Solar Heating Enhanced Selective Recovery of Metal Ions Through Flowing Electrodes Enabled by Hybrid Carbon Nanostructures

Abstract Capacitive deionization (CDI) based on flowing electrodes is a promising technique for large-scale recycling of valuable yet toxic ions from wastewater. The selectivity between a target and competing ions is, however, unsatisfying due to insufficient differences in transport kinetics for different types. Herein, a photothermal-enhanced CDI system is constructed for the selective recovery of Ni2+ (a typical element in electroplating and battery industries), in which the transport kinetics are enhanced to varying extents for various types of ions under solar irradiation. The strategy is based on the photothermal effect of a microporous hybrid of carbon nanoplatelets and nanotubes, whereby the temperature rises efficiently upon irradiation with sunlight. With a temperature increase from 10 °C to 55 °C, the Ni2+ recovery rate is increased by 250%, the selectivity toward Ni2+ is increased by 53%, while the energy consumption is decreased by 51%. Furthermore, it is found that divalent cations containing moderate 3d-orbital electrons (Ni2+, Mn2+, and Co2+) exhibit the strongest sensitivity to temperature, suggesting a more favorable adsorption tendency toward these ions at elevated temperatures. The photothermal enhanced CDI system, based on porous and microcrystalline carbons, provides a powerful approach to treat various wastewater containing value-added resources.