Electrochimica Acta 72 (2012) 68–73 Contents lists available at SciVerse ScienceDirect Electrochimica Acta j ourna l ho me pag e: www.elsevier.com/locate/electacta Surface modification and electrochemical behaviour of undoped nanodiamonds Jianbing Zang a,b , Yanhui Wang a,∗ , Linyan Bian a , Jinhui Zhang a , Fanwei Meng a , Yuling Zhao a , Shubin Ren b , Xuanhui Qu b a State Key Laboratory of Metastable Material Science & Technology, College of Material Science & Engineering, Yanshan University, Qinhuangdao 066004, PR China b State Key Laboratory for Advanced Metals and Materials, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, PR China a r t i c l e i n f o Article history: Received 25 December 2011 Received in revised form 25 March 2012 Accepted 31 March 2012 Available online 12 April 2012 Keywords: Nanodiamond Annealing Surface modification Electrochemical activity a b s t r a c t Surface modifications of undoped nanodiamond (ND) particles were carried out through different anneal- ing treatments. The methods of Fourier transform infrared spectroscopy, Raman spectroscopy, and transmission electron microscopy were used to characterize the ND surface before and after the annealing process. The electrochemical properties of the modified ND powders in aqueous solution were investi- gated with Fe(CN) 6 3-/4- as a redox probe. When the annealing temperature was below 850 ◦ C, vacuum annealing removed parts of the oxygen-containing surface functionalities from the ND surface and pro- duced more sp 2 carbon atoms in the shell. The charge transfer of the Fe(CN) 6 3-/4- redox couple decreased with increasing annealing temperature. Re-annealing in air restored the original surface conditions: few sp 2 -bonded carbon atoms and similar surface functionalities, and thus the electrochemical activity. When ND was annealed in vacuum at 900–1100 ◦ C, more serious graphitization produced a continuous fullerenic shell wrapped around a diamond core, which had a high conductivity and electrochemical activity. This provides a novel nanoparticle with high conductivity and high stability for electrochemical applications. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction It is well known that conductive diamond film electrodes pos- sess unique electrochemical properties such as a wide potential window and low background current in aqueous or non-aqueous electrolytes, high chemical and electrochemical stabilities, and excellent corrosion stability [1]. Boron doped diamond film elec- trodes fabricated by the chemical vapour deposition technique are the most widely studied and well reported in the literature [2–5] due to the p-type semiconducting characteristic originated from B-doping. Hydrogen-terminated undoped diamond films are also found to exhibit a surface conductivity (SC), and many different types of devices that use the electronic properties of diamond are currently in research and development [6–10]. Although the mechanism is still unclear and gives rise to controversial discus- sion, the “electrochemical transfer doping model”, in which the SC is attributed to the hydrogen termination and surface adsorbates layer, has received more attention [6,10,11]. Most recently, detonation-synthesized nanodiamond (ND) powders have been incorporated into electrodes and biosensors [12–16]. Diamond nanoparticles with an average grain dimension ∗ Corresponding author. Tel.: +86 13780373375; fax: +86 335 8387679. E-mail address: diamond wangyanhui@163.com (Y. Wang). of 3–9 nm have a giant specific surface of 250–300 m 2 /g and a cluster structure of a dense diamond core and a relatively loose shell with non-diamond phase and surface functional groups [17]. X-ray and neutron diffraction measurements as well as high reso- lution transmission electron microscopy (HRTEM) confirmed that the core of the nanoparticles is sp 3 bonded diamond lattice [18]; however, the nature of the outer layer is still unclear. Nevertheless the sp 2 character does occur in the shell, and a complex arrange- ment related to the surface functional groups and surface carbon atoms depends on the history of ND production and treatment [18–21]. Clearly the large contribution of surface atoms causes significant dependence of the ND properties on the state of the surface. Previous work by our group investigated the electrochemistry of ND powders in Fe(CN) 6 3-/4- solution and in NO 2 - solution [12,13]. Holt et al. [14,22,23] demonstrated that undoped 5 nm diamond nanoparticles show redox behaviour and attributed the electro- chemical activity to the surface chemistry of the particles. Zhao et al. [15] described a glucose biosensor based on electrochemical pretreatment of undoped nanocrystalline diamond modified gold electrode, where the ND was found to greatly promote the oxy- gen reduction reaction. These reports reveal that electron transport does occur between the ND particles and the electrolyte; however, it is difficult to determine the nature of the electrochemical activ- ity because it may be influenced by implicated surface states, for 0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2012.03.169