Polymer-assisted formation of giant polyoxomolybdate structures

A highly ordered, porous nanoscale network structure of polyoxomolybdate wa s prepared from the slow decomposition of an unstable precursor compound Mo O2(OH)(OOH) in the presence of PEO-containing triblock copolymer gels or se rnidilute/concentrated poly(ethylene oxide) (PEO) homopolymer solutions. Sm all-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) m easurements of the 1-mum size crystals revealed an extremely ordered primit ive cubic (pc) structure made of polyoxomolybdates. Scanning electron micro scopy (SEM) measurements showed that the overall size of these single cryst als was close to 1 mum, in agreement with estimates from the scattering pea k widths. Evidence from both scattering measurements and transmission elect ron microscope (TEM) measurements suggested that the system formed a highly porous primitive cubic network similar to that of certain zeolite structur es. However, the observed lattice constant of 5 nm was much larger. The fun ction of the PEO-containing polymer network was found to be very subtle and complex. Presumably, PEO acted simultaneously as a weak reducing agent and as a viscous matrix to ensure sufficient time for the formation of long-ra nge ordered structures, resulting in the growth of extremely uniform but pr obably hollow "nanospheres". We suggest that this new material may find uni que applications as a high-efficiency absorbent or catalyst. Furthermore, t he current synthetic method may open up new pathways to prepare similar fun ctional nanomaterials.