Tuning visible-light-driven photocatalytic activity of PrMnO3 perovskites for tetracycline degradation: mechanistic insights and performance analysis.

A praseodymium-based perovskite (PrMnO3) was synthesised via a simple sol-gel route and investigated as a visible-light-active photocatalyst for the degradation of tetracycline. Compared to La, Ce, and Nd based systems, Pr-based materials have received relatively less attention in antibiotic removal, which forms the basis of this study. The structural and physicochemical properties were comprehensively analysed using XRD, FTIR, Raman, FESEM-EDX, XPS, BET, zeta potential, UV-vis DRS, Mott-Schottky, EIS and PL techniques. XRD confirmed the formation of an orthorhombic perovskite phase (Pnma) with an average crystallite size of ∼19.8 nm, while spectroscopic analyses verified the presence of MnO6 octahedra. The material exhibited a porous and agglomerated morphology with a relatively high surface area (70.375 m2 g-1). Optical characterisation indicated a band gap of ∼2.23 eV, while Mott-Schottky analysis confirmed the n-type semiconducting nature of the material with a flat-band potential of 0.83 V vs. NHE. XPS results revealed mixed-valence states (Pr3+/Pr4+ and Mn3+/Mn4+) and oxygen vacancies, which are beneficial for charge separation. The photocatalytic performance of PrMnO3 under visible light showed a maximum tetracycline degradation efficiency of 91.04% (k = 0.016 min-1) within 120 min at near-neutral pH (6.92) in deionised water, with slightly lower efficiency observed in real water matrices (river and tap water). Also, the catalyst maintained excellent stability and reusability, with negligible structural changes after repeated cycles, as evidenced by XRD and FTIR analyses. The reaction followed pseudo-first-order kinetics. Mechanistic insights obtained from LC-MS analysis, radical scavenging experiments, and band structure evaluation reveal that the degradation process is primarily governed by hydroxyl radicals (˙OH) and photogenerated holes (h+), while electrons play a crucial role in facilitating charge separation and sustaining the photocatalytic cycle. Overall, the results demonstrate that PrMnO3 is a promising and efficient photocatalyst for tetracycline removal under visible-light irradiation.