Zn-Al layered double hydroxide / polyurethane as a novel nanocomposite for cefixime antibiotic adsorption

Wastewater contaminated with antibiotics requires innovative solutions to remove such pollutants efficiently. In this work, Zn-Al layered double hydroxide (LDH) adsorbent supported on polyurethane (PU) (Zn-Al LDH/PU) was synthesized using a simple co-precipitation method. The synthesized material was characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), zeta potential, and hydrodynamic size. This adsorbent was investigated for the removal of cefixime (CFX), which is a model third-generation cephalosporin antibiotic. The LDH phase showed a typical hexagonal layered morphology with layer sizes larger than 200 nm in diameter. CFX adsorption on PU, Zn-Al LDH and Zn-Al LDH/PU showed a maximum adsorption capacity of 94.43, 57.17, and 115.69 mg/g, respectively. The Redlich-Peterson and Baudu isotherm models were found to be the best fit models for CFX adsorption of Zn-Al LDH and Zn-Al/PU, respectively. The equilibrium time was found to be 175 and 250 min for CFX adsorption of Zn-Al LDH and Zn-Al/PU, respectively. CFX adsorption kinetics on Zn-Al LDH/PU best fitted the pseudo-second order model indicating chemisorption and diffusion limited adsorption process. Numerous types of bonding between functional groups of CFX and both Zn-Al LDH and PU could explain the adsorption mechanism. The selectivity study of CFX adsorption on Zn-Al LDH/PU using Sulfamethoxazole and Ciprofloxacin with different concentrations was investigated and discussed. The recyclability of this Zn-Al LDH/PU was also studied. Also, the effect of temperature was investigated at (23, 35, 45, 55 °C) and the thermodynamic parameters (∆H°, ∆S° and ∆G°) were calculated showing exothermic and spontaneous adsorption process.The methyl thiazolyl tetrazolium (MTT) assay indicated that the biocompatibility of Zn-Al LDH nanostructures was enhanced following modification with PU, demonstrating regulated and minimal cytotoxic effects towards normal liver cell line (WRL-68). The Zn-Al LDH/PU can be considered as a promising low-cost adsorbent for CFX antibiotic from wastewater streams.