Synthesis of Bio‐Based Hydroxyethyl Cellulose Superabsorbent Hydrogel for Successful Removal of Methylene Blue From Aqueous Medium

ABSTRACT To make bio‐based superabsorbent hydrogel (Bio‐SAH), hydroxyethyl cellulose (HEC) and 2‐acrylamide‐2‐methylepropanesulphonic acid (AAMPSA) were used as the polymer and monomer, respectively. This was done using free radical copolymerization. The synthesized Bio‐SAH was characterized by SEM, FT‐IR, and rheometer. A batch adsorption study was carried out to study the removal efficiency of Bio‐SAH toward methylene blue (MB) in an aqueous medium. The swelling properties of the superabsorbent were investigated by varying concentrations of AAMPSA, keeping the concentration of HEC constant and very high values of % swelling were observed in all three prepared hydrogels (For H 1 , % swelling was 2946, for H 2 it was 2163% and in the case of H 3 swelling was found to be 1183%). We studied various parameters in detail, including the effect of time, temperature, pH, dye initial concentration, and hydrogel dosage. We found the prepared hydrogel's adsorption capacity to be very close to the theoretical value. The kinetic study revealed that the adsorption process follows pseudo‐second‐order kinetics. Thermodynamic parameters calculated through Langmuir isotherm were ∆ G ° (−9.52 kJ mol −1 ), ∆H° (16.72 kJ mol −1 ), and ∆ S ° (0.08 J mol −1 K −1 ). We recycled and reused the hydrogel five times, with almost 95% removal efficiency for MB dye. Rheological tests were investigated at various temperatures and it has also been observed that at high temperatures, viscosity decreases significantly as compared to that at low temperatures. Also, storage moduli ( G ′) were found to be larger than loss moduli ( G ″) for the whole range of angular frequency thus, indicating that the viscous properties of the hydrogel were less dominant as compared to elastic properties, making the hydrogel material more solid‐like mocked plastic material, which confirms its suitability for environmental applications.