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Adsorption of hexavalent chromium ions from aqueous solution by graphene nanosheets: kinetic and thermodynamic studies
Goharshadi, E. K. & Moghaddam, M. B.
Abstract
In the present study, a batch system was used
to investigate the adsorption of chromium (VI) ions from
an aqueous solution by graphene nanosheets. Graphene is
decorated with functional groups containing oxygen such
as epoxy and hydroxyl on the basal plane. The large negative
charge density available on graphene causes effective
adsorption of chromium (VI) ions from aqueous solutions.
The adsorption capacity and rate of chromium (VI) ions at
different temperatures, adsorbent dosages, initial concentrations,
and contact times were evaluated. The kinetic
study illustrated that the adsorption of chromium (VI) ions
onto graphene obeys the pseudo-second-order model with
activation energy of 21.91 kJ mol-1. The chromium (VI)
ions adsorption was well explained using Dubinin–Radushkevich
isotherm model. The values of standard
enthalpy, entropy, and Gibbs free energy changes at 25 °C
were calculated as 686.07 kJ mol-1, 2.38 kJ mol-1K-1,
and -22.43 kJ mol-1, respectively. In this work, graphene
was prepared via a green method. Transmission electron
microscopy, Fourier transform-infrared spectroscopy,
energy-dispersive X-ray analysis, powder X-ray diffraction,
Boehm’s titration, and N2 adsorption–desorption
techniques revealed a high-quality few-layer nanosheets of
graphene with surface area and inter-planar spacing of
594.7 m2 g-1 and 3.6 Å, respectively.
Keywords
Chromium (VI) removal; Graphene; Dubinin–Radushkevich isotherm; Thermodynamics
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