Experimental and Theoretical Studies of Green Synthesized Cu2O Nanoparticles Using Datura Metel L

In biomedical applications, Cu₂O nanoparticles are of great interest. The bioengineered route is eco-friendly for the synthesis of nanoparticles. Therefore, in the present study, there is an attempt to synthesis Cu₂O nanoparticles using Datura metel L. The synthesized nanoparticles were characterized by UV–Vis, XRD, and FT-IR. UV–Vis results suggest the presence of hyoscyamine, atropine in Datura metel L, and also, nanoparticles formation has been confirmed by the presence of absorption peak at 790 nm. The average crystallite size (19.56 nm) was obtained by XRD. FT-IR was also used to confirm the different functional groups. Fourier Power Spectrum was also employed to examine the synthesized nanomaterials spectrum data to emphasize the peak of the prominent frequencies. Density functional theory (DFT) was also utilized to assess the energy of the substance over time, which appears to indicate a stable molecule. Furthermore, calculated energies, thermodynamic properties (such as enthalpies, entropies, and Gibbs-free energies), modeled structures of complexes, crystals, and clusters, and predicted yields, rates, and regio- and stereospecificity of reactions were all in good agreement with experimental results. Overall, the results show that the successful production of Cu₂O nanoparticles with Datura metel L. corresponds to theoretical research.

     

A facile strategy to synthesize bimetallic Au/Ag nanocomposite film by layer-by-layer assembly technique

A facile strategy has been developed for the preparation of bimetallic gold–silver (Au–Ag) nanocomposite films by alternating absorption of poly-(ethyleneimine)–silver ions and Au onto substrates and subsequent reduction of the silver ions. The composition, micro-structure and properties of the {PEI–Ag/Au}_n nanocomposite films were characterized by ultraviolet visible spectroscopy (UV–vis), transmisson electron microscopy (TEM), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), surface enhanced Raman scattering (SERS) and cyclic voltammetry (CV). The UV–vis characteristic absorbances of {PEI–Ag/Au}_n nanocomposite thin film increase almost linear with the number of bilayers, which indicates a process of uniform assembling. Appearance of a double plasmon bands in the visible region and the lack of apparent core–shell structures in the TEM images confirm the formation of bimetallic Au–Ag nanoparticles. The result of XPS also demonstrates the existence of Ag and Au nanoparticles in the nanocomposite films. TEM and FESEM images show that these Ag and Au nanoparticles in the films possess sphere structure with the size of 20–25 nm. The resulting {PEI–Ag/Au}_n films inherit the properties from both the metal Ag and Au, which exhibits a unique performance in SERS and electrocatalytic activities to the oxidation of dopamine. As a result, the {PEI–Ag/Au}_n films are more attractive compared to {PEI–Ag/PSS}_n and {PEI/Au}_n films.     

Fabrication of L10 FePtAg nanoparticles and a study of the effect of Ag during the annealing process

L1₀ ferromagnetic phase FePt nanoparticles containing Ag atoms (FePtAg) were synthesized by means of a liquid phase process, followed by annealing. The addition of Ag to FePt nanoparticles permits annealing to be conducted at a lower temperature (350 °C). This is further accompanied by a subsequent transformation in the crystal phase from the FCC superparamagnetic phase to the FCT (L1₀) ferromagnetic phase. The effects of annealing temperature and the Ag atoms inside the nanoparticles on the magnetic properties of the FePt nanoparticles have been studied. Using electron spectroscopy for the chemical analysis (ESCA), Ag atoms in the L1₀ phase FePtAg nanoparticles were found to be localized on the surface region of the annealed nanoparticles. The Ag atoms function to inhibit the oxidation of FePt, causing the particles to become more stable and to have ferromagnetic properties.     

Synthesis and characterization of bovine femur bone hydroxyapatite containing silver nanoparticles for the biomedical applications

Bovine femur bone hydroxyapatite (HA) containing silver (Ag) nanoparticles was synthesized by thermal decomposition method and subsequent reduction of silver nitrate with N,N-dimethylformamide (DMF) in the presence of poly(vinylacetate) (PVAc). The structural, morphological, and chemical properties of the HA–Ag nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). TEM images showed that the Ag nanoparticles with size ranging from 8 to 20 nm and were arranged at the periphery of HA crystals. Bactericidal activity of HA–Ag with different concentration of Ag nanoparticles immobilized on the surface of HA was investigated against gram-positive Staphylococcus aureus (S. aureus, non-MRSA), Methicillin resistant S. aureus (MRSA) and gram-negative Escherichia coli (E. coli) by the disc diffusion susceptibility test. The HA–Ag nanoparticles showed that broad spectrum activity against non-MRSA, MRSA, and E. coli bacterial strains.     

Latex-mediated synthesis of ZnS nanoparticles: green synthesis approach

A low-cost, green synthesis of ZnS nanoparticles is reported using 0.3 % latex solution prepared from Jatropha curcas L. ZnS nanoparticles were characterized by X-ray diffraction, selected area electron diffraction, transmission electron microscopy, energy dispersive analysis of X-rays, UV–vis optical absorption and photoluminescence techniques. Fourier Transform Infrared Spectroscopy was performed to find the role of cyclic peptides namely curcacycline A (an octapeptide), curcacycline B (a nonapeptide) and curcain (an enzyme) as a possible reducing and stabilizing agents present in the latex of J. curcas L. The average size of ZnS nanoparticles was found to be 10 nm. Latex of J. curcas L. itself acts as a source of sulphide (S⁻²) ions that are donated to Zn ions under present experimental conditions. Source of sulphide (S⁻²) ions is still unclear, but we speculate that cysteine or thiol residues present in enzyme curcain may be donating these sulphide (S⁻²) ions.     

An insight into the effect of composition for enhance catalytic performance of biogenic Au/Ag bimetallic nanoparticles

A comprehensive knowledge of composition‐activity property relationship of nanoparticulate materials is highly desirable for applications in various catalysis reactions. We have addressed a facile green aqueous approach for preparation of Au, Ag monometallic, Au/Ag alloy as well as core‐shell bimetallic nanoparticles. The phytochemicals present in lemon grass leaves extract were employed both as natural reducing and capping agents at room temperature. X‐ray diffraction pattern, UV‐Vis spectroscopy, and energy dispersive X‐ray studies confirmed the formation of bimetallic system. The ensuing Au core/Ag shell and Au/Ag alloy bimetallic nanoparticles were crystalline and spherical in nature with identical average diameter of ~ 18 nm as measured via transmission electron microscopy. The bimetallic systems incredibly display higher catalytic potential than their monometallic counterparts which were vividly reckoned on structural effect, lattice compression, and synergistic electronic effect.     

Facile preparation of Au/Ag bimetallic hollow nanospheres and its application in surface-enhanced Raman scattering

In this paper, an Au/Ag bimetallic hollow nanostructure was obtained by using SiO₂ nanospheres as sacrificial templates. The nanostructure was fabricated via a three steps method. SiO₂@Au nanospheres were first synthesized by the layer-by-layer technique, and then they were coated with a layer of Ag particles, finally, the Au/Ag bimetallic hollow nanospheres were obtained by dissolution of the SiO₂ core by exposure in HF solution. Several characterizations, such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and UV visible absorption spectroscopy were used to investigate the prepared nanostructures. The effectiveness of these Au/Ag bimetallic hollow nanospheres as substrates toward surface-enhanced Raman scattering (SERS) detection was evaluated by using rhodamine 6G (R6G) as a probe molecule. We show that such Au/Ag bimetallic hollow nanospheres structure films which consisting of larger interconnected aggregates are highly desirable as SERS substrates in terms of high Raman intensity enhancement. The Au/Ag bimetallic hollow nanostructured aggregate, interconnected nanostructured aggregate and nanoscale roughness are important factors responsible for this large SERS enhancement ability.     

Laser ablation of silver and gold in liquid ammonia

Laser ablation of a silver (Ag) and/or gold (Au) target was performed in liquid ammonia (l-NH₃) at 233 K using nanosecond laser pulses of 1064, 532 and 355 nm wavelengths. An “in situ” monitoring of the ablation process by UV/vis/NIR spectroscopy has shown the evolution of the surface plasmon extinction band of silver or gold nanoparticles and thus confirmed their formation. While sols of Au nanoparticles in l-NH₃ are quite stable in air, those of Ag nanoparticles undergo oxidation to Ag(I) complexes with NH₃ ligands. On the other hand, formation of solvated electrons, namely of the (e⁻)NH₃ solvates, has not been unequivocally confirmed under the conditions of our laser ablation/nanoparticle fragmentation experiment, since only very weak vis/NIR spectral features of these solvates were observed with a low reproducibility. Reference experiments have shown that the well-known chemical production of these solvates is hindered by the presence of Ag and Au plates. Ag and Au targets can thus possibly act as electron scavengers in our ablation experiments.     

Individual SERS substrate with core–satellite structure decorated in shrinkable hydrogel template for pesticide detection

Individual Au@PNIPAM/Ag composite has been designed and fabricated as surface‐enhanced Raman scattering (SERS) substrate in this paper. Because of the high porosity of the polymer shell and the driving force of the Au core to Ag⁺(H₂O)_n (n = 1–4) in aqueous solution, chemical reactions can be carried out while aggregation is completely avoided. Also, this makes the formation of vast and monodisperse Ag nanoparticles within PNIPAM and increases the colloidal stability. The Au cores with different sizes and the vast Ag nanoparticles then form core–satellite structures that can generate plasmon resonance. Moreover, this kind of individual Au@PNIPAM/Ag composite can be seen directly through Raman optical microscope, and uncertain effects on SERS signals resulting from variability of the configurations are minimized because these individual composite particles are relatively uniform. Importantly, the gaps between the Au and Ag nanoparticles can decrease because the PNIPAM shrinks from swollen to collapse state, so the substrate can also be used for inspecting pesticide residues accurately and rapidly. Copyright © 2014 John Wiley & Sons, Ltd.     

Metal nanoparticle-doped coloured films on glass and polycarbonate substrates

In a program on the development of metal (e.g. Au, Ag, Cu and their alloy) nanoparticles in sol-gel derived films, attempts were made to synthesize different coloured coatings on glasses and plastics. The absorption position of surface plasmon resonance (SPR) band arising from the embedded metal nanoparticles was tailored by controlling the refractive index of the matrix for the development of different colours. Thus different coloured (pink to blue) coatings on ordinary sheet glasses were prepared by generating Au nanoparticles in mixed SiO₂-TiO₂ matrices having refractive index values ranging from about 1.41 to 1.93. In another development,in situ generation of Ag nanoparticles in the inorganic-organic hybrid host leads to the formation of different abrasion resistant coloured coatings (yellow to pink) on polycarbonate substrates after curing. As expected, the SPR peak of Ag or Au is gradually red-shifted due to the increase of refractive index of the coating matrices causing a systematic change of colour     

Design of Enhanced Catalysts by Coupling of Noble Metals (Au,Ag) with Semiconductor SnO2 for Catalytic Reduction of 4‐Nitrophenol

The reduction of 4‐nitrophenol (Nip) into 4‐aminophenol (Amp) by NaBH₄, which is catalyzed by both binary and ternary yolk–shell noble‐metal/SnO₂ heterostructures, is reported. The binary heterostructures contain individual Au or Ag nanoparticles (NPs) and the ternary heterostructures contain both Au and Ag NPs. The Au@SnO₂ yolk–shell NPs are synthesized via a silica seeds‐mediated hydrothermal method. Subsequently, the Au@SnO₂@Ag and Au@SnO₂@Au yolk–shell–shell (YSS) NPs are synthesized, whereby SnO₂ is located between the Au and Ag NPs. The morphology, composition, and optical properties of the as‐prepared samples are analyzed. For the binary heterostructures, the rate of the reduction reaction increases with decreasing particle size. The catalytic results demonstrate the synergistic effect of Au and Ag in the ternary metal–semiconductor heterostructures, which is beneficial to the catalytic reduction of Nip into Amp. Both the binary and ternary heterostructures exhibit significantly better catalytic performances than the corresponding bare Au and Ag NPs. It is envisaged that the current synthesized strategy will promote further interest in the field of bimetal NP‐based catalysis.     

Insight into growth of Au–Pt bimetallic nanoparticles: an in situ XAS study

Au–Pt bimetallic nanoparticles have been synthesized through a one‐pot synthesis route from their respective chloride precursors using block copolymer as a stabilizer. Growth of the nanoparticles has been studied by simultaneous in situ measurement of X‐ray absorption spectroscopy (XAS) and UV–Vis spectroscopy at the energy‐dispersive EXAFS beamline (BL‐08) at Indus‐2 SRS at RRCAT, Indore, India. In situ XAS spectra, comprising both X‐ray near‐edge structure (XANES) and extended X‐ray absorption fine‐structure (EXAFS) parts, have been measured simultaneously at the Au and Pt L₃‐edges. While the XANES spectra of the precursors provide real‐time information on the reduction process, the EXAFS spectra reveal the structure of the clusters formed in the intermediate stages of growth. This insight into the formation process throws light on how the difference in the reduction potential of the two precursors could be used to obtain the core–shell‐type configuration of a bimetallic alloy in a one‐pot synthesis method. The core–shell‐type structure of the nanoparticles has also been confirmed by ex situ energy‐dispersive spectroscopy line‐scan and X‐ray photoelectron spectroscopy measurements with in situ ion etching on fully formed nanoparticles.     

Photoluminescence of Cu:ZnS, Ag:ZnS, and Au:ZnS nanoparticles applied in Bio-LED

In this work, transition elements, including Cu²⁺, Ag⁺, and Au³⁺, were used to dope in zinc sulfide (ZnS) by chemical solution synthesis to prepare Cu:ZnS, Ag:ZnS, and Au:ZnS nanoparticles, respectively. Transition elements doping ZnS nanoparticles form the electronic energy level between the conduction band and valance band, which will result in the green light emission. There is a zinc sulfide emission shift from blue (~3.01 eV) to green light (~2.15 eV). We also found that Au:ZnS nanoparticles will emit a green light (~2.3 eV) and a blue light (~2.92 eV) at the same time because the mechanism of blue light emission was not broken after Au element had been doped. Furthermore, we used sodium chlorophyllin copper salt to simulate chlorophyll in biological light emission devices (Bio-LED). We combined copper chlorophyll with Cu:ZnS, Ag:ZnS, and Au:ZnS nanoparticles by a self-assembly method. Then, we measured its photoluminescence spectroscopy and X-ray photoelectron spectroscopy to study its emission spectrum and bonding mode. We found that Au:ZnS nanoparticles are able to emit green and blue light to excite the red light emission of copper chlorophyll, which is a potential application of Bio-LED.     

Preparation of large-area surface-enhanced Raman scattering active Ag and Ag/Au nanocomposite films

Ag films on tinning glass substrates were fabricated by modified silver-mirror (Tollen’s) reaction with the advantage of low-cost, simple and quick fabrication process. The obtained Ag films were served as sacrificial materials for preparation of Ag/Au nanocomposite films by immersing in a chlorauric acid (HAuCl₄) solution at room temperature. After a short time of galvanic replacement reaction, Ag/Au bimetallic nanostructures were synthesized with “concave” structures. The morphology, properties and composition of the Ag and Ag/Au nanocomposite films were analyzed by using scanning electron microscopy (SEM), UV-visible spectroscopy, X-ray diffraction (XRD), energy-dispersive X-ray spectrometry (EDS) and surface enhanced Raman scattering (SERS). SEM images displayed that the large area of Ag film and Ag/Au bimetallic nanostructures experienced structural evolution process during galvanic reaction. The UV-Vis spectra showed the absorbencies characterization of Ag film and Ag/Au nanocomposite films. SERS measurements using methylene blue as an analyte showed that SERS intensities of bimetallic films were enhanced significantly compared with that of pure Ag films. The SERS enhancement ability of Ag/Au bimetallic films was dependent on the immersion time for galvanic replacement reaction.     

Silver,gold and the corresponding core shell nanoparticles: synthesis and characterization

Simple strategies for producing silver and gold nanoparticles (AgNP and AuNP) along with the corresponding core shell nanoparticles (Au–Ag and Ag–Au) by reduction of the metal salts AgBF₄ and HAuCl₄ by NaBH₄ in water will be presented. The morphologies of the obtained nanoparticles are determined by the order of addition of reactants. The obtained NPs, with sizes in the range 3–40 nm, are characterized by transmission electronic microscopy (TEM) and UV–Vis absorption spectroscopy, so as to evaluate their qualities. Moreover, a direct electrochemical detection protocol based on a cyclic voltammetry in water solution that involves the use of glassy carbon electrode is also applied to characterize the prepared NPs. The developed NPs and the related electroanalytical method seem to be with interest for future sensing and biosensing applications including DNA sensors and immunosensors.     

Protection of iron against corrosion by coverage with Au nanoparticles and n-hexylthiol mixed films

Through a one-step thermal reaction, Au nanoparticles were synthesized and self-assembled mixed films of Au nanoparticles and n-hexylthiol were prepared on iron surface. The size distribution and shape of Au nanoparticles were examined using transmission electron microscopy (TEM). Results of two electrochemical methods - electrochemical impedance spectroscopy (EIS) and polarization curves indicate that self-assembled mixed films can form on the iron surface and prevent it from corrosion effectively. Energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) measurements were applied to identify the formation of the mixed films on iron surface.     

Biosynthesis of gold and silver nanoparticles by natural precursor clove and their functionalization with amine group

We report a simple and cost effective way for synthesis of metallic nanoparticles (Au and Ag) using natural precursor clove. Au and Ag nanoparticles have been synthesized by reducing the aqueous solution of AuCl₄ and AgNO₃ with clove extract. One interesting aspect here is that reduction time is quite small (few minutes instead of hours as compared to other natural precursors). We synthesized gold and silver nanoparticles of different shape and size by varying the ratio of AuCl₄ and AgNO₃ with respect to clove extract, where the dominant component is eugenol. The evolution of Au and Ag nanoparticles from the reduction of different ratios of AuCl₄ and AgNO₃ with optimised concentration of the clove extract has been evaluated through monitoring of surface plasmon behaviour as a function of time. The reduction of AuCl₄ and AgNO₃ by eugenol is because of the inductive effect of methoxy and allyl groups which are present at ortho and para positions of proton releasing –OH group as two electrons are released from one molecule of eugenol. This is followed by the formation of resonating structure of the anionic form of eugenol. The presence of methoxy and allyl groups has been confirmed by FTIR. To the best of our knowledge, use of clove as reducing agent, the consequent very short time (minutes instead of hours and without any scavenger) and the elucidation of mechanism of reduction based on FTIR analysis has not been attempted earlier.     

Synthesis and characterization of composite Au/TiO2 nanoparticles by laser irradiation

Composite Au/TiO₂ nanoparticles were synthesized by laser ablation of gold plate in TiO₂ sol. The nanoparticles were characterized by UV-visible spectroscopy, transmission electron microscopy, X-ray diffraction, and atomic force microscopy. The peak of surface plasmon is at 550 nm with a red shift of 30 nm compared with that of Au nanoparticles in water. Monolayers of composite Au/TiO₂ nanoparticles were obtained by dip-coating technique. The XRD pattern of Au/TiO₂ powders resembles a mixture of anatase TiO₂ and gold.     

The mechanism of metal nanoparticle formation in plants: limits on accumulation

Metal nanoparticles have many potential technological applications. Biological routes to the synthesis of these particles have been proposed including production by vascular plants, known as phytoextraction. While many studies have looked at metal uptake by plants, particularly with regard to phytoremediation and hyperaccumulation, few have distinguished between metal deposition and metal salt accumulation. This work describes the uptake of AgNO₃, Na₃Ag(S₂O₃)₂, and Ag(NH₃)₂NO₃ solutions by hydroponically grown Brassica juncea and the quantitative measurement of the conversion of these salts to silver metal nanoparticles. Using X-ray absorption near edge spectroscopy (XANES) to determine the metal speciation within the plants, combined with atomic absorption spectroscopy (AAS) for total Ag, the quantity of reduction of Ag^I to Ag⁰ is reported. Transmission electron microscopy (TEM) showed Ag particles of 2–35 nm. The factors controlling the amount of silver accumulated are revealed. It is found that there is a limit on the amount of metal nanoparticles that may be deposited, of about 0.35 wt.% Ag on a dry plant basis, and that higher levels of silver are obtained only by the concentration of metal salts within the plant, not by deposition of metal. The limit on metal nanoparticle accumulation, across a range of metals, is proposed to be controlled by the total reducing capacity of the plant for the reduction potential of the metal species and limited to reactions occurring at an electrochemical potential greater than 0 V (verses the standard hydrogen electrode).     

Plasmonics properties of trimetallic Al@Al2O3@Ag@Au and Al@Al2O3@AuAg nanostructures

Bimetallic and trimetallic nanoparticles have attracted significant attention in recent times due to their enhanced electrochemical and catalytic properties compared to monometallic nanoparticles. The numerical calculations using Mie theory has been carried out for three-layered metal nanoshell dielectric–metal–metal (DMM) system consisting of a particle with a dielectric core (Al@Al₂O₃), a middle metal Ag (Au) layer and an outer metal Au (Ag) shell. The results have been interpreted using plasmon hybridization theory. We have also prepared Al@Al₂O₃@Ag@Au and Al@Al₂O₃@AgAu triple-layered core–shell or alloy nanostructure by two-step laser ablation method and compared with calculated results. The synthesis involves temporal separations of Al, Ag, and Au deposition for step-by-step formation of triple-layered core–shell structure. To form Al@Ag nanoparticles, we ablated silver for 40 min in aluminium nanoparticle colloidal solution. As aluminium oxidizes easily in water to form alumina, the resulting structure is core–shell Al@Al₂O₃. The Al@Al₂O₃ particle acts as a seed for the incoming energetic silver particles for multilayered Al@Al₂O₃@Ag nanoparticles is formed. The silver target was then replaced by gold target and ablation was carried out for different ablation time using different laser energy for generation of Al@Al₂O₃@Ag@Au core–shell or Al@Al₂O₃@AgAu alloy. The formation of core–shell and alloy nanostructure was confirmed by UV–visible spectroscopy. The absorption spectra show shift in plasmon resonance peak of silver to gold in the range 400–520 nm with increasing ablation time suggesting formation of Ag–Au alloy in the presence of alumina particles in the solution.