Mesoporous carbon materials derived from artocarpus heterophyllus for water desalination and defluoridation using capacitive deionization

Abstract

Sustainable clean water for human use can be attained through cost-effective water purification technologies whereby capacitive deionization (CDI) technology is among them. To attain high CDI performance porous carbon materials with high surface area, specific capacitance, and good chemical stability are essential. In this study, high surface area mesoporous carbon has been synthesized from jackfruit peels (Artocarpus heterophyllus) through chemical activation method. Two different activation routes were used; carbonization followed by KOH activation and direct activation with H 3 PO 4 . In KOH activation route, the activation process was done by varying activation temperature from 600 to 800 ˚C and KOH to carbon ratio (KOH/C) from 1 to 3 for 1 h. In H 3 PO 4 route, activation was done by varying concentration of H 3 PO 4 from 10 to 35% and activation temperature from 450 to 550 ˚C for 1 h. The textural properties of the synthesized jackfruit activated carbon (JFAC) and electrochemical characteristics of the fabricated electrodes were found to be influenced by activating agent ratio/concentration and activation temperature. The synthesized JFAC possess a honey comb-like structure with plentiful mesopores at a pore size range of 3.0-5.0 nm which are beneficial for electrosorption. The BET surface area and pore volume of the carbonized jackfruit peels (JFC) increased from 607 to 2681 m 2 /g and 0.52 to 2.61 cm 3 /g respectively, upon activation with KOH/C ratio of 2 at 800 °C. Nitrogen adsorptiondesorption studies revealed that the synthesized JFAC is mainly mesopores characterized by type IV isotherms according to IUPAC classification. Desalination experiments were carried out with 30 to 500 mg/L NaCl solution in batch mode at a flow rate of 2.5 mL/min while applying a voltage of 1.2, 1.4 and 2.0 V to the cell. The electrosorption capacity and saltremoval efficiency increased with increasing BET surface area and applied potential. Among the samples studied, carbon produced with KOH/C ratio of 1 at 700 ˚C (JFAC-1-700) exhibited the highest specific capacitance of 307 F/g, high salt removal efficiency and electrosorption capacity of 5.74 mg/g when voltage of 2 V was applied. When JFAC electrodes were studied for natural water defluoridation, it was found that JFAC CDI electrodes could remove fluoride (Fˉ) from natural water containing low Fˉ concentrations to the permissible limits set by the World Health Organization (WHO). Maximum Fˉ adsorption efficiency (62%) and electrosorption capacity (0.13 mg/g) were attained with applied voltage of 2 V and the pH of water remained unaffected. These results indicated that the Artocarpus heterophyllus peels can be the promising CDI electrode materials for low salinity water desalination and defluoridation.