**4. Conclusions**

An Fe-doped ZnO nanoparticles-based sunlight-assisted photocatalytic system was developed for the degradation of the fluoroquinolone antibiotic ciprofloxacin in water, assessing its best performance parameters like pH, temperature, and catalyst dosage. The degradation of ciprofloxacin was proved both spectrophotometrically as well as microbiologically by the loss of antibiotic activity of the photocatalytically treated water. The developed Fe-doped ZnO nanoparticles-based photocatalytic system can potentially be used for the degradation of other fluoroquinolones and other antibiotics as well as other organic contaminants in water. Antibiotic residues in aquatic systems have the potential to induce resistance in bacteria, which has further the potential to infect humans and thereby become a serious threat to human health. The developed system has therefore potential to contribute to containing antibiotic resistance.

**Author Contributions:** S.K.T., A.J.T. and C.S.L. created the original study plan. S.D., S.G. and A.J.M. designed and executed the experiments under the guidance of S.K.T., A.M. helped in the microbiology experiments. S.D., S.G. and A.J.M. wrote the manuscript. S.K.T., A.J.T., and C.S.L. reviewed and edited the manuscript. All authors read and approved the manuscript.

**Funding:** This work was supported by Department of Science & Technology, Government of India (DST/TM/WTI/2K15/75C) and Swedish Research Council (Grant Number (Grant No. 2012-02889 and 2017-01327).

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