Investigating replacement core-shell strategies for optimizing photocatalytic chromium reduction with MOF-on-MOF heterostructure on steel mesh

While cerium-based metal-organic frameworks (Ce-MOFs) exhibit inherent limitations in standalone photocatalytic efficacy, their potential amplifies when integrated into heterostructures with other semiconductors, leveraging the advantageous heterojunction effects. This study systematically explores the establishment of heterojunctions between Ce-MOFs and zirconium-based frameworks, delineating the performance variance based on the positioning of Ce-MOFs within the MOF-on-MOF architecture. When situated as the outer shell in these configurations, Ce-MOFs significantly enhance the photocatalytic capabilities compared to their placement in the core. Further, immobilizing these composite structures onto steel substrates demonstrates remarkable efficiency in the purification of hexavalent chromium from water under visible light exposure. Initially, Ce-MOF-801-on-ZrMOF-801 and Zr-MOF-801-on-Ce-MOF-801 heterojunctions were synthesized to explore their combined and MOF-on-MOF effects. Subsequently, Ce-MOF-801-on-Zr-MOF-801 was applied onto a steel mesh substrate using the spraying method. The results demonstrated exceptional efficiency in Cr(VI) extraction and remarkable durability. Crucially, leaching tests and ICP-OES analysis confirmed the material's strong adhesion to the substrate, enabling repeated use. Impressively, even after multiple cycles, the material efficiently purified Cr(VI) from water within 120 min under visible light. With all these merits, the Cr(VI) removal efficiency of Ce-MOF801-on-Zr-MOF-801/mesh with an initial Cr(VI) concentration of 5 ppm is near 100% for 2 h. This work presents a feasible and promising route to filter suitable photocatalyst materials by using mesh substrates for fixing environmental issues.