Preparation And Modification Of Sodium Alginate Composite Hydrogel Beads And Their Study On Adsorption Properties For Copper Or Uranium In Wastewater

Sodium alginate contains a large number of carboxyl groups and it can be crosslinked through calcium ions to form hydrogels,leading to a wide use in adsorption of heavy metal ions.However,the practical application of alginate hydrogel is limited due to its poor physical properties and the ability to adsorb metal ions.In order to enhance the physical and adsorption properties of the alginate hydrogel,three different alginate-based composite hydrogel beads were prepared by modification or combined with other materials in this paper,and then they were applied to study the adsorption properties of copper ions or uranyl ions in the wastewater.In the third chapter,we prepared Fe₃O₄/sodium alginate coated chitosan hydrogel beads for removal of Cu（Ⅱ）and U（Ⅵ）from aqueous solutions.Covering the chitosan on the surface of the microspheres solved the problem which is difficult to combine chitosan with sodium alginate.The introduction of Fe₃O₄ magnetic nanoparticles was to enhance the thermal stability of the gel beads and to use their magnetic separation properties.The FTIR and XRD spectra proved the successful preparation of beads;The SEM image and EDX spectra analysis showed that Cu²⁺ or UO₂²⁺ were adsorbed on the surface of the microspheres.The effects of pH value,initial concentration and sorption time were studied by the batch adsorption experiment;The adsorption kinetics and adsorption isotherms were studied by fitting the experimental data;The reproducible properties of the beads were investigated by the desorption experiment.The results showed that the beads had good adsorption properties for Cu（Ⅱ）or U（Ⅵ）.In the fourth chapter,the NaOH solution was used for modifying chitosan/alginate/Fe₃O₄ composite gel beads briefly.We compared the mechanical properties and Cu²⁺ adsorption performance of the microspheres before and after modification:The mechanical properties of the hydrogel beads after the NaOH modification were obviously stronger than that before the modification,which was confirmed by the stress-strain curves obtained from texture analyzer;The adsorption capacity of the beads for Cu²⁺ after the modification was remarkably better than that before the modification,which was verified by the batch adsorption test.In the fifth chapter,we prepared sodium alginate/graphene oxide/polyvinyl alcohol composite hydrogel beads and applied them to the investigation of adsorption properties of Cu（Ⅱ）or U（Ⅵ）.Among them,the graphene oxide is used for strengthening the physical properties of the microspheres,and polyvinyl alcohol is used for increasing the flexibility of the beads and for dispersing the graphene oxide in the gel beads.In this chapter,we compared the adsorption properties of the microspheres for Cu²⁺ and UO₂²⁺:the adsorption capacity of the beads for UO₂²⁺ is obviously stronger than that of the Cu²⁺,which was confirmed by comparing the proportion of U and Cu elements in the EDX element analysis and the intension of the U element and the Cu element peak in the X ray photoelectron spectroscopy.The difference in adsorption capacity obtained from characterization was in concert with the results we calculated from the adsorption experiments.