1. Key Laboratory of Eco-Environment-Related Polymer Materials of Ministry of Education, Key Laboratory of Polymer Materials of Gansu Province, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, P. R. China
2. College of Petrochemical Engineering, Longdong University, Qingyang 745000, P. R. China
3. College of Chemistry and Chemical Engineering, Key Laboratory of Hexi Corridor Resources Utilization of Gansu Universities, Hexi University, Zhangye 734000, P. R. China