Preparation of Ni/Co Composite Materials Based on Cucurbit[6]uril and Their Photothermal Synergistic Catalysis for Nitrogen Reduction to Ammonia under Mild Conditions

Cucurbit[n]urils, owing to their unique structural features, exhibit versatility in performing tasks such as adsorption, detection, and catalysis. However, the scope of their catalytic applications remains limited, primarily because most Cucurbituril-based catalytic reactions take place in either aqueous or organic phases. In this study, we have successfully synthesized porous honeycomb composites of cucurbit[6]uril with cobalt and nickel (denoted as Q[6]@Co and Q[6]@Ni, respectively) and applied them in a photothermal synergistic heterogeneous gas-solid reaction for the reduction of nitrogen to ammonia under mild conditions. This represents a groundbreaking achievement, as it is the first instance where a cucurbit[n]uril-based material has demonstrated catalytic functionality in its solid-state form, thereby introducing a novel concept for the design and application of cucurbit[n]uril-based photocatalysts. To characterize the structure of these composites, we employed a range of techniques including XAFS (X-ray Absorption Fine Structure), TEM (Transmission Electron Microscopy), SEM (Scanning Electron Microscopy), XPS (X-ray Photoelectron Spectroscopy), and H2-TPR (Hydrogen Temperature-Programmed Reduction). Our findings revealed that Q[6]@Ni exhibits higher photothermal catalytic ammonia synthesis activity compared to Q[6]@Co. This enhanced activity is attributed to the strong metal-support interaction (MSI) between Ni and Q[6], which facilitates electron transfer and nitrogen activation. Furthermore, the thermal source promotes the transition of electrons from the valence band to the conduction band, thereby enhancing the cleavage of the N≡N bond. Notably, the band gaps of Q[6]@Co and Q[6]@Ni are significantly reduced. In particular, Q[6]@Ni demonstrates the highest efficiency in electron-hole pair separation, as evidenced by PL (Photoluminescence) and EIS (Electrochemical Impedance Spectroscopy) measurements. Overall, Q[6]@Co/Ni provides an effective pathway for nitrogen reduction under mild conditions and advances the application of Cucurbituril-based materials in photothermal catalysis. This work also contributes to the development of environmentally sustainable ammonia synthesis technology.