Preparation Of Fluorescence Molecules Intercalated Layered Double Hydroxides And Their Application Sensors

This thesis describes a systematic study on preparation of the layered double hydroxide (LDH) intercalated with organic luminescence molecules (OLM). The interlayer molecular orientation of OLM, fluorescence properties and application of the OLM/LDH composites in the filed of sensors have been investigated thoroughly. Fluorescence polarization method was applied to determine the preferential orientation of OLM in the interlayer region of LDH. The photoluminescent properties of OLM in the LDH gallery can be tuned by changing the interlayer microenvironment. The preparation of highly oriented photoluminescence films of OLM/LDH composites opens avenues for their applications in the fields of photoluminescent materials, polarized luminescent materials and sensors.Theα-NAA andβ-NAA intercalated Zn2Al LDH composites were prepared by the ion-exchange method and their thin films on Si substrates were obtained by the solvent evaporation method respectively. The XRD and SEM show that theα-NAA LDH andβ-NAA LDH thin films are well c-oriented assembly with ab-plane of LDH microcrystals parallel to the substrate. UV-vis absorption and fluorescence spectra (emission, lifetime and time resolution) indicate that the intercalated NAA exists in its monomer form and depolarization factors exhibit no influence on its fluorescence emission process. Fluorescence polarization method was applied to investigate the preferential orientation ofα-NAA andβ-NAA in the LDH gallery, and the results show thatα-NAA andβ-NAA are accommodated between sheets of Zn2Al LDH as monomeric units with a tilt angleψ(the angle between the transition moment of NAA with respect to the normal to the LDH layers) of 60°and 65°, respectively.The influences of microenvironment on the photoluminescence properties of interlayer chromophores have been studied. The a-NAA and 1-heptanesulfonic acid sodium (HES) with different molar ratios were co-intercalated in the galleries of a Zn2Al LDH. The fluorescence wavelength, emission intensity and lifetime correlate with the orientation ofα-NAA remarkably and can be finely controlled by varying the fluorophore content in a rigid and constrained environment of the host. The optimal luminous intensity and the longest fluorescence lifetime of a-NAA-HES/LDH (x%, x stands for the molar percentage of a-NAA) can be obtained with x value ranging in 15%-20%. In addition, fluorescein (FLU) and surfactants with different alkyl chain length ((CH2)nSO3) were co-intercalated in the galleries of a Zn2Al LDH. The orientation of FLU and its photoluminescence properties are related to the microenvironment of LDH gallery, which can be tuned by simply changing the alkyl chain length of the surfactant. The optimal luminous intensity, anisotropy, the longest fluorescence lifetime and the strongest photostability of FLU-(CH2)nSO3/LDH film can be obtained with n=7, due to the "size-matching" rule between the organic dye and surfactant.Furthermore, the application of OLM/LDH composites in the field of electrochemical and photochemical sensors has been investigated. The FLU-HES/LDH thin film modified electrode exhibits electrocatalytic performances for dopamine (DA) with rather high sensitivity and selectivity. The FLU-HES/LDH (x=1.25×10-2%) modified electrode possesses a wide linear range, low detection limit, excellent reproducibility and stability for the determination of DA. In addition, the optical pH sensor with FLU-HES/LDH film thickness of 300 nm exhibits a broad linear dynamic range for solution pH, good repeatability and reversibility, high photostability and storage stability as well as fast response time.