Preparation of biomass-based hydrogels and their efficient heavy metal removal from aqueous solution
Mingyue Zhang, Yaru Zhou, Fangling Wang, Zeshao Chen, Xu Zhao, Weidong Duan, Guangting Yin, Xinling Yang, Junfeng Li, Quanyu Yin, Mingqin Zhao
Abstract
In this work, a porous tobacco straw-based polyacrylic acid hydrogel STS-PAA with high adsorption performance was prepared by polymerizing pretreated waste tobacco straw (TS) with acrylic acid/potassium acrylate by UV radiation initiation. The adsorption performance of metal ions was investigated. The effects of different temperatures (25°C, 35°C, and 45°C), adsorption times (1–420 min), pH values (2.0–6.0) and initial concentrations (0.25–4.0 mmol L −1 ) of metal ions on the adsorption amount of heavy metal ions were investigated. The results showed that the hydrogel had a high removal rate of Pb 2+ , Cd 2+ and Hg 2+ in aqueous solution. The adsorption of Pb 2+ was particularly effective. When C 0 = 4.0 mmol L −1 , pH = 6, the equilibrium adsorption amount of Pb 2+ , Cd 2+ and Hg 2+ reached 1.49 mmol g −1 , 1.02 mmol L −1 and 0.94 mmol g −1 , respectively. The chemical structure and morphology of the hydrogels were characterized by FT-IR, EDS, SEM and XPS. The Langmuir model fits well with the adsorption system. The kinetic data suggest the adsorption of Pb 2+ , Cd 2+ and Hg 2+ follow the pseudo-first-order model. This indicates that STS-PAA adsorption of three heavy metal ions is monolayer physical adsorption. Thermodynamic analysis shows that the adsorption of Pb 2+ , Cd 2+ and Hg 2+ by STS-PAA is an endothermic (ΔH>0) entropy increase (ΔS>0) non-spontaneous reaction.