Synthesis And Adsorption Selectivity Of Nicosulfuron Molecularly Imprinted Membranes

Molecular imprinting technique has been paid more and more attention due to itspredetermination, specific recognition and practicability. Along with the the development ofmolecular imprinted polymer molecularly imprinted membrane （MIM） has been a newresearch field and became a research hotspot in functionalized separation membrane. Thisthesis aims to synthesize herbicide molecularly imprinted membranes and investigate theirspecific recognition to template molecules in order to develop new application of MIM in theherbicide detection in food and in environment.In the first part, polymer molecularly imprinted composite membranes （MICM） usingherbicide nicosulfuron （N₁） as the template molecule were synthesized via photo-initiatedpolymerization supported on nylon microporous filter paper with different ratio of methacr-ylic acid （MAA） and acrylamide （AM） as monomers. The optimal conditions for thepreparation of molecularly imprinted composite membranes were determined. The structureand the surface morphology of the membranes were studied by infrared spectroscopy （FT-IR）,scanning electron microscopy （SEM） and thermogravimetric analysis （TGA）. Static equilib-rium binding and competitive recognition properties of the membranes to nicosulfuron and itsanalogues （pyrazosulfuron ethyl （P2） and bensulfuron methyl （B3）） were examined. Thebinding mechanism was proposed and the recognition capability was determined according tothe equilibrium binding experiment and Scatchard analysis of MICM. It has been showed thatthe nicosulfuron-imprinted membranes （MAA: AM=4:1） had the best adsorption capacityto N₁(363.21μg g^-1)and the best recognition capacity to N₁compared to its analogues. Thebiggest selectivity factors of αN₁/P2and αN₁/B3were1.28and1.83and the imprinted factorreached to2.34. The Scatchard plot revealed that one class of binding sites was mainlyproduced in the imprinted composite membrane in the studied concentration range ofnicosulfuron. The equilibrium dissociation constant Kdand the apparent maximum numberQ_maxwere calculated to be9.55mmol L^-1and82.50μmol g^-1. The results of this studyimplied that the molecularly imprinted composite membranes could be used as separationmembranes for nicosulfuron enrichment.In the second part, the polymer molecularly imprinted composite membranes wereprepared by photo-initiated polymerization on polyvinylidene fluoride （PVDF） microporousfilter paper using herbicide chlorimuron-ethyl as the template molecule with different ratio of methacrylic acid （MAA） and acrylamide （AM）. The structure and the surface morphology themembranes were examined by FT-IR and TGA. The equilibrium binding experiment showedthat MICM （MAA: AM=4:1） had the best binding capacity to the template(361.9μg g^-1).Scatchard plot revealed that one class of binding sites was mainly produced in MICM in thestudied concentration range of chlorimuron-ethyl. The equilibrium dissociation constant Kdand the apparent maximum number Q_maxwere calculated to be9.71mmol L^-1and80.36μmol g^-1, respectively, according to the slope and intercept of its Scatchard plot. The swell-ing study of MICM in different solvent showed that the swelling properties of MICM inacetonitrile（ACN）was4.06%, indicating that MICM could be used in ACN solution systemfor long time.In the third part, organic-inorganic hybrid nicosulfuron molecularly imprinted loadingmembranes （HMIM） were fabricated using nicosulfuron as the template molecule, TEOS asthe inorganic phase, methacrylic acid as the organic phase, glass fiber as loading film,respectively. The effects of different ratio of substrates, hydrolysis time, temperature, mixingtime of organic phase and inorganic phase and coupling agent on the quality and theadsorption capacity of the HMIM were investigated. The structure and the surfacemorphology of HMIM were studied by FT-IR and SEM. The adsorption properties and thespecific recognition of the molecularly imprinted hybrid membranes to nicosulfuron and itsanalogues （P2and B3） were tested by equilibrium binding experiments. The selectivitycoefficients of HMIM, kN₁/P2and kN₁/B3, were2.98and3.32and the relative selectivitycoefficient, k′N₁/P2and k′N₁/B3, were1.32and2.71, respectively. In certain concentration range,the binding kinetics of organic-inorganic hybrid molecularly imprinted glass fiber loadingmembranes to nicosulfuron was studied. The Scatchard plot revealed that one class of bindingsites was mainly produced in the imprinted composite membrane in the studied concentrationrange of nicosulfuron. The equilibrium dissociation constant Kdand the apparent maximumnumber Q_maxwere calculated to be6.30mmol L^-1and127.71μmol g^-1, respectively. Thesynthesis and recognition mechanism of HMIM were speculated.In the forth part, organic-inorganic hybrid nicosulfuron molecularly imprinted loadingmembranes （HMIM） were produced on the surface of glass, using nicosulfuron as templatemolecule, TEOS as inorganic phase, methacrylic acid as the organic phase, respectively. Thestructure and the surface morphology of the HMIM were studied by FT-IR and SEM, whichshowed that the HMIM had uniform structure. The studies of adsorption properties and selectivity recognition of HMIM to N₁and its analogues （P2and B3） indicated that HMIM hadthe best binding capacity to N₁(15.00μg g^-1), the selectivity coefficients of HMIM, kN₁/P2and kN₁/B3（2.94and4.35） and the relative selectivity coefficient, k′N₁/P2and k′N₁/B3（1.46and1.54）, respectively.In the fifth part, methods of multiwavelength-high performance liquid chromatographywith diode array detector （HPLC-DAD） was studied to test various components of strawberryand apricot from different regions simultaneously, including water soluble organic acids（citric acid and succinic acid, malic acid） and vitamins （vitamin C, vitamin B1, vitamin B2）.0.5mmol· L^-1phosphoric acid and acetonitrile were used as mobile phase. Flow rate of themobile phase ratio was changed with different time at the wavelengths of210nm,254nmand270nm. The results showed the organic acids and vitamins could be achieved a rapid andefficient separation.In summary, nicosulfuron molecularly imprinted P （MAA-co-AM） composite membra-nes, nicosulfuron molecularly imprinted organic-inorganic hybrid loading membranes on thesurface of glass fiber and glass and chlorimuron-ethyl molecularly imprinted P （MAA-co-AM）composite membranes were successfully prepared. The adsorption and recognitionexperiments showed that MICM and HMIM had very good selective recognition propertiesand could be used as separation membranes for template molecules enrichment. Themulticomponents in food could be tested simultaneously and efficiently using the method ofthe multi-wavelength HPLC with diode array detector （HPLC-DAD）.