Polyaniline-modified activated carbon electrodes for capacitive deionisation

• The conductivity of AC/PANI was higher than that of the original AC.
• Higher specific capacitance of AC/PANI CV was found.
• Fast ion removal rate was observed.

A composite of activated carbon particles (AC) and the conducting polymer polyaniline (PANI) was synthesised by in-situ polymerisation. The resultant composite was used as electrodes in the capacitive deionisation. The PANI presence was confirmed by Fourier transform infrared spectroscopy (FTIR). The morphology and porous structure were investigated by scanning electron microscopy (SEM) and N2 adsorption–desorption measurement. Electrochemical behaviour was studied by a cyclic voltammetry (CV) test. The results showed that the electrodes made of the composite had an ion removal capacity of 3.15 mg/g, which was much higher than that of AC only electrodes (1.98 mg/g) at the initial concentration of around 250 mg/L. Moreover, a faster ion removal rate was found for the composite electrodes with an absorption rate constant of 0.67, more than twice as high as the original activated carbon electrodes (0.23). The combination of two materials reduced the number of micropores and increased conductivity. It was believed that PANI formed conducting chains that connected micro-AC particles together and blocked most of the micropores. Weak acid functional groups at the surface of AC acted as dopant for PANI to increase its conductivity. It was found that the ion electrosorption by AC/PANI composite follows the Langmuir adsorption model.