Gas-Phase Cryogenic Vibrational Spectroscopy of Metal Oxide Cluster Ions: Structure-Reactivity Relationship

Gas phase cryogenic ion trap vibrational spectroscopy in combination with high level quantum chemical calculations provides an ideal arena to investigate structure- reactivity relationships of pure- and bi- metallic oxide clusters as a function of size, charge-state and coordination environment. In the last decades, characterization of binary metal oxide nanomaterials has received special attention, mainly because catalytically inactive materials can be activated by doping with a second metal. Precisely controlled conditions and the absence of perturbing interactions with an environment allow the gas phase clusters to serve as powerful model systems for nanomaterials. Moreover, the active site(s) of these reactive intermediates can be unambiguously identified by their characteristic vibrational signatures. Such insights ultimately allow for a molecular level understanding of the reaction mechanisms at play at reactive surfaces in heterogeneous catalysis. Iron is the most common impurity in naturally occurring zeolites. Atomic Fe- substituted small Al-oxide clusters [(Al2O3)nFeO]+ function as model system for Fe- doped zeolites. The influence of an Fe-atom in an Al-oxide network is investigated in terms of structural change and preferred coordination site in Chapter 4. The results demonstrate that the Fe-atom prefers to occupy a position in the outer ring of the cluster and induces substantial change in the cluster structure for the smallest cluster studied (n=1), but not for the larger ones. Furthermore, a structural evolution from planar (n=1) over quasi-2D (n=2) to cage type (n≥3) structures is observed with increasing cluster size. The insights correlate with reported results of Fe-doped nanoparticles and nanocrystals, where the dopant Fe-atom is mostly found to replace the under-coordinated surface Al-atoms of the Al2O3 network. In Chapter 5 the active site(s) of heteronuclear metal oxide clusters towards oxygen atom transfer (OAT) reactions is identified. [AlVOx=3,4]●+ and [VPOx=3,4]●+ radical cations are studied in the context of CO to CO2 conversion (chapter 5.1) and ethylene to formaldehyde oxidation (chapter 5.2), respectively. In both cases, the oxygen atom bound to the main group atom, either Al or P, in contrast to the transition metal atom (V) takes part in the OAT cycle. The results presented in Chapter 6 reveal that the oxygen-deficient Ti3+ centre, which represents a model system for an oxygen vacancy at a titania surface, is the active site for CO2 adsorption. The first two CO2 molecules adsorb chemically on [Ti3O6] ̅, forming asymmetric bidentate-bridged and symmetric tridentate-bridged binding motifs. The tridentate-bridged binding motif, which is reported here for the first time, plays a central role in the oxygen exchange mechanism on a defective anatase surface and activation of CO2 on wet titania surfaces

Edge Detecting New Physics the Voronoi Way

We point out that interesting features in high energy physics data can be determined from properties of Voronoi tessellations of the relevant phase space. For illustration, we focus on the detection of kinematic "edges" in two dimensions, which may signal physics beyond the standard model. After deriving some useful geometric results for Voronoi tessellations on perfect grids, we propose several algorithms for tagging the Voronoi cells in the vicinity of kinematic edges in real data. We show that the efficiency is improved by the addition of a few Voronoi relaxation steps via Lloyd's method. By preserving the maximum spatial resolution of the data, Voronoi methods can be a valuable addition to the data analysis toolkit at the LHC.Comment: 6 pages, 7 figure

Quasi-spherical gravitational collapse and the role of initial data, anisotropy and inhomogeneity

In this paper, the role of anisotropy and inhomogeneity has been studied in quasi-spherical gravitational collapse. Also the role of initial data has been investigated in characterizing the final state of collapse. Finally, a linear transformation on the initial data set has been presented and its impact has been discussed.Comment: RevTex, 7 Latex pages, No figure

Comparative Analysis of Hexavalent Chromium Biosorption Efficiency Using Dead and Live Aspergillus nomius Biomass

Daily industrial activities especially in developing countries produce and discharge wastes containing heavy metals into the water resources making them polluted, threatening human health and the ecosystem. One such heavy metal is Chromium, the hexavalent form of which is extremely toxic and carcinogenic. Biosorption, the process of passive cation binding by dead or living biomass, represents a potentially cost-effective way of eliminating toxic heavy metals from industrial wastewater. The potential of microorganisms to remove metal ions in solution has been extensively studied; in particular, live and dead fungi have been recognized as a promising class of low-cost adsorbents for the removal of heavy metal ions. Fungal biomass has various advantages; hence, it needs to be explored further to take its maximum advantage in wastewater treatment. In this study, we discuss the live and dead fungi characteristics of sorption, factors influencing heavy metal removal. Biosorption studies were performed with both dead and live biomass and the effectiveness of Cr (VI) biosorption was compared for each parameter. It was observed that biosorption was maximum (approximately): 82% while using sulfuric acid as the pre-treatment agent (hence only dead biomass) and also maximum of 96.5% at 1 N. The optimum pH for maximum biosorption was 6 when dead biomass was used, while it was 2 when live biomass was used. Maximum Chromium removal of 86% was obtained using 2 g live biomass whereas 0.5 g of dead biomass was enough to obtain the maximum efficiency.96% chromium was removed at 25° C using dead biomass, whereas, maximum removal of about 84% was obtained when live biomass was used for biosorption and it took place at 35° C. Maximum Cr (VI) removal of about 95% was obtained when dead biomass was used and 69% when live biomass was used, both at 1mg/L metal concentration. 0.5 g of dead biomass in 100 ml, 1 mg/L solution, was optimum for Cr (VI) removal, while for live biomass, maximum Cr (VI) biosorption of 63% was obtained when 1.5 g of it was used in 300 ml solution. It was finally concluded that dead fungal biomass has better biosorption potentials and also some other inherent advantages over live biomass