developed to check the charge kinetics behavior at the photocatalysis process.
Explicitly, the photogenerated charge carriers are examined by characterizing the
band structure and light absorption. Based on charge separation and migration, the
characterization techniques are mostly concentrated on charge dynamics (photoexcited charge carrier separation and lifetime efficiency). Moreover, several advanced
techniques have been widely designed to check surface reactions, such as the
molecular desorption/adsorption, reaction paths, reactant dissociation, and intermediate product.
1.4.1 Charge Carrier Transfer Kinetics
Besides charge transfer kinetics, the charge separation, migration, and recombination processes normally occur in an ultra-small timescale. The transient absorption
spectroscopy, which measures the signals for charges at the ground/excited state, and
the recombination rate of photogenerated charge carriers, has been broadly utilized
in a photocatalytic mechanism study (Berera et al. 2009). However, transient
absorption spectroscopy cannot fully reflect the photocatalytic process under simulated solar light irradiation owing to the robust pulsed laser used as excitation
sources (Berera et al. 2009). Therefore, photoelectrochemical measurements have
been used to check the charge kinetics behavior and average dynamic parameters of
a photocatalytic system (Sato 1998). Moreover, the recombination of
photogenerated carriers is measured by the time-resolved/steady-state
photoluminescence spectroscopy (Anpo and Kamat 2010). Generally, the low intensity in the steady-state photoluminescence spectroscopy shows a low chance of
recombination rate of charge carrier. For time-resolved photoluminescence spectroscopy, a rapid photoluminescence degeneration with a short lifetime shows a low
recombination of electrons with holes.
1.4.2 Band Structure and Light Absorption
Ultraviolet-visible diffuse reflectance spectroscopy is used to quantify the optical
band gaps of semiconductors and light absorption of semiconductor photocatalyst
materials. In contrast to ultraviolet-visible spectroscopy, the synchrotron-based soft
X-ray spectroscopy is used to measure the electronic structure of complex materials,
wherein the VBM and CBM are measured by the X-ray emission and absorption
spectroscopy, respectively (Kapilashrami et al. 2014). Synchrotron radiation-based
X-ray spectroscopy provides the ability to analyze the band structure of
photocatalyst materials, while modifying the wavelength of the incident light allows
the study of element-selective photocatalyst materials (Vayssieres 2010).
8
F. Opoku et al.
Explicitly, the photogenerated charge carriers are examined by characterizing the
band structure and light absorption. Based on charge separation and migration, the
characterization techniques are mostly concentrated on charge dynamics (photoexcited charge carrier separation and lifetime efficiency). Moreover, several advanced
techniques have been widely designed to check surface reactions, such as the
molecular desorption/adsorption, reaction paths, reactant dissociation, and intermediate product.
1.4.1 Charge Carrier Transfer Kinetics
Besides charge transfer kinetics, the charge separation, migration, and recombination processes normally occur in an ultra-small timescale. The transient absorption
spectroscopy, which measures the signals for charges at the ground/excited state, and
the recombination rate of photogenerated charge carriers, has been broadly utilized
in a photocatalytic mechanism study (Berera et al. 2009). However, transient
absorption spectroscopy cannot fully reflect the photocatalytic process under simulated solar light irradiation owing to the robust pulsed laser used as excitation
sources (Berera et al. 2009). Therefore, photoelectrochemical measurements have
been used to check the charge kinetics behavior and average dynamic parameters of
a photocatalytic system (Sato 1998). Moreover, the recombination of
photogenerated carriers is measured by the time-resolved/steady-state
photoluminescence spectroscopy (Anpo and Kamat 2010). Generally, the low intensity in the steady-state photoluminescence spectroscopy shows a low chance of
recombination rate of charge carrier. For time-resolved photoluminescence spectroscopy, a rapid photoluminescence degeneration with a short lifetime shows a low
recombination of electrons with holes.
1.4.2 Band Structure and Light Absorption
Ultraviolet-visible diffuse reflectance spectroscopy is used to quantify the optical
band gaps of semiconductors and light absorption of semiconductor photocatalyst
materials. In contrast to ultraviolet-visible spectroscopy, the synchrotron-based soft
X-ray spectroscopy is used to measure the electronic structure of complex materials,
wherein the VBM and CBM are measured by the X-ray emission and absorption
spectroscopy, respectively (Kapilashrami et al. 2014). Synchrotron radiation-based
X-ray spectroscopy provides the ability to analyze the band structure of
photocatalyst materials, while modifying the wavelength of the incident light allows
the study of element-selective photocatalyst materials (Vayssieres 2010).
8
F. Opoku et al.