Morphology-controlled synthesis of silver nanostructures via a solvothermal method

Silver nanostructures have been synthesized by a simple solvothermal method in the presence of poly(vinylpyrrolidone) (PVP). Typically, different exotic agents (NaOH, KBr, NaCl) are added into the reaction system. The anions (OH⁻, Cl⁻, Br⁻) from these agents can combine Ag⁺ to form silver salt colloids (AgOH, AgBr and AgCl), decreasing the concentration of free Ag⁺ in the initial formation of silver seeds. However, different release rates of Ag⁺ from these colloids to the solution in the subsequent reaction may play different roles in the growth of silver seeds. The as-prepared silver nanostructures were characterized by UV–vis absorption spectrum, X-ray diffraction (XRD) and field emission scanning electron microscope (FSEM). It is found that silver nanostructures with various shapes can be obtained by the addition of different exotic agents. Finally, our work provides a simple route to synthesize silver nanostructures with controllable morphologies.     

Room temperature aqueous synthesis of bipyramidal silver nanostructures

The proposed strategy demonstrates a simple method to synthesize the pentagonal right bipyramidal silver nanostructures in aqueous phase at room temperature. Aqueous synthesis enables the materials for direct use in biological systems. The sharp edges of silver nanostructures multiply SERS (surface enhanced Raman spectroscopy) signals by many folds. We have explored a combination of a cationic surfactant, namely, cetyl tri-methyl ammonium bromide (CTAB) and a well-known polymer, polyvinyl pyrrolidone (PVP) for capping preferential crystallographic facets of silver nanosurface. The structural transformation of these anisotropic nanostructures was studied by following various factors, such as, effect of Ag seed concentration, the ratio of concentration of CTAB to the concentration of silver nitrate, the effect of PVP, the ascorbic acid concentration dependence and the effect of pH. CTAB functions as template directing agent while PVP acts as a shape directing agent. Zeta potential measurements and Fourier Transform Infra-red (FTIR) spectral analysis reveal that PVP substitutes CTAB over the facets of silver nanobypiramids.     

Potato extract as reducing agent and stabiliser in a facile green one-step synthesis of ZnO nanoparticles

A facile green recipe was developed to synthesise highly pure, safe and durable zinc oxide nanoparticles (ZnO Nps) using homemade starch-rich potato extract. The ZnO Nps were synthesised using zinc nitrate and potato extract, and the whole reaction is carried out for 30 min at 80 °C. In the synthesis, starch-rich potato extract acted as the reducing agent and as a stabilising layer on freshly formed ZnO Nps. Hexagonal (wurtzite) shaped ZnO Nps with size about 20 ± 1.2 nm were synthesised and characterised using X-ray diffraction, transition electron microscope and scanning microscopy analyses. Fourier transform infrared spectral analysis indicated that highly pure ZnO nanopowders were obtained at higher temperatures. The use of environmentally benign and renewable material as the respective reducing and protecting agents, starch-rich potato extract, as well as a gentle solvent medium (H₂O), offered a simple and quite efficient procedure for the synthesis of ZnO Nps in neutral medium with promising potential for biological and biomedical applications.     

Preparation of ultrafine silver powder using ascorbic acid as reducing agent and its application in MLCI

The preparation of ultrafine silver powder with chemical reduction method was investigated. Ascorbic acid was employed as reducing agent. Reaction of AgNO₃ with ascorbic acid gives polyhedron monodispersed ultrafine silver powder. Effect of reaction temperature on particles was studied. The average congeris sizes (D₅₀) reduces linearly from 3.1 μm to 1.0 μm as the reaction temperature increases from 20 °C to 60 °C. The silver powder having excellent dispersibility and different size was prepared through different pH value or different dosage surfactant. The TG/DTA of silver was discussed with thermal analyzer. As-prepared silver powder was applied in ferrite multi-layer chip inductor (MLCI). The silver end termination has high adhesion strength, excellent solderability and solder leaching resistance behavior.     

Effect of reducing agent on the synthesis of nickel nanoparticles

Synthesis of nickel nano-particles with a coating of a hydrophilic surfactant has been carried out by use of sodium borohydride and sodium formaldehyde sulfoxylate (SFS) in aqueous medium. It is observed that an ideal temperature range for formation of nickel nanoparticles is between 50 and 100 °C. Phase-pure nano-nickel can be obtained by use of SFS. X-ray diffraction measurements (XRD) revealed broad pattern for fcc crystal structure of nickel metal with particle diameter of about 10-15 nm. Scanning Electron Microscopy (SEM) showed that there is clustering of spherical particles in dry state and Transmission Electron Microscopy (TEM) gave a particle size of about less than 10 nm.     

Biomolecule assisted hydrothermal synthesis of chainlike network of silver sulfide nanostructures

A L-cysteine assisted hydrothermal route has been utilized for the growth of Ag2S nanostructures with chainlike network. It was observed that the experimental parameters such as the synthesis temperature and variation in the molar ratio of the anionic and cationic precursors play critical role in determining the morphology and crystal structure of the products. X-ray diffraction study revealed the formation of monoclinic acanthite Ag2S. L-cysteine was acting as complexing agent as well as sulfur source. The branching fractal morphology was explained through Cayley tree model and structure of L-cysteine.     

Low dimensional silver nanostructures: synthesis, growth mechanism, properties and applications

This work presents a review of the recent advances on the low-dimensional (LD) silver nanostructures (e.g., one-dimensional nanorods and nanowires, and two-dimensional nanoplates and nanodisks). First, the methods, either physical or chemical, for the synthesis of silver LD nanostructures are introduced. Then, the use is discussed of advanced experimental techniques (e.g., transmission electron microscope, high-resolution transmission electron microscope, scanning electron microscope, atomic force microscope, ultraviolet-visible and Raman spectra) and theoretical techniques at different time and length scales from quantum mechanics (e.g., ab initio simulation and density function theory) to molecular dynamics method for understanding the principles of governing particle growth, as well as discrete dipolar approximate method for understanding the optical properties of different shapes and sizes of silver LD nanostructures. Subsequently, the functional applications of the LD silver nanostructures in different areas such optical, electronic, and sensing, particularly for those related to surface plasma resonance are summarized based on the recent findings. Finally, some perspectives and comments for future investigation of silver nanostructures are also briefly discussed.     

NiB deposits on p-silicon using borohydride as a reducing agent

A solution, with various deposition parameters optimized to deposit electroless NiB films on p-silicon, has been developed, using sodium borohydride as the reducing agent. This has been done with a view to replace the existing silver–aluminum back contact for crystalline silicon solar cells with NiB films. The deposition has been studied by varying the temperature, time of deposition and the concentration of the reducing agent used, keeping the pH of the solution unchanged. Sheet resistance of the deposited films were measured to confirm the growth. Preliminary studies on contact resistance between NiB film and p-Si have been carried out.     

A study on gold nanoparticle synthesis using oleylamine as both reducing agent and protecting ligand

The growth kinetics and mechanism of a gold nanoparticle synthesis using water as a single phase solvent and oleylamine as both reducing agent and monolayer protection agent were studied. FT-IR and 1H NMR spectroscopic analysis revealed a conversion of oleylamine ligands to oleylamides when gold(III) was reduced to gold(I) and gold atoms. During the reaction, it was found by UV-Vis absorption spectroscopy and transmission electron microscopic study that oleylamine ligands formed large complex aggregates with gold salt instantly upon mixing these two agents together. At an elevated temperature of 80 degrees C, the complex decomposed first into very small particles and then the small particles recombined together into larger and thermally stable particles with an average core size around 9-10 nm. The oleylamide ligands formed a protecting monolayer around the nanoparticles through a hydrogen bonding network between the amide groups. The recombination of small particles into larger ones was found to follow a logistic model, as confirmed by a nonlinear regression fitting of the UV-Vis absorption data of the reaction solution with the mathematical model.     

Synthesis of hollow silver nanostructures by a simple strategy

Various silver nanostructures with hollow interiors, including nanoscaled cubic or quasi-cubic boxes, tubes, triangular rings, trapeziform rings and hybrid structures composed of tubes and cubic boxes, were synthesized via an extremely simple route. The method involved the modification of the solid silver nanocrystals by dithiol, and subsequent dissolving of the interior metal and assembly of the outer surface. In the whole process, only one simple step of pretreatment was needed before the transformation from Ag solid nanostructures to their corresponding hollow nanostructures. According to the morphological, spectral and structural changes in the evolution from silver solid nanostructures to their corresponding hollow nanostructures, a layer-by-layer assembly mechanism was proposed. The method is believed to open up a simple and versatile route to the fabrication of metallic hollow nanostructures with various morphologies according to the starting templates.     

Controllable synthesis of self-assembled Cu2S nanostructures through a template-free polyol process for the degradation of organic pollutant under visible light

Cu₂S nanostructures were fabricated by polyol method and then characterized by X-ray diffractometer, scanning electron microscopy, transmission electron microscopy (TEM) and high resolution TEM. The morphologically different Cu₂S nanostructures such as vertically nanorod arrays, nanoflowers assembled by nanorod arrays, nanoparticles and nanowires, can be successfully synthesized under different experimental conditions. The growth mechanism for the different nanostructures is proposed. The photocatalytic activity of the prepared samples was evaluated based on the degradation of organic pollutant, active brilliant red X-3B (X-3B), under visible light. Among the Cu₂S nanostructures, self-assembled nanoflowers have the highest photocatalytic activity. In addition, the prepared Cu₂S nanostructures are found to be able to decolorize X-3B with iron ions for the formation of Fenton reagent. This study provides a more choice to prepare self-assembled nanostructures for the application of environmental pollution control.     

Synthesis of silver nanoparticles using surfactin: A biosurfactant as stabilizing agent

Surfactin, a lipopeptide biosurfactant, was used to stabilize the formation of silver nanoparticles. Synthesis of silver nanoparticles using a borohydrate reduction was performed at three pH levels (pH 5, 7 and 9) and two different temperatures in the presence of surfactin. The nanomaterials were characterized by UV-vis spectroscopy, X-ray diffraction and transmission electron microscopy. The nanoparticles were synthesized at different pH conditions and temperature and remained stable for 2 months. The UV-vis spectra showed a surface plasmon resonance vibration band at 428 nm for all samples. TEM micrographs revealed that the mean nanoparticle size decreased with increase of pH from 5 to 9 (i.e. 17.8 ± 9.8, 6.9 ± 1.5 and 4.3 ± 1.1 nm) at 4 °C. However, at room temperature, size increased with pH (4.9 ± 1.4, 6.5 ± 1.6, 9.7 ± 4.3 nm at pH 5, 7 and 9 respectively). This report describes the use of a renewable, environmentally compatible, biodegradable surfactant as a stabilizing agent for the synthesis of silver nanoparticles.     

Tungsten film as a hard and compatible carrier for antibacterial agent of silver

Silver-containing tungsten (W–Ag) films for antibacterial applications were deposited on glass, silicon, and 316L stainless-steel substrates by magnetron sputtering with the silver target current of 0–2.0 A. The addition of silver improves adhesion of the films on glass substrate due to the reduced residual stress in the films. SEM and EDX analyses reveal Ag-rich tiny dots (~?20 nm) at the surface of W–Ag films with high silver contents. In XRD patterns, silver peaks are present for the samples deposited at 1.5 and 2.0 A, and tungsten grain size is decreased from?~?23 to 10 nm by silver addition. XPS analysis shows that tungsten is slightly oxidized (WO₃) at the top surface of the film, and silver presents mainly in metallic state. The low Ag/W ratios and the small surface roughness (<?8 nm) indicate that silver segregation at the film surface is not obvious. Microhardness of the samples with ≤?6.7 at.% silver is nearly seven times that of the stainless steel (~?250 HV). The coated samples are hydrophobic tested by contact angle measurement. The potentiodynamic polarization and the soaking test simulating the inflammatory state show that even corrosion occurs and silver addition decreases corrosion resistance of the films. The antibacterial ratio of the coated samples increases with silver content, being 91% at 4.2 at.% silver content tested by agar plate counting method. In agar disk diffusion assay, no inhibition zone is observed for all samples. The antibacterial property of the W–Ag films is localized, long-lasting, and reusable, which would be beneficial for their potential biomedical and environmental applications.     

Zinc stannate nanostructures: hydrothermal synthesis

Nanostructured binary semiconducting metal oxides have received much attention in the last decade owing to their unique properties rendering them suitable for a wide range of applications. In the quest to further improve the physical and chemical properties, an interest in ternary complex oxides has become noticeable in recent times. Zinc stannate or zinc tin oxide (ZTO) is a class of ternary oxides that are known for their stable properties under extreme conditions, higher electron mobility compared to its binary counterparts and other interesting optical properties. The material is thus ideal for applications from solar cells and sensors to photocatalysts. Among the different methods of synthesizing ZTO nanostructures, the hydrothermal method is an attractive green process that is carried out at low temperatures. In this review, we summarize the conditions leading to the growth of different ZTO nanostructures using the hydrothermal method and delve into a few of its applications reported in the literature.     

Zinc stannate nanostructures: hydrothermal synthesis

Abstract

Nanostructured binary semiconducting metal oxides have received much attention in the last decade owing to their unique properties rendering them suitable for a wide range of applications. In the quest to further improve the physical and chemical properties, an interest in ternary complex oxides has become noticeable in recent times. Zinc stannate or zinc tin oxide (ZTO) is a class of ternary oxides that are known for their stable properties under extreme conditions, higher electron mobility compared to its binary counterparts and other interesting optical properties. The material is thus ideal for applications from solar cells and sensors to photocatalysts. Among the different methods of synthesizing ZTO nanostructures, the hydrothermal method is an attractive green process that is carried out at low temperatures. In this review, we summarize the conditions leading to the growth of different ZTO nanostructures using the hydrothermal method and delve into a few of its applications reported in the literature.     

Hydrothermal synthesis and characterization of TiO2 nanostructures using LiOH as a solvent

In the present study, we performed hydrothermal method as a simple and efficient route for the synthesis of rutile TiO₂ nanostructures in various concentrations of lithium hydroxide solutions. TiO₂ nanopowders with average sizes of 15 and 23 nm were prepared using 4 M and 7 M LiOH solutions. X-ray diffraction analysis (XRD), transmission electron microscope (FEG-STEM), scanning electron microscopy (SEM), and Brunauer–Emmet–Teller (BET) analyses were used in order to characterize the obtained products and comparison of the morphology of the powders obtained in different concentrations of LiOH solvent. It was shown that alkali solution concentration has affected the crystallinity, agglomeration ratio, particle size and specific surface area of the obtained rutile phases.     

Cauliflower-like CuI nanostructures: Green synthesis and applications as catalyst and adsorbent

Cauliflower-like CuI nanostructures is realized by an ampicillin-assisted clean, nontoxic, environmentally friendly synthesis strategy at room temperature. The morphology, composition, and phase structure of as-prepared powders were characterized by field emission scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results show that ampicillin plays dual roles, reducing and morphology-directing agents, in the formation of the products. A possible growth mechanism of the cauliflower-like CuI nanostructures is tentatively proposed. The preliminary investigations show that the cauliflower-like CuI structure not only exhibits high catalytic activity with respect to coupling reaction between benzylamine and iodobenzene but also possesses high removal capacity for Cd (II), which may be ascribed to the high specific surface area of the special configuration. To the best of our knowledge, it is the first report that cauliflower-like CuI nanoparticles act as catalyst for coupling reaction and adsorbent for heavy metal ion.     

A comparative study of eco-friendly silver nanoparticles synthesis using Prunus domestica plum extract and sodium citrate as reducing agents

Through the current comparative study, colloidal silver nanoparticles (AgNPs) were synthesized with various morphologies and sizes using Prunus domestica (P-dom) extract and sodium citrate as green and chemical reducing agents, respectively. AgNPs were synthesized employing different concentrations of the reducing agents in an aqueous solution at various pH values (3–10) and temperatures (25–85 °C). The UV–visible absorption spectrum indicated characteristic SPR peaks of AgNPs at 380–450 nm. Fourier transform infrared spectroscopy revealed aqueous-soluble polyols (such as glycosides, phenols, and flavanols) participation in Ag ions reduction to the corresponding AgNPs at various pH values. The crystallinity of AgNPs was detected by an X-ray diffractometer. Different morphologies (polygonal, oval, and spherical) of the AgNPs with varying pH values were confirmed conducting transmission electron microscopy (TEM). Average particle sizes of 16–50 nm were determined using scanning electron microscopy, TEM, and dynamic light scattering assessments for AgNPs synthesized at various reaction conditions. This study is a demonstration for a facile, cheap, and eco-friendly stimuli-sensitive preparation of the AgNPs.     

Solvothermal synthesis of Ce-doped tungsten oxide nanostructures as visible-light-driven photocatalysts

Cerium (Ce)-doped tungsten oxide nanostructures have been generated by using a simple solvothermal method with cerium chloride salts and tungsten hexachloride as precursors. The as-synthesized samples were characterized by electron microscopy, x-ray diffraction and x-ray photoelectron spectrometry. The photocatalytic activities of the samples were evaluated by degradation of methyl orange in an aqueous solution under visible light irradiation. Results showed that the as-synthesized samples underwent morphological evolution with decreasing W/Ce molar ratio, from one-dimensional bundled nanowires through straighter, shorter and thicker bundled nanorods to two-dimensional bundled blocks, then to a mixture of bundled nanorods and agglomerated nanoparticles, and finally to particle agglomerates. The Ce-doped tungsten oxides exhibited better photocatalytic activities than that of the undoped tungsten oxide. The cerium-doped tungsten oxide bundled blocks synthesized with a W/Ce molar ratio of 15:1 possessed the most effective photocatalytic activity among the tested samples. These novel nanomaterials may find potential applications as visible-light-driven photocatalysts.     

Controllable synthesis of ZnO nanostructures using dodecythiol as ligands: A phase-transfer strategy

We report an unparallel route to synthesize ZnO nanocrystallines by using dodecythiol as ligand. Different from other reported solvotherml synthetic routes, the route reported here related to a two-phase reaction system. Primary ZnO particles were generated in aqueous phase and spontaneously capped by dissolved thiol molecules. When a critical size was reached, the thiol-capped particles transferred from aqueous to thiol phase, and their growth was stopped there. After calcining the thiol-capped precursor particles, ZnO nanoparticles were obtained. The derived ZnO nanocrystallines were characterized with X-ray diffraction, energy dispersion X-ray analysis, transmission electron microscopy techniques.