Topics in Current Chemistry (2020) 378:2
1 3
transformation of titanium dioxide to titanate was complete even at 120 °C. However, increase of the temperature to 180 °C led to a shift of the characteristic diffraction at around 10° 2θ to a higher angler (~ 12°), suggesting a narrow interlayer spacing between the layers of walls. Suzuki and Yoshikawa assigned the characteristic
XRD reflection peak at 2θ = ~ 10° of the hydrothermally synthesized H 2 Ti 3 O 7 .nH 2 O
NTBs to an interlayer distance of 0.92 nm [100]. An interesting parenthetical fact
can be added at this point. The high-temperature XRD pattern obtained at 100 °C
was almost identical with the one at room temperature, but at 200 °C, the reflection
was shifted to 11.2°. This narrowing of the interlayer space to 0.79 nm was linked
to the removal of the water moieties between the layers of the wall. It is worth mentioning that thermogravimetric analysis of the NTBs showed that above 200 °C, the
weight loss was very limited.
Going a step further, the team of Tanthapanichakoon [117] chose to study the
effect of temperature during the synthesis with or without US pre-treatment by using
raw particles of an ~ 400-nm diameter, due to the fact that this raw TiO 2 gave higher
S BET compared to the raw one with average particle size of 1 μm. The resulted specific surface areas and the morphology of the sample are presented in Fig. 17.
As can be observed, the effect of US pretreatment on the structural and morphological features is loud and clear, and, additionally, it had a key effect on the
product purity and shape homogeneity, as confirmed by microscopy analysis. At
90 °C, NTBs, nanosheets, and remaining un-transformed crystals were detected
either without or with US pretreatment (Fig. 18). Moreover, the use of sonication
did not lead to higher S BET . The effect of US was dramatically more pronounced at
a synthesis temperature of 120 °C. The length of the NTBs was much higher and
the S BET almost doubled in value. The purity was also enhanced, since no un-transformed crystals were detected after US pre-treatment. Analogous outcomes were
derived when the synthesis was performed at 150 °C after US pre-treatment. Further
increase to 180 °C had a negative impact on the S BET and the desired morphology,
with the US irradiation not leading to a specific effect. The predominant shape of the
particles was of nanowires/fibers/rods in both cases, although with a smaller diameter in the case of US irradiation. The shape change was in good agreement with the
angle shift of the XRD pattern, as was discussed above. It can be suggested that the
thermal effects when the synthesis temperature is higher than 150 °C overcome the
effects of the US pre-treatment.
3 PART B
3.1 Ball‑Milling‑Derived Nanomaterials
The utilization of ball milling (BM) in order to obtain TiO 2 nanoparticles includes different possible pathways with regard to the used raw material. The latter can be either
elemental Ti, either TiO 2, or a different source of titanium like a mineral. The duration and the power of the BM plays a crucial role, as does the atmosphere in which
the process takes place. The achievement of high temperature is found to be in some
54
Reprinted from the journal
1 3
transformation of titanium dioxide to titanate was complete even at 120 °C. However, increase of the temperature to 180 °C led to a shift of the characteristic diffraction at around 10° 2θ to a higher angler (~ 12°), suggesting a narrow interlayer spacing between the layers of walls. Suzuki and Yoshikawa assigned the characteristic
XRD reflection peak at 2θ = ~ 10° of the hydrothermally synthesized H 2 Ti 3 O 7 .nH 2 O
NTBs to an interlayer distance of 0.92 nm [100]. An interesting parenthetical fact
can be added at this point. The high-temperature XRD pattern obtained at 100 °C
was almost identical with the one at room temperature, but at 200 °C, the reflection
was shifted to 11.2°. This narrowing of the interlayer space to 0.79 nm was linked
to the removal of the water moieties between the layers of the wall. It is worth mentioning that thermogravimetric analysis of the NTBs showed that above 200 °C, the
weight loss was very limited.
Going a step further, the team of Tanthapanichakoon [117] chose to study the
effect of temperature during the synthesis with or without US pre-treatment by using
raw particles of an ~ 400-nm diameter, due to the fact that this raw TiO 2 gave higher
S BET compared to the raw one with average particle size of 1 μm. The resulted specific surface areas and the morphology of the sample are presented in Fig. 17.
As can be observed, the effect of US pretreatment on the structural and morphological features is loud and clear, and, additionally, it had a key effect on the
product purity and shape homogeneity, as confirmed by microscopy analysis. At
90 °C, NTBs, nanosheets, and remaining un-transformed crystals were detected
either without or with US pretreatment (Fig. 18). Moreover, the use of sonication
did not lead to higher S BET . The effect of US was dramatically more pronounced at
a synthesis temperature of 120 °C. The length of the NTBs was much higher and
the S BET almost doubled in value. The purity was also enhanced, since no un-transformed crystals were detected after US pre-treatment. Analogous outcomes were
derived when the synthesis was performed at 150 °C after US pre-treatment. Further
increase to 180 °C had a negative impact on the S BET and the desired morphology,
with the US irradiation not leading to a specific effect. The predominant shape of the
particles was of nanowires/fibers/rods in both cases, although with a smaller diameter in the case of US irradiation. The shape change was in good agreement with the
angle shift of the XRD pattern, as was discussed above. It can be suggested that the
thermal effects when the synthesis temperature is higher than 150 °C overcome the
effects of the US pre-treatment.
3 PART B
3.1 Ball‑Milling‑Derived Nanomaterials
The utilization of ball milling (BM) in order to obtain TiO 2 nanoparticles includes different possible pathways with regard to the used raw material. The latter can be either
elemental Ti, either TiO 2, or a different source of titanium like a mineral. The duration and the power of the BM plays a crucial role, as does the atmosphere in which
the process takes place. The achievement of high temperature is found to be in some
54
Reprinted from the journal