A Novel Mn-Based Film with Oxygen Vacancy for Efficient and Selective K⁺ Separation

In this study, a novel electrical Mn-based film was developed for selective potassium (K+) separation, in which delaminated MnOx was obtained with the assistance of Ho3+ using a facile coprecipitation method and coated on carbon paper with poly(vinylidene fluoride) (PVDF) and graphitized carbon black. With the scanning electron microscope (SEM) and transmission electron microscope (TEM) observations, it was found that abundant multiphase interfaces and lattice dislocations appeared on the bulk of Ho-MnOx. Brunauer–Emmett–Teller (BET) analysis verified that the delamination assisted by Ho3+ increased the specific surface area from 110.3 m2/g (MnOx) to 166.8 m2/g (1% Ho-MnOx), which should be beneficial for the exposing of more electrochemical active areas and active sites for K+ adsorption and separation. Particularly, 1% Ho-MnOx had a high concentration of oxygen vacancies and showed a better K+ adsorption ability than MnOx. It was considered that the adsorption of K+ was mainly affected by the ion memory toward K+ for the 1% Ho-MnOx. In addition, the 1% Ho-MnOx film had good stable retention and regeneration capability for the separation of K+; after 10 cycles of adsorption and desorption, the film still retained 87.24% of the maximum adsorption capacity for K+. It is expected to provide an effective preparation method to obtain a high-performance K+ removal film electrode for the separation of K+ under a low concentration.