ARTICLE IN PRESS JID: JTICE [m5G;July 1, 2015;22:20] Journal of the Taiwan Institute of Chemical Engineers 000 (2015) 1–8 Contents lists available at ScienceDirect Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice Optimization of physico-chemical parameters for the photo-oxidation of neutral red on the spinel Co 2 SnO 4 H. Bouchaaba a , B. Bellal b,∗ , R. Maachi a , M. Trari b , N. Nasrallah a , A. Mellah a a Laboratory of Engineering Reaction, Faculty of Mechanic and Engineering Processes USTHB, BP 32, Algeria b Laboratory of Storage and Valorization of Renewable Energies, Faculty of Chemistry (USTHB) BP 32, Algeria article info Article history: Received 4 January 2015 Revised 28 May 2015 Accepted 7 June 2015 Available online xxx Keywords: Spinel Co 2 SnO 4 Neutral red Sunlight Kinetic Langmuir–Hinshelwood model abstract The spinel Co 2 SnO 4 is prepared by chemical route to assess its feasibility for the oxidation of neutral red under visible illumination. The diffuse reflectance gives a band gap of 1.72 eV, properly matched to the sun spectrum. The electrons in the conduction band (0.16 V SCE ), determined from the capacitance measurement, permit the formation of O 2 − radicals, responsible of the neutral red oxidation. The dye concentration, catalyst dose, agitation speed and light flux are optimized. A degradation of 85% is obtained under sunlight within 45 min for 10 mg/L concentration. The oxidation follows a pseudo second order kinetic with an apparent rate constant of 11.5 × 10 −3 L/mg/min according to the Langmuir–Hinshelwood model. © 2015 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. 1. Introduction In recent decades, a growing activity has been observed for the water pollution by the industrial activities of dyes, pesticides, phar- maceutical compounds and heavy metals [1,2]. The conventional methods like the membrane separation, reverse osmosis, advanced oxidation processes (AOPs), and solvent extraction [3,4] have been applied so far for the water treatment. However, such techniques of- ten become inefficient at low concentrations [5]. Dye-containing wastewaters are discharged from the textile in- dustry and represent a serious threat for the environment with about 20% of the world pollution. They affect dramatically the aquatic life and disturb the eco-system for concentration as low as 5 mg/L by in- hibiting the photosynthesis [6]. To remedy to such situation, efficient and inexpensive techniques have to be developed to treat the indus- trial effluents before landfills in the aquatic medium. However, depending on the nature and the concentration of the dye, the decontamination method is limited either because of the expensive cost of operations or by the inefficiency of the technique to achieve a high degree of purification, thus respecting the stan- dards of the water quality imposed by the World Health Organization (WHO). So, the urgency of seeking new energy sources for the water treatment is highly encouraged [7]. In this respect, the photocatalysis emerged as an attractive alternative for the water remediation [8,9]; ∗ Corresponding author. Tel.: +213 21 24 79 55; fax: +213 21 24 80 08. E-mail address: bachirbellal60@gmail.com (B. Bellal). the advantage resides in its simplicity since the technique does not require any special set up and can mineralize the organic matter by radicals to a large extend [10,11]. The principle is based on the absorp- tion by a semiconductor, of light radiation with energy higher than the band gap (E g ). This energy causes the excitation of an electron to the conduction band (CB) and concomitantly generates a “hole” in the valence band (VB) giving the semiconductor photoredox proper- ties [12–14]. The simultaneous presence of the catalyst, oxygen and visible light favor the oxidation of organic compounds. In this respect, Algeria has a huge solar potential with an aver- age insolation of ∼6 kWh/m 2 /day and a sunshine duration going over ∼3000 h/year. Our group has been working on the dyes removal by both adsorption [15] and photocatalysis [16]. In continuation, we are interesting by the photooxidation of neutral red under both artifi- cial and sun lights. Many commercial dyes resist to biodegradation and the photocatalysis is highly recommended in such a case [17,18]. Neutral red (NR, tolylene red chloride, C 15 H 16 N 4 •HCl, C.I.50040) is a cationic dye soluble in water. It is a pH indicator whose color changes from red to yellow over the pH range (6.8–8) and is widely used in the textile industry as tracer. On the other hand, a survey of the literature [19–23] shows that considerable efforts were focused on developing effective photocata- lysts and attention would be, therefore, directed to the spinels fam- ily which has the required properties for the photoelectrochemical (PEC) conversion [24,25]. To our knowledge, the spinel Co 2 SnO 4 has not yet been assessed photocatalytically, it is selected because of its chemical stability over a wide pH range and optical gap, close to the ideal value for terrestrial applications. This work deals with the http://dx.doi.org/10.1016/j.jtice.2015.06.011 1876-1070/© 2015 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Please cite this article as: H. Bouchaaba et al., Optimization of physico-chemical parameters for the photo-oxidation of neutral red on the spinel Co 2 SnO 4 , Journal of the Taiwan Institute of Chemical Engineers (2015), http://dx.doi.org/10.1016/j.jtice.2015.06.011