Direct regeneration of hydrogels based on lemon peel and its isolated microcrystalline cellulose: Characterization and application for methylene blue adsorption

In this study, we developed a facile and eco-friendly fabrication of hydrogels based on lemon peel (LP) and its isolated microcrystalline cellulose (LPMCC) by direct co-dissolving in 1-butyl-3-methylimidazolium chloride (BmimCl), followed by direct regeneration in distilled water to form hydrogels. The influence of LP addition on the structure and methylene blue (MB) adsorption of the hydrogels was systematically investigated. The hydrogels displayed a physically cross-linked network through hydrogen bonding interactions. Compared with pure LPMCC hydrogel, the introduction of LP increased the porosity and improved the thermal stability of the hydrogels. The adsorption process of MB on the hydrogels conformed better to the pseudo-second-order kinetic (R2 > 0.993) and Langmuir isotherm models (R2 > 0.996). The MB adsorption process was feasible, spontaneous and exothermic in nature, and was influenced by initial MB concentration, pH, temperature, ionic type and strength. Notably, the introduction of LP improved MB adsorption capacity of the hydrogels. This work develops a facile approach of agricultural by-products based hydrogels using pure cellulose as the structural skeleton and untreated lignocellulose components as the structure modifier.