Preparation And Adsorption Of Heavy Metal Ions On Silicate Nanocomposites Based On ATRP

With the development of nanomaterials and nanotechnology,nano-adsorbents have been widely studied in the field of heavy metal wastewater treatment.In recent years,it is an important research to reduce the preparation cost,improve the adsorption capacity and separation efficiency of nanomaterials.In this paper,four new nanocomposites,e.g,Mg₃Si₂O₅?OH?4-SH,Mg₃Si₂O₅?OH?₄-g-PEI,Ni₃Si₂O₅?OH?4-g-PAMPS and Ni₃Si₂O₅?OH?₄-g-P4VP were designed and prepared on the basis of abundant silicate materials.Their adsorption properties of heavy metal ions in water were studied,including kinetics,thermodynamics,adsorption balance,regeneration and reuse,then adsorption mechanism was also explored.The main results were following:?1?The sulfhydryl functionalized Mg₃Si₂O₅?OH?4-SH nanocomposites were prepared on the basis of synthesized magnesium silicate nanotubes and modified by MPTMS.The adsorption behavior of Hg?II?in aqueous solution was studied.The results showed that Mg₃Si₂O₅?OH?4-SH still maintains the original mesoporous structure compared with the unmodified material,but the pore size distribution was narrower,the pore size was smaller,the specific surface area reduced.The sulfhydryl modification effectively improved the adsorption performance of Mg₃Si₂O₅?OH?4-SH nanotubes for Hg?II?.The adsorption capacity increased nearly three times,to 0.147 mmol/g,and it had wider p H adaptability.The co-existing ions Ca²⁺,Mg²⁺,K⁺,SO₄^2-had little effect on the adsorption of Hg?II?by Mg₃Si₂O₅?OH?4-SH,but the effect of Cl^-ions was very remarkable,which was attributed to the formation of complex between Hg?II?and Cl^-ions.The adsorption of Mg₃Si₂O₅?OH?4-SH on Hg?II?was a pseudo second-order kinetic process.Langmuir adsorption isotherm model could describe the isotherm adsorption equilibrium well.Mg₃Si₂O₅?OH?₄-SH adsorbent could be reused for 8 times,and the regeneration capacity retained at 90%.?2?The Mg₃Si₂O₅?OH?₄-g-PEI nanocomposite was prepared by siliconizing firstly and grafting PEI onto the surface of magnesium silicate nanotubes.The results showed that the structure of Mg₃Si₂O₅?OH?₄ was basically unchanged before and after modification,and the thickness of PEI polymer layer on its surface was about 16nm.Its adsorption behavior of Cu?II?in aqueous solution was studied.The results showed that PEI improved the adsorption capacity for Cu?II?,up to 0.7631mmol/g,and made it more suitable for p H value?from 3 to 5?.The adsorption kinetics of Mg₃Si₂O₅?OH?₄-g-PEI for Cu?II?was in accordance with the pseudo first order?PFO?adsorption kinetics model.Langmuir isotherm adsorption model fitted its adsorption process well.Its adsorption process of Cu?II?was spontaneous and endothermic.Its adsorption heat was 21.29KJ/mol,and the increase of temperature was conducive to its adsorption.After five adsorption desorption cycles,its adsorption capacity of Mg₃Si₂O₅?OH?₄-g-PEI for Cu?II?maintained above 90%.?3?The Ni₃Si₂O₅?OH?₄-g-PAMPS nanocomposite was prepared by ATRP method,which was based on the synthesis of nickel silicate nanotubes and grafted with 2-acrylamide-2-methylpropane sulfonic acid?AMPS?.Its adsorption of Pb?II?was further studied.The results showed that the tubular structure of Ni₃Si₂O₅?OH?₄ was basically unchanged before and after modification,and the thickness of PAMPS polymer brush was about 8 nm.With the increase of initial p H,the zeta potential of the solution decreased,while its adsorption capacity of Pb?II?increased rapidly,with the maximum adsorption capacity of 0.3283 mmol/g.In the presence of coexisting ions Cu?II?and Mg?II?,the adsorption of Pb?II?by Ni₃Si₂O₅?OH?₄-g-PAMPS showed good selectivity.The adsorption kinetics of Ni₃Si₂O₅?OH?₄-g-PAMPS for Pb?II?was in accordance with the pseudo second order?PSO?kinetic model.The analysis of Weber Morris and Boyd model showed that the diffusion in particles and the diffusion of liquid film jointly affect its adsorption of Pb?II?.Langmuir isotherm adsorption model could fit its adsorption process of Pb?II?well.The thermodynamic analysis showed that its adsorption process of Pb?II?was spontaneous and endothermic,and its adsorption heat was 20.32 k J/mol,which was consistent with the experimental phenomenon.Increasing the temperature was conducive to the adsorption.The adsorption mechanism showed that the adsorption of Ni₃Si₂O₅?OH?₄-g-PAMPS was mainly through the interaction of the oxygen atom of the-SO₃^-group on the PAMPs chain with Pb?II?ion.After four adsorption cycles,the adsorption capacity of Ni₃Si₂O₅?OH?₄-g-PAMPS for Pb?II?remains above 0.34mmol/g,which indicated that Ni₃Si₂O₅?OH?₄-g-PAMPS had good regeneration performance and adsorption stability.?4?The magnetic Ni3Si2O5?OH?4-g-P4VP nanocomposite was prepared by partially reducing Ni3Si2O5?OH?4 nanotubes with sodium borohydride,and then modifying by 4-vinylpyridine?4VP?with ATRP method.The results showed that the structure of the magnetic Ni3Si2O5?OH?4-g-P4VP material after reduction and grafting was unchanged obviously,and the thickness of P4VP polymer brush on the surface was about 5nm.The pH of the solution significantly affected the adsorption of Cr?VI?by magnetic Ni3Si2O5?OH?4-g-P4VP.There was a narrow optimal pH value,about 3.The maximum adsorption capacity was 1.4865mmol/g.The adsorption process of Cr?VI?by magnetic Ni₃Si₂O₅?OH?₄-g-P4VP was in accordance with the pseudo second-order adsorption kinetic model.The analysis of Weber-Morris and Boyd model showed that the diffusion in particles and the diffusion in liquid film jointly affect its adsorption of Cr?VI?.Freundlich and Redlich Peterson models could well fit the equilibrium adsorption of Cr?VI?ion on magnetic Ni3Si2O5?OH?4-g-P4VP.The adsorption of Cr?VI?was a spontaneous and endothermic process.Increasing the temperature was conducive to the adsorption,and the adsorption heat was 18.37kj/mol.XPS analysis showed that Cr?VI?and Cr?III?coexisted on the surface of Ni3Si2O5?OH?4-g-P4VP adsorbent,and some Cr?VI?anions were reduced to Cr?III?during the adsorption process.The adsorption capacity of magnetic Ni₃Si₂O₅?OH?₄-g-P4VP decreased by less than 9%after 8 times,which indicated that the material had good adsorption capacity and stability,and could achieve rapid separation,recovery and reuse under the effect of external magnetic field...