Highly chlorinated aromatics, such as 2,4,5 trichlorophenol (TCP), are examples of organic chemicals commonly used in industry and agriculture, toxic to humans and other organisms, and highly recalcitrant to biodegradation. Nano-scale TiO2 is a well-known photocatalyst for free-radical reactions that can partially degrade chlorinated organics to biodegradable products, but it also is used as a biocide to kill microorganisms. Photobiocatalysis marries TiO2 photocatalysis with biodegradation in such a way that the free-radical reactions generate biodegradable products without also killing the microorganisms that carry out biodegradation of the products. Thus, photobiocatalysis is a nano-biotechnology for the complete biodegradation of highly recalcitrant organic chemicals. We describe successful approaches for photobiocatalysis of TCP, a highly chlorinated aromatic that resists biodegradation and also is toxic to bacteria that are able to biodegrade it.