Removal of basic fuchsin from aqueous solution using polyacrylamide and gellan gum-based hydrogels

Hydrogels have emerged as promising “smart sorbents” for wastewater treatment due to their simple fabrication, environmentally friendly nature, and quick regeneration. In the present study, hydrogels comprising polyacrylamide and gellan gum/acrylamide (GG-co-pAAm) were synthesized through free-radical polymerization, incorporating varying percentages of gellan gum as a biopolymer backbone. The hydrogels were characterized using scanning electron microscopy and Fourier transform infrared spectroscopy. The swelling behavior of the synthesized hydrogels was evaluated in tap and distilled water at neutral pH and within the pH range of 4.2–11.2. Swelling at neutral pH was 2623% for pAAm, 2104% for (GG-co-pAAm)-10%, and 1841% for (GG-co-pAAm)-20% hydrogel samples in distilled water, while high swelling was observed at high pH for all the samples. Maximum dye adsorption was observed for (GG-co-pAAm)-20% compared to (GG-co-pAAm)-10% and PAAm. The adsorption process was influenced by changes in pH, and dye adsorption increased with an increase in the solution's pH. Different kinetic and isotherm models were used to investigate adsorption mechanisms. The pseudo-second-order kinetics and Freundlich isotherm model were found to be the best fits for kinetics and isotherms, respectively. Grafting parameters such as %G and %GE, along with various factors like temperature, initial dye concentration, contact time, and pH, were investigated. Thermodynamic analysis indicated the exothermic and spontaneous nature of BF adsorption, with negative ∆ H o values of − 6.720 for pAAm, − 9.465 for (GG-co-pAAm)-10%, and − 15.434 for (GG-co-pAAm)-20%. The adsorption capacity of the hydrogels increased with an increasing gellan gum concentration in the synthesized hydrogel, resulting in a 59% removal efficiency for polyacrylamide, 88% for (gellan gum-co-polyacrylamide)-10%, and 93% for (gellan gum-co-polyacrylamide)-20%. The swelling behavior of the hydrogels showed Fickian-type diffusion. The adsorbent was successfully regenerated with acetone and retained a removal capacity of ≥ 85% even after five consecutive cycles, demonstrating its reusability. Overall, the (GG-co-AAm) sorbent exhibits potential as an alternative to conventional adsorbents for wastewater treatment. Graphical abstract