6.5 Adsorption
97
to the saturation of the adsorption sites. The initial concentration of MO has a complicated influence on the adsorption capacity of the carbon materials. To put more
light on this, the effect of this parameter on the color removal was investigated.
Figure 6.13b shows that graphene adsorbent outperforms the graphite, so that the
color removal performance of the graphene and graphite at an initial MO concentration of 0.05 g L
−1 are 98% and 70%, respectively. Moreover, the color removal
performance of both carbon materials strongly depends on the initial concentration
of MO. For instance, the color removal performance of the graphene drops from
98% to 25% by increasing the MO initial concentration from 0.05 to 0.3 g L
−1 . The
greater performance of the 3D graphene can be attributed to its higher values of the
specific surface area and density of edge sites, in comparison with those of graphite.
It should be considered that both the surface and wrinkles exist on graphene
nanosheets may provide effective sites for the adsorption of organic pollutants consisting of one or more aromatic rings. However, the mechanisms involved in interaction between organic pollutants and these adsorption sites are complex, since they
depend on the structure of graphene material used and the properties of the sorbate
[111]. The flat surface of graphene can provide a unique platform for π–π interaction with aromatic molecules, and a high hydrophobic attraction toward dyes. Structural defects such as wrinkles, surface functional groups and edges of the graphene
nanosheets can also contribute to the overall adsorption mechanism [112]. The electrolytic 3D graphene possesses a high mechanical and chemical stability as well as a
high surface area and edge sites making it attractive for dye adsorption applications.
Figures 6.13c and d present the influence of the amount of adsorbents on the MO
adsorption and the color removal performance of the graphite and 3D graphene
materials, repectively, from which contradictory behaviors can be observed: for
both adsorbents, by increasing the adsorbent dosage, the MO adsorption capacity
decreases while the color removal performance increases. To explain this, we need
to consider that a greater deal of active sites becomes available for the adsorption of
MO at an increased adsorbent dosage. Therefore, the color removal, consequently,
increases. However, since there is a constant initial MO concentration of 50 mg L
−1 ,
the MO adsorption per unit mass of the adsorbent decreases by the increase of the
adsorbent dosage [98]. This behavior was also reported by Wang et al. [78].
As it can be observed from Fig. 6.14, by increasing the adsorption time, the
absorbance of MO dye solution decreases. For instance, the absorbance intensity has
values of 1.62 and 0.06 at the beginning and after 15 min of the adsorption, respectively, using the graphene material. In contrast, the absorbance remains constant at
the value of 0.44 after 15 min adsorption using the graphite adsorbent. These observations indicate the efficient dye removal achieved by the use of molten salt-produced
graphene.
97
to the saturation of the adsorption sites. The initial concentration of MO has a complicated influence on the adsorption capacity of the carbon materials. To put more
light on this, the effect of this parameter on the color removal was investigated.
Figure 6.13b shows that graphene adsorbent outperforms the graphite, so that the
color removal performance of the graphene and graphite at an initial MO concentration of 0.05 g L
−1 are 98% and 70%, respectively. Moreover, the color removal
performance of both carbon materials strongly depends on the initial concentration
of MO. For instance, the color removal performance of the graphene drops from
98% to 25% by increasing the MO initial concentration from 0.05 to 0.3 g L
−1 . The
greater performance of the 3D graphene can be attributed to its higher values of the
specific surface area and density of edge sites, in comparison with those of graphite.
It should be considered that both the surface and wrinkles exist on graphene
nanosheets may provide effective sites for the adsorption of organic pollutants consisting of one or more aromatic rings. However, the mechanisms involved in interaction between organic pollutants and these adsorption sites are complex, since they
depend on the structure of graphene material used and the properties of the sorbate
[111]. The flat surface of graphene can provide a unique platform for π–π interaction with aromatic molecules, and a high hydrophobic attraction toward dyes. Structural defects such as wrinkles, surface functional groups and edges of the graphene
nanosheets can also contribute to the overall adsorption mechanism [112]. The electrolytic 3D graphene possesses a high mechanical and chemical stability as well as a
high surface area and edge sites making it attractive for dye adsorption applications.
Figures 6.13c and d present the influence of the amount of adsorbents on the MO
adsorption and the color removal performance of the graphite and 3D graphene
materials, repectively, from which contradictory behaviors can be observed: for
both adsorbents, by increasing the adsorbent dosage, the MO adsorption capacity
decreases while the color removal performance increases. To explain this, we need
to consider that a greater deal of active sites becomes available for the adsorption of
MO at an increased adsorbent dosage. Therefore, the color removal, consequently,
increases. However, since there is a constant initial MO concentration of 50 mg L
−1 ,
the MO adsorption per unit mass of the adsorbent decreases by the increase of the
adsorbent dosage [98]. This behavior was also reported by Wang et al. [78].
As it can be observed from Fig. 6.14, by increasing the adsorption time, the
absorbance of MO dye solution decreases. For instance, the absorbance intensity has
values of 1.62 and 0.06 at the beginning and after 15 min of the adsorption, respectively, using the graphene material. In contrast, the absorbance remains constant at
the value of 0.44 after 15 min adsorption using the graphite adsorbent. These observations indicate the efficient dye removal achieved by the use of molten salt-produced
graphene.