Core-shell structure of polypyrrole grown on W18O49 nanorods for high performance gas sensor operating at room temperature

In this work, uniform core-shell structure of polypyrrole wrapped on tungsten oxide nanorods (PPy@W₁₈O₄₉ core-shell nanorods) were synthesized via a two-step process for gas-sensing applications. The core-nanorods of W₁₈O₄₉ were first grown by solvothermal method with tungsten hexachloride (WCl₆) as precursor. The PPy-shell layer was then formed uniformly on the solvothermally synthesized W₁₈O₄₉ nanorods by in-situ chemical polymerization of pyrrole monomer (Py), with sodium dodecyl benzene sulfonic acid (DBSA) as dopant and ammonium persulfate (APS) as oxidant. High dispersion of Py achieving in ethanol is proved to be crucial to form the uniform PPy-shell layer, and the layer thickness of PPy-shell is highly controlled by adjusting the Py concentration in polymeric solution. The morphology and structure of the nanocomposite were characterized systematically; it shows that the composite exhibits perfect core-shell structure of one-dimensional (1D) nanorods with average diameter of around 70–90 nm. The NH₃-sensing properties of the sensors based on the PPy@W₁₈O₄₉ core-shell nanorods were investigated at operating temperature of 15–130 °C over NH₃ concentration ranging from 1 to 200 ppm. The response magnitude of the PPy@W₁₈O₄₉ sensor can be affected seriously by temperature fluctuation, even in room temperature range (15–30 °C), and meanwhile, a temperature-dependent p-n response characteristic reversal is observed for the heteronanorods sensor. At much low room temperature of 15 °C, the present PPy@W₁₈O₄₉ nanorods show quick and sensitive response to NH₃ gas mainly due to the ultrathin, uniform PPy shell and the special heterojunction effect between p-type PPy and n-type W₁₈O₄₉. The underlying gas-sensing mechanism is analyzed.     

An easy and eco-friendly method to fabricate three-dimensional Pd-M (Cu,Ni) nanonetwork structure decorated on the graphene nanosheet with boosted ethanol electrooxidation activity in alkaline medium

A new rapid and facile strategy for the preparation of Pd-Ni/G and Pd-Cu/G catalysts with a three-dimensional porous structure are presented in this paper. Both catalysts are formed using the same strategies in two steps: 1) The reduction of Ni(OH)₂ and Cu(OH)₂ to the metallic form on the surface of G/GC Electrode using the Zn/HCl reducer, 2) The galvanic displacement of Ni and Cu by Pd²⁺. Afterwards, three-dimensional Pd nanonetwork is generated on the glassy carbon electrode via the galvanic displacement. Compared to the other routes, this strategy depicts several advantages (e.g. fast way, facile, surfactant and reductant free, cheap, and eco-friendly.) Both catalysts are applied towards Ethanol Oxidation Reaction (EOR). Both porous structures show higher electrocatalytic activity and stability toward EOR compared to the commercial Pd/C. The extraordinary catalytic activity and durability of the both proposed catalysts for EOR can be related to the two vital reasons:1) The combination of Ni and Cu with Pd will efficiently promote the catalytic performance of Pd-Ni/G and Pd-Cu/G samples due to synergetic effects. 2) The porous structure of the as-prepared catalysts renders a high surface area and leads easier mass transport through the pores.     

Bioinspired study of energy and electron transfer in photovoltaic system

ABSTRACT

This study focuses on understanding the fundamentals of energy transfer and electron transport in photovoltaic devices with uniquely designed nanostructures by analysing energy transfer in purple photosynthetic bacteria using dye-sensitised solar cell systems. Förster resonance energy transfer between the xanthene dye (donor of energy) and a new polymethine dye (acceptor of energy) was studied in dye-sensitised solar cells, which leads to a doubling of energy conversion efficiency in comparison to the cell with only the polymethine dye. The electron transport in the two different nanostructures of zinc oxide (nanorods and nanosheets) was investigated by spectroscopic methods (UV-vis spectrometer, time-resolved photoluminescence spectroscopy) and electrochemical potentiostat methods. The nanosheet structure of zinc oxide showed high short circuit current and long diffusion length. This fundamental study will lead to efficient artificial photosystem designs.     

Interior-architectured ZnO nanostructure for enhanced electrical conductivity via stepwise fabrication process

Fabrication of ZnO nanostructure via direct patterning based on sol-gel process has advantages of low-cost, vacuum-free, and rapid process and producibility on flexible or non-uniform substrates. Recently, it has been applied in light-emitting devices and advanced nanopatterning. However, application as an electrically conducting layer processed at low temperature has been limited by its high resistivity due to interior structure. In this paper, we report interior-architecturing of sol-gel-based ZnO nanostructure for the enhanced electrical conductivity. Stepwise fabrication process combining the nanoimprint lithography (NIL) process with an additional growth process was newly applied. Changes in morphology, interior structure, and electrical characteristics of the fabricated ZnO nanolines were analyzed. It was shown that filling structural voids in ZnO nanolines with nanocrystalline ZnO contributed to reducing electrical resistivity. Both rigid and flexible substrates were adopted for the device implementation, and the robustness of ZnO nanostructure on flexible substrate was verified. Interior-architecturing of ZnO nanostructure lends itself well to the tunability of morphological, electrical, and optical characteristics of nanopatterned inorganic materials with the large-area, low-cost, and low-temperature producibility.     

Studying the adsorption of DNA nanostructures on graphene in the aqueous phase using molecular dynamic simulations

DNA nanostructures can undergo large structural fluctuations and deviate from their intended configurations. In this work, two model DNA nanostructures (i.e., Nan and Kai) were designed based on the shape of the two Chinese characters of the name of Nankai University, and additional single-stranded DNA fragments were added to interact with graphene. During four 50-ns molecular dynamic simulations in aqueous solution, the DNA nanostructures adsorbed onto graphene demonstrated more stable conformations with lower root mean square deviations and smaller coordinate changes in the z-axis direction than the DNA nanostructures that were not adsorbed onto graphene. The interaction analyses and energetic calculations show that π-π interactions between single-stranded DNA and graphene are necessary for adsorption of the DNA nanostructures. Overall, this work examined the interactions between DNA and graphene at a large spatial scale with the hope that it provides a new strategy to stabilize DNA nanostructures.     

Three-dimensional ZnO@TiO2 core-shell nanostructures decorated with plasmonic Au nanoparticles for promoting photoelectrochemical water splitting

A novel three-dimensional (3D) core-shell nanostructure decorated with plasmonic Au nanoparticles (NPs) was prepared for photoelectrochemical water splitting. In the new nanostructure, ZnO nanorods (NRs) are perpendicular to ZnO nanosheets (NSs), and the ZnO NSs-NRs are coated with a thin TiO₂ shell formed by liquid phase deposition. The plasmonic Au NPs were formed in situ on the surface of ZnO NSs-NRs@TiO₂ by thermal reduction. A thin TiO₂ shell and uniformly distributed Au NPs were successfully obtained. The photoconversion efficiency and photocurrent density of the 3D ZnO NSs-NRs@TiO₂-Au nanostructure respectively reached 0.48% and 1.73 mA cm⁻² at 1.23 V vs. reversible hydrogen electrode, 4.80 and 4.33 times higher than those of ZnO NSs, respectively. The thin TiO₂ shell effectively promoted charge separation, while the surface plasmon resonance effects of the Au NPs improved the photocurrent density. The findings suggest that the 3D ZnO NSs-NRs@TiO₂-Au nanostructure is a promising photoanode for photoelectrochemical water splitting.     

Hierarchical NiCo2O4 and NiCo2S4 nanomaterials as electrocatalysts for methanol oxidation reaction

In this work, Ni foam supported hierarchical NiCo₂O₄ nanomaterials are successfully prepared through a hydrothermal process and subsequent calcination process, then the hierarchical NiCo₂O₄ is converted to hierarchical NiCo₂S₄ through a hydrothermal anion exchange process. The hierarchical nanomaterials are constructed by a nanorod core and nanoribbons shell. The morphology evolution mechanism of the hierarchical NiCo₂O₄ is studied by exploratory experiments, the results show that the morphology evolution from nanorod to hierarchical nanostructure undergo a solid–solid process, and the calcination temperature is crucial for the formation of the hierarchical nanostructure. The hierarchical NiCo₂O₄ and NiCo₂S₄ nanomaterials are both used as electrocatalysts for methanol oxidation reaction in alkaline electrolyte, and the electrocatalytic activity of the NiCo₂S₄ is higher than that of the NiCo₂O₄. Cycling test shows the good stability of the NiCo₂S₄, and the slight loss of activity during cycling is caused by the surface oxidation of NiCo₂S₄ in alkaline electrolyte. This work indicate that the hierarchical NiCo₂S₄ is a promising non-noble metal electrocatalyst for direct methanol fuel cells.     

Enhancing upconversion of Nd3+ through Yb3+-mediated energy cycling towards temperature sensing

Photon upconversion of lanthanides has been a powerful means to convert low-energy photons into high-energy ones. However, in contrast to the mostly investigated lanthanide ions, it has remained a challenge for the efficient upconversion of Nd³⁺ due to the deleterious concentration quenching effect. Here we report an efficient strategy to enhance the upconversion of Nd³⁺ through the Yb³⁺-mediated energy cycling in a core-shell-shell nanostructure. Both Nd³⁺ and Yb³⁺ are confined in the interlayer, and the presence of Yb³⁺ in the Nd-sublattice provides a more matched energy for the upconversion transitions occurring at the intermediate state of Nd³⁺ towards much better population at its emissive levels. Moreover, this design also minimizes the possible cross-relaxation processes at both intermediate level and the emissive levels of Nd³⁺ which are the primary factors limiting the upconversion performance for the Nd³⁺-doped materials. Such energy cycling-enhanced upconversion shows promise in temperature sensing.     

Advances and perspectives on one-dimensional nanostructure electrode materials for potassium-ion batteries

Potassium-ion batteries (PIBs) have aroused considerable interest as a promising next-generation advanced large-scale energy storage system due to the abundant potassium resources and high safety. However, the K⁺ with large ionic radius brings restricted diffusion kinetics and severe volume expansion in electrode materials, resulting in inferior actual rate characteristics and rapid capacity fading. Designing electrode materials with one-dimensional (1D) nanostructure can effectively enhance various electrochemical properties due to the well-guided electron transfer pathways, short ionic diffusion channels and high specific surface areas. In this review, we summarize the recent research progress and achievements of 1D nanostructure electrode materials in PIBs, especially focusing on the development and application of cathode and anode materials. The nanostructure, synthetic methods, electrochemical performances and structure-performance correlation are discussed in detail. The advanced characterizations on the reaction mechanisms of 1D nanostructure electrode materials in PIBs are briefly summarized. Furthermore, the main future research directions of 1D nanostructure electrode materials are also predicted, hoping to accelerate their development into the practical PIBs market.     

Total scattering atomic pair distribution function: new methodology for nanostructure determination

The conventional X-ray diffraction (XRD) methods probe for the presence of long-range order towards a solution of the average crystal structure. Experimentally, structural information about long-range, periodic atomic ordering is reflected in the Bragg scattering while local atomic structural deviations from the average structure mainly affect the diffuse scattering intensities. In order to obtain structural information about both average and local atomic structures, a technique that takes in account both Bragg and diffuse scattering needs to be employed, such as the total scattering atomic pair distribution function (PDF) technique. This article introduces a PDF-based methodology that can be applied to extract precise structural information about nanoparticles such as the size of the crystalline core region, the degree of crystallinity, the atomic structure of the core region, local bonding, and the degree of the internal disorder, as a function of the nanoparticle diameter. This article sheds light on a new PDF-based methodology that can yield precise quantitative structural information about small nanocrystals from XRD data, and also describes the essential aspects of this proposed methodology as well as its great potential. This method is generally applicable to the characterisation of the nanoscale solid, many of which may exhibit complex disordered structure.