Surface Of Ag Nanoparticles Research Articles

Uncovering strong π-metal interactions on Ag and Au nanosurfaces under ambient conditions via in-situ surface-enhanced Raman spectroscopy

Uncovering strong π-metal interactions on Ag and Au nanosurfaces under ambient conditions via in-situ surface-enhanced Raman spectroscopy

Synergistic effect of modest pores and lithiophilic surface on 3D current collectors for stable Li metal anodes

The increasing demand for high energy density battery systems has accelerated the development of lithium metal batteries, and it is imperative to seek strategies for alleviating the large volume change and inhibiting dendrite growth of the Li metal anode. 3D porous anode current collectors cooperated with surface modification have been considered as effective methods. Herein, we develop 3D porous Cu with modest pores by powder metallurgy method, combined with surface modification by lithiophilic Ag nanoparticles. The obtained ingenious porous structure ensures the reduction of local current density when served as the Li anode current collector, while the Ag nanoparticle layer provides numerous lithiophilic nucleation sites. Smooth and uniform Li plating morphologies are confirmed on the PM Cu@AgNP electrode surface, and the PM Cu@AgNP-Li symmetric cell presents a stable cycle of 1600 h, which effectively inhibits the Li dendrite growth. When coupled with the LiFePO 4 cathode, the assembled full cell exhibits superb capacity retention and stability for 600 cycles at 0.5 C. This facile and rational strategy with synergistic effect of modest pores and surface lithiophilicity provides a way to achieve highly stable Li metal anodes for next-generation Li batteries. • Powder metallurgy method is introduced to prepare the Li metal anode current collector. • Synergistic effect of the structure and lithiophilicity makes stable Li anode. • An average pore size of 21.2 µm is modest for the porous current collector. • Surface Ag nanoparticles significantly reduce Li nucleation overpotential.

In vitro antibacterial and cytotoxicity assessment of magnetron sputtered Ti1.5ZrTa0.5Nb0.5W0.5 refractory high-entropy alloy doped with Ag nanoparticles

The aim of the current study is to develop and evaluate antibacterial and biocompatible refractory high-entropy alloy (RHEAs) film using RF magnetron sputtering technique. For this purpose, Ti1.5ZrTa0.5Nb0.5W0.5 RHEA film and its Ag nanoparticle doped analog (with an Ag content of 9 atomic %) were deposited on Ti6Al4V substrate. The microstructural characterization revealed the homogenous distribution of the constituent elements and amorphous structure of the deposited films. The antibacterial activity of Ag nanoparticles doped RHEA film was compared with that of undoped film and uncoated Ti6Al4V. The results indicated that doping Ag nanoparticles reduced the colony forming unit of P. Aeruginosa and S. Aureus bacteria by 98.5% and 90.9%, respectively. In addition, healthy C2C12 mouse muscle myoblast cells adhered and proliferated perfectly on the surface of antibacterial Ag nanoparticles doped RHEA film with no indication of toxic effect, demonstrating promising biocompatibility in addition to its strong antibacterial property.

An Electrochromic Ag-Decorated WO3-x Film with Adjustable Defect States for Electrochemical Surface-Enhanced Raman Spectroscopy.

Electrochemical surface-enhanced Raman scattering (EC-SERS) spectroscopy is an ultrasensitive spectro-electrochemistry technique that provides mechanistic and dynamic information on electrochemical interfaces at the molecular level. However, the plasmon-mediated photocatalysis hinders the intrinsic electrochemical behavior of molecules at electrochemical interfaces. This work aimed to develop a facile method for constructing a reliable EC-SERS substrate that can be used to study the molecular dynamics at electrochemical interfaces. Herein, a novel Ag-WO3−x electrochromic heterostructure was synthesized for EC-SERS. Especially, the use of electrochromic WO3−x film suppresses the influence of hot-electrons-induced catalysis while offering a reliable SERS effect. Based on this finding, the real electrochemical behavior of p-aminothiophenol (PATP) on Ag nanoparticles (NPs) surface was revealed for the first time. We are confident that metal-semiconductor electrochromic heterostructures could be developed into reliable substrates for EC-SERS analysis. Furthermore, the results obtained in this work provide new insights not only into the chemical mechanism of SERS, but also into the hot-electron transfer mechanism in metal-semiconductor heterostructures.

Efficient and continuous chemical conversion in a thin membrane comprising three-dimensional network trapping Ag nanoparticles

In this work, we report a novel and highly efficient catalytic membrane (PES/PNM-Ag) comprising well-dispersed silver nanoparticles (NPs). The membrane can be straightforwardly constructed via dynamic loading expansible hybrid microgels PNM-Ag into a commercially-available poly(ether sulfone) (PES) membrane with asymmetric structure. Characterization results of PNM-Ag and PES/PNM-Ag indicate that a nanoscale three-dimensional network embedded with Ag NPs was developed in membrane pores by swollen microgels. The flat-sheet membrane reactor assembled with PES/PNM-Ag can efficiently and continuously catalyze the reduction of 4-nitrophenol (apparent reaction rate constant reaching 1.12 s−1) and showed good stability. The improved catalytic activity was attributed to fully accessible surface of Ag NPs as well as the unique structure of the membrane, in which the reactant was restricted to flow through immobilized catalyst. Present strategy hints to design other noble metal NPs loaded catalytic membranes for efficient conversion of nitro-aromatic pollutants.

Self‐Assembly Silver Nanoparticles Decorated on Gold Nanoislands for Label‐Free Localized Surface Plasmon Resonance Biosensing

AbstractA nanostructure of self‐assembly silver nanoparticles decorated on gold nanoislands (SAM Ag@AuNIs) is proposed in this article as a sensitive sensing medium for localized surface plasmon resonance (LSPR) biosensing applications. A wide tunable plasmonic sensing range from 472 to 552 nm is found by adjusting the Au–Ag atomic ratio. Biotin is employed as an indicator to investigate the potential biosensing applicability and site‐specific bioactivity of the SAM Ag@AuNIs. In virtue of a white light common‐path sensing system, direct adsorption of biotin on the SAM Ag@AuNIs is measured in label‐free manner with detection limit (LOD) of 2.9 pg mL−1 (11.87 × 10−12 m). It is 105‐fold better than that of TiN film, which is previously reported to provide excellent LSPR LOD after functionalization with biotin. The experimental and computational results indicate that the biotin molecule can selectively immobilize onto the Ag nanoparticles (AgNPs) surface through S–Ag bonding, resulting in site‐specific functionalization. Meanwhile, the geometry of AgNPs/AuNIs provided a coupling effect that helps to improve the sensitivity. Here, AgNPs are, for the first time, reported to be directly functionalized with biotin. The SAM Ag@AuNIs can serve as a desirable plasmonic medium in the biosensing community based on the exceptionally good LOD of biotin.

A Multilayer Interlaced Ag Nanosheet Film Prepared by an Electrodeposition Method on a PPy@PEDOT:PSS Film: A Strategy to Prepare Sensitive Surface-Enhanced Raman Scattering Substrates.

A highly sensitive multilayer interlaced silver (Ag) nanosheet (MISN) film was prepared on a PPy@PEDOT:PSS film via an electrodeposition method for surface-enhanced Raman scattering (SERS) applications. After the PPy@PEDOT:PSS film was pretreated with ascorbic acid solution, many sparse Ag nanoparticles (NPs) could be directly reduced on the surface of the PPy@PEDOT:PSS film in AgNO3 solution. Then, the MISN film was directionally grown along the surface of sparse Ag NPs by using an electrochemical galvanostatic method to form a Ag/PPy@PEDOT:PSS film for a SERS substrate. The results indicated that with the increase in electrodeposition time, the density of Ag nanosheets was also increased for boosting the SERS effect. Accordingly, owing to the directional growth of Ag NPs, the increase in the length–width ratio of single Ag nanosheets would further promote the SERS signal of the substrate. Moreover, the maximum enhancement factor of the SERS substrate could reach to 12,478, and the minimum limit of detection of melamine solution was down to 5.42 ng/mL. The SERS sensitivity of the Ag nanosheet film reached 100.65. This method of preparing the SERS substrate provides a novel and robust strategy for the low-cost and high-sensitivity detection in biomedicine, drugs, and food.

Construction of Ag/3D-reduced graphene oxide nanocomposite with advanced catalytic capacity for 4-nitrophenol and methylene blue

The Ag nanoparticles decorated three dimentional (3D) reduced graphene oxide (Ag/3D-rGO) nanocomposite was prepared by a one-pot green hydrothermal method in the absence of any extra additive. It was found that the formation of Ag/3D-rGO cylinder depend on the GO dispersion concentration strongly. The obtained 3D Ag/rGO nanocomposite was of superior catalytic performance for the catalytic reduction of 4-nitropenol and catalytic degradation of methyl-blue at room temperature. The corresponding catalytic kinetics constants are 1.18577 min−1 for 4-nitrophenol and 0.83581 min−1 for methylene blue due to the naked surface of Ag nanoparticles and the charge transfer effect between anchored Ag nanoparticles and 3D-rGO. Both of the above kinetics constants are much higher than the reported counterparts. The outstanding catalytic performance along with the favorable kinetics parameters make the 3D Ag/rGO nanocomposite to be a promising heterogeneous catalyst in environmental protection and chemical engineering industry.

Study of the Adsorption of Human Hemoglobin to Silver (Ag) Nanoparticle Surface for the Detection of the Unfolding of Hemoglobin

Study of the Adsorption of Human Hemoglobin to Silver (Ag) Nanoparticle Surface for the Detection of the Unfolding of Hemoglobin

Neutral and charged forms of inubosin B in aqueous solutions at different pH and on the surface of Ag nanoparticles

One of the strategies to combat neurodegenerative diseases such as Alzheimer's and Parkinson's diseases, or to heal brain injuries is based on the regeneration of neurons. Inubosin B is acridine alkaloid with neuroregenerative potential. The understanding of its physico-chemical properties and structure in solution can be useful for drug formulations. We have determined pKa,1 5.30 and pKa,2 9.45 constants for inubosin B. The presence of both acidic and basic sites in the molecule of inubosin B does not lead to formation of zwitterion. In neutral form, inubosin B exists as “a free base”, which is lipophilic and easily extractable to chloroform and n-octanol. Moreover, by comparison of experimental and calculated UV–vis and NMR spectra, we have proven the existence of inubosin B in “free base” form and revealed the conformers of inubosin B in water. Inubosin B was adsorbed on silver surface providing the strongest surface enhanced Raman (SERS) spectrum in neutral pH. Based on relative intensity conservation and density functional theory (DFT) calculation, we propose that inubosin B is adsorbed on the silver surface in free base form.

Silver Oxygen Reduction Electrocatalyst in Alkaline Medium: Aging and Protective Coating

The oxygen reduction reaction (ORR) is a key process in anion exchange membrane fuel cells. The alkaline conditions should allow silver‐based cost‐efficient catalysts to replace platinum group metal materials. However, Ag electrochemical stability or lack of stability in alkaline medium is still to be demonstrated. Herein, Ag catalyst nanoparticles (NPs) are characterized by identical location transmission electron microscopy and X‐ray photoelectron spectroscopy after electrochemical cycling, revealing the losses of activity and surface. Herein, a facile method for enhancing the chemical stability of Ag catalysts in an alkaline environment by depositing a protective polydopamine (PDA) coating is reported. It is enhanced via crosslinking with polyethyleneimine (PEI), on the surface of Ag NPs. The enhanced electrochemical stability of Ag PDA–PEI nanocatalyst via the analysis of ORR polarization curves during accelerated stress test cycling is demonstrated, with at least one order of magnitude higher durability than the standard Pt/C catalyst. Moreover, electrochemical measurements indicate that the protective PDA–PEI coating has good permeability to O2, with a positive effect on the ORR activity of Ag NPs.

Kinetic Study on the Adsorption of 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane on Ag Nanoparticles in Chloroform: Implications for the Charge Transfer Complex of Ag–F4TCNQ

In this study, the kinetics of the adsorption of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) on the surface of Ag nanoparticles (Ag NPs) in chloroform has been intensively investi...

Toward white light emission from plasmonic-luminescent hybrid nanostructures

Abstract We study the light emission of plasmonic-luminescent hybrid nanostructures consisting of Ag nanoparticles (NPs) embedded in europium oxide (EuOX). The Ag NPs present a bidimensional organization in the nanostructures and they optically behave as oblate spheroids. The photoluminescence (PL) spectral response of the nanostructures evolves from a narrow red emission characteristic of Eu3+ ions in absence of Ag NPs to a broad blue-green emission band associated with Eu2+ ions when the layer of Ag NPs is present. This behavior is not related to a change in the Eu2+/Eu3+ ratio, which is verified by compositional analysis. Instead, a detailed investigation of the PL emission of the nanostructures suggests that the coupling of the Ag NPs to the Eu2+ ions present in the EuOX layer, which manifests itself in an efficient sensitization of these ions, enhances their broad visible emission. In particular, the longitudinal mode of the Ag NPs surface plasmon is considered to be responsible for the efficient energy transfer for the non-normal incidence excitation PL configuration used. Finally, the use of a capping amorphous Al2O3 layer allows improving the robustness of hybrid nanostructures and further enhances their PL emission. These findings provide a new path to actively control the selective excitation of Eu2+ and Eu3+ ions via a controlled coupling with the surface plasmon resonance modes of the Ag NPs and points to these nanostructures as promising building blocks for the development of integrable white light sources.

Structure and photocatalytic properties of the composite of Al-doped porous ZnO hollow micro-spheres and Ag nanoparticles

Al-doped porous ZnO hollow micro-spheres were prepared using a sol-gel method with a template of agglomerates of polystyrene (PS) nanospheres, and the composite of these ZnO hollow micro-spheres and Ag nanoparticles was prepared with further photo-deposition. The effects of Al doped on the structure and the optical properties of the specimen were investigated by means of x-ray diffractometer, SEM, TEM, an UV-Vis diffuse reflectance analyzer, and photoluminescence (PL) spectroscopy. Different doping concentrations of Al affect not only the existing form of Al atoms in the crystal but also the concentration of the intrinsic defects of ZnO, thus influencing the morphology of the hollow micro-spheres. The appropriate amount of Al doping provides the hollow spheres with a porous, loose morphology, showing the largest specific surface area, which significantly improves the absorbance of light and the number of reaction sites in photocatalysis. For the composite specimen, the introduction of Ag nanoparticles improves the absorbance of light in the visible region because of the surface plasmon resonance: in the PL measurements, because many electrons in the ZnO crystal flow to the surface of Ag nanoparticles due to the difference of energy levels between Ag and ZnO crystals, the intensity of the intrinsic and defect-related emissions of ZnO is reduced. The photocatalytic properties of the specimens were evaluated with the degradation of a methyl orange dye solution under simulated solar irradiation at room temperature. The specimen of porous ZnO hollow micro-spheres with 3% Al dopant concentration demonstrates excellent photocatalytic performance due to its large specific surface area. However, with the designed energy structure, the composite of porous ZnO hollow micro-spheres and Ag nanoparticles exhibits the best photocatalytic performance among the specimens tested by separating electrons and holes in the ZnO crystal.

Vibrational analysis of α-lipoic acid and its adsorption behavior study by SERS

FT-IR and Raman spectra of α-Lipoic acid (LA), a molecule present in almost all eukaryotic cells that exhibits intracellular metabolic properties, were recorded and analyzed by means of both experimental and DFT based theoretical methods. Moreover, the adsorption behavior of LA on silver (Ag) nanoparticles surface at different concentrations was thoroughly investigated by SERS and the lowest detectable concentration of LA was found to be of 10−9 M. The analyte concentration dependence on SERS evidenced that at concentrations between 10−2 M and 10−7 M the LA molecule is chemisorbed on the Ag nanoparticles surface through the carboxyl group and is predominantly perpendicular with respect to the metal surface, whereas at lower concentrations (up to 10−9 M) a reorientation of the adsorbed species takes place.

Photococatalytic anticancer performance of naked Ag/AgCl nanoparticles

Ag/AgCl as a plasmonic photocatalyst has an excellent performance in dye degradation, but its photocatalytic ability in cancer therapy has not been well researched. Hence, we synthesized bio-compatible and surfactant-free Ag/AgCl nanoparticle to investigate their photocatalytic efficacy. AgCl can be oxidized by FeCl3 on the surface of Ag nanoparticles (NPs), which will naturally form a Schottky junction. Thus, Ag as a co-catalyst can easily trap the photo-generated charge carriers and then provide free electrons, which will decrease the influence of the recombination process and increase photocatalytic efficacy. Besides that, the light irradiation will stimulate the surface plasmon resonance of Ag nanoparticle, which can enhance visible light absorption by the material. Our photocatalyst can generate Reactive oxygen species (ROS) which generate oxidative stress to cellular systems and result in apoptosis. Compared to pure Ag nanoparticle, AgCl coated on Ag nanoparticle has a larger range of working wavelength and higher photocatalytic efficacy, moreover, it has less dark cytotoxicity than pure AgCl nanoparticle based on our results. The photocatalytic efficacy of Ag/AgCl nanoparticle can eliminate over 75% HeLa cells under 30 min of light irradiation.

Role of polystyrene microplastics in sunlight-mediated transformation of silver in aquatic environments: Mechanisms, kinetics and toxicity

Sunlight-oxidative ageing is a common and critical process for microplastics (MPs) in aquatic environments. O2•−, 1O2, and •OH generation has been widely proven in this process, which can alter metal speciation based on its reduction and oxidation potential. Herein, chemical speciation of Ag mediated by polystyrene (PS) MPs was determined under simulated sunlight irradiation. The O2•− generation on the PS MPs surfaces is the vital factor for Ag+ reduction, regardless of acid or base conditions. The 1O2 and •OH are dominant factors, and 1O2 played a more important role than •OH for its higher formation amount, causing oxidative dissolution of newly formed Ag0 nanoparticles (NPs). The Ag NPs can hetero-aggregate with PS MPs through electrostatic interactions with O–containing groups (C–O, C–OH and CO), and co-precipitate from the water phase. This hetero-aggregation can stabilize Ag NPs by inhibiting Ag NPs surface photooxidation and suppressing Ag+ release. Transformation of Ag species (from Ag+ to Ag0 NPs) mediated by sunlight with PS MPs significantly suppressed acute toxicity of Ag+ to Escherichia coli, Selenastrum capricornutum, Daphnia magna and zebrafish. This study emphasized that PS MPs play an important role in the speciation, migration and toxicity of Ag+ in freshwater environments.

Influence of excitation wavelength, solution pH, incubation time, absolute configuration (S and R) and constitutional isomerism (ortho-, meta- and para-) on the adsorption on the surface of Ag nanoparticles of N-benzylamino(boronphenyl)methylphosphonic acid analogues

Five analogs of N-benzylamino(boronophenyl)methylphosphonic acid, which is a potential inhibitor of kinase and protease enzymes whose activation has been detected during tumor growth, proliferation, and invasion were synthetized. These compounds were adsorbed on the surface of Ag nanoparticles (AgNPs) with a diameter of ~ 15 nm from an aqueous solution under various environmental conditions, including excitation wavelengths (488.0, 632.8, and 785.0 nm), pH values of the solutions (from pH = 5 to pH = 11), absolute configuration (S and R), and constitutional isomerism (ortho–, meta–, and para–). Using surface-enhanced Raman scattering (SERS) technique, specific conclusions were drawn about the dynamic nature of these compounds at the solid/liquid interface, which is biologically important as the boronic acid motif acts as a transition state analog that forms hydrogen and covalent bonds in the active site of the enzyme.

Application of Alanine Scanning to Determination of Amino Acids Essential for Peptide Adsorption at the Solid/Solution Interface and Binding to the Receptor: Surface-Enhanced Raman/Infrared Spectroscopy versus Bioactivity Assays.

The article describes the application of the alanine-scanning technique used in combination with Raman, surface-enhanced Raman, attenuated total reflection Fourier transform infrared, and surface-enhanced infrared absorption (SEIRA) spectroscopies, which allowed defining the role of individual amino acid residues in the C-terminal 6–14 fragment of the bombesin chain (BN6–14) on the path of its adsorption on the surface of Ag (AgNPs) and Au nanoparticles (AuNPs). A reliable analysis of the SEIRA spectra of these peptides was possible, thanks to a curve fitting of these spectra. By combining alanine-scanning with biological activity studies using cell lines overexpressing bombesin receptors and the intracellular inositol monophosphate assay, it was possible to determine which peptide side chains play a significant role in binding a peptide to membrane-bound G protein-coupled receptors (GPCRs). Based on the analysis of spectral profiles and bioactivity results, conclusions for the specific peptide–metal and peptide–GPCR interactions were drawn and compared.

In situ photochemical deposition of Ag nanoparticles on polyester fiber membranes as flexible SERS substrates for sensitive detection of sodium saccharin in soft drinks

Flexible surface-enhanced Raman scattering (SERS) substrates, specifically paper-based SERS substrates, are generally employed in many practical applications. However, paper-based SERS substrate quantitation is still challenging because of the inferior uniformity originating from the irregular morphology of the paper. The present study synthesized Ag nanoparticles (NPs) via the in situ photochemical reduction of Ag+ ions on a titanium dioxide (TiO2) film at the polyester fiber membranes (PFMs) surface. This generated many “hot spots” that presented significant SERS activity with an enhancement factor of 2.1 × 109. Sodium saccharin (SS) bonded to the Ag NPs surface via the carbonyl oxygen and ring nitrogen atoms. A SERS sensor with photochemically deposited Ag NPs was prepared for the sensitive and rapid detection of SS in soft drinks with a limit of detection of 0.3 mg/L. The recovery rate ranged from 93% to 103%, indicating that this method is reliable in actual sample detection with simple pretreatment steps and can be potentially applied for the on-site detection of food additives for food safety.