Applied Catalysis B: Environmental 156–157 (2014) 1–7 Contents lists available at ScienceDirect Applied Catalysis B: Environmental j ourna l h om epage: www.elsevier.com/locate/apcatb Dimethyl phthalate degradation at novel and efficient electro-Fenton cathode Yi Wang a , Yuhui Liu a , Tianfu Liu a , Shuqin Song b , Xuchun Gui b , Hong Liu a,c,∗ , Panagiotis Tsiakaras d,∗∗ a KLGHEI of Environment and Energy Chemistry/The Key Lab of Low-carbon Chemistry & Energy Conservation of Guangdong Province, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275, China b State Key Laboratory of Optoelectronic Materials and Technologies/The Key Lab of Low-carbon Chemistry & Energy Conservation of Guangdong Province, School of Physics and Engineering, Sun Yat-sen University, Guangzhou, China c Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 401122, China d Department of Mechanical Engineering, School of Engineering, University of Thessaly, Pedion Areos, 38334 Volos, Greece a r t i c l e i n f o Article history: Received 18 September 2013 Received in revised form 17 February 2014 Accepted 20 February 2014 Available online 28 February 2014 Keywords: Carbon nanotube sponge Electro-Fenton H2O2 generation Dimethyl phthalate a b s t r a c t A novel three-dimensional porous carbon nanotube sponge (CNTS) with high electrical conductivity was prepared, characterized and investigated as the catalytic cathode for oxygen reduction and employed for an electro-Fenton process to degrade dimethyl phthalate (DMP) in aqueous solution. For comparison, the conventional electro-Fenton cathode, graphite gas diffusion electrode (GDE) and graphite electrode, was also tested. Experiments showed that the side reaction of H 2 evolution was avoided and the H 2 O 2 accumulation concentration arrived at the maximal value at CNTS cathode as the cathode potential was set at -0.5 V (vs. SCE). The apparent rate constant for DMP degradation was 0.057 min -1 at CNTS cathode, much higher than 0.005 min -1 at graphite cathode and 0.011 min -1 at graphite GDE. Meanwhile, CNTS possessed desirable stability without performance decay after 20 times reaction. It was also found that more negative cathode potential than -0.5 V could cause the side reaction of H 2 evolution and thus leading to a deteriorated DMP degradation. Moreover, the initial DMP concentration affected the apparent rate constant of DMP degradation. Compared to the case of higher initial DMP concentration, DMP degraded faster in the case of lower initial DMP concentration. The pH value and initial Fe 2+ concentration for DMP degradation at CNTS cathode were optimized to be 3.0 and 0.5 mmol L -1 , respectively. The CNTS is promising to be potentially used as the cathode for electro-Fenton system to remove organic pollutants in wastewater. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Advanced oxidation processes (AOPs) are promising technol- ogy for effluent purification when the contaminants are difficult to remove by biological processes [1–4]. Among AOPs, the Fenton oxi- dation process [5–8], whose high performance is based on the high oxidation power and the non-selective oxidation ability of hydroxyl free radicals ( • OH) generated from Fenton’s reagents (H 2 O 2 + Fe 2+ ), has received tremendous attention in recent years. The Fenton’s reaction mechanism for the formation of •OH is complicated, while the main reaction can be described as follows: ∗ Corresponding author: Tel.: +86 23 63063783; fax: +86 23 84113365. ∗∗ Corresponding author: Tel.: +30 24210 74065; fax: +30 24210 74050. E-mail addresses: liuhong@cigit.ac.cn (H. Liu), tsiak@uth.gr (P. Tsiakaras). Fe 2+ + H 2 O 2 → • OH + OH - + Fe 3+ (1) The high oxidative efficiency of Fenton oxidation process has been well established, while its application is limited by the stor- age and shipment of concentrated hydrogen peroxide (H 2 O 2 ). To solve these problems, electro-Fenton process [9–13] is developed to eliminate or minimize this drawback. In electro-Fenton process, H 2 O 2 can be in situ supplied electrochemically through oxygen reduction reaction (ORR), and ferrous ions (Fe 2+ ) can be regenerated at cathode in acidic aqueous solution. Therefore, H 2 O 2 production from ORR at cathode is crucial to the electro-Fenton process [14]. It should be noted that ORR has two possible reaction pathways involving two or four electrons transfer, which can be expressed by Eqs. (2) and (3), respectively [15,16]. O 2 + 2H + + 2e → H 2 O 2 0.695 V (vs. NHE) (2) http://dx.doi.org/10.1016/j.apcatb.2014.02.041 0926-3373/© 2014 Elsevier B.V. All rights reserved.