Electric field enhanced in situ silica nanoparticles grafted activated carbon cloth electrodes for capacitive deionization

Abstract Activated carbon clothes (ACCs) were modified by in situ deposition of silica nanoparticles (SiO2 NPs) to enhance the dielectric property of ACC surface and used as electrodes in the capacitive deionization (CDI) system. Four different concentrations of tetraethyl orthosilicate precursors were used as silica source and the effect of concentration on the CDI performance was investigated. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis revealed the presence of Si-O bonds on the ACC surface and Raman analysis confirmed the graphitic structure of the ACC was intact after grafting with SiO2 NPs. SiO2 NPs coated ACC electrodes revealed better desalination efficiency and average salt removal rate (ASRR) than pristine ACC. Specifically, ACC electrodes coated with 45 mM silica (SiO2-III) exhibited the highest specific capacitance of 97.4 ± 0.1F/g, average desalination efficiency of 70 % with ASRR of 0.075 ± 0.008 mg/cm2/min using 200 ppm NaCl. Moreover, CDI Ragone’s plot verified the highest desalination rate was achieved with 45 mM SiO2 coated ACC electrodes. Furthermore, different salt concentrations and applied potentials upon desalination performances were also investigated. Moreover, post characterization of used pristine ACC and SiO2-III electrodes exhibited the sign of substantial electrode oxidation for pristine ACC but less on SiO2 NPs coated ACC electrodes. SiO2 NPs decorated ACC electrodes were not only enhanced localized electric field around dielectric coating of SiO2 NPs but also prevented the surface oxidation of the electrodes.