Intermediate Nanostructures Research Articles

Evidence and importance of intermediate nanostructures in the journey from molecular precursors to allophane and imogolite nanocrystals

Nanoparticles often-called proto-imogolites have been identified as an intermediate in the formation process of imogolite nanotubes as early as 1979. Their composition and structure are now well documented in the case of synthetic imogolite. One specific characteristic of proto-imogolite is that they have a curved shape with a local structure close to the one of imogolite. During a growth stage, they evolve toward nanocrystals (allophane, imogolite). Their thorough characterization has so far been difficult. Using synchrotron Small Angle X-ray Scattering coupled with Raman spectroscopy, we observe that proto-imogolites form during the initial stage of the co-precipitation of aluminum and silicon molecular precursors thanks to a reorganization process. The shape of the initial proto-imogolites, before the growth stage, depends on the synthesis conditions and controls the characteristics of the final product. We show using cryo-TEM images that, at the end of the growth stage, non-tubular nanostructures continue to coexist with nanotubes. Protocols to quantify remaining non-tubular nano-objects and purify the samples are discussed.

Beyond the standard model of solubilization: Non-ionic surfactants induce collapse of lipid vesicles into rippled bilamellar nanodiscs

HypothesisAlthough solubilization of lipid membranes has been studied extensively, questions remain regarding the structural pathways and metastable structures involved. This study investigated whether the non-ionic detergent Triton X-100 follows the classical solubilization pathway or if intermediate nanostructures are formed. ExperimentsSmall angle X-ray and neutron scattering (SAXS/SANS) was used in combination with transmission electron cryo-microscopy and cryo-tomography to deduce the structure of mixtures of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) vesicles and Triton X-100. Time-resolved SAXS and dynamic light scattering were used to investigate the kinetics of the process. FindingsUpon addition of moderate detergent amounts at low temperatures, the lipid vesicles implode into ordered rippled bilamellar disc structures. The bilayers arrange in a ripple phase to accommodate packing constraints caused by inserted TX-100 molecules. The collapse is suggested to occur through a combination of water structure destabilization by detergents flipping across the membrane and osmotic pressure causing interbilayer attraction internally. The subsequently induced ripples then stabilize the aggregates and prevent solubilization, supported by the observation that negatively charged vesicles undergo a different pathway upon TX-100 addition, forming large bicelles. The findings demonstrate the richness in assembly pathways of simple lipids and detergents and stimulate considerations for the use of certain detergents in membrane solubilization.

Interspecific hybridization explains rapid gorget colour divergence in Heliodoxa hummingbirds (Aves: Trochilidae).

Hybridization is a known source of morphological, functional and communicative signal novelty in many organisms. Although diverse mechanisms of established novel ornamentation have been identified in natural populations, we lack an understanding of hybridization effects across levels of biological scales and upon phylogenies. Hummingbirds display diverse structural colours resulting from coherent light scattering by feather nanostructures. Given the complex relationship between feather nanostructures and the colours they produce, intermediate coloration does not necessarily imply intermediate nanostructures. Here, we characterize nanostructural, ecological and genetic inputs in a distinctive Heliodoxa hummingbird from the foothills of eastern Peru. Genetically, this individual is closely allied with Heliodoxa branickii and Heliodoxa gularis, but it is not identical to either when nuclear data are assessed. Elevated interspecific heterozygosity further suggests it is a hybrid backcross to H. branickii. Electron microscopy and spectrophotometry of this unique individual reveal key nanostructural differences underlying its distinct gorget colour, confirmed by optical modelling. Phylogenetic comparative analysis suggests that the observed gorget coloration divergence from both parentals to this individual would take 6.6-10 My to evolve at the current rate within a single hummingbird lineage. These results emphasize the mosaic nature of hybridization and suggest that hybridization may contribute to the structural colour diversity found across hummingbirds.

Self-Confined Nucleation of Iron Oxide Nanoparticles in a Nanostructured Amorphous Precursor.

Crystallization from solution is commonly described by classical nucleation theory, although this ignores that crystals often form via disordered nanostructures. As an alternative, the classical theory remains widely used in a "multistep" variant, where the intermediate nanostructures merely introduce additional thermodynamic parameters. However, this variant still requires validation by experiments addressing indeed proper time and spatial scales (millisecond, nanometer). Here, we used in situ X-ray scattering to determine the mechanism of magnetite crystallization and, in particular, how nucleation propagates at the nanometer scale within amorphous precursors. We find that the self-confinement by an amorphous precursor slows down crystal growth by 2 orders of magnitude once the crystal size reaches the amorphous particle size (∼3 nm). Thus, not only the thermodynamic properties of transient amorphous nanostructures but also their spatial distribution determine crystal nucleation.

A molecular dynamics study of the thermal transport in silicon/germanium nanostructures: From cross-plane to in-plane

Thermal transport in silicon/germanium (Si/Ge) nanostructures has been widely studied in both the cross-plane and in-plane configurations. It remains unknown, however, how heat transports in the intermediate configurations. Here we conduct nonequilibrium molecular dynamics simulations to study the thermal conductance of Si/Ge nanostructures that gradually change from a cross-plane to an in-plane configuration. The thermal conductances of the cross-plane and in-plane Si/Ge nanostructures are found to be (1.57 ± 0.01) × 108 and (1.60 ± 0.02) × 108 W/m2-K respectively at 300 K, both smaller than those of the intermediate nanostructures at the same temperature. As temperature increases, the thermal conductances of the nanostructures decrease, with those of the intermediate nanostructures exhibiting a stronger temperature dependence. The thermal conductances are inconsistent with the trend of the overlap of the vibrational density of states (VDOS) but agree well with the trend of the integrated VDOS in the middle region of the nanostructures.

Transition mechanisms of three-dimensional nanostructures formed from geometrically constraining (AB)f star block copolymers

The self-assembly behavior of (AB)f star copolymers under a cylindrical confinement has been investigated using self-consistent field theory. Aiming to study the influence of the pore diameter on the order-order transitions as volume fraction varies, the phase diagram with respect to the volume fraction and the pore size is constructed. An interesting transition sequence of ordered nanostructures, H2A→P2A→L2A→ P3CB→H3CB, is predicted, which is corresponding to the phase transition of C→ G→L→G→C in bulk. Notably, this transition sequence is universal for both linear (AB diblock and BAB triblock) and star-like (AB)f block copolymer. In particular, we explore the formation mechanism of helical nanostructures as the volume fraction increases, where the P phase plays an important role in forming helical structures as an intermediate nanostructure. Finally, we construct the two-dimensional phase diagram, including pore size and volume fraction, of (AB)f star-like block under confinement at different number of arms, where P nanostructures was found to surrounded by other nanophases suggesting the importance of P nanostructure in the transition sequence.

Stability and Reactivity: Positive and Negative Aspects for Nanoparticle Processing.

Nanoparticles exist far from the equilibrium state due to their high surface energy. Nanoparticles are therefore extremely unstable and easily change themselves or react with active substances to reach a relatively stable state in some cases. This causes desired changes or undesired changes to nanoparticles and thus makes them exhibit a high reactivity and a poor stability. Such dual nature (poor stability and high reactivity) of nanoparticles may result in both negative and positive effects for nanoparticle processing. However, the existing studies mainly focus on the high reactivity of nanoparticles, whereas their poor stability has been neglected or considered inconsequential. In fact, in some cases the unstable process, which is derived from the poor stability of nanoparticles, offers an opportunity to design and fabricate unique nanomaterials, such as by chemically transforming the "captured" intermediate nanostructures during a changing process, assembling destabilized nanoparticles into larger ordered assemblies, or shrinking/processing pristine materials into the desired size or shape via selective etching. In this review, we aim to present the stability and reactivity of nanoparticles on three levels: the foundation, concrete manifestations, and applications. We start with a brief introduction of dangling bonds and the surface chemistry of nanoparticles. Then, concrete manifestations of the poor stability and high reactivity of nanoparticles are presented from four perspectives: dispersion stability, thermal stability, structural stability, and chemical stability/reactivity. Next, we discuss some issues regarding the stability and reactivity of nanomaterials during applications. Finally, conclusions and perspectives on this field are presented.

Defect-enhanced performance of a 3D graphene anode in a lithium-ion battery

Morphological defects were generated in an undoped 3D graphene structure via the involvement of a ZnO and Mg(OH)2 intermediate nanostructure layer placed between two layers of vapor-deposited graphene. Once the intermediate layer was etched, the 3D graphene lost support and shrank; during this process many morphological defects were formed. The electrochemical performance of the derived defective graphene utilized as the anode of a lithium (Li)-ion battery was significantly improved from ∼382 mAh g−1 to ∼2204 mAh g−1 at 0.5 A g−1 compared to normal 3D graphene. The derived defective graphene exhibited an initial capacity of 1009 mAh g−1 and retention of 83% at 4 A g−1 for 500 cycles, and ∼330 mAh g−1 at a high rate of 20 A g−1. Complicated defects such as wrinkles, pores, and particles formed during the etching of the intermediate layer, were considered to contribute to the improvement of the electrochemical performance.

Domain Structures of Ni and NiFe (Oxy)Hydroxide Oxygen-Evolution Catalysts from X-ray Pair Distribution Function Analysis

Ni–Fe (oxy)hydroxides, Ni(1–z)FezOxHy, are among the fastest-known water oxidation catalysts in alkaline media on a per-cation basis. At current densities relevant for electrolysis (e.g., >0.5 A/cm–2), mass and electron transport through catalyst films with high mass loading are critical and depend substantially on the extended and intermediate catalyst architecture. Here we use X-ray pair distribution function (PDF) analysis to determine the intermediate nanostructures of electrodeposited Ni(1–z)FezOxHy films. We report the effects of electrodeposition technique (pulsed versus continuous), electrochemical cycling, and Fe content on the structure of the catalyst film. The PDF patterns for Ni(1–z)FezOxHy films are best simulated by model structures consisting of brucite-like β-Ni(OH)2 fragments 1 to 3 layers in thickness. Only the oxidation state of the film significantly affects the intralayer scattering behavior (i.e., metal–oxygen bond distance). The interlayer interactions, however, are affected by Fe ...

(Invited) Porous Hollow PtNi/C Nanoparticles and Their Many Facets

Porous hollow PtM/C electrocatalysts (where M is a 3d transition metal element) have proven to enhance remarkably the oxygen reduction reaction (ORR) kinetics in proton exchange membrane fuel cells. However, their mechanism of formation, the nature of adequate alloying elements and carbon supports as well as the rationale for their interesting electrocatalytic properties remain open questions. Herein, we describe the mechanism of formation and growth of porous hollow PtNi/C NPs using operando wide angle X-ray scattering, scanning transmission electron microscopy and X-ray energy dispersive spectroscopy 1. The results show that Ni-rich NPs covered by a NixByOz shell form first before acting as a sacrificial template for the deposition of Pt2+ ions via galvanic replacement (Figure 1). Finally, the solid Ni-rich core@Pt-rich shell NPs are transformed into alloy hollow PtNi/C NPs via the nanoscale Kirkendall effect (a vacancy mediated interdiffusion mechanism). Density Functional Theory (DFT) calculations were then used to gain insights on the impact of atomic vacancies on the surface structure and the reactivity of the porous hollow PtNi/C nanoparticles 2. The DFT and experimental results show that porous hollow PtM/C nanoparticles feature unique catalytic advantages (i) open percolated structure exposing two catalytic surfaces (inner and outer), and (ii) structural defects that distort the metal lattice and produce catalytic sites that are highly active for both electrooxidation (COadsmonolayer electrooxidation, methanol and ethanol electrooxidation) and electroreduction (ORR) reactions. 1. R. Chattot, T. Asset, J. Drnec, P. Bordet, J. Nelayah, L. Dubau, F. Maillard, Nano Lett. (2017). DOI: 10.1021/acs.nanolett.7b00119 2. O. Le Bacq, A. Pasturel, R. Chattot, B. Previdello, J. Nelayah, T. Asset, L. Dubau, F. Maillard, ChemCatChem. (2017). DOI: 10.1002/cctc.201601672 Figure 1.Conventional and scanning transmission electron microscopy images and elemental maps of the different intermediate nanostructures forming during the synthesis of hollow PtNi/C nanoparticles. Figure 1

Optical properties of hybrid quantum-well–dots nanostructures grown by MOCVD

The deposition of In x Ga1–x As with an indium content of 0.3–0.5 and an average thickness of 3–27 single layers on a GaAs wafer by metalorganic chemical vapor deposition (MOCVD) at low temperatures results in the appearance of thickness and composition modulations in the layers being formed. Such structures can be considered to be intermediate nanostructures between ideal quantum wells and quantum dots. Depending on the average thickness and composition of the layers, the wavelength of the photoluminescence peak for the hybrid InGaAs quantum well–dots nanostructures varies from 950 to 1100 nm. The optimal average In x Ga1–x As thicknesses and compositions at which the emission wavelength is the longest with a high quantum efficiency retained are determined.

Long conducting polymer nanonecklaces with a ‘beads-on-a-string’ morphology: DNA nanotube-template synthesis and electrical properties

Complex and functional nanostructures are always desired. Herein, we present the synthesis of novel long conducting polymer nanonecklaces with a 'beads-on-a-string' morphology by the DNA nanotube-template approach and in situ oxidative polymerization of the 3-methylthiophene monomer with FeCl3 as the oxidant/catalyst. The length of the nanonecklaces is up to 60 μm, and the polymer beads of around 20-25 nm in diameter are closely packed along the axis of the DNA nanotube template with a density of ca. 45 particles per μm. The formation of porous DNA nanotubes impregnated with FeCl3 was also demonstrated as intermediate nanostructures. The mechanisms for the formation of both the porous DNA nanotubes and the conducting polymer nanonecklaces are discussed in detail. The as-synthesized polymer/DNA nanonecklaces exhibit good electrical properties.

Intercrystal self-assembly for the design of high-quality nickel molybdate nanocrystals.

Nanowire of nickel molybdate hydrate, being recognized as an emerging supercapacitor material, was synthesized from the intercrystal self-assembly process (commonly referred to as oriented aggregation or attachment). The detailed lattice image of a NiMoO4·0.75H2O nanowire and the intermediate nanostructure before reaching the interplanar binding were successfully captured by means of high-resolution transmission and scanning electron microscopies. NiMoO4·0.75H2O possessed highly crystalline surface and internal nanostructures.

Understanding the stability and reactivity of ultrathin tellurium nanowires in solution: An emerging platform for chemical transformation and material design

The stability and reactivity of nanomaterials are of crucial importance for their application, but the long-term effects of stability and reactivity of nanomaterials under practical conditions are still not well understood. In this study, we first established a comprehensive strategy to investigate the stability of a highly reactive nanomaterial from the viewpoint of reaction kinetics with ultrathin tellurium nanowires (TeNWs) as a model material in aqueous solution through an accelerated oxidation process. This allowed us to propose a new approach for the design and synthesis of other unique one-dimensional nanostructures by a chemical transformation process using the intermediate nanostructures “captured” during the dynamic oxidation process under different conditions. In essence, the oxidation of ultrathin TeNWs is a gas-solid reaction which involves liquid, gas and solid phases. It has been demonstrated that the oxidation process of ultrathin TeNWs in aqueous solution can be divided into three stages, namely oxygen limiting, ultrathin TeNWs limiting and mass transfer resistance limiting stages. The apparent oxidation kinetics for ultrathin TeNWs is approximately in accord with a first order reaction kinetics model and has an apparent activation energy as low as 13.53 kJ·mol−1, indicating that ultrathin TeNWs are thermodynamically unstable. However, the unstable nature of ultrathin TeNWs is actually an advantage since it can act as an excellent platform to help us synthesize and design one-dimensional functional nanomaterials-with special structures and distinctive properties-which are difficult to obtain by a direct synthesis method.

Cooperative self-assembly and crystallization into fractal patterns by PNIPAM-based nonlinear multihydrophilic block copolymers under alkaline conditions

Hierarchical two-dimensional patterned nanomaterials fabricated by bottom-up self-assembly are of great interests in practical applications. A series of nonlinear multihydrophilic block copolymers (MHBCs), consisting of poly(N-isopropylacrylamide) (PNIPAM), poly(acrylic acid) (PAA) and/or poly(vinyl pyrrolidone) (PVP) segments, were employed to fabricate well-defined fractal patterns under alkaline conditions by a simple solvent evaporation process. The formation of fractal patterns was discovered to obey a diffusion-limited aggregation process by needle-shaped intermediate nanostructures, which are actually nanohybrids formed by the cooperative self-assembly and crystallization of polymers and alkalis. The ability of MHBCs to form fractal patterns is closely related to their structural architectures, and is also significantly influenced by temperature, alkaline concentration, alkali type and substrate. Upon evaporation, PAA segments serve as the growing scaffolds of alkali crystallization along with the occurrence of self-contraction and intermolecular association of PNIPAM segments. PVP segments are not necessary for fractal patterning, which, however, can prompt the self-assembly into more perfect dendritic patterns in the case of a proper structural linking sequence. The observations reported here can provide a better understanding of molecular self-assembly toward complex patterns at multiple length scales, which may gain potential applications in advanced devices, sensors and microprinting.

Ascorbate-Assisted Growth of Hierarchical ZnO Nanostructures: Sphere, Spindle, and Flower and Their Catalytic Properties

A simple solution-based method to prepare mainly flowerlike zinc oxide (ZnO) nanostructures using the ascorbate ion as a shape-directing/capping agent at relatively low temperature (ca. 30 and 60 degrees C) was described. However, we observed that different shapes of hierarchical ZnO nanostructures such as flowerlike, spindlelike, and spherical could be obtained with an increase in the synthesis temperature from 60 to 90 degrees C. The effects of other organic capping agents on the shape of hierarchical ZnO nanostructures were also studied. FTIR, FESEM, and XRD characterization were performed on the formed ZnO nanostructures to understand the role of ascorbate in the growth of flowerlike morphology. The nucleation and growth process can regulate by changing the metal precursor and ascorbate ion concentrations. We were able to identify intermediate nanostructures such as spherical/quasi-spherical and spindle that are very much on the pathway of formation of large, flowerlike ZnO nanostructures. Electron microscopy results indicated that these spherical/quasi-spherical ZnO nanoparticles might aggregate through oriented attachment to produce spindlelike and flowerlike nanostructures. On the basis of these results, a possible growth mechanism for the formation of flowerlike ZnO nanostructures was described. The optical properties of these differently shaped ZnO nanostructures were also described. The catalytic activities of the as-synthesized spherical and flowerlike ZnO nanostructures were tested in the Friedel-Crafts acylation reaction of anthracene with benzoyl chloride. The catalysis results indicated that the catalytic activity of flowerlike ZnO nanostructures is slightly higher than the spherical counterpart.

Nanorings from the Self-Assembly of Amphiphilic Molecular Dumbbells

We have prepared amphiphilic dumbbell molecules consisting of hydrophobic alkyl chains and hydrophilic oligoether dendrons at each end of the rod segment. The molecular dumbbells, in aqueous solution, self-assemble into toroids as an intermediate nanostructure between spherical and long cylindrical micelles. The formation of toroidal structure is likely to originate from side by side connections of discrete bundles through the combination of strong hydrophobic interactions and anisotropic aggregation of rod segments.