1. Gansu Key Laboratory of Environmental Friendly, Composites and Biomass Utilization, College of Chemical Engineering, Northwest University for Nationalities, Lanzhou, Gansu 730030, P. R. China
2. Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, P. R. China
3. Gansu Key Laboratory of Polymer Materials, College of Chemistry and Chemical Engineering, Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Education, Northwest Normal University, Lanzhou, Gansu 730070, P. R. China