A "sense and shoot" approach has been developed for the photocatalytic degradation of organic contaminants from aqueous solutions. The presence of aromatic compounds such as chlorinated phenols is readily detected from the quenching of visible emission of ZnO semiconductor film. The emission quenching is quantitative and can be analyzed on the basis of adsorption equilibrium between ZnO and organic molecules. High apparent association constant values (K-a = (1-5) x 10(4) M-1) make possible the detection of these organic molecules at very low concentration levels. For example, 1 ppm of 4-chlorocatechol in water results in a 15% decrease of ZnO emission. Interestingly, the same ZnO film is capable of degrading aromatic compounds present in water under UV irradiation. The concept of adopting a strategy of simultaneous sensing and degradation in photocatalysis is illustrated in this paper.