Electric field assisted ion adsorption with nanoporous SWCNT electrodes

The permeable single wall carbon nanotube (SWCNT) film electrodes of high electrical conductivity for filtration of ions are promising for future water treatment technology. The permeable SWCNT film electrodes were obtained by the use of the Zn/Al-based dispersant-aided SWCNT ink. The G band peak position and I_D/I_G value of Raman spectra do not change before and after the polarization of the SWCNT electrodes, showing the robustness of permeable SWCNT film electrodes. The analysis of N₂ adsorption isotherms showed that microporosity and specific surface area of the SWCNT electrodes were larger than those of the pristine SWCNT, due to the debundling of SWCNTs and removal of the caps of SWCNT on the dispersion treatment. Application of the electric voltage above − 3 V to the SWCNT electrodes enhanced markedly the adsorption-mediated permeability of K⁺ ions, reaching the removability of 90%. The removability dependence of Na⁺ ions on the initial ion concentration showed that the SWCNT permeation electrodes filter was efficient for diluted Na⁺ ionic solution. The ions of smaller Stokes radius were adsorbed for the mixed ionic solution of Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺, suggesting that the inner tube space of SWCNT electrodes is important for adsorption of ions.