Bi2O3-sensitized hierarchically mesoporous ZnO nanoparticles for Hg (II) reduction

Herein, an affordable and novel approach to design Bi2O3-sensitized hierarchically mesoporous ZnO nanoparticles (NPs) with a variety of Bi2O3 contents is achieved for Hg(II) reduction upon visible light exposure. TEM images of both ZnO and 3% Bi2O3/ZnO samples exhibit nanoscale spherical-like structures with a regular shape and a particle size of -30 nm. The incorporation of Bi2O3 on hierarchically mesoporous ZnO networks allows visible light to be harvested in a broad range, and the mesoporous 3% Bi2O3/ZnO heterostructure demonstrates the best photocatalytic efficiency for Hg(II) reduction with a value of -100% after 60 min. The photoreduction rate over the 3% Bi2O3/ZnO heterostructure is enhanced 10 and 20 times more than that of TiO2-P25 and ZnO NPs. The rate constant of the 3% Bi2O3/ZnO heterostructure is 16.8 and 33.6 fold larger than that of TiO2-P25 and ZnO NPs. The superior Hg(II) photoreduction performance could be ascribed to the synergistic effect, excellent visible-light harvest, large surface area, and pore volume provided by incorporating Bi2O3 and the heterojunction design between p-type Bi2O3 and n-type ZnO. This alignment of the electronic bands provides charge carrier separation, thereby decreasing the recombination rate. Finally, the mechanisms and kinetics for the photocatalytic reduction of Hg(II) are proposed.

Automated summary

An affordable and novel approach to design Bi2O3-sensitized hierarchically mesoporous ZnO nanoparticles for Hg(II) reduction under visible light exposure has been achieved. The mesoporous 3% Bi2O3/ZnO heterostructure demonstrated the best photocatalytic efficiency for Hg(II) reduction, outperforming TiO2-P25 and ZnO NPs in terms of photoreduction rate and rate constant. The superior performance is attributed to the synergistic effect, visible-light harvest, large surface area, pore volume, and heterojunction design between Bi2O3 and ZnO, leading to efficient charge carrier separation and reduced recombination rate. Proposed mechanisms and kinetics for the photocatalytic reduction of Hg(II) are also discussed.