Co-reporter:Adam J. Biacchi, Dimitri D. Vaughn II, and Raymond E. Schaak
Journal of the American Chemical Society August 7, 2013 Volume 135(Issue 31) pp:11634-11644
Publication Date(Web):July 3, 2013
DOI:10.1021/ja405203e
Tin sulfide, SnS, is a narrow band gap semiconductor comprised of inexpensive, earth abundant, and environmentally benign elements that is emerging as an important material for a diverse range of applications in solar energy conversion, energy storage, and electronics. Relative to many comparable systems, much less is known about the factors that influence the synthesis or morphology-dependent properties of SnS nanostructures. Here, we report the synthesis of colloidal SnS cubes, spherical polyhedra, and sheets and demonstrate their activity for the photocatalytic degradation of methylene blue. We also study their morphology-dependent polymorphism using an in-depth crystallographic analysis that correlates high-resolution TEM data of individual nanocrystals with ensemble-based electron diffraction and powder XRD data. These studies reveal that the crystal structure adopted by the SnS cubes and spherical polyhedra is expanded along the a and b axes and contracted along c, converging on a pseudotetragonal cell that is distinct from that of orthorhombic α-SnS, the most stable polymorph. All of the peaks observed in powder XRD patterns that are often interpreted as originating from a mixture of metastable zincblende-type SnS and α-SnS can instead be accounted for by this single-phase pseudotetragonal modification, and this helps to rationalize discrepancies that exist between theoretical predictions of SnS polymorph stability and interpretations of experimental diffraction data. This same crystallographic analysis also indicates the morphologies of the nanocrystals and the facets by which they are bound, and it reveals that the SnS cubes form through selective overgrowth of spherical polyhedral seeds.
Co-reporter:Joshua M. McEnaney
Inorganic Chemistry 2015 Volume 54(Issue 3) pp:707-709
Publication Date(Web):November 12, 2014
DOI:10.1021/ic502394u
Transition-metal silicides are part of an important family of intermetallic compounds, but the high-temperature reactions that are generally required to synthesize them preclude the formation of colloidal nanoparticles. Here, we show that palladium, copper, and nickel nanoparticles react with monophenylsilane in trioctylamine and squalane at 375 °C to form colloidal Pd2Si, Cu3Si, and Ni2Si nanoparticles, respectively. These metal silicide nanoparticles were screened as electrocatalysts for the hydrogen evolution reaction, and Pd2Si and Ni2Si were identified as active catalysts that require overpotentials of −192 and −243 mV, respectively, to produce cathodic current densities of −10 mA cm–2.
Co-reporter:Christopher W. Roske; Eric J. Popczun; Brian Seger; Carlos G. Read; Thomas Pedersen; Ole Hansen; Peter C. K. Vesborg; Bruce S. Brunschwig; Raymond E. Schaak; Ib Chorkendorff; Harry B. Gray;Nathan S. Lewis
The Journal of Physical Chemistry Letters 2015 Volume 6(Issue 9) pp:1679-1683
Publication Date(Web):April 20, 2015
DOI:10.1021/acs.jpclett.5b00495
The electrocatalytic performance for hydrogen evolution has been evaluated for radial-junction n+p-Si microwire (MW) arrays with Pt or cobalt phosphide, CoP, nanoparticulate catalysts in contact with 0.50 M H2SO4(aq). The CoP-coated (2.0 mg cm–2) n+p-Si MW photocathodes were stable for over 12 h of continuous operation and produced an open-circuit photovoltage (Voc) of 0.48 V, a light-limited photocurrent density (Jph) of 17 mA cm–2, a fill factor (ff) of 0.24, and an ideal regenerative cell efficiency (ηIRC) of 1.9% under simulated 1 Sun illumination. Pt-coated (0.5 mg cm–2) n+p-Si MW-array photocathodes produced Voc = 0.44 V, Jph = 14 mA cm–2, ff = 0.46, and η = 2.9% under identical conditions. Thus, the MW geometry allows the fabrication of photocathodes entirely comprised of earth-abundant materials that exhibit performance comparable to that of devices that contain Pt.
Co-reporter:Dimitri D. Vaughn II, Jose Araujo, Praveen Meduri, Juan F. Callejas, Michael A. Hickner, and Raymond E. Schaak
Chemistry of Materials 2014 Volume 26(Issue 21) pp:6226
Publication Date(Web):October 8, 2014
DOI:10.1021/cm5029723
The synthesis of transition metal nitride nanoparticles is challenging, in part because the unreactive nature of the most common nitrogen reagents necessitates high-temperature and/or high-pressure reaction conditions. Here we report the solution-phase synthesis and characterization of antiperovskite-type Cu3PdN nanocrystals that are multifaceted, uniform, and highly dispersible as colloidal solutions. Colloidal Cu3PdN nanocrystals were synthesized by reacting copper(II) nitrate and palladium(II) acetylacetonate in 1-octadecene with oleylamine at 240 °C. The Cu3PdN nanocrystals were evaluated as electrocatalysts for the oxygen reduction reaction (ORR) under alkaline conditions, where both Cu3N and Pd nanocrystals are known to be active. The ORR activity of the Cu3PdN nanocrystals appears to be superior to that of Cu3N and comparable to that of Pd synthesized using similar methods, but with significantly improved mass activity than Pd control samples. The Cu3PdN nanocrystals also show greater stability than comparably synthesized Pd nanocrystals during repeated cycling under alkaline conditions.
Co-reporter:Thomas R. Gordon and Raymond E. Schaak
Chemistry of Materials 2014 Volume 26(Issue 20) pp:5900
Publication Date(Web):August 11, 2014
DOI:10.1021/cm502396d
Hybrid nanoparticles composed of multiple material systems provide a platform for studying the coupling between nanoparticles with distinct properties. Here, we describe a nontraditional synthetic pathway to Au-In2O3 hybrid nanoparticles that contain two distinct plasmonic domains: Au, with a localized surface plasmon resonance (LSPR) in the visible, and In2O3, with a LSPR in the mid-infrared. The hybrid nanocrystals are produced by slowly introduce In(III) stock solution to Au nanoparticle seeds using a syringe pump. Rather than forming through a traditional heterogeneous seeded-growth process, a series of in situ and ex situ studies reveal an alternate multistep pathway. The Au nanoparticles first combine with In to form an alloy of Au and In, which is colloidally stable up to 300 °C in 1-octadecene. The Au-In alloy nanoparticles then transform into intermetallic AuIn2 nanoparticles that are surrounded by a shell of amorphous indium oxide (AuIn2@InOx), followed by the final Au-In2O3 heterodimers upon complete phase segregation.
Co-reporter:Joshua M. McEnaney, J. Chance Crompton, Juan F. Callejas, Eric J. Popczun, Adam J. Biacchi, Nathan S. Lewis, and Raymond E. Schaak
Chemistry of Materials 2014 Volume 26(Issue 16) pp:4826
Publication Date(Web):July 17, 2014
DOI:10.1021/cm502035s
Amorphous molybdenum phosphide (MoP) nanoparticles have been synthesized and characterized as electrocatalysts for the hydrogen-evolution reaction (HER) in 0.50 M H2SO4 (pH 0.3). Amorphous MoP nanoparticles (having diameters of 4.2 ± 0.5 nm) formed upon heating Mo(CO)6 and trioctylphosphine in squalane at 320 °C, and the nanoparticles remained amorphous after heating at 450 °C in H2(5%)/Ar(95%) to remove the surface ligands. At mass loadings of 1 mg cm–2, MoP/Ti electrodes exhibited overpotentials of −90 and −105 mV (−110 and −140 mV without iR correction) at current densities of −10 and −20 mA cm–2, respectively. These HER overpotentials remained nearly constant over 500 cyclic voltammetric sweeps and 18 h of galvanostatic testing, indicating stability in acidic media under operating conditions. Amorphous MoP nanoparticles are therefore among the most active known molybdenum-based HER systems and are part of a growing family of active, acid-stable, non-noble-metal HER catalysts.
Co-reporter:Matthew R. Buck, Adam J. Biacchi, and Raymond E. Schaak
Chemistry of Materials 2014 Volume 26(Issue 3) pp:1492
Publication Date(Web):January 17, 2014
DOI:10.1021/cm4041055
Fatty acid salts of transition metals are known to undergo thermal decomposition in high-boiling organic solvents. Although it is a straightforward, promising approach for generating colloidal metal oxide nanocrystals in high yield, its widespread implementation is hindered by irreproducibility. Subtle structural variations and impurities are often introduced during preparation of the carboxylate precursors, which exhibit strong influence on thermal decomposition, and the resulting nucleation and growth of oxide nanocrystals. Here, we studied the colloidal synthesis of wurtzite-type CoO (wz-CoO) nanostructures via thermal decomposition of Co(II) oleate complex [Co(OL)]2. Using Fourier transform infrared spectroscopy, we discovered that the conventional method for preparing [Co(OL)]2 gives rise to an isolable impurity containing a free hydroxide moiety. Furthermore, [Co(OL)]2 did not thermally decompose within the expected temperature range when the impurity was removed. In contrast, pencil-shaped wz-CoO nanorods were synthesized when no measures were taken to remove the impurity, suggesting that the hydroxide functionality may facilitate the thermal decomposition. These insights enabled us to prepare size-and shape-controlled wz-CoO nanocrystals using purified [Co(OL)]2 solutions, by incorporating additives that mimic the action of the hydroxide impurity. We also demonstrate a simplified pathway to wz-CoO nanocrystals that does not require chemical additives for thermolysis.
Co-reporter:Joshua M. McEnaney, J. Chance Crompton, Juan F. Callejas, Eric J. Popczun, Carlos G. Read, Nathan S. Lewis and Raymond E. Schaak
Chemical Communications 2014 vol. 50(Issue 75) pp:11026-11028
Publication Date(Web):30 Jul 2014
DOI:10.1039/C4CC04709E
Amorphous tungsten phosphide (WP), which has been synthesized as colloidal nanoparticles with an average diameter of 3 nm, has been identified as a new electrocatalyst for the hydrogen-evolution reaction (HER) in acidic aqueous solutions. WP/Ti electrodes produced current densities of −10 mA cm−2 and −20 mA cm−2 at overpotentials of only −120 mV and −140 mV, respectively, in 0.50 M H2SO4(aq).
Co-reporter:Eric J. Popczun;Carlos G. Read;Christopher W. Roske; Nathan S. Lewis; Raymond E. Schaak
Angewandte Chemie International Edition 2014 Volume 53( Issue 21) pp:5427-5430
Publication Date(Web):
DOI:10.1002/anie.201402646
Abstract
Nanoparticles of cobalt phosphide, CoP, have been prepared and evaluated as electrocatalysts for the hydrogen evolution reaction (HER) under strongly acidic conditions (0.50 M H2SO4, pH 0.3). Uniform, multi-faceted CoP nanoparticles were synthesized by reacting Co nanoparticles with trioctylphosphine. Electrodes comprised of CoP nanoparticles on a Ti support (2 mg cm−2 mass loading) produced a cathodic current density of 20 mA cm−2 at an overpotential of −85 mV. The CoP/Ti electrodes were stable over 24 h of sustained hydrogen production in 0.50 M H2SO4. The activity was essentially unchanged after 400 cyclic voltammetric sweeps, suggesting long-term viability under operating conditions. CoP is therefore amongst the most active, acid-stable, earth-abundant HER electrocatalysts reported to date.
Co-reporter:Juan F. Callejas, Joshua M. McEnaney, Carlos G. Read, J. Chance Crompton, Adam J. Biacchi, Eric J. Popczun, Thomas R. Gordon, Nathan S. Lewis, and Raymond E. Schaak
ACS Nano 2014 Volume 8(Issue 11) pp:11101
Publication Date(Web):September 24, 2014
DOI:10.1021/nn5048553
Nanostructured transition-metal phosphides have recently emerged as Earth-abundant alternatives to platinum for catalyzing the hydrogen-evolution reaction (HER), which is central to several clean energy technologies because it produces molecular hydrogen through the electrochemical reduction of water. Iron-based catalysts are very attractive targets because iron is the most abundant and least expensive transition metal. We report herein that iron phosphide (FeP), synthesized as nanoparticles having a uniform, hollow morphology, exhibits among the highest HER activities reported to date in both acidic and neutral-pH aqueous solutions. As an electrocatalyst operating at a current density of −10 mA cm–2, FeP nanoparticles deposited at a mass loading of ∼1 mg cm–2 on Ti substrates exhibited overpotentials of −50 mV in 0.50 M H2SO4 and −102 mV in 1.0 M phosphate buffered saline. The FeP nanoparticles supported sustained hydrogen production with essentially quantitative faradaic yields for extended time periods under galvanostatic control. Under UV illumination in both acidic and neutral-pH solutions, FeP nanoparticles deposited on TiO2 produced H2 at rates and amounts that begin to approach those of Pt/TiO2. FeP therefore is a highly Earth-abundant material for efficiently facilitating the HER both electrocatalytically and photocatalytically.Keywords: electrocatalysis; hydrogen evolution reaction; metal phosphides; nanoparticles; photocatalysis;
Co-reporter:James M. Hodges, Adam J. Biacchi, and Raymond E. Schaak
ACS Nano 2014 Volume 8(Issue 1) pp:1047
Publication Date(Web):December 13, 2013
DOI:10.1021/nn405943z
Colloidal hybrid nanoparticles are an important class of materials that incorporate multiple nanoparticles into a single system through solid-state interfaces, which can result in multifunctionality and the emergence of synergistic properties not found in the individual components. These hybrid structures are typically produced using seeded-growth methods, where preformed nanoparticles serve as seeds onto which additional domains are added through subsequent reactions. For hybrid nanoparticles that contain more than two domains, multiple configurations with distinct connectivities and functionalities are possible, and these can be considered as nanoparticle analogues of molecular isomers. However, accessing one isomer relative to others in the same hybrid nanoparticle system is challenging, particularly when the formation of a target isomer is disfavored relative to more stable or synthetically accessible configurations. Here, we show that an iron oxide shell installed onto the Pt domain of Pt–Fe3O4 hybrid nanoparticles serves as a solid-state protecting group that can direct the nucleation of a third domain to an otherwise disfavored site. Under traditional conditions, Ag nucleates exclusively onto the Pt domain of Pt–Fe3O4 heterodimers, resulting in the formation of the Ag–Pt–Fe3O4 heterotrimer isomer. When the Pt surface is covered with an iron oxide protecting group, the nucleation of Ag is redirected onto the Fe3O4 domain, producing the distinct and otherwise inaccessible Pt–Fe3O4–Ag isomer. Similar results are obtained for the Au–Pt–Fe3O4 system, where formation of the favored Au–Pt–Fe3O4 configuration is blocked by the iron oxide protecting group. The thickness of the iron oxide shell that protects the Pt domain can be systematically tuned by adjusting the ratio of oleic acid to iron pentacarbonyl during the synthesis of the Pt–Fe3O4 heterodimers, and this insight is important for controllably implementing the protecting group chemistry.Keywords: colloidal hybrid nanoparticles; heterodimers; heterotrimers; nanocrystals; nanoparticle isomers; nanoparticle synthesis; protecting group; Pt−Fe3O4; seeded growth
Co-reporter:Dimitri D. Vaughn II and Raymond E. Schaak
Chemical Society Reviews 2013 vol. 42(Issue 7) pp:2861-2879
Publication Date(Web):05 Nov 2012
DOI:10.1039/C2CS35364D
Germanium nanoparticles have excited scientists and engineers because of their size-dependent optical properties and their potential applications in optoelectronics, biological imaging and therapeutics, flash memories, and lithium-ion batteries. In order to further develop these applications and to gain deeper insights into their size-dependent properties, robust and facile synthetic methods are needed to controllably synthesize Ge nanoparticles. However, when compared to other II–VI, IV–VI, and III–V semiconductor systems, colloidal routes to Ge NPs with uniform sizes and shapes are much less mature. In this Review Article, we highlight the progress that has been made in this field and provide insights into the strategies used for the colloidal synthesis of size and shape-controlled germanium nanomaterials. We also survey some of the potential applications of these materials in optoelectronics, biological imaging, and energy conversion and storage. Finally, we discuss the colloidal synthesis of other germanium-containing compounds, emphasizing technologically relevant germanium chalcogenides that include GeS, GeSe, and GeTe.
Co-reporter:Eric J. Popczun ; James R. McKone ; Carlos G. Read ; Adam J. Biacchi ; Alex M. Wiltrout ; Nathan S. Lewis
Journal of the American Chemical Society 2013 Volume 135(Issue 25) pp:9267-9270
Publication Date(Web):June 13, 2013
DOI:10.1021/ja403440e
Nanoparticles of nickel phosphide (Ni2P) have been investigated for electrocatalytic activity and stability for the hydrogen evolution reaction (HER) in acidic solutions, under which proton exchange membrane-based electrolysis is operational. The catalytically active Ni2P nanoparticles were hollow and faceted to expose a high density of the Ni2P(001) surface, which has previously been predicted based on theory to be an active HER catalyst. The Ni2P nanoparticles had among the highest HER activity of any non-noble metal electrocatalyst reported to date, producing H2(g) with nearly quantitative faradaic yield, while also affording stability in aqueous acidic media.
Co-reporter:Matthew J. Bradley, Adam J. Biacchi, and Raymond E. Schaak
Chemistry of Materials 2013 Volume 25(Issue 9) pp:1886
Publication Date(Web):March 18, 2013
DOI:10.1021/cm4005163
Colloidal hybrid nanoparticles contain multiple domains that are directly fused together through a solid–solid interface, which facilitates synergistic interactions between the components that can lead to enhanced properties, as well as multifunctionality in a single particle. By nucleating one nanoparticle on the surface of another, a growing number of these hybrid nanoparticles can be synthesized. However, to rapidly expand the materials diversity of such systems, alternative routes to heterogeneous seeded nucleation are needed. Here, we show that solution-mediated chemical transformation reactions, which are well established for pseudomorphically transforming colloidal metal nanoparticles into derivative metal-containing phases, can also be applied to colloidal hybrid nanoparticles. Specifically, we show that Pt–Fe3O4 heterodimers react with Pb(acac)2 and Sn(acac)2 at 180–200 °C in a mixture of benzyl ether, oleylamine, oleic acid, and tert-butylamine borane to form PtPb–Fe3O4 and Pt3Sn–Fe3O4 heterodimers, respectively. This chemical transformation reaction introduces intermetallic and alloy components into the heterodimers, proceeds with morphological retention, and preserves the solid–solid interface that characterizes these hybrid nanoparticle systems. In addition, the PtPb–Fe3O4 heterodimers spontaneously aggregate to form colloidally stable (PtPb–Fe3O4)n nanoflowers via a process that is conceptually analogous to a molecular condensation reaction. These reactions add to the growing toolbox of predictable manipulations of colloidal hybrid nanoparticles, ultimately expanding their materials diversity and range of potential applications.Keywords: chemical transformation; colloidal hybrid nanoparticles; intermetallic nanoparticles; Pt−Fe3O4;
Co-reporter:Dimitri D. Vaughn II, Du Sun, Jarrett A. Moyer, Adam J. Biacchi, Rajiv Misra, Peter Schiffer, and Raymond E. Schaak
Chemistry of Materials 2013 Volume 25(Issue 21) pp:4396
Publication Date(Web):September 26, 2013
DOI:10.1021/cm402795r
Iron–germanium (Fe–Ge) is a complex alloy system that includes several structurally and compositionally diverse phases that exhibit a range of interesting magnetic properties that can change significantly when reduced to nanoscale dimensions. Fe–Ge nanostructures have been synthesized using chemical and physical deposition methods but have not previously been accessible as solution-synthesized colloidal materials. Here, we show that colloidal Fe–Ge nanostructures can be synthesized via the hot injection of an oleylamine solution of Fe(CO)5 into a solution containing GeI4, oleylamine, oleic acid, and hexamethyldisilazane. This approach effectively merges recent advances in the synthesis of colloidal Ge nanocrystals with methods routinely used to synthesize metal and alloy nanoparticles. At 260 °C, spherical nanocrystals of Ni2In-type Fe3Ge2 form. Heating the solution at 300 °C transforms the spherical Fe3Ge2 nanocrystals into CoGe-type FeGe nanowires. The Fe3Ge2 nanocrystals are ferromagnetic with Tc ≈ 265 K, whereas the FeGe nanowires are only weakly magnetic.Keywords: colloidal nanoparticle synthesis; iron germanium; magnetic nanocrystals; metal germanide alloys; nanocrystals; nanowires;
Co-reporter:Carlos G. Read, Adam J. Biacchi, and Raymond E. Schaak
Chemistry of Materials 2013 Volume 25(Issue 21) pp:4304
Publication Date(Web):September 26, 2013
DOI:10.1021/cm4024452
Colloidal hybrid nanoparticles, which contain multiple inorganic domains that are joined together through solid–solid interfaces, exhibit particle multifunctionality as well as new and enhanced properties that can emerge from the particle–particle interactions. These hybrid nanoparticles are typically synthesized using heterogeneous seeded nucleation of one nanoparticle on the surface of another as well as using phase segregation, surface dewetting of core–shell nanoparticles, and the fusion of premade nanoparticles. However, to expand the materials diversity and the potential range of applications of such systems, alternative routes to heterogeneous seeded nucleation are needed. Here, we show that solution–liquid–solid and related supersaturation-precipitation strategies, traditionally used in the synthesis of 1D structures such as nanowires and nanorods, can also be applied to the synthesis of colloidal hybrid nanoparticles. Specifically, we show that colloidal Au and Ag nanoparticles can serve as seeds for the growth of colloidal Au–Ge and Ag–Ge heterodimers upon reaction with Ge(HMDS)2 (Ge(II)bis(hexamethyldisilylamide)) at ∼290 and ∼320 °C, respectively. By modifying the size of the seed nanoparticles and the amount of Ge(HMDS)2, the widths and lengths of the Ge domains can be systematically tuned. Additionally, the Ge domains can serve as site-selective templates for the galvanic deposition of metal nanoparticles, forming trimeric Au–Ge–(Ag)n nanostructures. This alternate route to colloidal hybrid nanoparticles facilitates the integration of previously inaccessible group IV elements, and it could open the door to the design and synthesis of a wide range of new functional colloidal nanostructures.Keywords: colloidal hybrid nanoparticles; germanium nanoparticles; gold nanoparticles; silver nanoparticles; SLS; solution−liquid−solid growth;
Co-reporter:Matthew R. Buck, Adam J. Biacchi, Eric J. Popczun, and Raymond E. Schaak
Chemistry of Materials 2013 Volume 25(Issue 10) pp:2163
Publication Date(Web):April 17, 2013
DOI:10.1021/cm4009656
Germanium telluride (GeTe) nanostructures are a demonstrated platform for studying the effects of scaling on reversible, amorphous-to-crystalline phase transitions that are important for data storage and computing applications, and for understanding ferroelectric behavior at the nanometer scale. Despite the interest in GeTe, and the apparent advantages of solution-phase processing, there is a dearth of information related to the synthesis of high-quality, morphology-controlled, colloidal GeTe. This paper describes the preparation of colloidal GeTe nanostructures in the presence of surface-stabilizing polymers, which mediate particle–particle interactions and prevent aggregation of GeTe crystallites more effectively than conventional molecular stabilizers. As a result, several novel GeTe nanostructures are formed, including faceted octahedral nanoparticles, amorphous GexTe1–x alloy nanospheres and single-crystal two-dimensional (2D) GeTe nanosheets. The colloidal stability conferred by the polymer may provide the key experimental degree of freedom necessary to achieve higher-order morphology control for GeTe and related materials.Keywords: GeTe; nanoparticle synthesis; nanoparticles; nanosheets; phase change materials;
Co-reporter:Elizabeth R. Essinger-Hileman, Eric J. Popczun and Raymond E. Schaak
Chemical Communications 2013 vol. 49(Issue 48) pp:5471-5473
Publication Date(Web):29 Apr 2013
DOI:10.1039/C3CC42496K
A material specific peptide bound to Fe2O3 facilitates the selective sequestration of Au from a colloidal mixture of Au and CdS nanoparticles; the Au–Fe2O3 precipitate can then be magnetically separated from the colloidal CdS, and the Au nanoparticles can be recovered upon release from the Fe2O3.
Co-reporter:Matthew R. Buck ; Raymond E. Schaak
Angewandte Chemie International Edition 2013 Volume 52( Issue 24) pp:6154-6178
Publication Date(Web):
DOI:10.1002/anie.201207240
Abstract
New synthetic innovations are rapidly being developed to address the demand for complex, next-generation nanomaterials with rigorously controlled architectures and interfaces. This Review highlights key strategies for the chemical transformation and stepwise synthesis of multicomponent inorganic nanostructures, with the existing nanoscale transformations categorized into classes of reactions that are related to those used in the synthesis of organic molecules. The application of concepts used in molecular synthesis—including site-selectivity, regio- and chemoselectivity, orthogonal reactivity, coupling reactions, protection/deprotection strategies, and procedures for separation and purification—to nanoscale systems is emphasized. Collectively, the resulting synthetic concept represents an emerging model for the synthesis of complex inorganic nanostructures on the basis of the guiding principles that underpin the multistep total synthesis of complex organic molecules and natural products.
Co-reporter:Matthew R. Buck ; Raymond E. Schaak
Angewandte Chemie 2013 Volume 125( Issue 24) pp:6270-6297
Publication Date(Web):
DOI:10.1002/ange.201207240
Abstract
Die rege Nachfrage nach komplexen Nanomaterialien mit präzise kontrollierten Architekturen und Grenzflächen hat zu einer enormen Entwicklung bei innovativen Syntheseverfahren geführt. Dieser Aufsatz beleuchtet Schlüsselstrategien für die chemische Umwandlung und schrittweise Synthese von anorganischen Mehrkomponenten-Nanostrukturen, wobei existierende Umwandlungsreaktionen im Nanobereich in Klassen eingeordnet werden, die den bei der Synthese von organischen Molekülen verwendeten entsprechen. Ein Schwerpunkt liegt auf der Übertragung von Konzepten aus der Molekülsynthese auf nanoskalige Systeme: Dazu gehören unter anderem Ortsselektivität, Regio- und Chemoselektivität, orthogonale Reaktivität, Kupplungsreaktionen, Strategien zum Schützen und Entschützen sowie Verfahren zur Trennung und Aufreinigung. Das so geschaffene Regelwerk stellt ein neues Modell für die “Totalsynthese” von komplexen anorganischen Nanostrukturen dar, dem die Prinzipien von mehrstufigen Totalsynthesen komplexer organischer Molekülverbindungen und Naturstoffe zugrundeliegen.
Co-reporter:Ian T. Sines, Dimitri D. Vaughn II, Adam J. Biacchi, Corinne E. Kingsley, Eric J. Popczun, and Raymond E. Schaak
Chemistry of Materials 2012 Volume 24(Issue 15) pp:3088
Publication Date(Web):June 28, 2012
DOI:10.1021/cm301734b
Single-crystal colloidal SnSe nanosheets react with a trioctylphosphine–tellurium complex to transform into porous single-crystal SnTe nanosheets with oriented nanocube protrusions. This chemical transformation reaction, which provides chemical and crystallographic guidelines for designing secondary nanostructural features into single crystal colloidal nanosheets and also results in two-dimensional nanosheets of a three-dimensionally bonded material, proceeds via a diffusion-mediated anion exchange pathway. Intermediate nanosheets reveal that SnTe nucleates with crystallographic alignment on the surface of the SnSe nanosheet, which ultimately is consumed to produce the porous SnTe nanosheet product. The anion exchange reaction is general, successfully converting a library of metal selenides and sulfides to the corresponding tellurides.Keywords: chemical transformation; nanosheets; porous nanostructures; SnSe; SnTe;
Co-reporter:Nathan E. Motl, James F. Bondi, and Raymond E. Schaak
Chemistry of Materials 2012 Volume 24(Issue 9) pp:1552
Publication Date(Web):April 19, 2012
DOI:10.1021/cm300511q
Co-reporter:DimitriD. Vaughn II, Du Sun, Scott M. Levin, Adam J. Biacchi, Theresa S. Mayer, and Raymond E. Schaak
Chemistry of Materials 2012 Volume 24(Issue 18) pp:3643
Publication Date(Web):August 28, 2012
DOI:10.1021/cm3023192
GeSe is a narrow band gap IV–VI semiconductor that has been attracting increasing attention as a potential alternative material for photovoltaics, along with other optical and electrical applications. However, unlike several other narrow band gap chalcogenide semiconductors, very few examples of GeSe nanostructures have been reported. One-dimensional nanostructures are particularly attractive, because they can serve as building blocks for nanostructured electronic devices. As a step toward both increasing the morphological diversity of GeSe nanomaterials and expanding the library of electronic materials that are accessible as one-dimensional nanostructures, we report here the colloidal synthesis and electrical properties of GeSe nanobelts. The GeSe nanobelts were synthesized by first heating a one-pot reaction mixture of GeI4, TOP-Se, oleylamine, oleic acid, and hexamethyldisilazane to 320 °C, then adding additional TOP-Se and heating for several additional hours. Aliquot studies revealed that an amorphous GeSex precursor forms first, and then dissolves with continued heating prior to rapid nucleation of the GeSe nanobelts. The resulting nanobelts, which were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD), had an average diameter of 77 ± 18 nm and lengths that ranged from 1–25 μm. Visible-NIR diffuse reflectance spectroscopy revealed an absorption edge near 1100 nm and an indirect band gap of approximately 1.1 eV. Individual GeSe nanobelts were aligned between Ti/Au electrodes using an electric field-assisted assembly process, and 2- and 4-point current–voltage measurements were conducted, indicating ohmic (linear) behavior with resistivity values of approximately 360 Ω-cm.Keywords: GeSe; IV−VI semiconductors; nanobelts; one-dimensional nanostructures;
Co-reporter:Dimitri D. Vaughn, Olivia D. Hentz, Shuru Chen, Donghai Wang and Raymond E. Schaak
Chemical Communications 2012 vol. 48(Issue 45) pp:5608-5610
Publication Date(Web):01 May 2012
DOI:10.1039/C2CC32033A
SnS nanoflowers containing hierarchically organized nanosheet subunits were synthesized using a simple solution route, and they function as lithium ion battery anodes that maintain high capacities and coulombic efficiencies over 30 cycles.
Co-reporter:Ian T. Sines, Dimitri D. Vaughn II, Rajiv Misra, Eric J. Popczun, Raymond E. Schaak
Journal of Solid State Chemistry 2012 Volume 196() pp:17-20
Publication Date(Web):December 2012
DOI:10.1016/j.jssc.2012.07.056
Mackinawite, a metastable 1:1 compound of iron and sulfur that adopts an anti-PbO-type structure, is of interest because of its relationship to known iron chalcogenide superconductors, as well as its biogeochemical relevance. Colloidal nanosheets of mackinawite-type FeS were synthesized by first generating an amorphous Fe–S precursor via the aqueous room-temperature co-precipitation of Fe2+ and S2−, then solvothermally crystallizing it in ethylene glycol at 200 °C in an autoclave. The product is highly crystalline, with lattice constants of a=3.674(3) Å and c=5.0354(3) Å. The nanosheets, with their surface normal oriented along the [0 0 1] direction, are irregularly faceted with edge lengths that range from 100 nm to over 1 μm and average thicknesses of approx. 30 nm. The samples showed a ferromagnetic background signal with no evidence of superconductivity.Grahpical abstractSingle-crystal colloidal nanosheets of mackinawite-type FeS were synthesized by the solvothermal crystallization of an amorphous Fe–S precursor.Highlights► Aqueous co-precipitation yields an amorphous Fe–S precursor. ► The amorphous precursor solvothermally crystallizes to form metastable mackinawite. ► Mackinawite-type FeS forms as single crystal colloidal nanosheets. ► Samples are ferromagnetic with no evidence of superconductivity.
Co-reporter:Raymond E. Schaak and Mary E. Williams
ACS Nano 2012 Volume 6(Issue 10) pp:8492
Publication Date(Web):October 3, 2012
DOI:10.1021/nn304375v
Colloidal hybrid nanoparticles merge multiple distinct materials into single particles, producing nanostructures that often exhibit synergistic properties and multifunctionality. As the complexity of such nanostructures continues to expand and the design criteria become increasingly stringent, the synthetic pathways required to access such materials are growing in sophistication. Multistep pathways are typically needed to generate complex hybrid nanoparticles, and these synthetic protocols have important conceptual analogies to the total synthesis framework used by chemists to construct complex organic molecules. This issue of ACS Nano includes a new nanoscale total synthesis: a five-step route to CoxOy–Pt–(CdSe@CdS)–Pt–CoxOy nanorods, a material which consists of CdSe@CdS nanorods that have Pt and cobalt oxide (CoxOy) at the tips. In addition to the conceptual analogies between molecular and nanoparticle total syntheses, there are practical analogies, as well, which are important for ensuring the reproducible and high-yield production of multicomponent nanostructured products with the highest possible purities. This Perspective highlights some of the practical considerations that are important for all nanoparticle syntheses but that become magnified significantly when multiple sequential reactions are required to generate a target product. These considerations include detailed reporting of reaction setups, experimental and workup procedures, hazards, yields of all intermediates and final products, complete data analysis, and separation techniques for ensuring high purity.
Co-reporter:Dr. Su-Il In;Dimitri D. Vaughn II ; Raymond E. Schaak
Angewandte Chemie 2012 Volume 124( Issue 16) pp:3981-3984
Publication Date(Web):
DOI:10.1002/ange.201108936
Co-reporter:Dr. Su-Il In;Dimitri D. Vaughn II ; Raymond E. Schaak
Angewandte Chemie International Edition 2012 Volume 51( Issue 16) pp:3915-3918
Publication Date(Web):
DOI:10.1002/anie.201108936
Co-reporter:Zachary L. Schaefer, Kaitlyn M. Weeber, Rajiv Misra, Peter Schiffer, and Raymond E. Schaak
Chemistry of Materials 2011 Volume 23(Issue 9) pp:2475
Publication Date(Web):April 7, 2011
DOI:10.1021/cm200410s
Nanoparticles of elemental nickel underpin a large number of magnetic and catalytic applications, and the possibility of tuning these properties via the formation of different allotropes is intriguing. While bulk elemental nickel adopts a face centered cubic (fcc) structure, a growing number of reports suggest that colloidal nickel nanoparticles can crystallize in the metastable hexagonal close packed (hcp) structure. However, there is some disagreement in the literature concerning the formation of hcp-Ni, particularly with respect to the crystallographically-related Ni3C phase. Most notable is a range of lattice constants and magnetic properties that have been attributed to hcp-Ni. Here, we show that reaction time can be used to tune the carbon content of a Ni3C1-x solid solution. Importantly, colloidal nanoparticles of Ni3C1-x can help to experimentally rationalize the range of lattice constants and magnetic properties reported for hcp-Ni and Ni3C, effectively bridging these two end-member systems. All samples, including those isolated immediately upon reduction of Ni2+ to Ni0, contained some carbon, as evidenced by XRD, XPS, TGA, DSC, TEM, and SQUID magnetometry. As reaction time increases, the average carbon content increases, and this correlates with a systematic increase in unit cell volume and a systematic decrease in saturation magnetization. These results also provide a straightforward pathway for tuning the magnetic properties of isomorphous Ni nanoparticles.Keywords: composition-tunable solid solution; magnetic nanoparticles; nickel; nickel carbide;
Co-reporter:Elizabeth R. Essinger-Hileman, Danielle DeCicco, James F. Bondi and Raymond E. Schaak
Journal of Materials Chemistry A 2011 vol. 21(Issue 31) pp:11599-11604
Publication Date(Web):24 Feb 2011
DOI:10.1039/C0JM03913F
Many binary late transition metal systems have large bulk miscibility gaps, and a variety of synthetic strategies have been developed to generate these non-equilibrium alloys as nanoparticles. While many of these methods strive to co-nucleate both elements by exploiting fast reduction kinetics or co-sequestration within a confined space, we show here that simple room-temperature borohydride co-reduction of appropriate aqueous metal salt solutions yields alloy nanoparticles in the bulk-immiscible Au–Rh, Au–Pt, Pt–Rh, and Pd–Rh systems. The compositions can be tuned across the entire Au1−xRhx, Au1−xPtx, Pt1−xRhx, and Pd1−xRhx solid solutions by varying the ratio of metal salt reagents, and they form in the presence of a variety of molecular and polymeric surface stabilizers. Reaction pathway studies on the model Au–Rh system suggest that the alloy nanoparticles form via a “conversion chemistry” mechanism: Au nanoparticle templates nucleate first, followed by diffusion of Rh to form homogeneous Au–Rh alloy nanoparticles. The alloy nanoparticles tend to be agglomerated, but this can be minimized by forming the nanoparticles directly on catalytically relevant high surface area carbon and biological supports, e.g. Vulcan carbon and wild-type M13 bacteriophage.
Co-reporter:James F. Bondi
European Journal of Inorganic Chemistry 2011 Volume 2011( Issue 26) pp:3877-3880
Publication Date(Web):
DOI:10.1002/ejic.201100276
Abstract
Colloidal nanoparticles of a prototype polar intermetallic compound, Au3Li, were synthesized by reacting Au nanoparticle seeds with n-butyllithium. X-ray and electron diffraction data are consistent with the L12 (Cu3Au) structure type expected for Au3Li. Composition analysis indicates a stoichiometry of approximately Au3Li0.7, which is within the reported composition range of the Au3Li phase. The Au3Li nanoparticles decompose in water to regenerate Au. The successful synthesis of Au3Li as colloidal nanoparticles demonstrates that polar intermetallic compounds containing highly electropositive elements are accessible by using low-temperature solution chemistry routes and that they are also amenable to nanostructuring.
Co-reporter:Arthur Mar;Julia Y. Chan;Myung-Hwan Whangbo;Gordon J. Miller;Mercouri G. Kanatzidis;Michael Shatruk
European Journal of Inorganic Chemistry 2011 Volume 2011( Issue 26) pp:
Publication Date(Web):
DOI:10.1002/ejic.201190075
Abstract
The front cover picture shows the clock tower, the “Campanile”, of Iowa State University where John Corbett did the ground-breaking research in polar intermetallics that forms the basis of his Viewpoint in this cluster issue. Superimposed on this background are structures and data to visualize the broad scope of topic. The complexity of structure is displayed by the ternary rare-earth cobalt gallides that contain interstitial atoms (top left, A. Mar et al.), a calcium-poor intermetallic phase of the Ca/Ni/Ge system (top right from the lab of T. Fässler), and a single crystal of a polymorph of thallium nickel gallide (bottom right, J. Chan et al.). The potentially general synthesis of colloidal nanoparticles – Au3Li from the lab of R. E. Schaak – is outlined mid left. The groups of M. H. Whangbo and G. Miller devote their contributions to the theoretical aspects of bonding (depicted top centre, the plots showing Au–Au bonding and antibonding interactions in Dy2Au2In and mid right, the effects of ionic interactions on the structural properties of isoelectronic intermetallic compounds, respectively). Representative of the range of properties discussed is the magnetic susceptibility of Yb5Ni4Ge10 (bottom left, M. G. Kanatzidis et al.). We thank the authors for the use of the graphics from their papers on the cover.
Co-reporter:Jacob S. Beveridge;Matthew R. Buck;James F. Bondi;Dr. Rajiv Misra; Peter Schiffer; Raymond E. Schaak; Mary Elizabeth Williams
Angewandte Chemie International Edition 2011 Volume 50( Issue 42) pp:9875-9879
Publication Date(Web):
DOI:10.1002/anie.201104829
Co-reporter:Jacob S. Beveridge;Matthew R. Buck;James F. Bondi;Dr. Rajiv Misra; Peter Schiffer; Raymond E. Schaak; Mary Elizabeth Williams
Angewandte Chemie 2011 Volume 123( Issue 42) pp:10049-10053
Publication Date(Web):
DOI:10.1002/ange.201104829
Co-reporter:Adam J. Biacchi and Raymond E. Schaak
ACS Nano 2011 Volume 5(Issue 10) pp:8089
Publication Date(Web):September 21, 2011
DOI:10.1021/nn2026758
The polyol process is one of the most common methods for synthesizing metal nanoparticles with controlled shapes and sizes due to its wide applicability and ease of use. These nanostructures often have unique morphology-dependent properties that are useful in a range of applications, including catalysis, plasmonics, and medical diagnostics and therapeutics. While many variations of the polyol process have been developed to produce shape-controlled nanoparticles, there has been no systematic investigation that defines the influence of the solvent on the shape and uniformity of the product. Here we show that proper selection of the polyol solvent can be used to manipulate the metal nanoparticle morphology. Each polyol has a different oxidation potential which, along with the metal reagent, defines the temperature at which particle formation takes place. For a given system, particle growth will vary between a kinetic and thermodynamic regime depending on the thermal conditions, which can be modulated through selection of the appropriate solvent. This strategy, which is demonstrated for the catalytically relevant rhodium system, facilitates the high-yield synthesis of monodisperse rhodium nanoparticles with shapes that include icosahedra, cubes, triangular plates, and octahedra.Keywords: nanoparticle synthesis; polyol process; rhodium nanoparticles; shape controlled-nanoparticles
Co-reporter:Dimitri D. Vaughn II, Su-Il In, and Raymond E. Schaak
ACS Nano 2011 Volume 5(Issue 11) pp:8852
Publication Date(Web):October 12, 2011
DOI:10.1021/nn203009v
The availability of high-quality colloidal nanosheets underpins a diverse range of applications and investigations into dimension-dependent physical properties. To facilitate this, synthetic methods that yield single-crystal colloidal nanosheets with regular shapes, uniform lateral dimensions, and tunable thicknesses are critically important. Most strategies that yield colloidal nanosheets achieve some, but not all, of these morphological characteristics. Here, we describe a synthetic pathway that generates colloidal nanosheets of SnSe with uniform lateral dimensions and tunable thicknesses. SnSe represents an excellent prototype system for studying the formation of colloidal nanosheets because of its layered crystal structure and the growing interest in its potential application as an absorption layer in low-cost photovoltaic devices. Freestanding colloidal SnSe nanosheets were synthesized by slowly heating a one-pot reaction mixture of SnCl2, oleylamine, trioctylphosphine selenide (TOP-Se), and hexamethyldisilazane (HMDS) to 240 °C. The SnSe nanostructures adopt a uniform square-like morphology with lateral dimensions of approximately 500 nm ×500 nm, and the average nanosheet thicknesses can be tuned from approximately 10 to 40 nm by adjusting the concentrations of the SnCl2 and TOP-Se reagents. Aliquot studies reveal fundamental insights into how the nanosheets form: they first “grow out” laterally via coalescence of individual nanoparticle building blocks to yield a single-crystal nanosheet template and then “grow up” vertically (through nanoparticle attachment to the nanosheet template) in a pseudo layer-by-layer fashion. Vertical growth is therefore limited, and can be controlled, by reagent concentration. Drop-cast films of the SnSe nanosheets are photoactive and have a bandgap of approximately 1 eV. These studies, demonstrated for SnSe but potentially applicable to other systems, establish a straightforward pathway for tuning the thicknesses of colloidal nanosheets while maintaining lateral uniformity.Keywords: colloidal nanosheets; nanoparticle coalescence; nanoparticle synthesis; narrow bandgap semiconductors; reaction pathway studies; tin selenide (SnSe)
Co-reporter:Dimitri D. Vaughn II ; Romesh J. Patel ; Michael A. Hickner
Journal of the American Chemical Society 2010 Volume 132(Issue 43) pp:15170-15172
Publication Date(Web):October 13, 2010
DOI:10.1021/ja107520b
Narrow-band-gap IV−VI semiconductors offer promising optoelectronic properties for integration as light-absorbing components in field-effect transistors, photodetectors, and photovoltaic devices. Importantly, colloidal nanostructures of these materials have the potential to substantially decrease the fabrication cost of solar cells because of their ability to be solution-processed. While colloidal nanomaterials formed from IV−VI lead chalcogenides such as PbS and PbSe have been extensively investigated, those of the layered semiconductors SnS, SnSe, GeS, and GeSe have only recently been considered. In particular, there have been very few studies of the germanium chalcogenides, which have band-gap energies that overlap well with the solar spectrum. Here we report the first synthesis of colloidal GeS and GeSe nanostructures obtained by heating GeI4, hexamethyldisilazane, oleylamine, oleic acid, and dodecanethiol or trioctylphosphine selenide to 320 °C for 24 h. These materials, which were characterized by TEM, SAED, SEM, AFM, XRD, diffuse reflectance spectroscopy, and I−V conductivity measurements, preferentially adopt a two-dimensional single-crystal nanosheet morphology that produces fully [100]-oriented films upon drop-casting. Optical measurements indicated indirect band gaps of 1.58 and 1.14 eV for GeS and GeSe, respectively, and electrical measurements showed that drop-cast films of GeSe exhibit p-type conductivity.
Co-reporter:Ian T. Sines
Journal of the American Chemical Society 2010 Volume 133(Issue 5) pp:1294-1297
Publication Date(Web):December 30, 2010
DOI:10.1021/ja110374d
Controlling the composition and phase formation of bulk and nanoscale solids underpins efforts to control physical properties. Here, we introduce a powerful new chemical pathway that facilitates composition-tunable synthesis, post-synthesis purification, and precise phase targeting in metal chalcogenide systems. When metal selenides and sulfides react with trioctylphosphine (TOP) at temperatures that range from 65 to 270 °C, selenium and sulfur are selectively extracted to produce the most metal-rich chalcogenide that is stable in a particular binary system. This general approach is demonstrated for SnSe2, FeS2, NiSe2, and CoSe2, which convert to SnSe, FeS, Ni3Se2, and Co9Se8, respectively. In-depth studies of the Fe−Se system highlight the precise phase targeting and purification that is achievable, with PbO-type FeSe (the most metal-rich stable Fe−Se phase) forming exclusively when other Fe−Se phases, including mixtures, react with TOP. This chemistry also represents a new template-based nanoparticle “conversion chemistry” reaction, transforming hollow NiSe2 nanospheres into hollow NiSe nanospheres with morphological retention.
Co-reporter:Matthew R. Buck, Ian T. Sines and Raymond E. Schaak
Chemistry of Materials 2010 Volume 22(Issue 10) pp:3236
Publication Date(Web):April 15, 2010
DOI:10.1021/cm1004483
Many Ge-based chalcogenide alloys, including GeTe, exhibit a reversible amorphous-to-crystalline phase change that is the basis for a wide range of current and next-generation technologies. Solution routes are attractive alternative strategies for synthesizing these materials, because they have the potential to impart morphology control on the crystallites and permit liquid-based processing of films and patterned structures. This paper describes a liquid-phase route to crystalline rhombohedral GeTe crystallites with cube-shaped morphologies and edge lengths of 1.0 ± 0.2 μm. The microcrystallites can be deposited onto planar substrates to produce highly textured (002) oriented films. During TEM imaging, the particles undergo electron beam induced fragmentation and, in some cases, partial amorphization. The GeTe crystallites are characterized by XRD, SEM, EDS (including element mapping), DSC, TEM, and electron diffraction.
Co-reporter:James F. Bondi, Rajiv Misra, Xianglin Ke, Ian T. Sines, Peter Schiffer and Raymond E. Schaak
Chemistry of Materials 2010 Volume 22(Issue 13) pp:3988
Publication Date(Web):June 11, 2010
DOI:10.1021/cm100705c
Au and the 3d transition metals are immiscible under equilibrium conditions, but nonequilibrium alloys and intermetallic compounds of these elements are of interest for their potential multifunctional optical, catalytic, and magnetic properties. Here we report an optimized synthesis of intermetallic compounds with nominal compositions of Au3Fe1−x, Au3Co1−x, and Au3Ni1−x as nanoparticles. Identification and optimization of the key synthetic variables (solvent, order of reagent addition, stabilizer, heating rate) led to the generation of nanoparticles with high phase purity and sample sizes of >30 mg, which is an order of magnitude larger than what was previously achievable. These intermetallic nanoparticles, which have diffraction patterns consistent with the L12 structure type, were characterized by powder XRD, TEM, EDS, electron diffraction, UV−visible spectroscopy, and SQUID magnetometry. Aliquot studies showed that Au3Fe1−x formed through the initial nucleation of Au nanoparticles, followed by subsequent incorporation of Fe. Magnetic studies of powdered samples identified Au3Fe1−x and Au3Co1−x as superparamagnetic with TB = 7.9 and 2.4 K, respectively. Au3Ni1−x is paramagnetic down to 1.8 K.
Co-reporter:Dimitri D. Vaughn II, James F. Bondi, and Raymond E. Schaak
Chemistry of Materials 2010 Volume 22(Issue 22) pp:6103
Publication Date(Web):November 1, 2010
DOI:10.1021/cm1015965
Nanoparticles of elemental germanium have interesting optical and electronic properties and relatively low toxicity, making them attractive materials for biological and optoelectronic applications. The most common routes to colloidal Ge nanoparticles include metathesis reactions involving Zintl salts, hydride reduction of Ge halides, and thermal decomposition of organogermane precursors. Here we describe an alternative “heat-up” method for the synthesis of size- and shape-tunable Ge nanoparticles that are both crystalline and air stable. The readily available reagents GeI4, oleylamine, oleic acid, and hexamethyldisilazane are combined in one pot and heated to 260 °C, where a rapid nucleation event occurs and multifaceted nanoparticles of crystalline Ge form. By varying the concentration of GeI4, the nanoparticle size can be tuned from 6 to 22 nm with narrow size distributions. Adding trioctylphosphine yields cube-shaped particles, and switching the solvent to octadecene yields one-dimensional nanostructures. The Ge nanoparticles, which are fully air stable for more than 6 months, were characterized by XRD, TEM, HRTEM, EDS, XPS, DRIFT, and UV−visible spectroscopy.
Co-reporter:M. E. Anderson, S. S. N. Bharadwaya and R. E. Schaak
Journal of Materials Chemistry A 2010 vol. 20(Issue 38) pp:8362-8367
Publication Date(Web):26 Aug 2010
DOI:10.1039/C0JM01424A
Bismuth antimony telluride, Bi0.5Sb1.5Te3, is a prototype thermoelectric alloy for which nanostructuring has been shown to improve the thermoelectric figure of merit. Most bulk-scale nanostructured thermoelectric materials are synthesized using either traditional solid-state routes or “top-down” physical methods such as ball milling, sputtering, etc. “Bottom-up” chemical methods represent an important alternative route to nanostructured thermoelectrics, but often produce small sample sizes that make transport measurements difficult. Here, nanostructured Bi0.5Sb1.5Te3 has been synthesized in half-gram quantities using a simple and scalable modified polyol process. Stoichiometric amounts of appropriate metal salts were combined in tetraethylene glycol with and without poly(vinylpyrrolidone) (PVP), reduced with sodium borohydride, and heated in solution and in powder form to obtain samples of crystalline Bi0.5Sb1.5Te3. The structure, composition, and morphology of the products were characterized using powder XRD, TEM, SEM, and EDS mapping data. The Seebeck coefficient, measured from 300–500 K for 1 cm sintered pellets of Bi0.5Sb1.5Te3, increased with temperature and was found to be +256 µV K−1 at 500 K. Bulk-scale nanostructured powders of other thermoelectrics could also be synthesized, including Bi2Te3, PbTe, Sb2Te3, AgSbTe2, and Pb1−xSnxTe.
Co-reporter:Nathaniel L. Henderson, Xianglin Ke, Peter Schiffer, Raymond E. Schaak
Journal of Solid State Chemistry 2010 Volume 183(Issue 3) pp:631-635
Publication Date(Web):March 2010
DOI:10.1016/j.jssc.2009.12.025
Europium titanate, EuTiO3, is a paraelectric/antiferromagnetic cubic perovskite with TN=5.5 K. It is predicted that compressive strain could induce simultaneous ferroelectricity and ferromagnetism in this material, leading to multiferroic behavior. As an alternative to epitaxial strain, we explored lattice contraction via chemical substitution of Eu2+ with the smaller Ca2+ cation as a mechanism to tune the magnetic properties of EuTiO3. A modified sol–gel process was used to form homogeneously mixed precursors containing Eu3+, Ca2+, and Ti4+, and reductive annealing was used to transform these precursors into crystalline powders of Eu1−xCaxTiO3 with x=0.00, 0.05, 0.10, 0.15, 0.25, 0.35, 0.50, 0.55, 0.60, 0.65, 0.80, and 1.00. Powder XRD data indicated that a continuous Eu1−xCaxTiO3 solid solution was readily accessible, and the lattice constants agreed well with those predicted by Vegard's law. SEM imaging and EDS element mapping indicated a homogeneous distribution of Eu, Ca, and Ti throughout the polycrystalline sample, and the actual Eu:Ca ratio agreed well with the nominal stoichiometry. Measurements of magnetic susceptibility vs. temperature indicated antiferromagnetic ordering in samples with x≤0.60, with TN decreasing from 5.4 K in EuTiO3 to 2.6 K in Eu0.40Ca0.60TiO3. No antiferromagnetic ordering above 1.8 K was detected in samples with x>0.60.Twelve members of the Eu1−xCaxTiO3 solid solution (0≤x≤1) were synthesized by first forming a homogeneously mixed precursor using a modified sol–gel process, followed by reductive annealing. Samples with x≤0.60 are antiferromagnetic, with TN decreasing as the level of calcium substitution increases.
Co-reporter:Zachary L. Schaefer;Matthew L. Gross; Michael A. Hickner; Raymond E. Schaak
Angewandte Chemie 2010 Volume 122( Issue 39) pp:7199-7202
Publication Date(Web):
DOI:10.1002/ange.201003213
Co-reporter:Zachary L. Schaefer;Matthew L. Gross; Michael A. Hickner; Raymond E. Schaak
Angewandte Chemie International Edition 2010 Volume 49( Issue 39) pp:7045-7048
Publication Date(Web):
DOI:10.1002/anie.201003213
Co-reporter:IanT. Sines;Rajiv Misra Dr.;Peter Schiffer ;RaymondE. Schaak
Angewandte Chemie 2010 Volume 122( Issue 27) pp:4742-4744
Publication Date(Web):
DOI:10.1002/ange.201001213
Co-reporter:IanT. Sines;Rajiv Misra Dr.;Peter Schiffer ;RaymondE. Schaak
Angewandte Chemie 2010 Volume 122( Issue 27) pp:
Publication Date(Web):
DOI:10.1002/ange.201003242
Co-reporter:Nathan E. Motl, Ebo Ewusi-Annan, Ian T. Sines, Lasse Jensen, and Raymond E. Schaak
The Journal of Physical Chemistry C 2010 Volume 114(Issue 45) pp:19263-19269
Publication Date(Web):October 25, 2010
DOI:10.1021/jp107637j
For plasmonic alloy nanoparticles, theoretical modeling and experimental characterization are both central to our capabilities involving predictable synthesis and targeted applications. This article uses composition-tunable colloidal Au−Cu nanoparticles as a model system for exploring the issue of reliable experimental determination of composition in plasmonic alloy nanoparticles and correlation of this experimental data with theoretical predictions. Highly uniform spherical Au1-xCux alloy nanoparticles were synthesized with compositions ranging from x = 0 to 0.5. The particle compositions were analyzed independently using both powder X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS), which represent two of the most common nanoparticle composition analysis techniques. The plasmon resonance frequencies, determined experimentally for each sample using UV−vis spectroscopy, red shift with increasing copper content as expected. These experimentally determined plasmon resonance frequencies were then compared to the values predicted theoretically based upon the XRD and EDS composition measurements. Although EDS and XRD are both found to be acceptable methods for experimentally determining the composition, careful data analysis suggests that XRD composition measurements are more accurate for smaller values of x, whereas EDS measurements are more accurate for larger values of x. In addition, some discrepancies between the experimentally determined plasmon resonance frequencies and those predicted by theory suggest inaccuracies in using a simple linear mixing rule to determine the dielectric constant of the Au−Cu alloys.
Co-reporter:IanT. Sines;Rajiv Misra Dr.;Peter Schiffer ;RaymondE. Schaak
Angewandte Chemie International Edition 2010 Volume 49( Issue 27) pp:4638-4640
Publication Date(Web):
DOI:10.1002/anie.201001213
Co-reporter:IanT. Sines;Rajiv Misra Dr.;Peter Schiffer ;RaymondE. Schaak
Angewandte Chemie International Edition 2010 Volume 49( Issue 27) pp:
Publication Date(Web):
DOI:10.1002/anie.201003242
Co-reporter:James F. Bondi ; Karl D. Oyler ; Xianglin Ke ; Peter Schiffer
Journal of the American Chemical Society 2009 Volume 131(Issue 26) pp:9144-9145
Publication Date(Web):June 16, 2009
DOI:10.1021/ja901372q
Elemental manganese has a complex crystal structure and unusual magnetic properties, making it an intriguing target for exploration in nanocrystalline form. However, because of its oxophilicity and the difficulty in reducing soluble metal salts to elemental Mn using the most common solution-phase reducing agents, it has been challenging to synthesize and stabilize elemental Mn nanoparticles using solution chemistry methods. Here we report the chemical synthesis of α-Mn nanoparticles using n-butyllithium as a reducing agent. The nanoparticles have been characterized by powder XRD, TEM, electron diffraction, infrared spectroscopy (DRIFT), XPS, and SQUID magnetometry. An amorphous manganese oxide layer bound by oleate ligands helps to render the nanoparticles air-stable. The oxide-coated α-Mn nanoparticles are paramagnetic.
Co-reporter:Qingsheng Liu ; Zhen Yan ; Nathaniel L. Henderson ; J. Chris Bauer ; D. Wayne Goodman ; James D. Batteas
Journal of the American Chemical Society 2009 Volume 131(Issue 16) pp:5720-5721
Publication Date(Web):April 6, 2009
DOI:10.1021/ja810151r
Solution chemistry methods have been used to synthesize bimetallic CuPt alloy nanoparticle catalysts with controllable sizes and shapes. By variation of the relative ratios of the oleylamine and oleic acid stabilizers, solvent, and reduction rate, the nanoparticles could be tuned from ∼2 nm spherical particles to nanorods with diameters of ∼2.5 nm and aspect ratios tunable from 5:1 to 25:1. These mixed-metal nanoparticles show excellent catalytic properties for CO oxidation, with light-off temperatures that are nearly 200 K below those of conventional supported Pt catalysts.
Co-reporter:Nathaniel L. Henderson, Matthew D. Straesser, Philip E. Sabato and Raymond E. Schaak
Green Chemistry 2009 vol. 11(Issue 7) pp:974-978
Publication Date(Web):07 Apr 2009
DOI:10.1039/B815443K
Binary intermetallic compounds have been synthesized in edible plant and seed oils through the reaction of molten metal dispersions of low-melting p-block metals with late transition metal powders. Specifically, apricot kernel, almond, safflower, and canola oils have been used to synthesize FeSn2, Ni3Sn4, CoSn3, CoGa3, Cu6Sn5, and Bi3Ni. This low-temperature strategy yields bulk-scale products that are highly crystalline, and the solvents used to synthesize them can be re-used several times.
Co-reporter:Kendra N. Avery, Janell E. Schaak and Raymond E. Schaak
Chemistry of Materials 2009 Volume 21(Issue 11) pp:2176
Publication Date(Web):May 7, 2009
DOI:10.1021/cm900869u
Co-reporter:Karl D. Oyler, Xianglin Ke, Ian T. Sines, Peter Schiffer and Raymond E. Schaak
Chemistry of Materials 2009 Volume 21(Issue 15) pp:3655
Publication Date(Web):July 10, 2009
DOI:10.1021/cm901150c
Transition metal chalcogenides are important materials because of their range of useful properties and applications, including as thermoelectrics, magnetic semiconductors, superconductors, quantum dots, sensors, and photovoltaics. In particular, iron chalcogenides have received renewed attention following the discovery of superconductivity in PbO-type β-FeSe and related solid solutions. This paper reports a low-temperature solution chemistry route to the synthesis of β-FeSe, β-FeTe, FeTe2, and several members of the β-Fe(Se,Te) solid solution. The samples were analyzed by powder XRD, TEM, EDS, SAED, SEM with elemental mapping, AFM, and SQUID magnetometry. Consistent with the layered crystal structures, the FeSe, FeTe, and Fe(Se,Te) products are predominantly two-dimensional single-crystal nanosheets with thicknesses of approximately 2−3 nm and edge lengths ranging from 200 nm to several micrometers. FeTe2 forms a mixture of nanosheets and one-dimensional sheet-derived nanostructures. None of the samples are superconducting, which could be due to size effects, nonstoichiometry, or low-level impurities.
Co-reporter:Ting-Hao Phan and Raymond E. Schaak
Chemical Communications 2009 (Issue 21) pp:3026-3028
Publication Date(Web):01 May 2009
DOI:10.1039/B902024A
Palladium is converted into palladium hydride, β-PdHx, in polyol solution using NaBH4 as a hydrogen source; nanocrystalline Pd reacts to form PdHx faster and at lower temperatures than bulk Pd, and can be made to release hydrogen to regenerate Pd.
Co-reporter:Brian M. Leonard, Mary E. Anderson, Karl D. Oyler, Ting-Hao Phan and Raymond E. Schaak
ACS Nano 2009 Volume 3(Issue 4) pp:940
Publication Date(Web):February 25, 2009
DOI:10.1021/nn800892a
Chemists rely on a toolbox of robust chemical transformations for selectively modifying molecules with spatial and functional precision to make them more complex in a controllable and predictable manner. This manuscript describes proof-of-principle experiments for a conceptually analogous strategy involving the selective, stepwise, and spatially controlled modification of inorganic nanostructures. The key concept is orthogonal reactivity: one component of a multicomponent system reacts with a particular reagent under a specific set of conditions while the others do not, even though they are all present together in the same reaction vessel. Using the chemical conversion of metal nanoparticles into intermetallic, sulfide, and phosphide nanoparticles as representative examples, the concept of orthogonal reactivity is defined and demonstrated for a variety of two- and three-component nanoscale systems. First, solution-phase reactivity data are presented and collectively analyzed for the reaction of metal nanoparticles (Ni, Cu, Rh, Pd, Ag, Pt, Au, Sn) with several metal salt and elemental reagents (Bi, Pb, Sb, Sn, S). From these data, several two- and three-component orthogonal systems are identified. Finally, these results are applied to the spatially selective chemical modification of lithographically patterned surfaces and striped template-grown metal nanowires.Keywords: intermetallic nanoparticles; metal nanoparticles; metal nanowires; orthogonal reactivity; patterned surfaces; synthesis
Co-reporter:Nam Hawn Chou and Raymond E. Schaak
Chemistry of Materials 2008 Volume 20(Issue 6) pp:2081
Publication Date(Web):February 28, 2008
DOI:10.1021/cm703640u
We describe a unified and general template-based strategy for synthesizing a library of morphology-controllable M−Sn (M = Co, Ni, Cu, Ag, Au, Pt, Ru) intermetallic nanorods. The reaction of β-Sn nanorod templates with appropriate metal salt solutions under reducing conditions yields single-crystal intermetallic nanorods of CoSn3, Ni3Sn4, Cu6Sn5, Ag4Sn, AuSn, PtSn, and RuSn2. Temperature plays a key role in maintaining the morphology of the β-Sn nanorod templates in the final M−Sn products and also selectively generating spherical nanocrystals vs dense nanorods vs hollow nanorods, in some cases (e.g., CoSn3) within the same system. These observations are linked to the diffusion process, and accordingly, the melting points of the transition elements used in this study can help us understand and predict the morphologies that can be formed, as well as the lowest temperature at which a particular intermetallic compound can form using low-temperature solution routes.
Co-reporter:Nathaniel L. Henderson and Raymond E. Schaak
Chemistry of Materials 2008 Volume 20(Issue 9) pp:3212
Publication Date(Web):April 22, 2008
DOI:10.1021/cm800245j
A variety of binary intermetallic compounds of late transition metals with low-melting post-transition metals have been synthesized in bulk quantities by reacting molten metal dispersions with fine metal powders in hot polyalcohol solvents. Fourteen distinct intermetallics were formed using this technique: SbSn, FeSn2, Cu6Sn5, CoSn3, Ni3Sn4, FeGa3, NiGa4, Cu9Ga4, CoGa3, Ni2In3, InSb, In5Bi3, InBi, and Bi3Ni. Notable among these are a low-temperature phase (α-CoSn3), textured intermetallic powders with anisotropic morphologies (α-CoSn3 and FeSn2), and superconductors (Bi3Ni and In5Bi3). Reaction pathway studies suggest that the molten low-melting metals diffuse into the larger higher melting powders, forming intermetallic compounds directly in a liquid-phase medium from bulk-scale powders of the constituent elements.
Co-reporter:J. Chris Bauer, Xiaole Chen, Qingsheng Liu, Ting-Hao Phan and Raymond E. Schaak
Journal of Materials Chemistry A 2008 vol. 18(Issue 3) pp:275-282
Publication Date(Web):22 Nov 2007
DOI:10.1039/B712035D
Multi-metal nanoparticles, particularly alloys and intermetallic compounds, are useful catalysts for a variety of chemical transformations. Supported intermetallic nanoparticle catalysts are usually prepared by depositing precursors onto a support followed by high-temperature annealing, which is necessary to generate the intermetallic compound but causes sintering and minimizes surface area. Here we show that solution chemistry methods for converting metal nanoparticles into intermetallic compounds are applicable to supported nanoparticle catalyst systems. Unsupported nanocrystalline Pt can be converted to nanocrystalline PtSn, PtPb, PtBi, and FePt3 by reaction with appropriate metal salt solutions under reducing conditions. Similar reactions convert Al2O3, CeO2, and carbon-supported Pt nanoparticles into PtSn, PtPb, PtSb, Pt3Sn, and Cu3Pt. These reactions generate supported alloy and intermetallic nanoparticles directly in solution without the need for high temperature annealing or additional surface stabilizers. These supported intermetallic nanoparticles are catalytically active for chemical transformations such as formic acid oxidation (PtPb/Vulcan) and CO oxidation (Pt3Sn/graphite). Notably, PtPb/Vulcan XC-72 was found to electrocatalytically oxidize formic acid at a lower onset potential (0.1 V) than commercial PtRu/Vulcan XC-72 (0.4 V).
Co-reporter:Yolanda Vasquez, Amanda E. Henkes, J. Chris Bauer, Raymond E. Schaak
Journal of Solid State Chemistry 2008 Volume 181(Issue 7) pp:1509-1523
Publication Date(Web):July 2008
DOI:10.1016/j.jssc.2008.04.007
The concept of nanocrystal conversion chemistry, which involves the use of pre-formed nanoparticles as templates for chemical transformation into derivative solids, has emerged as a powerful approach for designing the synthesis of complex nanocrystalline solids. The general strategy exploits established synthetic capabilities in simple nanocrystal systems and uses these nanocrystals as templates that help to define the composition, crystal structure, and morphology of product nanocrystals. This article highlights key examples of “conversion chemistry” approaches to the synthesis of nanocrystalline solids using a variety of techniques, including galvanic replacement, diffusion, oxidation, and ion exchange. The discussion is organized according to classes of solids, highlighting the diverse target systems that are accessible using similar chemical concepts: metals, oxides, chalcogenides, phosphides, alloys, intermetallic compounds, sulfides, and nitrides.Nanocrystal conversion chemistry uses pre-formed nanoparticles as templates for chemical transformation into derivative solids, helping to define the composition, crystal structure, and morphology of product nanocrystals that have more complex features than their precursor templates. This article highlights the application of this concept to diverse classes of solids, including metals, oxides, chalcogenides, phosphides, alloys, intermetallics, sulfides, and nitrides.
Co-reporter:Raymond E. Schaak
Journal of Solid State Chemistry 2008 Volume 181(Issue 7) pp:1507-1508
Publication Date(Web):July 2008
DOI:10.1016/j.jssc.2008.06.035
Co-reporter:Amanda E. Henkes, Raymond E. Schaak
Journal of Solid State Chemistry 2008 Volume 181(Issue 12) pp:3264-3268
Publication Date(Web):December 2008
DOI:10.1016/j.jssc.2008.08.028
A solution precursor route has been used to synthesize a series of nanocrystalline rare-earth borates. Amorphous precursor powders are precipitated during an aqueous reaction between RE3+ and NaBH4, and the isolated powders can be annealed in air at 700 °C to form YBO3, NdBO3, SmBO3, EuBO3, GdBO3, and HoBO3. YBO3:Eu formed using this strategy shows red-orange emission properties that are similar to high-quality nanocrystals prepared by other methods. The materials have been characterized by FTIR spectroscopy, powder XRD, SEM, DSC, UV–Vis fluorimetry, and TEM with EDS and element mapping.Amorphous nanoscopic precursor powders are formed through the aqueous reaction of RE3+ with NaBH4. Once isolated, the powders can be annealed at 700 °C in air to form a series of nanocrystalline REBO3 orthoborates. Nanocrystalline YBO3:Eu formed using this strategy shows red-orange emission properties when excited with UV light.
Co-reporter:Zachary L. Schaefer, Xianglin Ke, Peter Schiffer and Raymond E. Schaak
The Journal of Physical Chemistry C 2008 Volume 112(Issue 50) pp:19846-19851
Publication Date(Web):2017-2-22
DOI:10.1021/jp8082503
Crystalline Ni3B with a fused porous nanoparticle network has been synthesized directly in solution using a modified polyol method. KBH4 serves both as a reducing agent for Ni2+ and as a boron source, while tetraethylene glycol serves as a solvent capable of achieving reaction temperatures that can crystallize Ni3B. The reaction pathway was studied using X-ray diffraction, transmission electron microscopy, and electron diffraction, and a nucleation−aggregation−smoothing mechanism is proposed. Amorphous Ni−B alloy nanoparticles form first and then aggregate into larger networks, which crystallize and smooth to form porous crystalline Ni3B nanoparticle networks. Structural characterization by X-ray diffraction indicates that the lattice constants for nanocrystalline Ni3B are shifted relative to single-crystal Ni3B, likely because of some carbon incorporation based on X-ray photoelectron spectroscopy data. Magnetic measurements suggest the formation of a small amount of nanocrystalline Ni, which provides further insight into the reaction pathway. Scanning electron microscopy and Brunauer−Emmett−Teller surface area measurements indicate a porous morphology, and thermal analysis shows that boronized nickel generated from Ni3B is more resistant to oxidation than a similar sample of pure Ni.
Co-reporter:Adam J. Biacchi ; Dimitri D. Vaughn ; II
Journal of the American Chemical Society () pp:
Publication Date(Web):July 3, 2013
DOI:10.1021/ja405203e
Tin sulfide, SnS, is a narrow band gap semiconductor comprised of inexpensive, earth abundant, and environmentally benign elements that is emerging as an important material for a diverse range of applications in solar energy conversion, energy storage, and electronics. Relative to many comparable systems, much less is known about the factors that influence the synthesis or morphology-dependent properties of SnS nanostructures. Here, we report the synthesis of colloidal SnS cubes, spherical polyhedra, and sheets and demonstrate their activity for the photocatalytic degradation of methylene blue. We also study their morphology-dependent polymorphism using an in-depth crystallographic analysis that correlates high-resolution TEM data of individual nanocrystals with ensemble-based electron diffraction and powder XRD data. These studies reveal that the crystal structure adopted by the SnS cubes and spherical polyhedra is expanded along the a and b axes and contracted along c, converging on a pseudotetragonal cell that is distinct from that of orthorhombic α-SnS, the most stable polymorph. All of the peaks observed in powder XRD patterns that are often interpreted as originating from a mixture of metastable zincblende-type SnS and α-SnS can instead be accounted for by this single-phase pseudotetragonal modification, and this helps to rationalize discrepancies that exist between theoretical predictions of SnS polymorph stability and interpretations of experimental diffraction data. This same crystallographic analysis also indicates the morphologies of the nanocrystals and the facets by which they are bound, and it reveals that the SnS cubes form through selective overgrowth of spherical polyhedral seeds.
Co-reporter:Dimitri D. Vaughn II and Raymond E. Schaak
Chemical Society Reviews 2013 - vol. 42(Issue 7) pp:NaN2879-2879
Publication Date(Web):2012/11/05
DOI:10.1039/C2CS35364D
Germanium nanoparticles have excited scientists and engineers because of their size-dependent optical properties and their potential applications in optoelectronics, biological imaging and therapeutics, flash memories, and lithium-ion batteries. In order to further develop these applications and to gain deeper insights into their size-dependent properties, robust and facile synthetic methods are needed to controllably synthesize Ge nanoparticles. However, when compared to other II–VI, IV–VI, and III–V semiconductor systems, colloidal routes to Ge NPs with uniform sizes and shapes are much less mature. In this Review Article, we highlight the progress that has been made in this field and provide insights into the strategies used for the colloidal synthesis of size and shape-controlled germanium nanomaterials. We also survey some of the potential applications of these materials in optoelectronics, biological imaging, and energy conversion and storage. Finally, we discuss the colloidal synthesis of other germanium-containing compounds, emphasizing technologically relevant germanium chalcogenides that include GeS, GeSe, and GeTe.
Co-reporter:J. Chris Bauer, Xiaole Chen, Qingsheng Liu, Ting-Hao Phan and Raymond E. Schaak
Journal of Materials Chemistry A 2008 - vol. 18(Issue 3) pp:NaN282-282
Publication Date(Web):2007/11/22
DOI:10.1039/B712035D
Multi-metal nanoparticles, particularly alloys and intermetallic compounds, are useful catalysts for a variety of chemical transformations. Supported intermetallic nanoparticle catalysts are usually prepared by depositing precursors onto a support followed by high-temperature annealing, which is necessary to generate the intermetallic compound but causes sintering and minimizes surface area. Here we show that solution chemistry methods for converting metal nanoparticles into intermetallic compounds are applicable to supported nanoparticle catalyst systems. Unsupported nanocrystalline Pt can be converted to nanocrystalline PtSn, PtPb, PtBi, and FePt3 by reaction with appropriate metal salt solutions under reducing conditions. Similar reactions convert Al2O3, CeO2, and carbon-supported Pt nanoparticles into PtSn, PtPb, PtSb, Pt3Sn, and Cu3Pt. These reactions generate supported alloy and intermetallic nanoparticles directly in solution without the need for high temperature annealing or additional surface stabilizers. These supported intermetallic nanoparticles are catalytically active for chemical transformations such as formic acid oxidation (PtPb/Vulcan) and CO oxidation (Pt3Sn/graphite). Notably, PtPb/Vulcan XC-72 was found to electrocatalytically oxidize formic acid at a lower onset potential (0.1 V) than commercial PtRu/Vulcan XC-72 (0.4 V).
Co-reporter:M. E. Anderson, S. S. N. Bharadwaya and R. E. Schaak
Journal of Materials Chemistry A 2010 - vol. 20(Issue 38) pp:NaN8367-8367
Publication Date(Web):2010/08/26
DOI:10.1039/C0JM01424A
Bismuth antimony telluride, Bi0.5Sb1.5Te3, is a prototype thermoelectric alloy for which nanostructuring has been shown to improve the thermoelectric figure of merit. Most bulk-scale nanostructured thermoelectric materials are synthesized using either traditional solid-state routes or “top-down” physical methods such as ball milling, sputtering, etc. “Bottom-up” chemical methods represent an important alternative route to nanostructured thermoelectrics, but often produce small sample sizes that make transport measurements difficult. Here, nanostructured Bi0.5Sb1.5Te3 has been synthesized in half-gram quantities using a simple and scalable modified polyol process. Stoichiometric amounts of appropriate metal salts were combined in tetraethylene glycol with and without poly(vinylpyrrolidone) (PVP), reduced with sodium borohydride, and heated in solution and in powder form to obtain samples of crystalline Bi0.5Sb1.5Te3. The structure, composition, and morphology of the products were characterized using powder XRD, TEM, SEM, and EDS mapping data. The Seebeck coefficient, measured from 300–500 K for 1 cm sintered pellets of Bi0.5Sb1.5Te3, increased with temperature and was found to be +256 µV K−1 at 500 K. Bulk-scale nanostructured powders of other thermoelectrics could also be synthesized, including Bi2Te3, PbTe, Sb2Te3, AgSbTe2, and Pb1−xSnxTe.
Co-reporter:Elizabeth R. Essinger-Hileman, Danielle DeCicco, James F. Bondi and Raymond E. Schaak
Journal of Materials Chemistry A 2011 - vol. 21(Issue 31) pp:NaN11604-11604
Publication Date(Web):2011/02/24
DOI:10.1039/C0JM03913F
Many binary late transition metal systems have large bulk miscibility gaps, and a variety of synthetic strategies have been developed to generate these non-equilibrium alloys as nanoparticles. While many of these methods strive to co-nucleate both elements by exploiting fast reduction kinetics or co-sequestration within a confined space, we show here that simple room-temperature borohydride co-reduction of appropriate aqueous metal salt solutions yields alloy nanoparticles in the bulk-immiscible Au–Rh, Au–Pt, Pt–Rh, and Pd–Rh systems. The compositions can be tuned across the entire Au1−xRhx, Au1−xPtx, Pt1−xRhx, and Pd1−xRhx solid solutions by varying the ratio of metal salt reagents, and they form in the presence of a variety of molecular and polymeric surface stabilizers. Reaction pathway studies on the model Au–Rh system suggest that the alloy nanoparticles form via a “conversion chemistry” mechanism: Au nanoparticle templates nucleate first, followed by diffusion of Rh to form homogeneous Au–Rh alloy nanoparticles. The alloy nanoparticles tend to be agglomerated, but this can be minimized by forming the nanoparticles directly on catalytically relevant high surface area carbon and biological supports, e.g. Vulcan carbon and wild-type M13 bacteriophage.
Co-reporter:Ting-Hao Phan and Raymond E. Schaak
Chemical Communications 2009(Issue 21) pp:NaN3028-3028
Publication Date(Web):2009/05/01
DOI:10.1039/B902024A
Palladium is converted into palladium hydride, β-PdHx, in polyol solution using NaBH4 as a hydrogen source; nanocrystalline Pd reacts to form PdHx faster and at lower temperatures than bulk Pd, and can be made to release hydrogen to regenerate Pd.
Co-reporter:Elizabeth R. Essinger-Hileman, Eric J. Popczun and Raymond E. Schaak
Chemical Communications 2013 - vol. 49(Issue 48) pp:NaN5473-5473
Publication Date(Web):2013/04/29
DOI:10.1039/C3CC42496K
A material specific peptide bound to Fe2O3 facilitates the selective sequestration of Au from a colloidal mixture of Au and CdS nanoparticles; the Au–Fe2O3 precipitate can then be magnetically separated from the colloidal CdS, and the Au nanoparticles can be recovered upon release from the Fe2O3.
Co-reporter:Dimitri D. Vaughn, Olivia D. Hentz, Shuru Chen, Donghai Wang and Raymond E. Schaak
Chemical Communications 2012 - vol. 48(Issue 45) pp:NaN5610-5610
Publication Date(Web):2012/05/01
DOI:10.1039/C2CC32033A
SnS nanoflowers containing hierarchically organized nanosheet subunits were synthesized using a simple solution route, and they function as lithium ion battery anodes that maintain high capacities and coulombic efficiencies over 30 cycles.
Co-reporter:Joshua M. McEnaney, J. Chance Crompton, Juan F. Callejas, Eric J. Popczun, Carlos G. Read, Nathan S. Lewis and Raymond E. Schaak
Chemical Communications 2014 - vol. 50(Issue 75) pp:NaN11028-11028
Publication Date(Web):2014/07/30
DOI:10.1039/C4CC04709E
Amorphous tungsten phosphide (WP), which has been synthesized as colloidal nanoparticles with an average diameter of 3 nm, has been identified as a new electrocatalyst for the hydrogen-evolution reaction (HER) in acidic aqueous solutions. WP/Ti electrodes produced current densities of −10 mA cm−2 and −20 mA cm−2 at overpotentials of only −120 mV and −140 mV, respectively, in 0.50 M H2SO4(aq).
.jpg)
