Polyethylene Glycol-Modified Layered Double Hydroxides: Synthesis, Characterization, and Study on Adsorption Characteristics for Removal of Acid Orange II from Aqueous Solution

The present study aimed to improve the adsorption characteristics of the pristine layered double hydroxide (LDH) by physicochemical modification using polyethylene glycol (PEG(400)), a nontoxic hydrophilic polymer. With this objective, LDH was synthesized and modified with different concentrations of PEG(400). The PEG-modified LDHs (LDH/PEGs) were characterized using X-ray diffraction, thermogravimetric analysis, Brunauer-Emmett-Teller surface area and porosity measurement, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and zeta potential measurements. The adsorption properties of the pristine LDH (PLDH) and the LDH/PEGs were studied for the removal of Acid Orange II from water, and the results were compared. The PLDH treated with 15% PEG solution showed similar to 30% increase in adsorption capacity as compared to the PLDH. The adsorption isotherm data were analyzed using Langmuir, Freundlich, and Temkin isotherm models. The values of thermodynamic parameters such as Delta S and Delta H showed the spontaneous and endothermic nature of the adsorption process. The adsorption kinetics data for both PLDH and the LDH/PEG adsorbents presented a good fit to the pseudo-second-order kinetic model.