Preparation Of Sulfhydryl Functionalized Separation Membrane And Its Application In The Removal Of Patulin

Food safety was a major problem concerning the national economy and people's livelihood,and it was also an important basis for ensuring the smooth export of China's agricultural products.But the excessive exposure of mycotoxin has become one of the major obstacle to the export of China's agricultural products.Patulin is a toxin fungal secondary metabolite,and it can cause a significant heathy threat to humans and animals.Therefore,many countries have specified a maximum limit of 50 ?g/L for patulin in fruits and their products.In this paper,the preparation and application of thiol-functionalized membrane were carried out based on the interaction between thiol group and patulin.Nylon membrane was used as the matrix membrane,the polydopamine(PDA)reaction platform was constructed by the deposition of PDA onto the surface of nylon membrane.Then several various thiol-functionalized membranes were prepared using the reaction characteristics of PDA coatings.High performance thiol-functionalized membrane was prepared by the optimization of preparation conditions,the relationship among the membrane morphology,chemical composition and the properties of membrane.The patulin removal efficiency,membrane adsorption and regeneration mechanism and dynamic filtration behavior was studied,which provided a theoretical foundation and technical support for the application of thiol-functionalized membrane for in fruit juice detoxification.The specific research contents are as follows:(1)Firstly,the PDA reaction platform was constructed by the deposition of PDA onto the surface of nylon membrane,and then three sulfhydryl molecules of L-cysteine,thiolated polyethyleneimine(PEI)and thiol-cyclodextrin were grafted separately.The results of XPS and Ellman's method for detecting thiol groups showed that these three sulfhydryl molecules were successfully grafted on the surface of membrane,and the thiol contents were 1.89?mol/g,2.18?mol/g and 2.35 ?mol/g,respectively.,It was found that the patulin removal efficiency of the thiol-functionalized membrane modified with L-cysteine,thiolated PEI and thiol-cyclodextrin were 33.1%,36.2%and 81.7%at the adsorption tempurature was 60?,respectively.Combined with the thiol contents of different thiol-functionalized membrane,it indicated that the more thiol groups grafted onto the surface of membrane,the higher patulin removal efficiency.(2)In order to increase the thiol contents on the surface of membrane,the branched PEI molecules was grafted onto the PDA coating as the intermediate layer,and then the thiol-functionalized membrane(HS-PEI-PDA/NY)was prepared by the amidation reaction between thiol group of L-cysteine and the amino group of PEI grafted on the membrane.The optimum conditions of membrane preparation were determined by the optimization of dopamine coating,different PEI molecules and amidation reaction conditions.The results of XPS and Ellman's method for detecting thiol groups showed that the highest thiol contents of thiol-functionalized membrane with PEI as the intermediate link layer was 12.57 ?mol/g,it was 435%higher than the thiol-cyclodextrin modified membrane(CD-S-PDA/NY).After optimization,when the adsorption tempurature was 60?,compared to the CD-SPDA/NY membrane,the patulin removal efficiency of thiol-functionalized membrane was 100%in the same time,it indicated that the HS-PEI-PDA/NY membrane has stronger adsorption capacity of patulin than the CD-S-PDA/NY membrane.(3)Taking HS-PEI-PDA/NY membrane as the research object,the effects of adsorption temperature,pH,time and initial concentration of patulin about patulin removal efficiency and the adsorption/regeneration mechanism of HS-PEI-PDA/NY membrane were studied.It was found that the patulin removal efficiency was up to 91.0%in the first 6 h by the HS-PEI-PDA/NY membrane.In the concentration rang of 50-10000 ?g/L,the patulin adsorption capacity of the HS-PEI-PDA/NY membrane was up to 1245.11 ?g/g.The kinetic and thermodynamic analysis of the patulin adsorption process showed that the pseudo-second-order kinetic model,liquid film diffusion model and Freundlich isotherm model were fitted for describing the adsorption process of patulin by the HS-PEI-PDA/NY membrane.It indicated that the adsorption process of HS-PEI-PDA/NY membrane for patulin was a chemical adsorption process,and the reaction site on the membrane surface is heterogeneous.The liquid diffusion was the main limiting step in the adsorption process.It indicated that the thiol-functionalized membrane could be regenerated by L-cysteine.After eight adsorption-desorption,the patulin removal of the regenerated membrane could be maintained at about 89.23%,while the adsorption of control membrane was only 17.33%.In this paper,the regeneration mechanism was systematically studied,which provided a theoretical foundation for the recycle application?(4)Taking HS-PEI-PDA/NY membrane as the research object,the effects of membrane number,temperature and initial filtration volume on the patulin removal efficiency were studied under dynamic filtration.The results showed that the removal efficiency of patulin was affected by various factors.In case of the initial liquid volume of 50 mL,the six-layer membrane was continuously treated 250 mL solution,the patulin removal efficiency could be maintained more than 50%.Compared to the static adsorption,the volume of patulin solution was increased under dynamic filtration,this may be the dynamic filtration process increased the effective exposure of patulin to the thiol groups on the membrane,and the certain pressure could also drive more thiol groups to bind to patulin,so the removal effect was improved.