Page 257 - Multifunctional Photocatalytic Materials for Energy

240 Multifunctional Photocatalytic Materials for Energy

(Fig. 11.1C) [45,46]. The newly synthesized dual-phase photocatalyst surface exhib-
ited an extraordinary affinity for dye adsorption, further facilitating efficient miner-
alization in UV and visible light because of sensitization with doped nitrogen. By
introducing a small amount of chloride or nitrate to the mixture of NH 4 HCO 3 , linoleic
acid (LA), trimethylamine, cyclohexane, and Ti(OBu) 4 , Li and coworkers success-
4 +
2 +
3 +
2 +
fully synthesized M-doped (M = Fe , Co , Sn , Ni ) 0D TiO 2 nanocrystallines
(Fig. 11.1D).
11.2.2 Rational synthesis of 1D TiO 2 nanostructures
One-dimensional (1D) nanostructures play an important role in the family of nano-
structured materials. Geometrically, they offer proper properties, which are difficult
to obtain with other dimensions. 1D TiO 2 nanostructures have been recognized as
the most ideal candidates for solar energy conversion because of their unique struc-
tural qualities, including good physicochemical stability, fast and long-distance charge
transport, and large surface-to-volume ratio [47]. Several advanced methods have been
reported for 1D TiO 2 nanostructured materials with remarkable morphology and size
types, for example, hydrothermal processes, chemical vapor deposition, electrochemi-
cal anodization, and electrospinning. In this section, we briefly discuss 1D TiO 2 nano-
materials with different morphologies.

11.2.2.1 TiO 2 nanotubes
Kasuga et al. [48–50] were the first to prepare TiO 2 NTAs by assembling amorphous
TiO 2 powders with an alkaline aqueous solution via a traditional hydrothermal pro-
cess. Various approaches have sprung up since then in which rutile TiO 2 powder and
NaOH were utilized. Geng's group successfully synthesized 1D TiO 2 nanotubes after
calcination at 400°C for 2 h. The as-prepared TiO 2 nanotubes were about 300 nm in
length and had a 4 and 10 nm inner and outer diameter, respectively (Fig. 11.2A),
and a random arrangement [51,58]. In order to obtain highly ordered TiO 2 nanotubes
aligned perpendicular to the surface of the electrode, the electrochemical anodization
Ti foil method was used. This method has been well established as a fast, easy, and
efficient way to prepare highly aligned TiO 2 NTAs (Fig. 11.2B) [52,59]. Based on dif-
ferent electrolytes, the TiO 2 NTAs can be categorized according to five generations (as
shown in Table 11.1). The traditional hydrothermal method still has several defects,
including long reaction times, limited applicability, and nonuniformity of the prepared
nanotubes. To improve these defects, Tang's group recently synthesized elongated
TiO 2 nanotubes with lengths up to tens of micrometers via an improved hydrothermal
method under stirring (Fig. 11.2F). 0.1 g of P25 powder was dispersed into a 15 mL
of NaOH (10 M) solution, then the mixture was transferred into a 25 mL Teflon-lined
stainless-steel autoclave under a specific rate of magnetic stirrer and a temperature of
130°C in oil bath for 24 h. Next the samples were taken out and cooled to ambient
temperature. The sodium titanate was collected by centrifugation and washed with de-
ionized water more than three times to reach pH = 9. Then the samples were subjected
+
−
+
to a H exchange process in a H solution three times to neutralize the OH . Finally,