Study Of Preparation And Performance Of Porous Materials For Removal Of Heavy Metal Ions In Water

Heavy metal ion pollution in water can exhibit serious impacts on ecosystems,organisms and humans.The issue of how to use effective means to treat heavy metal ion pollution in water has always been of concern.There are many methods to remove heavy metal ions,such as chemical precipitation,membrane separation,ion exchange and adsorption.Compared with other methods,adsorption is widely used because of its low cost,easy operation,and good performance.The key to the removal of heavy metal ions by adsorption is to develop efficient,inexpensive and green adsorbents.Therefore,exploring preparation of new porous adsorbent materials with large specific surface area,high density of adsorption active sites and adsorption functional groups is an inevitable trend to solve this problem.In this paper,two functionalized metal-organic frameworks（MOFs）and a functionalized chitosan carbonized core-shell material were synthesized by solvothermal method and the adsorption properties of heavy metal ions on them were explored.The details are as follows:1.Metal organic framework MIL-101（Cr）was synthesized by solvothermal method and was functionalized using phosphomolybdic acid（PMA）by impregnation method to obtain phosphomolybdic acid functionalized MIL-101（Cr）adsorbent（PMA/MIL-101（Cr））.FTIR,BET,XRD,SEM,TEM,XPS methods were used to characterize the structure and morphology of the as-prepared PMA/MIL-101（Cr）and the performance of it toward adsorption of Pb（II）was studied.The results show that PMA was successfully loaded on MIL-101.Under the conditions of pH range（2.0-6.0）and adsorption equilibrium time of 150minutes,PMA/MIL-101 exhibits better adsorption performance and selectivity for Pb（II）.The adsorption capacity of Pb（II）is 550.00 mg·g^-1,and the selectivity coefficients for Pb（II）/Cd（II）and Pb（II）/Cr（III）are 7.98 and 11.10,respectively;The adsorption isotherm of Pb（II）on PMA/MIL-101 accords with the Langmuir model,and the adsorption kinetics conforms to the pseudo-second-order kinetics model,which shows that the process is dominated by chemical adsorption and which is also consistent with the results of Dubinin-Radushkevich isothermal model.PMA/MIL-101 has a large specific surface area(1341.05 m²·g^-1)and is rich in high-density adsorption active sites,which ensure its high adsorption capacity for heavy metal ions and thus showing potential application prospects for removing heavy metal ion contamination.2.Metal-organic framework compound HKUST-1 was synthesized by solvothermal method,and then amino-functionalized HKUST-1 adsorbent（TETA-[Cu₃（BTC）₂]）was prepared by amino functionalization of HKUST-1 with triethylene tetramine（TETA）.The structure of TETA-[Cu₃（BTC）₂]was characterized by FTIR,BET,SEM,EDX and XRD and its adsorption performances for Pb（II）and Cd（II）were also explored.The results show that:TETA was successfully grafted onto HKUST-1.TETA-[Cu₃（BTC）₂]possesses characteristics of mesoporous material,large specific surface area(976.82 m²·g^-1)and higher adsorption capacities for Pb（II）and Cd（II）.Under the optimum adsorption pH（Pb（II）5.0,Cd（II）7.0）and adsorption equilibrium time（Pb（II）120 min and Cd（II）90 min）,the adsorption isotherms of TETA-[Cu₃（BTC）₂]for Pb（II）and Cd（II）fit well with Langmuir model and the corresponding calculated maximum adsorption capacity for Pb（II）is 310.56 m²·g^-1 and for Cd（II）is 256.41 m²·g^-1.The fitting results of adsorption kinetics of Pb（II）and Cd（II）both fit the pseudo-second-order adsorption kinetics model,indicating that the processes are dominated by chemisorption.The high adsorption capacities of TETA-[Cu₃（BTC）₂]for heavy metal ions due to its high density of amino functional groups and high specific surface area make it potentially promising for removal of heavy metal ions from aqueous solutions.3.The phosphomolybdic acid-functionalized chitosan carbonized core-shell structure adsorbent（PMA/CoO_x@C）was synthesized by hydrothermal carbonization method.The structure and morphology of the adsorbent were characterized by SEM,HRTEM,XRD,Raman,FTIR and XPS methods and adsorption performance of the sorbent for Pb（II）,Cd（II）and Cr（III）were studied,which including the effect of pH on the adsorption capacity,adsorption kinetics,adsorption isotherm,and selectivity for heavy metal ions.The experimental results show that PMA/CoO_x@C has a complete core-shell structure and good mesoporous properties.The average particle size of the core-shell material is 1390 nm,and the specific surface area is 35.96 m²·g^-1;Under conditions of pH（6.0）and adsorption equilibrium time（360 min）,Pb（II）,Cd（II）and Cr（III）exhibit good adsorption effects on PMA/CoO_x@C.The adsorption kinetics of the three heavy metal ions are all in accordance with the pseudo-second-order kinetic model.The adsorption isotherms of Pb（II）and Cd（II）conform to the Langmuir model,while the Cr（III）adsorption isotherm follows the Freundlich model.The active sites of PMA and cobalt oxide in the PMA/CoO_x@C material act synergistically with some of the hydroxyl groups and amino groups retained by the hydrothermal carbonization process,thus exhibiting excellent adsorption effects for heavy metal ions and promising to become a novel green adsorbent for removing heavy metal ions from water.