1. School of Metallurgy and Environment, Central South University, Changsha 410083, P. R. China
2. School of Chemistry and Chemical Engineering, Central South University, Changsha 410083, P. R. China
3. Chinese National Engineering Research Center for Control and Treatment of Heavy Metal Pollution, Changsha 410083, P. R. China
4. School of Physics and Electronics, Central South University, Changsha 410083, P. R. China