1. School of Chemistry and Environment, Yunnan Minzu University, Kunming 650504, Yunnan, P. R. China
2. Faculty of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming 650500, P. R. China
3. Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650039, Yunnan, P. R. China