Alkoxy-modified terpyridine complexes as efficient photocatalysts for diclofenac potassium degradation in pharmaceutical wastewater

Abstract

This study explores the synthesis and application of terpyridine-based metal complexes (C1–C6) for the degradation of diclofenac potassium (DCF), a widely used pharmaceutical pollutant. Terpyridine (TPY) ligands and their metal complexes were synthesized and characterized using FTIR, UV-Vis, ¹H NMR, ¹³C NMR spectroscopy, and mass spectrometry. The novelty of this study lies in the fact that, for the first time, such structures were investigated/explored as potential photocatalysts for the degradation of DCF. The study demonstrates that the target complex compounds exhibit remarkable catalytic efficiency, facilitating the effective degradation of the target pollutant, DCF. The catalytic efficiency of the complexes (C1–C6) in the degradation process was investigated under optimized conditions, including pH and catalyst concentration. A detailed mechanistic study was conducted to elucidate the pathways involved in diclofenac degradation. Kinetic parameters were determined, demonstrating the reaction followed pseudo first-order kinetics. Furthermore, the recyclability of the TPY complexes was assessed over multiple degradation cycles, confirming their stability and reusability. Moreover, computational chemistry techniques utilizing density functional theory (DFT) efficiently explain the electrical properties of the target molecules. The molecular electrostatic potential (MEP) is a theoretical model widely utilized in catalyst chemistry to examine potential sites for nucleophilic and electrophilic attacks on photocatalysts and pollutants using a reactivity map. The density of states (DOS) indicated that C5 exhibited enhanced photoactivity owing to the more prominent localization and delocalization of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). The adsorption route of DCF on C2, C4, and C5 was accurately predicted using molecular electrostatic potential (MEP) descriptors. This study highlights the potential of TPY-based catalysts as efficient and sustainable materials for the remediation of pharmaceutical contaminants in water systems. The enhanced photocatalytic performance is attributed to the optimized electronic structure and the strategic incorporation of alkoxy-functionalized TPY scaffolds. Compared to previous studies on methylene blue (MB) degradation, the newly synthesized complexes exhibit significantly higher efficiency, particularly in the degradation of DCF, demonstrating superior reaction kinetics and recyclability. These findings underscore their promise as next-generation photocatalysts for environmental applications.