Showing papers by "Yury Gogotsi published in 2012"
TL;DR: Evidence is presented for the exfoliation of the following MAX phases by the simple immersion of their powders, at room temperature, in HF of varying concentrations for times varying between 10 and 72 h followed by sonication.
Abstract: Herein we report on the synthesis of two-dimensional transition metal carbides and carbonitrides by immersing select MAX phase powders in hydrofluoric acid, HF. The MAX phases represent a large (>60 members) family of ternary, layered, machinable transition metal carbides, nitrides, and carbonitrides. Herein we present evidence for the exfoliation of the following MAX phases: Ti2AlC, Ta4AlC3, (Ti0.5,Nb0.5)2AlC, (V0.5,Cr0.5)3AlC2, and Ti3AlCN by the simple immersion of their powders, at room temperature, in HF of varying concentrations for times varying between 10 and 72 h followed by sonication. The removal of the “A” group layer from the MAX phases results in 2-D layers that we are labeling MXenes to denote the loss of the A element and emphasize their structural similarities with graphene. The sheet resistances of the MXenes were found to be comparable to multilayer graphene. Contact angle measurements with water on pressed MXene surfaces showed hydrophilic behavior.
3,080 citations
TL;DR: The rational control of the mechanical, chemical, electronic and optical properties of nanodiamonds through surface doping, interior doping and the introduction of functional groups are discussed.
Abstract: Nanodiamonds have excellent mechanical and optical properties, high surface areas and tunable surface structures. They are also non-toxic, which makes them well suited to biomedical applications. Here we review the synthesis, structure, properties, surface chemistry and phase transformations of individual nanodiamonds and clusters of nanodiamonds. In particular we discuss the rational control of the mechanical, chemical, electronic and optical properties of nanodiamonds through surface doping, interior doping and the introduction of functional groups. These little gems have a wide range of potential applications in tribology, drug delivery, bioimaging and tissue engineering, and also as protein mimics and a filler material for nanocomposites.
2,351 citations
TL;DR: In this paper, Li insertion into a 2D layered Ti-C-based material (MXene) with an oxidized surface, formed by etching Al from Ti₂AlC in HF at room temperature, was reported.
1,165 citations
TL;DR: This work provides the first quantitative picture of the structure of an ionic liquid adsorbed inside realistically modelled microporous carbon electrodes and shows how the separation of the positive and negative ions occurs inside the porous disordered carbons, yielding much higher capacitance values than with simpler electrode geometries.
Abstract: Lightweight, low-cost supercapacitors with the capability of rapidly storing a large amount of electrical energy can contribute to meeting continuous energy demands and effectively levelling the cyclic nature of renewable energy sources1. The excellent electrochemical performance of supercapacitors is due to a reversible ion adsorption in porous carbon electrodes. Recently, it was demonstrated that ions from the electrolyte could enter sub nanometre pores, greatly increasing the capacitance2, 3, 4. However, the molecular mechanism of this enhancement remains poorly understood. Here we provide the first quantitative picture of the structure of an ionic liquid adsorbed inside realistically modelled microporous carbon electrodes. We show how the separation of the positive and negative ions occurs inside the porous disordered carbons, yielding much higher capacitance values (125 F g−1) than with simpler electrode geometries5. The proposed mechanism opens the door for the design of materials with improved energy storage capabilities. It also sheds new light on situations where ion adsorption in porous structures or membranes plays a role.
883 citations
TL;DR: In this article, the optimal pore size of nanoporous carbon electrodes is discussed in terms of the maximal stored energy density. But, the authors focus on the choice of the optimal size of the pore and not on the effect of size dispersion.
Abstract: This paper focuses on the choice of the optimal pore size and the effect of pore size dispersion, which is important for the rational design of nanoporous supercapacitors. Optimization of the pore size of nanoporous carbon electrodes is discussed in terms of the maximal stored energy density. By applying a previously developed theory, and supporting it by newly performed experiments, we find that the energy density is a non-monotonic function of the pore size of monodisperse porous electrodes. The ‘optimal’ pore size that provides the maximal energy density increases with increasing operating voltage and saturates at high voltages. We also analyse how the pore size distribution affects the voltage dependent capacitance and the stored energy density, and show that the latter is maximized for monodisperse electrodes.
438 citations
TL;DR: The measured adsorption capacity for four materials tested negatively correlates with known metrics for pore structure of the carbon powders such as total pore volume and BET-area, but is positively correlated with the volume of pores of sizes <1 nm, suggesting the relevance of these sub-nanometer pores for ion adsorptive capacity.
Abstract: Capacitive deionization (CDI) is a water desalination technology in which salt ions are removed from brackish water by flowing through a spacer channel with porous electrodes on each side. Upon applying a voltage difference between the two electrodes, cations move to and are accumulated in electrostatic double layers inside the negatively charged cathode and the anions are removed by the positively charged anode. One of the key parameters for commercial realization of CDI is the salt adsorption capacity of the electrodes. State-of-the-art electrode materials are based on porous activated carbon particles or carbon aerogels. Here we report the use for CDI of carbide-derived carbon (CDC), a porous material with well-defined and tunable pore sizes in the sub-nanometer range. When comparing electrodes made with CDC with electrodes based on activated carbon, we find a significantly higher salt adsorption capacity in the relevant cell voltage window of 1.2–1.4 V. The measured adsorption capacity for four materi...
388 citations
TL;DR: In this paper, the electronic and elastic properties of two-dimensional early transition metal carbides and nitrides derived from the MAX phases were investigated by first principles calculations utilizing the generalized gradient approximation within the density functional theory.
Abstract: Recently, we reported on the facile synthesis of a number of two-dimensional early transition metal carbides and nitrides, derived from the MAX phases, that we labeled MXenes. Herein, we report on the electronic and elastic properties—investigated by first principles calculations utilizing the generalized gradient approximation within the density functional theory—of the following two-dimensional transition metal carbides: Ti2C, Ti3C2, Ti4C3, V2C, Cr2C, Zr2C, Hf2C, and Ta2C, Ta3C2, and Ta4C3. Similar to the MAX phases, the MXenes are found to be metallic and possess high elastic moduli when stretched along the basal planes.
385 citations
Abstract: A new MXene phase, Ti2C, obtained by aluminum extraction from Ti2AlC and exfoliation of the reaction product, was electrochemically studied vs. Lithium. Li-ions insertion into the 2-D structure was characterized by in situ XRD measurements. Additional electrochemical kinetic characterizations of Ti2C, using a cavity micro-electrode, showed that the electrochemical reactions involve two different phenomena: one diffusion-limited, the other not. A Ti2C/activated carbon asymmetric cell was assembled to highlight the high rate performance of the MXene. The cell was cycled between 1.0 V and 3.5 V, and showed good capacity retention during 1000 galvanostatic charge/discharge cycles at rates up to 10C.
314 citations
TL;DR: In this article, the authors demonstrate that the microwave absorption capacity of carbon materials is highly dependent on their chemical composition and structure, and that the increase of oxygen content in graphite oxides (GO) and/or graphene-based materials remarkably decreases its microwave absorption due to the size decrease of the π-π conjugated structure in these materials, and vice versa.
247 citations
TL;DR: In this paper, the electrochemical flow capacitor (EFC) is proposed to provide rapid charging/discharging while enabling the decoupling of the power and energy ratings, and the energy is stored in the electric double layer of charged carbon particles.
Abstract: Availability of grid-scale electric energy storage systems with response rates on the order of seconds plays a key role in wide implementation of renewable energy sources. Here, a new concept called the electrochemical flow capacitor (EFC) is presented. This new concept shares the major advantages of both supercapacitors and flow batteries, providing rapid charging/discharging while enabling the decoupling of the power and energy ratings. Like in supercapacitors, energy is stored in the electric double layer of charged carbon particles. A flowable carbon-electrolyte mixture is employed as the active material for capacitive energy storage, and is handled in a similar fashion to flow or semi-solid batteries (i.e., for charging/discharging, it is pumped into an electrochemical cell, and for storage, it is pumped into reservoirs). This study presents the proof-of-concept of this technology and reports initial EFC performance data obtained under static and intermittent flow operations.
229 citations
TL;DR: In this paper, the capacitive performance of onion-like carbon (OLC) was studied as a function of the synthesis temperature and compared with diamond soot, carbon black, and activated carbon.
TL;DR: The enhanced mechanical properties and the increased mineralization capability with higher ND-ODA concentration suggest that these biodegradable composites may potentially be useful for a variety of biomedical applications, including scaffolds for orthopedic regenerative engineering.
TL;DR: Observations confirm key aspects of a predicted electric double layer structure from an analytical Landau-Ginzburg-type continuum theory incorporating ion correlation effects, and provide a new baseline for understanding the fundamental nanoscale response of RTILs at charged interfaces.
Abstract: The nanoscale interactions of room temperature ionic liquids (RTILs) at uncharged (graphene) and charged (muscovite mica) solid surfaces were evaluated with high resolution X-ray interface scattering and fully atomistic molecular dynamics simulations. At uncharged graphene surfaces, the imidazolium-based RTIL ([bmim+][Tf2N–]) exhibits a mixed cation/anion layering with a strong interfacial densification of the first RTIL layer. The first layer density observed via experiment is larger than that predicted by simulation and the apparent discrepancy can be understood with the inclusion of, dominantly, image charge and π-stacking interactions between the RTIL and the graphene sheet. In contrast, the RTIL structure adjacent to the charged mica surface exhibits an alternating cation–anion layering extending 3.5 nm into the bulk fluid. The associated charge density profile demonstrates a pronounced charge overscreening (i.e., excess first-layer counterions with respect to the adjacent surface charge), highlighti...
TL;DR: A novel synthesis route for monolithic carbide-derived carbon materials, including micro-, meso-, and macroporous structures with extremely high specific surface area is described.
Abstract: Porous carbon materials are crucial components in catalysis, gas storage, electronics, and biochemistry. A hierarchical pore architecture in these materials is essential to achieve high surface areas combined with advanced mass transport kinetics. Widely used approaches for the generation of microor mesopores are activation and nanocasting. In contrast, macroporous carbon materials are primarily obtained by carbonization of polymeric precursor gels or replication of larger templates. A relatively new class of microand mesoporous carbon material with tunable porosity are carbide-derived carbon materials (CDCs). High-temperature chlorination of carbides leads to selective removal of metalor semi-metal atoms and allows control over the pore size of the resulting CDCs in a subngstrcm range by changing synthesis conditions or the carbide precursor. These materials have been studied for applications in gas storage and as electrode materials in supercapacitors because of their high specific surface areas. Recently, metal etching from pyrolyzed pre-ceramic components (polysilsesquioxanes or polysilazanes) was found to be a useful route towards carbide-derived carbon materials with enhanced porosity and gas-storage properties. A significant step towards ultrahigh specific surface area combined with a hierarchical mesoporous–microporous system was achieved using nanocasting of silica templates (SBA-15 or KIT-6) with polycarbosilane precursors and subsequent chlorine treatment of the resulting ordered mesoporous silicon carbides. These ordered mesoporous CDCs offer specific surface areas as high as 2800 mg 1 and total pore volumes of up to 2 cmg . Their mesostructure can be easily controlled by changing the silica hard template, resulting in excellent performance in protein adsorption, gas storage, and as electrodes for supercapacitors. However, such carbon materials are available only as nonstructured micrometer-sized powders and cannot be shaped into films without the addition of binders or the use of high mechanical stress, leading to structural deformation. Chlorine treatment of mechanically mixed Si/SiC precursors was found to be a useful route towards monolithic CDC with a hierarchical pore system. The presence of a free metal phase in the precursor system provides the opportunity to introduce a secondary macroporosity of 3 mm sized channels with a volume of 0.23 cmg 1 along with the microporous carbide-derived carbon material system. The introduction of large transport pores in polymerbased CDCs might be an alternative way to form materials that combine high surface areas with efficient fluid transport. The current literature describes a variety of routes for the production of highly macroporous ceramics from precursor polymers with controllable cell and window sizes. In particular, direct blowing of polycarbosilanes was found to be a useful approach for the generation of silicon carbide foams that might be suitable materials for the production of hierarchical CDCs. In the following, we describe a novel synthesis route for monolithic carbide-derived carbon materials, including micro-, meso-, and macroporous structures with extremely high specific surface area. They can be obtained by hightemperature chlorination of macroporous polymer-derived silicon carbide (SiC-PolyHIPE). A soft-templating approach starting from a high internal phase emulsion (HIPE) was used with an external oil phase consisting of liquid polycarbosilane SMP-10 and the cross-linker paradivinylbenzene. Using Span-80 as surfactant to stabilize the internal water phase, the application of oxidic or carbon hard templates and the corresponding template removal under harsh conditions is no longer necessary. After cross-linking the polymer chains, the resulting PolyHIPEs were pyrolyzed to silicon carbides at maximum temperatures of 700, 800, and 1000 8C and subsequently converted into CDCs by chlorine treatment at the maximum pyrolysis temperature (Supporting [*] M. Oschatz, L. Borchardt, Dr. I. Senkovska, N. Klein, Dr. R. Frind, Prof. Dr. S. Kaskel Department of Inorganic Chemistry Dresden University of Technology Bergstrasse 66, 01062 Dresden (Germany) E-mail: stefan.kaskel@chemie.tu-dresden.de
TL;DR: In this paper, the interaction of interfacial water with graphitic carbon at the atomic scale is studied as a function of the hydrophobicity of epitaxial graphene, and it is shown that the graphene-water contact angle is controlled by the average graphene thickness.
Abstract: The interaction of interfacial water with graphitic carbon at the atomic scale is studied as a function of the hydrophobicity of epitaxial graphene. High resolution x-ray reflectivity shows that the graphene-water contact angle is controlled by the average graphene thickness, due to the fraction of the film surface expressed as the epitaxial buffer layer whose contact angle (contact angle \ensuremath{\theta}${}_{\mathrm{c}}$ $=$ 73\ifmmode^\circ\else\textdegree\fi{}) is substantially smaller than that of multilayer graphene (\ensuremath{\theta}${}_{c}$ $=$ 93\ifmmode^\circ\else\textdegree\fi{}). Classical and ab initio molecular dynamics simulations show that the reduced contact angle of the buffer layer is due to both its epitaxy with the SiC substrate and the presence of interfacial defects. This insight clarifies the relationship between interfacial water structure and hydrophobicity, in general, and suggests new routes to control interface properties of epitaxial graphene.
TL;DR: In this article, flexible electrospun titanium carbide (TiC) nano-felts were converted into carbide-derived carbon (CDC) by dry chlorination at temperatures between 200 and 1000°C and used as binder-free supercapacitor electrodes.
TL;DR: A review of the state-of-the-art tools currently available for intracellular SERS can be found in this paper, where various types of SERS probes are considered, including colloidal gold and silver nanoparticles, metallized optical fibers, and tip-enhanced Raman probes.
Abstract: Surface-enhanced Raman spectroscopy (SERS) is a promising and powerful label free technique for high resolution analysis of single cells. For intracellular analysis, there is a need for SERS-active nanoprobes that are minimally invasive to cells, do not affect cell viability, and provide reproducible signals. This work reviews the state-of-the-art tools currently available for intracellular SERS. Various types of SERS probes are considered, including colloidal gold and silver nanoparticles, metallized optical fibers, and tip-enhanced Raman probes. We also discuss recently developed SERS-active nanopipettes implemented on the basis of pulled glass microcapillaries. Finally, the critical aspects of selecting an optimal SERS nanoprobe for single-cell analysis depending on a particular application are summarized. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this paper, the wear and dry friction of epoxy-ND composites prepared from as-received and aminated nanodiamond (ND) across the length scale range from macro to nano.
Abstract: Owing to its superior mechanical properties, nanodiamond (ND) holds great potential to improve tribological characteristics of composites. In this study, we report on the wear and dry friction of epoxy-ND composites prepared from as-received and aminated ND across the length scale range from macro to nano. Comparison of macroscale, microscale, and nanoscale frictional behavior shows that ND is highly effective in improving the wear resistance and friction coefficients of polymer matrices across the different length scales. Although with both types of ND wear resistance and friction coefficients of epoxy-ND composites were significantly improved, aminated ND outperformed as-received ND, which we account to the formation of a strong interface between aminated ND and the epoxy matrix. This study also shows that agglomerates within epoxy-ND composites containing 25 vol.% ND were able to wear an alumina counterbody, indicating very high hardness and Young’s modulus of these agglomerates, that can eventually replace micron sized diamonds currently used in industrial abrasive applications.
Carnegie Mellon University1, Coe College2, Corning Inc.3, University of Washington4, Lehigh University5, Duke University6, University of Texas at Austin7, University of Illinois at Urbana–Champaign8, Northwestern University9, University of California, Riverside10, Drexel University11, Rensselaer Polytechnic Institute12, Alfred University13, Oak Ridge National Laboratory14, University of Maine15, University of California, Santa Barbara16, University of Pittsburgh17, North Carolina State University18, The Coca-Cola Company19, University of California, Davis20, University of Central Florida21, Pennsylvania State University22, Stanford University23, Toyota24, Toyota Technological Institute25, Pacific Northwest National Laboratory26
TL;DR: In this article, a group of researchers met to discuss emerging topics in ceramic science and to identify grand challenges in the field, and reached a consensus on eight challenges for the future: understanding rare events in ceramic microstructures, understanding the phase-like behavior of interfaces, predicting and controlling heterogeneous micro-structures with unprecedented functionalities.
Abstract: In March 2012, a group of researchers met to discuss emerging topics in ceramic science and to identify grand challenges in the field. By the end of the workshop, the group reached a consensus on eight challenges for the future:—understanding rare events in ceramic microstructures, understanding the phase-like behavior of interfaces, predicting and controlling heterogeneous microstructures with unprecedented functionalities, controlling the properties of oxide electronics, understanding defects in the vicinity of interfaces, controlling ceramics far from equilibrium, accelerating the development of new ceramic materials, and harnessing order within disorder in glasses. This paper reports the outcomes of the workshop and provides descriptions of these challenges.
TL;DR: In this article, it was shown that the steric effect is involved when ions are adsorbed into pores and highlighted the importance of controlling ion size/pore size relationship for optimisation of the capacitive performance of EDLC devices.
TL;DR: In this article, a novel strategy to obtain the graphene-supported palladium catalyst for the hydrodesulfurization of carbonyl sulfide (COS) in coal gas is presented.
Abstract: In this work, a novel strategy to obtain the graphene-supported palladium catalyst for the hydrodesulfurization of carbonyl sulfide (COS) in coal gas is presented. By employing the low temperature dielectric barrier discharge (DBD) plasma, well-dispersed Pd nanoparticles with particle size of about 2 nm supported on graphene sheets (PL-Pd/GS) have been synthesized through a facile one-step route, in which the graphite oxides and PdCl2 were simultaneously reduced in hydrogen plasma. The as-prepared PL-Pd/GS catalyst shows higher catalytic efficiency in the COS hydrogenation, compared to a traditional Pd/C catalyst, as well as Pd/GS reduced by hydrogen at high temperature or by ethylene glycol reduction in liquid phase. Characterizations using XRD, FT-IR, Raman, and HRTEM techniques reveal that the improved performance of PL-Pd/GS for COS conversion is attributed to small size and uniform dispersion of Pd nanoparticles on graphene sheets resulting from the efficient low temperature treatment in DBD plasma. This finding inspires the in situ preparation of various metal–graphene sheets catalysts by taking advantage of plasma, and paves a new avenue to make use of graphene sheets as a support material to improve catalytic activity.
TL;DR: In this article, it was shown that a composite's Young's modulus can be improved by nanodiamonds amino groups without any additions of curing agent, achieving a nanoindentation of up to ∼18 GPa.
TL;DR: In this article, the pore volume and specific surface area of carbide-derived carbon with no significant change in pore size up to 1500 °C were investigated, and the results demonstrate that vacuum treatment can be used to further tune pore structure and potentially the surface functionality for supercapacitor electrodes, gas chromatography, sorption, sensing and other applications.
TL;DR: In this article, the authors investigated charge induced expansion effects of spherical exohedral carbons, that is, onion-like carbons (OLC, diameter: 5-7 nm) and carbon black (diameter: ≈40 nm).
Abstract: High power electrochemical double layer capacitors (also called supercapacitors) rely on highly conductive electrode materials witha large specific surface area, which is easily accessible for ions. Exohedral materials with a large ion-accessible outer surface andlittle or no porosity within the particles are particularly attractive for supercapacitor electrodes because they decrease mass transportlimitations and enable very high charge/discharge rates. This study focuses on the investigation of charge induced expansioneffects of spherical exohedral carbons, that is, onion-like carbons (OLC, diameter: 5–7 nm) and carbon black (diameter: ≈40 nm).Employing electrochemical in-situ dilatometry we studied the expansion behavior within ±1 V potential window
TL;DR: In this paper, a free-standing nanohybridged buckypaper with high carbon nanotube (CNT) contents was fabricated using polymer single crystal-decorated CNTs as the precursor.
Abstract: Herein we report fabrication of uniform, free-standing nanohybrid buckypaper with high carbon nanotube (CNT) contents (13–70%) using polymer single crystal-decorated CNTs as the precursor. Polyethylene single crystals were periodically grown on CNT surfaces, forming a nanohybrid shish kebab (NHSK) structure. Vacuum filtering a NHSK suspension led to polymer single crystal-decorated buckypaper (named as NHSK paper) with a wide range of CNT contents and uniform CNT dispersion. Porosity, surface roughness, and conductivity of NHSK paper can be controlled by tuning the polymer single crystal size. Because of the hierarchical roughness created by intra- and inter-NHSK nanostructure, NHSK paper with controlled kebab size exhibits both superhydrophobicity and high surface water adhesion, which mimics the rose petal effect. We anticipate that this unique NHSK paper can find applications in sensors, electrochemical devices, and coatings.
TL;DR: In this article, single-walled carbon nanotube (SWCNT) nanorings have been fabricated on a large scale using a Pickering emulsion-based process.
TL;DR: In this paper, a free-standing films of ordered mesoporous silicon and titanium carbide-derived carbons have been synthesized using a novel soft templating approach without employing hydrofluoric acid.
TL;DR: In this paper, small-angle neutron scattering (SANS) and neutron contrast variation were used to study the structure of four nanoporous carbons prepared by thermo-chemical etching of titanium carbide TiC in chlorine at 300, 400, 600, and 800°C with pore diameters ranging between ∼4 and ∼11 A.
TL;DR: This multifunctional magnetic system will be useful not only for micro and nanorheological studies, but it will find much broader applications requiring remote controlled manipulation of micro and nano objects.
Abstract: We report on the development of a multifunctional magnetic rotator that has been built and used during the last five years by two groups from Clemson and Drexel Universities studying the rheological properties of microdroplets. This magnetic rotator allows one to generate rotating magnetic fields in a broad frequency band, from hertz to tens kilohertz. We illustrate its flexibility and robustness by conducting the rheological studies of simple and polymeric fluids at the nano and microscale. First we reproduce a temperature-dependent viscosity of a synthetic oil used as a viscosity standard. Magnetic rotational spectroscopy with suspended nickel nanorods was used in these studies. As a second example, we converted the magnetic rotator into a pump with precise controlled flow modulation. Using multiwalled carbon nanotubes, we were able to estimate the shear modulus of sickle hemoglobin polymer. We believe that this multifunctional magnetic system will be useful not only for micro and nanorheological studies, but it will find much broader applications requiring remote controlled manipulation of micro and nanoobjects.
TL;DR: Series of silicon carbonitride ceramics are utilized to obtain hierarchically porous carbide-derived carbons (CDCs) for cytokine removal and the removal rate is proportional to the surface area of pores larger than the size of the protein molecule.
Abstract: Series of silicon carbonitride ceramics are utilized to obtain hierarchically porous carbide-derived carbons (CDCs) for cytokine removal. The removal rate of TNF-α and IL-6, as two examples of pro- and anti-inflammatory cytokines, is proportional to the surface area of pores larger than the size of the protein molecule