Core-shell nanoparticles: synthesis and applications in catalysis and electrocatalysis.

Core-shell nanoparticles (CSNs) are a class of nanostructured materials that have recently received increased attention owing to their interesting properties and broad range of applications in catalysis, biology, materials chemistry and sensors. By rationally tuning the cores as well as the shells of such materials, a range of core-shell nanoparticles can be produced with tailorable properties that can play important roles in various catalytic processes and offer sustainable solutions to current energy problems. Various synthetic methods for preparing different classes of CSNs, including the Stöber method, solvothermal method, one-pot synthetic method involving surfactants, etc., are briefly mentioned here. The roles of various classes of CSNs are exemplified for both catalytic and electrocatalytic applications, including oxidation, reduction, coupling reactions, etc.

Seed-induced growth of flower-like Au-Ni-ZnO metal-semiconductor hybrid nanocrystals for photocatalytic applications.

The combination of metal and semiconductor components in nanoscale to form a hybrid nanocrystal provides an important approach for achieving advanced functional materials with special optical, magnetic and photocatalytic functionalities. Here, a facile solution method is reported for the synthesis of Au-Ni-ZnO metal-semiconductor hybrid nanocrystals with a flower-like morphology and multifunctional properties. This synthetic strategy uses noble and magnetic metal Au@Ni nanocrystal seeds formed in situ to induce the heteroepitaxial growth of semiconducting ZnO nanopyramids onto the surface of metal cores. Evidence of epitaxial growth of ZnO{0001} facets on Ni {111} facets is observed on the heterojunction, even though there is a large lattice mismatch between the semiconducting and magnetic components. Adjustment of the amount of Au and Ni precursors can control the size and composition of the metal core, and consequently modify the surface plasmon resonance (SPR) and magnetic properties. Room-temperature superparamagnetic properties can be achieved by tuning the size of Ni core. The as-prepared Au-Ni-ZnO nanocrystals are strongly photocatalytic and can be separated and re-cycled by virtue of their magnetic properties. The simultaneous combination of plasmonic, semiconducting and magnetic components within a single hybrid nanocrystal furnishes it multifunctionalities that may find wide potential applications.

Sustainable wood electronics by iron-catalyzed laser-induced graphitization for large-scale applications.

Ecologically friendly wood electronics will help alleviating the shortcomings of state-of-art cellulose-based "green electronics". Here we introduce iron-catalyzed laser-induced graphitization (IC-LIG) as an innovative approach for engraving large-scale electrically conductive structures on wood with very high quality and efficiency, overcoming the limitations of conventional LIG including high ablation, thermal damages, need for multiple lasing steps, use of fire retardants and inert atmospheres. An aqueous bio-based coating, inspired by historical iron-gall ink, protects wood from laser ablation and thermal damage while promoting efficient graphitization and smoothening substrate irregularities. Large-scale (100 cm2), highly conductive (≥2500 S m-1) and homogeneous surface areas are engraved single-step in ambient atmosphere with a conventional CO2 laser, even on very thin (∼450 µm) wood veneers. We demonstrate the validity of our approach by turning wood into highly durable strain sensors, flexible electrodes, capacitive touch panels and an electroluminescent LIG-based device.

Facile synthesis of near-monodisperse Ag@Ni core-shell nanoparticles and their application for catalytic generation of hydrogen.

Magnetically recyclable Ag-Ni core-shell nanoparticles have been fabricated via a simple one-pot synthetic route using oleylamine both as solvent and reducing agent and triphenylphosphine as a surfactant. As characterized by transmission electron microscopy (TEM), the as-synthesized Ag-Ni core-shell nanoparticles exhibit a very narrow size distribution with a typical size of 14.9 ± 1.2 nm and a tunable shell thickness. UV-vis absorption spectroscopy study shows that the formation of a Ni shell on Ag core can damp the surface plasmon resonance (SPR) of the Ag core and lead to a red-shifted SPR absorption peak. Magnetic measurement indicates that all the as-synthesized Ag-Ni core-shell nanoparticles are superparamagnetic at room temperature, and their blocking temperatures can be controlled by modulating the shell thickness. The as-synthesized Ag-Ni core-shell nanoparticles exhibit excellent catalytic properties for the generation of H(2) from dehydrogenation of sodium borohydride in aqueous solutions. The hydrogen generation rate of Ag-Ni core-shell nanoparticles is found to be much higher than that of Ag and Ni nanoparticles of a similar size, and the calculated activation energy for hydrogen generation is lower than that of many bimetallic catalysts. The strategy employed here can also be extended to other noble-magnetic metal systems.

Enhanced mechanical energy conversion with selectively decayed wood.

Producing electricity from renewable sources and reducing its consumption by buildings are necessary to meet energy and climate change challenges. Wood is an excellent "green" building material and, owing to its piezoelectric behavior, could enable direct conversion of mechanical energy into electricity. Although this phenomenon has been discovered decades ago, its exploitation as an energy source has been impaired by the ultralow piezoelectric output of native wood. Here, we demonstrate that, by enhancing the elastic compressibility of balsa wood through a facile, green, and sustainable fungal decay pretreatment, the piezoelectric output is increased over 55 times. A single cube (15 mm by 15 mm by 13.2 mm) of decayed wood is able to produce a maximum voltage of 0.87 V and a current of 13.3 nA under 45-kPa stress. This study is a fundamental step to develop next-generation self-powered green building materials for future energy supply and mitigation of climate change.

Structural Characterization and Analysis of High-Strength Laminated Composites from Recycled Newspaper and HDPE.

Recycled newspaper (NP) shows excellent potential as a reinforcement for polymer composites. Herein, high-strength laminated composites were prepared by using NP laminas as reinforcement and high-density polyethylene (HDPE) films as matrix. Physical and mechanical properties of the laminated composites were measured. It was found that the flexural strength of the composites had a good linear relationship to its density, with R2 = 0.9853. The flexural and tensile strength of the composites at the maximum density (1.40 g/cm3) reached up to 95.6 ± 2.4 MPa and 99.4 ± 0.8 MPa, respectively. SEM results showed that NP layer inside the composite became compact at the hot pressing time of 40 min, because the melted HDPE permeated into the NP layers to bond the NP fibers. Quantitative description of the composite porosity was conducted according to the density of the composite. The 24-h water absorption of the composite was highly related to its porosity, with R2 = 0.8994. This study reveals that density of laminated composites is an important parameter, which could be used to forecast the mechanical strength, and its derived value, porosity of the composites, could be used to predict the water absorption behavior of the composite.

Hierarchical Porous Wood Cellulose Scaffold with Atomically Dispersed Pt Catalysts for Low-Temperature Ethylene Decomposition.

Despite the excellent catalytic properties of individual nanoparticles and atomic clusters, the current capabilities to assemble them into a complex system are insufficient for many practical applications. An objective of this work is to develop a fabrication technology that allows for the simultaneous control of the nanoparticle surface chemistry, elemental distribution, microscale geometry, and large-scale assembly. Using a cellulose structure derived from wood, we fabricate hierarchical porous cellulose scaffolds combining with cerium-doped TiO2. This hybrid material serves as the support for atomically dispersed Pt catalysts and is used to successfully decompose ethylene at 0 °C. The fabrication concept developed in this work would allow mitigating the conflict between the required large active surfaces and the difficulties in handling nanopowders in environmental catalysis, including food preservation and indoor air purification. We thus discover a promising route to manufacture multifunctional materials with complex structures by combining a controllable chemical synthesis with the nature-designed wood scaffold.

Bioinspired Struvite Mineralization for Fire-Resistant Wood.

High-performance wood materials have attracted significant attention in recent years because of excellent property profiles achieved by relatively easy top-down processing of a renewable resource. A crucial flaw of the renewable wood scaffolds is the low flame retardancy, which we tackled by bioinspired mineralization in an eco-friendly processing step. The formation of the biomineral struvite, commonly found in urinary tract stones, was used for the infiltration of hierarchical wood structures with the necessary ions followed by an in situ synthesis of struvite by ammonium steam fumigation. Struvite decomposes prior to wood, which absorbs heat and releases nonflammable gas and amorphous MgHPO4 resulting from the degradation, which promotes insulating char formation. As a result, the mineralized wood can hardly be ignited and the treatment strongly suppresses the heat release rate and smoke production.

Dictating anisotropic electric conductivity of a transparent copper nanowire coating by the surface structure of wood.

In this article, a robust, air-stable, flexible and transparent copper (Cu) nanowire (NW) network coating on the surface of the wood is presented, based on a fusion welding of the Cu NWs by photonic curing. Thereby, an anisotropic conductivity can be achieved, which is originating from the structural organization of the wood body and its surface. Furthermore, the Cu NWs are protected from oxidation or wear by a commercially available paraffin wax-polyolefin, which also results in surface water repellency. The developed processing steps present a facile and flexible routine for applying Cu NW transparent conductors to abundant biomaterials and solve current manufacturing obstacles for corrosion-resistant circuits while keeping the natural appearance of the substrate. It may open a venue for more extensive utilization of materials from renewable resources such as wood for electronic devices in smart buildings or mobility applications.

Highly Efficient UV Protection of the Biomaterial Wood by A Transparent TiO2/Ce Xerogel.

Titanium dioxide is widely used in sunscreens because of its strong ultraviolet (UV) light absorbing capabilities and its resistance to discoloration under UV exposure. However, when deposited as a thin film, the high refractive index of titanium dioxide typically results in whiteness and opacity, which limits the use of titanium dioxide for material surfaces, for which long-term natural appearance is of high relevance. Since the whitish appearance is due to the strong light scattering and reflection on the interface of oxide particles and air, one can increase the transparency of TiO2 coatings by forming a continuous TiO2 layer. The purpose of the present article is 2-fold. First, we show that, in the presence of cerium ammonium nitrate, titanium dioxide can be turned from a white powder into a TiO2/Ce xerogel via a facile bottom-up fabrication process. Second, we demonstrate that the transparent TiO2/Ce xerogel can diminish surface deterioration induced by UV light and preserve the natural appearance of the highly abundant biomaterial wood. Furthermore, EPR spectroscopy revealed that the TiO2/Ce xerogel coating suppresses free radical generation on wood surfaces upon UV irradiation. Our research expands the applicability of the protective effect of titanium dioxide to coatings for natural engineering materials, which will become increasingly important in future bioeconomies.

Controllable synthesis of Cu-Ni core-shell nanoparticles and nanowires with tunable magnetic properties.

Cu seeds were used to direct the epitaxial growth of Ni shell to form Cu-Ni core-shell cubes, tetrahexahedrons and nanowires. The controllable epitaxial growth of Ni shells on Cu cores provided selectively exposed surfaces and morphologies as well as tunable magnetic properties.

Direct synthesis of graphene 3D-coated Cu nanosilks network for antioxidant transparent conducting electrode.

Transparent conducting film occupies an important position in various optoelectronic devices. To replace the costly tin-doped indium oxide (ITO), promising materials, such as metal nanowires and graphene, have been widely studied. Moreover, a long-pursued goal is to consolidate these two materials together and express their outstanding properties simultaneously. We successfully achieved a direct 3D coating of a graphene layer on an interlacing Cu nanosilks network by the low pressure chemical vapor deposition method. High aspect ratio Cu nanosilks (13 nm diameter with 40 µm length) were synthesized through the nickel ion catalytic process. Large-size, transparent conducting film was successfully fabricated with Cu nanosilks ink by the imprint method. A magnetic manipulator equipped with a copper capsule was used to produce high Cu vapor pressure on Cu nanosilks and realize the graphene 3D-coating. The coated Cu@graphene nanosilks network achieved high transparency, low sheet resistance (41 Ohm sq(-1) at 95% transmittance) and robust antioxidant ability. With this technique, the transfer process of graphene is no longer needed, and a flexible, uniform and high-performance transparent conducting film could be fabricated in unlimited size.

Effect of component distribution and nanoporosity in CuPt nanotubes on electrocatalysis of the oxygen reduction reaction.

Pt-based bimetallic electrocatalysts hold great potential in the oxygen reduction reaction (ORR) in current fuel-cell prototypes. However, they also face challenges from drastic dealloying of less-noble metals and coalescence of small nanoparticles. Porous and structure-ordered nanotubes may hold the potential to improve the stability of bimetallic electrocatalysts. Herein, we report a method to prepare CuPt nanotubes and porous Cu3 Pt intermetallic nanorods through a controlled galvanic replacement reaction and heat treatment process. The effect of the geometric features and compositional segregation on the electrocatalysis of the ORR was clarified. The outstanding performance of the Cu3 Pt/C-700 catalyst in the ORR relative to that of CuPt/C-RT was mainly attributed to the nanoporosity of the catalyst, whereas the enhanced specific activity on CuPt/C-RT after potential cycling was attributed to the interaction between the CuPt alloyed core and the Pt shell in the tube wall.

Facile preparation of well-dispersed CeO2-ZnO composite hollow microspheres with enhanced catalytic activity for CO oxidation.

In this article, well-dispersed CeO2-ZnO composite hollow microspheres have been fabricated through a simple chemical reaction followed by annealing treatment. Amorphous zinc-cerium citrate hollow microspheres were first synthesized by dispersing zinc citrate hollow microspheres into cerium nitrate solution and then aging at room temperature for 1 h. By calcining the as-produced zinc-cerium citrate hollow microspheres at 500 °C for 2 h, CeO2-ZnO composite hollow microspheres with homogeneous composition distribution could be harvested for the first time. The resulting CeO2-ZnO composite hollow microspheres exhibit enhanced activity for CO oxidation compared with CeO2 and ZnO, which is due to well-dispersed small CeO2 particles on the surface of ZnO hollow microspheres and strong interaction between CeO2 and ZnO. Moreover, when Au nanoparticles are deposited on the surface of the CeO2-ZnO composite hollow microspheres, the full CO conversion temperature of the as-produced 1.0 wt % Au-CeO2-ZnO composites reduces from 300 to 60 °C in comparison with CeO2-ZnO composites. The significantly improved catalytic activity may be ascribed to the strong synergistic interplay between Au nanoparticles and CeO2-ZnO composites.

Injection synthesis of Ni-Cu@Au-Cu nanowires with tunable magnetic and plasmonic properties.

A facile nonaqueous injection method has been developed for the construction of one-dimensional nanostructure consisting of a magnetic alloy (Ni-Cu) core and a plasmonic alloy (Au-Cu) shell. The obtained Ni-Cu@Au-Cu nanowires exhibit tunable optical and magnetic properties.

Poly(dimethylsiloxane) oil absorbent with a three-dimensionally interconnected porous structure and swellable skeleton.

Cleanup of oil spills is a worldwide challenge to prevent serious environmental pollution. A new kind of poly(dimethylsiloxane) (PDMS) oil absorbent with high absorption capacity and excellent reusability was prepared and used for oil/water separation. The preparation process of PDMS oil absorbents involves direct curing of a PDMS prepolymer in a p-xylene solution in the presence of commercial sugar particles, which is simple and economic. PDMS oil absorbents have interconnected pores and a swellable skeleton, combining the advantages of porous materials and gels. Absorption capacities of PDMS oil absorbents are 4-34 g/g for various oils and organic solvents, which are 3 times that reported previously. Owing to their hydrophobicity and oleophilicity, the as-obtained PDMS oil absorbents can selectively collect oils or organic solvents from water. The absorption process can be finished within tens of seconds. Furthermore, the absorbed oils or organic solvents can be recovered by compressing the oil absorbents, and after 20 absorbing/recovering cycles, PDMS oil absorbents show little loss of their absorption capacities and own weights.

Facile synthesis of Cu and Cu@Cu-Ni nanocubes and nanowires in hydrophobic solution in the presence of nickel and chloride ions.

A highly shape selective synthesis of Cu and Cu@Cu-Ni nanocubes and nanowires has been developed by modulating the coordination chemistry of transition metal ions with a trioctylphosphine (TOP)-Cl(-) ligand pair in oleylamine under mild organic solvent conditions. The as-prepared nanocubes have a face-centered cubic (fcc) phase and are covered by six {100} facets, whereas the as-prepared nanowires have a multi-twinned structure and grow along the [110] direction. Both the Ni(2+) and Cl(-) ions, along with TOP, play vital roles in determining the final morphology of the as-prepared nanocrystals (NCs). TOP can be used to selectively generate single-crystal seeds at the initial stage, which then grow into nanocubes in the presence of Cl(-) ions, while the absence of TOP leads to the formation of multi-twined crystal seeds that finally develop into nanowires. Moreover, Ni can be incorporated to form a Cu-Ni alloy shell over a Cu core at higher temperatures in a one-pot process, which makes diamagnetic Cu NCs magnetically responsive and has a significant influence on their optical properties.

Template-free synthesis of amorphous double-shelled zinc-cobalt citrate hollow microspheres and their transformation to crystalline ZnCo2O4 microspheres.

A novel and facile approach was developed for the fabrication of amorphous double-shelled zinc-cobalt citrate hollow microspheres and crystalline double-shelled ZnCo2O4 hollow microspheres. In this approach, amorphous double-shelled zinc-cobalt citrate hollow microspheres were prepared through a simple route and with an aging process at 70 °C. The combining inward and outward Ostwald ripening processes are adopted to account for the formation of these double-shelled architectures. The double-shelled ZnCo2O4 hollow microspheres can be prepared via the perfect morphology inheritance of the double-shelled zinc-cobalt citrate hollow microspheres, by calcination at 500 °C for 2 h. The resultant double-shelled ZnCo2O4 hollow microspheres manifest a large reversible capacity, superior cycling stability, and good rate capability.

Copper nanowires as fully transparent conductive electrodes.

In pondering of new promising transparent conductors to replace the cost rising tin-doped indium oxide (ITO), metal nanowires have been widely concerned. Herein, we demonstrate an approach for successful synthesis of long and fine Cu nanowires (NWs) through a novel catalytic scheme involving nickel ions. Such Cu NWs in high aspect ratio (diameter of 16.2 ± 2 nm and length up to 40 µm) provide long distance for electron transport and, meanwhile, large space for light transmission. Transparent electrodes fabricated using the Cu NW ink achieve a low sheet resistance of 1.4 Ohm/sq at 14% transmittance and a high transparency of 93.1% at 51.5 Ohm/sq. The flexibility and stability were tested with 100-timebending by 180°and no resistance change occurred. Ohmic contact was achieved to the p- and n-GaN on blue light emitting diode chip and bright electroluminescence from the front face confirmed the excellent transparency.