Improved CO2 Photoreduction Activity and Selectivity Using an Indirect Z-Scheme Heterojunction of ZIF-67 and Bi4O5Br2 Nanostructures

Developing highly efficient photocatalysts for CO2 reduction is critical for addressing global warming and energy supply issues. However, both single-component metal-organic frameworks (MOFs) and conventional semiconductor catalysts face significant challenges, such as severe charge recombination, poor CO2 adsorption capacity, and low utilization of solar energy in the photocatalytic reduction of CO2. To address these limitations, the formation of Z-scheme heterojunction photocatalyst has been proved to be an effective way to suppress the recombination of photoinduced carriers. In this work, an indirect Z-scheme heterojunction photocatalytic system, namely, Cu-doped-ZIF-67Co/Bi4O5Br2, is prepared by means of ion-doping and in situ growth strategy. Electrochemical characterization demonstrated the formation of p-type ZIF-67CoCu nanocubes and n-type Bi4O5Br2 nanosheets. The indirect Z-scheme band structure of the heterojunction was well-defined by X-ray photoelectron spectroscopy (XPS), Mott–Schottky test, and ultraviolet photoelectron spectroscopy (UV). The optimal Cu-doping ratio (molar ratio) and composite ratio (mass ratio): 1% ZIF-67CoCu(1:1)/Bi4O5Br2 exhibits excellent photocatalytic CO2 reduction performance, a remarkable rate of 6469.88 μmol·g–1·h–1, and a high CO selectivity of 97%. Compared to individual ZIF-67CoCu and Bi4O5Br2, the performance of reduction of CO2 to CO is improved by 4.19 and 8.64 times, respectively. Density functional theory calculations and in situ diffuse reflectance infrared Fourier transform spectroscopy results had shown that the existence of Cu in ZIF-67 facilitates the desorption of CO and the reduction process features the key CO* intermediate during the photoreduction of CO2 to CO on 1% ZIF-67CoCu/Bi4O5Br2. This study provides an exciting example for the design and understanding of the ion-doped MOFs and the semiconductor construction of indirect Z-scheme photocatalytic system for promoting photocatalytic capacity.