88
M. H. Köhler et al.
as population growth, climate change, political decisions, and our current lifestyle
[2]. About 80% of current residuals’ water, from industry to city sewers, returns
to water bodies without the proper treatment [3]. A consequence is the increasing
contamination and degradation of aqueous environments. Not to mention that health
issues related to contaminated water tend to weigh even more on the low-income
population.
This is a humanitarian challenge that needs urgent technological solutions. In this
direction, scientists are making efforts to find cheaper, greener materials to be used
in water purification plants. A wide variety of methods have been employed, such as
screening, filtration, centrifugation, crystallization, sedimentation and separation by
gravity, flotation, precipitation, coagulation, oxidation, solvent extraction, evaporation, distillation, reverse osmosis (RO), ion exchange, electrodialysis, electrolysis,
and adsorption. These distinct methods employ a large variety of materials. However,
many of these materials cannot remove some pollutants, especially at natural water
pH or in high trace level concentration [4].
In this sense, one of the most significant tasks of modern material science is to
develop a material able to adsorb a broad spectrum of water pollutants. Among the
several materials proposed in recent years, graphene and other carbon-based nanostructures arise as the most prominent for water purification [4, 5]. It all started in
the early 50s when Radushkevich obtained carbon nanotubes (CNTs) by decomposition of carbon monoxide (CO) in iron [6]. Oberlinv and co-workers also produced
CNTs from benzene decomposition back in the 70s [7]. However, the scientific and
technological possibilities of carbon-based nanostructures only became notorious
after Ijima’s work on the fabrication of CNTs in the early 90s [8]. A decade after,
the hypothesis of a hierarchical self-assembly of carbon foams from nanostructured
graphite was first discussed by Umemoto and co-workers [9], giving rise to the
idea of two-dimensional (2D) carbon-based nanostructures. In 2004, a seminal work
by Novoselov et al. [10] revolutionized materials science. They were able to strip
graphene sheets out of graphite with a Scotch Tape, isolating this 1-carbon atomthick nanostructure. The technique was awarded the 2010 Nobel Prize in Physics and
represents one of the greatest revolutions in the chemical, physical, and engineering
sciences of our century. The extraordinary graphene properties, as mechanical flexibility, chemical and thermal stability, and, especially, its high surface area [11], make
this material one of the most promising for new water purification technologies.
Pure graphene sheets, or pristine graphene, will interact with contaminants mainly
by van der Waals (vdW) forces, since their carbon atoms are highly stabilized in an
sp
2 configuration. This property is useful, for instance, to separate heavy metals
from water. These ions are naturally observed in aqueous environments. However,
we are facing an increase in this kind of pollutant in water supplies due to humanmade phenomena, as mining and mineral processing [12] and the excessive use of
pesticides [13]. Graphene can be very effective in separating ions from water, but
for some pollutants, the energetic penalty for leaving bulk solution and be absorbed
in graphene’s surface is too high. A solution to adsorb polar pollutants is to decorate pristine graphene with specific functional groups. This increases the number of
M. H. Köhler et al.
as population growth, climate change, political decisions, and our current lifestyle
[2]. About 80% of current residuals’ water, from industry to city sewers, returns
to water bodies without the proper treatment [3]. A consequence is the increasing
contamination and degradation of aqueous environments. Not to mention that health
issues related to contaminated water tend to weigh even more on the low-income
population.
This is a humanitarian challenge that needs urgent technological solutions. In this
direction, scientists are making efforts to find cheaper, greener materials to be used
in water purification plants. A wide variety of methods have been employed, such as
screening, filtration, centrifugation, crystallization, sedimentation and separation by
gravity, flotation, precipitation, coagulation, oxidation, solvent extraction, evaporation, distillation, reverse osmosis (RO), ion exchange, electrodialysis, electrolysis,
and adsorption. These distinct methods employ a large variety of materials. However,
many of these materials cannot remove some pollutants, especially at natural water
pH or in high trace level concentration [4].
In this sense, one of the most significant tasks of modern material science is to
develop a material able to adsorb a broad spectrum of water pollutants. Among the
several materials proposed in recent years, graphene and other carbon-based nanostructures arise as the most prominent for water purification [4, 5]. It all started in
the early 50s when Radushkevich obtained carbon nanotubes (CNTs) by decomposition of carbon monoxide (CO) in iron [6]. Oberlinv and co-workers also produced
CNTs from benzene decomposition back in the 70s [7]. However, the scientific and
technological possibilities of carbon-based nanostructures only became notorious
after Ijima’s work on the fabrication of CNTs in the early 90s [8]. A decade after,
the hypothesis of a hierarchical self-assembly of carbon foams from nanostructured
graphite was first discussed by Umemoto and co-workers [9], giving rise to the
idea of two-dimensional (2D) carbon-based nanostructures. In 2004, a seminal work
by Novoselov et al. [10] revolutionized materials science. They were able to strip
graphene sheets out of graphite with a Scotch Tape, isolating this 1-carbon atomthick nanostructure. The technique was awarded the 2010 Nobel Prize in Physics and
represents one of the greatest revolutions in the chemical, physical, and engineering
sciences of our century. The extraordinary graphene properties, as mechanical flexibility, chemical and thermal stability, and, especially, its high surface area [11], make
this material one of the most promising for new water purification technologies.
Pure graphene sheets, or pristine graphene, will interact with contaminants mainly
by van der Waals (vdW) forces, since their carbon atoms are highly stabilized in an
sp
2 configuration. This property is useful, for instance, to separate heavy metals
from water. These ions are naturally observed in aqueous environments. However,
we are facing an increase in this kind of pollutant in water supplies due to humanmade phenomena, as mining and mineral processing [12] and the excessive use of
pesticides [13]. Graphene can be very effective in separating ions from water, but
for some pollutants, the energetic penalty for leaving bulk solution and be absorbed
in graphene’s surface is too high. A solution to adsorb polar pollutants is to decorate pristine graphene with specific functional groups. This increases the number of