Fig. 2a shows that the TiO2 nanobelts have the width of 50-200 nm, the thickness of 20-40 nm, and the length of tens of micrometers [6]. After the acid etching process, the surface-coarsened TiO2 nanobelts are obtained (Fig. 2b), which have a large specific surface area and can offer abundant nucleation sites for the assembling of