Three-dimensional porous hydrogel based on hyperbranched polyethyleneimine functionalized apple pomace derived cellulose for efficient removal of methyl orange

The efficient reuse of agricultural wastes such as apple pomace has always been a research focus because it increases the economic added value of apple pomace and reduces environmental pollution. Using cellulose, the main component of apple pomace, is an important way to reuse apple pomace resources. Cellulose is widely used as a good adsorption material to remove dyes from water. However, the effective adsorption sites of cellulose are few, and the binding force between adsorption functional groups and dyes is weak, resulting in the unsatisfactory adsorption performance of cellulose. To solve these problems, first, cellulose from apple pomace was oxidized to easily modified dialdehyde cellulose (DAC), and a series of factors was optimized to obtain DAC with high aldehyde content. Second, an HPEI-DAC hydrogel with a three-dimensional porous structure characterized by FTIR, XPS and SEM was prepared by crosslinking hyperbranched polyethyleneimine (HPEI) containing many amine groups with DAC. Because of its special topological structure and increasingly stronger adsorption sites, the HPEI-DAC hydrogel exhibited good adsorption performance for methyl orange (MO). The effects of the DAC/HPEI ratio, synthesis temperature, pH value and HPEI-DAC dosage on the adsorption property of HPEI-DAC for MO were studied. The HPEI-DAC hydrogel exhibited an adsorption capacity as high as 416.72 mg/g for MO. For the MO adsorption process, the adsorption kinetics and equilibrium data were consistent with the pseudo-second-order and Langmuir isotherm models, respectively. Moreover, the HPEI-DAC hydrogel could be easily regenerated and showed good reusability. After six cycles of adsorption/desorption, the adsorption capacity of the HPEI-DAC hydrogel remained at the initial value of 70 %. Therefore, the HPEI-DAC hydrogel can be considered a good adsorption material for treating azo dye wastewater.