Editorial pubs.acs.org/CR
Introduction: Nanoparticle Chemistry
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high activity and selectivity while efficiently using expensive precious metal components.4 Magnetic nanoparticles are actively studied for MRI imaging, therapy, and magnetic data storage. Some magnetic compounds also show excellent catalytic properties. Wu, Mendoza-Garcia, Li, and Sun provide a thorough review of the diverse field of magnetic nanoparticles that include various magnetic metals, metallic alloys, metal oxides, and multicomponent nanostructures.5 This issue presents several reviews covering different aspects of semiconductor nanoparticles. The excitonic properties of nanometer sized semiconductor crystallites have only been elucidated relatively recently. During the early 1980s, Ekimov and Efros6 as well as Brus8 arrived at the concept of quantum confinement that gave a start to the field of semiconductor quantum dots. The electronic structure and photophysical properties of quantum dots, as well as their applications in electronic and optoelectronic devices, are thoroughly reviewed in the article written by Pietryga, Park, Lim, Fidler, Bae, Brovelli, and Klimov.7 Quantum dots have been successfully commercialized as luminescent tags for bioimaging and display applications. The advantage of quantum dots as emitter materials originates from their narrow and symmetric emission spectra. Several leading display manufacturers recently released flat panel TVs that use colloidally synthesized quantum dots to expand the color gamut and improve the energy efficiency of LCD displays.9 The adoption of quantum dots for consumer products brings stringent requirements for materials quality, stability, manufacturing costs, and environmental friendliness. One possible way to reduce manufacturing costs is to run syntheses in aqueous mediums instead of using costly organic solvents. Jing, Kershaw, Li, Huang, Li, Rogach, and Gao discuss advances in the aqueous synthesis of semiconductor nanocrystals, their properties, and applications.10 Many semiconductor quantum dots contain cadmium or lead that bring toxicity concerns. This is not a problem in fundamental studies and for some practical applications, but applications in consumer products would greatly benefit from the development of nontoxic quantum dots composed of only inexpensive, earth-abundant elements. Reiss, Carrière, Lincheneau, Vaure, and Tamang provide a detailed review of the activities and achievements in the area of heavy-metal-free quantum dots that have excellent prospects for commercial applications.11 Knowles, Gamelin, and co-workers focus on a broad class of copper-containing semiconductor nanoparticles12 and review advances in synthesis and optical properties of nanoparticles made of doped semiconductors with optical properties that may be particularly suitable for use in luminescent solar concentrators. As-synthesized nanoparticles can be engaged in various postsynthetic chemical transformations, similar to the addition
anoparticle chemistry is a relatively young branch of chemical research. Even 30 years ago, these words would have sounded puzzling to many scientists despite the fact that nanoparticles, primarily in the form of dust and smoke, have always existed in nature. Nanoparticles were utilized in construction materials, pigments, and stained glass well before their nature and properties were uncovered and understood.1 For more than a century, transition metal nanoparticles were widely used as heterogeneous catalysts and generated impressive revenues for petrochemical companies. Despite these all-pervading examples, nanoparticle chemistry did not evolve into a rigorous academic field until the end of the 20th century, when the availability of electron microscopy and other modern characterization techniques equipped researchers with tools suitable for analyzing nanometer sized objects. One can find many scattered examples of early nanoparticle research, but the field gained most of its momentum in the 1980s and 1990s, when the plasmonic and excitonic properties of metal and semiconductor nanoparticles attracted widespread attention, first from a fundamental point of view and then by prospects for new technologies. Since many fundamental studies and technological applications required nanoparticles with uniform sizes and shapes, the research community recognized the need for novel chemistries for nanoparticle synthesis, purification, and postsynthetic modifications. Nanoparticles can be synthesized using a variety of methods. They typically come as dispersions in various hosts, such as a glass or liquid solvent, but can also be synthesized in the gas phase to form an aerosol. It turned out that solution-phase syntheses are most convenient and versatile, and a majority of recent research has focused on making nanoparticles via colloidal techniques using polar and nonpolar solvents as the reaction medium. Mastering nanoparticle synthesis required a deep understanding of nucleation and growth processes that spurred active research in related areas of materials characterization and modeling. This work is far from complete, with many exciting discoveries yet to come. This thematic issue of Chemical Reviews updates readers on state-of-the-art developments in nanoparticle chemistry. Metal nanoparticles are arguably the most studied class of nanoparticle systems. Early works date back to the 19th century, including Michael Faraday’s synthesis of colloidal gold in the 1850s.2 Mie described the interaction of light with metal nanoparticles in 1908.3 There are examples of ancient Romans using gold nanoparticles to prepare stained glass.1 In recent years, nanoparticle plasmonics has advanced, enabling precise engineering of plasmonic properties using chemical synthesis. Many recent studies have focused on the catalytic properties of metal nanoparticles. Different crystal surfaces have different catalytic activities, and by using shape-controlled nanoparticle synthesis, it is possible to control the types of surface facets and thus engineer catalytic activity and selectivity. In this issue, Gilroy, Ruditskiy, Peng, Qin, and Xia discuss the synthesis, properties, and applications of bimetallic nanoparticles, which show high potential as heterogeneous catalysts that combine © 2016 American Chemical Society
Special Issue: Nanoparticle Chemistry Published: September 28, 2016 10343
DOI: 10.1021/acs.chemrev.6b00566 Chem. Rev. 2016, 116, 10343−10345
Chemical Reviews
Editorial
ordinary solids, nanoparticles can form various packings, from simple fcc to fascinatingly complex quasicrystalline lattices. Such self-assembled nanoparticle superlattices are often used as an active component of thin-film electronic and optoelectronic devices including light-emitting diodes, photodetectors, transistors, solar cells, and so forth. Boles, Engel, and Talapin review various aspects in nanocrystal self-assembly, including synthesis methodology, structural characterization, theoretical descriptions of interparticle interactions, thermodynamics and kinetics of the formation of nanocrystal superstructures, as well as collective properties of nanocrystal assemblies.21 After two decades of extensive research and development, nanoparticles have become practical and technologically important materials. Reaching this stage would not be possible without tremendous progress in nanoparticle chemistry. The community is developing rigorous methodologies to control size, shape, and surface structure for a large number of functional materials. These synthetic developments are complemented by work aimed at a deep understanding of fundamental electronic, magnetic, and other processes in nanoparticles. The commercial prospects for this class of materials look promising and bright. The global quantum dots market accrued a revenue of $316 million in 2013 and is expected to grow to about $5 billion by 2020.22 Quantum dots have applications in the display, solid-state lighting, solar, biomedical, anticounterfeiting, and sensor sectors. Lighting and displays each represent a potential $100 billion global market by 2020, resulting in significant opportunities for quantum dots. Oxide nanoparticles are widely used in cosmetics and sunscreens, while the market for gold nanoparticles is expected to exceed $8 billion by 2022, with major revenues generated in the electronics and medical diagnostics sectors.23 If these forecasts prove to be reasonably accurate, we will witness numerous exciting discoveries and developments in nanoparticle chemistry in the coming years. We would like to thank all the authors who made this thematic issue a great success, as well as the editorial staff of Chemical Reviews for their hard work in handling the manuscripts. It is our sincere hope that you will find this thematic issue interesting, useful, and inspiring.
and substitution reactions well-known in molecular chemistry, but applied to small crystalline particles. De Trizio and Manna offer a detailed discussion of one class of such transformations, namely cation exchange reactions, and demonstrate the utility of these reactions for synthesizing novel nanomaterials.13 In many cases, nanoparticle shape directly impacts its physical properties, such as the frequency of surface plasmon resonance in gold and silver nanoparticles, or luminescence polarization in semiconductor nanorods. Wang, Dong, and Buhro cover one-dimensional nanostructures represented by semiconductor nanorods and nanowires synthesized via a chemical process known as solution−liquid−solid synthesis,14 while Nasilowski, Mahler, Lhuillier, Ithurria, and Dubertret discuss the chemistry, physics, and applications of twodimensional nanomaterials, such as semiconductor disks and nanoplatelets.15 These materials show great promise as emitters for displays and optical gain media for lasers.16 Wang, Feng, Bai, Zhang, and Yin cover yet another very interesting family of hollow nanostructures.17 Hollow nanoparticles of plasmonic metals and nanoshells exhibit plasmon resonance in the near-IR spectral range, making them suitable for photothermal cancer therapy. Hollow nanostructures are also being explored for drug delivery. The above reviews cover nanomaterials synthesized and handled in the solution phase, which have seen the most advancements in recent years. However, solution-based synthetic techniques have some limitations, primarily associated with limited stability of reactants and solvents at the high temperatures required for some hard-to-crystallize nanomaterials. This fundamental problem can be addressed by moving away from solution chemistry and employing solid-state reactions or synthesizing nanoparticles in the gas phase. Kortshagen, Sankaran, Pereira, Girshick, Wu, and Aydil provide a comprehensive review of plasma-assisted synthesis of crystalline nanoparticles in the gas phase.18 The advances in nanoparticle chemistry are closely related to progress in the development of characterization techniques for both ex situ, in situ, and in vivo studies of nanoparticles. In addition to electron microscopy, X-ray scattering and scanning probe microscopy techniques have proven to be extremely valuable for characterizing nanomaterials in academic and industrial settings. Small-angle X-ray scattering (SAXS) is a powerful method used to obtain information about nanoparticle size, shape, and size distribution averaged over a large ensemble of nanoparticles. SAXS has been successfully implemented for in situ studies of nanoparticle synthesis in real time under realistic experimental conditions. Li, Senesi, and Lee offer the readers an authoritative review covering the fundamentals of SAXS and the applications of this technique for nanoparticle research.19 To the best of our knowledge, it is the first review on this topic, and many scientists will find it useful. Scanning tunneling microscopy (STM) is a unique technique that allows peeking inside individual nanoparticles to reveal the details of their electronic structure. Swart, Liljeroth, and Vanmaekelbergh review state-of-the-art techniques in STM and other scanning probe microscopy methods that are becoming popular tools in nanoparticle research. These methods provide valuable information complementary to that obtained from spectroscopic studies at the ensemble and singleparticle levels.20 Self-organization phenomena help assemble individual nanoparticles into macroscopic materials. Similar to the atoms in
Dmitri V. Talapin*
The University of Chicago Argonne National Laboratory
Elena V. Shevchenko
Argonne National Laboratory
AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected]. Notes
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS. 10344
DOI: 10.1021/acs.chemrev.6b00566 Chem. Rev. 2016, 116, 10343−10345
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Biographies
(4) Gilroy, K. D.; Ruditskiy, A.; Peng, H.-C.; Qin, D.; Xia, Y. Bimetallic Nanocrystals: Syntheses, Properties, and Applications. Chem. Rev. 2016, DOI: 10.1021/acs.chemrev.6b00211. (5) Wu, L.; Mendoza-Garcia, A.; Li, Q.; Sun, S. Organic Phase Syntheses of Magnetic Nanoparticles and Their Applications. Chem. Rev. 2016, DOI: 10.1021/acs.chemrev.5b00687. (6) Ekimov, A. I.; Efros, A. L.; Onushchenko, A. A. Quantum size effect in semiconductor microcrystals. Solid State Commun. 1985, 56 (11), 921−924. (7) Pietryga, J. M.; Park, Y.-S.; Lim, J.; Fidler, A. F.; Bae, W. K.; Brovelli, S.; Klimov, V. I. Spectroscopic and Device Aspects of Nanocrystal Quantum Dots. Chem. Rev. 2016, DOI: 10.1021/ acs.chemrev.6b00169. (8) Brus, L. Electronic wave functions in semiconductor clusters: experiment and theory. J. Phys. Chem. 1986, 90 (12), 2555−2560. (9) Talapin, D. V.; Steckel, J. Quantum dot light-emitting devices. MRS Bull. 2013, 38 (9), 685−695. (10) Jing, L.; Kershaw, S. V.; Li, Y.; Huang, X.; Li, Y.; Rogach, A. L.; Gao, M. Aqueous Based Semiconductor Nanocrystals. Chem. Rev. 2016, DOI: 10.1021/acs.chemrev.6b00041. (11) Reiss, P.; Carrière, M.; Lincheneau, C.; Vaure, L.; Tamang, S. Synthesis of Semiconductor Nanocrystals, Focusing on Nontoxic and Earth-Abundant Materials. Chem. Rev. 2016, DOI: 10.1021/acs.chemrev.6b00116. (12) Knowles, K. E.; Hartstein, K. H.; Kilburn, T. B.; Marchioro, A.; Nelson, H. D.; Whitham, P. J.; Gamelin, D. R. Luminescent Colloidal Semiconductor Nanocrystals Containing Copper: Synthesis, Photophysics, and Applications. Chem. Rev. 2016, DOI: 10.1021/acs.chemrev.6b00048. (13) De Trizio, L.; Manna, L. Forging Colloidal Nanostructures via Cation Exchange Reactions. Chem. Rev. 2016, DOI: 10.1021/ acs.chemrev.5b00739. (14) Wang, F.; Dong, A.; Buhro, W. E. Solution−Liquid−Solid Synthesis, Properties, and Applications of One-Dimensional Colloidal Semiconductor Nanorods and Nanowires. Chem. Rev. 2016, DOI: 10.1021/acs.chemrev.5b00701. (15) Nasilowski, M.; Mahler, B.; Lhuillier, E.; Ithurria, S.; Dubertret, B. Two-Dimensional Colloidal Nanocrystals. Chem. Rev. 2016, DOI: 10.1021/acs.chemrev.6b00164. (16) She, C.; Fedin, I.; Dolzhnikov, D. S.; Demortière, A.; Schaller, R. D.; Pelton, M.; Talapin, D. V. Low-Threshold Stimulated Emission Using Colloidal Quantum Wells. Nano Lett. 2014, 14 (5), 2772−2777. (17) Wang, X.; Feng, J.; Bai, Y.; Zhang, Q.; Yin, Y. Synthesis, Properties, and Applications of Hollow Micro-/Nanostructures. Chem. Rev. 2016, DOI: 10.1021/acs.chemrev.5b00731. (18) Kortshagen, U. R.; Sankaran, R. M.; Pereira, R. N.; Girshick, S. L.; Wu, J. J.; Aydil, E. S. Nonthermal Plasma Synthesis of Nanocrystals: Fundamental Principles, Materials, and Applications. Chem. Rev. 2016, DOI: 10.1021/acs.chemrev.6b00039. (19) Li, T.; Senesi, A. J.; Lee, B. Small Angle X-ray Scattering for Nanoparticle Research. Chem. Rev. 2016, DOI: 10.1021/acs.chemrev.5b00690. (20) Swart, I.; Liljeroth, P.; Vanmaekelbergh, D. Scanning probe microscopy and spectroscopy of colloidal semiconductor nanocrystals and assembled structures. Chem. Rev. 2016, DOI: 10.1021/acs.chemrev.5b00678. (21) Boles, M. A.; Engel, A.; Talapin, D. V. Self-Assembly of Colloidal Nanocrystals: From Intricate Structures to Functional Materials. Chem. Rev. 2016, DOI: 10.1021/acs.chemrev.6b00196. (22) Quantum Dot Market forecast, https://www. alliedmarketresearch.com/quantum-dots-market (accessed Aug-16, 2016). (23) Gold Nanoparticles Market, https://www.gminsights.com/ industry-analysis/gold-nanoparticles-market.
Dmitri Talapin is a professor in the Department of Chemistry and James Franck Institute at the University of Chicago and a scientist at the Center for Nanoscale Materials at Argonne National Laboratory. He received his doctorate degree from Hamburg University in Germany under the supervision of Horst Weller. He was a postdoctoral fellow at IBM T.J. Watson Research Center from 2003 to 2005 and a staff scientist at the Molecular Foundry at Lawrence Berkeley National Laboratory from 2005 to 2007. He joined the University of Chicago faculty in 2007. His current research interests include synthesis of inorganic nanostructures and their applications for electronic and optoelectronic devices. (Group website: https:// talapinlab.uchicago.edu/)
Elena Shevchenko is a scientist at the Center for Nanoscale Materials at Argonne National Laboratory. She received her first degree in chemistry at the Belorussian State University and her Ph.D. from the University of Hamburg in 2003 with Horst Weller. From 2003 to 2005 she was a joint postdoctoral fellow at Columbia University and IBM T.J. Watson Research Center. In 2005, she moved to the Molecular Foundry at Lawrence Berkeley National Laboratory as a staff scientist. Her research interests include synthesis of nanoscale materials with controllable size and shape, design of multifunctional materials through self-assembly of nanoparticles, and study of the collective properties of such materials.
REFERENCES (1) Heiligtag, F. J.; Niederberger, M. The fascinating world of nanoparticle research. Mater. Today 2013, 16 (7−8), 262−271. (2) Faraday, M. The Bakerian Lecture: Experimental Relations of Gold (and Other Metals) to Light. Philosophical Transactions of the Royal Society of London 1857, 147, 145−181. (3) Mie, G. Beiträge zur Optik trüber Medien, speziell kolloidaler Metallösungen. Ann. Phys. 1908, 330 (3), 377−445. 10345
DOI: 10.1021/acs.chemrev.6b00566 Chem. Rev. 2016, 116, 10343−10345
