Regular article Concurrent growth, structural and photocatalytic properties of hybridized C, N co-doped TiO 2 mixed phase over g-C 3 N 4 nanostructured Mohamad Azuwa Mohamed a, ⁎, Juhana Jaafar b, ⁎, M.F. M. Zain c , Lorna Jeffery Minggu a , Mohammad B. Kassim a,d , Mohd Nur Ikhmal Salehmin a , Mohamad Saufi Rosmi e , W.N. W. Salleh b , Mohd Hafiz Dzarfan Othman b a Solar Hydrogen Group, Fuel Cell Institute (SELFUEL), Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia b Advanced Membrane Technology Research Centre, Universiti Teknologi Malaysia, 81310 Skudai, Johor Bahru, Malaysia c Sustainable Construction Materials and Building Systems (SUCOMBS) Research Group, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Malaysia d School of Chemical Sciences & Food Technology, Faculty of Science & Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia e Department of Chemistry, Faculty of Science and Mathematics, Universiti Pendidikan Sultan Idris, 35900 Tanjung Malim, Perak, Malaysia abstract article info Article history: Received 10 June 2017 Received in revised form 27 August 2017 Accepted 28 August 2017 A concurrent and facile sol-gel assisted low temperature calcination approach to homogeneous growth of TiO 2 mixed phase nanoparticles over g-C 3 N 4 for designing visible-light-driven photocatalyst is demonstrated in this study. The structural and morphological studies revealed a well-interconnected g-C 3 N 4 /TiO 2 mixed phase heterojunction photocatalyst was achieved through a sol-gel process and calcination at 400 °C. The well-inter- connected g-C 3 N 4 /TiO 2 mixed phase heterojunction photocatalyst has strong visible light absorption capability due to the presence of an in-situ nitrogen and carbon dopants. The noticeably increased in the visible-light-pho- tocatalytic activity performance is ascertained mainly due to the improvement of electron-hole separation and charge carrier migration. © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Sol-gel synthesis G-C 3 N 4 Doping Heterojunction Photocatalysis Recently, a non-metal graphitic carbon nitride (g-C 3 N 4 ) has been proposed as a solution to overcome the issues related to the use of TiO 2 as a photocatalyst [1–3]. This non-metal semiconductor has attracted a wide attention owing to its narrower band gap of 2.73 eV rel- ative to TiO 2 and hence, can be applied as a visible light driven photocatalyst. It is also featured to have a high stability and favorable electronic structure [4]. However, the key issues related to a fast charge recombination rate and poor conductivity need to be addressed to im- prove the g-C 3 N 4 photocatalytic performance [5]. By combining TiO 2 and g-C 3 N 4 , researchers have been able to produce a composite that has a higher photocatalytic activity compared to a pristine TiO 2 or g- C 3 -N 4 [6–9]. Moreover, g-C 3 N 4 provides higher surface area which is de- sirable as a template for TiO 2 and more active sites for adsorption and reaction [10–12]. Previously, researchers have been synthesizing a composite of TiO 2 and g-C 3 N 4 by thermal treatment [13] or by heating an ethanol solution of titanium tetrachloride with C 3 N 4 [14]. A multi-heterojunction of g- C 3 N 4 loaded a-TiO 2 /c-TiO 2 nanocomposite was also proposed by using sequential gas-phase and wet-chemical synthesis techniques [15]. However, to date there is no report on a concurrent synthesis of well-in- terconnected g-C 3 N 4 and C, N co-doped TiO 2 (anatase/rutile) mixed phase. It has been shown that a mixed phase of anatase/rutile TiO 2 can improve the charge carrier separation and consequently reduce the electron recombination [16–18]. Therefore, the present study pro- poses a simple concurrent growth and highly scalable method for pro- ducing a photocatalyst consisted of a homogeneous and well- interconnected g-C 3 N 4 and TiO 2 (anatase/rutile) mixed phase with en- hanced photocatalytic properties. Details of the synthesis, characteriza- tion and photocatalytic properties evaluation are explained in Section S1-S4 (Supplementary data). The occurrence, phase and crystallinity of pristine g-C 3 N 4 and g- C 3 N 4 /TiO 2 are shown in Fig. 1(a). The pristine g-C 3 N 4 exhibited two sig- nificant diffraction peaks at 2θ = 13.1–13.4° (100) and 27.4–27.6° (002), which were attributed to the in-planar repeat period for the hole-to-hole distance among the N-bridged tri-s-triazine units [19], and the typical inter-planar stacking of the conjugated aromatic sheets that indicated the peak characteristic of g-C 3 N 4 , respectively [3,12,15, 20]. On the other hand, the g-C 3 N 4 /TiO 2 exhibited diffraction patterns of TiO 2 mixed phase (anatase/rutile) [18] at [(011), (004), (020)] and [(110), (101), (211), (130)], which were attributed to the anatase and rutile phases, respectively. Notably, the broad peak at 2θ = 24–30° in g-C 3 N 4 /TiO 2 was due to the characteristic diffraction peaks of g-C 3 N 4 Scripta Materialia 142 (2018) 143–147 ⁎ Corresponding authors. E-mail addresses: p89056@siswa.ukm.edu.my, mazuwa2@gmail.com (M.A. Mohamed), juhana@petroleum.utm.my, juhana@utm.my (J. Jaafar). http://dx.doi.org/10.1016/j.scriptamat.2017.08.044 1359-6462/© 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Scripta Materialia journal homepage: www.elsevier.com/locate/scriptamat