Three-dimensional hierarchical CuO gas sensor modified by Au nanoparticles

The three-dimensional hierarchical CuO and Au nanoparticles were synthesized by the hydrothermal method, respectively. The hierarchical CuO and the Au nanoparticles samples were characterized by X-ray diffraction and scanning electronic microscope, respectively. The as-synthesized CuO was assembled regularly from the nanosheets with thickness of 100 nm. The size of Au nanoparticles ranged from 50 to 200 nm. The hierarchical CuO gas sensors modified by different concentration of gold were fabricated. All the Au-loaded CuO gas sensors enhanced the response to ethanol and xylene while reducing the response to methanol, acetone, and formaldehyde. The results indicate that the Au nanoparticles prepared with PVP as surfactant can improve the selectivity of CuO gas sensors to ethanol gas for other common organic volatile gases. The improvement of gas sensing is mainly attributed to the different catalytic efficiency of the Au nanoparticles for different reactions. Meanwhile, the related mechanisms are discussed.

Dispersion of Active Au Nanoparticles on Mesoporous SBA-15 Materials

Chemical modification(CM)and deposition-precipitation(DP)methods were used for the dispersion of active Au nanoparticles on mesoporous silica materials in this work.XRD,TEM,N2 adsorption isotherms and UV-Vis absorption spectra were used to characterize in detail Au-SBA-15 materials prepared by the two methods. The analysis results showed that high loading(1.7%,by mass)and uniform Au nanoparticles(approximately 3 nm) were dispersed in the channels of mesoporous SBA-15 by the CM method.While for the DP method,most of Au nanoparticles with the size of 10—15nm were aggregated outside of the channels of SBA-15 and the actual loading of Au was only 0.38%(by mass).

Green-chemistry Compatible Approach to TiO_2-supported PdAu Bimetallic Nanoparticles for Solvent-free 1-Phenylethanol Oxidation under Mild Conditions

Ti O2-supported Pd Au bimetallic nanoparticles(NPs) with small size and good dispersity were prepared by the room-temperature ionic liquid-assisted bimetal sputtering, which is simple, environmentally friendly, and free of additives and byproducts. Pd/Au atomic ratio can be tuned by controlling the sputtering conditions simply. High catalytic activity was found in Pd Au–NPs–Ti O2 hybrids for solvent-free selective oxidation of 1-phenylethanol using O2 as the oxidant at the low temperature of 50 °C and low pressure of 1 atm. It was found that Pd/Au ratio strongly affected the catalytical activity, and the highest conversion of about 35 % and turnover frequency of about 421 h-1were achieved at 1:1 of Pd/Au atomic ratio. The synergistic effect in Pd Au NPs was also discussed based on the comprehensive characterization results.The present approach may offer an alternative platform for future development of green-chemistry compatible bimetallic nanocatalysts.

Tailoring the surface structures of iron oxide nanorods to support Au nanoparticles for CO oxidation

Iron oxide supported Au nanomaterials are one of the most studied catalysts for low-temperature CO oxidation.Catalytic performance not only critically depends on the size of the supported Au nanoparticles(NPs)but also strongly on the chemical nature of the iron oxide.In this study,Au NPs supported on iron oxide nanorods with different surface properties throughβ-FeOOH annealing,at varying temperatures,were synthesized,and applied in the CO oxidation.Detailed characterizations of the interactions between Au NPs and iron oxides were obtained by X-ray diffraction,transmission electron microscopy(TEM),and X-ray photoelectron spectroscopy.The results indicate that the surface hydroxyl group on the Au/FeOOH catalyst,before calcination(Au/FeOOH-fresh),could facilitate the oxygen adsorption and dissociation on positively charged Au,thereby contributing to the low-temperature CO oxidation reactivity.After calcination at 200℃,under air exposure,the chemical state of the supported Au NP on varied iron oxides partly changed from metal cation to Au0,along with the disappearance of the surface OH species.Au/FeOOH with the highest Au0 content exhibits the highest activity in CO oxidation,among the as-synthesized catalysts.Furthermore,good durability in CO oxidation was achieved over the Au/FeOOH catalyst for 12 h without observable deactivation.In addition,the advanced identical-location TEM method was applied to the gas phase reaction to probe the structure evolution of the Au/iron oxide series of the catalysts and support structure.A Au NP size-dependent Ostwald ripening process mediated by the transport of Au(CO)x mobile species under certain reaction conditions is proposed,which offers a new insight into the validity of the structure-performance relationship.

Improved Plasmonic Hot‑Electron Capture in Au Nanoparticle/Polymeric Carbon Nitride by Pt Single Atoms for Broad‑Spectrum Photocatalytic H_(2)Evolution

ABSTRACT Rationally designing broad-spectrum photocatalysts to harvest whole visible-light region photons and enhance solar energy conversion is a“holy grail”for researchers,but is still a challenging issue.Herein,based on the common polymeric carbon nitride(PCN),a hybrid co-catalysts system comprising plasmonic Au nanoparticles(NPs)and atomically dispersed Pt single atoms(PtSAs)with different functions was constructed to address this challenge.For the dual co-catalysts decorated PCN(PtSAs–Au_(2.5)/PCN),the PCN is photoexcited to generate electrons under UV and short-wavelength visible light,and the synergetic Au NPs and PtSAs not only accelerate charge separation and transfer though Schottky junctions and metal-support bond but also act as the co-catalysts for H_(2) evolution.Furthermore,the Au NPs absorb long-wavelength visible light owing to its localized surface plasmon resonance,and the adjacent PtSAs trap the plasmonic hot-electrons for H_(2) evolution via direct electron transfer effect.Consequently,the PtSAs–Au_(2.5)/PCN exhibits excellent broad-spectrum photocatalytic H_(2) evolution activity with the H_(2) evolution rate of 8.8 mmol g^(−1) h^(−1) at 420 nm and 264μmol g^(−1) h^(−1) at 550 nm,much higher than that of Au_(2.5)/PCN and PtSAs–PCN,respectively.This work provides a new strategy to design broad-spectrum photocatalysts for energy conversion reaction.

Transient competition between photocatalysis and carrier recombination in TiO_2 nanotube film loaded with Au nanoparticles

Highly ordered TiO2 nanotube array （TNA） films are fabricated by using an anodic oxidation method. Au nanoparticles （NPs） films are decorated onto the top of TNA films with the aid of ion-sputtering and thermal annealing. An enhanced photocatalytic activity under ultraviolet C （UVC, 266 nm） light irradiation is obtained compared with that of the pristine TNA, which is shown by the steady-state photoluminescence （PL） spectra. Furthermore, a distinct blue shift in the nanosecond time-resolved transient photoluminescence （NTRT-PL） spectra is observed. Such a phenomenon could be well explained by considering the competition between the surface photocatalytic process and the recombination of the photo-generated carriers. The enhanced UV photocatalytic activities of the Au-TNA composite are evaluated through photo-degradation of methyl orange （MO） in an aqueous solution with ultraviolet-visible absorption spectrometry. Our current work may provide a simple strategy to synthesize defect-related composite photocatalytic devices.

Surface Plasmon Resonance Enhanced Scattering of Au Colloidal Nanoparticles

Suspended gold nanoparticles have been synthesized via electrochemical method. The strongest resonance scattering peak is at 485 nm, which results from the surface plasmon resonance. When the excited wavelength is at 242 nm (12.4 × 1014 Hz), there have been a 1/2 fraction frequency scattering peak at 485 nm (1/2 × 12.4 × 1014 Hz) and a 1/3 fraction frequency scattering peak at 726 nm (1/3 × 12.4 × 1014 Hz) displayed. Emission spectra with different particle diameters were compared, the intensity of scattering light increases with the particle size. The frequency-dependent scattering average cross section of small particle was calculated from Mie theory. The model calculation is in agreement with the experimental results.

Novel Au nanoparticles-inlaid titanium paper for PEM water electrolysis with enhanced interfacial electrical conductivity

Proton-exchange membrane water electrolysis(PEM WE)is a particularly promising technology for renewable hydrogen produc-tion.However,the excessive passivation of the gas diffusion layer(GDL)will seriously affect the high surface-contact resistance and result in energy losses.Thus,a mechanism for improving the conductivity and interface stability of the GDL is an urgent issue.In this work,we have prepared a hydrophilic and corrosion resistant conductive composite protective coating.The polydopamine(PDA)film on the Ti surface,which was obtained via the solution oxidation method,ensured that neither micropores nor pinholes existed in the final hybrid coatings.In-situ reduced gold nanoparticles(AuNPs)improved the conductivity to achieve the desired interfacial contact resistance and further enhanced the corrosion resistance.The surface composition of the treated samples was investigated using scanning electron microscopy(SEM),transmis-sion electron microscopy(TEM),X-ray diffraction(XRD),and Fourier transform infrared spectroscopy(FTIR).The results indicated that the optimized reaction conditions included a pH value of 3 of HAuCl_(4) solution with PDA deposition(48 h)on papers and revealed the lowest con-tact resistance(0.5 mΩ·cm^(2))and corrosion resistance(0.001μA·cm^(−2))in a 0.5 M H_(2)SO_(4)+2 ppm F−solution(1.7 V vs.RHE)among all the modified specimens,where RHE represents reversible hydrogen electrode.These findings indicated that the Au-PDA coating is very appropriate for the modification of Ti GDLs in PEM WE systems.

Study on the Electrical Conductivity of Au Nanoparticle/Chloroform and Toluene Suspensions

Au nanoparticles capped by hexadecanethiol and dodecanethiol were chemically synthesized. The characteristics of electrical conductivity for the capped nanoparticles dissolved in chloroform and toluene solvents were investigated. The electrical conductivity of the samples is conspicuously Au nanoparticle concentration dependent. The results show that a rapid conductivity increases when the nanoparticle concentration increases from low value to a moderate value of 5.47 g/L and 11.22 g/L, which is capped by hexadecanethiol and dodecanethiol in chloroform solvent, and 2.77 g/L and 7.88 g/L in toluene solvent. The room-temperature dc conductivity σ dc of Au nanoparticle capped by hexadecanethiol is smaller than that capped by dodecanethiol in the whole range of Au nanoparticle concentrations. The conductivity of Au nanoparticle suspensions increases almost linearly in the temperature range in above two solvents.

Synthesis of Ni@Au Core-shell Nanoparticles and Its Applications in Ullmann Reaction as a Synergistic Catalyst

The Ni@Au core-shell nanoparticles had been successfully synthesized from aqueous solution by one-step route at room temperature. The Ni@Au nanoparticles can be an excellent catalyst for Ullmann reaction. The advantage of Ni@Au is that the catalyst does not need additional reducing agents. The Au shell can effectively protect the Ni core from oxidation. The Ni core and Au shell have both composited in structure and cooperated in function.

Improved hydrogen oxidation reaction under alkaline conditions by Au–Pt alloy nanoparticles

This work demonstrates the outstanding performance of alloyed Au1 Pt1 nanoparticles on hydrogen oxidation reaction(HOR)in alkaline solution.Due to the weakened hydrogen binding energy caused by uniform incorporation of Au,the alloyed Au1Pt1/C nanoparticles exhibit superior HOR activity than commercial PtRu/C.On the contrary,the catalytic performance of the phase-segregated Au2Pt1/C and Au1Pt1/C bimetallic nanoparticles in HOR is significantly worse.Moreover,Au1Pt1/C shows a remarkable durability with activity dropping only 4% after 3000 CV cycles,while performance attenuation of commercial PtRu/C is high up to 15% under the same condition.Our results indicate that the alloyed Au1Pt1/C is a promising candidate to substitute commercial PtRu/C for hydrogen oxidation reaction in alkaline electrolyte.

Direct Electrochemistry and Electrocatalysis of Hemoglobin at PAMAM Dendrimer-MWNTs-Au Nanoparticles Composite Film Modified Glassy Carbon Electrode

The direct electron transfer of hemoglobin at the PAMAM-MWNTs-AuNPs composite film modified glassy carbon electrode was studied. In a phosphate buffer solution（PBS, pH=7.0）, the formal potential（E^0） of Hb was -0.105 V versus SCE, the electron transfer rate constant was 4.66 s-1. E^0＇ of Hb at the modified electrode was linearly varied in a pH range of 5.0-8.0 with a slope of-49.2 mV/pH. The Hb/PAMAM-MWNTs-AuNPs/GCE gave an excellent electrocatalytic response to the reduction of hydrogen peroxide. The catalytic current increased linearly with H2O2 concentration in a range of 1.0× 10^-6 to 2.2× 10^-3 mol/L. The detection limit was 2.0× 10^-7 mol/L at a signal to noise ratio of 3. The Michaelis-Menten constant（Km^app） was 2.95 mmol/L.

The enhancement of 21.2%-power conversion efficiency in polymer photovoltaic cells by using mixed Au nanoparticles with a wide absorption spectrum of 400 nm–1000 nm

Au nanoparticles （NPs） mixed with a majority of bone-like, rod, and cube shapes and a minority of irregu- lar spheres, which can generate a wide absorption spectrum of 400 nm-1000 nm and three localized surface plas- mon resonance peaks, respectively, at 525, 575, and 775 nrn, are introduced into the hole extraction layer poly（3,4- ethylenedioxythiophene）：poly（4-styrenesulfonate） （PEDOT：PSS） to improve optical-to-electrical conversion performances in polymer photovoltaic ceils. With the doping concentration of Au NPs optimized, the cell performance is significantly improved： the short-circuit current density and power conversion efficiency of the poly（3-hexylthiophene）： [6,6]-phenyl- C60-butyric acid methyl ester cell are increased by 20.54% and 21.2%, reaching 11.15 mA.cm-2 and 4.23%. The variations of optical, electrical, and morphology with the incorporation of Au NPs in the cells are analyzed in detail, and our results demonstrate that the cell performance improvement can be attributed to a synergistic reaction, including： 1） both the local- ized surface plasmon resonanceand scattering-induced absorption enhancement of the active layer, 2） Au doping-induced hole transport/extraction ability enhancement, and 3） large interface roughness-induced efficient exciton dissociation and hole collection.

Detection of HBV and HCV Coinfection by TEM with Au Nanoparticle Gene Probes

Gold（Au） nanoparticle HBV DNA or HCV cDNA gene probes were prepared and were used to detect HBV DNA and HCV RNA extracted from positive serum of patients with HBV and HCV coinfection directly by transmission electron microscopy （TEM）. PCR identifying HBV and HCV in serum of patients with HBV and HCV coinfection was established. Alkanethiol-modified oligonucleotide was bound with self-made Au nanoparticles to form nanoparticle HBV DNA or HCV cDNA gene probes through covalent binding of Au-S. HBV DNA and HCV RNA extracted from positive serum of patients with HBV and HCV coinfection was added to the detection system composed of nanoparticle HBV DNA and（or） HCV cDNA gene probes, The results showed that HBV DNA and HCV RNA could be specifically amplified by PCR. The zones of DNA amplification appeared in 431 bp and 323 bp respectively. When HBV DNA and HCV RNA extracted from positive serum of patients with HBV and HCV coinfection were added to the detection system, TEM displayed the nanoparticles self-assembled into large network aggregates. It was concluded that the detection of HBV and HCV coinfection by TEM was convenient and efficient with high specificity and sensitivity.

Microwave Synthesis of Au Nanoparticles with the System of AuCl_4-CH_3CH_2OH

The Au nanoparticles has been prepared by microwave high-pressure procedure with alcohol as the reducing agent. The color of colloidal Au nanoparticles is blue-violet. The maximum absorption spectrum of colloidal Au is at 580 nm, and the resonance scattering peak is at 580 nm. Using this method, the colloidal Au of long-time stability can be prepared Simply and quickly.

Highly Sensitive SnO_2 Nanorods Ethanol Sensors with the Adsorption of Au Nanoparticles

Flower-liked SnO_2 nanorods were prepared by a hydrothermal method.The sensors were fabricated using SnO_2 nanorods adsorption of Au nanoparticles through sputtering deposition.We found that the loading of a small amount of Au nanoparticles on the surface of SnO_2 nanorods can effectively enhance and functionalize the gas sensing performance of SnO_2 nanorods,which due to the Au adsorption make the surface-depletion effect more pronounced.Such enhanced surface depletion increases the sensitivity,lowers the operation temperature and decreases the response time.

Au-nanocluster-loaded human serum albumin nanoparticles with enhanced cellular uptake for fluorescent imaging

Protein-directed fluorescent Au nanoclusters have been widely studied owing to their potential applications in sensing,imaging,and drug and gene delivery.However,the use of nanoclusters in drug delivery is limited by low cellular uptake.In this study,human serum albumin-directed Au nanoclusters served as building blocks to obtain protein nanoparticles by desolvation.The nanoparticles had a decent quantum yield(QY),high colloidal stability and low cytotoxicity,and they could be readily conjugated with biological molecules.The cellular uptake of the Au nanoclusters and nanocluster-loaded protein nanoparticles were studied by confocal fluorescence microscopy.Agglomeration of the protein-directed Au nanoclusters into 50–150-nm nanoparticles dramatically increased the cellular uptake.

Preparation and Catalytic Performance of Microporous Polymer/Au Nanoparticles Composite Microspheres

Polystyrene crosslinked microspheres were prepared by soap-free emulsion polymerization using styrene (St) and divinylbenzene (DVB) as monomers;then,the microporous structure was knitted by the Friedel-Crafts alkylation reaction,and the Au nanoparticles (AuNPs) were loaded into the pores through thermal reduction,to obtain AuNPs/ hyper-crosslinked microporous polymer composite microspheres.SEM and particle-size test results show that the microspheres show good monodispersity.The micropore analysis indicates that the specific surface area and the pore volume of the microporous polymer microspheres decrease with increasing DVB content,and when the DVB content is 0.1%,the specific surface area reaches a maximum of 1 174.6 m2/g.After loading AuNPs,the specific surface area and the amount of micropores of the composite microspheres decrease obviously.The results of XRD and XPS analyses suggest that HAuCl4 is reduced to AuNPs.The composite microspheres show a good catalytic performance for the reduction catalyst of 4-nitrophenol.

Microwave-Assisted Au and Ag Nanoparticle Synthesis: An Energy Phase-Space Projection Analysis

Microwave-assisted synthesis of gold and silver nanoparticles, as a function of Green Chemistry, non Green Chemistry, and four applicator types are reported. The applicator types are Domestic microwave ovens, commercial temperature controlled microwave chemistry ovens (TCMC), digesters, and axial field helical antennae. For each of these microwave applicators the process energy budget where estimated (Watts multiplied by process time = kJ) and energy density (applied energy divided by suspension volume = kJ·ml-1) range between 180 ± 176.8 kJ, and 79.5 ± 79 kJ·ml-1, respectively. The axial field helical field an-tenna applicator is found to be the most energy efficient (0.253 kJ·m-1 per kJ, at 36 W). Followed by microwave ovens (4.47 ± 3.9 kJ·ml-1 per 76.83 ± 39 kJ), and TCMC ovens (2.86 ± 2.3 kJ·m-1 per 343 ± 321.5 kJ). The digester applicators have the least energy efficiency (36.2 ± 50.7 kJ·m-1 per 1010 ± 620 kJ). A comparison with reconstructed ‘non-thermal’ microwave oven inactivation microorganism experiments yields a power-law signature of n = 0.846 (R2 = 0.7923) four orders of magnitude. The paper provides a discussion on the Au and Ag nanoparticle chemistry and bio-chemistry synthesis aspects of the microwave applicator energy datasets and variation within each dataset. The visual and analytical approach within the energy phase-space projection enables a nanoparticle synthesis route to be systematically characterized, and where changes to the synthesis are to be mapped and compared directly with historical datasets. In order to help identify lower cost nanoparticle synthesis, in addition to potentially reduce synthesis energy to routes informed changes to potentially reduce synthesis energy budget, along with nanoparticle morphology and yield.

Au Nanoparticle Formation from Amorphous Au/Si Multilayer

By direct observations of transmission electron microscopy (TEM), irreversible morphological transformations of as-deposited amorphous Au/Si multilayer (a-Au/a-Si) were observed on heating. The well arrayed sequence of the multilayer changed to zigzag layered structure at 478 K (=Tzig). Finally, the zigzag structure transformed to Au nanoparticles at 508 K. The distribution of the Au nanoparticles was random within the thin film. In situ X-ray diffraction during heating can clarify partial crystallization Si (c-Si) in the multilayer at 450 K (= ), which corresponds to metal induced crystallization (MIC) from amorphous Si (a-Si) accompanying by Au diffusion. On further heating, a-Au started to crystallize at around 480 K (=Tc) and gradually grew up to 3.2 nm in radius, although the volume of c-Si was almost constant. Continuous heating caused crystal Au (c-Au) melting into liquid AuSi (l-AuSi) at 600 K (= ), which was lower than bulk eutectic temperature ( ). Due to the AuSi eutectic effect, reversible phase transition between liquid and solid occurred once temperature is larger than . Proportionally to the maximum temperatures at each cycles (673, 873 and 1073 K), both and Au crystallization temperature approaches to . Using a thermodynamic theory of the nanoparticle formation in the eutectic system, the relationship between and the nanoparticle size is explained.