Topics in Current Chemistry (2020) 378:29
1 3
those on the commercial scale, the use of gases such as air is recommended in
contrast to argon which has been reported to be quite effective by researchers on
the laboratory scale.
7. It will be important to select optimum power dissipation for both the ultrasonic
and UV irradiations from the perspective of restricting cavitational effects to the
optimum possible extent and in terms of restricting the overall costs of the treatment.
5 Concluding Remarks
The aim of this article was to demonstrate the beneficial effects of using ultrasound
during the catalyst synthesis processes as well as the actual application of ultrasound
in the photocatalytic oxidation. The key benefits in the catalyst synthesis process
include lower particle size, higher surface area and better control over the morphology of the particles. The synthesis conditions in terms of ultrasonic power and
time of application play a key role in determining the benefits and economics of the
process. The application of ultrasound has been established to be beneficial for all
forms of photocatalysts, including bare, composite and doped photocatalysts. Ultrasound often opens alternative synthesis routes for efficiently obtaining nanocatalysts
[101] that are also active in the visible light region, making it very attractive proposition for commercial applications in wastewater treatment.
In the case of SPC treatment, it is important to note that the beneficial effects
are generally observed when free radical formation and the attack of free radicals
on the pollutants are the controlling mechanisms. The extent of intensification (less
than the additive effect or the synergistic effect) typically depends on the pollutant in question and mostly on the utilization of the generated free radicals and the
problems of catalyst poisoning in the individual operation. It should be noted that
ultrasonic power is an important factor in determining the efficiency of the process,
and the choice of power presents a trade-off between economic aspects and degradation efficiency. Optimum power dissipation will usually be recommended, using
multiple transducers, thus giving lower intensities of irradiation. Also, operation at
a lower frequency (e.g. in the range 20–100 kHz) would be more suited for ultrasound. Additional operating parameters, such as pH and temperature, also need to
be optimized as these are strongly dependent on the specific pollutant in question.
Typically, doped photocatalysts perform better under SPC conditions than do bare
catalyst. Similarly, the enhancement of charge transfer and abatement of electron
hole recombination based on modifications, such as using GO sheets or CNTs as a
support for the catalyst, has an additional synergistic effect on the SPC degradation
efficiency. The use of solar irradiation instead of UV light is preferable for the applicability and possibility of a scale-up of the process; using doping to enhance the
light adsorption spectrum to include visible light is practical for this purpose. The
addition of radical promoters, such as H 2 O 2 , can also be advantageous although the
exact effect needs to be established for specific compounds.
Overall, the application of ultrasound offers a lucrative approach for improving the catalyst synthesis process, and the actual application of ultrasound in the
100
Reprinted from the journal
1 3
those on the commercial scale, the use of gases such as air is recommended in
contrast to argon which has been reported to be quite effective by researchers on
the laboratory scale.
7. It will be important to select optimum power dissipation for both the ultrasonic
and UV irradiations from the perspective of restricting cavitational effects to the
optimum possible extent and in terms of restricting the overall costs of the treatment.
5 Concluding Remarks
The aim of this article was to demonstrate the beneficial effects of using ultrasound
during the catalyst synthesis processes as well as the actual application of ultrasound
in the photocatalytic oxidation. The key benefits in the catalyst synthesis process
include lower particle size, higher surface area and better control over the morphology of the particles. The synthesis conditions in terms of ultrasonic power and
time of application play a key role in determining the benefits and economics of the
process. The application of ultrasound has been established to be beneficial for all
forms of photocatalysts, including bare, composite and doped photocatalysts. Ultrasound often opens alternative synthesis routes for efficiently obtaining nanocatalysts
[101] that are also active in the visible light region, making it very attractive proposition for commercial applications in wastewater treatment.
In the case of SPC treatment, it is important to note that the beneficial effects
are generally observed when free radical formation and the attack of free radicals
on the pollutants are the controlling mechanisms. The extent of intensification (less
than the additive effect or the synergistic effect) typically depends on the pollutant in question and mostly on the utilization of the generated free radicals and the
problems of catalyst poisoning in the individual operation. It should be noted that
ultrasonic power is an important factor in determining the efficiency of the process,
and the choice of power presents a trade-off between economic aspects and degradation efficiency. Optimum power dissipation will usually be recommended, using
multiple transducers, thus giving lower intensities of irradiation. Also, operation at
a lower frequency (e.g. in the range 20–100 kHz) would be more suited for ultrasound. Additional operating parameters, such as pH and temperature, also need to
be optimized as these are strongly dependent on the specific pollutant in question.
Typically, doped photocatalysts perform better under SPC conditions than do bare
catalyst. Similarly, the enhancement of charge transfer and abatement of electron
hole recombination based on modifications, such as using GO sheets or CNTs as a
support for the catalyst, has an additional synergistic effect on the SPC degradation
efficiency. The use of solar irradiation instead of UV light is preferable for the applicability and possibility of a scale-up of the process; using doping to enhance the
light adsorption spectrum to include visible light is practical for this purpose. The
addition of radical promoters, such as H 2 O 2 , can also be advantageous although the
exact effect needs to be established for specific compounds.
Overall, the application of ultrasound offers a lucrative approach for improving the catalyst synthesis process, and the actual application of ultrasound in the
100
Reprinted from the journal