1. Membrane and Separation Research Center, Korea Research Institute of Chemical Technology, P.O. Box 107, Yuseong, Daejeon 305-606, South Korea, and Department of Chemical and Biomolecular Engineering, National Research Laboratory for Environmental Catalysis, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, South Korea