Co-reporter:Georgiy Akopov, Inwhan Roh, Zachary C. Sobell, Michael T. Yeung, Lisa Pangilinan, Christopher L. Turner, and Richard B. Kaner
Journal of the American Chemical Society November 29, 2017 Volume 139(Issue 47) pp:17120-17120
Publication Date(Web):November 15, 2017
DOI:10.1021/jacs.7b08706
Tungsten tetraboride is an inexpensive, superhard material easily prepared at ambient pressure. Unfortunately, there are relatively few compounds in existence that crystallize in the same structure as tungsten tetraboride. Furthermore, the lack of data in the tetraboride phase space limits the discovery of any new superhard compounds that also possess high incompressibility and a three-dimensional boron network that withstands shear. Thus, the focus of the work here is to chemically probe the range of thermodynamically stable tetraboride compounds with respect to both the transition metal and the boron content. Tungsten tetraboride alloys with a variable concentration of boron were prepared by arc-melting and investigated for their mechanical properties and thermal stability. The purity and phase composition were confirmed by energy dispersive X-ray spectroscopy and powder X-ray diffraction. For variable boron WBx, it was found that samples prepared with a metal to boron ratio of 1:11.6 to 1:9 have similar hardness values (∼40 GPa at 0.49 N loading) as well as having a similar thermal oxidation temperature of ∼455 °C. A nearly single phase compound was successfully stabilized with tantalum and prepared with a nearly stoichiometric amount of boron (4.5) as W0.668Ta0.332B4.5. Therefore, the cost of production of WB4 can be decreased while maintaining its remarkable properties. Insights from this work will help design future compounds stable in the adaptable tungsten tetraboride structure.
Co-reporter:Cheng-Wei Lin, Rebecca L. Li, Shauna Robbennolt, Michael T. Yeung, Georgiy Akopov, and Richard B. Kaner
Macromolecules August 8, 2017 Volume 50(Issue 15) pp:5892-5892
Publication Date(Web):July 20, 2017
DOI:10.1021/acs.macromol.7b00633
Polyaniline is known for reversible acidic doping. However, despite extensive work, little experimental evidence exists for the initial doping mechanism mainly due to the difficulty of synthesizing polyaniline with a uniform chain length. In this study, we partially dope aniline tetramers in order to investigate the initial stage of doping in both solution and the solid state. In solution, we discovered a method for visualizing the doping level due to solvent density differences. The optical results in both the liquid and solid state suggest that the partially doped aniline tetramers are physical mixtures of aniline tetramer in the emeraldine base and emeraldine salt forms. Electron paramagnetic resonance confirms the formation of spinless bipolarons as the major carriers. Therefore, we postulate that the doping mechanism proceeds via a continual increase in the number of doubly doped tetraanilines.
Co-reporter:Jee Y. Hwang;Mengping Li;Maher F. El-Kady
Advanced Functional Materials 2017 Volume 27(Issue 15) pp:
Publication Date(Web):2017/04/01
DOI:10.1002/adfm.201605745
The global supercapacitor market has been growing rapidly during the past decade. Today, virtually all commercial devices use activated carbon. In this work, it is shown that laser treatment of activated carbon electrodes results in the formation of microchannels that can connect the internal pores of activated carbon with the surrounding electrolyte. These microchannels serve as electrolyte reservoirs that in turn shorten the ion diffusion distance and enable better interaction between the electrode surfaces and electrolyte ions. The capacitance can be further increased through fast and reversible redox reactions on the electrode surface using a redox-active electrolyte, enabling the operation of a symmetric device at 2.0 V, much higher than the thermodynamic decompostion voltage of water. This simple approach can alleviate the low energy density of supercapacitors which has limited the widespread use of this technology. This work represents a clear advancement in the processing of activated carbon electrodes toward the next-generation of low-cost supercapacitors.
Co-reporter:Georgiy Akopov;Michael T. Yeung
Advanced Materials 2017 Volume 29(Issue 21) pp:
Publication Date(Web):2017/06/01
DOI:10.1002/adma.201604506
For decades, borides have been primarily studied as crystallographic oddities. With such a wide variety of structures (a quick survey of the Inorganic Crystal Structure Database counts 1253 entries for binary boron compounds!), it is surprising that the applications of borides have been quite limited despite a great deal of fundamental research. If anything, the rich crystal chemistry found in borides could well provide the right tool for almost any application. The interplay between metals and the boron results in even more varied material's properties, many of which can be tuned via chemistry. Thus, the aim of this review is to reintroduce to the scientific community the developments in boride crystal chemistry over the past 60 years. We tie structures to material properties, and furthermore, elaborate on convenient synthetic routes toward preparing borides.
Co-reporter:Christina O. Baker;Xinwei Huang;Wyatt Nelson
Chemical Society Reviews 2017 vol. 46(Issue 5) pp:1510-1525
Publication Date(Web):2017/03/06
DOI:10.1039/C6CS00555A
Polyaniline is a conducting polymer with incredible promise, but it has had limited use due to poor reaction control and processability associated with conventional morphologies. Polyaniline nanofibers, on the other hand, have demonstrated, through manufacturing techniques discovered during the past decade, increased processability, higher surface area, and improved consistency and stability in aqueous dispersions, which are finally allowing for expanded commercial development of this promising polymer. This review explores some intriguing applications of polyaniline nanofibers, as well as the advantages and remaining challenges in developing better products using polyaniline in this new morphology.
Co-reporter:Yuanlong Shao;Jianmin Li;Yaogang Li;Hongzhi Wang;Qinghong Zhang
Materials Horizons (2014-Present) 2017 vol. 4(Issue 6) pp:1145-1150
Publication Date(Web):2017/10/30
DOI:10.1039/C7MH00441A
A quasi-solid-state micro-supercapacitor with cellular graphene film as the active material and polyvinyl alcohol/H3PO4 as the gel electrolyte is demonstrated as a new type of flexible energy storage device. The 3D porous graphene films not only serve as high performance supercapacitor electrodes, but also provide an abundant ion reservoir for the gel electrolyte. The quasi-solid-state micro-supercapacitor exhibits excellent electrochemical performance.
Co-reporter:Yuanlong Shao;Jianmin Li;Yaogang Li;Hongzhi Wang;Qinghong Zhang
Materials Horizons (2014-Present) 2017 vol. 4(Issue 6) pp:1145-1150
Publication Date(Web):2017/10/30
DOI:10.1039/C7MH00441A
A quasi-solid-state micro-supercapacitor with cellular graphene film as the active material and polyvinyl alcohol/H3PO4 as the gel electrolyte is demonstrated as a new type of flexible energy storage device. The 3D porous graphene films not only serve as high performance supercapacitor electrodes, but also provide an abundant ion reservoir for the gel electrolyte. The quasi-solid-state micro-supercapacitor exhibits excellent electrochemical performance.
Co-reporter:Jee Y. Hwang, Maher F. El-Kady, Mengping Li, Cheng-Wei Lin, Matthew Kowal, Xu Han, Richard B. Kaner
Nano Today 2017 Volume 15(Volume 15) pp:
Publication Date(Web):1 August 2017
DOI:10.1016/j.nantod.2017.06.009
•Simple laser technique is used for the direct writing of high-energy supercapacitors.•The electrode design involves 3D graphene scaffold doped with Fe3O4 nanoparticles.•The addition of a redox electrolyte increases the voltage window and capacitance.•The key is designing both electrode and electrolyte to store charge simultaneously.•The technique allows for printing multiple microscale supercapacitors at the same time.Supercapacitors are evolving into an important component in energy storage technology with the capability for storing and discharging energy very quickly and effectively. State-of-the-art supercapacitors feature activated carbon electrodes impregnated with a non-aqueous electrolyte (typically acetonitrile) that operate at voltages between 2.2–2.7 V. Unfortunately, activated carbons have low specific capacitance (100–120 F g−1) in organic electrolytes which severely limits the energy density of supercapacitors. In addition, organic solvents are often flammable leading to safety and environmental concerns. Aqueous electrolytes, on the other hand, are safer, cheaper and have higher ionic conductivity, promising higher capacitance electrodes. However, the low voltage window enforced by the low decomposition voltage of water around 1.23 V is a major challenge. Here, we demonstrate symmetric supercapacitors operating at an ultrahigh voltage of 1.8 V that can provide specific electrode capacitances up to 716 F g−1, which is higher than traditional activated carbon electrodes. This is possible through designing both the electrode and electrolyte to work synergistically towards improving not only the capacitance of the electrodes, but also the voltage and cycling stability of the supercapacitor. We also demonstrate by using a simple laser technique the possibility of fabricating micro-supercapacitors with great potential for miniaturized electronics. This work provides an effective strategy for designing and fabricating aqueous supercapacitors that hold promise for a sustainable energy future.Download high-res image (197KB)Download full-size image
Co-reporter:Jiahui Li, Yuanlong Shao, Qiuwei Shi, Chengyi Hou, Qinghong Zhang, Yaogang Li, Richard B. Kaner, Hongzhi Wang
Nano Energy 2017 Volume 38(Volume 38) pp:
Publication Date(Web):1 August 2017
DOI:10.1016/j.nanoen.2017.06.013
•Developing a continuous and stable way to transfer GO ink and write large-area rGO film by Chinese brush.•Large-area folded and wavy rGO film were fabricated with a controllable writing process.•All-solid-state single/foldable supercapacitors have been directly written by Chinese brush.•Three series/parallel connection of foldable supercapacitors were obtained and shows 2.4 V output voltage and 258.6 mF cm−2 areal capacitance.Chinese brush, made of a bundle of animal hairs in a quasi-parallel arrangement, is an effective tool that can be used to continuously place low-viscosity ink onto different substrates with high ink mass loading. Here, we demonstrate a highly effective approach to coat graphene onto rough and even crumpled substrates by using a Chinese brush. By combining forces including Laplace pressure differential, asymmetric retention and gravity, the low-viscosity graphene oxide ink can be sufficiently transferred onto different substrates through the brush hairs in a controlled manner. The as-prepared graphene films are used as electrodes for all-solid-state foldable supercapacitors. Using series and/or parallel connections, the energy storage performance of the foldable all-solid-state supercapacitors can be tailored to provide different output voltages and currents. The voltage of the three series connected devices with gel electrolyte can be extended to 2.4 V. A parallel connected foldable all-solid-state supercapacitor exhibits promising electrochemical performance, such as high areal capacitance of 258.6 mF cm−2, good energy density of 23.1 μW h cm−2 and power density of 0.2 mW cm−2. This work offers an alternative method of GO ink transfer, graphene film production and the fabrication of flexible electronics.We demonstrate a highly effective approach to coating graphene films onto rough or even crumpled substrates by using a Chinese brush. The produced graphene films are used as electrodes for all-solid-state foldable supercapacitors. By making series or parallel connections, the energy storage performance of the all-solid-state foldable supercapacitors can be adjusted to different output voltages and currents.Download high-res image (151KB)Download full-size image
Co-reporter:Thomas Farrell, Kan Wang, Cheng-Wei Lin, Richard B. Kaner
Polymer 2017 Volume 129(Volume 129) pp:
Publication Date(Web):27 October 2017
DOI:10.1016/j.polymer.2017.09.032
•Polyaniline forms composites with SWCNTs via simple ultrasonication.•The polyaniline/SWCNT composites can easily form blends with other polymers.•Polymer/SWCNT composites form conductive and transparent films via spin-coating.•Conformation of polyaniline chains is determined by the solvent used.Traditionally, in situ polymerization has been used to make polymer-carbon nanotube composites. Here, we report a simple method of mixing polyaniline with single-walled carbon nanotubes in a variety of organic solvents via ultrasonication. The maximum loading fraction of SWCNTs in the composites is determined by the conformation of the polyaniline chains. The type of solvent used has the greatest influence on the conformation of the polyaniline chains. Furthermore, the composites can be easily blended with poly(methyl methacrylate) (PMMA), to form polyblends. The electrical conductivities and transparencies of the polyblend films are reported.Download high-res image (185KB)Download full-size image
Co-reporter:S. Rasool Azari;Mohammad S. Rahmanifar
Journal of the Iranian Chemical Society 2017 Volume 14( Issue 12) pp:2579-2590
Publication Date(Web):06 September 2017
DOI:10.1007/s13738-017-1192-z
Aqueous supercapacitors based on neutral solutions have the advantages of high-ionic conductivity, being environmentally friendly, safe, and low cost. However, the operating potential window for most aqueous electrolytes is far lower than that of organic electrolytes that are commonly used in commercial supercapacitors. In this work, we report on the fabrication of a wide potential window, high-energy aqueous asymmetric supercapacitor, without sacrificing power, by using a nanostructured LiMn2O4/reduced graphene oxide (LMO–rGO) nanocomposite. We synthesized the uniformly distributed LMO in the LMO–rGO nanocomposite using a co-precipitation route followed by a low-temperature hydrothermal treatment. In a three-electrode cell setup, the specific capacitance of the LMO–rGO nanocomposite electrode at 1 A/g (1.2 mA/cm2) is 268.75 F/g (258 mF/cm2), which shows a dramatic improvement over the sum of the specific capacitances of pristine LMO (162.5 F/g) and pure rGO (29.94 F/g) electrodes in their relative ratios, when used alone. This finding suggests a synergistic coupling of LMO and rGO in the nanocomposite. We also assembled the LMO–rGO nanocomposite, as the positive electrode, with activated carbon, as the negative electrode, into an asymmetric cell configuration. The device shows an ultra-wide potential window of 2.0 V in a neutral aqueous Li2SO4 electrolyte, with a maximum energy density of 29.6 Wh/kg (which approaches the commercial lead-acid batteries), power density of up to 7408 W/kg, and an excellent cycle life (5% loss after 6000 cycles). These findings confirm that an LMO–rGO nanocomposite is a promising material to meet the demands of real world energy storage.
Co-reporter:Yuanlong Shao;Maher F. El-Kady;Cheng-Wei Lin;Guanzhou Zhu;Kristofer L. Marsh;Jee Youn Hwang;Qinghong Zhang;Yaogang Li;Hongzhi Wang
Advanced Materials 2016 Volume 28( Issue 31) pp:6719-6726
Publication Date(Web):
DOI:10.1002/adma.201506157
Co-reporter:Michael T. Yeung;Jialin Lei;Reza Mohammadi;Christopher L. Turner;Yue Wang;Sarah H. Tolbert
Advanced Materials 2016 Volume 28( Issue 32) pp:6993-6998
Publication Date(Web):
DOI:10.1002/adma.201601187
Co-reporter:Georgiy Akopov; Michael T. Yeung; Christopher L. Turner; Reza Mohammadi
Journal of the American Chemical Society 2016 Volume 138(Issue 17) pp:5714-5721
Publication Date(Web):April 26, 2016
DOI:10.1021/jacs.6b02676
Alloys of tungsten tetraboride (WB4) with the group 4 transition metals, titanium (Ti), zirconium (Zr), and hafnium (Hf), of different concentrations (0–50 at. % on a metals basis) were synthesized by arc-melting in order to study their mechanical properties. The phase composition and purity of the as-synthesized samples were confirmed using powder X-ray diffraction (PXRD) and energy dispersive X-ray spectroscopy (EDS). The solubility limit as determined by PXRD is 20 at. % for Ti, 10 at. % for Zr, and 8 at. % for Hf. Vickers indentation measurements of WB4 alloys with 8 at. % Ti, 8 at. % Zr, and 6 at. % Hf gave hardness values, Hv, of 50.9 ± 2.2, 55.9 ± 2.7 and 51.6 ± 2.8 GPa, respectively, compared to 43.3 GPa for pure WB4 under an applied load of 0.49 N. Each of the aforementioned compositions are considered superhard (Hv > 40 GPa), likely due to extrinsic hardening that plays a key role in these superhard metal borides. Furthermore, these materials exhibit a significantly reduced indentation size effect, which can be seen in the plateauing hardness values for the W1–xZrxB4 alloy. In addition, W0.92Zr0.08B4, a product of spinoidal decomposition, possesses nanostructured grains and enhanced grain hardening. The hardness of W0.92Zr0.08B4 is 34.7 ± 0.65 GPa under an applied load of 4.9 N, the highest value obtained for any superhard metal at this relatively high loading. In addition, the WB4 alloys with Ti, Zr, and Hf showed a substantially increased oxidation resistance up to ∼460 °C, ∼510 °C, and ∼490 °C, respectively, compared to ∼400 °C for pure WB4.
Co-reporter:Andrew T. Lech, Christopher L. Turner, Jialin Lei, Reza Mohammadi, Sarah H. Tolbert, and Richard B. Kaner
Journal of the American Chemical Society 2016 Volume 138(Issue 43) pp:14398-14408
Publication Date(Web):October 10, 2016
DOI:10.1021/jacs.6b08616
Rhenium diboride (ReB2), containing corrugated layers of covalently bonded boron, is a superhard metallic compound with a microhardness reaching as high as 40.5 GPa (under an applied load of 0.49 N). Tungsten diboride (WB2), which takes a structural hybrid between that of ReB2 and AlB2, where half of the boron layers are planar (as in AlB2) and half are corrugated (as in ReB2), has been shown not to be superhard. Here, we demonstrate that the ReB2-type structure can be maintained for solid solutions of tungsten in ReB2 with tungsten content up to a surprisingly large limit of nearly 50 atom %. The lattice parameters for the solid solutions linearly increase along both the a- and c-axes with increasing tungsten content, as evaluated by powder X-ray and neutron diffraction. From micro- and nanoindentation hardness testing, all of the compositions within the range of 0–48 atom % W are superhard, and the bulk modulus of the 48 atom % solid solution is nearly identical to that of pure ReB2. These results further indicate that ReB2-structured compounds are superhard, as has been predicted from first-principles calculations, and may warrant further studies into additional solid solutions or ternary compounds taking this structure type.
Co-reporter:Georgiy Akopov, Michael T. Yeung, Zachary C. Sobell, Christopher L. Turner, Cheng-Wei Lin, and Richard B. Kaner
Chemistry of Materials 2016 Volume 28(Issue 18) pp:6605
Publication Date(Web):September 12, 2016
DOI:10.1021/acs.chemmater.6b02632
Solid solutions of mixed metal dodecaborides of ZrB12, YB12, and ScB12 were prepared by arc-melting and studied for their mechanical properties. Zr1–xYxB12 formed an essentially perfect solid solution, closely following Vegard’s law. Zr1–xScxB12 and Y1–xScxB12 undergo a face centered-cubic to body-centered tetragonal transition at 90–95 at. % Sc as determined by powder X-ray diffraction and transmission electron microscopy. The compounds Zr0.5Y0.5B12, Zr0.5Sc0.5B12, and Y0.5Sc0.5B12 are superhard (Vickers hardness ≥ 40 GPa) and demonstrate an increase in hardness to 45.8 ± 1.3, 48.0 ± 2.1, and 45.2 ± 2.1 GPa under a load of 0.49 N, respectively, compared to 40.4 ± 1.8, 40.9 ± 1.6, and 41.7 ± 2.2 GPa for pure ZrB12, YB12, and ScB12, respectively. In addition, Zr0.5Y0.5B12, Zr0.5Sc0.5B12, and Y0.5Sc0.5B12 solid solutions show a substantial increase in oxidation resistance to approximately 630, 685, and 695 °C, respectively, when compared to other superhard metal borides (e.g., ∼400 °C for WB4) and their alloys and the traditional cutting tools material tungsten carbide (∼400 °C). Moreover, Zr0.5Y0.5B12, Zr0.5Sc0.5B12, and Y0.5Sc0.5B12 have relatively low densities of 3.52, 3.32, and 3.18 g/cm3, respectively, comparable to or even lower than that of diamond (3.52 g/cm3) and significantly lower than those of other superhard borides such as ReB2 (12.67 g/cm3) and WB4 (8.40 g/cm3) and traditional cutting tools materials, e.g., WC (15.77 g/cm3), making them of potential interest for lightweight protective coatings and/or as materials for cutting and machining.
Co-reporter:Reza Mohammadi, Christopher L. Turner, Miao Xie, Michael T. Yeung, Andrew T. Lech, Sarah H. Tolbert, and Richard B. Kaner
Chemistry of Materials 2016 Volume 28(Issue 2) pp:632
Publication Date(Web):December 21, 2015
DOI:10.1021/acs.chemmater.5b04410
By creation of solid solutions of the recently explored low-cost superhard boride, tungsten tetraboride (WB4), the hardness can be increased. To illustrate this concept, various concentrations of molybdenum (Mo) in WB4, that is, W1–xMoxB4 (x = 0.00–0.50), were systematically synthesized by arc melting from the pure elements. The as-synthesized samples were characterized using energy-dispersive X-ray spectroscopy (EDS) for elemental analysis, powder X-ray diffraction (XRD) for phase identification, Vickers microindentation for hardness testing, and thermal gravimetric analysis for determining the thermal stability limit. While the EDS analysis confirmed the elemental purity of the samples, the XRD results indicated that Mo is completely soluble in WB4 over the entire concentration range studied (0–50 at. %) without forming a second phase. When 3 at. % Mo is added to WB4, Vickers hardness values increased by about 15% from 28.1 ± 1.4 to 33.4 ± 0.9 GPa under an applied load of 4.90 N and from 43.3 ± 2.9 to 50.3 ± 3.2 GPa under an applied load of 0.49 N. Thermal gravimetric analysis revealed that the powders of this superhard solid solution, W0.97Mo0.03B4, are thermally stable in air up to ∼400 °C. These results indicate that the hardness of superhard transition-metal borides may be enhanced by making solid solutions with small amounts of other transition metals, without introducing a second phase to their structures.
Co-reporter:Xinwei Huang, Kristofer L. Marsh, Brian T. McVerry, Eric M. V. Hoek, and Richard B. Kaner
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 23) pp:14334-14338
Publication Date(Web):May 27, 2016
DOI:10.1021/acsami.6b05293
Azide-functionalized graphene oxide (AGO) was covalently anchored onto commercial reverse osmosis (RO) membrane surfaces via azide photochemistry. Surface modification was carried out by coating the RO membrane with an aqueous dispersion of AGO followed by UV exposure under ambient conditions. This simple process produces a hydrophilic, smooth, antibacterial membrane with limited reduction in water permeability or salt selectivity. The GO-RO membrane exhibited a 17-fold reduction in biofouling after 24 h of Escherichia coli contact and almost 2 times reduced BSA fouling after a 1 week cross-flow test compared to its unmodified counterpart.
Co-reporter:Zhijuan Zhao, Xiangping Chen, Cankun Zhang, Wen Wan, Zhifa Shan, Bo Tian, Qiongyu Li, Hao Ying, Pingping Zhuang, Richard B. Kaner, Weiwei Cai
Carbon 2016 Volume 106() pp:279-283
Publication Date(Web):September 2016
DOI:10.1016/j.carbon.2016.05.038
What causes graphene etching is still controversial. Here we report a special etching phenomenon on the outer surface of a copper (Cu) pocket, while large-size graphene domains grow slowly on the inner surface. A systematic study along a time axis was conducted to investigate this etching process through isotope-tracing. When millimeter-size graphene domains on the inner surface joined together, the original monolayer graphene with a few residual multilayers stayed behind on the outer surface, indicating that multilayer graphene formed in the interim subsequently disappeared. Combined with our previous work, we conclude that the etching phenomenon is analogous to a counter diffusion process that keeps a stable monolayer of graphene on both sides of the Cu foil. Low C solubility and poor C saturation in Cu appear to drive this counter diffusion and help keep the stable state. Furthermore, we used a fast-growth process to break this stable state and realized 85% coverage rates of bilayer graphene growth on the outer surface of a Cu pocket. This work sheds light on the graphene diffusion mechanism and self-limited growth mechanism on Cu substrates.
Co-reporter:Georgiy Akopov, Michael T. Yeung, Christopher L. Turner, Rebecca L. Li, and Richard B. Kaner
Inorganic Chemistry 2016 Volume 55(Issue 10) pp:5051
Publication Date(Web):April 26, 2016
DOI:10.1021/acs.inorgchem.6b00627
Alloys of metal dodecaborides—YB12 with HfB12—were prepared via arc-melting in order to stabilize the metastable HfB12 high-pressure phase under ambient pressure. Previously, HfB12 had been synthesized only under high-pressure (6.5 GPa). Powder X-ray diffraction (PXRD) and energy-dispersive X-ray spectroscopy (EDS) were used to confirm the purity and phase composition of the prepared samples. The solubility limit for HfB12 in Y1–xHfxB12 (cubic UB12 structure type) was determined to be ∼35 at. % Hf by PXRD and EDS analysis. The value of the cubic unit cell parameter (a) changed from 7.505 Å (pure YB12) to 7.454 Å across the solid solution range. Vickers hardness increased from 40.9 ± 1.6 GPa for pure YB12 to 45.0 ± 1.9 GPa under an applied load of 0.49 N for the Y1–xHfxB12 solid solution composition with ∼28 at. % Hf, suggesting both solid solution hardening and extrinsic hardening due to the formation of secondary phases of hafnium.
Co-reporter:Georgiy Akopov, Zachary C. Sobell, Michael T. Yeung, and Richard B. Kaner
Inorganic Chemistry 2016 Volume 55(Issue 23) pp:12419-12426
Publication Date(Web):November 17, 2016
DOI:10.1021/acs.inorgchem.6b02311
We report ambient pressure stabilization of a previously synthesized high-pressure (6.5 GPa) phase, GdB12, in a Zr1–xGdxB12 solid solution (with ∼54 at. % Gd solubility, as determined by both powder X-ray diffraction and energy-dispersive spectroscopy). Limited solubilities of Sm (∼15 at. % Sm), Nd (∼7 at. % Nd), and Pr (∼4 at. % Pr), in ZrB12 were also achieved. Previous attempts at preparing these rare-earth borides were unsuccessful even under high pressure. On the basis of insights provided from the unit cell sizes observed via solid solutions, at least 6.5 GPa of pressure would be needed to synthesize these rare-earth borides since Sm, Nd, and Pr atomic radii are larger than that of Gd. The solid-solution formation for Zr1–xGdxB12 and Zr1–xSmxB12 can be seen in the change of the unit cell of each of the solid solutions relative to their pure parent compounds as well as in the change of color of the respective alloys. For Zr0.45Gd0.55B12 and Zr0.70Sm0.30B12, the cubic unit cell parameter (a) reached a value of 7.453 and 7.428 Å, respectively, compared to 7.412 Å for pure ZrB12.
Co-reporter:Morteza Sarparast;Abolhassan Noori;Hoda Ilkhani;S. Zahra Bathaie
Nano Research 2016 Volume 9( Issue 11) pp:3229-3246
Publication Date(Web):2016 November
DOI:10.1007/s12274-016-1201-z
Biotemplated metal nanoclusters have garnered much attention owing to their wide range of potential applications in biosensing, bioimaging, catalysis, and nanomedicine. Here, we report the synthesis of stable, biocompatible, water-soluble, and highly fluorescent bovine serum albumin-templated cadmium nanoclusters (CdNCs) through a facile one-pot green method. We covalently conjugated hyaluronic acid (HA) to the CdNCs to form a pH-responsive, tumortargeting theranostic nanocarrier with a sustained release profile for doxorubicin (DOX), a model anticancer drug. The nanocarrier showed a DOX encapsulation efficiency of about 75.6%. DOX release profiles revealed that 74% of DOX was released at pH 5.3, while less than 26% of DOX was released at pH 7.4 within the same 24-h period. The nanocarrier selectively recognized MCF-7 breast cancer cells expressing CD44, a cell surface receptor for HA, whereas no such recognition was observed with HA receptor-negative HEK293 cells. Biocompatibility of the nanocarrier was evaluated through cytotoxicity assays with HEK293 and MCF-7 cells. The nanocarrier exhibited very low to no cytotoxicity, whereas the DOX-loaded nanocarrier showed considerable cellular uptake and enhanced MCF-7 breast cancer cell-killing ability. We also confirmed the feasibility of using the highly fluorescent nanoconjugate for bioimaging of MCF-7 and HeLa cells. The superior targeted drug delivery efficacy, cellular imaging capability, and low cytotoxicity position this nanoconjugate as an exciting new nanoplatform with promising biomedical applications.
Co-reporter:Yuanlong Shao, Maher F. El-Kady, Lisa J. Wang, Qinghong Zhang, Yaogang Li, Hongzhi Wang, Mir F. Mousavi and Richard B. Kaner
Chemical Society Reviews 2015 vol. 44(Issue 11) pp:3639-3665
Publication Date(Web):22 Apr 2015
DOI:10.1039/C4CS00316K
The demand for flexible/wearable electronic devices that have aesthetic appeal and multi-functionality has stimulated the rapid development of flexible supercapacitors with enhanced electrochemical performance and mechanical flexibility. After a brief introduction to flexible supercapacitors, we summarize current progress made with graphene-based electrodes. Two recently proposed prototypes for flexible supercapacitors, known as micro-supercapacitors and fiber-type supercapacitors, are then discussed. We also present our perspective on the development of graphene-based electrodes for flexible supercapacitors.
Co-reporter:Lisa J. Wang;Maher F. El-Kady;Sergey Dubin;Jee Youn Hwang;Yuanlong Shao;Kristofer Marsh;Brian McVerry;Matthew D. Kowal;Mir F. Mousavi
Advanced Energy Materials 2015 Volume 5( Issue 18) pp:
Publication Date(Web):
DOI:10.1002/aenm.201500786
Supercapacitors are known for their rapid energy charge–discharge properties, often ten to a hundred times faster than batteries. However, there is still a demand for supercapacitors with even faster charge–discharge characteristics to fulfill the requirements of emerging technologies. The power and rate capabilities of supercapacitors are highly dependent on the morphology of their electrode materials. An electrically conductive 3D porous structure possessing a high surface area for ions to access is ideal. Using a flash of light, a method to produce highly interconnected 3D graphene architectures with high surface area and good conductivity is developed. The flash converted graphene is synthesized by reducing freeze-dried graphene oxide using an ordinary camera flash as a photothermal source. The flash converted graphene is used in coin cell supercapacitors to investigate its electrode materials properties. The electrodes are fabricated using either a precoating flash conversion or a postcoating flash conversion of graphene oxide. Both techniques produce supercapacitors possessing ultra-high power (5–7 × 105 W kg−1). Furthermore, optimized supercapacitors retain >50% of their capacitance when operated at an ultrahigh current density up to 220 A g−1.
Co-reporter:Wanmei Sun, Michael T. Yeung, Andrew T. Lech, Cheng-Wei Lin, Chain Lee, Tianqi Li, Xiangfeng Duan, Jun Zhou, and Richard B. Kaner
Nano Letters 2015 Volume 15(Issue 7) pp:4834-4838
Publication Date(Web):June 15, 2015
DOI:10.1021/acs.nanolett.5b02013
High surface area in h-WO3 has been verified from the intracrystalline tunnels. This bottom-up approach differs from conventional templating-type methods. The 3.67 Å diameter tunnels are characterized by low-pressure CO2 adsorption isotherms with nonlocal density functional theory fitting, transmission electron microscopy, and thermal gravimetric analysis. These open and rigid tunnels absorb H+ and Li+, but not Na+ in aqueous electrolytes without inducing a phase transformation, accessing both internal and external active sites. Moreover, these tunnel structures demonstrate high specific pseudocapacitance and good stability in an H2SO4 aqueous electrolyte. Thus, the high surface area created from 3.67 Å diameter tunnels in h-WO3 shows potential applications in electrochemical energy storage, selective ion transfer, and selective gas adsorption.
Co-reporter:Xin-Gui Li, Yaozu Liao, Mei-Rong Huang and Richard B. Kaner
Chemical Science 2015 vol. 6(Issue 3) pp:2087-2101
Publication Date(Web):21 Jan 2015
DOI:10.1039/C4SC03890H
A novel polyfluoranthene (PFA) exhibiting strong visual fluorescence emission, a highly amplified quenching effect, and widely controllable electrical conductivity is synthesized by the direct cationic oxidative polymerization of fluoranthene in a dynamic interface between n-hexane and nitromethane containing fluoranthene and FeCl3, respectively. A full characterization of the molecular structure signifies that the PFAs have a degree of polymerization from 22–50 depending on the polymerization conditions. A polymerization mechanism at the interface of the hexane/nitromethane biphasic system is proposed. The conductivity of the PFA is tunable from 6.4 × 10−6 to 0.074 S cm−1 by doping with HCl or iodine. The conductivity can be significantly enhanced to 150 S cm−1 by heat treatment at 1100 °C in argon. A PFA-based chemosensor shows a highly selective sensitivity for Fe3+ detection which is unaffected by other common metal ions. The detection of Fe3+ likely involves the synergistic effect of well-distributed π-conjugated electrons throughout the PFA helical chains that function as both the fluorophore and the receptor units.
Co-reporter:Xin-Gui Li, Yaozu Liao, Mei-Rong Huang and Richard B. Kaner
Chemical Science 2015 vol. 6(Issue 12) pp:7190-7200
Publication Date(Web):17 Sep 2015
DOI:10.1039/C5SC03041B
Strongly fluorescence-emitting oligofluoranthene (OFA) nanorods are readily synthesized by a direct template-free chemical oxidative oligomerization of fluoranthene in nitromethane containing ferric chloride as an oxidant. The OFAs likely consist of five fluoranthene units containing cyclic pentamers with crystalline order and tunable electrical conductivity across 12 orders of magnitude. The OFA nanorods are heat-resistant materials and efficient precursors for macroporous carbon materials with high carbon yield in argon at 1100 °C. In particular, the optimal ring-like pentamer shows 12.2 times stronger cyan fluorescence-emission than recognized highly fluorescent fluoranthene under the same conditions, which makes the OFAs into ideal strong fluorescent emitters, tunable conductors, and high carbon-yield precursors for the preparation of sensors and carbon materials. These findings demonstrate an advance in the direct synthesis of oligomers from fused-ring aromatic hydrocarbons and provide a potential direction to optimize the synthesis and functionalities of wholly aromatic nanomaterials.
Co-reporter:Afshin Pendashteh, Seyyed Ebrahim Moosavifard, Mohammad S. Rahmanifar, Yue Wang, Maher F. El-Kady, Richard B. Kaner, and Mir F. Mousavi
Chemistry of Materials 2015 Volume 27(Issue 11) pp:3919
Publication Date(Web):April 20, 2015
DOI:10.1021/acs.chemmater.5b00706
The search for faster, safer, and more efficient energy storage systems continues to inspire researchers to develop new energy storage materials with ultrahigh performance. Mesoporous nanostructures are interesting for supercapacitors because of their high surface area, controlled porosity, and large number of active sites, which promise the utilization of the full capacitance of active materials. Herein, highly ordered mesoporous CuCo2O4 nanowires have been synthesized by nanocasting from a silica SBA-15 template. These nanowires exhibit superior pseudocapacitance of 1210 F g–1 in the initial cycles. Electroactivation of the electrode in the subsequent 250 cycles causes a significant increase in capacitance to 3080 F g–1. An asymmetric supercapacitor composed of mesoporous CuCo2O4 nanowires for the positive electrode and activated carbon for the negative electrode demonstrates an ultrahigh energy density of 42.8 Wh kg–1 with a power density of 15 kW kg–1 plus excellent cycle life. We also show that two asymmetric devices in series can efficiently power 5 mm diameter blue, green, and red LED indicators for 60 min. This work could lead to a new generation of hybrid supercapacitors to bridge the energy gap between chemical batteries and double layer supercapacitors.
Co-reporter:Xinwei Huang, Brian T. McVerry, Catalina Marambio-Jones, Mavis C. Y. Wong, Eric M. V. Hoek and Richard B. Kaner
Journal of Materials Chemistry A 2015 vol. 3(Issue 16) pp:8725-8733
Publication Date(Web):11 Mar 2015
DOI:10.1039/C5TA00900F
We demonstrate that poly(n-2-hydroxyethyl aniline) (n-PANi), a derivative of polyaniline (PANi), provides an effective chlorine tolerant PANi-based ultrafiltration (UF) membrane. n-PANi was synthesized from its monomer via chemical oxidative polymerization. Unlike PANi, n-PANi can be dissolved in N-methyl-2-pyrollidone (NMP) up to 30 wt% to form a casting solution which is stable for months without the aid of an anti-gelling agent. Membranes formed from n-PANi show high resistance to chlorine, even when exposed to 250 ppm sodium hypochlorite for 30 days while PANi membranes completely lose their ability to reject bovine serum albumin (BSA, 6 nm) after 2 days. Spectroscopic studies indicate that the benzenoid groups in PANi membranes are oxidized while n-PANi membranes maintain their chemical structure. n-PANi membranes display high hydrophilicity with a contact angle of ∼36 degrees which contributes to their ultra-low adhesion of E. coli. Cross-flow fouling tests with 1.5 g L−1 BSA fouling solution reveal that n-PANi membranes exhibit low-fouling properties with only 11% flux decline and 91% flux recovery, superior to PANi and commercial polysulfone (PSf) membranes.
Co-reporter:K. L. Marsh, M. Souliman and R. B. Kaner
Chemical Communications 2015 vol. 51(Issue 1) pp:187-190
Publication Date(Web):04 Nov 2014
DOI:10.1039/C4CC07324J
A simple method is presented for exfoliating and suspending hexagonal boron nitride using a co-solvent approach. A 60 w/w% concentration of tert-butanol in water is very effective at exfoliating boron nitride especially when compared to the individual components alone as indicated by UV-vis and transmission electron microscopy. Molecular weight and surface tension are found to play inverse roles in the exfoliation.
Co-reporter:Seyyed E. Moosavifard, Maher F. El-Kady, Mohammad S. Rahmanifar, Richard B. Kaner, and Mir F. Mousavi
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 8) pp:4851
Publication Date(Web):February 11, 2015
DOI:10.1021/am508816t
The increasing demand for energy has triggered tremendous research efforts for the development of lightweight and durable energy storage devices. Herein, we report a simple, yet effective, strategy for high-performance supercapacitors by building three-dimensional pseudocapacitive CuO frameworks with highly ordered and interconnected bimodal nanopores, nanosized walls (∼4 nm) and large specific surface area of 149 m2 g–1. This interesting electrode structure plays a key role in providing facilitated ion transport, short ion and electron diffusion pathways and more active sites for electrochemical reactions. This electrode demonstrates excellent electrochemical performance with a specific capacitance of 431 F g–1 (1.51 F cm–2) at 3.5 mA cm–2 and retains over 70% of this capacitance when operated at an ultrafast rate of 70 mA cm–2. When this highly ordered CuO electrode is assembled in an asymmetric cell with an activated carbon electrode, the as-fabricated device demonstrates remarkable performance with an energy density of 19.7 W h kg–1, power density of 7 kW kg–1, and excellent cycle life. This work presents a new platform for high-performance asymmetric supercapacitors for the next generation of portable electronics and electric vehicles.Keywords: 3D highly ordered electrodes; asymmetric supercapacitor; copper oxide; nanoporous
Co-reporter:Mohammad A. Kiani, Mohammad S. Rahmanifar, Maher F. El-Kady, Richard B. Kaner and Mir F. Mousavi
RSC Advances 2015 vol. 5(Issue 62) pp:50433-50439
Publication Date(Web):26 May 2015
DOI:10.1039/C5RA08170J
Using nanoparticles, instead of microparticles, as active electrode materials in lithium ion batteries could provide a solution to slow charging rates due to long ion diffusion pathways in conventional bulk materials. In this work, we present a new strategy for the synthesis of high purity lithium nickel manganese oxide (LiNi0.5Mn1.5O4) nanoparticles as a high-voltage cathode. A sonochemical reaction is used to synthesize nickel hydroxide and manganese dioxide nanoparticles followed by a solid-state reaction with lithium hydroxide. The product shows a single spinel phase and uniform spherical nano-particles under the appropriate calcination conditions. The LiNi0.5Mn1.5O4 exhibits a high voltage plateau at about 4.7–4.9 V in the charge/discharge process and delivers a discharge capacity of more than 140 mA h g−1 and excellent cycling performance with 99% capacity retention after 70 cycles. The synthesized nano-particles show improved electrochemical performance at high rates. This electrode delivers a power density as high as 26.1 kW kg−1 at a discharge rate of 40 C. This power performance is about one order of magnitude higher than traditional lithium ion batteries. These findings may lead to a new generation of high power lithium ion batteries that can be recharged in minutes instead of hours.
Co-reporter:Maher F. El-Kady;Mengping Li;Andrew T. Lech;Jee Youn Hwang;Mir F. Mousavi;Lindsay Chaney;Melanie Ihns
PNAS 2015 Volume 112 (Issue 14 ) pp:4233-4238
Publication Date(Web):2015-04-07
DOI:10.1073/pnas.1420398112
Supercapacitors now play an important role in the progress of hybrid and electric vehicles, consumer electronics, and military
and space applications. There is a growing demand in developing hybrid supercapacitor systems to overcome the energy density
limitations of the current generation of carbon-based supercapacitors. Here, we demonstrate 3D high-performance hybrid supercapacitors
and microsupercapacitors based on graphene and MnO2 by rationally designing the electrode microstructure and combining active materials with electrolytes that operate at high
voltages. This results in hybrid electrodes with ultrahigh volumetric capacitance of over 1,100 F/cm3. This corresponds to a specific capacitance of the constituent MnO2 of 1,145 F/g, which is close to the theoretical value of 1,380 F/g. The energy density of the full device varies between
22 and 42 Wh/l depending on the device configuration, which is superior to those of commercially available double-layer supercapacitors,
pseudocapacitors, lithium-ion capacitors, and hybrid supercapacitors tested under the same conditions and is comparable to
that of lead acid batteries. These hybrid supercapacitors use aqueous electrolytes and are assembled in air without the need
for expensive “dry rooms” required for building today’s supercapacitors. Furthermore, we demonstrate a simple technique for
the fabrication of supercapacitor arrays for high-voltage applications. These arrays can be integrated with solar cells for
efficient energy harvesting and storage systems.
Co-reporter:Jee Y. Hwang, Maher F. El-Kady, Yue Wang, Lisa Wang, Yuanlong Shao, Kristofer Marsh, Jang M. Ko, Richard B. Kaner
Nano Energy 2015 Volume 18() pp:57-70
Publication Date(Web):November 2015
DOI:10.1016/j.nanoen.2015.09.009
•This work demonstrates a simple one-step process for the synthesis and processing of laser-scribed graphene/RuO2 nanocomposites into 3D electrodes that exhibit ultrahigh specific capacitances up to 1139 F g−1.•The technique enables the direct laser writing of hybrid micro-supercapacitors in single step for the first time, with energy density comparable to Li-thin battery.•Graphene/RuO2 hybrid electrodes can be integrated into an asymmetric electrochemical capacitor operating at a maximum cell voltage of 1.8 V in an aqueous electrolyte.•This simple approach opens up the way for a general strategy for making a wide range of composite materials for a variety of applications.Carbon materials are widely used in supercapacitors because of their high surface area, controlled porosity and ease of processing into electrodes. The combination of carbon with metal oxides results in hybrid electrodes with higher specific capacitance than pure carbon electrodes, which has so far limited the energy density of supercapacitors currently available commercially. However, the preparation and processing of carbon/metal oxide electrodes into supercapacitors of different structures and configurations, especially for miniaturized electronics, has been challenging. Here, we demonstrate a simple one-step process for the synthesis and processing of laser-scribed graphene/RuO2 nanocomposites into electrodes that exhibit ultrahigh energy and power densities. Hydrous RuO2 nanoparticles were successfully anchored to graphene surfaces through a redox reaction of the precursors, graphene oxide, and RuCl3 using a consumer grade LightScribe DVD burner with a 788 nm laser. This binder-free, metal current collector-free graphene/RuO2 film was then used directly as a hybrid electrochemical capacitor electrode, demonstrating much-improved cycling stability and rate-capability with a specific capacitance up to 1139 F g−1. We employed these hybrid electrodes for building aqueous-based symmetric and asymmetric cells that can deliver energy densities up to 55.3 Wh kg−1, placing them among the best performing hybrid electrochemical capacitors. Furthermore, this technique was used for the direct writing of interdigitated hybrid micro-supercapacitors in a single step for the first time, with great potential for miniaturized electronics. This simple approach provides a general strategy for making a wide range of composite materials for a variety of applications.
Co-reporter:Andrew T. Lech;Christopher L. Turner;Reza Mohammadi;Sarah H. Tolbert
PNAS 2015 112 (11 ) pp:3223-3228
Publication Date(Web):2015-03-17
DOI:10.1073/pnas.1415018112
Superhard metals are of interest as possible replacements with enhanced properties over the metal carbides commonly used in
cutting, drilling, and wear-resistant tooling. Of the superhard metals, the highest boride of tungsten—often referred to as
WB4 and sometimes as W1–xB3—is one of the most promising candidates. The structure of this boride, however, has never been fully resolved, despite the
fact that it was discovered in 1961—a fact that severely limits our understanding of its structure–property relationships
and has generated increasing controversy in the literature. Here, we present a new crystallographic model of this compound
based on refinement against time-of-flight neutron diffraction data. Contrary to previous X-ray–only structural refinements,
there is strong evidence for the presence of interstitial arrangements of boron atoms and polyhedral bonding. The formation
of these polyhedra—slightly distorted boron cuboctahedra—appears to be dependent upon the defective nature of the tungsten-deficient
metal sublattice. This previously unidentified structure type has an intermediary relationship between MB2 and MB12 type boride polymorphs. Manipulation of the fractionally occupied metal and boron sites may provide insight for the rational
design of new superhard metals.
Co-reporter:Yue Wang, Jaime A. Torres, Adam Z. Stieg, Shan Jiang, Michael T. Yeung, Yves Rubin, Santanu Chaudhuri, Xiangfeng Duan, and Richard B. Kaner
ACS Nano 2015 Volume 9(Issue 10) pp:9486
Publication Date(Web):August 31, 2015
DOI:10.1021/acsnano.5b03465
Vertically oriented structures of single crystalline conductors and semiconductors are of great technological importance due to their directional charge carrier transport, high device density, and interesting optical properties. However, creating such architectures for organic electronic materials remains challenging. Here, we report a facile, controllable route for producing oriented vertical arrays of single crystalline conjugated molecules using graphene as the guiding substrate. The arrays exhibit uniform morphological and crystallographic orientations. Using an oligoaniline as an example, we demonstrate this method to be highly versatile in controlling the nucleation densities, crystal sizes, and orientations. Charge carriers are shown to travel most efficiently along the vertical interfacial stacking direction with a conductivity of 12.3 S/cm in individual crystals, the highest reported to date for an aniline oligomer. These crystal arrays can be readily patterned and their current harnessed collectively over large areas, illustrating the promise for both micro- and macroscopic device applications.Keywords: graphene; oligoaniline; organic single crystal; selective growth patterning; vertical alignment;
Co-reporter:Yaozu Liao, Thomas P. Farrell, Gregory R. Guillen, Minghua Li, James A. T. Temple, Xin-Gui Li, Eric M. V. Hoek and Richard B. Kaner
Materials Horizons 2014 vol. 1(Issue 1) pp:58-64
Publication Date(Web):03 Sep 2013
DOI:10.1039/C3MH00049D
Highly dispersible polypyrrole (PPy) nanospheres were synthesized and used to produce polysulfone (PSf) nanocomposite ultrafiltration membranes by a non-solvent induced phase separation (NIPS) process. The composite networks formed between PPy and PSf lead to higher porosity, hydrophilicity, surface charge, thermal stability, and water permeability, but slightly lower protein rejection. Nanocomposite membranes containing up to 20% PPy nanospheres were >10 times more permeable than pure PSf membranes, while the bovine serum albumin (BSA) rejection decreased from 94 to 82%. With nanoscale pores, high porosity, improved hydrophilicity, and tunable surface charge properties, the PPy/PSf nanocomposite membranes hold great promise for advanced protein separation, dialysis, water filtration and other macro molecular separations.
Co-reporter:Brian T. McVerry;Mavis C. Y. Wong;Kristofer L. Marsh;James A. T. Temple;Catalina Marambio-Jones;Eric M. V. Hoek
Macromolecular Rapid Communications 2014 Volume 35( Issue 17) pp:1528-1533
Publication Date(Web):
DOI:10.1002/marc.201400226
Co-reporter:Kwang Man Kim, Nguyen Vu Ly, Jung Ha Won, Young-Gi Lee, Won Il Cho, Jang Myoun Ko, Richard B. Kaner
Electrochimica Acta 2014 Volume 136() pp:182-188
Publication Date(Web):1 August 2014
DOI:10.1016/j.electacta.2014.05.054
Three kinds of polydimethylsiloxane (PDMS)-based grafted and ungrafted copolymers such as poly[dimethylsiloxane-co-(siloxane-g-acrylate)] (PDMS-A), poly(dimethylsiloxane-co-phenylsiloxane) (PDMS-P), and poly[dimethylsiloxane-co-(siloxane-g-ethylene oxide)] (PDMS-EO) are used as additives to standard liquid electrolyte solutions to enhance the lithium-ion battery performance at low temperatures. Liquid electrolyte solutions with PDMS-based additives are electrochemically stable under 5.0 V and have adequate ionic conductivities of 10−4 S cm−1 at -20 °C. Particularly, liquid electrolytes with PDMS-P and PDMS-EO exhibit higher ionic conductivities of around 5 × 10−4 S cm−1 at -20 °C, indicating a specific resisting property against the freezing of the liquid electrolyte components. As a result, the addition of PDMS-based additives to liquid electrolytes improves the capacity retention ratio and rate-capability of lithium-ion batteries at low temperatures.
Co-reporter:Maher F. El-Kady and Richard B. Kaner
ACS Nano 2014 Volume 8(Issue 9) pp:8725
Publication Date(Web):September 12, 2014
DOI:10.1021/nn504946k
One of the fundamental issues with graphene for logic applications is its lack of a band gap. In this issue of ACS Nano, Shim and colleagues introduce an effective approach for modulating the current flow in graphene by forming p–n junctions using lasers. The findings could lead to a new route for controlling the electronic properties of graphene-based devices. We highlight recent progress in the direct laser synthesis and patterning of graphene for numerous applications. We also discuss the challenges and opportunities in translating this remarkable progress toward the direct laser writing of graphene electronics at large scales.
Co-reporter:Julio M. D’Arcy, Maher F. El-Kady, Pwint P. Khine, Linghong Zhang, Sun Hwa Lee, Nicole R. Davis, David S. Liu, Michael T. Yeung, Sung Yeol Kim, Christopher L. Turner, Andrew T. Lech, Paula T. Hammond, and Richard B. Kaner
ACS Nano 2014 Volume 8(Issue 2) pp:1500
Publication Date(Web):February 3, 2014
DOI:10.1021/nn405595r
Nanostructures of the conducting polymer poly(3,4-ethylenedioxythiophene) with large surface areas enhance the performance of energy storage devices such as electrochemical supercapacitors. However, until now, high aspect ratio nanofibers of this polymer could only be deposited from the vapor-phase, utilizing extrinsic hard templates such as electrospun nanofibers and anodized aluminum oxide. These routes result in low conductivity and require postsynthetic template removal, conditions that stifle the development of conducting polymer electronics. Here we introduce a simple process that overcomes these drawbacks and results in vertically directed high aspect ratio poly(3,4-ethylenedioxythiophene) nanofibers possessing a high conductivity of 130 S/cm. Nanofibers deposit as a freestanding mechanically robust film that is easily processable into a supercapacitor without using organic binders or conductive additives and is characterized by excellent cycling stability, retaining more than 92% of its initial capacitance after 10 000 charge/discharge cycles. Deposition of nanofibers on a hard carbon fiber paper current collector affords a highly efficient and stable electrode for a supercapacitor exhibiting gravimetric capacitance of 175 F/g and 94% capacitance retention after 1000 cycles.Keywords: conducting polymer; nanofibers; poly(3,4-ethylenedioxythiophene); supercapacitor; vapor-phase polymerization
Co-reporter:Jonathan K. Wassei and Richard B. Kaner
Accounts of Chemical Research 2013 Volume 46(Issue 10) pp:2244
Publication Date(Web):January 10, 2013
DOI:10.1021/ar300184v
Since the first reported isolation of graphene by peeling graphite with cellophane tape in 2004, there has been a paradigm shift in research. In just nine years, graphene has had a major impact on fields ranging from physics and chemistry to materials science and engineering leading to a host of interdisciplinary advances in nanotechnology. Graphene is attractive because it possesses many extraordinary characteristics that are a direct consequence of its unique atomic structure, as discussed here.For over a decade, our group has been exploring new routes to synthesize graphene so that this potentially important material can be scaled up for use in practical applications. We have made several significant discoveries starting with the synthesis of few-layer graphene from intercalation/exfoliation reactions that upon sonication produce carbon nanoscrolls. Next, we developed high-throughput methods for producing chemically converted graphene from graphene oxide using either aqueous or anhydrous hydrazine. Recently, we introduced an inexpensive process that uses the laser in an optical drive to deoxygenate graphite oxide layers to create laser scribed graphene.The impetus of this Account is to discuss both synthetic routes to graphene and their applications. The first part highlights both our top-down and bottom-up routes to graphene, which includes intercalation/exfoliation, chemical reduction with hydrazine and other organic reagents, chemical vapor deposition, and laser scribed graphene. In the later part, we emphasize the significance of these contributions to the field and how each approach has afforded us unique opportunities to explore graphene’s properties. This has resulted in new applications such as practical chemical sensors, flash memory storage devices, transparent conductors, distributed ignition, and supercapacitors.
Co-reporter:Brian T. McVerry, James A. T. Temple, Xinwei Huang, Kristofer L. Marsh, Eric M. V. Hoek, and Richard B. Kaner
Chemistry of Materials 2013 Volume 25(Issue 18) pp:3597
Publication Date(Web):August 22, 2013
DOI:10.1021/cm401288r
A simple, scalable method for fabricating fouling-resistant ultrafiltration membranes is described. A self-doped, sulfonated form of polyaniline was blended into polysulfone (PSf) ultrafiltration (UF) membranes to enhance hydrophilicity and fouling resistance. Polyaniline in its base form was sulfonated with fuming sulfuric acid, yielding sulfonated polyaniline (SPANi) with a degree of sulfonation of ∼0.5 confirmed by XPS. The SPANi polymer was dedoped and dissolved in a solution of polysulfone in N-methylpyrollidone at varying concentrations. During phase inversion to form membranes, SPANi is redoped and precipitated within the PSf membrane films in a facile one-step process. Composite membranes containing increasing amounts of SPANi were compared to the pure PSf membranes to determine changes in performance, hydrophilicity, and antifouling characteristics. The composite membranes exhibit fluxes similar to those of the pure PSf membrane and maintain rejection properties similar to those of current UF membranes. Captive bubble contact angle measurements and atomic force microscopy suggest increasing membrane hydrophilicity with increasing SPANi content. During flux decline and recovery experiments, SPANi/PSf composite membranes exhibited higher flux recovery than a pure PSf membrane, with the best performing membrane regaining 95% of its original flux after being washed with deionized water, demonstrating a high resistance to irreversible fouling.Keywords: antifouling properties; hydrophilic additive; low-fouling; polyaniline; ultrafiltration membranes;
Co-reporter:Xin-Gui Li, Yaozu Liao, Mei-Rong Huang, Veronica Strong and Richard B. Kaner
Chemical Science 2013 vol. 4(Issue 5) pp:1970-1978
Publication Date(Web):10 Jan 2013
DOI:10.1039/C3SC22107E
Electron-rich oligofluoranthene has been successfully synthesized by a one-step direct chemical oxidative oligomerization of fluoranthene. Key advantages include easy synthesis, high synthetic yield and low cost when compared with electropolymerization. Oligofluoranthene in solution is a very strong cyan fluorescence emitter with 12.2 times higher intensity than the fluoranthene monomer. The strong fluorescence can be effectively quenched by specific electron-deficient species, enabling the fabrication of low-cost, high-performance chemosensors for the selective detection of Fe(III) ions and the explosive 2,4,6-trinitrophenol (picric acid). A concentration range of >9 orders of magnitude with exceedingly low detection limits down to 10−12 M is possible. No sample enrichment is needed likely due to the synergistic effects of well-distributed π-conjugated electrons with a conical stereo configuration that may enhance the detection ability. Common interferents appear to have little effect as Fe(III) can be selectively detected in both tap water and seawater containing many other metal ions and picric acid can be detected at low concentrations even in the presence of inorganic acids.
Co-reporter:Yaozu Liao, Deng-Guang Yu, Xia Wang, Wei Chain, Xin-Gui Li, Eric M. V. Hoek and Richard B. Kaner
Nanoscale 2013 vol. 5(Issue 9) pp:3856-3862
Publication Date(Web):27 Feb 2013
DOI:10.1039/C3NR00441D
Electro-active switchable ultrafiltration membranes are of great interest due to the possibility of external control over permeability, selectivity, anti-fouling and cleaning. Here, we report on hybrid single-walled carbon nanotube (SWCNT)–polyaniline (PANi) nanofibers synthesized by in situ polymerization of aniline in the presence of oxidized SWCNTs. The composite nanofibers exhibit unique morphology of core–shell (SWCNT–PANi) structures with average total diameters of 60 nm with 10 to 30 nm thick PANi coatings. The composite nanofibers are easily dispersed in polar aprotic solvents and cast into asymmetric membranes via a nonsolvent induced phase separation. The hybrid SWCNT–PANi membranes are electrically conductive at neutral pH and exhibit ultrafiltration-like permeability and selectivity when filtering aqueous suspensions of 6 nm diameter bovine serum albumin and 48 nm diameter silica particles. A novel flash welding technique is utilized to tune the morphology, porosity, conductivity, permeability and nanoparticle rejection of the SWCNT–PANi composite ultrafiltration membranes. Upon flash welding, both conductivity and pure water permeability of the membranes improves by nearly a factor of 10, while maintaining silica nanoparticle rejection levels above 90%. Flash welding of SWCNT–PANi composite membranes holds promise for formation of electrochemically tunable membranes.
Co-reporter:Yaozu Liao, Xin-Gui Li, Eric M. V. Hoek and Richard B. Kaner
Journal of Materials Chemistry A 2013 vol. 1(Issue 48) pp:15390-15396
Publication Date(Web):28 Oct 2013
DOI:10.1039/C3TA13902F
Development of electro-ultrafiltration membranes is an attractive target. We report electrically conducting ultrafiltration membranes by blending single-walled carbon nanotube/polyaniline (SWCNT/PANi) nanofibers into a polysulfone (PSf) matrix. By selecting the amount of nanofibers and applying a flash welding technique, the chemical structure, porosity, thermal stability, conductivity, hydrophilicity, permeability, and bovine serum albumin (BSA) rejection of these composite ultrafiltration membranes can be controlled. Addition of SWCNT/PANi nanofibers to the composites enhances the initial water permeability by 2.5–7.3 times and increases the hydrophilicity, and maintains considerable rejection of BSA from 39.8–73.7%. An electrical conductivity between 0.1 and 3.4 × 10−6 S cm−1 can be maintained over a broad pH range from 0.52–10.2. By regulating the flash welding intensity, the conductivity, permeability, and BSA rejection can be enhanced up to 600, 2, and ∼1.5 times, respectively.
Co-reporter:Yue Wang, Xin N. Guan, Che-Yu Wu, Ming-Tien Chen, Hsin-Hsi Hsieh, Henry D. Tran, Shu-Chuan Huang and Richard B. Kaner
Polymer Chemistry 2013 vol. 4(Issue 17) pp:4814-4820
Publication Date(Web):15 Jul 2013
DOI:10.1039/C3PY00672G
Copolymerization of aniline with substituted anilines can synergistically combine high electrical conductivity with good solubility and functionality. Here, we report the synthesis of a variety of polyaniline-based copolymer nanofibers with uniform diameters. The relationship between the feed ratio and the final composition is examined by NMR and UV-vis spectra. The conductivity of the copolymers can be tuned over a six order-of-magnitude range by varying the composition of the two building blocks. The copolymer nanofibers exhibit excellent colloidal stability with zeta-potential values as high as 40 mV, which enables them to be spray-coated to form transparent, conductive thin films with good optical properties. This simple process is scalable, and can lead to flexible or patterned films, which may be helpful for applications in organic electronics, optoelectronics, sensors, and energy storage devices.
Co-reporter:Maher F. El-Kady;Veronica Strong;Sergey Dubin
Science 2012 Vol 335(6074) pp:1326-1330
Publication Date(Web):16 Mar 2012
DOI:10.1126/science.1216744
Co-reporter:Giacomo Mariani, Yue Wang, Ping-Show Wong, Andrew Lech, Chung-Hong Hung, Joshua Shapiro, Sergey Prikhodko, Maher El-Kady, Richard B. Kaner, and Diana L. Huffaker
Nano Letters 2012 Volume 12(Issue 7) pp:3581-3586
Publication Date(Web):June 14, 2012
DOI:10.1021/nl301251q
Three-dimensional core–shell organic–inorganic hybrid solar cells with tunable properties are demonstrated via electropolymerization. Air-stable poly(3,4-ethylenedioxythiophene) (PEDOT) shells with controlled thicknesses are rapidly coated onto periodic GaAs nanopillar arrays conformally, preserving the vertical 3D structure. The properties of the organic layer can be readily tuned in situ, allowing for (1) the lowering of the highest occupied molecular orbital level (|ΔE| ∼ 0.28 eV), leading to the increase of open-circuit voltage (VOC), and (2) an improvement in PEDOT conductivity that results in enhanced short-circuit current densities (JSC). The incorporation of various anionic dopants in the polymer during the coating process also enables the tailoring of the polymer/semiconductor interface transport properties. Systematic tuning of the device properties results in a JSC of 13.6 mA cm–2, VOC of 0.63 V, peak external quantum efficiency of 58.5%, leading to a power conversion efficiencies of 4.11%.
Co-reporter:Yue Wang ; Jinglin Liu ; Henry D. Tran ; Matthew Mecklenburg ; Xin N. Guan ; Adam Z. Stieg ; B. C. Regan ; David C. Martin
Journal of the American Chemical Society 2012 Volume 134(Issue 22) pp:9251-9262
Publication Date(Web):May 25, 2012
DOI:10.1021/ja301061a
Single crystals of doped aniline oligomers are produced via a simple solution-based self-assembly method. Detailed mechanistic studies reveal that crystals of different morphologies and dimensions can be produced by a “bottom-up” hierarchical assembly where structures such as one-dimensional (1-D) nanofibers can be aggregated into higher order architectures. A large variety of crystalline nanostructures including 1-D nanofibers and nanowires, 2-D nanoribbons and nanosheets, 3-D nanoplates, stacked sheets, nanoflowers, porous networks, hollow spheres, and twisted coils can be obtained by controlling the nucleation of the crystals and the non-covalent interactions between the doped oligomers. These nanoscale crystals exhibit enhanced conductivity compared to their bulk counterparts as well as interesting structure–property relationships such as shape-dependent crystallinity. Furthermore, the morphology and dimension of these structures can be largely rationalized and predicted by monitoring molecule–solvent interactions via absorption studies. Using doped tetraaniline as a model system, the results and strategies presented here provide insight into the general scheme of shape and size control for organic materials.
Co-reporter:Reza Mohammadi ; Miao Xie ; Andrew T. Lech ; Christopher L. Turner ; Abby Kavner ; Sarah H. Tolbert
Journal of the American Chemical Society 2012 Volume 134(Issue 51) pp:20660-20668
Publication Date(Web):November 21, 2012
DOI:10.1021/ja308219r
To enhance the hardness of tungsten tetraboride (WB4), a notable lower cost member of the late transition-metal borides, we have synthesized and characterized solid solutions of this material with tantalum (Ta), manganese (Mn), and chromium (Cr). Various concentrations of these transition-metal elements, ranging from 0.0 to 50.0 at. %, on a metals basis, were made. Arc melting was used to synthesize these refractory compounds from the pure elements. Elemental and phase purity of the samples were examined using energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), and microindentation was utilized to measure the Vickers hardness under applied loads of 0.49–4.9 N. XRD results indicate that the solubility limit is below 10 at. % for Cr and below 20 at. % for Mn, while Ta is soluble in WB4 above 20 at. %. Optimized Vickers hardness values of 52.8 ± 2.2, 53.7 ± 1.8, and 53.5 ± 1.9 GPa were achieved, under an applied load of 0.49 N, when ∼2.0, 4.0, and 10.0 at. % Ta, Mn, and Cr were added to WB4 on a metals basis, respectively. Motivated by these results, ternary solid solutions of WB4 were produced, keeping the concentration of Ta in WB4 fixed at 2.0 at. % and varying the concentration of Mn or Cr. This led to hardness values of 55.8 ± 2.3 and 57.3 ± 1.9 GPa (under a load of 0.49 N) for the combinations W0.94Ta0.02Mn0.04B4 and W0.93Ta0.02Cr0.05B4, respectively. In situ high-pressure XRD measurements collected up to ∼65 GPa generated a bulk modulus of 335 ± 3 GPa for the hardest WB4 solid solution, W0.93Ta0.02Cr0.05B4, and showed suppression of a pressure-induced phase transition previously observed in pure WB4.
Co-reporter:Yao Zu Liao;Veronica Strong;Yue Wang;Xin-Gui Li;Xia Wang
Advanced Functional Materials 2012 Volume 22( Issue 4) pp:726-735
Publication Date(Web):
DOI:10.1002/adfm.201102013
Abstract
Blue light-emitting oligotriphenylene nanofibers are synthesized by oxidizing triphenylene using ferric chloride. By adjusting the monomer concentration, the acid used, and the temperature employed, the average diameter and length of the nanofibers can be readily tuned from 50 to 200 nm and 0.5 to 5 μm, respectively. Structural characterization, electrical conductivity, thermal stability, and fluorescence of oligotriphenylene, along with a proposed nanofiber formation mechanism, are presented. Both oligotriphenylene nanofiber dispersions and oligotriphenylene/polysulfone composite films are developed as fluorescent sensors for detecting traces of nitro-based explosives including nitromethane, nitrobenzene, and 2,4,6-trinitrophenol, as well as an electron-deficient metal ion, Fe(III). The sensors exhibit much better selectivity and sensitivity compared to conventional sensors, with detection limits down to 1.0 nm with a detection range covering ∼4 orders of magnitude. The detection mechanism of the fluorescent sensors is also disscussed.
Co-reporter:Julio M. D'Arcy, Henry D. Tran, Adam Z. Stieg, James K. Gimzewski and Richard B. Kaner
Nanoscale 2012 vol. 4(Issue 10) pp:3075-3082
Publication Date(Web):27 Feb 2012
DOI:10.1039/C2NR00010E
A procedure for depositing thin films of carbon nanostructures is described that overcomes the limitations typically associated with solution based methods. Transparent and conductively continuous carbon coatings can be grown on virtually any type of substrate within seconds. Interfacial surface tension gradients result in directional fluid flow and film spreading at the water/oil interface. Transparent films of carbon nanostructures are produced including aligned ropes of single-walled carbon nanotubes and assemblies of single sheets of chemically converted graphene and graphite oxide. Process scale-up, layer-by-layer deposition, and a simple method for coating non-activated hydrophobic surfaces are demonstrated.
Co-reporter:Yaozu Liao, Veronica Strong, Wei Chian, Xia Wang, Xin-Gui Li, and Richard B. Kaner
Macromolecules 2012 Volume 45(Issue 3) pp:1570-1579
Publication Date(Web):January 31, 2012
DOI:10.1021/ma2024446
Sulfonated polyaniline (SPANi), a self-doped conjugated polymer, has received great interest in recent years; however, controlling its shape, size, and conductivity at the nanoscale remains a significant challenge. Here, we report an initiator-assisted route to SPANi nanostructures by rapidly copolymerizing o-aminobenzenesulfonic acid with aniline or its derivatives in the presence of a catalytic amount of the initiator–aniline dimer. UV–vis, FT-IR, and XRD spectra reveal that the chemical compositions of the SPANi nanostructures are similar to that of conventional SPANi possessing an agglomerated morphology. By regulating the comonomer molar ratios, the aniline derivatives used and the acidic media employed, the morphology of the SPANi changes from 1-D nanofibers, nanosticks, nanothorns, and nanorods to 2-D nanoplates and 3-D porous nanospheres. The length and aspect ratio of the SPANi nanofibers can reach values up to 4.5 μm and 60, respectively. These SPANi nanostructures are readily processable in both organic and aqueous solvents and demonstrate 6 orders of magnitude enhanced conductivity at pH values of 5.5–6.0 when compared to conventional polyaniline.
Co-reporter:Veronica Strong, Sergey Dubin, Maher F. El-Kady, Andrew Lech, Yue Wang, Bruce H. Weiller, and Richard B. Kaner
ACS Nano 2012 Volume 6(Issue 2) pp:1395
Publication Date(Web):January 13, 2012
DOI:10.1021/nn204200w
Engineering a low-cost graphene-based electronic device has proven difficult to accomplish via a single-step fabrication process. Here we introduce a facile, inexpensive, solid-state method for generating, patterning, and electronic tuning of graphene-based materials. Laser scribed graphene (LSG) is shown to be successfully produced and selectively patterned from the direct laser irradiation of graphite oxide films under ambient conditions. Circuits and complex designs are directly patterned onto various flexible substrates without masks, templates, post-processing, transferring techniques, or metal catalysts. In addition, by varying the laser intensity and laser irradiation treatments, the electrical properties of LSG can be precisely tuned over 5 orders of magnitude of conductivity, a feature that has proven difficult with other methods. This inexpensive method for generating LSG on thin flexible substrates provides a mode for fabricating a low-cost graphene-based NO2 gas sensor and enables its use as a heterogeneous scaffold for the selective growth of Pt nanoparticles. The LSG also shows exceptional electrochemical activity that surpasses other carbon-based electrodes in electron charge transfer rate as demonstrated using a ferro-/ferricyanide redox couple.Keywords: electrocatalysis; flexible electronics; gas sensor; graphene; graphene/Pt composite; graphite oxide; laser patterning
Co-reporter:Julio M. D'Arcy, Richard B. Kaner
Materials Today 2011 Volume 14(Issue 4) pp:175
Publication Date(Web):April 2011
DOI:10.1016/S1369-7021(11)70095-5
PEDOT nanostructures from the vapor phase
Co-reporter:Veronica Strong, Yue Wang, Ani Patatanyan, Philip G. Whitten, Geoffrey M. Spinks, Gordon G. Wallace, and Richard B. Kaner
Nano Letters 2011 Volume 11(Issue 8) pp:3128-3135
Publication Date(Web):July 5, 2011
DOI:10.1021/nl2011593
Despite the many attractive properties of conjugated polymers, their practical applications are often limited by the lack of a simple, scalable, and nondisruptive patterning method. Here, a direct, scalable, high-resolution patterning technique for conducting polymers is demonstrated that does not involve photoresists, masks, or postprocessing treatment. Complex, well-defined patterns down to sub-micrometer scales can be created from nanofibrous films of a wide variety of conducting polymers by photothermally welding the nanofibers using a low-energy infrared laser. The welding depth, structural robustness, and optical properties of the films are readily controlled. In addition, the electrical properties such as conductivity can be precisely tuned over a 7-order of magnitude range, while maintaining the characteristic tunable electronic properties in the nonwelded polyaniline regions.
Co-reporter:Yaozu Liao, Chen Zhang, Ya Zhang, Veronica Strong, Jianshi Tang, Xin-Gui Li, Kourosh Kalantar-zadeh, Eric M. V. Hoek, Kang L. Wang, and Richard B. Kaner
Nano Letters 2011 Volume 11(Issue 3) pp:954-959
Publication Date(Web):February 2, 2011
DOI:10.1021/nl103322b
An initiator is applied to synthesize single-walled carbon nanotube/polyaniline composite nanofibers for use as high-performance chemosensors. The composite nanofibers possess widely tunable conductivities (10−4 to 102 S/cm) with up to 5.0 wt % single-walled carbon nanotube (SWCNT) loadings. Chemosensors fabricated from the composite nanofibers synthesized with a 1.0 wt % SWCNT loading respond much more rapidly to low concentrations (100 ppb) of HCl and NH3 vapors compared to polyaniline nanofibers alone (120 s vs 1000 s). These nanofibrillar SWCNT/polyaniline composite nanostructures are promising materials for use as low-cost disposable sensors and as electrodes due to their widely tunable conductivities.
Co-reporter:Henry D. Tran, Julio M. D'Arcy, Yue Wang, Peter J. Beltramo, Veronica A. Strong and Richard B. Kaner
Journal of Materials Chemistry A 2011 vol. 21(Issue 11) pp:3534-3550
Publication Date(Web):25 Nov 2010
DOI:10.1039/C0JM02699A
The number of different nano- and micro-scale structures produced from the chemical oxidation of aniline into “polyaniline” is rivaled by few other organic materials. Nanoscale structures such as fibers, tubes, aligned wires, flowers, spheres and hollow spheres, plates, and even those resembling anatomical organs, insects, and sea animals have been observed for the products produced when aniline is oxidized. This feature article examines these different structures and the small and subtle changes in reaction parameters that result in their formation. These changes can often result in drastic differences in the polymer's nanoscale morphology. Because a nanomaterial's properties are highly dependent on the type of morphology produced, understanding polyaniline's propensity for forming these structures is crucial towards tailoring the material for different applications as well as improving its synthetic reproducibility. The different approaches to commonly observed polyaniline nanostructures are presented in this article along with some of the highly debated aspects of these processes. The article ends with our approach towards resolving some of these contentious issues and our perspective on where things are headed in the years to come.
Co-reporter:Jonathan K. Wassei, Kitty C. Cha, Vincent C. Tung, Yang Yang and Richard B. Kaner
Journal of Materials Chemistry A 2011 vol. 21(Issue 10) pp:3391-3396
Publication Date(Web):31 Jan 2011
DOI:10.1039/C0JM02910F
Anionic dopants have been used to reduce the overall sheet resistance of carbon nanotube and graphene films for transparent conductor applications. These enhanced electronic properties are attributed to an increased number of p-type charge carriers. While there have been many reports of its use, there is little reported insight into the chemical interactions of a commonly used dopant, thionyl chloride (SOCl2), with pristine graphene and its chemically converted derivatives. Here, we explore the effects of thionyl chloride on the physical and chemical properties of graphene and hybrid graphene–carbon nanotube films, focusing on how the changes in conductivity correlate to the morphology of chemically converted graphene and carbon nanotube composites.
Co-reporter:Yue Wang;Henry D. Tran
Macromolecular Rapid Communications 2011 Volume 32( Issue 1) pp:35-49
Publication Date(Web):
DOI:10.1002/marc.201000280
Co-reporter:Yaozu Liao ; Chen Zhang ; Xia Wang ; Xin-Gui Li ; Samuel J. Ippolito ; Kourosh Kalantar-zadeh
The Journal of Physical Chemistry C 2011 Volume 115(Issue 32) pp:16187-16192
Publication Date(Web):July 1, 2011
DOI:10.1021/jp2053585
The simple synthesis of one-dimensional (1D) semiconducting nanostructures with high charge-carrier transport is an important aim for the fabrication of organic electronic devices. Here, we report an initiator-assisted chemical processing technique that creates 1D nanocomposites consisting of a nanofibrillar polyaniline (PANi) shell built around a core of single-walled carbon nanotubes (SWCNTs). These nanostructured composites are produced by in situ polymerization of aniline in the presence of SWCNTs. The homogeneously dispersed SWCNTs in the nanofibrillar PANi matrix provides relatively high conductivities (up to 95 S cm–1) at low loadings (≤5 wt %). The partially ordered arrangement of the semiconducting nanostructures is improved through self-assembly of the 1D nanocomposites at microelectrodes using a dielectrophoretic technique. Field effect devices fabricated from the nanocomposites demonstrate four times larger carrier mobilities than that of pure PANi nanofibers, with values up to 2.85 cm2 V–1 s–1 due to the strong confinement of free carriers by the fibers in the axial direction and a facile charge-transfer reaction between the two components.
Co-reporter:Christina O. Baker, Brian Shedd, Ricky J. Tseng, Alfredo A. Martinez-Morales, Cengiz S. Ozkan, Mihri Ozkan, Yang Yang, and Richard B. Kaner
ACS Nano 2011 Volume 5(Issue 5) pp:3469
Publication Date(Web):April 6, 2011
DOI:10.1021/nn200992w
Controlling reaction temperature for a set time enables the size of gold nanoparticles autoreduced on the surface of polyaniline nanofibers to be controlled. The size of the gold nanoparticles can be used to tune the electrical bistable memory effect in gold/polyaniline nanofiber composite devices. Turn-on voltages and on/off ratios improve with decreasing nanoparticle size, making this a promising method to enhance performance and create smaller devices. Long-term stability of the composites can be improved by the addition of stabilizers following autoreduction of the gold nanoparticles.Keywords: bistable memory devices; gold nanoparticles; nanoparticle size/growth control; organic−inorganic nanocomposite; polyaniline nanofibers
Co-reporter:Reza Mohammadi;Andrew T. Lech;Miao Xie;Beth E. Weaver;Michael T. Yeung;Sarah H. Tolbert;
Proceedings of the National Academy of Sciences 2011 108(27) pp:10958-10962
Publication Date(Web):June 20, 2011
DOI:10.1073/pnas.1102636108
Tungsten tetraboride (WB4) is an interesting candidate as a less expensive member of the growing group of superhard transition metal borides. WB4 was successfully synthesized by arc melting from the elements. Characterization using powder X-ray diffraction (XRD) and
energy-dispersive X-ray spectroscopy (EDX) indicates that the as-synthesized material is phase pure. The zero-pressure bulk
modulus, as measured by high-pressure X-ray diffraction for WB4, is 339 GPa. Mechanical testing using microindentation gives a Vickers hardness of 43.3 ± 2.9 GPa under an applied load of
0.49 N. Various ratios of rhenium were added to WB4 in an attempt to increase hardness. With the addition of 1 at.% Re, the Vickers hardness increased to approximately 50 GPa
at 0.49 N. Powders of tungsten tetraboride with and without 1 at.% Re addition are thermally stable up to approximately 400 °C
in air as measured by thermal gravimetric analysis.
Co-reporter:Jonathan K. Wassei;Vincent C. Tung;Steven J. Jonas;Kitty Cha;Bruce S. Dunn;Yang Yang
Advanced Materials 2010 Volume 22( Issue 8) pp:897-901
Publication Date(Web):
DOI:10.1002/adma.200902360
Co-reporter:Jonathan K. Wassei, Richard B. Kaner
Materials Today 2010 Volume 13(Issue 3) pp:52-59
Publication Date(Web):March 2010
DOI:10.1016/S1369-7021(10)70034-1
New electronic devices such as touch screens, flexible displays, printable electronics, solid-state lighting and thin film photovoltaics have led to a rapidly growing market for flexible transparent conductors. Standard indium tin oxide films are unlikely to satisfy future needs due to losses in conductivity on bending and the escalating cost of indium which is in limited supply. Recent advances in the synthesis and characterization of graphene indicate that it may be suitable for many electronic applications including as a transparent conductor. Graphene hybrids with, for example, carbon nanotubes, may prove to be especially interesting.
Co-reporter:Sabah K. Bux, Marc Rodriguez, Michael T. Yeung, Crystal Yang, Adam Makhluf, Richard G. Blair, Jean-Pierre Fleurial and Richard B. Kaner
Chemistry of Materials 2010 Volume 22(Issue 8) pp:2534
Publication Date(Web):March 16, 2010
DOI:10.1021/cm903410s
Nanostructured silicon has recently been identified as an attractive material for a wide variety of uses from energy conversion and storage to biological applications. Here we present a new, rapid method of producing high-purity, nanostructured, unfunctionalized silicon via solid-state metathesis (SSM) in a matter of seconds. The silicon forms in a double displacement reaction between silicon tetraiodide and an alkaline earth silicide precursor. The products are characterized using powder X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive spectroscopy (EDS). Depending on the silicide precursor used, two different morphologies are obtained, either nanoparticles or dendritic nanowires. The variations in the morphologies are attributed to differences in the kinetics of the reactions.
Co-reporter:Sabah K. Bux, Jean-Pierre Fleurial and Richard B. Kaner
Chemical Communications 2010 vol. 46(Issue 44) pp:8311-8324
Publication Date(Web):05 Oct 2010
DOI:10.1039/C0CC02627A
Recent studies indicate that nanostructuring can be an effective method for increasing the dimensionless thermoelectric figure of merit (ZT) in materials. Most of the enhancement in ZT can be attributed to large reductions in the lattice thermal conductivity due to increased phonon scattering at interfaces. Although significant gains have been reported, much higher ZTs in practical, cost-effective and environmentally benign materials are needed in order for thermoelectrics to become effective for large-scale, wide-spread power and thermal management applications. This review discusses the various synthetic techniques that can be used in the production of bulk scale nanostructured materials. The advantages and disadvantages of each synthetic method are evaluated along with guidelines and goals presented for an ideal thermoelectric material. With proper optimization, some of these techniques hold promise for producing high efficiency devices.
Co-reporter:J.B. Levine, J.B. Betts, J.D. Garrett, S.Q. Guo, J.T. Eng, A. Migliori, R.B. Kaner
Acta Materialia 2010 Volume 58(Issue 5) pp:1530-1535
Publication Date(Web):March 2010
DOI:10.1016/j.actamat.2009.10.060
Abstract
The search for superhard materials, driven by their widespread use in industrial applications, highlights one of the most difficult problems in the field of materials science: the accurate characterization of a material’s intrinsic physical properties. This paper reports on the full elastic tensor of two polycrystalline isotropic specimens and one specimen of ReB2 consisting of highly oriented grains. The high-monocrystal bulk modulus value extracted from the grain-oriented specimen, measured by resonant ultrasound spectroscopy, validates the ultra-incompressibility of ReB2. An observed hardness of 40 GPa and a Debye temperature of 731 K were calculated for the ReB2 crystal, confirming its superhard and super-stiff properties. All the measured moduli of the ReB2 grain-oriented crystal exceed the comparable ones for the polycrystal by amounts that cannot be explained by averaging over direction, which may reveal why recent measurements reported on ReB2 containing excess boron yield values that are not as hard or incompressible as the crystal.
Co-reporter:Yaozu Liao, Xin-Gui Li, and Richard B. Kaner
ACS Nano 2010 Volume 4(Issue 9) pp:5193
Publication Date(Web):September 7, 2010
DOI:10.1021/nn101378p
Water-dispersible polypyrrole nanospheres with diameters of less than 100 nm were synthesized in high yield without any templates, surfactants, or functional dopants by the introduction of 2,4-diaminodiphenylamine as an initiator into a reaction mixture of pyrrole monomer, oxidant, and acid. The initiator plays a critical role in tailoring the nanostructures of polypyrrole. 2,4-Diaminodiphenylamine interacts with acid to form cations, which combine with various anions to self-assemble resulting in different size nanomicelles. These nanomicelles, stabilized by initiator molecules, act as templates to encapsulate pyrrole and oxidant leading to the formation of nanospheres during polymerization. When smaller acids are used, smaller diameter sphere-like polypyrrole nanostructures are obtained. The as-synthesized polypyrrole nanospheres can then be used to fabricate highly conducting nitrogen-doped carbon nanospheres with controllable sizes of 50−220 nm with monodispersities up to 95% after pyrolysis. The size of the carbon nanospheres decreases by 20−30 nm due to carbonization when compared to the original polymer nanospheres. The molecular structures, morphologies, and electrical properties along with the formation mechanism of the polypyrrole and carbon nanospheres are discussed.Keywords: carbon; conducting polymers; nanoparticles; self-assembly; synthesis
Co-reporter:Henry D. Tran;Julio M. D’Arcy;Alexander K. Tucker-Schwartz;Rain P. Wong;Vincent C. Tung;Yang Yang
PNAS 2010 Volume 107 (Issue 46 ) pp:19673-19678
Publication Date(Web):2010-11-16
DOI:10.1073/pnas.1008595107
The method employed for depositing nanostructures of conducting polymers dictates potential uses in a variety of applications
such as organic solar cells, light-emitting diodes, electrochromics, and sensors. A simple and scalable film fabrication technique
that allows reproducible control of thickness, and morphological homogeneity at the nanoscale, is an attractive option for
industrial applications. Here we demonstrate that under the proper conditions of volume, doping, and polymer concentration,
films consisting of monolayers of conducting polymer nanofibers such as polyaniline, polythiophene, and poly(3-hexylthiophene)
can be produced in a matter of seconds. A thermodynamically driven solution-based process leads to the growth of transparent
thin films of interfacially adsorbed nanofibers. High quality transparent thin films are deposited at ambient conditions on
virtually any substrate. This inexpensive process uses solutions that are recyclable and affords a new technique in the field
of conducting polymers for coating large substrate areas.
Co-reporter:Dan Li, Jiaxing Huang and Richard B. Kaner
Accounts of Chemical Research 2009 Volume 42(Issue 1) pp:135
Publication Date(Web):November 6, 2008
DOI:10.1021/ar800080n
Known for more than 150 years, polyaniline is the oldest and potentially one of the most useful conducting polymers because of its facile synthesis, environmental stability, and simple acid/base doping/dedoping chemistry. Because a nanoform of this polymer could offer new properties or enhanced performance, nanostructured polyaniline has attracted a great deal of interest during the past few years. This Account summarizes our recent research on the syntheses, processing, properties, and applications of polyaniline nanofibers. By monitoring the nucleation behavior of polyaniline, we demonstrate that high-quality nanofibers can be readily produced in bulk quantity using the conventional chemical oxidative polymerization of aniline. The polyaniline nanostructures formed using this simple method have led to a number of exciting discoveries. For example, we can readily prepare aqueous polyaniline colloids by purifying polyaniline nanofibers and controlling the pH. The colloids formed are self-stabilized via electrostatic repulsions without the need for any chemical modification or steric stabilizer, thus providing a simple and environmentally friendly way to process this polymer. An unusual nanoscale photothermal effect called “flash welding”, which we discovered with polyaniline nanofibers, has led to the development of new techniques for making asymmetric polymer membranes and patterned nanofiber films and creating polymer-based nanocomposites. We also demonstrate the use of flash-welded polyaniline films for monolithic actuators. Taking advantage of the unique reduction/oxidation chemistry of polyaniline, we can decorate polyaniline nanofibers with metal nanoparticles through in situ reduction of selected metal salts. The resulting polyaniline/metal nanoparticle composites show promise for use in ultrafast nonvolatile memory devices and for chemical catalysis. In addition, the use of polyaniline nanofibers or their composites can significantly enhance the sensitivity, selectivity, and response time of polyaniline-based chemical sensors. By combining straightforward synthesis and composite formation with exceptional solution processability, we have developed a range of new useful functionalities. Further research on nanostructured conjugated polymers holds promise for even more exciting discoveries and intriguing applications.
Co-reporter:Henry D. Tran;Dan Li
Advanced Materials 2009 Volume 21( Issue 14-15) pp:
Publication Date(Web):
DOI:10.1002/adma.200990047
Co-reporter:Henry D. Tran;Dan Li
Advanced Materials 2009 Volume 21( Issue 14-15) pp:1487-1499
Publication Date(Web):
DOI:10.1002/adma.200802289
Abstract
This Progress Report provides a brief overview of current research activities in the field of one-dimensional (1D) conducting polymer nanostructures. The synthesis, properties, and applications of these materials are outlined with a strong emphasis on recent literature examples. Chemical methods that can produce 1D nanostructures in bulk quantities are discussed in the context of two different strategies: 1) procedures that rely on a nanoscale template or additive not inherent to the polymer and 2) those that do not. The different sub-classifications of these two strategies are delineated and the virtues and vices of each area are discussed. Following this discussion is an outline of the properties and applications of 1D conducting polymer nanostructures. This section focuses on applications in which nanostructured conducting polymers are clearly advantageous over their conventional counterparts. We conclude with our perspective on the main challenges and future research directions for this new class of nanomaterials. This Progress Report is not intended as a comprehensive review of the field, but rather a summary of select contributions that we feel will provide the reader with a strong basis for further investigation into this fast emerging field.
Co-reporter:Sergey N. Tkachev;Jonathan B. Levine;Alexer Kisliuk;Alexei P. Sokolov;Shuqi Guo;Justin T. Eng
Advanced Materials 2009 Volume 21( Issue 42) pp:4284-4286
Publication Date(Web):
DOI:10.1002/adma.200900232
Co-reporter:Jonathan B. Levine;Sarah H. Tolbert
Advanced Functional Materials 2009 Volume 19( Issue 22) pp:3519-3533
Publication Date(Web):
DOI:10.1002/adfm.200901257
Abstract
Dense transition metal borides have recently been identified as superhard materials that offer the possibility of ambient pressure synthesis compared to the conventional high pressure, high temperature approach. This feature article begins with a discussion of the relevant physical properties for this class of compounds, followed by a summary of the synthesis and properties of several transition metal borides. A strong emphasis is placed on correlating mechanical properties with electronic and atomic structure of these materials in an effort to better predict new superhard compounds. It concludes with a perspective of future research directions, highlighting some recent results and presenting several new ideas that remain to be tested.
Co-reporter:Michelle B. Weinberger, Jonathan B. Levine, Hsiu-Ying Chung, Robert W. Cumberland, Haider I. Rasool, Jenn-Ming Yang, Richard B. Kaner and Sarah H. Tolbert
Chemistry of Materials 2009 Volume 21(Issue 9) pp:1915
Publication Date(Web):April 14, 2009
DOI:10.1021/cm900211v
Interest in new ultraincompressible hard materials has prompted studies of transition metal diboride solid solutions. We have synthesized pure RuB2 and solid solutions of Os1−xRuxB2. The mechanical properties of these materials are investigated using in situ high-pressure X-ray diffraction and Vickers hardness testing techniques. Both bulk moduli and hardness vary linearly with composition in accordance with Vegard’s law, whereas the differing behavior among end-members can be explained by relativistic effects, core electron density, and differences in the cohesive energy of the parent metals. The results provide a refinement of the rules previously reported for the design of new superhard materials.
Co-reporter:Zhongfen Ding, Sabah K. Bux, Daniel J. King, Feng L. Chang, Tai-Hao Chen, Shu-Chuan Huang and Richard B. Kaner
Journal of Materials Chemistry A 2009 vol. 19(Issue 17) pp:2588-2592
Publication Date(Web):27 Feb 2009
DOI:10.1039/B820226E
Alloys of bismuth telluride (Bi2Te3) are commonly used in thermoelectric devices. These materials possess a hexagonal layered structure comprised of five atom thick stacks of Te–Bi–Te–Bi–Te held together by weak van der Waals forces. Lithium cations can be intercalated between the layers using the reducing power of solvated electrons in liquid ammonia. After intercalation, lithium can be removed by exfoliation to create a stable colloidal suspension of thin sheets of Bi2Te3 or Bi2Se3 in water. Zeta potential measurements indicate that the colloids are charge stabilized. These colloidal suspensions can be deposited onto a variety of substrates to create two-dimensional thin films. Atomic force microscopy indicates that initially individual layers are deposited. The films are partially oriented as observed using X-ray powder diffraction. Annealing at temperatures as low as 85 °C can produce highly oriented films. Thus intercalation, exfoliation and deposition from a charge-stabilized colloid can provide a scalable process for synthesizing bulk quantities of nanostructured thermoelectric materials.
Co-reporter:Matthew J. Allen, Minsheng Wang, Sergio A. V. Jannuzzi, Yang Yang, Kang L. Wang and Richard B. Kaner
Chemical Communications 2009 (Issue 41) pp:6285-6287
Publication Date(Web):04 Sep 2009
DOI:10.1039/B911972H
Here we report chemically induced folding of thin graphene flakes. The folding occurs spontaneously when an intercalating species interrupts the adhesion between graphene and a supporting substrate. The morphology of induced folds suggests that the conjugated π network is capable of extremely sharp curvature. Adjacent folds are often parallel, suggesting preferential deformation along certain crystallographic planes.
Co-reporter:Jesse D. Fowler, Matthew J. Allen, Vincent C. Tung, Yang Yang, Richard B. Kaner and Bruce H. Weiller
ACS Nano 2009 Volume 3(Issue 2) pp:301
Publication Date(Web):January 27, 2009
DOI:10.1021/nn800593m
We report the development of useful chemical sensors from chemically converted graphene dispersions using spin coating to create single-layer films on interdigitated electrode arrays. Dispersions of graphene in anhydrous hydrazine are formed from graphite oxide. Preliminary results are presented on the detection of NO2, NH3, and 2,4-dinitrotoluene using this simple and scalable fabrication method for practical devices. Current versus voltage curves are linear and ohmic in all cases, studied independent of metal electrode or presence of analytes. The sensor response is consistent with a charge transfer mechanism between the analyte and graphene with a limited role of the electrical contacts. A micro hot plate sensor substrate is also used to monitor the temperature dependence of the response to nitrogen dioxide. The results are discussed in light of recent literature on carbon nanotube and graphene sensors.Keywords: 2,4-dinitrotoluene; ammonia; hydrazine; micro hot plate; nitrogen dioxide
Co-reporter:Yue Wang, Henry D. Tran and Richard B. Kaner
The Journal of Physical Chemistry C 2009 Volume 113(Issue 24) pp:10346-10349
Publication Date(Web):May 27, 2009
DOI:10.1021/jp903583e
Aligned bundles of conducting polymer nanowires are generated in situ during the polymerization of o-anisidine. The presence of an appropriate initiator, a prolonged reaction time, and careful tuning of reaction conditions are crucial parameters for producing aligned nanowires. Mechanistic studies suggest hydrogen bonding between the substituents on the monomer and the polymer backbone is important for promoting alignment.
Co-reporter:C. O. Baker;B. Shedd;P. C. Innis;P. G. Whitten;G. M. Spinks;G. G. Wallace;R. B. Kaner
Advanced Materials 2008 Volume 20( Issue 1) pp:155-158
Publication Date(Web):
DOI:10.1002/adma.200602864
Co-reporter:Henry D. Tran, Ian Norris, Julio M. D’Arcy, Hamilton Tsang, Yue Wang, Benjamin R. Mattes and Richard B. Kaner
Macromolecules 2008 Volume 41(Issue 20) pp:7405-7410
Publication Date(Web):October 4, 2008
DOI:10.1021/ma800122d
A bulk, template-free method to synthesize nanofibers of substituted polyanilines is presented. The morphology of the substituted polyanilines changes from agglomerates or micron-sized spheres to a nanofiber network when an initiator, such as p-phenylenediamine, is introduced into the conventional reagents used to synthesize these polymers. UV−vis spectroscopy and cyclic voltammetry reveal that the oxidation state and chemical composition of the substituted polyaniline nanofibers do not differ significantly from that of conventional polyaniline derivatives possessing an agglomerated morphology. Gel permeation chromatography indicates that the nanofibers formed possess an unusually low polydispersity compared to substituted polyanilines synthesized by other methods. Open-circuit potential measurements obtained during the synthesis of these polyaniline derivatives confirm that there is a significant increase in the reaction rate of the polymerization which is directly related to nanofiber formation. This synthetic method appears quite general as a wide variety of substituted aniline monomers have been polymerized into nanofibrillar polymers.
Co-reporter:Henry D. Tran, Yue Wang, Julio M. D’Arcy and Richard B. Kaner
ACS Nano 2008 Volume 2(Issue 9) pp:1841
Publication Date(Web):September 3, 2008
DOI:10.1021/nn800272z
Introducing small amounts of additives into polymerization reactions to produce conducting polymers can have a profound impact on the resulting polymer morphology. When an oligomer such as aniline dimer is added to the polymerization of aniline, the nanofibers produced are longer and less entangled than those typically observed. The addition of aniline dimer can even induce nanofiber formation under synthetic conditions that generally do not favor a nanofibrillar morphology. This finding can be extended to both the synthesis of polythiophene and polypyrrole nanofibers. The traditional oxidative polymerization of thiophene or pyrrole only produces agglomerated particles. However, when minute amounts of thiophene or pyrrole oligomers are added to the reaction, the resulting polymers possess a nanofibrillar morphology. These results reveal important insights into a semirigid rod nucleation phenomenon that has hitherto been little explored. When polyaniline nucleates homogeneously, surface energy requirements necessitate the formation of ordered nuclei which leads to the directional polymerization of aniline. This ultimately leads to the one-dimensional nanofibrillar morphology observed in the final product. The synthetic procedures developed here are simple, scalable, and do not require any templates or other additives that are not inherent to the polymer.Keywords: 1-D nanostructures; conducting polymers; polyaniline; polypyrrole; polythiophene
Co-reporter:Dan Li and Richard B. Kaner
Journal of Materials Chemistry A 2007 vol. 17(Issue 22) pp:2279-2282
Publication Date(Web):01 May 2007
DOI:10.1039/B700699C
Using the conducting polymer, polyaniline, as a prime example, this article highlights the important role of nucleation on the aggregation of nanoparticles. We demonstrate that during synthesis, irreversible aggregation of nanoparticles can be triggered by heterogeneous nucleation on pre-formed particles. Aggregation can be prevented by mediating the nucleation behavior via experimental conditions including mechanical agitation, reaction temperature and the use of additives. These findings may provide a valuable guide in the synthesis of many other nanostructures.
Co-reporter:Hyuncheol Kim, H. Thomas Hahn, Lisa M. Viculis, Scott Gilje, Richard B. Kaner
Carbon 2007 Volume 45(Issue 7) pp:1578-1582
Publication Date(Web):June 2007
DOI:10.1016/j.carbon.2007.02.035
Composites between graphite and polystyrene have been synthesized starting from potassium intercalated graphite and styrene vapor. This in situ polymerization process can be used to make electrically conductive composites containing well-dispersed thin graphite sheets. The conductivities of the composites increase as the number of ordered carbon layers increases. With only 10% graphite in a polystyrene matrix, an electrical conductivity up to 1.3 × 10−1 S/cm can be obtained. The key is synthesizing a material with at least four ordered graphite layers (a stage IV complex) separated by polystyrene. This composite shows an improvement in conductivity over a control composite made by radical polymerization of styrene containing the same amount of dispersed graphite which had a conductivity of 5.0 × 10−3 S/cm. Characterization of the complexes by powder X-ray diffraction, scanning electron microscopy and electrical conductivity is presented.
Co-reporter:Henry D. Tran;Koo Shin;Julio M. D'Arcy;Robert W. Kojima;Won G. Hong;Bruce H. Weiller
Macromolecular Rapid Communications 2007 Volume 28(Issue 24) pp:2289-2293
Publication Date(Web):30 OCT 2007
DOI:10.1002/marc.200700581
A template-free method for the production of polypyrrole nanofibers is presented. By adding a small amount of bipyrrole into the oxidative polymerization of pyrrole, a drastic change in the morphology of the observed material is observed from large, granular particles to nanofibrils with an average diameter of 20 nm. This simple procedure allows for the production of polypyrrole nanofibers without the presence of surfactants or other structural directing agents. The polypyrrole nanofibers can form stable water dispersions which can be cast into films of sufficient quality to function as chemical sensors for analytes such as ammonia.
Co-reporter:Abby Kavner;Hsiu-Ying Chung;Robert W. Cumberland;Jonathan B. Levine;Jenn-Ming Yang;Michelle B. Weinberger;Sarah H. Tolbert
Science 2007 Volume 318(Issue 5856) pp:1550
Publication Date(Web):07 Dec 2007
DOI:10.1126/science.1147704
Abstract
Dubrovinskaia et al. question our demonstration that rhenium diboride (ReB2) is hard enough to scratch diamond. Here, we provide conclusive evidence of a scratch through atomic force microscopy depth profiling and elemental mapping. With high hardness, high-bulk modulus, and the ability to withstand extreme differential stress, ReB2 and related materials should be investigated regardless of their cost, which is not prohibitive.
Co-reporter:Hsiu-Ying Chung;Michelle B. Weinberger;Abby Kavner;Jonathan B. Levine;Jenn-Ming Yang;Sarah H. Tolbert
Science 2007 Volume 316(Issue 5823) pp:436-439
Publication Date(Web):20 Apr 2007
DOI:10.1126/science.1139322
Abstract
The quest to create superhard materials rarely strays from the use of high-pressure synthetic methods, which typically require gigapascals of applied pressure. We report that rhenium diboride (ReB2), synthesized in bulk quantities via arc-melting under ambient pressure, rivals materials produced with high-pressure methods. Microindentation measurements on ReB2 indicated an average hardness of 48 gigapascals under an applied load of 0.49 newton, and scratch marks left on a diamond surface confirmed its superhard nature. Its incompressibility along the c axis was equal in magnitude to the linear incompressibility of diamond. In situ high-pressure x-ray diffraction measurements yielded a bulk modulus of 360 gigapascals, and radial diffraction indicated that ReB2 is able to support a remarkably high differential stress. This combination of properties suggests that this material may find applications in cutting when the formation of carbides prevents the use of traditional materials such as diamond.
Co-reporter:Henry D. Tran and Richard B. Kaner
Chemical Communications 2006 (Issue 37) pp:3915-3917
Publication Date(Web):07 Aug 2006
DOI:10.1039/B605928G
Nanofibrous mats of a wide variety of polyaniline derivatives can be synthesized without the need for templates or functional dopants by simply introducing an initiator into the reaction mixture of a rapidly mixed reaction between monomer and oxidant.
Co-reporter:Jiaxing Huang and Richard B. Kaner
Chemical Communications 2006 (Issue 4) pp:367-376
Publication Date(Web):07 Dec 2005
DOI:10.1039/B510956F
Polyaniline nanofibers are shown to form spontaneously during the chemical oxidative polymerization of aniline. The nanofibrillar morphology does not require any template or surfactant, and appears to be intrinsic to polyaniline synthesized in water. Two approaches—interfacial polymerization and rapidly-mixed reactions—have been developed to prepare pure nanofibers. The key is suppressing the secondary growth that leads to agglomerated particles. The effects of different dopant acids and solvents are discussed. Changing the dopant acid can be used to tune the diameters of the nanofibers between about 30 and 120 nm. Changing the organic solvent in interfacial polymerization reactions has little effect on the product. A brief discussion of the processibility of the nanofibers is presented. The possibility of creating nanofibrillar structures for selected polyaniline derivatives is also demonstrated.
Co-reporter:J. J. Mack;L. M. Viculis;A. Ali;R. Luoh;G. Yang;H. T. Hahn;F. K. Ko;R. B. Kaner
Advanced Materials 2005 Volume 17(Issue 1) pp:
Publication Date(Web):13 JAN 2005
DOI:10.1002/adma.200400133
Thin graphite nanoplatelets synthesized by an intercalation/exfoliation process are incorporated into a polymer fiber matrix by an electrospinning process, creating ultrafine nanocomposite fibrils (see Figure). Uniform nanofibers of average diameter 300 nm show a modest increase in thermal stability with increasing weight percentage of graphite nanoplatelets. The mechanical properties of the fibrils are examined, and the normalized Young's modulus is found to increase two-fold upon addition of 4 wt.-% graphite nanoplatelets.
Co-reporter:Lisa M. Viculis, Julia J. Mack, Oren M. Mayer, H. Thomas Hahn and Richard B. Kaner
Journal of Materials Chemistry A 2005 vol. 15(Issue 9) pp:974-978
Publication Date(Web):10 Jan 2005
DOI:10.1039/B413029D
Graphite nanoplatelets with thicknesses down to 2–10 nm are synthesized by alkali metal intercalation followed by ethanol exfoliation and microwave drying. Graphite that has already been intercalated and exfoliated with an oxidizing acid is reintercalated with an alkali metal to form a first stage compound, as confirmed by powder X-ray diffraction. This can be achieved either by heating graphite and potassium or caesium at 200 °C, or at room temperature using a sodium–potassium alloy. Reaction of the intercalated graphite with ethanol causes exfoliation of the graphene layers. Microwave radiation aids in drying and results in further separation of the sheets. Thermogravimetric analysis indicates that the graphite nanoplatelets are approximately 150 °C less stable in air than pristine graphite. High aspect ratio graphite nanoplatelets offer promise as reinforcements for high strength carbon–carbon composites.
Co-reporter:Dan Li and Richard B. Kaner
Chemical Communications 2005 (Issue 26) pp:3286-3288
Publication Date(Web):25 May 2005
DOI:10.1039/B504020E
Aqueous polyaniline colloids can be readily prepared by purifying polyaniline nanofibers and controlling the pH and self-stabilized via electrostatic repulsions without the need for any chemical modification or steric stabilizer, thus providing a simple and environmentally friendly way to process the conducting polymer in its conductive state both in bulk and at the nanometre level.
Co-reporter:Jiaxing Huang;Shabnam Virji;Bruce H. Weiller Dr.
Chemistry - A European Journal 2004 Volume 10(Issue 6) pp:
Publication Date(Web):29 JAN 2004
DOI:10.1002/chem.200305211
The conjugated polymer polyaniline is a promising material for sensors, since its conductivity is highly sensitive to chemical vapors. Nanofibers of polyaniline are found to have superior performance relative to conventional materials due to their much greater exposed surface area. A template-free chemical synthesis is described that produces uniform polyaniline nanofibers with diameters below 100 nm. The interfacial polymerization can be readily scaled to make gram quantities. Resistive-type sensors made from undoped or doped polyaniline nanofibers outperform conventional polyaniline on exposure to acid or base vapors, respectively. The nanofibers show essentially no thickness dependence to their sensitivity.
Co-reporter:Jiaxing Huang
Angewandte Chemie International Edition 2004 Volume 43(Issue 43) pp:
Publication Date(Web):2 NOV 2004
DOI:10.1002/anie.200460616
Stirring stuff: The morphological evolution of polyaniline from nanofibers to agglomerates during its chemical polymerization shows that the key to producing pure nanofibers is to suppress secondary growth after formation of the nanofibers. A simple and effective method for the synthesis of nanofibers was thus developed in which the polymerization is carried out in a rapidly mixed single-phase reaction (see scheme).
Co-reporter:Jiaxing Huang
Angewandte Chemie 2004 Volume 116(Issue 43) pp:
Publication Date(Web):2 NOV 2004
DOI:10.1002/ange.200460616
Geschüttelt oder gerührt: Die morphologische Entwicklung von Polyanilin von Nanofasern zu Agglomeraten zeigt, dass reine Nanofasern zugänglich sind, indem man ihr weiteres Wachstum unterdrückt. Eine sehr einfache und hocheffiziente Methode für die Synthese von Nanofasern wurde entwickelt, bei der die Polymerisation als Einphasenreaktion unter schnellem Mischen verläuft (siehe Schema).
Co-reporter:J. Huang;V.M. Egan;H. Guo;J.-Y. Yoon;A.L. Briseno;I.E. Rauda;R.L. Garrell;C.M. Knobler;F. Zhou;R.B. Kaner
Advanced Materials 2003 Volume 15(Issue 14) pp:
Publication Date(Web):21 JUL 2003
DOI:10.1002/adma.200304835
Co-reporter:Z. Ding;L. Viculis;J. Nakawatase;R. B. Kaner
Advanced Materials 2001 Volume 13(Issue 11) pp:
Publication Date(Web):31 MAY 2001
DOI:10.1002/1521-4095(200106)13:11<797::AID-ADMA797>3.0.CO;2-U
Co-reporter:Veronica Egan, Robert Bernstein, Laura Hohmann, Thu Tran and Richard B. Kaner
Chemical Communications 2001 (Issue 9) pp:801-802
Publication Date(Web):05 Apr 2001
DOI:10.1039/B008996F
Polyaniline doped with R-(−)- or
S-(+)-camphorsulfonic acid produces an inexpensive chiral
substrate; the presence or absence of water can be used to invert the
dopant-induced circular dichroism (CD) absorbance at 450 nm, shedding light
on conflicting literature reports.
Co-reporter:Yue Wang ; Henry D. Tran ; Lei Liao ; Xiangfeng Duan
Journal of the American Chemical Society () pp:
Publication Date(Web):July 14, 2010
DOI:10.1021/ja1014184
While nanostructures of organic conductors have generated great interest in recent years, their nanoscale size and shape control remains a significant challenge. Here, we report a general method for producing a variety of oligoaniline nanostructures with well-defined morphologies and dimensionalities. 1-D nanowires, 2-D nanoribbons, and 3-D rectangular nanoplates and nanoflowers of tetraaniline are produced by a solvent exchange process in which the dopant acid can be used to tune the oligomer morphology. The process appears to be a general route for producing nanostructures for a variety of other aniline oligomers such as the phenyl-capped tetramer. X-ray diffraction of the tetraniline nanostructures reveals that they possess different packing arrangements, which results in different nanoscale morphologies with different electrical properties for the structures. The conductivity of a single tetraaniline nanostructure is up to 2 orders of magnitude higher than the highest previously reported value and rivals that of pressed pellets of conventional polyaniline doped with acid. Furthermore, these oligomer nanostructures can be easily processed by a number of methods in order to create thin films composed of aligned nanostructures over a macroscopic area.
Co-reporter:Christina O. Baker, Xinwei Huang, Wyatt Nelson and Richard B. Kaner
Chemical Society Reviews 2017 - vol. 46(Issue 5) pp:NaN1525-1525
Publication Date(Web):2017/01/18
DOI:10.1039/C6CS00555A
Polyaniline is a conducting polymer with incredible promise, but it has had limited use due to poor reaction control and processability associated with conventional morphologies. Polyaniline nanofibers, on the other hand, have demonstrated, through manufacturing techniques discovered during the past decade, increased processability, higher surface area, and improved consistency and stability in aqueous dispersions, which are finally allowing for expanded commercial development of this promising polymer. This review explores some intriguing applications of polyaniline nanofibers, as well as the advantages and remaining challenges in developing better products using polyaniline in this new morphology.
Co-reporter:K. L. Marsh, M. Souliman and R. B. Kaner
Chemical Communications 2015 - vol. 51(Issue 1) pp:NaN190-190
Publication Date(Web):2014/11/04
DOI:10.1039/C4CC07324J
A simple method is presented for exfoliating and suspending hexagonal boron nitride using a co-solvent approach. A 60 w/w% concentration of tert-butanol in water is very effective at exfoliating boron nitride especially when compared to the individual components alone as indicated by UV-vis and transmission electron microscopy. Molecular weight and surface tension are found to play inverse roles in the exfoliation.
Co-reporter:Sabah K. Bux, Jean-Pierre Fleurial and Richard B. Kaner
Chemical Communications 2010 - vol. 46(Issue 44) pp:NaN8324-8324
Publication Date(Web):2010/10/05
DOI:10.1039/C0CC02627A
Recent studies indicate that nanostructuring can be an effective method for increasing the dimensionless thermoelectric figure of merit (ZT) in materials. Most of the enhancement in ZT can be attributed to large reductions in the lattice thermal conductivity due to increased phonon scattering at interfaces. Although significant gains have been reported, much higher ZTs in practical, cost-effective and environmentally benign materials are needed in order for thermoelectrics to become effective for large-scale, wide-spread power and thermal management applications. This review discusses the various synthetic techniques that can be used in the production of bulk scale nanostructured materials. The advantages and disadvantages of each synthetic method are evaluated along with guidelines and goals presented for an ideal thermoelectric material. With proper optimization, some of these techniques hold promise for producing high efficiency devices.
Co-reporter:Matthew J. Allen;Minsheng Wang;Sergio A. V. Jannuzzi;Yang Yang;Kang L. Wang
Chemical Communications 2009(Issue 41) pp:
Publication Date(Web):2009/10/13
DOI:10.1039/B911972H
Here we report chemically induced folding of thin graphene flakes. The folding occurs spontaneously when an intercalating species interrupts the adhesion between graphene and a supporting substrate. The morphology of induced folds suggests that the conjugated π network is capable of extremely sharp curvature. Adjacent folds are often parallel, suggesting preferential deformation along certain crystallographic planes.
Co-reporter:Xin-Gui Li, Yaozu Liao, Mei-Rong Huang and Richard B. Kaner
Chemical Science (2010-Present) 2015 - vol. 6(Issue 3) pp:NaN2101-2101
Publication Date(Web):2015/01/21
DOI:10.1039/C4SC03890H
A novel polyfluoranthene (PFA) exhibiting strong visual fluorescence emission, a highly amplified quenching effect, and widely controllable electrical conductivity is synthesized by the direct cationic oxidative polymerization of fluoranthene in a dynamic interface between n-hexane and nitromethane containing fluoranthene and FeCl3, respectively. A full characterization of the molecular structure signifies that the PFAs have a degree of polymerization from 22–50 depending on the polymerization conditions. A polymerization mechanism at the interface of the hexane/nitromethane biphasic system is proposed. The conductivity of the PFA is tunable from 6.4 × 10−6 to 0.074 S cm−1 by doping with HCl or iodine. The conductivity can be significantly enhanced to 150 S cm−1 by heat treatment at 1100 °C in argon. A PFA-based chemosensor shows a highly selective sensitivity for Fe3+ detection which is unaffected by other common metal ions. The detection of Fe3+ likely involves the synergistic effect of well-distributed π-conjugated electrons throughout the PFA helical chains that function as both the fluorophore and the receptor units.
Co-reporter:Xin-Gui Li, Yaozu Liao, Mei-Rong Huang, Veronica Strong and Richard B. Kaner
Chemical Science (2010-Present) 2013 - vol. 4(Issue 5) pp:NaN1978-1978
Publication Date(Web):2013/01/10
DOI:10.1039/C3SC22107E
Electron-rich oligofluoranthene has been successfully synthesized by a one-step direct chemical oxidative oligomerization of fluoranthene. Key advantages include easy synthesis, high synthetic yield and low cost when compared with electropolymerization. Oligofluoranthene in solution is a very strong cyan fluorescence emitter with 12.2 times higher intensity than the fluoranthene monomer. The strong fluorescence can be effectively quenched by specific electron-deficient species, enabling the fabrication of low-cost, high-performance chemosensors for the selective detection of Fe(III) ions and the explosive 2,4,6-trinitrophenol (picric acid). A concentration range of >9 orders of magnitude with exceedingly low detection limits down to 10−12 M is possible. No sample enrichment is needed likely due to the synergistic effects of well-distributed π-conjugated electrons with a conical stereo configuration that may enhance the detection ability. Common interferents appear to have little effect as Fe(III) can be selectively detected in both tap water and seawater containing many other metal ions and picric acid can be detected at low concentrations even in the presence of inorganic acids.
Co-reporter:Xin-Gui Li, Yaozu Liao, Mei-Rong Huang and Richard B. Kaner
Chemical Science (2010-Present) 2015 - vol. 6(Issue 12) pp:NaN7200-7200
Publication Date(Web):2015/09/17
DOI:10.1039/C5SC03041B
Strongly fluorescence-emitting oligofluoranthene (OFA) nanorods are readily synthesized by a direct template-free chemical oxidative oligomerization of fluoranthene in nitromethane containing ferric chloride as an oxidant. The OFAs likely consist of five fluoranthene units containing cyclic pentamers with crystalline order and tunable electrical conductivity across 12 orders of magnitude. The OFA nanorods are heat-resistant materials and efficient precursors for macroporous carbon materials with high carbon yield in argon at 1100 °C. In particular, the optimal ring-like pentamer shows 12.2 times stronger cyan fluorescence-emission than recognized highly fluorescent fluoranthene under the same conditions, which makes the OFAs into ideal strong fluorescent emitters, tunable conductors, and high carbon-yield precursors for the preparation of sensors and carbon materials. These findings demonstrate an advance in the direct synthesis of oligomers from fused-ring aromatic hydrocarbons and provide a potential direction to optimize the synthesis and functionalities of wholly aromatic nanomaterials.
Co-reporter:Yuanlong Shao, Maher F. El-Kady, Lisa J. Wang, Qinghong Zhang, Yaogang Li, Hongzhi Wang, Mir F. Mousavi and Richard B. Kaner
Chemical Society Reviews 2015 - vol. 44(Issue 11) pp:NaN3665-3665
Publication Date(Web):2015/04/22
DOI:10.1039/C4CS00316K
The demand for flexible/wearable electronic devices that have aesthetic appeal and multi-functionality has stimulated the rapid development of flexible supercapacitors with enhanced electrochemical performance and mechanical flexibility. After a brief introduction to flexible supercapacitors, we summarize current progress made with graphene-based electrodes. Two recently proposed prototypes for flexible supercapacitors, known as micro-supercapacitors and fiber-type supercapacitors, are then discussed. We also present our perspective on the development of graphene-based electrodes for flexible supercapacitors.
Co-reporter:Xinwei Huang, Brian T. McVerry, Catalina Marambio-Jones, Mavis C. Y. Wong, Eric M. V. Hoek and Richard B. Kaner
Journal of Materials Chemistry A 2015 - vol. 3(Issue 16) pp:NaN8733-8733
Publication Date(Web):2015/03/11
DOI:10.1039/C5TA00900F
We demonstrate that poly(n-2-hydroxyethyl aniline) (n-PANi), a derivative of polyaniline (PANi), provides an effective chlorine tolerant PANi-based ultrafiltration (UF) membrane. n-PANi was synthesized from its monomer via chemical oxidative polymerization. Unlike PANi, n-PANi can be dissolved in N-methyl-2-pyrollidone (NMP) up to 30 wt% to form a casting solution which is stable for months without the aid of an anti-gelling agent. Membranes formed from n-PANi show high resistance to chlorine, even when exposed to 250 ppm sodium hypochlorite for 30 days while PANi membranes completely lose their ability to reject bovine serum albumin (BSA, 6 nm) after 2 days. Spectroscopic studies indicate that the benzenoid groups in PANi membranes are oxidized while n-PANi membranes maintain their chemical structure. n-PANi membranes display high hydrophilicity with a contact angle of ∼36 degrees which contributes to their ultra-low adhesion of E. coli. Cross-flow fouling tests with 1.5 g L−1 BSA fouling solution reveal that n-PANi membranes exhibit low-fouling properties with only 11% flux decline and 91% flux recovery, superior to PANi and commercial polysulfone (PSf) membranes.
Co-reporter:Jonathan K. Wassei, Kitty C. Cha, Vincent C. Tung, Yang Yang and Richard B. Kaner
Journal of Materials Chemistry A 2011 - vol. 21(Issue 10) pp:NaN3396-3396
Publication Date(Web):2011/01/31
DOI:10.1039/C0JM02910F
Anionic dopants have been used to reduce the overall sheet resistance of carbon nanotube and graphene films for transparent conductor applications. These enhanced electronic properties are attributed to an increased number of p-type charge carriers. While there have been many reports of its use, there is little reported insight into the chemical interactions of a commonly used dopant, thionyl chloride (SOCl2), with pristine graphene and its chemically converted derivatives. Here, we explore the effects of thionyl chloride on the physical and chemical properties of graphene and hybrid graphene–carbon nanotube films, focusing on how the changes in conductivity correlate to the morphology of chemically converted graphene and carbon nanotube composites.
Co-reporter:Henry D. Tran, Julio M. D'Arcy, Yue Wang, Peter J. Beltramo, Veronica A. Strong and Richard B. Kaner
Journal of Materials Chemistry A 2011 - vol. 21(Issue 11) pp:NaN3550-3550
Publication Date(Web):2010/11/25
DOI:10.1039/C0JM02699A
The number of different nano- and micro-scale structures produced from the chemical oxidation of aniline into “polyaniline” is rivaled by few other organic materials. Nanoscale structures such as fibers, tubes, aligned wires, flowers, spheres and hollow spheres, plates, and even those resembling anatomical organs, insects, and sea animals have been observed for the products produced when aniline is oxidized. This feature article examines these different structures and the small and subtle changes in reaction parameters that result in their formation. These changes can often result in drastic differences in the polymer's nanoscale morphology. Because a nanomaterial's properties are highly dependent on the type of morphology produced, understanding polyaniline's propensity for forming these structures is crucial towards tailoring the material for different applications as well as improving its synthetic reproducibility. The different approaches to commonly observed polyaniline nanostructures are presented in this article along with some of the highly debated aspects of these processes. The article ends with our approach towards resolving some of these contentious issues and our perspective on where things are headed in the years to come.
Co-reporter:Zhongfen Ding, Sabah K. Bux, Daniel J. King, Feng L. Chang, Tai-Hao Chen, Shu-Chuan Huang and Richard B. Kaner
Journal of Materials Chemistry A 2009 - vol. 19(Issue 17) pp:NaN2592-2592
Publication Date(Web):2009/02/27
DOI:10.1039/B820226E
Alloys of bismuth telluride (Bi2Te3) are commonly used in thermoelectric devices. These materials possess a hexagonal layered structure comprised of five atom thick stacks of Te–Bi–Te–Bi–Te held together by weak van der Waals forces. Lithium cations can be intercalated between the layers using the reducing power of solvated electrons in liquid ammonia. After intercalation, lithium can be removed by exfoliation to create a stable colloidal suspension of thin sheets of Bi2Te3 or Bi2Se3 in water. Zeta potential measurements indicate that the colloids are charge stabilized. These colloidal suspensions can be deposited onto a variety of substrates to create two-dimensional thin films. Atomic force microscopy indicates that initially individual layers are deposited. The films are partially oriented as observed using X-ray powder diffraction. Annealing at temperatures as low as 85 °C can produce highly oriented films. Thus intercalation, exfoliation and deposition from a charge-stabilized colloid can provide a scalable process for synthesizing bulk quantities of nanostructured thermoelectric materials.
Co-reporter:Dan Li and Richard B. Kaner
Journal of Materials Chemistry A 2007 - vol. 17(Issue 22) pp:NaN2282-2282
Publication Date(Web):2007/05/01
DOI:10.1039/B700699C
Using the conducting polymer, polyaniline, as a prime example, this article highlights the important role of nucleation on the aggregation of nanoparticles. We demonstrate that during synthesis, irreversible aggregation of nanoparticles can be triggered by heterogeneous nucleation on pre-formed particles. Aggregation can be prevented by mediating the nucleation behavior via experimental conditions including mechanical agitation, reaction temperature and the use of additives. These findings may provide a valuable guide in the synthesis of many other nanostructures.
Co-reporter:Yaozu Liao, Xin-Gui Li, Eric M. V. Hoek and Richard B. Kaner
Journal of Materials Chemistry A 2013 - vol. 1(Issue 48) pp:NaN15396-15396
Publication Date(Web):2013/10/28
DOI:10.1039/C3TA13902F
Development of electro-ultrafiltration membranes is an attractive target. We report electrically conducting ultrafiltration membranes by blending single-walled carbon nanotube/polyaniline (SWCNT/PANi) nanofibers into a polysulfone (PSf) matrix. By selecting the amount of nanofibers and applying a flash welding technique, the chemical structure, porosity, thermal stability, conductivity, hydrophilicity, permeability, and bovine serum albumin (BSA) rejection of these composite ultrafiltration membranes can be controlled. Addition of SWCNT/PANi nanofibers to the composites enhances the initial water permeability by 2.5–7.3 times and increases the hydrophilicity, and maintains considerable rejection of BSA from 39.8–73.7%. An electrical conductivity between 0.1 and 3.4 × 10−6 S cm−1 can be maintained over a broad pH range from 0.52–10.2. By regulating the flash welding intensity, the conductivity, permeability, and BSA rejection can be enhanced up to 600, 2, and ∼1.5 times, respectively.
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