a matrix for use in a method of photocatalytically decomposing organic compounds in a fluid includes a fiber glass mat substrate carrying a photocatalytic material . the fiber glass mat is made of randomly oriented glass fibers that have been substantially filamentized and needled whereby the filaments are interlocked . adhesion of the photocatalytic material to the substrate is provided without requiring heat cleaning of the fiber glass by controlling the organic content of the fiber glass mat to be less than 1 . 0 percent by weight as measured by loss on ignition . this is achieved by using sizing compositions that preferably have little or no film forming polymer content .