Modification Of Au Nanoparticles Research Articles

Hierarchically Structured Nanotube Arrays as Heterogenous Photocatalysts for Highly Efficient Broadband Photoinduced Controlled Radical Polymerization

Highly ordered TiO2 nanotube arrays (TNTAs) and their heterostructure nanocomposites by structural engineering design were utilized as heterogeneous photocatalysts for highly efficient broadband photoinduced controlled radical polymerization (photoCRP), including photoATRP and PET-RAFT. Highly efficient broadband UV-visible light responsive photoCRP was achieved by combining the acceleration effects of electron transfer derived from the distinctive highly ordered nanotube structure of TNTAs and the localized surface plasmon resonance (LSPR) effect combined with the formation of the Schottky barrier via modification of Au nanoparticles. This polymerization system was capable to polymerize acrylate and methacrylate monomers with high conversion, "living" chain-ends, tightly regulated molecular weights, and outstanding temporal control properties. The heterogeneous nature of the photocatalysts enabled simple separation and effective reusability in subsequent polymerizations. These results highlight the modular design of highly efficient catalysts to optimize the controlled radical polymerization process.

Atomically dispersed Au anchored on CeO2 to enhancing the antioxidant activity

The modification of Au nanoparticles can improve the antioxidant activity of CeO2, however, nano Au/CeO2 has also met some problems such as low atomic utilization, the limit of reaction conditions, and high cost. Au single atom catalysts can well solve the above-mentioned problems, but there are some contradictory results about the activity of single atom Au1/CeO2 and nano Au/CeO2. Here, we synthesized rod-like Au single atom Au/CeO2 (0.4% Au1/CeO2) and nano Au/CeO2 (1% Au/CeO2, 2% Au/CeO2 and 4% Au/CeO2), and their antioxidant activity from strong to weak is 0.4% Au1/CeO2, 1% Au/CeO2, 2% Au/CeO2 and 4% Au/CeO2, respectively. The higher antioxidant activity of 0.4% Au1/CeO2 is mainly due to the high Au atomic utilization ratio and the stronger charge transfer between Au single atoms and CeO2, resulting in the higher content of Ce3+. Due to the coexistence of Au single atoms and Au NPs in 2% Au/CeO2, the antioxidant activity 2% Au/CeO2 is higher than that of 4% Au/CeO2. And the enhancement effect of Au single atoms was not affected by the concentration of ·OH and material concentration. These results can promote the understanding of the antioxidant activity of 0.4% Au1/CeO2 and promote its application.

An electrochemiluminescence immunosensor based on signal magnification of luminol using OER-activated NiFe2O4@C@CeO2/Au as effective co-reaction accelerator

In this work, a novel, label-free electrochemiluminescence (ECL) immunosensor was constructed for the ultrasensitive detection of carbohydrate antigen 15–3 (CA15-3) by the combined use of NiFe2O4@C@CeO2/Au hexahedral microbox and luminol luminophore. The synthesis of the co-reaction accelerator (NiFe2O4@C@CeO2/Au) was related to the calcination of FeNi-based metal–organic framework (MOF), as well as the ingrowth of CeO2 nanoparticles and modification of Au nanoparticles. To be specific, the electrical conductivity will be boosted due to the Au nanoparticles, the synergetic effect generated between CeO2 and calcination FeNi-MOF could offer better activity of oxygen evolution reaction (OER). Herein, the NiFe2O4@C@CeO2/Au hexahedral microbox as a co-reaction accelerator has excellent OER activity and production of reactive oxygen species (ROS), thus increasing the ECL intensity of luminol in a neutral medium without other co-reactants such as H2O2. Because of these benefits, the constructed ECL immunosensor was applied to detect CA15-3 as an example under optimum conditions, the designed ECL immunosensor exhibited high-level selectivity and sensitivity for CA15-3 biomarker within a linear response range of 0.01–100 U mL−1 and an ultralow detection limit of 0.545 mU mL−1 (S/N = 3), demonstrating its potentially valuable application in the area of clinical analysis.

GaAs Nanowire Photodetectors Based on Au Nanoparticles Modification.

A high-performance GaAs nanowire photodetector was fabricated based on the modification of Au nanoparticles (NPs). Au nanoparticles prepared by thermal evaporation were used to modify the defects on the surface of GaAs nanowires. Plasmons and Schottky barriers were also introduced on the surface of the GaAs nanowires, to enhance their light absorption and promote the separation of carriers inside the GaAs nanowires. The research results show that under the appropriate modification time, the dark current of GaAs nanowire photodetectors was reduced. In addition, photocurrent photodetectors increased from 2.39 × 10-10 A to 1.26 × 10-9 A. The responsivity of GaAs nanowire photodetectors correspondingly increased from 0.569 A∙W-1 to 3.047 A∙W-1. The reasons for the improvement of the photodetectors' performance after modification were analyzed through the energy band theory model. This work proposes a new method to improve the performance of GaAs nanowire photodetectors.

Dual-mode electrochemical immunoassay for Non-small cell lung cancer detection based on CoSe2-GO-Au and poly(MB)-Au

Combining the Potentiostatic Electrolysis i-t curve (i-t) and Differential Pulse Voltammetry (DPV), using CoSe2-GO-Au as the sensing substrate and poly(MB)-Au as the secondary antibody marker, the dual-mode electrochemical immunosensor was manufactured for the analysis and detection of Cytokeratin 19 Fragment Antigen (CYFRA 21-1). Cobalt selenide (CoSe2) had favourable catalytic activity of H2O2, which could provide an electrochemical signal through i-t. The huge specific surface area and excellent conductivity of graphene oxide (GO) provided a platform for the combination of CoSe2 and prevented the agglomeration of CoSe2. With the modification of Au nanoparticles, the conductivity of CoSe2-GO had been improved and the binding rates of Ab1 had been increased, which further expanded the electrochemical signal. Meanwhile, precious metal polymerized methylene blue (poly(MB)-Au) with good redox property was used as electrochemical probe, which could solve the shortcoming of MB falling off the electrode. Under the best experimental conditions, the sensitive detection of the CYFRA 21-1 was realized through the test methods of two modes. The dual-mode electrochemical immunosensor presented a linear current signal in 1 pg/mL–100 ng/mL with the detection limit of 0.36 pg/mL (i-t) and 0.24 pg/mL (DPV). To sum up, the prepared dual-mode electrochemical immunosensor provided a guarantee for the sensitive detection of CYFRA 21-1 in this experiment.

Electron Transfer Strategies to Regulate Carriers' Separation for Intensive Pyroelectric Dynamic Therapy With Simultaneous Photothermal Therapy.

Endogenic heat shock proteins and uneven local heat distribution are two main problems in traditional tumor hyperthermia therapy strategies. Aiming at solving these problems, we designed Au–SnSe–PVP nanomaterials (ASNPs) by modifying Au nanoparticles (Au-NPs) and biocompatible PVP on SnSe nanorods via a new reactive oxygen species production strategy. The ASNPs with excellent photothermal conversion performance can produce thermoelectric effects in response to temperature differences during photothermal conversion. The modification of Au-NPs can attract free electron (e–) to accumulate and promote the separation of e– and holes (h+) in the thermoelectric process, thereby further promoting e–-rich Au-NPs-induced H2O2 homolysis and h+–H2O half-reaction to generate hydroxyl radicals, realizing the synergistic application of photothermal therapy and pyroelectric dynamic therapy in tumor treatment.

Piezo-enhanced charge carrier separation over plasmonic Au-BiOBr for piezo-photocatalytic carbamazepine removal

The piezo-photocatalytic effect of Au decorated bismuth oxybromide (BiOBr) was investigated to elucidate the regulation of built-in electric field on charge carrier dynamics and exploit the potential of multi-field coupled environmental purification. Physicochemical properties of Au-BiOBr such as the piezoelectricity, photoresponse characteristics, and charge separation efficiencies were thoroughly analyzed, meanwhile the degradation of carbamazepine (CBZ) was chosen to evaluate the catalytic performance of this system. The piezo-photocatalytic removal of CBZ reached 95.8% within 30 min, and the rate constant is 1.73 times higher than the sum of individual piezo- and photocatalytic ones. The results attribute to not only the modification of Au nanoparticles that accelerates charge transfer and improves light absorption, but also, more importantly, the piezoelectric effect of BiOBr that amplifies the built-in electric field and modulates the band structure alignment. This work demonstrates a promising environmental remediation strategy via the co-utilization of solar and mechanical energy in nature.

Simultaneous visible and ultraviolet photoresponse improvement of MoS2/ZnO heterostructure photodetector via direct resonant coupling of Au nanoparticles localized surface plasmon resonance

Localized surface plasmon resonance (LSPR) as a unique property of metal nanoparticles (NPs) has been widely applied to enhance the performance of optoelectronic devices. However, limited by the specific resonance frequency of plasmonic NPs, the LSPR of NPs can only improve the photoresponse performance of photodetectors at specific wavelength. In this work, a simple strategy is proposed to simultaneously improve the performance of the p-MoS2/n-ZnO heterostructure photodetector in visible and ultraviolet (UV) light regions by modifying Au NPs. The Ilight/Idark ratio of the photodetector is considerably increased after the functionalization with plasmonic Au NPs under visible and UV light illumination due to the direct resonant coupling of LSPR. In particular, the photocurrent of the photodetector increases 14.8 times after Au NPs modification under 532 nm illumination, giving rise to an obvious increase in responsivity, external quantum efficiency and specific detectivity. Moreover, the modification of Au NPs facilitates the rapid separation of electrons and holes due to the generation of surface depletion regions located at Au/MoS2 and Au/ZnO interfaces. Consequently, the photoresponse speed is also drastically improved after Au NPs decoration in both visible and ultraviolet light regions. The strategy of direct resonant coupling of Au NPs LSPR with two photosensitive materials proposed in this work will provide a new avenue for optimizing the performance of optoelectronic devices.

Au modified spindle-shaped cerium phosphate as an efficient co-reaction accelerator to amplify electrochemiluminescence signal of carbon quantum dots for ultrasensitive analysis of aflatoxin B1

In various detection methods of aflatoxin B1 (AFB1), false positives and false negatives are common due to the low sensitivity, expensive equipment or improper pretreatment during operation. Here, a sandwich electrochemiluminescence (ECL) immunosensor armed with a synergistic co-reaction acceleration strategy was employed for the ultra-sensitive detection of AFB1. Benefiting from the catalytic properties of Ce3+/Ce4+ redox pairs, cerium phosphate@gold (CePO4@Au), for the first time, was introduced into the immunosensor as a new type of co-reaction accelerator, and it significantly improved the ECL intensity of the nitrogen doped hydrazide conjugated carbon dots (NHCDs)-H2O2 system. CePO4@Au has the ability to promote the decomposition of H2O2 and accelerate the formation of O2•−. The more of O2•− reacts with NHCDs to produce a stronger and more robust ECL signal response. Furthermore, the spindle-shaped sensing interface formed by oxidation cerium and phosphate has a high loading area and good biocompatibility, and the modification of Au nanoparticles further achieves the stable binding of the capture antibody. Striving for further improvement, Ag modifies Barium titanate (BaTiO3), as the signal carrier with amplification ability, loads with a large number of anodic luminescent carbon quantum dots, were adopted as detection markers for the construction of sandwich ECL biosensors. The co-reaction amplification system achieves high precision quantitative detection of AFB1 in the linear range of 0.01 pg/mL–100 ng/mL, and the detection limit is 9.55 fg/mL. In addition, the constructed biosensor also showed good stability, reproducibility and specificity, with a promising application prospect.

Au Nanoparticle Modification Induces Charge-Transfer Channels to Enhance the Electrocatalytic Hydrogen Evolution Reaction of InSe Nanosheets.

Electrocatalytic water splitting for hydrogen production is an efficient, clean, and sustainable strategy to solve energy and environmental problems. As the important alternative materials for noble metals (Pt, Ir, etc.), two-dimensional (2D) materials have been widely applied for electrocatalysis, although the practical performance is restricted by low carrier mobility and slow reaction kinetics. Here, we adopt the strategy of Au nanoparticle modification to achieve the enhanced hydrogen evolution reaction (HER) performance of InSe nanosheets. Experimental results prove that the HER performance of InSe nanosheets is significantly enhanced under the modification of Au nanoparticles, and the overpotential (392 mV) and Tafel slope (59 mV/dec) are significantly reduced compared to sole InSe nanosheets (580 mV and 148.2 mV/dec). First-principles calculations have found that the InSe/Au system exhibits metallicity because the free electrons provided by the Au particles are injected into the InSe, thereby improving its conductivity. The difference charge density and localized charge density of InSe/Au show that Au nanoparticle loading can induce the formation of Au-Se electron-transfer channels with electrovalent bond characteristics, which effectively promotes the charge transfer. Meanwhile, the standard free-energy calculation of the HER process shows that the InSe/Au heterojunction has a H* adsorption/desorption Gibbs free energy [(|ΔGH*|) = 0.59 eV] closer to the optimal value. This study reveals the theoretical mechanism of metal modification to improve the performance of electrocatalytic HER and is expected to motivate the development of a new strategy for enhancing the catalytic activity of 2D semiconductor materials.

Au nanoparticles/SnO2/ZnIn2S4-based biosensor for photoelectrochemical/electrochemical dual-signal detection of RNase A by combining the enzymolysis of DNA probe and the generation of molybdophosphate precipitate

We report here photoelectrochemical/electrochemical dual-signal detection of ribonuclease A (RNase A) by integrating the enzymolysis of a DNA probe with the generation of molybdophosphate precipitate. SnO2 nanoparticles-decorated ZnIn2S4 nanosheets as a novel photoactive material output a photocurrent higher than SnO2 and ZnIn2S4 alone resulting from the improved electron-hole separation. The modification of Au nanoparticles (AuNPs) on SnO2/ZnIn2S4 can not only enable facile immobilization of a ribonucleotide uracil (rU) containing single strand DNA probe but also boost the photocurrent exciton-plasmon coupling effect. The rU-DNA probe is immobilized on the AuNPs/SnO2/ZnIn2S4-based photoelectrode to construct a biosensor. The immobilized rU-DNA probe is cleaved by RNase A and then incubated with molybdate. When RNase A is present, the DNA chain becomes shorter, and less molybdophosphate precipitates are formed on the electrode. The hindrance of interfacial electron transfer by molybdophosphate precipitate enables “signal-on” photoelectrochemical detection of RNase A, with a linear range from 1 to 104 pg mL−1 and a detection limit of 0.2 pg mL−1. In addition, the electroactivity of molybdophosphate precipitate enables “signal-off” electrochemical detection of RNase A, with a linear range from 10 to 5 × 103 pg mL−1 and a detection limit of 2 pg mL−1. This work not only develops an efficient photoactive material but also offers a reliable detection of RNase A in photoelectrochemical/electrochemical dual mode.

Enhanced electron–hole separation in SnS2/Au/g-C3N4 embedded structure for efficient CO2 photoreduction

The use of semiconductor photocatalytic reduction technology has higher efficiency and lower energy consumption for CO2 reduction, but its existence of some mismatched energy band positions and relatively slow charge-hole separation greatly limits its practical application. In this paper, a SnS2/Au/g-C3N4 embedded structure model with carbon and nitrogen hybridization is proposed to gain an in-depth understanding of the role of hybridization and precious metal modification in photocatalysis. Carriers were investigated from the perspective of kinetics through photocurrent, LSV curve, and FL spectroscopy. After modification of Au nanoparticles, the photo-excited electrons showed a slower decay process, indicating that the separation of carriers was enhanced, which was further confirmed by impedance and PL spectroscopy. SEM, AFM and TEM analysis confirmed that the 2D face-to-face SnS2/Au/g-C3N4 embedded structure was successfully prepared and the Au nanoparticles were evenly distributed. Au nanoparticles not only act as a bridge for electron transport in 2D semiconductor materials to accelerate electron transport, but generate more excited electrons by themselves under the radiation of sunlight, which effectively improves the separation efficiency of electron-hole pairs and enhances the photocatalyst activity. DFT calculations show that the Z-type mechanism and the intercalated energy level of the SnS2/Au/g-C3N4 embedded structure expand the light absorption and improve the carrier separation efficiency. As expected, the photocatalyst activity with CO and CH4 the evolution rate of up 93.81 µmol·g−1·h−1 and 74.98 µmol·g−1·h−1 under visible light irradiation, respectively, while the photocatalytic activity is negligible loss after 30 h photoreduction. This work reveals the role of embedded structure and precious metal modification in the separation and transmission of electron-hole, opening up new perspective for achieving high-efficiency solar CO2 reduction performance.

Highly sensitive and selective acetone sensor based on three-dimensional ordered WO3/Au nanocomposite with enhanced performance

With the development of medical science, analyzing the concentration of the volatile organic compounds (VOCs) in expiration has been considered as a rapid, convenient and noninvasive method for medical diagnosis. The detection of diabetes with acetone as a marker has received extensive attention, but the development of a highly sensitive acetone sensor remains various challenges to improve the sensing performance with nanostructure-controllable novel materials. In this work, an acetone sensor based on three-dimensional inverse opal (3DIO) tungsten oxide (WO3) composite modified with Au (WO3/Au) was obtained through a simple sacrificial template synthesis, which provided more active sites with macropore architecture. Moreover, with modification of Au nanoparticles (NPs), it is obvious that gas sensing property with “spillover effects” and catalytic action was obtained. The 3DIO WO3/Au gas sensor exhibited good selectivity to acetone, and showed great test performance from 100 ppb to 100 ppm. A corresponding actual detection limit of 100 ppb at 410 °C was realized, which could allow real-time and reliable diagnosis of diabetic by acetone monitoring. Furthermore, it also showed good stability and faster response and recovery times compared with pure WO3 sensors. The 3DIO WO3/Au gas sensor shows great potential in practical application of a noninvasive and more accurate monitoring and detection of diabetes.

“Grafting to” approach for surface modification of AuNPs with RAFT-mediated synthesized smart polymers: Stimuli-responsive behaviors of hybrid nanoparticles

Core-shell nanoparticles with Au core and poly((2-dimethylamino)ethyl methacrylate) (PDMAEMA) or poly(N-isopropylacrylamide) (PNIPAAm) shell were fabricated via “grafting to” approach. Reversible addition-fragmentation chain transfer (RAFT) polymerization was used to synthesize functional narrow-dispersed polymers. Thiol-capped RAFT agent was used followed by reduction of RAFT agent by NaBH4 to produce thiol-terminated polymers. Then, thiolated polymers were dissolved in medium containing colloidal Au nanoparticles (AuNPs) and polymers were grafted onto surface of AuNPs by formation of Au-S bonds. 1H NMR was used to approve the synthesis of thiolated polymers and GPC showed that both polymers had Mn of about 15000 g/mol and dispersity of about 1.3. Fabrication of Au@polymer nanoparticles was studied by UV-vis. spectroscopy, TGA and TEM. Stimuli-responsive behavior of hybrid nanoparticles was studied by monitoring hydrodynamic diameter of samples versus temperature in aqueous media at different pH values. According to results, Au@PDMAEMA nanoparticles showed a pH-dependent thermoresponsive behavior. They showed no volume phase transition temperature (VPTT) at pH = 2 while a VPTT of 44 and 40 °C was detected at pH = 8 and 10 respectively. However, pH had no mentionable effect on thermoresponsive behavior of Au@PNIPAAm nanoparticles and they showed a VPTT of 34 °C at different pH values.

Heterogeneous three-dimensional TiO2/ZnO nanorod array for enhanced photoelectrochemical water splitting properties

A 3D heterogeneous TiO2/ZnO array was successfully synthesized on FTO substrate via hydrothermal process. The 3D TiO2/ZnO array exhibited enhanced light absorption, decreased interface transfer resistance, enlarged carriers’ density compared to TiO2 photoanode, and TiO2/ZnO array prepared with 10 mM Zn(NO3)2 exhibited the best performance. The maximum photocurrent density reached to ~ 1.1 mA/cm2 and further increased to ~ 2.0 mA/cm2 at 1.23 V vs RHE with the modification of Au nanoparticles. This work demonstrated a promising method for preparing heterogeneous three-dimensional TiO2/ZnO nanorod array with excellent PEC performance for water splitting.

Gold nanoparticles as intermediate ligands for polymer monolithic capillary microextraction of trace rare earth elements followed by inductively coupled plasma mass spectrometry detection

In this work, a novel method of Au nanoparticles (NPs) modified polymer monolithic capillary microextraction (CME) on-line coupling with inductively coupled plasma-mass spectrometry (ICP-MS) was developed for the determination of trace rare earth elements (REEs) in environmental and biological samples. The poly(glycidyl methacrylate-ethylene dimethacrylate) monolithic capillary was prepared, functionalized with thiol ligands for the attaching of Au NPs, and then modified with mercaptosuccinic acid to provide massive carboxyl groups which have high affinity to REEs. With the modification of Au NPs, the adsorption capacity of the monolith towards target REEs has been improved by 3 to 6.5 times. Under the optimized conditions, the limits of detection of the developed method for REEs were in the range of 0.16 (Tb)–0.85 (Gd) ngL−1. The enrichment factor was 25-fold with the sample throughput of 10h−1. And the relative standard deviations were between 2.7 (Lu) and 9.8% (Dy) (c=10ngL−1, n=9). The accuracy of the method was validated by the analysis of a standard stock solution of GSB04-1789-2004 and a Certified Reference Material of GBW07301a stream sediment. The proposed method was applied for the analysis of trace REEs in seawater samples as well as human whole blood with good recoveries. The prepared monolith is featured with strong anti-interference ability, superior adsorption capacity as well as long lifespan, and the developed monolithic CME-ICP-MS is sensitive, simple and rapid for the analysis of trace/ultra-trace REEs in environmental and biological samples with complex matrix.

Au nanoparticles modified branched TiO2 nanorod array arranged with ultrathin nanorods for enhanced photoelectrochemical water splitting

Au nanoparticles modified branched TiO2 (Au/B-TiO2) arrays were synthesized and the crystallization and morphology of the branches could be well controlled by simply altering the reaction times. The B-TiO2 array composed of ultra-thin nanorod with thickness of ∼5 nm showed enhanced photoelectrochemical performances compared to TiO2 nanorod array due to decreased resistance and increased carriers' transfer efficiency. Further, after the modification of Au nanoparticles, the photocurrent density was ∼2.5 mA/cm2 at 1.23 V vs RHE, which was much higher than that of B-TiO2 and TiO2 nanorod array due to enhanced light harvesting ability, enhanced carriers' density that resulted from the synergistic effect of branched structure of TiO2 and SPR surface plasmon resonance (SPR) effect of Au nanoparticles.

Electrocatalytic Activity of Au Core Au-Pt Alloy Shell Nanoparticles Prepared on Ionic Liquid Surface Via Metal Sputtering Deposition

Pt-based bimetallic nanoparticles (NPs) have been considered to be promising materials as electrocatalysts for improving the performance of fuel cells such as a direct methanol fuel cell because of decreasing CO poisoning on Pt surface and enhancing reactivity of Pt via a ligand effect. The compositional control of electrocatalyst surface is of significant importance to effectively utilize noble metals and to improve the electrocatalytic activities, because electrochemical reactions only occurs on the surface of particle catalysts. In our previous study, we have reported a facile method to synthesize noble metal NPs by metal sputter deposition on room temperature ionic liquids (RTILs) under vacuum condition.(1) This RTIL/metal sputtering technique was also useful to prepare core-shell-structured particles of Au@In2O3 and Pt@In2O3, which were prepared by the successive sputter deposition of noble metals and Indium into RTILs. Recently we have reported that a monolayer of Au nanoparticles was formed on the RTIL surface with single step deposition process when Au sputter deposition was carried out onto the surface of RTILs containing hydroxyl-functionalized cations.(2)In this study, we report the synthesis of Au core-AuPt alloy shell NPs monolayer by the sequential sputter deposition of Au and Pt onto hydroxyl-functionalized RTILs. The surface coverage of Pt atoms on individual Au NPs could be controlled with variation of Pt sputtering time. Original Au NPs monolayer was prepared by the sputter deposition of Au on the surface of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate (HyEMI-BF4) used as a RTIL with a discharge current of 10 mA under argon pressure of 20 Pa for 150 s. The subsequent sputter deposition of Pt was carried out on thus-obtained Au NPs monolayer. The sputtering condition used for Pt deposition was the same as that used for Au deposition except for sputtering time. The sputter deposition of Au changed the color of RTIL surface from colorless to reddish blue due to the Au film formation. By subsequent sputter deposition of Pt, the film on the solution surface tuned brownish. Extinction spectra of films showed an LSPR peak at 540 nm, the intensity of which was lessened with an increase in the Pt sputtering time and finally vanished after Pt sputter deposition for 80 min or more. This result suggested that the sputter deposition of Pt onto Au film caused surface modification of individual Au NPs. From TEM measurement, it was found that the films prepared by sputter deposition of Au and Pt were monolayers composed of spherical particles, the size of which increased with elapse of Pt sputtering time from 4.2 to 4.8 nm. Since pure Pt particles were not observed in the film, it was suggested that sputtered Pt species were simply deposited on individual Au particles floated on the RTIL surface without additional nucleation. The XPS measurement revealed that deposited Pt formed the surface layer composed of Au-Pt alloy on Au cores. The cyclic voltammograms of Au-Pt bimetallic NPs monolayers transferred on HOPG electrodes were measured in an N2-saturated 0.5 mol dm-3 H2SO4aqueous solution, in which a cathodic peak assigned to the reduction of Au oxide monolayer appeared at 1.2 V vs. RHE along with a pair of redox peaks attributable to the adsorption/desorption of hydrogen on Pt surface at ca. 0.02-0.04 V vs. RHE. The electrochemical surface areas (ECSA) of Au and Pt were obtained by measuring charges flowed in reduction of Au oxide monolayer and in hydrogen desorption on Pt surface, respectively. The fraction of Pt ECSA was higher than the Pt content in particles, regardless of Pt sputtering time, indicating that Pt atoms were predominantly deposited on the surface of Au particles. The methanol oxidation activity of the Au-Pt NPs monolayers was evaluated by a cyclic voltammetry in a 0.5 mol dm-3 KOH aqueous solution containing 0.5 mol dm-3methanol. The obtained voltammograms exhibited an anode peak at ca. 0.9 V vs. RHE, assignable to methanol oxidation (Fig. 1). The peak current intensity of methanol oxidation for Au-Pt bimetallic films was dependent on the Pt sputtering time but was larger than those of monometallic counterparts, indicating that the electrocatalytic activity for methanol oxidation was enhanced by the modification of Au NPs monolayer with AuPt alloy shell layer. The maximum intensity was obtained for the Au-Pt NPs film prepared with Pt sputtering time for 80 min. References T. Torimoto, et al., Appl. Phys. Lett., 89, 243117 (2006).T. Torimoto, et al., Phys. Chem. Chem. Phys., 17, 13150 (2015). Figure 1

Thiol-modified gold nanoparticles deposited on silica support using dip coating

In our work, we have prepared thin layers of gold nanoparticles deposited via dip coating technique on silica glass substrate. The prepared thin layers were modified by two different ligands, namely 1,4-dithiothreitol (sample Au-DTT NPs) and l-glutathione (sample Au-GSH NPs). The spectral, structural and magnetic properties of the prepared samples were investigated. The modification of Au nanoparticles with thiol ligands leads to change of their plasmon resonance fields, as indicated by UV–vis spectra. The magnetic measurements showed that the magnetization of the samples is composed from two magnetic contributions: diamagnetic contribution and low field ferromagnetic contribution. Our experimental results show that the charge transfer between Au and S atoms gives rise to the ferromagnetic behaviour of prepared thin layers.

More conductive polypyrrole electrodeposited on substrates with close-packed gold nanoparticles

Recently, conductive polymers (CPs) of polypyrrole (PPy) have been widely applied in supercapacitors, gas sensors, photocatalyses and innovative cancer therapies. Chemical and electrochemical oxidation polymerizations are two general pathways for the preparation of PPy. The principal advantage of the electrochemical method is related to the prepared PPy with a better conductivity and its long-term stability. In this work, PPy films are innovatively electrodeposited on Pt substrates modified with Au nanoparticles (NPs) prepared by using sonoelectrochemical deposition-dissolving cycles (SEDDC). The modification of Au NPs demonstrates a catalytic electro-oxidation pathway for the polymerization of PPy. Encouragingly, the conductivity of PPy electrodeposited on this Au NPs-deposited Pt substrate is significantly increased by more than 6-fold of magnitude, as compared with that of PPy electrodeposited on a polished Pt substrate. The increased conductivity of PPy is consistent with its increased oxidation degree, oxidation level and longer conjugating length, and with its dopant ions being more stable during polymerization, which are revealed from analyses of Raman and X-ray photoelectron spectroscopies.