1. School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710119, P. R. China
2. Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Main Building, Cardiff CF10 3AT, U.K.
3. State Key Lab of Loess and Quaternary Geology (SKLLQG), Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, P. R. China
4. School Water and Environment, Key Lab Subsurface Hydrol Ecol Effects Arid Reg, Minist Educ, Chang’an University, Xi’an 710054, P. R. China