Efficient degradation of tetrabromobisphenol A by heterostructured Ag/Bi5Nb3O15 material under the simulated sunlight irradiation

Heterostructured metallic silver-layered bismuth niobate two-component system (Ag/Bi(5)Nb(3)O(15)) was developed for the first time by a mild hydrothermal method combined with photodeposition. The Ag/Bi(5)Nb(3)O(15) exhibited single-crystalline orthorhombic structure with small particle size (50-200 nm) and octahedral as well as sheet-like shape; additionally, it possessed photoresponse in both UV and visible region. As a novel alternative photocatalysts to TiO(2), the photocatalytic activity of the Ag/Bi(5)Nb(3)O(15) was evaluated by the degradation of tetrabromobisphenol A, a member from the family of the brominated flame retardant, under solar simulating Xe lamp irradiation, and enhanced photocatalytic activity in compared to Bi(5)Nb(3)O(15) itself and Degussa P25 was obtained.     

Femtosecond response of a free-standing LT-GaAs photoconductive switch

We present a novel, free-standing low-temperature GaAs (LT-GaAs) photoconductive switch and demonstrate its femtosecond performance. A 1-microm-thick layer of a single-crystal LT-GaAs was patterned into 5-10-microm-wide and 15-30-microm-long bars, separated from their GaAs substrate and, subsequently, placed across gold coplanar transmission lines deposited on a Si substrate, forming a photoconductive switch. The switch was excited with 110-fs-wide optical pulses, and its photoresponse was measured with an electro-optic sampling system. Using 810-nm optical radiation, we recorded an electrical transient as short as 360 fs (1.25 THz, 3-dB bandwidth) and established that the photo-carrier lifetime in our LT-GaAs was 150 fs. Our free-standing devices exhibited quantum efficiency of the order of approximately 7%, and their photoresponse amplitude was a linear function of the applied voltage bias, as well as a linear function of the excitation power, below a well-defined saturation threshold.     

Low-voltage-driven pentacene thin-film transistors with cross-linked poly(4-vinylphenol)/high-k Bi55b3O15 hybrid dielectric for phototransistor

This paper describes the fabrication of pentacene thin-film transistors (TFTs) with an organic/inorganic hybrid gate dielectric, consisting of cross-linked poly(4-vinylphenol) (PVP) and Bi5Nb3O15. A 300-nm-thick Bi5Nb3O15 dielectric film, grown at room temperature, exhibits a high dielectric constant (high-k) value of 40 but has an undesirable interface with organic semiconductors (OSC). To form better interfaces with OSC, a cross-linked PVP dielectric was stacked on the Bi5Nb3O15 dielectric. It is shown that, with the introduction of a hybrid dielectric, our devices not only can be operated at a low voltage (- -5 V) but also have improved electrical characteristics and photoresponse, including a field-effect mobility of 0.72 cm2/V x s, current sub-threshold slopes of 0.29 V/decade, and a photoresponse of 4.84 at a gate bias V(G) = 0 V under 100 mW/cm2 AM 1.5 illumination.     

A method to construct a third-generation horseradish peroxidase biosensor: self-assembling gold nanoparticles to three-dimensional sol-gel network

A novel method for fabrication of horseradish peroxidase biosensor has been developed by self-assembling gold nanoparticles to a thiol-containing sol-gel network. A cleaned gold electrode was first immersed in a hydrolyzed (3-mercaptopropyl)-trimethoxysilane (MPS) sol-gel solution to assemble three-dimensional silica gel, and then gold nanoparticles were chemisorbed onto the thiol groups of the sol-gel network. Finally, horseradish peroxidase (HRP) was adsorbed onto the surface of the gold nanoparticles. The distribution of gold nanoparticles and HRP was examined by atomic force microscopy (AFM). The immobilized horseradish peroxidase exhibited direct electrochemical behavior toward the reduction of hydrogen peroxide. The performance and factors influencing the performance of the resulting biosensor were studied in detail. The resulting biosensor exhibited fast amperometric response (2.5 s) to H2O2. The detection limit of the biosensor was 2.0 micromol L(-1), and the linear range was from 5.0 micromol L(-1) to 10.0 mmol L(-1). Moreover, the studied biosensor exhibited high sensitivity, good reproducibility, and long-term stability.     

Photosensitive gold-nanoparticle-embedded dielectric nanowires

Noble-metal nanoparticles embedded in dielectric matrices are considered to have practical applications in ultrafast all-optical switching devices owing to their enhanced third-order nonlinear susceptibility, especially near the surface-plasmon-resonance (SPR) frequency. Here we present the use of a microreactor approach to the fabrication of a self-organized photosensitive gold nanoparticle chain encapsulated in a dielectric nanowire. Such a hybrid nanowire shows pronounced SPR absorption. More remarkably, a strong wavelength-dependent and reversible photoresponse has been demonstrated in a two-terminal device using an ensemble of gold nanopeapodded silica nanowires under light illumination, whereas no photoresponse was observed for the plain silica nanowires. These results show the potential of using gold nanopeapodded silica nanowires as wavelength-controlled optical nanoswitches. The microreactor approach can be applied to the preparation of a range of hybrid metal-dielectric one-dimensional nanostructures that can be used as functional building blocks for nanoscale waveguiding devices, sensors and optoelectronics.     

Effect of nanosized gold particle addition to supported metal oxide catalyst in methanol oxidation

Gold has rarely been utilized as a catalytic component because of its poor affinity to chemical species. It is however known that nanosized gold particles promote the dissociation of oxygen or hydrogen. In this study, alumina-supported metal oxide catalysts were prepared by impregnation method and applied to methanol oxidation. The dispersion form and size of the gold particles were observed by transmission electron microscopy (TEM). In the results, the maximum catalytic activity was obtained over the ZnO/Al2O3 catalyst, and the optimum loading was 4 wt%. Furthermore, nano-sized gold particles at various loadings were added to ZnO/Al2O3 catalyst by deposition method. The gold particles on Au/ZnO/Al2O3 catalyst were well dispersed and the catalyst activity was remarkably increased compared to ZnO/Al2O3 catalyst. The role of gold particles in the increased catalytic activity is discussed and a possible mechanism is presented.     

二钛酸钾纳米薄膜的原位合成及其性能研究

以Ti(n-OC4H9)4和CH3COOK为前驱体,采用溶胶-凝胶法在较低温度下原位合成了高光催化活性的K2Ti2O5纳米薄膜;采用TG-DSC,XRD,Raman光谱和AFM研究了K2Ti2O5薄膜的晶体生长过程;采用电化学方法测量了薄膜的光电响应.结果表明:原料在约259℃发生反应,在低于414℃的固态反应阶段生成K2Ti2O5晶核,在414℃～600℃的结晶阶段制得K2Ti2O5纳米薄膜,薄膜的颗粒表面非常平整,薄膜的晶粒是沿着一个晶面取向生长;薄膜均匀、致密、透明;在空气中紫外光照时,K2Ti2O5薄膜能很有效的降解OTS(C18H37SiCl3)单分子膜(SAMs),光催化活性比溶胶-凝胶法制备的TiO2薄膜高,光激发和光电响应能力也比TiO2薄膜强.     

Enhancement in the photodetection of ZnO nanowires by introducing surface-roughness-induced traps

We investigated the enhanced photoresponse of ZnO nanowire transistors that was introduced with surface-roughness-induced traps by a simple chemical treatment with isopropyl alcohol (IPA). The enhanced photoresponse of IPA-treated ZnO nanowire devices is attributed to an increase in adsorbed oxygen on IPA-induced surface traps. The results of this study revealed that IPA-treated ZnO nanowire devices displayed higher photocurrent gains and faster photoswitching speed than transistors containing unmodified ZnO nanowires. Thus, chemical treatment with IPA can be a useful method for improving the photoresponse of ZnO nanowire devices.     

Effect of oxygen annealing on the ultraviolet photoresponse of P-NiO-nanoflower/n-ZnO-nanowire heterostructures

A transparent ultraviolet (UV) sensor using nanoheterojunctions (NHJs) composed of p-type NiO nanoflowers (NFs) and n-type ZnO nanowires (NWs) was prepared through a sequential low-temperature hydrothermal-growth process. The devices that were annealed in an oxygen (O2) ambient exhibited better rectification behavior (I forward/I reverse = 427), a lower forward threshold voltage (V(th) = 0.98 V), a lower leakage current (1.68 x 10(-5) A/cm2), and superior sensitivity (I uv/I dark = 57.8; I visible/I dark = 1.25) to UV light (lambda = 325 nm) than the unannealed devices. The remarkably improved device performances and optoelectronic characteristics of the annealed p-NiO-NF/n-ZnO-NW NHJs can be associated with their fewer structural defects, fewer interfacial defects, and better crystallinity. A stable and repeatable operation of dynamic photoresponse was also observed in the annealed devices. The excellent sensitivity and repeatable photoresponse to UV light of the hydrothermally grown p-NiO-NF/n-ZnO-NW NHJs annealed in a suitable O2 ambient indicate that they can be applied to nano-integrated optoelectronic devices.     

Inkjet printing of nanoporous gold electrode arrays on cellulose membranes for high-sensitive paper-like electrochemical oxygen sensors using ionic liquid electrolytes

A simple approach to the mass production of nanoporous gold electrode arrays on cellulose membranes for electrochemical sensing of oxygen using ionic liquid (IL) electrolytes was established. The approach, combining the inkjet printing of gold nanoparticle (GNP) patterns with the self-catalytic growth of these patterns into conducting layers, can fabricate hundreds of self-designed gold arrays on cellulose membranes within several hours using an inexpensive inkjet printer. The resulting paper-based gold electrode arrays (PGEAs) had several unique properties as thin-film sensor platforms, including good conductivity, excellent flexibility, high integration, and low cost. The porous nature of PGEAs also allowed the addition of electrolytes from the back cellulose membrane side and controllably produced large three-phase electrolyte/electrode/gas interfaces at the front electrode side. A novel paper-based solid-state electrochemical oxygen (O(2)) sensor was therefore developed using an IL electrolyte, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF(6)). The sensor looked like a piece of paper but possessed high sensitivity for O(2) in a linear range from 0.054 to 0.177 v/v %, along with a low detection limit of 0.0075% and a short response time of less than 10 s, foreseeing its promising applications in developing cost-effective and environment-friendly paper-based electrochemical gas sensors.     

Chemical solution approaches to YBa2Cu3O7_delta-Au nanocomposite superconducting thin films

We explore the feasibility of preparing YBa2CU3O7-Au (YBCO-Au) nanocomposite thin films by chemical solution deposition (CSD). Two approaches were used: (i) A standard in-situ methodology where Au metallorganic salts are added into the precursor solution of YBCO trifluoroacetate (TFA) salts and (ii) a novel approach where stable colloidal solutions of preformed gold nanoparticles (5-15 nm) were homogeneously mixed with TFA-YBCO solutions. A detailed analysis of the microstructure of the films showed that in both cases, there is a strong tendency of gold nanoparticles to migrate to the film surface. However the kinetics of this migration evidences important differences and in the case of preformed nanoparticles their size remains unchanged (a few nanometers) whereas for the in-situ nanocomposites gold ripening leads to large particles (hundreds of nanometers). The grown YBCO-Au films showed good superconducting characteristics (J(c) 2 MA/cm2 at 77 K) but the absence of Au inclusions inside the YBCO matrix explains the fact that no enhancement of vortex pinning was observed.     

Biocatalytically induced growth of gold nanoshells: using enzyme reaction for the controllable fabrication of nanomaterials

In the present work, the enzymatically controlled growth process of gold nanoshells (GNSs) in the presence of O2/glucose/glucose oxidase (GOx) and its chloroaurate ion electron acceptor is described. The biocatalytically stimulated growth process is one of the bio-inspired synthetic procedures directed by biological molecules which occur under ambient conditions. It is found that hydrogen peroxide (H2O2) could enlarge the gold nanoparticles (GNPs) on the surface of GNSs precursor composites, of which the preadsorbed GNPs serve as nucleation sites for further gold deposition. Here, GOx is harnessed for its unparalled level of catalytic activity and substrate specificity while H2O2 is produced as a by-product during the oxidation of D-glucose to gluconic acid by GOx. Then the bio-generated H2O2 is used as the reducing agent in the catalytic deposition process of GNSs formation. During the procedure, the localized surface plasmon resonance peaks range across hundreds of nanometers from visible to near infrared region accompanying by the resultant formation of uniform and continuous core-shell nanostructures. The corresponding optical, morphological and enzyme kinetic properties are all well investigated. The novel protocol offers a new perspective for the bio-directed synthesis method in nanotechnology.     

Multichannel electrochemiluminescence of luminol in neutral and alkaline aqueous solutions on a gold nanoparticle self-assembled electrode

The electrochemiluminescence (ECL) behavior of luminol on a gold nanoparticle self-assembled electrode in neutral and alkaline pH conditions was studied under conventional cyclic voltammetry (CV). The gold nanoparticle self-assembled electrode exhibited excellent electrocatalytic property and redox reactivity to the luminol ECL system. In neutral solution, four ECL peaks were observed at 0.69, 1.03, -0.45, and -1.22 V (vs SCE) on the curve of ECL intensity versus potential. Compared with a bulk gold electrode, two anodic and one cathodic ECL peaks were greatly enhanced, and one new cathodic ECL peak appeared. In alkaline solution, two anodic ECL peaks were obtained at 0.69 and 1.03 V, which were much stronger than those on a bulk gold electrode. These ECL peaks were found to depend on gold nanoparticles on the surface of the electrode, potential scan direction and range, the presence of O(2) or N(2), the pH and concentration of luminol solution, NaBr concentration, and scan rate. The emitter of all ECL peaks was identified as 3-aminophthalate by analyzing the ECL spectra. The spatial distribution of the luminol ECL peaks on the gold nanoparticle self-assembled electrode was studied by CCD. The surface state of the gold nanoparticle self-assembled electrode was characterized by scanning electron microscopy (SEM) and UV-visible reflection spectra. The mechanism for the formation of these ECL peaks has been proposed. The results indicate that the gold nanoparticle self-assembled electrode could lead to novel ECL properties, and strong luminol ECL in neutral and alkaline solutions could be obtained on such an electrode, which is of great analytical potential.     

Fabrication of a novel hydrogen peroxide biosensor based on C@Au composite

A promising hydrogen peroxide (H2O2) biosensor was fabricated by the immobilization of hemoglobin (Hb) on C@Au composite surface. The composite with carbon spheres and gold shell (C@Au) was synthesized via the seed-growth assembly technique. The assembly of the gold shell on carbon sphere surfaces was characterized by scanning electron miscroscopy (SEM). Owing to the unique structure and large surface area of the gold shell, the composite offered an effective interface for the immobilization of hemoglobin to fabricate a H2O2 biosensor. The obtained biosensor showed a wide linear range from 5.0 microM to 135 microM with a detection limit of 1.67 microM at 3sigma, and the apparent Michaelis-Menten constant (Km(app)) of the immobilized Hb was calculated to be 88.6 microM. Moreover, the biosensor also exhibited good reproducibility and long-term stability. Therefore, this kind of composite can provide an ideal matrix for protein immobilization and biosensor fabrication.     

Preparation of controllable core-shell gold nanoparticles and its application in detection of silver ions

We report a novel shell technique to prepare controllable core-shell nanoparticles. In this technique, the shell is formed when the core reacts with metal ions and Na(2)S(2)O(3) and the size of the core and thickness of the shell can be controlled. Transmission electron microscopy and X-ray diffraction reveal that the shell consists of insoluble complex salts comprising Au(2)S, AuAgS, and Ag(3)AuS(2). The resulting core-shell nanoparticles obtained at different reaction stages demonstrate that the formation of Au(2)S, AuAgS, and Ag(3)AuS(2) shell proceeds from the outside. The morphological evolution of the particles changes significantly with reaction time demonstrating that formation of the shell results from diffusion in the solid shell. The core-shell nanoparticles produced by this technique can be used as nanosensors to detect Ag(+) in aqueous media with high selectivity and sensitivity. The excellent selectivity for Ag(+) is demonstrated by comparing the response to other metal ions. In addition, our evaluation indicates that gold nanorods offer higher sensitivity than gold nanospheres.     

Complete oxidation of ethylene over supported gold nanoparticle catalysts

Complete oxidation of ethylene was performed over supported noble metals or transition metals oxide catalysts and on monoliths under atmospheric pressure. Gold nanoparticles on Al2O3 or MxOy(M = Mo, Fe, Mn) were prepared by impregnation, coprecipitation, deposition, and dispersion methods. Nanoparticles prepared by impregnation method were irregular and very large above 25 nm, but those by coprecipitation and deposition method were uniformly nanosized at 4-5 nm. The gold nanoparticle were outstandingly active in catalyzing oxidation of ethylene. The activity order of these catalysts with preparation methods was deposition > coprecipitation > impregnation, and Au/Co3O4 prepared by deposition method showed the best performance in ethylene oxidation. The addition of gold particles to MxOy/Al2O3 catalyst enhanced the ethylene oxidation activity significantly. The main role of the gold nanoparticles apparently was to promote dissociative adsorption of oxygen and to enhance the reoxidation of the catalyst.     

Controlled growth of vertically oriented hematite/Pt composite nanorod arrays: use for photoelectrochemical water splitting

Highly ordered and vertically grown Pt-doped α-Fe(2)O(3) nanorod arrays on a gold substrate were successfully prepared by the electrochemical co-deposition method using an anodized aluminum oxide template. The effect of the Pt doping in α-Fe(2)O(3) nanorod arrays on their water splitting ability was investigated for the first time. The elemental maps obtained by energy dispersive spectroscopy showed that the Pt was uniformly dispersed in the α-Fe(2)O(3) nanorod arrays. The photoelectrochemical properties of the α-Fe(2)O(3)/Pt composite nanorod arrays as a function of the Pt content were studied by measuring their photocurrent-potential behavior in 1 M NaOH electrolyte under AM 1.5 100 mW cm(-2) illumination. The Pt-doped α-Fe(2)O(3) nanorod arrays show an improvement in solar-to-hydrogen conversion efficiency (～5%) for photoelectrochemical water splitting compared to undoped samples. To the best of our knowledge, it is the highest value yet obtained from α-Fe(2)O(3).     

Superoxide dismutase-based third-generation biosensor for superoxide anion

A third-generation biosensor for superoxide anion (O2-) was developed by immobilizing superoxide dismutase (SOD) on a self-assembled monolayer of cysteine on gold electrode; i.e., a SOD/cysteine-modified gold electrode (SOD/Cys/Au) was fabricated. A rapid and direct electron transfer of SOD was realized at the gold electrode by using the cysteine molecule as an electron-transfer promoter. The promoted direct electron transfer of SOD and biomolecular recognition by the exploitation of specific and significant enzyme-substrate reactivity of SOD toward O2- combined with the low operating potential enabled a sensitive measurement of O2-. At SOD/Cys/Au, O2- could be specifically oxidized and reduced to O2 and hydrogen peroxide, respectively, through the inherent catalytic reaction of SOD. This allowed us to measure O2- by polarizing the electrode both anodically and cathodically. We could successfully measure O2- by suitably polarizing the electrode, typically at 300 and -200 mV versus Ag/AgCl without the virtual interference from physiological levels of H2O2, ascorbic acid, uric acid, and metabolites of neurotransmitters. The response mechanism of SOD/Cys/Au to O2- and its sensor characteristics are also presented and discussed.     

Monodisperse α-Fe(2)O(3)@SiO(2)@Au core/shell nanocomposite spheres: synthesis, characterization and properties

A new hybrid spherical structure α-Fe(2)O(3)@SiO(2)@Au with a size of about 141?nm was designed, with a hematite cubic core surrounded by a thick silica shell and further decorated with gold nanoparticles. The monodisperse α-Fe(2)O(3)@SiO(2) spheres were first prepared by a sol-gel process based on the modified St?ber method. Subsequently, the surface of the α-Fe(2)O(3)@SiO(2) particles was functionalized by-NH(2) functional groups. The electrostatic attraction of -NH(2) groups will attach the negatively charged Au nanoparticles to the amino-functionalized α-Fe(2)O(3)@SiO(2) nanospheres in order to prepare α-Fe(2)O(3)@SiO(2) monodisperse hybrid spheres. The M(H) hysteresis loop for α-Fe(2)O(3)@SiO(2) and α-Fe(2)O(3)@SiO(2)@Au spheres indicates that the nanocomposite spheres exhibit superparamagnetic characteristics at room temperature. The optical properties and the application of these hybrid nanocomposites as catalysts for the conversion of CO to CO(2) have also been studied.     

A novel nanostructured iron oxide-gold bioelectrode for hydrogen peroxide sensing

Fe(3)O(4) nanoparticles covalently linked to a gold electrode have been used for immobilizing catalase (CAT) enzyme to sense the presence of various concentrations of H(2)O(2). These nanoparticles ranging from 20 to 30 nm were synthesized by thermal co-precipitation of ferric and ferrous chlorides. SEM and XRD have been used for morphological and structural characterization of Fe(3)O(4) nanoparticles. CAT enzyme was linked covalently to the surface of iron oxide using carbodiimide in phosphate buffer (pH 7.4) at 4?°C. The enzyme-iron oxide link was confirmed by FT-IR spectroscopy. Sensing studies carried out using cyclic voltammetry showed a linear response of the CAT/nano Fe(3)O(4)/Au bioelectrode towards H(2)O(2) between 1.5 and 13.5 μM with a very sharp response time of 2 s.