A mild one-step method for enhancing optical absorption of amine-functionalized metal-organic frameworks

Metal-organic frameworks (MOFs) are of significant interest for photocatalysis using visible light. Here we discuss HOMO/LUMO gap modification of amine-functionalized MOFs through a mild one-step method. DFT calculation reveals the formation of covalent bond between TiO2 and the amine from NH2-MIL-125, narrowing the HOMO/LUMO gap of NH2-MIL-125 by raising its HOMO level. After CdS quantum dots (QDs) deposited on this MOF@TiO2 core-shell structure, this composite catalyst can act as an efficient visible-light-driven catalyst for NO removal. The integral coating of amorphous TiO2 onto MOF octahedrons constructs a mesoporous protection shell upon MOF frameworks, providing a superior accommodation for embedding CdS QDs. Integrating MOF with TiO2 also reduces undesirable electron-hole recombination by facilitating charge transfer to amorphous TiO2. Possible mechanism of photocatalytic oxidation of NO over CdS/NH2-MIL-125@TiO2 catalysts is proposed. This work illustrates the possibility of tuning the optical response of NH2-MOFs under very mild condition, and demonstrates the potential usage of MOF-based heterostructured photocatalysts.