this problem. Paper Micro-sized ZnO tetrapodal particles added to pilot paper production. The most common are one-dimensional nanostructures, such as nanorods, nanotubes, nanofibers, nanowires, but also nanoplates, nanosheets, nanospheres, tetrapods. ZnO is strongly oxidative, chemically stabile, with enhanced photocatalytic activity, and has a large free-exciton binding energy. It is non-toxic, abundant, biocompatible, biodegradable, environmentally friendly, low cost, and compatible with simple chemical synthesis. ZnO faces limits to its widespread use in photocatalysis under solar radiation. Several approaches have been suggested to overcome this limitation, including doping for reducing the band gap and improving charge carrier separation. Water splitting Photocatalytic water splitting separates water into hydrogen and oxygen: The most prevalently investigated material, , is inefficient. Mixtures of and nickel oxide (NiO) are more active. NiO allows a significant explоitation of the visible spectrum. One efficient photocatalyst in the UV range is based on sodium tantalite (NaTaO3) doped with lanthanum and loaded with a nickel oxide cocatalyst. The surface is grooved with nanosteps from doping with lanthanum (3–15 nm range, see nanotechnology). The NiO particles are present on the edges, with the oxygen evolving from the grooves. Self-cleaning glass 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. Disinfection and cleaning Water disinfection/decontamination, a form of solar water disinfection (SODIS). Adsorbents attract organics such as tetrachloroethylene. Adsorbents are placed in packed beds for 18 hours. Spent adsorbents are placed in regeneration fluid, essentially removing organics still attached by passing hot water opposite to the flow of water during adsorption. The regeneration fluid passes through fixed beds of silica gel photocatalysts to remove and decompose remaining organics. self-sterilizing coatings (for application to food contact surfaces and in other environments where microbial pathogens spread by indirect contact). Magnetic nanoparticle oxidation of organic contaminants agitated using a magnetic field. Sterilization of surgical instruments and