Whereas the chemistry of fullerenes is well‐established, the chemistry of single‐walled carbon nanotubes (SWNTs) is a relatively unexplored field of research. Investigations into the bonding of ...moieties onto SWNTs are important because they provide fundamental structural insight into how nanoscale interactions occur. Hence, understanding SWNT chemistry becomes critical to rational, predictive manipulation of their properties. Among the strategies discussed include molecular metal complexation with SWNTs to control site‐selective chemistry in these systems. In particular, work has been performed with Vaska's and Wilkinson's complexes to create functionalized adducts. Functionalization should offer a relatively simple means of tube solubilization and bundle exfoliation, and also allows for tubes to be utilized as recoverable catalyst supports. Solubilization of oxidized SWNTs has also been achieved through derivatization by using a functionalized organic crown ether. The resultant adduct yielded concentrations of dissolved nanotubes on the order of 1 g L−1 in water and at elevated concentrations in a range of organic solvents, traditionally poor for SWNT manipulation. To further demonstrate chemical processability of SWNTs, we have subjected them to ozonolysis, followed by treatment with various independent reagents, to rationally generate a higher proportion of oxygenated functional groups on the nanotube surface. This protocol has been found to purify nanotubes. More importantly, the reaction sequence has been found to ozonize the sidewalls of these nanotubes. Finally, SWNTs have also been chemically modified with quantum dots and oxide nanocrystals. A composite heterostructure consisting of nanotubes joined to nanocrystals offers a unique opportunity to obtain desired physical, electronic, and chemical properties by adjusting synthetic conditions to tailor the size and structure of the individual sub‐components, with implications for self‐assembly.
A variety of molecular organic and inorganic‐inspired methodologies can be used to chemically functionalize carbon nanotubes. These include metal coordination and solution‐phase ozonolysis, as well as the formation of nanotube–nanocrystal heterostructures. The figure illustrates an optimized geometry for crown ether functionalized (5,5) single‐walled carbon nanotubes.
Single-crystalline perovskite BaZrO3 submicrometer-sized particles were synthesized using a simple, scaleable molten salt method. In this paper, in addition to a time-dependent particle evolution ...study, we explored primarily the effects of different experimental processing parameters, such as the identity of the salt, annealing temperatures, overall reaction times, cooling rates, and the chemical nature of the precursor in determining their impact upon the purity, size, shape, and morphology of the as-obtained products. We also discuss the role of additional experimentally controllable factors such as the heating rate applied, the amount of salt used, the molar ratios of precursors involved, and the use of surfactant. By a judicious choice of experimental parameters and conditions, we describe herein a rational means of producing pure products with a reproducible composition and morphology.
Nanoscale structures, such as nanoparticles, nanorods, nanowires, nanocubes, and nanotubes, have attracted extensive synthetic attention as a result of their novel size-dependent properties. Ideally, ...the net result of nanoscale synthesis is the production of structures that achieve monodispersity, stability, and crystallinity with a predictable morphology. Many of the synthetic methods used to attain these goals have been based on principles derived from semiconductor technology, solid state chemistry, and molecular inorganic cluster chemistry. We describe a number of advances that have been made in the reproducible synthesis of various ternary oxide nanomaterials, including alkaline earth metal titanates, alkali metal titanates, bismuth ferrites, ABO(4)-type oxides, as well as miscellaneous classes of ternary metal oxides.
In this work, we have put forth a facile hydrothermal approach to synthesize an array of one-dimensional (1D) Mn-doped Zn2SiO4 nanostructures. Specifically, we have probed and correlated the effects ...of controllable reaction parameters such as the pH and Mn dopant concentrations with the resulting crystal structures and morphologies of the products obtained. Based upon our results, we find that careful tuning of the pH versus the Mn dopant level gives rise to opposite trends with respect to the overall size of the resulting one-dimensional nanostructures. Significantly, we have highlighted the role of the Mn dopant ion concentration as a potentially generalizable reaction parameter in solution-based synthesis for controlling morphology and hence, the observed optical behavior. Indeed, such a strategy can be potentially generalized to systems such as but not limited to Mn-doped ZnS, CdS, and CdSe quantum dots (QD), which, to the best of our knowledge, denote promising candidates for a variety of optoelectronic applications. Specifically, we have carefully optimized the synthesis conditions in order to generate a series of chemically well-defined Mn-doped Zn2SiO4 not only possessing Mn concentrations ranging from 3% to 8% but also characterized by highly crystalline, monodisperse wire-like motifs measuring ∼30 nm in diameter and ∼700 nm in length. Optically, the photoluminescence signals associated with the 1D series yielded a volcano-shaped relationship between PL intensities and the Mn dopant level. In additional experiments, we have immobilized CdSe quantum dots (QDs) onto the external surfaces of our as-synthesized Mn-doped Zn2SiO4 nanowires, in order to form novel composite heterostructures. The optical properties of the CdSe QD-Mn:Zn2SiO4 heterostructures have been subsequently examined. Our results have demonstrated the likely co-existence of both energy transfer and charge transfer phenomena between the two constituent components of our as-prepared composites. Specifically, when both components are photoexcited, both energy transfer and charge transfer were found to plausibly occur, albeit in opposite directions. When the CdSe QDs are excited alone for example, charge transfer probably takes place from the CdSe QDs to the dopant Mn2+ ions. We believe that our as-processed heterostructures are therefore promising as a tunable light-harvesting motif. Essentially, these materials have broadened the effective light absorption range for optical 'accessibility', not only through their incorporation of dopant-tunable Zn2SiO4 possessing complementary absorption properties to those of the QDs but also through their integration of CdSe QDs with size-tailorable optical behavior.
Solution‐based, anionic doping represents a convenient strategy with which to improve upon the conductivity of candidate anode materials such as Li4Ti5O12 (LTO). As such, novel synthetic ...hydrothermally‐inspired protocols have primarily been devised herein, aimed at the large‐scale production of unique halogen‐doped, micron‐scale, three‐dimensional, hierarchical LTO flower‐like motifs. Although fluorine (F) doping has been explored, the use of chlorine (Cl) dopants is the primary focus here. Several experimental variables, such as dopant amount, lithium hydroxide concentration, and titanium butoxide purity, were probed and perfected. Furthermore, the Cl doping process did not damage the intrinsic LTO morphology. The analysis, based on interpreting a compilation of SEM, XRD, XPS, and TEM‐EDS results, was used to determine an optimized dopant concentration of Cl. Electrochemical tests demonstrated an increased capacity via cycling of 12 % for a Cl‐doped sample as compared with pristine LTO. Moreover, the Cl‐doped LTO sample described in this study exhibited the highest discharge capacity yet reported at an observed rate of 2C for this material at 143mAh g−1. Overall, these data suggest that the Cl dopant likely enhances not only the ion transport capabilities, but also the overall electrical conductivity of our as‐prepared structures. To help explain these favorable findings, theoretical DFT calculations were used to postulate that the electronic conductivity and Li diffusion were likely improved by the presence of increased Ti3+ ion concentration coupled with widening of the Li migration channel.
Flower power: Solution‐based, anionic doping represents a convenient strategy with which to improve upon the conductivity of candidate anode materials such as Li4Ti5O12. Here, Cl doping was optimized and fully characterized, with the resulting materials tested for application in lithium ion batteries.
Fuel cells (FCs) convert chemical energy into electricity through electrochemical reactions. They maintain desirable functional advantages that render them as attractive candidates for renewable ...energy alternatives. However, the high cost and general scarcity of conventional FC catalysts largely limit the ubiquitous application of this device configuration. For example, under current consumption requirements, there is an insufficient global reserve of Pt to provide for the needs of an effective FC for every car produced. Therefore, it is absolutely necessary in the future to replace Pt either completely or in part with far more plentiful, abundant, cheaper, and potentially less toxic first row transition metals, because the high cost-to-benefit ratio of conventional catalysts is and will continue to be a major limiting factor preventing mass commercialization. We and other groups have explored a number of nanowire-based catalytic architectures, which are either Pt-free or with reduced Pt content, as an energy efficient solution with improved performance metrics versus conventional, currently commercially available Pt nanoparticles that are already well established in the community. Specifically, in this Perspective, we highlight strategies aimed at the rational modification of not only the physical structure but also the chemical composition as a means of developing superior electrocatalysts for a number of small-molecule-based anodic oxidation and cathodic reduction reactions, which underlie the overall FC behavior. In particular, we focus on efforts to precisely, synergistically, and simultaneously tune not only the size, morphology, architectural motif, surface chemistry, and chemical composition of the as-generated catalysts but also the nature of the underlying support so as to controllably improve performance metrics of the hydrogen oxidation reaction, the methanol oxidation reaction, the ethanol oxidation reaction, and the formic acid oxidation reaction, in addition to the oxygen reduction reaction.
The rational synthesis of Cu@TiO2 core@shell nanowire (NW) structures was thoroughly explored using a microwave-assisted method through the tuning of experimental parameters such as but not limited ...to (i) controlled variation in molar ratios, (ii) the effect of discrete Ti precursors, (iii) the method of addition of the precursors themselves, and (iv) time of irradiation. Uniform coatings were obtained using Cu/Ti molar ratios of 1:2, 1:1, 2:1, and 4:1, respectively. It should be noted that although relative molar precursor concentrations primarily determined the magnitude of the resulting shell size, the dependence was nonlinear. Moreover, additionally important reaction parameters, such as precursor identity, the means of addition of precursors, and the reaction time, were individually explored with the objective of creating a series of optimized reaction conditions. As compared with Cu NWs alone, it is evident that both of the Cu@TiO2 core–shell NW samples, regardless of pretreatment conditions, evinced much better catalytic performance, up to as much as 20 times greater activity as compared with standard Cu NWs. These results imply the significance of the Cu/TiO2 interface in terms of promoting CO2 hydrogenation, because TiO2 alone is known to be inert for this reaction. Furthermore, it is additionally notable that the N2 annealing pretreatment is crucial in terms of preserving the overall Cu@TiO2 core@shell structure. We also systematically analyzed and tracked the structural and chemical evolution of our catalysts before and after the CO2 reduction experiments. Indeed, we discovered that the core@shell wire motif was essentially maintained and conserved after this high-temperature reaction process, thereby accentuating the thermal stability and physical robustness of our as-prepared hierarchical motifs.
A number of complementary, synergistic advances are reported herein. First, we describe the 'first-time' synthesis of ultrathin Ru
2
Co
1
nanowires (NWs) possessing average diameters of 2.3 ± 0.5 nm ...using a modified surfactant-mediated protocol. Second, we utilize a combination of quantitative EDS, EDS mapping (along with accompanying line-scan profiles), and EXAFS spectroscopy results to probe the local atomic structure of not only novel Ru
2
Co
1
NWs but also 'control' samples of analogous ultrathin Ru
1
Pt
1
, Au
1
Ag
1
, Pd
1
Pt
1
, and Pd
1
Pt
9
NWs. We demonstrate that ultrathin NWs possess an atomic-level geometry that is fundamentally dependent upon their intrinsic chemical composition. In the case of the PdPt NW series, EDS mapping data are consistent with the formation of a homogeneous alloy, a finding further corroborated by EXAFS analysis. By contrast, EXAFS analysis results for both Ru
1
Pt
1
and Ru
2
Co
1
imply the generation of homophilic structures in which there is a strong tendency for the clustering of 'like' atoms; associated EDS results for Ru
1
Pt
1
convey the same conclusion, namely the production of a heterogeneous structure. Conversely, EDS mapping data for Ru
2
Co
1
suggests a uniform distribution of both elements. In the singular case of Au
1
Ag
1
, EDS mapping results are suggestive of a homogeneous alloy, whereas EXAFS analysis pointed to Ag segregation at the surface and an Au-rich core, within the context of a core-shell structure. These cumulative outcomes indicate that only a combined consideration of both EDS and EXAFS results can provide for an accurate representation of the local atomic structure of ultrathin NW motifs.
EDS and EXAFS spectroscopy are used as complementary techniques to investigate the local structure of bimetallic ultrathin nanowires. Results highlight the importance of using a combined approach to achieve an accurate understanding of these systems.
We have demonstrated near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy as a particularly useful and effective technique for simultaneously probing the surface chemistry, surface ...molecular orientation, degree of order, and electronic structure of carbon nanotubes and related nanomaterials. Specifically, we employ NEXAFS in the study of single‐walled carbon nanotube and multi‐walled carbon nanotube powders, films, and arrays, as well as of boron nitride nanotubes. We have focused on the advantages of NEXAFS as an exciting, complementary tool to conventional microscopy and spectroscopy for providing chemical and structural information about nanoscale samples.
The future utility of nanoscale materials depends much on finding methods that allow the intrinsic properties of such materials to be carefully and accurately determined. NEXAFS spectroscopy will likely become a useful tool to the nanoscientist, since a variety of chemical and structural information can be obtained on nanoscale samples, such as buckypapers fashioned from single‐walled carbon nanotubes (see picture).
We have synthesized several morphologies and crystal structures of MgWO
using a one-pot hydrothermal method, producing not only monoclinic stars and large nanoparticles but also triclinic wool balls ...and sub-10 nm nanoparticles. Herein we describe the importance of reaction parameters in demonstrating morphology control of as-prepared MgWO
. Moreover, we correlate structure and composition with the resulting photoluminescence and radioluminescence properties. Specifically, triclinic-phase samples yielded a photoluminescence emission of 421 nm, whereas monoclinic-phase materials gave rise to an emission maximum of 515 nm. The corresponding radioluminescence data were characterized by a broad emission peak, located at 500 nm for all samples. Annealing the wool balls and sub-10 nm particles to transform the crystal structure from a triclinic to a monoclinic phase yielded a radioluminescence (RL) emission signal that was two orders of magnitude greater than that of their unannealed counterparts. Finally, to confirm the practical utility of these materials for biomedical applications, a series of sub-10 nm particles, including as-prepared and annealed samples, were functionalized with biocompatible PEG molecules, and subsequently were found to be readily taken up by various cell lines as well as primary cultured hippocampal neurons with low levels of toxicity, thereby highlighting for the first time the potential of this particular class of metal oxides as viable and readily generated platforms for a range of biomedical applications.
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