Abstract:
Traditional water supplies are increasingly inadequate due to climate change and population growth, making the need for effective wastewater treatment crucial. Desalination of brackish water is necessary but costly. Among various strategies, capacitive deionization (CDI) stands out for its low energy consumption and environmental sustainability. CDI removes salt ions from solutions, storing them in electric double layers, without membranes and at lower pressures, thus offering a promising method for reducing freshwater scarcity. However, CDI systems face limitations due to low charge efficiency and reduced influent concentrations in carbon electrodes. Ion exchange membranes (IEMs) in membrane CDI (MCDI) are a popular solution, but this research aims to enhance CDI performance without IEMs. The dissertation focuses on improving CDI energy and salt removal efficiency and evaluating performance across various material designs. Six different CDI materials were developed: Activated carbon with (i) physical activation (ACpa), (ii) physio-chemical activation (ACpc), and shape-dependent polyaniline (PANI) with (iii) Nanorod (NR-PANI), (iv) Nanotube (NT-PANI), (v) Nanofiber (NF-PANI), and (vi) AC-PANI composite using the best-performing AC and PANI materials as electrodes. The study assessed the desalination performance (Na+/Cl-) and heavy metal deionization (Ni2+/Cl- and Co3+/NO3-) of these materials, focusing on their impact on electrode performance in water using CDI. Structural and chemical properties were analyzed using techniques such as field emission scanning electron microscopy (FE-SEM), Brunauer–Emmet–Teller (BET) analysis, energy dispersive X-ray (EDX), and Fourier-transform infrared spectroscopy (FTIR). Electrochemical properties were evaluated using cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) tests, revealing no faradic response behavior.
The AC-PANI composite electrode demonstrated the highest specific capacitance (165 F/g) at a current density of 0.7A/g, outperforming PANI (NT-PANI=110 F/g, NR-PANI=70 F/g, NF-PANI=50 F/g) and AC (ACpc=123 F/g, ACpa=80 F/g). It also exhibited the highest electrosorption capacity (147 mg/g) for removing saline ions from a 100 ppm NaCl solution, surpassing ACpc (96 mg/g), ACpa (80 mg/g), NF-PANI (73 mg/g), NR-PANI (70 mg/g), and NT-PANI (84 mg/g) electrodes. Furthermore, the AC-PANI composite showed outstanding electrosorption for removing heavy metal ions (Ni2+ and Co3+) from 100 ppm NiCl2 and Co(NO3-)3 solutions. This research confirms the superior CDI performance of the AC-PANI composite for desalination and deionization compared to individual AC and PANI electrodes, suggesting its potential for improving CDI systems in the desalination of brackish water.