Self-Assembly of CDs@NH2-MOF(Ni)/n-Bu4NBr and its Catalytic Performance for CO2 Fixation with Epoxides

Metal–organic frameworks (CDs@NH2-MOF(Ni)) with carbon dots as the core were synthesised successfully by a one-pot method. The synthesised CDs@NH2-MOF(Ni) contain a large number of amine functional groups and a large surface area for capturing CO2. The FT-IR spectra showed that there exists a large number of carboxylate and amine groups on the surface of the carbon dots, and analysis by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetric, and Brunauer–Emmett–Teller surface area analysis confirmed that the CDs had successfully entered the CDs@NH2-MOF(Ni). The cycloaddition reaction of propylene oxide (PO) and CO2 was carried out using CDs@NH2-MOF(Ni)/tetra-n-butylammonium bromide (TBAB) and NH2-MOF(Ni)/TBAB as catalytic systems, respectively. The reaction results showed that the two catalytic systems have good catalytic performance for the cycloaddition reaction of PO and CO2. Compared with that of the NH2-MOF(Ni)/TBAB system, both the conversion of PO and the yield of propylene carbonate (PC) are improved in the CDs@NH2-MOF(Ni)/TBAB system. Finally, the optimum catalytic reaction conditions, such as time, temperature, CO2 pressure, and five cycles of catalytic effect, were also discussed. Meanwhile, the mechanism of the catalytic system CDs@NH2-MOF(Ni)/TBAB in the cycloaddition reaction of PO and CO2 was proposed in this work.