1. Dept. of Chemistry, Faculty of Mathematics and Natural Science, State Univ. of Padang, Padang, West Sumatera 25131, Indonesia; Graduate School of Environmental Science, Hokkaido Univ., N10W5, Sapporo, Hokkaido 060-0810, Japan.
2. Graduate School of Environmental Science, Hokkaido Univ., N10W5, Sapporo, Hokkaido 060-0810, Japan.
3. Dept. of Chemical Engineering, Univ. of Vigo, Vigo 36310, Spain.