Selectivity in the photocatalytic properties of the composites of TiO 2 nanoparticles with B- and N-doped graphenes K. Gopalakrishnan, Hrushikesh M. Joshi, Prashant Kumar, L.S. Panchakarla, C.N.R. Rao ⇑ International Centre for Materials Science, Chemistry and Physics of Materials Unit, New Chemistry Unit and CSIR Centre of Excellence in Chemistry, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore 560064, India article info Article history: Received 18 March 2011 In final form 14 June 2011 Available online 17 June 2011 abstract Photodegradation of two dyes, methylene blue (MB) and rhodamine B (RB), adsorbed over composites of TiO 2 nanoparticles with pure graphene as well as boron- and nitrogen-doped graphenes has been inves- tigated. MB which is a good electron donor and has a low ionization energy interacts strongly with electron-deficient boron-doped graphene resulting in fast degradation of the dye. On the other hand, RB which is not such a good electron donor and has a higher ionization energy, interacts strongly with electron-rich nitrogen-doped graphene causing a faster degradation of the dye. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Titanium dioxide is a versatile material with properties that are useful in energy conversion [1,2], photocatalysis involving photo- degradation of organic contaminants [3] and in other areas [4]. Upon irradiation of TiO 2 with ultraviolet light, electron–hole pairs are produced by the absorption of photons, thus enabling splitting of water to produce hydrogen [5]. Electron–hole recombination in a short span of time marginally decreases its photocatalytic activity. Carbonaceous materials have been used as anchors for TiO 2 and other semiconducting nanoparticles [6,7], giving rise to enhanced photocatalytic activity because of the increase in surface area [8]. It is believed that photoexcited electrons from TiO 2 transfer to nano- carbons such as carbon nanotubes or graphene and hinder the recombination process, thereby enhancing the oxidative reactivity [9]. Chen et al. [10] find that TiO 2 -graphene oxide composites de- grade methyl orange photocatalytically. In this process, graphene oxide is reduced by the electron transferred from TiO 2 . Most studies of the TiO 2 -graphene composites have concentrated on electron transfer between TiO 2 and graphene oxide or graphene although there are indications that the electronic structure of the nanocar- bons may play a crucial role in the photocatalysis [11]. We consid- ered it important to examine the nature of interaction of graphene with TiO 2 as well as with adsorbed molecules to understand the photocatalytic properties. Since the electronic properties of graph- ene can be conveniently tuned chemically by doping with nitrogen and boron, thereby changing the effective band gap of the compos- ites, we have investigated the photocatalytic properties of TiO 2 by using chemically doped graphenes as supports. With this purpose, we have studied the interaction of TiO 2 nanoparticles with B- and N-doped graphenes and also the interaction of the graphenes with two dye molecules possessing widely different electron-donating abilities or ionization energies. The molecules investigated are methylene blue (I) and rhodamine B (II), the former with a very low ionization energy of 5.3 eV [12]. Rhodamine B has ionization en- ergy of 6.7 eV [13]. It was felt that the study would show whether the photodegradation of these dye molecule by the TiO 2 -graphene composites depends on the electronic properties of graphene. 0009-2614/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2011.06.033 ⇑ Corresponding author. Fax: +91 80 22082760. E-mail address: cnrrao@jncasr.ac.in (C.N.R. Rao). Chemical Physics Letters 511 (2011) 304–308 Contents lists available at ScienceDirect Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett