Oxygen-Vacancy-Activated CO₂ Splitting over Amorphous Oxide Semiconductor Photocatalyst

Gaseous oxides generated during industrial processes, such as carbon oxides (CO x ) and nitrogen oxides (NO x ), have important effects on the Earth’s atmosphere. It is highly desired to develop a low-cost and efficient route to convert them to harmless products. Here, direct splitting of gaseous oxides was proposed on the basis of photocatalysis by an amorphous oxide semiconductor. As an example, splitting of CO 2 into carbon and oxygen was achieved over amorphous zinc germanate (α-Zn-Ge-O) semiconductor photocatalyst under 300 W Xe lamp irradiation. Electron paramagnetic resonance and 18 O isotope labeling indicated that the splitting of CO 2 was achieved via photoinduced oxygen vacancies on α-Zn-Ge-O reacting and thus filling with O of CO 2, while the photogenerated electrons reduced the carbon species of CO 2 to solid carbon. Under irradiation, such a defect reaction is sustainable by continuous photogenerated hole oxidation of surface oxygen atoms on α-Zn-Ge-O to form oxygen vacancies and to release O 2 . When we used H 2 O or NO in place of CO 2, H 2 and O 2 or N 2 and O 2 were evolved, respectively, indicating the same mechanism can also split H 2 O or NO.