Terpyridine complexes as superior catalysts for methylene blue dye degradation: Synthesis, characterization, mechanistic insights, kinetic study and recyclability assessment

This manuscript investigates the catalytic potential of terpyridine-based metal complexes (C1–C6) in the efficient degradation of methylene blue dye. The synthesized terpyridine complexes were characterized using various spectroscopic techniques, and their catalytic activity was evaluated in the degradation of methylene blue dye under different experimental conditions. The study reveals that the target complex compounds exhibit notable catalytic efficiency, leading to the effective degradation of the envisioned dye. The reaction kinetics, mechanism, and the influence of various parameters on the catalytic performance were systematically explored. Among different synthesized complexes, Zn-complexes showed better performance than Fe-complexes. Remarkably, the complex C5 showed the best photocatalytic efficiency with a degradation of 79.84 % at optimized conditions of initial dye concentration = 15 mg/L, catalyst dosage = 10 mg, pH = 4, and temperature = 323 K. The recyclability test indicated good stability of the photocatalyst over five cycles with a very small loss of photocatalytic efficiency (∼11.64 %) and the photocatalytic reaction followed pseudo-first order kinetics with a high-rate constant of 0.009 min⁻¹. The trapping experiment revealed the active role of hydroxyl radicals (OH•) and superoxide anions (•O₂⁻) as reactive species on the basis of which a plausible degradation mechanism is proposed. This research contributes valuable insights into the development of terpyridine-based catalysts for the degradation of organic dyes, paving the way for further advancements in the field of catalysis and environmental remediation.