Simultaneous photodegradation of two textile dyes using TiO 2 as a catalyst D. Lonc ˇarevic ´ 1 • J. Dostanic ´ 1 • V. Radonjic ´ 1 • Lj. Z ˇ ivkovic ´ 2 • D. M. Jovanovic ´ 1 Received: 30 November 2015 / Accepted: 21 January 2016 / Published online: 10 February 2016 Ó Akade ´miai Kiado ´, Budapest, Hungary 2016 Abstract The simultaneous photocatalytic degradation of two dyes: methylene blue (MB), a cationic dye, and arylazo pyridone dye (SD), an anionic dye was investigated using sol–gel prepared TiO 2 particles. The paper shows the main dif- ference in degradation kinetics between single dye solution and binary dye solu- tions. The effects of competitive adsorption and the concentration of the dyes on degradation rate were analyzed. The preferential adsorption capacity of TiO 2 toward MB was attributed to electrostatic interactions between the cationic dye and neg- atively charged TiO 2 surface, while repulsion between the negatively charged surface of the catalyst and SD dye results in its lower adsorption capacity. The TiO 2 surface charge and accordingly adsorption affinity of investigated dyes were found to be the main factors affecting degradation rate of the dyes. In the single dye system, the catalyst showed considerably higher degradation activity toward MB than to SD. In binary dye systems, the presence of SD did not affect the degradation of MB. On the other hand, the degradation efficiency of SD was found to be highly influenced by initial MB concentration and absorption ability of MB. In addition, higher MB concentration induces the production of a higher amount of reaction products, which also determine the SD degradation rate. Three kinetic regimes for the photodegradation of SD in binary mixtures were observed, used as a starting point to elucidate most influencing parameters for SD reaction kinetics. Electronic supplementary material The online version of this article (doi:10.1007/s11144-016-0990-0) contains supplementary material, which is available to authorized users. & D. Lonc ˇarevic ´ dloncarevic@nanosys.ihtm.bg.ac.rs 1 Department of Catalysis and Chemical Engineering, Institute of Chemistry, Technology and Metallurgy, University of Belgrade, Njegos ˇeva 12, 11000 Belgrade, Serbia 2 Vinc ˇa Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11001 Belgrade, Serbia 123 Reac Kinet Mech Cat (2016) 118:153–164 DOI 10.1007/s11144-016-0990-0