Please cite this article in press as: Vahidzadeh, E., et al. Synthesis of a nitrogen-doped titanium dioxide–reduced graphene oxide nanocomposite for photocatalysis under visible light irradiation. Particuology (2018), https://doi.org/10.1016/j.partic.2017.12.013 ARTICLE IN PRESS G Model PARTIC-1118; No. of Pages 10 Particuology xxx (2018) xxx–xxx Contents lists available at ScienceDirect Particuology j our na l ho me page: www.elsevier.com/locate/partic Synthesis of a nitrogen-doped titanium dioxide–reduced graphene oxide nanocomposite for photocatalysis under visible light irradiation Ehsan Vahidzadeh a , Shohreh Fatemi a,∗ , Amideddin Nouralishahi b a School of Chemical Engineering, College of Engineering, University of Tehran, P.O. Box 11365-4563, Tehran, Iran b Caspian Faculty of Engineering, College of Engineering, University of Tehran, P.O. Box 11365-4563, Tehran, Iran a r t i c l e i n f o Article history: Received 22 August 2017 Received in revised form 10 December 2017 Accepted 13 December 2017 Available online xxx Keywords: N-doped TiO2 Photocatalyst Reduced graphene oxide Visible light irradiation Nanocomposite Nanoparticle a b s t r a c t A nitrogen-doped titanium dioxide–reduced graphene oxide (N-TiO 2 –RGO) nanocomposite has been synthesized by the combination of a hydrothermal method and a thermal treatment under a NH 3 /N 2 atmosphere. The resulting composites are characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, diffuse reflectance absorption spec- troscopy, energy-dispersive X-ray spectroscopy, and Raman characterization techniques. The sequence of the thermal treatment and hydrothermal treatment processes is shown to influence the photocatalytic activity of nitrogen-doped composites. The composites synthesized by using this method show better photocatalytic activities toward the degradation of acetaldehyde under visible light irradiation compared with P25, N-TiO 2 , and TiO 2 –RGO. By applying the thermal treatment process after the hydrothermal pro- cess, nitrogen atoms can be simultaneously doped in the lattice of TiO 2 nanoparticles and on the surface of reduced graphene oxide sheets. The conversion of acetaldehyde, as the model molecule of volatile organic compounds, is measured in a continuous stirred-tank reactor until the steady state condition is reached. The conversion of 50 ppm acetaldehyde, in an air flow under illumination from an 80 W Hg lamp with a UV cut-off filter, reaches 62% after a 1-h reaction using a 0.07 g N-TiO 2 –RGO sample with an optimum loading of 2 wt% graphene oxide. In comparison, the photocatalytic activity of P25 for the degradation of acetaldehyde under visible light irradiation is only 8% under the same reaction conditions. The reac- tion rates for acetaldehyde degradation are calculated and predicted with pseudo-first-order reaction kinetics, and the activity result of the best N-TiO 2 –RGO sample is 12.3 times higher than for P25. © 2018 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved. Introduction The photocatalytic degradation of volatile organic compounds (VOCs) is a promising environmental technology that provides a variety of advantages, such as operation under room conditions. Titanium dioxide (TiO 2 ) is the most common semiconductor and has been used as a photocatalyst in the degradation and oxida- tion of hazardous materials to nontoxic compounds (Wang et al., 2015). However, two major problems limit the large-scale applica- tion of the photocatalytic degradation technology. First, the band gap of TiO 2 is approximately 3.2 eV, which means it can only absorb ultraviolet light, so it only uses 4% of the solar energy spectrum. Sec- ond, under UV illumination, an electron is excited from the valence band to the conduction band of the semiconductor, which leaves a ∗ Corresponding author. E-mail address: shfatemi@ut.ac.ir (S. Fatemi). hole behind. This photo-generated electron–hole pairs are respon- sible for the photocatalytic activity (Yin et al., 2013). Unfortunately, in the case of TiO 2 , these photo-generated electron and hole pairs recombine rapidly (before they can migrate to the surface of the photocatalyst to take part in the photocatalytic oxidation reac- tion) and dramatically reduce the photocatalytic activity (Yin et al., 2013). Thus, several efforts have been made recently to enhance the photocatalytic activity of TiO 2 . The most common strategy that has been adopted is to extend the optical absorption of TiO 2 to the visible light region by doping with transition metals (V, Co, Ni, Fe) (Umebayashi, Yamaki, Itoh, & Asai, 2002) or nonmetallic dopants (N, F, B) (Di Valentin & Pacchioni, 2013). In particular, nitrogen is the most common nonmetallic ele- ment that has been incorporated into the TiO 2 structure to tune its photocatalytic efficiency. Asahi, Morikawa, Ohwaki, Aoki, and Taga (2001) proposed that the p orbitals of nitrogen mixed with the valance band O2p orbitals, which leads to a narrowing of the band gap. There are several ways of doping nitrogen into the TiO 2 https://doi.org/10.1016/j.partic.2017.12.013 1674-2001/© 2018 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.