Extracellular synthesis of silver nanoparticles using the leaf extract of Coleus amboinicus Lour.

In the present investigation, Coleus amboinicus Lour. leaf extract-mediated green chemistry approach for the synthesis of silver nanoparticles was described. The nanoparticles were characterized by ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The influence of leaf extract on the control of size and shape of silver nanoparticles is reported. Upon an increase in the concentration of leaf extract, there was a shift in the shape of nanoparticles from anisotrophic nanostructures like triangle, decahedral and hexagonal to isotrophic spherical nanoparticles. Crystalline nature of fcc structured nanoparticles was confirmed by XRD spectrum with peaks corresponding to (1 1 1), (2 0 0), (2 2 0) and (3 1 1) planes and bright circular spots in the selected-area electron diffraction (SAED). Such environment friendly and sustainable methods are non-toxic, cheap and alternative to hazardous chemical procedures.     

Green synthesis of silver nanoparticles using marine polysaccharide: Study of in-vitro antibacterial activity

The present contribution deals with one pot method for synthesis of silver nanoparticles through green route using sulfated polysaccharide isolated from marine red algae (Porphyra vietnamensis). The obtained silver nanoparticles showed surface plasmon resonance centered at 404 nm with average particle size measured to be 13 ± 3 nm. FTIR spectra revealed the involvement of sulfate moiety of polysaccharide for reduction of silver nitrate. The capping of anionic polysaccharide on the surface of nanoparticles was confirmed by zeta potential measurement (−35.05 mV) and is responsible for the electrostatic stability. The silver nanoparticles were highly stable at wide range of pH (2-10) and electrolyte concentration (up to 10⁻² M of NaCl). The dose dependent effect of synthesized silver nanoparticles revealed strong antibacterial activity against gram negative bacteria as compared to gram positive bacteria.     

Green synthesis and characteristic of core-shell structure silver/starch nanoparticles

An eco-friendly method was put forward to synthesize Ag nanoparticles (Ag NPs) by using biodegradable starch as a stabilizing agent. The silver ion from AgNO₃ was reduced by glucose in soluble starch solution. Morphological observation and characterization of Ag NPs were performed by using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and UV–vis absorption spectroscopy. HRTEM showed that Ag NPs were covered by starch layer to form spherical core-shell Ag/starch NPs with diameter ranging from 5 to 20 nm. XRD pattern confirmed the presence of Ag NPs with face-centered cubic (fcc) structure. All these results indicated that starch played an important role in stabilizing Ag NPs.     

Formation of size and shape tunable gold nanoparticles in solution by bio-assisted synthesis with bovine serum albumin in native and denaturated state

We have successfully controlled the size and shape of gold nanoparticles (GNPs) through a one-step bio-assisted procedure by using bovine serum albumin (BSA) protein as both reducing and stabilizing agent. We found that the growing process of GNPs can be directly manipulated by simply controlling the BSA concentration in solution and the reaction temperature. The GNPs formation was followed both experimentally by UV–vis–NIR spectroscopy and transmission electron microscopy (TEM) and theoretically by finite difference time domain (FDTD) simulations. The surface plasmon resonance of as-prepared GNPs suits the needs of many biological applications.     

Synthesis and structure of large single crystalline silver hexagonal microplates suitable for micromachining

We report a simple one-step synthesis method of large single crystalline Ag (111) hexagonal microplates with sharp edges and a size of up to tens of microns. Single silver crystals were produced by reduction silver nitrate aqueous solution with 4-(methylamino)phenol sulfate. Scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, selected area electron diffraction and optical microscopy techniques were combined to characterize the crystals. It is shown that the microplates can be easily dispersed and transferred as single objects onto different substrates and subsequently used as a high quality plasmonic starting material for micromachining of future nanocomponents, using modern top-down techniques like focused-ion beam milling and gas injection deposition.     

One-step chemical bath deposition and photocatalytic activity of Cu2O thin films with orientation and size controlled by a chelating agent

Nanocrystalline cuprous oxide (Cu₂O) thin films were prepared via a one-step chemical bath deposition (CBD) method. The effects of a chelating agent on the orientation, morphology, crystallite size, and photocatalytic activity of the thin films were carefully examined using X-ray diffractometry, scanning electron microscopy, and UV–vis spectrophotometry. The results confirmed that the crystallite size as well as the orientation of the films was dependent on the volume of trisodium citrate (TSC), demonstrating that the band gap ranged from 2.71 eV to 2.49 eV. The morphology and number density of the thin films also depended on the volume of TSC. In addition, the obtained Cu₂O thin films could degrade methyl orange (MO) efficiently in the presence of H₂O₂ under visible-light irradiation, and the mechanism for the enhanced photocatalytic activity of the Cu₂O thin films with the assistance of H₂O₂ was also explored in detail.     

Biological synthesis of silver nanoparticles using the fungus Aspergillus flavus

The fungus, Aspergillus flavus when challenged with silver nitrate solution accumulated silver nanoparticles on the surface of its cell wall in 72 h. These nanoparticles dislodged by ultrasonication showed an absorption peak at 420 nm in UV-visible spectrum corresponding to the plasmon resonance of silver nanoparticles. The transmission electron micrographs of dislodged nanoparticles in aqueous solution showed the production of reasonably monodisperse silver nanoparticles (average particle size: 8.92 ± 1.61 nm) by the fungus. X-ray diffraction spectrum of the nanoparticles confirmed the formation of metallic silver. The Fourier transform infrared spectroscopy confirmed the presence of protein as the stabilizing agent surrounding the silver nanoparticles. These protein-stabilized silver nanoparticles produced a characteristic emission peak at 553 nm when excited at 420 nm in photoluminescence spectrum. The use of fungus for silver nanoparticles synthesis offers the benefits of eco-friendliness and amenability for large-scale production.     

Biological synthesis of very small silver nanoparticles by culture supernatant of Klebsiella pneumonia: The effects of visible-light irradiation and the liquid mixing process

This study has investigated different visible-light irradiation's effect on the formation of silver nanoparticles from silver nitrate using the culture supernatant of Klebsiella pneumonia. Our study shows that visible-light emission can significantly prompt the synthesis of silver nanoparticles. Also, the study experimentally investigated the liquid mixing process effect on silver nanoparticle synthesis by visible-light irradiation. This study successfully synthesized uniformly dispersed silver nanoparticles with a uniform size and shape in the range of 1-6 nm with an average size of 3 nm. Furthermore, the study investigated the mechanism of the reduction of silver ions by culture supernatant of K. pneumonia, and used X-ray diffraction to characterize silver chloride as an intermediate compound. Silver chloride was prepared synthetically and used as a substrate for the synthesis of silver nanoparticles by culture supernatant of K. pneumonia. The silver nanoparticles have been prepared from silver chloride during this investigation for the first time.     

Effects of geometric structure, orientation and size on structural stability and thermal behavior of zinc oxide nanowires

The structural stability, orientation effect and melting characteristic of zinc oxide (ZnO) nanowires are simulated by using the molecular dynamics with many-body tightbinding potential. The structural stability is affected by the geometric shape of the cross section of a nanowire. The nanowire with a hexagonal cross section is more stable than that with another cross section type, namely, a rectangular, triangular, rhombohedral, octagonal, and circular cross section. The structural stability and melting temperature of a nanowire is sensitive to its diameter because of the surface energy and unfavorable coordination. Remarkably, it is observed that hexagonal ZnO nanowires transform to metastable circular-type structures at temperatures lower than the melting point.     

Green synthesis of silver nanoparticles using biopolymers,carboxymethylated-curdlan and fucoidan

There is a growing need in developing a reliable and eco-friendly methodology for the synthesis of metallic nanoparticles, which may be applied for many nanotechnological applications. Natural compounds such as biopolymers are one of the resources which could be used for this purpose. The present study involves the development of a simple, ecological and user-friendly method in synthesizing silver nanoparticles by using carboxymethylated-curdlan or fucoidan as reducing and stabilizing agents. Reduction of silver ions by these biopolymers occurred when heating at 100 °C, led to the formation of silver nanoparticles in the range of 40–80 nm in dimensions. The silver nanoparticles were formed readily within 10–15 min. Morphological observation and characterization of the silver nanoparticles were performed by using dynamic light scattering (DLS), high-resolution transmission electron microscopy (HRTEM), and UV–vis absorption spectrophotometer. The size of silver nanoparticles can be controlled by using different concentrations of carboxymethylated-curdlan, fucoidan or silver nitrate. This way of silver nanoparticles preparation is easy, fast, user-friendly and suitable for large-scale production.     

Effect of Fe on the synthesis and electrochemical performance of nanostructured MnO2

Different MnO₂ nanostructures were synthesized in stoichiometric KMnO_4/MnSO₄ aqueous solutions in the absence/presence of Fe³⁺ at temperature ranging from 30 °C to 180 °C. The phase structures, morphologies and electrochemical properties of the as-prepared MnO₂ products were investigated using X-ray powder diffraction, scanning electron microscope, N₂ physical adsorption and cyclic voltammetry techniques. The results showed that the presence of Fe³⁺ addition had a significant effect on the phase structural evolution, morphological features and electrochemical properties of the MnO₂ products. Fe³⁺ was found to greatly prevent the epitaxial growth and crystallization of MnO₂ nucleus, which in turn influenced textual characteristics. The electrochemical performance of the nanostructured MnO₂ products had a complex relationship with the phase structures, specific surface area as well as pore characteristics. MnO₂ prepared in the presence of Fe³⁺ (KMF-MnO₂) showed relatively higher specific capacitance compared to that of MnO₂ prepared in the absence of Fe³⁺ (KM-MnO₂). Maximum capacitance of 214 F g⁻¹ was obtained for KMF-MnO₂ prepared at 30 °C at a scan rate of 2 mV s⁻¹ in 0.1 M Na₂SO₄ electrolyte.     

Green synthesis of zinc oxide nanoparticles by aloe barbadensis miller leaf extract: Structure and optical properties

Biological methods for nanoparticle synthesis using microorganisms, enzymes, and plants or plant extracts have been suggested as possible ecofriendly alternatives to chemical and physical methods. In this paper, we report on the synthesis of nanostructured zinc oxide particles by both chemical and biological method. Highly stable and spherical zinc oxide nanoparticles are produced by using zinc nitrate and Aloe vera leaf extract. Greater than 95% conversion to nanoparticles has been achieved with aloe leaf broth concentration greater than 25%. Structural, morphological and optical properties of the synthesized nanoparticles have been characterized by using UV-Vis spectrophotometer, FTIR, Photoluminescence, SEM, TEM and XRD analysis. SEM and TEM analysis shows that the zinc oxide nanoparticles prepared were poly dispersed and the average size ranged from 25 to 40 nm. The particles obtained have been found to be predominantly spherical and the particle size could be controlled by varying the concentrations of leaf broth solution.     

Size-dependent melting point of nanoparticles based on bond number calculation

An integrated model based on bond number and bond strength in a system with a cubo-octahedral structure is developed to predict the size-dependent thermal characteristics of nanoparticles. Without any adjustable parameters, this model can be used to predict the melting point and cohesive energy of low-dimensional materials, suggesting that both depend on the size and on the atomic distance. The good agreement of the theoretical prediction with the experimental and molecular dynamic simulation results confirms the validity of the cubo-octahedron in describing the thermodynamic behaviors of nanoparticles even without considering their crystalline structures.     

Green synthesis of silver nanoparticles using aqueous solution of Ficus benghalensis leaf extract and characterization of their antibacterial activity

The present study reports an environmentally friendly and rapid method for synthesis of silver nanoparticles. Although several articles have been reported for the synthesis of silver nanoparticles from plant extract, here we have developed a green synthetic method for silver nanoparticles using Ficus benghalensis leaf extract which acts as a reducing and capping agent. It was observed that use of Ficus benghalensis leaf extract makes a fast and convenient method for the synthesis of silver nanoparticles and can reduce silver ions into silver nanoparticles within 5 min of reaction time without using any harsh conditions. Silver nanoparticles so prepared were characterized by using UV-visible spectroscopy, transmission electron microscope-energy dispersive spectra (TEM-EDS) and X-ray diffraction (XRD). Further, these nanoparticles show effective antibacterial activity toward E.coli MTCC1302 due to high surface to volume ratio.     

Sol-gel synthesis, structure and photoluminescence properties of nanocrystalline Lu2MoO6:Eu

In this paper, we reported the obtention of Eu³⁺ ion doped Lu₂MoO₆ powders synthesized by a sol-gel method, and followed by annealing at different temperatures. The structure and photoluminescence properties of these powders were investigated. The X-ray diffraction pattern suggests that Lu₂MoO₆ powder has a monoclinic structure. It was observed that the UV-visible and photoluminescence spectra of Lu₂MoO₆:Eu nanocrystallines varied systematically with the calcination temperature. The near-UV absorption edge shifts to long wavelength direction with the decreasing of the calcination temperature, while the peak of MoO₅ excitation band shifts in an opposite way. The decline of the crystallinity and the introduced lattice defect were considered to respond for these variations. Additionally, due to the efficient red light emission under near-UV light excitation, the powder can be a candidate as red phosphor for white-light-emitting diodes.     

Effect of citrate on poly(vinyl pyrrolidone)-stabilized gold nanoparticles formed by PVP reduction in microwave (MW) synthesis

Colloidal PVP (poly(vinyl pyrrolidone))–stabilized gold nanoparticles (PVP–AuNPs) are synthesized in aqueous solution with PVP as a reducing and stabilizing agent using a short microwave (MW) heating duration of 1 min. The size and uniformity of the synthesized PVP–AuNPs can be varied by modifying the concentration of sodium citrate (Na₃Ct), which acts predominantly as mediator of the stability of PVP–AuNP formation during the rapid synthesis. Due to the increase in the Na₃Ct concentration, the number of citrate ions adsorbed on the growing surface of AuNPs increase, and less reactive gold solute complexes are formed, leading to slow stable reactions that produce small, uniform colloidal PVP–AuNPs. We therefore demonstrate that by adjusting the Na₃Ct concentration used in the PVP reduction, the diameter of PVP–AuNPs was varied from 19.47 ± 3.97 nm to 7.94 ± 0.14 nm when using constant concentrations of chloroauric acid (HAuCl₄) and PVP.     

Green synthesis of gold nanoparticles using ethanolic leaf extract of Centella asiatica

Here, we report a novel use of the ethanolic leaf extract of Centella asiatica to produce gold nanoparticles by reduction of AuCl₄⁻ ions. The phytochemicals present in the leaf extract served as effective reducing and capping agent. The gold nanoparticles obtained were characterized by UV-visible spectra, transmission electron microscopy (TEM) and X-ray diffraction (XRD). TEM studies showed the particles to be of various shapes and sizes. Selected-area electron diffraction (SAED) pattern and high-resolution TEM image confirmed a fcc phase and high crystallinity of the particles. The XRD patterns showed a (1 1 1) preferential orientation of the gold nanoparticles. Fourier transform infra-red spectroscopy (FTIR) measurements showed the GNPs having a coating of phenolic compounds indicating a possible role of biomolecules responsible for capping and efficient stabilization of the gold nanoparticles. As no synthetic reagents were used in this method, the synthesized gold nanoparticles have potential for application in bio-molecular imaging and therapy.     

Synthesis of gold nanoparticles using aqueous extract of Calotropis procera latex

This is an account of the use of aqueous extract of the latex of Calotropis procera for the synthesis of gold nanoparticles. UV-Vis spectroscopic studies of the products resulting from reaction between the aqueous latex extract and chlorauric acid indicated the successful synthesis of gold nanoparticles. Reaction parameters viz. concentration of latex extract and reaction time were optimized for maximum yield of gold nanoparticles. Effect of reaction temperature on the synthesis rate of the particles and their optical properties was also studied. Transmission electron microscopic (TEM) studies of the particles revealed the dominance of spherical particles. Mean particle size distribution was found to be 22 ± 10 nm. Crystalline nature of the particles was confirmed from X-ray diffractrograms. FT-IR analysis and protein coagulation test of the gold nanoparticles confirmed capping behaviour of the latex proteins that contributed to their long term stability (6 months) in aqueous medium. Toxicity of the particles was tested on three cell lines, HeLa, A549 and BHK21. The method exploits a cheap and easily available biomaterial not explored so far for the synthesis of metallic nanoparticles.     

Solvothermal synthesis of LiFePO4 nanoplates with (010) plane and the uniform carbon coated on their surface by esterification reaction

A facile solvothermal synthesis and esterification reaction combined with a high temperature calcination technique has been developed to prepare the uniform carbon coating LiFePO₄ nanoplates. The carbon coating LiFePO₄ nanoplates are investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), transmission electron microscope (TEM), galvanostatic intermittent titration technique (GITT) and galvanostatic charge–discharge test. A reasonable growth mechanism of LiFePO₄ nanoplates is proposed on the basis of time dependent experimental results. The results show that each nanoplate is a LiFePO₄ single crystal with the large (010) plane. According to Raman spectroscopy analysis, carbon is uniformly coated on the surface of LiFePO₄ nanoplates. Electrochemical test results also indicate that the carbon coating LiFePO₄ nanoplates exhibit a high reversible specific capacity of 144.8 mAh g⁻¹ at 0.5 C and 116.9 mAh g⁻¹ under lower discharging rate at −20 °C.     

Controllable synthesis of hydroxyapatite nanocrystals via a dendrimer-assisted hydrothermal process

The morphology and size of hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (denoted HAP) can be controlled under hydrothermal treatment assisted with different dendrimers, such as carboxylic terminated poly(amidoamine) (PAMAM) and polyhydroxy terminated PAMAM. The structure and morphology were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR) and transmission electron microscopy (TEM). IR spectra were also used to investigate the complexation of Ca²⁺ with PAMAM. The results revealed that the inner cores of the PAMAM dendrimers are hydrophilic and potentially open to calcium ions, since interior nitrogen moieties serve as complexation sites, especially in case of the polyhydroxy terminated PAMAM. And the reasonable mechanism of crystallization was proposed that it can be attributed to the localization of nucleation site: external or interior PAMAM. Additionally, the PAMAM dendrimer with carboxylic and polyhydroxy groups has an effective influence on the size and shape of hydroxyapatite (HAP) nanostructures. Different crystal morphology was accomplished by adsorption of different dendrimers onto specific faces of growing crystals, altering the relative growth rates of the different crystallographic faces and leading to different crystal habits.