Preparation And Adsorption Of Heavy Metal Ions Of Functional Dendritic Mesoporous Silica Nanoparticles

The rapid development of urbanization and the rapid improvement of industrialization have also brought about many problems in environmental governance.Heavy metal pollutants from electroplating,mining,metal processing and other industries are discharged into the soil with industrial wastewater,which not only destroys the ecological balance of nature,but also poses a great threat to human life,health and safety.At present,the main treatment methods for wastewater containing heavy metals include chemical sedimentation,membrane separation,coagulation,flocculation,electrochemical and other methods.However,high cost,high energy consumption,secondary pollution and other drawbacks limit the application of these methods in actual industrial production.Due to the advantages of low cost,simple operation,sustainable and environmentally friendly,adsorption method has been widely concerned by researchers at home and abroad.The key to the treatment of sewage containing heavy metals by adsorption method is to develop heavy metal ion adsorbents with good adsorption effect,high efficiency,no secondary pollution and recyclable.Based on this,this paper prepared and functionalized three-dimensional dendriform mesoporous nano-silica(DMSNs)with unique threedimensional morphology,open pore structure and high internal surface area,and explored its application in the adsorption of Cu(Ⅱ),Cd(Ⅱ),Pb(Ⅱ)and other heavy metal ions.The specific work content is as follows:1.Based on micelle self-assembly mechanism,DMSNs were prepared quickly and conveniently by hydrothermal synthesis method with ethyl orthosilicate(TEOS)as raw material,cetyltrimethyl ammonium bromide(CTAB)and sodium trifluoroacetate(FC2)as structural auxiliaries and triethanolamine as catalyst.The influence of reaction time,molar ratio of FC2 to CTAB and temperature on DMSNs channels was systematically discussed.It was found that with the passage of reaction time,the pore structure of DMSNs evolved from open center-radial dendritic pores to tiny mesoporous pores similar to traditional nano silica particles.Moreover,the increase of the molar ratio of FC2 to CTAB and the increase of temperature promote the transformation process of DMSNs pore structure.In addition,the size of DMSNs particle is positively correlated with the molar ratio of the structural additives.Aiming at the application of adsorbing heavy metal ions,the advantages and disadvantages of two removal methods of structural additives,calcination and extraction,were compared.The experiment proved that the calcination method had a better effect on the removal of structural additives of DMSNs,but destroyed the silicon hydroxyl group in the structure of DMSNs.The extraction method could effectively remove the structural additives while retaining the silicon hydroxyl group site of DMSNS.Moreover,DMSNs treated by extraction had stronger adsorption capacity for heavy metal ions.The research results of this work provide theoretical reference for the control of DMSNs pore and particle size,and the removal of DMSNs structural additives used for adsorption of heavy metal ions.2.Amino-functionalized dendritic mesoporous nano-silica(DMSNs-NH2)and mercaptofunctionalized dendritic mesoporous nano-silica(DMSNs-SH)were prepared in one pot by using silane coupling agent as modifier,and these two functionalized materials were used as adsorbent.The adsorption behavior of Cu(Ⅱ),Pb(Ⅱ)and Cd(Ⅱ)in aqueous solution by DMSNs-NH2 and DMSNs-SH is systematically discussed.The optimal feeding ratio of DMSNs-NH2 and DMSNs-SH for preparation was clarified,and the effects of pH value,contact time,temperature and initial concentration of heavy metal ions on the adsorption of heavy metal ions by the two adsorbents were explored.The adsorption kinetics of heavy metal ions by DMSNs-NH2 and DMSNs-SH were analyzed using the quasi-first-order kinetic model,quasi-second-order kinetic model and intra-particle diffusion model.The results showed that the adsorption behavior was dominated by chemical action,and the surface and internal diffusion of heavy metal ions in the adsorbent had a great influence on the adsorption rate.Langmuir adsorption isotherm model,Freundlich model and Temkin model were used to fit the adsorption data.It was found that Langmuir model and Temkin model had better fitting effect.At 25℃,The maximum adsorption capacity of DMSNs-NH2 for Cu(Ⅱ)is 56.39 mg/g,and the maximum adsorption capacity of DMSNs-SH for Cd(Ⅱ)is 51.31 mg/g.The adsorption of DMSNs-NH2 and DMSNs-SH on heavy metal ions tends to be monolayer adsorption,and the adsorption heat has a good linear relationship with the coverage of adsorption sites.The thermodynamic behaviors of heavy metal ions adsorbed by two kinds of adsorbents were investigated.The calculated thermodynamic parameters showed that the adsorption of heavy metal ions by DMSNs-NH2 and DMSNs-SH was a spontaneous,endothermic and entropyincreasing process.XPS analysis showed that the complexation reaction between functional groups and heavy metal ions was the main adsorption mechanism.The results of adsorptiondesorption cycle experiments show that the two adsorbents have good recycling properties.