One-Pot Synthesis of Schiff Bases by Defect-Induced TiO2-x-Catalyzed Tandem Transformation from Alcohols and Nitro Compounds.

Schiff bases that are generally formed from condensation reactions of aldehydes (or ketones) and amino groups could also be produced by a photodriven one-pot tandem reaction between alcohols and nitro compounds, in our case. Herein, TiO2-x porous cages derived from NH2-MIL-125 by a self-sacrificing template route are used to study the organic transformation and exhibit 100% conversion efficiency of nitrobenzene and 100% selectivity for Schiff bases in the system of benzyl alcohol (5 mL) and nitrobenzene (41 µL) upon light irradiation, but hydrogen by dehydrogenation of benzyl alcohol cannot be detected. Successful occurrence of the organic transformation is mainly attributed to Ti(III)-oxygen vacancy associates. Surface oxygen vacancy-related Ti(III) sites are responsible for binding with nitro groups, and low-coordinated Ti5c sites selectively adsorb hydroxyl groups of benzyl alcohol. The Ti(III) and oxygen vacancy associates capture photogenerated electrons for achievement of multielectron reduction of nitrobenzene and the subsequent Schiff base condensation reaction with the as-formed benzaldehyde.

Novel Wax Valves To Improve Distance-Based Analyte Detection in Paper Microfluidics.

Microfluidic paper-based analytical devices (µPADs) have been extensively studied for disease diagnostics, food quality control, and environmental monitoring due to the advantages of low cost, portability, and simplicity. The lack of flow controllability has triggered the development of valves for such devices. This paper reports the µPADs integrating novel wax valves for distance-based detection. The valves are printed on paper and can be manually opened by organic solvents within seconds. The opened valve does not influence the flow. The µPADs with wax valves were then applied in the distance-based detection of potassium iodate and glucose. The valves allow mixing of reagents and subsequent incubation in the loading zone, resulting in a shorter detection time and larger linear detection range. This study has demonstrated a linear detection range of 0.05-0.5 mM for potassium iodate, while linear ranges of 1-5 and 2.5-80 mg/dL are achieved for glucose when total detection time is 15 and 25 min, respectively. The lower detection limit is only 1/11 of that in a previous study. The detection ranges of iodate and glucose assays cover the concentrations of iodate in salt/milk and glucose in human saliva, respectively. Due to the simplicity, reliability, and ability for high-density integration, the µPADs with wax valves are of great potential in point-of-care (sampling) applications.

Pt9 Ni Wavelike Nanowires with High Activity for Oxygen Reduction Reactions.

Platinum (Pt)-based nanostructures are the most efficient catalysts for the oxygen reduction reaction (ORR) in acid media. Here, Pt9 Ni wavelike nanowires (W-NWs) have been synthesized by etching Pt3 Ni@PtNi2 core-shell nanowires with 2,5-dihydroxyterephthalic acid for 24 hours. Compared to the commercial Pt/C catalyst, the free-standing Pt9 Ni W-NWs show improvements of up to 9.3 times for mass activity and 12.6 times for specific activity, respectively.

CTAB-Assisted Fabrication of Bi2WO6 Thin Nanoplates with High Adsorption and Enhanced Visible Light-Driven Photocatalytic Performance.

Two-dimensional thin Bi2WO6 nanoplates have been fabricated using a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal method. We investigated the proposed formation mechanism based on the crystalline structures of the thin Bi2WO6 nanoplates. The high adsorption ability and excellent visible-light driven photocatalytic activities of the Bi2WO6 nanoplates were illustrated, in view of exposed (001) facets of nanoplates possessing faster separation of photo-generated charge carriers and increased catalytically active sites. Such a cost-effective way to obtain Bi2WO6 nanoplates offers new possibilities for the design of adsorptive semiconductor photocatalysts with strengthened photocatalytic activities.

Green and Tunable Decoration of Graphene with Spherical Nanoparticles Based on Laser Ablation in Water: A Case of Ag Nanoparticle/Graphene Oxide Sheet Composites.

A simple and green strategy is presented to decorate graphene with nanoparticles, based on laser ablation of targets in graphene auqeous solution. Ag and graphene oxide (GO) are chosen as model materials. The surface of GO sheets is strongly anchored with spherical Ag nanoparticles. The density and size of the Ag nanoparticles can be easily tuned by laser ablation conditions. Further, the GO sheets can be decorated with other nanoparticles from simple metals or semiconductors to multicomponent hybrids. Additionally, the Ag nanoparticle/GO sheet colloids can be utilized as blocks to build three-dimensional structures, such as sandwich membranes by evaporation-induced self-assembly. These graphene-based composite materials could be very useful in catalysis, sensors, and nanodevices. Particularly, the Ag nanoparticle/GO sheet sandwich composite membranes exhibit excellent surface-enhanced Raman scattering performance and possess the huge potential in trace-detecting persistent organic pollutants in the environment.

Three-dimensional plasmonic nanoclusters.

Assembling nanoparticles into well-defined structures is an important way to create and tailor the optical properties of materials. Most advances in metamaterials research to date have been based on structures fabricated in two-dimensional planar geometries. Here, we show an efficient method for assembling noble metal nanoparticles into stable, three-dimensional (3-D) clusters, whose optical properties can be highly sensitive or remarkably independent of cluster orientation, depending on particle number and cluster geometry. Some of the clusters, such as tetrahedra and icosahedra, could serve as the optical kernels for metafluids, imparting metamaterial optical properties into disordered media such as liquids, glasses, or plastics, free from the requirement of nanostructure orientation.

Measuring the unusually slow ionic diffusion in polyaniline via study of yolk-shell nanostructures.

We demonstrate a unique capability in partially oxidizing the oligoaniline shell on gold nanoparticles to polyaniline. Because of the solubility difference, the unreacted inner shell section can be selectively dissolved by 2-propanol, giving yolk-shell nanostructures and, thus, making it possible for assessing the oxidized section. The ionic diffusion through the polymer shell is found to be the rate-determining step in the overall process. Conservative estimates show that the diffusion coefficient of AuCl(4)(-) is at least 700 times slower than that of the typical rate values in traditional studies. It is most likely caused by the lack of micropores in the polymer structures. Such mircopores are hard to avoid in preparing polymer membranes by casting or drying of polymers dissolved in organic solvents. We can rule out the presence of irregular pores on the basis of the uniformly oxidized shell section. With the nanoscale shells, the system is sensitive enough to detect minute changes in the shell or small differences among the individual nanoparticles. Even with a small increase in porosity, for example, when the polyaniline shell is swollen using small amounts of DMF (3%, 5%, or 10% in aqueous solutions), the diffusion coefficient of AuCl(4)(-) increases to 4, 11, and 17 times, respectively. Thus, our study demonstrates a new methodology for studying the diffusion of ions in hydrophobic polymers.

Developing mutually encapsulating materials for versatile syntheses of multilayer metal-silica-polymer hybrid nanostructures.

New methods to self-assemble polystyrene-block-poly(acrylic acid) (PSPAA) on silica via electrostatic interaction and to deposit silica on PSPAA shells are developed. The mutual encapsulation of silica and PSPAA allows versatile syntheses of well-controlled nanohybrids.

Controlling reversible elastic deformation of carbon nanotube rings.

We show that bundles of carbon nanotubes can be coiled into ring structures by controlling the contraction of their polymer shells. With the robust carbon nanotubes, we demonstrate their reversible transformation between circular and compressed rings in a colloid.

Chiral transformation: from single nanowire to double helix.

We report a new type of water-soluble ultrathin Au-Ag alloy nanowire (NW), which exhibits unprecedented behavior in a colloidal solution. Upon growth of a thin metal (Pd, Pt, or Au) layer, the NW winds around itself to give a metallic double helix. We propose that the winding originates from the chirality within the as-synthesized Au-Ag NWs, which were induced to untwist upon metal deposition.

Cu Nanocluster-Loaded TiO2 Nanosheets for Highly Efficient Generation of CO-Free Hydrogen by Selective Photocatalytic Dehydrogenation of Methanol to Formaldehyde.

Safe storage and transportation of H2 is a fundamental requirement for its wide applications in the future. Controllable release of high-purity H2 from a stable storage medium such as CH3OH before use offers an efficient way of achieving this purpose. In our case, Cu nanoclusters uniformly dispersed onto (001) surfaces of TiO2 nanosheets (TiO2/Cu) are selectively prepared by thermal treatment of HKUST-1 loaded TiO2 nanosheets. One of the TiO2/Cu composites, TiO2/Cu_50, exhibits remarkably high activity toward the selective dehydrogenation of CH3OH to HCHO with a H2 evolution rate of 17.8 mmol h-1 per gram of catalyst within a 16-h photocatalytic reaction (quantum efficiency at 365 nm: 16.4%). Theoretical calculations reveal that interactions of Cu nanoclusters with TiO2 could affect their electronic structures, leading to higher adsorption energy of CH3OH at Ti sites and a lower barrier for the dehydrogenation of CH3OH by the synergistic effect of Cu nanoclusters and TiO2, and lower Gibbs free energy for desorption HCHO and H2 as well.

Effect of Furfurylation on Hierarchical Porous Structure of Poplar Wood.

Some wood properties (such as permeability and acoustic properties) are closely related to its hierarchical porous structure, which is responsible for its potential applications. In this study, the effect of wood impregnation with furfuryl alcohol on its hierarchical porous structure was investigated by microscopy, mercury intrusion porosimetry and nuclear magnetic resonance cryoporometry. Results indicated decreasing lumina diameters and increasing cell wall thickness of various cells after modification. These alterations became serious with enhancing weight percent gain (WPG). Some perforations and pits were also occluded. Compared with those of untreated wood, the porosity and pore volume of two furfurylated woods decreased at most of the pore diameters, which became more remarkable with raising WPG. The majority of pore sizes (diameters of 1000~100,000 nm and 10~80 nm) of macrospores and micro-mesopores of two furfurylated woods were the same as those of untreated wood. This work could offer thorough knowledge of the hierarchical porous structure of impregnatedly modified wood and pore-related properties, thereby providing guidance for subsequent wood processing and value-added applications.

N-CND modified NH2-UiO-66 for photocatalytic CO2 conversion under visible light by a photo-induced electron transfer process.

A N-CNDs/NH2-UiO-66 composite is successfully prepared by introducing N-CNDs into the synthetic system of NH2-UiO-66. Excited electrons in the LUMO of the N-CNDs are smoothly transferred to Zr4+ of NH2-UiO-66 upon visible light irradiation. The composite exhibits enhanced photocatalytic performance for CO2 reduction in an acetonitrile/ethanol mixture via the PET process.

Topological Formation of a Mo-Ni-Based Hollow Structure as a Highly Efficient Electrocatalyst for the Hydrogen Evolution Reaction in Alkaline Solutions.

A Mo-Ni alloy has been demonstrated to be a benchmark noble-metal-free catalyst for the hydrogen evolution reaction (HER) in alkaline solutions. Nevertheless, further improvement on its catalytic activity is desired to meet industrial requirements. In this study, Mo-Ni-based hollow structures (MoNi-HS), backboned by MoO3- x nanosheets and decorated with metallic MoNi4 nanoparticles, were obtained via a topological transformation process by annealing MoNi-oxide hollow precursors in a reducing atmosphere. This hollow structure allowed for a large proportion of catalytic surface exposed in the electrolyte, leading to highly efficient utilization of active sites in the catalyst. As a result, robust catalytic activity toward HER was recorded in 1 M KOH electrolyte: a low overpotential of 38 mV to deliver a current density of 10 mA/cm2 and a very small Tafel slope of 31.4 mV per dec. Such a remarkable performance of MoNi-HS even outperformed the catalytic activity of the commercial Pt/C electrocatalyst, addressing an effective strategy to promote the catalytic performance of noble-metal-free catalysts.

Nanoplate-Built ZnO Hollow Microspheres Decorated with Gold Nanoparticles and Their Enhanced Photocatalytic and Gas-Sensing Properties.

Hierarchical porous ZnO microspheres decorated with gold nanoparticles (AuNPs) were successfully synthesized by a facile solvothermal route. The hierarchical ZnO superstructure was constructed of interconnected nanoplates with numerous voids. Photoluminescence, X-ray photoelectron spectroscopy, and electron paramagnetic resonance measurements demonstrated that the main defects were oxygen vacancies (V(O)(•)) with minor interstitial oxygen (O(i)(-)) in the hierarchical ZnO hollow microspheres. The as-prepared hierarchical ZnO hollow microspheres and the AuNPs used to decorate them were examined for their photocatalytic degradation ability and as gas sensors. The photodegradation results demonstrated that the degradation rate constant on rhodamine B for undecorated ZnO microspheres was 0.43 min(-1), which increased to 1.76 min(-1) for AuNP-decorated ZnO microspheres. The AuNP-functionalized ZnO microspheres displayed superior sensing properties, with a 3-fold enhancement in their gas response to 1 ppb of dibutyl phthalate.

Induced coiling action: exploring the intrinsic defects in five-fold twinned silver nanowires.

Growth of polythiophene (PTh) on five-fold twinned Ag nanowires (NWs) is not symmetrical due to preferred etching of their intrinsic defects. This imbalance of polymer formation leads to consistent bending action along the etched NWs, coiling the resulting Ag-PTh nanocomposites into planar spirals. We studied the etching intermediates and also the effects of the surface ligands in order to understand the symmetry-breaking action. The defect-dependent etching chemistry offers a new means to induce motion and a novel perspective in the ordered occurrence of certain defects. We demonstrate that Ag can be deposited back onto the coiled Ag-PTh composite to form metallic spirals.

Assembly of colloidal nanoparticles directed by the microstructures of polycrystalline ice.

We show that the microstructures of polycrystalline ice can serve as a confining template for one-dimensional assembly of colloidal nanoparticles. Upon simply freezing an aqueous colloid, the nanoparticles are excluded from ice grains and form chains in the ice veins. The nanoparticle chains are transferable and can be strengthened by polymer encapsulation. After coating with polyaniline shells, simple sedimentation is used to remove large aggregates, enriching single-line chains of 40 nm gold nanoparticles with a total length of several micrometers. When gold nanorods were used, they formed one-dimensional aggregates with specific end-to-end conformation, indicating the confining effects of the nanoscale ice veins at the final stage of freezing. The unbranched and ultralong plasmonic chains are of importance for future study of plasmonic coupling and development of plasmonic waveguides.