Study of sugar cane bagasse fly ash as electrode material for capacitive deionization

• Sugar cane bagasse fly ash (SCBFA) was successfully employed as CDI electrodes.
• Thermal treatment of SCBFA strongly improved electrosorption of salts.
• Higher presence of surface oxygen groups was detected for the SCBFA heated at 200 °C.
• T200 showed the highest specific capacitance (55 F g−1) and salt removal (6.2 mg g−1).
• The extremely low cost of the SCBFA makes it highly competitive for CDI applications.

An abundant low-cost biowaste material such as sugar cane bagasse fly ash (SCBFA) was evaluated in this work as a capacitive deionization (CDI) electrode for brackish water desalination applications. A thermal treatment of SCBFA at different temperatures (200–800 °C) was explored as a way to improve structural and electrochemical properties. Pyrolysis at 200 °C resulted in an increase of the surface oxygen groups (SOG) that drastically improved electrode wettability. As a consequence, not only specific capacitance values increased (from 33 to 55 F g−1) but also maximum salt adsorption capacity (mSAC, from 2.9 to 5.3 mg g−1). Higher temperatures led to higher specific surface areas materials but also to the decomposition of SOG. This resulted in lower mSAC values but still higher than pre-heated SCBFA. Under brackish water concentrations (40 mM NaCl) the observed mSAC values reached 6.2 mg g−1, showing the potential of the T200 material as CDI electrode.

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