Adsorption characteristics of beta-lactam cefixime onto nanosilica fabricated from rice HUSK with surface modification by polyelectrolyte

Abstract

The present study aims to investigate adsorption of beta-lactam cefixime (CEF) onto strong polycation, polydiallyldimethylammonium chloride (PDADMAC) modified nanosilica (PMNS). Nanosilica fabricated from rice husk with purity greater than 99.6% was confirmed by X-ray fluorescence (XRF) spectroscopy while a particle size of 20 nm was determined by transmission electron microscopy (TEM). The specific surface area of nanosilica by Brunauer - Emmett – Teller (BET) method was 160.5 m2/g. The surface of nanosilica was modified by pre-adsorption of PDADMAC at pH 10 and 100 mM KCl in order to enhance highly positive charge of PMNS. The effective conditions for removal CEF using PMNS were found to be contact time 90 min, pH 4 and adsorbent dosage 10 mg/mL. Under the optimum adsorption conditions, CEF removal from aqueous solution increased significantly from 24.55% to 93.51%. Adsorption isotherms of CEF onto PMNS at different salt concentrations were fitted well by two-step model while adsorption kinetics agreed well with the pseudo-second-order kinetic model. Adsorption of CEF onto PMNS decreased with an increase of ionic strength, demonstrating that adsorption of CEF onto PMNS is mainly controlled by electrostatic attraction between anionic CEF molecules and positively charged PMNS surface. After four regenerations of PMNS, the removal of CEF still reached to 90%. The removal of CEF from an actual hospital wastewater using PMNS was higher than 75%. Our results suggest that PMNS is a novel adsorbent to remove antibiotics from aqueous solutions.