1. College of Science, Gansu Agricultural University, Lanzhou, Gansu 730070, P. R. China
2. Key Laboratory of Eco-Environmental Polymer Materials of Gansu Province, Key Laboratory of Eco-functional Polymer Materials of the Ministry of Education, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, P. R. China
3. Lanzhou Seventh Middle School, Lanzhou, Gansu 730070, P. R. China
4. Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 32827, Republic of Korea