6.5 Adsorption
87
6.5 Adsorption
Graphene potentially possesses interesting tunable electrical [40], mechanical [41],
thermal [42] and chemical [43] properties. As the result, graphene may have a combination of interesting properties such as large specific surface area [44], high conductivity and flexibility [45, 46] as well as unique optical [47, 48] and thermal [49, 50]
properties. Due to these capabilities, graphene can potentially be applicable in many
applications including electronics [51], energy conversion and storage devices [45,
52], medicine [53], composites [54, 55], and microfluidics [56] and also as adsorbent
for removal of organic and inorganic poullants from the environment [57].
In applications such as supercapacitor or adsorbent, the interaction of graphene
with its surrounding environment is of significant importance, and therefore, the
graphene edge sites can be of particular interest. It is because the presence of dangling
bonds makes the edge sites of graphene at least two times more reactive than the basal
plane [58]. When the graphene material is exposed to the surrounding environment,
the less stable dangling bonds located on the edge sites can be functionalized by
oxygen-containing groups or other reactive species available in the environment [59].
This characteristic provides the graphene’s edge sites with interesting properties such
as a high specific electrochemical capacitance [60, 61] and adsorption capacity [98].
As discussed in Chap. 4, 3D graphene nanosheets with a high density of edge sites
can be produced in molten salts in an economic and efficient way. This graphene
material can be considered as an efficient adsorbent for the removal of inorganic
poullants or organic dyes.
It is a demanding application, since a wide variety of organic dyes are globally used
by many industries such textile, food and drink, pharmaceutical, cosmetic, leather,
tannery, ink and paper sections for coloring purposes, generating large volumes of
wastewater that contain synthetic dyestuffs. The increasing presence of bioactive
dyes in water resources has created a global threat to the biodiversity of our planet
[62, 63].
There are many different dyes, but among them, azo dyes are the most abundant
which represent around 70% of the global dye production. These dyes contain one
or more azo bonds (−N = N−) which are often linked to naphthalenic or benzene
rings containing lateral—OH and/or −SO
−
3 groups [63]. Large volumes of colored
effluents, which often contain a high concentration of azo dyes, are daily discharged
by various industries mentioned above into bodies of water around the world. This
causes aesthetic problems and provides a barrier for the penetration of sunlight into
the water. It also causes health issues for aquatic organisms due to the toxicity, carcinogenicity, mutagenicity of such dyes and also and their degradation by-products,
like aromatic amines [64–68]. Moreover, azo dyes are highly resistance to biodegradation in the aquatic environment, and therefore, cannot be eliminated naturally or
by physicochemical or biological treatments conducted in treatment plants. For the
removal of dyes from industrial effluents, various techniques are employed including
coagulation [65, 66], ion exchange [67, 68], chemical reduction [69, 70], membrane
separation [71, 72], biological treatments [73, 74] and adsorption [75–79]. Among
87
6.5 Adsorption
Graphene potentially possesses interesting tunable electrical [40], mechanical [41],
thermal [42] and chemical [43] properties. As the result, graphene may have a combination of interesting properties such as large specific surface area [44], high conductivity and flexibility [45, 46] as well as unique optical [47, 48] and thermal [49, 50]
properties. Due to these capabilities, graphene can potentially be applicable in many
applications including electronics [51], energy conversion and storage devices [45,
52], medicine [53], composites [54, 55], and microfluidics [56] and also as adsorbent
for removal of organic and inorganic poullants from the environment [57].
In applications such as supercapacitor or adsorbent, the interaction of graphene
with its surrounding environment is of significant importance, and therefore, the
graphene edge sites can be of particular interest. It is because the presence of dangling
bonds makes the edge sites of graphene at least two times more reactive than the basal
plane [58]. When the graphene material is exposed to the surrounding environment,
the less stable dangling bonds located on the edge sites can be functionalized by
oxygen-containing groups or other reactive species available in the environment [59].
This characteristic provides the graphene’s edge sites with interesting properties such
as a high specific electrochemical capacitance [60, 61] and adsorption capacity [98].
As discussed in Chap. 4, 3D graphene nanosheets with a high density of edge sites
can be produced in molten salts in an economic and efficient way. This graphene
material can be considered as an efficient adsorbent for the removal of inorganic
poullants or organic dyes.
It is a demanding application, since a wide variety of organic dyes are globally used
by many industries such textile, food and drink, pharmaceutical, cosmetic, leather,
tannery, ink and paper sections for coloring purposes, generating large volumes of
wastewater that contain synthetic dyestuffs. The increasing presence of bioactive
dyes in water resources has created a global threat to the biodiversity of our planet
[62, 63].
There are many different dyes, but among them, azo dyes are the most abundant
which represent around 70% of the global dye production. These dyes contain one
or more azo bonds (−N = N−) which are often linked to naphthalenic or benzene
rings containing lateral—OH and/or −SO
−
3 groups [63]. Large volumes of colored
effluents, which often contain a high concentration of azo dyes, are daily discharged
by various industries mentioned above into bodies of water around the world. This
causes aesthetic problems and provides a barrier for the penetration of sunlight into
the water. It also causes health issues for aquatic organisms due to the toxicity, carcinogenicity, mutagenicity of such dyes and also and their degradation by-products,
like aromatic amines [64–68]. Moreover, azo dyes are highly resistance to biodegradation in the aquatic environment, and therefore, cannot be eliminated naturally or
by physicochemical or biological treatments conducted in treatment plants. For the
removal of dyes from industrial effluents, various techniques are employed including
coagulation [65, 66], ion exchange [67, 68], chemical reduction [69, 70], membrane
separation [71, 72], biological treatments [73, 74] and adsorption [75–79]. Among