**4. Conclusions**

Successfully, theBiF3 powder sample was prepared via the precipitation route simply by washing the purchased powder of Bi2O3 several times into the concentrated HF solution. After several washes through the concentrated HF solution, the Bi2O3 powder was systematically transformed into BiF3 powder in conjunction with each washing. An intermediate phase of Bi1.2F2.4O0.6 was identified for the 1st and 2nd washing of the Bi2O3 powder, which completely vanished after the 3rd washing and converted into the BiF3 powder sample. The photocatalytic performance of the as-prepared BiF3 powder was tested and compared with the Bi2O3 powder on a hazardous industrial waste solution of MB dye. The BiF3 powder rapidly decomposed the MB solution under the visible light illumination as compared to the purchased Bi2O3 powder sample. Usually, POP is used vastly in the construction as well as the building of sculptures and, therefore, is always exposed to water as well as air pollutants. Therefore, to check the self-cleaning activity from such pollutants and introduce the photocatalytic properties in POP, BiF3 powders were added according to 0%, 1%, 5%, and 10% by wt% in the POP matrix. The photocatalytic and self-cleaning properties of these POP–BiF3 composites were demonstrated by using a well-known photocatalysis indicator ink of Rz under visible light exposure. Due to the photocatalytic effect of POP–BiF3 composites under the solar illumination, the blue color of the Rz ink turned into Rf of the pink color. The long-time illumination of visible light resulted from the reduction in the pink color Rf molecules into the colorless product. Photocatalytic performances were improved linearly for the incorporation of BiF3 up to 10% of the concentration in the POP matrix.

**Author Contributions:** Conceptualization, V.P.S. and R.V.; methodology, V.P.S., R.V., S.-H.P. and M.K.; validation, V.P.S., M.S. and D.M.; formal analysis, V.P.S., M.S. and D.M.; investigation, V.P.S., M.K., M.S. and D.M.; resources, R.V., K.-S.S. and S.-H.P.; data curation, V.P.S. and M.K.; writing, V.P.S., R.V., S.-H.P. and M.K.; writing—review and editing, V.P.S., R.V., S.-H.P. and M.K.; visualization, V.P.S., R.V., S.-H.P. and M.K.; supervision, R.V., K.-S.S. and S.-H.P.; project administration, R.V., K.-S.S. and S.-H.P.; funding acquisition, K.-S.S. and S.-H.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the 2021 Yeungnam University Research Grant. **Acknowledgments:** V. P. Singh and Rahul Vaish acknowledge the NPIU and AICTE for the CRS gran<sup>t</sup> under the TEQIP III program for research-related work.RV thanks the CSIR, New Delhi, India, for the financial support under the sponsored research project scheme.

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