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/AI 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 similar to 9.5. By raising coprecipitation pH upto 11, Mg/Al ratio successfully increased in final LDH product upto 15.4. Under controlled initial Mg/AI ratio and coprecipitation pH, various LDHs with Mg/AI ratio between I and 16, which corresponded to layer charge density between 0.5 and 6(+)/100 angstrom(2), were obtained. The charge density and surface charge of LDHs exhibited linear correlation, showing zeta potential value 16-40 mV at neutral pH. (C) 2016 Elsevier B.V. All rights reserved.