1. Science and Technology Administration Department; Xi'an Polytechnic University; Xi'an 710048 China
2. State Key Laboratory of Solid Lubrication; Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences; Lanzhou 730000 China
3. Key Laboratory for Utility of Environment Friendly Composites and Biomass in Universities of Gansu Province, College of Chemical Engineering; Northwest University for Nationalities; Lanzhou 730030 China