Thermoplastic surface modification is achieved with photocatalysts, such as titanium dioxide, tungsten oxide and mixtures thereof. A uniform coating of a powdered photocatalyst is applied to a thermoplastic surface that is wetted with an organic solvent. The coating is in a range between approximately 1.5 mg/cm2 to approximately 2.5 mg/cm2. After the uniform coating of photocatalyst is dried, the thermoplastic surface is heated to a temperature above its softening temperature, usually in a range between approximately 80° C. to approximately 130° C.; then, a mild pressure is applied to imbed the photocatalyst into the surface of the thermoplastic sheet. The method of modification is inexpensive, long-lasting and non-detrimental to the thermoplastic surface. A surface is provided with improved aesthetic appearance, extended lifetime and sustained protection from undesirable growth of nuisance organisms, such as algae, fungus, bacteria, mold, mildew and the like.