NOVELTY - A photocatalytic method for detoxification and/or disinfection of materials in fluid, involves: providing photocatalyst comprising substrate (17') having curved portion(s) (14) and stress (18, 19)-induced bandgap shifted semiconductor thin film (16) overlying curved portion(s); contacting semiconductor thin film with fluid to be detoxified and/or disinfected; and while semiconductor thin film is in contact with fluid, exposing photocatalyst to light, to cause generation of oxidizing species at surface of photocatalyst in contact with fluid and detoxification and/or disinfection of fluid.    USE - As a photocatalytic method for detoxification and/or disinfection of materials, in a fluid selected from gaseous fluid (preferably air), or liquid fluid (preferably water) (claimed). The electrical activity induced in the band-shifted titania by visible light is also useful in photoelectrolysis (i.e. generation of hydrogen production from water and light), photovoltaics (i.e. generation of electrical power from sunlight), point-of-use photoelectrolysis for use in internal combustion engines, continual tuning of stress and bandgap properties for telecomm devices, water desalination (where the product of combustion of the hydrogen and oxygen gases from photoelectrolysis is desalinated water), photocatalytic disinfection and detoxification of e.g. a medium or biological agent, and alteration and improving magnetic properties of thin films applied to hard drive disks for data storage.    ADVANTAGE - In the photocatalytic method using the thin semiconductor film, the curved portion of the substrate either in the form of fiber or substantially spherical body induces regions of stress of at least 1 GPa in the semiconductor thin film; and causes the bandgap of the semiconductor thin film to be shifted to lower values, decreased or broadened and allows more efficient conversion of the light into oxidizing species. Thus, when in the photocatalysis titania semiconductor film is used having a bandgap of 3 that requires light of 390 nm that is in ultra-violet region, whereas the sunlight is very low in intensity; the deposition of the titania film in the curved portions on the substrate induces stress (both tensile and compressive) in the thin titania film to shift and lower the bandgap energy into the longer wavelengths that are more abundant in sunlight i.e. matches the band gap of the titania more efficiently with the solar spectrum at the earth's surface, and allows more efficient conversion of the solar spectrum of light into electricity and promotes photocatalysis. The undulated coating also serves to self-focus and concentrate the incident light required for the process, and increases photocatalytic surface area. The stress-inducing template profiles also provide a mechanical lock to the coating so that the stress can exist without causing delamination of the coating from the substrate. The self-focusing provided by the nano-lens shape of the titania on the corrugated substrate improves performance in low light level applications. In addition, the same stress-induced thin film bandgap shifting works with other semiconductors such as amorphous silicon to provide similar benefits. The method can be applied both in terrestrial and space environments. The semiconductor (preferably titania thin film) does not cause scatter or diffraction due to its sub-wavelength spatial period, and allows low temperature deposition onto polymers. The sinusoidal interface at the high and low index thin film and substrate respectively further causes effective index that varies gradually from one index to the other, with gradient index benefits of improved transmission and reduced reflection. As the photocatalyst is a thin film, it reduces the probability of recombination of the hole and electron pairs that occurs in bulk semiconductors in the absence of an anode (or cathode) and electrolyte. The concentration of the illumination is largely independent of incident illumination angle, which reduces or eliminates the need to track the sun in the sky. The additional effective surface created by the substrate stress-inducing profiles facilitates and improves heat dissipation. Further, the substrate shape is used to increase or control the stress in the titania film.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for an apparatus for photocatalytic detoxification and/or disinfection of materials, comprising: a polymeric fiber or substantially spherical body bearing a stress-induced bandgap shifted semiconductor thin film on its surface, which when exposed to light while in contact with a fluid, generates oxidizing species effective to cause detoxification and/or disinfection of the fluid.    DESCRIPTION OF DRAWING(S) - The figure shows stress in coated layer of titania coated onto nano-cylindrical polycarbonate embossed template.    Pitch between undulations (12)    Thickness of semiconductor/titania coating (13)    Radius of curvature of undulations (14)    Peak to valley height of undulations (15)    Semiconductor/titania film (16)    Undulations (17)    Substrate (17')    Tensile stress in apex of undulations (18)    Compressive stress in trough of undulations (19)