Preparation Of Polysaccharide-based Composite Materials And Study Of Their Heavy Metal Ion Adsorption Propertie

With the rapid development of economy in our country,industrial pollution is becoming increasingly serious.How to deal with heavy metal ion water pollution has become an important problem.Among the various treatment methods of heavy metal ions in water environment,adsorption treatment has the advantages of simple operation and good treatment effect.In this study,the exploration of functional modification of polysaccharide group adsorbent materials was carried out.On the one hand,the natural macromolecular polysaccharide materials with wide sources,easy to use,and rich active sites,including sodium alginate and chitosan,were used as substrates to prepare polysaccharide group easily separated adsorbent materials.On the other hand,hexavalent chromium[Cr（Ⅵ）]and divalent lead[Pb（Ⅱ）]were selected as characteristic pollutants.In this paper,sodium alginate and chitosan of high molecular chain polysaccharide were used as substrates to prepare polysaccharide functionalized composite adsorbors.SEM,EDS-Mapping,XRD,Zeta potential,FT-IR,BET,ICP-OES and XPS were used to characterize the adsorbors.To investigate the adsorption mechanism of phosphoric acid functionalized sodium alginate matrix composite gel sphere,sponge loaded sodium alginate matrix composite and sponge loaded chitosan matrix composite on heavy metal ions,and to provide new ideas for effective removal of heavy metal ions and application of polysaccharide matrix composite materials.The main research results are as follows:（1）Sodium alginate,a natural polysaccharide,was used as raw material,and THPS was used as modifier to prepare microbeads with a diameter of 1-2 mm by the impregnation method at room temperature.Phosphoric acid functionalized sodium alginate composite gel spheres（SAB-THPS）were prepared.Compared with alginate composite gel sphere（SAB）,the adsorption performance of SAB-THPS on Cr（VI）was significantly improved.The Langmuir isothermal model showed that the maximum adsorption capacity of Cr（VI）could reach 145.77mg/g,and the adsorption rate of Cr（VI）was extremely fast.When the initial concentration was20,50 and 100 mg/L,the adsorption equilibrium time was 2.5,6.5 and 20 min,respectively,and the residual Cr（VI）concentration after adsorption was lower than 0.5 mg/L,which was the national minimum wastewater discharge standard.For SAB-THPS,the main adsorption mechanism involves the chemical reduction of Cr（VI）to Cr（III）,as well as ion-exchange interactions and electrostatic interactions through-OH and-COOH groups.（2）Based on the discussion of sodium alginate composite material above,the environmentally friendly polysaccharide sodium alginate was selected as the matrix to explore the adsorption performance of different ion cross-linked sodium alginate composite gel spheres（SAB-Ca/Al/Ni/Cu）for Pb（Ⅱ）.The effect of different ion crosslinking on the adsorption performance of Pb（Ⅱ）was compared by orthogonal test,SEM,Zeta potential and XPS,and the Ca²⁺cross-linking was selected.At the same time,the sponge-based materials were further studied from the exploration of bead-like materials,and the sponge-supported sodium alginate matrix composite（SA-Ca@NSP）was prepared.It was found that the adsorption performance of SA-Ca@NSP on Pb（Ⅱ）was significantly improved,and the isotherm fitting was consistent with the Langmuir model.The maximum adsorption capacity was 459.58 mg/g,which was higher than that of SA@NSP（368.56 mg/g）of uncrosslinked calcium.（3）Based on the above research on sponge-based materials,the porous layered nano-sponge（NSP）with easy loading structure was selected as the carrier to load natural polysaccharide polymer chitosan（CS）,supplemented by cheap and non-toxic polyvinyl alcohol（PVA）as the precipitation agent.After PVA modification,the composite material has good mechanical strength and rich hydroxyl groups on the surface.To facilitate the immobilization of chitosan and further improve the stability of the material structure,the sponge carrier loaded chitosan matrix composite（CS/PVA-THPS@NSP）was prepared.The adsorption performance of CS/PVA-THPS@NSP on Cr（VI）was significantly improved,and the maximum adsorption capacity was up to 403.75 mg/g.The kinetic fit was in accordance with the fitting second-order model,and the adsorption isotherm fit was in accordance with the Langmuir model.The adsorption mechanism was mainly chemical precipitation and ion exchange.Moreover,for Cr（VI）solution with initial concentration of 50 mg/L,the residual concentration of 0.05 mg/L after adsorption can reach the national wastewater standard,and the maximum adsorption capacity can be reached within 30min,which has the characteristics of rapid adsorption.