Preparation and NH3 gas-sensing properties of Ag/β-AgVO3 nanorods

NH3 gas sensors operating at room temperature, consisting of Ag nanoparticles decorated β-AgVO3 nanorods (Ag/β-AgVO3 NRs), were fabricated via a facile hydrothermal method without the need for a template. The surface characteristics and compositions of Ag/β-AgVO3 NRs were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Ag nanoparticles, ranging in diameter from approximately 20 to 40 nm, were dispersed on the surface of monoclinic β-AgVO3 NRs with diameters ranging from 50 to 105 nm and lengths from 0.3 to 1.3 μm. The NH3 gas sensing properties of Ag/β-AgVO3 NRs were studied under both dry air and humid conditions at room temperature. Comparative analysis demonstrated that the Ag/β-AgVO3 NRs exhibited a strong response to NH3 gas under 70% relative humidity (RH) at room temperature compared to α-AgVO3 NRs. Specifically, the response of the Ag/β-AgVO3 NRs to 5 ppm NH3 increased by 2.25 times as the RH varied from 20% to 80% at room temperature. This enhanced response was attributed to the effects of formation of nanoheterojunctions, nano-metallic Ag activity and the conductivity of NH4+ and OH- ions induced by the presence of humidity. The room temperature NH3 gas sensors based on Ag/β-AgVO3 NRs demonstrated strong responses to low NH3 concentrations, high selectivity, good reproducibility, and long-term stability, and show promise for the development of low-power and cost-effective NH3 gas sensors for practical applications even under high humidity.

Fabrication of a Plasmonic Heterojunction for Degradation of Oxytetracycline Hydrochloride and Removal of Cr(VI) from Water

A novel Ag/Ag2CO3/BiVO4 plasmonic photocatalyst was successfully prepared by depositing Ag nanoparticles on the surface of Ag2CO3/BiVO4 through the photoreduction reaction. Due to the existence of this novel heterojunction photocatalyst structure, not only can it prevent the photogenerated charge recombination, but the unique properties of Ag also have a great advantage in the absorption of light. The Ag/Ag2CO3/BiVO4 photocatalyst showed good catalytic performance in the degradation of oxytetracycline hydrochloride (OTH) and removal of Cr6+, and the degradation rate of OTH reached 98.0% after 150 min of illumination. The successful preparation of Ag/Ag2CO3/BiVO4 was confirmed by a series of characterization methods, and the importance of •OH and h+ radicals in the degradation of OTH was demonstrated. In addition, the photocatalytic mechanism of Ag/Ag2CO3/BiVO4 photocatalyst was systematically studied in terms of degradation of OTH and reduction of Cr6+. This study is of great importance for the development of novel plasmonic heterojunction photocatalysts and to meet future environmental requirements.

Femtosecond laser self-assembly for silver vanadium oxide flower structures

Flower-like silver vanadium oxide (SVO) micropatterns were realized by femtosecond laser in situ writing from its precursor. Self-assembled petals irradiated by a femtosecond laser were observed standing on the substrate along the scanned routine assisted by the formation of silver seeds and plasmonic-mediated effects. By controlling the concentration of ammonium monovanadate and the laser exposure time, a different thickness of petals was manipulated from ∼100  nm to micrometers. The SVO products were confirmed Ag₄V₂O₇, AgVO₃, and part of Ag₃VO₄ by x-ray diffraction (XRD) measurement. Photon-driven self-assembly for in situ fabrication of microstructures looks to be an effective and facile technique for SVO and other functional compounds.

A novel three-dimensional heterojunction photocatalyst for the photocatalytic oxidation of crystal violet and reduction of Cr6

A novel 3-D heterojunction photocatalyst Ag₂CO₃/BiVO₄ was successfully fabricated. It exhibits excellent photocatalytic performances for the photocatalytic oxidation of crystal violet and reduction of Cr⁶⁺, which is ascribed to the suppression of charge recombination, and increasing lifetime of the charge carriers confirmed by the result of time-resolved fluorescence emission decay spectra and photoelectrochemical measures. The electron spin resonance result also suggests that heterojunction structure can improve separation efficiency of photogenerated carriers and favor to form •OH radicals. Moreover, ten intermediates and products for the photocatalytic oxidation degradation of crystal violet are identified by GC-MS.

The structural conversion from α-AgVO3 to β-AgVO3: Ag nanoparticle decorated nanowires with application as cathode materials for Li-ion batteries

The majority of electrode materials in batteries and related electrochemical energy storage devices are fashioned into slurries via the addition of a conductive additive and a binder. However, aggregation of smaller diameter nanoparticles in current generation electrode compositions can result in non-homogeneous active materials. Inconsistent slurry formulation may lead to inconsistent electrical conductivity throughout the material, local variations in electrochemical response, and the overall cell performance. Here we demonstrate the hydrothermal preparation of Ag nanoparticle (NP) decorated α-AgVO₃ nanowires (NWs) and their conversion to tunnel structured β-AgVO₃ NWs by annealing to form a uniform blend of intercalation materials that are well connected electrically. The synthesis of nanostructures with chemically bound conductive nanoparticles is an elegant means to overcome the intrinsic issues associated with electrode slurry production, as wire-to-wire conductive pathways are formed within the overall electrode active mass of NWs. The conversion from α-AgVO₃ to β-AgVO₃ is explained in detail through a comprehensive structural characterization. Meticulous EELS analysis of β-AgVO₃ NWs offers insight into the true β-AgVO₃ structure and how the annealing process facilitates a higher surface coverage of Ag NPs directly from ionic Ag content within the α-AgVO₃ NWs. Variations in vanadium oxidation state across the surface of the nanowires indicate that the β-AgVO₃ NWs have a core-shell oxidation state structure, and that the vanadium oxidation state under the Ag NP confirms a chemically bound NP from reduction of diffused ionic silver from the α-AgVO₃ NWs core material. Electrochemical comparison of α-AgVO₃ and β-AgVO₃ NWs confirms that β-AgVO₃ offers improved electrochemical performance. An ex situ structural characterization of β-AgVO₃ NWs after the first galvanostatic discharge and charge offers new insight into the Li⁺ reaction mechanism for β-AgVO₃. Ag⁺ between the van der Waals layers of the vanadium oxide is reduced during discharge and deposited as metallic Ag, the vacant sites are then occupied by Li⁺.

Efficient photocatalytic degradation of ibuprofen in aqueous solution using novel visible-light responsive graphene quantum dot/AgVO3 nanoribbons

Single crystalline, non-toxicity, and long-term stability graphene quantum dots (GQDs) were modified onto the AgVO3 nanoribbons by a facile hydrothermal and sintering technique which constructs a unique heterojunction photocatalyst. Characterization results indicate that GQDs are well dispersed on the surface of AgVO3 nanoribbons and GQD/AgVO3 heterojunctions are formed, which can greatly promote the separation efficiency of photogenerated electron-hole pairs under visible light irradiation. By taking advantage of this feature, the GQD/AgVO3 heterojunctions exhibit considerable improvement on the photocatalytic activities for the degradation of ibuprofen (IBP) under visible light irradiation as compared to pure AgVO3. The photocatalytic activity of GQD/AgVO3 heterojunctions is relevant with GQD ratio and the optimal activity is obtained at 3wt% with the highest separation efficiency of photogenerated electron-hole pairs. Integrating the physicochemical and photocatalytic properties, the factors controlling the photocatalytic activity of GQD/AgVO3 heterojunctions are discussed in detail. Moreover, potential photocatalytic degradation mechanisms of IBP via GQD/AgVO3 heterojunctions under visible light are proposed.

Template-free synthesis of β-Na0.33V2O5microspheres as cathode materials for lithium-ion batteries

Hierarchical nanosheet-assembled β-Na_0.33V₂O₅microspheres have been fabricated by a solvothermal method with subsequent calcination in air, and exhibit high specific capacity and good rate capability.

Ultrafine β-AgVO3 nanoribbons derived from α-AgVO3 nanorods by water evaporation method and its application for lithium ion batteries

Monoclinic β-AgVO₃ nanoribbons with thickness of 10–20 nm, width of 80–100 nm and length of several hundred micrometers have been successfully prepared by a water evaporation method without using any template and organic surfactant.