Egg White Protein–Soybean Protein Isolate Hierarchical Network Hydrogel for Enhanced Adsorption of Methylene Blue

Abstract

In terms of environmental protection and the sustainable development of society, the constraint of dye concentrations in industrial wastewater is vitally important for the development of every country. In this study, egg white protein (EWP)–soybean protein isolate (SPI) hierarchical-network hydrogel beads reinforced with calcium alginate are devised using a one-step chemical crosslinking. The prepared EWP/SPI beads, with a specific surface area of 26.55 m2∙g−1, possess a self-floating ability that enhances their solid–liquid separation of methylene blue (MB) from industrial sewage and achieves adsorption equilibrium within 60 min. The investigation of adsorption behavior indicates that the results fitted well with the Langmuir isotherm mode and pseudo-first-order kinetic model. Based on the pseudo-first-order kinetic model and the Langmuir model, the equilibrium adsorption capacity and maximum adsorption capacity of the EWP/SPI hydrogel beads towards MB are 187.495 and 336.265 mg∙g−1, respectively. Furthermore, the favorable regeneration of the EWP/SPI hydrogel is demonstrated, with a removal efficiency towards MB decreasing from 94% to 82% (10 mg dose, 100 mg∙L−1 MB, pH 7, 25 °C) after five adsorption–desorption cycles. The resulting EWP/SPI hydrogel beads with hydrophilicity exhibited good self-floating stability (above 80%) in wastewater for 7 days, suggesting their potential for recycling in diverse complex environments. Therefore, the inexpensive and sustainable floating EWP/SPI hydrogel beads provide a new insight for organic pollutant treatment in wastewater.