Mesoporous silica iron-doped as stable and efficient heterogeneous catalyst for the degradation of C.I. Acid Orange 7 using sono–photo-Fenton process Xin Zhong a , Sebastien Royer b , Hui Zhang a,⇑ , Qianqian Huang a , Luojing Xiang a,b , Sabine Valange b , Joel Barrault b a Department of Environmental Engineering, Wuhan University, P.O. Box C319, Luoyu Road 129#, Wuhan 430079, China b LACCO, Université de Poitiers-CNRS, 40 Avenue du Recteur Pineau, F-86022 Poitiers Cedex, France article info Article history: Received 2 September 2010 Received in revised form 13 April 2011 Accepted 15 April 2011 Available online 10 May 2011 Keywords: Sono–photo-Fenton Fe 2 O 3 /SBA-15 GC–MS Degradation pathway abstract Iron-containing mesostructured silica (Fe 2 O 3 /SBA-15) was prepared and used as heterogeneous catalyst in the integrated sono–photo-Fenton process. The effect of hydrogen peroxide concentration, initial pH, Fe 2 O 3 /SBA-15 loading, ultrasonic power, and initial solution concentration on the decolorization of C.I. Acid Orange 7 (AO7) by the integrated heterogeneous sono–photo-Fenton process was investigated in order to optimize process efficiency. The results showed that the decolorization efficiency increased with the increase of hydrogen peroxide concentration, ultrasonic power, Fe 2 O 3 /SBA-15 loading, but decreased with the increase of initial pH and initial dye concentration. Catalyst stability was evaluated by measur- ing iron leaching in solution. The particles size distribution of spent catalyst evidenced a remarkable size reduction during reaction, leading to more reactive surface and higher mass transfer rate. The main reac- tion intermediates were separated and identified using GC–MS and a possible degradation pathway was proposed. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Over the past several years, the treatment of hazardous organic pollutants containing wastewater by advanced oxidation processes (AOPs) has attracted continuous interest. Among the various AOPs, Fenton process based on the use of H 2 O 2 with Fe(II) ions is well known as a powerful source of reactive radicals Å OH, which are able to degrade various refractory compounds [1]. Compared to other AOPs, Fenton-based process involves mild operating reaction con- ditions thanks to the redox properties of the metallic cations used [2,3], but the iron removal required additional separation steps, resulting in increased overall costs [4]. In order to overcome the major drawbacks of the homogeneous process, heterogeneous Fen- ton-type systems using Fe-containing catalyst have been prepared to catalyze the oxidation of various organic compounds [5]. Unfor- tunately, the catalyst can suffer from poisoning during the oxida- tion process, due to reaction intermediates adsorption on its surface, thereby leading to progressively inactive surface [6]. In parallel, ultrasonic irradiation (US) has been paid great atten- tion, especially for refractory pollutants degradation in wastewater treatment [7]. Generally, most of researches focused on the ‘‘hot spots’’ theory to illustrate the chemical effects due to the cavitation [8]. The nucleation, cyclic growth, and finally collapse of the microbubbles generated by ultrasonic irradiation lead to localized high temperatures and pressures [9]. The resulting generation of highly potent chemical oxidants, such as free radicals ( Å OH, Å H, and Å O 2 ), through the use of ultrasound irradiation makes it a promising process for the degradation of pollutants [10]. Unfortu- nately, high organic compounds degradation and mineralization degree by using ultrasound alone are rarely achieved, and the cost of ultrasound irradiation remains high [11]. Interestingly, ultra- sound irradiation favors the removal of reactive intermediates or by-products from the catalyst surface, thereby providing clean and reactive surfaces for subsequent reactions over heterogeneous catalytic systems [12]. Moreover, fragmentation of the catalyst in small particles that provide a higher surface area, as well as higher mass transfer, also account for the main advantages of ultrasound system over other AOPs [13]. In this way, advanced oxidation tech- nologies integration is advantageous in water treatment in order to avoid the disadvantages associated to each individual process [14]. Indeed, promising results have been reported in the literature con- cerning the simultaneous combination of ultrasound and Fenton- like systems in the degradation of various organic compounds, such as phenolic solutions [15], chlorophenols [16,17], MTBE [18], p-chlorobenzoic acid [19], dyes [20] and 2,4-dichlorophenol [21]. The combination of UV irradiation with ultrasound enhanced Fenton-like system not only increases the rate and number of generated reactive radicals, but also reduces mass transfer resis- tance due to acoustic streaming and turbulence [22]. Melero and 1383-5866/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2011.04.024 ⇑ Corresponding author. Tel.: +86 27 68775837; fax: +86 27 68778893. E-mail address: eeng@whu.edu.cn (H. Zhang). Separation and Purification Technology 80 (2011) 163–171 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur