Novel Carbon-Based Nanoadsorbents for Removal of Synthetic Textile Dyes from Wastewaters - Green Chemistry for Dyes Removal from Wastewater - page 44

of both polymers and small molecules via π-π stacking or van der Waals
interactions [75]. As a result, interest in RGO has also spread across many
disciplines.
Undoubtedly the discovery of graphene has brought about enormous
opportunities for science and technology. Because of their perfect sp 2
hybrid carbon nanostructure, large specific surface area, and strong inter-
actions with other molecules or atoms, graphene nanomaterials have
recently attracted the interest of researchers as a new type of adsorbent
for the removal of harmful contaminants from aqueous systems. Large
numbers of experimental studies have already been carried out on the
adsorption of different dye pollutants by graphene nanomaterials, as will
be discussed in the following section.

2.3 Adsorpton of Textile Dyes by Carbon

Nanoadsorbents

2.3.1 Adsorption by CNTs and Their Composites

2.3.1.1 CNTs

Numerous investigations have been undertaken to evaluate the adsorption
potential of CNTs for treatment of dye-contaminated waters (Table 2.2).
Ya o et al. [78] explored the possibility of using CNTs for removal of
Methylene Blue from its aqueous solution. The adsorption equilibrium
data were well described by the Langmuir model, implying monolayer
coverage of dye molecules onto the adsorbent surface. The maximum dye
adsorption capacity increased from 35.4 mg g -1 at 273 K to 64.7 mg g -1 at
333 K, indicating an endothermic nature of the adsorption process.
Shirmardi et al. [79] studied the performance of SWCNTs as adsor-
bent for the removal of Acid Red 18 from aqueous solutions. The adsorp-
tion equilibrium data showed an excellent fit to the Langmuir isotherm
model, with a maximum monolayer dye adsorption of 166.66 mg g -1 . In
another study, Moradi [80] investigated the adsorption of Basic Red 46
onto SWCNTs. Adsorption of Basic Red 46 was strongly dependent on the
initial solution pH with maximum uptake occurring at about pH 9. The
adsorption process was spontaneous and exothermic in nature but domi-
nated by physisorption. The maximum dye uptake capacity was deter-
mined to be 38.35 mg g -1 at 298 K.
Kuo et al. [81] tested the adsorption efficiency of MWCNTs for remov-
ing direct dyes (Direct Yellow 86 and Direct Red 224) from their aqueous