Solar light driven degradation of norfloxacin using as-synthesized Bi3+ and Fe2+ co-doped ZnO with the addition of HSO5−: Toxicities and degradation pathways investigation

In this study, solar light responsive Bi3+ and Fe2+ doped ZnO were synthesized and used for photocatalytic degradation of norfloxacin (NOR), an emerging water pollutant. Analysis with Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and UV–vis diffuse reflectance spectroscopy (DRS) confirmed coupling of dopants (i.e., Bi3+ and Fe2+) or co-dopants (Bi3+/Fe2+) with ZnO and suggested small narrow size as well as highly crystalline and porous nature of the doped ZnO. Metal ions doping lowered band gap energy and inhibited recombination of electron-hole pair in the as-synthesized ZnO. Consequently, BiFe-ZnO showed enhanced photocatalytic activity and reusability, giving 80% removal of NOR as compared to 36% by un-doped ZnO at a reaction time of 120 min. The analysis with photoluminescence (PL) technique verified high yield of OH from solar light activation of BiFe-ZnO compared to Bi-ZnO, Fe-ZnO and ZnO. Performance of the as-prepared photocatalysts was promoted with the added HSO5− and increased with increasing [HSO5−]0. Degradation of NOR by BiFe-ZnO with the added HSO5− was due to OH and SO4− and NOR showed high reactivity with OH and SO4−. The removal efficiency of NOR was inhibited using OH and SO4− scavengers. Photocatalytic activity of the as-synthesized photocatalysts with the added HSO5− was highly dependent on [NOR]0, [pH]0, co-existing ions, and natural organic matter. Degradation pathways were suggested from the pattern of NOR degradation and identified transformation products. The mineralization of NOR as well as formation of non-toxic end product suggests co-doped ZnO with added HSO5− to be a potential technology for treating antibiotics contaminated water.