Synthesis,Exfoliation,Surface-modification And Fluorescence Detection Of Layered Rare Earth Hydroxides

Layered rare earth hydroxides（LREHs）represent a new family of layered host compounds that incorporate attractive physical and chemical properties of rare earth elements with the wide tunability of guest anions.The compounds have attracted a lot of research attention,and potential applications have been found in various fields such as optics,catalysis,bio-medicine and so on.Synthesis,structural characterization,exfoliation,fluorescence detection research of organic aromatic compounds were introduced in this paper.Five kinds of rare earth elements,Cerium（Ce）,Samarium（Sm）,Europium（Eu）,Terbium（Tb）and Dysprosium（Dy）,of layered hydroxide were prepared,and their formulae were determined by elemental analysis,X-ray spectroscopy（EDX）and rare earth titration.The formulae are as follows:1:Ce₂（OH）₄.i（SO₄）0.9·2.3H₂O2:Sm（OH）_2.6Cl_0.4· 1.8H₂O3:Eu（OH）_2.6Cl_0.4·1.4H₂O4:Tb（OH）_2.6Cl_0.4·1.0H₂O5:Dy（OH）_2.5Cl_0.5·0.5H₂OWe further confirm that layered rare earth hydroxides were synthesized by TEM and SEM,and their morphology can be observed clearly.The shape of layered europium hydroxide（LEuH）is close to the rectangle,whose the size is large and uniform,but thickness was thick,about 106-207 nm long,about 52-167 nm wide,and 0.0236 μm thickness.Layered cerium hydroxide is flake,shape of diamond,but have different size,the length is around 96.6 nm-1.0 μm range,and about 11.5 nm thick.Layered terbium hydroxide（LTbH）is plate shaped,whose characteristic is the shape size inhomogeneity,smaller size and moderate sheet thickness,the size is around 222.1-605.9nm,and about 54.4nm thickness.Layered samarium hydroxide（LSmH）has thinner and larger-size dimension,the size is about （2.5）μm,and thickness is 4-5nm,and many places have foldings.The morphology of layered dysprosium hydroxide（LDyH）is preferable,and size and thickness is moderate,the size is about 180nm,the thickness is about 20nm,and show flower shaped structure,which is unique.Fluorescent characterizations show the rare earth element characteristic peak obviously and strong fluorescence emission.In order to further study the properties of rare earth europium hydroxide,exfoliation experiment was carried out through different methods,and by TEM,SEM and XRD characterization to prove that was stripped completely.Fluorescence characterizations show that the fluorescence intensity was increased after exfoliation.Then we use terephthalic acid（p-PTA）to make surface modification of layered europium hydroxide.By adjusting the reaction temperature,the molar ratio of terephthalic acid and layered europium hydroxide,the variation tendency of fluorescence intensity was observed and it was found that the fluorescence intensity enhanced.Elemental analysis,differential thermal/thermo-gravimetric analysis（DTA-TG）and infrared spectroscopy indicated that the surface of LEuH was modified with p-PTA,and TEM showed that the shape and size of LEuH did not change obviously after the modification of p-PTA.The application of rare earth luminescent material is mainly magnetic and luminescent.Trivalent rare earth ion usually can provide guest molecules with Lewis acid sites,enhancing the interaction between host and guest,which can serve as a good fluorescence detection.Therefore,in order to take advantage of this characteristic,we use LEuH to detect terephthalic acid and 2,6-pyridine dicarboxylic acid（DPA）.After joining p-PTA,the p-PTA carboxylate would coordinate with Eu³⁺,thus increasing the fluorescence intensity of LEuH.In theory,the carboxylate of DPA may also coordinate with Eu³⁺ so as to enhance the fluorescence intensity of LEuH.But the present experimental results show that LEuH can be used to detect p-PTA,but is still not possible to detect DPA.