Formation Of Metal Nanoparticles Research Articles

Use of carboxymethyl cellulose as binder for the production of water-soluble catalysts

Bio-based polymers are materials of high interest given the harmful environmental impact that involves the use of non-biodegradable fossil products for industrial applications. These materials are also particularly interesting as bio-based ligands for the preparation of metal nanoparticles (MNPs), employed as catalysts for the synthesis of high value chemicals. In the present study, Ru (0) and Rh(0) Metal Nanoparticles supported on Sodium Carboxymethyl cellulose (MNP(0)s-CMCNa) were prepared by simply mixing RhCl3x3H2O or RuCl3 with an aqueous solution of CMCNa, followed by NaBH4 reduction. The formation of MNP(0)s-CMCNa was confirmed by FT-IR and XRD, and their size estimated to be around 1.5 and 2.2 nm by TEM analysis. MNP(0)s-CMCNa were employed for the hydrogenation of (E)-cinnamic aldehyde, furfural and levulinic acid. Hydrogenation experiments revealed that CMCNa is an excellent ligand for the stabilization of Rh(0) and Ru(0) nanoparticles allowing to obtain high conversions (>90 %) and selectivities (>98 %) with all substrates tested. Easy recovery by liquid/liquid extraction allowed to separate the catalyst from the reaction products, and recycling experiments demonstrated that MNPs-CS were highly efficiency up to three times in best hydrogenation conditions.

Untargeted metabolomics and molecular docking studies on green silver nanoparticles synthesized by Sarocladium subulatum: Exploring antibacterial and antioxidant properties

The biological synthesis of silver nanoparticles (Ag-NPs) with fungi has shown promising results in antibacterial and antioxidant properties. Fungi generate metabolites (both primary and secondary) and proteins, which aid in the formation of metal nanoparticles as reducing or capping agents. While several studies have been conducted on the biological production of Ag-NPs, the exact mechanisms still need to be clarified. In this study, Ag-NPs are synthesized greenly using an unstudied fungal strain, Sarocladium subulatum AS4D. Three silver salts were used to synthesize the Ag-NPs for the first time, optimized using a cell-free extract (CFE) strategy. Additionally, these NPs were assessed for their antimicrobial and antioxidant properties. Various spectroscopic and microscopy techniques were utilized to confirm Ag-NP formation and analyze their morphology, crystalline properties, functional groups, size, stability, and concentrations. Untargeted metabolomics and proteome disruption were employed to explore the synthesis mechanism. Computational tools were applied to predict metabolite toxicity and antibacterial activity. The study identified 40 fungal metabolites capable of reducing silver ions, with COOH and OH functional groups playing a pivotal role. The silver salt type impacted the NPs' size and stability, with sizes ranging from 40 to 52 nm and zeta potentials from −0.9 to −30.4 mV. Proteome disruption affected size and stability but not shape. Biosynthesized Ag-NPs using protein-free extracts ranged from 55 to 62 nm, and zeta potentials varied from −18 to −27 mV. Molecular docking studies and PASS results found no role for the metabolome in antibacterial activity. This suggests the antibacterial activity comes from Ag-NPs, not capping or reducing agents. Overall, the research affirmed the vital role of specific reducing metabolites in the biosynthesis of Ag-NPs, while proteins derived from biological extracts were found to solely affect their size and stability.

The Effect of Reduction Pretreatments on the Size of Supported Pt and Pd Nanoparticles Prepared by Strong Electrostatic Adsorption

AbstractSupported catalyst synthesis involves pretreatment (drying, reduction) of metal complexes to form metal nanoparticles. This study has been undertaken to explore the effect of reduction temperature, heating rate, and water partial pressure on final particle size of Pt and Pd supported on a total of four carbon and oxide supports. Supported nanoparticles were synthesized by strong electrostatic adsorption (SEA) and dry impregnation (DI); the former method was hypothesized to yield greater nanoparticle stability in thermochemical reducing environments stemming from the strong interaction of the precursor with the support during impregnation. Reduced samples were characterized by in-situ and ex-situ XRD and STEM. The DI-derived samples generally showed an expected increase of particle size with increased reduction temperature, and severe particle coalescence in humid hydrogen, while the SEA-derived samples did not sinter at the elevated reduction temperatures (up to 500 °C) and were remarkably stable in the humid reducing environment. Graphical Abstract

Efficient degradation of acetaminophen by activated peroxymonosulfate using Mn/C composites: Performance and mechanism

The synthesis of manganese oxide (MnOx) composites often leads to particle aggregation and the formation of larger metal nanoparticles, which greatly reduces the efficient use of manganese (Mn) as catalyst. Additionally, the structurally unstable Mn matrix composites increase the risk of metal precipitation during the reaction process. To address these issues, a series of Mn-carbon (Mn/C) co-doped composites (Mn@CA400, Mn@CA500, and Mn@CA600) were synthesized using potassium permanganate (KMnO4) and citric acid (CA) as precursors. The Mn@CA400 exhibited exceptional catalytic activity towards peroxymonosulfate (PMS) resulting in complete removal of 10 mg/L acetaminophen (ACT) within 10 min. Furthermore, Mn@CA400 demonstrated significant selectivity and resistance in complex matrices to interference for pollutant degradation. The results showed that Mn@CA400 exhibited higher catalytic activity and better stability compared with the reported Mn-based composites. Quenching experiments, electron paramagnetic resonance (EPR), solvent exchange experiments, and electrochemical analysis confirmed that singlet oxygen (1O2) and electron transfer pathways were responsible for ACT degradation. The mechanism analysis revealed that ACT could be degraded under three pathways. The current study not only presents an effective method to solve the problem of metal agglomeration and precipitation in the synthesis of MnOx composites but also establishes an efficient and selective oxidation system. In addition, it greatly improves the understanding of PMS activation and ACT degradation mechanisms.

(Invited) Transforming Metal-Containing Secondary Resources into Functional Materials for Electrochemical Energy Applications

Transforming metal-containing waste into functional materials for electrochemical energy applications presents an innovative and sustainable solution to address the growing issue of waste management and resource conservation. By utilizing end-of-life products, off-specification materials, waste materials, and spent materials as secondary resources, this approach can effectively reduce environmental impacts and promote the development of clean energy technologies.Gas-diffusion electrocrystallization (GDEx) is a novel electrochemical technology that can be used as a step to selectively recover and convert valuable metals from metal-containing waste streams into functional materials for electrochemical energy applications. By leveraging the electrochemical reduction of gases, such as O2 or CO2, for the in-situ production of oxidizing (H2O2) or reducing agents (H2 and CO)—which may also result in the formation of other chemical species, e.g., alkali (OH–) in aqueous media, GDEx facilitates the precipitation of soluble metal precursors. This process results in the formation of metal nanoparticles with controlled compositions, crystal structures, sizes, morphologies, and compositions, tailored for specific electrochemical applications.In this talk, the principles of the GDEx process will be explained and examples will be provided of its applicability in the direct transformation of metals contained in secondary resources for the production of functional materials for electrochemical applications. Specifically, the production of electrocatalysts for methanol oxidation from the recycling of automotive catalysts leachates will be conveyed, as well as the production of active battery materials for Li-ion batteries, and the recovery of lithium from geothermal brines.Gas Diffusion Electrocrystallization (GDEx) is a novel and sustainable approach to transform waste materials into functional materials for electrochemical energy applications. This innovative method enables the recovery and synthesis of valuable metal nanoparticles (NPs) from waste streams, such as end-of-life products and industrial leachates, for use in electrocatalysis, energy storage, and fuel cells.GDEx will be conveyed as a sustainable and scalable technology for the recovery of critical metals, contributing to a circular economy and reducing the environmental impact of mining and refining activities. The opportunity for producing materials with enhanced performance will be portrayed, together with the portent of a customizable and flexible solution which can be integrated with existing recycling chains.AcknowledgementThis research has received funding from the European Union’s Horizon 2020 and Horizon Europe research and innovation programmes under grant agreements 958302 (PEACOC Project), 101069685 (Rhinoceros Project), 101069644 (LICORNE Project), 101058163 (CRM-Geothermal Project), and 101091715 (FIREFLY Project).ReferencesPrato M.R.A., Van Vught V., Chayambuka K., Pozo G., Eggermont S., Fransaer J., Dominguez-Benetton X. (2020) Synthesis of material libraries using gas diffusion electrodes. J. Mater. Chem. A, 8:11674-11686. DOI:10.1039/D0TA00633E.Martinez Mora O., Pozo G., Leon-Fernandez L.F., Fransaer J., Dominguez-Benetton X. (2023) Synthesis of platinum group metal nanoparticles assisted by CO2 reduction and H2 cogeneration at gas-diffusion electrodes. RSC Sustain., 2023, Accepted Manuscript. DOI: 10.1039/D3SU00046J

Designing Multidimensional and Interconnected Multi-Element Nanostructures by Exsolution-Self-Assembly in a Complex Concentrated Oxide

Complex concentrated oxides (CCOs) are an emerging material class that includes high-entropy oxide (HEOs) and entropy-stabilized oxides (ESOs), whose unprecedented properties stem from disorder-induced distributions in electronic structure and chemistry caused by stabilizing many-cation (typically > 5) solid solutions [1-2]. Integrating these materials into composites with nanoscale tunability will enable tailored (multi)functionality beyond what is possible in a single phase [3]. Here, we demonstrate a novel, highly extensible approach, exsolution self-assembly (ESA), to realize CCO-based nanocomposite thin films with intricate multi-element nanostructures [4]. Using pulsed-laser deposition (PLD), we selectively reduce cations in a 6-cation model perovskite CCO, inducing defect-interaction-driven exsolution and simultaneous self-assembly of metal nanorods and metal-oxide core-shell nanoparticles, depending on film growth conditions. ESA using a CCO precursor enables novel multielement composite morphologies with finely tuned sub-phase chemical composition that are not possible by conventional exsolution or self-assembly independently. By mapping the distribution of distinct sub-phase structure and chemistry with sub-nanoscale electron microscopy and atom probes, we show that Ellingham's model of cation reducibility predicts nanostructure chemical composition while mass transport via extended defects governs local morphology formation. Importantly for various applications, the electronic conductivity of our nanocomposites exceeds 0.1 S/cm at room temperature, with transport correlated to nanostructure formation primarily through B-site cation mixed valency and site occupancy in the CCO matrix.A correlated analysis using aberration-corrected scanning transmission electron microscopy (STEM) imaging, energy dispersive X-ray spectroscopy (EDS), electron energy-loss spectroscopy (EELS), geometric phase analysis (GPA) strain mapping, atom probe tomography (APT) with 3D mass spectrometry, and X-ray photoemission spectroscopy (XPS) was performed to elucidate the fundamental nanostructure formation mechanisms underlying the highly tailorable synthesis approach. We show that the method achieves uniform bulk exsolution with short process time and is manipulated by tuning readily accessible PLD conditions. Detailed characterization resolved the impact of increasing oxygen vacancy concentration and varying cation reducibility on nanostructure self-assembly. For example, metal nanorods grow from the bottom of the thin film to the top surface, with growth restricted by compressive stress exerted by the matrix in the in-plane direction. Metal-oxide core-shell nanoparticles embedded in the matrix form via seed growth effect triggered by metal nanoparticle formation followed by subsequent reduction of additional mobile cations. This work demonstrates a route towards vast morphological tunability and compositional complexity through nanocomposite design of CCO thin films. Given CCOs’ vast combinatorial space, ESA is expected to be highly extensible via application to novel compositions and crystal structures, with the understanding presented here enabling one to take advantage of chemical complexity in a rational way.

Electrochemical Top-Down Synthesis of Nanostructured Electrocatalysts for Polymer Electrolyte Membrane Fuel Cells

Nanostructured catalysts are a promising class of materials to meet the requirements for the energy transition away from fossil fuels towards alternative, carbon-free, energy carriers, such as hydrogen. These catalyst materials boost the efficiency of energy conversion devices, such as fuel cells or electrolyzers, by accelerating their fundamental electrochemical reactions. Bottom-up synthetic routes for nanostructured materials often involve multiple synthesis steps and the use of surfactants, reducing agents or stabilizers. This results in complex and extensive synthesis protocols.[1] In recent years, a novel top-down synthesis approach to form metal nanoparticles has been established, in which bulk metal wires are immersed in an electrolyte and subsequently subjected to a high alternating potential. This leads to the generation of nanoparticles dispersed in the electrolyte.[2] There is no need for reducing agents, surfactants, or precursor solutions. The complete synthesis can be performed in one pot involving one main step with consequent washing and drying of the nanoparticles.In this study, we synthesized Pt-based nanoparticles supported on Vulcan® carbon support (Pt/C) and tested their electrochemical activity towards the oxygen reduction reaction (ORR) for polymer electrolyte membrane fuel cells (PEMFCs). Firstly, we elucidated the influence of synthesis parameters such as potential amplitude, frequency, electrolyte composition, and concentration on the size and shape of Pt nanoparticles.[3] We continued with the synthesis of more complex nanostructures, such as Pt alloy nanoparticles. This introduces strain and ligand effects at the surface of the nanoparticles, which increases the electrocatalytic activity for the ORR. We demonstrated the facile, simple, and surfactant-free synthesis of highly active PtxPr/C[4] and PtxCu/C, as two examples for Pt alloy catalysts for the ORR, and give an outlook on other systems, such as PtxGd/C.

An Overview of Heterogeneous Catalysts Based on Hypercrosslinked Polystyrene for the Synthesis and Transformation of Platform Chemicals Derived from Biomass.

Platform chemicals, also known as chemical building blocks, are substances that serve as starting materials for the synthesis of various value-added products, which find a wide range of applications. These chemicals are the key ingredients for many fine and specialty chemicals. Most of the transformations of platform chemicals are catalytic processes, which should meet the requirements of sustainable chemistry: to be not toxic for humans, to be safe for the environment, and to allow multiple reuses of catalytic materials. This paper presents an overview of a new class of heterogeneous catalysts based on nanoparticles of catalytically active metals stabilized by a polymer matrix of hypercrosslinked polystyrene (HPS). This polymeric support is characterized by hierarchical porosity (including meso- and macropores along with micropores), which is important both for the formation of metal nanoparticles and for efficient mass transfer of reactants. The influence of key parameters such as the morphology of nanoparticles (bimetallic versus monometallic) and the presence of functional groups in the polymer matrix on the catalytic properties is considered. Emphasis is placed on the use of this class of heterogeneous catalysts for the conversion of plant polysaccharides into polyols (sorbitol, mannitol, and glycols), hydrogenation of levulinic acid, furfural, oxidation of disaccharides, and some other reactions that might be useful for large-scale industrial processes that aim to be sustainable. Some challenges related to the use of HPS-based catalysts are addressed and multiple perspectives are discussed.

Effect Of Microwave In The Green Synthesis Of Colloidal Bismuth Nanoparticles

In this study, bismuth nanoparticles were synthesized and prepared using citrus aurantifolia green synthesis method. The effect of microwave heating was examined. Citrus aurantifolia was used to reduce metal ions and nanoparticle formation due to the presence of various biomolecules needed. microwave was chosen because it can accelerate and form more stable nanoparticles. Bismuth nanoparticles were successfully synthesized with UV-Vis wavelength at 276 nm and nanoparticle average size is 4.66 nm. This result also shows a better TEM result image when with microwave because there is no impurity from bioreductor.

Single-Atom Catalysts for Selective Oxygen Reduction: Transition Metals in Uniform Carbon Nanospheres with High Loadings.

Transition metal single-atom catalysts (SACs) in uniform carbon nanospheres have gained tremendous interest as electrocatalysts owing to their low cost, high activity, and excellent selectivity. However, their preparation typically involves complicated multistep processes that are not practical for industrial use. Herein, we report a facile one-pot method to produce atomically isolated metal atoms with high loadings in uniform carbon nanospheres without any templates or postsynthesis modifications. Specifically, we use a chemical confinement strategy to suppress the formation of metal nanoparticles by introducing ethylenediaminetetraacetic acid (EDTA) as a molecular barrier to spatially isolate the metal atoms and thus generate SACs. To demonstrate the versatility of this synthetic method, we produced SACs from multiple transition metals, including Fe, Co, Cu, and Ni, with loadings as high as 3.87 wt %. Among these catalytic materials, the Fe-based SACs showed remarkable catalytic activity toward the oxygen reduction reaction (ORR), achieving an onset and half-wave potential of 1.00 and 0.831 VRHE, respectively, comparable to that of commercial 20 wt % Pt/C. Significantly, we were able to steer the ORR selectivity toward either energy generation or hydrogen peroxide production by simply changing the transition metal in the EDTA-based precursor.

Fe-Co Alloy Nanoparticles Dispersed in Polymer-Derived Carbon Support: Effect of Initial Polymer Nature on the Size, Structure and Magnetic Properties.

Fe-Co alloy nanoparticles with different sizes, supported by carbon derived from several polymers, namely polyacrylonitrile, polyvinyl alcohol and chitosan, have been synthesized by a one-pot method involving simultaneous metal nanoparticle formation and polymer carbonization. The method involves the joint dissolution of metal salts and a polymer, followed by annealing of the resulting dried film. Detailed XRD analysis confirmed the formation of Fe-Co alloy nanoparticles in each sample, regardless of the initial polymer used. Transmission electron microscopy images showed that the Fe-Co nanoparticles were all spherical, were homogeneously distributed within the carbon support and varied by size depending on the initial polymer nature and synthesis temperature. Fe-Co nanoparticles supported by polyacrylonitrile-derived carbon exhibited the smallest size (6-12 nm), whereas nanoparticles on chitosan-derived carbon support were characterized by the largest particle size (13-38 nm). The size dependence of magnetic properties were studied by a vibrating sample magnetometer at room temperature. For the first time, the critical particle size of Fe-Co alloy nanoparticles with equiatomic composition has been experimentally determined as 13 nm, indicating the transition of magnetic properties from ferromagnetic to superparamagnetic.

Revitalizing platinum: Alkali-promoted formation of active metallic nanoparticles from inert Pt entities for enhanced benzene combustion

Pt-based catalysts play a crucial role in the catalytic combustion of benzene. Previous studies have highlighted the significance of metal Pt atoms as the active phase in benzene combustion, while oxidized Pt sites exhibit lower activity. In practical catalysts synthesized through wet chemical methods, a range of metal species is present, including highly dispersed oxidized metal atoms, small oxidized metal clusters, and metal nanoparticles. This paper explores an effective strategy to enhance metal utilization and develop high-performance platinum-based catalysts for benzene catalytic combustion by introducing alkali metals. This approach transforms low-activity oxidized metal atoms and small oxidized metal clusters into active small metal nanoparticles. The introduction of K-O groups displaces Pt from oxygen vacancy trapping sites on antimony-doped tin oxide (ATO) support, enhancing Pt mobility and converting them into active metallic Pt nanoparticles, ultimately improving benzene combustion. These findings highlight the role of alkali metals in promoting catalytic activity and provide insights for designing high-performance noble-metal-based catalysts.

Preparation of Dual‐activity Enzyme‐metal‐nanoparticles Conjugate Catalysts for Cascade Processes

AbstractThe fabrication of novel systems where enzymatic and metallic actives sites directly interact represents an elegant strategy for sustainable processes. One of the new strategies involves the in situ formation of metal nanoparticles on a protein network as scaffold. This biological entity is the key element because it conserves the biological catalytic efficiency and induces the final metallic nanoparticles generation on the structure. This method allows to obtain bifunctional enzyme‐metallic catalysts with excellent versatility and efficiency in a different reaction and experimental conditions. In this concept article, the relevant aspects in terms of fabrication of enzyme‐metal nanoparticles hybrids and recently reported examples of successful application in cascade processes will be described.

From biomolecules to biogeochemistry: Exploring the interaction of an indigenous bacterium with gold

Specialised microbial communities colonise the surface of gold particles in soils/sediments, and catalyse gold dissolution and re-precipitation, thereby contributing to the environmental mobility and toxicity of this ‘inert’ precious metal. We assessed the proteomic and physiological response of Serratia proteamaculans, the first metabolically active bacterium enriched and isolated directly from natural gold particles, when exposed to toxic levels of soluble Au3+ (10 μM). The results were compared to a metal-free blank, and to cultures exposed to similarly toxic levels of soluble Cu2+ (0.1 mM); Cu was chosen for comparison because it is closely associated with Au in nature due to similar geochemical properties. A total of 273 proteins were detected from the cells that experienced the oxidative effects of soluble Au, of which 139 (51%) were upregulated with either sole expression (31%) or had synthesis levels greater than the Au-free control (20%). The majority (54%) of upregulated proteins were functionally different from up-regulated proteins in the bacteria-copper treatment. These proteins were related to broad functions involving metabolism and biogenesis, followed by cellular process and signalling, indicating significant specificity for Au. This proteomic study revealed that the bacterium upregulates the synthesis of various proteins related to oxidative stress response (e.g., Monothiol-Glutaredoxin, Thiol Peroxidase, etc.) and cellular damage repair, which leads to the formation of metallic gold nanoparticles less toxic than ionic gold. Therefore, indigenous bacteria may mediate the toxicity of Au through two different yet simultaneous processes: i) repairing cellular components by replenishing damaged proteins and ii) neutralising reactive oxygen species (ROS) by up-regulating the synthesis of antioxidants. By connecting the fields of molecular bacteriology and environmental biogeochemistry, this study is the first step towards the development of biotechnologies based on indigenous bacteria applied to gold bio-recovery and bioremediation of contaminated environments.

Role of Kinetics and Thermodynamics in Controlling the Crystal Structure of Nickel Nanoparticles Formed on Reduced Graphene Oxide: Implications for Energy Storage and Conversion Applications

Ultrafast heating has emerged recently to speed up the synthesis processes of nanoparticles and control their morphology. However, it is not clear how the heating rate affects the formation of metal nanoparticles, particularly those formed on substrates. Here, we explored the formation of nickel (Ni) nanoparticles on graphene oxide (GO) substrates under slow (20 °C/min) and ultrafast (103 °C/s) heating rates. The experiments were performed in situ on heating microchip devices using an aberration-corrected transmission electron microscope. Interestingly, the GO structure was the most effective in controlling the stability of nanoparticles when ultrafast heating was employed, leading to a hexagonally close-packed Ni phase (hcp-Ni) because of less lattice mismatch with the graphitic substrate. On the contrary, fcc-Ni nanoparticles formed under a slow heating process where no strong correlation with the GO crystal structure was observed. Additionally, ultrafast heating resulted in smaller-size nanoparticles which could be ascribed to rapid reduction, nucleation rate, and higher diffusion barrier of hcp-Ni crystals on rGO. Nevertheless, the stability of the crystal structure of the nickel nanoparticles remains unaffected by their size. These results indicate the crucial role of the substrate on crystal structure during the nonequilibrium processing of materials and the competing effects of thermodynamics versus kinetics in creating novel phases of materials for energy storage and conversion applications.

PENENTUAN KANDUNGAN ANTIOKSIDAN DAN FENOLIK TOTAL DARI EKSTRAK TUMBUHAN SEBAGAI BIOREDUKTOR DALAM PEMBENTUKAN NANOPARTIKEL PERAK

The formation of metal nanoparticles (silver, gold, platinum) by biological methods (green synthesis) has advantages over chemical and physical methods because it is easier, faster, simpler, and environmentally friendly. One of the substances used in this method is plant extracts. The presence of secondary metabolites that act as antioxidants such as phenolics and flavonoids play roles in the formation of silver nanoparticles. In this study, phytochemical screening was carried out from several herbal plants as bioreductors in the formation of silver nanoparticles, such as Phyllanthus buxifolius, Pachira aquatica, Peperomia pellucida, Ageratum conyzoides, and Piper crocatum leaf extracts. The total antioxidant content was determined using the modified phenanthroline method, and the total phenolic content determined using the Folin-Ciocalteu method. The formation of silver nanoparticles was carried out by mixing silver nitrate solution with each plant extract. Colloidal silver nanoparticles formed were then measured for their absorption spectra. The results of the antioxidant content of the five consecutive samples were 26,90 ± 0,19; 26,09 ± 0,14; 18,25 ± 0,02; 42,76 ± 0,14; dan 30,94 ± 0,14 mg AA/g, while the total phenolic contents were 48,44 ± 0,45; 21,08 ± 0,92; 17,42 ± 0,27; 57,71 ± 0,47; dan 49,83 ± 0,60 mg GA/g. Silver nanoparticles mediated by Ageratum conyzoides leaf extracts provided the highest absorbance value compared to other plants. The antioxidants and phenolic contained in the extract acts as reducing agent from silver ions into silver nanoparticles.

Green synthesis, characterization and antibacterial activity of Tin (IV) oxide nanoparticles using root extract of Cassia tora

Synthesis of nanoparticles via green resources is a pollutant free, easy, ecofriendly, and low cost method. Nanoparticles synthesized by using plant materials are generally non-toxic. Aqueous root extract of plant, Cassia tora showed the presence of phytochemical constituents like alkaloids, flavonoids, phenols, tannins, saponins etc. which are directly involved in the reduction of metal salts hence forming metal nanoparticles. Thermal treatment of these metal nanoparticles changes them to their oxides. Tin (IV) oxide nanoparticles prepared via this route were first characterized and then evaluated for their antibacterial potential against three species of Gram negative bacteria viz., Salmonella typhi, Escherichia coli &Shigella flexineri and two speices of Gram positive bacteria viz. Bacillus cereus & Staphylococcus aureus. The current study reports the synthesis and characterization of Tin (IV) oxide nanoparticles using Cassia tora root extract.Synthesized nanoparticles were evaluated for their antibacterial activity. Results of antimicrobial activity showed excellent antibacterial property against Gram negative bacteria than Gram positive bacteria. Research has proved that green methods are more effective for generation of nanoparticles than the traditional methods, used in past as there are less chances of failure and shows enhanced biological activity.

Atomically Dispersed NiNx Site with High Oxygen Electrocatalysis Performance Facilely Produced via a Surface Immobilization Strategy

Nonprecious-metal heterogeneous catalysts with atomically dispersed active sites demonstrated high activity and selectivity in different reactions, and the rational design and large-scale preparation of such catalysts are of great interest but remain a huge challenge. Current approaches usually involve extremely high-temperature and tedious procedures. Here, we demonstrated a straightforward and scalable preparation strategy. In two simple steps, the atomically dispersed Ni electrocatalyst can be synthesized in a tens grams scale with quantitative yield under mild conditions, and the active Ni sites were produced by immobilizing preorganized NiNx complex on the substrate surface via organic thermal reactions. This catalyst exhibits excellent catalysis performances in both oxygen evolution and reduction reactions. It also exhibited tunable catalysis activity, high catalysis reproducibility, and high stability. The atomically dispersed NiNx sites are tolerant at high Ni concentration, as the random reactions and metal nanoparticle formation that generally occurred at high temperatures were avoided. This strategy illustrated a practical and green method for the industrial manufacture of nonprecious-metal single-site catalysts with a predictable structure.

Litchi‐derived platinum group metal‐free electrocatalysts for oxygen reduction reaction and hydrogen evolution reaction in alkaline media

AbstractWithin the framework of the circular economy, the waste litchi's skins were upgraded and transformed into electrocatalysts for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). The waste litchi's skins were pyrolyzed, activated, and then used as carbon support for fabricating metal–nitrogen–carbons (M–N–Cs) which belong to a promising class of platinum group metal‐free electrocatalysts. The activated char was functionalized with transition metal (Fe, Ni, and Co)‐ phthalocyanine (Pc) in monometallic and bimetallic fashion by subjecting it to a thermal treatment at 600 and 900°C. The samples functionalized at 900°C showed higher performance for HER due to the formation of metal nanoparticles, whereas the samples functionalized at 600°C showed higher performance for ORR. Particularly, sample Ni–Co 900 had an overpotential of −0.38 V for HER, while the sample Fe 600 was the most active electrocatalyst for ORR by demonstrating the onset potential of ∼0.9 V (a half‐wave potential of ∼0.81 V) with the least production of unwanted peroxide anion.

Ex-Solution Hybrids Functionalized on Oxide Nanofibers for Highly Active and Durable Catalytic Materials

Ex-solution catalysts containing spontaneously formed metal nanoparticles socketed on the surface of reservoir oxides have recently been employed in various research fields including catalysis and sensing, due to the process efficiency and outstanding chemical/thermal stability. However, since the ex-solution process accompanies harsh reduction heat treatment, during which many oxides undergo phase decomposition, it restricts material selection and further advancement. Herein, we propose an elaborate design principle to uniformly functionalize ex-solution catalysts at porous oxide frameworks via an electrospinning process. As a case study, we selected the ex-solved La0.6Ca0.4Fe0.95Co0.05-xNixO3-δ (x = 0, 0.025 and 0.05) and SnO2 nanofibers as ex-solution hybrids and main frameworks, respectively. We confirmed superior dimethyl sulfide (C2H6S) gas sensing characteristics with excellent long-cycling stability. In particular, the high catalytic activities of ex-solved CoNiFe ternary nanoparticles, strongly socketed on reservoir oxide, accelerate the spillover process of O2 to dramatically enhance the response toward sulfuric analytes with exceptional tolerance. Altogether, our contribution represents an important stepping-stone to a rational design of ex-solved particle-reservoir oxide hybrids functionalized on porous oxide scaffolds for a variety of applications.