“…In recent years, considerable effort has been devoted to fabricating various TiO 2 nanostructures and morphologies, including TiO 2 spheres [31,32], nanorods [33], nanotubes [34,35], sheets [36], nanofibers [37], and other hierarchical nanostructures [38,39]. Among them, 3D TiO 2 nanostructures has been considered to be a promising candidate in the fields of photocatalysis [40], sensor [41], lithium ion battery [42], solar cell [43], and so on, due to its high surface area, low density, high light-harvesting efficiency and good surface permeability [44]. Numerous 3D TiO 2 nanostructures have been synthesized in the past a few years.…”