1 3
Topics in Current Chemistry (2020) 378:2
the initial TiO 2 P25 and the TiNTBs produced by combining high-energy sonication
and hydrothermal treatment can be seen in Fig. 15.
The crystallinity and the chemical composition of the nanorods were investigated by XRD and energy-dispersive spectroscopy (EDS) analysis. It was concluded
that the chemical composition was H 2 Ti 4 O 9 .H 2 O (JCPDS 36-0655), while traces of
rutile fractions were also observed. Considering that the TiO 2 P25 consisted of 70%
anatase phase and around 30% rutile phase, the transformation of the latter phase is
preferable, while the former type is more stable under the hydrothermal treatment
conditions. The EDS elemental analysis showed the absolute absence of Na.
The authors also studied the effect of the higher sonication power (380 W) without the hydrothermal and acid treatment. 15 min of US irradiation did not reveal the
ability to alter the shape of the spherical particles. Increase of the irradiation time to
30 min led to swelled nanoparticles with an average diameter of 100 nm, probably as
a result of the spherical particles merging. By increasing the duration of irradiation
to 60 min, the observed morphology was found to be nanorods like, with lengths in
between 100 and 300 nm. By hydrothermal and acidic treatment after the 60 min
of US irradiation, the length of the nanorod-like particles increased up to 600 nm.
Additionally, the diameter of the tubes was also smaller, but the shape homogeneity was not so perfect. Based on these observations, it can be proposed that the US
effects can originate the reaction of the TiO 2 nanoparticles with the base, by promoting the cleavage of the Ti–O–Ti lattice bond and the intercalation of Na
+
at the
lattice. The spherical forms are swollen and transformed to nanorods by increasing
their length. Calcination at 300 and 450 °C of the sample obtained after the twostep process was not accompanied with notable shape alterations (Fig. 15c, d). On
the contrary, calcination at 600 °C led to morphology transformation of the hollow
tubular structures to rod-like structured nanoparticles (Fig. 15e).
Interesting outcomes regarding the vital role of the precursor’s particle size
were derived by using two other commercial TiO 2 powders instead of P25. When
the size of the initial particles was around 10 nm (Hombikat UV100, Fig. 16a),
the formed NTBs had inner and outer diameters and lengths of 3–6, 7–10, and
up to 400 nm, respectively (Fig. 16b). When particles of a bigger average size
of 200 nm (BCC100, Fig. 16c) were used as precursor, instead of tubular-shaped
particles, sheet-like structures with rolled edges were obtained together with
untransformed particles that were slightly changed in size and shape (Fig. 16d).
This was linked to the fact that the formed sheet-like structures cannot transform/
roll to tubes, perhaps due to a hindrance effect by the larger particles.
Tanthapanichakoon and his colleagues showed and analyzed how the ultrasonication pretreatment can influence controllably the length of the titania NTBs [117,
118]. Interestingly, they used a commercial precursor (KISHIDA) of a low specific
surface area (8 m
2
/g) and relatively large particles (400 nm) compared to the previous reports. By using a titanium horn (probably low-frequency, not specified in the
article), the suspension of TiO 2 in a 10 M NaOH aqueous solution was sonicated
prior the hydrothermal treatment for 8 min with different supplied powers, from 0
to 38.1 W. After thermal treatment for 3 days at 150 °C, the obtained suspension
was treated/washed with HCl and H 2 O. TEM analysis revealed that no US irradiation led to TiNTBs (herein referred to as short) with multilayered walls (2–6 layers
51
Reprinted from the journal
Topics in Current Chemistry (2020) 378:2
the initial TiO 2 P25 and the TiNTBs produced by combining high-energy sonication
and hydrothermal treatment can be seen in Fig. 15.
The crystallinity and the chemical composition of the nanorods were investigated by XRD and energy-dispersive spectroscopy (EDS) analysis. It was concluded
that the chemical composition was H 2 Ti 4 O 9 .H 2 O (JCPDS 36-0655), while traces of
rutile fractions were also observed. Considering that the TiO 2 P25 consisted of 70%
anatase phase and around 30% rutile phase, the transformation of the latter phase is
preferable, while the former type is more stable under the hydrothermal treatment
conditions. The EDS elemental analysis showed the absolute absence of Na.
The authors also studied the effect of the higher sonication power (380 W) without the hydrothermal and acid treatment. 15 min of US irradiation did not reveal the
ability to alter the shape of the spherical particles. Increase of the irradiation time to
30 min led to swelled nanoparticles with an average diameter of 100 nm, probably as
a result of the spherical particles merging. By increasing the duration of irradiation
to 60 min, the observed morphology was found to be nanorods like, with lengths in
between 100 and 300 nm. By hydrothermal and acidic treatment after the 60 min
of US irradiation, the length of the nanorod-like particles increased up to 600 nm.
Additionally, the diameter of the tubes was also smaller, but the shape homogeneity was not so perfect. Based on these observations, it can be proposed that the US
effects can originate the reaction of the TiO 2 nanoparticles with the base, by promoting the cleavage of the Ti–O–Ti lattice bond and the intercalation of Na
+
at the
lattice. The spherical forms are swollen and transformed to nanorods by increasing
their length. Calcination at 300 and 450 °C of the sample obtained after the twostep process was not accompanied with notable shape alterations (Fig. 15c, d). On
the contrary, calcination at 600 °C led to morphology transformation of the hollow
tubular structures to rod-like structured nanoparticles (Fig. 15e).
Interesting outcomes regarding the vital role of the precursor’s particle size
were derived by using two other commercial TiO 2 powders instead of P25. When
the size of the initial particles was around 10 nm (Hombikat UV100, Fig. 16a),
the formed NTBs had inner and outer diameters and lengths of 3–6, 7–10, and
up to 400 nm, respectively (Fig. 16b). When particles of a bigger average size
of 200 nm (BCC100, Fig. 16c) were used as precursor, instead of tubular-shaped
particles, sheet-like structures with rolled edges were obtained together with
untransformed particles that were slightly changed in size and shape (Fig. 16d).
This was linked to the fact that the formed sheet-like structures cannot transform/
roll to tubes, perhaps due to a hindrance effect by the larger particles.
Tanthapanichakoon and his colleagues showed and analyzed how the ultrasonication pretreatment can influence controllably the length of the titania NTBs [117,
118]. Interestingly, they used a commercial precursor (KISHIDA) of a low specific
surface area (8 m
2
/g) and relatively large particles (400 nm) compared to the previous reports. By using a titanium horn (probably low-frequency, not specified in the
article), the suspension of TiO 2 in a 10 M NaOH aqueous solution was sonicated
prior the hydrothermal treatment for 8 min with different supplied powers, from 0
to 38.1 W. After thermal treatment for 3 days at 150 °C, the obtained suspension
was treated/washed with HCl and H 2 O. TEM analysis revealed that no US irradiation led to TiNTBs (herein referred to as short) with multilayered walls (2–6 layers
51
Reprinted from the journal