基金This work was supported by the National Natural Science Foundation of China （Grant No. 20877104） the Key Research Project of Guangdong Province （No. 2009B030802006）+1 种基金 and the National Science and Technology Key Project for Water Protection, China （Grant No. 2009ZX07211-002-3） The authors are indebted to Kaylin Huang from USA and Roy Luo from MTC Industries, Inc., Edgewood, NY, USA for helpful comments in the preparation of this manuscript.
