Texture effect of layered double hydroxides on chemisorption of Orange II

The chemisorption properties of hydrotalcite (HT) with novel macroporous properties have been investigated for azo dye, Orange II (O-II), and compared to coprecipitated HT and their calcined derivatives. Adsorption isotherms satisfactorily fit the Langmuir model. Adsorption capacities of the layered double hydroxides (LDH) macroporous structures are very high, particularly for the calcined materials (4.34 mmol/g) compared to standard HT (0.504 mmol/g), showing that accessibility to the LDH layer surface insures better sorptive properties. For both synthetic materials, the calcination/reconstruction process gives rise to highest concentrations of adsorbed O-II and a partial intercalation of O-II molecules in the structure as shown by the expansion of the basal spacing (d=2.4nm). Conversely, the uncalcined HT phases mainly display a surface exchange chemisorption process.