Photocatalysts are substances initiating a chemical process under the influence of light in which inorganic or organic pollutants are removed by oxidation. When applied to outside surfaces, for instance, of façades, tiles, roofs, sanitary ceramics, glass or textile membranes, they can dissolve depositions of pollutant particles and exert a cleansing effect. Photocatalysts added to drinking water and waste water can achieve their cleansing effect in the same way in water treatment. Normally, nanoparticles of titanium oxide are used for these self-cleansing photocatalytic effects. This photocatalyst has the benefit of being inexpensive and available in large quantities. However, its drawback is that it works only under UV light. As the UV fraction of daylight is only four percent, the efficiency of titanium oxide-based photocatalysts is too low for the mass applications listed above. Efficiency is improved when the photocatalyst can be activated also by visible light. The Institute of Inorganic Chemistry (AOC) successfully developed a photocatalyst on the basis of tin tungstate which is active in daylight. In a model experiment, dyes simulating pollutants, such as methyl blue, disperse black or methyl orange, were used as model substances for photocatalytic reactions. They were degraded in daylight up to 20 times faster than by the commercial photocatalyst made out of titanium oxide. Even the best current photocatalysts active in daylight described in science, such as BiVO4 or Ag3PO4, are outperformed. The factor of economic interest to materials producers is especially the simple, water-based, inexpensive production of photocatalysts. The economic potential of the new photocatalysts is high, thanks to their wide usability especially in large markets, such as water treatment, and in the chemical and building industries.