Removal of Methylene Blue from Aqueous Solutions Using Poly(vinyl alcohol)/Montmorillonite Nanocomposite Hydrogels: Taguchi Optimization

Abstract

Nanocomposite hydrogel adsorbents on the basis of poly(vinyl alcohol) containing 0, 4, 8 and 12 wt% (based on dry basis) of montmorillonite were prepared using a cyclic freezing–thawing process. The capabilities of the adsorbents in adsorbing of a cationic dye, methylene blue, were studied in aqueous solutions having different temperatures, pH and concentrations. The Taguchi method was utilized to optimize the controllable factors, including the montmorillonite loading level, the solution temperature and pH and also the methylene blue concentration in adsorption solution. The prepared nanocomposite hydrogel adsorbents were characterized by Fourier transform infrared spectroscopy and their gel content and swelling values were also measured. The results showed that the gel content and swelling of nanocomposite hydrogel adsorbents had a direct and inverse dependency to the loading level of incorporated montmorillonite to adsorbent, respectively. The successful dye adsorption by the prepared nanocomposite hydrogel adsorbents was confirmed by the Fourier transform infrared spectroscopy. Based on the Taguchi method, the optimized conditions for methylene blue adsorption were found as: montmorillonite loading level of 12 wt%, adsorption temperature of 50 °C, pH of the aqueous solution of 9 and methylene blue concentration in adsorption solution of 5 mg/L. The percentage contribution of each parameter on the removal of methylene blue was determined using the Analysis of Variance method and the following order was found: temperature > concentration of methylene blue in solution > montmorillonite loading level in adsorbent > pH.