Insights in the adsorption of eco-friendly starch hydrogel

This work prepared a class of starch hydrogel with and without lignin from sugarcane bagasse (5% wt.) and trisodium citrate as a crosslinking agent. The physical and chemical properties of the hydrogels were characterized by Fourier-transformed infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Thermogravimetric analysis (TGA), and X-ray diffractometry (XRD) techniques. Besides, the swelling degree and the pH of zero point charge (pH(zpc)) were evaluated. Hydrogels were tested for the adsorption of potentially toxic elements (PTEs) and dye (methylene blue) by chromatography and UV-vis, respectively. FTIR confirmed that the reticulation of the starch structure successfully occurred, while the inclusion of lignin promoted new interactions that increased pore size, swelling degree, and pH(zpc) of the developed hydrogels. The adsorption of cationic metals at pH < pHzpc showed low removal but presented complete adsorption of oxyanion chromium. Moreover, the adsorption of methylene blue presented removal higher than 90%, further enhanced by lignin presence, which presented an adsorption capacity of 99.4 mg.g(-1) at 70 min. The hydrogels presented a better fit to the Freundlich isotherm model, indicating that removal is favorable. Thus, using lignin in the hydrogels can enhance their performance and be an alternative to developing new eco-friendly materials.