Au Nanosheets Research Articles

Synthesis of Au-nanoparticle-loaded 1T@2H-MoS2 nanosheets with high photocatalytic performance

Although nanosheets of the transition metal dichalcogenides MoS2 have been the subject of extensive attention and research due to their unique properties, little research has been conducted on hybrid-phase MoS2 (1T@2H-MoS2), which has high photocatalytic properties. In this study, we prepared 1T@2H-MoS2 nanosheets loaded with Au nanoparticles (NPs) which exhibited high photocatalytic properties by a simple hydrothermal method, and the photocatalytic degradation of methylene blue by the 1T@2H-MoS2/Au nanosheets under visible light was 91.2%. This high degradation efficiency was due to the introduction of the Au NPs to produce localised surface plasmon resonance, which enhances the visible light absorption of 1T@2H-MoS2. The combination of a high content of the 1T phase and the Au NPs accelerates the transfer of photogenerated electrons, which inhibits the recombination of photogenerated electron–hole pairs and allows more electrons to participate in the catalytic reaction. The results showed that loading Au NPs on the 1T@2H-MoS2 nanosheets promoted the conversion of the 2H phase to the 1T phase, which effectively improved the visible light catalytic performance.

Skin-Attachable, Stretchable Electrochemical Sweat Sensor for Glucose and pH Detection.

As part of increased efforts to develop wearable healthcare devices for monitoring and managing physiological and metabolic information, stretchable electrochemical sweat sensors have been investigated. In this study, we report on the fabrication of a stretchable and skin-attachable electrochemical sensor for detecting glucose and pH in sweat. A patterned stretchable electrode was fabricated via layer-by-layer deposition of carbon nanotubes (CNTs) on top of patterned Au nanosheets (AuNS) prepared by filtration onto stretchable substrate. For the detection of glucose and pH, CoWO4/CNT and polyaniline/CNT nanocomposites were coated onto the CNT-AuNS electrodes, respectively. A reference electrode was prepared via chlorination of silver nanowires. Encapsulation of the stretchable sensor with sticky silbione led to a skin-attachable sweat sensor. Our sensor showed high performance with sensitivities of 10.89 μA mM-1 cm-2 and 71.44 mV pH-1 for glucose and pH, respectively, with mechanical stability up to 30% stretching and air stability for 10 days. The sensor also showed good adhesion even to wet skin, allowing the detection of glucose and pH in sweat from running while being attached onto the skin. This work suggests the application of our stretchable and skin-attachable electrochemical sensor to health management as a high-performance healthcare wearable device.

Photochemical strategies for the green synthesis of ultrathin Au nanosheets using photoinduced free radical generation and their catalytic properties.

Two-dimensional gold nanosheets represent a class of materials with excellent chemical and structural properties, which are often prepared using a template or toxic CO in organic solvents. Here, we report methylene blue (MB) radicals as a reducing agent to grow freestanding hexagonal ultrathin Au nanosheets with well-tuned thicknesses in water. This is the first time that carbon organic radicals have been used as a reducing agent in metal nanosheet synthesis. Notably, no template is used throughout the synthesis process, and the yield of Au nanosheets is very high. It is found that MB is decisive in the growth of Au nanosheets because no Au nanosheets are obtained in the absence of MB with the same reaction parameters. The resulting nanosheets exhibit excellent catalytic activity during H2O2 decomposition to generate nontoxic O2. Thus, folic acid-conjugated oxygen generating nanosheets could detect cancer cells in serum samples with high sensitivity through pressure signals. Furthermore, the nanosheets exhibit highly efficient activity and selectivity toward the hydrogenation of α,β-unsaturated aldehydes. We anticipate that using MB radicals for the high-yield synthesis of 2D materials in this unique system has demonstrated their effectiveness and provides a green alternative route for producing other 2D nanomaterials.

Ultrathin silver telluride nanowire films and gold nanosheet electrodes for a flexible resistive switching device.

We demonstrated a flexible resistive switching device based on ultrathin Ag2Te nanowire (NW) films and Au nanosheet (NS) electrodes by exploiting a monolayer assembly on the water surface for macroscale two-dimensional structures. Firstly, ultrathin TeNWs (diameter ≈ 10 nm) are rapidly assembled on the water surface as a form of monolayer and transferred to fabricate TeNW films on various substrates with any available size. An assembled TeNW film was used as a template to produce a Ag2TeNW film through chemical transformation. A well-aligned Ag2TeNW film device showed reversible resistive switching properties when the Ag composition of the silver telluride NW becomes stoichiometric Ag2Te. Additionally, a non-stoichiometric Ag2+δTeNW film shows an increased On/Off ratio. For a flexible memory device, ultrathin AuNSs (thickness ≤20 nm) were adopted as working electrodes, since thermally deposited gold electrodes tend to crack under strain, which can fail to maintain the electrical properties. A paper-like flexibility of AuNS proved its capability as optimal electrodes of ultrathin Ag2TeNW film-based resistive memory devices.

Fully Elastic Conductive Films from Viscoelastic Composites.

We investigated, for the first time, the conditions where a thermoplastic conductive composite can exhibit completely reversible stretchability at high elongational strains (ε = 1.8). We studied a composite of Au nanosheets and a polystyrene-block-polybutadiene-block-polystyrene block copolymer as an example. The composite had an outstandingly low sheet resistance (0.45 Ω/sq). We found that when a thin thermoplastic composite film is placed on a relatively thicker chemically cross-linked elastomer film, it can follow the reversible elastic behavior of the bottom elastomer. Such elasticity comes from the restoration of the block copolymer microstructure. The strong adhesion of the thermoplastic polymer to the metallic fillers is advantageous in the fabrication of mechanically robust, highly conductive, stretchable electrodes. The chemical stability of the Au composite was used to fabricate high luminescence, stretchable electrochemiluminescence displays with a conventional top-bottom electrode setup and with a horizontal electrode setup.

Fully stretchable and highly durable triboelectric nanogenerators based on gold-nanosheet electrodes for self-powered human-motion detection

A patchable triboelectric nanogenerator (TENG) is highly promising for self-powered human-motion detection, but it may undergo repeated stretching/releasing cycles during daily activities of a human, which may lead to mechanical fracture of each component and degradation in electrical output performance of the TENG device. Here, we report a fully stretchable and durable triboelectric nanogenerator (TENG) with gold (Au) nanosheets (NSs) embedded into both PDMS matrix and micropyramid-patterned PDMS. It was found that a new design of the Au NS electrodes dramatically improves the mechanical flexibility and stretchability, enabling to achieve the outstanding output stability of the Au NS electrode-based TENG (Au NS-TENG) during 10,000 cycles of repeated pushing and stretching tests. Our fully stretchable and durable Au NS-TENGs were successfully applied to the hand joints that can be used in the self-powered human-motion detection processes for wearable applications.

Morphologically Controlled Au Nanosheets Assisted by Ferulic Acid

Morphologically Controlled Au Nanosheets Assisted by Ferulic Acid

Morphologically Controlled Au Nanosheets Assisted by Ferulic Acid

Morphologically Controlled Au Nanosheets Assisted by Ferulic Acid

(Invited) Synthesis and Applications of Novel Two-Dimensional Nanomaterials

In this talk, I will summarize the recent research on synthesis, characterization and applications of two-dimensional nanomaterials in my group. I will introduce the synthesis and characterization of novel low-dimensional nanomaterials, such as graphene-based composites including the first-time synthesized hexagonal-close packed (hcp) Au nanosheets (AuSSs) on graphene oxide, surface-induced phase transformation of AuSSs from hcp to face-centered cubic (fcc) structures, the synthesis of ultrathin fcc Au@Pt and Au@Pd rhombic nanoplates through the epitaxial growth of Pt and Pd on the hcp AuSSs, respectively, the first-time synthesis of 4H hexagonal phase Au nanoribbons (NRBs) and their phase transformation to fcc Au RNBs as well as the epitaxial growth of Ag, Pt and Pd on 4H Au NRBs to form the 4H/fcc Au@Ag, Au@Pt and Au@Pd core–shell NRBs, and the epitaxial growth of metal and semiconductor nanostructures on solution-processable transition metal dichalcogenide (TMD) nanoshees at ambient conditions, single- or few-layer metal dichalcogenide nanosheets and hybrid nanomaterials, the large-amount, uniform, ultrathin metal sulfide and selenide nanocrystals, other 2D nanomaterials, nanodots prepared from 2D nanomaterials, and self-assembled 2D nanosheets and chiral nanofibers from ultrathin low-dimensional nanomaterials. Then I will demonstrate the applications of these novel nanomaterials in chemical and bio-sensors, solar cells, water splitting, hydrogen evolution reaction, electric devices, memory devices, conductive electrodes, other clean energy, etc.

Study of gold nanostructures of various dimensions: Au NWs, Au nanosheets, Au nanocylinders

Using atomistic simulations, we study the impact of stretching on the structural evolution of 1D monatomic gold nanochains (MACs) undergoing elongation using SIESTA (Spanish Initiative for Electronic Simulation with Thousands of Atoms), the computational code based on DFT. Further we extend our work to the study of 2D gold nanosheets and 3D gold nanocylinders. Since the study of stretching of gold nanosheets and nanocylinders using DFT is computationally demanding, we will be using many body Gupta Potential.It will be seen that during the stretching of nanosheets different defects will arise while stretching of gold nanocylinders leads to gold monoatomic chain formation.

Preparation of Au nanosheets supported on Ni foam and its electrocatalytic performance towards NaBH4 oxidation

The unique Au nanosheets (Au NSs) are electrodeposited uniformly on Ni foam substrate via a one-step potentiostatic electrodeposition technique. The electrode is characterized by scanning electron microscopy equipped with energy dispersive X-ray spectrometer and X-ray diffractometer. It shows a unique open structure allowing the full utilization of Au surface active sites. NaBH4 electrooxidation in KOH solution on the Au NSs/Ni foam electrode are studied by linear sweep voltammetry and chronoamperometry. The electrode exhibits a high catalytic performance outperforming the Au particles made by the same method. At the oxidation potential of 0V, the current density of 827mAcm−2 can be achieved on Au NSs/Ni foam electrode, and only 219mAcm−2 was obtained on Au NPs/Ni foam electrode, indicating that the catalytic activity is increased by 278%, which is attributed to the porous 3D structure, ensuring the full utilization of Au surfaces. Besides, H2 generated by NaBH4 hydrolysis can quickly diffuse away from the electrode, preventing surface active sites of Au from blocking by adsorbed gas bubbles.

A sensitive SERS substrate based on Au/TiO2/Au nanosheets

Sensitive SERS substrates based on Au/TiO2/Au nanosheet have been prepared by physically sputtering Au nanoparticles onto fabricated TiO2 nanosheets. The Au/TiO2/Au nanosheets show much stronger SERS signal as compared to normal Au/Ti substrates by increasing surface area and effectively inducing plasmonic coupling between adjoining Au nanoparticles. In addition, influence factors such as concentration of probe solution and deposition time of gold nanoparticles were discussed. This study provides an easy-prepared and label-free substrate for the detection of biomolecule.

Two-dimensional structure Au nanosheets are super active for the catalytic reduction of 4-nitrophenol.

Two-dimensional structure Au nanosheets with a polygon morphology and controlled thicknesses of ∼15 nm, ∼35 nm, and ∼50 nm were successfully synthesized by a one-step solution reduction method. Scanning and transmission electron microscopy (SEM and TEM), selected area electron diffraction (SEAD) analyses, and X-ray diffraction (XRD) were used to thoroughly study the structure and the formation mechanism of the nanosheets. The catalytic activity of the Au nanosheets was investigated for the reduction of 4-nitrophenol (4-NP) by UV-visible absorption spectroscopy. Against all expectation, the Au nanosheets with such a big lateral (more than 1 μm) size exhibited superior catalytic activity on the selective reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of NaBH4. On the other hand, the catalytic activity does closely depend on the thickness of the nanosheets; that is, it decreases with increasing thickness. The reaction can be completed in less than 1 min when catalyzed by Au nanosheets about 15 nm thick. The 100% conversion efficiency was further demonstrated after two catalytic cycles with the thinnest Au nanosheets.

Yucca-derived synthesis of gold nanomaterial and their catalytic potential.

AuNPs ranging in 20 to 300 nm size were synthesized at a room temperature using Yucca filamentosa leaf extract. Diverse nanomaterial morphologies were obtained by varying the extract concentration, reaction pH, and temperature. While low volumes of extract (0.25 and 0.5 mL) induced the formation of microscale Au sheets with edge length greater than 1 μm, high volumes yielded spherical particles ranging from 20 to 200 nm. Varying pH of the solution significantly influenced the particle shape with the production of largely spherical particles at pH 5 to 6 and truncated triangles at pH 2. Separation of multidimensional nanostructures was achieved using a novel method of sucrose density gradient centrifugation. The catalytic function of Yucca-derived AuNPs was demonstrated by degradation of a wastewater dye: methylene blue using spectrophotometric measurements over time. Treatment with Au nanosheets and spheres demonstrated methylene blue degradation approximately 100% greater than the activity in control at 60 min.

Thickness-Controlled Synthesis of Ultrathin Au Sheets and Surface Plasmonic Property

Thickness-controlled synthesis of nanosheets of nonlayered materials is of scientific significance yet greatly underdeveloped because of the lack of controllable means of inducing anisotropic growth of 2D structures. Here we report a novel 2D template-directed synthesis of ultrathin single-crystalline Au nanosheets with well-tuned thicknesses of several to tens of nanometers, large areas (>100 μm(2)), and atomically flat surfaces. The 2D template is composed of hundred-nanometer-thick water layers sandwiched by lamellar bilayer membranes of a self-assembled nonionic surfactant, dodecylglyceryl itaconate, which appears as an iridescent solution as a result of Bragg reflection of visible light from the periodic lamellar planes. The large-area, ultrathin single-crystalline Au nanosheets enable the fabrication of plasmonic devices. For the first time, the property of surface plasmon polaritons on a patterned single-crystalline Au nanosheet was investigated, and a long propagation length approaching the theoretical expectation was found.

Highly Stretchable Patterned Gold Electrodes Made of Au Nanosheets

Multilayered Au nanosheets are suggested as a novel class of material for fabricating stretchable electrodes suitable for organic-based electronic devices. The electrodes show no difference in resistivity during repeated stretching cycles of up to ϵ = 40%.

Green Synthesis of Noble Nanometals (Au, Pt, Pd) Using Glycerol under Microwave Irradiation Conditions

A newer application of glycerol in the field of nanomaterials synthesis has been developed from both the economic and environmental points of view. Glycerol can act as a reducing agent for the fabrication of noble nanometals, such as Au, Pt, and Pd, under microwave irradiation. Their shapes can be changed by adding different surfactants. In the presence of CTAB, Au nanosheets were formed within 2 min where the size of Au nanosheets can be controlled by the microwave irradiation time and glycerol content.

Facile Fabrication of Au–F127 Nanocolloids with Different Morphologies and their Potential Bioapplications

Three kinds of novel facile fabrication routes to prepare Au–F127 nanocolloids with different morphologies including rambutan-like Au–F127 hybrid nanospheres, Au@F127 core–shell nanostructure, and multiple shapes of Au nanosheets are reported. The different Au–F127 nanocolloids are characterised by transmission electron microscopy, electron diffraction patterns, and UV-vis spectroscopy. The different formation mechanisms of the Au–F127 nanocolloids with different morphologies are discussed. The intrinsic properties and application potential of Au–F127 nanocolloids are determined by their size, shape, composition, and structure. A biosensor made of rambutan-like Au–F127 hybrid nanospheres exhibited a good electrocatalytic activity for the reduction of hydrogen peroxide. The Au@F127 core–shell nanoparticles exhibited good blood compatibility attributable to the surface hydrophilicity of the F127 layer. These strategies open up the exciting possibility of using F127 in synthesis of gold nanomaterials of variable morphology, and provide a promising platform for biomedical applications in future.

Spectroscopic Properties of Multilayered Gold Nanoparticle 2D Sheets

We report the fabrication technique and optical properties of multilayered two-dimensional (2D) gold nanoparticle sheets ("Au nanosheet"). The 2D crystalline monolayer sheet composed of Au nanoparticles shows an absorption peak originating from a localized surface plasmon resonance (LSPR). It was found that the absorption spectra dramatically change when the monolayers are assembled into the multilayers on different substrates (quartz or Au). In the case of the multilayers on Au thin film (d = 200 nm), the LSPR peak is shifted to longer wavelength at the near-IR region by increasing the number of layers. The absorbance also depends on the layer number and shows the nonlinear behavior. On the other hand, the multilayers on quartz substrate show neither such LSPR peak shift nor nonlinear response of absorbance. The layer number dependence on metal surfaces can be interpreted as the combined effects between the near-field coupling of the LSPR and the far-field optics of the stratified metamaterial films, as proposed in our previous study. We also report the spectroscopic properties of hybrid multilayers composed of two kinds of monolayers, i.e., Au nanosheet and Ag nanosheet. The combination of the different metal nanoparticle sheets realizes more flexible plasmonic color tuning.

Effect of additives on the morphology of single-crystal Au nanosheet synthesized using the polyol process

Triangular and hexagonal-shaped single-crystal Au nanosheets were prepared by the reduction of HAuCl4 with the polyol method, after addition of a polyvinylpyrolidone (PVP) capping agent and salts. Both capping agent and salts played a crucial role during nanosheet growth. The high PVP concentration was found to result in a mixed Au morphology of sheets and spherical particles, which could be tailored with the addition of salts to provide solely nanosheets. The main product is always nanosheets after the salts have been added. The selective adsorption of PVP and salt ions onto certain crystallographic facets is thought to be important in the proposed growth mechanism. This synthetic route is simple and fast, and can be extended to other morphology metal particles with careful salt and capping agent selection.