Carbon-cobalt nanostructures 1 and 2 were prepared by pyrolysis of the cisdichlorobis(
1,10-phenanthroline-N,N')-cobalt(II) complex 3 in the absence or presence
of anthracene respectively. DFT calculation was used to estimate ligand dissociation energy
of cobalt complex, the energy cost for the formation of cobalt particles which catalyze
the formation of carbon nanostructures. FE-SEM analysis indicates that 1 and 2
contain 3D nanostructure hierarchical porous graphitic carbons HPCGs wrapping cobalt
particles in spheres and rods, with mesopores and macropores ranging from 10-100 nm.
TEM analysis indicated that nanostructures 1 and 2 consist of graphite layers as well as
single wall and bamboo multiple wall carbon nanotubes. Crystalline cobalt catalyst nanoparticles
were found wrapped in ordered graphene layers and also at the tips of the
bamboo-shaped disordered multiwall carbon nanotubes. TEM also showed porous surfaces.
Both nanostructures 1 and 2 were used as adsorbents to uptake malachite green
dye (MG) from aqueous solution. Adsorption isotherms of MG by adsorbents 1 and 2
were fitted in terms of Langmuir, Freundlich, Temkin, and D-R models. The adsorption
capacity of 2 (492 mg/g) was higher than that of 1 (200 mg/g). Thermodynamic adsorption
studies indicated that the sorption process was spontaneous and exothermic. A
pseudo-first order model has been adopted to describe the kinetics of the adsorption process
as well as the activated thermodynamic parameters. Column kinetic adsorption of
MG by 2 was best fitted by the Thomas model. The column capacity was found to be 64
mg. The adsorbent can be regenerated and proved efficient for three consecutive cycles.
Keywords: Carbon nanostructure, cobalt complex, complexation energy, malachite green, adsorption isotherm,
thermodynamics, kinetic, column.
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