Synthesis,Charaterization And Structural Analysis Of Layered Double Hydroxides Containing Europium And Complexes

A possible way to increase the photosynthetic effective of plants is toconvert the ultraviolet (UV) and green (G) component in sunlight intoblue (B) and red (R). The plastic farm film containing specialphotoluminescent materials is called light-conversion farm film, whichcan considerably increase the growth of plants.Layered double hydroxides (LDHs) have selectivity absorption ofinfrared light owing to their special layers structure and chemicalcomposition. So, LDHs have been used as a new additive in the plasticfarm film to enhance temperature of greenhouse. However, the commonLDHs don't have luminescent properties. But novel layered doublehydroxide (LDH) phases containing rare earth (RE) have been preparedby ion-exchange method using complexes as guest anions. It issuggestion that it is possible to synthesis a novel dual-function additivesfor plastics farm film with selectivity absorbing infrared wavelength andlight conversion function by ion exchange or intercalation method in thebase of LDHs.Rare earths have better optical, electronic and magnetic propertiesdue to their distinctive 4f shell electronic structure. So, the aim of ourinvestigation focuses on the synthesis inorganic/organic hybrid materialswith dual-functional by the method of intercalation the rare earth or rareearth ligand into LDHs structure.In this thesis, in order to getting dual-functional LDHs materials,two strategies are designed. (1) First, Al³⁺ cations within LDHs layerswere replacement of Eu³⁺ by using the isomorphous substitution; then intercalation of organic anions intercalate into LDHs interlayer by theion-exchange method, to enhance the luminescence of LDHs doped withEu³⁺ ions. (2) The rare earth complexes were prepared; it was intercalatedinto MgAl-NO₃ LDHs precursor by ion-exchange method. The details areas follow:1. Preparation and luminescence of LDHs doped with Eu³⁺ ionsThe samples of MgAl-hydrotalcites containing Eu³⁺ (MgAlEu-CO₃LDHs) were prepared by co-precipition and through hydrothermaltreatment. Various preparative factors such as system pH value, content,aging time and temperature, were studies. Through controlling thereaction condition, the results of product may give rise to high purity andbetter crystal form of MgAlEu-CO₃ LDHs. MgAlEu-CO₃ LDHs hold thelayered structure and have infrared absorption at 600～1350 cm^-1. Underexcitation by 399 nm, there are three sharp emissions peaked at 594, 620and 700 nm in emission spectrum of MgAlEu-CO₃ LDHs, which belongto the ⁵D₀→⁷F_J(J=1,2,4) transition of Eu³⁺ ion. Besides, the luminescentintensity changed with the increasing of Eu³⁺/Al³⁺ molar ratio. All ofresults revealed that a few Al³⁺ ions within layers of LDHs were replacedby Eu³⁺ ions in our sample. It was found that the MgAlEu-CO₃ LDHs is anovel dual-function material with selectivity absorbing infraredwavelength and red emitting.2. Preparation and luminescence of Eu-LDHs intercalated organiciigandBenzoate, terephthalte, salicylate and pyridine-2,6-dicarboxylic(DPA)were intercalated into the interlayer MgAlEu-NO₃ LDHs precursor byion-exchange method. It is still good layered structure and infrared absorption. At the same time, organic anions intercalation LDHs enhancethe relative intensity of red luminescent of Eu³⁺ ion.Pyfidine-2,6-dicarboxylic (DPA) Pillared MgAlEu-LDHs have the bestluminescence in above hybrid materials. The samples thus obtained werecharacterized by XRD and FT-IR, then combining the mulliken chargedensity of organic guest anions using an ab initio(HF/6-31G) method byGaussian 03w, the supermolecule structure model of organic guest anionsintercalated MgAlEu-LDHs were build, and its luminescent mechanismwas also discussed.3. Synthesis and properties of europium ligand intercalation in LDHsHaving been prepared, Eu(DPA)₃^3- complex was intercalated into theinterlayer of MgAl-NO₃ LDHs by ion-exchange method throughhydrothermal treatment (MgAl-Eu(DPA)₃ LDHs). The analyses indicatedthat Eu(DPA)₃^3- complex as an entirety intercalated into LDHs interlayerspace, and Eu(DPA)₃^3- molecules steadily arranged with C3 axisperpendicular to the layer plane. The luminescence studies showed thatMgAl-Eu(DPA)₃ LDHs have keeping typical red luminescence of Eu³⁺ion and exhibits enhanced red luminescence compared with those of purepowder samples.