Co-reporter:Lauren E. Marbella, Xing Yee Gan, Derrick C. Kaseman, and Jill E. Millstone
Nano Letters April 12, 2017 Volume 17(Issue 4) pp:2414-2414
Publication Date(Web):March 17, 2017
DOI:10.1021/acs.nanolett.6b05420
Recently, a wide variety of new nanoparticle compositions have been identified as potential plasmonic materials including earth-abundant metals such as aluminum, highly doped semiconductors, as well as metal pnictides. For semiconductor compositions, plasmonic properties may be tuned not only by nanoparticle size and shape, but also by charge carrier density which can be controlled via a variety of intrinsic and extrinsic doping strategies. Current methods to quantitatively determine charge carrier density primarily rely on interpretation of the nanoparticle extinction spectrum. However, interpretation of nanoparticle extinction spectra can be convoluted by factors such as particle ligands, size distribution and/or aggregation state which may impact the charge carrier information extracted. Therefore, alternative methods to quantify charge carrier density may be transformational in the development of these new materials and would facilitate previously inaccessible correlations between particle synthetic routes, crystallographic features, and emergent optoelectronic properties. Here, we report the use of 77Se solid state nuclear magnetic resonance (NMR) spectroscopy to quantitatively determine charge carrier density in a variety of Cu2–xSe nanoparticle compositions and correlate this charge carrier density with particle crystallinity and extinction features. Importantly, we show that significant charge carrier populations are present even in nanoparticles without spectroscopically discernible plasmonic features and with crystal structures indistinguishable from fully reduced Cu2Se. These results highlight the potential impact of the NMR-based carrier density measurement, especially in the study of plasmon emergence in these systems (i.e., at low dopant concentrations).Keywords: charge carrier; doping; metal chalcogenide; nanoparticle; NMR; Plasmonic;
Co-reporter:Ashley M. Smith;Kathryn A. Johnston;Scott E. Crawford;Lauren E. Marbella
Analyst (1876-Present) 2017 vol. 142(Issue 1) pp:11-29
Publication Date(Web):2016/12/19
DOI:10.1039/C6AN02206E
Colloidal inorganic nanoparticles are being used in an increasingly large number of applications ranging from biological imaging to television displays. In all cases, nanoparticle surface chemistry can significantly impact particle physical properties, processing, and performance. The first step in leveraging this tunability is to develop analytical approaches to describe surface chemical features. Some of the most basic descriptors of particle surface chemistry include the quantity, identity, and arrangement of ligands appended to the particle core. Here, we review approaches to quantify molecular ligand densities on nanoparticle surfaces and consider fundamental barriers to the accuracy of this analysis including parameters such as dispersity in colloidal nanoparticle samples, particle–ligand interactions, and currently available analytical techniques. Techniques reviewed include widely studied methods such as optical, atomic, vibrational, and nuclear magnetic resonance spectroscopies as well as emerging or niche approaches including electrospray-differential mobility analysis, pH-based methods, and X-ray photoelectron spectroscopy. Collectively, these studies elucidate surface chemistry architectures that accelerate both fundamental understanding of nanoscale physical phenomena and the implementation of these materials in a wide range of technologies.
Co-reporter:Lauren E. Marbella, Scott E. Crawford, Michael J. Hartmann and Jill E. Millstone
Chemical Communications 2016 vol. 52(Issue 58) pp:9020-9023
Publication Date(Web):31 Mar 2016
DOI:10.1039/C6CC00464D
Here, we use solution and solid-state 31P NMR to study the ligand environment of water soluble, phosphine-terminated gold nanoparticles. The resulting spectra indicate that particle-bound phosphine ligands occupy an unexpectedly monodisperse ligand environment. This uniformity then facilitates one of the first descriptions of distinct 31P–197Au coupling in colloidal nanoparticles.
Co-reporter:Patrick J. Straney;Christopher M. Andolina
Israel Journal of Chemistry 2016 Volume 56( Issue 4) pp:257-261
Publication Date(Web):
DOI:10.1002/ijch.201500033
Abstract
Copper-containing nanomaterials are attractive due to the natural abundance, low cost, and unique catalytic properties of copper metal. Copper may also be used as a representative system to study the formation of mixed metal nanoparticles containing 3d transition metals. These elements pose challenges to traditional metal nanoparticle synthesis strategies due to competing formation of both oxides and hydroxides, depending on metal identity. Here, we analyze copper deposition pathways on gold nanoprism substrates using a combination of electron microscopy and X-ray photoelectron spectroscopy techniques, demonstrating conditions for both core@shell and island growth modes. Elemental analysis by X-ray photoelectron spectroscopy and Auger electron spectroscopy indicate that the final nanoparticle products contain metallic copper. Together, these results elucidate important trends for incorporating 3d transition metals into traditional colloidal syntheses of multimetallic nanostructures.
Co-reporter:Rowan K. Leary, Anjli Kumar, Patrick J. Straney, Sean M. Collins, Sadegh Yazdi, Rafal E. Dunin-Borkowski, Paul A. Midgley, Jill E. Millstone, and Emilie Ringe
The Journal of Physical Chemistry C 2016 Volume 120(Issue 37) pp:20843-20851
Publication Date(Web):April 18, 2016
DOI:10.1021/acs.jpcc.6b02103
Catalytic and optical properties can be coupled by combining different metals into nanoscale architectures in which both the shape and the composition provide fine-tuning of functionality. Here, discrete, small Pt nanoparticles (diameter = 3–6 nm) were grown in linear arrays on Au nanoprisms, and the resulting structures are shown to retain strong localized surface plasmon resonances. Multidimensional electron microscopy and spectroscopy techniques (energy-dispersive X-ray spectroscopy, electron tomography, and electron energy-loss spectroscopy) were used to unravel their local composition, three-dimensional morphology, growth patterns, and optical properties. The composition and tomographic analyses disclose otherwise ambiguous details of the Pt-decorated Au nanoprisms, revealing that both pseudospherical protrusions and dendritic Pt nanoparticles grow on all faces of the nanoprisms (the faceted or occasionally twisted morphologies of which are also revealed), and shed light on the alignment of the Pt nanoparticles. The electron energy-loss spectroscopy investigations show that the Au nanoprisms support multiple localized surface plasmon resonances despite the presence of pendant Pt nanoparticles. The plasmonic fields at the surface of the nanoprisms indeed extend into the Pt nanoparticles, opening possibilities for combined optical and catalytic applications. These insights pave the way toward comprehensive nanoengineering of multifunctional bimetallic nanostructures, with potential applications in plasmon-enhanced catalysis and in situ monitoring of chemical processes via surface-enhanced spectroscopy.
Co-reporter:Michael J. Hartmann, Jill E. Millstone, and Hannu Häkkinen
The Journal of Physical Chemistry C 2016 Volume 120(Issue 37) pp:20822-20827
Publication Date(Web):April 4, 2016
DOI:10.1021/acs.jpcc.6b02126
Magnetic properties of Co13 and Co55 nanoclusters, passivated by surface ligand shells that exhibit varying electronic interactions with the metal, are studied using density functional theory. The calculations show that the chemical nature of the bond between the ligand and the metal core (X-type or L-type) impacts the total magnetic moment of Co nanoclusters dramatically. Furthermore, the chemical identity of the ligand within each binding motif then provides a fine handle on the exhibited magnetic moment of the cluster. Thus, ligand shell chemistry is predicted to not only stabilize Co nanoclusters, but provide a powerful approach to control their magnetic properties, which combined enable a variety of magnetism-based applications.
Co-reporter:Kathryn A. Johnston, Ashley M. Smith, Lauren E. Marbella, and Jill E. Millstone
Langmuir 2016 Volume 32(Issue 16) pp:3820-3826
Publication Date(Web):April 14, 2016
DOI:10.1021/acs.langmuir.6b00232
Here, we compare the ligand exchange behaviors of silver nanoparticles synthesized in the presence of two different surface capping agents: poly(vinylpyrrolidone) (MW = 10 or 40 kDa) or trisodium citrate, and under either ambient or low-oxygen conditions. In all cases, we find that the polymer capping agent exhibits features of a weakly bound ligand, producing better ligand exchange efficiencies with an incoming thiolated ligand compared to citrate. The polymer capping agent also generates nanoparticles that are more susceptible to reactions with oxygen during both synthesis and ligand exchange. The influence of the original ligand on the outcome of ligand exchange reactions with an incoming thiolated ligand highlights important aspects of silver nanoparticle surface chemistry, crucial for applications ranging from photocatalysis to antimicrobials.
Co-reporter:Julia R. Bursten
The Journal of Physical Chemistry Letters 2016 Volume 7(Issue 10) pp:1917-1918
Publication Date(Web):May 19, 2016
DOI:10.1021/acs.jpclett.6b00694
Co-reporter:Scott E. Crawford; Christopher M. Andolina; Ashley M. Smith; Lauren E. Marbella; Kathryn A. Johnston; Patrick J. Straney; Michael J. Hartmann
Journal of the American Chemical Society 2015 Volume 137(Issue 45) pp:14423-14429
Publication Date(Web):November 6, 2015
DOI:10.1021/jacs.5b09408
Small gold nanoparticles (∼1.4–2.2 nm core diameters) exist at an exciting interface between molecular and metallic electronic structures. These particles have the potential to elucidate fundamental physical principles driving nanoscale phenomena and to be useful in a wide range of applications. Here, we study the optoelectronic properties of aqueous, phosphine-terminated gold nanoparticles (core diameter = 1.7 ± 0.4 nm) after ligand exchange with a variety of sulfur-containing molecules. No emission is observed from these particles prior to ligand exchange, however the introduction of sulfur-containing ligands initiates photoluminescence. Further, small changes in sulfur substituents produce significant changes in nanoparticle photoluminescence features including quantum yield, which ranges from 0.13 to 3.65% depending on substituent. Interestingly, smaller ligands produce the most intense, highest energy, narrowest, and longest-lived emissions. Radiative lifetime measurements for these gold nanoparticle conjugates range from 59 to 2590 μs, indicating that even minor changes to the ligand substituent fundamentally alter the electronic properties of the luminophore itself. These results isolate the critical role of surface chemistry in the photoluminescence of small metal nanoparticles and largely rule out other mechanisms such as discrete (Au(I)—S—R)n impurities, differences in ligand densities, and/or core diameters. Taken together, these experiments provide important mechanistic insight into the relationship between gold nanoparticle near-infrared emission and pendant ligand architectures, as well as demonstrate the pivotal role of metal nanoparticle surface chemistry in tuning and optimizing emergent optoelectronic features from these nanostructures.
Co-reporter:Lauren E. Marbella; Daniel M. Chevrier; Peter D. Tancini; Olabobola Shobayo; Ashley M. Smith; Kathryn A. Johnston; Christopher M. Andolina; Peng Zhang; Giannis Mpourmpakis
Journal of the American Chemical Society 2015 Volume 137(Issue 50) pp:15852-15858
Publication Date(Web):December 15, 2015
DOI:10.1021/jacs.5b10124
We report the identification, description, and role of multinuclear metal–thiolate complexes in aqueous Au–Cu nanoparticle syntheses. The structure of these species was characterized by nuclear magnetic resonance spectroscopy, mass spectrometry, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy techniques. The observed structures were found to be in good agreement with thermodynamic growth trends predicted by first-principles calculations. The presence of metal−thiolate complexes is then shown to be critical for the formation of alloyed Au–Cu architectures in the small nanoparticle regime (diameter ∼2 nm). In the absence of mixed metal–thiolate precursors, nanoparticles form with a Cu–S shell and a Au-rich interior. Taken together, these results demonstrate that prenucleation species, which are discrete molecular precursors distinct from both initial reagents and final particle products, may provide an important new synthetic route to control final metal nanoparticle composition and composition architectures.
Co-reporter:Lauren E. Marbella and Jill E. Millstone
Chemistry of Materials 2015 Volume 27(Issue 8) pp:2721
Publication Date(Web):March 11, 2015
DOI:10.1021/cm504809c
Solution phase noble metal nanoparticle growth reactions are comprised of deceptively simple steps. Analytical methods with high chemical, spatial, and temporal resolution are crucial to understanding these reactions and subsequent nanoparticle properties. However, approaches for the characterization of solid inorganic materials and solution phase molecular species are often disparate. One powerful technique to address this gap is nuclear magnetic resonance (NMR) spectroscopy, which can facilitate routine, direct, molecular-scale analysis of nanoparticle formation and morphology in situ, in both the solution and the solid phase. A growing body of work indicates that NMR analyses should yield an exciting complement to the existing canon of routine nanoparticle characterization methods such as electron microscopy and optical absorption spectroscopy. Here, we discuss recent developments in the application of NMR techniques to the study of noble metal nanoparticle growth, surface chemistry, and physical properties. Specifically, we describe the unique capabilities of NMR in resolving hard–soft matter interfaces with both high chemical and high spatial resolution.
Co-reporter:Ashley M. Smith, Lauren E. Marbella, Kathryn A. Johnston, Michael J. Hartmann, Scott E. Crawford, Lisa M. Kozycz, Dwight S. Seferos, and Jill E. Millstone
Analytical Chemistry 2015 Volume 87(Issue 5) pp:2771
Publication Date(Web):February 6, 2015
DOI:10.1021/ac504081k
We use nuclear magnetic resonance spectroscopy methods to quantify the extent of ligand exchange between different types of thiolated molecules on the surface of gold nanoparticles. Specifically, we determine ligand density values for single-moiety ligand shells and then use these data to describe ligand exchange behavior with a second, thiolated molecule. Using these techniques, we identify trends in gold nanoparticle functionalization efficiency with respect to ligand type, concentration, and reaction time as well as distinguish between functionalization pathways where the new ligand may either replace the existing ligand shell (exchange) or add to it (“backfilling”). Specifically, we find that gold nanoparticles functionalized with thiolated macromolecules, such as poly(ethylene glycol) (1 kDa), exhibit ligand exchange efficiencies ranging from 70% to 95% depending on the structure of the incoming ligand. Conversely, gold nanoparticles functionalized with small-molecule thiolated ligands exhibit exchange efficiencies as low as 2% when exposed to thiolated molecules under identical exchange conditions. Taken together, the reported results provide advances in the fundamental understanding of mixed ligand shell formation and will be important for the preparation of gold nanoparticles in a variety of biomedical, optoelectronic, and catalytic applications.
Co-reporter:Michael J. Hartmann
The Journal of Physical Chemistry C 2015 Volume 119(Issue 15) pp:8290-8298
Publication Date(Web):April 3, 2015
DOI:10.1021/jp5125475
Co-reporter:Patrick J. Straney ; Lauren E. Marbella ; Christopher M. Andolina ; Noel T. Nuhfer
Journal of the American Chemical Society 2014 Volume 136(Issue 22) pp:7873-7876
Publication Date(Web):May 23, 2014
DOI:10.1021/ja504294p
Nanoscale platinum materials are essential components in many technologies, including catalytic converters and fuel cells. Combining Pt with other metals can enhance its performance and/or decrease the cost of the technology, and a wide range of strategies have been developed to capitalize on these advantages. However, wet chemical synthesis of Pt-containing nanoparticles (NPs) is challenging due to the diverse metal segregation and metal–metal redox processes possible under closely related experimental conditions. Here, we elucidate the relationship between Pt(IV) speciation and the formation of well-known NP motifs, including frame-like and core–shell morphologies, in Au–Pt systems. We leverage insights gained from these studies to induce a controlled transition from redox- to surface chemistry-mediated growth pathways, resulting in the formation of Pt NPs in epitaxial contact and linear alignment along a gold nanoprism substrate. Mechanistic investigations using a combination of electron microscopy and 195Pt NMR spectroscopy identify Pt(IV) speciation as a crucial parameter for understanding and controlling the formation of Pt-containing NPs. Combined, these findings point toward fully bottom-up methods for deposition and organization of NPs on colloidal plasmonic substrates.
Co-reporter:Lauren E. Marbella;Christopher M. Andolina;Ashley M. Smith;Michael J. Hartmann;Andrew C. Dewar;Kathryn A. Johnston;Owen H. Daly
Advanced Functional Materials 2014 Volume 24( Issue 41) pp:6532-6539
Publication Date(Web):
DOI:10.1002/adfm.201400988
We demonstrate the synthesis of discrete, composition-tunable gold-cobalt nanoparticle alloys (% Co = 0–100%; diameter = 2–3 nm), in contrast with bulk behavior, which shows immiscibility of Au and Co at room temperature across all composition space. These particles are characterized by transmission electron microscopy and 1H NMR techniques, as well as inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy. In particular, 1H NMR methods allow the simultaneous evaluation of composition-tunable magnetic properties as well as molecular characterization of the colloid, including ligand environment and hydrodynamic diameter. These experiments also demonstrate a route to optimize bimodal imaging modalities, where we identify AuxCoyNP compositions that exhibit both bright NIR emission (2884 m −1cm−1) as well as some of the highest per-particle T 2 relaxivities (12200 mm NP −1s−1) reported to date for this particle size range.
Co-reporter:Christopher M. Andolina ; Andrew C. Dewar ; Ashley M. Smith ; Lauren E. Marbella ; Michael J. Hartmann
Journal of the American Chemical Society 2013 Volume 135(Issue 14) pp:5266-5269
Publication Date(Web):April 2, 2013
DOI:10.1021/ja400569u
Discrete gold nanoparticles with diameters between 2 and 3 nm show remarkable properties including enhanced catalytic behavior and photoluminescence. However, tunability of these properties is limited by the tight size range within which they are observed. Here, we report the synthesis of discrete, bimetallic gold–copper nanoparticle alloys (diameter ≅ 2–3 nm) which display photoluminescent properties that can be tuned by changing the alloy composition. Electron microscopy, X-ray photoelectron spectroscopy, inductively coupled plasma mass spectrometry, and pulsed-field gradient stimulated echo 1H NMR measurements show that the nanoparticles are homogeneous, discrete, and crystalline. Upon varying the composition of the nanoparticles from 0% to 100% molar ratio copper, the photoluminescence maxima shift from 947 to 1067 nm, with excitation at 360 nm. The resulting particles exhibit brightness values (molar extinction coefficient (ε) × quantum yield (Φ)) that are more than an order of magnitude larger than the brightest near-infrared-emitting lanthanide complexes and small-molecule probes evaluated under similar conditions.
Co-reporter:Patrick J. Straney, Christopher M. Andolina, and Jill E. Millstone
Langmuir 2013 Volume 29(Issue 13) pp:4396-4403
Publication Date(Web):March 21, 2013
DOI:10.1021/la400227k
Seedless initiation has been used as a simple and sustainable alternative to seed-mediated production of two canonical anisotropic gold nanoparticles: nanorods and nanoprisms. The concentration of reducing agent during the nucleation event was found to influence the resulting product morphology, producing nanorods with lengths from 30 to 630 nm and triangular or hexagonal prisms with vertex-to-vertex lengths ranging from 120 to over 700 nm. The seedless approach is then used to eliminate several chemical reagents and reactions steps from classic particle preparations while achieving almost identical nanoparticle products and product yields. Our results shed light on factors that influence (or do not influence) the evolution of gold nanoparticle shape and present a dramatically more efficient route to obtaining these architectures. Specifically, using these methods reduces the total amount of reagent needed to produce nanorods and nanoprisms by as much as 90 wt % and, to the best of our knowledge, has yielded the first report of spectroscopically discernible, colloidal gold nanoplates synthesized using a seedless methodology.
Co-reporter:Lauren E. Marbella, Scott E. Crawford, Michael J. Hartmann and Jill E. Millstone
Chemical Communications 2016 - vol. 52(Issue 58) pp:NaN9023-9023
Publication Date(Web):2016/03/31
DOI:10.1039/C6CC00464D
Here, we use solution and solid-state 31P NMR to study the ligand environment of water soluble, phosphine-terminated gold nanoparticles. The resulting spectra indicate that particle-bound phosphine ligands occupy an unexpectedly monodisperse ligand environment. This uniformity then facilitates one of the first descriptions of distinct 31P–197Au coupling in colloidal nanoparticles.
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