Topics in Current Chemistry (2019) 377:22
1 3
that Kronos has good absorption properties, but the absorbed radiation is not
efficiently employed to convert the molecules of BPA. Aeroxide P 25 absorbs
less radiation, but this energy is more efficiently used to degrade the pollutant.
The comparison among these figures reveals that the challenge lies not only in
improving the light absorption of the doped catalyst, but also in developing a
material that can more efficiently use the harvested energy. It should be stressed
that the performance of a photocatalyst for the degradation of a particular compound cannot be extrapolated to substrates of a different chemical structure [117],
and that the former analysis is valid under the operating conditions of the study.
Another example that illustrates the convenience of calculating efficiency
parameters to compare reactors with different configurations is presented in
Table 6 (data extracted from [118]). A fixed-film reactor (FFR) (or wall reactor)
with TiO 2 immobilized onto the reactor window is compared with a fixed-bed
reactor (FBR) filled with TiO 2 -coated glass rings. The degradation of the model
pollutant clofibric acid in water was evaluated under artificial UV radiation. The
same experimental setup was employed in both systems.
Under the same incident radiation, the FBR renders a reaction rate value about
15% lower than the FFR. Consequently, ph is also 15% lower for the FBR. Nevertheless, the value of the photon absorption rate in the FBR is much lower (almost
50%) than the value obtained in the FFR. Therefore, the quantum efficiency of
the FBR is 1.5 times higher. This analysis indicates that the absorbed radiation is
lower in the FBR but it is more efficiently employed for the degradation reaction.
Hence, a possible strategy for increasing the reaction rate in the FBR would be
to increase the number of TiO 2 coatings over the glass rings, and thus improve
radiation absorption in this type of reactor.
7 Conclusions
This review presents a methodology for the modeling of photocatalytic reactors
for chemical pollution abatement in water and air. The photocatalytic degradation
of model pollutants in three of the most widely used reactor configurations has
been analyzed: wall reactors with the catalyst immobilized onto the reactor window, slurry reactors with suspended catalyst particles in aqueous suspension, and
fixed-bed reactors filled with catalyst-coated filling material.
The evaluation of the local absorption rate of photons inside the reactors is
fundamental for estimating the reaction rate of the electron–hole generation and
obtaining the intrinsic kinetics of the photocatalytic process. Additionally, the
analysis of the absorbed radiation is essential to understanding the phenomena
occurring in photocatalytic reactors and for making improvements in the reactors
design, the absorption properties of catalytic materials, and the operating conditions of the processes.
From the results reported, it can be concluded that the proposed methodology
has proven to be adequate to simulate the performance of photocatalytic reactors
of different types, shapes, sizes, and configurations.
296
Reprinted from the journal
1 3
that Kronos has good absorption properties, but the absorbed radiation is not
efficiently employed to convert the molecules of BPA. Aeroxide P 25 absorbs
less radiation, but this energy is more efficiently used to degrade the pollutant.
The comparison among these figures reveals that the challenge lies not only in
improving the light absorption of the doped catalyst, but also in developing a
material that can more efficiently use the harvested energy. It should be stressed
that the performance of a photocatalyst for the degradation of a particular compound cannot be extrapolated to substrates of a different chemical structure [117],
and that the former analysis is valid under the operating conditions of the study.
Another example that illustrates the convenience of calculating efficiency
parameters to compare reactors with different configurations is presented in
Table 6 (data extracted from [118]). A fixed-film reactor (FFR) (or wall reactor)
with TiO 2 immobilized onto the reactor window is compared with a fixed-bed
reactor (FBR) filled with TiO 2 -coated glass rings. The degradation of the model
pollutant clofibric acid in water was evaluated under artificial UV radiation. The
same experimental setup was employed in both systems.
Under the same incident radiation, the FBR renders a reaction rate value about
15% lower than the FFR. Consequently, ph is also 15% lower for the FBR. Nevertheless, the value of the photon absorption rate in the FBR is much lower (almost
50%) than the value obtained in the FFR. Therefore, the quantum efficiency of
the FBR is 1.5 times higher. This analysis indicates that the absorbed radiation is
lower in the FBR but it is more efficiently employed for the degradation reaction.
Hence, a possible strategy for increasing the reaction rate in the FBR would be
to increase the number of TiO 2 coatings over the glass rings, and thus improve
radiation absorption in this type of reactor.
7 Conclusions
This review presents a methodology for the modeling of photocatalytic reactors
for chemical pollution abatement in water and air. The photocatalytic degradation
of model pollutants in three of the most widely used reactor configurations has
been analyzed: wall reactors with the catalyst immobilized onto the reactor window, slurry reactors with suspended catalyst particles in aqueous suspension, and
fixed-bed reactors filled with catalyst-coated filling material.
The evaluation of the local absorption rate of photons inside the reactors is
fundamental for estimating the reaction rate of the electron–hole generation and
obtaining the intrinsic kinetics of the photocatalytic process. Additionally, the
analysis of the absorbed radiation is essential to understanding the phenomena
occurring in photocatalytic reactors and for making improvements in the reactors
design, the absorption properties of catalytic materials, and the operating conditions of the processes.
From the results reported, it can be concluded that the proposed methodology
has proven to be adequate to simulate the performance of photocatalytic reactors
of different types, shapes, sizes, and configurations.
296
Reprinted from the journal