Influence of the Alumina Interface layer in Silica@Layered Double Hydroxide Core-Shell Particles

Abstract

We have studied the nature of the silica-layered double hydroxide (LDH) interface in silica@ aluminum layered double hydroxide (silica@LDH) core-shell systems. This interface affects the composition of the LDH outer layer and the behavior upon calcination. By combining powder X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and solid state magic-angle spinning nuclear magnetic resonance spectroscopy (ssMAS-NMR) we have demonstrated that the silica-LDH interface consists primarily of alumina. This interface is shown to require a consistent amount of aluminum which is removed from the outer LDH shell. By increasing the amount of aluminum used in the synthesis, Al-containing LDHs of desired M2+/Al3+ composition can be formed. However, upon calcination the composition further changes due to the irreversible migration of aluminum ions from the LDH platelets into the interface. This is in stark contrast to the reversible transitions observed when LDHs are calcined to their layered double oxides (LDOs) and then reconstructed back to LDHs.