Electrochemical Fabrication Of Metal Organic Frameworks Composite Coatings And Its Application In Safety Detection Of Food Contact Materials

Food contact materials（FCMs）are widely used in food manufacturing,processing,packaging and transporting.However,it must be warned that FCMs may also cause potential food safety problems resulted from the residue and migration of their internal harmful substances while used in our lives.Therefore,it is significant for food safety to study an efficient separation and enrichment method coupled with a sensitive detector of harmful substances in FCMs because of their very low migration amount and complicated migration matrix.In this aspect,headspace-solid phase microextraction（HS-SPME）become preferred pretreatment method for complex matrix samples because it integrates sampling,purification,concentration and enable to combine with other detection instruments.Among them,the development of efficient extraction coatings has always been the focus in the application of this technology.Metal organic framework materials（MOFs）have been considered as an ideal adsorption material for microextraction coating originated from their high porosity,large specific surface area,adjustable channel structure,and special metal active sites.Unfortunately,the current preparation of MOFs coatings mostly adopts physical methods,which is not only tedious and time-consuming,but also has a certain limitations in its stability and service life.In this study,a mild and controllable electrochemical synthesis was introduced to directly deposit MOFs composite coatings on stainless steel wires which coupled with HS-SPME and gas chromatography（GC）to determination of volatile organic compounds（VOCs）and plasticizers（PAEs）migrated from real ion exchange resins for the food industry and red wine corks,respectively.The specific content is as follows:（1）A polythiophene/metal organic framework（PEDOT/Ui O-66）composite coating prepared on stainless steel wire by electrochemical method was coupled with HS-SPME-GC for simultaneous determination of seven kinds of VOCs including methyl cyclohexane,benzene,toluene,o-xylene,p-xylene,styrene and divinyl-benzene.The effects of electrolyte composition and electrochemical parameters on the preparation of composite coatings were investigated.The coatings were characterized by FT-IR,XRD,XPS,SEM and TG.The extraction conditions were optimized,indicating that the coating could reach quickly adsorption equilibrium for seven kinds of VOCs（about 5 min）in the extraction conditions of room temperature（20°C）,slight stirring(100 r min^-1)and 0.3 g m L^-1Na Cl solution,which proved its good extraction efficiency.The adsorption curve showed thatπ-πinteraction maybe play a role in the adsorption of composite coatings for VOCs.Under the optimal experimental conditions,the determination method of seven kinds of VOCs were established which had a wide linear range(0.09-100 ng m L^-1),low detection limit(0.03-0.06 ng m L^-1),good reproducibility（RSDs are 2.6%-12.3%）,satisfied recoveries（84.5-117.2%）,and have been successfully applied to the migration detection of VOCs in four types of real ion-exchange resins for the food industry.（2）A cauliflower-shaped Fe-MOFs was prepared by controlled cathodic electrodeposition method.The obtained Fe-MOFs was characterized by XPS,EDS,SEM,FT-IR,TG,and electrochemical measurements,indicating its morphology,structure and electrochemical activities varied with the applied cathodic potential.The electrochemical synthesis process was investigated thoroughly and the electrodeposition mechanism of the Fe-MOFs was proposed,revealing the change of cathodic potential would cause the difference of redox states for reaction components near to the electrode surface,especially for the iron ions can achieve the conversion of multiple valence states,making Fe-MOFs materials enable to be designed within a certain degree.In addition,Fe-MOFs was directly deposited on multi-walled carbon nanotube modified stainless steel wire to prepare MWCNTs/Fe-MOFs composite coating fibers for determination of diethyl phthalate（DEP）and dibutyl phthalate（DBP）.Under the optimal experimental conditions,the methods for the determination of two kinds of PAEs were established and successfully used to detect the migration amounts of DEP and DBP in three types of real wine corks.