This study investigates the UV-C photodegradation kinetics of ofloxacin (OFX) and norfloxacin (NFX) in relation to their fluorescence lifetimes and pH-dependent speciation. While NFX consistently follows first-order kinetics under all conditions, OFX exhibits zero-order kinetics at pH 4 and 10, attributed to saturation of photon absorption sites. OFX degrades fastest under basic conditions, whereas NFX is more stable in acidic media and degrades more rapidly near neutral pH. Fluorescence lifetimes measured at pH 4 show that OFX (τF = 7.08 ns) is intrinsically more photostable than NFX (τF = 2.04 ns), although in river water, environmental factors such as dissolved organic matter and reactive oxygen species accelerate OFX degradation. Zwitterionic forms of both antibiotics display enhanced photoreactivity due to a favorable electronic structure and higher UV absorbance. Although UV-C irradiation was used, these controlled experiments provide mechanistic insights relevant to the environmental fate of fluoroquinolones.
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