Preparation Of MOFs Modified Alginate Composite Hydrogel And Its Adsorption Performance For Heavy Metal Ions

The heavy metals in factory wastewater are discharged directly without treatment,and the water pollution caused by heavy metals is very harmful to the environment and human health.Effective treatment of heavy metals pollution is one of environmental goals pursued by countries all over the world.Therefore,it is an urgent to develop an effective and economical method to remove heavy metal ions from wastewater.The adsorption technology is the preferred choice for removing heavy metal ions due to its simple operation,safety,high removal efficiency and recyclability.Biopolymer materials have attracted widespread attention in the field of adsorption because of their wide range of sources,renewable and easily degradable.Sodium alginate is one of the natural biomass materials,its surface contains abundant hydroxyl and carboxyl groups,which interact with multivalent cations(except Mg2+)to form threedimensional hydrogel beads.Metal organic framework polymers(MOFs)have the advantages of high specific surface area,structural diversity and abundant active sites.MOFs can be used to modify sodium alginate to improve its adsorption capacity and selectivity.In this paper,two kinds of MOFs modified sodium alginate composite hydrogel adsorbents were prepared to remove Cu(Ⅱ)and Pb(Ⅱ)from aqueous solution,the main research contents were as follows:1.Polyvinyl alcohol/sodium alginate@ZIF-8 composite hydrogel(PVA/SA@ZIF-8)was synthesized by in-situ method at room temperature to remove Cu(Ⅱ)from aqueous solution.SEM,FTIR,TGA,XRD and XPS characterization methods were used to explore the structure of adsorbents.The experimental results showed that the adsorption sites of Cu(Ⅱ)were increased by introducing PVA and ZIF-8 to modify the hydrogel.The experimental data of Cu(Ⅱ)adsorption could be simulated by pseudosecond-order kinetic model(R2=0.9967)and Langmuir isothermal model(R2=0.9992).The excellent adsorption capacity of PVA/SA@ZIF-8 for Cu(Ⅱ)was 165.23 mg/g.In the competition experiments of coexisting Cd(Ⅱ),Ni(Ⅱ),Co(Ⅱ),Cu(Ⅱ)and Mn(Ⅱ),it had excellent selectivity for Cu(Ⅱ),and it showed excellent reusability in five adsorption-desorption experiments.Therefore,PVA/SA@ZIF-8 hydrogel is a simple and effective adsorption material for removing Cu(Ⅱ)from aqueous solution.2.Sodium alginate-melamine@ZIF-67 composite hydrogel(SAME@ZIF-67)was synthesized to remove Pb(Ⅱ)from aqueous solution.The experimental results showed that ME and ZIF-67 introduced abundant functional groups into the sodium alginate hydrogel,increased the adsorption sites for Pb(Ⅱ)and improved the adsorption performance.The fitting of SA-ME@ZIF-67 to remove Pb(Ⅱ)experimental data accorded with pseudo-second-order kinetic model(R2=0.9977)and Langmuir isothermal model(R2=0.9990-0.9997).According to the Langmuir model the adsorption capacity of S A-ME@ZIF-67 material for Pb(Ⅱ)was as high as 628.93 mg/g at 308.15 K.Thermodynamic studies showed that the adsorption process of Pb(Ⅱ)is endothermic and spontaneous.Even after five cycles,the removal efficiency of SA-ME@ZIF-67 remained above 85%.Thus,SA-ME@ZIF-67 hydrogel has great potential in the treatment of wastewater polluted by Pb(Ⅱ).