Please cite this article in press as: N. Kaneva, et al., Photocatalytic purification of dye contaminated sea water by lanthanide (La 3+ , Ce 3+ , Eu 3+ ) modified ZnO, Catal. Today (2015), http://dx.doi.org/10.1016/j.cattod.2014.12.008 ARTICLE IN PRESS G Model CATTOD-9391; No. of Pages 7 Catalysis Today xxx (2015) xxx–xxx Contents lists available at ScienceDirect Catalysis Today j our na l ho me page: www.elsevier.com/locate/cattod Photocatalytic purification of dye contaminated sea water by lanthanide (La 3+ , Ce 3+ , Eu 3+ ) modified ZnO Nina Kaneva, Assya Bojinova ∗ , Karolina Papazova ∗∗ , Dimitre Dimitrov Laboratory of Nanoparticle Science and Technology, Department of General and Inorganic Chemistry, Faculty of Chemistry and Pharmacy, University of Sofia, 1 James Bourchier Blvd., 1164 Sofia, Bulgaria a r t i c l e i n f o Article history: Received 2 July 2014 Received in revised form 2 December 2014 Accepted 13 December 2014 Available online xxx Keywords: ZnO Powders Rare earth Photocatalysis Textile dye a b s t r a c t The photocatalytic degradation of the textile dye Reactive Black 5 in distilled and sea water by Ln mod- ified ZnO is studied for the first time under UV-light irradiation. The bleaching process is investigated from different aspects: the type of rare earth element, La 3+ concentration and annealing temperature. The observed dye degradation rate increases with the La content up to 2 mol % and then decreases (2.5 and 3.0 mol%). It is found out that Ln modified ZnO photocatalyst achieves contaminants mineralization within a short irradiation time. The optimal dopants concentration and annealing temperature are exper- imentally established-powders, modified with 2 mol% La 3+ and annealed at 100 ◦ C, are the most efficient in Reactive Black 5 photodegradation in comparison with pure and (Ce 3+ , Eu 3+ ) modified ZnO. © 2015 Published by Elsevier B.V. 1. Introduction In the past decade, rare earths (RE) doped photocatalysts attract great attention as a useful approach for achieving improved photo- catalytic efficiency. Recent investigations report photodegradation of: azo (X-3B) dye by Ln-TiO 2 sol [1]; 4-nitrophenol by (La 3+ , Nd 3+ and Sm 3+ ) modified ZnO nanoparticles [2]; phenol under Vis light irradiation by rare earth-doped (Eu, Ce, Nd) ZnO hierarchical micro/nanospheres [3]; metasystox by La-modified ZnO nanorods [4]. Several research groups report various synthesis methods of RE doped ZnO, such as polymer pyrolysis [2], facile chemical pre- cipitation [3,5], wet chemical precipitation method [6], sol–gel [7,8], magnetron sputtering [9], pulsed laser deposition [10], hydrothermal method [11,12], micro emulsion templating [13], co- precipitation [14–16], forced hydrolysis [17–19], electrode position [20,21], photolithography and wet chemical etching [22,23]. In particular, because of their unique 4f-electronic configuration and spectral characteristics, lanthanides are ideal dopants for mod- ifying the crystal structure, electronic structure, optical properties and surface adsorption of ZnO and preparation of novel promising ∗ Corresponding author. Tel.: +359 2 8161 479; fax: +359 2 962 5438. ∗∗ Corresponding author. E-mail addresses: nhasb@wmail.chem.uni-sofia.bg (A. Bojinova), cpapazova@outlook.com (K. Papazova). photocatalysts. The doping of rare earth ions into ZnO lattice unfor- tunately faces the two difficulties [2] described below. The first is the limited Ln 3+ dopants concentration in ZnO lattice due to the differences in ionic radius and charge between Ln ions and Zn 2+ ions. The second is the inappropriate energy level position of Ln 3+ ion, related to the valence and conduction bands of ZnO host. Meanwhile, in recent years La-doped TiO 2 photocatalysts has attracted much attention [24–26]. Unfortunately, to the best of our knowledge, there is insufficient information available on the application of RE modified ZnO for photodegradation of organic pollutants in more real conditions. 2. Experimental 2.1. Reagents and materials Zinc oxide commercial powder (>99.0%), Ce(NO 3 ) 3 ·6H 2 O (>99.0%), La 2 O 3 (>99.0%), Eu 2 O 3 (>99.0%) and absolute ethanol were obtained from Fluka. Reactive Black 5 (C 26 H 21 N 5 Na 4 O 19 S 6 ,  max = 595 nm, dye con- tent ca. 55% from Sigma–Aldrich) was chosen as modal pollutant in the photocatalytic experiments, due to its large scale application in practice. It is diazo compound with four phenyl groups, which when dissolved in water, has a dark blue color due to connection between aromatic rings and azo groups [27]. RB5 is one of the most common dyes that have been used in textile industries for cotton, viscose, wool and polyamide fabrics dyeing. It is also used as a stain dye in http://dx.doi.org/10.1016/j.cattod.2014.12.008 0920-5861/© 2015 Published by Elsevier B.V.