Kinetic and thermodynamic studies of Direct Red 23 removal using zero-valent nanoparticles immobilized on multi walled carbon nanotubes from aqueous solution

Abstract

In the present study nanoscale zero valent iron (nZVI) has been immobilized on multi-walled carbon nanotubes (MWCNTs) and used to remove Direct Red 23 (DR 23) from aqueous solution. The effect of parameters such as, initial dye concentration, solution pH, adsorbent content, temperature and contact time on the adsorption process have been investigated. The studied adsorbent exhibits high efficiency for dye adsorption and the equilibrium state is achieved in 6 min. For equilibrium studies, three isotherm models, namely Langmuir, Freundlich and Temkin are used. It is found that Langmuir fits very well with experimental data. The kinetic studies suggest the process following pseudo second-order kinetics and involvement of the particle-diffusion mechanism. The value of different thermodynamic parameters, like Gibb’s free energy change, enthalpy change and entropy change of the adsorption process have also been evaluated. The adsorption of DR 23 has been found to be endothermic.