19 research outputs found
Graphene: Microwave Enabled One‐Pot, One‐Step Fabrication and Nitrogen Doping of Holey Graphene Oxide for Catalytic Applications (Small 27/2015)
No full textPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/112226/1/smll201570159.pd
Direct Production of Graphene Nanosheets for Near Infrared Photoacoustic Imaging.
No full textHummers method is commonly used for the fabrication of graphene oxide (GO) from graphite particles. The oxidation process also leads to the cutting of graphene sheets into small pieces. From a thermodynamic perspective, it seems improbable that the aggressive, somewhat random oxidative cutting process could directly result in graphene nanosheets without destroying the intrinsic π-conjugated structures and the associated exotic properties of graphene. In Hummers method, both KMnO4 and NO2þ (nitronium ions) in concentrated H2SO4 solutions act as oxidants via different oxidation mechanisms. From both experimental observations and theoretical calculations, it appears that KMnO4 plays a major role in the observed oxidative cutting and unzipping processes. We find that KMnO4 also limits nitronium oxidative etching of graphene basal planes, therefore slowing down graphene fracturing processes for nanosheet fabrication. By intentionally excluding KMnO4 and exploiting pure nitronium ion oxidation, aided by the unique thermal and kinetic effects induced by microwave heating, we find that graphite particles can be converted into graphene nanosheets with their π-conjugated aromatic structures and properties largely retained. Without the need of any postreduction processes to remove the high concentration of oxygenated groups that results from Hummers GO formation, the graphene nanosheets as-fabricated exhibit strong absorption, which is nearly wavelength-independent in the visible and near-infrared (NIR) regions, an optical property typical for intrinsic graphene sheets. For the first time, we demonstrate that strong photoacoustic signals can be generated from these graphene nanosheets with NIR excitation. The photo-to-acoustic conversion is weakly dependent on the wavelength of the NIR excitation, which is different from all other NIR photoacoustic contrast agents previously reported.This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in ACS Nano, copyright © American Chemical Society after peer review. To access the final edited and published work see https://dx.doi.org/10.1021/nn403429v
P-Doped Porous Carbon as Metal Free Catalysts for Selective Aerobic Oxidation with an Unexpected Mechanism
No full textAn extremely simple and rapid (seconds) approach is reported to directly synthesize gram quantities of P-doped graphitic porous carbon materials with controlled P bond configuration. For the first time, it is demonstrated that the P-doped carbon materials can be used as a selective metal free catalyst for aerobic oxidation reactions. The work function of P-doped carbon materials, its connectivity to the P bond configuration, and the correlation with its catalytic efficiency are studied and established. In direct contrast to N-doped graphene, the P-doped carbon materials with higher work function show high activity in catalytic aerobic oxidation. The selectivity trend for the electron donating and withdrawing properties of the functional groups attached to the aromatic ring of benzylic alcohols is also different from other metal free carbon based catalysts. A unique catalytic mechanism is demonstrated, which differs from both GO and N-doped graphene obtained by high temperature nitrification. The unique and unexpected catalytic pathway endows the P-doped materials with not only good catalytic efficiency but also recyclability. This, combined with a rapid, energy saving approach that permits fabrication on a large scale, suggests that the P-doped porous materials are promising materials for “green catalysis” due to their higher theoretical surface area, sustainability, environmental friendliness and low cost.This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Nano, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/acsnano.5b07054.Peer reviewe
Microwave enabled synthesis of carbon based materials with controlled structures: applications from multifunctional drug delivery to metal free catalysis
No full textGraphene is a single-layered sheet of sp2- bonded carbon atoms arranged in a honeycomb structure, whose discovery won the 2010 Nobel Prize in physics. Due to its excellent electronic, optical, thermal and mechanical properties, and its large surface area and low mass, graphene holds great potential for a broad range of applications. It seems that the research in graphene has now proceeded from the initial phase of developing myriad strategies for the synthesis of graphene sheets to the use of graphene in various research fields. However, it is still challenging to controllably produce solution processable highly conductive graphene sheets in large quantity, at low cost, and energy saving process, with optimal sheet size, layer thickness, defects (vacancies and holes) and molecular structures (oxygen-containing groups and non-defective graphene domains). All these structural parameters determine their electronic, thermal and mechanical properties of graphene, which are key warrants for their practical application in various devices. As examples, fundamental studies and high-frequency electronics require pristine graphene. However, "bulk" applications such as flexible macro-electronics, and mechanically and electronically reinforced composites, require large quantities of solution-processable highly conductive large graphene sheets manufactured at low cost. On the other hand, holey graphene, referring to graphene with nanoholes in their basal plane, demonstrates much better performance in their application as metal-free catalysts and in energy storage. Finally, there is a surge of interests in nanosized graphene sheets for various biological applications due to their unique size effects, edge effects, and even quantum confinement effects. As one part of this thesis, we have demonstrated that by understanding the oxidation mechanism of nitronium ions and KMnO4, which were both used in the widely used Hummers method for fabrication of graphene oxides, we developed various microwave chemistries for rapid (30-40 seconds) and controllable fabrication of graphene with controlled lateral sizes, holey structures, and oxidation levels. As examples, by intentionally excluding KMnO4 in the reaction system while controlling the concentration of nitronium ions and microwave irradiation power and time, we can rapidly and directly fabricate graphene nanosheets with uniform lateral sizes. The as-fabricated graphene nanosheets largely retain the intrinsic properties of graphene. These nanosheets exhibit strong and wavelength-independent absorption in NIR regions, which ensures their applications in Near-Infrared (NIR) photoacoustic imaging, photothermal treatment, and multifunctional drug delivery. On the other hand, by including KMnO4 in the recipe and still taking advantage of the unique thermal and kinetic effects of microwave heating, we developed approaches to directly fabricate micrometer sized graphene oxide with controlled holey structures. Taking one step further; we have also developed microwave chemistry to dope these graphene oxide sheets with/without holes in their basal planes with N controllable bond configurations. We have shown that the N-doping and holey structure of graphene is important for their excellent electrochemical catalytic performance in oxygen reduction reaction (ORR). In the drive towards green and sustainable chemistry, there is an ever-increasing interest in developing the heteroatom-doped carbon-based catalysts to replace the metal-based catalysts for organic reactions. Compared to ORR, studies that use doped and/or co-doped carbon materials as catalysts for selective organic synthesis is in the early stages of development. This might be due to lack of systematic studies about how the electronic and geometrical structures, surface functionalities, and therefore, the interface properties of graphene-based materials determine their catalytic performance. Also lacking is the inability to synthesize these doped carbon catalysts in bulk quantity with simple and cost effective approaches. In the second part of this dissertation, we have reported extremely simple and rapid (seconds) approaches to directly synthesize gram quantities of single or multiple heteroatom-doped graphitic porous carbon materials from abundant and cheap biomass molecules (inositol or phytic acid) with controlled doping configuration. The porous structure of the catalyst is beneficial for efficient mass transport and dramatically increases edges and surface area, and therefore creates more accessible catalytic centers. Furthermore, we have also explored the catalytic center of these heteroatom-doped carbon catalysts (especially phosphorus-doped and phosphorus, sulfur-codoped) to gain a fundamental understanding of how the heteroatom (P and S) configuration affect the catalytic properties of carbon material in ORR and industry oxidation reactions, such as benzyl alcohol oxidation. This fundamental understanding will help us to design more efficient heteroatom-doped carbon catalysts.Ph.D.Includes bibliographical referencesby Mehulkumar Pate
Localized current activated sintering of titanium nickelides
No full textIncludes bibliographical references (p. 88-93).This research thesis discusses the processing of 50 at. % Ni-Ti elemental powders through Ball Milling (a Mechanical Alloying process) route and locally sintering of titanium nickelides via Current-Activated Tip-based Sintering (CATS), a novel sintering process. CATS process facilitates much higher current densities than any conventionally available sintering process, which can bolster rapid sintering and intermetallic phase transformation rates. For the first time CATS was employed to tip-sinter equi-atomic mechanically alloyed Ni-Ti powder system at varying current intensities (50 A -- 100 A) and cumulative current exposure time (1 second -- 100 seconds). The effect of current and sintering time conditions on the evolution of the locally sintered Ni-Ti microstructure and its properties are discussed. Harder Ti2Ni phase shows significant effect on NiTi mechanical properties (i.e. micro-hardness). With increasing current exposure time at constant current intensities shows an enhancement in the sintered process zone. It was discovered that current intensity, cumulative exposure time and distance from the tip/material interface have direct implication to degree of sintering, intermetallic phase transformations, and microstructural properties of titanium nickelides. This research studies displays the full/near full densification of titanium nickelides in extraordinary short times at locations exposed to exceptional ultra-high current densities
Hyperloop Network Design: The Swiss Case
No full textPrevious studies on Hyperloop network design, do not show any application of detailed network design process. The current study focuses on network design of Hyperloop considering the case of Switzerland. The study estimates the costs from the literature and estimates demand of network from the Swiss National Passenger Transport Model. These estimates along with a few fixed stations are considered as inputs for the network design process. The overall sequential network design process is performed in three phases i.e. (i) Network Generation (ii) Route Design & Frequency Setting (iii) Assignment. Output generated from each of the phases has been used as an input for the subsequent phase. The network generation phase develops the structure of the network, while the route design phase defines the lines and respective frequencies. The network design is also evaluated with the help of Cost-Benefit Analysis (CBA) in accordance with Swiss CBA norms. The findings show that the overall process develops positive results with respect benefit to cost ratio. The sensitivity analysis is also performed with all the phases of network design including cost-benefit analysis. The results show a linear relation of benefit to cost ratio with each cost, value of time and discount rate.Civil Engineering | Transport and Plannin
A Review of Internal Combustion Engine Design
No full textThe most successful inventions of human includes internal combustion engine (I C Engine) as top of the list. The recent emphasis on fuel economy, pollution control and other automobile fields like low friction body profile has also stimulated theoretical searches for an automobile. Studies have found no alternative type that promises to have significant advantages in fuel economy or pollution control than conventional I C Engines. But from these studies, it appears that the conventional types of spark-ignition and Diesel engines will remain in their present predominant position in land and sea transportation and for industrial and portable power for the foreseeable future. And so, here is an approach to have combined design aspects for all basic I C Engine components in one paper. Design aspects includes components like, piston, piston rings, cylinder, cylinder head, connecting rod, crank and crank shaft, cam and cam shaft along with valve and valve gear mechanism. A paper can be the base for future detailed designing work of I C Engine along with stress analysis and simulation
A Review of Palm Oil Biodiesel under Long-Term Storage Conditions
No full textPalm-oil biodiesel is widely used as alternative to diesel; the influences of long-term oxidative degradation on its burning characteristics are a matter of some concern. To further our understanding of this issue, this study investigated the heat release, carbon residue, flash point, and cetane index, oxidative stability, Density, Viscosity, Total acid no. of palm-oil biodiesel in a constant-temperature water bath after long-term storage.
DOI: 10.17762/ijritcc2321-8169.15016
Phthalocyanine-loaded graphene nanoplatform for imaging-guided combinatorial phototherapy
No full textOlena Taratula,1 Mehulkumar Patel,2 Canan Schumann,1 Michael A Naleway,1 Addison J Pang,1 Huixin He,2 Oleh Taratula1 1Department of Pharmaceutical Sciences, College of Pharmacy, Oregon State University, Portland, OR, USA; 2Department of Chemistry, Rutgers University-Newark, Newark, NJ, USA Abstract: We report a novel cancer-targeted nanomedicine platform for imaging and prospect for future treatment of unresected ovarian cancer tumors by intraoperative multimodal phototherapy. To develop the required theranostic system, novel low-oxygen graphene nanosheets were chemically modified with polypropylenimine dendrimers loaded with phthalocyanine (Pc) as a photosensitizer. Such a molecular design prevents fluorescence quenching of the Pc by graphene nanosheets, providing the possibility of fluorescence imaging. Furthermore, the developed nanoplatform was conjugated with poly(ethylene glycol), to improve biocompatibility, and with luteinizing hormone-releasing hormone (LHRH) peptide, for tumor-targeted delivery. Notably, a low-power near-infrared (NIR) irradiation of single wavelength was used for both heat generation by the graphene nanosheets (photothermal therapy [PTT]) and for reactive oxygen species (ROS)-production by Pc (photodynamic therapy [PDT]). The combinatorial phototherapy resulted in an enhanced destruction of ovarian cancer cells, with a killing efficacy of 90%–95% at low Pc and low-oxygen graphene dosages, presumably conferring cytotoxicity to the synergistic effects of generated ROS and mild hyperthermia. An animal study confirmed that Pc loaded into the nanoplatform can be employed as a NIR fluorescence agent for imaging-guided drug delivery. Hence, the newly developed Pc-graphene nanoplatform has the significant potential as an effective NIR theranostic probe for imaging and combinatorial phototherapy. Keywords: graphene nanosheets, phthalocyanine, photothermal therapy, photodynamic therapy, theranostic 
