Titanium dioxide takes part in self-cleaning glass. Free radicals generated from  oxidize organic matter. The rough wedge-like  surface can be modified with a hydrophobic monolayer of octadecylphosphonic acid (ODP).  surfaces that were plasma etched for 10 seconds and subsequent surface modifications with ODP showed a water contact angle greater than 150◦. The surface was converted into a superhydrophilic surface (water contact angle = 0◦) upon UV illumination, due to rapid decomposition of octadecylphosphonic acid coating resulting from  photocatalysis. Due to  's wide band gap, light absorption by the semiconductor material and resulting superhydrophilic conversion of undoped  requires ultraviolet radiation (wavelength <390 nm) and thereby restricts self-cleaning to outdoor applications.