5,7,12,14-Pentacenetetrone as a cation storage electrode enabling preferential extraction and recovery of Ca2+and Mg2+

Due to the abundance of calcium and magnesium in the Earth's crust, Ca2+ and Mg2+ are universally present in natural saline water sources and industrial wastewater generated while converting calcium- and magnesiumcontaining ores to chemicals. The ability to extract Ca2+ and Mg2+ from these water sources can offer new opportunities in (waste)water treatment because their extraction can mitigate scaling problems in various water treatment applications and the extracted ions can be used to store captured CO2 as CaCO3 and MgCO3. In this study, we investigated the feasibility of using an ion-storage electrode to electrochemically extract Ca2+ and Mg2+ from feed water and recover them in a separate cell as useful chemicals. We demonstrate that 5,7,12,14pentacenetetrone (PT) can preferentially extract Ca2+ and Mg2+ over Na+ while maintaining a stable capacity over a wide pH range (pH 3-12). Due to PT's stability in basic media, it is possible to recover the extracted Ca2+ as CaCO3 in basic media where Na+ is highly soluble. As a result, although PT's divalent ion selectivity is modest, the co-extracted and co-released Na+ does not interfere with the separation and collection of CaCO3. This work presents a new route to electrochemically extract and convert Ca2+ and Mg2+ into valuable chemicals.