Topics in Current Chemistry (2019) 377:22
1 3
of Eq. (11) results from the assumption of low contaminant concentration or, alternatively, of linear adsorption at the catalyst surface.
2.2 Photocatalytic Kinetics in Gas Phase
The most frequently reported kinetic expressions for photocatalytic reactions in gas
phase, summarized in Table 3, consider hydroxyl radical attack as the main mechanism for the degradation of pollutants. Hypotheses similar to those for the liquid
phase are assumed, with two exceptions: (i) water vapor is a variable of the reacting system, and (ii) adsorption competition among water and other species for the
actives sites of the catalyst must be considered.
3 Wall Reactors
In this configuration, the photocatalyst is immobilized on the reactor walls, represented by flat or curved extended surfaces of an inert support in contact with the
contaminated phase to be treated. This type of photoreactor is frequently employed
for kinetic studies in gas and liquid phases [4, 27, 28].
3.1 Evaluation of Photon Absorption
A medium is considered as participating in radiative transfer if it absorbs, emits,
or scatters a ray as it travels through the medium. In this case, the radiative transfer
equation (RTE) governs the distribution of the radiation intensity. In photocatalytic
Table 2 Common photocatalytic kinetic expressions in liquid-phase photocatalytic reactions involving
direct hole attack
Case
Photocatalytic reaction rate
Equations
References
Complete expression
r X =
1 C X
1+K X C X
⎛
⎜
⎜
⎝
1 −
�
1 +
2 ∫
e
a,s
d(1+K X C X )
C X
⎞
⎟
⎟
⎠
(10)
[12–14]
Linear adsorption isotherms/
low contaminant concentration
r X = 1 C X
⎛
⎜
⎜
⎝
1 −
�
1 +
2 ∫
e
a,s
d
C X
⎞
⎟
⎟
⎠
(11)
[12–14]
With 2 =
2
1
or
= 1:
[15–17]
Linear adsorption isotherms/
low contaminant concentration and high irradiation
level
r X = −
√
∫
e
a,s
dC X
(12)
[14]
Linear adsorption isotherms/
low contaminant concentration and low irradiation level
r X = − ∫
e
a,s
d
(13)
[14]
For intermediate
generation rate:
[18]
270
Reprinted from the journal
1 3
of Eq. (11) results from the assumption of low contaminant concentration or, alternatively, of linear adsorption at the catalyst surface.
2.2 Photocatalytic Kinetics in Gas Phase
The most frequently reported kinetic expressions for photocatalytic reactions in gas
phase, summarized in Table 3, consider hydroxyl radical attack as the main mechanism for the degradation of pollutants. Hypotheses similar to those for the liquid
phase are assumed, with two exceptions: (i) water vapor is a variable of the reacting system, and (ii) adsorption competition among water and other species for the
actives sites of the catalyst must be considered.
3 Wall Reactors
In this configuration, the photocatalyst is immobilized on the reactor walls, represented by flat or curved extended surfaces of an inert support in contact with the
contaminated phase to be treated. This type of photoreactor is frequently employed
for kinetic studies in gas and liquid phases [4, 27, 28].
3.1 Evaluation of Photon Absorption
A medium is considered as participating in radiative transfer if it absorbs, emits,
or scatters a ray as it travels through the medium. In this case, the radiative transfer
equation (RTE) governs the distribution of the radiation intensity. In photocatalytic
Table 2 Common photocatalytic kinetic expressions in liquid-phase photocatalytic reactions involving
direct hole attack
Case
Photocatalytic reaction rate
Equations
References
Complete expression
r X =
1 C X
1+K X C X
⎛
⎜
⎜
⎝
1 −
�
1 +
2 ∫
e
a,s
d(1+K X C X )
C X
⎞
⎟
⎟
⎠
(10)
[12–14]
Linear adsorption isotherms/
low contaminant concentration
r X = 1 C X
⎛
⎜
⎜
⎝
1 −
�
1 +
2 ∫
e
a,s
d
C X
⎞
⎟
⎟
⎠
(11)
[12–14]
With 2 =
2
1
or
= 1:
[15–17]
Linear adsorption isotherms/
low contaminant concentration and high irradiation
level
r X = −
√
∫
e
a,s
dC X
(12)
[14]
Linear adsorption isotherms/
low contaminant concentration and low irradiation level
r X = − ∫
e
a,s
d
(13)
[14]
For intermediate
generation rate:
[18]
270
Reprinted from the journal