In this Progress Report, we update covalent chemical strategies commonly used for the focused functionalization of single‐walled carbon nanotube (SWNT) surfaces. In recent years, SWNTs have been ...treated as legitimate nanoscale chemical reagents. Hence, herein we seek to understand, from a structural and mechanistic perspective, the breadth and types of controlled covalent reactions SWNTs can undergo in solution phase, not only at ends and defect sites but also along sidewalls. We explore advances in the formation of nanotube derivatives that essentially maintain and even enhance their performance metrics after precise chemical modification. We especially highlight molecular insights (and corresponding correlation with properties) into the binding of functional moieties onto carbon nanotube surfaces. Controllable chemical functionalization suggests that the unique optical, electronic, and mechanical properties of SWNTs can be much more readily tuned than ever before, with key implications for the generation of truly functional nanoscale working devices.
Rational covalent functionalization of single‐walled carbon nanotube (SWNT) surfaces can be used to carefully manipulate properties of SWNTs and enhance their performance in a wide range of diverse applications. In this review, we update on a number of diverse chemical strategies for productively functionalizing SWNTs at their ends, defect sites, and sidewalls. Potential applications in the fields of polymer composites and biological devices are also discussed.
As-prepared, single-crystalline bismuth ferrite nanoparticles show strong size-dependent magnetic properties that correlate with: (a) increased suppression of the known spiral spin structure (period ...length of ∼62 nm) with decreasing nanoparticle size and (b) uncompensated spins and strain anisotropies at the surface. Zero-field-cooled and field-cooled magnetization curves exhibit spin-glass freezing behavior due to a complex interplay between finite size effects, interparticle interactions, and a random distribution of anisotropy axes in our nanoparticle assemblies.
A simple and effective template-mediated protocol has been developed for the large-scale, room-temperature preparation of high-aspect-ratio, single-crystalline Tb-doped CePO4 nanowires, measuring ∼12 ...nm in diameter and over 10 μm in length. Moreover, we also isolated sheaf-like bundles of nanostructures. The synthesis mechanism likely involved a crystal splitting step. The resulting nanowires demonstrated an intense redox-sensitive green photoluminescence, which was exploited, in addition to their inherently high biocompatibility and low toxicity, for potential applications in biological imaging and labeling of cells.
Environmentally friendly synthetic methodologies have gradually been implemented as viable techniques in the synthesis of a range of nanostructures. In this work, we focus on the application of ...green‐chemistry principles to the synthesis of complex metal oxide and fluoride nanostructures. In particular, we describe advances in the use of the molten‐salt synthetic methods, hydrothermal protocols, and template‐directed techniques as environmentally sound, socially responsible, and cost‐effective methodologies that allow us to generate nanomaterials without the need to sacrifice sample quality, purity, and crystallinity, while allowing control over size, shape, and morphology.
What's small and green? The answer to this question is discussed in this Review, which highlights some of the techniques currently being used in groups worldwide to prepare novel and useful nanoscale materials in an environmentally friendly manner. Molten‐salt processes (used to prepare the orthorhombic Bi2Fe4O9 structures shown), hydrothermal syntheses, and templating techniques are but some of the methods designed to utilize safer precursors, produce less‐harmful byproducts, and generate less waste.
A size- and shape-dependent morphological transformation was demonstrated during the hydrothermal soft chemical transformation, in neutral solution, of titanate nanostructures into their anatase ...titania counterparts. Specifically, lepidocrocite hydrogen titanate nanotubes with diameters of ∼10 nm were transformed into anatase nanoparticles with an average size of 12 nm. Lepidocrocite hydrogen titanate nanowires with relatively small diameters (average diameter range of ≤ 200 nm) were converted into single-crystalline anatase nanowires with relatively smooth surfaces. Larger diameter (>200 nm) titanate wires were transformed into analogous anatase submicron wire motifs, resembling clusters of adjoining anatase nanocrystals with perfectly parallel, oriented fringes. Our results indicate that as-synthesized TiO2 nanostructures possessed higher photocatalytic activity than the commercial titania precursors from whence they were derived.
With the increased interest in the development of hydrogen fuel cells as a plausible alternative to internal combustion engines, recent work has focused on creating alkaline fuel cells (AFC), which ...employ an alkaline environment. Working in alkaline as opposed to acidic media yields a number of tangible benefits, including (i) the ability to use cheaper and plentiful precious-metal-free catalysts, due to their increased stability, (ii) a reduction in the amount of degradation and corrosion of Pt-based catalysts, and (iii) a longer operational lifetime for the overall fuel cell configuration. However, in the absence of Pt, no catalyst has achieved activities similar to those of Pt. Herein, we have synthesized a number of crystalline ultrathin PtM alloy nanowires (NWs) (M = Fe, Co, Ru, Cu, Au) in order to replace a portion of the costly Pt metal without compromising on activity while simultaneously adding in metals known to exhibit favorable synergistic ligand and strain effects with respect to the host lattice. In fact, our experiments confirm theoretical insights about a clear and correlative dependence between measured activity and chemical composition. We have conclusively demonstrated that our as-synthesized alloy NW catalysts yield improved hydrogen oxidation reaction (HOR) activities as compared with a commercial Pt standard as well as with our as-synthesized Pt NWs. The Pt7Ru3 NW system, in particular, quantitatively achieved an exchange current density of 0.493 mA/cm2, which is higher than the corresponding data for Pt NWs alone. Additionally, the HOR activities follow the same expected trend as their calculated hydrogen binding energy (HBE) values, thereby confirming the critical importance and correlation of HBE with the observed activities.
We describe the preparation and characterization of (a) discrete, individual motifs and (b) arrays of crystalline and pure semiconducting transition metal sulfide (CuS, PbS, and CdS) nanowires, ...synthesized via an inexpensive, generalizable, simplistic, and ambient modified template-directed technique. We have demonstrated control over the diameters and lengths of our one-dimensional (1-D) nanostructures through corresponding variations in the template membrane’s pore size and thickness. We have not only successfully generated cubic-phase 1-D CdS nanowires but also produced, at slightly elevated temperatures, unusual CdS cactus-like, hierarchical nanostructures, consisting of tiny nanoneedles projecting out from the outer surfaces of parent CdS nanotube motifs. Opto-vibrational properties of all of these metal sulfide nanomaterials have been extensively studied. In addition, our results indicate that our as-prepared hexagonal-phase CdS cactus-like nanotubes evinced a higher photocatalytic degradation activity than that of both cubic CdS nanowires and their commercial bulk counterparts.
We report on the synthesis, characterization, and electrocatalytic performance of ultrathin Pt nanowires with a diameter of less than 2 nm. An acid-wash protocol was employed in order to yield highly ...exfoliated, crystalline nanowires with a diameter of 1.3 ± 0.4 nm. The electrocatalytic activity of these nanowires toward the oxygen reduction reaction was studied in relation to the activity of both supported and unsupported Pt nanoparticles as well as with previously synthesized Pt nanotubes. Our ultrathin, acid-treated, unsupported nanowires displayed an electrochemical surface area activity of 1.45 mA/cm2, which was nearly 4 times greater than that of analogous, unsupported platinum nanotubes and 7 times greater than that of commercial supported platinum nanoparticles.
We report on the synthesis, characterization, and electrochemical performance of novel, ultrathin Pt monolayer shell–Pd nanowire core catalysts. Initially, ultrathin Pd nanowires with diameters of ...2.0 ± 0.5 nm were generated, and a method has been developed to achieve highly uniform distributions of these catalysts onto the Vulcan XC-72 carbon support. As-prepared wires are activated by the use of two distinctive treatment protocols followed by selective CO adsorption in order to selectively remove undesirable organic residues. Subsequently, the desired nanowire core–Pt monolayer shell motif was reliably achieved by Cu underpotential deposition followed by galvanic displacement of the Cu adatoms. The surface area and mass activity of the acid and ozone-treated nanowires were assessed, and the ozone-treated nanowires were found to maintain outstanding area and mass specific activities of 0.77 mA/cm2 and 1.83 A/mgPt, respectively, which were significantly enhanced as compared with conventional commercial Pt nanoparticles, core–shell nanoparticles, and acid-treated nanowires. The ozone-treated nanowires also maintained excellent electrochemical durability under accelerated half-cell testing, and it was found that the area-specific activity increased by ∼1.5 fold after a simulated catalyst lifetime.
An ambient, surfactant-based synthetic means was used to prepare ultrathin binary (d ∼ 2 nm) Pd–Ni nanowires, which were subsequently purified using a novel butylamine-based surfactant-exchange ...process coupled with an electrochemical CO adsorption and stripping treatment to expose active surface sites. We were able to systematically vary the chemical composition of as-prepared Pd–Ni nanowires from pure elemental Pd to Pd0.50Ni0.50 (atomic ratio), as verified using EDS analysis. The overall morphology of samples possessing >60 atom % Pd consisted of individual, discrete one-dimensional nanowires. The electrocatalytic performances of elemental Pd, Pd0.90Ni0.10, Pd0.83Ni0.17, and Pd0.75Ni0.25 nanowires in particular were examined. Our results highlight a “volcano”-type relationship between chemical composition and corresponding ORR activities with Pd0.90Ni0.10, yielding the highest activity (i.e., 1.96 mA/cm2 at 0.8 V) among all nanowires tested. Moreover, the Pd0.90Ni0.10 sample exhibited outstanding methanol tolerance ability. In essence, there was only a relatively minimal 15% loss in the specific activity in the presence of 4 mM methanol, which was significantly better than analogous data on Pt nanoparticles and Pt nanowires. In addition, we also studied ultrathin, core–shell Pt∼Pd0.90Ni0.10 nanowires, which exhibited a specific activity of 0.62 mA/cm2 and a corresponding mass activity of 1.44 A/mgPt at 0.9 V. Moreover, our as-prepared core–shell electrocatalysts maintained excellent electrochemical durability. We postulate that one-dimensional Pd–Ni nanostructures represent a particularly promising platform for designing ORR catalysts with high performance.
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