Direct Sonochemical Synthesis
of Manganese Octahedral Molecular Sieve (OMS-2) Nanomaterials Using
Cosolvent
Systems, Their Characterization, and Catalytic Applications
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Abstract
A rapid, direct sonochemical method has successfully
been developed to synthesize cryptomelane-type manganese octahedral
molecular sieve (OMS-2) materials. Very high surface area of 288 ±
1 m<sup>2</sup>/g and small particle sizes in the range of 1–7
nm were produced under nonthermal conditions. No further processing
such as calcination was needed to obtain the pure cryptomelane phase.
A cosolvent system was utilized to reduce the reaction time and to
obtain higher surface areas. Reaction time was reduced by 50% using
water/acetone mixed phase solvent systems. The cryptomelane phase
was obtained with 5% acetone after 2 h of sonication at ambient temperature.
Reaction time, temperature, and acetone concentration were identified
as the most important parameters in the formation of the pure cryptomelane
phase. OMS materials synthesized using the above-mentioned method
were characterized by X-ray diffraction (XRD), nitrogen sorption,
scanning electron microscopy (SEM), transmission electron microscopy
(TEM), and Fourier transformation infrared spectroscopy (FTIR). OMS-2
materials synthesized using sonochemical methods (K-OMS-2<sub>SC</sub>) possess greater amounts of defects and hence show excellent catalytic
performances for oxidation of benzyl alcohol as compared to OMS-2
synthesized using reflux methods (K-OMS-2<sub>REF</sub>) and commercial
MnO<sub>2</sub>