Thermal, optical and dielectric properties of Zn–Al layered double hydroxide

Zn–Al–NO 3–layered double hydroxide (Zn–Al–NO 3–LDH) was prepared by the co-precipitation method at a constant pH of 7 and a ratio of Zn/Al = 4. A thermal treatment was performed for LDH at various temperatures. Powder XRD patterns showed that the layered structure of the LDH samples was stable below 200 °C, which was also confirmed by thermogravimetric (TGA) and differential thermal (DTA) analyses. Infrared spectra of the samples showed the characteristic peaks of LDH, and changes of these peaks were observed when thermal treatment was performed above 150 °C. Diffuse reflectance spectroscopy of the samples showed more than one energy gap at calcination temperatures below200 °C. In samples calcined at 200 °C and above only one energy gap was observed at approximately 3.3 eV. The photocatalytic activity was found to increase with the increase of the ZnO crystal size, which can be achieved by increasing the calcination temperature of the samples. Because of the presence of water molecules and anionic NO 3 − in the interlayer of the LDH, the dielectric response of the calcined LDH can be described by an anomalous low frequency dispersion using the second type of Universal Power Law for calcination temperatures below 200 °C. The dielectric response of the calcined LDH above 150 °C displays the dielectric relaxation behaviour of ZnO because of the formation of a ZnO phase in the LDH within this temperature range. The following figure shows the summary of my work: Thermal degradation of Zn–Al–NO 3–LDH through (a) TGA/DTG and (b) TGA/DTA analyses. (c) Optical properties of Zn–Al–NO 3–LDH before thermal treatment. (d) Optical properties of Zn–Al–NO 3–LDH after thermal treatment (at calcination temperature of 500 °C). (e) Dielectric response of Zn–Al–NO 3–LDH at various calcined temperatures. [Display omitted] ► Zn–Al–NO 3–LDH is prepared by using the co-precipitation method. ► LDH structure is well preserved at calcination temperatures below 180 °C. ► Photocatalytic activity of LDH will improve as its calcined temperature increases. ► Dielectric response of LDH can be described by anomalous low frequency dispersion.