Facile synthesis of ultrasmall monodisperse “raisin–bun”-type MoO3/SiO2 nanocomposites with enhanced catalytic properties

Abstract

We report the preparation of ultrasmall monodisperse MoO3/SiO2 nanocomposites in reverse microemulsions formed by Brij-58/cyclohexane/water. The nanocomposites are of "raisin-bun"-type with 1.0 ± 0.2 nm MoO3 homogeneously dispersed in 23 ± 2 nm silica spheres. Characterization is carried out based on transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectrometry (EDS), X-ray powder diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectrometry (ICP-OES), N2 sorption measurement, and NH3 temperature-programmed desorption (NH3-TPD). The as-prepared MoO3/SiO2 nanocomposites are microporous and exhibit enhanced catalytic activities for acetalization of benzaldehyde with ethylene glycol and can be repeatedly used 5 times without obvious deactivation. The catalytic performance improvement is attributed to the unique structure and ultrasmall size of the nanocomposites.

Core–Shell Poly (Ionic Liquid)@Mesoporous Silica Chemiluminescent Nanoprobes for Sensitive Intracellular Hydrogen Peroxide Imaging

“…This result is consistent with the DLS characterization. The hump at 22 on X‐ray diffraction (XRD) pattern (Figure S3, Supporting Information) proves the existence of mesoporous silica shell . The adsorption–desorption isotherm obtained on PIL@mSiO 2 shows a type IV behavior with a capillary condensation in the relative pressure range of 0.5–0.9 (Figure e), indicating the presence of a porosity organization.…”

MoO3 subnanoclusters on ultrasmall mesoporous silica nanoparticles: an efficient catalyst for oxidative desulfurization

“…According to the results of TEM image and particle size distribution histogram, the particle diameter of UMSN of C-1 was only 14.2 AE 4.9 nm and MoO 3 was unable to be seen under HRTEM. Since MoO 3 particles of 1 nm were observable, 22 the MoO 3 size of C-1 was supposed to be less than 1 nm, i.e., subnanometer. With the increasing amount of ammonium molybdate, the MoO 3 size was raised from subnanometer to nanometer (1.2 AE 0.2 nm, C-2).…”

“…Besides, the synthesis principle is similar to our former works where the same structure with multi-cores dispersed inside SiO 2 was obtained. 22,24 The formation mechanism of the subnano-MoO 3 /UMSN was shown in Scheme 1. The spherical reverse micelles consist of surfactant (CTAB), cosurfactant (n-butanol), oil phase (cyclohexane), and aqueous phase (ammonia and ammonium molybdate solution).…”

“…26 The MoO 3 was formed in situ from the pyrolysis of the ammonium molybdate encapsulated in silica during the sol-gel process. 22 The size of MoO 3 can be easily controlled through changing the precursor concentration. Subnanoclusters would form with low precursor concentration.…”

“…21 It is well known that decreasing the particle size of porous support to shorten the channel length could reduce the mass transfer resistance and improve the catalytic activity. 22 Ultrasmall mesoporous silica nanoparticles (UMSN, <25 nm), 23 have more advantages over the conventional mesoporous silica nanoparticles (MSN) as support because the decrease of their particle size shortens the access path and increases the specic area. In addition, the mesopores of UMSN make the internal active sites accessible to some big molecules, like DBT, which are difficult to enter microporous channels due to size limitation.…”