Self-Cleaning and Multifunctional Sol-Gel Coatings

Zhang et al [105] published a review on superhydrophobic surfaces considering several aspects to develop self-cleaning coatings with antireflection (AR) properties. They reported the preparation of multilayer stacks with an inner 

Si02 coating and an outer Ti02 coating. The self-cleaning effect is related to the photoinduced superhydrophilicity of thin nanoporous Ti02 films. 

Other multifunctional coating [106] develops transparent superhydrophobic surfaces. Trimethylsiloxane (TMS) surface-functionalized silica nanoparticles embedded in an organosihca gel matrix were used to obtain the films, which present appropriate roughness and low surface energy without any additional hydrophobic capping layer. The amount of nanoparticles and silica gel binder determine water repellence and the thermomechanical stability of the coated surfaces. 

Ti02 is the photocatalyst par excellence. It is an n-type semiconductor that occupies an intermediate energy position within broadband semiconductors. It is extremely effective in oxidation and reduction processes and shows a very high stability in highly humid atmospheres and even in contact with aqueous solutions. 

Sol-gel process is an easy chemical method for obtaining Ti02 coatings in anatase phase, the most efficient for photocatalysis, at much lower temperatures. 

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