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1.  Stretchable and Flexible High-Strain Sensors Made Using Carbon Nanotubes and Graphite Films on Natural Rubber 
Sensors (Basel, Switzerland)  2014;14(1):868-876.
Conventional metallic strain sensors are flexible, but they can sustain maximum strains of only ∼5%, so there is a need for sensors that can bear high strains for multifunctional applications. In this study, we report stretchable and flexible high-strain sensors that consist of entangled and randomly distributed multiwall carbon nanotubes or graphite flakes on a natural rubber substrate. Carbon nanotubes/graphite flakes were sandwiched in natural rubber to produce these high-strain sensors. Using field emission scanning electron microscopy, the morphology of the films for both the carbon nanotube and graphite sensors were assessed under different strain conditions (0% and 400% strain). As the strain was increased, the films fractured, resulting in an increase in the electrical resistance of the sensor; this change was reversible. Strains of up to 246% (graphite sensor) and 620% (carbon nanotube sensor) were measured; these values are respectively ∼50 and ∼120 times greater than those of conventional metallic strain sensors.
PMCID: PMC3926590  PMID: 24399158
piezoresistive sensor; soft wearable sensors; electro-mechanical properties; film composite; stretchable device; carbon nanotubes; health monitoring
2.  A Versatile High-Permittivity Phantom for EIT 
Phantoms are frequently used in medical imaging systems to test hardware, reconstruction algorithms, and the interpretation of data. This report describes and characterizes the use of powdered graphite as a means of adding a significant reactive component or permittivity to useful phantom media for electrical impedance imaging. The phantom materials produced have usable complex admittivity at the electrical impedance tomography (EIT) frequencies from a few kilohertz to 1 MHz, as measured by our EIT system (ACT4) and by a commercial bioimpedance analyzer (BIS 4000, Xitron). We have also studied a commercial ultrasound coupling gel, which is highly electrically conductive and semisolid but that permits objects to move within it. The mixture of agar–graphite and gel–graphite, increases in permittivity and conductivity are proportional to the graphite concentration. We also report the use of a porous polymer membrane to simulate skin. A thin layer of this membrane increased resistance and the characteristic frequency of the phantoms, providing a promising candidate to simulate the effect of skin and the layered structure of a breast or other anatomical structure. The graphite also provides a realistic level of “speckle” in ultrasound images of the phantom, which may be useful in developing dual-mode imaging systems with ultrasound and the EIT.
PMCID: PMC2769077  PMID: 18990630
Electrical impedance tomography (EIT); graphite powder; high-permittivity phantom; porous polymer
3.  Capacity fade in Sn–C nanopowder anodes due to fracture 
Journal of Power Sources  2012;197(2):246-252.
► Detailed microscopy was performed on Sn/C anodes before and after cycling. ► Significant fracture of the Sn was observed during cycling. ► The Sn volume average and surface area must be low to prevent fracture.
Sn based anodes allow for high initial capacities, which however cannot be retained due to the severe mechanical damage that occurs during Li-insertion and de-insertion. To better understand the fracture process during electrochemical cycling three different nanopowders comprised of Sn particles attached on artificial graphite, natural graphite or micro-carbon microbeads were examined. Although an initial capacity of 700 mAh g−1 was obtained for all Sn–C nanopowders, a significant capacity fade took place with continuous electrochemical cycling. The microstructural changes in the electrodes corresponding to the changes in electrochemical behavior were studied by transmission and scanning electron microscopy. The fragmentation of Sn observed by microscopy correlates with the capacity fade, but this fragmentation and capacity fade can be controlled by controlling the initial microstructure. It was found that there is a dependence of the capacity fade on the Sn particle volume and surface area fraction of Sn on carbon.
PMCID: PMC3208070  PMID: 22241941
Sn–C; Anodes; Nanostructured; Fracture
4.  X-ray absorption spectroscopy by full-field X-ray microscopy of a thin graphite flake: Imaging and electronic structure via the carbon K-edge 
We demonstrate that near-edge X-ray-absorption fine-structure spectra combined with full-field transmission X-ray microscopy can be used to study the electronic structure of graphite flakes consisting of a few graphene layers. The flake was produced by exfoliation using sodium cholate and then isolated by means of density-gradient ultracentrifugation. An image sequence around the carbon K-edge, analyzed by using reference spectra for the in-plane and out-of-plane regions of the sample, is used to map and spectrally characterize the flat and folded regions of the flake. Additional spectral features in both π and σ regions are observed, which may be related to the presence of topological defects. Doping by metal impurities that were present in the original exfoliated graphite is indicated by the presence of a pre-edge signal at 284.2 eV.
PMCID: PMC3388357  PMID: 23016137
carbon; graphene; nanostructure; NEXAFS; X-ray microscopy
5.  Effect of Graphite Concentration on Shear-Wave Speed in Gelatin-Based Tissue-Mimicking Phantoms 
Ultrasonic imaging  2011;33(2):134-142.
Elasticity-based imaging modalities are becoming popular diagnostic tools in clinical practice. Gelatin-based, tissue mimicking phantoms that contain graphite as the acoustic scattering material are commonly used in testing and validating elasticity-imaging methods to quantify tissue stiffness. The gelatin bloom strength and concentration are used to control phantom stiffness. While it is known that graphite concentration can be modulated to control acoustic attenuation, the impact of graphite concentrationon phantom elasticity has not been characterized in these gelatin phantoms. This work investigates the impact of graphite concentration on phantom shear stiffness as characterized by shear-wave speed measurements using impulsive acoustic-radiation-force excitations. Phantom shear-wave speed increased by 0.83 (m/s)/(dB/(cm MHz)) when increasing the attenuation coefficient slope of the phantom material through increasing graphite concentration. Therefore, gelatin-phantom stiffness can be affected by the conventional ways that attenuation is modulated through graphite concentration in these phantoms.
PMCID: PMC3128385  PMID: 21710828
Acoustic radiation force; ARFI; attenuation coefficient slope; elasticity; graphite; phantom; shear wave; stiffness
6.  Quality of Graphite Target for Biological/Biomedical/Environmental Applications of 14C-Accelerator Mass Spectrometry 
Analytical Chemistry  2010;82(6):2243-2252.
Catalytic graphitization for 14C-accelerator mass spectrometry (14C-AMS) produced various forms of elemental carbon. Our high-throughput Zn reduction method (C/Fe = 1:5, 500 °C, 3 h) produced the AMS target of graphite-coated iron powder (GCIP), a mix of nongraphitic carbon and Fe3C. Crystallinity of the AMS targets of GCIP (nongraphitic carbon) was increased to turbostratic carbon by raising the C/Fe ratio from 1:5 to 1:1 and the graphitization temperature from 500 to 585 °C. The AMS target of GCIP containing turbostratic carbon had a large isotopic fractionation and a low AMS ion current. The AMS target of GCIP containing turbostratic carbon also yielded less accurate/precise 14C-AMS measurements because of the lower graphitization yield and lower thermal conductivity that were caused by the higher C/Fe ratio of 1:1. On the other hand, the AMS target of GCIP containing nongraphitic carbon had higher graphitization yield and better thermal conductivity over the AMS target of GCIP containing turbostratic carbon due to optimal surface area provided by the iron powder. Finally, graphitization yield and thermal conductivity were stronger determinants (over graphite crystallinity) for accurate/precise/high-throughput biological, biomedical, and environmental14C-AMS applications such as absorption, distribution, metabolism, elimination (ADME), and physiologically based pharmacokinetics (PBPK) of nutrients, drugs, phytochemicals, and environmental chemicals.
PMCID: PMC2837469  PMID: 20163100
7.  High-yield Synthesis of Multiwalled Carbon Nanotube by Mechanothermal Method 
Nanoscale Research Letters  2009;4(4):296-302.
This study reports on the mechanothermal synthesis of multiwalled carbon nanotube (MWCNTs) from elemental graphite powder. Initially, high ultra-active graphite powder can be obtained by mechanical milling under argon atmosphere. Finally, the mechanical activation product is heat-treated at 1350°C for 2–4 h under argon gas flow. After heat-treatment, active graphite powders were successfully changed into MWCNTs with high purity. The XRD analyses showed that in the duration 150 h of milling, all the raw materials were changed to the desired materials. From the broadening of the diffraction lines in the XRD patterns, it was concluded that the graphite crystallites were nanosized, and raising the milling duration resulted in the fineness of the particles and the increase of the strain. The structure and morphology of MWCNTs were investigated using scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The yield of MWCNTs was estimated through SEM and TEM observations of the as-prepared samples was to be about 90%. Indeed, mechanothermal method is of interest for fundamental understanding and improvement of commercial synthesis of carbon nanotubes (CNTs). As a matter of fact, the method of mechanothermal guarantees the production of MWCNTs suitable for different applications.
PMCID: PMC2893906  PMID: 20596448
Carbon nanotubes; Mechanothermal; Nanotechnology; Advanced materials; Outstanding structure
8.  High-yield Synthesis of Multiwalled Carbon Nanotube by Mechanothermal Method 
Nanoscale Research Letters  2009;4(4):296-302.
This study reports on the mechanothermal synthesis of multiwalled carbon nanotube (MWCNTs) from elemental graphite powder. Initially, high ultra-active graphite powder can be obtained by mechanical milling under argon atmosphere. Finally, the mechanical activation product is heat-treated at 1350°C for 2–4 h under argon gas flow. After heat-treatment, active graphite powders were successfully changed into MWCNTs with high purity. The XRD analyses showed that in the duration 150 h of milling, all the raw materials were changed to the desired materials. From the broadening of the diffraction lines in the XRD patterns, it was concluded that the graphite crystallites were nanosized, and raising the milling duration resulted in the fineness of the particles and the increase of the strain. The structure and morphology of MWCNTs were investigated using scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The yield of MWCNTs was estimated through SEM and TEM observations of the as-prepared samples was to be about 90%. Indeed, mechanothermal method is of interest for fundamental understanding and improvement of commercial synthesis of carbon nanotubes (CNTs). As a matter of fact, the method of mechanothermal guarantees the production of MWCNTs suitable for different applications.
PMCID: PMC2893906  PMID: 20596448
Carbon nanotubes; Mechanothermal; Nanotechnology; Advanced materials; Outstanding structure
9.  The microwave-assisted ionic liquid nanocomposite synthesis: platinum nanoparticles on graphene and the application on hydrogenation of styrene 
Nanoscale Research Letters  2013;8(1):414.
The microwave-assisted nanocomposite synthesis of metal nanoparticles on graphene or graphite oxide was introduced in this research. With microwave assistance, the Pt nanoparticles on graphene/graphite oxide were successfully produced in the ionic liquid of 2-hydroxyethanaminium formate [HOCH2CH2NH3][HCO2]. On graphene/graphite oxide, the sizes of Pt nanoparticles were about 5 to 30 nm from transmitted electron microscopy (TEM) results. The crystalline Pt structures were examined by X-ray diffraction (XRD). Since hydrogenation of styrene is one of the important well-known chemical reactions, herein, we demonstrated then the catalytic hydrogenation capability of the Pt nanoparticles on graphene/graphite oxide for the nanocomposite to compare with that of the commercial catalysts (Pt/C and Pd/C, 10 wt.% metal catalysts on activated carbon from Strem chemicals, Inc.). The conversions with the Pt nanoparticles on graphene are >99% from styrene to ethyl benzene at 100°C and under 140 psi H2 atmosphere. However, ethyl cyclohexane could be found as a side product at 100°C and under 1,520 psi H2 atmosphere utilizing the same nanocomposite catalyst.
PMCID: PMC3854513  PMID: 24103100
Graphene; Pt nanoparticle; Ionic liquid; Microwave; Hydrogenation of styrene
10.  Role of Peroxide Ions in Formation of Graphene Nanosheets by Electrochemical Exfoliation of Graphite 
Scientific Reports  2014;4:4237.
This study demonstrates a facile, mild and environmentally-friendly sustainable (soft processing) approach for the efficient electrochemical exfoliation of graphite using a sodium hydroxide/hydrogen peroxide/water (NaOH/H2O2/H2O) system that can produce high-quality, anodic few-layer graphene nanosheets in 95% yield at ambient reaction conditions. The control experiment conducted using NaOH/H2O revealed the crucial role of H2O2 in the exfoliation of graphite. A possible exfoliation mechanism is proposed. The reaction of H2O2 with hydroxyl ions (HO−) leads to the formation of highly nucleophilic peroxide ions (O22−), which play a crucial role in the exfoliation of graphite via electrochemical-potential-assisted intercalation and strong expansion of graphite sheets.
PMCID: PMC3937785  PMID: 24577336
11.  High yield production and purification of few layer graphene by Gum Arabic assisted physical sonication 
Scientific Reports  2013;3:1378.
Exploiting the emulsification properties of low cost, environmentally safe Gum Arabic we demonstrate a high yield process to produce a few layer graphene with a low defect ratio, maintaining the pristine graphite structure. In addition, we demonstrate the need for and efficacy of an acid hydrolysis treatment to remove the polymer residues to produce 100% pure graphene. The scalable process gives yield of up to 5 wt% graphene based on 10 g starting graphite. The graphene product is compared with reduced graphene oxide produced through Hummer's method using UV-visible spectroscopy, SEM, TEM, and Raman spectroscopy. The two graphene materials show significant difference in these characterizations. Further, the film fabricated from this graphene exhibits 20 times higher electrical conductivity than that of the reduced graphene oxide. Sonication processing of graphite with environmentally approved biopolymers such as Gum Arabic opens up a scalable avenue for production of cheap graphene.
PMCID: PMC3594761  PMID: 23478744
12.  A nano-graphite cold cathode for an energy-efficient cathodoluminescent light source 
The development of new types of light sources is necessary in order to meet the growing demands of consumers and to ensure an efficient use of energy. The cathodoluminescence process is still under-exploited for light generation because of the lack of cathodes suitable for the energy-efficient production of electron beams and appropriate phosphor materials. In this paper we propose a nano-graphite film material as a highly efficient cold cathode, which is able to produce high intensity electron beams without energy consumption. The nano-graphite film material was produced by using chemical vapor deposition techniques. Prototypes of cathodoluminescent lamp devices with a construction optimized for the usage of nano-graphite cold cathodes were developed, manufactured and tested. The results indicate prospective advantages of this type of lamp and the possibility to provide advanced power efficiency as well as enhanced spectral and other characteristics.
PMCID: PMC3778399  PMID: 24062975
cathodoluminescence; electron field emission; light source; nano-graphite; vacuum electronics
13.  Acquisition and analysis of GFAAS data 
Since its inception as an analytical technique some 30 years ago atomic absorption spectrometry has become a firmly established method for the analysis of trace metals. Graphite furnace atomic absorption spectrometry provides the analyst with the capability of analysis of solutions containing μg l-1 levels of the analyte, but, because of the transient nature of the signals, a sophisticated approach to the data aquisition and handling of data is required. Most modern commercial graphite furnace atomic absorption spectrometers have built in microprocessors for this purpose but they often have limited capability for extensible user programs and limited data storage facilities. In this communication we describe the use of an Apple IIe microcomputer for the acquisition of data from a Pye Unicam SP9 graphite furnace atomic absorption spectrometer. Details of the interface which utilizes an in-house designed AD converter, and an overview of the Pascal and assembler programs employed are given. The system allows the user to record, store and dump the graphical display of the furnace signalsfor all analyses performed. Files containing details of peak height, and area are formatted on an eight-column spreadsheet. Details of sample type, concentrations of standards, dilutions and replication are entered from the keyboard. The calibration graph is constructed using a moving quadratic fit routine and the concentrations of the analyte in unknown solutions calculated. In addition to this, greater processing power and integration of the data into other analytical schemes can be achieved by exporting the data to other software packages and computers. Details of data transfer between the Apple IIe and an Amstrad PC 1512 are given. Some examples of the use of the system in the development of an analytical methodfor silver in plant material are given.
PMCID: PMC2547752  PMID: 18925199
14.  Understanding the nature of “superhard graphite” 
Scientific Reports  2012;2:471.
Numerous experiments showed that on cold compression graphite transforms into a new superhard and transparent allotrope. Several structures with different topologies have been proposed for this phase. While experimental data are compatible with most of these models, the only way to solve this puzzle is to find which structure is kinetically easiest to form. Using state-of-the-art molecular-dynamics transition path sampling simulations, we investigate kinetic pathways of the pressure-induced transformation of graphite to various superhard candidate structures. Unlike hitherto applied methods for elucidating nature of superhard graphite, transition path sampling realistically models nucleation events necessary for physically meaningful transformation kinetics. We demonstrate that nucleation mechanism and kinetics lead to M-carbon as the final product. W-carbon, initially competitor to M-carbon, is ruled out by phase growth. Bct-C4 structure is not expected to be produced by cold compression due to less probable nucleation and higher barrier of formation.
PMCID: PMC3384968  PMID: 22745897
15.  Use of Activated Graphitized Carbon Chips for LC/MS and MSMS Analysis of Tryptic Glycopeptides 
Protein glycosylation has a significant medical importance as changes in glycosylation patterns have been associated with a number of diseases. Therefore, monitoring potential changes in glycan profiles, and the microheterogeneities associated with glycosylation sites are becoming increasingly important in the search for disease biomarkers. Highly efficient separations and sensitive methods must be developed to effectively monitor changes in the glycoproteome. These methods must not discriminate against hydrophobic or hydrophilic analytes. The use of activated graphitized carbon as a desalting media and a stationary phase for the purification and the separation of glycans, and as a stationary phase for the separation of small glycopeptides has previously been reported. Here, we describe the use of activated graphitized carbon as a stationary phase for the separation of hydrophilic tryptic glycopeptides, employing a chip-based liquid chromatographic system. The capabilities of both activated graphitized carbon and C18 LC chips for the characterization of the glycopeptides appeared to be comparable. Adequate retention time reproducibility was achieved for both packing types in the chip format. However, hydrophilic glycopeptides were preferentially retained on the activated graphitized carbon chip, thus allowing the identification of hydrophilic glycopeptides which were not effectively retained on C18 chips. On the other hand, hydrophobic glycopeptides were better retained on C18 chips. Characterization of the glycosylation sites of glycoproteins possessing both hydrophilic and hydrophobic glycopeptides is comprehensively achieved using both media. This is feasible considering the limited amount of sample required per analysis (< 1 pmol). The performance of both media was also appeared comparable when analyzing a 4-protein mixture. Similar sequence coverage and MASCOT ion scores were observed for all proteins when using either stationary phase.
PMCID: PMC3658454  PMID: 19145579
Activated graphitized carbon chip; Glycopeptides; LC/MSMS
16.  Pencil Drawn Strain Gauges and Chemiresistors on Paper 
Scientific Reports  2014;4:3812.
Pencil traces drawn on print papers are shown to function as strain gauges and chemiresistors. Regular graphite/clay pencils can leave traces composed of percolated networks of fine graphite powders, which exhibit reversible resistance changes upon compressive or tensile deflections. Flexible toy pencils can leave traces that are essentially thin films of graphite/polymer composites, which show reversible changes in resistance upon exposure to volatile organic compounds due to absorption/desorption induced swelling/recovery of the polymer binders. Pencil-on-paper devices are low-cost, extremely simple and rapid to fabricate. They are light, flexible, portable, disposable, and do not generate potentially negative environmental impact during processing and device fabrication. One can envision many other types of pencil drawn paper electronic devices that can take on a great variety of form factors. Hand drawn devices could be useful in resource-limited or emergency situations. They could also lead to new applications integrating art and electronics.
PMCID: PMC3898045  PMID: 24448478
17.  A simple mechanical technique to obtain carbon nanoscrolls from graphite nanoplatelets 
Nanoscale Research Letters  2013;8(1):403.
A simple approach for the bulk production of carbon nanoscrolls (CNSs) is described. This method is based on the application of shear-friction forces to convert graphite nanoplatelets into carbon nanoscrolls using a bi-axially oriented polypropylene (BOPP) surface. The combined action of shear and friction forces causes the exfoliation of graphite nanoplatelets and the simultaneous roll-up of graphite layers. Evidence of the CNS formation is given by optical microscopy, scanning electron microscopy, and transmission electron microscopy. These investigations reveal that the CNSs have a long tube-like and fusiform structure with a hollow core surrounded by few layers of graphene. Micro-Raman spectroscopy shows that the produced structures are not defect free, and optical spectroscopy reveals distinctive features due to the presence of two weak absorption bands at 224 and 324 nm.
PMCID: PMC3849441  PMID: 24229076
Carbon nanoscrolls; Shear stress; Bi-axially oriented polypropylene; Graphite nanoplatelets
18.  Flexible Temperature Sensor Array Based on a Graphite-Polydimethylsiloxane Composite 
Sensors (Basel, Switzerland)  2010;10(4):3597-3610.
This paper presents a novel method to fabricate temperature sensor arrays by dispensing a graphite-polydimethylsiloxane composite on flexible polyimide films. The fabricated temperature sensor array has 64 sensing cells in a 4 × 4 cm2 area. The sensor array can be used as humanoid artificial skin for sensation system of robots. Interdigitated copper electrodes were patterned on the flexible polyimide substrate for determining the resistivity change of the composites subjected to ambient temperature variations. Polydimethylsiloxane was used as the matrix. Composites of different graphite volume fractions for large dynamic range from 30 °C to 110 °C have been investigated. Our experiments showed that graphite powder provided the composite high temperature sensitivity. The fabricated temperature sensor array has been tested. The detected temperature contours are in good agreement with the shapes and magnitudes of different heat sources.
PMCID: PMC3274235  PMID: 22319314
composite; temperature sensor array; flexible substrate
19.  Visualizing the chemistry and structure dynamics in lithium-ion batteries by in-situ neutron diffraction 
Scientific Reports  2012;2:747.
We report an in-situ neutron diffraction study of a large format pouch battery cell. The succession of Li-Graphite intercalation phases was fully captured under an 1C charge-discharge condition (i.e., charge to full capacity in 1 hour). However, the lithiation and dilithiation pathways are distinctively different and, unlike in slowing charging experiments with which the Li-Graphite phase diagram was established, no LiC24 phase was found during charge at 1C rate. Approximately 75 mol. % of the graphite converts to LiC6 at full charge, and a lattice dilation as large as 4% was observed during a charge-discharge cycle. Our work demonstrates the potential of in-situ, time and spatially resolved neutron diffraction study of the dynamic chemical and structural changes in “real-world” batteries under realistic cycling conditions, which should provide microscopic insights on degradation and the important role of diffusion kinetics in energy storage materials.
PMCID: PMC3475991  PMID: 23087812
20.  Enhanced performance and interfacial investigation of mineral-based composite phase change materials for thermal energy storage 
Scientific Reports  2013;3:1908.
A novel mineral-based composite phase change materials (PCMs) was prepared via vacuum impregnation method assisted with microwave-acid treatment of the graphite (G) and bentonite (B) mixture. Graphite and microwave-acid treated bentonite mixture (GBm) had more loading capacity and higher crystallinity of stearic acid (SA) in the SA/GBm composite. The SA/GBm composite showed an enhanced thermal storage capacity, latent heats for melting and freezing (84.64 and 84.14 J/g) was higher than those of SA/B sample (48.43 and 47.13 J/g, respectively). Addition of graphite was beneficial to the enhancement in thermal conductivity of the SA/GBm composite, which could reach 0.77 W/m K, 31% higher than SA/B and 196% than pure SA. Furthermore, atomic-level interfaces between SA and support surfaces were depicted, and the mechanism of enhanced thermal storage properties was in detail investigated.
PMCID: PMC3664896  PMID: 23712069
21.  Rice husks as a sustainable source of nanostructured silicon for high performance Li-ion battery anodes 
Scientific Reports  2013;3:1919.
The recovery of useful materials from earth-abundant substances is of strategic importance for industrial processes. Despite the fact that Si is the second most abundant element in the Earth's crust, processes to form Si nanomaterials is usually complex, costly and energy-intensive. Here we show that pure Si nanoparticles (SiNPs) can be derived directly from rice husks (RHs), an abundant agricultural byproduct produced at a rate of 1.2 × 108 tons/year, with a conversion yield as high as 5% by mass. And owing to their small size (10–40 nm) and porous nature, these recovered SiNPs exhibits high performance as Li-ion battery anodes, with high reversible capacity (2,790 mA h g−1, seven times greater than graphite anodes) and long cycle life (86% capacity retention over 300 cycles). Using RHs as the raw material source, overall energy-efficient, green, and large scale synthesis of low-cost and functional Si nanomaterials is possible.
PMCID: PMC3665957  PMID: 23715238
22.  Effect of applied voltage, initial concentration and natural organic matter on sequential reduction/oxidation of nitrobenzene by graphite electrodes 
Environmental science & technology  2012;46(11):6174-6181.
Carbon electrodes are proposed in reactive sediment caps for in situ treatment of contaminants. The electrodes produce reducing conditions and H2 at the cathode and oxidizing conditions and O2 at the anode. Emplaced perpendicular to seepage flow, the electrodes provide the opportunity for sequential reduction and oxidation of contaminants. The objectives of this study are to demonstrate degradation of nitrobenzene (NB) as a probe compound for sequential electrochemical reduction and oxidation, and to determine the effect of applied voltage, initial concentration and natural organic matter on the degradation rate. In H-cell reactors with graphite electrodes and buffer solution, NB was reduced stoichiometrically to aniline (AN) at the cathode with nitrosobenzene (NSB) as the intermediate. AN was then removed at the anode, faster than the reduction step. No common AN oxidation intermediate was detected in the system. Both the first order reduction rate constants of NB (kNB) and NSB (kNSB) increased with applied voltage between 2V and 3.5 V (when the initial NB concentration was 100 µM, kNB=0.3 d−1 and kNSB=0.04 d−1at 2V; kNB=1.6 d−1 and kNSB=0.64 d−1at 3.5 V) but stopped increasing beyond the threshold of 3.5V. When initial NB concentration decreased from 100 to 5 µM, kNB and kNSB became 9 and 5 times faster, respectively, suggesting that competition for active sites on the electrode surface is an important factor in NB degradation. Presence of natural organic matter (in forms of either humic acid or Anacostia River sediment porewater) decreased kNB while slightly increased kNSB, but only to a limited extent (~factor of 3) for dissolved organic carbon content up to 100 mg/l. These findings suggest that electrode-based reactive sediment capping via sequential reduction/oxidation is a potentially robust and tunable technology for in situ contaminants degradation.
PMCID: PMC3374338  PMID: 22571797
23.  Colloidal graphite/graphene nanostructures using collagen showing enhanced thermal conductivity 
In the present study, the exfoliation of natural graphite (GR) directly to colloidal GR/graphene (G) nanostructures using collagen (CL) was studied as a safe and scalable process, akin to numerous natural processes and hence can be termed “biomimetic”. Although the exfoliation and functionalization takes place in just 1 day, it takes about 7 days for the nano GR/G flakes to stabilize. The predominantly aromatic residues of the triple helical CL forms its own special micro and nanoarchitecture in acetic acid dispersions. This, with the help of hydrophobic and electrostatic forces, interacts with GR and breaks it down to nanostructures, forming a stable colloidal dispersion. Surface enhanced Raman spectroscopy, X-ray diffraction, photoluminescence, fluorescence, and X-ray photoelectron spectroscopy of the colloid show the interaction between GR and CL on day 1 and 7. Differential interference contrast images in the liquid state clearly reveal how the GR flakes are entrapped in the CL fibrils, with a corresponding fluorescence image showing the intercalation of CL within GR. Atomic force microscopy of graphene-collagen coated on glass substrates shows an average flake size of 350 nm, and the hexagonal diffraction pattern and thickness contours of the G flakes from transmission electron microscopy confirm ≤ five layers of G. Thermal conductivity of the colloid shows an approximate 17% enhancement for a volume fraction of less than approximately 0.00005 of G. Thus, through the use of CL, this new material and process may improve the use of G in terms of biocompatibility for numerous medical applications that currently employ G, such as internally controlled drug-delivery assisted thermal ablation of carcinoma cells.
PMCID: PMC3956625  PMID: 24648728
graphene; collagen; colloid; nanostructures; biomimetic; carbon; nanomaterials; heat; thermal ablation; thermal conductivity
24.  Graphite pneumoconiosis 
Ranasinha, K. W., and Uragoda, C. G. (1972).Brit. J. industr. Med.,29, 178-183. Graphite pneumoconiosis. In this survey, which is the first of its kind in the graphite industry, 344 workers in a large mine in Ceylon were investigated for pulmonary lesions; 22·7% of them had radiographic abnormalities, which included small rounded and irregular opacities, large opacities, and significant enlargement of hilar shadows. They had worked considerably longer in the industry and were, on average, older than the rest. Only 19·2% of the affected workers had respiratory symptoms, of which dyspnoea and cough were the most frequent. Digital clubbing was seen in 21·9%.
In an age and sex matched control group, comprising 327 persons from a neighbouring village, only 8 (2·4%) showed radiographic abnormalities.
Graphite pneumoconiosis closely resembles coal miners' pneumoconiosis in many respects. It does not appear to be a pure silicosis, neither could it be considered a true carbon pneumoconiosis. It is likely that massive fibrosis is associated with tuberculous infection.
PMCID: PMC1009396  PMID: 5021997
25.  Physicochemical Characterization, and Relaxometry Studies of Micro-Graphite Oxide, Graphene Nanoplatelets, and Nanoribbons 
PLoS ONE  2012;7(6):e38185.
The chemistry of high-performance magnetic resonance imaging contrast agents remains an active area of research. In this work, we demonstrate that the potassium permanganate-based oxidative chemical procedures used to synthesize graphite oxide or graphene nanoparticles leads to the confinement (intercalation) of trace amounts of Mn2+ ions between the graphene sheets, and that these manganese intercalated graphitic and graphene structures show disparate structural, chemical and magnetic properties, and high relaxivity (up to 2 order) and distinctly different nuclear magnetic resonance dispersion profiles compared to paramagnetic chelate compounds. The results taken together with other published reports on confinement of paramagnetic metal ions within single-walled carbon nanotubes (a rolled up graphene sheet) show that confinement (encapsulation or intercalation) of paramagnetic metal ions within graphene sheets, and not the size, shape or architecture of the graphitic carbon particles is the key determinant for increasing relaxivity, and thus, identifies nano confinement of paramagnetic ions as novel general strategy to develop paramagnetic metal-ion graphitic-carbon complexes as high relaxivity MRI contrast agents.
PMCID: PMC3369907  PMID: 22685555

Results 1-25 (532618)