Graphene oxide/Mg-Zn-Al layered double hydroxide for efficient removal of doxycycline from water: Taguchi approach for optimization

Abstract

Graphene oxide/Mg-Zn-Al layered double hydroxide (GMZA) was synthesized and applied for the adsorptive removal of doxycycline. The material was characterized by FTIR, Raman, XRD, XPS, SEM with EDX, TEM and TGA-DTA. The variables of the adsorption process (contact time, pH, adsorbent dose and initial concentration) were optimized by Taguchi method. The optimum levels of variables were: contact time = 90 min; pH = 8; adsorbent dose = 15 mg and initial concentration of doxycycline = 100 mg/L. The material showed enhanced adsorption capacity (429.33 mg/g) for doxycycline. The equilibrium adsorption data fitted well to Freundlich isotherm model with R2 > 0.99 and χ2 ≤ 0.40. The pseudo-second order kinetic model was the best fit model with R2 > 0.998 and χ2 ≤ 0.20. The thermodynamic parameters suggested the endothermic and spontaneous nature of adsorption process. The adsorption mechanism was explained on the basis of kinetic data, FTIR and Raman spectroscopy. The results suggested the involvement of electrostatic interaction, π-π interaction and H-bonding in the adsorption of doxycycline on the adsorbent. Adsorption/desorption test demonstrated that the material can be used upto 5 cycles.