As-prepared Ag Research Articles

Creation of Controllable High-Density Defects in Silver Nanowires for Enhanced Catalytic Property.

Structural defects have been proven to determine many of the materials' properties. Here, we demonstrate a unique approach to the creation of Ag nanowires with high-density defects through controllable nanoparticles coalescence in one-dimensional pores of mesoporous silica. The density of defects can be easily adjusted by tuning the annealing temperature during synthetic process. The high-density defects promote the adsorption and activation of more reactants on the surface of Ag nanowires during catalytic reactions. As a result, the as-prepared Ag nanowires exhibit enhanced activities in catalyzing dehydrogenative coupling reaction of silane in terms of apparent activation energy and turnover frequency (TOF). We show further that the silane conversion rate can be enhanced by maximizing the defect density and thus the number of active sites on the Ag nanowires, reaching a remarkable TOF of 8288 h(-1), which represents the highest TOF that has been achieved by far on Ag catalysts. This work not only proves the important role of structural defects in catalysis but also provides a new and general strategy for constructing high-density defects in metal catalysts.

Homogeneous synthesis of Ag nanoparticles-doped water-soluble cellulose acetate for versatile applications

We report a facile and efficient approach for synthesis of well-dispersed and stable silver nanoparticles (Ag NPs) using water-soluble cellulose acetate (CA) as both reductant and stabilizer. Partially substituted CA with highly active hydroxyl groups and excellent water-solubility is able to reduce silver ions in homogeneous aqueous medium effectively. The synthesized Ag NPs were characterized by UV⿿vis spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and energy dispersive X-ray spectroscope analysis. The as-prepared Ag NPs were well-dispersed, showing a surface plasmon resonance peak at 426nm. The resulted Ag NPs@CA nanohybrids exhibit high catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4. Meanwhile, the nanohybrids are also effective in inhibiting the growth of bacterial. This environmentally friendly method promotes the use of renewable natural resources to prepare a variety of inorganic-organic materials for catalysis, antibacterial, sensors and other applications.

High Yield Seedless Synthesis of Uniform Silver Nanoparticles with Different Sizes.

Currently, seed-mediated growth method is the dominant strategy for synthesis of silver nanoparticles (Ag NPs) with different sizes. However, it is complicated for the researchers with limited chemistry-training. In this work, monodisperse, quasi-spherical Ag NPs with different sizes were successfully produced in high yield by adding a trace amount of NaBH4 solution into the mixtures of AgNO3, ascorbic acid and cetyltrimethylammonium chloride (CTAC) as surfactants. It was found that the sizes of as-prepared Ag NPs can be tuned from 20 nm to 50 nm by adjusting the NaBH4 concentration at optimal pH (about 6.33) and CTAC concentration (0.02-0.06 M). The surface-enhanced Raman scattering (SERS) activity of 50 nm Ag NPs shows an enhanced enhancement factor for 4-aminothiophenol (4-ATP) molecules (2.5 x 10(7) for a(1) mode). Moreover, Raman signals (a(g) mode) of 4,4'-dimercaptoazobenzene (DMAB) molecules were also observed due to the laser-induced transformation of 4-ATP molecules on the surfaces of 50 nm Ag NPs during SERS measurement. Furthermore, the transformation of probe molecules on the surfaces of metal NPs during SERS measurement have to be considered.

Enhanced CO selectivity and stability for electrocatalytic reduction of CO2 on electrodeposited nanostructured porous Ag electrode

Nanostructured electrocatalysts for CO2 reduction have attracted much attention due to their unique properties compared to their bulk counterparts. Here we report the synthesis of porous Ag foams on a polished Ag substrate via electrodeposition using the hydrogen bubble dynamic template. The as-prepared porous Ag foams has an average pore size of 10–25μm with the porous wall composed of 40–100nm Ag nanoparticles. CV tests indicate that the competing hydrogen evolution reaction remarkably slow down on porous Ag electrode and the onset potential of CO2 reduction occurs at 0.15V less than that on the Ag foil electrode. Moreover, the high current density and CO faradaic efficiency of over 90% were stable over the course of several hours, whereas Ag foil electrode exhibited the drop of CO faradaic efficiency from 74.4% to 58.6% under identical conditions. We found that the enhanced activity and stability are the result of a large electrochemical surface area (approximately 120 times larger) which can provide more active sites. The noteworthy difference between the two electrodes suggests that the nanostructured surface of porous Ag foams is likely to not only favor the formation of CO2− intermediate but also suppress the competitive reaction of hydrogen evolution.

Ag-Ag2S Hybrid Nanoprisms: Structural versus Plasmonic Evolution.

Recently, Ag-Ag2S hybrid nanostructures have attracted a great deal of attention due to their enhanced chemical and thermal stability, in addition to their morphology- and composition-dependent tunable local surface plasmon resonances. Although Ag-Ag2S nanostructures can be synthesized via sulfidation of as-prepared anisotropic Ag nanoparticles, this process is poorly understood, often leading to materials with anomalous compositions, sizes, and shapes and, consequently, optical properties. In this work, we use theory and experiment to investigate the structural and plasmonic evolution of Ag-Ag2S nanoprisms during the sulfidation of Ag precursors. The previously observed red-shifted extinction of the Ag-Ag2S hybrid nanoprism as sulfidation occurs contradicts theoretical predictions, indicating that the reaction does not just occur at the prism tips as previously speculated. Our experiments show that sulfidation can induce either blue or red shifts in the extinction of the dipole plasmon mode, depending on reaction conditions. By elucidating the correlation with the final structure and morphology of the synthesized Ag-Ag2S nanoprisms, we find that, depending on the reaction conditions, sulfidation occurs on the prism tips and/or the (111) surfaces, leading to a core(Ag)-anisotropic shell(Ag2S) prism nanostructure. Additionally, we demonstrate that the direction of the shift in the dipole plasmon is a function of the relative amounts of Ag2S at the prism tips and Ag2S shell thickness around the prism.

Noble metal nanoclusters and their in situ calcination to nanocrystals: Precise control of their size and interface with TiO2 nanosheets and their versatile catalysis applications

In this work, we present a new versatile strategy to prepare noble metal (Au, Ag and Cu) nanoclusters on TiO2 nanosheets in large scales with exposed (001) facets with controlled size, crystalline interface, and loading amount. By precise in situ calcination, the metal (M = Au, Ag, and Cu) nanocrystals with controllable size and better crystalline interface with the TiO2 support have been prepared. The potential application of the as-prepared Au, Ag, and Cu nanoclusters on TiO2 nanosheets as potential heterogeneous catalysts for organic synthesis, such as catalytic reduction of 4-nitrophenol to 4-aminophenol, has been demonstrated. After calcination, Au, Ag, and Cu nanocrystals were found to be proficient cocatalysts for photocatalytic H2 evolution, particularly the Au cocatalyst. Based on precise high-resolution transmission electron microscopy (HRTEM) and inductively coupled plasma optical emission spectrometry (ICP-OES) analyses, the flexible control of their size and loading amount as well as their intimate contact with the TiO2 nanosheet enhanced the photocatalytic H2 evolution activity and the sensitivity of the photocurrent response of the film. Furthermore, this aqueous-directed synthesis of metal nanoclusters on a support will generate further interest in the field of nanocatalysis.

In-situ electrochemical shell-isolated Ag nanoparticles-enhanced Raman spectroscopy study of adenine adsorption on smooth Ag electrodes

Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) is employed to investigate the electrochemical behavior of adenine molecules on smooth Ag electrodes. To attain this goal, pinhole-free shell-isolated Ag nanoparticles (Ag SHINs) have been synthesized and then used as signal “amplifiers” in the gap-mode configuration (Ag SHINs are coupled with a Ag electrode surface). The as-prepared Ag SHINs exhibit remarkable plasmonic performance under 488, 532, and 633nm excitations as revealed by finite-difference time-domain (FDTD) simulations and SHINERS experiments. Furthermore, wavelength-dependent SHINERS investigation of adenine on Ag electrodes is excellently combined with the electrochemical technique. With outstanding chemical stability and plasmonic property, the Ag SHINs are extraordinarily suitable for fundamental studies at various electrochemical interfaces.

A facile method for the synthesis of large-size Ag nanoparticles as efficient SERS substrates

Silver nanoparticles (Ag NPs) enjoy a reputation as an ultrasensitive substrate for surface-enhanced Raman spectroscopy (SERS). However, large-scale synthesis of Ag NPs in a controlled manner is a challenging task for a long period of time. Here, we reported a simple seed-mediated method to synthesize Ag NPs with controllable sizes from 50 to 300 nm, which were characterized by scanning electron microscopy (SEM) and UV–Vis spectroscopy. SERS spectra of Rhodamine 6G (R6G) from the as-prepared Ag NPs substrates indicate that the enhancement capability of Ag NPs varies with different excitation wavelengths. The Ag NPs with average sizes of ~150, ~175, and ~225 nm show the highest SERS activities for 532, 633, and 785-nm excitation, respectively. Significantly, 150-nm Ag NPs exhibit an enhancement factor exceeding 108 for pyridine (Py) molecules in electrochemical SERS (EC-SERS) measurements. Furthermore, finite-difference time-domain (FDTD) calculation is employed to explain the size-dependent SERS activity. Finally, the potential of the as-prepared SERS substrates is demonstrated with the detection of malachite green. Copyright © 2016 John Wiley & Sons, Ltd.

Egg White Templated Synthesis of Ag and Au@Ag Alloy Microspheres for Surface-Enhanced Raman Spectroscopy Research.

Herein, we report the green synthesis of Ag and Au@Ag microspheres by using the aqueous extracts of the egg white as well as their application as substrates for surface-enhanced Raman spectroscopy (SERS) detection. Both microspheres are prepared via the green synthesis method (room temperature, in aqueous solution and a benign reducer). The as-prepared urchin-like Ag microspheres have an average diameter of 600-800 nm, which is made up of some nanopricks with an average length of 10-40 nm. Meanwhile, the Au@Ag architectures prepared by galvanic replacement keep nearly similar size, which is also composed of some compact nanoparticles with an average diameter of about 10-40 nm. These products are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electronic microscopy (TEM), and Fourier transform infrared spectrophotometer (FTIR). The study on SERS activities is also carried out for both microspheres. It is found that Au@Ag microspheres possess much higher SERS activity than Ag microspheres. Our work may shed light on the design and synthesis of self-assembled 3D micro/nano-architectures for the use of SERS, catalysis, biosensors, nanomedicine, etc.

Contribution of oligomer/carbon dots hybrid semiconductor nanoribbon to surface-enhanced Raman scattering property

The hybrid Ag-(PS-PSS)/C-dots nanobelts (NBs) have been prepared by decorating Ag nanoparticles (NPs) on surface of the ultra-long, semiconducting (PS-PSS)/C-dots nanoribbons (NRs) via an electroless plating method. The as-prepared Ag-(PS-PSS)/C-dots NB has been demonstrated to be an excellent substrate for surface-enhanced Raman scattering (SERS) with a detection limit of 10−14M and an enhancement factor of 3.35×108 while using rhodamine 6G as probe molecules. Moreover, we have investigated the application of Ag-(PS-PSS)/C-dots NBs as SERS substrate for detection of coumarins. Further, the Ag-(PS-PSS)/C-dots NB could be used as a sacrificial template to form a novel kind of hollow porous Ag nanotubes (NTs) by simply removing the inner NR in tetrahydrofuran. However, the obtained Ag NTs show a weaker SERS effect compared to that of the Ag-(PS-PSS)/C-dots NBs, which indicates that the inner organic/C-dots NR plays an essential role in SERS property of the Ag-(PS-PSS)/C-dots NBs. Here the organic (PS-PSS)/C-dots NR not only acts as a dielectric support for Ag NPs to reduce the surface plasmon damping at the Ag-NR interface due to the high electrical conductivity but also their large surface area are favorable for creating more “hot-spots”. In addition, the embedded sp2-hybridized C-dots in NR can adsorb more aromatic R6G molecules via π–π interaction, which also drives R6G molecules approaching to the “hot-spots”, thus enhancing the SERS signals. Based on our results, it is believed that the employment of semiconducting organic (PS-PSS)/C-dots ribbon-like structures to fabricate sensitive SERS substrates is an interesting new approach.

Heat generation and stability of a plasmonic nanogold system

The surface plasmon resonance (SPR) of Au nanostructures can be precisely tuned in the visible to near-infrared (vis–NIR) region with the size and morphology. The photothermal effect induced by the SPR can raise the temperature of Au nanostructures and the surrounding matrix under external illumination. In this work, hollow Au nanostructures such as nanoboxes and nanorings with a tunable SPR in the region of 650–1100 nm were obtained by a replacement reaction between HAuCl4 and the as-prepared Ag nanostructures as the sacrificed templates. Compared with the solid Au nanorods, studies on the photothermal conversion and stability of hollow Au nanostructures were systematically carried out with the assistance of the near-infrared (NIR) lasers available. Under NIR laser irradiation, the temperatures of the colloidal Au nanostructures increased rapidly from ~30 °C to ~65 °C. Combining the experimental results with a finite-different time-domain (FDTD) numerical simulation, the heat generation of different Au nanostructures was investigated. With the consideration of the concentration of the Au nanostructures, it is indicated that hollow Au nanostructures are superior to solid Au nanorods in photothermal conversion. On increasing the NIR laser power (3 W), Au nanorods undergo a shape deformation from nanorods to spherical nanoparticles, while the SPR and morphology of hollow Au nanoboxes and nanorings maintain high stability, promising to be candidates for nanoheaters. This work provides a standard to design optimized plasmonic nanoheaters.

Controlled preparation of Ag nanoparticle films by a modified photocatalytic method on TiO2 films with Ag seeds for surface-enhanced Raman scattering

Uniform Ag nanoparticle (NP) films were synthesized by a modified photocatalytic method on TiO2 films with Ag seeds for surface-enhanced Raman scattering, which combine the advantages of the spurting method (high nucleation density) and the traditional photocatalytic method (suitable particle size). The Ag seeds were prepared by magnetron sputtering with different time, which would adjust the distribution and transfer of electrons on the surface of TiO2 film in the process of photocatalytic reduction. The distribution and morphology of Ag NP films can be adjusted by the sputtering time and the UV irradiation time. The Raman enhancement of as-prepared Ag NP films was calculated by finite-difference time-domain to validate the experiment data. It is found that the Ag NP films synthesized on TiO2 films with suitable pre-deposited Ag seeds exhibit a much higher Raman enhancement activity than the optimum Ag NP film synthesized directly on the TiO2 film without Ag seeds.

Green synthesis of silver nanoparticles for selective toxicity towards cancer cells.

Therapeutic applications of nanoparticles (NPs) are rapidly increasing for their utility in medicine, especially cancer therapy. The present study investigated the green synthesis of silver NPs (Ag NPs) of 10 nm size using Sargassum vulgare and its preferential ability to kill cancerous human myeloblastic leukemic cells HL60 and cervical cancer cells HeLa as compared with normal peripheral blood mononuclear cells. DNA fragmentation study and annexin V marker fluorescence-activated cell sorting (FACS) analysis revealed the Ag NP-induced cell death is through apoptosis. Transmission electron micrographs have showed the endocytosis of Ag NPs into the nucleus. Ag NPs inhibited the lipid peroxidation-induced reactive oxygen species generation, thus preventing the irradiation-related carcinogenesis. This study suggested that a mechanism underlying the toxicity of Ag NPs towards cancer cells is due to DNA damage and apoptosis. The authors' findings revealed the potential utility of as-prepared Ag NPs in the treatment of cancer as prophylactic agent with antioxidant property and chemotherapeutic agent for their selective toxicity to cancer cells.

Electrochemical Synthesis and Deposition of Surface-Enhanced Raman Scattering-Active Silver Microstructures on a Screen-Printed Carbon Electrode

We demonstrated a series of Ag microstructures with controlled morphologies directly deposited on a screen-printed carbon electrode by using electrochemical procedures in the presence of different electrolytes. Scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and high-resolution X-ray diffractometry were used for characterizing as-prepared Ag substrates. Thereafter, the potential of the flower-like Ag microstructures for use in surface-enhanced Raman scattering (SERS) applications was investigated. The flower-like Ag microstructures provided a more intense SERS signal because of extremely intense local electromagnetic fields. The enhancement factor value was approximately 1.2 × 106 for 4-mercaptobenzoic acid molecules. The percentage of relative standard deviation of SERS signals was lower than 2.1%. Determining the SERS spectra of 4,4′-dimercapto-azobenzene, 5,5′-dithiobis-2-nitrobenzoic acid, adenine, and single-stranded DNA (fumarylacetoacetate hydro...

The synthesis, activity, stability and the charge transfer identification of Ag:AgBr/γ-Al2O3 photocatalyst for organic pollutant decomposition in water

Highly stable Ag:AgBr/γ-Al2O3 photo-catalyst was obtained by dispersing AgBr sol on hollow γ-Al2O3 microsphere. Metallic Ag nanoparticles were in situ generated on AgBr crystals by a photo-reduction method. The activity of catalyst was characterized by MO and phenol decomposition. The light irradiation response, the life times of the photo-induced charges, and the charge separation and transition were determined by the UV–vis diffuse reflection spectra, open circuit voltage decay spectra and transient photocurrent responses. The as-prepared Ag:AgBr/γ-Al2O3 catalyst can response to visible light irradiation. Charge separation was clarified to correlate with electrons transferring from Ag to AgBr surface and the consequent reaction with ads-O2 to generate O2− species. It was found that the O2− rather than OH played a dominant role in the photocatalytic oxidation of MO and phenol in water. However, the electrons trended to transfer from AgBr to Ag intrinsically without light irradiation. Therefore, the electron transfer between Ag and AgBr reaching the dynamic equilibrium was the key factor for obtaining a high stable Ag/AgBr catalyst which can be obtained by optimizing the Ag:AgBr ratio. Loading amount of Ag:AgBr on γ-Al2O3 was optimized to 30wt.% and the metallic Ag content was stabilized at 9wt.% of Ag:AgBr catalyst.

Plasma-induced brightening and coarsening of tarnished Ag nanoparticles

The recovery of the optical properties of tarnished silver nanoparticles (Ag NPs) has been demonstrated using exposure to plasma. As-prepared Ag NPs on a SiO2 substrate exhibited an intense localized surface plasmon resonance (LSPR) in the UV–vis optical extinction spectrum. The LSPR band weakened gradually when an Ag NP sample was stored in ambient air forming tarnished Ag. X-ray photoelectron spectroscopy (XPS) and ion-beam analysis revealed the presence of impurity elements, such as N and S. In addition, the shape of the valence-band XPS spectra changed significantly with exposure to ambient air. Ar plasma treatments recovered the intense LSPR and the XPS spectral shape. We conclude that both the reduction of Ag2S to Ag and the morphological change toward isolated Ag NPs most likely lead to their recovery. A simulation based on the Mie theory, as well as direct observation with an atomic force microscope, supports our findings.

Graphene Oxide-Supported Ag Nanoplates as LSPR Tunable and Reproducible Substrates for SERS Applications with Optimized Sensitivity.

Nanoparticles and nanohybrids with well-defined structures, along with tunable localized surface plasmon resonance (LSPR) properties and optimized sensitivity, are crucial and highly desired for surface-enhanced Raman spectroscopy (SERS) applications. In this article, we report on a very promising and flexible SERS platforms with a tunable LSPR response and sensitivity based on Ag nanoplates and graphene oxide (GO). The SERS detection sensitivity can be easily optimized and significantly improved by fine-tuning the LSPR band of the Ag nanoplate/GO substrates (to enhance the SERS response) during sample preparation. We applied the as-prepared SERS platform for sensitive SERS detection of 4-mercaptobenzoic acid and 4-aminothiophenol and found that the SERS signal varied markedly (by ∼10-15-fold) with the fine-tuning of the LSPR band. The SERS enhancement factor of the Ag nanoplate/GO complexes was more than 10(4) times larger than that obtained using spherical Ag nanoparticles. The as-prepared Ag nanoplate/GO platforms, because of their excellent stability and tunable LSPR properties, will find promising practical SERS applications.

Dextrin-mediated synthesis of Ag NPs for colorimetric assays of Cu2+ ion and Au NPs for catalytic activity

A facile one-pot approach for rapid synthesis of silver and gold nanoparticles (Ag NPs and Au NPs) with narrow size distribution and good stability was described by reducing silver nitrate and chloroauric acid with polysaccharide dextrin. Here, dextrin was used as both a reducing and stabilizing agent for synthesis of NPs. The as-synthesized Ag NPs and Au NPs were characterized by UV–visible absorption spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The Ag NPs and Au NPs exhibited an absorption maxima at 404 and 547nm respectively. TEM images showed NPs in the range of 8–28nm. The crystallinity of the NPs was measured by XRD analysis. Furthermore, the as-prepared Ag NPs revealed colorimetric sensor property for detection of Cu2+ ions based on changes in absorbance resulting from metal ion-induced aggregation of NPs or direct deposition of metal ions onto NPs. The as-prepared Au NPs exhibited a notable catalytic activity toward the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4.

Facile Synthesis of Ag3PO4 Nanospheres with Enhanced Photocatalytic Properties for the Degradation of Methylene Blue Under Visible Light Irradiation

A facile and simple sodium hexametaphosphate complex method is proposed for the synthesis of Ag 3 PO 4 nanospheres with highly uniform in size. The morphology, structure, and photoabsorption of the Ag 3 PO 4 nanospheres were characterized. Furthermore, the photocatalytic activities for the decomposition of methylene blue (MB) were also analyzed and the results show that the as-prepared Ag 3 PO 4 nanospheres exhibit excellent visible light driven photocatalytic activities for the photodecomposition of organic contaminants in comparation with microsized Ag 3 PO 4 particles and N-doped TiO 2 under visible light irradiation.

Ag nanoparticle-decorated 3D flower-like TiO2 hierarchical microstructures composed of ultrathin nanosheets and enhanced photoelectrical conversion properties in dye-sensitized solar cells

A double-layer TiO2 (Ag–TiO2-DL) photoanode with various loading amounts of Ag nanoparticles were designed with an underlayer composed of P25 TiO2 nanoparticles and an overlayer of 3D flower-like TiO2 hierarchical microstructures (TiO2-HS) and used to make a serious of dye-sensitized solar cells (DSSCs). The resulting nanostructures are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV–visible spectroscopy, N2 adsorption–desorption isotherms, and Raman spectroscopy. The influences of different loading amounts of Ag on the structure and performance of the DSSCs are investigated. Results indicate that the short current density (Jsc), open-circuit voltage (Voc) and charge lifetime of DSSCs containing Ag nanoparticles are significantly improved. Especially, the as-prepared Ag–TiO2-DL film at the nominal Ag loading of 0.8 wt% showed the highest photoelectric conversion efficiency of 8.98%, which exceeds that of pure TiO2-DL of 6.22%. Thus superior cell efficiency is mostly due to the increase of current density, attributed to that (i) a higher efficiency of light harvesting through the light scattering of overlayer; (ii) the efficient separation of photo-induced electrons and holes due to these novel hierarchical microstructures; (iii) the surface Plasmon resonance effect of Ag nanoparticles, which enhance the efficient charge separation and high carrier mobility.