Synthesis And Heavy Metal Ion Adsorption Studies Of A Magnetic Hydrogel

Humans have suffered a lot from exponential increase of using heavy metals in industrial processes. Thus, the removal of heavy metal ions of contaminated water bodies is imminent. Among the techniques used for heavy metal removal, adsorption is regarded as a more reliable choice with its advantages such as high efficiency, easy operation, variety of adsorption material, low cost and so on.This research aimed to seek a kind of adsorbent which can be simply prepared and has good adsorption capacity of heavy metal ions, and also can be easily recycled, providing a new way to solve the problem of water heavy metal contamination. In this study, a novel poly (L-cysteine/2-hydroxyethyl acrylate/)(P(Cys/HEA)) hydrogel was developed via60Co-γ-induced radiation copolymerization and utilized for in situ Fe3O4nanoparticles loading to prepare magnetic hydrogel Fe3O4P (Cys/HEA). The surface morphology, component structure of Fe3O4-P (Cys/HEA) hydrogel and its adsorption performance and adsorption mechanisms of Pb2+, Cd2+, Cu2+, and Cr3+were studied through batch experiments investigating the effects of pH, time, temperature, initial metal ion concentration and competition properties and a series of analysis methods, such as FT-IR, SEM, TGA and XPS characterization method. Seperation and regeneration studies were also carried out for further investigating the potential application of Fe3O4-P (Cys/HEA) hydrogel for the removal of heavy metal ions from wastewater.The conclusions are as follows:1. A novel P (Cys/HEA) hydrogel with Cys and HEA as monomers was successfully synthesized via60Co-y-induced radiation copolymerization at-78℃. Then the copolymer P (Cys/HEA) hydrogel was utilized for in situ Fe3O4nanoparticles loading to prepare magnetic hydrogel Fe3O4(Cys/HEA).2. SEM results showed that the hydrogel had a three-dimensional network structure and the pore size varied in the range of10～30μ m, and had been successfully loaded by Fe3O4nanoparticles; FTIR analysis showed that P (Cys/HEA) and Fe3O4-P (Cys/HEA) hydrogels were indeed a copolymer of Cys and HEA with amine and sulfhydryl groups; VSM results showed that the saturation magnetization was15emu/g, and the prepared magnetic hydrogel responded well to external magnetic fields without any permanent magnetization; XRD analysis showed that Fe3O4loaded was of spinel type and the diameter was15nm; TGA analysis indicated that thermal stability was related with both the skeleton, structure and chemical composition of hydrogel; XPS test showed that heavy metal ions were effectively absorbed onto the magnetic hydrogel.3.The swelling ratio of P(Cys/HEA) of different components was in the range of2.0-4.6. The adsorption of heavy metal ions by P(Cys/HEA) hydrogel contained both physical and chemical adsorption.When water accounted for70%(v./v.) and the Cys accouted for10%(mol/mol)(B-10), the prepared hydrogel showed both best swelling property and adsorption capacity.4. Contrast experiment showed that Fe3O4-P(Cys/HEA) hydrogel exhibited slight increase of adsorption capacity, which can be explained by the large surface areas and high activities caused by the size quantization effect of Fe3O4nanoparticles loaded into hydrogel’s network.5. The isotherm experimental data fitted better to the Langmuir model than the Freundlich model, demonstrating that the heavy metal ions on Fe3O4-P(Cys/HEA) were removed through Langmuir monolayer adsorption. The calculated RL values revealed that the adsorption process was favorable.The adsorption kinetics followed pseudo-second-order kinetic model, indicating that the adsorption rate was controlled by chemical adsorption, and the adsorption rates followed the order Cr3+>Cu2+> Cd2+>Pb2+. According to the competitive adsorption results, the priority order in multi-component adsorption was Pb2+> Cu2+>Cd2+>Cr3+, this may be that the competitive adsorption of the four heavy metal ions on Fe3O4-P(Cys/HEA) is mainly affected by the metal electronegativity. The heavy metal with larger electronegativity tended to be preferentially adsorbed.6. The magnetic hydrogel was pH sensitive but barely affected by temperature, and the optimal pH values obtained from the adsorption experiments for Pb2+, Cd2+, Cu2+, and Cr3+were5.13、6.07、5.01and5.13, respectively, which were very close to the initial pH values of the heavy metal solutions.7. The adsorption mechanism included both physical and chemical adsorption. The physical adsorption mainly depended on the three-dimensional network structure of the hydrogel. And the chemical adsorption depended on the functional groups of the hydrogel, and the chemical adsorption was a combined reaction caused by-NH2and—H including chelation and ion exchange interaction.8. The composite hydrogels can readily be removed with the applied magnetic field, and heavy metal ions absorbed also can be separated from water simultaneously. Fe3O4-P(Cys/HEA) was regenerated with an efficiency of greater than90%using O.lmol/L eathylene diamine tetraacetic acid. In addition, the adsorption capacity of hydrogel could still be maintained more than85%after three cycles, indicating that the novel magnetic hydrogel had potential applications for removing heavy metal ions from wastewater.