Adsorption of Direct red 81 dye onto friendly prepared iron oxide/multi-walled carbon nanotubes nanocomposite: kinetics and thermodynamic studies

This paper describes the synthesis of an iron oxide/multi-walled carbon nanotubes (Fe2
O3/MWCNT) nanocomposite for the removal of Direct red 81 dye as an organic pollutant. The nanocomposite
was characterized using various techniques, including X-ray diffraction, Fourier-transform infrared
spectroscopy, thermogravimetric analysis, UV-visible spectrophotometry, scanning electron micros
copy, and transmission electron microscopy. The study demonstrates the feasibility of preparing a
nanocomposite through a simple impregnation followed by a decomposition solid-state reaction,
which reduces time and chemical costs. The characteristics of the nanocomposite and the kinetics of
the adsorptive removal of the organic dye are described in detail, including the factors that govern
adsorptive behavior such as pH, temperature, initial concentration of the dye, and adsorbent dosage.
The results show that the efficiency of the adsorption process increases with increasing concentra
tion of reactants and temperature. The study used Langmuir and Freundlich adsorption isothermal
models, and the equilibrium data revealed that the Langmuir model fit linearly with the Direct red
81 adsorption, with the highest adsorption capacity being 73.05 mg/g. Additionally, the kinetics of
the process fit linearly with the pseudo-second-order model. The thermodynamic studies showed
that the adsorption process was endothermic and spontaneous, with a negative value of free energy
change indicating favorable adsorption. Finally, a reusability study showed that the prepared com
posite had good decolorization performance over four consecutive cycles, indicating its potential
as an effective and efficient adsorbent for the removal of organic pollutants