In order to further confirm the crystalline quality and the formation of the chemical bonds in the TNFs and TNFG, The Raman spectrum was recorded in the range of 200–2500 cm1. Fig. 1B shows the Raman spectrum of GO, TNFs and TNFG-2. Only for the TNFs, the four peaks observed in the low frequency region were assigned to the E1g (148.5 cm1), B1g (400 cm1), A1g (517 cm1) and Eg (638 cm1) modes of the anatase phase respectively [45,46].