Highly efficient and selective adsorption of malachite green onto granular composite hydrogel

•3D structured composite hydrogel can be obtained in the form of granules.•The hydrogel can be prepared at room temperature and atmosphere conditions.•The hydrogel shows fast, high and pH-independent adsorption properties to MG.•The hydrogel shows excellent adsorption selectivity for cationic dyes.

A series of granular composite hydrogels were prepared at room temperature and atmospheric oxygen via a facile in-situ polymerization using chitosan as the grafting backbone, acrylic acid (AA) and itaconic acid (IA) as the monomers, and attapulgite (APT) as the inorganic component. The resulting AA–IA–APT hydrogel is well characterized to possess a three-dimensional structured polymeric network and can be used for the adsorption of malachite green in single or mixed dye solution due to its anionic characteristics. The introduction of a small amount of APT (5 wt%) into the hydrogel can not only accelerate the adsorption rate, but also improve the adsorption capacity. The adsorption isotherm obeys the Langmuir model, with the saturation adsorption capacity of 2433 mg/g for the composite hydrogel AA–IA–APT5. The as-prepared composite hydrogel shows almost a constant and high adsorption capacity in a wide pH range from 4.0 to 10.0 and, can be regenerated and reused for several times. Furthermore, the composite hydrogel shows high adsorption selectivity for cationic dyes in the case of mixed dyes.

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