Study on the coating of nano-scale SiO 2 film on the surface of nanocrystalline Mg-Al layered double hydroxides

The coating process of a nano-scale SiO 2 film on the nanocrystalline Mg-Al layered double hydroxides via a sol-gel process was investigated. The uniform and dense SiO 2 film with a thickness of about 5 nm on the nano-LDHs particles was characterized by the solubility test in the dilute HNO 3 or HCl acid, TEM and FT-IR, XRD, TG and DSC. The chemical shifts of binding energies of Al 2p, Mg 2p, Si 2s and O 1s on the coated particles indicate that the coating of the SiO 2 nano-film on the surface of the nano-LDHs proceeds through the formation of Mg-O-Si and Al-O-Si bonds. The thermal analysis shows that both the SiO 2 -coated nano-LDHs and the nano-LDHs have a similar mass loss process, in which there are three obvious stages of mass loss in the temperature range of 40-700°C. Furthermore, the more the coated amount of SiO 2 on the surface of the nano-LDHs is, the less the mass loss of the samples is at 700°C.The nano LDHs have two obvious endothermic peaks at 244.67°C and 430.13°C, whose corresponding heat absorption capacities are 412.28 J/g and 336.30 J/g, respectively. In contrast, the coated nano-LDHs have only one endothermic peak at 243.60°C with a heat absorption capacity of 221.25 J/g.