Layered double hydroxide/sepiolite heterostructured materials: preparation and applications

Oral presentation given at the 8th Mid-European Clay Conference, held in Kosice (Slovakia) on July 4-8th, 2016. S6: application and treatment of clays and other industrial minerals.There is an increasing interest in the development of nanostructured materials based on the combination of diverse type of inorganic particulate solids with the aim to produce a new generation of functional materials for diverse applications. In this context, fibrous clays have been used as support of nanoparticles, as for instance metal oxides (e.g., TiO2, Fe3O4,..). This communication will introduce a new type of heterostructured materials in which layered double hydroxides (LDH) are assembled to sepiolite fibrous clay [1]. In this way, Mg-Al and Zn-Al LDH have been generated in presence of sepiolite clay, becoming linked to the fibrous silicate through the silanol groups present at its external surface. The synthesis procedure allows to tune the sepiolite:LDH relative ratio, being also possible to prepare the LDH in the presence of anionic organic species to produce the corresponding intercalation compounds. Changes in the textural properties deduced from the N2adsorption-desorption isotherms can be interpreted by the effect of sepiolite for providing a stable support where nanometric LDH particles remain attached decreasing the amount of N2 adsorbed and therefore its specific surface area. This methodology has been patented [2] and it is now applied to the preparation of diverse materials that can be of interest in diverse areas of application. For example, MgAl-LDH heterostructures show the preservation of adsorption properties ascribed to both type of inorganic components with the possibility of adsorbing simultaneously both cationic and anionic species. This has been tested in the removal of various dye pollutants. The thermal transformation of assembled ZnAl-LDH in the corresponding mixed metal oxide shows the presence of the generated nanoparticles that remain bonded ontothe silicate, confirming the interest of the approach in view to prepare highly disperse metal oxide catalysts supported on sepiolite using LDH of different composition as precursors. The assembled LDH preserves its ion-exchange capacity which can be profited to incorporate anionic species useful for other applications. Thus, the anionic herbicide known as MCPA (2-methyl-4-chlorophenoxyacetic acid) has been intercalated in the supported LDH by ion-exchange as well by co-precipitation of the LDH in presence of MCPA and the clay. The release of the herbicide from these heterostructured materials has been tested in comparison to that from the herbicide intercalated in the LDH alone.CICYT (Spain, project MAT2012-31759 & MAT2015-71117-R) and the EU COST Action MP1202