Direct Sonochemical Synthesis of Manganese Octahedral Molecular Sieve (OMS-2) Nanomaterials Using Cosolvent Systems, Their Characterization, and Catalytic Applications

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 m²/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_SC) 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_REF) and commercial MnO₂

Structure and Oxidation Activity Correlations for Carbon Blacks and Diesel Soot

This work focuses on a comprehensive investigation of structure–activity relationships for a diesel engine soot sample (Corning) and 10 commercially available carbon black samples. Particle sizes were determined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Specific surface area was determined by nitrogen sorption studies, while the microstructure was investigated by X-ray diffraction (XRD) peak profile analysis, Raman spectroscopy, and TEM. Oxidation activity of these samples was studied using thermogravimetric analysis (TGA) under an oxidative (10% O₂) environment consistent with the typical oxygen levels in the diesel engine exhaust. Various structural parameters, such as the average particle size, specific surface area, degree of organization, and average crystallite stacking height, were correlated with the TGA oxidation activity data. In general, samples with low particle size, high surface area, highly amorphous nature (low degree of organization), and low crystallite stacking height showed high oxidation activity. A second diesel engine soot sample (Corning), which was collected at different operating conditions, was used to validate the obtained structure–activity correlations. Overall, our rigorous analysis for a large number of samples with multiple techniques indicated unique and novel correlations/trends between soot structure and reactivity