Diameter Au Nanoparticles Research Articles

Ppb level triethylamine detection of yolk-shell SnO2/Au/Fe2O3 nanoboxes at low-temperature

Yolk-shell nanostructures with high specific surface area and more active areas become the development direction of gas sensors. In this work, yolk-shell SnO2/Au/Fe2O3 nanoboxes with specific surface area of 38.3 m2 g−1 were successfully prepared. The size of Fe2O3 nanocubes was about 300 nm, the thickness of SnO2 was about 20 nm and the diameter of Au nanoparticles was about 12 nm. Benefiting from the distinctive structure and catalytic activity of precious metals, the as-prepared SnO2/Au/Fe2O3 yolk-shell nanostructures showed outstanding response to triethylamine (TEA) gas at 240 °C. The response value to 100 ppm TEA gas was 126.84, which was about 6 times and 14 times of the Au/Fe2O3 and Fe2O3 samples. In addition, yolk-shell SnO2/Au/Fe2O3 nanoboxes also exhibited a low detection limit (50 ppb), good response and recovery character (7/10 s). This experiment provided novel ideas for the design of new nanostructures for gas sensors.

Size-Selective Electrophoretic Deposition of Gold Nanoparticles Mediated by Hydroquinone Oxidation.

Here we describe the size-selective, hydroquinone (HQ)-mediated electrophoretic deposition of 4 and 15 nm diameter citrate-stabilized Au nanoparticles (NPs) onto a glass/indium-tin-oxide (ITO) electrode. Protons liberated from HQ during electrochemical oxidation at the Au NP surface during collisions with the glass/ITO electrode lead to Au NP deposition through neutralization of the citrate stabilizer surrounding the Au NPs, protonation of the glass/ITO electrode, or some combination of the two. Interestingly, the 4 nm Au NPs deposit at about 300-400 mV more negative potential than that of 15 nm diameter Au NPs because of faster HQ oxidation kinetics at the 4 nm NPs, leading to lower overpotentials. This allows for selective deposition of the 4 nm Au NPs over 15 nm Au NPs in a solution containing a mixture of the two by controlling the electrode potential. Controlled pH experiments indicate that significant NP deposition occurs on glass/ITO at a pH of ∼3, giving insight into the local pH needed from HQ oxidation in order to deposit the Au NPs. Experiments performed at different ionic strengths confirm that migration is a major mode of mass transport of the NPs to the glass/ITO. Long deposition times lead to films of densely packed Au NPs that are mostly free from NP-NP contact, indicating that some electrostatic repulsion between the NPs remains during the deposition. This simple method of Au NP deposition may find use for separation of Au NPs and electrode device preparation for a variety of sensor and electrocatalysis applications.

Enhanced Photocatalytic Degradation of Methylene Blue by Using Au-TiO<sub>2</sub>

In this work, Au-TiO2 nanoparticles (NPs) were synthesized in a single step by flame spray pyrolysis (FSP) method. X-ray diffraction (XRD) results indicated that phase structures of all samples TiO2 were the mixture of anatase and rutile phases. High resolution transmission electron microscopy (HRTEM) showed that dark spots of Au NPs deposited on larger TiO2 nanoparticles. HRTEM results indicated TiO2 NPs were average crystallite size in the range of 10–30 nm whereas the average diameter of Au NPs was about 5–10 nm. UV–Vis absorption spectroscopy technique showed peaks attributable of surface plasmon resonance (SPR) to Au NPs loaded on TiO2 in the wavelength of 500–630 nm. The Au-TiO2 NPs showed excellent photocatalytic activity for the degradation of methylene blue (MB) under UV-Vis irradiation. It was found that 0.25 mol% Au-TiO2 which was a better photocatalyst than others under the same reaction conditions. The results showed that Au NPs-loading could effectively improve the photocatalytic activities of TiO2.

Control of Au Nanoparticles Structural and Optical Properties by Laser Radiation and Thermal Annealing

The aim of this study is to show the possibility to control structural and optical properties of Au nanoparticles (AuNPs) by changing their size and concentration and make comparison between methods of their formation. 1.4 nm thick Au films were formed on borosilicate glass substrates by the vacuum evaporation method. AuNPs were formed on the surface of the substrate by two methods. First is the irradiation by the Nd:YAG laser pulses with intensities from 75 to 180 MW/cm2. Second is thermal annealing, at temperature T=400 °C and the time of curing was varied from 24 to 72 hours. The irradiation of Au film by laser leads to formation of AuNPs. The increase of intensity of laser radiation causes the disappearing of small Au nanoparticles and growing of big nanoparticles from 113-180 nm due to the agglomeration of small particles into big ones and, correspondingly, concentration of particles decreases. In contrast, thermal annealing at T=400 °C from 48 to 72 hours leads to the island formation with the non-spherical shape and their dividing into several islands according to the spinodal dewetting model. As a result, the mean diameter of AuNPs is decreased from 161 to 85 nm but concentration increases.

Efficiency Enhancement of Perovskite Solar Cells with Plasmonic Nanoparticles: A Simulation Study.

Recently, hybrid organic-inorganic perovskites have been extensively studied due to their promising optical properties with relatively low-cost and simple processing. However, the perovskite solar cells have some low optical absorption in the visible spectrum, especially around the red region. In this paper, an improvement of perovskite solar cell efficiency is studied via simulations through adding plasmonic nanoparticles (NPs) at the rear side of the solar cell. The plasmonic resonance wavelength is selected to be very close to the spectrum range of lower absorption of the perovskite: around 600 nm. Both gold and silver nanoparticles (Au and Ag NPs) are selected to introduce the plasmonic effect with diameters above 40 nm, to get an overlap between the plasmonic resonance spectrum and the requested lower absorption spectrum of the perovskite layer. Simulations show the increase in the short circuit current density (Jsc) as a result of adding Au and Ag NPs, respectively. Enhancement in Jsc is observed as the diameter of both Au and Ag NPs is increased beyond 40 nm. Furthermore, there is a slight increase in the reflection loss as the thickness of the plasmonic nanoparticles at the rear side of the solar cell is increased. A significant decrease in the current loss due to transmission is achieved as the size of the nanoparticles increases. As a comparison, slightly higher enhancement in external quantum efficiency (EQE) can be achieved in case of adding Ag NPs rather than Au NPs.

Controlled Hetero‐Architectures of Au‐Nanoparticles‐Decorated ZnO Nanowires for Enhanced Field Electron Emission Displays

AbstractThe spitzer shaped pointed ZnO nanowires of diameter 120 nm and length ∼5‐6 μm synthesized via hydrothermal techniques were decorated with Au nanoparticles of diameter < 20 nm along their textural boundaries. The turn‐on field (Eon) of 1.56 V/μm required to draw current density of 10 μA/cm2 from ZnO nanowires was reduced further to 0.96 V/μm after controlled decoration of Au nanoparticle, is significantly lower than pristine/doped ZnO nanostructures, Ag@ZnO, Au@ZnO, Au@CuO, and MoS2@TiO2 heterostructure based field emission (FE) devices. The orthodoxy test confirmed the feasibility of field‐enhancement factor (βFE) of 4477 for Au/ZnO/ITO emitters. The enhanced FE behavior are attributed to pointed nanotips, individual dispersion of Au nanoparticles along the textural boundaries of ZnO nanowires, and enhanced energy well formation at their interface. Moreover, the density of state increases enormously due to the hetero‐structured interface of Au@ZnO and a significant amount of electrons from both Au and ZnO contribute for enhanced emission current density (2.1 mA/cm2 @ 1.92 V/μm), and greatly stable electron emission. Our experiments suggest that the tunable hetero‐architectures of Au nanoparticles@ZnO nanowires hold the promises for applications in display screens and intense electron source.

Conductive Atomic Force Microscopy Study of the Resistive Switching in Yttria-Stabilized Zirconia Films with Au Nanoparticles.

We report on the investigation of the resistive switching (RS) in the ultrathin (≈5 nm in thickness) yttria-stabilized zirconia (YSZ) films with single layers of Au nanoparticles (NPs) by conductive atomic force microscopy (CAFM). Besides the butterfly-type hysteresis loops in the current-voltage (I-V) curves of the contact of the CAFM probe to the investigated film surface corresponding to the bipolar RS, the negative differential resistance (NDR) has been observed in the I-V curves of the AFM probe contact to the YSZ films with Au NPs in the conductive (“ON”) state. The NDR has been related to the resonant tunneling of electrons through the size-quantized energy states in the ultrafine (1 to 2 nm in diameter) Au NPs built in the conductive filaments in the YSZ films.

Aggregation-Dependent Oxidation of Metal Nanoparticles.

Here we describe the effect of aggregation on the oxidation of citrate-stabilized Au nanoparticles (NPs) attached electrostatically to amine-functionalized glass/ITO electrodes. When the Au NPs are attached to the electrode from a solution with pH greater than ∼3.0, they are well-separated on the electrode and oxidize in bromide-containing electrolyte at 0.698, 0.757, and 0.943 V (vs Ag/AgCl) for 4, 15, and 50 nm diameter Au NPs, respectively, in line with their size-dependent oxidation behavior. In solutions below pH 3.0, the Au NPs aggregate in solution and attach to the electrode in the aggregated form. The solution UV-vis spectra and scanning electron microscopy images of the electrodes show clear evidence of aggregation. The oxidation potential for aggregated 4 and 15 nm diameter Au NPs shifts positive by a maximum of 230 and 180 mV, respectively. The magnitude of the shift depends on the extent of aggregation, which was controlled by the solution pH and time. NP aggregation leads to a significant reduction in the surface area-to-volume ratio, which is likely responsible for the positive shift in the oxidation potential. The oxidation potential does not shift at all for aggregated 50 nm diameter Au NPs.

Highly efficient PeLEDs using gold nanoparticles modified PEDOT:PSS as the hole injection layer

Organic-inorganic hybrid perovskite light-emitting diodes (PeLEDs) have attracted increasing attentions recently due to their great potential in flat panel display and lightening as well as other advantages such as low cost, ease of fabrication, high color purity, and tunable emission from the visible to infrared wavelengths. Improving the electroluminescent efficiency and the device stability of PeLEDs became hot spots in recent studies. To achieve highly efficient PeLEDs, two critical criteria must be satisfied: pinhole-free perovskite film to suppress leakage currents and optimized device structures with minimum injection barriers that guarantee balanced charge injection into perovskites. Over the last decades, metallic nanostructures have been focused on improving the efficiency of organic optoelectronic devices, which is mainly based on the optical and electrical effects of metal nanoparticles (NPs), including localized surface plasmon resonance (LSPR)-enhanced fluorescence, electrical properties, interface effect, light scattering, and so on. However, there is few research dedicated to the metal plasmonic enhanced electroluminescence of perovskite. Driven by this motivation, metal NPs may provide many advantages in improving the performance of PeLEDs through optimizing the device structure. In this work, gold nanoparticles (Au NPs) aqueous solution (with Au NPs diameter of ~20 nm) was first synthesized by ″Frens″ method. And then, the Au NPs modified poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), which was obtained by mixing Au NPs aqueous solution with PEDOT:PSS with a desired volume ratio of 0.2:1, was introduced into CH3NH3PbBr3-based PeLEDs as the hole injection layer. It should be noted that the ~20 nm Au NPs was fully covered by ~45 nm PEDOT:PSS layer in order to avoid direct contact with the active layer of CH3NH3PbBr3, which is critical to prevent excitions quenching by a nonradiative energy transfer process at the surfaces of the metal NPs. Results show that, the photoluminescence (PL) and electroluminescence (EL) of CH3NH3PbBr3 film are both enhanced by ~2.41 fold and ~1.48 fold by the Au NPs, respectively. For the Au NPs modified PeLEDs with structure of ITO/Au NPs: PEDOT:PSS/PVK:CH3NH3PbBr3:TPBi/TPBi/Cs2CO3/Al, the turn-on voltage was ~3.0 V, the maximum luminance was ~16050 cd/m2, and the maximum current efficiency was ~7.02 cd/A, compared to the performance of the reference PeLEDs without Au NPs modification which exhibited the turn-on voltage of ~3.2 V, the maximum luminance of ~7156 cd/m2, and the maximum current efficiency of ~4.74 cd/A. By studying the underlying mechanisms, we found that the absorption spectra of Au NPs and PL spectra of CH3NH3PbBr3 film overlapped to each other very well, indicating that the LSPR effect of Au NPs could accelerate radiative decay rate of CH3NH3PbBr3 excitions accumulated at PEDOT:PSS/CH3NH3PbBr3 interface, which is helpful in making full use of CH3NH3PbBr3 excitions by avoiding them being quenched by interfacial excess charge carriers or anode. Our studies have provided an alternative way to further improve the EL efficiency of PeLEDs through interface modification with Au NPs, which is of great importance in both fundamental study of LSPR effect of Au NPs, and their potential applications in PeLEDs.

Fermi energy dependence of the optical emission in core/shell InAs nanowire homostructures

InAs nanowires grown by vapor–liquid–solid (VLS) method are investigated by photoluminescence. We observe that the Fermi energy of all samples is reduced by ∼20 meV when the size of the Au nanoparticle used for catalysis is increased from 5 to 20 nm. Additional capping with a thin InP shell enhances the optical emission and does not affect the Fermi energy. The unexpected behavior of the Fermi energy is attributed to the differences in the residual donor (likely carbon) incorporation in the axial (low) and lateral (high incorporation) growth in the VLS and vapor–solid (VS) methods, respectively. The different impurity incorporation rate in these two regions leads to a core/shell InAs homostructure. In this case, the minority carriers (holes) diffuse to the core due to the built-in electric field created by the radial impurity distribution. As a result, the optical emission is dominated by the core region rather than by the more heavily doped InAs shell. Thus, the photoluminescence spectra and the Fermi energy become sensitive to the core diameter. These results are corroborated by a theoretical model using a self-consistent method to calculate the radial carrier distribution and Fermi energy for distinct diameters of Au nanoparticles.

Size-Dependent Electrophoretic Deposition of Catalytic Gold Nanoparticles.

Here we describe size-dependent electrophoretic deposition (EPD) of citrate-stabilized Au nanoparticles (NPs) onto indium-tin-oxide-coated glass (glass/ITO) electrodes as studied by linear sweep stripping voltammetry (LSSV) and scanning electron microscopy (SEM). LSSV allows both the determination of the Au NP coverage and NP size from the peak area and the peak potential, respectively. Two-electrode EPD in aqueous solutions of Au NPs plus H2O2 reveal that a minimum potential of 1.5 V is needed for significant deposition of 4 nm diameter Au NPs as opposed to 2.0 V for 33 nm diameter Au NPs. EPD at 0.4 V in a solution of Au NPs prepared with a short 5 min reaction time led to the successful capture of 1-2 nm diameter Au NPs with appreciable coverage. In all cases, deposition did not occur in the absence of H2O2. Three-electrode experiments with a real reference electrode revealed the same size selective deposition with potential and that the amount of Au deposited depends on the deposition time and H2O2 concentration. The deposition occurs indirectly by oxidation of H2O2, which liberates protons and neutralizes the citrate stabilizer, leading to precipitation of the Au NPs onto the glass/ITO electrode. Studies on pH stability show that larger Au NPs aggregate at lower pH compared to smaller Au NPs. More importantly, though, 4 nm diameter Au NPs are much more catalytic for H2O2 oxidation, which is the main reason for the size selective deposition.

Tetrazole-Stabilized Gold Nanoparticles for Catalytic Applications

Abstract Herein, we report on a proof-of-concept application of tetrazole-stabilized Au nanoparticles (NPs) for CO oxidation. After impregnation of the support material TiO2 with the tetrazole-stabilized Au NPs (diameter<5 nm), a thermal heat treatment under oxygen is used to remove the tetrazole from the NP surface. The resulting surfactant-free NPs are used in the CO oxidation and show enhanced catalytic activity in comparison to the untreated samples demonstrating the potential of tetrazole-stabilized NPs for various catalytic applications.

Morphology-selective synthesis of active and durable gold catalysts with high catalytic performance in the reduction of 4-nitrophenol

A series of novel catalysts consisting of nanosized Au particles confined in micro-mesoporous ZSM-5/SBA-15 (ZSBA) materials with platelet (PL), rod (RD), and hexagonal-prism (HP) morphologies have been synthesized in situ. These catalysts possess both SBA-15 and ZSM-5 structures and exhibit excellent stability of their active sites by confinement of the Au nanoparticles (NPs) within ZSBA. The catalysts have been characterized in depth to understand their structure–property relationships. The gold NP dimensions and the pore structure of the catalysts, which were found to be sensitive to calcination temperature and synthetic conditions, are shown to play vital roles in the reduction of 4-nitrophenol. Au/ZSBA-PL, with short mesochannels (210 nm) and a large pore diameter (6.7 nm), exhibits high catalytic performance in the reduction of 4-nitrophenol, whereas Au/ZSBA-HP and Au/ZSBA-RD, with long mesochannels and relatively smaller pore sizes, show poor catalytic activities. In the case of catalysts with different gold NP sizes, Au/ZSBA-PL-350 with an Au NP diameter of 4.0 nm exhibits the highest reaction rate constant (0.14 min-1) and turnover frequency (0.0341 s-1). In addition, the effect of the reaction parameters on the reduction of 4-nitrophenol has been systematically investigated. A possible mechanism for 4-nitrophenol reduction over the Au/ZSBA catalysts is proposed.

In-situfabrication of gold nanoparticle functionalized probes for tip-enhanced Raman spectroscopy by dielectrophoresis

We report the use of dielectrophoresis to fabricate in-situ probes for tip-enhanced Raman spectroscopy (TERS) based on Au nanoparticles. A typical conductive atomic force microscope (AFM) was used to functionalize iridium-coated conductive silicon probes with Au nanoparticles of 10-nm diameter. Suitable TERS probes can be rapidly produced (30 to 120 s) by applying a voltage of 10 Vpp at a frequency of 1 MHz. The technique has the advantage that the Au-based probes are ready for immediate use for TERS measurements, minimizing the risks of tip contamination and damage during handling. Scanning electron microscopy and energy dispersive x-ray spectroscopy were used to confirm the quality of the probes, and used samples of p-ATP monolayers on silver substrates were used to demonstrate experimentally TERS measurements.

Aqueous Solution-Based Fe3O4 Seed-Mediated Route to Hydrophilic Fe3O4-Au Janus Nanoparticles.

Hydrophilic Fe3O4-Au Janus nanoparticles have been synthesized through a facile aqueous solution-based Fe3O4 seed-mediated chemical reduction route, where Au nanoparticles can be in situ formed on surfaces of PVP-modified Fe3O4 nanoparticles by adopting the well-known citrate reduction route. The diameter of Au nanoparticles can be controllably tuned in the range of 3-12 nm by simply changing the initial molar ratio between sodium citrate and auric acid. The as-fabricated hydrophilic Fe3O4-Au Janus nanoparticles have shown excellent catalytic performance with high catalytic activity and recyclability due to the synergetic effect between Au and Fe3O4 nanoparticles.

Growth and Deposition of Au Nanoclusters on Polymer-wrapped Graphene and Their Oxygen Reduction Activity.

The development of a non-Pt electrocatalyst with a high performance for the oxygen reduction reaction (ORR) is one of the central issues in polymer electrolyte fuel cells science. Au-nanoparticles (Au-NPs) with a diameter of <2 nm are one of the promising substitutes of Pt-NPs; however, it is still a challenge to synthesize such a small-sized Au-NPs with a narrow diameter distribution on a carbon support without using capping agents. We here describe a facile method to deposit uniform Au-NPs (diameter = 1.6 nm and 3.3 nm) on the stacked-graphene (<10 layers) coated with poly[2,2′-(2,6-pyridine)-5,5′-bibenzimidazole] without using any capping agents. The obtained Au-NPs exhibit an excellent ORR activity with the onset potential at −0.11 V and −0.09 V (vs. Ag/AgCl) for 1.6 nm and 3.3 nm, respectively. On the other hand, inhomogeneous Au-NPs with 4.6 nm in average diameter shows the onset potential at −0.15 V (vs. Ag/AgCl).

Changes in the characteristics of nonvolatile memory depending on Au nanoparticle size for p- and n-type channels

Nonvolatile memory capacitors were fabricated using immobilized Au nanoparticles (NPs) on p- and n-type doped Si substrates with Au NPs of diameter 3 and 2 nm immobilized by self-assembled monolayers on the Si surface, and the charge density and data retention of the programmed nonvolatile memories were found to change dramatically depending on both nanoparticle size and channel type (p-/n-). In the case of capacitors fabricated on p-Si substrates, large charge density was observed in devices using 3 nm Au NPs under low electric fields, and devices using 2 nm Au NPs were found to exhibit larger charge densities compared with devices using 3 nm Au NPs under high electric fields. Additionally, data retention was better for p-Si devices using 2 nm Au NPs compared with 3 nm Au NPs. However, data retention was worse for n-Si devices than for p-Si devices.

Size Dependent Plasmonic Effect on BiVO4 Photoanodes for Solar Water Splitting.

Plasmonic nanostructures show great promise in enhancing the solar water splitting efficiency due to their ability to confine light to extremely small volumes inside semiconductors. While size plays a critical role in the plasmonic performance of Au nanoparticles (AuNPs), its influence on plasmon-assisted water splitting is still not fully understood. This holds especially true for low band gap semiconductors, for which interband excitations occur in wavelength regions that overlap with plasmonic resonances. Here, BiVO4 films are modified with AuNPs of diameters varying from 10 to 80 nm to study the size dependence of the plasmonic effect. Plasmon resonance energy transfer (PRET) is found to be the dominant effect in enhancing the water splitting efficiency of BiVO4. “Hot electron” injection effect is weak in the case of BiVO4/AuNP. This is attributed to the interband excitation of BiVO4, which is unfavourable for the hot electrons accumulation in BiVO4 conduction band. The resonant scattering effect also contributes to the enhanced water splitting efficiency for the larger diameter AuNPs. It is also for the first time found that higher PRET effect can be achieved at larger off-normal irradiation angle.

MOCVD Growth of High-Quality and Density-Tunable GaAs Nanowires on ITO Catalyzed by Au Nanoparticles Deposited by Centrifugation.

High-quality and density-tunable GaAs nanowires (NWs) are directly grown on indium tin oxide (ITO) using Au nanoparticles (NPs) as catalysts by metal organic chemical vapor deposition (MOCVD). Au catalysts were deposited on ITO glass substrate using a centrifugal method. Compared with the droplet-only method, high-area density Au NPs were uniformly distributed on ITO. Tunable area density was realized through variation of the centrifugation time, and the highest area densities were obtained as high as 490 and 120 NP/μm2 for 10- and 20-nm diameters of Au NPs, respectively. Based on the vapor–liquid–solid growth mechanism, the growth rates of GaAs NWs at 430 °C were 18.2 and 21.5 nm/s for the highest area density obtained of 10- and 20-nm Au NP-catalyzed NWs. The growth rate of the GaAs NWs was reduced with the increase of the NW density due to the competition of precursor materials. High crystal quality of the NWs was also obtained with no observable planar defects. 10-nm Au NP-induced NWs exhibit wurtzite structure whereas zinc-blende is observed for 20-nm NW samples. Controllable density and high crystal quality of the GaAs NWs on ITO demonstrate their potential application in hybrid a solar cell.

Localized surface plasmon enhanced photoluminescence of ZnO nanosheets by Au nanoparticles

ZnO nanosheets were synthesized by a facile low temperature hydrothermal method and the Au nanoparticles were decorated on the surface of ZnO nanosheets by an in-situ solution method. The ZnO nanostructures had sheet-like morphology with relatively uniform size and possessed high crystallinity. The average diameter of Au nanoparticles decorated on the ZnO nanosheets was around 10–20nm. The ultraviolet emission from Au decorated ZnO nanosheets was greatly enhanced and the green emission was significantly suppressed compared with the bare ZnO nanosheets. This excellent photoluminescence performance was attributable to the surface-plasmon-mediated sequential transfer of defect energy from ZnO to Au and electron transfer from excited Au to ZnO.