Capacitive Deionization with Titania and Amine Modified Activated Biochar

Abstract

Capacitive deionization based on electrosorption has become a viable process for brackish water desalination. In this study, activated biochar was employed as a low-cost carbon-based electrode material with comparable adsorption capacity to activated carbon and other biomass derived materials. Modification of the activated biochar was done by amine functional group grafting and metal oxide incorporation to improve ionic transport, and cation/anion selectivity, reducing the co-ion effect. Cation and anion selective electrodes were prepared by using titanium dioxide, and 3-aminopropyltriethoxysilane (3-APTES) via diazonium salt activation. These modified biochar electrodes were physically characterized by SEM-EDX, TEM, XPS, and XRD. Cyclic voltammetry, galvanostatic charge/discharge measurements, and impedance spectroscopy were performed to analyze the electrochemical property of both types of electrodes. This study investigated salt removal capacity of NaCl and NaF solutions using chloride and fluoride ion-selective electrode. Three different asymmetrical CDI cell designs (TB cathode – AmB anode, TB cathode – AcB anode, and AcB cathode – AmB anode) and two symmetrical cell designs AcB anode – AcB cathode and TB anode – TB cathode) were tested. Titania, amine, and activated biochar electrodes are denoted as TB, AmB, and AcB, respectively. It was found that a symmetric cell design with titania modified biochar electrodes show a 30% better removal capacity than the other cell designs. This work shows that biochar can be modified and explored broadly as an inexpensive alternative electrode material for capacitive deionization.