Adsorptive removal of gemifloxacin from aqueous solution using mesoporous Fe-incorporated silica pillared clay followed by thermal regeneration

Abstract

Fe-incorporated silica pillared clay (Fe/Si-PILC) was prepared by SiO2-pillaring of local clay (Iran), followed by Fe doping through a cost-effective process. The characterization tests were carried out on Fe/Si-PILC, Si-PILC, and the raw clay using BET-PSD, XRF, XRD, FTIR, DR-UV-Visible, TG, FESEM, and TEM, and the results confirmed the successful pillaring and Fe-incorporation processes. Gemifloxacin (GMF) adsorption from aqueous systems and the thermal regeneration of saturated sorbent were then investigated. The pillaring process increased the specific surface area by 15 times and the basal spacing by 3.5 times, resulting in a mesoporous structure with high thermal stability. GMF adsorption on Fe/Si-PILC was relatively fast (equilibrium time: 2 h), pH-dependent (optimum pH: 7), influenced by electrostatic interactions. Fe incorporation increased the adsorption capacity for GMF (3–22 % at different pHs in the range of 3–11). The pseudo-second order and Sips isotherm models provided the best fit to kinetic and equilibrium data. According to the Sips isotherm model, the maximum monolayer adsorption capacities of Fe/Si-PILC at 25, 40, and 55 °C were 349.8, 330.8, and 313.1 mg/g, respectively. The adsorption was exothermic and affected by hydrogen bonding, electrostatic interactions, and Lewis acid/base interactions. The prepared adsorbent was thermally stable, and heating under air flow at 500 ℃ for 15 min was sufficient to regenerate the GMF-saturated sorbent in five consecutive cycles.