Thadathil S. Sreeremya

Shape-Selective Oriented Cerium Oxide Nanocrystals Permit Assessment of the Effect of the Exposed Facets on Catalytic Activity and Oxygen Storage Capacity

The catalytic performance of a range of nanocrystalline CeO2 samples, prepared to have different morphologies, was measured using two accepted indicators; oxygen storage and diesel soot combustion. The same powders were characterized in detail by HR-TEM, XRD, XPS, and Raman methods. The study demonstrates that activity is determined by the relative fraction of the active crystallographic planes, not by the specific surface area of the powders. The physical study is a step toward quantitative evaluation of the relative contribution to activity of the different facets. The synthetic protocol permits fabrication of CeO2 nanostructures with preferentially grown active planes, and therefore has potential in developing catalytic applications and in nanocompositing.

One-pot synthesis of ultra-small cerium oxide nanodots exhibiting multi-colored fluorescence

CeO(2) nanodots of diameter 2nm have been synthesized by the thermolysis of cerium acetate in diphenylether in the presence of an oleic acid surfactant. The surfactant coating enabled them to be easily dispersible in nonpolar solvents. The CeO(2) dots exhibited size dependant optical properties such as a red shift in absorption and band gap. As a result, the surfactant coated CeO(2) nanocrystals emit photons in the visible region with broad photoluminescence spectra resulting in multi-colored fluorescence, which originates from defects associated with CeO(2) nanocrystals approaching molecular dimensions.

Facile synthetic strategy of oleophilic zirconia nanoparticles allows preparation of highly stable thermo-conductive coolant

We report a simple one-step method of fabricating monodisperse zirconium oxide nanoparticles by decomposing a zirconium oleate complex in a high boiling organic solvent. The X-ray and transmission electron microscopy of nanocrystals indicated the formation of monoclinic zirconia. The surfactant capped zirconia nanoparticles produced excellent dispersions in oils. The suitability of the nanofluids in heat transport was carefully investigated by measuring suspension stability, thermal conductivity and viscosity as a function of temperature. The effect of particle loading and temperature on the thermal conductivity of the oil based nanofluids and other promising features indicated potential application of ZrO2 based nanofluids in the heat transport sector. A thermal conductivity enhancement of ∼10.3% was achieved with 1.7 vol% zirconia nanoparticle loading at room temperature. The TC of the nanofluids was remarkably higher than the same predicted by Maxwell and Hamilton–Crosser models.

Tailoring the surface properties of cerium oxide nanoabrasives through morphology control for glass CMP

Nanosized cerium oxide (CeO2) particles possessing different morphologies like nanorods, nanocubes and nanospheres have been successfully synthesized by a simple one step, surfactant free, precipitation technique and by hydrothermal methods. The diverse morphology motifs were further utilized for the planarization of silicate glass with an initial surface roughness of ∼40 nm and we observed a strong morphology dependence of the abrasive in glass polishing. Polishing efficiency of the nanoabrasives in terms of the mass removal and surface roughness was investigated using a table top lapping machine. Surface roughness analysis by atomic force microscopy reveals that the ceria nanostructure with a mixed morphology of rods and cubes could produce a surface finish of ∼3 A. The surface properties of the abrasive were found to play a key role in polishing as evidenced by X-ray photoelectron spectroscopy and Raman spectral analysis. The powder contact angle/hydrophilicity of the nanopowders followed the same trend as that of the dipolar (200) plane and [Ce3+]. This work has shown promise in polishing efficiency with nano CeO2 slurry to achieve nanolevel planarity on glass substrates, which is desirable for the global planarization of complex device topography.

Concentration quenching in cerium oxide dispersions via a Förster resonance energy transfer mechanism facilitates the identification of fatty acids

The energy exchange phenomena of cerium oxide based nanoparticles in a medium have been studied by means of a meticulous approach. A concentration dependent non-radiative pathway has been revealed for the particles due to the close proximity between them which causes the extinction of fluorescence. The calibration plot, according to the Stern–Volmer equation, showed a good linear relationship within the acceptable error limit, and the value of Q, denoting the exchange interaction, was close to 6, implying dipolar coupling between particles. Theoretical analysis of spectroscopic data showed that Forster resonance energy transfer (FRET) is the dominant mechanism responsible for the interparticle excitation transfer and the Forster radius (R0) calculated was 68.6 A°. The distance dependence of FRET has been utilized to analyse the conformation and chain length of fatty acids by interrupting the energy transfer efficiency among the particles, and thus a simple analytical tool based on FRET for the qualitative as well as quantitative assessment of fatty acids has been projected.

Size-tunable hydrophilic cerium oxide nanoparticles as a ‘turn-on’ fluorescence sensor for the rapid detection of ultralow concentrations of vitamin C

The novel perspective of cerium dioxide as a fluorescence sensor has been demonstrated in the present study. The green coloured emission associated with the nano-dimensions of ceria has been adopted as an analytical tool to sense vitamin C, which is a biologically important molecule, in dilute concentrations. Ultrafine ceria nanoparticles of average size 2.2 nm have been fabricated by a surfactant assisted thermal decomposition strategy. The particular fashion of attachment of the oleic acid surfactant with ceria resulted in the surface hydrophobicity of the nanoparticles which in turn prevents their interaction with a hydrophilic molecule like vitamin C in the reaction media. In order to tackle the incompatibility of the nanoparticles with water, a hydrophilic surfactant coating has been grafted over their surface via bilayer surface functionalisation. The success of the accomplished strategy has been confirmed by thermogravimetric analyses, zeta potential and contact angle measurements. The redox properties of ceria and its optical properties served as a probe to quantify vitamin C in the concentration range 10−7 to 10−4 M with a very low limit of detection (LoD) of 500 nM. The designed sensor exhibits a rapid ‘turn on’ fluorescence response within 30 seconds and the reversibility of its fluorescence even after 5 cycles of vitamin C addition corroborates its reusability. The high selectivity of the sensor to detect vitamin C again highlights its suitability as an analytical tool. The realistic application of the sensor has also been displayed by the quantification of vitamin C in pharmaceutical formulations within acceptable error limits.

Morphological evolution and growth of cerium oxide nanostructures by virtue of organic ligands as well as monomer concentration

Morphologically diverse nanostructures based on ceria have been fabricated by adopting a non-hydrolytic thermal decomposition strategy. It was assessed that parameters like the precursor concentration, characteristics of the surfactant and their molar ratio were crucial in controlling the evolution of morphology. Within the provided experimental conditions, a collection of nanopatterns including butterfly-shaped structures, plates, rods and bundles have been obtained. By means of transmission electron microscopy, X-ray diffraction studies and thermogravimetric analyses, a shape-guiding mechanism based on (111)-oriented attachment has been put forward to rationalize the morphological progression. Also, an attempt has been made to correlate the optical properties exhibited by the structural motifs with their diversity in morphology. In general, the present study illustrates the facile tuning of the nano-construction of ceria on the grounds of modest synthetic strategies.