Novel Visible Light Photocatalytic and Photoelectrochemical (PEC) Activity of Carbon-doped Zinc Oxide/Reduced Graphene Oxide: Supercritical Methanol Synthesis with Enhanced Photocorrosion Suppression Ahmad Tayyebi a, b , Tayyebeh Soltani a , Byeong-Kyu Lee a, * , Mohammad Outokesh b, ** , Meysam Tayebi c a Department of Civil and Environment Engineering, University of Ulsan, Daehakro 93, Namgu, Ulsan, 680-749, Republic of Korea b Department of Energy Engineering, Sharif University of Technology, P.O. Box 11365-8639, Tehran, Iran c Chemical Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad, Iran article info Article history: Received 14 April 2017 Received in revised form 22 June 2017 Accepted 29 June 2017 Available online 30 June 2017 Keywords: Carbon doping Reduced graphene oxide Photoelectrochemical Supercritical methanol Photocorrosion Photocatalytic degradation abstract Carbon-doped zinc oxide/reduced graphene oxide (C-ZnO/rGO) was prepared by a facile one-pot su- percritical methanol method. The synthesized C-ZnO/rGO nanocomposite with flower-like ZnO micro- rods (MRs) synergistically inherited all the advantages of carbon doping and rGO heterojunction and exhibited high photocatalytic activity for the photodegradation of methyl orange (MO) under visible light. The x-ray diffraction (XRD) results indicated that in presence of GO, a new carbon-doped phase was formed at the high temperature and pressure of supercritical methanol. The x-ray photoelectron spec- troscopy (XPS) at low binding energies demonstrated that the valence band of C-ZnO-rGO is up-shifted by 0.35 ± 0.05 eV compared to that of ZnO MRs and narrowed the band-gap down to 2.9 eV. Under visible light irradiation, C-ZnO/rGO showed photocatalytic degradation of MO that was greatly increased by 4.5-fold compared to that of pure ZnO MRs. Measuring the photoelectrochemical (PEC) performance illustrated that C-ZnO/rGO showed higher photocurrent density in UV and visible region compared with those of ZnO MRs electrode. In addition, the incorporation of graphene sheets greatly suppressed the photocorrosion and photocurrent density decay of C-ZnO/rGO to only 0.5% and 10%, compared with 27% and 70% for neat ZnO MRs, respectively. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Due to its high catalytic activity, low cost, and environmental friendliness, zinc oxide (ZnO) has been applied for different research fields including gas sensors [1], photodetectors [2], bio- imaging [3], solar cell [4], light-emitting diodes (LEDs) [5], and environment applications [6e8]. However, the large band gap (3.0e3.2 eV) of unmodified zinc oxide made it too inefficient to generate electron-hole from sunlight due to the small number of sufficiently energetic photons [8,9]. Recent efforts have focused on improving the photocatalytic activity of ZnO by tailoring its struc- ture, including morphology, surface defects, and oxygen vacancies [9e12]. Previous studies reported that morphology greatly in- fluences the band gap tailoring of ZnO nanostructures [13]. For example, Kang et al. reported that ZnO NRs showed higher pho- tocatalytic performance in comparison to nanoparticles, nano- sheets and nanospheres [14]. Doping ZnO with non-metal atoms has received strong atten- tion by extending the optical absorption to the visible-light region and tailoring its band gap. For example, the photocatalytic perfor- mance of the ZnO nanostructure was improved by doping of ni- trogen [15,16], sulfur [17], and carbon [18,19]. Carbon-doped ZnO (C-ZnO) was synthesized using various methods such as sol-gel, solvothermal, hydrothermal and thermal plasma. However, obsta- cles in the preparation of C-ZnO, such as the addition of the carbon source [20], formation of undesired by-products, and time- consuming synthesis procedure [18], necessitate alternative methods capable of modifying the ZnO structure, which is a vital in improving its photocatalytic activity. * Corresponding author. ** Corresponding author. E-mail addresses: bklee@ulsan.ac.kr (B.-K. Lee), outokesh@sharif.ir (M. Outokesh). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom http://dx.doi.org/10.1016/j.jallcom.2017.06.316 0925-8388/© 2017 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 723 (2017) 1001e1010