Superior photocatalytic activity of porous wurtzite ZnO nanosheets with exposed {0 0 1} facets and a charge separation model between polar (0 0 1) and (001¯) surfaces

• Porous wurtzite ZnO nanosheets with exposed {0 0 1} facets were synthesized.
• The porous ZnO nanosheets show higher photocatalytic activity than ZnO nanorods.
• The highly reaction activity results from the {0 0 1} facets and a high surface area.
• The highly reactive ZnO {0 0 1} facets were found to be polar surfaces.
• A charge separation model between polar (0 0 1) and (001¯) surfaces was proposed.

Porous ZnO nanosheets with exposed {0 0 1} facets coated on Zn foils have been synthesized by annealing sheet-like Zn5(OH)8Cl2·H2O–Zn2OCl2·2H2O precursor coated on Zn foils at 400 °C for 60 min. The precursors were synthesized by heating ZnCl2 solution on zinc foil at 340 °C for 60 min. Photocatalytic activity of porous ZnO nanosheets in degradation of methyl orange was studied, and the results indicate that the porous ZnO nanosheets show superior photoreactivity, compared to ZnO nanorods as a benchmarking material. The superior photocatalytic activity is attributed to the exposed {0 0 1} facets and a high specific surface area. The exposed {0 0 1} facets were found to be polar surfaces by periodic density functional theory calculations, and thus a charge separation model between polar (0 0 1) and (001¯) surfaces was proposed. There is an internal electric field between positive Zn–ZnO (0 0 1) and negative O–ZnO (001¯) surfaces due to the spontaneous polarization. The internal electric field provides a driving force for charge separation. The reduction and oxidation reactions take place on the positive (0 0 1) and negative (001¯) polar surfaces, respectively. The charge separation model can deepen understanding of charge transfer in the semiconductor nanocrystal with highly photocatalytic activities and offer guidance to design more effective photocatalysts and new type of solar cells, photoelectrodes or photoelectric devices.

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