Preparation And Mass Transfer Mechanism Of Cd(Ⅱ) Ion And Co(Ⅱ) Ion Imprinted Composite Membrane

With the development of urban modernization and industrial production rapidly,environmental pollution is becoming increasingly serious.The discharge of heavy metal ion wastewater is an important factor that has caused water pollution and has posed huge harm to human society.The traditional methods for treating wastewater with heavy metal ion which existing some problems,such as complicated process,poor selectivity or cause secondary pollution easily etc.Therefore,it is urgent to find an adsorption separation material with high selectivity for heavy metal ions in sewage to overcome the abovementioned problems.Metal ion imprinted composite membranes appeared to be an emerging technology which provides new ideas for the separation and removal of metal ions,it is not only combines the advantages of metal ion imprinting technology and membrane separation technology,but also is an important branch of the development of metal ion imprinting technology.Based on the metal ion imprinting technique and Cd（Ⅱ）ions and Co（Ⅱ）ions as template ions,this paper prepared three types of metal ion imprinted composite membranes and corresponding non-imprinted composite membranes by surface imprinting method.These performances of adsorption and permeation selection were systematically studied,and the osmotic mass transfer mechanism of Cd（Ⅱ）ions and Co（Ⅱ）ions was established.The research content mainly includes the following aspects:（1）Combined with the surface imprinting method,Cd（Ⅱ）ions as template ions and using the traditional functional monomers in the laboratory,Cd（Ⅱ）ion imprinting composite membranes(Cd（Ⅱ）-IICM_1～26)and non-imprinted composite membrane(NICM_1～26)were prepared.Of which 4-vinylpyridine as the functional monomer and Nylon-6 membrane as the supporting membrane,the molar ratio of template ion,functional monomer and crosslinking agent is 1:4:20,Cd（Ⅱ）-IICM₆ of optimal imprinting membrane was prepared by soaking in solvent which is caused by methanol/water（v:v=1:1）for 180 s.The adsorption capacity of the membrane can reach 376.98 mg·g^-1,and the imprint factor of 1.56.Isothermal adsorption experiments showed that the adsorption performance of Cd（Ⅱ）-IICM₆ conforms to the Freundlich model,indicating that Cd（Ⅱ）-IICM₆ has adsorption sites with bilayer distribution.Kinetic fitting showed that the adsorption of Cd（Ⅱ）-IICM₆ to Cd（Ⅱ）ions is a process dominated by chemical adsorption.Permeation selectivity experiments confirmed that Cd（Ⅱ）-IICM₆ has better permeation selectivity for Cd（Ⅱ）ions.（2）The group of pyridine used as the matrix and synthesized a new functional monomer N,N’-pyridine-2,6-bis（2-methacrylamide）（PMA）with nitrogen heterocycle,the surface imprinting technology was adopted,and single-factor experimental method was used to optimize imprinting system,Cd（Ⅱ）ion imprinting composite membranes(Cd（Ⅱ）-PMA-IICM_1～25)and non-imprinting composite membranes(PMA-NICM_1～25)were prepared.The structure morphology,the adsorption performance and permeation selection performance of Cd（Ⅱ）-PMA-IICM₁₇ were characterized by SEM,BET,adsorption experiments and permeation experiments,respectively.The results showed that the optimal process is as follows:using PTFE microporous membrane as the supporting membrane,CH₃OH:H₂O（v:v=1:3）as solvent,and the molar ratio of template ion,functional monomer and crosslinking agent is 1:4:50,the membrane immersion time is 180 s.Adsorption experiments showed that the adsorption behavior of Cd（Ⅱ）-PMA-IICM₁₇and PMA-NICM₁₇ for Cd（Ⅱ）ions in solution is more fitted by the Freundlich isotherm adsorption model and pseudo-second-order kinetic model:indicating that the adsorption process of imprinted composite membrane for Cd（Ⅱ）is closer to bilayer adsorption,which is mainly controlled by chemical adsorption.Permeability experiments showed that Cd（Ⅱ）-PMA-IICM₁₇ and PMA-NICM₁₇ have better permeation selectivity for template Cd（Ⅱ）ions,and the permeation process follows the"promoting permeation"mass transfer mechanism.（3）The group of Nitrogen-containing heterocyclic ring（pyrrole）as the host,a new functional monomer N-methylpyrrolidinyl acrylamide（PMMA）was synthesized.Using surface imprinting technology,Co（Ⅱ）ion imprinted composite membrane(Co（Ⅱ）-PMMA-IICM_1²7)and the corresponding non-imprinted composite membrane(PMMA-NICM_1²7)were prepared.The optimal conditions for preparing the imprinted membrane are optimized:the molar ratio of template ion,functional monomer and crosslinking agent is 1:4:50,Nylon-6 is the supporting membrane,and DMF/H₂O（v:v=1:1）is solvent,the soaking time is 180 s.The Co（Ⅱ）-PMMA-IICM₁₆ has best adsorbing capacity at 428.24 mg·g^-1 and imprinting factor was 2.36 for Co（Ⅱ）ions which prepared under the optimal conditions.The results of SEM and BET studies indicated that Co（Ⅱ）-PMMA-IICM₁₆ is a typical mesoporous material.The adsorption experiments and permeation selectivity experiments showed that the adsorption process of Co（Ⅱ）-PMMA-IICM₁₆ for Co（Ⅱ）ions conforms to the pseudo-second-order kinetic adsorption model and Langmuir isotherm adsorption model,and the permeation processes of Co（Ⅱ）-PMMA-IICM₁₆to Co（Ⅱ）/Cd（Ⅱ）and Co（Ⅱ）/Cu（Ⅱ）follow the“delayed”permeation mass transfer mechanism,with relative permeability selectivity coefficients of 2.11 and 1.55,respectively.