Copper Claims First As Near-Infrared Photocatalyst

Photocatalysts that work by absorbing sunlight are beneficial in enhancing chemical reactions, such as splitting water into hydrogen and oxygen and the detoxification of organic pollutants in wastewater. In a search to improve photocatalyst efficiency, a research team led by Baibiao Huang of Shandong University, in China, has found a copper mineral, Cu₂(OH)PO₄, that is the first photocatalyst known to be active in the near-infrared portion of the solar spectrum (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201301306). Most photocatalysts, such as titanium dioxide for example, are activated by ultraviolet light. But UV light makes up only about 5% of sunlight. Chemists must add a dye or dopant atoms to the photocatalyst to make use of the visible part of the solar spectrum. Although an improvement, that strategy still leaves out most near-IR light, which makes up about 45% of sunlight. The secret to the new copper catalyst’s reactivity is its crystal lattice, which is made of distorted trigonal bipyramidal and octahedral geometric sites. This arrangement helps separate reactive electron-hole pairs generated when the copper(II) ions absorb near-IR light, in addition to UV and visible light. The researchers tested the catalyst by using it to decompose the fungicide 2,4-dichlorophenol in aqueous solution. They suggest that the dual coordination environment is a promising model for developing other sunlight-driven photocatalysts.