Scientists in Russian Academy of Sciences, Moscow have revealed a variety of transformations taking place on carbon surface under the influence of metal nanoparticles and microwaves.
Graphene "cut and paste" with metal nanoparticles was carried out under microwave irradiation. The study revealed unique processes occurring on the carbon layers under the influence of metal nanoparticles heated by microwave irradiation. Understanding the processes taking place in Metal/Carbon systems is crucial for development of new generation of highly efficient catalysts for organic synthesis and chemical industry. The authors described the key transformations responsible for catalyst evolution in connection with preparation of nanostructured Metal/Carbon systems .
Figure 1. Metal nanoparticles heated to high temperature initiate the process of "cutting" of the carbon layers (etching of graphene), cyclization of nanoribbons, formation of cycloparaphenylenes, and nanotube growth.
Copyright : Ananikov Laboratory (AnanikovLab.ru)
The study, carried out in the laboratory of Prof. V.P.Ananikov at Zelinsky Institute of Organic Chemistry of Russian Academy of Sciences, discovered a variety of processes occurring on the surface of carbon material upon a contact with hot metal nanoparticles. Metal nanoparticles, heated by microwave radiation, caused significant morphological changes of the carbon surface: formation of patterns of pits and channels, penetration inside the carbon material and direct growth of carbon nanotubes.
As it is widely accepted now, discovery and systematic study of carbon nanotubes was one of the prominent groundbreaking points at the beginning of nanotechnology era. Carbon nanotubes are nanoscale tubular structures consisting of carbon atoms arranged in the interconnected six-membered rings within a cylindrical wall.
From a certain point of view carbon nanotube may be represented as a graphene sheet (flat sheet of monoatomic thickness) rolled into a cylinder and carbon-glued at the edges. Direct access to carbon nanotubes starting from graphene (and especially starting from much cheaper precursor – graphene layers in graphite) would be an outstanding process of great practical interest. The questions appear: how easy is to cut graphite sheets and to roll them up? Does it violate thermodynamic factors?
The present study, published in the ACS Catalysis journal, discovered a series of processes mediated in metal-carbon systems under microwave irradiation. "Cutting" of carbon slices by hot metal particles was clearly observed by field-emission scanning electron microscopy (FE-SEM). "Pasting" of carbon atoms into a new location has resulted in a growth of carbon nanotubes on the surface of graphite – the process was also observed in the experiment under an inert atmosphere.
In the theoretical modeling the authors considered the following possibility: at the first stages graphene sheet can be cut into nanoribbons of one aromatic ring wide (Figure 1). Then, each nanoribbon is rolled into cycloparaphenylenes – these molecules are known and were described previously. On the later stages, cycloparaphenylene rings are joined together to form the nanotube. Important stages of this process were modeled by quantum chemical calculations involving density functional theory.
As shown by theoretical modeling, the energy of such process depends strongly on the initial state of the edges of graphene sheet. If the edges are capped with hydrogen (reaction 1, Figure 2), the overall process of nanotube formation reaction is accompanied by releasing of 20 hydrogen molecules and it is energetically unfavorable (increase in energy is ~2.5 kcal/mol per one carbon atom).
Reaction (2) involves partially hydrogenated graphene edges and it is energetically more favorable (energy decrease is ~1.5 kcal/mol per one carbon atom). The most favorable process from thermodynamic point of view is the formation of a nanotube from a fully dehydrogenated graphene sheet (reaction 3). This process was accompanied by an energy decrease of ~4.6 kcal/mol per one carbon atom.
Important findings, described in the article, deal with transformation of carbon support in Metal/Carbon catalysts. For a long time it was considered that carbon support is an inert (innocent) material used only for supporting (anchoring) of metal nanoparticles. The present study has clearly shown that it is not always the case. Metal particles do interact with carbon support and the interaction leads to amazing modification of the morphology of Metal/Carbon systems. Understanding the nature of this interaction plays a key role in developing efficient and stable catalytic systems. Evolution of the catalyst during chemical transformation may be responsible for deactivation of the catalyst and loss of catalytic activity.
 Evgeniy O. Pentsak, Evgeniy G. Gordeev, Valentine P. Ananikov, «Noninnocent Nature of Carbon Support in Metal/Carbon Catalysts: Etching/Pitting vs Nanotube Growth under Microwave Irradiation», ACS Catalysis, 2014, Vol. 4, pp. 3806−3814.
On-line link: http://dx.doi.org/10.1021/cs500934g
Cover picture: http://pubs.acs.org/action/showLargeCover?jcode=accacs&vol=4&issue=11
Valentine Ananikov | ResearchSEA
From ancient fossils to future cars
21.10.2016 | University of California - Riverside
Study explains strength gap between graphene, carbon fiber
20.10.2016 | Rice University
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.
In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...
'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.
Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
21.10.2016 | Health and Medicine
21.10.2016 | Information Technology
21.10.2016 | Materials Sciences