Improved adsorption performance of rubber-based hydrogel: optimisation through response surface methodology, isotherm, and kinetic studies

Batch adsorption experiments were carried out for the removal of methylene blue (MB) cationic dye from its aqueous solution using rubber-based hydrogel. In this work, the adsorption of two rubber-based hydrogels, namely maleated liquid natural rubber/acrylic acid hydrogel (LNR-g-MaH/AAc) and maleated liquid natural rubber/acrylic acid/montmorillonite hydrogel (LNR-g-MaH/AAc/MMT), was optimised by response surface methodology (RSM) using a central composite rotatable design (CCRD). The effects of various parameters, such as adsorbent mass and initial concentrations of MB, were examined. The hydrogels were characterised using field emission scanning electron microscopy, thermogravimetric analysis (TGA), and fourier-transform infrared (FTIR). A total of 13 experiments were conducted to establish a quadratic model. Among those two rubber-based hydrogels, LNR-g-MaH/AAc/MMT hydrogel had higher optimum adsorption efficiency with 99.07% of dye removal percentage. The optimum dye performance of LNR-g-MaH/AAc hydrogel was also effective as the dye removal percentage was about 95.46%. Those responses were recorded when the adsorbent mass and initial concentration of MB were optimally set as 0.55 g, and 5.50 mg L-1, respectively. The Freundlich isotherm model was found to be best fitted to adsorption for those two hydrogels. The maximum adsorption capacities were 1.85 mg/g for LNR-g-MaH/AAc and 9.74 mg/g for LNR-g-MaH/AAc. Two kinetic models were tested to correlate the experimental data and the sorption was discovered to fit well with the pseudo-second-order kinetic model. It was found that by introducing of montmorillonite (MMT) could improve the adsorption ability of the LNR-g-MaH/AAc hydrogel.