Multi-cationic layered double hydroxides: Calcined products as photocatalysts for decomposition of NO_x

Several multi-cationic layered double hydroxides were synthesized by hydrothermal method and their calcined products were evaluated for the photodegradation of NO_x. The synthetic samples were characterized by powder X-ray diffraction (XRD), BET specific surface area and scanning electron microscopy (SEM). From the XRD results, it was found that doping of lanthanum in LDH structures led to poor crystallinity. Nickel zinc titanium oxide phases were observed in the XRD patterns when the samples were heated at higher temperatures. Doping the samples with Ni prevented the formation of pure zinc titanate phase. Lanthanum doping also affected the formation of nickel zinc titanium oxide. The photocatalytic activity of calcined samples was measured using decomposition of NO_x molecules. Photocatalytic properties decreased with increasing calcination temperatures as a result of grain growth. Formation of ZnO phase after calcination led to effective photocatalytic decomposition of NO_x molecules. Nickel zinc titanium oxide showed lower photocatalytic activity compared to pure zinc titanate. The specific surface areas of La containing LDHs were found to be higher compared to other LDHs containing different cations as a result of smaller crystal size in the former.