Bi quantum dots obtained via in situ photodeposition method as a new photocatalytic CO2 reduction cocatalyst instead of noble metals: Borrowing redox conversion between Bi2O3 and Bi

Abstract

Metal Bi is applied as the cocatalyst instead of noble metals, for the first time, in photocatalytic CO2 reduction and exhibits significant increase in CO yield compared to that of pristine photocatalyst, about 4.8 times. In situ photodeposition method is used to prepare metal Bi. Surprisingly, the average size of metal Bi obtained is ca. 5 nm and can be considered as quantum dots level, which is very difficult to be realized for noble metals via in situ photodeposition. Unfortunately, such small Bi is unstable in air, making it very difficult for the preservation. Another fortunate phenomenon is discovered, the unstable metal Bi can be stored via using the form of Bi/Bi2O3 quantum dots (Bi2O3 is main body of white Bi/Bi2O3 composites). When carried out the photocatalytic CO2 reduction, the white Bi/Bi2O3 can be easily transformed into grey Bi/Bi2O3 composites (the main body of grey Bi/Bi2O3 composites is metal Bi) to improve the photocatalytic CO2 reduction rate. This reason is that CB level of Bi2O3 quantum dots has shifted to a more negative position due to quantum confinement effect compared to the standard redox potential of Bi2O3/Bi (0.37 eV), leading to Bi2O3 easily to be reduced to metal Bi under the effect of photogenerated electrons derived from TiO2. This work demonstrated the mutual conversion between storage and utilization may offer an attractive approach for the application of unstable quantum dot materials or single atom materials.