Adsorption Characteristics Of Modified Montmorillonite On Copper Ions In Water

Cu（Ⅱ）contamination has become an international environmental concern.Adsorption is efficient,simple,economical and widely used.Montmorillonite has gained international attention as a potential adsorbent due to its large specific surface area,high cation exchange capacity,easy modification,low cost and no secondary environmental pollution,etc.It can be used as an excellent adsorbent for Cu（Ⅱ）removal.Therefore,the adsorption capacity of the adsorbent can be further enhanced by modifying the montmorillonite with modifiers.In this thesis,modified montmorillonite was designed and prepared for the removal of Cu（Ⅱ）from water.The main results obtained were as follows:（1）The experimental and theoretical studies on the adsorption of Cu（Ⅱ）on the surface of montmorillonite（P-Mt）were reported.Effects of batch adsorption experimental parameters were studied.Density Functional Theory（DFT）and Molecular Dynamics（MD）simulations were used to study the adsorption of Cu（Ⅱ）on P-Mt（001）surface.The adsorption reached equilibrium within 80 min,and the adsorption capacity was 35.23 mg·g^-1at 25°C.The adsorption data of Cu（Ⅱ）were consistent with pseudo-second-order kinetic and Langmuir isotherm models.The activation energy（E_a）was 2.96 k J·mol^-1,which implied the nature of physical adsorption.The influence of coexisting cations on the adsorption capacity of Cu（Ⅱ）was Mg（Ⅱ）>Co（Ⅱ）>Ca（Ⅱ）>Na（I）.The simulation results demonstrated that there were no significant differences in the adsorption energy of Cu（Ⅱ）at the four adsorption sites on the P-Mt（001）surface.Cu（Ⅱ）had more electron transfer than Na（I）.The diffusion coefficient of Cu（Ⅱ）in the aqueous solution system containing P-Mt was 0.85×10^-10m²·s^-1.A considerable amount of Cu（Ⅱ）ions were adsorbed at a distance of 0.26?and 2.25?from the P-Mt（001）surface.The simulation results provided strong supporting evidence for experimental conclusions.（2）The montmorillonite（P-Mt）was modified with sodium dodecyl benzene sulfonate（SDBS）to form sodium dodecyl benzene sulfonate-montmorillonite（SDBS-Mt）for the purpose of enhancing the removal performance of Cu（Ⅱ）from aqueous solution.The materials were characterized by means of XRD,SEM-EDS,BET,FT-IR and XPS to analyze the surface morphology and structure.SDBS-Mt displayed a higher adsorption capacity than P-Mt.The adsorption kinetic model and the adsorption isotherm model were depicted by the pseudo-second-order kinetic equation and the Langmuir equation,respectively.The order of influence of coexisting cations on the adsorption of Cu（Ⅱ）was Ni（Ⅱ）>Mg（Ⅱ）>Co（Ⅱ）>Zn（Ⅱ）>Na（I）>K（I）.In addition,the adsorbent has certain regeneration performance after 5 cycles of experiments.A combination of experiment,characterization and DFT analysis showed that the main mechanisms of Cu（Ⅱ）adsorption by SDBS-Mt may include electrostatic attraction,ion exchange and complexation of sulfonate groups.In brief,SDBS-Mt may be a simple and low-cost adsorbent for the treatment of Cu（Ⅱ）in aqueous solution.（3）Zinc oxide-montmorillonite composite（ZnO-Mt）was prepared through ion exchange followed by heat treatment to form a highly effective adsorbent for the removal of Cu（Ⅱ）from aqueous solution.The structure and morphology of the composite were investigated by XRD,SEM-EDS,FT-IR,BET,TEM,TGA and XPS.It was found that Zinc oxide was successfully coated on montmorillonite.The composite had a superior removal effect on Cu（Ⅱ）in aqueous solution with an adsorption capacity of 192.89 mg·g^-1.The adsorption kinetic model and the adsorption isotherm model were described by the pseudo-second-order kinetic equation and the Langmuir equation,respectively.The activation energy（E_a）was 84.18 k J·mol^-1,indicating that the adsorption was dominated by chemisorption.In addition,Zn O-Mt can be applied in a wide p H range（3–8）and exhibited satisfactory selectivity for the adsorption of Cu（Ⅱ）in the presence of coexisting cations.The removal efficiency of Zn O-Mt for Cu（Ⅱ）remained 72%of the fresh adsorbent after five cycles.Finally,a combination of experiment,characterization and DFT analysis showed that the mechanism of Cu（Ⅱ）removal was mainly surface complexation,ion exchange and electrostatic attraction.Therefore,Zn O-Mt composite is a promising and efficient adsorbent for the removal of Cu（Ⅱ）from aqueous solution.