Synthesis Of Noble Metal Nanoparticles Research Articles

Opportunities and Challenges in the Synthesis of Noble Metal Nanoparticles via the Chemical Route in Microreactor Systems.

The process of noble metal nanoparticle synthesis is complex and consists of at least two steps: slow nucleation and fast autocatalytic growth. The kinetics of these two processes depends on the reductant "power" and the addition of stabilizers, as well as other factors (e.g., temperature, pH, ionic strength). Knowing these parameters, it is possible to synthesize materials with appropriate physicochemical properties, which can be simply adjusted by the type of the used metal, particle morphology and surface property. This, in turn, affects the possibility of their applications in various areas of life, including medicine, catalysis, engineering, fuel cells, etc. However, in some cases, the standard route, i.e., the chemical reduction of a metal precursor carried out in the batch reactor, is not sufficient due to problems with temperature control, properties of reagents, unstable or dangerous intermediates and products, etc. Therefore, in this review, we focused on an alternative approach to their chemical synthesis provided by microreactor systems. The use of microreactors for the synthesis of noble metal nanomaterials (e.g., Ag, Au, Pt, Pd), obtained by chemical reduction, is analyzed, taking into account investigations carried out in recent years. A particular emphasis is placed on the processes in which the use of microreactors removed the limitations associated with synthesis in a batch reactor. Moreover, the opportunities and challenges related to the synthesis of noble nanomaterials in the microreactor system are underlined. This review discusses the advantages as well as the problems of nanoparticle synthesis in microreactors.

Synthesis of sustainable silver nanoparticles using plant extract and their antimicrobial, anticancer, and photocatalytic dye degradation efficiency analysis

The green synthesis of noble metal nanoparticles has gained a lot of interest in the area of nanotechnology, because of its high therapeutic properties. The present study focussed on the synthesis of the silver nanoparticles (Ag-NPs) using Ceropegia debilis leaf extract and characterized by various physio-chemical techniques and surface morphological studies. The prepared Ag-NPs exhibit a face-centred cubic structure, spherical morphology, and high purity as shown by XRD, SEM, and EDS analyses. The average size of the Ag-NPs was confirmed by TEM study as 18.6 ± 7.5 nm. The synthesized Ag-NPs show remarkable antioxidant activity of 72.1% compared to standard BHT 86.9%. Furthermore, Ag-NPs show remarkable cytotoxic properties against MCF 7 and A 549 cell line of 37.19% and 33.33%, respectively at 250 µg/mL. The antibacterial activity of Ag-NPs was investigated against the human pathogen and intestinal pathogen Staphylococcus aureus and Escherichia coli by agar disc diffusion method. Moreover, the synthesised Ag-NPs exhibit good antifungal properties against the fungal specimen Trichoderma viride assessed by well diffusion technique. In addition, Ag-NPs serve as an excellent nanocatalyst in the removal of toxic methylene blue dye (93.2%) from industrial wastewater under sunlight irradiation.

Green synthesis of silver nanoparticles using Illicium verum extract: Optimization and characterization for biomedical applications

Abstract The synthesis of noble metal nanoparticles is currently experiencing substantial development and considerable attention. Plant extracts are commonly used for the biological synthesis of nanoparticles because they contain biologically active constituents. In our present study, silver nanoparticles (AgNPs) were synthesized using an aqueous Illicium verum (Star anise) extract to evaluate their antimicrobial, antioxidant, and cytotoxicity activities. For maximum yields of AgNPs, the extract (2.5 ml), silver ions (500 µM), and pH (8) were shown to be the ideal nanoparticle production parameters. The visual colour shifted from pale brown to dark brown when the ultraviolet-visible spectrophotometer was used to validate the synthesis of AgNPs. A transmission electron microscope was utilized to evaluate nanoparticles’ physical nature. The presence of silver metal with face-centred cubic symmetry was confirmed by X-ray diffraction analysis. Fourier-transform infrared spectroscopy was used to identify the functional groups in charge of reducing silver ions (Ag+) and the stability of AgNPs produced using the I. verum aqueous extract. The agar well diffusion method investigated the antibacterial activity of I. verum silver nanoparticles (Iv-AgNPs) against pathogenic bacteria and fungi. At higher doses (100 µg·mL−1), the highest zone of inhibition was observed, and spherical AgNPs demonstrated the antibacterial activity. The I. verum extract and Iv-AgNPs enhanced (70%) their free radical scavenging activity at 500 µg·mL−1 according to the 2,2-diphenyl-1-picrylhydrazyl assay. Moreover, the cytotoxicity of Iv-AgNPs against the HCT-116 human colon cancer cell line indicated cell inhibition in a dose-dependent manner. Ultimately, the findings of this study indicate that techniques used to produce AgNPs are environmental friendly, cost-effective, harmless, uncomplicated, and can effectively tackle a broad spectrum of medical and nutritional concerns.

A universal strategy for green and surfactant-free synthesis of noble metal nanoparticles.

We propose a universal, green, and surfactant-free strategy to synthesize noble metal particles with high monodispersity using gaseous H2 as a reducing agent in a solution at 60 °C. The prepared Pt nanoparticles have a 24 mV more positive half-wave potential than the commercially available Pt/C in the oxygen reduction reaction, while showing high durability with negligible half-wave potential decay after 10 000 cycles of testing.

Photochemical Synthesis of Noble Metal Nanoparticles: Influence of Metal Salt Concentration on Size and Distribution.

This paper explores the photochemical synthesis of noble metal nanoparticles, specifically gold (Au) and silver (Ag) nanoparticles, using a one-component photoinitiator system. The synthesis process involves visible light irradiation at a wavelength of 419 nm and an intensity of 250 mW/cm2. The radical-generating capabilities of the photoinitiators were evaluated using electron spin resonance (ESR) spectroscopy. The main objective of this study was to investigate how the concentration of metal salts influences the size and distribution of the nanoparticles. Proposed mechanisms for the photochemical formation of nanoparticles through photoinitiated radicals were validated using cyclic voltammetry. The results showed that the concentration of AgNO3 significantly impacted the size of silver nanoparticles, with diameters ranging from 1 to 5 nm at 1 wt% and 3 wt% concentrations, while increasing the concentration to 5 wt% led to an increase in the diameter of silver nanoparticles to 16 nm. When HAuCl4 was used instead of AgNO3, it was found that the average diameters of gold nanoparticles synthesized using both photoinitiators at different concentrations ranged between 1 and 4 nm. The findings suggest that variations in HAuCl4 concentration have minimal impact on the size of gold nanoparticles. The photoproduction of AuNPs was shown to be thermodynamically favorable, with the reduction of HAuCl4 to Au0 having ∆G values of approximately -3.51 and -2.96 eV for photoinitiators A and B, respectively. Furthermore, the photoreduction of Ag+1 to Ag0 was demonstrated to be thermodynamically feasible, with ∆G values of approximately -3.459 and -2.91 eV for photoinitiators A and B, respectively, confirming the effectiveness of the new photoinitiators on the production of nanoparticles. The synthesis of nanoparticles was monitored using UV-vis absorption spectroscopy, and their sizes were determined through particle size analysis of transmission electron microscopy (TEM) images.

Origin for the chloride and citrate ions tuned morphology of Pd particles

Capping agents such as halide and citrate (CA) are crucial in the colloidal synthesis of noble metal nanoparticles (NPs) with desirable shape for specific catalytic reaction. Halide ions have been shown to stabilize the cubic NP while CA ions favor the octahedral NP regardless of the noble metals, but the mechanism remains unclear. We combine DFT calculations and Wulff construction to understand how the morphology of Pd particle changes with Cl and CA chemical potential (μ). Three main factors are identified to affect the morphology of Pd particle: μ of adsorbate, its number per unit area (NAS/S), and rigidity or flexibility. Increasing μ of adsorbate or its NAS/S causes decreased surface free energy and increased exposed surface area. Moreover, rigid adsorbates (PdClx) occupy a larger surface area for surfaces with high atomic density such as Pd(111), leading to cubic Pd particle at high μCl. Conversely, flexible adsorbates (CA) that can adjust their structure based on the surface occupy smaller surface area on Pd(111), favoring octahedral Pd particle. This work reveals the origin for capping agent tuned morphology of Pd NP, and the insights can be used to guide metal NP synthesis with desired morphology for catalytic reactions of technological interest.

Review of Biological methods of AgNPs Synthesis

Recently, noble metal nanoparticle synthesis has become more advanced thanks to the growth of nanotechnology. The abundance and diversity of the biomolecules that function as capping and reducing agents in biological synthesis methods make them more advantageous than other traditional synthesis techniques in terms of cost and safety. Due to their safety and environmental friendliness, biosynthesized silver nanoparticles (AgNPs) show potential uses in a variety of disciplines. The results of reported studies on the green synthesis of Ag NPs employing various stem, fruit, and seed components have been compiled together with their effects on the morphological characteristics. This review is crucial for figuring out how to synthesize Ag NPs in a method that is regulated, less expensive, and ecologically benign.

Evaluation of cytotoxic activity against A549 human lung cancer cells using green synthesized N-Cholyl D-Penicillamine encapsulated silver and gold nanoparticles

Synthesis of noble metal nanoparticles (MNPs) using a biocompatible template provides a biologically safe, cost effective, and environment friendly approach in view of biomedical applications. In this manusctipt, synthesis of gold and silver nanoparticles (Au and Ag NPs) using N-cholyl D-penicilamine (NCPA) as an effective reducing and stabilizing agent at below the critical micellar concerntration (CMC) under sunlight exposure has been reported. The formation of NPs were optimized by changing the concentration of NCPA and pH of the medium. The synthesized Au and Ag NPs were characterized by UV-visible, FT-IR, DLS, Zeta potential and HR-TEM techniques. The average size of Au and Ag NPs were found to be 10.3 ± 0.4 and 9.1 ± 0.6 nm, respectively and exhibit stability for more than six month. The prepared NPs showed low toxicity on human erythrocytes (RBCs) even at their higher concentrations (120 μg/mL). The anticancer activity of NCPA capped NPs on A549 cells were investigated by cell viability assay, apoptosis analysis using MTT assay and Acridine Orange/Propidium Iodide (AO/PI) dual fluorescent staining asay. The results obtained from these studies suggest that the synthesized NPs showed potent cytotoxicity on A549 cells in a dose-dependent manner. Further, AgNPs showed better cytotoxicity as compared to AuNPs.

Characterization, catalytic, and recyclability studies of nano-sized spherical palladium particles synthesized using aqueous poly-extract (turmeric, neem, and tulasi)

Green synthesis of noble metal nanoparticles (NPs) has gained immense significance compared to other metal ions owing to their unique properties. Among them, palladium ‘Pd’ has been in the spotlight for its stable and superior catalytic activity. This work focuses on the synthesis of Pd NPs using the combined aqueous extract (poly-extract) of turmeric (rhizome), neem (leaves), and tulasi (leaves). The bio-synthesized Pd NPs were characterized to study its physicochemical and morphological features using several analytical techniques. Role of Pd NPs as nano-catalysts in the degradation of dyes (1 mg/2 mL stock solution) was evaluated in the presence of a strong reducing agent (sodium borohydride; SBH). In the presence of Pd NPs and SBH, maximum reduction of methylene blue (MB), methyl orange (MO), and rhodamine-B (Rh–B) dyes was observed under 20nullmin (96.55 ± 2.11%), 36nullmin (96.96 ± 2.24%), and 27nullmin (98.12 ± 1.33%), with degradation rate of 0.1789 ± 0.0273 min−1, 0.0926 ± 0.0102 min−1, and 0.1557 ± 0.0200 min−1, respectively. In combination of dyes (MB + MO + Rh–B), maximum degradation was observed under 50nullmin (95.49 ± 2.56%) with degradation rate of 0.0694 ± 0.0087 min−1. It was observed that degradation was following pseudo-first order reaction kinetics. Furthermore, Pd NPs showed good recyclability up to cycle 5 (72.88 ± 2.32%), cycle 9 (69.11 ± 2.19%) and cycle 6 (66.21 ± 2.72%) for MB, MO and Rh–B dyes, respectively. Whereas, up to cycle 4 (74.67 ± 0.66%) during combination of dyes. As Pd NPs showed good recyclability, they can be used for several cycles thus influencing the overall economics of the process.

Biogenic synthesis of noble metal nanoparticles using Melissa officinalis L. and Salvia officinalis L. extracts and evaluation of their biosafety potential

In this study we targeted the noble metal nanoparticles (MNPs) biogenic synthesis capacity of two medicinal species with therapeutic potential, namely Melissa officinalis L. (lemon balm) and Salvia officinalis L. (sage), cultivated in Romania. Plant material was extracted by maceration, microwave assisted extraction (MAE) and ultrasound assisted extraction (UAE). Bright field scanning transmission electron microscopy and energy dispersive X-ray spectroscopy (BFSTEM-EDS) techniques were used in order to investigate particles shape, dispersion and chemical elemental analysis. The total polyphenol content for both simple extracts and nanostructured mixtures was determined using the Folin-Ciocalteu method and antioxidant activity using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. Identification and quantification of secondary metabolites of M. officinalis and S. officinalis were performed by ultra-high performance liquid chromatography (UHPLC). The Allium assay was used to evaluate the potential cytogenotoxic activity, for both simple and nanostructured phytochemical complexes, in the case of S. officinalis L. species being performed for the first time. Spherical shaped MNPs with diameters of about 20 nm were biosynthesised in lemon balm extracts. Larger AuNPs were phytosynthesized in sage extract obtained by UAE. Compared to the simple extracts, the antioxidant capacity as well as the amount of total polyphenols in the nanostructured extracts decreased, substantiating the involvement of bioorganic material in the reduction of metal ions. Low frequency of chromosomal aberrations corresponding to crude extracts and extracts supplemented with MNPs, suggest the cytoprotective, antigenotoxic, and safe use of these plant species as potential therapeutic forms in various diseases.

Urethane functions can reduce metal salts under hydrothermal conditions: synthesis of noble metal nanoparticles on flexible sponges applied in semi-automated organic reduction.

We report an additive-free one-pot hydrothermal synthesis of Au, Ag, Pd, and alloy AuPd nanoparticles (NPs) anchored on commercial polyurethane (PU) foams. While unable to reduce the precursor metal salts at room temperature, PU is able to serve as a reducing agent under hydrothermal conditions. The resulting NP@PU sponge materials perform comparably to reported state-of-the-art reduction catalysts, and are additionally very well suited for use in semi-automated synthesis: the NP anchoring is strong enough and the support flexible enough to be used as a 'catalytic sponge' that can be manipulated with a robotic arm, i.e., be repeatedly dipped into and drawn out of solutions, wrung out, and re-soaked.

Surfactant Mediated Synthesis of Noble Metal Nanoparticles and Their Cytotoxic Effects on Breast Cancer Cells

Surfactant Mediated Synthesis of Noble Metal Nanoparticles and Their Cytotoxic Effects on Breast Cancer Cells

Acrylamide: New Organic Solvent with Chemically Tunable Viscosity for Rapid Gram-Scale Synthesis of Gold Nanoparticles.

Noble metal nanoparticles have demonstrated various biomedical, optical, and electronic applications owing to their unique chemical and physical properties. However, their gram-scale synthesis remains a challenge. We have developed a method for the gram-scale synthesis of gold nanoparticles (AuNPs) using acrylamide (AAm) as a solvent. AAm possesses unique properties such as low melting temperature, high solvating power, and high solubility of its polymer (polyacrylamide(pAAm)) in water. The viscosity of the AAm solvent can be chemically tuned by the polymerization of AAm and addition of a low-volatile diluent, which can stabilize highly concentrated as-synthesized AuNPs in gram quantities. The synthesized AuNPs are substantially stable and catalytically active under high ionic strength conditions owing to the pAAm protection on the particle surface. Further, the synthesis mechanism of the AuNPs has been thoroughly investigated. The versatility of the synthesis method is proved by synthesizing other mono-(Ag and Pd) and bimetallic (Au + Pd and Ag + Pd) nanoparticles using the AAm solvent with controlled viscosity. Importantly, the productivity of this synthetic strategy is the highest among the previously reported gram-scale synthesis methods of AuNPs. To the best of our knowledge, our study presents the use of acrylic monomer as a solvent for the gram-scale synthesis of noble metal nanoparticles for the first time. This study significantly extends the list of solvents with chemically tunable viscosity by including other acrylic reagents for nanomaterial synthesis, functionalization, and catalytic, optical, and electrical reactions under highly localized reaction conditions.

Biogenic synthesis of spherical-shaped noble metal nanoparticles using Vicia faba extract (X@VF, X = Au, Ag) for photocatalytic degradation of organic hazardous dye and their in vitro antifungal, antibacterial and anticancer activities

• A cost effective green Vicia faba method used to obtain gold and silver nanoparticles. • SEM images conferred the spherical and oval morphology of samples. • AuNPs and AgNPs showed excellent antibacterial (against gram-negative and gram-positive strains) and antifungal activities. • AuNPs and AgNPs exhibited dose dependent anticancer activity (on AGS-3 and MCF-7 cell lines) and high biocompatibility towards normal cells (Beas-2B cell line). • Excellent photocatalytic pollutant degradation was observed in the Ag and Au nanoparticles. In recent years, industrial wastewater pollution, including organic pollution and harmful bacteria, has endangered the health of humans and other organisms. For this purpose, we designed an eco-friendly and cost-effective technique for the synthesis of noble metal nanoparticles using natural reducing, stabilizing, and capping agents. In the present study, gold (AuNPs@ VF ) and silver nanoparticles (AgNPs@ VF ) were synthesized using the extract of Vicia faba , and evaluated for catalytic, antibacterial, antifungal, and anticancer activities. Optimizing synthesis conditions (pH, temperature, reaction time, and concentration) for the best outcomes was conducted. The synthesized AuNPs@ VF and AgNPs@ VF were characterized using UV-Vis, XRD, EDS, TEM, and FESEM. The homogeneous, oval-spherical morphology and regular products with a size in the range of 30-60 nm were observed from XRD and FESEM techniques. The photocatalytic performance of AuNPs@ VF and AgNPs@ VF were calculated by degradation of methyl orange (MO) pollution under UV-light irradiation. The AuNPs@ VF (91.4%) and AgNPs@ VF (80.4%) showed high photocatalytic degradation in the shortest possible time. In order to evaluate antifungal, antibacterial, and drug resistance activities, seven ATCC bacteria (gram-positive and gram-negative bacteria), resistant pathogens strains, and eight fungal strains were selected. The results showed that among these two metal nanoparticles, silver nanoparticles showed a very high antibacterial activity, which can be considered an antibacterial agent. This is despite the fact that the antifungal activity of gold nanoparticles was better than silver nanoparticles. Moreover, the cytotoxicity effects of AuNPs@ VF and AgNPs@ VF on MCF-7, AGS-3, and normal Beas-2B cell lines were examined by MTT assay. The cytotoxicity result showed that the biosynthesized AuNPs@VF and AgNPs@VF displayed a significant dose-dependent inhibitory effect with IC50 values of 58.65, 46.38 µg/mL on MCF-7 and 22.91, 9.73 µg/mL on AGS-3, respectively compared cisplatin as the positive control. Also, the results showed that the synthesized nanoparticles acted selectively on the normal cell and were safe on the human epithelial cells.

Dendronized Gelatin-Mediated Synthesis of Gold Nanoparticles

Thermoresponsive dendronized gelatins (GelG1) or gelatin methacrylates (GelG1MA) were used as precursors to modulate the efficient reduction of Au(III) to form stable gold nanoparticles (AuNPs) through UV irradiation. These dendronized gelatins were obtained through the amidation of gelatin or gelatin methacrylates with dendritic oligoethylene glycols (OEGs). Crowded OEG dendrons along the gelatin backbones create a hydrophobic microenvironment, which promotes the reduction of Au(III). Gelatin backbones act as ligands through the electron-rich groups to facilitate the reduction, while the dendritic OEGs provide shielding effects through crowding to form a hydrophobic microenvironment, which not only enhances the reduction but also stabilize the formed AuNPs through encapsulation. The effects of dendron coverage on the dendronized biomacromolecules and their thermoresponsiveness on the reduction kinetics were examined. Dendronized gelatin/AuNPs hydrogels were further prepared through the in situ photo-crosslinking of GelG1MA. The modification of natural macromolecules through dendronization presented in this report facilitates a novel platform for the environmentally friendly synthesis of noble metal nanoparticles, which may form a new strategy for developing smart nano-biosensors and nano-devices.

Citrus limetta Risso peel mediated green synthesis of gold nanoparticles and its antioxidant and catalytic activity

Green synthesis of noble metal nanoparticles is now receiving great attention because of their numerous applications such as optics, catalysis, and biomedicine. In this work, gold nanoparticles were synthesized from peel extract of sweet lime (Citrus limetta Risso), which is usually discarded as a bio-waste. Bioactive components present in the fruit peel extract act as reducing and capping agents for the synthesis of gold nanoparticles from chloroauric acid (HAuCl4). The visual color change from light yellow to ruby red suggested the formation of gold nanoparticles, which was further confirmed by the maximum absorption peak at 530 nm of colloidal suspension measured by UV–vis spectroscopy. XRD spectra indicated the crystalline nature of prepared gold nanoparticles. The average crystallite size of gold nanoparticles measured from prominent peaks of XRD was found to be around 64 nm (size range: 50–80 nm), which was further supported by FESEM analysis. The components responsible for the reduction of chloroauric acid into gold nanoparticles were analyzed by FTIR, which suggested the presence of several phytochemicals e.g. phenol, carboxylic acid, amines, and alkynes in the fruit peel extract. Green prepared gold nanoparticle was further evaluated for its antioxidant and catalytic activity. Green gold nanoparticles exhibited excellent antioxidant activity evident by scavenging/inhibition of free oxygen/nitrogen radical generation. Furthermore, green gold nanoparticles demonstrated excellent catalytic activity indicated by the reduction of 4-nitrophenol into 4-aminophenol. This study highlights the significance of bio-waste for the production of nanostructure of noble metals for numerous applications.

Characterization and Biological Activities of Silver Nanoparticles Synthesized using Grewia tiliifolia Vahl Leaf Extract

Background: An eco-friendly approach for the synthesis of noble metal nanoparticles employing various plant extracts has become of great interest in the field of nanotechnology. In the present study, the efficacy of Grewia tiliifolia leaf extract in reducing 1mM silver nitrate to silver nanoparticles(AgNPs) has been reported for the first time and also we investigated the anticancer, antituberculosis and antioxidant activity. Methods: Characterization of biosynthesized AgNPs using G. tiliifolia leaf extract was evaluated by Uv-Vis, FTIR, XRD, DLS and TEM with SAED. Efficacy of biosynthesized AgNPs using G. tiliifolia leaf extract was tested for cytotoxicity against A549 Lung cancer cell lines by MTT Assay and also against the infectious agent Mycobacterium tuberculosis using MABA Assay. Further antioxidant activity was evaluated by DPPH radical scavaging assay. Results: The biosynthesis of AgNPs was evident by color change of reaction mixture from dark yellow to reddish-brown. Biofabricated AgNPs was further confirmed by characteristic surface plasmon absorption peak at 409nm by UV-vis analysis. FTIR data reveals the presence of phytochemicals involved in bioreduction and biocapping of AgNPs, XRD analysis depicted crystallographic nature of AgNPs. Further, size, charge, and polydispersity nature were studied using DLS (40.2nm with polydispersity index 0.361) and Zeta potential (-35.8mV). The morphology of AgNPs was determined by TEM analysis with size ranging from 11-34nm. The plant derived AgNPs exhibited a cytotoxic effect on the Lung cancer cell line with IC50 value of 23.45µg/ml and also found to be effective against M. tuberculosis with a MIC of 6.25µg/ml in comparison to the leaf extract (MIC 50µg/ml). Antioxidant activity observed by AgNPs was moderate with IC50 value 49.60 µg/ml. Conclusion: The findings indicate that the AgNPs synthesized from leaf extract of G. tiliifolia are eco-friendly, cost-effective, non-toxic and can be the effective natural anticancer, antituberculosis agents and antioxidant agent.

Solid–Solution–Solid (SSS) phase transitions for Gram-Scale and High-Throughput synthesis of noble metal nanoparticles in deep eutectic solvents

Modern colloidal chemistry has enabled the controlled synthesis of various noble metal nanoparticles with unique physical and chemical properties. However, solution-based synthesis still suffers from limited productivity, particularly in industrial applications. We have developed the gram-scale synthesis of gold nanoparticles (AuNPs) using a polymerizable deep eutectic solvent (DES) via solid–solution–solid phase transitions. The DES plays two important roles, as a designer solvent. First, the solvating power of the DES allows the precursors to dissolve easily, even at high concentrations. Second, the concomitant polymerization of the DES with the synthesis of highly concentrated AuNPs and their consequent fixation in the polymer matrix is crucial for their stabilization. This rapid one-pot synthesis provides the highest productivity, among the other previously reported gram-scale syntheses of AuNPs. The procedure can be easily extended to conduct multiple reactions in a high-throughput manner. The chemical and physical properties and synthesis mechanisms of the AuNPs are thoroughly investigated. The synthesis of other noble metal (Pd, Ag, Au) nanoparticles, which are mono- and bimetallic, has also been demonstrated using the DES. As a practical application, a large-area transparent display is demonstrated using AuNPs synthesized in the DES, implying the scope for further industrial applications.

Solid-solid synthesis of covalent organic framework as a support for growth of controllable ultrafine Au nanoparticles

Covalent organic frameworks (COFs) are promising supports for the synthesis of noble metal nanoparticles (NM NPs) with controllable sizes and dispersities. However, it is still challenging to synthesize COFs using green and efficient routes. Herein, COFs (TpMA) were prepared by ball milling, which required less solvent and time. They were then used as a support for the growth of ultrafine Au NPs. Using the COFs as supports, five size-controlled ultrafine Au NPs (2.5 ± 0.55– 4.32 ± 1.39 nm) were synthesized (Au@TpMA). It was found that the Au NPs exhibited remarkable dispersibility owing to the support of TpMA. The reduction of 4-nitrophenol to 4-aminophenol was used as a model reaction to evaluate the performance of the Au@TpMA catalyst, which showed excellent catalytic activity for the reduction of 4-nitrophenol. The Au@TpMA catalyst exhibited good stability and recyclability, and the reduction rate was 95% at the end of six successive experiments. In addition, in the presence of the Au@TpMA catalyst, the maximum pseudo-first-order reaction rate constant of 4-nitrophenol was 0.2379 min−1. From the results of this study, we hope that using COFs-based supports prepared by ball milling for the size-controlled synthesis of NM NPs provides a path forward for the mechanical synthesis of other COFs.

Spectroscopic Study of Phytosynthesized Ag Nanoparticles and Their Activity as SERS Substrate

The affordable and scalable synthesis of noble metal nanoparticles that are biocompatible without additional functionalization steps has been a growing field of research, stimulated by numerous prospective applications of these NPs. In the case of phytosynthesized or biogenic noble metal NPs, the mechanism of NP stabilization by biomolecules contained in each particular plant extract or living organism determines the possible applications of these NPs. In this work, we investigated Ag NPs synthesized in water with plant extracts of common toothwort (Lathraea squamaria) and two species of pepper (Capsicum annuum and Capsicum chinense). From FTIR and XPS, we drew conclusions about the composition of the functional groups and molecules that stabilize NPs in each extract, such as polysaccharide compounds (pectins, cellulose, glycosides and phenolic acids). Distinct characteristic IR features of amide I and amide II proteins were observed, which are common in plant extracts, while features of amide III were not distinctly observed in our extracts. A Raman spectroscopy study revealed weak own-SERS activity of the biomolecules of the extract and high efficiency of the NPs in the enhancement of “external” analytes, such as dyes and antibodies. This is the first report of the efficient SERS application of phytosynthesized Ag NPs.