Flower-like Ag Research Articles

A novel AgNFs/MOF/CFC substrate-based flexible SERS sensor for high-sensitive detection of dye molecules

Metal–organic framework (MOF) materials have been increasingly used owing to their high porosity, chemical stability, and semiconducting properties. With the help of MOF materials, MOF-based SERS substrates can exhibit high sensitivity. Herein, we proposed a flower-like Ag nanoparticles (AgNFs)/metal–organic framework (MOF)/ carbon fiber cloth (CFC) substrate-based surface-enhanced Raman scattering (SERS) sensor for the high-sensitive detection of dye molecules. MOF is used as a signal amplifier to accelerate the approach of dye molecules near AgNFs on the MOF surface and anchor AgNFs on the substrate surface. The detection occurred on the AgNFs/MOF/CFC SERS substrate, providing an enhancement factor (EF) of 5.53 × 107. Benefitting from the signal amplification function of AgNFs/MOF/CFC and the superiority of SERS, this sensor represented high sensitivity performance and a wide detection range. Importantly, the combination of Co elements with silver in the AgNFs/MOF/CFC composite substrate enhances the resistance of Ag to oxidation by atmospheric moisture resulting in excellent stability (the substrate maintained good SERS activity after 45 days of exposure to air) of the SERS substrate. The basic performance of the substrate was evaluated using rhodamine 6 G (R6G). (Detection limit reached 10−12 M) The detection limit of TC was 0.1 ppm. This method provides a potential and cost-effective strategy to develop advanced SERS sensing devices to effectively monitor pollutants in environmental waters.

Highly ordered Si-based ZnO/Ag bilayer structure for recyclable SERS substrates with ultra-sensitivity

Compositing semiconductors with noble metal is considered as an effective strategy for improving SERS enhancement attributed to synergistic contribution of LSPR and CT mechanisms. In this work, highly ordered ZnO/Ag bilayer structures on p-type silicon wafers are prepared by photolithography and electrochemical self-assembly. The synergistic effect of EM and CT for SERS enhancement is identified by the Raman, PL spectra and 3D FDTD simulation. Flower-like Ag deposited on coarse ZnO films exhibits high SERS sensitivity. The ultra-low concentration of R6G molecules as low as 10−15 M can be detected, and the EF is estimated to be 8.08 × 1013. Due to the excellent photocatalytic property of ZnO, the bilayer structures possess steady and effective UV-cleaning performance. After being UV irradiated for 10 min, this SERS substrate can be re-used for many times. And the detecting RSD is about 4.11 %. The multi-functional ZnO/Ag bilayer structures with a wide direct bandgap has the prominent capacity to provide an efficient charge transfer path to possess trace detection ability for many probe molecules.

Designing of Ag decorated ZnO catalyst for on-demand and sustainable H2 production at room temperature

Growing energy demand, expansion of population, and fast depletion of fossil fuels motivate the development of feasible and safe ways to store and supply sustainable energy. Hydrogen is regarded as a promising sustainable fuel for addressing global energy and environmental issues due to its high energy efficiency and negligible greenhouse gas emissions. However, hydrogen storage is considered as a stumbling block in the implementation of the hydrogen economy. In this regard, sodium borohydride (SB), a chemical metal hydride is one of the most auspicious material due to its high volumetric hydrogen density, low capital investment, and low potential risk. In the present investigation, Ag NPs decorated ZnO catalyst were prepared by a one-pot strategy in an ethylene glycol (EG) medium. All Ag-NPs decorated ZnO catalysts showed higher activity than pristine ZnO under dark conditions, whereas, flower-like Ag NPs decorated ZnO catalyst exhibited the highest catalytic activity for H2 generation from hydrolysis of SB. A maximum value of 123 mLg−1min-1 as the turnover frequency is obtained with 22 kJ mol−1 activation energy, which is comparable to well-known high-cost NPS like Pt, Pd, and Ru. The prepared sample exhibited good reusability and 100% conversion even after the 5th cycle.

Toward Flexible Metal Semiconductor Sandwich Surface-Enhanced Raman scattering (SERS) sensors Pesticide Duplex Detection

The overuse of mixed pesticides poses a threat to both the ecosystem and human health, yet general pesticide detection methods are complex in terms of steps, such as the need for pretreatment and cleaning. Surface-enhanced Raman scattering (SERS) has been used for real-life trace detection of residues due to its rapid detection and ultra-high sensitivity. Here, we prepared a novel Ti3C2Tx (MXene)-noble metal hybrid flexible substrate with a layer of MXene on top of flower-like Ag nanoparticles (AgNFs), and finally grew Au nanoparticles (AuNPs) by galvanic replacement and self-reduction reactions. The limit of detection (LOD) can be as low as 2 × 10-12 M by detecting 4-mercaptobenzoic acid (4MBA). For efficient sampling, transparent and flexible platform made of polydimethylsiloxane (PDMS) were used for the extraction and detection of thiabendazole (TBZ), thiram, methyl parathion (MP) and their mixtures. Notably, the lowest concentrations detected by swabbing on the tomato surface (3.7 ng/mL, 2.8 ng/mL) were lower than the EU maximum permissible limits of pesticides on raw fruits and vegetables (4.0 mg/L, 6.33 mg/mL). This high performance Ti3C2Tx-noble metal hybrid flexible substrate offers a great advantage in the trace detection of molecules.

Electrodeposited Cobalt Nanosheets on Smooth Silver as a Bifunctional Catalyst for OER and ORR: In Situ Structural and Catalytic Characterization.

Developing earth-abundant, cost-effective, and active bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is key to boosting sustainable energy systems such as electrolyzers and lithium-air batteries. However, the performance of promising cobalt-based materials is impaired by the external effects of binders and carbon additives as well as inhomogeneous electrode fabrication. In this work, binder- and carbon-free flower-like Co-decorated Ag catalytic nanosheets were in situ-synthesized via a simple electrodeposition approach. The morphology, composition, and structure of Co/Ag before and after OER were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Co/Ag thin film electrodes with various Co contents exhibited a bifunctional activity toward ORR and OER due to a synergistic effect. XPS analysis suggested the formation of Co3O4 as the main active species for OER. In particular, Co (83%)/Ag surface revealed a 60 mV lower ORR overpotential than a pure Ag surface and even lower than drop-casted Co3O4 nanoparticles on Ag surface. Only 1.5% peroxide was generated, suggesting a four-electron transfer ORR. In addition, the OER onset potential on Co/Ag is 60 mV less than Co3O4. Tafel slopes of 71 and 75 mV dec-1 were obtained for ORR and OER, respectively. Importantly, the three-dimensional (3D) growth mechanism of a cobalt layer (∼1 nm) on a well-defined atomic smooth Ag surface is unraveled by in situ electrochemical scanning tunneling microscopy (EC-STM). EC-STM suggests that Co prefers to nucleate at the step edges of Ag and grows in a 3D, forming nanoparticles, where the deposition/dissolution process of the Co adlayer on Ag is reversible. This investigation may provide insights into design strategies of efficient oxygen electrocatalysts.

A comprehensive melamine sponge decorated with 3D flowerlike Ag/NiCo-layered double hydroxide for wastewater remediation

In this work, 3D flowerlike Ag NPs/NiCo-layered double hydroxide (NiCo-LDH) decorated on melamine sponge was fabricated through a facile hydrothermal and in-situ reduction method. 3D flowerlike Ag NPs/NiCo-LDH were demonstrated to immobilize on the skeleton of polydopamine-pretreated melamine sponge. The melamine sponge decorated with 3D flowerlike Ag NPs/ NiCo-LDH presented outstanding catalytic activity for reduction of various water-soluble organic dyes in the appearance of NaBH4 as reducing agent, including 4-nitrophenol (4-NP), rhodamine B (RhB), methylene blue (MB) and methyl orange (MO), respectively. Owing to the appearance of Ag NPs, the melamine sponge decorated with 3D flowerlike Ag NPs/NiCo-LDH also showed efficient antibacterial activities against Gram-positive Staphylococcus aureus and Bacillus cereus, and Gram-negative Escherichia coli and Pseudomonas aeruginosa, suggesting its broad-spectrum antibacterial property. Moreover, the melamine sponge decorated with 3D flowerlike Ag NPs/ NiCo-LDH could also achieve the separation process for insoluble oils/organics from water by a facile surface modification technology after being treated toward low-surface-energy chemical of octadecylamine. The octadecylamine-coated sponge exhibited superhydrophobicity (WCA=158.6°) and superoleophilicity (OCA=0°), which could adsorb a wide range of oils/organics without the adsorption of any water, thus realizing the process of oil/water separation. The novel comprehensive melamine sponge demonstrates a new strategy for the remediation of complex polluted water.

Selective Adsorption and Photocatalytic Clean‐Up of Oil by TiO2 Thin Film Decorated with p‐V3D3 Modified Flowerlike Ag Nanoplates (Adv. Mater. Interfaces 14/2022)

Selective Adsorption and Photocatalytic Clean-Up of Oil In article number 2102126, Josiah Shondo, Salih Veziroglu, Franz Faupel, O. Cenk Aktas, and co-workers develop a novel surface named as “three-in-one (3-in-1) surface” since it is composed of 1) a highly photocatalytic layer, 2) micro- and nano-structures, and 3) a low surface energy layer. This 3-in-1 surface selectively adsorbs the oil and similar petroleum products (clean-up via photocatalysis) while it exhibits extreme water repellence.

Selective Adsorption and Photocatalytic Clean‐Up of Oil by TiO2 Thin Film Decorated with p‐V3D3 Modified Flowerlike Ag Nanoplates

AbstractVarious methods are developed and used to treat oil‐contaminated water, including mechanical separation, chemical treatment, biological treatment, membrane filtration, and sorption. Oil clean‐up via selective sorption of the oil by an engineered surface is the most accepted technique due to its high removal efficiency and low cost. Here, a multifunctional surface providing highly selective oil sorption and clean‐up capability via the photocatalytic decomposition is proposed. This novel surface is named as the “three‐in‐one (3‐in‐1) surface” since it is composed of 1) a highly photocatalytic layer, 2) micro‐ and nanostructures, and 3) a low surface energy layer. First, the TiO2 photocatalytic layer is prepared by magnetron sputtering. Then flowerlike Ag nanoplates are photocatalytically deposited on the sputtered TiO2 layer. Afterward, a low surface energy layer, poly‐1,3,5‐trivinyl‐1,3,5‐trimethylcyclotrisiloxane (p‐V3D3), is over‐coated on Ag/TiO2 surface by initiated chemical vapor deposition (iCVD) while retaining the topographical features of the surface (micro‐ and nanoscale surface structures). The p‐V3D3/Ag/TiO2 surface demonstrates a high selective adsorption to oil whereas simultaneously it shows extreme repellency to water. The p‐V3D3/Ag/TiO2 surface can also be photocatalytically cleaned up and this may find applications in various technology fields including water treatment, microfluidics, self‐cleaning, and water harvesting.

Enriching surface-enhanced Raman spectral signatures in combined static and plasmonic electrical fields in self-powered substrates

Promoting the quality of surface-enhanced Raman spectra (SERS) holds immense significance in various research fields, such as high-sensitive detection or real-time in situ monitoring. However, obtaining rich molecular information from the vibration modes in SERS remains difficult due to the surface selection rules. Herein, we develop an electrically enhanced, composite SERS substrate by combining flower-like Ag nanostructures with a piezoelectric-dielectric polymeric film. The piezoelectricity generated in the polymeric film transforms into combined quasi-static electrical fields with multi-directional distributions and intensified plasmonic hotspots in the Ag nanoflowers. Molecules adsorbed on the Ag nanoflowers are propelled by the quasi-static electrical fields and deviate from the absorption equilibrium states, a key criterion to present additional SERS peaks. In addition, the intensified hotpots generate SERS peaks with higher intensities (> ~ 2 times). Dual-enhanced SERS in both the intensity and the number of vibration peaks e.g., 3 peaks more for 4-Mpy, are obtained from a variety of widely used molecular Raman probes as well as pesticide contaminants. The universality of the dual enhancement effects from our SERS design with increasing detection sensitivity demonstrates high applicability in the rapid and on-site detection of real samples. The changes to SERS spectra, and thus the molecular vibrational fingerprints, in the combined static and plasmonic electrical fields may also inspire scientific understanding in photoelectrical catalytic processes.

Shape-diversified silver nanostructures on Al foil fabricated in micellar template for high performance surface enhanced Raman scattering applications

Highly effective surface-enhanced Raman substrates with shape-diversified silver nanostructures on Al foil (AlF) were fabricated by galvanic replacement reaction in micellar template which is easy to control, simple and cost-effective. Due to the localized surface plasmon resonance (LSPR) of silver nanostructures, the substrates were used as surface enhanced Raman substrates. The shape-diversified silver nanostructures on AlF exhibited stronger surface enhanced Raman scattering (SERS) effects compared with flowerlike Ag nanostructures on ITO glass substrate fabricated by electrodeposition in micellar template. The maximum Raman enhancement factor of 109 fold was obtained, which is 236 times larger than the flowerlike silver nanostructures on ITO glass substrate. The scanning electron microscope (SEM) images show that the size and shape of the nanostructures and surface morphology make a valuable contribution to SERS. Raman enhancement experiments of three Raman probes were studied, which shows that different vibrational modes of Raman probe affect SERS effect. The fabricated shape-diversified silver nanostructures on AlF fabricated by galvanic replacement reaction in micellar template are cheap, controllable and simple. It could be potentially useful in SERS field such as imaging applications and highly sensitive molecule detecting.

Surface Plasmonic Resonance and Z-Scheme Charge Transport Synergy in Three-Dimensional Flower-like Ag–CeO2–ZnO Heterostructures for Highly Improved Photocatalytic CO2 Reduction

The design and engineering of plasmonic metal nanocomposite photocatalysts offer an operative approach for highly efficient CO2 photoreduction. Herein, the authors report a plasmonic 3D flower-like...

Bio-inspired self-cleaning carbon cloth based on flower-like Ag nanoparticles and leaf-like MOF: A high-performance and reusable substrate for SERS detection of azo dyes in soft drinks

Surface-enhanced Raman scattering (SERS) enables azo dye monitoring become rapid and efficient. However, the high cost, low efficiency and poor recyclability of SERS substrate limit its practical application. Herein, we propose a facile strategy to develop self-cleaning carbon cloth as a high-performance and reusable SERS substrate through in-situ growth of leaf-like metal-organic framework (L-MOF) and one-step electro-deposition of flower-like Ag nanoparticles (CC-L-MOF@F-Ag) followed by chemical modification for SERS detection of congo red (CR), chrysoidine (CYD) and acid orange II (AO II) in soft drinks. Taking advantages of superhydrophobicity and SERS-active F-Ag, the prepared self-cleaning CC-L-MOF@F-Ag not only avoids the diffusion-random problem and further boosts sensitivity, but also yields excellent self-cleaning property through facile washing with water, endowing its good reusability and stability. Furthermore, this substrate can realize quantitative detection of CR, CYD and AO II with low limits of detection (0.013 μM for CR, 0.017 μM for CYD and 0.0067 μM for AO II) and wide linear detection range (0.1 – 1000 μM for CR, 0.1 – 1000 μM for CYD and 0.01 – 100 μM for AO II). Meanwhile, CR, CYD and AO II in six soft drinks were also successfully detected with satisfactory recoveries. This method provides a potential and cost-effective strategy to develop advanced SERS sensing device for effective monitoring azo dyes in soft drinks.

In Situ Recyclable Surface-Enhanced Raman Scattering-Based Detection of Multicomponent Pesticide Residues on Fruits and Vegetables by the Flower-like MoS2@Ag Hybrid Substrate.

Pesticides, extensively used in agriculture production, have received enormous attention because of their potential threats to the environment and human health. Hence, in this study, a kind of highly sensitive and stable hybrid surface-enhanced Raman scattering (SERS)-active substrates constructed with flower-like two-dimensional molybdenum sulfide and Ag (MoS2@Ag) has been developed, and then the above substrate was sequentially utilized in the recyclable detection of pesticide residues on several kinds of fruits and vegetables. In the first place, the excellent photocatalytic performance of the MoS2@Ag hybrid substrate was demonstrated, which was attributed to the inhibition of electron-hole combination after the formation of Schottky barrier between the Ag NPs and MoS2 matrix. Thereafter, two calibration curves with ultra-low limits of detection (LOD) as 6.4 × 10-7 and 9.8 × 10-7 mg/mL were established for the standard solutions of thiram (tetramethylthiuram disulfide, TMTD) and methyl parathion (MP), and then the recyclable assay of their single and mixed residues on eggplant, Chinese cabbage, grape, and strawberry was successfully realized. It is interesting to note that the detection recoveries from 95.5 to 63.1% for TMTD and 92.3 to 62.6% for MP are greatly dependent on the size and surface roughness of these foods. In a word, the MoS2@Ag composite matrix shows attractive SERS and photocatalysis performance, and it is expected to have the potential application on food safety monitoring.

Flower-like Ag coated with molecularly imprinted polymers as a surface-enhanced Raman scattering substrate for the sensitive and selective detection of glibenclamide.

Flower-like Ag was formed by nanosheet self-assembly as a SERS-active substrate and was utilized for the preparation of flower-like Ag@molecularly imprinted polymers (MIPs) as a surface-enhanced Raman scattering (SERS) sensor. Based on the combination of the molecular imprinting technique and SERS technology, the flower-like Ag@MIPs with high sensitivity and excellent selectivity were used as SERS substrates for the detection of glibenclamide. The imprinted layer could effectively protect the flower-like Ag from oxidation and thereby may improve the stability of the SERS substrate. The intensities of the characteristic peaks obtained for the flower-like Ag@MIPs were higher than that of flower-like Ag. By applying the flower-like Ag@MIPs as an efficient and ultra-sensitive SERS platform, glibenclamide was quantitatively detected in trace concentrations as low as 1 ng mL-1. Furthermore, the SERS enhancement for the flower-like Ag@MIPs was due to the synergetic effect between electromagnetic enhancement and chemical enhancement. We believe that this reliable method can open up new opportunities for practical chemosensor or biosensor applications.

Spontaneous Growth of 3D Silver Mesoflowers on Poly(4-vinylpyridine) Brushes-Grafted-Graphene Oxide Films and Facile Creation of Nanoporosities over their Surface.

Fabricating three-dimensional (3D) hierarchical noble-metal particles by spontaneous redox reactions between graphene and noble-metal salts still remains a great challenge. Herein, the fact that graphene oxide (GO) itself acts as both a platform for grafting polymer brushes and a reducing agent to reduce [Ag(NH3 )2 ]+ ions is taken advantages of. 3D flower-like Ag mesoparticles (Ag mesoflowers, Ag MFs) with tunable size and shapes can spontaneous grow on poly(4-vinylpyridine) brushes-grafted-graphene oxide (P4VP-g-GO) films in Ag(NH3 )2 OH solution without the use of any additional reducing agent. The residual Ag(NH3 )2 OH on 3D Ag MFs surface can be further reduced by NaBH4 , causing abundant nanoporosities over the entire Ag MFs. The resulting Ag nanoporous MFs (Ag NMFs) with larger surface-to-volume ratio and higher nanoscale roughness exhibit ultrasensitivity in surface-enhanced Raman spectroscopy (SERS) detection, and the detection limit for 4-aminothiophenol is as low as 10-13 m.

Graphene oxide-highly anisotropic noble metal hybrid systems for intensified surface enhanced Raman scattering and direct capture and sensitive discrimination in PCBs monitoring

Graphene oxide (GO)-anisotropic noble metal hybrid systems were developed as highly sensitive and reproducible surface enhanced Raman scattering (SERS) platform, in which ultrathin GO was embedded between two metallic layers of flower-like Ag nanoparticles (AgNFs) and gold nanostars (AuNSts). Due to multi-dimensional plasmonic coupling effect, the well-designed AgNFs-GO-AuNSts sandwich structures possessed ultrahigh sensitivity with the detection limit of R6G as low as 1.0 × 10−13 M and high enhancement factor of 2.59 × 107. Additionally, the GO interlayer could function as protective shell to suppress the oxidation of bottom silver layer and efficiently position the target analytes within hot spots. These features endow the substrate with high stability and excellent reproducibility (Signal variations < 7%). Particularly, the GO sandwiched substrate can be explored for the direct capture and sensitive detection of polychlorinated biphenyls (PCBs) without any organic modifier as molecule harvester. This minimum detected concentration was estimated as low as 3.4 × 10-6 M. The detection method based on GO mediated sandwich substrate avoids complicated surface modification manipulations and improves the substrate cleanness. Moreover, the resultant sandwich substrates can be used to recognize fingerprint peaks of different PCBs in their complex mixture, revealing great potential applications in SERS-based simultaneous detection of multiple pollutants with low affinity.

Characterization studies of heavily doped Ag-SnS thin films prepared by magnetron co-sputtering technique

Heavily Ag doped SnS films were deposited by magnetron co-sputtering technique with in-situ substrate temperature of 400 °C. Structural analysis confirmed the formation of single phase of SnS without any traces of secondary phases, with a slight shift in 2θ due to the effect of doping. Ag diffraction peaks with the preferential orientation along (1 1 1) and (2 0 0) directions elucidate the presence of excess amount of Ag. SEM analysis reveals flower-like Ag clusters on the surface of SnS nanoparticles. Heavy doping modifies the slope of optical absorption of semiconductor nature of SnS, with a small shift in the energy band gap.

Facile synthesis of flower-like Ag nanocube@mesoporous SiO2 and their sensitive SERS performance

Developing facile strategy to synthesize novel nanostructure substrate with superior surface enhanced Raman scattering (SERS) efficiency and identifying the optimal geometry parameter for high enhancement factor (EF) and perfect absorption status of molecules are significant aspects for the intended application of SERS. In the present work, flower-like Ag nanocube@mesoporous SiO2 (AgNC@MSiO2) nanostructure with highly rough surface was designed and prepared by restricting the nucleation region of silica on the surface of Ag nanocube modified with two different kinds of molecules (4MPAA and PAA). The novel hybrid nanostructure exhibited outstanding optical performance. Attributing to the efficient anchor of 2-naphthalenethiol (2NT) on rough silica surface and migration of the molecules through the numerous pores, a large EF of about 5.85 × 106 was achieved. It was found that the limit of detection for 2NT by the as-prepared AgNC@MSiO2 could be as low as 10−8 M with a linear dynamic region from 10−6 to 10−4 M. These results show that the AgNC@MSiO2 nanostructure presented here could be a promising candidate for classical SERS sensors.

Enhanced second harmonic generation by double plasmon resonances in mesoscale flower-like silver particles

We investigate second harmonic generation (SHG) response of mesoscale silver (Ag) particles. The flower-like Ag mesoparticles and Ag micro-hemispheres on an indium tin oxide coated glass substrate were prepared by a simple electrochemical deposition method. We find that the mesoscale Ag particles show a strong SHG response associated with their geometries. The dependence of the SHG on the excitation wavelength reveals that the multi-resonant response occurring at the emission wavelengths plays an important role in SHG enhancement.

Fabrication of a Flowerlike Ag Microsphere Film with Applications in Catalysis and as a SERS Substrate

Three‐dimensional flowerlike Ag microstructures were assembled in situ on a substrate to fabricate Ag microflower (Ag MF) films. The morphology and size of the Ag MFs can be easily controlled by varying the reaction time. The mechanism of growth of Ag MFs was investigated by SEM. The shape evolution revealed that the Ag MFs are assembled from thin nanosheets composed of Ag nanoparticles (NPs), and the elemental composition of the NPs was evidenced by energy‐dispersive X‐ray spectroscopic analysis. The potential of the film as a catalyst in the reduction of nitrophenols was investigated. The reusability of the catalyst was estimated by recycling catalysis of 4‐nitrophenol. Moreover, the Ag MF film could be used as a versatile substrate for surface‐enhanced Raman scattering (SERS) for detection of Rhodamine 6G with a detection limit as low as 1 × 10–7 m. The results demonstrated that the Ag MF film exhibits excellent SERS enhancement ability and catalytic activity.