Preparation And Heavy Metal Adsorption Studies Of A Novel Hydrogel

With the rapid development of modern industry, excessive emission of heavy metal ions is more severe. Heavy metal ions are bioaccumulative and difficult to degradate in the environment, and they can easily be enriched through the food chain, especially through polluting the water, which can be a direct threat to the environment and human health. In recent years, many severe blood lead poisoning events and river heavy metal pollution incidents have appeared in China. Thus, the removal of heavy metal ions of contaminated water bodies is imminent. Adsorption method has been a research focus in the removal of heavy metal ions from water, and the choice of the adsorbent has a decisive effect on removal efficiency. Most problems the common adsorbent faces are recycling and modification treatment, so the purpose of this research is to seek a kind of adsorbent which can be simply prepared and has good adsorption capacity of heavy metal ions, also can be easily recycled, providing a new way to solve the problem of water heavy metal contamination. In this paper, a novel poly(Hydroxyethyl methacrylate/Maleamic acid)(p(HEA/MALA)) hydrogel was synthesized by60Co-y induced copolymerization. The surface morphology, thermal stability, group and elemental composition of p(HEA/MALA) hydrogel were analysized by FT-IR, SEM, TGA and XPS characterization methods. The adsorption performance of the hydrogel were studied through batch experiments investigating the effects of pH, time, temperature, initial metal ion concentration and competition properties. The desorption and reuse of the hydrogel were explored by different desorbents. And its adsorption mechanism was discussed, the conclusions are as follows:1. A novel p(HEA/MALA) hydrogel with HEA and MALA as monomers was successfully synthesized using a60Co gamma source for24h to a total dose of30kGy at-78℃. SEM photos showed that p(HEA/MALA) hydrogel was a three-dimensional network polymer material having a certain pore structure. FT-IR and TGA analysis confirmed that the p(HEA/MALA) hydrogel was indeed a copolymer of HEA and Maleamic acid.2. The swelling performance of p(HEA/MALA) of different components showed that the swelling properties of the hydrogel were less affected by the hydrogel structure, which were mainly due to the proportion of HEA and MALA in hydrogel. The adsorption capacity experiments of the hydrogel illustrated that the adsorption of heavy metal ions on p(HEA/MALA) contains both chemical adsorption, which is affected by the functional groups, and physical adsorption, which is related to the adsorbent’s structure.3. The adsorption kinetics of Pb2+, Cd2+, Ni2+, Cu2+and Zn2+ions on p(HEA/MALA) followed pseudo-second-order kinetic model, the adsorption rate was controlled by chemical adsorption, and the adsorption rates followed the order Zn2+> Cd2+> Pb2+> Ni2+> Cu2+. The isotherm experimental data fitted better to the Langmuir model (R2>0.98) than the Freundlich model, demonstrating that the Pb2+, Cd2+, Ni2+, Cu2+and Zn2+on p(HEA/MALA) were removed through Langmuir monolayer adsorption.4. The adsorption process of p(HEA/MALA) hydrogel for heavy metal ions is endothermic reaction, in which the adsorption capacity decreased with the increase of temperature. Besides, the adsorption capacities of Pb2+, Cd2+, Ni2+, Cu2+and Zn2+on p(HEA/MALA) barely increased with the increase of pH from1to2, and increased rapidly with the increase of pH from2to4, but then leveled off (pH>4), suggesting that the adsorption mechanisms of Pb2+, Cd2+, Ni2+, Cu2+and Zn2+by p(HEA/MALA) hydrogel at different pH values may be the combined action of electrostatic interaction, chelation and ion-exchange. 5. The desorption capacity of EDTA-Na2was better than HNO3. The desorption efficiency by EDTA-Na2was more than92%. And the hydrogel could be reused3times.6. According to the competitive adsorption results, the priority order in multi-component adsorption was Pb2+> Cu2+> Ni2+> Zn2+> Cd2+, this may be that the competitive adsorption of the five heavy metal ions on p(HEA/MALA) is mainly affected by the metal electronegativity. The heavy metal with larger electronegativity has stronger competitiveness.7. The adsorption mechanism of Pb2+, Cd2+, Ni2+, Cu2+and Zn2+by p(HEA/MALA) is chemical adsorption-based, supplemented by physical adsorption. The physical adsorption is mainly dependent on the three-dimensional network structure of the hydrogel. And the chemical adsorption depends on the functional groups of the hydrogel. The specific mechanism of chemical adsorption is the the electrostatic interaction between the heavy metal ions and the functional groups in hydrogel, chelation between the metal ions and-NH2and ion exchange interaction between the heavy metal ions and-COOH groups.