Highly porous egg white/polyethyleneimine hydrogel for rapid removal of heavy metal ions and catalysis in wastewater

The water pollution caused by the heavy metal ions have raised potent damages to the water ecosystem and human health. It is thus important to develop materials that can capture the heavy metal ions effectively and efficiently in the wastewater to resolve this issue. Herein, a highly porous functional hydrogel from the egg white (EW) integrated with polyethyleneimine (PEI) was prepared and examined for the adsorptive removal of the Cu2+, Pb2+ and Cd2+ ions in aqueous solutions. A systematic study was performed to illustrate the EW/PEI hydrogel's excellent affinity to the metallic ions in both the mono- and competitive adsorption systems. The maximum adsorption capacities for the Cu2+, Pb2+ and Cd2+ ions in the mono-adsorption system were determined to be 7.494, 2.194 and 3.705 mmol g−1, respectively with the adsorption rates and isotherms complying with the pseudo-second order kinetics and Langmuir isotherm model, respectively. Furthermore, in situ reduction turned the adsorbed Cu2+ ions into uniformly distributed Cu nanoparticles (NPs) in the EW/PEI hydrogel. This material can serve as an excellent catalyst as confirmed by a ~98% conversion of 4-nitrophenol (20 mmol) to 4-aminophenol in 10 min at the ambient temperature. The EW/PEI hydrogel and the Cu NPs-decorated EW/PEI hydrogel catalyst can be regenerated easily as proved by the consecutive adsorption/desorption and catalysis experiments for several repetitions, respectively. Therefore, the current study highlights the application of the EW/PEI hydrogel as an effective and practical approach for capturing and recycling/utilizing the toxic metal ions in the wastewater.