In recent studies, α-FeOOH has been found to degrade some recalcitrant organic
compounds at neutral to alkaline pH values under UV irradiation. It first absorbs UV
light to produce electrons and holes and subsequently reacts with H 2 O and H 2 O 2 to
produce ●OH radicals. The hydroxyl radicals can also be generated by breaking up
the FeO–OH bond through UV irradiation. Importantly, the incorporation of
graphene and α-FeOOH enables the composite to have visible light response and
absorption characteristics, and the photo-generated electrons are also transported to
graphene sheets to reduce their recombination and enhance the photocatalytic
activity. Wang et al. [75] prepared GO/α-FeOOH composite by reducing Fe
(II) onto GO via in situ self-assembly process. They demonstrated that the
as-prepared catalyst had a high activity on oxidizing phenol under visible light
irradiation in a wide pH range. Liu et al. [76] synthesized α-FeOOH@GCA by
incorporating GO-CNTs and α-FeOOH nanoparticles using a facile in situ hydrolysis route. Compared with pristine α-FeOOH, the composite was proved to show
more effective in H 2 O 2 activity and more excellent performance on degrading OII.
10.3 Conclusions and Outlook
In summary, various iron-based oxides/graphene composites have been explored to
obtain more effective, environmental friendly, cheaper, and more toxic catalyst in
order to solve the problem of increasingly dye pollution in water. The synergistic
effect of graphene and iron (hydr)oxides semiconductors enhances the
photocatalytic activity of iron (hydr)oxides to degrade a large number of water dye
pollutants such as methyl blue, phenol, and so forth. The combination of the sizedependent property of nanomaterials and the excellent properties of graphene endow
the composites exhibiting much more functionalities, such as large surface area,
wide pH reaction range, wide sunlight response and absorption, high adsorption
capacity, high speed of electron transportation, low recombination of electrons and
holes, and so on. The iron (hydr)oxides have various bandgap ranging from 0.1 eV
(Fe 3 O 4 ) to 2.8 eV (FeOOH) and the potential of the minimum conductive band is
more negative than the water reduction potential (H
+ /H 2 ) or the potential of the
maximum valence band is more positive than the water oxidation potential (H 2 O/
O 2 ). A variety of synthetic methods have been studied to produce iron (hydr)oxidesbased composites. However, there are still some problems needed to be overcome
for large-scale application. For instance, it is difficult to obtain high purified
graphene with precisely controlling the defects and defect sites. The recombination
of electrons and holes and restacking of graphene to graphite are not completely
solved. It still needs to be further researched to find new methods to overcome the
problems mentioned above.
The exploration of new catalysts and treatment technique of the organic pollutants in wastewater is an exciting and difficult work for scientific researchers.
Considering the recycling of catalysts, magnetic materials may attract more attention
due to that they not only possess the catalytic performance but also can be magnetic
254
10 Heterogeneous Photo-Fenton Technology
compounds at neutral to alkaline pH values under UV irradiation. It first absorbs UV
light to produce electrons and holes and subsequently reacts with H 2 O and H 2 O 2 to
produce ●OH radicals. The hydroxyl radicals can also be generated by breaking up
the FeO–OH bond through UV irradiation. Importantly, the incorporation of
graphene and α-FeOOH enables the composite to have visible light response and
absorption characteristics, and the photo-generated electrons are also transported to
graphene sheets to reduce their recombination and enhance the photocatalytic
activity. Wang et al. [75] prepared GO/α-FeOOH composite by reducing Fe
(II) onto GO via in situ self-assembly process. They demonstrated that the
as-prepared catalyst had a high activity on oxidizing phenol under visible light
irradiation in a wide pH range. Liu et al. [76] synthesized α-FeOOH@GCA by
incorporating GO-CNTs and α-FeOOH nanoparticles using a facile in situ hydrolysis route. Compared with pristine α-FeOOH, the composite was proved to show
more effective in H 2 O 2 activity and more excellent performance on degrading OII.
10.3 Conclusions and Outlook
In summary, various iron-based oxides/graphene composites have been explored to
obtain more effective, environmental friendly, cheaper, and more toxic catalyst in
order to solve the problem of increasingly dye pollution in water. The synergistic
effect of graphene and iron (hydr)oxides semiconductors enhances the
photocatalytic activity of iron (hydr)oxides to degrade a large number of water dye
pollutants such as methyl blue, phenol, and so forth. The combination of the sizedependent property of nanomaterials and the excellent properties of graphene endow
the composites exhibiting much more functionalities, such as large surface area,
wide pH reaction range, wide sunlight response and absorption, high adsorption
capacity, high speed of electron transportation, low recombination of electrons and
holes, and so on. The iron (hydr)oxides have various bandgap ranging from 0.1 eV
(Fe 3 O 4 ) to 2.8 eV (FeOOH) and the potential of the minimum conductive band is
more negative than the water reduction potential (H
+ /H 2 ) or the potential of the
maximum valence band is more positive than the water oxidation potential (H 2 O/
O 2 ). A variety of synthetic methods have been studied to produce iron (hydr)oxidesbased composites. However, there are still some problems needed to be overcome
for large-scale application. For instance, it is difficult to obtain high purified
graphene with precisely controlling the defects and defect sites. The recombination
of electrons and holes and restacking of graphene to graphite are not completely
solved. It still needs to be further researched to find new methods to overcome the
problems mentioned above.
The exploration of new catalysts and treatment technique of the organic pollutants in wastewater is an exciting and difficult work for scientific researchers.
Considering the recycling of catalysts, magnetic materials may attract more attention
due to that they not only possess the catalytic performance but also can be magnetic
254
10 Heterogeneous Photo-Fenton Technology