A coupling technology of capacitive deionization and MoS/nitrogen-doped carbon spheres with abundant active sites for efficiently and selectively adsorbing low-concentration copper ions.

Conventional techniques like electrodialysis, evaporation concentration cannot efficiently and selectively separate valuable heavy metals ions (VHMI) from electroplating rinse wastewater due to VHMI's low concentration and other ions' competitive adsorption. To realize the separation, a coupling technology was proposed which combines capacitive deionization (CDI) technique suitable for separating low-concentration ions and the few-layer molybdenum disulfide/N-doped carbon spheres (FL-MoS/NCS) composite capable of selectively adsorbing copper ions (Cu), a representative VHMI. The FL-MoS/NCS composite was successfully prepared by one-pot method and used as the cathode and anode in a CDI cell. Electrosorption experiments in the CDI cell showed that the FL-MoS/NCS electrode (cathode) can efficiently adsorb low-concentration Cu (23.63 mg/L) with a saturated adsorption capacity of 1199.63 mg/g at 0.8 V. In the competitive environment (Cu/Na/Fe), the FL-MoS/NCS electrode can selectively adsorb Cu still with a high adsorption capacity of 1071.6 mg/g greatly outnumbering that of Na (199.2 mg/g) and Fe (262.8 mg/g), despite the high concentrations of both NaCl (500 mg/L) and FeCl (80 mg/L). Furthermore, the XPS test and competitive adsorption results proved that the efficient and selective adsorption of the FL-MoS/NCS electrode for Cu was synergistically promoted by electrical double layer (EDL) and complexation of Cu with FL-MoS/NCS.