Adsorption Studies of Cd (II) from Water by Acid Modified Multiwalled Carbon Nanotubes

Abstract

This work aims to decorate carbon nanotubes with oxygenated functional groups for effective removal of Cadmium ions from aqueous media. For that purpose Carbon nanotubes (CNT) was oxidized by nitric acid to give MCNT- HNO3. The CNT and MCNT- HNO3 were characterized by SEM, TEM, FT-IR, Boehm titration, nitrogen adsorption–desorption analysis, point of zero charge and surface pH. The adsorption experiments of Cd(II) onto sorbents were studied using the batch technique and factors affecting the adsorption capacities of Cd(II) were investigated and discussed. The isotherm data were analyzed using Langmuir and Freundlich equations. The equilibrium data fitted well Langmuir isotherm for both CNT and MCNT- HNO3. The kinetic results were analyzed using pseudo-first order, pseudo-second order, intraparticle diffusion and the Boyd equations. The rate constants, equilibrium capacities and related correlation coefficients (R2) for each kinetic model were calculated and discussed. Highest values of R2 were obtained on applying the pseudo second-order with both carbons. Although intraparticle diffusion plays impotent role in rate-controlling step in the adsorption process of Cd(II) onto the investigated sorbents, film diffusion is also controlling this process. The thermodynamic parameters including ΔG°, ΔH° and ΔS° for the adsorption processes of Cd(II) on the carbons were calculated, and the negative value of ΔG° indicated the spontaneous nature of adsorption. The desorption studies revealed that the regeneration of MCNT- HNO3 can be easily achieved.