Photocatalytic performance of K0.5Na0.5NbO3 rods and cuboids for solar-driven methylene blue degradation in wastewater treatment

This study explores the morphology-dependent photocatalytic performance of lead-free K 0.5 Na 0.5 NbO 3 (KNN) perovskites for solar-assisted wastewater treatment. Phase-pure KNN cuboids were obtained by hydrothermal synthesis, while molten salt-derived KNN rods contained minor K 6 Nb 10.8 O 30 impurities. The KNN rods showed higher surface area (2.39 vs. 1.69 m 2 /g), narrower band gap (3.26 vs. 3.39 eV), and higher aspect ratio (10–20:1). Under natural sunlight irradiation, KNN rods achieved 84.4% methylene blue (10 mg/L) degradation at 5 g/L catalyst loading, outperforming KNN cuboids (75.5% at 4 g/L). Kinetic analysis revealed that this enhanced efficiency is driven by a faster pseudo-first-order reaction rate (k = 0.0083 min −1 ) and superior resistance to surface passivation. Furthermore, although KNN primarily absorbs UV light due to its wide band gap, natural sunlight contains sufficient UV radiation (∼5% of the solar spectrum) to effectively activate this photocatalytic degradation process. These results highlight KNN’s potential as a sustainable, high-efficiency photocatalyst for energy-efficient wastewater treatment.