| 1. |
- Ngoc Pham, Tung, et al.
(author)
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Industrially benign super-compressible piezoresistive carbon foams with predefined wetting properties : from environmental to electrical applications
- 2014
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In: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 4
-
Journal article (peer-reviewed)abstract
- In the present work electrically conductive, flexible, lightweight carbon sponge materials derived from open-pore structure melamine foams are studied and explored. Hydrophobic and hydrophilic surface properties - depending on the chosen treatment conditions - allow the separation and storage of liquid chemical compounds. Activation of the carbonaceous structures substantially increases the specific surface area from ,4 m2 g21 to ,345 m2 g21 , while retaining the original three-dimensional, open-pore structure suitable for hosting, for example, Ni catalyst nanoparticles. In turn the structure is rendered suitable for hydrogenating acetone to 2-propanol and methyl isobutyl ketone as well for growing hierarchical carbon nanotube structures used as electric double-layer capacitor electrodes with specific capacitance of ,40 F/g. Mechanical stress-strain analysis indicates the materials are super-compressible (.70% volume reduction) and viscoelastic with excellent damping behavior (loss of 0.69 6 0.07), while piezoresistive measurements show very high gauge factors (from ,20 to 50) over a large range of deformations. The cost-effective, robust and scalable synthesis - in conjunction with their fascinating multifunctional utility - makes the demonstrated carbon foams remarkable competitors with other three-dimensional carbon materials typically based on pyrolyzed biopolymers or on covalently bonded graphene and carbon nanotube frameworks.
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| 2. |
- Aldea, Steliana, et al.
(author)
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Crystallization of Nano-Calcium Carbonate : The Influence of Process Parameters
- 2016
-
In: Chemie Ingenieur Technik. - : Wiley-VCH Verlagsgesellschaft. - 0009-286X .- 1522-2640. ; 88:11, s. 1609-1616
-
Journal article (peer-reviewed)abstract
- Precipitated calcium carbonate was synthesized by carbonation of calcium hydroxide in the presence and absence of ultrasound (conventional stirring) at atmospheric as well as at elevated pressures and different initial concentrations of Ca(OH)2. Spherical morphology of the formed calcite was favored at high Ca(OH)2 concentrations and low CO2 pressures. The presence of ultrasound did not show any influence on the reaction rate in case of efficient mixing. A small increase of the reaction rate was observed at lower CO2 pressures. Elevated pressures in combination with ultrasound did not lead to notable changes of reaction rate or particle morphology.
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| 3. |
- Alene Asres, Georgies, et al.
(author)
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A novel WS2 nanowire-nanoflake hybrid material synthesized from WO3 nanowires in sulfur vapor
- 2016
-
In: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 6:25610
-
Journal article (peer-reviewed)abstract
- In this work, WS2 nanowire-nanoflake hybrids are synthesized by the sulfurization of hydrothermally grown WO3 nanowires. The influence of temperature on the formation of products is optimized to grow WS2 nanowires covered with nanoflakes. Current-voltage and resistance-temperature measurements carried out on random networks of the nanostructures show nonlinear characteristics and negative temperature coefficient of resistance indicating that the hybrids are of semiconducting nature. Bottom gated field effect transistor structures based on random networks of the hybrids show only minor modulation of the channel conductance upon applied gate voltage, which indicates poor electrical transport between the nanowires in the random films. On the other hand, the photo response of channel current holds promise for cost-efficient solution process fabrication of photodetector devices working in the visible spectral range.
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| 4. |
- Asres, Georgies Alene, et al.
(author)
-
High photoresponse of individual WS2 nanowire-nanoflake hybrid materials
- 2018
-
In: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 112:23
-
Journal article (peer-reviewed)abstract
- van der Waals solids have been recognized as highly photosensitive materials that compete conventional Si and compound semiconductor based devices. While 2-dimensional nanosheets of single and multiple layers and 1-dimensional nanowires of molybdenum and tungsten chalcogenides have been studied, their nanostructured derivatives with complex morphologies are not explored yet. Here, we report on the electrical and photosensitive properties of WS2 nanowire-nanoflake hybrid materials we developed lately. We probe individual hybrid nanostructured particles along the structure using focused ion beam deposited Pt contacts. Further, we use conductive atomic force microscopy to analyze electrical behavior across the nanostructure in the transverse direction. The electrical measurements are complemented by in situ laser beam illumination to explore the photoresponse of the nanohybrids in the visible optical spectrum. Photodetectors with responsivity up to similar to 0.4 AW(-1) are demonstrated outperforming graphene as well as most of the other transition metal dichalcogenide based devices. Published by AIP Publishing.
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| 5. |
- Asres, Georgies Alene, et al.
(author)
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Ultrasensitive H2S gas sensors based on p-type WS2 hybrid materials
- 2018
-
In: Nano Reseach. - : Springer. - 1998-0124 .- 1998-0000. ; 11:8, s. 4215-4224
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Journal article (peer-reviewed)abstract
- Owing to their higher intrinsic electrical conductivity and chemical stability with respect to their oxide counterparts, nanostructured metal sulfides are expected to revive materials for resistive chemical sensor applications. Herein, we explore the gas sensing behavior of WS2 nanowire-nanoflake hybrid materials and demonstrate their excellent sensitivity (0.043 ppm-1) as well as high selectivity towards H2S relative to CO, NH3, H2, and NO (with corresponding sensitivities of 0.002, 0.0074, 0.0002, and 0.0046 ppm-1, respectively). Gas response measurements, complemented with the results of X-ray photoelectron spectroscopy analysis and first-principles calculations based on density functional theory, suggest that the intrinsic electronic properties of pristine WS2 alone are not sufficient to explain the observed high sensitivity towards H2S. A major role in this behavior is also played by O doping in the S sites of the WS2 lattice. The results of the present study open up new avenues for the use of transition metal disulfide nanomaterials as effective alternatives to metal oxides in future applications for industrial process control, security, and health and environmental safety.
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| 6. |
- Bourajoini, Hasna, et al.
(author)
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Calcium manganese oxide catalysts for water oxidation : Unravelling the influence of various synthesis strategies
- 2016
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In: Materials research bulletin. - : Elsevier. - 0025-5408 .- 1873-4227. ; 79, s. 133-137
-
Journal article (peer-reviewed)abstract
- Abstract Three different mixed oxide catalysts primarily consisting of calcium and manganese oxides targeting artificial photosynthesis were synthesized and studied. According to the results, their catalytic activity for water oxidation was enhanced by the presence of mixed valence states of Mnn+ ions (3.0 ≤ n ≪ 4.0), while the specific surface area had negligible effect.
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| 7. |
- Bukhanko, Natalia, et al.
(author)
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Continuous gas phase synthesis of 1-ethyl chloride from ethyl alcohol and hydrochloric acid over Al2O3-based catalysts: the ‘green’ route
- 2013
-
In: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 1:8, s. 883-893
-
Journal article (peer-reviewed)abstract
- The synthesis of 1-ethyl chloride in the gas-phase mixture of ethanol and hydrochloric acid over ZnCl2/Al2O3 catalysts was studied in a continuous reactor using both commercial and tailor-made supports. The catalytic materials were characterized by the means of structural (XPS, TEM, XRD, and BET) and catalytic activity (selectivity and conversion) measurements. The reaction parameters such as temperature, pressure, and feedstock flow rates were optimized for the conversion of ethanol to ethyl chloride. The new tailor-made highly porous Al2O3-based catalyst outperformed its commercial counterpart by exhibiting high conversion and selectivity (98%) at the temperature of 325 °C. Long-term stability tests (240 h) confirmed the excellent durability of the tailor-made alumina catalysts. The process demonstrated here poses an efficient and economic “green” large-scale on-site synthesis of this industrially important reactant in industry, where bioethanol is produced and 1-ethyl chloride is necessary, e.g., for ethylation of cellulose and synthetic polymer products. On-site in situ production of ethyl chloride avoids the problems associated with the transportation and storage of toxic and flammable 1-ethyl chloride.
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| 8. |
- Bukhanko, Natalia, et al.
(author)
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Gas phase synthesis of isopropyl chloride from isopropanol and HCl over alumina and flexible 3-D carbon foam supported catalysts
- 2017
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In: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 542:25, s. 212-225
-
Journal article (peer-reviewed)abstract
- Isopropyl chloride synthesis from isopropanol and HCl in gas phase over ZnCl2 catalysts supported on Al2O3 as well as flexible carbon foam was studied in a continuous reactor. A series of catalytic materials were synthesised and characterised by BET, XPS, SEM, TEM, XRD and NH3-TPD methods. Catalytic activity tests (product selectivity and conversion of reactants) were performed for all materials and optimal reaction conditions (temperature and feedstock flow rates) were found. The results indicate that the highest yield of isopropyl chloride was obtained over 5 wt.% ZnCl2 on commercial Al2O3 (No. II) (95.3%). Determination of product mixture compositions and by-product identification were done using a GC-MS method. Carbon foam variant catalyst, 5 wt.% ZnCl2/C, was found to perform best out of the carbon-supported materials, achieving ∼75% yield of isopropyl chloride. The kinetic model describing the process in a continuous packed bed reactor was proposed and kinetic parameters were calculated. The activation energy for the formation of isopropyl chloride reaction directly from isopropanol and HCl was found to be ∼58 kJ/mol.
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| 9. |
-
Dehydroisomerization of α-pinene over metal supported Si-SBA-15 mesoporous molecular sieves
- 2013
-
Editorial proceedings (peer-reviewed)abstract
- The effective dispersion of active metal species on mesoporous Si-SBA-15 is acquired by means of deposition-precipitation method. In order to achieve this, the surface of Si-SBA-15 was first modified with TiO2 via grafting method, followed by deposition-precipitation method (DP) to obtain a fine dispersion of metallic nanoparticles over TiO2 modified Si-SBA-15. The structural features of the synthesized materials were characterized by means of X-ray diffraction (XRD), nitrogen sorption (BET), XPS and HR-TEM. A valuable platform chemical, p-cymene, was produced over the prepared catalyst by dehydroisomerization of α-pinene under vapour-phase conditions. A stable catalyst for one-spot synthesis of renewable p-cymene from α-pinene was developed.
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| 10. |
- Eta, Valerie, et al.
(author)
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Synthesis of dimethyl carbonate from methanol and carbon dioxide : Circumventing thermodynamic limitations
- 2010
-
In: Industrial & Engineering Chemistry Research. - : American Chemical Society. - 0888-5885 .- 1520-5045. ; 49:20, s. 9609-17
-
Journal article (peer-reviewed)abstract
- The synthesis of dimethyl carbonate from methanol and CO2 catalyzed by ZrO2 doped with KCl was investigated using chemical traps for water to circumvent thermodynamic limitations. The reaction, promoted by magnesium, occurred via the formation of carbonated magnesium methoxide (CMM) which adsorbed on the surface of ZrO2. The surface migration of the oxygen atom of ZrO2 to the surface methoxy groups of CMM resulted in the formation of dimethyl carbonate. The resulting MgO then reacted with methanol forming water and regenerating magnesium methoxide. The water formed reacted with the dehydrating agent, thus shifting the equilibrium toward a higher yield of DMC. The yield of 7.2 mol % DMC and 13.6 mol % conversion of methanol was obtained when methanol reacted with CO2 at 150 °C and 9.5 MPa for 8 h. The plausible reaction pathway is described.
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| 11. |
- Fu, Qilin, 1986-, et al.
(author)
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Suppressing tool chatter with novel multi-layered nanostructures of carbon based composite coatings
- 2015
-
In: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 223, s. 292-298
-
Journal article (peer-reviewed)abstract
- Multi-layered nanostructured Cu and Cu-CNx composites synthesized by plasma-enhanced chemical vapour deposition were applied in the clamping area of a milling tool to suppress regenerative tool chatter. Scanning electron microscopy analysis showed a multi-layered nanostructure with excellent conformality, i.e. coating is not only uniform on planar surfaces but also around corners of the substrate. Cu:CuCNx nanostructured multilayers with thicknesses of approximately 0.5:1.6 mu m were obtained. With a diameter of 20 mm, the milling tool performed slotting processes at an overhang length of 120 mm. Modal analysis showed that a coating, with a thickness of approximately 300 mu m, can add sufficient damping without losing stiffness of the tool, to increase the critical stability limit by 50% or 100% depending on cutting direction.
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| 12. |
- Gemo, Nicola, et al.
(author)
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Reactivity aspects of SBA15-based doped supported catalysts : H2O2 direct synthesis and disproportionation reactions
- 2013
-
In: Topics in catalysis. - New York : Springer. - 1022-5528 .- 1572-9028. ; 56:9-10, s. 540-549
-
Journal article (peer-reviewed)abstract
- Pd and PdAu catalysts supported on SBA15 and SiO2 were prepared and investigated for H2O2 direct synthesis in a batch autoclave (10 °C and 17.5 bar) and in the absence of halides and acids. The SiO2 supported catalysts exhibited inferior performances compared to the mesoporous ordered SBA15. A good control of both the catalysts dispersion and nanoparticle stability was achieved using SBA15. Catalysts were doped with bromine, a promoter in the H2O2 direct synthesis. Productivity and selectivity decreased when bromine was incorporated in the catalysts, thus indicating a possible poisoning due to the grafting process. A synergetic effect between Pd and Au was observed both in presence and absence of bromopropylsilane grafting on the catalyst surface. Three modifiers of the SBA15 support (Al, CeO2 and Ti) were chosen to elucidate the influence of the surface properties on metal dispersion and catalytic performance. Higher productivity and selectivity were achieved incorporating Al into the SBA15 framework, whereas neither Ti nor CeO2 improved H2O2 yields. The enhanced performance observed for the Prau/Al–SBA15 catalysts was attributed to the increased number of Brønsted acid sites. A modification of this catalyst with bromine was confirmed to impair both productivity and selectivity, possibly due to the broader particle size distribution and the poor stability of the metal nanoparticles, as demonstrate by transmission electron microscopy (TEM) images. H2O2 disproportionation was also investigated. A much slower reaction rate was observed compared to the H2O2 production, suggesting that the major contributor in the process of H2O2 destruction must be connected to the hydrogenation reaction.
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| 13. |
- Gemo, Nicola, et al.
(author)
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The influence of catalyst amount and Pd loading on the H2O2 synthesis from hydrogen and oxygen
- 2015
-
In: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 5:7, s. 3545-3555
-
Journal article (peer-reviewed)abstract
- Palladium catalysts with an active metal content from 0.3 to 5.0 wt.% and supported on a strongly acidic, macroporous resin were prepared by ion-exchange/reduction method. H2O2 direct synthesis was carried out in the absence of promoters (acids and halides). The total Pd amount in the reacting environment was varied by changing A) the catalyst concentration in the slurry and B) the Pd content of the catalyst. In both cases, smaller amounts of the active metal enhance the selectivity towards H2O2, at any H-2 conversion, with option B) better than A). In case A), the Pd(II)/Pd(0) molar ratio (XPS) in the spent catalysts was found to decrease at lower catalyst Pd content. With these catalysts and this experimental set-up the dynamic H-2(1)/Pd molar ratio, the metal loading and the metal particle size were the key factors controlling the selectivity, which reached 57% at 60% H-2 conversion, and 80% at lower conversion.
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| 14. |
- Gemo, Nicola, et al.
(author)
-
TiO2 nanoparticles vs. TiO2 nanowires as support in hydrogen peroxide direct synthesis : the influence of N and Au doping
- 2016
-
In: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 6:105, s. 103311-103319
-
Journal article (peer-reviewed)abstract
- The performance of Pd on titania support were evaluated in the direct synthesis of hydrogen peroxide. The equipment used was a high pressure, semi-batch apparatus equipped with a special injection system. Pd (1 wt%) catalysts on TiO2 materials with different nature were prepared by wet impregnation method. Three aspects were investigated: (a) the structure of the support (nanoparticles vs. nanowires); (b) the addition of a second active metal (Au); (c) the influence of N-doping of the support. All samples were characterized by means of XPS, TEM and XRD analyses. TiO2 nanoparticle supported catalyst demonstrated higher H2O2 selectivity and higher turnover frequency (TOF) than the catalysts based on TiO2 nanowires. The addition of Au to the Pd TiO2 nanowire catalyst improved the H2O2 selectivity due to altered particle size and electronic effects. Both N-doped versions of the catalysts gave rise to higher H2O2 selectivity than the parent non-doped ones. The synthetic procedure was the source of this observation: larger mean Pd nanoparticles were present, thus favouring the formation of H2O2 as the primary product.
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| 15. |
- Halonen, Niina, et al.
(author)
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Low-temperature growth of multi-walled carbon nanotubes by thermal CVD
- 2011
-
In: Physica status solidi. B, Basic research. - Malden : Wiley-Blackwell. - 0370-1972 .- 1521-3951. ; 248:11, s. 2500-2503
-
Journal article (peer-reviewed)abstract
- Low-temperature thermal chemical vapor deposition (thermal CVD) synthesis of multi-walled carbon nanotubes (MWCNTs) was studied using a large variety of different precursor compounds. Cyclopentene oxide, tetrahydrofuran, methanol, and xylene: methanol mixture as oxygen containing heteroatomic precursors, while xylene and acetylene as conventional hydrocarbon feedstocks were applied in the experiments. The catalytic activity of Co, Fe, Ni, and their bi-as well as tri-metallic combinations were tested for the reactions. Low-temperature CNT growth occurred at 400 degrees C when using bi-metallic Co-Fe and tri-metallic Ni-Co-Fe catalyst (on alumina) and methanol or acetylene as precursors. In the case of monometallic catalyst nanoparticles, only Co (both on alumina and on silica) was found to be active in the low temperature growth (below 500 degrees C) from oxygenates such as cyclopentene oxide and methanol. The structure and composition of the achieved MWCNTs products were studied by scanning and transmission electron microscopy (SEM and TEM) as well as by Raman and X-ray photoelectron spectroscopy (XPS) and by X-ray diffraction (XRD). The successful MWCNT growth below 500 degrees C is promising from the point of view of integrating MWCNT materials into existing IC fabrication technologies. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 16. |
- Hedman, Daniel, 1989-
(author)
-
A Theoretical Study: The Connection between Stability of Single-Walled Carbon Nanotubes and Observed Products
- 2017
-
Licentiate thesis (other academic/artistic)abstract
- Over the past 20 years’ researchers have tried to utilize the remarkable properties of single-walled carbon nanotubes (SWCNTs) to create new high-tech materials and devices, such as strong light-weight composites, efficient electrical wires and super-fast transistors. But the mass production of these materials and devices are still hampered by the poor uniformity of the produced SWCNTs. These are hollow cylindrical tubes of carbon where the atomic structure of the tube wall consists of just a single atomic layer of carbon atoms arranged in a hexagonal grid. For a SWCNT the orientation of the hexagonal grid making up the tube wall is what determines its properties, this orientation is known as the chirality of a SWCNT. As an example, tubes with certain chiralities will be electrically conductive while others having different chiralities will be semiconducting.Today’s large scale methods for producing SWCNTs, commonly known as growth of SWCNTs, gives products with a large spread of different chiralities. A mixture of chiralities will give products with a mixture of different properties. This is one of the major problems holding back the use of SWCNTs in future materials and devices. The ultimate goal is to achieve growth where the resulting product is uniform, meaning that all of the SWCNTs have the same chirality, a process termed chirality-specific growth. To achieve chirality-specific growth of SWCNTs requires us to obtain a better fundamental understanding about how they grow, both from an experimental and a theoretical point of view.This work focuses on theoretical studies of SWCNT properties and how they relate to the growth process, thereby giving us vital new information about how SWCNTs grow and taking us ever closer to achieving the ultimate goal of chirality-specific growth. In this thesis, an introduction to the field is given and the current state of the art experiments focusing on chirality-specific growth of SWCNTs are presented. A brief review of the current theoretical works and computer simulations related to growth of SWCNTs is also presented. The results presented in this thesis are obtained using first principle density functional theory. The first study shows a correlation between the stability of SWCNT-fragments and the observed products from experiments. Calculations confirm that in 84% of the investigated cases the chirality of experimental products matches the chirality of the most stable SWCNT-fragments (within 0.2 eV). Further theoretical calculations also reveal a previously unknown link between the stability of SWCNT-fragments and their length. The calculations show that at specific SWCNT-fragment lengths the most stable chirality changes. Thus, introducing the concept of a switching length for SWCNT stability. How these new results link to the existing understanding of SWCNT growth is discussed at the end of the thesis.
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| 17. |
- Järvinen, Topias, et al.
(author)
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An energy harvester based on UV-polymerized short-alkyl-chain-modified [DBU][TFSI] ionic liquid electrets
- 2024
-
In: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 12:3, s. 1746-1752
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Journal article (peer-reviewed)abstract
- Three short-alkyl-chain-modified [DBU][TFSI] ionic liquids (ILs) were synthesized and utilized in electrets. The electrets were prepared by mixing a UV-curable polymer with the ionic liquids followed by polymerization while applying an external electric field, thus forming spatially separated anions and cations in the proximity of opposing surfaces of the composite slabs. The immobilized surplus surface charge was measured by periodically engaging the electret with a metal counter electrode plate and detecting the displacement current using a charge amplifier. The results show that electrets based on polymerized [DBU][TFSI] ILs have a separated surface charge density of up to 64 nC × cm−2, which equals an energy harvesting density of 7.0 nJ × cm−2. Control measurements repeated after a few days to assess the stability and reproducibility of the systems showed that while charge separation reverses over time to some extent, the polymerized ionic liquid samples are resilient to exposure to atmospheric conditions and could be utilized in this type of energy harvesting scheme.
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| 18. |
- Khajavizadeh, Lida, 1978-
(author)
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Materials Design for the Improvement of SiC Field Effect Gas Sensor performance in High Temperature Process Control applications
- 2023
-
Doctoral thesis (other academic/artistic)abstract
- Following growing concerns about the effect these last decades of accelerating energy consumption, escalating use of natural (not the least fossil) resources, and waste generation has had on earth’s climate, human health, and the environment, industry is facing mounting pressure to increase the energy-, resource-, and cost-efficiency of both processes and products while drastically reducing pollutant emissions. In response, industry is, besides increasing their utilization of renewable energy and introducing new bio-based products, taking advantage of the rapid development in 5G technology and associated wireless interconnectivity to move towards full automation of production processes and facilities. With the ability to connect and collect information from a large number of instruments and process steps as well as to analyse huge amounts of multi-dimensional data, entire production lines can be automatically controlled and/or adapted, e.g., through the application of machine learning, for optimized efficiency and minimized greenhouse gas and pollutant emissions. In order to fully benefit from this so-called 4th industrial revolution and the Industrial Internet of Things (IIoT), however, access to cost-efficient and long-term reliable means for measuring various process parameters in multiple locations is required.The basis for this thesis is therefore the characterization of silicon carbide-based Metal Oxide Semiconductor Field Effect Transistor (MOSFET) gas sensors for their applicability in real-time monitoring of process gases/ gas mixtures and pollutant emissions in high-temperature applications, e.g., control of flue gas/ exhaust after-treatment systems, as well as investigations performed to gain a better understanding of the corresponding sensing mechanisms and to improve sensor performance in terms of e.g., long-term reliability.Besides demonstrating the general applicability of SiC MOSFET gas sensors in ammonia (NH3) slip detection and control of Selective Catalytic Reduction and similar flue gas/ exhaust emissions abatement systems to minimize the release of nitrogen oxides into the atmosphere from the energy production and transport sectors, sensors for the selective monitoring of nitrogen oxides with negligible interference from (sensitivity/ cross-sensitivity to) ammonia have been developed. Through variation of the gold/ iridium composition of the MOSFET gate contact, the interaction of which with gaseous substances in the ambient determines the sensor signal, sensors selective to ammonia and nitrogen oxides (NOx; NO and NO2), respectively, could be developed. Furthermore, as both sensor-types exhibit decent sensitivity to the respective substance over a common temperature interval, the realization of simultaneous NH3 and NOx monitoring with one and the same sensor probe would be facilitated. In relating the sensor response under different conditions to the composition and micro- (/nano-) structure of the gate contact material another piece in the puzzle towards an understanding of the ammonia sensing mechanism of field effect sensor devices could also be obtained.Through the investigation of co-deposited platinum group metals/ metal oxides in different ratios it was also shown possible to improve the long-term stability of carbon monoxide (CO) sensors intended for emissions monitoring and combustion control in industrial processes. Both the materials composition and structure were thereby evaluated and their effect on other important sensor parameters, e.g., sensitivity and temperature dependence, analysed. To further improve sensitivity and selectivity of CO as well as NH3 sensors for combustion control and ammonia slip monitoring applications, respectively, the sensor characteristics were also studied under different ambient conditions, e.g., variations in oxygen concentration, and related to the microstructure of the deposited gate materials. From the simultaneous tuning of film structure and operating temperatures, the selectivity could be enhanced for both the CO and NH3 sensors.In summary, the obtained research results from this thesis work have contributed to a further understanding of the sensing mechanisms of silicon carbide-based MOSFET sensors for CO, NOx, and NH3 monitoring and through the tuning of materials properties and sensor operation parameters generated improvements in sensor reliability, sensitivity, and selectivity of importance to the further realization of sensors for process control and emissions reduction applications.
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| 19. |
- Kordás, Krisztián, et al.
(author)
-
Nanoparticle Dispersions
- 2013
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In: Springer Handbook of Nanomaterials. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783642205941 - 9783642205958 ; , s. 729-776
-
Book chapter (peer-reviewed)abstract
- This chapter aims to provide an insight into the physics and chemistry of nanoparticle–liquid systems. The first part of the chapter discusses parameters and effects that influence dispersion stability (Sect. 20.1), including particle size and shape as well as the interactions at the interface between the solid and liquid phases. Section 20.2 summarizes the practical aspects of making a dispersion, collecting and listing hundreds of examples from contemporary literature. Because of the broad spectrum of materials in question, the survey is limited to dispersions of inorganic nanoparticles including metals, their oxides/sulfides, some (compound) semiconductors, as well as nanostructured carbon particles such as fullerenes, nanotubes, and graphene/graphite (Sect. 20.3). Dispersions of polymers of either synthetic or biological origin lie beyond the scope of this work. Since a very large fraction of applications are related to various surface coatings using dispersions as the source of nanoparticles, Sect. 20.4 is devoted to drying phenomena and particle self-ordering.
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| 20. |
- Kordas, Krisztian, et al.
(author)
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On the Interaction of Metal Nanoparticles with Supports
- 2015
-
In: Topics in catalysis. - : Springer Science+Business Media B.V.. - 1022-5528 .- 1572-9028. ; 58:14-17, s. 1127-1135
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Journal article (peer-reviewed)abstract
- Metal nanoparticles supported on surfaces often undergo sintering even at moderate temperatures. The degree of sintering is typically influenced by the surface chemistry indicating that besides the commonly believed Ostwald ripening also other processes associated with metal surface diffusion are responsible for the nanoparticle size growth. In addition to the deterioration in metal dispersion, carbon supports can show chemical instability leading to their partial degradation in the proximity of the nanoparticles both in reducing and oxidizing environments at elevated temperatures. This work reports a study of Pd, Pt and Ni nanoparticles anchored on carbon (activated carbon, graphite and carbon nanotubes) as well as titania (nanoparticles and microparticles) surfaces frequently applied as catalyst materials in heterogeneous catalysis and photocatalysis, and evaluate the potential events causing metal sintering and degradation of the supports using transmission electron microscopy analysis.
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| 21. |
- Kukkola, Jarmo, et al.
(author)
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Electrical transport through single-wall carbon nanotube-anodic aluminum oxide-aluminum heterostructures
- 2010
-
In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 21:3, s. 35707-
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Journal article (peer-reviewed)abstract
- Aluminum foils were anodized in sulfuric acid solution to form thick porous anodic aluminum oxide (AAO) films of thickness approximately 6 microm. Electrodes of carboxyl-functionalized single-wall carbon nanotube (SWCNT) thin films were inkjet printed on the anodic oxide layer and the electrical characteristics of the as-obtained SWCNT-AAO-Al structures were studied. Nonlinear current-voltage transport and strong temperature dependence of conduction through the structure was measured. The microstructure and chemical composition of the anodic oxide layer was analyzed using transmission and scanning electron microscopy as well as x-ray photoelectron spectroscopy. Schottky emission at the SWCNT-AAO and AAO-Al interfaces allowed by impurity states in the anodic aluminum oxide film together with ionic surface conduction on the pore walls of AAO gives a reasonable explanation for the measured electrical conduction. Calcined AAO is proposed as a dielectric material for SWCNT-field effect transistors.
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| 22. |
- Kukkola, Jarmo, et al.
(author)
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Gas sensors based on anodic tungsten oxide
- 2011
-
In: Sensors and actuators. B, Chemical. - : Elsevier B V. - 0925-4005 .- 1873-3077. ; 153:2, s. 293-300
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Journal article (peer-reviewed)abstract
- Nanostructured porous tungsten oxide materials were synthesized by the means of electrochemical etching (anodization) of tungsten foils in aqueous NaF electrolyte. Formation of the sub-micrometer size mesoporous particles has been achieved by infiltrating the pores with water. The obtained colloidal anodic tungsten oxide dispersions have been used to fabricate resistive WO3 gas sensors by drop casting the sub-micrometer size mesoporous particles between Pt electrodes on Si/SiO2 substrate followed by calcination at 400 °C in air for 2 h. The synthesized WO3 films show slightly nonlinear current–voltage characteristics with strong thermally activated carrier transport behavior measured at temperatures between −20 °C and 280 °C. Gas response measurements carried out in CO, H2, NO and O2 analytes (concentration from 1 to 640 ppm) in air as well as in Ar buffers (O2 only in Ar) exhibited a rapid change of sensor conductance for each gas and showed pronounced response towards H2 and NO in Ar and air, respectively. The response of the sensors was dependent on temperature and yielded highest values between 170 °C and 220 °C.
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| 23. |
- Kukkola, Jarmo, et al.
(author)
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Inkjet-printed gas sensors : metal decorated WO3 nanoparticles and their gas sensing properties
- 2012
-
In: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 22:34, s. 17878-17886
-
Journal article (peer-reviewed)abstract
- Inkjet deposition is an attractive technology to localize nanomaterials in an area-selective manner on virtually any kind of surfaces. Great advantages of the method are effective usage of materials, low processing temperatures and few required manufacturing steps, thus enabling rapid prototyping and bulk production with reasonably low cost. A number of different electrical devices such as light emitting diodes, transistors and solar cells have already been demonstrated, reflecting the versatility of inkjet printing. In this paper, we collect the contemporary results on inkjet deposited gas sensors and show examples of such gas sensing devices based on surface modified WO3 nanoparticles for efficient discrimination of various gaseous analytes from sub-ppm up to nearly 0.1% concentration levels in air.
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| 24. |
- Kukkola, Jarmo, et al.
(author)
-
Room temperature hydrogen sensors based on metal decorated WO3 nanowires
- 2013
-
In: Sensors and actuators. B, Chemical. - : Elsevier. - 0925-4005 .- 1873-3077. ; 186, s. 90-95
-
Journal article (peer-reviewed)abstract
- The emerging hydrogen economy has created a demand for the development of improved hydrogen sensors operating at room temperature. In this work, we present hydrogen detectors based on metal decorated WO3 nanowires that were able to detect 1000 ppm of H-2, even at room temperature (30 degrees C), with relatively short recovery time and high sensitivity. The nanowires were synthesized by a hydrothermal process and decorated with PdO and PtOx nanoparticles by decomposition of Pd(acac)(2) and Pt(acac)(2) precursors. The gas responses were tested for H-2, NO, H2S and CO analyte gases in an air buffer at 150,200 and 250 degrees C (H-2 also at 30,70 and 130 degrees C).
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| 25. |
- Leino, Anne-Riikka, et al.
(author)
-
Low-temperature catalytic oxidation of multi-walled carbon nanotubes
- 2013
-
In: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 57, s. 99-107
-
Journal article (peer-reviewed)abstract
- When in a pure form, carbon nanotubes are known to be stable in air up to ∼800 K making them attractive for a large variety of applications. In this work, we report a significant decrease of ignition temperature (in some cases occurring at ∼500 K) and a reduction in the apparent activation energy for oxidation in air as a result of impregnation with nanoparticles (<2 nm) of metal (Pt, Pd, Ni and Co) acetylacetonates or by decoration with corresponding oxides. Surprisingly, defects introduced by partial oxidation of the carbon nanotubes do not in practice have any influence on the enhancement of further oxidation. Reduction temperatures of metal oxides with H2 were close to those of other carbon supported catalyst materials. However, the carbon nanotubes showed a tendency for low temperature gasification in the presence of hydrogenation catalyst metals (Pt, Pd).
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| 26. |
- Leino, Ewelina, et al.
(author)
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Influence of the synthesis parameters on the physico-chemical and catalytic properties of cerium oxide for application in the synthesis of diethyl carbonate
- 2013
-
In: Materials Chemistry and Physics. - : Elsevier. - 0254-0584 .- 1879-3312. ; 143:1, s. 65-75
-
Journal article (peer-reviewed)abstract
- Synthesis of cerium (IV) oxide by means of room temperature precipitation method was carried out. The effect of preparation variables such as synthesis time, calcination temperature and pH of the solution on resulting CeO2 properties was discussed. Moreover, the comparison of CeO2 samples prepared in a static and rotation mode of synthesis is presented. The solid catalysts were characterized by means of X-ray powder diffraction, scanning electron microscopy, transmission electron microscope, nitrogen physisorption, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy using pyridine as a probe molecule and temperature programmed desorption of CO2. Significant variations in physicochemical properties of CeO2 by varying the preparation conditions were observed. Furthermore, the catalytic performances of CeO2 catalysts were compared in the synthesis of diethyl carbonate starting from ethanol and CeO2 using butylene oxide as a dehydrating agent. The dependence of CeO2 properties on its catalytic activity is evaluated in detail. (C) 2013 Elsevier B.V. All rights reserved.
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| 27. |
- Leino, Ewelina, et al.
(author)
-
The influence of various synthesis methods on the catalytic activity of cerium oxide in one-pot synthesis of diethyl carbonate starting from CO2, ethanol and butylene oxide
- 2013
-
In: Catalysis Today. - : Elsevier. - 0920-5861 .- 1873-4308. ; 210, s. 47-54
-
Journal article (peer-reviewed)abstract
- Different synthesis methods such as homogeneous precipitation at room temperature and supercritical water (T > 647 K and P > 22.1 MPa) were employed for cerium oxide preparation. Additionally, deposition of ceria on silica mesoporous material, SBA-15, was carried out. The obtained materials were characterized by means of X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen physisorption, X-ray photoelectron spectroscopy and CO2 temperature programmed desorption. Considerable variations in physico-chemical properties of the resulting materials were observed. The catalytic activities of pristine cerium oxide and ceria loaded on SBA-15 support were compared. The test reaction was synthesis of diethyl carbonate starting from carbon dioxide and ethanol using butylene oxide as the dehydrating agent.
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| 28. |
- Lin, Jhih-Fong, et al.
(author)
-
Trifluoroacetylazobenzene for optical and electrochemical detection of amines
- 2015
-
In: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 3:8, s. 4687-4694
-
Journal article (peer-reviewed)abstract
- In this work, we demonstrate the solution processing of optical and electrochemical dye sensors based on 4-(dioctylamino)-4'-(trifluoroacetyl) azobenzene and its application in sensing different amine compounds. Distinct optical response of the sensors exposed to ammonia, tetramethylammonium hydroxide, ethylamine, cadaverine and putrescine (typical compounds upon the decomposition of proteins) is observed. Incorporation of inkjet deposited thin films of the dye as sensors in food packages of ground meat and salmon is found as a feasible route to detect the appearance of biogenic amines produced by the degrading food products. Furthermore, we demonstrate an electrochemical amine sensor based on (trifluoroacetyl) azobenzene dye added in carbon nanotube-Nafion (R) composites. The electrochemical sensor exploits the reaction between the dye and amines to detect amines in electrolytes, while the carbon nanotubes provide large surface for adsorption and also provide a percolating electrical network for allowing efficient charge transfer at the electrode electrolyte interface.
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| 29. |
- Mohl, Melinda, et al.
(author)
-
Formation of CuPd and CuPt Bimetallic Nanotubes by Galvanic Replacement Reaction
- 2011
-
In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:19, s. 9403-9409
-
Journal article (peer-reviewed)abstract
- A galvanic replacement reaction has been successfully applied to prepare CuPd and CuPt bimetallic nanotubes. The nanotubes were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) techniques. Ultralong, single crystalline copper nanowires (NWs) with a diameter of similar to 64 nm and a length of several micrometers were used as template material. By controlling the amount of noble metal salt added, nanotubes with different compositions were obtained. After the replacement of Cu with Pt, nanotubes composed of a PtCu alloy were formed. EDS analysis revealed that the Pt content increased until about 66%. No further increase in the molar ratio resulted in any additional Pt incorporation into the alloy. As for the replacement of Cu with Pd, the thickening of the nanotubes was observed indicating that nanotubes composed of Pd nanoparticles were formed. Bacicscattered electron imaging and SEM-EDS revealed CuPd nanotubes with approximately 2.3% Cu content. These remarks indicate different evolution mechanism for the nanotubes in the two systems.
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| 30. |
- Mohl, Melinda, et al.
(author)
-
Titania nanofibers in gypsum composites : an antibacterial and cytotoxicology study
- 2014
-
In: Journal of Material Chemistry B. - : Royal Society of Chemistry. - 2050-750X .- 2050-7518. ; 2:10, s. 1307-1316
-
Journal article (peer-reviewed)abstract
- Further developments of antibacterial coatings based on photocatalytic nanomaterials could be a promising route towards potential environmentally friendly applications in households, public buildings and health care facilities. Hereby we describe a simple chemical approach to synthesize photocatalytic nanomaterial-embedded coatings using gypsum as a binder. Various types of TiO2 nanofiber-based photocatalytic materials (nitrogen-doped and/or palladium nanoparticle decorated) and their composites with gypsum were characterized by means of scanning (SEM) and transmission (TEM) electron microscopy as well as electron and X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) techniques. These gypsum-based composites can be directly applied as commercially available paints on indoor walls. Herein we report that surfaces coated with photocatalytic composites exhibit excellent antimicrobial properties by killing both methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) under blue light. In the case of MSSA cells, the palladium nanoparticle-decorated and nitrogen-doped TiO2 composites demonstrated the highest antimicrobial activity. For the MRSA strain even pure gypsum samples were proven to be efficient in eradicating Gram-positive human pathogens. The cytotoxicity of freestanding TiO2 nanofibers was revealed by analyzing the viability of HeLa cells using MTT and fluorescent cell assays.
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| 31. |
- Mäklin, Jani, et al.
(author)
-
Thermal diffusivity of aligned multi-walled carbon nanotubes measured by the flash method
- 2011
-
In: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 248:11, s. 2508-2511
-
Journal article (peer-reviewed)abstract
- Thermal diffusivity of freestanding catalytic chemical vapor deposition (CCVD) grown multi-walled carbon nanotube (MWCNT) forests (height of 1.5 and 1.9 mm) was characterized in the temperature range between 25 and 200 degrees C. Copper and Al-alloy metal blocks were used as references for validation of the experimental setup. The measurements were carried out along the MWCNT alignment direction with a thermal property analyzer that uses the flash method. The thermal diffusivities measured at room temperature for as-grown and post-annealed (2 h at 480 degrees C in open air) samples were found to be similar to 0.45 and similar to 0.23 cm(2)/s, respectively. In both cases, the thermal diffusivity values were slightly decreasing with increasing temperature. The observed decrease in diffusivity after annealing is most probably due to the loss of amorphous carbon in the specimens and also because of the increased defect density in the nanotube walls resulting in a more pronounced phonon scattering in the lattice. The measured thermal diffusivities for as-grown samples agree with data reported elsewhere for similar MWCNT materials [W. Yi et al., Rev. B 59, 9015 (1999) and T. Borca-Tasciuc et al., J. Appl. Phys. 98, 054309 (2005)]. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 32. |
- Ngoc Pham, Tung, et al.
(author)
-
Catalytic Hydrogenation of d-Xylose Over Ru Decorated Carbon Foam Catalyst in a SpinChem® Rotating Bed Reactor
- 2016
-
In: Topics in catalysis. - New York : Springer. - 1022-5528 .- 1572-9028. ; 59:13-14, s. 1165-1177
-
Journal article (peer-reviewed)abstract
- In this work the activity of ruthenium decorated carbon foam (Ru/CF) catalyst was studied in three phase hydrogenation reaction of d-xylose to d-xylitol. The developed catalyst was characterized by using scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectrometry and nitrogen adsorption–desorption measurement. Kinetic measurements were carried out in a laboratory scale pressurized reactor (Parr®) assisted by SpinChem® rotating bed reactor (SRBR), at pre-defined conditions (40–60 bar H2 and 100–120 °C). The study on the influence of reaction conditions showed that the conversion rate and selectivity of hydrogenation reaction of d-xylose was significantly affected by temperature. These results have been proved by a competitive kinetics model which was found to describe the behavior of the novel system (Ru/CF catalyst used together with the SRBR) very well. Besides, it was revealed that the catalytic activity as well as the stability of our Ru/CF-SRBR is comparable with the commercial ruthenium decorated carbon catalyst (Ru/AC) under identical reaction conditions. Moreover, all steps from catalyst preparation and catalyst recycling as well as catalytic testing can be performed in an easy, fast and elegant manner without any loss of materials. Briefly, the developed Ru/CF catalyst used together with the SRBR could be used an excellent alternative for the conventional Raney nickel catalyst in a slurry batch reactor and offers an attractive concept with obvious industrial applicability.
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| 33. |
- Ngoc Pham, Tung, et al.
(author)
-
Robust hierarchical 3D carbon foam electrode for efficient water electrolysis
- 2017
-
In: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 7
-
Journal article (peer-reviewed)abstract
- Herein we report a 3D heterostructure comprising a hierarchical macroporous carbon foam that incorporates mesoporous carbon nanotubes decorated with cobalt oxide nanoparticles as an unique and highly efficient electrode material for the oxygen evolution reaction (OER) in electrocatalytic water splitting. The best performing electrode material showed high stability after 10 h, at constant potential of 1.7 V vs. RHE (reversible hydrogen electrode) in a 0.1 M KOH solution and high electrocatalytic activity in OER with low overpotential (0.38 V vs RHE at 10 mA cm(-2)). The excellent electrocatalytic performance of the electrode is rationalized by the overall 3D macroporous structure and with the firmly integrated CNTs directly grown on the foam, resulting in a large specific surface area, good electrical conductivity, as well as an efficient electrolyte transport into the whole electrode matrix concurrent with an ability to quickly dispose oxygen bubbles into the electrolyte. The eminent properties of the three-dimensional structured carbon matrix, which can be synthesized through a simple, scalable and cost effective pyrolysis process show that it has potential to be implemented in large-scale water electrolysis systems.
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| 34. |
- Nitze, Florian, 1981-
(author)
-
Synthesis and characterization of palladium based carbon nanostructure-composites and their clean-energy application
- 2013
-
Doctoral thesis (other academic/artistic)abstract
- Carbon nanostructures are a wide field with many applications. The use of carbon nanostructures as support in heterogeneous catalysis is a key development that led together with the use of nanoparticles to a significant cost reduction of catalysts. Catalysts designed in this way are widely applied in fuel cell technologies. For portable devices especially low temperature fuel cells are desirable with low hazards for the user. One technology which fulfills these requirements is the direct formic acid fuel cell (DFAFC). DFAFC have many promising characteristics, such as high electromotive force and easy fuel handling. However, they still suffer from too low power output and lifetime for commercialization.This thesis focusses on two main aspects: the synthesis of carbon nanostructures by chemical vapor deposition (CVD) and their application as catalyst support. The materials are investigated by many different techniques ranging from transmission electron microscopy (TEM) to fuel cell tests.Different carbon nanostructures could be synthesized by catalytic CVD on palladium (Pd) nanoparticles. Multi-walled carbon nanotubes (MWCNTs), carbon nanofibers (CNFs) and helical carbon nanofibers (HCNFs) were grown, selectively, dependent on temperature, using acetylene as carbon precursor. Especially HCNF raised further interest due to their unique structure. A growth model for HCNFs was developed based on an anisotropic extrusion model. The synthesis conditions for HCNFs were optimized until an almost 100 % purity with very high efficiency was obtained.The unique helical but fiber-like structure made the material very interesting as support for heterogeneous catalysis. Several catalysts based on Pd nanoparticle decorated HCNFs were developed. The synthesis methods ranged from standard methods like the polyol method to phase-transfer methods. The catalysts showed very promising results for the electro-oxidation of methanol, ethanol and formic acid. This makes them highly attractive for fuel cell applications. The catalysts were tested in DFAFC. The superiority of HCNF-based catalysts is attributed to the good attachment of nanoparticles to the defect-rich and easy to functionalize surface of HCNFs in combination with adequate film forming properties during electrode preparation.
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| 35. |
- Pham, Ngoc Tung, 1977-
(author)
-
Three-dimensional structured carbon foam : synthesis and applications
- 2016
-
Doctoral thesis (other academic/artistic)abstract
- Recently, due to the unique properties and structures such as large geometric surface area, electrical conductivity and light weight, 3D structured carbon materials have been attracting extensive attention from scientists. Moreover, the materials, which can provide well-defined pathways for reactants to easily access active sites, are extremely useful for energy conversion as well as environmental and catalysis applications. To date, many precursors have been used for fabrication of 3D structured carbon materials including pitch, carbon nanotubes, graphene, and polymer foams.This thesis, as shown in the thesis title, focus on two main aspects: the study of the characteristics of melamine based carbon foam synthesized at different conditions and their applications. In paper I, it was revealed that through a simple, one-step pyrolysis process, flexible carbon foam synthesized from melamine foam (BasotectÒ, BASF) was obtained. Additionally, through a pyrolysis-activation process, activated carbon foam which possesses hydrophilic nature and high surface area was successfully synthesized. The characteristics of carbon foam such as the hydrophobic/hydrophilic nature, electrical conductivity, mechanical properties and surface chemistry were studied. It was shown that carbon foam could be successfully used as an absorbent in environmental applications e.g. removing of spill oil from water (paper I) or as support for heterogeneous catalysts, which in turn was used not only in gas phase reactions (paper I and IV) but also in an aqueous phase reaction (paper II). Importantly, when combined with a SpinChem® rotating bed reactor (SRBR) (paper II), the monolithic carbon foam/SRBR system brought more advantages than using the foam alone. Additionally, the work in paper III showed the potential of carbon foam in an energy conversion application as anode electrode substrate in alkaline water electrolysis. In summary, the versatility of the carbon foam has been proven through abovementioned lab scale studies and due to the simple, scalable and cost effective pyrolysis and activation processes used for the production, it has potential to be used in large-scale applications.
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| 36. |
- Pitkanen, O., et al.
(author)
-
Low-Temperature Growth of Carbon Nanotubes on Bi- and Tri-metallic Catalyst Templates
- 2013
-
In: Topics in catalysis. - : Springer. - 1022-5528 .- 1572-9028. ; 56:9-10, s. 522-526
-
Journal article (peer-reviewed)abstract
- Low temperature growth process of carbon nanotubes (CNTs) over bi-metallic (Co-Fe) and tri-metallic (Ni-Co-Fe) catalysts on Si/Al/Al2O3 substrates is carried out from acetylene precursor using hydrogen, ammonia or nitrogen as a carrier in a low pressure chemical vapor deposition system. Using the tri-metallic Ni-Co-Fe catalyst template, vertically aligned CNTs of similar to 700 nm length could be grown already at 450 A degrees C within 10 min using ammonia as a carrier. Within the same period of time, on bi-metallic Co-Fe catalyst templates, similar to 250 nm long aligned nanotubes emerged already at 400 A degrees C in nitrogen carrier. At low temperatures most of the catalyst materials were elevated from the support by the grown nanotubes indicating tip growth mechanism. The structure of catalyst layers and nanotube films was studied using scanning and transmission electron microscopy and atomic force microscopy.
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| 37. |
- Pitkänen, Olli, et al.
(author)
-
Evaluation of short alkyl chain modified [DBU][TFSI] based ionic liquids as supercapacitor electrolytes
- 2024
-
In: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 475
-
Journal article (peer-reviewed)abstract
- The need of new electrolytes with wide electrochemical window, good stability and conductivity has promoted novel ionic liquids (ILs) as new solutions for supercapacitors. In this work, four hydrophobic room temperature ionic liquids based on organic superbase-derived cations and Trifluoromethanesulfonimide (TFSI) anion were synthetized. The structures of the novel ILs were analyzed, characterized and their performance as a supercapacitor electrolyte was evaluated. The ILs have high decomposition temperatures of up to 490 °C and electrochemical window up to 4.8 V. It was found that there was an optimal chemical structure providing the best stability and operational potential window coupled with moderate conductivity. The IL with the shortest alkyl chain structure provided the highest conductivity but suffered from instability. The performance of the ILs with longer alkyl chains was hindered by lower conductivities and, in the case of the largest chemical structures, also by reduced cyclic stabilities in open air. However, the ionic liquid with moderate alkyl chain length was found to be stable even in open air providing decent conductivity, which can be utilized in future research to develop other hydrophobic ionic liquids suitable as supercapacitor electrolytes.
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| 38. |
- Raut, Dilip G., et al.
(author)
-
A morpholinium ionic liquid for cellulose dissolution
- 2015
-
In: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 130, s. 18-25
-
Journal article (peer-reviewed)abstract
- A series of substituted morpholinium ionic salts and allyl ammonium acetates were prepared. Amongst those, N-allyl-N-methylmorpholinium acetate ([AMMorp][OAc]) was found to dissolve cellulose readily without any pre-processing of native cellulose. At 120 degrees C, [AMMorp][OAc] could dissolve 30 wt%, 28 wt% and 25 wt% of cellulose with degree of polymerization (DPn) - 789, 1644 and 2082 respectively, in 20 min. Importantly, SEC analysis indicated that no discernible changes occurred in terms of the degree of polymerization of the different celluloses after regeneration. Furthermore, when comparing the cellulose dissolution capability of these newly synthesized ionic liquids, it is evident that the combination of all three constituents - the morpholinium cation, the existence of an allyl group and choosing the acetate anion are essential for efficient cellulose dissolution. The structure and morphology of the regenerated cellulosic materials were characterized by SEM, XRD, TGA, CP/MAS C-13 NMR and FTIR, respectively.
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| 39. |
- Rautio, Anne-Riikka, et al.
(author)
-
Electric double-layer capacitors based on multiwalled carbon nanotubes : can nanostructuring of the nanotubes enhance performance?
- 2015
-
In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:7, s. 3538-3544
-
Journal article (peer-reviewed)abstract
- Supercapacitors prepared from chemically modified and vacuum filtered buckypapers were studied. The aim was to evaluate how its pore structure impacts the specific capacitance, energy, and power density in different electrolytes. The specific capacitance varies in a linear fashion with the specific surface area for nanotubes modified by the means of catalytic, low-temperature partial catalytic oxidation using cobalt oxide nanoparticles decorating the nanotubes. In contrast, electrodes composed of nanotubes preactivated in CO2 demonstrated only a minor increase in their specific capacitance, despite the observed significant increase in specific surface area. The radically improved surface area was a result of emergence and deposition of soot on the nanotubes during the activation process, as revealed by transmission electron microscopy. Among six different types of electrode materials, the CoOx decorated materials proved to have the highest specific capacitance (similar to 25 F/g in aqueous KOH and similar to 15 F/g in triethylsulfonium bis(trifluoromethylsulfonyl)imide ionic liquid). Thus, highly structured carbon nanotubes giving rise to energy and power storage densities comparable with commercial and other multiwalled carbon nanotube based electric double-layer capacitor devices were obtained.
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| 40. |
- Reinik, Janek, et al.
(author)
-
Alkaline modified oil shale fly ash : Optimal synthesis conditions and preliminary tests on CO(2) adsorption
- 2011
-
In: Journal of Hazardous Materials. - Amsterdam : Elsevier. - 0304-3894 .- 1873-3336. ; 196, s. 180-186
-
Journal article (peer-reviewed)abstract
- Environmentally friendly product, calcium-silica-aluminum hydrate, was synthesized from oil shale fly ash, which is rendered so far partly as an industrial waste. Reaction conditions were: temperature 130 and 160°C, NaOH concentrations 1, 3, 5 and 8M and synthesis time 24h. Optimal conditions were found to be 5M at 130°C at given parameter range. Original and activated ash samples were characterized by XRD, XRF, SEM, EFTEM, (29)Si MAS-NMR, BET and TGA. Semi-quantitative XRD and MAS-NMR showed that mainly tobermorites and katoite are formed during alkaline hydrothermal treatment. Physical adsorption of CO(2) on the surface of the original and activated ash samples was measured with thermo-gravimetric analysis. TGA showed that the physical adsorption of CO(2) on the oil shale fly ash sample increases from 0.06 to 3-4mass% after alkaline hydrothermal activation with NaOH. The activated product has a potential to be used in industrial processes for physical adsorption of CO(2) emissions.
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| 41. |
- Reinik, Janek, et al.
(author)
-
DIRECT CO2 SEQUESTRATION ONTO ALKALINE MODIFIED OIL SHALE FLY ASH
- 2014
-
In: Gorûcie slancy. - : Estonian Academy Publishers. - 0208-189X .- 1736-7492. ; 31:1, s. 79-90
-
Journal article (peer-reviewed)abstract
- The present study focuses on the direct chemical adsorption of CO2 onto alkaline hydrothermally activated oil shale fly ash (OSFA). The CO2 chemisorption experiments were conducted in a high-pressure reactor at a temperature of 150 degrees C and CO2 partial pressure of 100 bar during a 24-hour period. Original, activated and chemisorbed OSFA samples were characterized by means of X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) coupled with energy-dispersive X-ray spectroscopy (EDS), specific surface area (BETN2) and high-resolution Si-29 magic angle spinning nuclear magnetic resonance (MAS-NMR). The results indicated moderate weight increase (max 5 wt%) and according to XRD and MAS-NMR analysis tobermorites had reacted with CO2, leading to calcite formation. The results also show that the alkaline hydrothermally activated OSFA has a potential to be used in industrial processes for direct chemical adsorption of CO2 from flue gases.
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| 42. |
- Riittonen, Toni, et al.
(author)
-
Continuous liquid-phase valorization of bio-ethanol towards bio-butanol over metal modified alumina
- 2015
-
In: Renewable energy. - : Elsevier. - 0960-1481 .- 1879-0682. ; 74, s. 369-378
-
Journal article (peer-reviewed)abstract
- Commercial mixed-phase aluminum oxide was used as a heterogeneous catalyst support, providing slightly basic properties which are well-suited for the condensation of bio-ethanol to C-4 hydrocarbons, such as 1-butanol. Different metals (Cu, Ni and Co), at various metal loadings were deposited on the support. Consequently, the catalytic reactions were carried out in a continuous laboratory-scale fixed bed reactor operated at 240 degrees C and 70 bar. The catalysts were characterized by means of XRD, TEM, FT-IR, XPS and ICP-OES. Different metals were found to give entirely different product distributions. With the best catalysts, the selectivities towards 1-butanol close to 70% were reached, while the ethanol conversion typically varied between 10 and 30% - strongly depending on the metal applied. It was observed that low loading of copper and high loading of nickel were responsible for the formation of 1-butanol, whereas cobalt and high loading of copper resulted in the production of ethyl acetate. The reaction was found to be extremely sensitive to catalyst preparation conditions and procedures such as metal loading, calcination/reduction temperature and, thereby, to the formation of corresponding crystallite structure.
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| 43. |
- Riittonen, Toni, et al.
(author)
-
One-pot liquid-phase catalytic conversion of ethanol to 1-butanol over aluminium oxide : the effect of the active metal on the selectivity
- 2012
-
In: Catalysts. - : MDPI. - 2073-4344. ; 2:1, s. 68-84
-
Journal article (peer-reviewed)abstract
- Direct catalytic valorization of bioethanol to 1-butanol over different alumina supported catalysts was studied. Thirteen (13) heterogeneous catalysts were screened in search for the optimal material composition for direct one-pot conversion of ethanol to 1-butanol. For the most promising catalyst, a 25% ethanol conversion with 80% selectivity (among liquid carbon products) to 1-butanol could be reached at 250 °C. Additionally, the reaction kinetics and mechanisms were further investigated upon use of the most suitable catalyst candidate.
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| 44. |
- Salminen, Eero, et al.
(author)
-
Alkaline modifiers as performance boosters in citral hydrogenation over supported ionic liquid catalysts (SILCAs)
- 2012
-
In: Catalysis Today. - : Elsevier. - 0920-5861 .- 1873-4308. ; 196:1, s. 126-131
-
Journal article (peer-reviewed)abstract
- Supported ionic liquid catalysts (SILCAs) consist of nano-scale catalytic species immobilized in an ionic liquid layer which, in turn, is immobilized on a solid support. In this work, novel SILCAs containing various inorganic alkaline modifiers (e.g. potassium hydroxide) were prepared and applied in citral hydrogenation reactions. The supported ionic liquid catalyst systems demonstrated enhanced reaction rates and improved selectivities toward citronellal in citral hydrogenation. With the addition of an alkaline modifier into ionic liquid layer, the catalyst selectivity increased from 16% to 74%. In fact, a highly selective reaction route toward citronellal was accomplished.
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| 45. |
- Samikannu, Ajaikumar, et al.
(author)
-
Effective dispersion of Au and Au-M (M = Co, Ni, Cu and Zn) bimetallic nanoparticles over TiO2 grafted SBA-15 : their catalytic activity on dehydroisomerization of α-pinene
- 2013
-
In: Microporous and Mesoporous Materials. - Amsterdam : Elsevier. - 1387-1811 .- 1873-3093. ; 173, s. 99-111
-
Journal article (peer-reviewed)abstract
- Mesostructured siliceous SBA-15 was synthesized via direct hydrothermal crystallization from acidic solution of poly-(ethylene glycol)-block-poly(propylene glycol)-block poly(ethylene glycol)-copolymer and tetraethyl orthosilicate. The amorphous surface of the calcined Si-SBA-15 was modified with 20wt.% of TiO2 by chemical grafting method using titanium isopropoxide as the titanium source in ethanol solution. Various metal nanoparticles Au, Au-M (M = Co, Ni, Cu and Zn) were supported on TiO2/SBA-15 by deposition-precipitation method (DP) using urea as the precipitating agent. The structural features of the synthesized materials were characterized by various physico-chemical techniques such as X-ray diffraction, nitrogen sorption, XPS and HR-TEM. BET results of Si-SBA-15 revealed the formation of mesoporous structure with an average pore size of 5.9nm, pore volume of 1.12 cm3/g and the specific surface area of 846 m2/g. HR-TEM results demonstrated that metal nanoparticles were highly dispersed over TiO2/SBA-15 and long range ordering of hexagonal mesopores of Si-SBA-15 was well retained after loading of 20 wt.% TiO2 and 3 wt.% of bimetallic nanoparticles. The catalytic performances of the prepared catalysts were studied on dehydroisomerization of α-pinene under gas phase conditions using hydrogen atmosphere. The stability and catalytic activity of Au-M-TiO2/SBA-15 (DP) catalysts upon conversion of α-pinene in to p-cymene was explored in comparison with the catalysts prepared by conventional method. AuNi-TiO2/SBA-15 catalysts prepared via DP method were found to be stable upon longer reaction time as well as superior in terms of conversion and selective towards the formation of p-cymene.
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| 46. |
- Sarkar, Anjana, 1978-, et al.
(author)
-
Photocatalytic activity of TiO2 nanoparticles : effect of thermal annealing under various gaseous atmospheres
- 2012
-
In: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 23:47, s. 475711-475719
-
Journal article (peer-reviewed)abstract
- The structure, composition and photocatalytic activity of TiO2 nanoparticles annealed in various gas atmospheres (N2, NH3 and H2) were studied in this work. The effect of treatment on crystal structure, particle size, chemical composition and optical absorbance were assessed by means of x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy and diffuse optical reflectance/transmittance measurements, respectively. Photocatalytic properties of the materials were evaluated by three different methods: degradation of methyl orange in water, killing of Staphylococcus aureus bacteria and photogeneration of radicals in the presence of 3-carboxy-2,2,5,5-tetramethyl pyrrolidine-1-oxyl (PCA) marker molecules. The results indicate that the correlation between pretreatment and the photocatalytic performance depends on the photocatalytic processes and cannot be generalized.
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| 47. |
- Sarkar, Anjana, et al.
(author)
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Photocatalytic reduction of CO2 with H2O over modified TiO2 nanofibers : Understanding the reduction pathway
- 2016
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In: Nano Reseach. - : Springer Science+Business Media B.V.. - 1998-0124 .- 1998-0000. ; , s. 1-13
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Journal article (peer-reviewed)abstract
- Nanosized metal (Pt or Pd)-decorated TiO2 nanofibers (NFs) were synthesized by a wet impregnation method. CdSe quantum dots (QDs) were then anchored onto the metal-decorated TiO2 NFs. The photocatalytic performance of these catalysts was tested for activation and reduction of CO2 under UV-B light. Gas chromatographic analysis indicated the formation of methanol, formic acid, and methyl formate as the primary products. In the absence of CdSe QDs, Pd-decorated TiO2 NFs were found to exhibit enhanced performance compared to Pt-decorated TiO2 NFs for methanol production. However, in the presence of CdSe, Pt-decorated TiO2 NFs exhibited higher selectivity for methanol, typically producing ∼90 ppmg−1·h−1 methanol. The CO2 photoreduction mechanism is proposed to take place via a hydrogenation pathway from first principles calculations, which complement the experimental observations.
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| 48. |
- Sifontes Herrera, Víctor A, et al.
(author)
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Sugar hydrogenation over a Ru/C catalyst
- 2011
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In: Journal of chemical technology and biotechnology (1986). - : Society of Chemical Industry. - 0268-2575 .- 1097-4660. ; 86:5, s. 658-668
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Journal article (peer-reviewed)abstract
- BACKGROUND: In recent years, exploitation of renewable resources has gained considerable attention. In this respect, polyols derived from the hydrogenation of sugar molecules are versatile molecules with a variety of uses, such as low-caloric sweeteners. The hydrogenation of D-maltose, D-galactose, L-rhamnose and L-arabinose was carried out on a finely dispersed Ru/activated carbon catalyst with the objective of studying the kinetics of the production of the corresponding polyols. The reactions were carried out in a stirred tank reactor at temperatures ranging from 90 to 130 °C and hydrogen pressures from 40 to 60 bar. RESULTS: Sugar conversions up to 100% were achieved. Some by-product formation affecting the quality of the selectivity was also observed at elevated operating conditions. The catalyst was characterized by scanning electron microcopy (SEM), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectrometry (ICP-OES) and nitrogen physisorption. Kinetic models based on the Langmuir Hinshelwood assumptions were proposed for the reactions and a nonlinear regression was performed to obtain the numerical values of the kinetic parameters. CONCLUSIONS: The kinetic models predicted well the sugar hydrogenation process and the kinetic parameters were established. The model can be used to predict the behaviour of batchwise operating slurry reactors. Copyright © 2011 Society of Chemical Industry
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| 49. |
- Simakova, Olga A, et al.
(author)
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Linoleic acid isomerization over mesoporous carbon supported gold catalysts
- 2010
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In: Catalysis Today. - : Elsevier B.V.. - 0920-5861 .- 1873-4308. ; 150:1-2, s. 32-6
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Journal article (peer-reviewed)abstract
- Gold catalyst supported on mesoporous carbon and silica were synthesized, characterized by TEM, XRD, XPS and tested in linoleic acid isomerization. Nature of the support affects the selectivity towards isomerization in relation to unwanted hydrogenation. In particular carbon support allowed much higher selectivity in double bond migration compared to silica. Effect of carbon surface oxidative pre-treatment on selectivity of catalyst was investigated.
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| 50. |
- Sterchele, Stefano, et al.
(author)
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Influence of Metal Precursors and Reduction Protocols on the Chloride-Free Preparation of Catalysts for the Direct Synthesis of Hydrogen Peroxide without Selectivity Enhancers
- 2016
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In: ChemCatChem. - : John Wiley & Sons. - 1867-3880 .- 1867-3899. ; 8:8, s. 1564-1574
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Journal article (peer-reviewed)abstract
- Different metal precursors and reducing agents were applied in the preparation of 1 wt % Pd catalysts supported on commercial ion-exchange resin (Lewatit K2621) and used in the direct synthesis of H2O2. The catalysts were characterized by using TEM and their performance was evaluated in the direct synthesis of H2O2 (in a batch and semi-batch reactor) to investigate the relationship between the catalyst preparation methods, morphology, and catalytic performance. As expected, both the choice of the Pd precursor and the reduction conditions had a strong influence on the size and size distribution of the resulting supported nanostructured metal nanoparticles and, consequently, on the catalytic performance. The best combination of metal precursor and reduction agent was [Pd(NH3)4]SO4 reduced with hydrogen. This catalyst had the largest average size of the Pd nanoparticles and the broadest size distribution.
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