Grafted natural melanin κ-carrageenan hydrogel bead adsorbents: New strategy for bioremediation of cationic dye contamination in aqueous solutions

Pollution of water resources has become a global environmental problem, and the massive discharge of high-color printing and dyeing wastewater has caused serious harm to the natural environment. In this work, we have used repeated alkali solubilization and acid precipitation for an agricultural and forestry by-product, bilberry kernel shells, to obtain Mountain apricot shell Melanin (Mas-Mel), which can be used for the adsorption of cationic dyes. By graft copolymerization with a natural sugar-based polymer, κ-carrageenan (κCA), in a mild manner, we have prepared the adsorbent, Mountain apricot shell Melanin /κ-carrageenan (Mas-Mel/κCA) hydrogel beads, which were physically and chemically analyzed using a variety of spectroscopic and microscopic techniques. The optimum conditions for methylene blue (MB) adsorption and malachite green (MG) on Mas-Mel/κCA hydrogel were: contact time 150 min, adsorbent dose 60 mg, pH 6–7. The results of the adsorption tests followed the Pseudo-second order kinetics (R2 = 0.97 and 0.95), and the maximum adsorption capacity of MB and MG based on the Langmuir isotherm model was 48.63 mg/g and 37.84 mg/g, respectively. In addition, the prepared hydrogel beads still exhibited a high reusability and removal rate (∼50 %) after three consecutive 400-minute cyclic adsorption-resolution cycles. Our results may provide a new strategy for the development of green bio-based adsorbent materials and industrial dye wastewater treatment.