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Magic impurities not magic nanotubes
17 July 2006
The electrocatalytic properties of some carbon nanotube electrodes are actually caused by impurities, report scientists in the UK.
Richard Compton and colleagues at the University of Oxford, analysed the anaesthetic known as halothane using a multiwalled carbon nanotube modified glassy carbon electrode. They compared the electrode's performance to that of other carbon electrodes using cyclic voltammetry, a technique used to study redox properties of chemicals and materials by measuring the currents generated in electrolytic solutions when known voltages are applied.
The researchers found that their modified electrode showed electrocatalytic properties and decided to investigate this phenomenon further. They were surprised to find that the catalytic properties were not due to the carbon nanotubes themselves, but to copper particle impurities introduced at the manufacturing stage. These nanoparticles, not completely removed by purification steps, were incorporated into or retained in the nanotube structure.
Compton believes that the catalytic effects of nanotube electrodes are often misreported in the literature because the underlying science is not thoroughly investigated. 'There is a widespread misconception within the electroanalytical community that carbon nanotubes allow the enhanced electrocatalytic detection of a huge list of analytes. Yet until recently nobody questioned what the cause of this apparent electrocatalysis was; apparently this is considered to be yet another "magical" property of the nanotubes.'
This study reports one type of mechanism underlying electrocatalysis, but there could be many others. Frank Marken, an expert in electrochemistry at the University of Bath, UK, says, 'these fascinating observations suggest there is more unresolved nanocarbon chemistry that deserves a better fundamental understanding.' Metal-carbon incorporated systems 'could be very interesting in other areas of catalysis where the catalyst has to be protected from leaching and degradation,' he added.
The authors hope that their work will prompt further investigations in the field of this nature. 'In turn this may then highlight yet more examples of real electrocatalytic analysis using carbon nanotubes which may have interesting and surprising causes and further our understanding of nanoscale materials in general,' said Compton.
Michele R Zgraggen
X Dai, G G Wildgoose and R G Compton, Analyst, 2006