Zn-Al layered double hydroxide prepared at different molar ratios: Preparation, characterization, optical and dielectric properties

摘要

The co-precipitation method was used to prepare Zn-Al-NO _3-LDH at different Zn ~2/Al ~3 molar ratios (2, 3, 4, 5 and 6) and pH value of 7.5. The structure, textural, composition and morphological properties were investigated using powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) and scanning electron microscope (SEM), respectively. The crystallinity of LDH samples were found to improve as molar ratio decreased which is attributed to the distortion of the hydroxide layers networks of the LDH crystal by the larger difference in ionic radii of Zn ~2 and Al ~3. The optical band gap energy of LDH samples were evaluated using absorbance data from UV-Vis-NIR Diffuse reflectance spectroscopy. Band gaps were affected by the variation of the Zn ~2/Al ~3 molar ratio is due to the formation of the low crystalline phases (ZnO and ZnAl _2O _4). The water molecules and anionic NO ~(3 -) in the LDH interlayer were responsible for the generation of the dielectric response. This response can be described by an anomalous low frequency dispersion using the second type of Universal Power Law. The dominance of ZnO dipoles and charge carriers (NO ~(3 -) ions) in the dielectric relaxation increases with the increasing molar ratio.