1. Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito exterior s/n, Cd. Universitaria, Del. Coyoacán C.P. 04510, Ciudad de México, Mexico
2. National Energy Technology Laboratory, United States Department of Energy, 626 Cochrans Mill Road, Pittsburgh, PA 15236, USA
3. College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, P. R. China