Please cite this article in press as: E. Kusiak-Nejman, et al., Graphene oxide-TiO 2 and reduced graphene oxide-TiO 2 nanocomposites: Insight in charge-carrier lifetime measurements, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.11.008 ARTICLE IN PRESS G Model CATTOD-10443; No. of Pages 7 Catalysis Today xxx (2016) xxx–xxx Contents lists available at ScienceDirect Catalysis Today journal homepage: www.elsevier.com/locate/cattod Graphene oxide-TiO 2 and reduced graphene oxide-TiO 2 nanocomposites: Insight in charge-carrier lifetime measurements Ewelina Kusiak-Nejman a,∗ , Agnieszka Wanag a , Łukasz Kowalczyk a , Joanna Kapica-Kozar a , Christophe Colbeau-Justin b , María G. Mendez Medrano b , Antoni W. Morawski a a West Pomeranian University of Technology, Szczecin, Institute of Inorganic Technology and Environment Engineering, Pulaskiego 10,70-322 Szczecin, Poland b Université Paris-Sud - Université Paris-Saclay, Laboratoire de Chimie Physique - CNRS UMR 8000, 91405 Orsay, France a r t i c l e i n f o Article history: Received 30 June 2016 Received in revised form 8 October 2016 Accepted 6 November 2016 Available online xxx Keywords: Titanium dioxide Graphene oxide Reduced graphene oxide Charge-carrier dynamics Lifetime of photoexcited electrons TRMC study a b s t r a c t A hybrid nanocomposites containing nanocrystalline TiO 2 and graphene related materials (graphene oxide and reduced graphene oxide) were successfully prepared elevated pressure using hydrothermal method. The structural and textural properties as well as the presence of different carbonaceous struc- tures on the surface of obtained nanocomposites have been characterized by means of XRD, FTIR/DRS and Raman spectroscopy. FTIR/DRS analysis allowed to find characteristic peaks of graphene oxide: epoxy stretching at 1229 cm −1 and alkoxy stretching vibration at 1059 cm −1 . In the spectrum of nanocomposites containing rGO, all the bands decreased or even disappear. It can be indicated that GO was successfully reduced to rGO. SEM studies showed difference between graphene oxide (aggregated, crumpled, non- transparent) and reduced graphene oxide (thin and transparent) flakes. The Time Resolved Microwave Conductivity analysis have been utilized to investigate the excess of charge-carrier lifetimes in TiO 2 - graphene oxide and TiO 2 -reduced graphene oxide hybrid nanocomposites. It was generally concluded that modification of starting TiO 2 with carbonaceous precursors leads to the slight increase of intensity of the TRMC signals, indicating that more electrons are induced in the conduction band of hybrid nanocom- posites. It is also worth mentioning that the decay of studied signals of modified powders depends on added carbon precursor, indicating that the type of deposited species may affect the slight or significant suppression of recombination or charge-carriers trapping. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Titanium dioxide is well-known and the most investigated material in photocatalysis [1,2]. TiO 2 can produce photoinduced electron–hole pairs under the ultraviolet (UV) light irradiation that eventually generates hydroxyl radicals on the photocatalyst sur- face, used for organic pollutants oxidation. The activity of TiO 2 is limited due to a fast recombination of photoinduced charge- carriers. The recombination of the electron–hole pairs can be effectively suppressed by combining the TiO 2 with graphene which can serve as a hole or electron trap, slowing charge recombina- tion in TiO 2 [3–5]. Graphene, as a zero band gap semiconductor displays an ambipolar electric field effect and charge-carriers can be tuned continuously between electrons and holes in concen- ∗ Corresponding author. E-mail address: ekusiak@zut.edu.pl (E. Kusiak-Nejman). trations as high as 10 13 cm −2 , with room temperature mobility up to 200 000 cm 2 V −1 s −1 [6,7]. In case of graphene oxide (GO) and reduced graphene oxide (rGO) electron transport is different due to the presence of substantial electronic disorder. GO can be treated as graphene with oxygen functional groups present on the surface and edges. Sp2 conjugated network of original graphene sheet is extended and disrupted by sp3 hybridized carbon-oxygen bonds. Reduction of GO further generates various types of defects in the graphene lattice, which limits charge-carrier transport [8–10]. However, electrical properties of rGO strongly depend on the amount of residual oxygen therefore amount of sp3 bonding, which represent transport barriers [11]. Accordingly, the electron transfer efficiency and decrease of the electron-hole pairs recombination for use of GO and rGO depend on the preparation conditions as well as reduction methods [8]. According to Kaiser et al. [12]. con- ductance measured for rGO at room temperature is dominated by two-dimensional electric field-assisted, thermally-driven (Pollak- Riess) variable-range hopping (VRH) through highly disordered http://dx.doi.org/10.1016/j.cattod.2016.11.008 0920-5861/© 2016 Elsevier B.V. All rights reserved.