F. A. Ofori, F. A. Sheikh, R. Appiah-Ntiamoah, X. Yang, and H. Kim, “A Simple Method of Electrospun Tungsten Trioxide Nanofibers with Enhanced Visible-Light Photocatalytic Activity”, Nano-Micro Lett, vol. 7, no. 3, pp. 291-297, Jun. 2015.