Valence regulation of ultrathin cerium vanadate nanosheets for enhanced photocatalytic CO₂ reduction to CO

Atomic valence state regulation is an advantageous approach for improving photocata-lytic efficiency and product selectivity. However, it is difficult to precisely control the ratio of the different valence states on the surface and the relationship between the surface valence change and catalytic efficiency in the photocatalytic reaction process is unclear. Herein, CeVO4 ultrathin nanosheets were fabricated by one-step solvothermal method with ethanolamine (MEA) as the structure-directing agent. The ratio of the concentrations of intrinsic Ce⁴⁺ and Ce³⁺ ions is precisely modulated from 19.82:100 to 13.33:100 changed by the volume of MEA added without morphology modification. The photocatalytic efficiency increases as the concentrations of intrinsic Ce⁴⁺ and Ce³⁺ ions decrease and CV3 (prepared with 3 mL of MEA) shows the highest CO generation rate approx-imately 6 and 14 times larger than CV (prepared without MEA) and CV1 (prepared with 1 mL of MEA), respectively, in the photocatalytic CO2 reduction. Interestingly, about 6.8% photo-induced Ce⁴⁺ ions were generated on the surface of the catalysts during the photocatalytic CO2 reduction without any phase and morphology changes for CV3. The photocatalytic reaction mechanism is proposed considering the intrinsic and photo-induced Ce⁴⁺ ions to obtain efficient photocatalysts.