Selectivity in environmental photocatalysis from nonspecific mineralization to precision directed contaminant transformation

Conventional environmental photocatalysis has been characterized by mineralization, i.e., oxidation in broad quantities of organics to CO 2 , water, and inorganic ions. This has been proven effective in controlled laboratory conditions, but it is not very effective in real-world systems. Toxic products are formed, matrix elements are competing for oxygen, energy is used extensively, and chemical recoveries lose their value. This review proposes a conceptual change, proposing selectivity-controlled photocatalysis as an appropriate and practical approach for the next generation of environmental remediation. In such a system, photocatalytic reactions are designed to produce detoxified, stable, and where feasible value-added products by controlling the process or materials level to manipulate such selectivity, surface defects, heterojunctions with tunable charge-carrier properties, and wavelength-dependent photoexcitation, as well as process parameters including photon flux, pH, dissolved oxygen, and reactor dynamics. Emphasis is given to pharmaceuticals and hormone disrupters at relevant concentrations, reactive nitrogen and sulfur species, and persistent organic pollutants. Photocatalyst stability in realistic water is also considered. The lack of a standardized selectivity metric and the need for ecotoxicological validation are two areas of research that must be addressed.