Adsorption Of Typical Pollutants In Water By Modified Sodium Alginate Gel Spheres

Sodium alginate(SA)is a kind of natural anionic polymer compound,which has the advantages of sufficient raw material source and green environmental protection.Its molecular chain has a variety of functional groups such as-COOH and-OH,which can be crosslinked with polyvalent metal ions to form three-dimensional hydrogel materials.This kind of materials has rich porous structure,which increases the contact area between pollutant and adsorbent and improves the removal efficiency.However,the limitations of simple sodium alginate gel limit its application.In this study,Chitosan(CS),Hydrotalcite(LDHs,MgAl type),Polyvinyl alcohol(PVA),Polyethylene imine(PEI)and Zr ions were introduced to realize the multi-functionalization of sodium alginate gel by embedding method,blending method,surface modification and other means.Three sodium alginate gel spheres,CS-LDHs-SA,CS-LDHs-SA-Zr and PVASA@PEI,have been obtained to remove several typical pollutants.The materials were characterized by Infrared spectroscopy(FTIR),Scanning electron microscopy(SEMEDS),X-ray diffraction(XRD),Elemental analysis,Specific surface area(BET)and X-ray photoelectron spectroscopy(XPS).The adsorption mechanism of the gel spheres was investigated by isotherm model,kinetic model fitting and thermodynamic analysis.The results are as follows:(1)CS-LDHs-SA gel spheres with polyethylene glycol(PEG)as pore-forming agent and Ca(Ⅱ)as crosslinking agent were prepared to adsorb heavy metals Cu(Ⅱ)and Pb(Ⅱ).The addition of inorganic material LDHs enhanced the mechanical strength of sodium alginate gel.The results of FTIR and SEM showed that chitosan was successfully loaded onto the surface of LDHs,and the easily agglutinated LDHs had a better dispersion effect in sodium alginate solution.Meanwhile,amino and amide groups were introduced into the gel.The specific surface area analysis results also showed that the addition of PEG made the gel have more pore size structure.Through batch adsorption experiments,it was found that the pH adaptation range of gel spheres was broadened,and the coexistence of Ca(Ⅱ)was not conducive to Cu(Ⅱ)and Pb(Ⅱ)adsorption.The adsorption effect of Cu(Ⅱ)and Pb(Ⅱ)on CS-LDHs-SA gel spheres was significantly improved,and the maximum adsorption capacity was 117 mg·g-1 and 155 mg·g-1 at 303 K,respectively.The adsorption mechanisms of CS-LDHs-SA toward Cu(Ⅱ)and Pb(Ⅱ)are mainly complexation and ion exchange.(2)Since Ca(Ⅱ)crosslinked CS-LDHs-SA gel spheres had poor adsorption effect on anions,Zr(Ⅳ)crosslinked CS-LDHs-SA-Zr gel spheres had been prepared by ion exchange for the adsorption of phosphoric acid.SEM-EDS showed that Ca(Ⅱ)was mostly exchanged into Zr(Ⅳ),and the distribution was uniform.It was also observed that the modified gel spheres had larger pore size structure.Batch adsorption experiments showed that the modified CS-LDHs-SA-Zr gel spheres had better adsorption effect on phosphoric acid than CS-LDHs-SA gel spheres.The maximum adsorption capacity was 28.6 mg·g-1(according to P)at 303 K.The optimal adsorption solution pH was 2,and the coexistence cation Ca(Ⅱ)promoted the adsorption.The main adsorption mechanisms are complexation and electrostatic attraction.(3)Polyvinyl imine(PEI)was crosslinked to the surface of polyvinyl alcohol and sodium alginate(PVA/SA)gel spheres,and multifunctional PVA/SA@PEI gel spheres with high mechanical strength and multiple functional groups were prepared,which were used to adsorb Cr(Ⅵ)and diclofenac sodium(DS).The results of FTIR and Elemental analysis showed that PEI was successfully cross-linked to gel spheres and the number of active groups was increased.The results of batch adsorption experiments showed that the maximum adsorption capacity of Cr(Ⅵ)and DS is 419 mg·g-1 和 72.8 mg·g-1 at 303 K,respectively,and pH=2 is the best for Cr(Ⅵ)adsorption while it is in favor of DS adsorption at acidic conditions.The adsorption mechanism of PVAS A@PEI gel spheres for Cr(Ⅵ)is mainly electrostatic attraction and reduction reaction,while the adsorption mechanism for DS is mainly electrostatic attraction and hydrogen bonding.The prepared materials have certain stability and good adsorption performance,and the results provided a basis for the development and utilization of this kind of materials.