This brief overview focuses on three of the main basic phenomena limiting the applications of photocatalysis using semiconductors for the treatment of water, so that this technology has really not gone beyond the demonstration stage aside from niche applications. These phenomena are: the recombination of photogenerated charges; the adsorption of trace organic pollutants; the spectral range of photocatalytic activity. The accomplishments and failures of the various and numerous attempts to overcome these fundamental limitations are summarized and discussed. The emphasis is on the methods susceptible to improve the use of photons, including those in the visible domain to better use solar irradiation if applicable, and to facilitate the contact between the semiconductor and the trace organic pollutants in liquid water. Despite numerous studies, these limitations have not yet been overcome for water purification, because additionally the photocatalysts must contain chemical elements that are both innocuous and inexpensive. However, combinations of TiO2 and activated carbon might provide materials of interest.

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