Unique Necklace‐Like Phenol Formaldehyde Resin Nanofibers: Scalable Templating Synthesis,Casting Films,and Their Superhydrophobic Property

1D necklace‐like nanostructures have exhibited different potential applications due to their unique geometry and property. However, their macroscopic and controllable synthesis has been a challenge. Herein, a facile and scalable template‐directed hydrothermal process is reported to synthesize a series of necklace‐like phenol‐formaldehyde resin (PFR) wrapped nanocables. The 1D templates involved in the synthesis can be various, such as tellurium nanowires (TeNWs), silver nanowires, and carbon nanotubes. After removal of the TeNWs template, pure PFR necklace‐like nanofibers with different morphologies can be prepared. Owning to their multiscale roughness and formed 3D network structures, such necklace‐like PFR nanofibers can be further used as building blocks for constructing robust superhydrophobic coatings with excellent mechanical properties on various substrates.     

Phase and Composition Tuning of 1D Platinum‐Nickel Nanostructures for Highly Efficient Electrocatalysis

Among various platinum (Pt)‐based nanostructures, porous or hollow ones are of great importance because they exhibit fantastic oxygen reduction reaction (ORR) enhancements and maximize atomic utilization by exposing both exterior and interior surfaces. Here, a new class of porous Pt₃Ni nanowires (NWs) with 1D architecture, an ultrathin Pt‐rich shell, high index facets, and a highly open structure is designed via a selective etching strategy by using the phase and composition segregated Pt‐Ni NWs as the starting material. The porous feature of Pt₃Ni NWs can be readily fulfilled by changing the Pt/Ni atomic ratio of the starting Pt‐Ni NWs. Such porous Pt₃Ni NWs show extraordinary activity and stability enhancements toward methanol oxidation reaction and ORR. The porous Pt₃Ni NWs can deliver ORR mass activity of 5.60 A mg^?1, which is 37.3‐fold higher than that of the Pt/C. They also show outstanding stability with negligible activity loss after 20 000 cycles. This study offers a unique approach for the design of complex nanostructures as efficient catalysts through precisely tailoring.     

Templating Synthesis of SnO2 Nanotubes Loaded with Ag2O Nanoparticles and Their Enhanced Gas Sensing Properties

A new kind of SnO₂ nanotubes loaded with Ag₂O nanoparticles can be synthesized by using Ag@C coaxial nanocables as sacrificial templates. The composition of silver in SnO₂ nanotubes can be controlled by tuning the compositions of metallic Ag in Ag@C sacrificial templates, and the morphology of tubular structures can be changed by use of nanocables with different thicknesses of carbonaceous layer. This simple strategy is expected to be extended for the fabrication of similar metal‐oxide doped nanotubes using different nanocable templates. In contrast to SnO₂@Ag@C nanocables as well as to other types of SnO₂ reported previously, the Ag₂O‐doped SnO₂ nanotubes exhibit excellent gas sensing behaviors. The dynamic transients of the sensors demonstrated both their ultra‐fast response (1–2 s) and ultra‐fast recovery (2–4 s) towards ethanol, and response (1–4 s) and recovery (4–5 s) towards butanone. The combination of SnO₂ tubular structure and catalytic activity of Ag₂O dopants gives a very attractive sensing behavior for applications as real‐time monitoring gas sensors with ultra‐fast responding and recovering speed.     

Replicating the Defect Structures on Ultrathin Rh Nanowires with Pt to Achieve Superior Electrocatalytic Activity toward Ethanol Oxidation

Metal nanostructures with an ultrathin Pt skin and abundant surface defects are attractive for electrocatalytic applications owing to the increased utilization efficiency of Pt atoms and the presence of highly reactive sites. This paper reports a conformal, layer‐by‐layer deposition of Pt atoms on defective Rh nanowires for the faithful replication of surface defects (i.e., grain boundaries) on the Rh nanowires. The thickness of the Pt shell can be controlled from one monolayer up to 5.3 atomic layers. This series of Rh@Pt_nL (n = 1–5.3) core–sheath nanowires show greatly enhanced activity and durability in catalyzing the ethanol oxidation reaction in an acidic medium. Among others, the Rh @ Pt_3.5L nanowires show the greatest mass activity (809 mA mg^?1_Pt) and specific activity (1.18 mA cm^?2) after loaded on carbon support, which are 3.7 and 3.4 times those of the commercial Pt/C, respectively. In situ Fourier transform infrared spectroscopy studies indicate an enhanced interaction between the outermost Pt layer and the Rh nanowire can promote C? C bond cleavage for complete oxidation of ethanol to CO₂ while depress the dehydrogenation of ethanol to acetic acid. As the Pt shell thickness is increased, the selectivity for the CO₂ pathway decreases while that for acetic acid is increased.     

Shape Control of Platinum Nanoparticles

The synthesis of shape controlled platinum nanoparticles has been investigated through an organometallic approach starting from the complex Pt₂(dba)₃ and using a long alkyl chain amine, hexadecylamine (HDA), as stabilizer. The influence of the experimental parameters (reactive gas and solvent nature, stabilizer/metal ratio, reactants concentration, temperature) on the shape of the Pt nanoparticles has been studied. Various shaped platinum nanostructures such as isolated nanoparticles, dendrites or crystalline nanowires were obtained, depending on the reaction conditions. This method takes profit of the mild conditions of chemistry in solution and allows obtaining regular nanostructures, most of them being homogeneous in shape as well as in size (isolated nanoparticles) or diameter/length (nanowires). Transmission electron microscopy and wide‐angle X‐ray scattering were used as characterization techniques. Beside the Knight‐shift effect of platinum, NMR solution investigations clearly evidenced the coordination of the amine at the Pt particles surface and its mobility. This mobility, increased when H₂ is used as reactive gas for the precursor decomposition, favors the particles coalescence into nanowires. This phenomenon is also favored by the “soft” template character of the amine in particular in toluene solution.     

Filling the Gaps between Graphene Oxide: A General Strategy toward Nanolayered Oxides

Despite extraordinary developments in the research of 2D inorganic nanomaterials, a scalable and generalized synthetic method toward 2D oxide materials that lack layered lattice structures is still challenging. Herein, an easy and versatile solution‐based route to synthesize oxides with layered nanostructures by combining sol–gel method with graphene oxide (GO) paper templates is reported. GO can stack together to form a paper‐like membrane, the gap between two GO layers provides ideal 2D space to template the growth of oxide nanolayers. By this simple strategy, the gaps are filled successfully with polycrystalline TiO₂, ZnO, Fe₂O₃, and amorphous SiO₂ nanolayers with thickness of 1–5 nm. Single or multilayers of the oxide‐based ceramic/glass nanolayers for applications in electronics, catalysts, energy storage, and gas separation can be expected; as an example, it is shown that layered Fe₂O₃ electrodes exhibit high performance for lithium‐ion battery due to enhanced electrical connections between the 2D nanolayers.     

Synthesis of Semiconducting Functional Materials in Solution: From II‐VI Semiconductor to Inorganic–Organic Hybrid Semiconductor Nanomaterials

This Feature Article provides a brief overview of the latest development and emerging new synthesis solution strategies for II–VI semiconducting nanomaterials and inorganic‐organic semiconductor hybrid materials. Research on the synthesis of II–VI semiconductor nanomaterials and inorganic–organic hybrid semiconducting materials via solution strategies has made great progress in the past few years. A variety of II–VI semiconductor and a new family of [MQ(L)_0.5] (M = Mn, Zn, Cd; Q = S, Se, Te; L = diamine, deta) hybrid nanostructures can be generated using solution synthetic routes. Recent advances have demonstrated that the solution strategies in pure solvent and a mixed solvent can not only determine the crystal size, shape, composition, structure and assembly properties, but also the crystallization pathway, and act as a matrix for the formation of a variety of different II–VI semiconductor and hybrid nanocomposites with diverse morphologies. These II–VI semiconductor nanostructures and their hybrid nanocomposites display obvious quantum size effects, unique and tunable optical properties.     

Gram‐Scale Synthesis of Ultrathin Tungsten Oxide Nanowires and their Aspect Ratio‐Dependent Photocatalytic Activity

Preparation of size‐tunable ultrathin W₁₈O₄₉ nanowires by an alcohol‐assisted solvothermal decomposition of tungstic acid is reported. The synthesis of ultrathin W₁₈O₄₉ nanowires can be achieved at large scale and low cost, while changing the molecular size of the used alcohols can control the nanowire morphology. With increasing the molecular size of the alcohol, the synthesized W₁₈O₄₉ nanowires have smaller diameters and longer lengths. The as‐prepared blue W₁₈O₄₉ nanomaterials show a very strong visible light absorption caused by oxygen defects and an aspect ratio‐dependent photocatalytic activity on the degradation of pollutant rhodamine B (RhB) under simulated solar light irradiation. It is found that the W₁₈O₄₉ nanowires with highest aspect ratio show the highest activity in the photodegradation of RhB, which could be related to their higher density of oxygen surface defects in combination with a higher adsorption capability of RhB. This new synthetic route of size tunable ultrathin W₁₈O₄₉ nanomaterials will enlarge their potential applications and can be possibly used in the pyrolyzing synthesis of other metal oxide nanomaterials.     

Co3O4 Nanostructures with Different Morphologies and their Field‐Emission Properties

We report an efficient method to synthesize vertically aligned Co₃O₄ nanostructures on the surface of cobalt foils. This synthesis is accomplished by simply heating the cobalt foils in the presence of oxygen gas. The resultant morphologies of the nanostructures can be tailored to be either one‐dimensional nanowires or two‐dimensional nanowalls by controlling the reactivity and the diffusion rate of the oxygen species during the growth process. A possible growth mechanism governing the formation of such nanostructures is discussed. The field‐emission properties of the as‐synthesized nanostructures are investigated in detail. The turn‐on field was determined to be 6.4 and 7.7 V μm^–1 for nanowires and nanowalls, respectively. The nanowire samples show superior field‐emission characteristics with a lower turn‐on field and higher current density because of their sharp tip geometry and high aspect ratio.     

Large‐Scale Synthesis and Characterization of TiO2‐Based Nanostructures on Ti Substrates

Na₂Ti₆O₁₃ nanoplates, nanowires, and continuous nanowire network films are hydrothermally formed on a large scale directly on Ti substrates for the first time. The morphology of the formed Na₂Ti₆O₁₃ nanostructures can be easily tuned by varying the experimental parameters of temperature, reaction duration, and the NaOH concentration. Our study demonstrates that the synthesized Na₂Ti₆O₁₃ nanostructures are easily converted into H₂Ti₃O₇ nanostructures—a desirable precursor for the fabrication of various TiO₂‐based nanomaterials—with shape preservation, by an ion‐exchange process. Anatase, a mixture of anatase and rutile, and rutile TiO₂ nanowires are formed when the H₂Ti₃O₇ nanowires are annealed at 450, 600, and 750 °C, respectively. The optical properties and the photocatalytic activity of H₂Ti₃O₇ nanowires and of the TiO₂‐based nanomaterials are also addressed. The approach described in this study provides a simple and novel method for the large‐scale synthesis of various TiO₂‐based nanostructured materials that grow directly on Ti substrates and are ready for a wide range of practical applications, such as the photodegradation of wastewater.     

Nanoparticles: Correlation Between Surface Chemistry and Electrocatalytic Properties of Monodisperse PtxNi1‐x Nanoparticles (Adv. Funct. Mater. 1/2011)

Monodisperse and homogeneous Pt_xNi_1‐x alloy nanoparticles of various compositions are synthesized via an organic solution approach in order to reveal the correlation between surface chemistry and their electrocatalytic properties. Atomic‐level microscopic analysis of the compositional profile and modeling of nanoparticle structure are combined to follow the dependence of Ni dissolution on the initial alloy composition and formation of the Pt‐skeleton nanostructures. The developed approach and acquired knowledge about surface structure‐property correlation can be further generalized and applied towards the design of advanced functional nanomaterials.     

Correlation Between Surface Chemistry and Electrocatalytic Properties of Monodisperse PtxNi1‐x Nanoparticles

Monodisperse and homogeneous Pt_xNi_1‐x alloy nanoparticles of various compositions are synthesized via an organic solution approach in order to reveal the correlation between surface chemistry and their electrocatalytic properties. Atomic‐level microscopic analysis of the compositional profile and modeling of nanoparticle structure are combined to follow the dependence of Ni dissolution on the initial alloy composition and formation of the Pt‐skeleton nanostructures. The developed approach and acquired knowledge about surface structure‐property correlation can be further generalized and applied towards the design of advanced functional nanomaterials.     

Excellent Field‐Emission Performances of Neodymium Hexaboride (NdB6) Nanoneedles with Ultra‐Low Work Functions

High‐quality NdB₆ nanostructures with a low work function are successfully synthesized via an one‐step catalyst‐free chemical vapor deposition process. Field emission properties of these nanostructures (curve nanowires, short‐straight nanorods, long‐straight nanowires, and nanoneedles) are systematically investigated and found to be strongly affected by the tip morphologies and temperatures. The nanoneedles with sharp tips demonstrate the lowest turn‐on (2.71 V/μm) and threshold (3.60 V/μm) electric fields, as well as a high current density (5.37 mA/cm²) at a field of 4.32 V/μm in comparision with other nanostructures. Furthermore, with an increase in temperature from room temperature to 623 K, the turn‐on field of the nanoneedles decreases from 2.71 to 1.76 V/μm, and the threshold field decreases from 3.60 to 2.57 V/μm. Such excellent performances make NdB₆ nanomaterials promising candidates for application in flat panel displays and nanoelectronics building blocks.     

Improved Hydrogen Production of Au–Pt–CdS Hetero‐Nanostructures by Efficient Plasmon‐Induced Multipathway Electron Transfer

The design of new functional materials with excellent hydrogen production activity under visible‐light irradiation has critical significance for solving the energy crisis. A well‐controlled synthesis strategy is developed to prepare an Au–Pt–CdS hetero‐nanostructure, in which each component of Au, Pt, and CdS has direct contact with the other two materials; Pt is on the tips and a CdS layer along the sides of an Au nanotriangle (NT), which exhibits excellent photocatalytic activity for hydrogen production under light irradiation (λ > 420 nm). The sequential growth and surfactant‐dependent deposition produce the three‐component Au–Pt–CdS hybrids with the Au NT acting as core while Pt and CdS serve as a co‐shell. Due to the presence of the Au NT cores, the Au–Pt–CdS nanostructures possess highly enhanced light‐harvesting and strong local‐electric‐field enhancement. Moreover, the intimate and multi‐interface contact generates multiple electron‐transfer pathways (Au to CdS, CdS to Pt and Au to Pt) which guide photoexcited electrons to the co‐catalyst Pt for an efficient hydrogen reduction reaction. By evaluating the hydrogen production rate when aqueous Na₂SO₃–Na₂S solution is used as sacrificial agent, the Au–Pt–CdS hybrid exhibits excellent photocatalytic activity that is about 2.5 and 1.4 times larger than those of CdS/Pt and Au@CdS/Pt, respectively.     

Surface State Mediated NIR Two‐Photon Fluorescence of Iron Oxides for Nonlinear Optical Microscopy

The development of fluorescent iron oxide nanomaterials is highly desired for multimodal molecular imaging. Instead of incorporating fluorescent dyes on the surface of iron oxides, a ligand‐assisted synthesis approach is developed to allow near‐infrared (NIR) fluorescence in Fe₃O₄ nanostructures. Using a trimesic acid (TMA)/citrate‐mediated synthesis, fabricated Fe₃O₄ nanostructures can generate a NIR two‐photon florescence (TPF) peak around 700 nm under the excitation by a 1230‐nm femtosecond laser. By tailoring the absorption of Fe₃O₄ nanostructures toward NIR band, the NIR‐TPF efficiency can be greatly increased. Through internal etching, surface peeling, and ligand replacement, spectroscopic results validated that such resonantly enhanced NIR‐TPF is mediated by surface states with strong NIR‐IR absorption. This TPF signal evolution can be generalized to other iron oxide nanomaterials like magnetite nanoparticles and α‐Fe₂O₃ nanoplates. Using the developed fluorescent Fe₃O₄ nanostructures, it is demonstrated that their TPF and third harmonic generation (THG) contrast in the nonlinear optical microscopy of live cells. It is anticipated that the synthesized NIR photofunctional Fe₃O₄ will serve as a versatile platform for dual‐modality magnetic resonance imaging (MRI) as well as a magnet‐guided theranostic agent.     

Tunable Synthesis of Various Wurtzite ZnS Architectural Structures and Their Photocatalytic Properties

Semiconductor ZnS with novel and complex 3D architectures such as nanorods (or nanowires) networks, urchinlike nanosturctures, nearly monodisperse nanospheres self‐assembled from nanorods and 1D nanostructures (rods and wires) had been synthesized in a binary solution by controlling the reaction conditions, such as the volume ratio of the mixed solvents and the reaction temperature. The morphology of ZnS changed from 3D architectural structures to 1D rodlike (or wirelike) shape when the temperature was increased from 160 to 200–240 °C. The possible growth mechanisms for the formation of nanospheres self‐assembled from nanorods are tentatively discussed according to the experimental results. The photocatalytic activity of various ZnS nanostructures has been tested by degradation of acid fuchsine under infrared light compared to that of commercial ZnS powders under infrared‐light irradiation and commercial TiO₂ powders under UV‐light irradiation, indicating that the as‐obtained ZnS nanostructures exhibit excellent photocatalytic activity for degradation of acid fuchsine.     

Hierarchical Self‐Organization of Nanomaterials into Two‐Dimensional Arrays Using Functional Polymer Scaffold

Fabrication of two and three‐dimensional nanostructures requires the development of new methodologies for the assembly of molecular/macromolecular objects on substrates in predetermined arrangements. Templated self‐assembly approach is a powerful strategy for the creation of materials from assembly of molecular components or nanoparticles. The present study describes the development of a facile, template directed self‐assembly of (metal/organic) nanomaterials into periodic micro‐ and nanostructures. The positioning and the organization of nanomaterials into spatially well‐defined arrays were achieved using an amphiphilic conjugated polymer‐aided, self‐organization process. Arrays of honeycomb patterns formed from conjugated C₁₂PPPOH film with homogenous distribution of metal/organic nanomaterials. Our approach offers a straightforward and inexpensive method of preparation for hybrid thin films without environmentally controlled chambers or sophisticated instruments as compared to multistep micro‐fabrication techniques.     

Endocytosis‐Enabled Construction of Silica Nanochannels Crossing Living Cell Membrane for Transmembrane Drug Transport

Artificial transmembrane channel (ATC) analogs are developed for overcoming biological membrane barriers and realizing transmembrane drug delivery, which are mostly studied within artificial lipid bilayers and thus lacked enough stability in practical applications on living cells. Here, natural endocytosis of silica‐based 1D nanomaterials (nanowires) with an ultrahigh aspect ratio is investigated. Enlightened by partially endocytosed ultralong silica nanowires, ATC that can penetrate living cell membranes for transmembrane transportation of small drug molecules is creatively constructed, resulting in enhanced drug delivery efficacy and decreased the half maximal inhibitory concentration. For the first time, an in‐depth study of the cellular uptake of 1D nanomaterials with ultrahigh aspect ratios (from 10 to 120) into living cells is carried out. Through confocal laser scanning microscopy observation, the endocytosis process of ultralong nanowires, including full uptake of short nanowires and partial uptake of longer nanowires, is clarified. Theoretical simulation is performed to give a fundamental understanding on the endocytosis mechanism of ultralong 1D silica nanowires. The simulation results demonstrate the time‐dependent internalization dynamics of the nanowires, which agrees well with our experimental results. This work not only clarifies the cellular interaction between 1D nanomaterials and living cells, but also pioneers the use of natural endocytosis of 1D nanomaterials for constructing ATC.     

Hydrogen‐Assisted Growth of Ultrathin Te Flakes with Giant Gate‐Dependent Photoresponse

Tellurium (Te), as an elementary material, has attracted intense attention due to its potentially novel properties. However, it is still a great challenge to realize high‐quality 2D Te due to its helical chain structure. Here, ultrathin Te flakes (5 nm) are synthesized via hydrogen‐assisted chemical vapor deposition method. The density functional theory calculations and experiments confirm the growth mechanism, which can be ascribed to the formation of volatile intermediates increasing vapor pressure of the source and promoting the reaction. Impressively, the Te flake‐based transistor shows high on/off ratio ≈10⁴, ultralow off‐state current ≈8 × 10^?13 A, as well as a negligible hysteresis due to reducing thermally activated defects at 80 K. Moreover, Te‐flake‐based phototransistor demonstrates giant gate‐dependent photoresponse: when gate voltage varies from ?70 to 70 V, I_on/I_off is increased by ≈40‐fold. The hydrogen‐assisted strategy may provide a new approach for synthesizing other high quality 2D elementary materials.     

Synthesis and Functionalization of Oriented Metal–Organic‐Framework Nanosheets: Toward a Series of 2D Catalysts

Synthesis of metal–organic frameworks (MOFs) is based on coordination‐driven self‐assembly of metal ions and organic ligands. However, to date, it remains difficult to adjust the coordination behaviors of MOFs and then control geometric shapes of nanostructures; especially their morphologies in 1D nanofibers or 2D nanosheets have seldom been explored. Here, a facile route at room temperature and ambient pressure is reported for the preparation of copper‐based MOFs with low‐dimensional shapes (i.e., nanofibers, nanorods, nanosheets, and nanocuboids), via thermodynamic and kinetic controls over the anisotropic growth. Importantly, the as‐prepared 2D MOF nanosheets with monocrystalline nature (100% exposed {010} facets) provide a material platform to the fabrication of 2D supported metal nanocatalysts. First, the MOF nanosheets can serve as a self‐templating solid precursor to prepare different CuO and CuO‐Cu₂O nanocomposites, or even Cu metals via thermolysis or reduction under controlled atmospheres. Upon their formation, second, ultrafine noble metal nanoparticles (e.g., Au, Ag, Pt, Pd, Au_0.4Pt_0.6, Au_0.4Pd_0.6, and Au_0.3Pt_0.3Pd_0.4) can be exclusively anchored on the external surfaces of the MOF nanosheets. To show their open accessibility, catalytic activities of the derived catalysts have been evaluated using CO₂ hydrogenation and 4‐nitrophenol reduction in gas phase and liquid phase, respectively.