Defect engineering in SPS TiO2-x coatings

Reduced TiO₂₋ₓ, also known as Black Titanium Oxide (BTO), has recently emerged as a visible-light-active photocatalyst. Among various synthesis methods, suspension plasma spraying (SPS) is gaining increasing attention. Due to the use of hydrogen as a plasma-forming gas, this method enables the in-situ synthesis of BTO in a relatively simple, one-step process. However, even though the potential of SPS in this field has already been explored, the exact influence of process parameters on the defective structure remains unclear. Thus, in this study, we demonstrate the relationship between suspension plasma spray parameters and defect formation in sub-stoichiometric TiO₂₋ₓ. The coatings were analyzed under scanning electron and light microscopes to examine their structure. Phase composition was investigated using Raman spectroscopy, while defective structures were identified through electron paramagnetic resonance and photoluminescence spectroscopy. The results revealed a relationship between process parameters and the formation of specific defects, namely F-centers. These observations confirmed that the defective structure can be controlled via suspension plasma spray parameters.