Photocatalytic activity of undoped and Mn- and Co-doped TiO2 nanocrystals incorporated in enamel coatings on stainless steel

A series of undoped and transition-metal (TM)-doped TiO2 nanocrystals (NCs) were synthesized and calcined at different temperatures, and fully characterized. Such NCs were employed as catalysts for the photodegradation of methylene blue, which enabled us to study the influence of both NC size and anatase/brookite/rutile phase ratio on the photocatalytic activity, as well as the effect of different TM dopants, namely Mn and Co. Then, the NCs were used as active additives for the fabrication of a new photocatalytic system composed of an enamel incorporating these NCs supported onto a stainless-steel sheet. NCs both in powder form and incorporated in enamels deposited on steel were characterized by transmission electron microscopy, X-ray diffraction, and reflectance and Raman spectroscopy. We demonstrate how the calcination of TiO2 NCs induces both a growth in the anatase ratio and formation of the rutile form, which leads to a photocatalytic activity increase. Similarly, doping with Mn and Co gives rise to an enhancement of the catalytic performance attributed to a displacement of the energy bandgap. The obtained material combines the resistance of steel and the photocatalytic activity of TiO2 deposited on enamel, which also operates as a corrosion protection layer for the former. The resulting smart photocatalytic surface presents many applications such as a self-cleaning coating and potential use for NOx photodegradation.