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

Abstract

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.