The invention relates to the purification of a fluid medium, for example air or water, and more particularly to the adsorption and/or degradation of organic pollutants in water and also to accelerate total organic carbon (TOC) reduction, chlorine destruction and ozone destruction. The invention describes a novel photocatalyst which comprises a layered nano-structured semiconductor doped with a material selected from the group consisting of a metal, a metal alloy, a metal oxide and mixtures thereof, said material being located between the layers of semiconductor, and the layered nano-structured semiconductor being attached to a substrate which may be easily removed from the fluid medium. The novel photocatalyst may be used together with a light source with a wavelength that will activate the photocatalyst for purification of fluids by adsorption and/or degradation of pollutants. An object of the present invention is to apply this invention to a practical fluid purification system for either commercial or domestic use, or by improving existing systems, for example for the purification of potable water or for treating water from natural sources such as reservoirs, streams, groundwater or even wastewater for reuse.