Enhanced capacitive deionization desalination provided by chemical activation of sugar cane bagasse fly ash electrodes

•Modified biowaste SCBFA was successfully employed as an AC precursor for CDI electrodes.•Activation of SCBFA by ZnCl2 provoked charge efficiency issues related with residual Zn.•Activation with KOH led to a surface area enlargement, a higher amount of SOG and an increase in specific capacitance.•Occurrence of alcohol/ether groups reduced carbon hydrophobocity improving salt adsorption kinetics.•SCBFA activated by KOH showed a competitive CDI performance with respect to a commercial activated carbon.

Sugar Cane Bagasse Fly Ash (SCBFA) is an abundant low-cost high content carbon bio-waste material. In this manuscript, different chemical activation agents, such as ZnCl2 and KOH, have been explored as a mean of improving physical and electrochemical properties of SCBFA as an electrode material for capacitive deionization (CDI). The study determined that the activation with high mass ratios of ZnCl2 led to a low electrosorption of salt and high charge density. These results seemed to be a consequence of the residual Zn that led to parasitic reactions reducing charge efficiency. An intensive cleaning procedure resulted in a higher electrosorption due to a reduction of Zn contain although complete Zn removal was not achieved and this might pose eventual environmental issues. KOH activation had a significant positive impact on enlarging the specific surface area and increasing the number of polar surface oxygen groups (SOG). These modifications led to a large increase in specific capacitance (from 12 to 72-86 F g−1) and salt adsorption capacity (48-74%). Moreover, SOG increment reduced the SCBFA hydrophobicity improving ion transport and leading to faster electrosorption kinetics. These findings support the potential of chemically activated SCBFA as a CDI electrode material for brackish water desalination.

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