Topics in Current Chemistry (2020) 378:6
1 3
The authors studied some optical characteristics such as the absorption spectrum
and scattering, absorption and extinction coefficients, as a basis for future designs
of photoreactors using this catalyst. Under white light and without any co-catalyst
present, NiFe 2 O 4 produced ca. five times larger amount of hydrogen than TiO 2 P25
after 8 h from an aqueous methanol solution.
In photocatalytic hydrogen evolution reactions, the presence of a co-catalyst,
most generally a noble metal, improves the hydrogen yield by boosting charge separation and acting as catalytic sites for H–H bond formation [148]. In addition, in the
case of some metals with appropriate particle size, the localized surface plasmon
resonance effect may enhance light absorption in the visible range [107]. In recent
work, Zeng and co-workers examined the combined effect of plasmonic gold nanoparticles and fluorescein sensitization on the activity of NiFe 2 O 4 photocatalysts for
visible-light-induced hydrogen production from water using triethanolamine as sacrificial reagent [149]. The presence of gold increased the hydrogen yield by a factor
of 5 at an optimum metal loading with respect to the pure ferrite, which the authors
ascribed to stronger absorption in the visible range and slower recombination on the
basis of UV–Vis and photoluminescence spectra, respectively. A synergistic effect
of fluorescein sensitizer and plasmonic Au co-catalyst further improved the photoactivity by one order of magnitude, with stable hydrogen production throughout six
photocatalytic cycles.
In contrast to the work by Gobara et al. [144] cited above, Rodríguez-Rodríguez and co-workers obtained a higher hydrogen yield with the spinel zinc ferrite ZnFe 2 O 4 compared to NiFe 2 O 4 [150]. The authors prepared nanosized Ni, Co
and Zn ferrites in oil-in-water microemulsions and tested them without any co-catalyst for photocatalytic hydrogen evolution from methanol aqueous solutions. The
photocatalytic activity followed the order ZnFe 2 O 4 > NiFe 2 O 4 > CoFe 2 O 4 , which is
mainly attributed to conduction band energies increasing in the reversed order on
the basis of UV–Vis spectra. A higher conduction band energy would thus imply a
stronger driving force for the transfer of electrons to protons. Dom and co-workers
used a microwave solid-state synthesis method to improve the activity of zinc ferrite by a factor of 4 with respect to the one obtained by a conventional solid-state
reaction [151]. Electrochemical measurements together with physicochemical and
optical characterizations let the authors conclude that the absence of agglomeration
of nanoparticles in the microwave method compared to the conventional one modified the electronic band positions and the electron mobility, resulting in improved
photocatalytic behaviour. Doping zinc ferrite may also lead to improved photocatalytic hydrogen production, as shown by Boudjemaa and co-workers, who prepared
M 0.2 Zn 0.8 Fe 2 O 4 spinels by a co-precipitation method, wherein M is Co, Ni or Cu
[152]. In this work, a considerable improvement of the activity of the zinc ferrite is
reported in the case Co doping and Ni doping, with the former giving the best results
of the series. In contrast, Cu doping resulted in a decrease of activity with respect to
ZnFe 2 O 4 . On the basis of electrochemical, photoelectrochemical and optical characterization, the authors mainly ascribe the effect of the guest cation on activity to its
influence on the electronic structure of the ferrites, with the bandgap values of the
different samples decreasing in the same order as the obtained hydrogen evolution
rates increase.
138
Reprinted from the journal
1 3
The authors studied some optical characteristics such as the absorption spectrum
and scattering, absorption and extinction coefficients, as a basis for future designs
of photoreactors using this catalyst. Under white light and without any co-catalyst
present, NiFe 2 O 4 produced ca. five times larger amount of hydrogen than TiO 2 P25
after 8 h from an aqueous methanol solution.
In photocatalytic hydrogen evolution reactions, the presence of a co-catalyst,
most generally a noble metal, improves the hydrogen yield by boosting charge separation and acting as catalytic sites for H–H bond formation [148]. In addition, in the
case of some metals with appropriate particle size, the localized surface plasmon
resonance effect may enhance light absorption in the visible range [107]. In recent
work, Zeng and co-workers examined the combined effect of plasmonic gold nanoparticles and fluorescein sensitization on the activity of NiFe 2 O 4 photocatalysts for
visible-light-induced hydrogen production from water using triethanolamine as sacrificial reagent [149]. The presence of gold increased the hydrogen yield by a factor
of 5 at an optimum metal loading with respect to the pure ferrite, which the authors
ascribed to stronger absorption in the visible range and slower recombination on the
basis of UV–Vis and photoluminescence spectra, respectively. A synergistic effect
of fluorescein sensitizer and plasmonic Au co-catalyst further improved the photoactivity by one order of magnitude, with stable hydrogen production throughout six
photocatalytic cycles.
In contrast to the work by Gobara et al. [144] cited above, Rodríguez-Rodríguez and co-workers obtained a higher hydrogen yield with the spinel zinc ferrite ZnFe 2 O 4 compared to NiFe 2 O 4 [150]. The authors prepared nanosized Ni, Co
and Zn ferrites in oil-in-water microemulsions and tested them without any co-catalyst for photocatalytic hydrogen evolution from methanol aqueous solutions. The
photocatalytic activity followed the order ZnFe 2 O 4 > NiFe 2 O 4 > CoFe 2 O 4 , which is
mainly attributed to conduction band energies increasing in the reversed order on
the basis of UV–Vis spectra. A higher conduction band energy would thus imply a
stronger driving force for the transfer of electrons to protons. Dom and co-workers
used a microwave solid-state synthesis method to improve the activity of zinc ferrite by a factor of 4 with respect to the one obtained by a conventional solid-state
reaction [151]. Electrochemical measurements together with physicochemical and
optical characterizations let the authors conclude that the absence of agglomeration
of nanoparticles in the microwave method compared to the conventional one modified the electronic band positions and the electron mobility, resulting in improved
photocatalytic behaviour. Doping zinc ferrite may also lead to improved photocatalytic hydrogen production, as shown by Boudjemaa and co-workers, who prepared
M 0.2 Zn 0.8 Fe 2 O 4 spinels by a co-precipitation method, wherein M is Co, Ni or Cu
[152]. In this work, a considerable improvement of the activity of the zinc ferrite is
reported in the case Co doping and Ni doping, with the former giving the best results
of the series. In contrast, Cu doping resulted in a decrease of activity with respect to
ZnFe 2 O 4 . On the basis of electrochemical, photoelectrochemical and optical characterization, the authors mainly ascribe the effect of the guest cation on activity to its
influence on the electronic structure of the ferrites, with the bandgap values of the
different samples decreasing in the same order as the obtained hydrogen evolution
rates increase.
138
Reprinted from the journal