Interfacial and build-in electric fields rooting in gradient polyelectrolyte hydrogel boosted heavy metal removal

With the aggravation of pollutants damage to the environment, it is crucial yet rather challenging to design powerful matrixes for nanomaterials with high ions permeability and migration, as well as multiple exposed active sites. However, most of the current nanomaterial matrixes just act as carrier supporters with introduced invalid mass. Here, a gradient natural polycation electrolyte (chitosan) hydrogel was engineered as nanomaterials matrix to boost anionic heavy metals removal such as antimonate (Sb(V)) and arsenate (As(V)) for the first time, based on the generated interfacial and build-in electric potentials due to the diffusion of counterions. The resulting dual electric potentials allow for rapid diffusion and removal efficiency of heavy metal ions. Exemplified by Sb(V) removal, the chitosan gradient hydrogel matrixes with embedded UiO-66 MOFs exhibited a 3-fold higher removal velocity than the homogeneous hydrogel matrix, and their removal efficiencies were also promoted by gathering on the high charge density side of hydrogels. In contrast to the other reported matrix materials without driving force, the gradient polyelectrolyte hydrogel can greatly boost the removal efficiency and shorten the treatment times. This study offers inspirations on eliminating heavy metal contaminations based on self-driving forces stemming from the heterogeneous structure of materials.