Carbon Materials and Technology
Debashis Chakraborty; Sourav Singha Roy; Sriparna Sarkar
Abstract
The production of aliphatic polyesters (via ROP of cyclic esters) and aliphatic polycarbonates (via ROCOP of CO2/epoxide) is an important synthetic pathway for the production of biodegradable and biocompatible polymers. The study focuses on the catalytic activity and selectivity of phenoxy-imine based ...
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The production of aliphatic polyesters (via ROP of cyclic esters) and aliphatic polycarbonates (via ROCOP of CO2/epoxide) is an important synthetic pathway for the production of biodegradable and biocompatible polymers. The study focuses on the catalytic activity and selectivity of phenoxy-imine based zinc compounds for the ROP of cyclic esters (rac-LA and -CL) and ROCOP of carbon dioxide and CHO/PO. The monoligated and bisligated zinc compounds have the same coordination number (four) but differed from each other in the binding mode of the ligand to the metal center (tridentate for monoligated and bidentate for bisligated compounds) and thus the compounds adopt different symmetry. For the ROP of rac-LA, the monoligated zinc compounds gave isotactic-enriched PLA while the bisligated zinc compounds gave heterotactic-enriched PLA. For the ROCOP of epoxide/CO2, isotactic-enriched polycarbonates were obtained with a notable difference in catalytic activity with the variation of the number of ligands attached to the zinc center. In addition, a correlation is established between the percentage of carbonate linkage in the polycarbonate chain and the substituent attached to the phenolate core.
Composite Materials
Elguja Kutelia; Kusman Dossumov; Gaukhar Yergasiyeva; David Gventsadze; Nikoloz Jalabadze; Teimuraz Dzigrashvili; Lili Nadaraia; Olga Tsurtsumia; Manshuk Mambetova
Abstract
This study first demonstrated the possibility of the production of catalyst supports in the form of granules and tablets composed of nanoparticles of Fe atom cluster-doped CNTs using mini-mold forming and spark plasma sintering (SPS) techniques respectively. The pilot samples of the novel catalyst system ...
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This study first demonstrated the possibility of the production of catalyst supports in the form of granules and tablets composed of nanoparticles of Fe atom cluster-doped CNTs using mini-mold forming and spark plasma sintering (SPS) techniques respectively. The pilot samples of the novel catalyst system containing 3% NiO active phase, synthesized on the granulated Fe cluster-doped CNTs carrier, were tested to determine their catalytic activity and coking resistance in the DRM reaction, in a wide range of temperatures up to 900oC. The developed novel catalyst systems’ samples were characterized before and after the catalyst reaction using SEM, EDX, XRD, and AES methods. It is shown that the temperature dependence of the catalytic activity of the 3% NiO catalyst, supported on the granulated Fe cluster-doped CNTs carrier, revealed two characteristic temperature ranges with different rates of efficiency. Particularly, at high reaction temperatures, starting from 700oC, the conversion rates of methane and carbon dioxide (42.4% and 45.6% respectively) have more than doubled at 850oC. Starting from 850oC to 900oC the latter tends to exceed the carbon dioxide conversion rate, and at 900oC it amounts to 95%.
Carbon Materials and Technology
Zacharias Fthenakis; Antonios Fountoulakis; Ioannis Petsalakis; Nektarios Lathiotakis
Abstract
This work is part of a systematic study on the energy barriers for the permeation of several molecules, like He, H2, CO, CO2, H2O, NH3, CH4 etc, through nanoporous single layer graphene, having pores with different shape, size, and type. In the present work, we focus on the permeation of CO2 through ...
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This work is part of a systematic study on the energy barriers for the permeation of several molecules, like He, H2, CO, CO2, H2O, NH3, CH4 etc, through nanoporous single layer graphene, having pores with different shape, size, and type. In the present work, we focus on the permeation of CO2 through graphene pores which are constructed when neighboring carbon atoms of the graphene layer are removed from the structure, and nitrogen atoms have replaced the carbon atoms in the boundary of the pore. The energy barriers for each different pore are calculated using 2 different ReaxFF potentials along a path which the molecule would ideally follow in order to pass from the one side of the membrane to the other through the pore. Using the calculated values of the energy barriers, we estimate permeances by employing the kinetic theory of gasses. We give estimates for the preferable sizes and structures of the pores for permeability and demonstrate the ability of nanoporous graphene for CO2 separation.
Carbon Materials and Technology
Sung Yong Kim; Megha Chitranshi; Anuptha Pujari; Vianessa Ng; Ashley Kubley; Ronald Hudepohl; Vesselin Shanov; Devanathan Anantharaman; Daniel Chen; Devika Chauhan; Mark Schulz
Abstract
This paper addresses the design of a reactor system for manufacturing carbon nanotube (CNT) fabric and carbon hybrid materials (CHM). A web or sock of CNT is formed in a reactor tube in the gas phase pyrolysis method. The sock exits the reactor tube and is wound layer by layer onto a drum to directly ...
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This paper addresses the design of a reactor system for manufacturing carbon nanotube (CNT) fabric and carbon hybrid materials (CHM). A web or sock of CNT is formed in a reactor tube in the gas phase pyrolysis method. The sock exits the reactor tube and is wound layer by layer onto a drum to directly form a nonwoven fabric. Metal nanoparticles and continuous microfibers can be integrated into the synthesis process to form CHM. Continuous direct manufacturing of fabric is an advantage of the method. However, the reliability of this manufacturing process in our particular reactor system is affected by several problems. These include occasional breaking of the sock, the need for daily cleaning of the ceramic reactor tube due to carbon deposits on the inside, sagging/bending of the reactor tube, and safety in handling the hydrogen gas produced from the reaction. Possible solutions to the problems are proposed. The importance of this research is that no other bulk material has the combination of properties of CNT hybrid fabric. If the properties can be further improved and customized, and if manufacturing of the material can be scaled-up at reasonable cost, many new commercial applications for nanotube custom materials could open up.
Nanomaterials & Nanotechnology
Carsten Strobel; Carlos Chavarin; Sebastian Leszczynski; Karola Richter; Martin Knaut; Johanna Reif; Sandra Voelkel; Matthias Albert; Christian Wenger; Johann Wolfgang Bartha; Thomas Mikolajick
Abstract
A new kind of transistor device with a graphene monolayer embedded between two n-type silicon layers is fabricated and characterized. The device is called graphene-base heterojunction transistor (GBHT). The base-voltage controls the current of the device flowing from the emitter via graphene to the collector. ...
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A new kind of transistor device with a graphene monolayer embedded between two n-type silicon layers is fabricated and characterized. The device is called graphene-base heterojunction transistor (GBHT). The base-voltage controls the current of the device flowing from the emitter via graphene to the collector. The transit time for electrons passing by the ultrathin graphene layer is extremely short which makes the device very promising for high frequency RF-electronics. The output current of the device is saturated and clearly modulated by the base voltage. Further, the silicon collector of the GBHT is replaced by germanium to improve the device performance. This enabled the collector current to be increased by almost three orders of magnitude. Also, the common-emitter current gain (Ic/Ib) increased from 10-3 to approximately 0.3 for the newly designed device. However, the ON-OFF ratio of the improved germanium based GBHT has so far been rather low. Further optimizations are necessary in order to fully exploit the potential of the graphene-base heterojunction transistor.
Carbon Materials and Technology
Sung Yong Kim; Megha Chitranshi; Anuptha Pujari; Vianessa Ng; Ashley Kubley; Ronald Hudepohl; Vesselin Shanov; Devanathan Anantharaman; Daniel Chen; Devika Chauhan; Mark Schulz
Abstract
The overall hypothesis for this paper is that accurately tuning the gas phase pyrolysis synthesis process and using appropriate raw materials will enable manufacturing different types of carbon hybrid materials (CHM). Optimizing multiple variables including particle melting and vaporization temperatures, ...
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The overall hypothesis for this paper is that accurately tuning the gas phase pyrolysis synthesis process and using appropriate raw materials will enable manufacturing different types of carbon hybrid materials (CHM). Optimizing multiple variables including particle melting and vaporization temperatures, fuel flow rate, gas flow rates, gas velocity, and sock wind-up speed is needed to achieve reliability of the synthesis process. Results from our specific reactor are presented to show how the process variables interact and how they affect CNT sock yield and stability. Metal nanoparticle (NP) injection enables the formation of hybrid materials. Several types of CHM materials created by incorporating different types of NPs into the carbon nanotube (CNT) synthesis process and CNT sock are discussed. Many possible combinations of metal NPs can be used in the process to customize the properties of CHM. However, it is a complex problem to determine what metal compounds can chemically join with CNT. Some of the first results testing the new CHM process are presented in this paper.
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