Preparation of composite hydrogels containing fly ash as low-cost adsorbent material and its use in dye adsorption

Recycling industrial wastes is necessary for the economy and the environment. Additionally, it is important to develop high-efficiency adsorbents to prevent severe water pollution caused by wastewater containing dye agents. Here, poly(2-acrylamido-2-methylpropane sulfonic acid)-fly ash composite hydrogel was synthesized with a variety of fly ash proportions with the radical polymerization method. The synthesized composite hydrogel was used for adsorption of methylene blue and methyl orange dyes from water containing dye agents. A variety of parameters such as initial dye concentration, solution pH, anion effects, temperature, contact time and adsorbent amount were investigated for optimization of the adsorption process. The poly(2-acrylamido-2-methylpropane sulfonic acid)-fly ash composite hydrogel was determined to be an effective adsorbent to remove both the cationic dye methylene blue (1438.68 mg g(-1)) and the anionic dye methyl orange (646.54 mg g(-1)). Experimental adsorption data were assessed with a variety of isotherm and kinetic models. It was determined that the adsorption of both dye molecules abided by the pseudo-second-order kinetic model. The thermodynamic parameters were determined as Delta H degrees = - 15.77 +/- 5.22 kJ mol(-1), Delta S = - 45.05 +/- 16.42 J mol(-1) K-1 and Delta G degrees < 0 for MB, Delta H degrees = - 20.13 +/- 4.83 kJ mol(-1), Delta S = - 72.87 +/- 15.20 J mol(-1) K-1 and Delta G degrees > 0 for MO. In conclusion, a material was synthesized that can be used as a single adsorbent composite material for both anionic and cationic dyes. In addition to the perfect adsorption capacity of this material, it offers reusability and a broad area of application for a variety of dye agents.