmission electron microscopy. The PDSA was successfully grafted with high density amine groups (AMPDSA) using a nonpolar solvent and tetraethyl orthosilicate as a co-hydrolyzer, at 80 °C, under reflux. The lowest and highest amine coverage was 5.83 µmol/m2 and 6.52 µmol/m2; respectively. Up to 80% removal efficiency was achieved in a solution containing 3.56 mg/L of cefixime at pH 3 with a 1 g/L adsorbent and contact time of 150 min (optimal condition). Successful sorption of cefixime on the AMPDSA adsorbent was confirmed by FTIR. The Kinetics of cefixime adsorption onto the AMPDSA was best explained using modified pseudo-first-order, pseudo-first-order, pseudo-second-order, and intra-particle diffusion models with higher correlation coefficient to the pseudo-second-order model. The equilibrium data were best fitted onto several two and three parameter isotherm models with higher correlation coefficient (R2) and lower residual sum of squares (RSS) for Khan equation. Accordingly, the maximum adsorption capacity was calculated to be 49.63 mg/g. Based on the findings of this study, AMPDSA is an effective and low-cost adsorbent which can be used as a beneficial agent to remove cefixime, and probably other pharmaceuticals, from aqueous solutions.