sentences:  Noxer block
  
  Noxer blocks are concrete pavers that feature a 5–7 mm thick coating of titanium dioxide (TiO2) atop a cement mortar layer.Titanium dioxide is a heterogeneous photocatalyst that uses sunlight to absorb and render oxides of nitrogen (NO and NO2) harmless by converting them to nitrate ions (NO3−), which are then either washed away by rain or soaked into the concrete to form stable compounds.