Surface-Sensitive Adsorption of Water and Carbon Dioxide on Magnetite: Fe₃O₄(111) versus Fe₃O₄(001)

The interaction of water with solid surfaces is important in many scientific fields such as corrosion, electrochemistry, geology, and heterogeneous catalysis. Chemistry at water/oxide interfaces plays a crucial role in surface's properties and reactivity. Employing model systems structurally and electronically characterized under well-defined conditions offers deep insights into the chemistry of the water/solid interfaces at an atomic level. This knowledge allows one to tune and optimize catalytic processes. Its strong relevance to the economical and environmental concerns (climate change) has driven growing worldwide attention to carbon dioxide (CO2). It is highly desirable to find a promising route to transform CO2 into valuable chemicals such as fuels for further applications. In this respect, iron oxides were considered as suitable catalysts for activation of CO2, not only because of their natural abundance, but also due to their important catalytic role in many industrial processes, such as the Fisher-Tropsch synthesis, the Haber process (NH3 synthesis), and the high-temperature water gas shift reaction. The thesis aims to investigate the interaction of water and CO2 on magnetite (Fe3O4) surfaces and the role of water on CO2 activation. I also investigated the influence of surface orientation ((111) vs (001)) on the adsorption behavior. Well-defined magnetite surfaces were prepared as thin ordered films on metal substrates (Pt(111) and Pt(001)). For structural characterization and reactivity studies we used Temperature Programmed Desorption (TPD), low energy electron diffraction (LEED), Temperature-Programmed LEED (TP LEED), and Infrared Reflection Absorption Spectroscopy (IRAS). First, I addressed the surface termination of the films using CO as a probe molecule. In the next step, individual adsorption of water and CO2 was studied. In the case of Fe3O4(111), water dissociates resulting in the formation of OsH and OwH hydroxyl groups, consisting of oxygen atoms from the magnetite surface (s) and water (w) molecule, respectively. These hydroxyl groups act as an anchor for the incoming water molecules to form a dimer complex, which ultimately forms (2x2) hexagonally ordered structure (seen by LEED) via hydrogen bond network. The latter is proved by DFT calculations to be thermodynamically favorable. In contrast to the (111) surface, the water molecularly adsorbs on Fe3O4(001)- (√2 × √2)R45°. Upon increasing coverage, water molecule starts to partially dissociate which reinforces the interaction between the formed dimer or trimer and the oxide surface. Water ordering directly observed by LEED suggests that the water ad-layer follows the symmetry of iron oxide underneath, thus ice-like layers are formed on (111) and (001) in hexagonal and square symmetry, respectively. This is the first time that water ordering has been experimentally observed in two different structures on the same oxide. We believe that the experimental results provide a strong basis for theoretical calculations of water/oxide interfaces, and can even serve as benchmarks for the investigation of ice nucleation on solid surfaces. When compared to water, CO2 molecules are rather weakly interacting with both Fe3O4(111) and (001) surfaces. However, strongly bound CO2 species may be formed as minority species at a low coverage regime, which are, most likely, related to surface defects. Based on isotopic experiments, there is no evidence of CO2 dissociation. TPD spectra on (111) facet manifest a competition between CO2 and residual gases (water and CO) from the UHV background. In fact, even traces of water may considerably alter CO2 interaction with the oxide. Therefore, careful precautions have to be taken while studying CO2 interaction with the oxide surface. The results show that on the (111) surface, CO2 may adsorb more strongly in the presence of surface hydroxyls, resulting in CO2 desorption at 250 K (compared to ∼200 K on the clean surface). According to the TPD results, a water pre-covered magnetite (001) surface enhances CO2 interaction, probably via the formation of bicarbonate species which decompose at ∼350 K. We believe that the results presented in this Thesis shed more light on the complex interaction of "simple" molecules with oxide surfaces

The Quality Characteristics of Camel Sausage Formulated with Different Levels of Whey Protein Powder

In this study camel sausage was formulated with different levels (1, 2, 3 and 4%) of whey protein powder (WPP). Raw and cooked sausage samples were evaluated for physical properties, cooking measurements, shrinkage, color parameters, emulsion capacity (EC) and emulsion stability (ES) and sensory attributes. Using whey protein powder increased pH value, moisture retention, emulsion capacity and emulsion stability while, the cooking loss and shrinkage were decreased. Camel sausages formulated with 4% whey protein powder (WPP) had higher emulsion stability and emulsion capacity, lower cooking loss, better color and more acceptable than other sausage samples. However addition of 4% whey protein powder can be improved the quality characteristics of camel sausages

Seed selection for information cascade in multilayer networks

Information spreading is an interesting field in the domain of online social media. In this work, we are investigating how well different seed selection strategies affect the spreading processes simulated using independent cascade model on eighteen multilayer social networks. Fifteen networks are built based on the user interaction data extracted from Facebook public pages and tree of them are multilayer networks downloaded from public repository (two of them being Twitter networks). The results indicate that various state of the art seed selection strategies for single-layer networks like K-Shell or VoteRank do not perform so well on multilayer networks and are outperformed by Degree Centrality

Pembuatan Silika High Grade dari Fly Ash Sawit dengan Proses Ekstraksi dan Cation Exchange

One alternative raw materials manufacture of high grade silica is using palm oil mill fly ash. This research aimed to study the effect of temperatureprocess, time and the ratio mass of zeolite and obtain optimum conditions cation exchange process (Fe) in a solution of sodium silicate with raw material palm oil mill fly ash. Palm oil mill fly ash is heated using oven at 105° C for 24 hours. Then fly ash reacted with 1,4N NaOH solution at 105° C for 50 minutes. Then obtained sodium silicate solution is reacted with Na-zeolite. The results of the optimization then precipitated using 10% H2SO4 and derived solidsilica. XRF analysis results showed solid silica has a purity of 96.129%

High-precision calculations of In I and Sn II atomic properties

We use all-order relativistic many-body perturbation theory to study 5s^2 nl configurations of In I and Sn II. Energies, E1-amplitudes, and hyperfine constants are calculated using all-order method, which accounts for single and double excitations of the Dirac-Fock wave functions.Comment: 10 pages, accepted to PRA; v2: Introduction changed, references adde

Calcium Levels in Ruffle-Ended and Smooth-Ended Maturation Ameloblasts

Scanning electron microscopy was used to distinguish the topographical characteristics of two maturation ameloblast types in freeze-dried blocks of enamel organ tissue. This distinction was based primarily upon the configuration of the distal ends of the ameloblasts and the presence or absence of wide intercellular spaces. Energy dispersive x-ray spectrometry was applied to compare calcium levels in various regions of tissue identified as constituting either ruffle-ended or smooth ended ameloblasts. Greater levels of calcium were found in the distal ends of the ruffle-ended cells than in their proximal ends. In addition, greater calcium levels were found in the distal ends of the ruffle-ended cells than the distal ends of the smooth-ended cells. The higher calcium levels in ruffle-ended cells correlates with the view that these cells are actively involved in control of movement of calcium to the enamel front

Secretory Ameloblasts and Calcium Distribution During Normal and Experimentally Altered Mineralization

The distribution of calcium in relation to secretory ameloblasts of the rat incisor was studied. An experimental model system in which enamel mineralization was temporarily inhibited by injecting sodium fluoride and cobalt chloride was used. Potassium pyroantimonate (PPA) cytochemistry, electron energy loss spectroscopy (EELS), and energy dispersive X-ray spectrometry (EDS) were used to clarify the role of the ameloblast in controlling calcium distribution during normal and experimentally altered enamel mineralization. Secretory ameloblasts chemically-preserved in glutaraldehyde either with or without PPA were analyzed for calcium; those preserved with PPA showed higher concentrations of calcium than did those preserved with glutaraldehyde only. Freeze-dried control and experimental tissues showed an increasing gradient of calcium from stratum intermedium cells to the distal ends of the ameloblasts. Calcium levels were reduced near the distal ends of the cells following fluoride and cobalt injections, while magnesium levels were increased markedly in the same region. This multi-method approach showed correlated calcium localization in specific regions of this cell in relation to changes in function. The study thus provides additional evidence for active involvement of the ameloblasts in enamel mineralization