Adsorptive Removal of Methylene Blue Dye from Aqueous Solutions by Polyvinyl Alcohol/Activated Carbon Nanocomposite Hydrogels

Polyvinyl alcohol/activated carbon (PVA/AC) nanocomposite hydrogels were prepared using a cyclic freezing-thawing process and successfully used to eliminate methylene blue dye from aqueous media. Characterization of the produced adsorbents was performed using Fourier transform infrared spectroscopy, X-ray diffraction, dynamic light scattering, field emission scanning electron microscopy, Brunauer-Emmett-Teller analysis and gel fraction tests. The swelling abilities of the adsorbents and also the methylene blue diffusion coefficients were determined in acidic, neutral and alkaline media. The contributions of four main factors, including the pH, loading level of activated carbon, initial concentration of methylene blue and temperature on the removal of methylene blue were investigated using the Taguchi method. The results revealed that by increasing the loading level of activated carbon in the adsorbent, the gel fraction was increased while the swelling ratio and methylene blue diffusion coefficient decreased. Meanwhile, by increasing the pH and temperature, the swelling ratio and methylene blue diffusion coefficient increased. The adsorption data showed that the initial concentration of methylene blue had little impact on the adsorption process, while the pH and activated carbon loading level were the most influential factors in the adsorption process. Additionally, the isotherm and kinetics studies demonstrated that the Langmuir isotherm model and the Webber-Morris kinetic model described appropriate fits to the adsorption process data.