Comparative desalination performance of activated carbon from coconut shell waste/carbon nanotubes composite in batch mode and single-pass mode

A combination of biomass-derived activated carbon and nano-carbonaceous materials has been considered as a sustainable approach to developing the highly electro-adsorptive electrode for desalination by capacitive deionization (CDI) technology. These composites can propose many enormous advantages such as non-toxicity, eco-friendly, high conductivity, and scalability. This work aimed to fabricate the composite coconut-shell-derived activated carbon/carbon nanotubes electrode with low CNTs content (1 wt%) for desalination. The nitrogen adsorption/desorption demonstrates the decrease of surface area of AC/CNTs-1% composite as compared to AC-pristine due to the blocking of micropores of AC. The SEM images evidenced good connection between CNTs and AC particles, where the fibrils of CNTs were featured as the electrical bridges to improve the electron transfer between the AC particles in the electrode structure. Comparison of the CDI performance of AC/CNTs-1% composite electrode in two regimes (batch mode and single-pass mode) in Ragone plot showed that the single-pass mode provided the essential factors of salt absorption capacity and average salt adsorption rate which shifted toward much upper and right regions, indicating the superior desalination performance. At the operation of 1.2 V, the batch mode and single-pass mode can deliver the salt absorption capacity of 10.93 mg g−1 and 11.97 mg g−1, respectively. The durability test of our CDI system in single-pass mode showed a stable performance on 100 cycles with the energy consumption of 0.284 kWh m−3 which is suitable for large-scale CDI applications using the renewable energy sources.