Visible-light photocatalysis in Cu2Se nanowires with exposed {111} facets and charge separation between (111) and ((1)over-bar(1)over-bar(1)over-bar) polar surfaces

The search for active narrow band gap semiconductor photocatalysts that directly split water or degrade organic pollutants under solar irradiation remains an open issue. We synthesized Cu2Se nanowires with exposed {111} facets using ethanol and glycerol as morphology controlling agents. The {111} facets were found to be the active facets for decomposing organic contaminants in the entire solar spectrum. Based on the polar structure of the Cu2Se {111} facets, a charge separation model between polar (111) and ((1) over bar(1) over bar(1) over bar) surfaces is proposed. The internal electric field between polar (111) and ((1) over bar(1) over bar(1) over bar) surfaces created by spontaneous polarization drives charge separation. The reduction and oxidation reactions occur on the positive (111) and negative ((1) over bar(1) over bar(1) over bar) polar surfaces, respectively. This suggests the surface-engineering of narrow band gap semiconductors as a strategy to fabricate photocatalysts with high reactivity in the entire solar spectrum. The charge separation model can deepen the understanding of charge transfer in other semiconductor nanocrystals with high photocatalytic activities and offer guidance to design more effective photocatalysts as well as new types of solar cells, photoelectrodes and photoelectric devices.