Three-Dimensional and Lamellar Graphene Oxide Membranes …
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possible applications of graphene-based materials for water treatment and purification, including the removal of dyes, organic solvents, pesticides, heavy metals, and
inorganic pollutants.
Another way to include polar groups is by using graphene oxide (GO). This
material differs from the standard pristine graphene once it has oxidized sites. A
GO compound can be obtained through chemical oxidation of carbon sources, such
as graphite, using oxidizing agents (e.g., KMnO 4 , H 2 SO 4 , etc.) to produce graphite
oxide. Then, distinct exfoliation methods can be used to yield GO nanosheets. The
possibility of large-scale production of GO makes it inexpensive in comparison with
other materials [14]. GO sheets have hexagonal structure as pristine graphene with
oxygen-based functionalized sites. It shows high electronic mobility, thermal conductivity, and remarkable mechanical strength, with the advantage of being highly stable
in water. As well, its surface can be easily functionalized by organic biomolecules,
strong π–π stacking, and vdW interactions.
Spontaneous self-assembly is one of the most prominent and efficient strategies
to build 2D or 3D macroscopic structures from nanosized chemical building blocks
[15]. It allows exploring the unique properties of nanomaterials, like GO, in macroscopic devices. One of the main quests in self-assembly is to control the resulting
morphology. In the case of GO, the control of the oxidation degree can be obtained
through reducing agents. This control over the polar-oxygenated functional sites
allows for GO manipulation in water and distinct 2D or 3D structures’ self-assembly
[14]. Reduced GO (rGO) sheet with a controlled number of functional groups is itself
a strategy to explore the separation properties of GO-based materials. As well, distinct
reducing agents can be employed to reduce and create new and unique binding sites
for pollutants.
A huge variety of structures are obtained by the assembly of GO/rGO nanosheets.
In suspension, these layers can be manipulated to obtain either lamellar or 3D nanostructures, as shown in Fig. 1. 2D lamellar multilayered structures of GO and rGO
have shown great potential for separation. These 2D materials have nanochannels that
can be tuned in size by distinct reducing agents [16, 17] to allow the flow of specific
atoms and molecules, controlling both water permeability and pollutant removal. As
well, the lamellar structures can be functionalized by distinct materials to achieve
specific adsorption and filtration properties [18, 19]. On the other hand, 3D-GObased macrostructures have shown high adsorption capacity and recyclability due to
their unique superficial area and porosity [20, 21]. Briefly stated, 3D-GO multifunctional structures are obtained by employing methods that prevent the GO/rGO sheets
to stack in the suspended solution. This 3D configuration keeps the GO/rGO sheet
properties, and increase applications based in characteristics that single sheets do
not have, as porosity. In this way, several studies have been dedicated to synthesize
3D-GO/rGO structures, as foam, sponges, and aerogels, with distinct morphology,
structure, and properties [20]. Both lamellar and 3D structures have physical–chemical properties that diverge from their chemical building blocks (i.e., the GO/rGO
nanosheets and the functionalization molecules), making them interesting materials
for new water treatment technologies.
89
possible applications of graphene-based materials for water treatment and purification, including the removal of dyes, organic solvents, pesticides, heavy metals, and
inorganic pollutants.
Another way to include polar groups is by using graphene oxide (GO). This
material differs from the standard pristine graphene once it has oxidized sites. A
GO compound can be obtained through chemical oxidation of carbon sources, such
as graphite, using oxidizing agents (e.g., KMnO 4 , H 2 SO 4 , etc.) to produce graphite
oxide. Then, distinct exfoliation methods can be used to yield GO nanosheets. The
possibility of large-scale production of GO makes it inexpensive in comparison with
other materials [14]. GO sheets have hexagonal structure as pristine graphene with
oxygen-based functionalized sites. It shows high electronic mobility, thermal conductivity, and remarkable mechanical strength, with the advantage of being highly stable
in water. As well, its surface can be easily functionalized by organic biomolecules,
strong π–π stacking, and vdW interactions.
Spontaneous self-assembly is one of the most prominent and efficient strategies
to build 2D or 3D macroscopic structures from nanosized chemical building blocks
[15]. It allows exploring the unique properties of nanomaterials, like GO, in macroscopic devices. One of the main quests in self-assembly is to control the resulting
morphology. In the case of GO, the control of the oxidation degree can be obtained
through reducing agents. This control over the polar-oxygenated functional sites
allows for GO manipulation in water and distinct 2D or 3D structures’ self-assembly
[14]. Reduced GO (rGO) sheet with a controlled number of functional groups is itself
a strategy to explore the separation properties of GO-based materials. As well, distinct
reducing agents can be employed to reduce and create new and unique binding sites
for pollutants.
A huge variety of structures are obtained by the assembly of GO/rGO nanosheets.
In suspension, these layers can be manipulated to obtain either lamellar or 3D nanostructures, as shown in Fig. 1. 2D lamellar multilayered structures of GO and rGO
have shown great potential for separation. These 2D materials have nanochannels that
can be tuned in size by distinct reducing agents [16, 17] to allow the flow of specific
atoms and molecules, controlling both water permeability and pollutant removal. As
well, the lamellar structures can be functionalized by distinct materials to achieve
specific adsorption and filtration properties [18, 19]. On the other hand, 3D-GObased macrostructures have shown high adsorption capacity and recyclability due to
their unique superficial area and porosity [20, 21]. Briefly stated, 3D-GO multifunctional structures are obtained by employing methods that prevent the GO/rGO sheets
to stack in the suspended solution. This 3D configuration keeps the GO/rGO sheet
properties, and increase applications based in characteristics that single sheets do
not have, as porosity. In this way, several studies have been dedicated to synthesize
3D-GO/rGO structures, as foam, sponges, and aerogels, with distinct morphology,
structure, and properties [20]. Both lamellar and 3D structures have physical–chemical properties that diverge from their chemical building blocks (i.e., the GO/rGO
nanosheets and the functionalization molecules), making them interesting materials
for new water treatment technologies.