Green biosorbents based on glutaraldehyde cross-linked alginate/sepiolite hydrogel capsules for methylene blue, malachite green and methyl violet removal

In the synthesis of alginate-based composites, new materials consisting of alginate (Alg) as biopolymer matrix, sepiolite (Sp) and glutaraldehyde as cross-linking agents were obtained. The removal of methylene blue (MB), malachite green (MG) and methyl violet (MV) from the aqueous medium by the adsorption process was investigated by using the synthesized new glutaraldehyde cross-linked alginate/sepiolite hydrogel capsules (Alg/Sp-g). Experimental parameters affecting the adsorption process such as dye concentration, contact time, amount of adsorbent, solution pH and temperature were studied, and Langmuir, Freundlich, Scatchard, Temkin and Dubinin-Radushkevich (D-R) adsorption isotherm models were used to investigate the obtained experimental data. It was determined that the adsorption of methylene blue, malachite green and methyl violet with Alg/Sp-g was more suitable for Langmuir isotherm model and pseudo-second-order kinetics. According to Langmuir isotherm, the maximum adsorption capacity of MB, MG and MV was found to be 294.1, 122.0 and 357.1 mg/g, respectively. It was observed that the adsorption kinetics fit the pseudo-second-order model. Thermodynamic evaluation of adsorption showed that adsorption is exothermic and adsorption is spontaneous. Recovery studies have shown that Alg/Sp-g composite has good adsorption/desorption performance.