Anuradha Mitra

TiO2 nanoparticles doped SiO2 films with ordered mesopore channels: a catalytic nanoreactor

Titanium dioxide (TiO2) incorporated ordered 2D hexagonal mesoporous silica (SiO2) films on a glass substrate were fabricated for use as a catalytic nanoreactor. Films were prepared using a tetraethyl orthosilicate (TEOS) derived SiO2 sol and a commercially available dispersion of TiO2 nanoparticles (NPs) in the presence of pluronic P123 as the structure directing agent. The effect of TiO2 doping (4-10 mol% with respect to the equivalent SiO2) into the ordered mesoporous SiO2 matrix was thoroughly investigated. The undoped SiO2 film showed a mesostructural transformation after heat-treatment at 350 °C whereas incorporation of TiO2 restricted such a transformation. Among all the TiO2 incorporated films, TEM showed that the 7 equivalent mol% TiO2 doped SiO2 film (ST-7) had an optimal composition which could retain the more organized 2D hexagonal (space group p6mm)-like mesostructures after heat-treatment. The catalytic activities of the TiO2 doped (4-10 mol%) films were investigated for the reduction of toxic KMnO4 in an aqueous medium. ST-7 film showed the maximum catalytic activity, as well as reusability. A TEM study on the resultant solution after KMnO4 reduction revealed the formation of MnO2 nanowires. It was understood that the embedded TiO2 NPs bonded SiO2 matrix increased the surface hydroxyl groups of the composite films resulting in the generation of acidic sites. The catalytic process can be explained by this enhanced surface acidity. The mesoporous channel of the ST-7 films with TiO2 doping can be used as a nanoreactor to form extremely thin MnO2 nanowires.

Atomically precise and monolayer protected iridium clusters in solution

The first atomically precise and monolayer protected iridium cluster in solution, Ir9(PET)6 (PET – 2-phenyethanethiol) was synthesized via a solid state method. The absence of a plasmonic band at ∼350 nm, expected in the UV/Vis spectra for spherical Ir particles of 10 nm size indicated that the synthesized cluster is smaller than this dimension. Small angle X-ray scattering (SAXS) showed that the cluster has a particle size of ∼2 nm in solution which was confirmed by transmission electron microscopy (TEM). The blue emission of the cluster is much weaker than many noble metal clusters investigated so far. X-ray photoelectron spectroscopy (XPS) measurements showed that all Ir atoms of the cluster are close to the zero oxidation state. The characteristic S–H vibrational peak of PET at 2560 cm−1 was absent in the FT-IR spectrum of the cluster indicating RS–Ir bond formation. The molecular formula of the cluster, Ir9(PET)6 was assigned based on the most significant peak at m/z 2553 in the matrix assisted laser desorption ionization mass spectrum (MALDI MS), measured at the threshold laser intensity. Density functional theory calculations on small Ir@SCH3 and Ir@PET clusters and comparison of the predictions with the IR and 1H-NMR spectra of Ir9(PET)6 suggested that the PET ligands have two distinct structural arrangements and are likely to be present as bridging thiolates –(Ir–SR–Ir)– and singly attached thiolates –(Ir–SR).

Mesoporous alumina films: effect of oligomer formation toward mesostructural ordering.

Alumina films with Im3̅m, Ia3d, and onion-like mesopores have been synthesized using a single sol composition derived from an modified alumina precursor (MAP), partial acetylacetone (acac) chelated aluminum secondary butoxide (ASB/acac = 1:0.5). We observed that MAP undergoes oligomerization with aging time and the differently aged MAP generates different micellar structures in the presence of P123 in alumina sols, and forms differently ordered mesostructured coatings. The time-dependent changes in the chemical nature of the MAP have been studied through ATR-FTIR spectroscopy. The nature of micellar transformations in the sols have been studied by transmission SAXS investigations. It has been observed that the size of the micelles gradually increases with time. On aging, MAP contains more bridging alkoxide groups with lesser hydrophilic characteristics; this reduces its interaction with the hydrophilic groups in the P123 micelle. Therefore, a mesostructure with low curvature is gradually formed in the sol due to the rigid nature of cross-linked MAP. Low angle XRD and TEM studies of the coatings obtained from the above sols have confirmed the generation of three distinctly different types of ordered mesoporous arrangements after heat treatments. The time-induced mesophase transformation mechanism has been proposed based upon the experimental results. The study reveals transformation of a modified Al alkoxide solution with respect to time and its successful use to obtain mesoporous alumina films of different ordered structures on glass.