Encapsulated Au Nanoparticles Research Articles

Gold nanoparticle microemulsion films with tunable surface plasmon resonance signal

Composite films were prepared by the dip-coating method. An organosol of Au nanoparticles (6.3±0.4 nm) was used as the reaction mixture. The nanoparticles were stabilized with sodium bis(2-ethylhexyl) sulfosuccinate (AOT). The prepared films were formed of an AOT layer with encapsulated Au nanoparticles (i.e. Au@AOT films). The films demonstrated a stable plasmon effect. The variation of the immersion number of the glass substrate from 1 to 10 allowed the adjustment of the plasmonic properties. The absorption intensity and maximum wavelength of the surface plasmon resonance were found to change from 0.183 to 0.245 and from 529±2 to 539±2 nm, respectively. The plasmonic properties were found to correlate with the film thickness, roughness, and morphology. An increase in the concentration of Au nanoparticles improves the film’s mechanical strength and wettability.

Discrimination of chiral amino acid enantiomers through photoelectrochemical sensing platform

Chirality plays fundamental functions in the activity of biological molecules and broad classes of chemical reactions, but its recognition and detection still remain a great challenge. Herein, inspired by the stereo-control characteristics of chiral amino acids adjacent to the active sites of natural enzymes, a photoelectrochemical (PEC) chiral sensor was constructed by encapsulating Au nanoparticles with the recognition unit l-Cysteine into mesoporous BiVO4 skeleton. The chiral sensor exhibits a high sensitivity and selectivity discrimination of 3,4-dihydroxyphenylalanine (DOPA) enantiomers. The possible mechanism of enantioselectivity was proposed with the guidance of DFT calculations, suggesting that the origin of chiral selectivity lies in the different hydrogen bonds forms between l-Cys and DOPA. This work provides a powerful strategy for constructing PEC chiral sensing device with excellent chiral recognition performance.

Localized Surface Plasmon Resonance Promotes Metal–Organic Framework‐Based Photocatalytic Hydrogen Evolution

AbstractCombining metal nanoparticles (NPs) featured with localized surface plasmon resonance (LSPR) with metal–organic framework (MOF)‐based photocatalysts is a novel means for achieving efficient separation of electron–hole pairs. Herein, the Au@NH2‐UiO‐66/CdS composites are successfully synthesized by encapsulating Au NPs with LSPR into the NH2‐UiO‐66 nanocage, further growing CdS NPs on the surface of the NH2‐UiO‐66, which exhibits higher photocatalytic activity in hydrogen evolution reaction under visible‐light irradiation than that of NH2‐UiO‐66/CdS and CdS, respectively. Transient absorption measurements reveal that MOF is not only a transit station for electrons generated from CdS to Au, but also a receiver for hot electrons generated from plasmonic Au in Au@MOF/CdS composites. Thus, the LSPR‐induced hot electron transfer from Au NPs is an important manifestation to prolong the carrier lifetime and enhance the photocatalytic performance. This work provides insights into investigating the photoinduced carrier dynamics of nanomaterials with LSPR effects for enhancing the MOF‐based photocatalytic performance.

Fabrication of noble metal (Au, Ag, Pt)/polythiophene/reduced graphene oxide ternary nanocomposites for NH3 gas sensing at room temperature.

Room temperature NH3 gas sensors composed of noble metal (Au, Ag or Pt)/polythiophene/reduced graphene oxide (Au, Ag or Pt/PTh/rGO) ternary nanocomposite films were fabricated using a simple one-pot redox reaction. The surface morphology and composition of Au, Ag or Pt/PTh/rGO ternary nanocomposite films were analyzed using Fourier transform infrared spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Compared with Ag/PTh/rGO and Pt/PTh/rGO ternary nanocomposite films, obviously bright Au nanoparticles were observed on the surface of the massive lamination PTh film which wrapped the rGO, and encapsulated Au nanoparticles were observed in the Au/PTh/rGO film. Comparative gas sensing results showed that the Au/PTh/rGO ternary nanocomposite film had the highest response compared with Ag/PTh/rGO and Pt/PTh/rGO ternary nanocomposite films at room temperature, especially when the testing concentration of NH3 gas was below 5 ppm. The Au/PTh/rGO ternary nanocomposite film also had a fast response time and good reproducibility. The combination of the high catalytic activity of naked Au nanoparticles and the formation of effective carrier transfer channels by encapsulated Au nanoparticles was responsible for the improved response of the Au/PTh/rGO ternary nanocomposite film.

Ion implanted Au nanoparticles in surface plasmon temperature sensing

Temperature dependence of surface plasmon (SP) resonance from implanted Au nanoparticles have been studied in an ambient-air environment from 75 °C to 175 °C. Implantation provides encapsulated Au nanoparticles in a quartz substrate. The SP peak shifts linearly with the temperature increase. The experimental results were confirmed by the Drude model explaining the controlling mechanisms of the peak change. The Au nanoparticles have a higher volume thermal expansion coefficient than the substrate. Therefore, the dominant mechanism was the volume thermal expansion coefficient. This study provides another aspect of temperature sensing in Au nanoparticles which can be provided by ion implantation.

Synthesis of Au nanoparticles using magnetite cored polyamine dendrimer template and its green catalysis for selective oxidation of alcohols

Magnetite cored PAMAM G3 dendrimer was synthesized and amide groups were reduced using LAH to afford amine groups enriched polyamine dendrimer; subsequently surface was grafted with succinic anhydride to attain carboxylic acid terminated polyamine dendrimer on magnetite core. This nanohybrid material was used as template to synthesize Au nanoparticle via sequestering metal ion followed by chemical reduction process. Analytical data evidenced that size and shape-controlled ultrafine gold nanoparticles of 1–2 nm size was achieved using this lower generation dendrimer template. Magnetite cored polyamine G3 dendrimer encapsulated Au nanoparticles was exploited as a green and sustainable catalyst for the selective oxidation of alcohol under mild reaction conditions and effectively reused for five catalytic cycles.

TiO2 encapsulated Au nanostars as catalysts for aerobic photo-oxidation of benzyl alcohol under visible light

Gold nanostar (AuNS) particles, characterized by pointed tips emerging from a central core, exhibit localized surface plasmon resonance (LSPR) with strongly amplified electric field upon illumination. Compared to Au nanospheres and nanorods, the absorbance is enhanced with the absorption band extending from 500 to above 1000 nm. However, they are easily reshaped by Ostwald ripening and therefore difficult to use in any application. This study shows that the AuNS particles can be effectively stabilized by encapsulation with TiO2 using a low temperature method. The synthesis parameters and capping solution were optimized to form nanostars. The encapsulated Au nanoparticles promoted the aerobic oxidation of benzyl alcohol to benzaldehyde at ambient temperature under visible light irradiation. AuNS@TiO2 showed significantly higher photocatalytic activity than Au nanospheres, Au nanorods or bulk TiO2 due to its enhanced LSPR. Encapsulation of the colloidal nanoparticles with TiO2 confers robustness to the resulting heterogeneous catalyst with retention of the metal particle size, morphology and associated LSPR properties.

Silica Encapsulated-Gold Nanoparticles as a Nano-reactor for Aerobic Oxidation of Benzyl alcohols and Tandem Oxidative A3 coupling Reactions in Water

In this work, the encapsulated-Au nanoparticles (NPs) into the silica hollow NPs were synthesized by microwave-assisted preparation of PEG-coated Au NPs, coating them with a layer of organically modified silica and removing the PEG around the Au NPs. The structure of these encapsulated NPs was characterized by TEM, SEM, XRD, FTIR, EDX, TGA, and ICP-OES. These NPs have shown excellent activities in the aerobic oxidation of benzyl alcohol derivatives and tandem oxidative A3 coupling reactions as a catalyst and reactor in the water at room temperature. Synthesis of a new silica/gold nanoparticles as catalytic nano-reactor for carrying out A3-coupling reaction in the water at ambient temperature

Photochromic organic cage-encapsulated Au nanoparticles: light-regulated cavities for catalytic reduction of 4-nitrophenol.

A diarylethene-based photochromic cage (DPC) with an adjustable cavity upon irradiation with UV and visible light has been designed and synthesized. Au nanoparticles encapsulated in the organic cage with open and closed states (Au@o-DPC and Au@c-DPC) showed different catalytic activities for the reduction of 4-nitrophenol.

Pressure-induced assemblies and structures of graphitic-carbon sheet encapsulated Au nanoparticles.

A novel strategy of using hydrostatic pressures to synthesize gold-carbon (Au-C) nanohybrid materials is explored. The stable face-centered-cubic (fcc) Au undergoes a structural phase transition to a mixture of primitive orthorhombic and cubic phases as the carbon phase acquires a highly ordered onion-like carbon (OLC) structure which encapsulates the Au nanoparticles, thereby exerting an additional pressure. Increasing the pressure results in a one dimensional (1-D) chain-like structure with the primitive cubic Au nanoparticles contained in an amorphous carbon matrix. The OLC structure allows the formation of quenchable Au nanoparticle phases with the primitive close packing and Au-C hybrids with new mesoscopic structures. Under pressure, we observe the formation of a hybrid material composed of a poorly conducting matrix made of amorphous carbon and conducting OLC-encapsulated Au nanoparticles. The electrical conductivity of this hybrid material under pressure reveals a percolation threshold. We present a new synthesis approach to explore the interplay between atomic and mesoscopic structures and the electrical conductivity of metal hybrid structures.

Tuning the Microenvironment of Gold Nanoparticles Encapsulated within MIL-101(Cr) for the Selective Oxidation of Alcohols with O2 : Influence of the Amino Terephthalate Linker.

This manuscript reports a comparative study of the catalytic performance of gold nanoparticles (NPs) encapsulated within MIL-101(Cr) with or without amino groups in the terephthalate linker. The purpose is to show how the amino groups can influence the microenvironment and catalytic stability of incorporated gold nanoparticles. The first influence of the presence of this substituent is the smaller particle size of Au NPs hosted in MIL-101(Cr)-NH2 (2.45±0.19 nm) compared with the parent MIL-101(Cr)-H (3.02±0.39 nm). Both materials are highly active to promote the aerobic alcohol oxidation and exhibit a wide substrate scope. Although both catalysts can achieve turnover numbers as high as 106 for the solvent-free aerobic oxidation of benzyl alcohol, Au@MIL-101(Cr)-NH2 exhibits higher turnover frequency values (12 000 h-1 ) than Au@MIL-101(Cr)-H (6800 h-1 ). Au@MIL-101(Cr)-NH2 also exhibits higher catalytic stability, being recyclable for 20 times with coincident temporal conversion profiles, in comparison with some decay observed in the parent Au@MIL-101(Cr)-H. Characterization by transmission electron microscopy of the 20-times used samples shows a very minor particle size increase in the case of Au@MIL-101(Cr)-NH2 (2.97±0.27 nm) in comparison with the Au@MIL-101(Cr)-H analog (5.32±0.72 nm). The data presented show the potential of better control of the microenvironment to improve the performance of encapsulated Au nanoparticles.

Impact of critical micelle concentration of macroRAFT agents on the encapsulation of colloidal Au nanoparticles

HypothesisReversible addition fragmentation chain transfer (RAFT) - assisted encapsulating emulsion polymerization (REEP) has received considerable attention as an efficient strategy to prepare colloidal stable shell@core nanoparticles. Generally, amphipathic macroRAFT agents are used but the effect of working above or below the critical micelle concentration (CMC) of macroRAFT agents needs to be addressed. Hence, it is necessary to understand if this parameter has an impact not only on the stability of the colloids but also on the molecular mass of the polymer shell. MethodsHere, the CMC of three different macroRAFT agent was determined and the effect of macroRAFT agents concentration on the colloidal stability of gold nanoparticles coated with macroRAFT agents (macroRAFT@Au) assessed. The subsequent chain extension from macroRAFT@Au NPs, resulting in encapsulated Au nanoparticles (copolymer@Au), has also been systematically studied. FindingsUsing the REEP approach it was possible to obtain stable encapsulated Au NPs. Moreover, this strategy opens the possibility of adjusting the macroRAFT agents concentration to tune the length of the polymer chains grown around Au cores which is of major interest for the design of biosensors based on responsive polymer shells, such as pH, temperature and photoluminescence quenching.

High-performance electrochemical biosensor for nonenzymatic H2O2 sensing based on Au@C-Co3O4 heterostructures

An ingenious and viable method for preparing heterogeneous Co3O4 dodecahedrons that contain carbon and encapsulated Au nanoparticles (Au@C-Co3O4) was proposed via pyrolysis of Au nanoparticle-encapsulated zeolitic imidazolate framework-67 (Au@ZIF-67). The obtained Au@C-Co3O4 possessed hierarchically porous structure, abundant active sites, excellent conductivity, and durability, all of which can significantly improve the analysis performance of the biosensor. Meanwhile, the fabricated electrode based on the porous Au@C-Co3O4 showed remarkable electrocatalytic performance towards H2O2 with a limit of detection of 19 nM and ultra-high sensitivity of 7553 μA mM−1 cm−2, even when the Au content in the composite was as low as 0.85 wt%. This novel biosensor was successfully used to monitor H2O2 concentration released from living cells, and the results can be used to identify cancer cells, thus advancing the use of transition metal oxides in the field of biosensing.

Size Stability and H2/CO Selectivity for Au Nanoparticles during Electrocatalytic CO2 Reduction.

In this paper, we show that Au nanoparticles (AuNPs) stabilized with either citrate or by low-generation dendrimers rapidly grow during electrocatalytic reduction of CO2. For example, citrate-stabilized AuNPs and AuNPs encapsulated within sixth-generation, hydroxyl-terminated, poly(amidoamine) dendrimers (G6-OH DENs) having diameters of ∼2 nm grow substantially in size (to 6-7 nm) and polydispersity during just 15 min of electrolysis at -0.80 V (vs RHE). This degree of instability makes it impossible to correlate the structure of AuNPs determined prior to electrocatalysis to their catalytic function. In contrast to the G6-OH dendrimer, the higher generation G8-OH analogue stabilizes AuNPs under the same conditions that lead to instability of the other two materials. More specifically, G8-OH DENs having an initial size of 1.7 ± 0.3 nm increase to only 2.2 ± 0.5 nm during electrolysis in 0.10 M NaHCO3 at -0.80 V (vs RHE). Even when the electrolysis is carried out at -1.20 V, the higher-generation dendrimer stabilizes encapsulated AuNPs. This is presumably due to the compactness of the periphery of the G8-OH dendrimer. Although the G8-OH dendrimer nearly eliminates AuNP growth, the surface of the AuNP is still accessible for electrocatalytic reactions. The smaller, more stable G8-OH DENs strongly favor formation of H2 over CO. Some previous reports have suggested that AuNPs in the ∼2 nm size range yield primarily CO, but we believe these findings are a consequence of the growth of the AuNPs during catalysis and do not reflect the true function of ∼2 nm AuNPs.

Metal Organic Frameworks as Versatile Hosts of Au Nanoparticles in Heterogeneous Catalysis

The present review describes the state of the art of the use of metal organic framework (MOF)-encapsulated Au nanoparticles (NPs) as heterogeneous catalysts. The purpose is to show that catalysts with very good performance, frequently among the most active Au catalysts reported so far, can be obtained by incorporation of Au NPs inside MOFs. The available data indicate that the high catalytic activity of MOF-encapsulated Au NPs derives from (i) small particle size, (ii) high dispersion and homogeneous distribution inside MOFs crystals, (iii) stabilization of particle size by confinement of Au NPs inside MOFs cages, and (iv) the synergy that can arise by the combination of the activity of Au NPs and MOFs. After some introductory sections presenting general issues commenting about the relevance of Au catalysis, how to determine the internal versus external location of Au NPs, and evidence in support for catalyst stability, this mini review covers reactions using Au@MOFs as catalysts for oxidations, reduction...

Macromol. Mater. Eng. 2/2017

Front Cover: A new approach to prepare free-standing biodegradable nanopillar arrays on flexible substrates is developed by using plasma etching with block copolymer micelles encapsulating Au nanoparticles as an etching mask. This method can offer a feasible route to create vertically-aligned nanostructures of various materials with dimensional controllability. This is reported by Gyeong Won Lee, Seunghyun Lee, Jang Hwan Kim, Sang-Gu Yim, Jooyeon Ryu, Eunji Lee, Jaebeom Lee, Seong Il Yoo, and Seung Yun Yang in article number 1600361.

Density-Controlled Freestanding Biodegradable Nanopillar Arrays Patterned via Block Copolymer Micelle Lithography

Vertically aligned polymer nanopillar arrays on substrates are receiving increasing interest as functional surfaces for a broad range of applications. However, methods for preparing polymeric nanopillar arrays have poor controllability of dimensional parameters and are limited to few polymers. Here, a new method to prepare freestanding biodegradable nanopillar arrays on different substrates, including flexible sheets, by plasma etching with polystyrene-block-poly(acrylic acid) (PS-PAA) block copolymer (BCP) micelles encapsulating Au nanoparticles ([email protected]) is reported. The adsorption density of the [email protected] micelles is controlled by the pH of the micelle solutions, affecting electrostatic interaction with the polyelectrolyte layers formed on a poly(lactic-co-glycolic acid) (PLGA) film coated on the substrates; thus, density-controlled PLGA nanopillar arrays are prepared using the micelle array as an etching mask during plasma etching. The height of the PLGA nanopillars is controlled by adjusting the plasma etching time, achieving high aspect ratios (>10) on inch-sized substrates. This new platform combining bottom-up (controlling absorption of BCP micelles used as etching mask) and top-down (plasma etching for nanopillar formation) approaches can be applied to prepare nanopillar arrays on substrates using different soft materials including biodegradable polymers.

Controlled-layer and large-area MoS2 films encapsulated Au nanoparticle hybrids for SERS.

In this work, a facile and effective method for controlled-layer and large-area MoS2 films encapsulated Au nanoparticle hybrids is developed. With accurate Ar plasma treatment time control, the large-area MoS2 layers can be obtained from monolayer to trilayer. The fabricated MoS2@Au NPs with higher surface area exhibit excellent Raman enhanced effect for aromatic organic molecules (rhodamine 6G and crystal violet) and achieve the best when the monolayer MoS2@AuNPs was obtained. The limit of detection is found to be as low as 1 × 10-10 M. The MoS2@AuNPs was characterized by SEM, EDS, AFM, Raman spectroscopy, UV-Vis, XRD and HRTEM.

Fe3O4@RGO@Au@C Composite with Magnetic Core and Au Enwrapped in Double-Shelled Carbon: An Excellent Catalyst in the Reduction of Nitroarenes and Suzuki–Miyaura Cross-Coupling

Magnetic core double-shelled carbon with Fe3O4 nanoparticles as the core, reduced graphene oxide (RGO) as the inner shell and carbon (C) layer as the outer shell, have been successfully designed and prepared. This tailor-making structure acts as an excellent capsule for encapsulating Au nanoparticles (Au NPs), which could effectively prevent Au NPs from aggregation and leaching. Because of its structural features, magnetic core-double-shell Fe3O4@RGO@Au@C architecture exhibits extremely high catalytic performance on two different kinds of organic reactions (1) reduction of nitroarenes, and (2) Suzuki–Miyaura cross coupling of phenyl boronic acid with aryl halides. Moreover, the synthesized catalyst can be easily recovered and reused for at least ten cycles due to its magnetically separable feature and good stability.

Fabrication of lotus-like Au@TiO2 nanocomposites with enhanced gas-sensing properties

The structure of lotus-like Au@TiO2 was directly fabricated via a simple and cost-effective hydrothermal method by carefully adjusting the molar ratio of Au to TiF4 in the precursor. (*) The crstal structure and morphology of the obtained louts-like Au@TiO2 were examined by X-ray diffraction (XRD), transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM), Brunauer-Emmett-Teller (BET) and X-ray photoelectron spectroscopy (XPS). The results indicated that perfect lotus-like Au@TiO2 hierarchical structure with Au pistil and TiO2 petal can be formed when the molar ratio of Au to TiF4 was 0.1875. Furthermore, the gas sensing test of the Au@TiO2 nanocomposites towards CO gas was also examined. The responses of the Au@TiO2-based sensors were higher than the pure TiO2-based sensor. Especially, the lotus-like 18.75 mol%Au@TiO2-based sensor presented a most outstanding gas sensing performance, including low optimal operating temperature, high sensitivity and selectivity as well as fast response and recovery time. Such sensing performance enhancement are ascribed to their unique lotus-like structures and the catalytic effect of the encapsulated Au nanoparticles (NPs).