Fine size control of platinum on carbon nanotubes: from single atoms to clusters

Synthesis of nanobelt-like 1-dimensional silver/nanocarbon hybrid materials for flexible and wearable electroncs

Most synthetic processes of metallic nanostructures were assisted by organic/inorganic or polymeric materials to control their shapes to one-dimension or two-dimension. However, these additives have to be removed after synthesis of metal nanostructures for applications. Here we report a straightforward method for the low-temperature and additive-free synthesis of nanobelt-like silver nanostructures templated by nanocarbon (NC) materials via bio-inspired shape control by introducing supramolecular 2-ureido-4[1H]pyrimidinone (UPy) groups into the NC surface. The growth of the Ag nanobelt structure was found to be induced by these UPy groups through observation of the selective formation of Ag nanobelts on UPy-modified carbon nanotubes and graphene surfaces. The synthesized NC/Ag nanobelt hybrid materials were subsequently used to fabricate the highly conductive fibres (>1000S/cm) that can function as a conformable electrode and highly tolerant strain sensor, as well as a highly conductive and robust paper (>10000S/cm after thermal treatment).

Recent Advances in Atomic Metal Doping of Carbon-based Nanomaterials for Energy Conversion

Nanostructured metal-contained catalysts are one of the most widely used types of catalysts applied to facilitate some of sluggish electrochemical reactions. However, the high activity of these catalysts cannot be sustained over a variety of pH ranges. In an effort to develop highly active and stable metal-contained catalysts, various approaches have been pursued with an emphasis on metal particle size reduction and doping on carbon-based supports. These techniques enhances the metal-support interactions, originating from the chemical bonding effect between the metal dopants and carbon support and the associated interface, as well as the charge transfer between the atomic metal species and carbon framework. This provides an opportunity to tune the well-defined metal active centers and optimize their activity, selectivity and stability of this type of (electro)catalyst. Herein, recent advances in synthesis strategies, characterization and catalytic performance of single atom metal dopants on carbon-based nanomaterials are highlighted with attempts to understand the electronic structure and spatial arrangement of individual atoms as well as their interaction with the supports. Applications of these new materials in a wide range of potential electrocatalytic processes in renewable energy conversion systems are also discussed with emphasis on future directions in this active field of research.

Fabrication, characterization, and stability of supported single-atom catalysts

Strong metal–support interactions are key requirements for development of stable single-atom catalysts with pronounced catalytic activity.

Phytochemically Functionalized Cu and Ag Nanoparticles Embedded in MWCNTs for Enhanced Antimicrobial and Anticancer Properties

Nanomedicine is an emerging field concerned with the use of precision engineered nanomaterials, which leads to the development of novel remedial and diagnostic modalities for human use. In this study, Cu(NO3)2 and AgNO3 precursors were reduced to copper nanoparticles (CuNPs) and silver nanoparticles (AgNPs) using Terminalia arjuna bark extracts under microwave irradiation in the presence of well-dispersed multi-walled carbon nanotubes (MWCNTs) in aqueous medium. The formation of CuNPs or AgNPs and their functionalization with MWCNTs via bioactive molecules of plant extract were evidenced from UV-Vis spectra, XRD, FTIR, FESEM, EDX, and TEM images. The phytochemically functionalized Cu-MWCNTs and Ag-MWCNTs nanomaterials showed enhanced biocide activity, and the inhibitory activity for bacteria was higher than that of fungus. Furthermore, these biohybrid nanomaterials are non-toxic to normal epithelial cells (Vero), whereas they are highly toxic for tested human cancer cells of MDA-MB-231, HeLa, SiHa, and Hep-G2. The cell viability was found to decrease with the increasing dose from 10 to 50 µg mL-1, as well as incubation time from 24 to 72 h. For instance, the cell viability was found to be ~91 % for normal Vero cells and ~76 % for cancer cells for lower dose of 10 µg mL-1.

Styrene hydrogenation performance of Pt nanoparticles with controlled size prepared by atomic layer deposition

Pt sub-nanoparticles supported on carbon nanotubes prepared by atomic layer deposition exhibit unusual catalytic performance for styrene hydrogenation.

Platinum-modified covalent triazine frameworks hybridized with carbon nanoparticles as methanol-tolerant oxygen reduction electrocatalysts

Covalent triazine frameworks, which are crosslinked porous polymers with two-dimensional molecular structures, are promising materials for heterogeneous catalysts. However, the application of the frameworks as electrocatalysts has not been achieved to date because of their poor electrical conductivity. Here we report that platinum-modified covalent triazine frameworks hybridized with conductive carbon nanoparticles are successfully synthesized by introducing carbon nanoparticles during the polymerization process of covalent triazine frameworks. The resulting materials exhibit clear electrocatalytic activity for oxygen reduction reactions in acidic solutions. More interestingly, the platinum-modified covalent triazine frameworks show almost no activity for methanol oxidation, in contrast to commercial carbon-supported platinum. Thus, platinum-modified covalent triazine frameworks hybridized with carbon nanoparticles exhibit selective activity for oxygen reduction reactions even in the presence of high concentrations of methanol, which indicates potential utility as a cathode catalyst in direct methanol fuel cells.

Covalent triazine frameworks are known catalysts for some catalytic reactions, but show no electrocatalytic activity. Here, the authors synthesize platinum modified covalent triazine frameworks hybridized with carbon nanoparticles, which are electro-active for oxygen reduction reactions.

Production of aviation fuel via catalytic hydrothermal decarboxylation of fatty acids in microalgae oil

A series of fatty acids in microalgae oil, such as stearic acid, palmitic acid, lauric acid, myristic acid, arachidic acid and behenic acid, were selected as the raw materials to produce aviation fuel via hydrothermal decarboxylation over a multi-wall carbon nanotube supported Pt catalyst (Pt/MWCNTs). It was found that Pt/MWCNTs catalysts exhibited higher activity for the hydrothermal decarboxylation of stearic acid with a 97% selectivity toward heptadecane compared to Pt/C and Ru/C under the same conditions. And Pt/MWCNTs is also capable for the decarboxylation of different fatty acids in microalgae oil. The reaction conditions, such as Pt/MWCNTs loading amount, reaction temperature and time were optimized. The activation energy of stearic acid decarboxylation over Pt/MWCNTs was calculated (114 kJ/mol).

Molecular catalysts confined on and within molecular layers formed on a si(111) surface with direct si-C bonds

Two examples of confined molecular catalysts are presented. PtCl(4) (2-) complexes are attached to a thiol-terminated monolayer by ligand exchange of Cl(-) with a thiolate group and incorporated in a multilayer of viologen moieties by ion exchange. All Cl(-) ligands are replaced by OH(-) or H(2) O before HER takes place. Ex situ and in situ XAFS measurements confirm that the Pt complexes accelerate HER without being converted into Pt particles.

Structure sensitivity and nanoscale effects in electrocatalysis

This review discusses the role of the detailed nanoscale structure of catalytic surfaces on the activity of various electrocatalytic reactions of importance for fuel cells, hydrogen production, and other environmentally important catalytic reactions, such as carbon monoxide oxidation, methanol and ethanol oxidation, ammonia oxidation, nitric oxide reduction, hydrogen evolution, and oxygen reduction. Specifically, results and insights obtained from surface-science single-crystal-based model experiments are linked to experiments on well-defined shape-controlled nanoparticles. A classification of structure sensitive effects in electrocatalysis is suggested, based both on empirical grounds and on quantum-chemical viz. thermochemical considerations. The mutual relation between the two classification schemes is also discussed. The review underscores the relevance of single-crystal modeling of nanoscale effects in catalysis, and points to the special role of two kinds of active sites for electrocatalysis on nanoparticulate surfaces: (i) steps and defects in (111) terraces or facets, and (ii) long-range (100) terraces or facets.

Tunable properties of PtxFe1-x electrocatalysts and their catalytic activity towards the oxygen reduction reaction

We present the controlled synthesis of bimetallic Pt(x)Fe(1-x) nanoparticles with tunable physical properties and a study of their catalytic activity towards the oxygen reduction reaction (ORR). Composition-induced variations in alloying extent and Pt d-band vacancies in Pt-Fe/C catalysts are systematically investigated. Density functional theoretical calculations are performed in order to realize the electronic effect caused by alloying Pt with Fe. The DFT computational observations revealed that iron donates electrons to platinum, when the Fe 3d and Pt 5d orbitals undergo hybridization. The Pt(x)Fe(1-x) catalysts with various Pt-to-Fe atomic ratios are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV), and X-ray absorption spectroscopy (XAS). TEM images indicate that the dispersion of the metal nanoparticles is uniform and the XAS technique provides significant insight on Pt d-band vacancies and the alloying extent of Pt and Fe in Pt(x)Fe(1-x) nanoparticles. Rotating-disk voltammetry of Pt(x)Fe(1-x) nanoparticle catalysts with various Pt : Fe atomic compositions (3 : 1, 1 : 1, and 1 : 3) revealed that the Pt(1)Fe(1)/C nanocatalyst showed a greater enhancement in ORR activity than platinum. The enhanced catalytic activity toward ORR is attributed to the higher alloying extent of platinum and iron as well as the promising electronic structure offered by the lower unfilled Pt d states in Pt(x)Fe(1-x) nanoparticles when compared to pure Pt.

PtRu nano-dandelions on thiolated carbon nanotubes: a new synthetic strategy for supported bimetallic core-shell clusters on the atomic scale

Core-shell PtRu clusters resembling dandelions were formed on thiolated carbon nanotubes by the difference in bond strength with surface thiol groups between Pt and Ru single atoms. The formation mechanism was clearly understood using a different release timing concept based on EXAFS and XPS analyses during heat treatment.