The peak intensity of (0 0 1) facets for WO 3 -001 nanosheet was obviously enhanced, which was caused by exposing the specific facets. By measuring the respective peak areas of the (1 0 0),(0 0 1) and (2 0 0) facets, the fraction of (0 0 1) facets from XRD patterns was estimated bythe following equation (Eq. 1).[27]