Hierarchically porous biocarbons prepared by microwave-aided carbonization and activation for capacitive deionization

Abstract Capacitive deionization (CDI) is an emerging technology for the energy-efficient and cost-effective removal of ions from salt water by electrosorption. To further enhance the capacitive deionization performance, sugarcane bagasse biowastes are used as raw materials to synthesize biomass-derived electrodes via microwave carbonization and activation assisted with potassium hydroxide in the flows of carbon dioxide, which has the advantages of reducing preparation time and saving energy. Experimentally, the effect of microwave power (500–800 W) has been studied on the morphology, the ratios of mesoporosity in the biocarbons and their corresponding desalination performance of CDI. Accordingly, the biocarbons which are activated at 700 W of microwave irradiation under carbon dioxide atmosphere (denoted as SB-CO2–700) possess the higher fraction of mesopore to total pore volume (ca. 64.1%) with surface area (764 m2 g−1). By using cyclic voltammetry, the specific capacitance of SB-CO2–700 is calculated to be ca. 123 F g−1 at 5 mV s−1. With the superior properties (greater fraction of mesopore to total pore volume, reasonable surface area and hierarchical porosity), the electrosorption capacity of SB-CO2–700 samples is estimated to be 11.4 mg g−1 in 10 mM of NaCl solution at 1.2 V. These low-cost biowastes-derived hierarchically porous carbons prepared by time and energy saving route may provide a potential electrode for CDI applications.