**4. Conclusions**

Distilled water was injected into the plasma jet to modify the solidification pathway of inflight melted TiO2 particles rather than adjusting the spray conditions. Results showed that the anatase phase was nucleated from melted TiO2 particles under a high cooling rate due to its lower surface energy comparing to the rutile phase, and photocatalytic TiO2 coatings with enhanced activity were obtained. Finally, the anatase content in TiO2 coatings was augmented to 19.9% from 4%, and the time constant of the activity was increased to 0.0046 h−<sup>1</sup> from 0.0017 h−1. In addition, the modification of the solidification pathway did not remarkably cause the loss of coating microhardness.

**Acknowledgments:** This work has been financially supported by Guangdong Natural Science Foundation (2016A030312015), Guangdong Academy of Sciences (2017GDASCX-0202, 2017GDASCX-0843, 2016GDASPT-0206, 2016GDASPT-0317).

**Author Contributions:** Kui Wen, Xuezhang Liu and Kesong Zhou conceived and designed the experiments; Kui Wen and Xuezhang Liu performed the experiments; Kui Wen, Xuezhang Liu, Min Liu and Chunming Deng analyzed the data; Xuezhang Liu and Kui Wen wrote and revised the paper respectively.

**Conflicts of Interest:** The authors declare no conflict of interest.
