Design rules applied to silver nanoparticles synthesis: A practical example of machine learning application

The synthesis of silver nanoparticles with controlled physicochemical properties is essential for governing their intended functionalities and safety profiles. However, synthesis process involves multiple parameters that could influence the resulting properties. This challenge could be addressed with the development of predictive models that forecast endpoints based on key synthesis parameters. In this study, we manually extracted synthesis-related data from the literature and leveraged various machine learning algorithms. Data extraction included parameters such as reactant concentrations, experimental conditions, as well as physicochemical properties. The antibacterial efficiencies and toxicological profiles of the synthesized nanoparticles were also extracted. In a second step, based on data completeness, we employed regression algorithms to establish relationships between synthesis parameters and desired endpoints and to build predictive models. The models for core size and antibacterial efficiency were trained and validated using a cross-validation approach. Finally, the features' impact was evaluated via Shapley values to provide insights into the contribution of features to the predictions. Factors such as synthesis duration, scale of synthesis and the choice of capping agents emerged as the most significant predictors. This study demonstrated the potential of machine learning to aid in the rational design of synthesis process and paves the way for the safe-by-design principles development by providing insights into the optimization of the synthesis process to achieve the desired properties. Finally, this study provides a valuable dataset compiled from literature sources with significant time and effort from multiple researchers. Access to such datasets notably aids computational advances in the field of nanotechnology.

Optimizing Green Synthesis of Hydrotalcite - Silver Nanoparticles using Syzygium Nervosum based Reducing Agent

Hydrotalcite-silver (HT-Ag) nanoparticles have been involved in various daily crucial applications, such as antibacterial, photocatalytic, adsorption, etc. There are many approaches to synthesizing silver nanoparticles (AgNPs) decorated on hydrotalcite (HT) surface and the most used approach is using a strong reducing agent. Thus, affordable but effective "green" reducing agents - Syzygium nervosum leaf extract, are taken into account in this work to solve several issues related to chemical reducing agents. This work aimed to assess the effect of Syzygium nervosum leaf extract as a reducing agent for green synthesis of AgNPs on HT through an optimizing process using response surface methodology (RSM) and the Box-Benken model. The optimal conditions for the synthesis of AgNPs on HT include a reaction time of 6.15 hours, a reaction temperature of 50 °C, and the ratio of diluted Syzygium nervosum leaf extract to reduce AgNO3 of 50.37 mL/mg. Under the optimal conditions, the yield of the reduction reaction reached 77.54 %, close to the theoretical value of 76.97 %. The optimization model was suitable for the experiment data. Besides, the morphology, density, and characteristics of AgNPs on the surface of HT layers have been determined by using Ultraviolet-visible spectroscopy, Field emission scanning electron microscopy (FESEM), High-resolution transmission electron microscopy (HR-TEM), selected area diffraction, X-ray diffraction, Dynamic light scattering (DLS), Infrared (IR) spectroscopy, Fluorescence emission spectroscopy (FE), Brunauer-Emmett-Teller (BET) methods. The spherical AgNPs were synthesized successfully on the surface of HT with the average particle size of 13.0±1.1 nm. Interestingly, HT-Ag hybrid materials can inhibit strongly the growth of E. coli, S. aureus as well as two antibiotic resistance bacterial strains, P. stutzeri B27, and antibiotic resistance E. coli. Especially, the antibacterial activity quantification and durability of the HT-Ag hybrid materials were also tested. Overall, the HT-Ag hybrid materials are very promising for application in material science and biomedicine fields.

Multidentate polyoxometalate modification of metal nanoparticles with tunable electronic states

To respond to the increasing demands for practical applications, stabilization and property modulation of metal nanoparticles have emerged as a key research subject. Herein, we present a viable protocol for preparing small metal nanoparticles (<5 nm; Ag, Pd, Pt, and Ru) via multidentate polyoxometalate (POM, [SiW9O34]10-) modification. In addition to enhancing stability, the POMs can modulate the electronic states of metal nanoparticles. Moreover, immobilization of the POM-modified metal nanoparticles on solid supports enables further tuning of the electronic states via a cooperative effect between the POMs and the supports without altering the particle size. Notably, POM-modified Pd nanoparticles on carbon support exhibited superior catalytic activity and selectivity in hydrogenation reactions in comparison with the catalyst without the POM modification.

Lukianov D, Gayanova TE, Voronova EV, Shishilov ON, Stepakhin VD. The Synthesis and Analysis of the Cytotoxicity of Al2O3-Supported Silver Nanoparticles Prepared by the Plasma Chemical Process Initiated by Pulsed MW Radiation in the Al2O3-Ag Powder Mixtures

An original plasma chemical process initiated by microwave discharge in a mixture of metal and dielectric powders was applied to prepare specific materials, which consisted of microsized spherical particles of aluminum oxide covered with silver nanoparticles. The prepared materials are highly uniform in shape, size distribution, and composition. Their cytotoxicity was investigated using the human cell lines MCF7, HEK293T, A549, and VA-13 and the bacterial strains E. coli JW5503 (ΔtolC) and E. coli K12. Their cytotoxicity was found not to exceed the cytotoxicity of the starting materials. Thus, the prepared materials can be considered highly promising for catalysis and biotechnology applications.

Catalytic Performance in Nitroarene Reduction of Nanocatalyst Based on Noble Metal Nanoparticles Supported on Polymer/s-Layer Protein Hybrids

We present a novel bionanocatalyst fabricated by the adsorption-reduction of metal ions on a polyurethane/S-layer protein biotemplate. The bioinspired support was obtained by the adsorption of S-layer proteins (isolated from Lentilactobacillus kefiri) on polyurethane particles. Silver and platinum nanoparticles were well-loaded on the surface of the support after the combination with metallic salts and reduction with H2 at room temperature. Transmission electron microscopy analysis revealed the strawberry-like morphology of the bionanocatalysts with a particle size, dn, of 2.39 nm for platinum and 9.60 nm for silver. Both systems catalyzed the hydrogenation of p-nitrophenol to p-aminophenol with high efficiency in water at mild conditions in the presence of NaBH4. Three different amounts of bionanocatalyst were tested, and in all cases, conversions between 97 and 99% were observed. The catalysts displayed excellent recyclability over ten cycles, and no extensive damage in their nanostructure was noted after them. The bionanocatalysts were stable during their production, storage, and use, thanks to the fact that the biosupport provides an effective driving force in the formation and stabilization of the metallic nanoparticles. The successful bioinspired production strategy and the good catalytic ability of the systems are encouraging in the search for nontoxic, simple, clean, and eco-friendly procedures for the synthesis and exploitation of nanostructures.

Impacts of Differentially Shaped Silver Nanoparticles with Increasingly Complex Hydrophobic Thiol Surface Coatings in Small-Scale Laboratory Microcosms

We investigated the impacts of spherical and triangular-plate-shaped lipid-coated silver nanoparticles (AgNPs) designed to prevent surface oxidation and silver ion (Ag+) dissolution in a small-scale microcosm to examine the role of shape and surface functionalization on biological interactions. Exposures were conducted in microcosms consisting of algae, bacteria, crustaceans, and fish embryos. Each microcosm was exposed to one of five surface chemistries within each shape profile (at 0, 0.1, or 0.5 mg Ag/L) to investigate the role of shape and surface composition on organismal uptake and toxicity. The hybrid lipid-coated AgNPs did not result in any significant release of Ag+ and had the most significant toxicity to D. magna, the most sensitive species, although the bacterial population growth rate was reduced in all exposures. Despite AgNPs resulting in increasing algal growth over the experiment, we found no correlation between algal growth and the survival of D. magna, suggesting that the impacts of the AgNPs on bacterial survival influenced algal growth rates. No significant impacts on zebrafish embryos were noted in any exposure. Our results demonstrate that the size, shape, and surface chemistry of AgNPs can be engineered to achieve specific goals while mitigating nanoparticle risks.

Silver Nanoparticle-Functionalized Postsynthetically Modified Thiol MOF UiO-66-NH-SH for Efficient CO2 Fixation

Thiols are essential functional groups imparting unique properties, such as reactivity and selectivity, to many vital enzymes and biomolecules. The integration of electronically soft thiol groups within metal-organic frameworks (MOFs) yields elevated reactivity and a pronounced affinity for soft metal ions. However, the scarcity of thiol-based ligands and synthetic challenges hinder the advancement of thiol-based MOFs. To bypass the difficulties of synthesizing thiol MOFs by a direct reaction between thiol-based ligands and corresponding metal salts, postsynthetic modification (PSM) of MOFs is an efficient strategy to introduce thiol functionality. Herein, we have introduced Ag nanoparticles in postsynthetically modified thiol MOFs UiO-66-NH-SH (1) (synthesized by reaction between UiO-66-NH2 and thioglycolic acid) and UiO-66-NH-SH (2) (synthesized by reaction between UiO-66-NH2 and 3-mercaptopropionic acid) to synthesize a series of heterogeneous catalysts for CO2 fixation. Catalysts Cat 1-2 and Cat 3 - 4 were synthesized from UiO-66-NH-SH (1) and UiO-66-NH-SH (2), respectively, by using varying concentrations of silver (AgNO3). Catalyst Ag@UiO-66-NH-SH (1) (Ag = 3.45%; namely Cat 2) shows the highest efficiency for the catalytic conversion of propargylic alcohol and terminal epoxide to the corresponding cyclic carbonates. Finally, a rationalized reaction mechanism is proposed by correlating our results with the current literature. This work presents a viable strategy to utilize the thiol functionality of MOFs (avoiding the complexities associated with synthesizing thiol MOFs directly from thiol ligands) as a platform for introducing catalytically active metal centers and applying them as a heterogeneous catalyst for CO2 fixation reactions.

Transition-Metal Catalyzed Synthesis of Pyrimidines: Recent Advances, Mechanism, Scope and Future Perspectives

Pyrimidine is a pharmacologically important moiety that exhibits diverse biological activities. This review reflects the growing significance of transition metal-catalyzed reactions for the synthesis of pyrimidines (with no discussion being made on the transition metal-catalyzed functionalization of pyrimidines). The effect of different catalysts on the selectivity/yields of pyrimidines and catalyst recyclability (wherever applicable) are described, together with attempts to illustrate the role of the catalyst through mechanisms. Although several methods have been researched for synthesizing this privileged scaffold, there has been a considerable push to expand transition metal-catalyzed, sustainable, efficient and selective synthetic strategies leading to pyrimidines. The aim of the authors with this update (2017-2023) is to drive the designing of new transition metal-mediated protocols for pyrimidine synthesis.

Catalytic Synthesis of Silanols by Hydroxylation of Hydrosilanes: From Chemoselectivity to Enantioselectivity

As a crucial class of functional molecules in organosilicon chemistry, silanols are found valuable applications in the fields of modern science and will be a potentially powerful framework for biologically active compounds or functional materials. It has witnessed an increasing demand for non-natural organosilanols, as well as the progress in the synthesis of these structural features. From the classic preparative methods to the catalytic selective oxidation of hydrosilanes, electrochemical hydrolysis of hydrosilanes, and then the construction of the most challenging silicon-stereogenic silanols. This review summarized the progress in the catalyzed synthesis of silanols via hydroxylation of hydrosilanes in the last decade, with a particular emphasis on the latest elegant developments in the desymmetrization strategy for the enantioselective synthesis of silicon-stereogenic silanols from dihydrosilanes.

Mechanistic elucidation of the catalytic activity of silver nanoclusters: exploring the predominant role of electrostatic surface

The core and the ligand shell of metal nanoclusters (MNCs) have an influential role in modulating their spectroscopic signatures and catalytic properties. The aspect of electrostatic interactions to regulate the catalytic properties of MNCs has not been comprehensively addressed to date. Our present work conclusively delineates the role of the metal core and the electrostatic surface of MNCs involved in the reduction of nitroarenes. A facile surface modification of mercaptosuccinic acid (MSA)-templated AgNCs has been selectively achieved through Mg2+ ions (Mg-AgNCs). Microscopic studies suggest that the size of Mg-AgNCs is ∼3.3 nm, which is considerably higher than that of MSA-templated AgNCs (∼1.75 nm), confirming the formation of a nano-assembled structure. Our spectroscopic and microscopic experiments revealed that the negatively charged AgNCs efficiently catalyze the reduction of 4-nitrophenol (4-NP) with a rate constant of 0.23 ± 0.01 min-1. However, upon surface modification, the catalytic efficiency almost doubles due to the formation of Mg-AgNCs. Catalysis through AgNCs and Mg-AgNCs collectively portrays the role of the core and electrostatic surfaces. Furthermore, the role of electrostatic interaction has been substantiated by varying the ionic strength of the medium, as well as employing different molecular systems. A quantitative assessment of the Debye screening length asserts the correlation between the ionic strength of the medium and the role of electrostatic interactions involved herein. This highly enhanced catalytic aspect has been utilized for the real sample analysis, wherein AgNCs unexpectedly outperform Mg-AgNCs. This approach of real sample analysis also emanates the role of electrostatics involved. This comprehensive investigation represents the influential role of the core and ligand shell of MNCs as well as the role of electrostatics on its catalytic activities, which is relevant for the rational design of highly efficient catalysts.

In Situ DRIFTS Analysis during Hydrogenation of 1-Pentyne and Olefin Purification with Ag Nanoparticles

The catalytic performance of nanoparticles (NPs) of Ag anchored on different supports was evaluated during the selective hydrogenation of 1-pentyne and the purification of a mixture of 1-pentene/1-pentyne (70/30 vol %). The catalysts were identified: Ag/Al (Ag supported on ɣ-Al2 O3 ), Ag/Al-Mg (Ag supported on ɣ-Al2 O3 modified with Mg), Ag/Ca (Ag supported on CaCO3 ) and Ag/RX3 (Ag supported on activated carbon-type: RX3). In addition, in situ DRIFTS analysis of 1-pentyne adsorption on each support, catalyst, and 1-pentyne hydrogenation were investigated. The results showed that the synthesized catalysts were active and very selective (≥85 %) for obtaining the desired product (1-pentene). Different adsorbed species (-C≡C- and -C=C-) were observed on the supports and catalysts surface using in situ DRIFT analysis, which can be correlated to the activity and high selectivity reached. The role of the supports and electronic properties over Ag improve the H2 dissociative chemisorption during the hydrogenation reactions; promoting the selectivity and the high catalytic performance. Ag/Al and Ag/Al-Mg were the most active catalysts. This was due to the synergism between the active Ag/Ag+ species and the supports (electronic effects). The results show that Ag/Al and Ag/Al-Mg catalysts have favorable properties and are promising for the alkyne hydrogenation and olefin purification reactions.

Alnafisah A, Beji L, Kouki N, Morlet-Savary F, Alminderej FM, Aroua LM, Lalevée J. 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.

Mapping the Progress in Surface Plasmon Resonance Analysis of Phytogenic Silver Nanoparticles with Colorimetric Sensing Applications

Nanotechnology is gaining enormous attention as the most dynamic research area in science and technology. It involves the synthesis and applications of nanomaterials in diverse fields including medical, agriculture, textiles, food technology, cosmetics, aerospace, electronics, etc. Silver nanoparticles (AgNPs) have been extensively used in such applications due to their excellent physicochemical, antibacterial, and biological properties. The use of plant extract as a biological reactor is one of the most promising solutions for the synthesis of AgNPs because this process overcomes the drawbacks of physical and chemical methods. This review article summarizes the plant-mediated synthesis process, the probable reaction mechanism, and the colorimetric sensing applications of AgNPs. Plant-mediated synthesis parameters largely affect the surface plasmon resonance (SPR) characteristic due to the changes in the size and shape of AgNPs. These changes in the size and shape of plant-mediated AgNPs are elaborately discussed here by analyzing the surface plasmon resonance characteristics. Furthermore, this article also highlights the promising applications of plant-mediated AgNPs in sensing applications regarding the detection of mercury, hydrogen peroxide, lead, and glucose. Finally, it describes the future perspective of plant-mediated AgNPs for the development of green chemistry.

Surface-exposed silver nanoclusters inside molecular metal oxide cavities

The surfaces of metal nanoclusters, including their interface with metal oxides, exhibit a high reactivity that is attractive for practical purposes. This high reactivity, however, has also hindered the synthesis of structurally well-defined hybrids of metal nanoclusters and metal oxides with exposed surfaces and/or interfaces. Here we report the sequential synthesis of structurally well-defined {Ag₃₀} nanoclusters in the cavity of ring-shaped molecular metal oxides known as polyoxometalates. The {Ag₃₀} nanoclusters possess exposed silver surfaces yet are stabilized both in solution and the solid state by the surrounding ring-shaped polyoxometalate species. The clusters underwent a redox-induced structural transformation without undesirable agglomeration or decomposition. Furthermore, {Ag₃₀} nanoclusters showed high catalytic activity for the selective reduction of several organic functional groups using H₂ under mild reaction conditions. We believe that these findings will serve for the discrete synthesis of surface-exposed metal nanoclusters stabilized by molecular metal oxides, which may in turn find applications in, for example, the fields of catalysis and energy conversion.

Electroless Deposition of Silver onto Silica Nanoparticles to Produce Lipophilic Core-Shell Nanoparticles

HYPOTHESIS

The colloidal stability of noble metal nanoparticles can be tuned for solvents of varying hydrophobicity by modifying the surface chemistry of the particles with different capping agent architectures. Challenges arise when attempting to separately control multiple nanoparticle properties due to the interdependence of this adsorption process on the surface chemistry and metal architecture. A surfactant-mediated, templated synthesis strategy should decouple control over size and stability to produce lipophilic nanoparticles from aqueous reagents.

EXPERIMENTS

A modified electroless plating process that produces oil-dispersible core-shell silver-silica nanoparticles is presented. Amine-terminated alkanes are utilized as the capping agents to generate lipophilic surface coatings and the particles are temporarily stabilized during the synthesis by adding a Pluronic surfactant that enhances dispersibility in the aqueous reaction medium. The evolution of shell morphology, composition, and colloidal stability was analyzed against capping agent architecture and concentration. The role of particle shape was also tested by interchanging the template geometry.

FINDINGS

The capping agents installed on the silver shell surface displayed both colloidal stability enhancements and a minimum effective capping concentration that is a function of molecular weight without influencing the shell composition. Particle geometry can be controlled by interchanging the silica template size and shape.

Biosynthesis of Silver Nanoparticles Utilizing Leaf Extract of Trigonella foenum-graecum L. for Catalytic Dyes Degradation and Colorimetric Sensing of Fe3+/Hg2

The aqueous Trigonella foenum-graecum L. leaf extract belonging to variety HM 444 was used as reducing agent for silver nanoparticles (AgNPs) synthesis. UV-Visible spectroscopy, Particle size analyser (PSA), Field emission scanning electron microscopy coupled to energy dispersive X-ray spectroscopy (FESEM-EDX) and High-resolution transmission electron microscopy (HRTEM) were used to characterize AgNPs. Selected area electron diffraction (SAED) confirmed the formation of metallic Ag. Fourier Transform Infrared Spectroscopy (FTIR) was done to find out the possible phytochemicals responsible for stabilization and capping of the AgNPs. The produced AgNPs had an average particle size of 21 nm, were spherical in shape, and monodispersed. It showed catalytic degradation of Methylene blue (96.57%, 0.1665 ± 0.03 min^-1), Methyl orange (71.45%, 0.1054 ± 0.002 min^-1), and Rhodamine B (92.72%, 0.2004 ± 0.01 min^-1). The produced AgNPs were excellent solid bio-based sensors because they were very sensitive to Hg²⁺ and Fe³⁺ metal ions with a detection limit of 11.17 µM and 195.24 µM, respectively. From the results obtained, it was suggested that aqueous leaf extract demonstrated a versatile and cost-effective method and should be utilized in future as green technology for the fabrication of nanoparticles.

Silver Nanoparticle-Incorporated Defect-Engineered Zr-based Metal-Organic Framework for Efficient Multicomponent Catalytic Reactions

Small-sized silver nanoparticles are incorporated into a thiol-functionalized stable Zr-based metal-organic framework (MOF). Thiol functionalization has been carried out using 2-mercapto benzoic acid (2-MBA) as the modulator, which promotes defect formation in the MOF structure. The incorporation of silver nanoparticles aided by the silver-sulfur interactions in this defective MOF gives rise to catalytic activity. Its catalytic efficiency in the highly atom-efficient A³ coupling reaction has been studied for a variety of substrates with impressive recyclability. The synergistic effect of the electron-rich silver core and electron-deficient surface of the thiol-bonded silver nanoparticle is key for this catalytic reaction.

Upcycling Bread Waste into a Ag-Doped Carbon Material Applied to the Detection of Halogenated Compounds in Waters

Bread waste is a major part of food wastage which could be upcycled to produce functional materials, following the principles of the circular bioeconomy. This work shows that bread waste can be recycled and valorized to produce a composite conductive material with excellent properties for chemical sensor applications. Here, dry bread is impregnated with an aqueous solution of a silver precursor and pyrolyzed to produce a porous carbon matrix containing Ag nanoparticles with diameters ranging from 20 to 40 nm. These particles perform as catalytic redox centers for the electrochemical detection of halide ions (Cl^-, Br^-, and I^-) and organohalide target molecules such as sucralose and trichloroacetic acid. A thorough analytical characterization is carried out to show the potential application of the developed material for the manufacturing of electrochemical sensor approaches. The material preparation is sustainable, low-cost, simple, and upscalable. These are ideal features for the large-scale manufacturing by screen-printing technologies of single-use electrochemical sensors for the rapid analysis of halogenated organic pollutants in waters.

Heptanuclear Silver Hydride Clusters as Catalytic Precursors for the Reduction of 4-Nitrophenol

We report on the design, synthesis, and characterization of the first silver hydride clusters solely protected and stabilized by dithiophosphonate ligands and their application for the in situ generation of silver nanoparticles towards the catalytic reduction of 4-nitrophenol in an aqueous system. The synthesis of the silver monohydride cluster involves the incorporation of an interstitial hydride using sodium borohydride. Poly-nuclear magnetic resonance and mass spectrometry were used to establish the structural properties. The structural properties were then confirmed with a single-crystal X-ray diffraction analysis, which showed a distorted tetracapped tetrahedron core with one hydride ion encapsulated within the core of the silver framework. Additionally, the synthesized heptanuclear silver hydride was utilized as a precursor for the in situ generation of silver nanoparticles, which simultaneously catalyzed the reduction of 4-nitrophenol. The mechanism of the catalytic activity was investigated by first synthesizing AgNPs, which was subsequently used as a catalyst. The kinetic study showed that the pseudo-first constant obtained using the cluster (2.43 × 10−2 s−1) was higher than that obtained using the synthesized AgNPs (2.43 × 10−2 s−1). This indicated that the silver monohydride cluster was more active owing to the release of the encapsulated hydride ion and greater reaction surface prior to aggregation.

Synergistic Effect in Ag/Fe–MnO2 Catalysts for Ethanol Oxidation

Here we report the synergistic effect of OMS-2 catalysts tested in ethanol oxidation, and the effects produced by both the addition of an Fe modifier in the catalyst preparation stage, and the introduction of Ag on its surface by the impregnation method. To analyze the action of each component, the Fe-modified, Ag-containing OMS-2 catalysts with different Mn/Fe ratios were prepared. Combined XPS and XRF elemental analysis confirms the states and distribution of the Ag- and Fe-containing species between the surface and bulk of the OMS-2 catalysts, which form highly dispersed Ag species on the surface of 0.05Fe–OMS-2, and are also incorporated into the OMS-2 crystalline lattice. The cooperative action of Ag and Fe modifiers improves both reoxidation ability (TPO results) and the amount of adsorbed oxygen species on the catalyst surface. The introduction of Ag to the OMS-2 and 0.05 Fe–OMS-2 surface allows a high level of activity (T80 = 150–155 °C) and selectivity (SAc80 = 93%) towards the acetaldehyde formation.

Supported Gold Nanoparticle-Catalyzed Selective Reduction of Multifunctional, Aromatic Nitro Precursors into Amines and Synthesis of 3,4-Dihydroquinoxalin-2-Ones

The synthesis of 3,4-dihydroquinoxalin-2-ones via the selective reduction of aromatic, multifunctional nitro precursors catalyzed by supported gold nanoparticles is reported. The reaction proceeds through the in situ formation of the corresponding amines under heterogeneous transfer hydrogenation of the initial nitro compounds catalyzed by the commercially available Au/TiO₂-Et₃SiH catalytic system, followed by an intramolecular C-N transamidation upon treatment with silica acting as a mild acid. Under the present conditions, the Au/TiO₂-TMDS system was also found to catalyze efficiently the present selective reduction process. Both transfer hydrogenation processes showed very good functional-group tolerance and were successfully applied to access more structurally demanding products bearing other reducible moieties such as chloro, aldehyde or methyl ketone. An easily scalable (up to 1 mmol), low catalyst loading (0.6 mol%) synthetic protocol was realized, providing access to this important scaffold. Under these mild catalytic conditions, the desired products were isolated in good to high yields and with a TON of 130. A library analysis was also performed to demonstrate the usefulness of our synthetic strategy and the physicochemical profile of the derivatives.

Controlled Synthesis of Platinum and Silver Nanoparticles Using Multivalent Ligands

Here, the controlled formation of platinum nanoparticles (PtNPs) and silver nanoparticles (AgNPs) using amine-functionalized multivalent ligands are reported. The effects of reaction temperature and ligand multivalency on the growth kinetics, size, and shape of PtNPs and AgNPs were systematically studied by performing a stepwise and a one-step process. PtNPs and AgNPs were prepared in the presence of amine ligands using platinum (II) acetylacetonate and silver (I) acetylacetonate, respectively. The effects of ligands and temperature on the formation of PtNPs were studied using a transmission electron microscope (TEM). For the characterization of AgNPs, additionally, ultraviolet-visible (UV-Vis) absorption was employed. The TEM measurements revealed that PtNPs prepared at different temperatures (160–200 °C, in a stepwise process) are monodispersed and of spherical shape regardless of the ligand multivalency or reaction temperature. In the preparation of PtNPs by the one-step process, ligands affect the shape of the PtNPs, which can be explained by the affinity of the ligands. The TEM and UV-Vis absorption studies on the formation of AgNPs with mono-, di-, and trivalent ligands showed narrower size distributions, while increasing the temperature from 80 °C to 120 °C and with a trivalent ligand in a one-step process.

Biosynthesis of silver nanoparticle composites based on hesperidin and pectin and their synergistic antibacterial mechanism

Silver nanoparticles (AgNPs) were widely used in the antibacterial field because of their excellent antibacterial properties. In this study, we used hesperidin and pectin as reductants and stabilizers, and prepared uniform and stable Hesperidin-Pectin AgNPs (HP-AgNPs) by a simple microwave-assisted process. Increasing the proportion of hesperidin, P-AgNPs, HP-AgNPs1, HP-AgNPs2 and H-AgNPs were obtained respectively. With the increase of hesperidin ratio, the mean particle size and zeta potential increased gradually. Fourier transform infrared spectroscopy (FTIR) analysis showed that Ag⁺ was reduced by hesperidin and pectin. Antibacterial tests showed that HP-AgNPs2 showed the MIC values of 66.7 μg/mL against E. coli. In addition, HP-AgNPs2 was selected to clarify its antibacterial mechanism against E. coli. Morphological experiments showed that HP-AgNPs2 stress caused damage to the cell wall of E. coli, as well as leakage of its contents and an increase in reactive oxygen species (ROS). On the other hand, the release of Ag⁺ during cell co-culture was studied and the results showed that most of the Ag⁺ released was taken up by E. coli. The synergistic effect of hesperidin and pectin resulted in a significant enhancement of the antibacterial properties of AgNPs. These preliminary data suggest that HP-AgNPs has good antibacterial activity and may be developed as an effective antibacterial nanomaterial.

A facile synthesis of palladium nanoparticles decorated bismuth oxybromide nanostructures with exceptional photo-antimicrobial activities

Assessing the interaction between microbes and nanocatalysts for finding an inclusive, proactive and deep understanding of nanoparticles-based toxicity is vital for discovering their broad range of applications. Palladium based photocatalysts owing to their unique fundamental characteristics and brilliant physicochemical potential have gained immense interest in environment remediation as disinfection system. In the present study, we report synthesis of a novel palladium nanoparticles decorated bismuth oxybromide (Pd/BiOBr) nanostructures using an energy efficient solution-based method, having excellent photocatalytic antibacterial action. The synthesized nanomaterials was thoroughly characterized using various analytical techniques. The photocatalytic antibacterial efficiency of Pd/BiOBr was evaluated against some common pathogenic strains of Gram-positive and Gram-negative bacteria (Pseudomonas fluorescens, Pseudomonas aeruginosa, Escherichia coli, Aeromonas salmonicida, Salmonella typhimurium, Klebsiella pneumoniae, Bacillus subtilis). In our results Pd/BiOBr showed excellent photocatalytic disinfection efficacy with > 99.9% bacterial inactivation. A very low concentration of Pd/BiOBr (0.5 µg/mL) effectively inhibited the bacterial growth in response to just 2 h of visible light irradiation, while 1 µg/mL of Pd/BiOBr completely killed all the tested bacterial strains proving their magnificent bactericidal potential. The developed materials with exceptional antibacterial broad range efficiency can be used in different photocatalytic disinfection systems including water purification systems, biofilm exclusion and combating differential antibiotic resistance.

Influence of Polyvinylpyrrolidone Concentration on Properties and Anti-Bacterial Activity of Green Synthesized Silver Nanoparticles

Environmentally green synthesis of stable polyvinyl pyrrolidone (PVP)-capped silver nanoparticles (PVP-AgNPs) was successfully carried out. The present study focused on investigating the influence of adding PVP during the synthesis process on the size, optical properties and antibacterial effect of silver nanoparticles produced. An aqueous extract of Eucalyptus camaldulensis leaves was used as a reducing agent. The effects of different PVP concentrations and reducing time on the synthesis of nanoparticles (NPs) were characterized by UV–Vis spectrophotometry, scanning electron microscopy (SEM), energy dispersive spectrum (EDX), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS) and nano tracker analysis (NTA). The addition of PVP was studied. The prepared PVP-AgNPs were spherical with an average size of 13 nm. FTIR analysis confirmed that PVP protects AgNPs by a coordination bond between silver nanoparticles and both N and O of PVP. DLS results indicated the good dispersion of silver nanoparticles. PVP-AgNPs were found to be stable for nearly 5 months. Antibacterial studies through the agar well diffusion method confirmed that silver nanoparticles synthesized using PVP had no inhibitor activity toward Gram-positive and Gram-negative bacteria as opposed to silver nanoparticles prepared without adding PVP, which showed a significant antibacterial activity towards some of the tested pathogens.

Synthesis of silver and gold nanoparticles-enzyme-polymer conjugate hybrids as dual-activity catalysts for chemoenzymatic cascade reactions

Novel hybrids containing silver or gold nanoparticles have been synthesized in aqueous media and at room temperature using enzymes or tailor-made enzyme-polymer conjugates, which directly induced the formation of inorganic silver or gold species. The choice of pH, protein, or bioconjugate strongly affected the final metallic nanoparticles hybrid formation. Using Candida antarctica lipase (CALB) in a solution, nanobiohybrids containing Ag₂O nanoparticles of 9 nm average diameter were obtained. The use of tailor-made bioconjugates, for example, the CALB modified with dextran-aspartic acid polymer (Dext6kDa), resulted in a nanobiohybrid containing smaller Ag(0)/Ag₂O nanoparticles. In the case of nanobiohybrids based on gold, Au(0) species were found in all cases. The Au-CALB hybrid contained spherical nanoparticles with 18 nm average diameter size, with a minor range of larger ones (>100 nm) while the AuNPs-CALB-Dext6kDa hybrid was formed by much smaller nanoparticles (9 nm, minor range of 22 nm), and also nanorods of 20-30/40-50 nm length. Using Thermomyces lanuginosus lipase (TLL), apart from the nanoparticle formation, nanoflowers with a diameter range of 100-200 nm were obtained. All nanobiohybrids maintained (dual) enzymatic and metallic activities. For instance, these nanobiohybrids exhibited exquisite dual-activity for hydrolysis/cycloisomerization cascades starting from allenic acetates. By merging the transition metal reactivity with the inherent lipase catalysis, allenic acetates directly converted to the corresponding O-heterocycles in enantiopure form catalysed by AgNPs-CALB-Dext6kDa, taking advantage of a kinetic resolution/cyclization pathway. These results showed the high applicability of these novel hybrids, offering new opportunities for the design of novel reaction cascades.

Modular terpene synthesis enabled by mild electrochemical couplings

The synthesis of terpenes is a large field of research that is woven deeply into the history of chemistry. Terpene biosynthesis is a case study of how the logic of a modular design can lead to diverse structures with unparalleled efficiency. This work leverages modern nickel-catalyzed electrochemical sp²-sp³ decarboxylative coupling reactions, enabled by silver nanoparticle-modified electrodes, to intuitively assemble terpene natural products and complex polyenes by using simple modular building blocks. The step change in efficiency of this approach is exemplified through the scalable preparation of 13 complex terpenes, which minimized protecting group manipulations, functional group interconversions, and redox fluctuations. The mechanistic aspects of the essential functionalized electrodes are studied in depth through a variety of spectroscopic and analytical techniques.

Migration of zeolite-encapsulated Pt and Au under reducing environments

Simulations reveal accelerated migration of Pt@zeolite by reducing adsorbates and the importance of PtCO in early stages of particle growth.

Polymer microgels for the stabilization of gold nanoparticles and their application in the catalytic reduction of nitroarenes in aqueous media

Polymer microgels containing a polystyrene core and poly(N-isopropylmethacrylamide) shell were synthesized in aqueous media following a free radical precipitation polymerization. Au nanoparticles were fabricated into the shell region of the core–shell microgels denoted as P(STY@NIPM) by the in situ reduction of chloroauric acid with sodium borohydride. Various characterization techniques such as transmission electron microscopy (TEM), ultraviolet–visible spectroscopy (UV-visible) and Fourier transform infrared spectroscopy (FTIR) were used for the characterization of Au–P(STY@NIPM). The catalytic potential of Au–P(STY@NIPM) toward the reductive reaction of 4-nitrophenol (4NP) under various reaction conditions was evaluated. The Arrhenius and Eyring parameters for the catalytic reduction of 4NP were determined to explore the process of catalysis. A variety of nitroarenes were converted successfully into their corresponding aminoarenes with good to excellent yields in the presence of the Au–P(STY@NIPM) system using NaBH₄ as a reductant. The Au–P(STY@NIPM) system was found to be an efficient and recyclable catalyst with no significant loss in its catalytic efficiency.

A core–shell microgel system was synthesized and used as a micro-reactor for the synthesis of gold nanoparticles. The resulting hybrid system has the ability to catalyze the reduction of various nitroarenes in aqueous media.

Xe Adsorption on Noble Metal Clusters: A Density Functional Theory Investigation

The adsorption mechanism of xenon on three noble metal clusters (M = Ag, Au, and Cu) has been investigated in the framework of density functional theory (DFT) within generalized gradient approximation (GGA-PBE). The ab initio calculations were performed with the quantum molecular dynamics (QMD) package ABINIT using the projector augmented (PAW) formalism. The spin-orbit coupling (SOC) and dispersion effects (Van der Waals DFT-D3) have been taken into account. According to these calculations, the M-Xe bonds are partly covalent and electrostatic and their contribution depends on the cluster size and nature. This study underlines the importance of using the SOC and the Van der Waals (VdW) effects. Based on these results, copper nanoparticles have the highest affinity for interaction with xenon compared with silver and gold.

Biomimetic synthesis of silver nanoparticles for treatment of N-Nitrosodiethylamine-induced hepatotoxicity

The development of bioengineered nanoparticles has attracted considerable universal attention in the field of medical science and disease treatment. Current studies were executed to evaluate the hepatoprotective activity of biosynthesized silver nanoparticles (AgNPs). Their characterization was performed by UV-Visible analysis, fourier transform infrared spectroscopy, transmission electron microscopy (TEM), scanning electron microscope (SEM), and Zeta analyses. In in vivo studies, albino rats (180 ± 10 g) were persuaded with model hepatic toxicant N-nitrosodiethylamine (NDEA) and subsequently cotreated with Morus multicaulis at 100 mg/kg and AgNPs at 100 µg/kg dose. NDEA administration elevates the levels of liver function test biomarkers, which were reinstated to normal by cotreatment of test drugs. The oxidative stress and concentration of drug-metabolizing enzyme increase after induction of toxicant (NDEA), these markers are restored toward normal after cotreatment of nano-drug. Treatments of M. multicaulis extract did not show such significant protection. The NDEA-treated groups showed a significant rise in the level of cytokines (interleukin [IL-6] and IL-10) and reached normal with subsequent treatment with AgNPs. Histopathological studies also exhibited the curative effect of AgNPs in the same manner. Thus current results strongly suggest that biomimetic AgNPs could be used as an effective drug against hepatic alteration.

Silver nanomaterials: synthesis and (electro/photo) catalytic applications

In view of their unique characteristics and properties, silver nanomaterials (Ag NMs) have been used not only in the field of nanomedicine but also for diverse advanced catalytic technologies. In this comprehensive review, light is shed on general synthetic approaches encompassing chemical reduction, sonochemical, microwave, and thermal treatment among the preparative methods for the syntheses of Ag-based NMs and their catalytic applications. Additionally, some of the latest innovative approaches such as continuous flow integrated with MW and other benign approaches have been emphasized that ultimately pave the way for sustainability. Moreover, the potential applications of emerging Ag NMs, including sub nanomaterials and single atoms, in the field of liquid-phase catalysis, photocatalysis, and electrocatalysis as well as a positive role of Ag NMs in catalytic reactions are meticulously summarized. The scientific interest in the synthesis and applications of Ag NMs lies in the integrated benefits of their catalytic activity, selectivity, stability, and recovery. Therefore, the rise and journey of Ag NM-based catalysts will inspire a new generation of chemists to tailor and design robust catalysts that can effectively tackle major environmental challenges and help to replace noble metals in advanced catalytic applications. This overview concludes by providing future perspectives on the research into Ag NMs in the arena of electrocatalysis and photocatalysis.

Ag-Catalyzed Multicomponent Synthesis of Heterocyclic Compounds: A Review

The investigation of the procedures for the multi-component synthesis of heterocycles has attracted the interest of organic and medicinal chemists. The use of heterogeneous catalysts, especially transition metal catalysts in organic synthesis, can provide a new, improved alternative to traditional methods in modern synthetic chemistry. The main focus is on the utilization of silver as a catalyst for the multi-component synthesis of heterocyclic compounds. The present review describes some important reported studies for the period of 2010 to 2020. Conclusion: The present review addresses some of the important reported studies on multi-component synthesis of heterocycles in the period of 2010-2020. These approaches were performed under classical and nonclassical conditions, using Ag salts, Ag NPs, Ag on the support, Ag as co-catalysts with other transition metals, ionic liquids, acidic or basic materials. Most of the reported reactions were performed under solvent-free conditions or in green solvents and the utilized catalysts were mostly recyclable. The main aim of the present review is to provide the organic chemists with the most appropriate procedures in the multi-component synthesis of desired heterocycles using silver catalysts.

Small RNAs as a New Platform for Tuning the Biosynthesis of Silver Nanoparticles for Enhanced Material and Functional Properties

Genetic engineering of nanoparticle biosynthesis in bacteria could help facilitate the production of nanoparticles with enhanced or desired properties. However, this process remains limited due to the lack of mechanistic knowledge regarding specific enzymes and other key biological factors. Herein, we report on the ability of small noncoding RNAs (sRNAs) to affect silver nanoparticle (AgNP) biosynthesis using the supernatant from the bacterium Deinococcus radiodurans. Deletion strains of 12 sRNAs potentially involved in the oxidative stress response were constructed, and the supernatants from these strains were screened for their effect on AgNP biosynthesis. We identified several sRNA deletions that drastically decreased AgNP yield compared to the wild-type (WT) strain, suggesting the importance of these sRNAs in AgNP biosynthesis. Furthermore, AgNPs biosynthesized using the supernatants from three of these sRNA deletion strains demonstrated significantly enhanced antimicrobial and catalytic activities against environmentally relevant dyes and bacteria relative to AgNPs biosynthesized using the WT strain. Characterization of these AgNPs using electron microscopy (EM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) revealed that the deletion of these small RNAs led to changes within the supernatant composition that altered AgNP properties such as the surface chemistry, surface potential, and overall composition. Taken together, our results demonstrate that modulating specific sRNA levels can affect the composition of supernatants used to biosynthesize AgNPs, resulting in AgNPs with unique material properties and improved functionality; as such, we introduce sRNAs as a new platform for genetically engineering the biosynthesis of metal nanoparticles using bacteria. Many of the sRNAs examined in this work have potential regulatory roles in oxidative stress responses; further studies into their targets could help provide insight into the specific molecular mechanisms underlying bacterial biosynthesis and metal reduction, enabling the production of nanoparticles with enhanced properties.

A Molecular Hybrid of an Atomically Precise Silver Nanocluster and Polyoxometalates for H2 Cleavage into Protons and Electrons

Atomically precise silver (Ag) nanoclusters are promising materials as catalysts, photocatalysts, and sensors because of their unique structures and mixed-valence states (Ag⁺ /Ag⁰ ). However, their low stability hinders the in-depth study of their intrinsic reactivity and catalytic property accompanying their redox processes. Herein, we demonstrate that a molecular hybrid of an atomically precise {Ag₂₇ }¹⁷⁺ nanocluster and polyoxometalates (POMs) can efficiently cleave H₂ into protons and electrons. The Ag nanocluster accommodates electrons through the redox reaction from {Ag₂₇ }¹⁷⁺ to {Ag₂₇ }¹³⁺ , and the POM ligands play the following important roles: (i) a significant stabilization of the typically unstable Ag nanocluster to preserve its structure during the redox reaction with H₂ , (ii) formation of a unique interface between the Ag nanocluster and metal oxides for efficient H₂ cleavage, and (iii) storage of the generated protons on the negatively charged basic surface.

Single-Particle Hyperspectral Imaging Reveals Kinetics of Silver Ion Leaching from Alloy Nanoparticles

Gold-silver alloy nanoparticles are interesting for multiple applications, including heterogeneous catalysis, optical sensing, and antimicrobial properties. The inert element gold acts as a stabilizer for silver to prevent particle corrosion, or conversely, to control the release kinetics of antimicrobial silver ions for long-term efficiency at minimum cytotoxicity. However, little is known about the kinetics of silver ion leaching from bimetallic nanoparticles and how it is correlated with silver content, especially not on a single-particle level. To characterize the kinetics of silver ion release from gold-silver alloy nanoparticles, we employed a combination of electron microscopy and single-particle hyperspectral imaging with an acquisition speed fast enough to capture the irreversible silver ion leaching. Single-particle leaching profiles revealed a reduction in silver ion leaching rate due to the alloying with gold as well as two leaching stages, with a large heterogeneity in rate constants. We modeled the initial leaching stage as a shrinking-particle with a rate constant that exponentially depends on the silver content. The second, slower leaching stage is controlled by the electrochemical oxidation potential of the alloy being steadily increased by the change in relative gold content and diffusion of silver atoms through the lattice. Interestingly, individual nanoparticles with similar sizes and compositions exhibited completely different silver ion leaching yields. Most nanoparticles released silver completely, but 25% of them appeared to arrest leaching. Additionally, nanoparticles became slightly porous. Alloy nanoparticles, produced by scalable laser ablation in liquid, together with kinetic studies of silver ion leaching, provide an approach to design the durability or bioactivity of alloy nanoparticles.