Solar photocatalytic degradation of RB5 by ferrite bismuth nanoparticles synthesized via ultrasound T. Soltani, M.H. Entezari ⇑ Department of Chemistry, Ferdowsi University of Mashhad, 91775 Mashhad, Iran article info Article history: Received 8 December 2012 Received in revised form 15 January 2013 Accepted 28 January 2013 Available online 7 February 2013 Keywords: Ultrasound Ferrit bismuth RB5 Degradation Mechanism abstract In this paper, the photocatalytic degradation of Reactive Black 5 (RB5) was investigated with ferrite bis- muth synthesized via ultrasound under direct sunlight irradiation. The intensity of absorption peaks of RB5 gradually decreased by increasing the irradiation time and finally vanished in 50 min in acidic med- ium. The formation of new intermediate was observed in basic medium. The relative concentration of RB5 in solution and on the surface of ferrite bismuth (BiFeO 3 ) nanoparticles was considered during the exper- iment in acidic and basic media. The effects of various parameters such as amount of catalyst, concentra- tion of dye, and pH of the solution have been studied on the dye degradation. The adsorption isotherm and the kinetic of photocatalytic degradation of RB5 were investigated. The adsorption constants in the dark and in the presence of sunlight irradiation were compared. The photocatalytic degradation mechanism of RB5 has been evaluated through the addition of some scavengers to the solution. In addi- tion, the stability and reusability of the catalyst were examined in this work. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Sixty to seventy percent of dyes used in the textiles industries contained azo dyes with one or more azo bonds (–N@N–). The in- tense use of azo dyes is related to their high solubility, stability and color variety and most important its simple dyeing procedure [1]. It is estimated about 15% of the total world production of dyes is lost and is released in the textile effluents during the dyeing pro- cess [2]. Some of these dyes not only are toxic, mutagenic [3] and carcinogenic [4] compounds, but also are resistant to aerobic biodegradation [5], and their half-lives under sunlight are greater than 2000 h [6]. These dyes even at low concentration stop the sunlight access to aquatic fauna and flora, and it reduces the pho- tosynthetic action within the ecosystem [7]. Hence, the textile industries are very important source of pollution of the aquatic system. Lately, there has been considerable attention for the removal of dyes by different methods. There are often used adsorption as a physical method [8], chlorination, ozonation as chemical methods [9] and biodegradation [10]. These removal methods are not effec- tive for a complete degradation and in some cases only provide separation of the dyes without any dye degradation, and creating a secondary waste problem. Advanced oxidation processes (AOPs) are based on generation of reactive species through illumination of UV or solar light of some active materials. This process can lead to oxidize organic pol- lutants to inorganic compounds [11]. From the practical point of view, photodegradation of pollutants using semiconductor and so- lar light is an economical process. Since, the solar energy is an abundant natural energy source, which can be used instead of arti- ficial light sources that is expensive and hazardous. TiO 2 is widely used for the degradation of many organic com- pounds under UV irradiation because of its low cost, high stability and high photocatalytic activities [12]. The band-gap energy of TiO 2 is 3.2 eV that can be activated by radiation of UV in the wave- length of 387.5 nm. It is known that only 4–5 percent of solar radi- ation is UV and this is a limitation for this catalyst which requires UV light for activation. Nowadays, the perovskite-type BiFeO 3 (BFO) has attracted con- siderable attention due to its narrowing band-gap energy (2.1 eV) [13], high chemical stability [14], and exhibiting a coexistence of simultaneous ferroelectric and magnetic order parameters [15]. In addition to potential electronic and magnetic applications, BFO powders have been used as a new visible-light photocatalyst [16]. Ultrasound has been successfully used for the synthesis of nanocrystalline materials due to its unique effects in recent years [17]. In our lab, the sono-synthesis of semiconductors with core– shell structure was carried out in short time and the product had appropriate adsorbability, and high catalytic activity [18–21]. Great attention has also been paid to the direct use of ultrasound for the degradation of wastewater. But, a complete mineralization of organic pollutants by ultrasonic irradiation alone is difficult. A significant decrease in the concentration of RB5 (94%) was 1350-4177/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ultsonch.2013.01.012 ⇑ Corresponding author. Fax: +98 511 8795457. E-mail address: moh_entezari@yahoo.com (M.H. Entezari). Ultrasonics Sonochemistry 20 (2013) 1245–1253 Contents lists available at SciVerse ScienceDirect Ultrasonics Sonochemistry journal homepage: www.elsevier.com/locate/ultson