Ordered nanostructured ceramic–metal composites through multifunctional block copolymer-metal nanoparticle self-assembly

A novel strategy for fabrication of ordered ceramic–metal nanocomposites was demonstrated by multifunctional block copolymer/metal nanoparticle self-assembly. Hybrid organic–inorganic block copolymer poly(3-methacryloxypropyl-T8-heptaisobutyl-polyhedral oligomeric silsesquioxane-block-N,N-dimethylaminoethyl methacrylate) was synthesized and used as a bi-functional structure directing agent for ligand-stabilized platinum nanoparticles to form ordered organic–inorganic nanocomposites with dense loading of inorganic species in both microphase separated domains. Subsequently, thin films of the hybrid material were converted to ordered silica (ceramic)–platinum (metal) nanocomposites via UV-assisted ozonolysis. This is the first time ordered ceramic–metal nanocomposites were achieved through a bottom-up approach, opening up opportunities for the design and synthesis of a broad range of ordered inorganic–inorganic nanocomposites.     

Preparation of PAMAM- and PPI-metal (silver, platinum, and palladium) nanocomposites and their catalytic activities for reduction of 4-nitrophenol

Dendrimer-metal (silver, platinum, and palladium) nanocomposites are prepared in aqueous solutions containing poly(amidoamine) (PAMAM) dendrimers with surface amino groups (generations 3, 4, and 5) or poly(propyleneimine) (PPI) dendrimers with surface amino groups (generations 2, 3, and 4). The particle sizes of the metal nanoparticles obtained are almost independent of the generation as well as the concentration of the dendrimer for both the PAMAM and the PPI dendrimers; the average sizes of silver, platinum, and palladium nanoparticles are 5.6-7.5, 1.2-1.6, and 1.6-2.0 nm, respectively. It is suggested that the dendrimer-metal nanocomposites are formed by adsorbing the dendrimers on the metal nanoparticles. Studies of the reduction reaction of 4-nitrophenol by these nanocomposites show that the rate constants are very similar between PAMAM and PPI dendrimer-silver nanocomposites, whereas the rate constants for the PPI dendrimer-platinum and -palladium nanocomposites are greater than those for the corresponding PAMAM dendrimer nanocomposites. In addition, it is found that the rate constants for the reduction of 4-nitrophenol involving all the dendrimer-metal nanocomposites decrease with an increase in the dendrimer concentrations, and the catalytic activity of dendrimer-palladium nanocomposites is highest.     

Synthesis and electrochemical characteristics of polymeric bimetallic Pt—Pd nanocatalysts

A method for the formation of catalytically active functional electrode nanocomposites with bimetallic platinum—palladium nanoparticles supported on a polymer matrix is described. The phase composition of nanocomposites was examined by X-ray powder diffraction, scanning electron microscopy and cyclic voltammetry were also applied in the study.     

Platinum-(diphenylamino styryl benzylazanediyl) diacetic acid derivatives nanocomposites: Synthesis and catalytic applications

Pt-(diphenylamino styryl benzylazanediyl) diacetic acid derivatives nanocomposites were synthesized via the alcohol reduction method and used as catalysts for hydrogenation of benzaldehydes including benzaldehyde, 3-phenoxybenzaldehyde, 4-hydroxybenzaldehyde, 4-anisaldehyde, and 4-dimethylaminobenzaldehyde. The nanocomposites characterized by UV-Vis, XRD and TEM have mean sizes of platinum cores from 1.8 to 2.9 nm. The size depends on the molar ratio of platinum and the organic compound in the nanocomposites. The Pt nanocomposites are stable not only in the colloidal solution but also during the catalytic hydrogenation process. The results of the catalytic hydrogenation of benzaldehyde derivatives demonstrate that the catalytic activity of the nanocomposites is much higher than that of Pt nanoparticles stabilized by Fréchet-type dendrimers under the same reaction conditions. High activity of the catalysts may be attributed to the relatively open dendritic shell of the nanocomposite, which provides large tunnels for the substrates moving from the surface to the active sites.     

Metal–Polymer Nanocomposites with Carbon Fillers for the Catalytic Oxidation of Formic Acid

Metal–polymer Pt–Pd nanocomposites on a Nafion polymer membrane modified with carbon nanotubes and carbon black are synthesized by the chemical reduction of ions in aqueous organic solutions of reverse microemulsions. The functional characteristics of the nanocomposites are studied by cyclic voltammetry and atomic force microscopy. The synthesized nanocomposites exhibit strong catalytic activity in the formic acid oxidation reaction. It is found that, at the optimum ratio of platinum metals, the catalytic activity of the metal–polymer composites is higher than that of the carbon nanocomposites.     

Formation of nanoparticles of platinum group metal alloys in composites based on nanodiamonds

Metal-carbon nanocomposites were synthesized from detonation nanodiamonds (ND) and platinum group metals under the IR pyrolysis conditions. The metal interacted with the nanodiamond surface. The size of metal nanoparticles was shown to depend on the amount of the metal introduced in the precursor. In ND/Pt-Ru, ND/Pt-Rh, ND/Pd-Ru, and ND/Pd-Rh nanocomposites, the metal phase was a solid solution. The lattice constants of the metal phases in the nanocomposites were determined. The quantity of the dissolved metal in the solid solution was evaluated.     

Catalysts with platinum–palladium nanoparticles on polymer matrix supports

The platinum–palladium/Nafion metal–polymer nanocomposites were synthesized by the chemical reduction of ions in the aqueous organic solutions of inverted microemulsions. The functional characteristics of the nanocomposites were studied by cyclic voltammetry, atomic force microscopy, and scanning electron microscopy. The nanocatalysts obtained exhibited high activity in the reactions of oxygen reduction and hydrogen oxidation. The influence of synthesis conditions on the catalytic activity of the metal–polymer nanocomposites was studied.     

Preparation and characterization of metal-chitosan nanocomposites

Various metal-chitosan nanocomposites were synthesized, including silver (Ag), gold (Au), platinum (Pt), and palladium (Pd) in aqueous solutions. Metal nanoparticles were formed by reduction of corresponding metal salts with NaBH4 in the presence of chitosan. And chitosan molecules adsorbing onto the surface of as-prepared metal nanoparticles formed the corresponding metal-chitosan nanocomposites. Transmission electron microscopy (TEM) images and UV-vis spectra of the nanocomposites revealed the presence of metal nanoparticles. Comparison of all the resulting particles size, it shows that silver nanoparticles are much larger than others (Au, Pt and Pd). In addition, the difference in particles size leads to develop different morphologies in the films cast from prepared metal-chitosan nanocomposites. Polarized optical microscopy (POM) images show a batonet-like structure for Ag-chitosan nanocomposites film, while for the films cast from other metal (Au, Pt, and Pd)-chitosan nanocomposites, some branched-like structures with a few differences among them were observed under POM observation.     

Platinum nanocomposites with mesoporous carbon nitride: synthesis and evaluation of the hydrogenation activity

Russian Chemical Bulletin - New platinum nanocomposites were synthesized by chemical reduction of H2PtCl6?6H2O in situ with a methanol—water mixture using mesoporous carbon nitride as a...     

Polyaniline/12-phosphotungstic acid/V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanocomposite and its platinum analog as oxygen reduction electrocatalysts

A guest-host nanocomposite based on electroconducting polyaniline doped with 12-phosphotungstic acid and V₂O₅ as well as its bifunctional analog containing not more than 5 mass% nanosized platinum were obtained. A study was carried out on the structure of these nanocomposites, their redox characteristics, and electrocatalytic activity in the reduction of oxygen. These nanocomposites were found to display catalytic properties in the electrochemical reduction of oxygen, while the presence of even a slight amount of nanosized platinum in the bifunctional composite leads to a significant increase in its electrocatalytic activity. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 5, pp. 307–314, September–October, 2007.     

Tuning selectivity in the gas phase hydrogenation of phenylacetylene over the platinum—mesoporous carbon nitride composites using organic modifiers

Russian Chemical Bulletin - The platinum nanocomposites with mesoporous carbon nitride (Pt/mpg-C3N4) were synthesized by in situ reduction of H2PtCl6·6H2O with aqueous methanol and studied as...     

Molecular sieving platinum nanoparticle catalysts kinetically frozen in nanoporous carbon

Highly active shape selective catalysts with excellent thermal stability are synthesized by entrapping well dispersed platinum nanoparticles in a polyfurfuryl alcohol derived nanoporous carbon matrix; these nanocomposites are excellent candidates for new catalytic applications including fuel cells, pharmaceutical synthesis and biomass conversion.     

Preparation and characterization of platinum (Pt) and palladium (Pd) nanoparticle decorated graphene sheets and their utilization for the elimination of basic fuchsin and indigo carmine dyes

In this study, graphene nano sheets, prepared with chemical oxidation and reduction routes via modified-Hummer method, were successfully decorated with platinum (Pt) and palladium (Pd) nanoparticles. Structural and morphological features of resulted graphene-metal nanocomposites were characterized with FT-IR, XRD, SEM and TEM methods. Anti-oxidant activity (AOA) values of nanocomposites were determined. The IC₅₀ values of Pt-graphene and Pd-graphene nanocomposites were found to be 46.1 and 90.2 μg/mL, respectively based on the ABTS method and 80.2 and 143.7 μg/mL according to the DPPH method. It was found that the graphene-metal nanocomposites exhibited superior free radical scavenging activity compared to several types of noble metal nano particles although the nanocomposites consist of much lower amount of active metal sites than the nano-crystalline metal powders. It was consequently reported that the graphene-metal nanocomposites could be successfully used for the photocatalytic elimination of fuchsin and indigo carmine dyes under light irradiation.     

Electrodeposition of platinum–nickel alloy nanocomposites on polyaniline-multiwalled carbon nanotubes for carbon monoxide redox

An electrochemical method was developed to deposit platinum (Pt)–nickel (Ni) alloy nanocomposites on polyaniline-multiwalled carbon nanotubes (Pt–Ni/PAN/MWCNTs). The material was characterized by various methods including field emission scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical techniques. An appreciably improved catalysis toward oxidation of carbon monoxide (CO) was observed at the Pt–Ni/PAN/MWCNTs nanocomposites (real ratio of Pt–Ni of 17:1), which was interpreted by a mechanism based on the bifunctional catalysis. The successful preparation of Pt–Ni/PAN/MWCNTs nanocomposites opens a new path to synthesize the promising catalysts for CO.     

Electrocatalytic properties of nanocomposites based on conducting polymers and titanium dioxide in oxygen reduction process

Electrochemical characteristics and electrocatalytic properties in the oxygen reduction reaction are studied on hybrid nanocomposites based on conducting polymers (polyaniline, polypyrrol) doped with phosphomolybdic acid (PMA), and TiO₂ and also their bifunctional analogs containing up to 5 wt % of nanosize platinum. It is found that the obtained nanocomposites in 0.5 M H₂SO₄ are capable of reversible electro-chemical redox transitions (in the range of potentials from ?0.6 to 1.0 V vs. Ag/AgCl), in which the main contribution is provided by the corresponding conducting polymer and dopant (PMA). It is shown that activity of the studied nanocomposites in the oxygen reduction reaction is caused by the joint catalytic effect of all their components: the polymer, TiO₂, H₃PMo₁₂O₄0, Pt.     

Metal–nitrogen coordination moieties in carbon for effective electrocatalytic reduction of oxygen

Oxygen reduction reaction is a critical process at the cathode of proton-exchange membrane fuel cells and metal–air batteries. Carbon-based single metal atom nanocomposites have emerged as effective alternatives to state-of-the-art platinum catalysts, in which the electrocatalytic activity is attributed largely to the formation of metal–nitrogen coordination moieties (MN_x) within the carbon matrix. In this review, we summarize recent progress in the studies of metal and nitrogen codoped carbon as single-atom catalysts toward oxygen reduction reaction within the context of the atomic configuration of the MN_x active sites and topologic characteristics of the carbon skeletons and include a perspective of the design and engineering of the nanocomposites for further enhancement of the electrocatalytic activity.     

Platinum/Carbon nanotube nanocomposite synthesized in supercritical fluid as electrocatalysts for low-temperature fuel cells

Carbon nanotube (CNT)-supported Pt nanoparticle catalysts have been synthesized in supercritical carbon dioxide (scCO(2)) using platinum(II) acetylacetonate as metal precursor. The structure of the catalysts has been characterized with transmission electron micrograph (TEM) and X-ray photoelectron spectroscopy (XPS). TEM images show that the platinum particles' size is in the range of 5-10 nm. XPS analysis indicates the presence of zero-valence platinum. The Pt-CNT exhibited high catalytic activity both for methanol oxidation and oxygen reduction reaction. The higher catalytic activity has been attributed to the large surface area of carbon nanotubes and the decrease in the overpotential for methanol oxidation and oxygen reduction reaction. Cyclic voltammetric measurements at different scan rates showed that the oxygen reduction reaction at the Pt-CNT electrode is a diffusion-controlled process. Analysis of the electrode kinetics using Tafel plot suggests that Pt-CNT from scCO(2) provides a strong electrocatalytic activity for oxygen reduction reaction. For the methanol oxidation reaction, a high ratio of forward anodic peak current to reverse anodic peak current was observed at room temperature, which implies good oxidation of methanol to carbon dioxide on the Pt-CNT electrode. This work demonstrates that Pt-CNT nanocomposites synthesized in supercritical carbon dioxide are effective electrocatalysts for low-temperature fuel cells.     

Electrocatalytic properties of multiwalled carbon nanotubes-based nanocomposites for oxygen electrodes

Metals (platinum, nickel, and lead) and oxides (manganese dioxide and molybdenum, chromium, cobalt, and niobium oxides) were deposited onto multiwalled carbon nanotubes by chemical and electrochemical methods. The resulting nanocomposites were tested as oxygen electrode materials for electrochemical power sources with alkaline electrolytes. A correlation was revealed between the catalytic activity of oxygen electrodes manufactured from composites based on carbon nanotubes with catalyst deposited, on the one hand, and the coefficient a in the Tafel equation for the oxygen evolution reaction on this catalyst, on the other. A possibility of predicting and evaluating the catalytic properties of oxygen electrode materials for power sources was suggested.     

Synthesis,morphology, and properties of hydroxyl terminated‐POSS/polyimide low‐k nanocomposite films

Polyhedral oligomeric silsequioxane (POSS), having eight hydroxyl groups for the preparation of nanocomposites with polyimide (PI) was synthesized by the direct hydrosilylation of allyl alcohol with octasilsesquioxane (Q₈M₈^H) with platinum divinyltetramethyl disiloxane Pt(dvs) as a catalyst. The structure of allyl alcohol terminated‐POSS (POSS‐OH) was confirmed by FTIR, NMR, and XRD. A high performance, low‐k PI nanocomposite from pyromellitic dianhydride (PMDA)‐4,4'‐oxydianiline (ODA) polyamic acid cured with POSS‐OH was also successfully synthesized. The incorporation of POSS‐OH into PI matrix reduced dielectric constant of PI without loosing mechanical properties. Furthermore, the effects of POSS‐OH on the morphology and properties of the PI/POSS‐OH nanocomposites were investigated using UV–vis, FTIR, XRD, SEM, AFM, transmission electron microscope (TEM), TGA, and contact angle. The homogeneous dispersion of POSS particles was confirmed by SEM, AFM, and TEM. The nanoindentation showed that the modulus increased upon increasing the concentration of POSS‐OH in PI, whereas the hardness did not increase very much with respect to loading of POSS, due to soft‐interphase around POSS molecules in the resulting nanocomposites. Overall results demonstrated the nanometer‐level integration of the polymer and POSS‐OH. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5887–5896, 2008     

In situ chemo-synthesized multi-wall carbon nanotube-conductive polyaniline nanocomposites: characterization and application for a glucose amperometric biosensor

A new glucose amperometric biosensor, based on electrodeposition of platinum nanoparticles onto the surface of multi-wall carbon nanotube (MWNT)-polyaniline (PANI) nanocomposites, and then immobilizing glucose oxidase (GOD) with covalent interaction and adsorption effect, was constructed in this paper. Firstly, the MWNT-PANI nanocomposites had been synthesized by in situ polymerization and were characterized through transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, and ultraviolet and visible (UV-vis) absorption spectra. The assembled process of the modified electrode was probed by scanning electron microscopy (SEM) and cyclic voltammetry (CV). Chronoamperometry was used to study the electrochemical performance of the resulting biosensor. The glucose biosensor exhibited a linear calibration curve over the range from 3.0 μM to 8.2 mM, with a detection limit of 1.0 μM and a high sensitivity of 16.1 μA mM⁻¹. The biosensor also showed a short response time (within 5 s). Furthermore, the reproducibility, stability and interferences of the biosensor were also investigated.