Magnetic Hollow Spheres Assembled from Graphene-Encapsulated Nickel Nanoparticles for Efficient Photocatalytic CO2 Reduction

The exploitation of efficient, robust, and easily recyclable catalysts is highly desirable for photochemical CO2 reduction to produce fuels and chemicals. Herein, we demonstrate the preparation of Ni@GC magnetic hollow spheres composed of metallic Ni nanoparticles surrounded by few-layered graphitic carbon (GC) for photocatalytic CO2 reduction with high efficiency. The Ni@GC hollow spheres were prepared by thermal annealing a Ni-containing metal–organic framework (Ni-MOF) under N2 atmosphere. A series of physiochemical characterizations reveal that the Ni@GC hollow spheres are successfully synthesized with large surface area and highly porous structure. In the presence of Ni–C bonding, the porous Ni@GC material can efficiently accelerate the separation and transportation of photoexcited charges, as well as improve CO2 adsorption. With the cooperation of a ruthenium photosensitizer under visible light irradiation, the Ni@GC catalyst exhibits a high CO2-to-CO conversion activity, giving a superior CO-production rate of 27 μmol h–1 (e.g., 9.0 mmol h–1 g–1). Moreover, the Ni@GC photocatalyst is highly stable and can be separated easily by a magnetic field for reuse. The possible photosensitized CO2 conversion mechanism is also proposed based on the relative energy levels of the Ni@GC catalyst and the ruthenium photosensitizer.