Studies On Fabrication And Properties Of Oriented Film Materials Based On Layered Double Hydroxides

In this dissertation, two types of layered double hydroxides-based filmmaterials with different orientation (ab plane of LDH platelets parallel toand perpendicular to the substrate respectively), have been fabricated byusing layered double hydroxides (LDHs) as host material and functionalspecies as guest. For the LDH/organic chromophore films, the effects ofhost-guest and guest-guest interactions on fluorescence properties wereinvestigated thoroughly. Moreover, the fluorescence film as a chemicalsensor for the determination of toxic metal ions was also explored. In thecase of the catalytic films with vertical orientation, the catalyticperformances towards the oxidation of mercaptan (catalytic activity,stability and recyclability) were evalued. The relationship between thestructure and catalytic behavior of the structured catalyst was revealed.The main results of this dissertation are as follows:1. LDH films with ab plane parallel to the substrate:(1) The influence of LDHs host material on thephotoluminescence properties of interlayer chromophore has beenstudied. The inorganic–organic composites films have been prepared by intercalation of fluorescent probe (ANS) into layered doublehydroxide (LDHs) with the different metal compositions. Thecomposite films obtained by the solvent evaporation method possessgood c-orientation (ab plane of LDH platelets parallel to the substrate).The result shows that the preferential orientation of the interlayer ANSmolecule, which is effected by metal species and M²⁺/Al³⁺ratio ofLDHs matrix, leads to variations in fluorescence performance ofcomposite films. Therefore, the luminescence behavior of compositefilms can be modulated via changing the type and ratio of cationspecies in LDHs matrix, which provides rational design andpreparation of luminescence materials.(2) The influence of microenvironment on the photoluminescenceproperties of interlayer chromophore has been studied. A fluorescentprobe (ANS) and a series of surfactants with different alkyl chainlengths were respectively cointercalated into the galleries of LDHs bythe anion exchange method. The composites films obtained by thesolvent evaporation method possess good c-orientation. Controllableluminescence behavior of ANS (wavelength, fluorescence efficiencyand lifetime) was achieved via varying the interlayer polarity, owing tothe "size-matching" rule between ANS and surfactant. Moreover, thefluorescence properties can be further tuned by changing the dispersiondegree of ANS accommodated in LDHs matrix, resulting in the optimal fluorescence film with a single molecular luminescence of ANS. Thiswork demonstrates tunable photoluminescence properties of compositefilms via changing the microenvironment of LDH gallery.(3) The application of the LDHs-based composite films in thefield of photochemical sensor was investigated. An inorganic-oganiccomposite film with a well c-orientation of LDHs microcrystals wasfabricated based on H-acid/LDHs film via the electrophoreticdeposition (EPD) method. The composite film as a fluorescencechemosensor for Hg²⁺at pH7.0exhibits a broad linear response range(1.0×10^-71.0×10^-5mol L^-1), low detection limit (6.3×10^-8mol L^-1)and high selectivity. The specific fluorescence response of the opticalsensor is attributed to the coordination between Hg(II) and H-acidimmobilized in the LDH matrix, accounting for the significantfluorescence quenching of the composite film. This work provides anovel approach to immobilize functional molecule into inorganiclayered matrix, for the purpose of technological applications inbiological analysis and environmental detection.2. LDH-based films with ab plane perpendicular to substrate:(1) A structured catalyst has been fabricated for mercaptansweetening based on immobilizing cobalt phthalocyanine tetrasulfonate(CoPcS) on a mixed metal oxide (denoted as MMO) film, whichderived from calcining the highly ordered LDHs film (ab plane of LDH platelets perpendicular to the substrate) preprared with the method ofin-situ growth. The structured catalyst possesses the desiredmechanical strength and high adhesion to the substrate. It was foundthat the structured catalyst exhibits a high conversion (85.7%) for theoxidation of mercaptan to disulphide, markedly higher than that of thecorresponding powder catalyst (38.7%), as a result of the synergisticeffect between the active center (CoPcS) and abundant moderate basicsites on MMO surface. In addition, the structured catalyst showssuperior catalysis-regeneration performance, which facilitates itsrepeatable and cyclic usage over a long period.(2) Mg/Ni/Al LDHs film has been prepared with the method ofin-situ growth, which was used as the precursor for fabricating astructured catalyst for mercaptan sweetening. It was found that a largenumber of moderate basic sites come into formation in the process ofcalcination owing to the synergistic effect between Mg and Ni,accounting for the largely enhanced catalytic activity (conversion92.8%) for the Mg/Ni/Al structured catalyst in comparison with Mg/Alone. In addition, the structured catalyst shows superiorcatalysis-regeneration performance. Therefore, this work provides afacile and effective method for the fabrication of structured catalystwith high catalytic activity, stability as well as recyclability, which canbe used as an eco-friendly catalyst for sweetening process in petroleum refining industry.