1 3
Topics in Current Chemistry (2020) 378:2
of the electrostatic forces/equilibria. Even though the above US-assisted hydrothermal approach successfully led to the preparation of NTBs significantly faster and
easily compared to the hydrothermal synthesis, there is a drawback. The synthesis
of the precursor starting with titanium butoxide hydrolysis is time-consuming and
complex.
In 2005, Joo et al. [115] reported the synthesis of TiO 2 nanorods of a diameter and length of 3.4 and 38 nm, respectively, by a nonhydrolytic ester elimination reaction between titanium(IV) isopropoxide (TTIP) and oleic acid [OA,
CH 3 (CH 2 ) 7 CH=CH(CH 2 ) 7 COOH]. The latter monosaturated fatty acid is among the
most common fatty acids in nature, produced both from vegetables and animals, and
in this work, it was utilized as surfactant and shape stabilizer during the synthesis.
Even though the authors concluded that the obtained crystallographic phase was of
anatase, they did not report the region of the XRD for angles lower than 20°. In
the following preparation method, TTIP was added to OA, and the suspension was
heated gradually until 270 °C within 20 min and was kept at this temperature for 2 h.
The initial clear solution of a yellow shade turned progressively to white. The yield
was around 70% wt, and the white powder consisted of nanorods and quasi-spherical
nanoparticles ~ 3-nm diameter (Fig. 14a, b). Interestingly, the authors were able to
separate the nanorods by conducting a size-selective precipitation from a hexane/
ethanol solution (Fig. 14c). They also showed that the nanorods’ diameter could be
controlled by adding different amounts of 1-hexadexylamine. Sonication for 30 min
(experimental conditions not specified) was applied for the removal of the surfactant
after the treatment of the powder with superhydride solution (lithium triethylborohydride in THF), but the effect of US was not explored. The finally obtained
nanorods presented a specific surface area of 198 m
2
/g and they were highly dispersible in water, a fact of a paramount importance for real-life applications. The
estimated bandgap of the nanorods was 3.33 eV, a value higher than that of 3.2 eV
of the bulk anatase, due to quantum size effect. Compared to commercial TiO 2 P25,
the obtained nanorods were found to possess a higher photocatalytic inactivation
Fig. 13 i: XRD patterns of titania particle precursors (a), titania whiskers (b), H 2 Ti 8 O 17 whiskers (c), and
nanotubes (d); TEM images of titanate (ii) and TiO 2 whiskers (iii), titania nanotubes (iv), and sample
obtained by thermal treatment (4 h, 110 °C) of the sonicated products followed by washing with water
for 5 min (v). Adapted with permission from [115]. Copyright (2005) American Chemical Society
49
Reprinted from the journal
Topics in Current Chemistry (2020) 378:2
of the electrostatic forces/equilibria. Even though the above US-assisted hydrothermal approach successfully led to the preparation of NTBs significantly faster and
easily compared to the hydrothermal synthesis, there is a drawback. The synthesis
of the precursor starting with titanium butoxide hydrolysis is time-consuming and
complex.
In 2005, Joo et al. [115] reported the synthesis of TiO 2 nanorods of a diameter and length of 3.4 and 38 nm, respectively, by a nonhydrolytic ester elimination reaction between titanium(IV) isopropoxide (TTIP) and oleic acid [OA,
CH 3 (CH 2 ) 7 CH=CH(CH 2 ) 7 COOH]. The latter monosaturated fatty acid is among the
most common fatty acids in nature, produced both from vegetables and animals, and
in this work, it was utilized as surfactant and shape stabilizer during the synthesis.
Even though the authors concluded that the obtained crystallographic phase was of
anatase, they did not report the region of the XRD for angles lower than 20°. In
the following preparation method, TTIP was added to OA, and the suspension was
heated gradually until 270 °C within 20 min and was kept at this temperature for 2 h.
The initial clear solution of a yellow shade turned progressively to white. The yield
was around 70% wt, and the white powder consisted of nanorods and quasi-spherical
nanoparticles ~ 3-nm diameter (Fig. 14a, b). Interestingly, the authors were able to
separate the nanorods by conducting a size-selective precipitation from a hexane/
ethanol solution (Fig. 14c). They also showed that the nanorods’ diameter could be
controlled by adding different amounts of 1-hexadexylamine. Sonication for 30 min
(experimental conditions not specified) was applied for the removal of the surfactant
after the treatment of the powder with superhydride solution (lithium triethylborohydride in THF), but the effect of US was not explored. The finally obtained
nanorods presented a specific surface area of 198 m
2
/g and they were highly dispersible in water, a fact of a paramount importance for real-life applications. The
estimated bandgap of the nanorods was 3.33 eV, a value higher than that of 3.2 eV
of the bulk anatase, due to quantum size effect. Compared to commercial TiO 2 P25,
the obtained nanorods were found to possess a higher photocatalytic inactivation
Fig. 13 i: XRD patterns of titania particle precursors (a), titania whiskers (b), H 2 Ti 8 O 17 whiskers (c), and
nanotubes (d); TEM images of titanate (ii) and TiO 2 whiskers (iii), titania nanotubes (iv), and sample
obtained by thermal treatment (4 h, 110 °C) of the sonicated products followed by washing with water
for 5 min (v). Adapted with permission from [115]. Copyright (2005) American Chemical Society
49
Reprinted from the journal