Block copolymer coated carbon nanotube membrane anodes for enhanced and multipurpose hybrid capacitive deionization

Carbon nanotube (CNT) membranes are widely used electrode materials in capacitive deionization (CDI) processes, while the limited electrosorption capacity and poor long-term stability need to improve. In this work, a pH-responsive block copolymer (BCP), poly (2-dimethylaminoethyl methacrylate)-block-polystyrene (PDMAEMA-b-PS) is combined with the selective swelling to fabricate a CNT membrane based multipurpose electrode. After BCP coating and selective swelling, the PDMAEMA blocks migrate onto the membrane surface and protonate during the CDI processes, which enhance the attraction between electrode and anions. Therefore, the BCP coated electrodes can be used as high performance anodes in the hybrid CDI (HCDI) module. Experiment results show that the initial solution pH values have significant influence on the CDI performance of the HCDI module. The maximum removal efficiencies of the HCDI module towards NaCl and NaH₂PO₄ are ~15 mg·g⁻¹ and ~38.7 mg·g⁻¹, respectively. Moreover, the chemical and mechanical stabilities of the anodes are significantly enhanced. No anode oxidation can be observed during CDI processes and the frequently occurred co-ion repulsion effect is suppressed. Considering these advantages, the combination of BCPs and selective swelling will be a promising candidate for the development of HCDI module.