Silver nanoparticles formed in bio- and chemical syntheses with biosurfactant as the stabilizing agent

In this work, the comparison of the physical properties of silver nanoparticles (AgNPs) obtained via the reduction of silver nitrate (AgNO₃) in biological and chemical (model) syntheses supplemented with the biosurfactant surfactin is described. In the studies, two strains of Bacillus subtilis (denoted T’1 and I’1a) were used. The biological synthesis of AgNPs was performed using supernatants obtained from cultures of bacteria growing on brewery effluents, molasses, and Luria–Bretani (LB) medium. In model experiments, ascorbic acid served as the reductant; surfactin acted as the stabilizing agent. The surfactin concentrations were adjusted to 5 and 30?mg/L, which corresponded to minimum and maximum surfactin concentrations as measured in the supernatants obtained from the B. subtilis cultures. The chemical synthesis was carried out at acidic as well as alkaline pH. Dynamic light scattering (DLS) revealed that in model and biological samples, single AgNPs were accompanied by aggregated structures. Transmission electron microscopy showed that the contribution of the aggregates in bacterial supernatants and in chemical synthesis is negligible under acidic conditions. However, in the alkaline environment, this contribution predominates. In the model experiments, smaller nanoparticles were formed with higher concentrations of surfactant. The presence of surfactin significantly increased the stability of AgNPs in both bio- and chemical syntheses.     

High-Fidelity,Narcissistic Self-Sorting in the Synthesis of Organometallic Assemblies from Poly-NHC Ligands

Highly selective, narcissistic self-sorting has been observed in the one-pot synthesis of three organometallic molecular cylinders of type [M₃{L-(NHC)₃}₂](PF₆)₃ (M=Ag⁺, Au⁺; L=1,3,5-benzene, triphenylamine, or 1,3,5-triphenylbenzene) from L-(NHC)₃ and silver(I) or gold(I) ions. The molecular cylinders contain only one type of tris-NHC ligand with no crossover products detectable. Transmetalation of the tris-NHC ligands from Ag⁺ to Au⁺ in a one-pot reaction with retention of the supramolecular structures is also demonstrated. High-fidelity self-sorting was also observed in the one-pot reaction of benzene-bridged tris-NHC and tetrakis-NHC ligands with Ag₂O. This study for the first time extends narcissistic self-sorting in metal–ligand interactions from Werner-type complexes to organometallic derivatives.     

Molten Ag2SO4‐based Ion‐Exchange Preparation of Ag0.5La0.5TiO3 for Photocatalytic O2 Evolution

Ag_0.5La_0.5TiO₃ with an ABO₃ perovskite structure was synthesized by a newly developed ion‐exchange method. Molten Ag₂SO₄ instead of traditional molten AgNO₃ was used as Ag⁺ source in view of its high decomposition temperature (1052 °C), thereby guaranteeing the complete substitution of Ag⁺ for Na⁺ in Na_0.5La_0.5TiO₃ with a stable ABO₃ perovskite structure at a high ion‐exchange temperature (700 °C). Under full‐arc irradiation, the O₂‐evolution activity of Ag_0.5La_0.5TiO₃ was about 1.6 times that of Na_0.5La_0.5TiO₃ due to the optimized electronic band structures and local lattice structures. On the one hand, the substitution of Ag⁺ for Na⁺ elevated the VBM and thus narrowed the band gap from 3.19 to 2.83 eV, thereby extending the light‐response range and, accordingly, enhancing the photoexcitation to generate more charge carriers. On the other hand, the substitution of Ag⁺ for Na⁺ induced a lattice distortion of the ABO₃ perovskite structure, thereby promoting the separation and migration of charge carriers. Moreover, under visible‐light irradiation, Ag_0.5La_0.5TiO₃ displayed notable O₂ evolution whereas Na_0.5La_0.5TiO₃ showed little O₂ evolution, thus demonstrating that the substitution of Ag⁺ for Na⁺ enabled the use of visible light to evolve O₂ photocatalytically. This work presents an effective route to explore novel Ag‐based photocatalysts.     

火焰原子吸收光谱法直接测定锡阳极泥中的银

建立了火焰原子吸收光谱法(FAAS)测定锡阳极泥中银含量的方法。文章考察了不同的测定介质、酸度对测定结果的影响。实验结果表明在选定条件下,锡阳极泥中的锡、锑、铅等杂质不干扰银的测定。方法加标回收率在99.2%~103%,精密度实验结果表明,相对标准偏差(RSD,n=11)均小于4%。操作过程简单,能满足生产的需要。     

火试金-重量法测定阳极铜中的金和银

阳极铜是铜电解过程的重要产品,其中含有一定量的金、银等贵金属,快速准确地测定阳极铜中的贵金属含量,具有重要的现实意义。采用火试金重量法可以同时且快速地测定出样品中的金量和银量,试样与适量的熔剂经高温熔融,铅将金、银富集起来形成铅扣,灰吹得到金、银合粒,用硝酸分金,重量法测得金量;用电感耦合等离子体发射光谱(ICP-OES)法测定分金液中的杂质量和金量,合粒质量减去金量及杂质量即为银量。此方法精密度好,准确度高。金、银的加标回收率在97.6%~102%,可以很好地满足阳极铜中金、银含量的测定。     

Coating Cellulosic Material with Ag Nanowires to Fabricate Wearable IR-Reflective Device for Personal Thermal Management: The Role of Coating Method and Loading Level

Textiles coated with silver nanowires (AgNWs) are effective at suppressing radiative heat loss without sacrificing breathability. Many reports present the applicability of AgNWs as IR-reflective wearable textiles, where such studies partially evaluate the parameters for practical usage for large-scale production. In this study, the effect of the two industrial coating methods and the loading value of AgNWs on the performance of AgNWs-coated fabric (AgNWs-CF) is reported. The AgNWs were synthesized by the polyol process and applied onto the surface of cotton fabric using either dip- or spray-coating methods with variable loading levels of AgNWs. X-ray diffraction, scanning electron microscopy (SEM), infrared (IR) reflectance, water vapor permeability (WVP), and electrical resistance properties were characterized. The results report the successful synthesis of AgNWs with a 30 μm length. The results also show that the spray coating method has a better performance for reflecting the IR radiation to the body, which increases with a greater loading level of the AgNWs. The antibacterial results show a good inhibition zone for cotton fabric coated by both methods, where the spray-coated fabric has a better performance overall. The results also show the coated fabric with AgNWs maintains the level of fabric breathability similar to control samples. AgNWs-CFs have potential utility for cold weather protective clothing in which heat dissipation is attenuated, along with applications such as wound dressing materials that provide antibacterial protection.     

The Quenching and Sonication Effect on the Mechanical Strength of Silver Nanowires Synthesized Using the Polyol Method

This study aims to determine the effect of fast cooling (quenching) on thermal properties, mechanical strength, morphology and size of the AgNWs. The synthesis of AgNWs was carried out at three different quenching-medium temperatures as follows: at 27 °C (ambient temperature), 0 °C (on ice), and −80 °C (in dry ice) using the polyol method at 130 °C. Furthermore, the AgNWs were sonified for 45 min to determine their mechanical strength. Scanning electron microscopy analysis showed that the quenched AgNWs had decreased significantly; at 27 °C, the AgNWs experienced a change in length from (40 ± 10) to (21 ± 6) µm, at 0 °C from (37 ± 8) to (24 ± 8) µm, and at −80 °C from (34 ± 9) to (29 ± 1) µm. The opposite occurred for their diameter with an increased quenching temperature: at 27 °C from (200 ± 10) to (210 ± 10) nm, at 0 °C from (224 ± 4) to (239 ± 8) nm, and at −80 °C from (253 ± 6) to (270 ± 10) nm. The lower the temperature of the quenching medium, the shorter the length and the higher the mechanical strength of AgNWs. The UV-Vis spectra of the AgNWs showed peak absorbances at 350 and 411 to 425 nm. Thermogravimetric analysis showed that AgNWs quenched at −80 °C have better thermal stability as their mass loss was only 2.88%, while at the quenching temperatures of 27 °C and 0 °C the mass loss was of 8.73% and 4.17%, respectively. The resulting AgNWs will then be applied to manufacture transparent conductive electrodes (TCEs) for optoelectronic applications.     

Antibacterial and Antifungal Studies of Biosynthesized Silver Nanoparticles against Plant Parasitic Nematode Meloidogyne incognita,Plant Pathogens Ralstonia solanacearum and Fusarium oxysporum

The possibility of using silver nanoparticles (AgNPs) to enhance the plants growth, crop production, and control of plant diseases is currently being researched. One of the most effective approaches for the production of AgNPs is green synthesis. Herein, we report a green and phytogenic synthesis of AgNPs by using aqueous extract of strawberry waste (solid waste after fruit juice extraction) as a novel bioresource, which is a non-hazardous and inexpensive that can act as a reducing, capping, and stabilizing agent. Successful biosynthesis of AgNPs was monitored by UV-visible spectroscopy showing a surface plasmon resonance (SPR) peak at ~415 nm. The X-ray diffraction studies confirm the face-centered cubic crystalline AgNPs. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques confirm the rectangular shape with an average size of ~55 nm. The antibacterial and antifungal efficacy and inhibitory impact of the biosynthesized AgNPs were tested against nematode, Meloidogyne incognita, plant pathogenic bacterium, Ralstonia solanacearum and fungus, Fusarium oxysporum. These results confirm that biosynthesized AgNPs can significantly control these plant pathogens.     

Facile Surfactant-, Reductant-, and Ag Salt-free Growth of Ag Nanoparticles with Controllable Size from 35 to 660 nm on Bulk Ag Materials

Morphologically and dimensionally controlled growth of Ag nanocrystals has long been plagued by surfactants or capping agents that complicate downstream applications, unstable Ag salts that impaired the reproducibility, and multistep seed injection that is troublesome and time-consuming. Here, we report a one-pot electro-chemical method to fast (∼2 min) produce Ag nanoparticles from commercial bulk Ag materials in a nitric acid solution, eliminating any need for surfactants or capping agents. Their size can be easily manipulated in an unprecedentedly wide range from 35 to 660 nm. Furthermore, the Ag nanoparticles are directly grown on the Ag substrate, highly desirable for promising applications such as catalysis and plasmonics. The mechanistic studies reveal that the concentration of Ag⁺ in the diffusion layer nearby the surface, controlled by the magnitude and duration of voltage, is critical in governing the nanoparticle formation (<1.3 mM) and its dimensional adjustability.