Star-concave iron-metal-organic frameworks with enhanced light trapping for boosting synergistic adsorption-photoreduction of the dominant chromium species

Creating a specific shape with hierarchically porous structure of metal-organic frameworks represents an effective strategy to enhance the adsorption and photocatalytic performance yet remains rather challenging. Herein, we present a facile linker competitive coordination induced interface assembly strategy to synthesize a series of star-concave metal-organic frameworks (MOFs) (Fe-MIL-101) with rich hierarchical pores. This strategy of star-concave Fe-MIL-101 depends on the electronegativity difference of the two linkers to produce an in-situ oriented growth with controllable kinetics nucleation and structural evolution. As a result, the optimized star-concave Fe-MIL-101-2 with multiple physical-chemical effects endows enhanced visible-light trapping, preferred charge separation, and optimized the local electronic structure. In comparison with the slightly concave Fe-MIL-101 and solid octahedron Fe-MIL-101-NH₂, the star-concave Fe-MIL-101-2 displays a clear superiority in the adsorption-photoreduction of Cr(VI) under visible-light irradiation. Furthermore, the X-ray absorption fine structure spectroscopy, finite element method, and density functional theory calculations are performed to reveal the local electronic structure of star-concave Fe-MIL-101-2, understanding the mechanisms behind the boosting synergistic adsorption-photoreduction of Cr(VI) removal performance. This work provides a new perspective for the rational construction of MOFs-based photocatalysts with high activity for Cr(VI) removal through shape engineering.