**2. Preparation of blue titanium oxide (TiO2) nanosheets**

The blue TiO2 nanosheets was prepared using simple hydrothermal assisted topochemical process as reported in the literature [31, 32]. Initially an appropriate amount of titanium boride was dissolved in 25 mL of hydrofluoric acid and transferred to Teflon lined autoclave for hydrothermal process at 180°C for 12 h. Upon completion of the hydrothermal process, the blue color precipitate is washed with double distilled water/ethanol and dried at 80°C for 12 h to obtain the blue TiO2 nanosheets.
