Cobalt Hydrogen-Bonded Organic Framework as a Visible Light-Driven Photocatalyst for CO₂ Cycloaddition Reaction

A novel cobalt hydrogen-bonded organic framework (Co-HOF, C₂₄H₁₄CoN₄O₈) was synthesized from a mixed linker, that is, 2,5-pyridinedicarboxylic acid (PDC) and 2,2'-bipyridyl (BPY) linkers and cobalt ion through a simple, one-pot, low-cost, and scalable solvothermal method. The Co-HOF was fully characterized using several analytical and spectroscopic techniques including single-crystal X-ray diffraction, diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray, and X-ray photoelectron spectroscopy. The Co-HOF exhibits high thermal and chemical stabilities compared to previously reported HOF materials. Moreover, Co-HOF shows excellent photocatalytic activity under visible light irradiation due to its narrow band gap of 2.05 eV. The cycloaddition reaction of CO₂ to variable epoxides was investigated to evaluate the photocatalytic performance of Co-HOF under visible light radiation and was found to produce the corresponding cyclic carbonates in yields up to 99.9%.