Effect of initial solution pH on the degradation of Orange II using clay-based Fe nanocomposites as heterogeneous photo-Fenton catalyst

Effect of initial solution pH on the discoloration and mineralization of 0.2 mM Orange 11 by using two clay-based Fe nanocomposites (Fe-B (Fe supported on bentonite clay) and Fe-Lap-RD (Fe supported on laponite clay)) as catalysts was studied in detail. It was found that the initial solution pH not only influences the photo-catalytic activity of Fe-B and Fe-Lap-RD but also the Fe leaching from the two catalysts. Both catalysts show the best photocatalytic activity at an initial solution pH of 3.0, and the activity of the catalysts decreases as the initial solution pH increases. At optimal conditions, 100% discoloration and mineralization of 0.2 mM Orange II are achieved in 60 and 120 min reaction in the presence of 10 mM H2O2, 1.0 g/L Fe-B, and 1 x 8 W UVC at initial solution pH of 3.0. 100% discoloration and 90% mineralization of 0.2mM Orange 11 are achieved when Fe-Lap-RD is used as catalyst under the same conditions. Both catalysts also display a reasonable good photocatalytic activity and negligible Fe leaching at an initial solution pH of 6.6 that is very close to neutral pH. This characteristic makes it possible for the Fe-B and Fe-Lap-RD to have a long-term stability. it also becomes feasible for the photo-Fenton process to treat the original wastewater without the need to pre-adjust the solution pH. (c) 2006 Elsevier Ltd. All rights reserved.