*2.4. Photocatalytic Degradation of Ciprofloxacin*

A 300 mL aqueous solution of ciprofloxacin with a concentration of 10 mg L−<sup>1</sup> was placed in a 500 mL borosilicate beaker with the required amount (see below) of Fe-doped ZnO and mixed by a magnetic stirrer. The mixture was kept undisturbed in dark for 30 min to allow equilibrium. The experiments were performed with different catalyst concentrations 100, 150 and 200 mg L−1, at pH 2, 3, 5.5, 7, 9, 10 and 11 (required pH was adjusted with 1 N HCl or 1 N NaOH), different reaction temperatures of 30 ◦C, 40 ◦C, 50 ◦C and 60 ◦C and different photocatalysts (TiO2 and ZnO) at a light intensity of 80,000 ± 3000 lux, which corresponds to 650 W/m2. At 15 min intervals, up to 210 min, collected samples were filtered through centrifugation (10,000 rpm, which corresponds to 9391 g force, 10 min, Eppendorf 5424) before spectrophotometric analysis (λmax-280 and 320 nm using a Shimadzu UV-1800 instrument (Japan) and the microbiology experiments for assessment of residual antibacterial activity. The time dependent decrease in absorbance values at λmax-280 and 320 nm suggests degradation of the antibiotic [14].
