Preparation of Hydrogels Based Radix Isatidis Residue Grafted with Acrylic Acid and Acrylamide for the Removal of Heavy Metals

Abstract

A series of hydrogels as biosorbents to remove heavy metal ions (Pb2+, Cu2+, and Cd2+) were prepared using Radix Isatidis residues as material grafted with acrylic acid and acrylamide. The surfaces of Radix Isatidis residue/acrylic acid-co-acrylamide (RIR/AA-co-AM), Radix Isatidis residue/polyacrylamide (RIR/PAM3), and Radix Isatidis residue/polyacrylic acid (RIR/PAA4) hydrogels have a sponge-like, three-dimensional, and highly microporous structure. The hydrogels all have considerable swelling properties and the swelling rate of RIR/PAA4 is the highest at 9240%. The hydrogels all possess high adsorptivity to Pb2+, Cu2+, and Cd2+. Under optimized conditions, the maximum adsorption capacity of RIR/AA-co-AM hydrogel is 655.4 mg/g for Pb2+, 367.2 mg/g for Cd2+, and 290.5 mg/g for Cu2+. The maximum adsorption capacity of RIR/AA-co-AM hydrogel for Cd2+ and Cu2+ is slightly lower than that of RIR/PAA4. In addition, the adsorption process of RIR/AA-co-AM for heavy metal ions conforms with the pseudo-second-order kinetic equation and Langmuir adsorption isotherm. Based on the microstructure analysis and adsorption kinetics, electrostatic adsorption and ion exchange are identified as the mechanisms for the hydrogels removal of heavy metal ions from water. It infers that hydrogels from Chinese herb residue can be used to effectively remove heavy metals from wastewater and improve the reutilization of Chinese herb residue.