Three-Dimensional and Lamellar Graphene Oxide Membranes …
99
antibiotic contaminants in water [83]. Silver phosphate/GO aerogel microspheres
that can photodegrade pharmaceuticals and pesticides were recently obtained [84].
Nd 2 O 3 nanoparticles [85] and rGO/rare-earth-metal-oxide [86] aerogels are also
promising functionalizations for dye removal.
Polyvinyl alcohol, a biocompatible polymer, bonded with iron oxide can be
used as a precursor to prepare an Fe 3 O 4 @Fe/GO aerogel. This membrane achieved
higher antibiotic activity in comparison with other 3D-GO/rGO materials and total
organic carbon removal from water [87]. Also, Fe 3 O 4 @Fe/GO nanocomposites can
be employed in the immobilization of pharmaceutical drugs, such as phenazopyridine [88], and heavy metals [89]. It is also possible to create a modified rGO
aerogel by exchanging the biopolymer for a polyethyleneimine (PEI). The resulting
Fe 3 O 4 @PEI/rGO aerogel has been shown to effectively remove a polar non-steroidal
anti-inflammatory drug from water [90]. An alternative membrane to adsorb similar
drugs was obtained through cobalt-based ferrite (CoFe 2 O 4 ) functionalization of
GO-based nanocomposites [91].
The possibilities of creating GO/rGO-based 3D structures for water purification
are numerous, as nanofiller membranes, foams, and sponges for water-pollutant separation. However, it is important to address some concerns about almost all current
synthesis routines. A significant issue is the reducing agents. Most of the chemicals
employed to reduce the disperse GO/rGO sheets into a 3D structure are toxic. For
instance, one of the most used reducing agents is hydrazine (N 2 H 4 ), which exhibits
excellent reducing capacity, but it is also a carcinogenic agent related to lung and
colon cancer [92] as well as basal cell carcinomas [93]. Another reducing agent
widely applied in 3D-GO synthesis is the sodium borohydride (NaBH 4 ), a highly
toxic compound that, in contact with water, starts a reaction that releases gases with
potential spontaneous ignition. The time required for the synthesis is also a challenge.
There are too many steps in current methods, taking several days—or weeks—to get
a sample. Besides that, in many cases, templates have to be employed. It is still necessary to create new chemical routines to obtain these membranes, using non-pollutant
reducing agents and speeding the process up to achieve large industrial production.
4 Computational Studies
Whether predicting new materials or exploring physical phenomena unlikely to
be explained through experiments, computer simulations have decisively advanced
materials science. The contribution becomes more evident when we scale down to
nanomaterials. They are expected to perform differently from bulk. For instance,
graphene exhibits extraordinary electronic and mechanical properties and extremely
high thermal conductivity. The latter was observed to even increase with the sample’s
length. Non-equilibrium molecular dynamics (NEMD) simulations showed that this
behavior is a consequence of the 2D nature of phonons in graphene, and to the
change of the phonon population at stationary non-equilibrium conditions [94],
providing a fundamental understanding of thermal transport in 2D materials. Theory
99
antibiotic contaminants in water [83]. Silver phosphate/GO aerogel microspheres
that can photodegrade pharmaceuticals and pesticides were recently obtained [84].
Nd 2 O 3 nanoparticles [85] and rGO/rare-earth-metal-oxide [86] aerogels are also
promising functionalizations for dye removal.
Polyvinyl alcohol, a biocompatible polymer, bonded with iron oxide can be
used as a precursor to prepare an Fe 3 O 4 @Fe/GO aerogel. This membrane achieved
higher antibiotic activity in comparison with other 3D-GO/rGO materials and total
organic carbon removal from water [87]. Also, Fe 3 O 4 @Fe/GO nanocomposites can
be employed in the immobilization of pharmaceutical drugs, such as phenazopyridine [88], and heavy metals [89]. It is also possible to create a modified rGO
aerogel by exchanging the biopolymer for a polyethyleneimine (PEI). The resulting
Fe 3 O 4 @PEI/rGO aerogel has been shown to effectively remove a polar non-steroidal
anti-inflammatory drug from water [90]. An alternative membrane to adsorb similar
drugs was obtained through cobalt-based ferrite (CoFe 2 O 4 ) functionalization of
GO-based nanocomposites [91].
The possibilities of creating GO/rGO-based 3D structures for water purification
are numerous, as nanofiller membranes, foams, and sponges for water-pollutant separation. However, it is important to address some concerns about almost all current
synthesis routines. A significant issue is the reducing agents. Most of the chemicals
employed to reduce the disperse GO/rGO sheets into a 3D structure are toxic. For
instance, one of the most used reducing agents is hydrazine (N 2 H 4 ), which exhibits
excellent reducing capacity, but it is also a carcinogenic agent related to lung and
colon cancer [92] as well as basal cell carcinomas [93]. Another reducing agent
widely applied in 3D-GO synthesis is the sodium borohydride (NaBH 4 ), a highly
toxic compound that, in contact with water, starts a reaction that releases gases with
potential spontaneous ignition. The time required for the synthesis is also a challenge.
There are too many steps in current methods, taking several days—or weeks—to get
a sample. Besides that, in many cases, templates have to be employed. It is still necessary to create new chemical routines to obtain these membranes, using non-pollutant
reducing agents and speeding the process up to achieve large industrial production.
4 Computational Studies
Whether predicting new materials or exploring physical phenomena unlikely to
be explained through experiments, computer simulations have decisively advanced
materials science. The contribution becomes more evident when we scale down to
nanomaterials. They are expected to perform differently from bulk. For instance,
graphene exhibits extraordinary electronic and mechanical properties and extremely
high thermal conductivity. The latter was observed to even increase with the sample’s
length. Non-equilibrium molecular dynamics (NEMD) simulations showed that this
behavior is a consequence of the 2D nature of phonons in graphene, and to the
change of the phonon population at stationary non-equilibrium conditions [94],
providing a fundamental understanding of thermal transport in 2D materials. Theory