Fluorescence Of Layered Double Hydroxides

Layered Double Hydroxides (LDHs), also called as hydrotalcite-like clays or anionic clays, are a family of inorganic lamellar compounds which are composed of cationic brucite-like host layers and exchangeable anions as guest molecular. LDHs have been the focus of researcher, because of their interesting properties and successful applications. With more properties discovered and applied in recent years, besides the traditional field of rheology, Catalytic technology and adsorption ,the study of LDHs has extended to the novel fields such as photochemistry, electrochemistry and the field of drug delivery.As one of the photochemistry properties, fluorescence of LDHs is of great potential value in some applied field, and it plays an important role in preparing photochemical and photophysical devices, providing complicated mechanism of intercalation processing by fluorescence spectra and describing the interactions between drug carriers and cells.The conventional methods to obtain the fluorescent LDHs composites are to exchange the interlayer anions with some fluorescent substances by intercalating, or adsorb the fluorescent substances to the surfaces of the layers. The fluorescent substances combined with LDHs included organic dyes or chromophores, fluorescent probes and labelling, rare earth complexes, inorganic nano-compounds and quantum dots, etc.In this paper, we report a new fluorescence behavior of pristine LDHs could also emit fluorescence both in suspension and powder state without any fluorescent substances intercalated. This conclusion is verified through fluorescence spectra and images of fluorescent microscope. In the excitation spectra, the spectral signatures show a peak near the wavelength 370 nm. Recorded after 370 nm excitation, the fluorescence spectrum of LDHs is characterized by the strong emission with one maximum at 430 nm. And, the dispersion state places no obvious influence on the fluorescence spectra of LDHs. However, the fluorescence lifetime in these two states differs from each other. The sample of the fluorescence images are visualized under a fluorescent microscope with UV light (excitation light at wavelength 360-370 nm) and a suitable light filter (WU filter). These results further prove the existence of fluorescence.Moreover, fluorescence behavior of pristine LDHs is found that it exists in all types of LDHs by further study. This result gives us a new method to prepare LDHs with fluorescence besides those conventional ones.Thirdly, by preparing layered double oxides, the product of LDHs calcined, and Eu-Zn-Al LDH, these two derivatives of LDHs are also verified of fluorescence properties existence.Finally, on the basis of study above, fluorescence of LDHs/anti-cancer drug composites are synthesised, and this property is studied by fluorescence spectrum. This new optical property will be expected to extend the potential applications of LDHs in drug delivery.