Plasmonic enhanced OLED efficiency upon silver-polyoxometalate core-shell nanoparticle integration into the hole injection/transport layer

Although organic light-emitting diodes (OLEDs) are considered a mature technology, further enhancements in their efficiency are of paramount importance for advancing their incorporation in high-quality displays and flexible, wearable, electronic devices. In this regard, we propose an innovative approach, focusing on strategic modifications to the hole transport layer (HTL) through the integration of core-shell nanoparticles. Silver nanoparticles (Ag-NPs) encapsulated in a tungsten polyoxometalate compound (POM) are embedded within the prototype poly(3,4-ethylenedioxythiophene)-poly(styrenesulphonate) (PEDOT:PSS) to form the modified HTL. Our work reveals the pivotal plasmonic role of Ag-NPs in enhancing OLED device performance based on commercially available conjugated polymers. Comprehensive analyses, including UV-Vis absorption spectroscopy, atomic force microscopy, photoluminescence spectroscopy, and electrical measurements, confirm the influence of the POM encapsulated Ag-NPs on improving the device efficiency. This is attributed to the synergistic influence of enhanced hole injection and conductivity and beneficial optical effects (i.e. the Localized Surface Plasmon Resonance (LSPR) and, likely, light scattering of the POM-Ag NPs in the core-shell configuration, depending on their diameter), contributing to enhanced carrier balance and exciton recombination rate. Comparison with POM gold NPs (POM-Au NPs) highlights the distinct advantages of POM-Ag NPs. Our work reveals the potential of this innovative approach to contribute to the evolution of high-performance OLEDs, ensuring a visually compelling and efficient future.

Dependence of copper(I) stability on long-range electromagnetic effects of Au under reducing atmospheres: the size effect of Au cores

It has been widely recognized that adjusting the size of Au particles has emerged as a significant approach in catalyst design, catalyst screening, and comprehension of reaction mechanisms. However, the essential factors of Au nanoparticles used only as an additive to enhance the activity of traditional multicomponent thermocatalysts have not been fully revealed. In this study, a series of Au@Cu2O core-shell nanocatalysts were synthesized through a controllable method, featuring core sizes ranging from 11 to 33 nm and an average shell thickness of approximately 55 nm. It was revealed that the size effect of Au cores plays a very vital role in the stability of the active Cu+ species under reducing atmospheres (H2, acetylene and formaldehyde) as well as the catalytic performance of the catalysts in the ethynylation of formaldehyde. The experimental findings revealed that Au@Cu2O core-shell catalysts with Au core sizes ranging from 11 to 16 nm exhibited a higher abundance of electron-deficient Cu+ species in the shell, which is attributed to the strong long-range electromagnetic effects of the Au core in the absence of photoexcitation or an applied electric field. Additionally, the active Cu+ species demonstrated remarkable stability under reducing atmospheres. Although the stability of Cu+ decreased slightly when the Au core size exceeded 16 nm, the Cu+ content remained above 80%. Notably, the Au@Cu2O catalysts with Au core sizes ranging from 11 to 16 nm exhibited excellent catalytic activity in the ethynylation of formaldehyde.

Plasmonic Ag@Cu2O core-shell nanostructures exhibiting near-infrared photothermal effect

This work was devoted to the investigation of the optical properties, structural characterization, and photothermal conversion performance of Ag@Cu2O nanostructures. The selection of anisotropic silver core, specifically Ag nanocubes, was driven by the possibility to tune LSPR across a broader range of the electromagnetic spectrum. The thickness of the Cu2O shell was intentionally changed through the variation in the Cu salt to the metal core nanoparticles ratios. The LSPRs of Ag(nanocube)@Cu2O core-shell nanoparticles can be fine-tuned to the spectral region to become resonant with the excitation wavelengths of 808 nm NIR laser. Due to the high refractive index of the deposited Cu2O, the redshifts of the plasmon band wavelength in the extinction spectra were observed. Consequently, the photothermal activities of the Ag(nanocube)@Cu2O core-shell NPs have been controlled by the shell thickness at the nanoscale. Ag@Cu2O nanoparticles with thickest shell (∼70 nm) exhibit the most efficient NIR photothermal effect under the irradiation of 808 nm laser at ambient conditions. Results of this work demonstrate that Ag@Cu2O hetero-nanostructures may be optimized and used for the efficient transformation of light into other forms of energy, specifically heat.

Electroactive and SERS-Active Ag@Cu2O NP-Programed Aptasensor for Dual-Mode Detection of Tetrodotoxin

Dual-mode nanotags with noninterference sensing signals improved the detection accuracy and sensitivity for the applications of tetrodotoxin (TTX) monitoring. Electroactive and surface-enhanced Raman scattering (SERS)-active Ag@Cu2O nanoparticles (NPs) were fabricated and displayed two electrooxidation signals at -0.13 and 0.17 V, attributed to the oxidization process of Cu+ and Ag0, respectively. Ag@Cu2O NPs were also found to exhibit stronger SERS performances than individual Ag NPs. The dielectric Cu2O shell with a large dielectric constant inhibited the attenuation of electromagnetic (EM) waves of Ag NPs, which strengthened the EM fields for SERS enhancement. The electron transfer from Ag to Cu2O to 4-aminothiophenol (4-ATP) also contributed to the SERS performances. Ag@Cu2O NPs were modified by TTX aptamers and assembled with MXene nanosheets (NSs) due to the large surface, good conductivity, and inherent Raman properties. The assemblies showed two-peaked electrooxidation signals and prominent SERS activity. An electrochemical detection curve was established by using the total peak intensity at -0.13 and 0.17 V as detection signals, and a ratiometric SERS detection curve was developed by applying the intensity at 1078 cm-1 (4-ATP) as the detection signal and 730 cm-1 (MXene NSs) as the reference signal. An electrochemical and SERS signal-programed dual-mode aptasensor was proposed for accurate TTX detection, with the limits of detection of 31.6 pg/mL for the electrochemical signal and 38.3 pg/mL for the SERS signal. The rational design of plasmonic metal-semiconductor heterogeneous nanocomposites had important prospects in establishing a multimodal biosensing platform for the quantitative and accurate detection of analytes in complex systems.

Self-assembled Cr2O3@nanogel/Au nanozymes to simulate peroxidase activity as a H2O2 sensor

The low temperature solvothermal method synthesized Cr₂O₃ NPs has not only peroxidase activity, but also oxidase activity. Then, the oxidase activity of Cr₂O₃ NPs is effectively shielded by nanogel immobilization using three monomers acrylamide, NIPAAM (N-isopropylacrylamide) and MBA (N,N'-methylene bisacrylamide) in HEPES (4-(2-hydroxyerhyl)piperazine-1-erhanesulfonic acid) buffer. Ultimately, the enzymatic activity of Cr₂O₃@nanogel/Au is significantly enhanced after doping Au NPs by SERS (Surface Enhanced Raman Spectroscopy) evaluation. A SERS strategy was proposed for the detection of H₂O₂ by Cr₂O₃@nanogel/Au. The linear range was 10^-8 mol·L^-1-10^-1 mol·L^-1.

Fabrication of porous ZnO/Co3O4 nanohybrids for the application of surface enhanced Raman scattering

With the growing use of various pesticides, it is important to develop facile and sensitive method to detect pesticides residues in food. Here, a semiconductor/magnetic hybrid material was used as surface enhanced Raman scattering (SERS) substrate to detect simulated residues. The representative sample of porous ZnO/Co₃O₄ nano-cube was fabricated by pyrolysis and calcination of Zn-Co ZIF, successively. The obtained hybrid of ZnO/Co₃O₄ was employed as substrate to detect of crystal violet (CV) and Rhodamine B (Rh B), and showed remarkable SERS performance. The detection limit of Rh B was 1 × 10^-10 M as well as CV of 1 × 10^-9 M. The results indicated that it was an ideal choice to improve the SERS property of transition metal oxide substrates by doping semiconductor. The semiconductor/magnetic hybrid material highlighted the obvious characteristics of low cost, facile preparation and ultra-low detection limit in the SERS measurements. The hybrids with the combination of semiconductor/magnetic properties showed a further widely application and development in SERS detection of pesticides residues.

Increasing charge transfer of SERS by the combination of amorphous Al2O3–Al thin film and ZnO nanorods decorated with Ag nanoparticles for trace detection of metronidazole

In this work, we study the charge transfer improvement by the combination of two semiconductors of SERS. The energy levels of the semiconductor, when combined, become intermediate energy levels that support the charge transfer from the HOMO to the LUMO level, amplifying the Raman signal of the organic molecules. The SERS substrates of Ag/a-Al₂O₃–Al/ZnO nanorods with high sensitivity are prepared for detecting dye rhodamine 6G (R6G) and metronidazole (MNZ) standard. The highly ordered vertically grown ZnO nanorods (NRs) are first developed on a glass substrate by a wet chemical bath deposition method. Then, ZnO NRs are covered with an amorphous oxidized aluminum thin film by a vacuum thermal evaporation method to produce a platform with a large surface area and high charge transfer performance. Finally, silver nanoparticles (NPs) are decorated onto this platform to form an active SERS substrate. The structure, surface morphology, optical properties, and elements in the sample are investigated by Raman spectroscopy, X-ray diffractometry, field-emission scanning electron microscopy (FE-SEM), ultraviolet-visible spectroscopy (UV-vis), reflectance spectroscopy, and energy dispersion X-ray spectroscopy (EDS). Rhodamine 6G is used as a reagent to evaluate the SERS substrates with an analytical enhancement factor (EF) of ∼1.85 × 10¹⁰ at the limit of detection (LOD) of 10⁻¹¹ M. These SERS substrates are used to detect metronidazole standard at a LOD of 0.01 ppm and an EF of 2.2 × 10⁶. The SERS substrate exhibits high sensitivity and stability for promising wide application in chemical, biomedical, and pharmaceutical detection.

In this work, we study the charge transfer improvement by the combination of two semiconductors of SERS.

Fabrication and Characterization of Au-Decorated MCM-41 Mesoporous Spheres Using Laser-Ablation Technique

This study reports the synthesis of Au-decorated MCM-41 mesoporous nanoparticles using a laser-ablation technique. It was observed that the number of Au attached to MCM-41 nanostructures was dependent on the amount of encapsulated Cationic surfactant (cetyl ammonium bromide (CTAB) volume. The chemical group of the prepared nanoparticles was analyzed by FT-IR spectroscopy, where different absorption peaks corresponding to Au and MCM-41 were observed. The observed band region was ∼1090, 966, 801, 2918, and 1847 cm^-1 for different samples, clearly confirming the successful preparation of MCM-41 with CTAB and Au-decorated MCM-41 nanoparticles using environmentally friendly laser-ablation approach. The surface morphology of the prepared nanoparticles were performed using TEM techniques. The TEM analysis of the MCM-41 specimen showed silica spheres with an average size of around 200 nm. Furthermore, Raman spectroscopy was done to evaluate the chemical structure of the prepared nanoparticles. It was seen that the prepared Au NPs decorated the MCM-41 system facilitated strong Raman peaks of CTAB. In addition, eight distinct Raman peaks were observed in the presence of Au NPs. This new functionalized method using the laser-ablation approach for mesoporous nanoparticles will participate effectively in multiple applications, especially the encapsulated molecule sensing and detection.

Enhancement of Cu+ stability under a reducing atmosphere by the long-range electromagnetic effect of Au

In conventional thermocatalytic reactions under a reducing atmosphere, stabilization of the active Cu⁺ component and inhibition of over-reduction into metallic Cu⁰ are extremely challenging. In this study, Au@Cu₂O core-shell nano-catalysts with different Cu₂O shell thicknesses were synthesized, and the effect of the Au nano-core on Cu⁺ stability under a reducing atmosphere and the catalytic performance of Cu⁺ in the ethynylation of formaldehyde were investigated. The Au nano-core facilitates Cu₂O dispersion and leads to an increase of 0.2-0.5 eV in electron binding energies of Cu₂O and Cu₂C₂ in the range of 27-55 nm, attributed to the long-range electromagnetic effect of Au NPs. Specifically, active Cu⁺ centers exhibit high stability under a reducing atmosphere due to the long-range electromagnetic effect of the Au nano-core. In the ethynylation of formaldehyde as a probe reaction, Cu⁺/(Cu⁰ + Cu⁺) on Au@Cu₂O catalysts remained at 88-91%. The catalytic performance in the ethynylation of formaldehyde revealed that the introduction of an Au nano-core into Cu-based catalysts increased the TOF from 0.37 to 0.7 h^-1, and decreased the activation energy from 42.6 to 38.1 kJ mol^-1. Additionally, the Cu⁺/(Cu⁰ + Cu⁺) ratios and the catalytic performance in the ethynylation of formaldehyde (BD yield = 65%, BD selectivity = 95%) on Au@Cu₂O catalysts remained constant after nine cycles, while pure Cu₂O readily deactivated due to the dramatically reduced Cu⁺/(Cu⁰ + Cu⁺) ratios and carbyne deposition. In summary, Cu⁺ in Cu-based catalysts showed high catalytic activity and stability during the ethynylation of formaldehyde due to the long-range electromagnetic effect of the Au nano-core.

Cuprous oxide coated silver/graphitic carbon nitride/cadmium sulfide nanocomposite heterostructure: Specific recognition of carcinoembryonic antigen through sandwich-type mechanism

The development of the effective diagnostic method for the determination of cancer biomarkers is one of the most promising strategies for early clinical diagnosis of cancer. Here, based on the preparation of heterogeneous cuprous oxide coated silver (Ag@Cu₂O) nanocomposites/graphitic carbon nitride (g-C₃N₄)/cadmium sulfide (CdS) nanoarrays structure, a highly sensitive photoelectrochemical (PEC) biosensor for the examination of carcinoembryonic antigen (CEA) has been constructed successfully. The combination of photoactive semiconductor materials g-C₃N₄ and CdS increases the electron transfer rate between them and enhances their photocurrent response, thus greatly increasing the concentration detection range. At the same time, the specific recognition between antigen and antibody is used to form a sandwich structure secondary antibody (Ab₂)/CEA/antibody (Ab₁). And because Ag@Cu₂O has the function of absorbing light and consuming electron donor. Therefore, the successful measurement of CEA was achieved by labeling Ag@Cu₂O on Ab₂ and finally immobilizing it on the sensor to correlate the current reduction with the CEA concentration. The sandwich PEC biosensor proposed by this signal amplification strategy under optimal conditions has good analytical performance for CEA, with a wide linear detection range (from 10^-5 to 1 ng/mL) and a low detection limit of 0.0011 pg/mL. The PEC biosensor constructed by this method showed high sensitivity, excellent anti-interference ability, favourable repeatability, and good stability.

Double profound enhancements of Cu2O nano-octahedrons connected by intertwined Ag nanovines for elevating SERS activity toward ultrasensitive pesticide detection

Recently, hybrid plasmonic metal/semiconductor-based surface-enhanced Raman scattering (SERS) has attracted ever-increasing attention due to its combined characteristics of electromagnetic (EM) enhancement and chemical (CM) enhancement, holding great potential for trace molecular detection. Herein, we demonstrate an interesting heterostructure by linking Cu₂O nano-octahedrons with intertwined Ag nanovines (NVs). The obtained Ag NVs/Cu₂O heterostructures exhibit excellent SERS activity, which is about 2.7 and 7.0 times higher than that of monodispersed Ag or Au nanoparticles (NPs) modified Cu₂O. The intertwined Ag NVs among adjacent Cu₂O octahedrons serve as efficient electron transport channels, which can obviously promote the separation of electrons and holes, reduce the recombination of photogenerated carriers, and then improve the CM enhancement effect. Meanwhile, the accumulated electrons on plasmonic NVs can effectively optimize the collective oscillation of electrons and further improve the EM enhancement. The optimal SERS substrate possesses fascinating multifunctional SERS properties, including ultra-low detection limit (CV, 10^-14 M), excellent anti-interference capability and selectivity. Finally, the established nanosensor can be effectively applied for the quantitative detection of pesticide thiram molecules in soil and biological samples, with low detection limits of 0.48 ng g^-1 and 10^-7 M, respectively. The proposed work demonstrates a high-performance SERS heterostructure with both improved CM enhancement and enhanced EM effect by linking adjacent Cu₂O nano-octahedrons with Ag NVs, which is particularly suitable for ultrasensitive residual pesticide detection in real-world environment.

Recent advancements and future submissions of silica core-shell nanoparticles

The core-shell silica-based nanoparticles (CSNPs) possess outstanding properties for developing next-generation therapeutics. CSNPs provide greater surface area owing to their mesoporous structure, which offers a high opportunity for surface modification. This review highlights the potential of core-shell silica-based nanoparticle (CSNP) based injectable nanotherapeutics (INT); its role in drug delivery, biomedical imaging, light-triggered phototherapy, Plasmonic enhancers, gene delivery, magnetic hyperthermia, immunotherapy, and potential as next-generation theragnostic. Specifically, the conceptual crosstalk on modern synthetic strategies, biodistribution profiles with a mechanistic view on the therapeutics loading and release modeling are dealt in detail. The manuscript also converses the challenges associated with CSNPs, regulatory hurdles, and their current market position.

Self-sustainable and recyclable ternary Au@Cu2O-Ag nanocomposites: application in ultrasensitive SERS detection and highly efficient photocatalysis of organic dyes under visible light

Ternary noble metal-semiconductor nanocomposites (NCs) with core-shell-satellite nanostructures have received widespread attention due to their outstanding performance in detecting pollutants through surface-enhanced Raman scattering (SERS) and photodegradation of organic pollutants. In this work, ternary Au@Cu2O-Ag NCs were designed and prepared by a galvanic replacement method. The effect of different amounts of Ag nanocrystals adsorbed on the surfaces of Au@Cu2O on the SERS activity was investigated based on the SERS detection of 4-mercaptobenzoic acid (4-MBA) reporter molecules. Based on electromagnetic field simulations and photoluminescence (PL) results, a possible SERS enhancement mechanism was proposed and discussed. Moreover, Au@Cu2O-Ag NCs served as SERS substrates, and highly sensitive SERS detection of malachite green (MG) with a detection limit as low as 10-9 M was achieved. In addition, Au@Cu2O-Ag NCs were recycled due to their superior self-cleaning ability and could catalyze the degradation of MG driven by visible light. This work demonstrates a wide range of possibilities for the integration of recyclable SERS detection and photodegradation of organic dyes and promotes the development of green testing techniques.

Synthesis of Fe3O4/Ag nanohybrid ferrofluids and their applications as antimicrobial and antifibrotic agents

To date, the search for creating stable ferrofluids with excellent properties for biomedical application is one of the challenging scientific and practical investigations. In this study, novel Fe3O4/Ag nanohybrid ferrofluids from iron sand were synthesized using a double-layer method. The Fe3O4/Ag nanocomposites exhibited stable crystallite sizes of 11.8 12.1 nm and 36.8-37.2 nm for Fe3O4 and Ag, respectively. The lattice parameters of the spinel structure Fe3O4 and face-centered cubic Ag were respectively 8.344 Å and 4.091 Å. With increasing Ag amount, the crystallite phase of Ag in the nanocomposites increased from 40.2% to 77.2%. The XPS results confirmed that Fe3O4/Ag nanocomposites were successfully prepared, where Fe3O4 mixed well with Ag via strong ionic bonding. The FTIR results confirmed the presence of Fe3O4/Ag, oleic acid, and dimethyl sulfoxide as the filler, first layer, and second layer, respectively. The as-prepared ferrofluids exhibited superparamagnetic behavior, where the saturation magnetization decreased with increasing Ag content. The Fe3O4/Ag nanohybrid ferrofluids exhibited excellent antimicrobial performance against Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Candida albicans. More importantly, the Fe3O4/Ag nanohybrid ferrofluids decreased the progression of liver fibrosis-related inflammation and fibrogenic activity on hepatic stellate cells.

Surface-Enhanced Raman Spectroscopy of Organic Molecules and Living Cells with Gold-Plated Black Silicon

Black silicon (bSi) refers to an etched silicon surface comprising arrays of microcones that effectively suppress reflection from UV to near-infrared (NIR) while simultaneously enhancing the scattering and absorption of light. This makes bSi covered with a nm-thin layer of plasmonic metal, i.e., gold, an attractive substrate material for sensing of bio-macromolecules and living cells using surface-enhanced Raman spectroscopy (SERS). The performed Raman measurements accompanied with finite element numerical simulation and density functional theory analysis revealed that at the 785 nm excitation wavelength, the SERS enhancement factor of the bSi/Au substrate is as high as 10⁸ due to a combination of electromagnetic and chemical mechanisms. This finding makes the SERS-active bSi/Au substrate suitable for detecting trace amounts of organic molecules. We demonstrate the outstanding performance of this substrate by highly sensitive and specific detection of a small organic molecule of 4-mercaptobenzoic acid and living C6 rat glioma cell nucleic acids/proteins/lipids. Specifically, the bSi/Au SERS-active substrate offers a unique opportunity to investigate the living cells' malignant transformation using characteristic protein disulfide Raman bands as a marker. Our findings evidence that bSi/Au provides a pathway to the highly sensitive and selective, scalable, and low-cost substrate for lab-on-a-chip SERS biosensors that can be integrated into silicon-based photonics devices.

Probing the charge-transfer of Ag/PEDOT:PSS/4-MBA by surface-enhanced raman scattering

A metal-organic semiconductor-molecule model was developed with Ag nanoparticles (NPs), poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and 4-mercaptobenzoic acid (4-MBA) via the layer-by-layer self-assembly method. In the SERS spectrum of the Ag/PEDOT:PSS/4-MBA system, structural changes in the PEDOT chain were discovered, which provides a deeper understanding of the charge transfer (CT) mechanism in SERS and helps in the development of a method to construct metal-organic semiconductor SERS substrates. A quantitative calculation of the degree of charge transfer (ρCT(κ)) determines the CT contribution of PEDOT:PSS to the SERS intensity of the Ag/PEDOT:PSS/4-MBA system. On this basis, we propose the formation of a resonance complex between Ag NPs and PEDOT:PSS to explore the CT mechanism, which is beneficial for studying interface CT and for understanding the CT mechanism in SERS. The introduction of organic semiconductors in this study not only broadens the research scope of SERS substrates but also contributes to the exploration of SERS mechanisms.

A balsam pear-shaped CuO SERS substrate with highly chemical enhancement for pesticide residue detection

Simple and traditional hydrothermal fabrication of a novel balsam pear-shaped CuO with high SERS enhancement is presented. XRD (X-ray diffraction), SEM (scanning electronic microscopy), TEM (transmission electron microscope), HRTEM (high-resolution transmission electron microscope), UV-Vis, and Raman are adopted to ensure that this balsam pear-shaped CuO with dense nanoparticle protuberance is successfully prepared. The LOD of this CuO SERS substrate is 4.79 μg L^-1 with R6G as molecular probe. By using DFT (density functional theory) calculation and FDTD (finite difference time domainmethod) simulation, both EM (electromagnetic enhancement) and CM (chemical enhancement) mechanisms are investigated, and the results show that these two-enhancement mechanisms can coexist in this balsam pear-shaped CuO. Finally, the prepared substrate has been applied for the determination of trace levels of paraquat in solution , and results show that its LOD for paraquat is 275 μg L^-1 (optimum Raman band: 1646 cm^-1 Raman shift), which is better than the government standard in China. A dexterous and facile way for fabrication of CuO SERS-active substrates with low cost and high performance, quite promising in detection of chemically hazardous substances and pesticide residue is provided. Graphical abstract.

Synthesis of Au@Cu2O Core-Shell Nanoparticles with Tunable Shell Thickness and Their Degradation Mechanism in Aqueous Solutions

Metal@semiconductor core-shell nanoparticles (NPs) are widely used in photocatalysts, sensors, and optical applications owing to their unique metal-semiconductor interface and the integration of the properties from both core and shell materials. Although many efforts have been made toward the precise synthesis of Au@Cu₂O core-shell structures, the chemical stability of Au@Cu₂O aqueous suspensions, which is of great significance in many related applications, is not mentioned in any published research. Herein we report the synthesis of Au@Cu₂O core-shell NPs with small shell thickness from 2 to 40 nm through a wet-chemistry method. The UV-vis absorption properties are found to be tunable with Cu₂O thickness in the range of 2-40 nm. Furthermore, the chemical stability of Au@Cu₂O core-shell nanoparticle suspensions in water/ethanol mixed solvents is investigated. It is found that water/ethanol mixed solvents with a larger amount of water are more likely to deteriorate the stability of Au@Cu₂O NPs by oxidizing Cu₂O to CuO. The results from this work may provide useful information for the preparation of metal@Cu₂O water-based suspensions that are expected to be used for SERS, photocatalyst, or photothermal applications.

Charge Transfer-Mediated Blue Luminescence in Plasmonic Ag-Cu2O Quantum Nanoheterostructures

Metal-semiconductor hybrid nanoheterostructures have the possibility to exhibit new synergic properties other than the combination of properties from discrete components due to the interaction of metal and semiconductor components at the interfaces. Here, we have synthesized Ag-Cu₂O eyeball-shaped quantum nanoheterostructures with diameter ranging between 8 and 12 nm using a single-step low-cost solvothermal process. It is observed that the presence of a minimum 3% of Ag is required for the formation of Ag-Cu₂O quantum nanoheterostructures. The formation of nanoheterostructures has introduced new synergic properties like intense blue luminescence and surface-enhanced Raman scattering due to the interactions between Ag and Cu₂O atoms at the interfaces. The significant presence of charge transfer through the interfaces is identified from the peak shift of Raman modes. The increase in the electron density at the metal surface due to the charge transfer and the recombination of these electrons with sp- or d-band holes of Ag could be the effective mechanism of the observed blue luminescence. The blue luminescence of Ag-Cu₂O quantum nanoheterostructures together with its low band gap value (≈2.3 eV) is believed to have important applications in optoelectronic devices.

Silver Nanocubes Coated in Ceria: Core/Shell Size Effects on Light-Induced Charge Transfer

Plasmonic sensitization of semiconductors is an attractive approach to increase light-induced photocatalytic performance; one method is to use plasmonic nanostructures in core@shell geometry. The occurrence and mechanism of synergetic effects in photocatalysis of such geometries are under intense debate and proposed to occur either through light-induced charge transfer (CT) or through thermal effects. This study focuses on the relation between the dimensions of Ag@CeO₂ nanocubes, the wavelength-dependent efficiency, and the mechanism of light-induced direct CT. A 4-mercaptobenzoic acid (4-MBA) linker between core and shell acts as a Raman probe for CT. For all Ag@CeO₂ nanocubes, CT increases with decreasing excitation wavelength, with notable increase at and below 514 nm. This is fully explainable by CT from silver to the 4-MBA LUMO, with the increase for excitation wavelengths that exceed the Ag/4-MBA LUMO gap of 2.28 eV (543 nm). A second general trend observed is an increase in CT yield with ceria shell thickness, which is assigned to relaxation of the excited electron further into the ceria conduction band, potentially producing defects.

Immobilizing Ag/Cu2O on cotton fabric to enhance visible light photocatalytic activity

Ag/Cu₂O composites were prepared by the solvothermal and photo-reduction method.

Shell isolated nanoparticle enhanced Raman spectroscopy for renewable energy electrocatalysis

This review covers the use of shell isolated nanoparticle enhanced Raman spectroscopy (SHINERS) to investigate heterogeneous electrocatalytic processes.

Surface-enhanced Raman scattering studies of Cu/Cu2O Core-shell NPs obtained by laser ablation

In order to perform SERS (surface-enhanced Raman scattering) measurements, spherical Cu/Cu₂O core-shell NPs with a rather rough rugged surface and well-defined crystallographic structures were fabricated using nanosecond Ce: Nd YAG pulsed laser ablation in liquid (PLAL). Raman, Fourier transform infrared (FTIR) spectroscopy and TEM imaging of the prepared NPs reveal the existence of additional minority CuO phase, not determined earlier through XRD patterns. The SERS activity of Cu/Cu₂O core-shell NPs substrates was investigated by using crystal violet (CV) and methylene blue (MB) as the analyte molecules under 532 nm excitation wavelength irradiation. The effect of localized surface plasmon resonance (LSPR) from Cu core contributing to the electromagnetic enhancement and Cu2O shell with a rough surface which itself contributes to chemical enhancement with adsorbed analyte molecule is due to a high overall SERS enhancement. The intensities of the totally and non-totally symmetric modes were used to calculate the degree of charge-transfer. The results demonstrate that the LSPR enhancement dominates charge-transfer resonance contribution in SERS of Cu/Cu2O-CV and Cu/Cu2O -MB systems. The reproducibility of the prepared SERS substrates was investigated and the SERS signals intensity variation was <28%.

Catalysis of Organic Pollutants Abatement Based on Pt-Decorated Ag@Cu2O Heterostructures

Pt-decorated Ag@Cu2O heterostructures were successfully synthesized using a simple and convenient method. The Pt nanoparticle density on the Ag@Cu2O can be controlled by changing the concentration of the Pt precursor. The synthesized Ag@Cu2O-Pt nanoparticles exhibited excellent catalytic performance, which was greatly affected by changes in the Ag@Cu2O-Pt structure. To optimize the material's properties, the synthesized Ag@Cu2O-Pt nanoparticles were used to catalyze toxic pollutants and methyl orange (MO), and nontoxic products were obtained by catalytic reduction. The Pt-decorated Ag@Cu2O nanoparticles showed excellent catalytic activity, which significantly decreased the pollutant concentration when the nanoparticles were used for catalytic reduction. The redistribution of charge transfer is the nanoparticles' main contribution to the catalytic degradation of an organic pollutant. This Pt-decorated Ag@Cu2O material has unique optical and structural characteristics that make it suitable for photocatalysis, local surface plasmon resonance, and peroxide catalysis.

Magnetism and plasmonic performance of mesoscopic hollow ceria spheres decorated with silver nanoparticles

We investigate the role of interfaces and surfaces in the magnetic and surface enhanced Raman spectroscopy (SERS) properties of CeO2 hollow spheres decorated with Ag nanoparticles (H-CeO2@Ag). The composites, H-CeO2@Ag, were synthesized using a newly developed two-step process. The CeO2 hollow sphere diameter ranges from 100 nm to 2 μm and the grafted Ag nanoparticle (NP) size varies from 5 to 50 nm with a controllable coverage ratio. Spectroscopic and microscopic characterization confirms the formation of an interface between the Ag and ceria and shows different charge rearrangements occurring at both the interface and the surface. Room temperature ferro-magnetism was observed in all composites, and is associated mostly with ceria surface defects. A strong SERS effect was reported with a detection limit down to 10-14 M for the rhodamine 6G analyte. Scanning transmission electron microscopy and electron energy loss spectroscopy investigation reveals that hot-spots are associated with the silver NP surfaces and also with the Ag/CeO2 interface. This interfacial hot spot occurs for metallic particles above 30 nm and is strongly red shifted with respect to the Ag surface plasmon. The strong SERS activity is then attributed to the presence of several types of hot-spots and the geometrical features (buoyant hollow sphere and size dispersion) of the composite.

Carrier Density-Dependent Localized Surface Plasmon Resonance and Charge Transfer Observed by Controllable Semiconductor Content

We discuss how the controllable carrier influences the localized surface plasmon resonance (LSPR) and charge transfer (CT) in the same system based on ultraviolet-visible and surface-enhanced Raman scattering (SERS) measurements. The LSPR can be easily tuned from 580 to 743 nm by changing the sputtering power of Cu₂S in the Ag and Cu₂S composite substrate. During this process, surprisingly, we find that the LSPR is proportional to the sputtering power of Cu₂S. This observation indicates that LSPR can be accurately adjusted by changing the content of the semiconductor, or even the carrier density. Moreover, we characterize the carrier density through the detection of the Hall effect to analyze the Raman shift caused by CT and obtain the relationships between them. These fundamental discussions provide a guideline for tunable LSPR and the investigation of CT.

Highly sensitive determination of iron (III) ion based on phenanthroline probe: Surface-enhanced Raman spectroscopy methods

In this paper, we introduced Raman spectroscopy techniques that were based on the traditional Fe³⁺ determination method with phenanthroline as a probe. Interestingly, surface-enhanced Raman spectroscopy (SERS)-based approach exhibited excellent sensitivities to phenanthroline. Different detection mechanisms were observed for the RR and SERS techniques, in which the RR intensity increased with increasing Fe³⁺ concentration due to the observation of the RR effect of the phenanthroline-Fe²⁺ complex, whereas the SERS intensity increased with decreasing Fe³⁺ concentration due to the observation of the SERS effect of the uncomplexed phenanthroline. More importantly, the determination sensitivity was substantially improved in the presence of a SERS-active substrate, giving a detection limit as low as 0.001μg/mL, which is 20 times lower than the limit of the UV-vis and RR methods. Furthermore, the proposed SERS method was free from other ions interference and can be used quality and sensitivity for the determination of the city tap water.

Self-Assembled Ag-Cu₂O Nanocomposite Films at Air-Liquid Interfaces for Surface-Enhanced Raman Scattering and Electrochemical Detection of H₂O₂

We employ a facile and novel route to synthesize multifunctional Ag-Cu₂O nanocomposite films through the self-assembly of nanoparticles at an air-liquid interface. In the ethanol-water phase, AgNO₃ and Cu(NO₃)₂ were reduced to Ag-Cu₂O nanoparticles by NaBH₄ in the presence of cinnamic acid. The Ag-Cu₂O nanoparticles were immediately trapped at the air-liquid interface to form two-dimensional nanocomposite films after the reduction reaction was finished. The morphology of the nanocomposite films could be controlled by the systematic regulation of experimental parameters. It was found that the prepared nanocomposite films serving as the substrates exhibited strong surface-enhanced Raman scattering (SERS) activity. 4-aminothiophenol (4-ATP) molecules were used as the test probes to examine the SERS sensitivity of the nanocomposite films. Moreover, the nanocomposite films synthesized by our method showed enhanced electrocatalytic activity towards hydrogen peroxide (H₂O₂) and therefore could be utilized to fabricate a non-enzymatic electrochemical H₂O₂ sensor.

SERS study of surface plasmon resonance induced carrier movement in Au@Cu2O core-shell nanoparticles

A plasmon induced carrier movement enhanced mechanism of surface-enhanced Raman scattering (SERS) was investigated using a charge-transfer (CT) enhancement mechanism. Here, we designed a strategy to study SERS in Au@Cu₂O nanoshell nanoparticles with different shell thicknesses. Among the plasmonically coupled nanostructures, Au spheres with Cu₂O shells have been of special interest due to their ultrastrong electromagnetic fields and controllable carrier transfer properties, which are useful for SERS. Au@Cu₂O nanoshell nanoparticles (NPs) with shell thicknesses of 48-56nm are synthesized that exhibit high SERS activity. This high activity originates from plasmonic-induced carrier transfer from Au@Cu₂O to 4-mercaptobenzoic acid (MBA). The CT transition from the valence band (VB) of Cu₂O to the second excited π-π* transition of MBA, and is of b₂ electronic symmetry, which was enhanced significantly. The Herzberg-Teller selection rules were employed to predict the observed enhanced b₂ symmetry modes. The system constructed in this study combines the long-range electromagnetic effect of Au NPs, localized surface plasmon resonance (LSPR) of the Au@Cu₂O nanoshell, and the CT contribution to assist in understanding the SERS mechanism based on LSPR-induced carrier movement in metal/semiconductor nanocomposites.

Increasing local field by interfacial coupling in nanobowl arrays

An increased local field is crucial to create hotspots when applied in detections, which usually means the fabrication of nanostructure arrays with strong electromagnetic couplings.