Redox Reactions at Nanodiamond Surfaces Revealed by Attenuated Total Reflectance InfraRed Spectroscopy

Katherine B. Holt 

University College London (UCL), 20 Gordon Street, London WC1H, United Kingdom

Abstract

Nanodiamond (ND) is formed by detonation of carbon-based explosives and consists of individual diamond nanoparticles of ~ 5 nm in diameter. This material is attracting much interest at present in possible biomedical applications such as drug delivery, intracellular imaging and biosensing. Our interest lies in its unexpected redox properties [1,2] as we find that when immobilized on an electrode it is able to undergo direct oxidation and reduction and can also undergo electron transfer with solution redox molecules such as IrCl62-.   As undoped diamond is an insulating material, with a band gap of 5.5 eV we have suggested that this redox activity must be associated with its surface. By necessity bonding at the surface is unsaturated and due to the acid treatment used in purification highly oxidized. The ND surface contains an array of different surface functionalities, such as carboxylic acid, alcohols, quinones and ketones etc. As these groups can undergo redox transformations they may be responsible for the observed redox activity.

This talk will discuss recent experiments to elucidate the mechanisms behind electron transfer at the ND surface. This study uses Attenuated Total Reflectance InfraRed (ATR IR) spectroscopy to monitor changes in the vibrational frequencies of the surface functional groups of the ND in the presence of redox probes. In ATR IR the IR beam is directed through an internal reflection element (IRE), on top of which a thin layer of the nanomaterial is immobilised. The IR beam is reflected internally at the surface of the IRE, but the beam also penetrates the immediate environment above the prism surface as an evanescent wave. An IR vibration spectrum of the material within range of the evanescent wave can therefore be obtained and as only a thin layer is probed, solvent absorption is minimised. Use of nanomaterials ensures that a high surface area is available to be probed, allowing good quality IR spectra of the redox-active surface functional groups to be obtained.

 [1] Electrochemistry of Undoped Diamond Nanoparticles: Accessing Surface Redox States, K. B. Holt, E. Millan-Barrios, D. J. Caruana, J. Am. Chem. Soc., (2009) 131, 13272+.

[2] Undoped diamond nanoparticles: origins of surface redox chemistry, K. B. Holt, Phys. Chem. Chem. Phys., (2010) 12, 2048

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Presentation: Keynote lecture at SMCBS'2011 International Workshop, by Katherine B. Holt
See On-line Journal of SMCBS'2011 International Workshop

Submitted: 2011-08-19 12:33
Revised:   2011-08-19 12:33
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