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Manganese Oxide Octahedral Molecular Sieves (OMS‐2) Multiple Framework Substitutions: A New Route to OMS‐2 Particle Size and Morphology Control
Author(s) -
King’ondu Cecil K.,
Opembe Naftali,
Chen Chunhu,
Ngala Katana,
Huang Hui,
Iyer Aparna,
Garcés Hector F.,
Suib Steven L.
Publication year - 2011
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201001020
Subject(s) - materials science , molecular sieve , manganese oxide , octahedron , manganese , morphology (biology) , particle size , oxide , chemical engineering , particle (ecology) , crystallography , nanotechnology , crystal structure , catalysis , metallurgy , organic chemistry , chemistry , oceanography , engineering , geology , biology , genetics
Self‐assembled multidoped cryptomelane hollow microspheres with ultrafine particles in the size range of 4–6 nm, and with a very high surface area of 380 m 2 g −1 have been synthesized. The particle size, morphology, and the surface area of these materials are readily controlled via multiple framework substitutions. The X‐ray diffraction and transmission electron microscopy (TEM) results indicate that the as‐synthesized multidoped OMS‐2 materials are pristine and crystalline, with no segregated metal oxide impurities. These results are corroborated by infrared (IR) and Raman spectroscopy data, which show no segregated amorphous and/or crystalline metal impurities. The field‐emission scanning electron microscopy (FESEM) studies confirm the homogeneous morphology consisting of microspheres that are hollow and constructed by the self‐assembly of pseudo‐flakes, whereas energy‐dispersive X‐ray (EDX) analyses imply that all four metal cations are incorporated into the OMS‐2 structure. On the other hand, thermogravimetric analyses (TGA) and differential scanning calorimetry (DSC) demonstrate that the as‐synthesized multidoped OMS‐2 hollow microspheres are more thermally unstable than their single‐doped and undoped counterparts. However, the in‐situ XRD studies show that the cryptomelane phase of the multidoped OMS‐2 hollow microspheres is stable up to about 450°C in air. The catalytic activity of these microspheres towards the oxidation of diphenylmethanol is excellent compared to that of undoped OMS‐2 materials.