Influence of anions on the photodegradation of antiviral drug: Comparative analysis of photocatalysts efficiency and a kinetic study

The susceptibility to photodegradation of antiviral drug, isoprinosine (IPN), at ambient conditions in milli-Q and in tap water was studied in the presence of selected inorganic anions (SO₄⁻², Cl⁻, NO₃⁻, and CO₃⁻²), as the main components of inorganic environmental matrices as well as real surface water without additional ions were introduced, as surface water naturally contains dissolved inorganic species. The study was performed with 2.0 mg/L concentration of IPN with solar light irradiance (500 W/m²) using TiO₂-P25, ZnO, and SnO₂ as photocatalysts, with IPN quantified by HPLC at 260 nm. The photocatalytic degradation of IPN followed pseudo-first-order kinetics. In Milli-Q water, the highest degradation rate constant 0.0334 min⁻¹ (R² = 0.8875 min⁻¹) was recorded using 20.0 mg/L of pure TiO₂ in the presence of NO₃⁻ ion (50.0 mg/L), while in tap water, TiO₂ exhibited enhanced activity in the presence of SO₄⁻² ions (0.0481 min⁻¹, R² = 0.9862). Complete removal of IPN was achieved using pure TiO₂ in the presence of CO₃⁻² in both milli-Q and tap water. SnO₂ showed limited photocatalytic activity, 25%, 21%, and 29% after 2 h in the presence of Cl⁻, CO₃⁻², and SO₄⁻² ions, respectively in milli-Q water except NO₃⁻ ions. It is likely due to its wide band gap and charge carrier recombination. While in surface water, ZnO exhibited the highest degradation efficiency (k t = 0.0053 min⁻¹, R² = 0.9272). Mineralization assessment based on total organic carbon analysis revealed partial organic carbon removal, indicating the formation of transformation products under the investigated conditions.