Photocatalytic reduction of CO2 based on a CeO2 photocatalyst loaded with imidazole fabricated N-doped graphene and Cu(II) as cocatalysts

Cocatalysts are vital for improving photocatalytic activity. Incorporating nitrogen atoms on a graphene frame using an imidazole cycle resulted in a new N-doped graphene (denoted as ING). Cerium(IV) oxide (CeO2) nanoparticles were dispersed on ING sheets, producing an ING/CeO2 hybrid material. The ING/CeO2 hybrid material was characterized using X-ray diffraction, transmission electron microscopy, Raman spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy and surface photovoltage spectroscopy. Copper(II) ions [Cu(II)] were adsorbed on the ING/CeO2 hybrid material to directly form Cu(II)/ING/CeO2, which could capture the photogenerated electrons to reduce carbon dioxide (CO2) to methanol (CH3OH) under incident light irradiation. The results showed that the yield from reducing CO2 to CH3OH during the photocatalytic process using Cu(II)/ING/CeO2 as the photocatalyst approached 385.8 μmol g−1 cat. h−1, whereas the yield was only 3.57 μmol g−1 cat. h−1 using ING/CeO2 as the photocatalyst. This shows that the Cu(II) ions play a vital role during photocatalytic reduction of CO2 by forming copper(I) ions [Cu(I)]. The percentage of ING in the ING/CeO2 hybrid material was investigated, and the results indicated that 3.6% of ING achieved an optimal yield of CH3OH during the photo-reduction process. The simultaneous roles of Cu(II) ions and ING sheets demonstrate a synergistic strategy for improving the photocatalytic CO2 reduction.