A pattern diagram of the newly-developed photocatalyst and its image taken with a transmission electron microscope (source: Osaka University)
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Osaka University announced Sept 26, 2017, that it has developed a completely metal-free photocatalyst that reacts to a wide band of sunlight.

When visible or near-infrared light is directed to the photocatalyst, it can efficiently generate hydrogen by using water. Because the catalyst is a composite made of black phosphorus and carbon nitride and does not contain any metal, it can reduce environmental load.

Conventional photocatalysts use ultraviolet light, which accounts for only about 4% of sunlight, lowering the efficiency of producing hydrogen by using water and sunlight. As a result, it is difficult to put them into practical use.

The new catalyst is the world's first photocatalyst that is driven by visible/near-infrared light and completely free of metal, according to the university. It was made by synthesizing a composite consisting of two constituents. One is layered black phosphorus that absorbs a large amount of ultraviolet, visible and near-infrared lights. The other is graphite-like carbon nitride (g-C3N4) consisting of several layers.

The black phosphorus works as a photosensitizer that reacts to visible and near-infrared lights, and g-C3N4 functions as a photosensitizer that reacts to visible light. Both of the black phosphorus and g-C3N4 have a layered structure, making it easy to form interfaces and, thus, facilitating charge transfer between the interfaces. As a result, charge separation efficiently progresses.

Osaka University found that P-N coupling takes place on the interface between the black phosphorus and g-C3N4 and forms an electron capturing part, producing hydrogen from water. The latest research results were published on the Sept 21 issue of Journal of the American Chemical Society.