Colloids and Surfaces A: Physicochem. Eng. Aspects 300 (2007) 315–320 Investigation of the electrosurface properties of NiO and Fe 2 O 3 in azole solutions I.B. Dmitrieva a,∗ , K.P. Tikhomolova b , A.S. Chukhno a , P.P. Prokopovich c , V.M. Starov c a Physics and Colloid Chemistry Department, St. Petersburg Academy of Chemistry and Pharmacology, 14, Prof Popova, St. Petersburg 197376, Russia b Chemistry Research Institute, St. Petersburg University, 2, Universitetskii pr., Petrodvorets 198904, Russia c Department of Chemical Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK Available online 3 February 2007 Abstract The electrokinetic study of heterogeneous system consisting of Ni(II) and Fe(III) oxide powders in aqueous azole solutions is presented. Diazole, triazole and tetrazole were used in our experiments. Various combinations of operating conditions such as pH, electrolyte and azole concentrations were employed. Zeta-potentials of powders with adsorbed azoles were obtained in order to investigate the interactions occurring between azoles and the oxide surfaces. In the presence of azoles the equilibration process of zeta-potential of oxide surfaces has a very special “damping oscillation” character and the equilibration process continues for around a week. However, kinetics of adsorption of azoles is completed in approximately 3 h. The latter shows a complex behaviour of adsorbed azoles on oxide surfaces. © 2007 Elsevier B.V. All rights reserved. Keywords: Nickel(II) oxide; Ferric(III) oxide; Azoles; Microelectrophoresis; Specific adsorption; Surface complexation 1. Introduction Analysis of double electric layer (DEL) formation mecha- nisms on solid surfaces in aqueous solutions in presence of biological active substances (BAS) is currently the subject of many researchers. This work is focussed on studying the BAS specific adsorption and electrokinetic properties of oxide sur- faces. We show that adsorption of azoles on oxide surfaces is substantially different from ion adsorption according to the classic ion-electrostatic theory. The adsorption of inorganic ions and surfactant ions are the major subjects under investigation in the literature. However, there are numerous classes of water soluble organic molecules, for example, heterocyclic molecules, with polar and non-polar groups, which are not defined as surfactants. There are only a few studies dedicated to the investigation of adsorption of such molecules [1,2], which have proven that adsorption mech- anism in such cases cannot be described in terms of adsorption either of inorganic ions or of surfactants. The specific adsorp- tion [1,2] was attributed to the formation of surface complexes of ∗ Corresponding author. E-mail address: dalexl@rol.ru (I.B. Dmitrieva). adsorbed BAS with the metal acting as an acceptor and adsorbed BAS behaving as a ligand. Formation of donor–acceptor bonds between an ion of the adsorbed BAS and the acceptor can lead to a number of specific phenomena in the adsorbed layer [1,2]. In the work presented here, azoles are the objects of inves- tigation of the specific adsorption of heterocyclic organic molecules. Azoles are unique and interesting objects for studies not only due to their acid–base properties changes in the order: diazole–triazole–tetrazole, but also due to their changing abili- ties to different types of interactions (Coulomb, donor–acceptor and Van der Waals). This influences the azoles aggregation mechanisms in solution and their ability to form complexes with metals both in solution and on surface. In this work, oxides of nickel(II) and iron(III) were used as model systems due to ability of nickel and iron to form complexes with azoles. These studies can help in solving vital problems such as transport of medicines inside organisms. The aim of the present study is to investigate the time depen- dences of changes of electrokinetic and adsorption properties of NiO and Fe 2 O 3 powders in aqueous solutions of 1,3-diazole, 1,2,4-triazole, 1,2,3,4-tetrazole and 5-methyl-1,2,3,4-tetrazole depending on aqueous phase composition (concentration of azoles, pH). 0927-7757/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2007.01.046