title: Tiocem
text: # Tiocem
  
  TioCem is a specialized cement with photocatalytic features, used on the surface of buildings to reduce air pollution caused by exposure of the cement to ultraviolet light (UV).
  
  ## Technology
  
  Photocatalysis is initiated by titanium dioxide $(TiO_2),$ which is added during the cement's production. Typical properties (i.e. strength) of cement applications (such as concrete) will be added to clean the air around the photocatalytic surface. Nitrogen dioxide $(NO_2)$ will be particularly abated when daylight activates the photocatalytic surfaces.
  
  The chemical process may be summarized as follows:
  
  * Titanium dioxide $(TiO_2)$ absorbs energy (UV radiation) and excites electrons (e-)
  
  $TiO_2$ + hν -> $TiO_2$ + h+ + e-
  
  * Oxygen existing in the air $(O_2)$ reacts with electrons (e-), generating super-oxide ions $(O_2-)$
  * Super-oxide ions $(O_2-)$ react with hydrogen ions (H+), generating the reactive hydroxyl radicals (OH•)
  
  $H_2O$ + h+ -> H+ + OH-
  
  * Nitrogen dioxide $(NO_2)$ reacts with the pollutant remover (OH•) and generates nitrate $(NO_3-),$ which reacts with the cement surface and is dissolved by water.
  
  Using materials like TioCem, the abatement of $NO_2$ could be measured by a test method using the Italian standard UNI 11247, which is being discussed as the basis of a European standard. This method involves test apparatus in which a mixture of air and pollutant flows in a chamber over a test object; the pollutant burden is measured with (and without) exposure to light. A defined level of $NO_2$ abatement is guaranteed by the label “TX Active” (plus an initial) and replication of the test results. Proof of the effective reduction of oxide-of-nitrogen exposure has been furnished under close-to-practical conditions by the PICADA (Photocatalytic Innovative Coverings Applications for Depollution Assessment) Project (supported by the European Union and other studies.
  
  ## Applications
  
  Since the photocatalytic effect is needed only on the surface of a building which is exposed to UV, Tiocem is used primarily in the top layer of a two-layer surface.
  
  The most effective fields for application are:
  
  * Pavement (stones and slabs)
  * Roofing tiles
  * Noise and screen barriers
  * Facades (wall cladding)
  * Rendering (dry mortar/exterior cement plaster)
  * Road construction (e.g. whitetopping)
  
  The abatement of $NO_2$ varies with changing climatic conditions. Field tests were carried out with pavements in Bergamo, Italy, on the inside walls of a tunnel in Rome and stucco in Stockholm. In all cases, the requirements of TX Active for $NO_2$ abatement were met.
  
  