Gaowu Qin

Enzyme-free amperometric sensing of hydrogen peroxide and glucose at a hierarchical Cu2O modified electrode

In this paper, an enzyme-free amperometric electrochemical sensor was fabricated by casting Nafion-impregnated Cu(2)O particles onto a glassy carbon electrode. A dual dependence of peak current on sweeping rate, which can be attributed for the accumulation of reaction products, was observed on the sensor. Electrochemical analysis of the particulate Cu(2)O for detecting H(2)O(2) and glucose is described, showing remarkable sensitivity in both cases. The estimated detection limits and sensitivities for H(2)O(2) (0.0039 μM, 52.3 mA mM(-1) cm(-2)) and glucose (47.2 μM, 0.19 mA mM(-1) cm(-2)) suggest that the response for H(2)O(2) detection was much higher than for glucose detection. Electron microscopy observation suggested that the hierarchical structures of Cu(2)O resulting from self-assembly of nanocrystals are responsible for the specific electrochemical properties.

Enhanced photoelectrochemical activity for Cu and Ti doped hematite: The first principles calculations

To improve photoelectrochemical (PEC) activity of hematite, the modification of energy band by doping 3d transition metal ions Cu and Ti into α-Fe2O3 were studied via the first-principles calculations with density function theory (DFT)+U method. The results show that the band gap of hematite is ∼2.1 eV and n-type dopant Ti improves the electric conductivity, confirmed by recent experiments. The p-type dopant Cu enhances the utilization ratio of solar energy, shifts both valance, and conduction band edges to a higher energy level, satisfying hydrogen production in the visible light driven PEC water splitting without voltage bias.

Energetics at the Surface of Photoelectrodes and Its Influence on the Photoelectrochemical Properties.

Photoelectrochemistry (PEC) holds potential as a direct route for solar energy storage. Its performance is governed by how efficiently photoexcited charges are separated and how fast the charges are transferred to the solution, both of which are highly sensitive to the photoelectrode surfaces near the electrolyte. While other aspects of a PEC system, such as the light-absorbing materials and the catalysts that facilitate charge transfer, have been extensively examined in the past, an underwhelming amount of attention has been paid to the energetics at the photoelectrode/electrolyte interface. The lack of understanding of this interface is an important reason why many photoelectrode materials fail to deliver the expected performance in harvesting solar energy in a PEC system. Using hematite (α-Fe2O3) as a material platform, we present in this Perspective how surface modifications can alter the energetics and the resulting consequences on the overall PEC performance. It has been shown that a detailed understanding of the photoelectrode/eletrolyte interfaces can contribute significantly to improving the performance of hematite, which enabled unassisted solar water splitting when combined with an amorphous Si photocathode.

High-Magnetization FeCo Nanochains with Ultrathin Interfacial Gaps for Broadband Electromagnetic Wave Absorption at Gigahertz

Superparamagnetic FeCo nanochains consisting of assembled ∼25 nm nanoparticles and ∼1 nm gaps are synthesized by facial wet-chemical route and exhibit significant electromagnetic absorption at gigahertz. Both the dielectric and magnetic loss factors present dual-resonance behaviors at 2-18 GHz frequencies, originated from the asymmetric architecture of the cubic FeCo particles that assembled in a one-dimensional chain structure. Theoretical analyses uncover that the origins of the enhancement of electromagnetic losses are ascribed to the high magnetization (228 emu/g) and the ultrathin gaps (∼1 nm), which enhances the Snoek limit and induces anisotropic dielectric polarizations, consequently constructing a proper electromagnetic match.

One-step fabrication of sub-10-nm plasmonic nanogaps for reliable SERS sensing of microorganisms

Nanoscale gaps in noble metal films can produce intense electromagnetic enhancement. When Raman-active molecules are positioned in these regions, their surface-enhanced Raman scattering (SERS) signals can be dramatically enhanced. However, the lack of convenient and reliable fabrication methods with ultrasmall nanogaps (<10 nm) severely block the application of SERS. Here, we propose a cost-effective and reproducible technique to fabricate the large-area Ag SERS-active substrates which are full of the high-density, sub-10-nm nanogaps by high pressure sputtering, and the enhancement factor (EF) is testified to improve by 10(3) times compared to the continuous Ag film with a smooth surface (the roughness is 0.5 nm) and without nanogaps. Since there are no chemicals used during fabrication, this substrate has a clean surface, which is crucial for acquiring reliable SERS spectra. This SERS-active substrate has then been applied to identify a series of microorganisms, and excellent, reproducible SERS spectra were obtained. Finally, a set of piecewise-linear equations is provided according to the correlation between SERS intensity and rhodamine 6G (R6G) concentration, and the detection limit is calculated to be 0.2×10(-8)M. These results suggest that the high pressure sputtering is an excellent, reliable technique for fabricating sub-10-nm plasmonic nanogaps, and the SERS-based methodology is very promising for being used in biological sensing field.

Microstructures and tensile properties of as-extruded Mg-Sn binary alloys

Abstract The microstructure and tensile properties of the Mg-1.0%Sn- x Y( x =1.5%, 3.0%, 3.5%, atom fraction) alloys extruded indirectly at 350 °C were investigated by means of optical microscopy, scanning electron microscopy and tensile test. The mean grain sizes of α -Mg matrix in the three extruded alloys are 6, 8 and 12 μm, respectively, slightly increasing with the addition of Y. The relationship between microstructure and strength was discussed in detail. The results show that the addition of Y has little effect on the grain refinement of the as-extruded Mg-Sn based alloys above. The only MgSnY phase is detected in the Mg-Sn-1.5%Y alloy, and the Sn 3 Y 5 phase in the Mg-Sn-3.5%Y alloy, whereas both of them simultaneously exist in the Mg-Sn-3.0%Y alloy. The particle shape of MgSnY and Sn 3 Y 5 phase, inherited from the solidification, has little change before and after hot extrusion. Mg-Sn-3.0%Y alloy has the highest ultimate tensile strength (UTS), 305 MPa, by over 50% compared with that of the other two alloys.

Assembled micro-nano particles with multiple interface polarizations for electromagnetic absorption at gigahertz

The usually utilized electromagnetic absorbers are fabricated by randomly dispersed fillers in polymer matrix, which limit the construction of multiple interfaces, thus influencing the optimization of absorption efficiency. In this Letter, the core/shell heterogeneous nanocapsules are chemically modified and subsequently conjugated on the micrometre-scale polymer units, forming a micro/nano-hybrided absorbent. Such a system creates multiple interfaces at sub-nanoscale, thus producing enhanced dielectric loss phenomena and resulting in an absorption efficiency of more than 90% over 2–18 GHz. The present study provides an effective concept to optimize the electromagnetic coupling and has important implications in the development of electromagnetic absorption materials.

Fabrication of long-range ordered, broccoli-like SERS arrays and application in detecting endocrine disrupting chemicals

Periodic broccoli-shaped Au and Ag surface-enhanced Raman spectroscopy (SERS) arrays were fabricated by combining ordered SiO2 colloidal crystal templates with the physical deposition technique. The SiO2 colloidal crystal-assisted Au and Ag SERS substrates have a long-range, adjustable periodic structure and a clean surface without incorporating any reductants or surfactant chemicals. Different from depositing directly on the flat substrates, the colloidal crystal-assisted nanostructure array has a larger effective surface area under the same projected area of laser irradiation, which exposes more “hot spots”. An increased roughness and a larger surface area have also been created as the highly bumpy surface feature of the broccoli-shaped SERS morphologies, resulting in a greater Raman amplification than the conventional metal film over nanosphere (MFON). SERS performances by Au and Ag SERS arrays reveal that the long-range broccoli-like morphology is a promising SERS platform as it is highly sensitive, reproducible and stable. The colloidal crystal-assisted Ag SERS array has a slightly higher enhancement factor (EF) than the Au SERS array, and they both are of the order of 107 enhancement. Compared to our previous work, which directly deposited noble metal nanoparticles onto flat substrates, the EF of the colloidal crystal-assisted SERS array is improved by one to two orders of magnitude. Finite-difference time-domain (FDTD) simulation was performed to estimate the electromagnetic field distribution. Finally, two endocrine disrupting chemicals (EDCs) (dioctyl phthalate (DOP) and dibutyl phthalate (DBP), homologous series) at different concentrations were successfully identified by Au and Ag SERS arrays with the detection limits of 0.24 × 10−9 M and 0.22 × 10−9 M, respectively. This study suggests that the broccoli-like Au and Ag SERS arrays are promising candidates for chemical sensing and this SERS substrate fabrication technique can be accessible to the standard industrial processes.

Gigahertz Dielectric Polarization of Substitutional Single Niobium Atoms in Defective Graphitic Layers

We synthesize two Nb/C composites with an order of magnitude difference in the density of single niobium atoms substituted into defective graphitic layers. The concentration and sites of single Nb atoms are identified using aberration-corrected scanning transmission electron microscopy and density functional theory. Comparing the experimental complex permittivity spectra reveals that a representative dielectric resonance at ∼16  GHz originates from the intrinsic polarization of single Nb atom sites, which is confirmed by theoretical simulations. The single-atom dielectric resonance represents the physical limit of the electromagnetic response of condensed matter, and thus might open up a new avenue for designing electromagnetic wave absorption materials. Single-atom resonance also has important implications in understanding the correlation between the macroscopic dielectric behaviors and the atomic-scale structural origin.

Nanoporous gold–alumina core–shell films with tunable optical properties

Tuning of the localized surface plasmon resonance (LSPR) of nanoporous metals is at the heart of manipulating light within extremely small volumes for the implementation of optical devices at the nanoscale. In this work, nanoporous gold-alumina core-shell films with fixed gold skeletons and different thicknesses of alumina shells are fabricated using chemical corrosion and subsequent atomic layer deposition. Optical transmission of the nanoporous composite films can be tailored through LSPR excitations of the three-dimensional gold skeleton and the alterable alumina shells as the covering dielectric. A 92 nanometer red-shift of the LSPR band is attained via its dielectric medium dependence and the comparable decay length with pore size. The widely tunable optical transmission and significantly improved stability thus suggest incorporating nanoporous gold-alumina into promising nano-devices with reliable performance. Low temperature surface decoration (<100 degrees C) provides a universal route to tune the optical properties while retaining the spatial geometry of the metallic nanostructures.