A high-performance carbon electrode is desirable for promoting electrochemical desalination efficiency in the membrane capacitive deionization (MCDI). Sugarcane bagasse (food waste) was employed in this study to prepare hierarchically porous biochars by microwave-assisted carbonization and activation with potassium hydroxide in N2 or CO2 atmosphere under varying flow rates (100-600 cm3 min−1). The sugarcane bagasse-derived biochars activated under CO2 flow of 300 cm3 min−1 (denoted as SBB-CO2-300) possessed the ratio of mesopores to total pore volume (Vmeso/Vtotal) of 56.7% with a specific surface area of 1019 m2 g−1. The electrochemical behavior of SBB-CO2-300 was demonstrated by a surpassing specific capacitance of 208 F g−1 at 5 mV s−1 by means of cyclic voltammetry. The desalination tests using a batch-mode MCDI at 1.2 V in a 5 mM NaCl solution indicated that the SBB-CO2-300 electrode exhibited an excellent electrosorption capacity of 28.9 mg g-1. The improvement in the electrochemical deionization performance of SBB-CO2-300 was attributed to the superior Vmeso/Vtotal ratio, high surface area, excellent capacitance behavior, and hierarchical pore structure. The biowaste-derived biochars prepared via facile microwave-assisted carbonization and CO2 activation route can provide a sustainable and high-efficiency carbon electrode for electrochemical deionization of brackish water.
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