Environmental Engineering Reference
In-Depth Information
2.3.2.1 Graphene
Liu et al, [115] reported the use of graphene as an adsorbent for removal
of Methylene Blue from its aqueous solution. The adsorption capacity
decreased with increasing adsorbent dose, while it increased with increas-
ing temperature. The maximum adsorption capacity increased from
153.85 mg g -1 to 204.08 mg g -1 with the rise in temperature from 293 K to
333 K. The adsorption kinetics was studied in terms of pseudo-first-order,
pseudo-second-order, Elovich and intraparticle diffusion models. It was
found that the pseudo-second-order mechanism was predominant and that
intraparticle diffusion was not the sole rate-controlling step. Adsorption
equilibrium data fitted well to the Langmuir isotherm model rather than
the Freundlich model. Estimation of the thermodynamic parameters indi-
cated that adsorption of Methylene Blue onto graphene was a spontaneous,
endothermic and physisorption process.
Adsorption of Cationic Red X-GRL onto graphene was studied by
Li  et al, [114]. The maximum dye adsorption capacity obtained from the
Langmuir isotherm equation was 153.85 mg g -1 at 293 K. Similar to the
investigations of Liu et al. [115], the adsorption process was spontaneous
and endothermic, and obeyed the pseudo-second-order rate equation.
Wu et al. [116] investigated the use of graphene for removal of Methyl
Blue. The amount of dye adsorbed was found to be strongly dependent
on the initial concentration of Methyl Blue, and the adsorption process
attained equilibrium after 1 h. Graphene showed a remarkably high dye
adsorption capacity of 1.52 g g -1 , which was mainly due to π-π stacking
interactions as inferred through fluorescence spectroscopy studies. The
researchers also investigated the possibility to regenerate and reuse gra-
phene and observed no significant changes in the efficiency of graphene, at
least during the first five cycles of the adsorption-desorption process.
In a very interesting study by Zhao et al. [117], a new graphene material
called “graphene sponge” was developed by hydrothermal treatment of GO
sheets in the presence of thiourea. The material had a very porous structure
and behaved like a sponge (hence the name). Graphene sponge showed
excellent mechanical properties, very good processability and structural
stability. The feasibility of using graphene sponge to remove cationic
(Methylene Blue, Rhodamine B) and anionic (Methyl Orange) dyes from
their aqueous solutions was investigated. Graphene sponge was found to
have an affinity for both cationic and anionic dyes. However, the sorption
capacity for basic dyes was much higher than for acidic dyes because of the
ionic charges on the dyes and surface characteristics of graphene sponge.
The maximum adsorption uptake was found to be 184, 72.5 and 11.5 mg g -1
for Methylene Blue, Rhodamine B and Methyl Orange, respectively.
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