Water Research 37 (2003) 3776–3784 Discoloration and mineralization of Reactive Red HE-3B by heterogeneous photo-Fenton reaction Jiyun Feng a , Xijun Hu a, *, Po Lock Yue a , Huai Yong Zhu b , Gao Qing Lu b a Department of Chemical Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong b Department of Chemical Engineering, University of Queensland, Brisbane, Qld 4702, Australia Received 17 September 2002; received in revised form 28 February 2003; accepted 3 May 2003 Abstract Discoloration and mineralization of Reactive Red HE-3B were studied by using a laponite clay-based Fe nanocomposite (Fe-Lap-RD) as a heterogeneous catalyst in the presence of H 2 O 2 and UV light. Our experimental results clearly indicate that Fe-Lap-RD mainly consists of Fe 2 O 3 (meghemite) and Fe 2 Si 4 O 10 (OH) 2 (iron silicate hydroxide) which have tetragonal and monoclinic structures, respectively, and has a high specific surface area (472 m 2 / g) as well as a high total pore volume (0.547 cm 3 /g). It was observed that discoloration of HE-3B undergoes a much faster kinetics than mineralization of HE-3B. It was also found that initial HE-3B concentration, H 2 O 2 concentration, UV light wavelength and power, and Fe-Lap-RD catalyst loading are the four main factors that can significantly influence the mineralization of HE-3B. At optimal conditions, complete discoloration of 100 mg/L HE-3B can be achieved in 30 min and the total organic carbon removal ratio can attain 76% in 120 min, illustrating that Fe-Lap-RD has a high photo-catalytic activity in the photo-assisted discoloration and mineralization of HE-3B in the presence of UV light (254 nm) and H 2 O 2 . r 2003 Elsevier Science Ltd. All rights reserved. 1. Introduction Advanced oxidation processes (AOPs) have been attracted wide interests in wastewater treatment since 1990s [1–11]. In principle, AOPs are based on the generation of OH radicals in water, which are highly oxidative and nonselective oxidants being able to oxidize organic compounds particularly unsaturated organic compounds such as azo dyes. Among AOPs, one of the most important processes to generate OH radicals is using the Fe 2+ /H 2 O 2 /UV system, where the catalyst of ferrous ions are dissolved in water so it is called homogeneous photo-Fenton system. In this system, Fe 2+ in solution functions as a homogeneous catalyst. The formation of OH radicals and regeneration of Fe 2+ by photo-reduction from Fe 3+ can be expressed by the following equations: Fe 2þ þ H 2 O 2 þUV-Fe 3þ þ dOH þ OH  ; ð1Þ FeðOHÞ 2þ þUV-Fe 2þ þ dOH: ð2Þ Many researchers have confirmed that homogeneous photo-Fenton process is a promising process in waste- water treatment [1–11]. However, it should be pointed out that homogeneous photo-Fenton process has a significant disadvantage. The removal of the sludge containing Fe ions at the end of wastewater treatment is costly and needs large amount of chemicals and manpower. This drawback limits the further application of homogeneous photo-Fenton reaction in wastewater treatment. To overcome the disadvantage of homogeneous photo-Fenton process, some attempts have been made to develop heterogeneous photo-Fenton or photo- Fenton-like process by coating Fe ions, Fe oxide or Cu onto porous solid as the catalyst, which is called heterogeneous catalyst because it does not dissolve in water [12–18]. Among these catalysts, one is based on ARTICLE IN PRESS *Corresponding author. Tel./fax: +852-2358-7134. E-mail address: kexhu@ust.hk (X. Hu). 0043-1354/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0043-1354(03)00268-9