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Competitive adsorption of dye species from aqueous solution onto melon husk in single and ternary dye systems
Olajire, A. A.; Giwa, A. A. & Bello, I. A.
Abstract
Polluted water may contain more than one dye
species. Consequently, the behavior of a particular dye in a
water system may be affected by the presence of the others.
In this study, the adsorption of methylene blue (MB) in
single dye system (SDS) and in ternary dye system (TDS)
comprising of MB, congo red and methyl orange onto
formaldehyde-treated melon husk (FMH) was investigated
as a function of pH, contact time and species concentrations.
Surface studies of FMH were investigated by Fourier
transform infrared and scanning electron microscopy. The
dye species adsorption equilibria were rapidly attained
after 60 (SDS) and 90 min (TDS) of contact times. The
adsorption kinetics were analyzed using pseudo first-order,
pseudo second-order and intraparticle diffusion models and
the adsorption data were well described by the pseudo
second-order model. The equilibrium adsorption data were
interpreted in terms of the Langmuir, Freundlich, Temkin,
Dubinin–Radushkevich, Harkin–Jura and Halsey isotherm
models and the goodness of fittings were inspected using
linear regression analysis (R2). Our results indicated that
the Langmuir model was best fitted, suggesting monolayer
adsorption. Thermodynamic study showed that the
adsorptions in SDS and TDS on FMH are favourable. The
change in entropy (ΔS°) and heat of adsorption (ΔH°) of
dye species on FMH in TDS were estimated as 82.2 J/
mol K and 17.95 kJ/mol. respectively while in SDS, they
were respectively -43.76 J/mol K and -21.84 kJ/mol.
The sorption process in both systems was thermodynamically
feasible with negative ΔG° values.
Keywords
Melon husk; Single dye system (SDS); Ternary dye system (TDS); Kinetics; Thermodynamics; Isotherms
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