Page 258 - Multifunctional Photocatalytic Materials for Energy

Multidimensional TiO 2 nanostructured catalysts for sustainable H 2 generation 241

Fig. 11.2 TEM image of TiO 2 nanotubes in Geng's work (A) [51]. Bottom image of TiO 2
NTAs substrate posttreated by calcination at 450°C in air for 3 h (B) [52]. SEM images of
first generation [53] in the HF electrolyte (C), third generation [54] in ethylene glycol/fluoride
electrolytes (D), and fifth generation [55] with two-step anodization in ethylene glycol/
fluoride electrolytes (E). SEM image of titanate nanotubes obtained at 500 rpm (F) by Tang's
group [56,57].

Table 11.1 Brief summary of various preparations of TiO 2 nanotubes

TiO 2 NTAs Electrolyte Morphology Refs.
First-generation 0.5 wt.% HF Short nanotube length: 200– [53]
(HF electrolyte) 500 nm; diameter: 10–100 nm;
and wall thickness: 13–27 nm
(Fig. 11.3C)
Second-generation 1 M Na 2 SO 4 / Rough wall with wing length: [64]
electrolytes (NH 4 ) 2 SO 4 + 0.5–2.4 μm; diameter: 100 nm; and
containing F − 0.5 wt.% NH 4 F wall thickness: 12 nm
Third-generation 0.5 wt.% Smooth and ultra-long tube length: [54]
organic electrolytes NH 4 F + 2 vol.% 5–1000 μm; diameter: 100 nm; and
containing F − H 2 O in ethylene wall thickness: 12 nm (Fig. 11.3D)
glycol
Fourth-generation 0.01–3 M HClO 4 Disordered tube length: 30 μm; [65]
fluoride-free diameter: 20–40 nm; and wall
electrolytes thickness: 10 nm (Fig. 11.3E)
Fifth-generation 0.5 wt.% Smooth and hexagonal tube length: [55,66]
multiple-step NH 4 F + 2 vol.% 2–10 μm; diameter: 100 nm;
anodization in H 2 O in ethylene and wall thickness: 15–20 nm
organic electrolytes glycol (Fig. 11.3F)
containing F −