Synthesis of hydrotalcite type layered double hydroxide with various Mg/Al ratio and surface charge under controlled reaction condition

In order to control Mg/Al ratio in hydrotalcite type layered double hydroxide (LDH), LDH was prepared through coprecipitation under varied synthetic parameters such as initial Mg/Al ratio (from 1 to 20) in metal solution and coprecipitation pH (9.5, 10, 10.5 and 11). Phase evolution of hydrotalcite or impurities was examined with powder X-ray diffraction pattern and the Mg/Al ratio in final product was evaluated with inductively coupled plasma-atomic emission spectroscopy. It was found that the nominal Mg/Al ratio did not correspond to the final values, showing narrow correlation range between 1 and 3 at relatively low pH ~ 9.5. By raising coprecipitation pH upto 11, Mg/Al ratio successfully increased in final LDH product upto 15.4. Under controlled initial Mg/Al ratio and coprecipitation pH, various LDHs with Mg/Al ratio between 1 and 16, which corresponded to layer charge density between 0.5 and 6(+)/100 Å2, were obtained. The charge density and surface charge of LDHs exhibited linear correlation, showing zeta potential value 16–40 mV at neutral pH.