Publications

Forthcoming
Aksay, I. A. ; Korkut, S. A. ; Kaczmarczyk, J. ; Gurdag, S. ; Korkmaz, D. Graphene dispersions, Forthcoming.Abstract
Method of making a composition comprising graphene sheets and at least one solvent, comprising dispersing a mixture of graphene sheets and graphite particles in a solvent, wherein the graphite particles have more than about 50 layers, separating the graphene sheets and the graphite particles to obtain a dispersion of graphene sheets that contains no more than 25% of graphite particles having more than about 50 layers, based on the total number of graphite particles and graphene sheets, and flocculating the dispersion of graphene sheets. The flocculated dispersion can be added to a polymer matrix to make a composite. The composite can be formed into articles.
Pope, M. A. ; Alain-Rizzo, V. ; Dabbs, D. M. ; Lettow, J. S. ; Aksay, I. A. Batteries incorporating graphene membranes for extending the cycle-life of lithium-ion batteries, Forthcoming.Abstract
Embodiments of the present invention relate to energy storage devices and associated methods of manufacture. In one embodiment, an energy storage device comprises an electrolyte. An anode is at least partially exposed to the electrolyte. A selectively permeable membrane comprising a graphene-based material is positioned proximate to the anode. The selectively permeable membrane reduces a quantity of a component that is included in the electrolyte from contacting the anode and thereby reduces degradation of the anode.
Aksay, I. A. ; Sallah, K. Conducting elastomers, Forthcoming.Abstract
The present invention relates to conducting elastomers and assocd. fabrication methods. In one embodiment, the conducting elastomer comprises a filler powder and a polymer. The filler powder includes carbon black and functionalized graphene sheets. The polymer has a mol. wt. of about 200 g/mol to about 5000 g/mol and is a liquid at room temperature.
Aksay, I. A. ; Dabbs, D. M. ; Pope, M. A. Electrodes incorporating composites of graphene and selenium-sulfur compounds for improved rechargeable lithium batteries. Forthcoming.Abstract
Embodiments of the present invention relate to battery electrodes incorporating composites of graphene and selenium-sulfur compds. for improved rechargeable batteries. In one embodiment, a conductive compn. comprises a conductive compn. having a Se-S compd., a conductive additive. The Se-S compd. is present as SexS8-x, wherein x is greater than zero and less than eight.
Aksay, I. A. ; Alain-Rizzo, V. ; Bozlar, M. ; Bozym, D. J. ; Dabbs, D. M. ; Szamreta, N. ; Ustundag, C. B. Electrohydrodynamically formed structures of carbonaceous material, Forthcoming.Abstract
A method for the electrohydrodynamic deposition of carbonaceous materials utilizing an electrohydrodynamic cell comprising two electrodes comprised of a conductive material, by first combining a solid phase comprising a carbonaceous material and a suspension medium, placing the suspension between the electrodes, applying an electric field in a first direction, varying the intensity of the electric field sufficiently to drive lateral movement, increasing the electric field to stop the lateral transport and fix the layers in place, then removing the applied field and removing the electrodes. Among the many different possibilities contemplated, the method may advantageously utilize: varying the spacing between the electrodes; removing the buildup from one or both electrodes; placing the electrodes into different suspensions; adjusting the concentration, pH, or temperature of the suspension(s); and varying the direction, intensity or duration of the electric fields.
2018
Aksay, I. A. ; Korkut, S. ; Pope, M. ; Punckt, C. Graphene-ionic liquid composites, 2018.Abstract
Method of making a graphene-ionic liquid composite. The composite can be used to make electrodes for energy storage devices, such as batteries and supercapacitors.
Prud'homme, R. K. ; Aksay, I. A. Thermal overload device containing a polymer composition containing thermally exfoliated graphite oxide and method of making the same, 2018.Abstract
A thermal overload device containing a polymer composite, which contains at least one polymer and a modified graphite oxide material, containing thermally exfoliated graphite oxide having a surface area of from about 300 m2/g to 2600 m2/g, and a method of making the same.
Aksay, I. A. ; Milius, D. L. ; Korkut, S. ; Prud'homme, R. K. Functionalized graphene sheets having high carbon to oxygen ratios, 2018.Abstract
Functionalized graphene sheets having a carbon to oxygen molar ratio of at least about 23:1 and method of preparing the same.
Aksay, I. A. ; Buyukdincer, B. ; Javaherian, N. ; Lettow, J. S. ; Pino, G. ; Redmond, K. ; Yildirim, I. O. Reinforced polymeric articles, 2018.Abstract
Polymeric article reinforced with a reinforcing component. The reinforcing component includes a composition made from at least one polymer and graphene sheets.
Crain, J. M. ; Lettow, J. S. ; Aksay, I. A. ; Korkut, S. ; Chiang, K. S. ; Chen, C. - H. ; Prud'homme, R. K. Printed electronics, 2018.Abstract
Printed electronic device comprising a substrate onto at least one surface of which has been applied a layer of an electrically conductive ink comprising functionalized graphene sheets and at least one binder. A method of preparing printed electronic devices is further disclosed.
Pan, S. ; Aksay, I. A. ; Prud'homme, R. K. Multifunctional graphene-silicone elastomer nanocomposite, method of making the same, and uses thereof, 2018.Abstract
A nanocomposite composition having a silicone elastomer matrix having therein a filler loading of greater than 0.05 wt %, based on total nanocomposite weight, wherein the filler is functional graphene sheets (FGS) having a surface area of from 300 m2/g to 2630 m2/g; and a method for producing the nanocomposite and uses thereof.
2017
Prud’homme, R. K. ; Aksay, I. A. Conductive circuit containing a polymer composition containing thermally exfoliated graphite oxide and method of making the same, 2017.Abstract
A conductive circuit containing a polymer composite, which contains at least one polymer and a modified graphite oxide material, containing thermally exfoliated graphite oxide having a surface area of from about 300 m2/g to 2600 m2/g, and a method of making the same.
Aksay, I. A. ; Milius, D. L. ; Korkut, S. ; Prud'homme, R. K. Functionalized Graphene Sheets having High Carbon to Oxygen Ratios, 2017.Abstract
The present invention relates to functionalized graphene sheets having low oxygen content and methods for their prepartion.
Alifierakis, M. ; Sallah, K. S. ; Aksay, I. A. ; Prevost, J. H. Reversible Cluster Aggregation and Growth Model for Graphene Suspensions. AIChE Journal 2017, 63, 5462-5473.Abstract
We present a reversible cluster aggregation model for 2-D macromolecules represented by line segments in 2-D; and, we use it to describe the aggregation process of functionalized graphene particles in an aqueous SDS surfactant solution. The model produces clusters with similar sizes and structures as a function of SDS concentration in agreement with experiments and predicts the existence of a critical surfactant concentration (C-crit) beyond which thermodynamically stable graphene suspensions form. Around C-crit, particles form dense clusters rapidly and sediment. At C << C-crit, a contiguous ramified network of graphene gel forms which also densifies, but at a slower rate, and sediments with time. The deaggregation-reaggregation mechanism of our model captures the restructuring of the large aggregates towards a graphite-like structure for the low SDS concentrations. (C) 2017 American Institute of Chemical Engineers
2016
Uralcan, B. ; Aksay, I. A. ; Debenedetti, P. G. ; Limmer, D. T. Concentration Fluctuations and Capacitive Response in Dense Ionic Solutions. Journal of Physical Chemistry Letters 2016, 7 2333-2338.Abstract
We use molecular dynamics simulations in a constant potential ensemble to study the effects of solution composition on the electrochemical response of a double layer capacitor. We find that the capacitance first increases with ion concentration following its expected ideal solution behavior but decreases upon approaching a pure ionic liquid in agreement with recent experimental observations. The nonmonotonic behavior of the capacitance as a function of ion concentration results from the competition between the independent motion of solvated ions in the dilute regime and solvation fluctuations in the concentrated regime. Mirroring the capacitance, we find that the characteristic decay length of charge density correlations away from the electrode is also nonmonotonic. The correlation length first decreases with ion concentration as a result of better electrostatic screening but increases with ion concentration as a result of enhanced steric interactions. When charge fluctuations induced by correlated ion-solvent fluctuations are large relative to those induced by the pure ionic liquid, such capacitive behavior is expected to be generic.
Bozym, D. J. ; Korkut, S. ; Pope, M. A. ; Aksay, I. A. Dehydrated Sucrose Nanoparticles as Spacers for Graphene-Ionic Liquid Supercapacitor Electrodes. ACS Sustainable Chemistry & Engineering 2016, 4 7167-7174.Abstract
The addition of dehydrated sucrose nano particles increases the gravimetric capacitance of electrochemical double-layer capacitor electrodes produced via the evaporative consolidation of graphene oxide-water-ionic liquid gels by more than two-fold. Dehydrated sucrose adsorbs onto graphene oxide and serves as a spacer, preventing the graphene oxide from restacking during solvent evaporation. Despite 61 wt % of the solids being electrochemically inactive dehydrated sucrose nanoparticles, the best electrodes achieved an energy density of similar to 13.3 Wh/kg, accounting for the total mass of all electrode components.
Aksay, I. A. ; Korkut, S. ; Pope, M. ; Punckt, C. Graphene-Ionic Liquid Composites, 2016.Abstract
Method of making a graphene-ionic liquid composite. The composite can be used to make electrodes for energy storage devices, such as batteries and supercapacitors. Disclosed and claimed herein is method of making a graphene-ionic liquid composite, comprising combining a graphene source with at least one ionic liquid and heating the combination at a temperature of at least about 130 °C.
Roy-Mayhew, J. D. ; Pope, M. A. ; Punckt, C. ; Aksay, I. A. Intrinsic Catalytic Activity of Graphene Defects for the Co-II/III(bpy)(3) Dye-Sensitized Solar Cell Redox Mediator. ACS Applied Materials & Interfaces 2016, 8 9134-9141.Abstract
We demonstrate that functionalized graphene, rich with lattice defects but lean with oxygen sites, catalyzes the reduction of Co-III(bpy)(3) as well as platinum does, exhibiting a rate of heterogeneous electron transfer, k(0), of similar to 6 x 10(-3) cm/s. We show this rate to be an order of magnitude higher than on oxygen-site-rich graphene oxide, and over 2 orders of magnitude higher than on the basal plane of graphite (as a surrogate for pristine graphene). Furthermore, dye-sensitized solar. cells using defect-rich graphene monolayers perform similarly to those using platinum nanoparticles as the catalyst.
Liu, J. ; Aksay, I. A. ; Kou, R. ; Wang, D. H. Mesoporous Metal Oxide Graphene Nanocomposite Materials, 2016.Abstract
A nanocomposite material formed of graphene and a mesoporous metal oxide having a demonstrated specific capacity of more than 200 F/g with particular utility when employed in supercapacitor applications. A method for making these nanocomposite materials by first forming a mixture of graphene, a surfactant, and a metal oxide precursor, precipitating the metal oxide precursor with the surfactant from the mixture to form a mesoporous metal oxide. The mesoporous metal oxide is then deposited onto a surface of the graphene.
Pan, S. Y. ; Aksay, I. A. ; Prud'homme, R. K. Multifunctional Graphene-Silicone Elastomer Nanocomposite, Method of Making the Same, and Uses Thereof, 2016.Abstract
A nanocomposite composition having a silicone elastomer matrix having therein a filler loading of greater than 0.05 wt %, based on total nanocomposite weight, wherein the filler is functional graphene sheets (FGS) having a surface area of from 300 m2/g to 2630 m2/g; and a method for producing the nanocomposite and uses thereof.
Crain, J. M. ; Lettow, J. S. ; Aksay, I. A. ; Korkut, S. ; Chiang, K. S. ; Chen, C. H. ; Prud'homme, R. K. Printed Electronics, 2016.Abstract
Printed electronic device comprising a substrate onto at least one surface of which has been applied a layer of an electrically conductive ink comprising functionalized graphene sheets and at least one binder. A method of preparing printed electronic devices is further disclosed.
Aksay, I. A. ; Buyukdincer, B. ; Javeherian, N. ; Lettow, J. S. ; Pino, G. ; Redmond, K. ; Yildirim, I. Reinforced Polymeric Articles, 2016.Abstract
The present invention relates to polymeric articles reinforced with a reinforcing agent made from compositions comprising at least one polymer and graphene sheets.
Aksay, I. A. ; Buyukdincer, B. ; Javaherian, N. ; Lettow, J. S. ; Pino, G. ; Redmond, K. ; Yildirim, I. O. Reinforced Polymeric Articles, 2016.Abstract
Polymeric article reinforced with a reinforcing component. The reinforcing component includes a composition made from at least one polymer and graphene sheets.
Punckt, C. ; Pope, M. A. ; Liu, Y. F. M. ; Aksay, I. A. Structure-Dependent Electrochemistry of Reduced Graphene Oxide Monolayers. Journal of the Electrochemical Society 2016, 163, H491-H498.Abstract
While graphene and other carbonaceous nanomaterials have shown promise in a variety of electrochemical applications, measurement of their intrinsic performance is often confounded with effects related to the complexities due to diffusion in a porous medium. To by-pass this limitation, we use effectively non-porous tiled monolayers of reduced graphene oxide as a model platform to study how rates of heterogeneous electron transfer evolve as a function of graphene structure/chemistry. A variety of electrochemical systems are investigated including the standard ferri/ferrocyanide redox probe, several common biomolecular redox systems as well as copper electrodeposition. We show that the rates of heterogeneous electron transfer can vary by as much as 3 orders of magnitude depending on the reduction or annealing conditions used and the redox system investigated. Performance changes are linked to graphene chemistry, and we show that the graphene oxide reduction procedure must be chosen judiciously to maximize the electrochemical performance for particular applications. (C) 2016 The Electrochemical Society. All rights reserved.
2015
Bozym, D. J. ; Uralcan, B. ; Limmer, D. T. ; Pope, M. A. ; Szamreta, N. J. ; Debenedetti, P. G. ; Aksay, I. A. Anomalous Capacitance Maximum of the Glassy Carbon-Ionic Liquid Interface through Dilution with Organic Solvents. J. Phys. Chem. Lett. 2015, 6 2644-2648.Abstract

We use electrochemical impedance spectroscopy to measure the effect of diluting a hydrophobic room temperature ionic liquid with miscible organic solvents on the differential capacitance of the glassy carbon − electrolyte interface. We show that the minimum differential capacitance increases with dilution and reaches a maximum value at ionic liquid contents near 5 − 10 mol% (i.e., ∼ 1 M). We provide evidence that mixtures with 1,2-dichloroethane, a low- dielectric constant solvent, yield the largest gains in capacitance near the open circuit potential when compared against two traditional solvents, acetonitrile and propylene carbonate. To provide a fundamental basis for these observations, we use a coarse-grained model to relate structural variations at the double layer to the occurrence of the maximum. Our results reveal the potential for the enhancement of double-layer capacitance through dilution.

Crain, J. M. ; Lettow, J. S. ; Aksay, I. A. ; Prud'homme, R. K. ; Korkut, S. Coatings Containing Functionalized Graphene Sheets and Articles Coated Therewith, 2015.Abstract
Coatings are provided containing functionalized graphene sheets and at least one binder. In one embodiment, the coatings are electrically conductive.
Zhang, C. ; Dabbs, D. M. ; Liu, L. - M. ; Aksay, I. A. ; Car, R. ; Selloni, A. Combined Effects of Functional Groups, Lattice Defects, and Edges in the Infrared Spectra of Graphene Oxide. J. Phys. Chem. C 2015, 119, 18167-18176.Abstract

Infrared spectroscopy in combination with density functional theory calculations has been widely used to characterize the structure of graphene oxide and its reduced forms. Yet, the synergistic effects of different functional groups, lattice defects, and edges on the vibrational spectra are not well understood. Here, we report first-principles calculations of the infrared spectra of graphene oxide performed on realistic, thermally equilibrated, structural models that incorporate lattice vacancies and edges along with various oxygen-containing functional groups. Models including adsorbed water are examined as well. Our results show that lattice vacancies lead to important blue and red shifts in the OH stretching and bending bands, respectively, whereas the presence of adsorbed water leaves these shifts largely unaffected. We also find unique infrared features for edge carboxyls resulting from interactions with both nearby functional groups and the graphene lattice. Comparison of the computed vibrational properties to our experiments clarifies the origin of several observed features and provides evidence that defects and edges are essential for characterizing and interpreting the infrared spectrum of graphene oxide.

Pope, M. A. ; Aksay, I. A. Four-Fold Increase in the Intrinsic Capacitance of Graphene through Functionalization and Lattice Disorder. J. Phys. Chem. C 2015, 119, 20369-20378.Abstract

Graphene has been heralded as a promising electrode material for high energy and power density electrochemical supercapacitors. This is in spite of recent work confirming the low double-layer capacitance (CDL) of the graphene/electrolyte interface limited by graphene’s low quantum capacitance (CQ), an effect known for the basal plane of graphite for over four decades. Consistent with this limit, much of the supercapacitor research implies the use of pristine graphene but, in contrast, uses a functionalized and defective graphene formed through the reduction of graphene oxide, without clarifying why reduced graphene oxide is needed to achieve high capacitance. Herein, we show that an optimal level of functionalization and lattice disorder in reduced graphene oxide yields a 4-fold increase in CDL over that of pristine graphene, suggesting graphene-based materials can indeed be tailored to engineer electrodes with significantly higher gravimetric capacitance limits exceeding 450 F/g than what has been achieved (∼ 274 F/g) thus far, even in nonaqueous electrolytes capable of high voltage operation.

Li, Y. ; Alain-Rizzo, V. ; Galmiche, L. ; Audebert, P. ; Miomandre, F. ; Louarn, G. ; Bozlar, M. ; Pope, M. A. ; Dabbs, D. M. ; Aksay, I. A. Functionalization of Graphene Oxide by Tetrazine Derivatives: A Versatile Approach toward Covalent Bridges between Graphene Sheets. Chem. Mater. 2015, 27, 4298-4310.Abstract

We have covalently grafted tetrazine derivatives to graphene oxide through nucleophilic substitution. Since the tetrazine unit is electroactive and nitrogen-rich, with a reduction potential sensitive to the type of substituent and degree of substitution, we used electrochemistry and X-ray photoelectron spectroscopy to demonstrate clear evidence for grafting through covalent bonding. Chemical modification was supported by Fourier transform infrared spectroscopy and thermal analysis. Tetrazines grafted onto graphene oxide displayed different mass losses compared to unmodified graphene and were more stable than the molecular precursors. Finally, a bridging tetrazine derivative was grafted between sheets of graphene oxide to demonstrate that the separation distance between sheets can be maintained while designing new graphene-based materials, including chemically bound, redox structures.

Hsieh, A. G. ; Punckt, C. ; Aksay, I. A. High-Rate Li+ Storage Capacity of Surfactant-Templated Graphene-TiO2 Nanocomposites. J. Electrochem. Soc. 2015, 162, A1566-A1573.Abstract
Graphene-TiO2 nanocomposites are a promising anode material for Li-ion batteries due to their good high-rate capacity, inherent safety, and mechanical and chemical robustness. However, despite a large number of scientific reports on the material, the mechanism of the enhanced high-rate Li+ storage capacity that results from the addition of graphene to TiO2 – typically attributed to improved electrical conductivity – is still not well understood. In this work, we focus on optimizing the processing of surfactant-templated graphene-TiO2 hybrid nanocomposites. Towards this end, we examine the influence of various processing parameters, in particular the surfactant-mediated colloidal dispersion of graphene, on the material properties and electrochemical performance of graphene-TiO2. We investigate the influence of electrode mass loading on Li+ storage capacity, focusing mainly on high-rate performance. Furthermore, we demonstrate an approach for estimating power loss during charge/discharge cycling, which offers a succinct method for characterizing the high-rate performance of Li-ion battery electrodes.
Liu, J. ; Aksay, I. A. ; Choi, D. W. ; Wang, D. H. ; Yang, Z. G. Nanocomposite of Graphene and Metal Oxide Materials, 2015.Abstract
Nanocomposite materials comprising a metal oxide bonded to at least one graphene material. The nanocomposite materials exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate greater than about 10 C.
Crain, J. M. ; Lettow, J. S. ; Aksay, I. A. ; Korkut, S. ; Chiang, K. S. ; Chen, C. H. ; Prud'homme, R. K. Printed Electronics, 2015.Abstract
Printed electronic device comprising a substrate onto at least one surface of which has been applied a layer of an electrically conductive ink comprising functionalized graphene sheets and at least one binder. A method of preparing printed electronic devices is further disclosed.
Aksay, I. A. ; Buyukdincer, B. ; Javaherian, N. ; Lettow, J. S. ; Pino, G. ; Redmond, K. ; Yildirim, I. Reinforced Polymeric Materials, 2015.Abstract
Polymeric article reinforced with a reinforcing component. The reinforcing component includes a composition made from at least one polymer and graphene sheets.
Liu, J. ; Aksay, I. A. ; Choi, D. W. ; Kou, R. ; Nie, Z. M. ; Wang, D. H. ; Yang, Z. G. Self-Assembled Multi-Layer Nanocomposite of Graphene and Metal Oxide Materials, 2015.Abstract
Nanocomposite materials having at least two layers, each layer consisting of one metal oxide bonded to at least one graphene layer were developed. The nanocomposite materials will typically have many alternating layers of metal oxides and graphene layers, bonded in a sandwich type construction and will be incorporated into an electrochemical or energy storage device.
Pope, M. A. ; Aksay, I. A. Structural Design of Cathodes for Li-S Batteries. Adv. Energy Mater. 2015, 5 1500124.Abstract

Battery technologies involving Li-S chemistries have been touted as one of the most promising next generation systems. The theoretical capacity of sulfur is nearly an order of magnitude higher than current Li-ion battery insertion cathodes and when coupled with a Li metal anode, Li-S batteries promise specific energies nearly five-fold higher. However, this assertion only holds if sulfur cathodes could be designed in the same manner as cathodes for Li-ion batteries. Here, the recent efforts to engineer high capacity, thick, sulfur-based cathodes are explored. Various works are compared in terms of capacity, areal mass loading, and fraction of conductive additive, which are the critical parameters dictating the potential for a device to achieve a specific energy higher than current Li-ion batteries (i.e., >200 Wh kg−1 ). While an inferior specific energy is projected in the majority of cases, several promising strategies have the potential to achieve >500 Wh kg−1 . The challenges associated with the limited cycle-life of these systems due to both the polysulfide shuttle phenomenon and the rapid degradation of the Li metal anode that is experienced at the current densities required to charge high specific energy batteries in a reasonable timeframe are also discussed.

Lee, Y. J. ; Huang, L. ; Wang, H. ; Sushko, M. L. ; Schwenzer, B. ; Aksay, I. A. ; Liu, J. Structural rearrangement and dispersion of functionalized graphene sheets in aqueous solutions. Colloids Interf. Sci. Comm. 2015, 8 1-5. Publisher's VersionAbstract

Surfactants are widely used for dispersing graphene and functionalized graphene sheets (FGS) in colloidal suspensions, but there have been few studies of the structure of the dispersed graphene–surfactant complexes in suspension and of their time evolution. Here, we combine experimental study of efficiencies of ionic surfactants/polymers in suspending FGS in water with characterization using atomic force microscopy, small angle neutron scattering, and molecular simulations to probe the detailed structures of FGSs. The small angle scattering technique provides quantitative measurement of structure of graphene sheets in the solution. This study suggests that in both ionic and nonionic surfactants, the dispersion tends to degrade over time through detachment of the surfactant molecules and structural rearrangements. Ionic surfactants with strong interfacial binding and large molecular weight increase the dispersing power by over an order of magnitude.

2014
Crain, J. M. ; Lettow, J. S. ; Aksay, I. A. ; Korkut, S. A. ; Chiang, K. S. ; Chen, C. - H. ; Prud'homme, R. K. Printed electronics, 2014.Abstract
Printed electronic device comprising a substrate onto at least one surface of which has been applied a layer of an electrically conductive ink comprising functionalized graphene sheets and at least one binder. A method of preparing printed electronic devices is further disclosed.
Prud'homme, R. K. ; Aksay, I. A. Conductive circuit containing a polymer composition containing thermally exfoliated graphite oxide and method of making the same, 2014.Abstract
A conductive circuit containing a polymer composite, which contains at least one polymer and a modified graphite oxide material, containing thermally exfoliated graphite oxide having a surface area of from about 300 m2/g to 2600 m2/g, and a method of making the same.
Aksay, I. A. ; Saville, D. A. ; Poon, H. F. ; Korkut, S. ; Chen, C. - H. Electrohydrodynamic printing and manufacturing, 2014.Abstract
An stable electrohydrodynamic filament is obtained by causing a straight electrohydrodynamic filament formed from a liquid to emerge from a Taylor cone, the filament having a diameter of from 10 nm to 100 µm. Such filaments are useful in electrohydrodynamic printing and manufacturing techniques and their application in liquid drop/particle and fiber production, colloidal deployment and assembly, and composite materials processing.
Tavakol, B. ; Bozlar, M. ; Punckt, C. ; Froehlicher, G. ; Stone, H. A. ; Aksay, I. A. ; Holmes, D. P. Buckling of dielectric elastomeric plates for soft, electrically active microfluidic pumps. Soft Matter 2014, 10, 4789-4794.Abstract
Elastic instabilities, when properly implemented within soft, mechanical structures, can generate advanced functionality. In this work, we use the voltage-induced buckling of thin, flexible plates to pump fluids within a microfluidic channel. The soft electrodes that enable electrical actuation are compatible with fluids, and undergo large, reversible deformations. We quantified the onset of voltage-induced buckling, and measured the flow rate within the microchannel. This embeddable, flexible microfluidic pump will aid in the generation of new stand-alone microfluidic devices that require a tunable flow rate.
Vijayakumar, M. ; Schwenzer, B. ; Shutthanandan, V. ; Hu, J. Z. ; Liu, J. ; Aksay, I. A. Elucidating graphene-ionic liquid interfacial region: A combined experimental and computational study. Nano Energy 2014, 3 152-158.Abstract
Graphene and ionic liquids are promising candidates for electrode materials and electrolytes, respectively, for modern energy storage devices such as supercapacitors. Understanding the interactions at the interfacial region between these materials is crucial for optimizing the overall performance and efficiency of supercapacitors. The interfacial region between graphene and an imidazolium-based ionic liquid is analyzed in a combined experimental and computational study. This dual approach reveals that the imidazolium-based cations mostly orient themselves parallel to the graphene surface due to pi-pi stacking interaction and form a primary interfacial layer, which is subsequently capped by a layer of anions from the ionic liquid. However, it also becomes apparent that the molecular interplay at the interfacial region is highly influenced by functional group defects on the graphene surface, in particular by hydroxyl groups. (C) 2012 Elsevier Ltd. All rights reserved.
Xiao, J. ; Meduri, P. ; Chen, H. H. ; Wang, Z. G. ; Gao, F. ; Hu, J. Z. ; Feng, J. ; Hu, M. ; Dai, S. ; Brown, S. ; et al. Energetics of Defects on Graphene through Fluorination. ChemSusChem 2014, 7 1295-1300.Abstract

Functionalized graphene sheets (FGSs) comprise a unique member of the carbon family, demonstrating excellent electrical conductivity and mechanical strength. However, the detailed chemical composition of this material is still unclear. Herein, we take advantage of the fluorination process to semiquantitatively probe the defects and functional groups on graphene surface. Functionalized graphene sheets are used as substrate for low-temperature (<150 °C) direct fluorination. The fluorine content has been modified to investigate the formation mechanism of different functional groups such as CF, CF2, OCF2 and (C=O)F during fluorination. The detailed structure and chemical bonds are simulated by density functional theory (DFT) and quantified experimentally by nuclear magnetic resonance (NMR). The electrochemical properties of fluorinated graphene are also discussed extending the use of graphene from fundamental research to practical applications.

Roy-Mayhew, J. D. ; Aksay, I. A. Graphene Materials and Their Use in Dye-Sensitized Solar Cells. Chemical Reviews 2014, 114, 6323-6348.
Punckt, C. ; Pope, M. A. ; Aksay, I. A. High Selectivity of Porous Graphene Electrodes Solely Due to Transport and Pore Depletion Effects. Journal of Physical Chemistry C 2014, 118, 22635-22642.Abstract
We contrast the performance of monolayer electrodes and thin porous film electrodes of highly reduced functionalized graphene to demonstrate that the introduction of electrode porosity gives rise to strong apparent electrocatalytic effects resulting in vastly improved electrode selectivity. This is despite graphene showing no intrinsic advantage over glassy carbon electrodes when used as a monolayer. The simultaneous electrooxidation of ascorbic acid, dopamine and uric acid is used as an experimental model electrolyte system. Our results suggest that a large number of reports claiming the superior surface chemistry of carbon nanomaterials as the reason for outstanding electrochemical characteristics should be revisited considering electrode morphology as a significant contributor to the observed behavior. Our experimental results are supported by numerical simulations explaining the porosity-induced electrode selectivity by the dominance of pore depletion over diffusion-limited currents.
2013
Aksay, I. A. ; Buyukdincer, B. ; Javaherian, N. ; Lettow, J. S. ; Pino, G. ; Redmond, K. ; Yildirim, I. O. Reinforced polymeric articles, 2013.Abstract
Polymeric article reinforced with a reinforcing component. The reinforcing component includes a composition made from at least one polymer and graphene sheets.
Liu, J. ; Aksay, I. A. ; Choi, D. ; Wang, D. ; Yang, Z. Nanocomposite of graphene and metal oxide materials, 2013.Abstract
Nanocomposite materials comprising a metal oxide bonded to at least one graphene material. The nanocomposite materials exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate greater than about 10 C.
Liu, J. ; Aksay, I. A. ; Choi, D. ; Kou, R. ; Nie, Z. ; Wang, D. ; Yang, Z. Self assembled multi-layer nanocomposite of graphene and metal oxide materials, 2013.Abstract
Nanocomposite materials having at least two layers, each layer consisting of one metal oxide bonded to at least one graphene layer were developed. The nanocomposite materials will typically have many alternating layers of metal oxides and graphene layers, bonded in a sandwich type construction and will be incorporated into an electrochemical or energy storage device.
Hsieh, A. G. ; Punckt, C. ; Korkut, S. ; Aksay, I. A. Adsorption of Sodium Dodecyl Sulfate on Functionalized Graphene Measured by Conductometric Titration. Journal of Physical Chemistry B 2013, 117, 7950-7958.Abstract
We report on the adsorption of sodium dodecyl sulfate (SDS) onto functionalized graphene sheets (FGSs) in an aqueous system, measured at broad SDS and FGS concentration ranges by conductometric surfactant titration. At dilute SDS concentrations (<12 mu M in bulk solution), there is evidence of a counterion exchange between hydronium ions (from the dissociation of acidic chemical functionalities on FGS) and sodium ions coadsorbing with dodecyl sulfate monomers onto FGSs. We find that, for FGS with a carbon-to-oxygen ratio of similar to 18, monolayer adsorption of SDS on FGS reaches full surface coverage by similar to 12 mu M SDS. Additionally, the critical surface aggregation concentration (csac) for surface micelle formation on FGS is measured to be similar to 1.5 mM SDS The transition from monolayer adsorption to surface micelle formation appears to occur at a similar SDS concentration on FGSs as on graphite, suggesting there is little difference in the surfactant adsorption behavior on both materials. We estimate that the FGS surface area available for SDS adsorption is similar to 600 m(2)/g which is significantly less than expected for FGSs in suspension and indicates the presence of regions on FGS on which SDS adsorption does not occur.
Jan, L. ; Punckt, C. ; Aksay, I. A. Cementation of Colloidal Particles on Electrodes in a Galvanic Microreactor. ACS Applied Materials & Interfaces 2013, 5 6346-6353.Abstract
We have studied the processes leading to the cementation of colloidal particles during their autonomous assembly on corroding copper electrodes within a Cu-Au galvanic rnicroreactor. We determined the onset of particle immobilization through particle tracking, monitored the dissolution of copper as well as the deposition of insoluble products of the corrosion reactions in situ, and showed that particle immobilization initiated after reaction products (RPs) began to deposit on the electrode substrate. We further demonstrated that the time and the extent of RP precipitation and thus the strength of the particle-substrate bond could be tuned by varying the amount of copper in the system and the microreactor pH. The ability to cement colloidal particles at locations undergoing corrosion illustrates that the studied colloidal assembly approach holds potential for applications in dynamic material property adaptation.
Jan, L. ; Punckt, C. ; Khusid, B. ; Aksay, I. A. Directed Motion of Colloidal Particles in a Galvanic Microreactor. Langmuir 2013, 29, 2498-2505.Abstract
The mechanisms leading to the deposition of colloidal particles in a copper-gold galvanic microreactor are investigated. Using in situ current density measurements and particle velocimetry, we establish correlations between the spatial arrangement and the geometry of the electrodes, current density distribution, and particle aggregation behavior. Ionic transport phenomena are responsible for the occurrence of strongly localized high current density at the edges and corners of the copper electrodes at large electrode separation, leading to a preferential aggregation of colloidal particles at the electrode edges. Preferential aggregation appears to be the result of a combination of electrophoretic effects and changes in bulk electrolyte flow patterns. We demonstrate that electrolyte flow is most likely driven by electrochemical potential gradients of reaction products formed during the inhomogeneous copper dissolution.
Hsieh, A. G. ; Korkut, S. ; Punckt, C. ; Aksay, I. A. Dispersion Stability of Functionalized Graphene in Aqueous Sodium Dodecyl Sulfate Solutions. Langmuir 2013, 29, 14831-14838.Abstract
The colloidal stability of functionalized graphene sheets (FGSs) in aqueous sodium dodecyl sulfate (SDS) solutions of different concentrations was studied by optical microscopy and ultraviolet visible light absorption after first dispersing the FGSs ultrasonically. In up to similar to 10 mu M SDS solutions, FGSs reaggregated within a few minutes, forming ramified structures in the absence of SDS and increasingly compact structures as the amount of SDS increased. Above similar to 10 mu M, the rate of reaggregation decreased with increasing SDS concentration; above similar to 40 mu M, the suspensions were colloidally stable for over a year. The concentration of similar to 40 mu M SDS lies 2 orders of magnitude below the critical surface aggregation concentration of similar to 1.8 mM SDS on FGSs but above the concentration (similar to 18 mu M) at which SDS begins to form a monolayer on FGSs. Neither surface micelle nor dense monolayer coverage is therefore required to obtain stable aqueous FGS dispersions. We support our experimental results by calculating the van der Waals and electrostatic interaction energies between FGSs as a function of SDS concentration and show that the experimentally observed transition from an unstable to a stable dispersion correlates with a transition from negative to positive interaction energies between FGSs in the aggregated state. Furthermore, our calculations support experimental evidence that aggregates tend to develop a compact structure over time.
Punckt, C. ; Muckel, F. ; Wolff, S. ; Aksay, I. A. ; Chavarin, C. A. ; Bacher, G. ; Mertin, W. The effect of degree of reduction on the electrical properties of functionalized graphene sheets. Applied Physics Letters 2013, 102.Abstract
We study the effect of carbon to oxygen ratio (C/O) on the electrical resistance of functionalized graphene sheets prepared by thermal exfoliation and reduction of graphite oxide at various temperatures. Using a 2-probe technique in conjunction with Kelvin probe force microscopy, we observe a transition from high-resistance (>400 k Omega/sq) nonlinear current/voltage characteristics at low C/O to low-resistance (<10 k Omega/sq) linear behavior at high C/O, indicating a transition from hopping to diffusive electron transport. Simultaneously, the metal-graphene contacts change from high-resistance Schottky-type behavior to nearly non-invasive metal-metal contact characteristics. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4775582]
Punckt, C. ; Pope, M. A. ; Aksay, I. A. On the Electrochemical Response of Porous Functionalized Graphene Electrodes. Journal of Physical Chemistry C 2013, 117, 16076-16086.Abstract
Electrodes used in electroanalysis, which are based on carbonaceous nanomaterials such as carbon nanotubes or graphene, often exhibit large degrees of porosity. By systematically varying the morphology of functionalized graphene electrodes from nearly flat to highly porous, we demonstrate experimentally that minute amounts of electrode porosity have surprisingly significant effects on the apparent reaction kinetics as determined by cyclic voltammetry, both in the reversible and the irreversible regime. We quantify electrode porosity using a coulometric approach and, with the help of numerical simulations, determine the correlation between electrode pore volume and apparent electrode kinetics. We show that in the reversible and quasi-reversible regime, the voltamperometric response constitutes a superposition of thin film diffusion-related effects within the porous electrode and of the standard flat electrode response. For irreversible kinetics, however, we show that diffusive coupling between the electrode and the electrolyte can, under suitably chosen conditions, result in effective electrocatalytic behavior. Confirming past theoretical work by Compton and others, our experiments demonstrate that for a comparison of electroanalytical data obtained with different electrode materials it is not sufficient to only consider differences in the materials' chemical structure but equally important to take into account differences in electrode morphology.
Liu, Y. F. M. ; Punckt, C. ; Pope, M. A. ; Gelperin, A. ; Aksay, I. A. Electrochemical Sensing of Nitric Oxide with Functionalized Graphene Electrodes. ACS Applied Materials & Interfaces 2013, 5 12624-12630.Abstract
The intrinsic electrocatalytic properties of functionalized graphene sheets (FGSs) in nitric oxide (NO) sensing are determined by cyclic voltammetry with FGS monolayer electrodes. The degrees of reduction and defectiveness of the FGSs are varied by employing different heat treatments during their fabrication. FGSs with intermediate degrees of reduction and high Raman I-D to I-G peak ratios exhibit an NO oxidation peak potential of 794 mV (vs 1 M Ag/AgCl), closely matching values obtained with a platinized Pt control (791 mV) as well as recent results from the literature on porous or biofunctionalized electrodes. We show that the peak potential obtained with FGS electrodes can be further reduced to 764 mV by incorporation of electrode porosity using a drop-casting approach, indicating a stronger apparent electrocatalytic effect on porous FGS electrodes as compared to platinized Pt. Taking into consideration effects of electrode Morphology, we thereby demonstrate that FGSs are intrinsically as catalytic toward NO oxidation as platinum. The lowered peak potential of porous FGS electrodes is accompanied by a significant increase in peak current, which we attribute either to pore depletion effects or an amplification effect due to subsequent electrooxidation reactions. Our results suggest that the development of sensor electrodes with higher sensitivity and lower detection limits should be feasible with FGSs.
Pope, M. A. ; Korkut, S. ; Punckt, C. ; Aksay, I. A. Supercapacitor Electrodes Produced through Evaporative Consolidation of Graphene Oxide-Water-Ionic Liquid Gels. Journal of the Electrochemical Society 2013, 160, A1653-A1660.Abstract
We use colloidal gels of graphene oxide in a water-ethanol-ionic liquid solution to assemble graphene-ionic liquid laminated structures for use as electrodes in electrochemical double layer capacitors. Our process involves evaporation of water and ethanol yielding a graphene oxide/ionic liquid composite, followed by thermal reduction of the graphene oxide to electrically conducting functionalized graphene. This yields an electrode in which the ionic liquid serves not only as the working electrolyte but also as a spacer to separate the graphene sheets and to increase their electrolyte-accessible surface area. Using this approach, we achieve an outstanding energy density of 17.5 Wh/kg at a gravimetric capacitance of 156 F/g and 3 V operating voltage, due to a high effective density of the active electrode material of 0.46 g/cm(2). By increasing the ionic liquid content and the degree of thermal reduction, we obtain electrodes that retain >90% of their capacitance at a scan rate of 500 mV/s, illustrating that we can tailor the electrodes toward higher power density if energy density is not the primary goal. The elimination of the electrolyte infiltration step from manufacturing makes,this bottom-up assembly approach scalable and well-suited for combinations of potentially any graphene material with ionic liquid electrolytes. (C) 2013 The Electrochemical Society. All rights reserved.
2012
Prud'homme, R. K. ; Aksay, I. A. ; Herrera-Alonso, M. Separation medium containing thermally exfoliated graphite oxide, 2012.Abstract
A separation medium, such as a chromatography filling or packing, containing a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m2/g to 2600 m2/g, wherein the thermally exfoliated graphite oxide has a surface that has been at least partially functionalized.
Prud'homme, R. K. ; O'Neil, C. ; Ozbas, B. ; Aksay, I. A. ; Register, R. ; Adamson, D. Functional graphene-polymer nanocomposites for gas barrier applications, 2012.Abstract
A gas diffusion barrier contains a polymer matrix and a functional graphene which displays no signature of graphite and/or graphite oxide, as determined by X-ray diffraction.
Prud'homme, R. K. ; Aksay, I. A. Gas storage cylinder formed from a composition containing thermally exfoliated graphite, 2012.Abstract
A gas storage cylinder or gas storage cylinder liner, formed from a polymer composite, containing at least one polymer and a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m2/g to 2600 m2/g.
Aksay, I. A. ; Yeh, T. C. - H. ; Saville, D. A. Supercapacitor and battery electrode containing thermally exfoliated graphite oxide, 2012.Abstract
A supercapacitor or battery electrode containing a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m2/g to 2600 m2/g.
Liu, J. ; Aksay, I. A. ; Choi, D. ; Wang, D. ; Yang, Z. Nanocomposite of graphene and metal oxide materials, 2012.Abstract
Nanocomposite materials comprising a metal oxide bonded to at least one graphene material. The nanocomposite materials exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate greater than about 10C.
Punckt, C. ; Jan, L. ; Jiang, P. ; Frewen, T. A. ; Saville, D. A. ; Kevrekidis, I. G. ; Aksay, I. A. Autonomous colloidal crystallization in a galvanic microreactor. Journal of Applied Physics 2012, 112.Abstract
We report on a technique that utilizes an array of galvanic microreactors to guide the assembly of two-dimensional colloidal crystals with spatial and orientational order. Our system is comprised of an array of copper and gold electrodes in a coplanar arrangement, immersed in a dilute hydrochloric acid solution in which colloidal micro-spheres of polystyrene and silica are suspended. Under optimized conditions, two-dimensional colloidal crystals form at the anodic copper with patterns and crystal orientation governed by the electrode geometry. After the aggregation process, the colloidal particles are cemented to the substrate by co-deposition of reaction products. As we vary the electrode geometry, the dissolution rate of the copper electrodes is altered. This way, we control the colloidal motion as well as the degree of reaction product formation. We show that particle motion is governed by a combination of electrokinetic effects acting directly on the colloidal particles and bulk electrolyte flow generated at the copper-gold interface. (C) 2012 American Institute of Physics.
Bozlar, M. ; Punckt, C. ; Korkut, S. ; Zhu, J. ; Foo, C. C. ; Suo, Z. G. ; Aksay, I. A. Dielectric elastomer actuators with elastomeric electrodes. Applied Physics Letters 2012, 101.Abstract
For many applications of dielectric elastomer actuators, it is desirable to replace the carbon-grease electrodes with stretchable, solid-state electrodes. Here, we attach thin layers of a conducting silicone elastomer to prestrained films of an acrylic dielectric elastomer and achieve voltage-actuated areal strains over 70%. The influence of the stiffness of the electrodes and the prestrain of the dielectric films is studied experimentally and theoretically. (C) 2012 American Institute of Physics.
Liu, L. M. ; Car, R. ; Selloni, A. ; Dabbs, D. M. ; Aksay, I. A. ; Yetter, R. A. Enhanced Thermal Decomposition of Nitromethane on Functionalized Graphene Sheets: Ab Initio Molecular Dynamics Simulations. Journal of the American Chemical Society 2012, 134, 19011-19016.Abstract
The burning rate of the monopropellant nitromethane (NM) has been observed to increase by adding and dispersing small amounts of functionalized graphene sheets (FGSs) in liquid NM. Until now, no plausible mechanisms for FGSs acting as combustion catalysts have been presented. Here, we report ab initio molecular dynamics simulations showing that carbon vacancy defects within the plane of the FGSs, fimctionalized with oxygen-containing groups, greatly accelerate the thermal decomposition of NM and its derivatives. This occurs through reaction pathways involving the exchange of protons or oxygens between the oxygen-containing functional groups and NM and its derivatives. FGS initiates and promotes the decomposition of the monopropellant and its derivatives, ultimately forming H2O, CO2, and N-2. Concomitantly, oxygen-containing functional groups on the FGSs are consumed and regenerated without significantly changing the FGSs in accordance with experiments indicating that the FGSs are not consumed during combustion.
Roy-Mayhew, J. D. ; Boschloo, G. ; Hagfeldt, A. ; Aksay, I. A. Functionalized Graphene Sheets as a Versatile Replacement for Platinum in Dye-Sensitized Solar Cells. ACS Applied Materials & Interfaces 2012, 4 2794-2800.Abstract
Several techniques for fabricating functionalized graphene sheet (FGS) electrodes were tested for catalytic performance in dye-sensitized solar cells (DSSCs). By using ethyl cellulose as a sacrificial binder, and partially thermolyzing it, we were able to create electrodes which exhibited lower effective charge transfer resistance (<1 Omega cm(2)) than the thermally decomposed chloroplatinic acid electrodes traditionally used. This performance was achieved not only for the triiodide/iodide redox couple, but also for the two other major redox mediators used in DSSCs, based on cobalt and sulfur complexes, showing the versatility of the electrode. DSSCs using these FGS electrodes had efficiencies (eta) equal to or higher than those using thermally decomposed chloroplatinic acid electrodes in each of the three major redox mediators: I (eta(FGS) = 6.8%, eta(Pt) = 6.8%), Co (4.5%, 4.4%), S (3.5%, 2.0%). Through an analysis of the thermolysis of the binder and composite material, we determined that the high surface area of an electrode, as determined by nitrogen adsorption, is consistent with but not sufficient for high performing electrodes. Two other important considerations are that (i) enough residue remains in the composite to maintain structural stability and prevent restacking of FGSs upon the introduction of the solvent, and (ii) this residue must not disperse in the electrolyte.
Li, X. L. ; Qi, W. ; Mei, D. H. ; Sushko, M. L. ; Aksay, I. ; Liu, J. Functionalized Graphene Sheets as Molecular Templates for Controlled Nucleation and Self-Assembly of Metal Oxide-Graphene Nanocomposites. Advanced Materials 2012, 24, 5136-5141.
Dabbs, D. M. ; Aksay, I. A. Multifunctional and Low-Density Inorganic Nanocomposites. JOM 2012, 64, 226-233.Abstract
We summarize our recent studies on the use of low-density nanoporous silica structures prepared through templating of a self-assembling disordered liquid-crystalline L (3) phase, as a matrix for use in numerous applications, including sensing, optical data storage, drug release, and structural. The silica matrix exhibits low density (0.5 g cm(-3) to 0.8 g cm(-3) for monoliths, 0.6 g cm(-3) to 0.99 g cm(-3) for fibers) coupled with high surface areas (up 1400 m(2) g(-1)) and void volumes (65% or higher). High-surface-area coatings are used to increase the sensitivity of mass-detecting quartz crystal microbalances to over 4000 times that of uncoated crystals. Monoliths, films, and fibers are produced using the templated silica gel. Once dried and converted to silica, the nanostructured material exhibits high fracture strength (up to 35 MPa in fibers) and Young's modulus (30 GPa to 40 GPa in fibers). These values are, respectively, two orders of magnitude and twice those of nanostructured silicas having comparable densities.
Ozbas, B. ; O'Neill, C. D. ; Register, R. A. ; Aksay, I. A. ; Prud'homme, R. K. ; Adamson, D. H. Multifunctional elastomer nanocomposites with functionalized graphene single sheets. Journal of Polymer Science Part B-Polymer Physics 2012, 50, 910-916.Abstract
We demonstrate the use of functionalized graphene sheets (FGSs) as multifunctional nanofillers to improve mechanical properties, lower gas permeability, and impart electrical conductivity for several distinct elastomers. FGS consists mainly of single sheets of crumbled graphene containing oxygen functional groups and is produced by the thermal exfoliation of oxidized graphite (GO). The present investigation includes composites of FGS and three elastomers: natural rubber (NR), styrenebutadiene rubber, and polydimethylsiloxane (PDMS). All of these elastomers show similar and significant improvements in mechanical properties with FGS, indicating that the mechanism of property improvement is inherent to the FGS and not simply a function of chemical crosslinking. The decrease in gas permeability is attributed to the high aspect ratio of the FGS sheets. This creates a tortuous path mechanism of gas diffusion; fitting the permeability data to the Nielsen model yields an aspect ratio of similar to 1000 for the FGS. Electrical conductivity is demonstrated at FGS loadings as low as 0.08% in PDMS and reaches 0.3 S/m at 4 wt % loading in NR. This combination of functionalities imparted by FGS is shown to result from its high aspect ratio and carbon-based structure. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012
Crain, J. M. ; Lettow, J. S. ; Aksay, I. A. ; Korkut, S. A. ; Chiang, K. S. ; Chen, C. - H. ; Prud'homme, R. K. Printed electronics, 2012.Abstract
Printed electronic device comprising a substrate onto at least one surface of which has been applied a layer of an elec. conductive ink comprising functionalized graphene sheets and at least one binder. A method of prepg. printed electronic devices is further disclosed.
Ozbas, B. ; Toki, S. ; Hsiao, B. S. ; Chu, B. ; Register, R. A. ; Aksay, I. A. ; Prud'homme, R. K. ; Adamson, D. H. Strain-induced crystallization and mechanical properties of functionalized graphene sheet-filled natural rubber. Journal of Polymer Science Part B-Polymer Physics 2012, 50, 718-723.Abstract
The effects of functionalized graphene sheets (FGSs) on the mechanical properties and strain-induced crystallization of natural rubber (NR) are investigated. FGSs are predominantly single sheets of graphene with a lateral size of several hundreds of nanometers and a thickness of 1.5 nm. The effect of FGS and that of carbon black (CB) on the strain-induced crystallization of NR is compared by coupled tensile tests and X-ray diffraction experiments. Synchrotron X-ray scattering enables simultaneous measurements of stress and crystallization of NR in real time during sample stretching. The onset of crystallization occurs at significantly lower strains for FGS-filled NR samples compared with CB-filled NR, even at low loadings. Neat-NR exhibits strain-induced crystallization around a strain of 2.25, while incorporation of 1 and 4 wt % FGS shifts the crystallization to strains of 1.25 and 0.75, respectively. In contrast, loadings of 16 wt % CB do not significantly shift the critical strain for crystallization. Two-dimensional (2D) wide angle X-ray scattering patterns show minor polymer chain alignment during stretching, in accord with previous results for NR. Small angle X-ray scattering shows that FGS is aligned in the stretching direction, whereas CB does not show alignment or anisotropy. The mechanical properties of filled NR samples are investigated using cyclic tensile and dynamic mechanical measurements above and below the glass transition of NR. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012
2011
Pan, S. Y. ; Aksay, I. A. Factors Controlling the Size of Graphene Oxide Sheets Produced via the Graphite Oxide Route. ACS Nano 2011, 5 4073-4083.Abstract
We have studied the effect of the oxidation path and the mechanical energy input on the size of graphene oxide sheets derived from graphite oxide. The cross-planar oxidation of graphite from the (0002) plane results in periodic cracking of the uppermost graphene oxide layer, limiting its lateral dimension to less than 30 mu m. We use an energy balance between the elastic strain energy associated with the undulation of graphene oxide sheets at the hydroxyl and epoxy sites, the crack formation energy, and the interaction energy between graphene layers to determine the cell size of the cracks. As the effective crack propagation rate in the cross-planar direction is an order of magnitude smaller than the edge-to-center oxidation rate, graphene oxide single sheets larger than those defined by the periodic cracking cell size are produced depending on the aspect ratio of the graphite particles. We also demonstrate that external energy input from hydrodynamic drag created by fluid motion or sonication, further reduces the size of the graphene oxide sheets through tensile stress buildup in the sheets.
Aksay, I. A. ; Milius, D. L. ; Korkut, S. ; Prud'homme, R. K. Functionalized graphene sheets having high carbon to oxygen ratios, 2011.Abstract
Functionalized graphene sheets having a C to O molar ratio of at least ∼23:1 and method of prepg. the same. [on SciFinder(R)]
Zhang, S. ; Shao, Y. Y. ; Liao, H. G. ; Liu, J. ; Aksay, I. A. ; Yin, G. P. ; Lin, Y. H. Graphene Decorated with PtAu Alloy Nanoparticles: Facile Synthesis and Promising Application for Formic Acid Oxidation. Chemistry of Materials 2011, 23, 1079-1081.
Zhang, S. ; Shao, Y. Y. ; Liu, J. ; Aksay, I. A. ; Lin, Y. H. Graphene-Polypyrrole Nanocomposite as a Highly Efficient and Low Cost Electrically Switched Ion Exchanger for Removing ClO4- from Wastewater. ACS Applied Materials & Interfaces 2011, 3 3633-3637.Abstract
Perchlorate (ClO4-) contamination is a widespread concern affecting water utilities. In the present study, functionalized graphene sheets were employed as the scaffold to synthesize a novel graphene-polypyrrole (Ppy) nanocomposite, which served as an excellent electrically switched ion exchanger for perchlorate removal. Scanning electron microscopy and electrochemical measurements showed that the 3D nanostructured graphene-Ppy nanocomposite exhibited a significantly improved uptake capacity for ClO4- compared with Ppy film alone. X-ray photoelectron spectroscopy confirmed the uptake and release process of ClO4- in graphene-Ppy nanocomposite. In addition, the presence of graphene substrate resulted in high stability of graphene-Ppy nanocomposite during potential cycling. The present work provides a promising method for large scale water treatment.
Xiao, J. ; Mei, D. H. ; Li, X. L. ; Xu, W. ; Wang, D. Y. ; Graff, G. L. ; Bennett, W. D. ; Nie, Z. M. ; Saraf, L. V. ; Aksay, I. A. ; et al. Hierarchically Porous Graphene as a Lithium-Air Battery Electrode. Nano Letters 2011, 11, 5071-5078.Abstract
The lithium-ir battery is one of the most promising technologies among various electrochemical energy storage systems. We demonstrate that a novel air electrode consisting of an unusual hierarchical arrangement of functionalized graphene sheets (with no catalyst) delivers an exceptionally high capacity of 15000 mAh/g in lithium-O-2 batteries which is the highest value ever reported in this field. This excellent performance is attributed to the unique bimodal porous structure of the electrode which consists of microporous channels facilitating rapid O-2 diffusion while the highly connected nanoscale pores provide a high density of reactive sites for Li-O-2 reactions. Further, we show that the defects and functional groups on graphene favor the formation of isolated nanosized Li2O2 particles and help prevent air blocking in the air electrode. The hierarchically ordered porous structure in bulk graphene enables its practical applications by promoting accessibility to most graphene sheets in this structure.
Korkut, S. ; Roy-Mayhew, J. D. ; Dabbs, D. M. ; Milius, D. L. ; Aksay, I. A. High Surface Area Tapes Produced with Functionalized Graphene. ACS Nano 2011, 5 5214-5222.Abstract
We describe a scalable method for producing continuous graphene networks by tape casting surfactant-stabilized aqueous suspensions of functionalized graphene sheets. Similar to all other highly connected graphene-containing networks, the degree of overlap between the sheets controls the tapes' electrical and mechanical properties. However, unlike other graphene-containing networks, the specific surface area of the cast tapes remains high (>400 m(2).g(-1)). Exhibiting apparent densities between 0.15 and 0.51 g.cm(-3), with electrical conductivities up to 24 kS.m(-1) and tensile strengths over 10 MPa, these tapes exhibit the best combination of properties with respect to density heretofore observed for carbon-based papers, membranes, or films.
Pope, M. A. ; Punckt, C. ; Aksay, I. A. Intrinsic Capacitance and Redox Activity of Functionalized Graphene Sheets. Journal of Physical Chemistry C 2011, 115, 20326-20334.Abstract
We present a general method for characterizing the intrinsic electrochemical properties of graphene sheets, such as the specific double-layer capacitance, in the absence of porosity-related artifacts and uncertainties. By assembling densely tiled monolayers of electrically insulating or conductive functionalized graphene sheets onto electrode substrates (gold and highly oriented pyrolytic graphite), we demonstrate our ability to isolate their intrinsic electrochemical response in terms of surface-specific double-layer capacitance and redox behavior. Using this system, the electrochemical properties of various types of graphene can be directly compared without the need to take into account changes in electrode morphology and electrolyte accessibility arising because of varying material properties.
Yan, L. ; Punckt, C. ; Aksay, I. A. ; Mertin, W. ; Bacher, G. Local Voltage Drop in a Single Functionalized Graphene Sheet Characterized by Kelvin Probe Force Microscopy. Nano Letters 2011, 11, 3543-3549.Abstract
We studied the local voltage drop in functionalized graphene sheets of sub mu m size under external bias conditions by Kelvin probe force microscopy. Using this noninvasive experimental approach, we measured ohmic current-voltage characteristics and an intrinsic conductivity of about 3.7 x 10(5) S/m corresponding to a sheet resistance of 2.7 k Omega/sq under ambient conditions for graphene produced via thermal reduction of graphite oxide. The contact resistivity between functionalized graphene and metal electrode was found. to be <6.3 x 10(-7) Omega cm(2).
Pan, S. ; Aksay, I. A. ; Prudhomme, R. K. Multifunctional graphene-silicone elastomer nanocomposite, method of making the same, and uses thereof, 2011.Abstract
In a nanocomposite compn. having a silicone elastomer matrix having therein a filler loading of greater than 0.05 wt %, based on total nanocomposite wt., the filler is functional graphene sheets (FGS) having a surface area of from 300 m2/g to 2630 m2/g; and a method for producing the nanocomposite and uses thereof. [on SciFinder(R)]
Yan, L. ; Punckt, C. ; Aksay, I. A. ; Mertin, W. ; Bacher, G. Potential Distribution in Functionalized Graphene Devices Probed by Kelvin Probe Force Microscopy. In Physics of Semiconductors: 30th International Conference on the Physics of Semiconductors; Ihm, J. ; Cheong, H., Ed. American Institute of Physics, 2011; Vol. 1399. Publisher's VersionAbstract
Kelvin probe force microscopy was used to study the impact of contacts and topography on the local potential distribution on contacted, individual functionalized graphene sheets (FGS) deposited on a SiO2/Si substrate. Negligible contact resistance is found at the graphene/Ti interface and a graphene resistance of 2.3 k Omega is extracted for a single sheet with sub-mu m size. Pronounced steps in the topography, which we attribute to a variation of the spacing between graphene and substrate, result in a significant change of the local resistivity.
Cao, Y. L. ; Li, X. L. ; Aksay, I. A. ; Lemmon, J. ; Nie, Z. M. ; Yang, Z. G. ; Liu, J. Sandwich-type functionalized graphene sheet-sulfur nanocomposite for rechargeable lithium batteries. Physical Chemistry Chemical Physics 2011, 13, 7660-7665.Abstract
A functionalized graphene sheet-sulfur (FGSS) nanocomposite was synthesized as the cathode material for lithium-sulfur batteries. The structure has a layer of functionalized graphene sheets/stacks (FGS) and a layer of sulfur nanoparticles creating a three-dimensional sandwich-type architecture. This unique FGSS nanoscale layered composite has a high loading (70 wt%) of active material (S), a high tap density of similar to 0.92 g cm(-3), and a reversible capacity of similar to 505 mAh g(-1) (similar to 464 mAh cm(-3)) at a current density of 1680 mA g(-1) (1C). When coated with a thin layer of cation exchange Nafion film, the migration of dissolved polysulfide anions from the FGSS nanocomposite was effectively reduced, leading to a good cycling stability of 75% capacity retention over 100 cycles. This sandwich-structured composite conceptually provides a new strategy for designing electrodes in energy storage applications.
Liu, J. ; Aksay, I. A. ; Choi, D. ; Kou, R. ; Nie, Z. ; Wang, D. ; Yang, Z. Self assembled multi-layer nanocomposite of graphene and metal oxide materials, 2011.Abstract
Nanocomposite materials having at least two layers, each layer consisting of one metal oxide bonded to at least one graphene layer were developed. The nanocomposite materials will typically have many alternating layers of metal oxides and graphene layers, bonded in a sandwich type construction and will be incorporated into an electrochem. or energy storage device. [on SciFinder(R)]
Liu, J. ; Choi, D. ; Kou, R. ; Nie, Z. ; Wang, D. ; Yang, Z. ; Aksay, I. A. Self assembled multi-layer nanocomposite of graphene and metal oxide materials, 2011.Abstract
Nanocomposite materials having at least two layers, each layer consisting of one metal oxide bonded to at least one graphene layer were developed. The nanocomposite materials will typically have many alternating layers of metal oxides and graphene layers, bonded in a sandwich type construction and will be incorporated into an electrochem. or energy storage device. [on SciFinder(R)]
Roy-Mayhew, J. ; Aksay, I. Semiconductor coated microporous graphene scaffolds for solar cells, 2011.Abstract
The invention refers to a high surface area scaffold to be used for a solar cell, made of a three-dimensional percolated network of functionalized graphene sheets. It may be used in the prepn. of a high surface area electrode by coating with a semiconductive material. Electronic devices can be made therefrom, including solar cells such as dye-sensitized solar cells. [on SciFinder(R)]
Kou, R. ; Shao, Y. Y. ; Mei, D. H. ; Nie, Z. M. ; Wang, D. H. ; Wang, C. M. ; Viswanathan, V. V. ; Park, S. ; Aksay, I. A. ; Lin, Y. H. ; et al. Stabilization of Electrocatalytic Metal Nanoparticles at Metal-Metal Oxide-Graphene Triple Junction Points. Journal of the American Chemical Society 2011, 133, 2541-2547.Abstract
Carbon-supported precious metal catalysts are widely used in heterogeneous catalysis and electrocatalysis, and enhancement of catalyst dispersion and stability by controlling the interfacial structure is highly desired. Here we report a new method to deposit metal oxides and metal nanoparticles on graphene and form stable metal-metal oxide-graphene triple junctions for electrocatalysis applications. We first synthesize indium tin oxide (ITO) nanocrystals directly on functionalized graphene sheets, forming an ITO-graphene hybrid. Platinum nanoparticles are then deposited, forming a unique triple-junction structure (Pt-ITO-graphene). Our experimental work and periodic density functional theory (DFT) calculations show that the supported Pt nanoparticles are more stable at the Pt-ITO-graphene triple junctions. Furthermore, DFT calculations suggest that the defects and functional groups on graphene also play an important role in stabilizing the catalysts. These new catalyst materials were tested for oxygen reduction for potential applications in polymer electrolyte membrane fuel cells, and they exhibited greatly enhanced stability and activity.
Castrillon, S. R. V. ; Giovambattista, N. ; Aksay, I. A. ; Debenedetti, P. G. Structure and Energetics of Thin Film Water. Journal of Physical Chemistry C 2011, 115, 4624-4635.Abstract
We present a molecular dynamics (MD) simulation study of the structure and energetics of thin films of water adsorbed on solid substrates at 240 K. By considering crystalline silica as a model hydrophilic surface, we systematically investigate the effect of film thickness on the hydrogen bonding, density, molecular orientation, and energy of adsorbed water films over a broad surface coverage range (delta). At the lowest coverage investigated (delta = 1 monolayer, >90% of water molecules form three hydrogen bonds (H-bonds) with surface silanol groups and none with other water molecules; when delta = 1 ML, the most probable molecular orientation is characterized by both the molecular dipole and the OH vectors being parallel to the surface. As 6 increases, water-water and water-surface interactions compete, leading to the appearance of an orientational structure near the solid-liquid interface characterized by the dipole moment pointing toward the silica surface. We find that the water-surface H-bond connectivity and energetics of the molecular layer nearest to the solid liquid interface do not change as delta increases. Interfacial water molecules, therefore, are able to reorient and form water-water H-bonds without compromising water-surface interactions. The surface-induced modifications to the orientational structure of the adsorbed film propagate up to similar to 1.4 nm from the solid-liquid interface when delta = 15.1 ML (a film that is similar to 2.3 run thick). For the thinner adsorbed films (delta <= 4.3 ML, thickness <= 0.8 nm) orientational correlations imposed by the solid liquid and liquid-vapor interfaces are observed throughout.
2010
Tang, Z. W. ; Wu, H. ; Cort, J. R. ; Buchko, G. W. ; Zhang, Y. Y. ; Shao, Y. Y. ; Aksay, I. A. ; Liu, J. ; Lin, Y. H. Constraint of DNA on Functionalized Graphene Improves its Biostability and Specificity. Small 2010, 6 1205-1209.
Punckt, C. ; Pope, M. A. ; Liu, J. ; Lin, Y. H. ; Aksay, I. A. Electrochemical Performance of Graphene as Effected by Electrode Porosity and Graphene Functionalization. Electroanalysis 2010, 22, 2834-2841.Abstract
Graphene-based electrodes have recently gained popularity due to their superior electrochemical properties. However, the exact mechanisms of electrochemical activity are not yet understood. Here, we present data from NADH oxidation and ferri/ferrocyanide redox probe experiments to demonstrate that both (i) the porosity of the graphene electrodes, as effected by the packing morphology, and (ii) the functional group and the lattice defect concentration play a significant role on their electrochemical performance.
Prud'homme, R. K. ; O'Neil, C. D. ; Ozbas, B. ; Aksay, I. A. ; Register, R. A. ; Adamson, D. H. Functional graphene-polymer nanocomposites for gas barrier applications, 2010.Abstract
A gas diffusion barrier contains a polymer matrix and a functional graphene which displays no signature of graphite and/or graphite oxide, as detd. by X-ray diffraction. [on SciFinder(R)]
Prud'homme, R. K. ; Ozbas, B. ; Aksay, I. A. ; Register, R. A. ; Adamson, D. H. Functional graphene-rubber nanocomposites, 2010.Abstract
A polymer compn., contg. a polymer matrix which contains an elastomer; and a functional graphene which displays no signature of graphite and/or graphite oxide, as detd. by x-ray diffraction, exhibits excellent strength, toughness, modulus, thermal stability and elec. cond. [on SciFinder(R)]
Roy-Mayhew, J. D. ; Bozym, D. J. ; Punckt, C. ; Aksay, I. A. Functionalized Graphene as a Catalytic Counter Electrode in Dye-Sensitized Solar Cells. ACS Nano 2010, 4 6203-6211.Abstract
When applied on the counter electrode of a dye-sensitized solar cell, functionalized graphene sheets with oxygen-containing sites perform comparably to platinum (conversion efficiencies of 5.0 and 5.5%, respectively, at 100 mW cm(-2) AM1.56 simulated light). To interpret the catalytic activity of functionalized graphene sheets toward the reduction of triiodide, we propose a new electrochemical impedance spectroscopy equivalent circuit that matches the observed spectra features to the appropriate phenomena. Using cyclic voltammetry, we also show that tuning our material by increasing the amount of oxygen-containing functional groups can improve its apparent catalytic activity. Furthermore, we demonstrate that a functionalized graphene sheet based ink can serve as a catalytic, flexible, electrically conductive counter electrode material.
Shao, Y. Y. ; Wang, J. ; Wu, H. ; Liu, J. ; Aksay, I. A. ; Lin, Y. H. Graphene Based Electrochemical Sensors and Biosensors: A Review. Electroanalysis 2010, 22, 1027-1036.Abstract
Graphene, emerging as a true 2-dimensional material, has received increasing attention due to its unique physicochemical properties (high surface area, excellent conductivity, high mechanical strength, and ease of functionalization and mass production). This article selectively reviews recent advances in graphene-based electrochemical sensors and biosensors. In particular, graphene for direct electrochemistry of enzyme, its electrocatalytic activity toward small biomolecules (hydrogen peroxide, NADH, dopamine, etc.), and graphene-based enzyme biosensors have been summarized in more detail; Graphene-based DNA sensing and environmental analysis have been discussed. Future perspectives in this rapidly developing field are also discussed.
Kang, X. H. ; Wang, J. ; Wu, H. ; Liu, J. ; Aksay, I. A. ; Lin, Y. H. A graphene-based electrochemical sensor for sensitive detection of paracetamol. Talanta 2010, 81, 754-759.Abstract
An electrochemical sensor based on the electrocatalytic activity of functionalized graphene for sensitive detection of paracetamol is presented. The electrochemical behaviors of paracetamol on graphene-modified glassy carbon electrodes (GCEs) were investigated by cyclic voltammetry and square-wave voltammetry. The results showed that the graphene-modified electrode exhibited excellent electrocatalytic activity to paracetamol. A quasi-reversible redox process of paracetamol at the modified electrode was obtained, and the over-potential of paracetamol decreased significantly compared with that at the bare GCE. Such electrocatalytic behavior of graphene is attributed to its unique physical and chemical properties, e.g., subtle electronic characteristics, attractive pi-pi interaction, and strong adsorptive capability. This electrochemical sensor shows an excellent performance for detecting paracetamol with a detection limit of 3.2 x 10(-8) M, a reproducibility of 5.2% relative standard deviation, and a satisfied recovery from 96.4% to 103.3%. The sensor shows great promise for simple, sensitive, and quantitative detection and screening of paracetamol. (C) 2010 Elsevier B.V. All rights reserved.
Liu, J. ; Aksay, I. A. ; Choi, D. ; Wang, D. ; Yang, Z. Nanocomposite of graphene and metal oxide materials, 2010.Abstract
Nanocomposite materials consist of a metal oxide bonded to at least one graphene material. The graphene layer has a carbon to oxygen ratio of (20-500):1 and a surface area of 600-2630 m2/g. The metal oxide can be an oxide of Ti, Sn, Ni, Mn, V, Si, or Co, preferably titania in the form of rutile or anatase, or tin oxide. The nanocomposite materials exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate of ⪆10 C. The nanocomposite material is prepd. by providing graphene in a first suspension; dispersing the graphene with a surfactant, esp. sodium dodecyl sulfate; adding a metal oxide precursor to the dispersed graphene to form a second suspension; and pptg. the metal oxide from the second suspension onto at least one surface of the dispersed graphene to form the nanocomposite material. The nanocomposite material can be used in an energy storage device, esp. in a lithium ion battery as electrode material. [on SciFinder(R)]
Liu, J. ; Aksay, I. A. ; Choi, D. ; Wang, D. ; Yang, Z. Nanocomposite of graphene and metal oxide materials and its use in energy storage devices, 2010.Abstract
Nanocomposite materials consists of a metal oxide bonded to at least one graphene material. The graphene layer has a carbon to oxygen ratio of (20-500):1 and a surface area of 600-2630 m2/g. The metal oxide can be an oxide of Ti, Sn, Ni, Mn, V, Si, or Co, preferably titania in the form of rutile or anatase, or tin oxide. The nanocomposite materials exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate of ⪆10 C. The nanocomposite material is prepd. by providing graphene in a first suspension; dispersing the graphene with a surfactant, esp. sodium dodecyl sulfate; adding a metal oxide precursor to the dispersed graphene to form a second suspension; and pptg. the metal oxide from the second suspension onto at least one surface of the dispersed graphene to form the nanocomposite material. The nanocomposite material can be used in an energy storage device, esp. in a lithium ion battery as electrode material. [on SciFinder(R)]
Shao, Y. Y. ; Zhang, S. ; Engelhard, M. H. ; Li, G. S. ; Shao, G. C. ; Wang, Y. ; Liu, J. ; Aksay, I. A. ; Lin, Y. H. Nitrogen-doped graphene and its electrochemical applications. Journal of Materials Chemistry 2010, 20, 7491-7496.Abstract
Nitrogen-doped graphene (N-graphene) is obtained by exposing graphene to nitrogen plasma. N-graphene exhibits much higher electrocatalytic activity toward oxygen reduction and H(2)O(2) reduction than graphene, and much higher durability and selectivity than the widely-used expensive Pt for oxygen reduction. The excellent electrochemical performance of N-graphene is attributed to nitrogen functional groups and the specific properties of graphene. This indicates that N-graphene is promising for applications in electrochemical energy devices (fuel cells, metal-air batteries) and biosensors.
Aksay, I. A. ; Bekircan, S. H. ; Crain, J. M. ; Gurdag, S. ; Guven, E. ; Javaherian, N. ; Lettow, J. S. ; Redmond, K. ; Tekmek, O. ; Vatansever, A. ; et al. Polymeric fibers and articles and forming reinforced fiber, 2010.Abstract
Fibers comprise a compn. including a polymer and graphene sheets. The fibers can be further formed into yarns, cords, and fabrics. The fibers can be polyamide, polyester, acrylic, acetate, modacrylic, spandex, lyocell fibers, and the like. Such fibers can take on a variety of forms, including, staple fibers, spun fibers, monofilaments, multifilaments, and the like. [on SciFinder(R)]
Aksay, I. A. ; Buyukdincer, B. ; Javaherian, N. ; Lettow, J. S. ; Pino, G. ; Redmond, K. ; Yildirim, I. O. Reinforced polymeric articles comprising a graphene sheet-reinforced polymers, 2010.Abstract
The reinforcing component of these articles includes a compn. made from at least one polymer and graphene sheets. [on SciFinder(R)]
Du, D. ; Zou, Z. X. ; Shin, Y. S. ; Wang, J. ; Wu, H. ; Engelhard, M. H. ; Liu, J. ; Aksay, I. A. ; Lin, Y. H. Sensitive Immunosensor for Cancer Biomarker Based on Dual Signal Amplification Strategy of Graphene Sheets and Multienzyme Functionalized Carbon Nanospheres. Analytical Chemistry 2010, 82, 2989-2995.Abstract
A novel electrochemical immunosensor for sensitive detection of cancer biomarker alpha-fetoprotein (AFP) is described that uses a graphene sheet sensor platform and functionalized carbon nanospheres (CNSs) labeled with horseradish peroxidase-secondary antibodies (HRP-Ab2). Greatly enhanced sensitivity for the cancer biomarker is based on a dual signal amplification strategy: first, the synthesized CNSs yielded a homogeneous and narrow size distribution, which allowed several binding events of HRP-Ab2 on each nanosphere. Enhanced sensitivity was achieved by introducing the multibioconjugates of HRP-Ab2-CNSs onto the electrode surface through "sandwich" immunoreactions. Second, functionalized graphene sheets used for the biosensor platform increased the surface area to capture a large amount of primary antibodies (Ab1), thus amplifying the detection response. On the basis of the dual signal amplification strategy of graphene sheets and the multienzyme labeling, the developed immunosensor showed a 7-fold increase in detection signal compared to the immunosensor without graphene modification and CNSs labeling. The proposed method could respond to 0.02 ng mL(-1) AFP with a linear calibration range from 0.05 to 6 ng mL(-1). This amplification strategy is a promising platform for clinical screening of cancer biomarkers and point-of-care diagnostics.
Wang, D. H. ; Kou, R. ; Choi, D. ; Yang, Z. G. ; Nie, Z. M. ; Li, J. ; Saraf, L. V. ; Hu, D. H. ; Zhang, J. G. ; Graff, G. L. ; et al. Ternary Self-Assembly of Ordered Metal Oxide-Graphene Nanocomposites for Electrochemical Energy Storage. ACS Nano 2010, 4 1587-1595.Abstract
Surfactant or polymer directed self-assembly has been widely investigated to prepare nanostructured metal oxides, semiconductors, and polymers, but this approach is mostly limited to two-phase materials, organic/inorganic hybrids, and nanoparticle or polymer-based nanocomposites. Self-assembled nanostructures from more complex, multiscale, and multiphase building blocks have been investigated with limited success. Here, we demonstrate a ternary self-assembly approach using graphene as fundamental building blocks to construct ordered metal oxide-graphene nanocomposites. A new class of layered nanocomposites is formed containing stable, ordered alternating layers of nanocrystalline metal oxides with graphene or graphene stacks. Alternatively, the graphene or graphene stacks can be incorporated into liquid-crystal-templated nanoporous structures to form high surface area, conductive networks. The self-assembly method can also be used to fabricate free-standing, flexible metal oxide-graphene nanocomposite films and electrodes. We have investigated the Li-ion insertion properties of the self-assembled electrodes for energy storage and show that the SnO2-graphene nanocomposite films can achieve near theoretical specific energy density without significant charge/discharge degradation.
Prud'homme, R. K. ; Aksay, I. A. ; Adamson, D. ; Abdala, A. Thermally exfoliated graphite oxide and polymer nanocomposites, 2010.Abstract
A modified graphite oxide material contains a thermally exfoliated graphite oxide with a surface area of from ∼300-2600 m2/g, wherein the thermally exfoliated graphite oxide displays no signature of the original graphite and/or graphite oxide, as detd. by x-ray diffraction. [on SciFinder(R)]

Pages