Synthesis of Mg–Al–Fe–NO3 layered double hydroxides via a mechano-hydrothermal route

• Hydrothermal treatment was combined with a pre-milling process.
• The synthesis route could be completed at low temperature.
• Resulting LDHs were well-crystallized and dispersed.
• Resulting LDHs have high removal efficiency for heavy metal pollutants.

Mg–Al–Fe–NO3 layered double hydroxides (LDHs) with a constant Mg2+/(Al3+ + Fe3+) molar ratio but varying Al3+/Fe3+ molar ratios were successfully synthesized by a mechano-hydrothermal (MHT) method from Mg(OH)2, Al(OH)3 and Fe(NO3)3·9H2O or Mg(NO3)2·6H2O as starting materials. The resulting LDHs (MHT-LDHs) were characterized by XRD, TEM, SEM, FT-IR, and zeta potential, size distribution and specific surface area analyses. It was found that pre-milling played a key role in the LDH formation during subsequent hydrothermal treatment. The MHT route is advantageous in terms of low reaction temperature compared with the conventional hydrothermal method, and the target products are of high crystallinity and good dispersion compared with the conventional mechanochemical (MC) method. The MHT-LDHs had higher specific surface area and zeta potential, and lower hydrodynamic diameter than LDHs obtained by MC method (MC-LDHs). Furthermore, the removal of Cr(VI) from aqueous solutions using the LDHs was examined, showing that the MHT-LDHs are of higher removal efficiency than MC-LDHs for the heavy metal pollutant.

High crystallized and well-dispersed Mg–Al–Fe–NO3 LDHs were synthesized via mechano-hydrothermal route. The LDHs show high removal efficiency for heavy metal pollutants from aqueous solutions. Figure optionsDownload as PowerPoint slide