Search Results (10)

The utilization of nano-sized drug delivery systems in herbal drug delivery systems has a promising future for improving drug effectiveness and overcoming issues connected with herbal medicine. As a consequence, the use of nanocarriers as novel drug delivery systems for the improvement of traditional medicine is critical to combating infectious diseases globally. In line with this, we herein report the biosynthesis of silver nanoparticles (AgNPs), gold nanoparticles (AuNPs), and bimetallic nanoparticles (BMNPs) as antibacterial agents against pathogenic bacterial strains using Annona squamosa L. leaf extract as a bio-reductant and bio-stabilizing agent. The as-synthesized metal nanoparticles were characterized by transmission electron microscopy (TEM), ultraviolet–visible (UV–Vis) absorption spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and the dynamic light scattering (DLS) method. The as-synthesized MNPs had an average particle size of 6.98 nm ± 2.86 nm (AgNPs), 21.84 ± 8.72 nm (AuNPs), and 2.05 nm ± 0.76 nm (BMNPs). The as-synthesized AgNPs and BMNPs showed good antibacterial activity against pathogenic bacterial strains of Gram-positive Staphylococcus aureus (ATCC 25923) and Gram-negative Escherichia coli (ATCC 25922). The obtained results offer insight into the development of benign nanoparticles as safe antibacterial agents for antibiotic therapy using Annona squamosa L. leaf extract. Full article

Microwave irradiation is widely used to intensify various chemical processes, including in the synthesis of nanomaterials. The purpose of this review is to present recent trends in the application of microwave heating for the preparation of monometallic, bimetallic, and more complicated metal nanoparticles. The advantages and drawbacks behind the use of microwave irradiation in the synthesis of unsupported and supported metal nanoparticles are summarized. Such metals as Ag, Au, Pt, Pd, Rh, Ir, Cu, Ni, Co, etc. are considered. Illustrative examples have been presented of the positive effects of microwave treatments, including the preparation of particles of different shapes and particles of immiscible metals. Full article

The electrocatalytic oxidation of glycerol by metal electrocatalysts is an effective method of low-energy-input hydrogen production in membrane reactors in alkaline conditions. The aim of the present study is to examine the proof of concept for the gamma-radiolysis-assisted direct growth of monometallic gold and bimetallic gold–silver nanostructured particles. We revised the gamma radiolysis procedure to generate free-standing Au and Au-Ag nano- and micro-structured particles onto a gas diffusion electrode by the immersion of the substrate in the reaction mixture. The metal particles were synthesized by radiolysis on a flat carbon paper in the presence of capping agents. We have integrated different methods (SEM, EDX, XPS, XRD, ICP-OES, CV, and EIS) to examine in detail the as-synthesized materials and interrogate their electrocatalytic efficiency for glycerol oxidation under baseline conditions to establish a structure–performance relationship. The developed strategy can be easily extended to the synthesis by radiolysis of other types of ready-to-use metal electrocatalysts as advanced electrode materials for heterogeneous catalysis. Full article

In the present project, fructose-stabilized gold, silver and gold–silver bimetallic colloids have been synthesized by the electrochemical reduction of HAuCl₄·3H₂O (Au precursor) and AgNO₃ (Ag precursor), employing the atmospheric pressure microplasma technique. X-Ray Diffraction patterns of gold–silver bimetallic particles exhibit (111), (200) and (220) planes identical to gold and silver NPs depicting FCC structures. The decrease in the peak intensities of Au–Ag (111) and Au–Ag (200) as compared to those of Au (111) and (200) is due to the formation of Au–Ag alloys. The FE-SEM image of gold–silver bimetallic NPs has revealed an adequate change in morphology as compared to the morphology of gold NPs and silver NPs. The majority of the gold–silver bimetallic NPs are spherical and are uniformly dispersed. The EDS spectra of (Au–Ag) confirm the presence of metallic gold and silver. The appearance of a single Surface Plasmon Resonance (SPR) peak in the UV–VIS absorption spectra of gold–silver colloids and its position in between the SPR peaks of the UV–VIS absorption spectra of gold and silver colloids justify the formation of gold–silver bimetallic alloy particles. In DLS measurements, the size distribution of gold–silver bimetallic colloids carries a narrow range 55 to 117 nm as compared to the size distribution of gold and silver colloids. The compatibility of the sizes of these colloids and the influenza virus belonging to the Orthomyxoviruses family (size range 80–300 nm with different morphologies) are assumed to stand responsible for an effective bio-conjunction with Influenza viruses. Au–Ag bimetallic nanostructures have synergistically improved their antiviral activity against H9N2 influenza virus as compared to monometallic AuNPs and AgNPs. Thus, the Au–Ag nanostructured alliance has been proven to be more effective and is capable of manifesting high antiviral efficacy. Full article

Wastewaters from precious metal industries contain high amounts of noble metals, but their efficient recycling is hindered by the wastewater complex composition. Here, we propose an innovative approach for the efficient recovery of noble metals contained in these metal-enriched wastewaters as precursors for the synthesis of noble metal nanoparticles (NPs) and supported metal catalysts. Silver NPs were synthesized from Ag-enriched wastewater and then deposited on TiO₂ to prepare photocatalysts. Then, further promotion of the photocatalytic activity of Ag-modified TiO₂ was achieved by the addition of as little as 0.5 wt.% of Au. STEM-EDS analyses proved that Au NPs were located on Ag or AgO_x nanoparticles. The contact between the two metal-containing NPs results in charge transfer effects, appreciable both in terms of oxidation states determined by XPS and of optical properties. In particular, the plasmon band of Au NPs shows photochromic effects: under UV light irradiation, bimetallic samples exhibit a blue-shift of the plasmon band, which is reversible under dark storage. The activity of the materials was tested towards ethanol photodegradation under UV light. Adding 0.5 wt.% Au NPs resulted in a promoted activity compared to Ag-TiO₂, thus showing synergistic effects between Au and Ag. Ethanol was completely converted already after 1 h of UV irradiation, acetaldehyde was formed as the main oxidation product and fully degraded in less than 180 min. Notably, bimetallic samples showed ethylene formation by a parallel dehydration mechanism. Full article

The present study reports a green chemistry approach for the rapid and easy biological synthesis of silver (Ag), gold (Au), and bimetallic Ag/Au nanoparticles using the callus extract of Lithospermum erythrorhizon as a reducing and capping agent. The biosynthesized nanoparticles were characterized with ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD) analysis, and transmission electron microscopy (TEM). Our results showed the formation of crystalline metal nanostructures of both spherical and non-spherical shape. Energy dispersive X-ray (EDX) spectroscopy showed the characteristic peaks in the silver and gold regions, confirming the presence of the corresponding elements in the monometallic particles and both elements in the bimetallic particles. Fourier-transform infrared (FTIR) spectroscopy affirmed the role of polysaccharides and polyphenols of the L. erythrorhizon extract as the major reducing and capping agents for metal ions. In addition, our results showed that the polysaccharide sample and the fraction containing secondary metabolites isolated from L. erythrorhizon were both able to produce large amounts of metallic nanoparticles. The biosynthesized nanoparticles demonstrated cytotoxicity against mouse neuroblastoma and embryonic fibroblast cells, which was considerably higher for Ag nanoparticles and for bimetallic Ag/Au nanoparticles containing a higher molar ratio of silver. However, fibroblast migration was not significantly affected by any of the nanoparticles tested. The obtained results provide a new example of the safe biological production of metallic nanoparticles, but further study is required to uncover the mechanism of their toxicity so that the biomedical potency can be assessed. Full article

Two noble metals, such as silver and gold alloy nanoparticles, were successfully synthesized by the microwave assisted method in the presence of the Asparagus racemosus root extract and were used as an antibacterial and immunomodulatory agent. The nanostuctures of the synthesized nanoparticles were confirmed by various spectroscopic and microscopic techniques. The UV-vis spectrum exhibits a distinct absorption peak at 483 nm for the bimetallic alloy nanoparticles. The microscopic analysis revealed the spherical shaped morphology of the biosynthesized nanoparticles with a particle size of 10–50 nm. The antibacterial potential of the green synthesized single metal (AgNPs and AuNPs) and bimetallic alloy nanoparticles was tested against five bacterial strains. The bimetallic alloy nanoparticles displayed the highest zone of inhibition against P. aeurgnosia and S.aureus strains when compared to single metal nanoparticles and plant extract. In addition, the inmmunomodulatory potential of the root extract of A. racemosus, AgNPs, AuNPs, and Ag-Au alloy NPs is achieved by measuring the cytokine levels in macrophages (IL-1β, IL-6, and TNF-α) and NK cells (IFN-γ) of NK92 and THP1 cells using the solid phase sandwich ELISA technique. The results showed that the root extract of A. racemosus, AgNPs, and AuNPs can reduce the pro-inflammatory cytokine levels in the macrophages cells, while Ag-Au alloy NPs can reduce cytokine responses in NK92 cells. Overall, this study shows that the microwave assisted biogenic synthesized bimetallic nanoalloy nanoparticles could be further explored for the development of antibacterial and anti-inflammatory therapies. Full article

The metal-organic zeolite imidazolate framework-8 (ZIF-8) supported gold-silver bimetallic catalysts with a core-shell structure (Au@Ag/ZIF-8 and Ag@Au/ZIF-8) and cluster structure (AuAg/ZIF-8) were successfully prepared by the deposition-redispersion method. Energy dispersive X-ray spectroscopy (EDS) elemental mapping images displayed that in the Au@Ag/ZIF-8 catalyst, Ag atoms were deposited on an exposed Au surface, and core-shell structured Au@Ag particles with highly dispersed Ag as the shell were formed. Additionally, the XPS investigation at gold 4f levels and silver 3d levels indicated that the Au and Ag particles of Au@Ag/ZIF-8, Ag@Au/ZIF-8, and AuAg/ZIF-8 were in a zero valence state. Among the resultant catalysts obtained in this study, Ag@Au/ZIF-8 catalysts showed the highest catalytic activity for the selective oxidation of benzyl alcohol, followed by AuAg/ZIF-8 and Au@Ag/ZIF-8. The turnover frequency (TOF) values were in the order of Ag@Au/ZIF-8 (28.2 h⁻¹) > AuAg/ZIF-8 (25.0 h⁻¹) > Au@Ag/ZIF-8 (20.0 h⁻¹) at 130 °C within 1 h under 8 bar O₂ when using THF as solvent. The catalysts of Au@Ag/ZIF-8 and Ag@Au/ZIF-8 with core–shell structures have higher benzaldehyde selectivities (53.0% and 53.3%) than the AuAg/ZIF-8 catalyst (35.2%) in the selective oxidation of benzyl alcohol into benzaldehyde. The effect of the solvent, reaction temperature, reaction time, and reaction pressure on benzyl alcohol conversion and benzaldehyde selectivity in benzyl alcohol selective oxidation over Au@Ag/ZIF-8, Ag@Au/ZIF-8, and AuAg/ZIF-8 were also investigated. All of the catalysts showed excellent performance at 130 °C under 8 bar O₂ within 1 h when using THF as the solvent in the selective oxidation of benzyl alcohol to benzaldehyde. Moreover, the catalysts can be easily recycled and used repetitively at least four times. Full article

In this work, a facile, environmentally friendly method was demonstrated for the synthesis of Ag-Au bimetallic nanoparticles (Ag-AuNPs) supported on reduced graphene oxide (RGO) with alginate as reductant and stabilizer. The prepared Ag-AuNPs/RGO was characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results indicated that uniform, spherical Ag-AuNPs was evenly dispersed on graphene surface and the average particle size is about 15 nm. Further, a non-enzymatic sensor was subsequently constructed through the modified electrode with the synthesized Ag-AuNPs/RGO. The sensor showed excellent performance toward H₂O₂ with a sensitivity of 112.05 μA·cm⁻²·mM⁻¹, a linear range of 0.1–10 mM, and a low detection limit of 0.57 μM (S/N = 3). Additionally, the sensor displayed high sensitivity, selectivity, and stability for the detection of H₂O₂. The results demonstrated that Ag-AuNPs/RGO has potential applications as sensing material for quantitative determination of H₂O₂. Full article

Herein we report a simple and green synthesis of smart Au and Ag@Au nanocomposite particles using poly(N-isopropylacrylamide)/polyethyleneimine (PNIPAm/PEI) core-shell microgels as dual reductant and templates in an aqueous system. The nanocomposite particles were synthesized through a spontaneous reduction of tetrachloroauric (III) acid to gold nanoparticles at room temperature, and in situ encapsulation and stabilization of the resultant gold nanoparticles (AuNPs) with amine-rich PEI shells. The preformed gold nanoparticles then acted as seed nanoparticles for further generation of Ag@Au bimetallic nanoparticles within the microgel templates at 60 °C. These nanocomposite particles were characterized by TEM, AFM, XPS, UV-vis spectroscopy, zeta-potential, and particle size analysis. The synergistic effects of the smart nanocomposite particles were studied via the reduction of p-nitrophenol to p-aminophenol. The catalytic performance of the bimetallic Ag@Au nanocomposite particles was 25-fold higher than that of the monometallic Au nanoparticles. Finally, the controllable catalytic activities of the Au@PNIPAm/PEI nanocomposite particles were demonstrated via tuning the solution pH and temperature. Full article