Layered Double Hydroxides With A High Aspect Ratio: Synthesis, Characterization And Application In Photocatalysis

Layered double hydroxides are a large group of materials applied for many catalysis reactions. Traditional synthesis routes can obtain but with much lower crystallinity, mixed interlayer anions and relative irregular morphology.In this study, a new route for synthesis of Mg/Al layered double hydroxide (Mg₆Al₂(OH)₁₆(CO₃)·4H₂O) has been introduced, which can be considered as a modified calcination-rehydration method. Under the hydrothermal conditions, LDHs with a high aspect ratio were synthesized and characterized by inductively coupled plasma-atom emission spectrometer (ICP-AES), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermal measurement (TG-DTG) and scanning electron microscopy (SEM). XRD patterns display the crystalline enhanced with the increase of hydrothermal temperature and aging time. TG-DTG curves show the more stable LDHs were synthesized at higher temperature. SEM images indicate the lateral size of the synthesized LDHs locates at ca. 1 - 6μm and the thickness at ca. 35 - 60 nm. And the particle size depends strongly on the treatment temperature and aging time. A buffer solution consisted of HCO₃^- and CO₃^2- keeps the pH of reaction system in a certain range and offers a low supersaturated reaction circumstance. This is of high importance for the formation of LDHs with a high aspect ratio.In the applications of photocatalic reaction, combination of titanium dioxide with the functional material is effective for improving the activity of catalyst. In this study, we try to use the high aspect ratio LDH material synthesised in our lab as a composite of commercial titanium dioxide (P-25), and apply it to remove of 2-nitrophenol pollution. A serials of combined catalyst of different ratio of P-25/LDH (wt%) were prepared to find the optimal one. The results show that, 20 mg composite catalyst with the ratio of 3:1 gives a 91.68% effectiveness in removing 80ml 20 mg/L 2-nitrophenol through 200 min (180 min under the Uv light).