1. Key Laboratory of Applied Surface and Colloid Chemistry (Shaanxi Normal University), Ministry of Education, School of Materials Science and EngineeringShaanxi Normal University Xi'an 710062 P. R. China
2. Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and EngineeringShaanxi Normal University Xi' an 710119 China
3. School of PhysicsNorthwest University Xi'an 710069 China
4. School of Materials Science and EngineeringNanyang Technological University 639798 Singapore