A Review of the Microstructural Location of Impurities in Polar Ice and Their Impacts on Deformation

Insoluble and soluble impurities, enclosed in polar ice sheets, have a major impact on the deformation behaviour of the ice. Macro- and Micro-scale deformation observed in ice sheets and ice cores has been retraced to chemical loads in the ice, even though the absolute concentration is negligible. And therefore the exact location of the impurities matters: Allocating impurities to specific locations inside the ice microstructure inherently determines the physical explanation of the observed interaction between chemical load and the deformational behaviour. Both, soluble and non-soluble impurities were located in grain boundaries, triple junctions or in the grain interior, using different methods, samples and theoretical approaches. While each of the observations is adding to the growing understanding of the effect of impurities in polar ice, the growing number of ambiguous results calls for a dedicated and holistic approach in assessing the findings. Thus, we here aim to give a state of the art overview of the development in microstructural impurity research over the last 20 years. We evaluate the used methods, discuss proposed deformation mechanisms and identify two main reasons for the observed ambiguity: 1) limitations and biases of measurement techniques and 2) the physical state of the analysed impurity. To overcome these obstacles we suggest possible approaches, such as the continuous analysis of impurities in deep ice cores with complementary methods, the implementation of these analyses into established in-situ ice core processing routines, a more holistic analysis of the microstructural location of impurities, and an enhanced knowledge-transfer via an open access data base

Boosting Photocatalytic Activity Using Vanadium Doped Titanium Oxide with Reduced Graphene Oxide (RGO)/Semiconductor Nanocomposites

Textile waste materials are increasing day by day with the depletion of water and increasing the concentration of ions present in the water that produce toxicity. The sustainability of the materials to rule out this toxicity can be done by Reduced Graphene Oxide synthesized by modified Hummer’s method. The composite of V-doped TiO2 and RGO was synthesized by hydrothermal method and V-doped TiO2/RGO and perfluorocarbon synthesized by sonication. The product was characterized by the powder X-ray Diffraction method. It has confirmed the synthesis of the product. Ultraviolet/visible spectroscopy was employed to study the photocatalytic activity of the product for the degradation of methylene blue which is an organic dye and hazardous to the environment

Ruthenium anchored on carbon nanotube electrocatalyst for hydrogen production with enhanced Faradaic efficiency

Developing efficient and stable electrocatalysts is crucial for the electrochemical production of pure and clean hydrogen. For practical applications, an economical and facile method of producing catalysts for the hydrogen evolution reaction (HER) is essential. Here, we report ruthenium (Ru) nanoparticles uniformly deposited on multi-walled carbon nanotubes (MWCNTs) as an efficient HER catalyst. The catalyst exhibits the small overpotentials of 13 and 17 mV at a current density of 10 mA cm(-2) in 0.5M aq. H2SO4 and 1.0M aq. KOH, respectively, surpassing the commercial Pt/C (16 mV and 33 mV). Moreover, the catalyst has excellent stability in both media, showing almost "zeroloss" during cycling. In a real device, the catalyst produces 15.4% more hydrogen per power consumed, and shows a higher Faradaic efficiency (92.28%) than the benchmark Pt/C (85.97%). Density functional theory calculations suggest that Ru-C bonding is the most plausible active site for the HER

N-DOPED MULTIWALLED CARBON NANOTUBES: FUNCTIONALIZATION, CHARACTERIZATION AND APPLICATION IN LI ION BATTERIES

The focus of this dissertation is to utilize chemical functionalization as a probe to investigate the reactivity of N-doped multiwalled carbon nanotubes (N-MWCNTs). The surface of N-MWCNTs, being a set of potentially reactive graphene edges, provides a large number of reactive sites for chemical modification, so considerable changes in chemical and physical properties can be envisaged. We observed that both reduction (dissolving metal reduction/alkylation) and oxidation (H2SO4/HNO3 and H2SO4/KMnO4 mixtures) of N-MWCNTs lead to formation of interesting spiral channels and spiraled carbon nanoribbons. A variety of techniques, including TGA, SEM, TEM, XRD and surface area measurements were used to analyze these new textural changes. We have developed methods to demonstrate that specific chemistry has occurred on these new structures. To this end, we introduced metal-binding ligands that could be used as probes in imaging and spectroscopic techniques including TEM, STEM, EDX, and EELS. A proposal for the underlying structure of N-MWCNTs responsible for the formation of the new textures is presented. We have investigated the performance of our materials as potential negative electrodes for rechargeable lithium ion batteries

Assessing the inhibitory potential of natural silicon oil on brass degradation in 1M H2SO4

Assessment of silicon oil as natural inhibitor on brass in 1 M H2SO4 acid solution has been studied using linear potentiodynamic polarization and gravimetric method in the inhibited concentration variation between 2% to 10% range. Tafel extrapolation techniques were used to obtain corrosion potential (Ecorr) and corrosion current density (Icorr). From all indication, the inhibitor is of mixed type. The adsorption behavior occurs on the surface of brass due to the presence of the absorbed complex atom from the oil. The calculated portion of the surface covered from the corrosion process follows Langmuir adsorption Isotherm

Adsorption and binding dynamics of graphene-supported phospholipid membranes using the QCM-D technique

We report on the adsorption dynamics of phospholipid membranes on graphene-coated substrates using the quartz crystal microbalance with dissipation monitoring (QCM-D) technique. We compare the lipid vescle interaction and membranne formation on gold and silicon dioxide QCM crystal surfaces with their graphene oxide (GO) and reduced (r)GO coated counterparts, and report on the different lipid structures obtained. We establish graphene derivative coatings as support surfaces with tuneable hydrophobicity for the formation of controllable lipid structures. One structure of interest formed are lipid monolayer membrannes which were formed on rGO, which are otherwise challenging to produce. We also demonstrate and monitor biotin-avidin binding on such a membranne, which will then serve as a platform for a wide range of biosensing applications. The QCM-D technique could be extended to both fundamental studies and applications of other covalent and non-covalent interactions in 2-dimensional materials

The Location of Impurities in Polar Ice

The distribution of natural impurities in polar ice is of considerable relevance to processes occurring in ice sheets and to the study of ice cores used to determine past climate. In this thesis a reliable method is developed using the scanning electron microscope equipped with a cold stage to directly locate and identify, with x-ray analysis, impurity in situ, The technique uses sublimation to collect impurities on the ice surface. Specimens of cold polycrystalline snow and ice from cores drilled in both Greenland and Antarctica are examined. The distribution is revealed to be heterogeneous and primarily dependent on the bulk ice impurity content In some samples dust particles are distributed preferentially at grain boundaries and are observed pinning grain boundaries. Soluble impurities are found dissolved in the lattice, at grain boundaries and coating bubbles Significant quantities of sulphuric acid are found in veins at crystal triple junctions only when sufficient acid is present in the ice to also coat the surrounding grain boundaries. Thus a smaller fraction resides in veins than previously thought. Factors such as grain size, fabric orientation, ice temperature and age are also likely to play a significant role in determining impurity distribution. The response of electrical conductivity to chemical impurity in the Dome C (Antarctica) ice core is quantified and is consistent with these observations. It is modelled by the presence of sulphuric acid at grain boundaries and possibly veins. A large proportion of the salt chloride in the core must be incorporated in the lattice to explain the measured conductivity. Limited diffusion of chloride and sulphate ions, but not sodium, is observed in the Dome C core causing broadening of peaks. Models reliant on normal grain growth to stimulate solute movement can explain this. This work reconciles differences between previous location studies, presents a consistent but not well-quantified description of impurity distribution and addresses possibilities of post-depositional solute movement

Graphite and Graphene-Oxide based PGM-free model catalysts for the Oxygen Reduction Reaction

The world currently relies heavily on fossil fuels such as coal, oil, and natural gas for its energy. Fossil fuels are non-renewable, that is, they draw on finite resources that will eventually dwindle, becoming too expensive or too environmentally damaging to retrieve. One alternative source of energy are fuel cells, electrochemical devices that convert chemical energy to cleanly and efficiently produce electricity. They can be used in a wide range of applications, including transportation, stationary, portable and emergency power sources. Their development has been slowed by the high cost of PGM electrocatalysts needed at both electrodes as well as sluggish oxygen reduction reaction (ORR) occurring at the cathode. To replace the costly PGM-based materials, a new generation of PGM-free ORR catalysts has emerged, composed by earth abundant elements such as carbon, nitrogen and transition metals. Current heterogeneous PGM-free catalysts are exceedingly difficult to study using standard analytical techniques. In the following studies, we use well- defined model systems based on graphitic systems such as graphite and graphene oxide. These extensively characterized materials are relatively simple to model, making them ideal platforms for understanding catalytic active sites. In the first study, we investigate a green, solvent-free and sustainable synthesis route to synthesize large amounts of active ORR electrocatalysts based on graphite. We show that the simple ball milling of expanded graphite in presence of metal and nitrogen precursors followed by a pyrolysis step can create active and selective catalysts towards the ORR. We report an improved activity of graphitebased electrocatalysts in alkaline medium with an onset potential (Eonset) up to ~0.89 V and a half-wave potential (E1/2) up to 0.72 V. In the second study, we demonstrate that removal of intercalated water using simple solvent treatments causes significant structural reorganization substantially impacting the ORR activity and stability of nitrogen-doped graphitic systems (NrGO). Contrasting reports describing ORR activity of NrGO-based catalysts in alkaline electrolytes, we demonstrate superior activity in acidic electrolyte with Eonset of ~0.9 V, E½ of 0.71 V, and selectivity for four-electron reduction \u3e95%. Further, durability testing showed E½ retention \u3e95% in N2- and O2-saturated solutions after 2000 cycles demonstrating highest ORR activity and stability reported to date for NrGO-based electrocatalysts in acidic media. In the third study, we report that the activity and selectivity (4e-) of NrGO catalysts for ORR is enhanced using simple solvent and electrochemical treatments. The solvents, which were chosen based on Hansen’s solubility parameters, drive a substantial change in the morphology of the functionalized graphene materials either by i) forming microporous holes in the graphitic sheets that lead to edge defects as well as enhanced oxygen transport, or ii) inducing 3D structure in the graphitic sheets that promote ORR. Additionally, the cycling of these catalysts has highlighted the multiplicity of the active sites, with different durability, leading to a more selective catalyst over time with little to no loss in performance. We demonstrate excellent ORR activity in an alkaline electrolyte with an Eonset up to ~1.08 V and a E1/2 up to 0.84 V. Further, durability testing showed E1/2 loss 2- and O2-saturated solutions after 10,000 cycles, demonstrating a high ORR activity and stability while improving the selectivity towards the 4-electron reduction. The results described in this study will allow for the synthesis of better performing graphitic ORR electrocatalyst with controlled activity and could lead to a better understanding of the active site formation in PGM-free electrocatalysts