All-biomass Cellulose/Casein Adsorbent Fabricated via the "Green Solvent System" of Ionic Liquid for the Efficient Removal of Cu(II), Cd(II) and Pb(II)

Abstract

Abstract The development of all-biomass adsorbents capable of effectively removing metal ions from wastewater is urgently required in accordance with the trend toward sustainable development and the requirements for environmental protection. In this study, a strategy was proposed to achieve convenient preparation of cellulose/casein composite hydrogel adsorbents (CE/CA) via adopting ionic liquid (IL) as a corporate solvent. The favorable solubility of IL and its negligible vapor pressure enabled the CE/CA to obtain a honeycomb-shaped surface structure while recycling IL in the material preparation process through simple vacuum evaporation technology. Consequently, the CE/CA exhibited a rapid adsorption rate (≤ 90 min) and extremely high adsorption capacities (≥ 230 mg g-1) toward Cu(II), Cd(II), and Pb(II), respectively. As indicated by the results of adsorption model fitting and XPS analysis, the binding of the CE/CA to the metal ions was primarily achieved through chemisorption and monolayer adsorption, and both cellulose and casein contributed to the high adsorption capacity of adsorbent through chelation. Lastly, the metal ions were removed at different concentrations (≥ 2 mg L-1) in simulated wastewater using the CE/CA. The results confirm that the aqueous solution treated with adsorbent can meet the safe drinking level standard (US EPA).