Bacterial indoleacetic acid-induced synthesis of colloidal Ag2O nanocrystals and their biological activities

The biosynthesis and biological activity of colloidal Ag₂O nanocrystals have not been well studied, although they have potential applications in many fields. For the first time, we developed a reducing agent free, cost-effective technique for Ag₂O biosynthesis using Xanthomonas sp. P5. The optimal conditions for Ag₂O synthesis were 50 °C, pH 8, and 2.5 mM AgNO₃. Using these conditions the yield of Ag₂O obtained at 10 h was about five times higher than that obtained at 12 h under unoptimized conditions. Ag₂O was characterized by FESEM-EDS, TEM, dynamic light scattering, XRD, and UV-Visible spectroscopy. Indoleacetic acid produced by the strain P2 was involved in the synthesis of Ag₂O. Ag₂O exhibited a broad antimicrobial spectrum against several human pathogens. Furthermore, Ag₂O exhibited 1,1-diphenyl-2-picrylhydrazyl (IC₅₀ = 25.1 µg/ml) and 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonate (IC₅₀ = 16.8 µg/ml) radical scavenging activities, and inhibited collagenase (IC₅₀ = 27.9 mg/ml). Cytotoxicity of Ag₂O was tested in fibroblast cells and found to be non-toxic, demonstrating biocompatibility.

Floatable superhydrophobic Ag2O photocatalyst without a modifier and its controllable wettability by particle size adjustment

In this research, a controlling mechanism of particle size on the wettability of Ag2O particles is reported, and an interesting floatable Ag2O photocatalyst with superhydrophobicity and superoleophilicity is prepared based on this mechanism. Stable superhydrophobic and superhydrophilic Ag2O without a low-surface-energy modifier can be obtained only by adjusting its particle size, and its wettability can switch mutually by changing the particle size. The wettability of Ag2O converts from superhydrophilic to hydrophobic when the average particle size is more than 1.08 μm. The operation parameters of the Ag2O crystallization process significantly influence the wettability of the Ag2O particles. The obtained superhydrophobic Ag2O floated on the water surface, and exhibited excellent photodegradation performance with various floating oils. This attractive superhydrophobic Ag2O photocatalyst is promising for practical applications, and provides a strategy for the development of functional photocatalysts and superhydrophobic materials.

Preparing cuprous oxide nanomaterials by electrochemical method for non-enzymatic glucose biosensor

Cuprous oxide (Cu₂O) nanostructure has been synthesized using an electrochemical method with a two-electrode system. Cu foils were used as electrodes and NH₂(OH) was utilized as the reducing agent. The effects of pH and applied voltages on the morphology of the product were investigated. The morphology and optical properties of Cu₂O particles were characterized using scanning electron microscopy, x-ray diffraction, and diffuse reflectance spectra. The synthesized Cu₂O nanostructures that formed in the vicinity of the anode at 2 V and pH = 11 showed high uniform distribution, small size, and good electrochemical sensing. These Cu₂O nanoparticles were coated on an Indium tin oxide substrate and applied to detect non-enzyme glucose as excellent biosensors. The non-enzyme glucose biosensors exhibited good performance with high response, good selectivity, wide linear detection range, and a low detection limit at 0.4 μM. Synthesized Cu₂O nanostructures are potential materials for a non-enzyme glucose biosensor.

Cathodic Corrosion of a Bulk Wire to Nonaggregated Functional Nanocrystals and Nanoalloys

A key enabling step in leveraging the properties of nanoparticles (NPs) is to explore new, simple, controllable, and scalable nanotechnologies for their syntheses. Among "wet" methods, cathodic corrosion has been used to synthesize catalytic aggregates with some control over their size and preferential faceting. Here, we report on a modification of the cathodic corrosion method for producing a range of nonaggregated nanocrystals (Pt, Pd, Au, Ag, Cu, Rh, Ir, and Ni) and nanoalloys (Pt₅₀Au₅₀, Pd₅₀Au₅₀, and Ag _xAu_{100- x}) with potential for scaling up the production rate. The method employs poly(vinylpyrrolidone) (PVP) as a stabilizer in an electrolyte solution containing nonreducible cations (Na⁺, Ca²⁺), and cathodic corrosion of the corresponding wires takes place in the electrolyte under ultrasonication. The ultrasonication not only promotes particle-PVP interactions (enhancing NP dispersion and diluting locally high NP concentration) but also increases the production rate by a factor of ca. 5. Further increase in the production rate can be achieved through parallelization of electrodes to construct comb electrodes. With respect to applications, carbon-supported Pt NPs prepared by the new method exhibit catalytic activity and durability for methanol oxidation comparable or better than the commercial benchmark catalyst. A variety of Ag _xAu_{100- x} nanoalloys are characterized by ultraviolet-visible absorption spectroscopy and high-resolution transmission electron microscopy. The protocol for NP synthesis by cathodic corrosion should be a step toward its further use in academic research as well as in its practical upscaling.

In Situ Synthesis of Gold Nanoparticles on Wool Powder and Their Catalytic Application

Gold nanoparticles (AuNPs) were synthesized in situ on wool powder (WP) under heating conditions. Wool powder not only reduced Au ions to AuNPs, but also provided a support for as-synthesized AuNPs. WPs were treated under different concentrations of Au ions, and corresponding optical features and morphologies of the treated WPs were investigated by UV-VIS diffuse reflectance absorption spectroscopy and scanning electron microscopy (SEM). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscope (TEM) were also employed to characterize the WP treated with AuNPs. The results demonstrate that AuNPs were produced in the presence of WP and distributed over the wool particles. The porous structure led to the synthesis of AuNPs in the internal parts of WP. Acid conditions and high temperature facilitated the synthesis of AuNPs by WP in aqueous solution. The reducibility of wool was improved after being converted to powder from fibers, due to exposure of more active groups. Moreover, the obtained AuNP-WP complexes showed significant catalytic activity to accelerate the reduction reaction of 4-nitrophenol (4-NP) by sodium borohydride (NaBH₄).

Efficient electrochemical water oxidation in neutral and near-neutral systems with a nanoscale silver-oxide catalyst

In electrocatalytic water splitting systems pursuing for renewable energy using sunlight, developing robust, stable and easily accessible materials operating under mild chemical conditions is pivotal. We present here a unique nanoparticulate type silver-oxide (AgOx-NP) based robust and highly stable electrocatalyst for efficient water oxidation. The AgOx-NP is generated in situ in a HCO3(-)/CO2 system under benign conditions. Micrographs show that they exhibit a nanoscale box type squared nano-bipyramidal configuration. The oxygen generation is initiated at low overpotential, and a sustained O2 evolution current density of >1.1 mA cm(-2) is achieved during prolonged-period water electrolysis. The AgOx-NP electrocatalyst performs exceptionally well in metal-ion free neutral or near-neutral carbonate, phosphate and borate buffers relative to recently reported Co-oxide and Ni-oxide based heterogeneous electrocatalysts, which are unstable in metal-ion free electrolytes and tend to deactivate with time and lose catalytic performance during long-term experimental tests.

The preparation of a recyclable catalyst of silver nanoparticles dispersed in a mesoporous silica nanofiber matrix

A recyclable catalyst of sliver nanoparticles well dispersed in mesoporous silica was successfully synthesized via a straight-forward strategy combining an electrospinning technique with post-calcination.

Dragon's blood-aided synthesis of Ag/Ag2O core/shell nanostructures and Ag/Ag2O decked multi-layered graphene for efficient As(iii) uptake from water and antibacterial activity

Excellent As(iii) uptake and antibacterial activities of Ag/Ag₂O core/shell and multi-layered graphene nanostructures obtained with the aid of Dragon's blood.

Functional Application of Noble Metal Nanoparticles In Situ Synthesized on Ramie Fibers

Different functions were imparted to ramie fibers through treatment with noble metal nanoparticles including silver and gold nanoparticles. The in situ synthesis of silver and gold nanoparticles was achieved by heating in the presence of ramie fibers in the corresponding solutions of precursors. The unique optical property of synthesized noble metal nanoparticles, i.e., localized surface plasmon resonance, endowed ramie fibers with bright colors. Color strength (K/S) of fibers increased with heating temperature. Silver nanoparticles were obtained in alkaline solution, while acidic condition was conducive to gold nanoparticles. The optical properties of treated ramie fibers were investigated using UV-vis absorption spectroscopy. Scanning electron microscopy (SEM) was employed to observe the morphologies of silver and gold nanoparticles in situ synthesized on fibers. The ramie fibers treated with noble metal nanoparticles showed remarkable catalytic activity for reduction of 4-nitrophenol (4-NP) by sodium borohydride. Moreover, the silver nanoparticle treatment showed significant antibacterial property on ramie fibers.

Facile synthesis of silver submicrospheres and their applications

Silver submicrospheres fabricated under an ambient condition can catalyze the reduction of 4-nitrophenol and improve significantly the Raman signal of crystal violet as surface-enhanced Raman scattering (SERS) substrate.