Influence of microwave radiation on the textural properties of layered double hydroxides

Abstract

Two series of layered double hydroxides (LDHs) with compositions Mg,Al–CO 3 and Mg,Cr–CO 3 were prepared by microwave and conventional hydrothermal treatment to study the role of microwave radiation on their physicochemical properties. Aging temperature was 125 °C in all cases. The samples were fully characterised by element chemical analysis, powder X-ray diffraction, differential thermal analysis and thermogravimetric analysis, 27Al MAS NMR, FT-IR and UV–Vis diffuse reflectance spectroscopies, and specific surface area and porosity assessment by N 2 adsorption at −196 °C. In all cases, the only crystalline phase obtained was hydrotalcite which crystallinity is further enhanced by microwave hydrothermal treatment than by conventional hydrothermal treatment. The microwave-aged samples also have larger amounts of interlayer water and smaller particle size than those prepared by conventional hydrothermal ageing. The textural properties of the solids are strongly modified during the ageing treatment, and large specific surface areas values are observed at shorter times for those samples subjected to microwave radiation.