Decontamination of methylene blue from aqueous media using alginate-bonded polyacrylamide/carbon black nanocomposite hydrogel

This work synthesized the novel alginate (Alg) based nanocomposite hydrogel using the free radical polymerization method to remove methylene blue (MB) from the aqueous solution. The successful grafting of acrylamide (AAm) monomer onto the alginate backbone was confirmed by the FTIR test. Different carbon black (CB) nanoparticle levels (0–12.5 wt.%) were embedded in a hydrogel matrix to enhance the removal efficiency, and its optimum value was obtained at 7.5 wt.%. FTIR, TGA, BET, and SEM analyses were performed to characterize synthesized adsorbents. TGA results showed that Alg-g-poly(AAm)/CB nanocomposite hydrogel has a higher thermal stability than Alg-g-poly(AAm) hydrogel. SEM analysis showed that incorporating CB into Alg-g-poly(AAm) considerably enhances roughness and surface area. Also, a higher surface area of Alg-g-poly(AAm)/CB (2.5 m²/g) was confirmed by BET analysis. The removal efficiency of nanocomposite hydrogel at optimum conditions of pH 6, initial concentration 10 mg/L, temperature 25 °C, and contact time 60 min was calculated at 94.63%. The kinetic and isotherm data were best fitted to pseudo-second-order and Langmuir models. The monolayer adsorption capacity for Alg-g-poly(AAm) and Alg-g-poly(AAm)/CB were calculated at 22.77 and 24.56 mg/g, respectively, showing CB's effectiveness in improving MB adsorption. The thermodynamic study showed that the removal process of MB by both adsorbents is spontaneous and exothermic, and entropy decreases. The synthesized adsorbents showed a good performance in textile wastewater treatment. Finally, it can be concluded that the synthesized adsorbents can be successfully applied for wastewater treatment application.