1 3
Topics in Current Chemistry (2020) 378:2
However, the most crucial driving force is believed to be the generation and
relaxation of mechanical stress that have a direct effect on the crystalline lattices
[3]. The theory of “hot spots” formation during ball milling is a widely accepted one
[7]. Hot spots can be created by the cracking of crystals, resulting in local temperature (up to 5000 K) and pressure, electric fields up to 108 V/m, crack propagation
with velocity close to that of sound (105 cm/s), and lifetimes for bond excitation
around 100 fs [3, 43, 44]. These effects are analogues of those of US irradiation in
a liquid, even though the formation of a hot spot results from the cavitation phenomena. And it is important that the high amount of added energy is localized
microscopically, even nanoscopically, without affecting the macroscopic system to
a great extent. This localized high amount of energy can lead to a diversity of consequences, such as lattice deformation, cleavage of bonds, or formation of radicals.
And these phenomena cannot be achieved by other synthetic approaches in solution.
Figure 2 presents the most important fields of mechanochemistry applications based
on the report by Elena Boldyreva [43]. More mechanistic aspects and fields of application of mechanochemistry can also be found elsewhere [3, 7, 35, 44]. Even though
Boldyreva did not consider US irradiation in her work, the latter can be utilized for
the same fields and applications when a liquid phase is required. The rapid growth
of the research interest around the application of mechanochemistry is due recent
discovery of unique effects. By the correct utilization of these effects, it is feasible
to obtain the desired nanostructured materials and enhance their crucial features by
simultaneously eliminating the environmental footprint of the synthesis and avoiding the usage of high energy and hazardous and non-recyclable chemicals.
1.5 TiO 2 : The Benchmark Semiconductor Photocatalyst
Titanium dioxide (TiO 2 ) can be regarded as one of the most popular semiconductor photocatalysts, for a wide range of applications; organic pollutant degradation,
hydrogen production, solar cells, photocatalysis, etc. It combines high photo-activity
for various reactions, high stability, low cost, and low toxicity for humans, animals,
and the environment. Use of titanium dioxide started intensively in 1972, when
Fujishima and Honda revealed photocatalytic water splitting by titania electrodes
[45]. Since then, numerous articles have focused on the use of TiO 2 and its composites for green-oriented heterogeneous catalysis, like valorization of biomass and
upgrading of obtained chemicals [1, 46, 47].
Another important property of titanium dioxide is its superhydrophilicity that is
crucial for solar fuel production and environmental remediation applications [48].
However, one crucial drawback arises due to the fact that TiO 2 has a wide bandgap
Fig. 2 Applications of mechanochemistry
35
Reprinted from the journal
Topics in Current Chemistry (2020) 378:2
However, the most crucial driving force is believed to be the generation and
relaxation of mechanical stress that have a direct effect on the crystalline lattices
[3]. The theory of “hot spots” formation during ball milling is a widely accepted one
[7]. Hot spots can be created by the cracking of crystals, resulting in local temperature (up to 5000 K) and pressure, electric fields up to 108 V/m, crack propagation
with velocity close to that of sound (105 cm/s), and lifetimes for bond excitation
around 100 fs [3, 43, 44]. These effects are analogues of those of US irradiation in
a liquid, even though the formation of a hot spot results from the cavitation phenomena. And it is important that the high amount of added energy is localized
microscopically, even nanoscopically, without affecting the macroscopic system to
a great extent. This localized high amount of energy can lead to a diversity of consequences, such as lattice deformation, cleavage of bonds, or formation of radicals.
And these phenomena cannot be achieved by other synthetic approaches in solution.
Figure 2 presents the most important fields of mechanochemistry applications based
on the report by Elena Boldyreva [43]. More mechanistic aspects and fields of application of mechanochemistry can also be found elsewhere [3, 7, 35, 44]. Even though
Boldyreva did not consider US irradiation in her work, the latter can be utilized for
the same fields and applications when a liquid phase is required. The rapid growth
of the research interest around the application of mechanochemistry is due recent
discovery of unique effects. By the correct utilization of these effects, it is feasible
to obtain the desired nanostructured materials and enhance their crucial features by
simultaneously eliminating the environmental footprint of the synthesis and avoiding the usage of high energy and hazardous and non-recyclable chemicals.
1.5 TiO 2 : The Benchmark Semiconductor Photocatalyst
Titanium dioxide (TiO 2 ) can be regarded as one of the most popular semiconductor photocatalysts, for a wide range of applications; organic pollutant degradation,
hydrogen production, solar cells, photocatalysis, etc. It combines high photo-activity
for various reactions, high stability, low cost, and low toxicity for humans, animals,
and the environment. Use of titanium dioxide started intensively in 1972, when
Fujishima and Honda revealed photocatalytic water splitting by titania electrodes
[45]. Since then, numerous articles have focused on the use of TiO 2 and its composites for green-oriented heterogeneous catalysis, like valorization of biomass and
upgrading of obtained chemicals [1, 46, 47].
Another important property of titanium dioxide is its superhydrophilicity that is
crucial for solar fuel production and environmental remediation applications [48].
However, one crucial drawback arises due to the fact that TiO 2 has a wide bandgap
Fig. 2 Applications of mechanochemistry
35
Reprinted from the journal