Assembly And Structural Characteristics Of Supramolecular UV Absorbents Based On Layered Double Hydroxides

In this thesis, the controllable preparation and structural characteristics of supramolecular UV absorbents based on Layered Double Hydroxides(LDHs) are reported. The influence of particle size of LDHs on UV absorption has been investigated. Several methods for synthesizing intercalated LDHs have been developed and the properties of the intercalated LDH UV absorbents have been fully characterized. The orientation and arrangement of the organic anions within the interlayer of the organo-LDHs have also been investigated. Zn-Al-CO3 Layered Double Hydroxides(LDHs) have been prepared by a new method involving separate nucleation and aging steps. The particle size in both a and c directions can be controlled by altering the concentration of the reactants, aging time and aging temperature. Under conditions of low concentration, long aging time and high temperature LDHs with large particle size and high crystallinity were obtained. Materials with different narrow ranges of particle size were prepared by altering the aging temperature. The degree of attenuation of ultraviolet-visible radiation in the range 200-800 nm through scattering by dispersions of the materials (0.02 wt.%) in water was found to increase with increasing particle size. Furthermore, linear relationships were found to exist between the degree of attenuation and the mean crystallite sizes in both a and c directions. The minimum values of mean crystallite size required to scatter radiation of different wavelengths were obtained by extrapolation. For scattering to occur at 290 nm, the crystallite size in the a direction must exceed 33 nm and that in the c direction must exceed 10 nm. At 800 nm, the corresponding values are 36 and 20 nm respectively. Intercalated LDH-based UV absorbents have been successfully assembled by ion exchange of a precursor in an organic solvent. The samples thereby obtained were characterized by XRD, FT-IR and TG-DTA. The results show that the original interlayer carbonate ions of the hydrotalcite precursor can be completely replaced by organic anions under controlled conditions. The interaction between the host layers and the guests, as well as the arrangement and orientation of guests between the layers was investigated. The resulting layered nanohybrids exhibit both physical screening by the LDH layers and UV absorbence by interlayer ions .Layered double hydroxides (LDHs) with interlayer organic anions were prepared using constant the pH coprecipitation method. A combination of XRD and TG-DTA was used to study in detail the effect of interlayer water content, layer charge density, composition of the host layer sheets, size and structure of the guest organic anions on the interlayer arrangement of the organo-LDHs. The results show that the orientation and arrangement of the organic anions within the interlayer of the organo-LDHs may be controlled and predicted.