Suzi Deng

α-Fe2O3 nanotubes-reduced graphene oxide composites as synergistic electrochemical capacitor materials

We present a facile approach for the fabrication of a nanocomposite comprising α-Fe(2)O(3) nanotubes (NTs) anchored on reduced graphene oxide (rGO) for electrochemical capacitors (ECs). The hollow tubular structure of the α-Fe(2)O(3) NTs presents a high surface area for reaction, while the incorporation of rGO provides an efficient two-dimensional conductive pathway to allow fast, reversible redox reaction. As a result, the nanocomposite materials exhibit a specific capacitance which is remarkably higher (~7 times) than α-Fe(2)O(3) NTs alone. In addition, the nanocomposites show excellent cycling life and large negative potential window. These findings suggest that such nanocomposites are a promising candidate as negative electrodes in asymmetrical capacitors with neutral electrolytes.

Plasmon-Enhanced Photocatalytic Properties of Cu2O Nanowire–Au Nanoparticle Assemblies

Cu(2)O-Au nanocomposites (NCs) with tunable coverage of Au were prepared by a facile method of mixing gold nanoparticles (Au NPs) with copper(I) oxide nanowires (Cu(2)O NWs) in various ratios. These Cu(2)O-Au NCs display tunable optical properties, and their photocatalytic properties were dependent on the coverage density of Au NPs. The photocatalytic activity of Cu(2)O-Au NCs was examined by photodegradation of methylene blue. The presence of Au NPs enhanced the photodegradation efficiency of Cu(2)O NCs. The photocatalytic efficiency of Cu(2)O-Au NCs initially increased with the increasing coverage density of Au NPs and then decreased as the surface of Cu(2)O became densely covered by Au NPs. The enhanced photocatalytic efficiency was ascribed to enhanced light absorption (by the surface plasmon resonance) and the electron sink effect of the Au NPs.

An effective surface-enhanced Raman scattering template based on a Ag nanocluster–ZnO nanowire array

An effective surface-enhanced Raman scattering (SERS) template based on a 3D hybrid Ag nanocluster (NC)-decorated ZnO nanowire array was fabricated through a simple process of depositing Ag NCs on ZnO nanowire arrays. The effects of particle size and excitation energy on the Raman scattering in these hybrid systems have been investigated using rhodamine 6G as a standard analyte. The results indicate that the hybrid nanosystem with 150 nm Ag NCs produces a larger SERS enhancement factor of 3.2 x 10(8), which is much higher than that of 10 nm Ag NCs (6.0 x 10(6)) under 532 nm excitation energy. The hybrid nanowire arrays were further applied to obtain SERS spectra of the two-photon absorption (TPA) chromophore T7. Finite-difference time-domain simulations reveal the presence of an enhanced field associated with inter-wire plasmon coupling of the 150 nm Ag NCs on adjacent ZnO nanowires; such a field was absent in the case of the 10 nm Ag NC-coated ZnO nanowire. Such hybrid nanosystems could be used as SERS substrates more effectively than assembled Ag NC film due to the enhanced light-scattering local field and the inter-wire plasmon-enhanced electromagnetic field.

Thiol-Capped ZnO Nanowire/Nanotube Arrays with Tunable Magnetic Properties at Room Temperature

The present study reports room-temperature ferromagnetic behaviors in three-dimensional (3D)-aligned thiol-capped single-crystalline ZnO nanowire (NW) and nanotube (NT) arrays as well as polycrystalline ZnO NT arrays. Besides the observation of height-dependent saturation magnetization, a much higher M(s) of 166 microemu cm(-2) has been found in NTs compared to NWs (36 microemu cm(-2)) due to larger surface area in ZnO NTs, indicating morphology-dependent magnetic properties in ZnO NW/NT systems. Density functional calculations have revealed that the origin of ferromagnetism is mainly attributed to spin-polarized 3p electrons in S sites and, therefore, has a strong correlation with Zn-S bond anisotropy. The preferential magnetization direction of both single-crystalline NTs and NWs lies perpendicular to the tube/wire axis due to the aligned high anisotropy orientation of the Zn-S bonds on the lateral (100) face of ZnO NWs and NTs. Polycrystalline ZnO NTs, however, exhibit a preferential magnetization direction parallel to the tube axis which is ascribed to shape anisotropy dominating the magnetic response. Our results demonstrate the interplay of morphology, dimensions, and crystallinity on spin alignment and magnetic anisotropy in a 3D semiconductor nanosystem with interfacial magnetism.

Room-Temperature Synthesis of Soluble Carbon Nanotubes by the Sonication of Graphene Oxide Nanosheets

The transformation of two-dimensional graphene oxide (GO) nanosheets into carbon nanotubes was achieved by sonicating GO in 70% nitric acid. Through the use of mass spectrometry to track the evolution of molecular fragments during the acid ultrasonication, it was observed that GO can be readily decomposed into polyaromatic hydrocarbons (PAHs). The cavitation-induced condensation of these PAHs results in their molecular reconstruction to form folded carbon nanostructures. UV-emitting, water-soluble carbon nanoparticles as well as carbon nanotubes that exhibit magnetic properties were fabricated under catalyst-free conditions.

Enhanced activity of H2O2-treated copper(II) oxide nanostructures for the electrochemical evolution of oxygen

The successful design and synthesis of earth-abundant and efficient catalysts for the oxygen evolution reaction (OER) will be a major step forward towards the use of electrochemical water splitting as an environmentally-friendly process for producing H2 fuel. Due to their poor activity, copper-based materials have not been considered apt for catalysing OER. In this work, we demonstrate that unique copper(II) oxide nanostructures obtained via hydrothermal synthesis and subsequent hydrogen peroxide treatment exhibit unusually high and sustainable OER activity. In 0.1 M KOH electrolyte, the CuO nanostructures catalyse OER with current densities of 2.6–3.4 mA cm−2 at 1.75 V (vs. RHE). The calculated turnover frequency (per Cu site) of ~2 × 10−3 s−1 for O2 production is markedly higher than that of high-surface area electrodeposited Cu metal nanoparticles by 40–68 times. The OER activity of the CuO nanostructures is also stable, approaching about half of 20% IrOx/Vulcan XC-72 after an hour-long OER. In situ Raman spectroscopy at OER-relevant potentials recorded compelling evidence that CuIII active species may be responsible for the unusual OER activity of the CuO nanostructures, as indicated by its signature vibration at 603 cm−1. This hitherto unobserved peak is assigned, with the aid of the model compound NaCuIIIO2, to the Cu–O stretching vibration of CuIII oxide. This feature was not found on electrodeposited Cu metal, which exhibited correspondingly weaker OER activity. The enhanced catalysis of O2 evolution by the CuO nanostructures is thus attributed to not just their higher surface area, but also the higher population of CuIII active sites on their surface.

Room temperature ferromagnetism at self-assembled monolayer modified Ag nanocluster-ZnO nanowire interface

Magnetic characterization of ZnO nanowires (NW) decorated with thiol-capped Ag nanoclusters (NCs) reveals spontaneous field-dependent magnetization and hysteresis at room temperature. The saturation magnetization is temperature independent for the 13nm thiol-capped Ag NCs but unexpectedly increases with temperature for the 4nm thiol-capped Ag NCs. The high magnetic moment results from the efficient dispersal of Ag NCs on the ZnO NW scaffold and charge transfer interaction between Ag and ZnO. The anomalous magnetic behavior in 4nm NCs may be due to the spin reorientation of Ag–S dipoles mediated by Zn–S dipoles.

Ultrathin Hexagonal Hybrid Nanosheets Synthesized by Graphene Oxide‐Assisted Exfoliation of β‐Co(OH)2 Mesocrystals

In the present study, we report the synthesis of a high-quality, single-crystal hexagonal β-Co(OH)2 nanosheet, exhibiting a thickness down to ten atomic layers and an aspect ratio exceeding 900, by using graphene oxide (GO) as an exfoliant of β-Co(OH)2 nanoflowers. Unlike conventional approaches using ionic precursors in which morphological control is realized by structure-directing molecules, the β-Co(OH)2 flower-like superstructures were first grown by a nanoparticle-mediated crystallization process, which results in large 3D superstructure consisting of ultrathin nanosheets interspaced by polydimethoxyaniline (PDMA). Thereafter, β-Co(OH)2 nanoflowers were chemically exfoliated by surface-active GO under hydrothermal conditions into unilamellar single-crystal nanosheets. In this reaction, GO acts as a two-dimensional (2D) amphiphile to facilitate the exfoliation process through tailored interactions between organic and inorganic molecules. Meanwhile, the on-site conjugation of GO and Co(OH)2 promotes the thermodynamic stability of freestanding ultrathin nanosheets and restrains further growth through Oswald ripening. The unique 2D structure combined with functionalities of the hybrid ultrathin Co(OH)2 nanosheets on rGO resulted in a remarkably enhanced lithium-ion storage performance as anode materials, maintaining a reversible capacity of 860 mA h g(-1) for as many as 30 cycles. Since mesocrystals are ubiquitous and rich in morphological diversity, the strategy of the GO-assisted exfoliation of mesocrystals developed here provides an opportunity for the synthesis of new functional nanostructures that could bear importance in clean renewable energy, catalysis, photoelectronics, and photonics.