Photo-Induced Construction and Recovery of Cu + Sites in Metal-Organic Frameworks.

The adjustment of the valence state of metal ions is crucial for various applications because peculiar activity originates from metal ions with specific valence. Cu + can interact with molecules possessing unsaturated bonds like CO via π-complexation, while Cu 2+ doesn't have such ability. Meanwhile, Cu + sites are easily oxidized to Cu 2+ , leading to the loss of activity. Despite great efforts, the development of a facile method to construct and recover Cu + sites remains a pronounced challenge. Here, for the first time a facile photo-induced strategy is reported to fabricate Cu + sites in metal-organic frameworks (MOFs) and recover Cu + after oxidation. The Cu 2+ precursor was loaded on NH 2 -MIL-125, a typical visible-light responsive Ti-based MOF. Visible light irradiation triggers the formation of Ti 3+ from Ti 4+ in framework, which reduces the supported Cu 2+ in the absence of any additional reducing agent, thus simplifying the process for Cu + generation significantly. Due to π-complexation interaction, the presence of Cu + results in remarkably enhanced CO capture capacity (1.16 mmol g -1 ) compared to NH 2 -MIL-125 (0.49 mmol g -1 ). More importantly, Cu + can be recovered conveniently via re-irradiation when it is oxidized to Cu 2+ , and the oxidation-recovery process is reversible.