TiO₂ anatase nanorods with non-equilibrium crystallographic {001} facets and their coatings exhibiting high photo-oxidation of NO gas

Development of highly active photocatalysts is mandatory for more widespread application of this alternative environmental technology. Synthesis of photocatalysts, such as anatase TiO₂, with more reactive, non-equilibrium, crystallographic facets is theoretically justified by a more efficient interfacial charge transfer to reactive adsorbed species, increasing quantum efficiency of photocatalyst. Air and vacuum calcinations of protonated trititanate nanotubes lead to their transformation to anatase nanorods. The nanorods synthesized by air calcination demonstrate photo-oxidation of NO gas more than three times superior to the one presented by the benchmark P-25 photocatalyst. This performance has been explained in terms of 50% higher specific surface area and, more importantly, through the predominance of more reactive, non-equilibrium, {001} crystallographic facets of the anatase nanorods. These facets present a high density of undercoordinated Ti cations, which favors adsorption of reactant species, and strained Ti-O-Ti bonds, leading to more efficient photo-oxidation reactions. Reduced Ti species, such as Ti³⁺, were not observed in the as-obtained nanorods, while reactive adsorbed molecules are scarce on the nanorods obtained through vacuum calcination. Dip-coating of TiO₂ anatase nanorods (air calcined) over soda-lime glass plates was used to prepare visible light transparent, superhydrophilic and highly adherent photocatalytic coatings with homogenously distributed nanopores.