3D printing of a photo-curable hydrogel to engineer mechanically robust porous structure for ion capture or sustained potassium ferrate(VI) release for water treatment

[Display omitted] •In-place UV irradiation-coupled with extrusion-type printer was used to crosslink hydrogel-based ink.•Crosslinked hydrogel-based inks showed a shear-thinning behavior with improved recoverable matrix.•A hierarchically porous capsule-like object was engineered, meeting a prerequisite for potential application in water purification.•3D-printed capsule-like object including ferrate were used for the degradation of toxic organic pollutants.•The printed capsule-like objects were stable and effective for more than one month. Contaminated water and scarcity of clean water are becoming progressively serious environmental concerns. Removal of hazardous pollutants from wastewater is vital and urgently needed attention for the protection of pure water resources. To tackle the aforementioned challenges, macroporous structures have great potential to be used in the treatment of heavy metal ions to improve the adsorption efficiency and sustainability of wastewater treatment methodologies. In this context, additive manufacturing technologies have gained considerable attention because of their ability to construct intricate macroporous shapes with multifunctionalities using diverse materials. Here, we used a photocrosslinking graft copolymerization of polyvinyl alcohol/acrylic acid-based ink using UV irradiation in the presence of Norrish type II photosensitizer through a hot-melt extrusion-type 3D printer to improve the printing quality of crosslinked ink. The photocured inks offered strong shear-thinning behavior that allowed layer-by-layer deposition to generate well-defined 3D structures, while having sufficiently high viscoelasticity to retain the shape after printing process. With an adequate viscosity at the higher extrusion shearing forces, the 3D printed structures could create multifaceted self-supporting scaffolds with an internal lattice structure that possesses high level of porosity. The hierarchically porous structure of 3D objects showed a recoverable structure yet robust matrix, offering more specific surface area, capable of effectively removing heavy metal ions from water with fast-responsiveness and a high capacity. The ferrate(VI)-contained 3D capsule-like object was also detected to be efficient regarding chemical oxygen demand reduction and decolorization of real wastewater. Such 3D-printed hierarchical macroporous objects can offer great prospects in the treatment of water and wastewater purification applications.