Catalysis Today 230 (2014) 152–157 Contents lists available at ScienceDirect Catalysis Today j o ur na l ho me page: www.elsevier.com/locate/cattod Photo-electrochemical properties of ZnO and TiO 2 layers in ionic liquid environment P. Dytrych a , P. Kluson a,∗ , P. Dzik b , M. Vesely b , M. Morozova a , Z. Sedlakova a , O. Solcova a a Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, Rozvojova 135, Prague 6, Czech Republic b Faculty of Chemistry, Brno University of Technology, Purkynova 118, Brno, Czech Republic a r t i c l e i n f o Article history: Received 20 July 2013 Received in revised form 10 October 2013 Accepted 11 October 2013 Available online 8 November 2013 Keywords: Room temperature ionic liquids Reverse micelles Piezoelectric jet printing Semiconducting metal oxides a b s t r a c t Photoinduced electrochemical functionality of uniform TiO 2 and ZnO films prepared by sol–gel method, in the former case in the reverse micelle environment, was studied using a specific type of ionic liquids as electrolytes. The coating part was arranged as piezoelectric ink-jet printing. Ionic liquids could be regarded as nanostructured fluids with two distinctive kinds of spatial domain: one ionic, the other non- polar. The driving force for the segregation of the nonpolar chains is energetic. They are excluded from the cohesive network of positive and negative charges that is formed by the charged groups of the ions in close contact. If side-chains are too short they do not disturb the ionic network significantly and, they do not possess enough conformational freedom to adopt low energy configuration. By increasing the chain- length the role of its spatial arrangement becomes important. Such features must be reflected in their specific behaviour as electrolytes in the contact with photoactive semiconducting thin films. Attention was also paid to the correlation of the values of generated photocurrent densities in layers with the fluidity and conductivity of the used ionic liquids. © 2013 Elsevier B.V. All rights reserved. 1. Introduction In the past years endless number of ZnO, CeO 2 , TiO 2 , etc. based functional materials have been described. In terms of their photo-induced functionality two types of mutually dependent sub- functionalities must be always considered. The primary function is associated with the photo-induced generation of the hole–electron pair. If the particular material is identified as sufficiently effec- tive in this manner it can be considered for the next step, for example as heterogeneous photocatalyst. Uniform functional films of nanoscopic metal oxides could be produced in many possible routines. One of such methods is the bottom-up generation of ordered structure nanoparticles in cores of reverse micelles [1,2]. The overall process is organized as the sol–gel method, the coating technique then as piezoelectric jet printing [3–6]. Undoubtedly titanium and zinc oxides are the most extensively studied transition-metal oxides. There are many possible applica- tions that might be taken into account depending on their structural and functional features. Here we report on the possible utiliza- tion of various types of room temperature ionic liquids (RTILs) as ∗ Corresponding author. Tel.: +420 220 390 340; fax: +420 220 920 661. E-mail addresses: kluson@icpf.cas.cz, p.kluson@seznam.cz, kluson@seznam.cz (P. Kluson). URL: http://www.icpf.cas.cz/hana (P. Kluson). electrolytes in the step of functional characterization of the pro- duced nanoscopic ZnO and TiO 2 films. Hundreds of structurally different ionic liquids are currently available. However, the most commonly used are those with the imidazolium type of cation combined either with hexafluorophosphate or tetrafluoroborate counter ions. Another attractive group of ILs might be ranked among quaternary ammonium salts (QAS) [7]. Ionic liquids could be regarded as nanostructured fluids with two distinctive kinds of spatial domain: one ionic, the other non-polar. The driving force for the segregation of the nonpolar chains is believed to be ener- getic. They are excluded from the cohesive network of positive and negative charges that is formed by the charged groups of the ions in close contact [8,9]. If the side-chains are too short, they do not disturb the ionic network significantly and, also, they do not possess enough conformational freedom to adopt a low energy configuration. However, increasing the chain-length the role of its spatial arrangement becomes much more important. Obviously such features must be also reflected in their specific behaviour as electrolytes in the contact with photoactive semiconducting thin films [10–13]. To the best of our knowledge electrochemical interactions of these types of RTILs with the reverse micelles templated semicon- ducting nanoparticles have not been reported yet. Special attention was also paid to the correlation of the values of generated photo- current densities in layers with the fluidity and conductivity of the used RTIL’s. 0920-5861/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cattod.2013.10.048