Preparation And Molecular Recognition Ability Of Surface Molecular Imprinted Polymers Based On Two Dimensional Nano-sheets

Molecular imprinted polymers (MIPs), described as artificial "locks" for "molecular keys", have the ability to recognize the used template from a mixture of closely related compounds. Due to the molecular recognition ability, MIPs have been proposed for promising applications in a wide variety of fields, such as solid-phase extraction, chiral separation, catalyst, and chemical/biological sensors. Compared with the conventional MIPs preparation through an inefficient entrapment method, the surface imprinted technique based on nano/micro materials provides an alternative way for improving mass transfer, increasing affinity binding and decreasing high diffusion barrier of the template by fixing MIPs on a support substrate. The surface imprinted materials have high surface-to-volume ratio, shallow recognition sites locating in the proximity of material surface, and is suitable to be modified and functionalized for integration of devices. The developing of surface imprinted methods is challenging to resolve the problem of traditional polymerization and has attracted significant interests in recent years.The research for the surface imprinted substrates is focused on the zero dimensional nanoparticles and three dimensional spheres. This thesis is selecting two dimensional nano-sheets materials:graphene and graphitic carbon nitride (g-CsN4) as the substrates, fabricating a series of new imprinted polymers based on the two dimensional nanomaterials, and constructing the molecular imprinted electrochemical and fluorescent senor for their functional application, which aims at determination of2,4-dinitrophenol (DNP) and chlorotetracycline (CTC).Graphene, the2D honeycomb lattice of sp2-bonded carbon atoms, have unique nanostructure, ultrahigh specific surface area (theoretical value2630m2g-1), extraordinary electronic conductivity, physical and chemical properties. It is favorable to the generation of the composites of graphene with thin MIP modification layers, providing a high loading capacity, improving the kinetics and accessibility to the target species. Graphene is also a promising candidate to detect a variety of molecules by charge transfer. These allow that MIP being deposited on graphene has a higher affinity and sensitivity to target analyte, and a more homogeneous distribution of recognition sites.A simple surface molecular imprinted approach was developed to synthesize composites of MIP with graphene oxide (GO) in aqueous solution, where DNP was used as the template, o-phenylenediamine (OPDA) as both a functional monomer and a cross-linker. Effects of the synthetic conditions including the polymerization temperature, the molar ratio of template to functional monomer, and the amount of initiator were investigated on the adsorption capacity of the GO-MIP composites. The GO-MIP composites were characterized with UV-vis, FT-IR, Raman spectroscopy, SEM and EDAX. The composites were demonstrated to have high adsorption capacity, excellent selectivity and site accessibility for the target pollutant DNP under optimal conditions. The composites were used to fabricate sensor for the determination of DNP, and the electrochemical behaviors of the sensor in the presence of DNP were investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and differential pulse voltammetry (DPV). Under optimal DPV conditions, there was a good linear correlation between the current of the cathodic peak and the concentration of DNP in the range of1.0-150.0μM. This proposed novel GO-MIP sensor is satisfactorily applied to determine DNP in practical water samples.A molecular imprinted polymer sensor was fabricated by directly eletropolymerizing monomer o-phenylenediamine in the presence of template (CTC), based on controlled electrochemical reduction of GO at cathodic potentials. In comparison with GO, the reduced GO (RGO) increased the cyclic voltammetric peak currents of [Fe(CN)6]3-/[Fe(CN)6]4-redox pair, which was influenced by the amount of used GO and the reduction time. Integrating the excellent response amplification of RGO and the special recognition of MIP, the new RGO-MIP sensor was used to detect CTC indirectly by using [Fe(CN)6]3-/[Fe(CN)6]4" redox pair as an electrochemical probe. The RGO-MIP sensor exhibited a wide-range linear correlation between the peak current variation of the DPV cathodic peak and the concentration of CTC in the range of10.0-500.0μM. The use of the RGO-MIP sensor gave satisfactory results in the analysis of tap water and laboratory wastewater samples. This indirect method provides a way for the determination of electrochemical inactive pollutants.A fluorescent imprinted senor is constructed base on g-C3N4selected as the substrate material. g-C3N4have a graphitic-like planar nanostructure, special optical and electrical properties. There still have no reports about the new imprinted material base on g-C3N4In this study, we develop a rapid and convenient method for a fluorescent g-C3N4-MIP sensor on the surface of g-C3N4, a product of melamine by high-temperature calcination, used DNP as template,3-aminopropyltriethoxysilane as monomer, tetraethyl orthosilicate as cross linker. The fluorescent of g-C3N4-MIP will be quenched during the rebinding process in the presence of template. The MIP sensor shows special recognition ability towards to template DNP. Therefore, the MIP sensor based on g-C3N4has promising applications in the sensitive and selective determination of organic compounds.