Preparation Of Poly(Vinyl Alcohol) Composite Hydrogels And The Research On The Adsorption Of Heavy Metals

Hydrogels had been attracted a great deal of attention due to their unique three-dimensional network structure, high adsorption capacity, fast adsorption rate and good regeneration properties in the treatment of heavy metals pollution field. In this work, in order to improve adsorption performance of the hydrogel for heavy metals, graphene oxide was used to prepare three kinds of composite hydrogel by an instantaneous gelation method. The influence of composite hydrogel on adsorption of heavy metal ions was investigated. Main contents and conclusions were as follows:1. Based on graphene oxide(GO), PVA/CS/GO composite hydrogel was prepared. The micromorphology and thermal stability of hydrogel beads were characterized by SEM and TGA respectively. The adsorption of Cu(II), Pb(II) and Cd(II) onto PVA/CS/GO hydrogel beads was studied. The results showed that p H, adorption time, adorption temperature and initial concentration of the solution affected the adsorption performance of the composite hydrogel for heavy metal ions. The optimum p H value was 5.5 for adorption of heavy metal ions solution and the equilibrium adsorption time was 200 min. The high temperature profited the adsorption. Compared with the PVA/CS hydrogel, maximum adsorption capacity of PVA/CS/GO composite hydrogel with 1wt% of GO was increased obviously. The data on adsorption were well matched by Langmuir isotherm and pseudo-second-order kinetic model, suggesting monolayer adsorption was more dominant during the adsorption process. And the adsorption rate was controlled by chemisorption. Thermodynamic studies indicated that the adsorption was spontaneous and endothermic process in nature. Besides, six consecutive adsorption-desorption cycles indicated the hydrogel was efficient and reusable adsorbents.2. Functional graphene oxide(PDA-r GO) was synthesized by reaction of dopamine and GO, and used to form PVA/CS/PDA-r GO composite hydrogel. Adsorption of Cu(II), Pb(II) and Cd(II) onto PVA/CS/ PDA-r GO hydrogel beads was investigated. The equilibrium adsorption time was 120 min. Compared with of the PVA/CS/GO composite hydrogel, the maximum adsorption capacity of PVA/CS/ PDA-r GO was further increased. The adsorption isotherms, kinetics and thermodynamics of composite hydrogel were studied in detail, which indicated that the adsorption of PVA/CS/PDA-r GO was monolayer adsorption, and controlled by chemisorption. Thermodynamic studies indicated that the adsorption was spontaneous and endothermic process in nature. Six consecutive adsorption-desorption cycles indicated the adsorbents was efficient and reusable. The competitive adsorption showed that PVA/CS/PDA-r GO beads had better adsorption selectivity for Pb(II) with the coexistence of Cu(II), Pb(II) and Cd(II).3. PVA/CS/Fe3O4-GO composite hydrogel was prepared by using Fe3O4-GO. Fe3O4-GO and hydrogel beads were characterized by FTIR, XRD and TGA respectively. The equilibrium adsorption time was 100 min, which was faster than that of PVA/CS/PDA-r GO and PVA/CS/GO composite hydrogel. PVA/CS/Fe3O4-GO were easy separated from solution after adsorption of heay metal ions. The maximum adsorption capacity of PVA/CS/Fe3O4-GO was comparable with that of PVA/CS/PDA-r GO. Adsorption data were well matched by Langmuir isotherm and pseudo-second-order kinetic model. The adsorption was spontaneous and endothermic process in nature. Six consecutive adsorption-desorption cycles indicated the adsorbents were efficient and reusable. The maximum adsorption capacity of Cr(Ⅲ), Ni(II) and Zn(II) adsorption were 128.75, 208.38 and 155.84 mg/g, respectively.