Adsorption of methylene blue from aqueous solution on modified ACFs by chemical vapor deposition

The adsorption behavior of activated carbon fibers (ACFs) modified by chemical vapor deposition (CVD) method on methylene blue (MB) was investigated in details. The Brunauer–Emmet–Teller (BET) surface area analysis, scanning electron microscope (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) analysis were employed to characterize the samples. The results showed that the pore size of the ACFs had a significant change after CVD modification. In addition, it was found that carbon nanotubes (CNTs) were well distributed on the surface of ACFs. FTIR analysis for modified ACFs after adsorption showed intensity changes of absorption peaks, in comparison to that before adsorption. The adsorption capacity at equilibrium increased with the increase of pH. Moreover, attempts were made to fit the isothermal data using Langmuir and Freundlich equations. The results manifested that the experimental data were well fitted by Freundlich equation. Furthermore, the adsorption kinetics was analyzed by pseudo-first-order, pseudo-second-order and intra-particle diffusion models. The results demonstrated that the kinetic data were well described by pseudo-second-order kinetic model. The adsorption rate was controlled by intra-particle diffusion and film diffusion and thermodynamic parameters including ΔG, ΔH and ΔS were also determined. This showed that the adsorption process was a spontaneous, endothermic and increasing randomness process. The calculated Ea was 28.33 kJ/mol, indicating that the adsorption could be a physisorption process.

► Activated carbon fibers were modified by growing CNTs on their surface with CVD.
► The adsorption of MB from aqueous solution on modified ACFs was investigated.
► Langmuir and Freundlich models well fitted the adsorption experimental results.
► The experimental data showed the pseudo-second-order kinetic model was well fitted.
► The adsorption is a spontaneous, endothermic and entropy drive physisorption.