Zn-Al layered double hydroxides as efficient photocatalysts for NOx abatement

Abstract

In this study,we report that layered double hydroxides (LDH) exhibited high photocatalytic activitiesin degrading NOx gases for the first time. ZnAl-CO3LDHs with a 1.5 to 3.0 Zn/Al ratio were prepared by a coprecipitation method both with and without hydrothermal treatment.Syntheses were carried out with high and low metal concentrations, the latter being the most favorablein obtaining pure LDHs in the whole Zn/Al ratio range. The samples were characterized by different techniques suchas PXRD, FT-IR, ICP mass, TGA, SBET, SEM and Diffuse reflectance (DR). The LDH particlesgrew as well-defined hexagonal nanolayers, whosesize and crystallization dependedon the synthetic procedure and the Zn/Al ratio. Those samples with lower crystallinity exhibit the highest specific surface area values (> 50 m2·g-1). The ZnAl-CO3LDHs were UV light responsive with band–gap valuescloseto 3.5 eV. The LDH photocatalysts show a high performance towards the photochemical oxidation process of NO gas, withefficiencies of around 55 %. Remarkably, the ZnAl-CO3photocatalysts exhibit an impressive selectivity towards the deNOx process, avoiding the emission of the toxic NO2gas into the atmosphere. Interestingly,these promising deNOx results are repeated when working for a long irradiation period or with the highest concentration of NO in polluted atmospheres.