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Topics in Current Chemistry (2019) 377:22
6 Photocatalytic Efficiency
6.1 Definitions
Reporting photocatalytic conversion or reaction rate data without a reference on energetic efficiency does not allow for objective comparison among different experiments.
Efficiency parameters are essential for determining reactor performance and comparing
different operating conditions or reactor configurations [62]. In this sense, the global
efficiency parameter T can be defined, for electrical-energy-driven systems, as the ratio
of the number of pollutant molecules decomposed to the electrical power (P) required
to operate the radiation source:
One interesting approach considers T as the product of individual efficiencies, each
amenable to quantitative measurement, analysis, and optimization [106, 107]:
where ele , the electrical efficiency, refers to the capacity of the radiation source to
transform electrical energy into radiant energy (photons); inc , the incidence efficiency, is the ratio between the photons that arrive at the reactor window to the photons supplied by the radiation source; abs , the radiation absorption efficiency, is
defined as the ratio of the number of absorbed photons to the total number of incident photons. This parameter strongly depends on the optical properties of the catalyst. Finally, rxn is the reaction efficiency, also called quantum efficiency. It relates
the moles of pollutant degraded per mol of photons absorbed by the catalyst. For
solar-energy-driven systems, the global efficiency reduces to:
It is important to note that both inc and abs are parameters related to the characteristics of the reactor and photocatalyst, and depend neither on the reaction taking place nor on the chosen operating conditions. On the contrary, the value of rxn
depends on both the specific reaction taking place and the photocatalyst used, and it
is strongly affected by the reactor operating conditions [108].
One of the most frequently reported parameters in the scientific literature is the
photonic efficiency ph , which relates the moles of reactant molecules degraded per
mol of incident photons. ph can be expressed in terms of the previously defined efficiencies as [108, 109]:
The electrical energy per order (EE/O) is another parameter used to evaluate the
efficiency of water or air treatment processes, and is especially useful for comparing
the costs of different systems for industrial applications. The EE/O is the electrical
energy in kilowatt-hours required to degrade a contaminant by one order of magnitude in a unit volume of contaminated water or air [110].
(52)
T =
observed reaction rate
P
.
(53)
T = ele inc abs rxn ,
(54)
T = inc abs rxn .
(55)
ph = abs rxn
293
Reprinted from the journal
Topics in Current Chemistry (2019) 377:22
6 Photocatalytic Efficiency
6.1 Definitions
Reporting photocatalytic conversion or reaction rate data without a reference on energetic efficiency does not allow for objective comparison among different experiments.
Efficiency parameters are essential for determining reactor performance and comparing
different operating conditions or reactor configurations [62]. In this sense, the global
efficiency parameter T can be defined, for electrical-energy-driven systems, as the ratio
of the number of pollutant molecules decomposed to the electrical power (P) required
to operate the radiation source:
One interesting approach considers T as the product of individual efficiencies, each
amenable to quantitative measurement, analysis, and optimization [106, 107]:
where ele , the electrical efficiency, refers to the capacity of the radiation source to
transform electrical energy into radiant energy (photons); inc , the incidence efficiency, is the ratio between the photons that arrive at the reactor window to the photons supplied by the radiation source; abs , the radiation absorption efficiency, is
defined as the ratio of the number of absorbed photons to the total number of incident photons. This parameter strongly depends on the optical properties of the catalyst. Finally, rxn is the reaction efficiency, also called quantum efficiency. It relates
the moles of pollutant degraded per mol of photons absorbed by the catalyst. For
solar-energy-driven systems, the global efficiency reduces to:
It is important to note that both inc and abs are parameters related to the characteristics of the reactor and photocatalyst, and depend neither on the reaction taking place nor on the chosen operating conditions. On the contrary, the value of rxn
depends on both the specific reaction taking place and the photocatalyst used, and it
is strongly affected by the reactor operating conditions [108].
One of the most frequently reported parameters in the scientific literature is the
photonic efficiency ph , which relates the moles of reactant molecules degraded per
mol of incident photons. ph can be expressed in terms of the previously defined efficiencies as [108, 109]:
The electrical energy per order (EE/O) is another parameter used to evaluate the
efficiency of water or air treatment processes, and is especially useful for comparing
the costs of different systems for industrial applications. The EE/O is the electrical
energy in kilowatt-hours required to degrade a contaminant by one order of magnitude in a unit volume of contaminated water or air [110].
(52)
T =
observed reaction rate
P
.
(53)
T = ele inc abs rxn ,
(54)
T = inc abs rxn .
(55)
ph = abs rxn
293
Reprinted from the journal