1. School of Chemistry and Chemical Engineering, Northwestern Polytechnical University Xi'an, Shaanxi 710072, P. R. China
2. Department of Ultrasonic Medicine, Tang Du Hospital, Air Force Medical University, No. 569 of Xin Si Road, Xi'an, Shaanxi 710038, P. R. China
3. Guangxi Key Laboratory of Chemistry and Engineering of Forest Products, Guangxi Minzu University, Nanning 530006, P. R. China