Facile synthesis of metal nanoparticles using conducting polymer colloids

We report a simple method to synthesize Ag, Au, and Pt nanoparticles with a reasonable size dispersity using water-dispersible conducting polymer colloids composed of polyaniline (PANI) and conventional polyelectrolyte. This facile synthesis results in single crystalline metal nanoparticles that are stable in an aqueous solution for at least several weeks. The process involves incrementally adding a metal ion solution to aqueous conducting polymer colloids and does not require reducing agents such as NaBH₄. In addition, the complete synthetic and purification procedure is carried out in an aqueous solution; therefore, it is environmentally benign and potentially suitable for large-scale production. We have also demonstrated synthesis of larger nanoparticles and nanosheets by varying the experimental parameters. With the tunable oxidation states of conducting polymers, we expect this synthetic platform can synthesize a wide range of nanostructured metals with specific size, shape and properties. Finally, the nanoparticles embedded in the conducting polymer matrix, the metal-polyaniline nanocomposite itself may be interesting since it represents a type of materials where metallic nanoislands are embedded in a semiconducting matrix.     

Nanosized catalysts as a basis for intensifications of technologies

This investigation of the catalytic properties of noble metal nanoparticles stabilized in hyper crosslinked polystyrene (HPS) matrix shows the prospect for their application in selective hydrogenation, selective oxidation and enantioselective hydrogenation, which represent key stages for the synthesis of the intermediates and final products of pharmaceutical industry. Commercial use of nanosized catalysts allows shortening the synthetic stages, increasing product yields, and improving the environmental safety of the existing industrial processes. In this review, the synthesis, structure and catalytic properties of mono (Pt, Ru, Pd), bi (Pt-Pd, Pt-Ru, Pd-Ru), and trimetallic (Pt-Pd-Ru) nanoparticles stabilized in the pores of a polymeric HPS matrix are discussed. Physicochemical investigations have shown that the formation of metalcontaining nanoparticles depends on the properties of the porous polymeric structure, the nature of the initial metal precursor, and the synthesis conditions. The use of nanosized catalysts is revealed to be effective in the most important field of fine organic synthesis: preparation of materials for medicine, vitamins, and food additives (e.g. in food and pharmaceutical industries).     

Greener synthesis and medical applications of metal oxide nanoparticles

Over the past decade, the subject of “greener chemistry" and chemical processes has been emphasized. The “greener chemistry” improves environmental efficiency in reducing the consumption of resources and energy and achieving a stable economic development of the environment. Nanotechnology is investigating nanoscale materials that have applications in the area of biotechnology and nanomedicine alongside several other significant applications such as cosmetics, drug delivery, and biosensors. The different shapes and sizes of nanoparticles can be synthesized with physical, chemical, or biological methods. The tendency to produce nanomaterials, especially metal oxides, and use them, is increasing because of their exciting properties in the nanoscale. However, metal oxide nanoparticles produced by chemical methods have significant concerns due to hazardous and toxic chemicals and their environmental damage. The production of metal oxide nanoparticles using the principles of greener chemistry has found a special place in research. Increased awareness of greener chemistry and biological processes has necessitated using environmentally friendly methods for the production of non-toxic nanomaterials. Plants and polymeric materials as renewable and inexpensive sources have received particular attention to prepare nano biomaterials. The use of plants to synthesize metal oxide nanoparticles because of the non-use toxic pollutants is one of the environmentally friendly methods, and that's why this type of synthesis is called greener synthesis. In this review, we exhibit a total sight of greener synthesis methods for producing metal oxide nanoparticles and their medical applications.     

Plant‐mediated synthesis of silver and gold nanoparticles and their applications

Nanobiotechnology deals with the synthesis of nanostructures using living organisms. Among the use of living organisms for nanoparticle synthesis, plants have found application particularly in metal nanoparticle synthesis. Use of plants for synthesis of nanoparticles could be advantageous over other environmentally benign biological processes as this eliminates the elaborate process of maintaining cell cultures. Biosynthetic processes for nanoparticles would be more useful if nanoparticles were produced extracellularly using plants or their extracts and in a controlled manner according to their size, dispersity and shape. Plant use can also be suitably scaled up for large‐scale synthesis of nanoparticles. In view of this, we have reviewed here the use of plants or their extracts in the synthesis of silver and gold nanoparticles for various human applications. Copyright © 2008 Society of Chemical Industry     

Colloid Science of Metal Nanoparticle Catalysts in 2D and 3D Structures. Challenges of Nucleation, Growth, Composition, Particle Shape, Size Control and Their Influence on Activity and Selectivity

Recent breakthroughs in the synthesis of nanosciences have achieved the control of size and shape of nanoparticles that are relevant for catalyst design. In this article, we review advances in the synthesis of nanoparticles, fabrication of two- and three-dimensional model catalyst systems, characterization, and studies of activity and selectivity. The ability to synthesize monodispersed platinum and rhodium nanoparticles 1–10 nm in size permitted us to study the influence of composition, structure, and dynamic properties of monodispersed metal nanoparticles on chemical reactivity and selectivity. We review the importance of the size and shape of nanoparticles to determine reaction selectivity in multi-path reactions. The influence of metal–support interaction has been studied by probing the hot electron flows through the metal–oxide interface in catalytic nanodiodes. Novel designs of nanoparticle catalytic systems are also discussed.     

Three strategies to stabilise nearly monodispersed silver nanoparticles in aqueous solution

ABSTRACT: Silver nanoparticles are extensively used due to their chemical and physical properties and promising applications in areas such as medicine and electronics. Controlled synthesis of silver nanoparticles remains a major challenge due to the difficulty in producing long-term stable particles of the same size and shape in aqueous solution. To address this problem, we examine three strategies to stabilise aqueous solutions of 15 nm citrate-reduced silver nanoparticles using organic polymeric capping, bimetallic core-shell and bimetallic alloying. Our results show that these strategies drastically improve nanoparticle stability by distinct mechanisms. Additionally, we report a new role of polymer functionalisation in preventing further uncontrolled nanoparticle growth. For bimetallic nanoparticles, we attribute the presence of a higher valence metal on the surface of the nanoparticle as one of the key factors for improving their long-term stability. Stable silver-based nanoparticles, free of organic solvents, will have great potential for accelerating further environmental and nanotoxicity studies.PACS: 81.07.-b; 81.16.Be; 82.70.Dd.     

Microgel electrospinning: A novel tool for the fabrication of nanocomposite fibers

We demonstrate for the first time herein that electrospinning of soluble crosslinked polymer particles (microgels) is feasible and that it can be used to obtain micron-sized fibers from these macromolecules. Most notably, the electrospinning approach is found to be successful also in the case of microgels bearing metal nanoclusters, and allows to prepare composite fibers containing a homogeneous dispersion of metal nanoparticles without alterations in the nanoparticle size and size distribution. Given the broad applicability of microgels as exotemplates and stabilisers for inorganic nanoparticles, the proposed preparation method stands out as a novel, general approach for the synthesis of potentially useful composite fibers containing inorganic nanoparticles.     

磁性壳聚糖微球的研究进展

磁性氧化铁纳米粒子（Fe3O4,γ-Fe2O3等）因具有尺寸小、超顺磁性和低毒性等特点,已经引起了生物化工、医药工业研究领域的广泛关注。磁性壳聚糖微球具有表面非常光滑的球形结构。近年来,已经制备出了平均粒径在10～2.5×105 nm之间的磁性壳聚糖微球,并在生物医药、食品工程和污水处理等许多领域已经取得了初步的应用,特别是在污水处理和酶固定化领域。本文综述了近年来磁性氧化铁纳米粒子和磁性壳聚糖微球的制备方法、磁性壳聚糖微球的改性方法及应用的最新研究成果。     

Some Aspects of Colloidal Nanoparticle Stability, Catalytic Activity, and Recycling Potential

In this review article, we examine many important aspects of the nanocatalysis field such as size and shape dependent nanocatalysis, the stability of nanoparticles during its catalytic function, and their recycling potential. We provide an overview of some of the work in the literature pertinent to these topics and also discuss some of our own work in these important areas. Some examples of how the catalytic activity is affected by the size of the nanoparticles are discussed as well as how the catalytic process affects the nanoparticle size after its catalytic function. The synthesis of platinum nanoparticles of different shapes is surveyed and the dependence of nanoparticle shape on the catalytic activity is discussed. In addition, changes in the nanoparticle shape and resulting changes in the catalytic activity are also discussed. The recycling potential of the metal nanocatalysts is also highlighted. In addition, a simple examination of the mechanism of nanocatalysis is discussed.     

Structure of reverse microemulsion-templated metal hexacyanoferrate nanoparticles

The droplet phase of a reverse microemulsion formed by the surfactant cetyltrimethylammonium ferrocyanide was used as a matrix to synthesize nanoparticles of nickel hexacyanoferrate by adding just a solution of NiCl₂ to the microemulsion media. Dynamic light scattering and small-angle neutron scattering measurements show that the reverse microemulsion droplets employed have a globular structure, with sizes that depend on water content. Transmission electron microscopy and electron diffraction are used to obtain information about the structure of the synthesized nanoparticles. The results show that the size and shape of the coordination compound nanoparticles correspond with the size and shape of the droplets, suggesting that the presented system constitutes an alternative method of the synthesis of metal hexacyanoferrate nanoparticles.     

Conifer-Derived Metallic Nanoparticles: Green Synthesis and Biological Applications

The use of metallic nanoparticles in engineering and biomedicine disciplines has gained considerable attention. Scientists are exploring new synthesis protocols of these substances considering their small size and lucrative antimicrobial potential. Among the most economical techniques of synthesis of metallic nanoparticles via chemical routes, which includes the use of chemicals as metal reducing agents, is considered to generate nanoparticles possessing toxicity and biological risk. This limitation of chemically synthesized nanoparticles has engendered the exploration for the ecofriendly synthesis process. Biological or green synthesis approaches have emerged as an effective solution to address the limitations of conventionally synthesized nanoparticles. Nanoparticles synthesized via biological entities obtained from plant extracts exhibit superior effect in comparison to chemical methods. Recently, conifer extracts have been found to be effective in synthesizing metallic nanoparticles through a highly regulated process. The current review highlights the importance of conifers and its extracts in synthesis of metallic nanoparticles. It also discusses the different applications of the conifer extract mediated metallic nanoparticles.     

Phyto-synthesized silver nanoparticles for biological applications

Silver nanoparticles (AgNPs) are valuable metal nanoparticles that exhibit exceptional properties compared to their bulk materials. Pronounced surface area, quantum confinement effect complemented by small particle dimension, and many other extraordinary characteristics make AgNPs suitable in a variety of applications. Different methods have been adopted to synthesize AgNPs. Biological methods can formulate AgNPs in an environmentally friendly manner without producing toxic waste. Among the biological methods, plants are simple and attractive sources for AgNP synthesis. Compared to AgNPs produced via other modes of synthesis, phyto-synthesized AgNPs, due to their safety features, have been found to be advantageous for a variety of applications, especially biological applications. Strong research efforts have investigated the utility of phyto-synthesized AgNPs for different applications. Investigators are coming up with innovative applications of phyto-synthesized AgNPs for the development of science and technology and to benefit humankind. The present article focuses on phyto-synthesized AgNPs for biological applications, with a brief review of their synthesis, mechanism, and size/shape control.     

New Trends in Nanoparticles: Syntheses and Their Applications to Fuel Cells,Health Care,and Magnetic Storage

This paper reviews important research on chemical and electrochemical synthesis and application of nanoparticles, especially our recent results in this field: (i) catalytic metal nanoparticles for micro-fuel cells, (ii) magnetic oxide nanoparticles for drug delivery systems, and (iii) magnetic metal nanoparticles for magnetic recording media. To fulfill the requirements of each application, we chose and modified those synthetic methods for obtaining suitable properties, e.g., morphology, catalytic activity, and magnetic properties. (i) For micro-fuel cells, electrodeposition is attractive because of its selective deposition onto current collectors and possible elimination of an annealing process. As a result, we have successfully synthesized Pt, PtRu alloy, and PdCo alloy, which consisted of dendritic structures macroscopically and of interconnected nanoparticles microscopically. (ii) For drug delivery systems, since magnetic nanoparticles should possess ferromagnetism, be dispersible in water, and be nontoxic, Fe₃O₄ nanoparticles synthesized by hydrolysis in aqueous media are suitable. As a result, we have successfully controlled the size (10–40 nm in diameter) and the magnetic properties of Fe₃O₄ nanoparticles by means of adjusting the molar ratio of ferrous to ferric ions in the precursor solution. (iii) For magnetic recording materials, since magnetic nanoparticles should possess high coercivity, a controlled shape, and a uniform small size, we have modified a chemical method for synthesizing FePt by adjusting the growth temperature. As a result, we have succeeded in synthesizing FePt nanoparticles with a controlled shape (cubic) and a uniform size (ca. 5.6 nm).     

Pseudomatrix synthesis of polymer-metal nanocomposite sols: Interaction of macromolecules with metal nanoparticles

The experimental and theoretical data on the effect of macromolecules on the formation of a metal phase during reduction of metal ions in a polymer solution and on the aggregative stability of sols with a narrow size distribution of metal nanoparticles and their small average size are summarized and analyzed. It has been shown that owing to the cooperativity, reversibility, and selectivity of noncovalent interactions of sufficiently long macromolecules with nanoparticles, the dispersion phase of such sols may be regarded as a macromolecule-nanoparticle complex, which forms once a certain size of the particles is achieved and in which the growth of particles ceases. The process of sol synthesis may be regarded as pseudomatrix. The theoretical model developed for the pseudomatrix process of metal phase formation in polymer solutions, which adequately describes the experimental data, makes it possible to control the synthesis conditions of sols of polymer-metal nanocomposites with preset dimensional characteristics of nanoparticles and to govern the aggregative stability of sols.     

Surface coverage of Pt atoms on PtCo nanoparticles and catalytic kinetics for oxygen reduction

The surface coverage of Pt atoms on PtCo nanoparticles and its effect on catalytic kinetics for oxygen reduction were investigated. The PtCo nanoparticles with different surface coverage of Pt atoms were synthesized with various methods, including normal chemical method, microemulsion synthesis, and ultrasound-assisted microemulsion. A model of Pt atoms filling into a spherical nanoparticle was proposed to explain the relationship of surface metal atoms and nanoparticle size. The catalytic activity of the PtCo nano-particles is highly dependent on the synthetic methods, even if they have the same chemical composition. The PtCo nano-particles synthesized with ultrasound-assisted microemulsion showed the highest activity, which is attributed to an increase of active surface coverage of Pt atoms on the metal nanoparticles. The rate of oxygen reduction at 0.5 V (vs. SCE) catalyzed by the PtCo synthesized with ultrasound-assisted micro-emulsion was about four times higher than that of the PtCo synthesized with normal chemical method. As demonstrated with rotating-ring disk electrode measurement, the PtCo nano-particles can catalyze oxygen 4-electron reduction to water without intermediate H₂O₂ detected.     

Recent Advances in Metal Nanoparticles Stabilization into Nanopores of Montmorillonite and Their Catalytic Applications for Fine Chemicals Synthesis

Metal nanoparticles supported montmorillonite with innovative characteristics has led to a new generation of heterogeneous “nanocatalyst.” Such catalysts are superior to the conventional catalysts because of several factors like: higher surface area; higher activity; higher selectivity and longer life and thus, developing a newer type of sustainable environmentally friendly catalysts. Metal clay supported nanocatalysts may find a wide range of applications in the area of fine and bulk chemical industries, pharmaceuticals, fuel cell, petroleum refineries, environmental catalysis, and many other fields. This article summarizes the recent advances in the synthesis and characterization of metal nanoparticles supported on modified montmorillonite and their catalytic applications for fine chemicals synthesis.     

Investigations of Structure Sensitivity in Heterogeneous Catalysis: From Single Crystals to Monodisperse Nanoparticles

Metal surface structure is often a crucial component in determining the activity and selectivity of heterogeneous catalytic reactions. Many important industrial reactions, such as ammonia synthesis, catalytic combustion, Fischer–Tropsch synthesis, and hydrocarbon reforming have been labeled as structure-sensitive. Metal single crystal studies utilizing ultra high vacuum techniques have repeatedly shown the importance of surface structure in reaction kinetics. Recent advances in the field of colloidal synthesis allow for fine control of the size and shape of metal nanoparticles, which permits catalytic studies of structure sensitivity to be performed on nanometer sized catalysts. It is clear that in order to optimize the performance of a catalyst, a complete molecular level understanding of the role of surface structure in the reaction of interest is essential. This article aims to review the importance of surface structure in heterogeneous catalysts, ranging from single crystals to size and shape controlled nanocatalysts.     

Comparative Antimicrobial Activity of Silver Nanoparticles Obtained by Wet Chemical Reduction and Solvothermal Methods

The synthesis of nanoparticles from noble metals has received high attention from researchers due to their unique properties and their wide range of applications. Silver nanoparticles (AgNPs), in particular, show a remarkable inhibitory effect against microorganisms and viruses. Various methods have been developed to obtain AgNPs, however the stability of such nanostructures over time is still challenging. Researchers attempt to obtain particular shapes and sizes in order to tailor AgNPs properties for specific areas, such as biochemistry, biology, agriculture, electronics, medicine, and industry. The aim of this study was to design AgNPs with improved antimicrobial characteristics and stability. Two different wet chemical routes were considered: synthesis being performed (i) reduction method at room temperatures and (ii) solvothermal method at high temperature. Here, we show that the antimicrobial properties of the obtained AgNPs, are influenced by their synthesis route, which impact on the size and shape of the structures. This work analyses and compares the antimicrobial properties of the obtained AgNPs, based on their structure, sizes and morphologies which are influenced, in turn, not only by the type or quantities of precursors used but also by the temperature of the reaction. Generally, AgNPs obtained by solvothermal, at raised temperature, registered better antimicrobial activity as compared to NPs obtained by reduction method at room temperature.     

High-throughput syntheses of nano-scaled mixed metal sulphides

The use of metal and mixed metal sulphides as heterogeneous catalysts is often hampered by an undefined composition formed by in situ sulphidation of oxides. Controlled synthesis methods are serial and thus slow, because high-throughput (HT) methods for the well-directed syntheses of exactly defined metal sulphides and especially mixed metal sulphides are still lacking. The present contribution presents the development of HT synthesis methods for a broad range of nano-scaled sulphides for various applications, such as heterogeneous catalysts or photocatalysts. The nano-scale regime for the particle sizes offers the possibilities of high surface area, appearance of quantum size effects and the possibility of modification of their properties as well as stabilisation of the particles by surface coating. Several precursor molecules have been tested, which hydrolyse under specific conditions and release sulphide ions for metal and mixed metal sulphide precipitation. Particle size confinement was achieved by w/o microemulsions using non-ionic surfactants. In a first step for the parallel synthesis of sulphides a 9-fold reactor assembly was developed, which offers the possibility of synthesis by precipitation and separation of the resulting materials by filtration in one setup.     

A simple plasma reduction for synthesis of Au and Pd nanoparticles at room temperature☆

A simple and fast plasma reduction method is developed for synthesis of Au and Pd metal nanoparticles. The scanning electron microscopy (SEM) analysis indicates a formation of aggregates of Au and Pd nanoparticles with branched structure. The transmission electron microscopy (TEM) image shows that the inclusive nanopar-ticles are al about 5 nm in size. Compared to conventional hydrogen reduction method, plasma method inhibits the agglomeration of metal particles. The room temperature operation is very helpful to limit the nanoparticle size. Most interestingly, plasma reduction produces more flattened metal particles. This plasma reduction does not require the use of any hazardous reducing chemicals, showing the great potential for the fabrication of noble metal nanoparticles.