1. Key Lab of Bioelectrochemistry and Environmental Analysis of Gansu; College of Chemistry and Chemical Engineering; Northwest Normal University; Lanzhou 730070 P. R. China
2. Department of Chemistry & Biochemistry; San Diego State University; San Diego CA 92182 USA
3. Department of Chemistry and Environmental Science; New Jersey Institute of Technology; New Jersey 07102 USA
4. School of Physical Science and Technology; Lanzhou University; Lanzhou, Gansu 730000 P. R. China