Selective uptake of La3+ ions with polyoxometalates-functionalized mesoporous SBA-15: An EXAFS study

Abstract

Abstract In this work, mesoporous materials based on inorganic/organic polyoxometalate (POMs) hybrids with the ability of further incorporating heterometallic lanthanum cations were designed. On the basis of the La3+ coordination to vacant organophosphonyle derivatives of POMs previously studied, herein POMs-grafted onto an amino-functionalized mesoporous SBA-15 ({NH2}-SBA-15) with incorporated La3+ ions were synthesized by varying the amounts of the latter. LIII-edge La EXAFS spectroscopy of the resulting materials provided local structural information around LaIII ions (i.e. number, nature and distances of neighboring atoms), which are comparable to that of the LaIII complexes of POMs hybrids. This technique, in addition with 31P CP-MAS NMR spectroscopy, gave definitive clues for a selective uptake of the incorporated La3+ ions by the POMs grafted onto the {NH2}-SBA-15 supports. This study is a clear demonstration that, due to their chelate effect, POMs hybrids act as efficient ligands for La3+ even in the presence of competitive adsorption sites. Consequently, a regular distribution of the La3+ ions along the channels of the SBA-15 is thus observed in these materials due to the nanostructuration of the POMs onto the support.