Isomer-dependent control of release and chloride uptake in pyridine dicarboxylate intercalated layered double hydroxide

In this study, we reveal a direct structure–performance relationship in layered double hydroxide (LDH) intercalated with pyridine dicarboxylate (PDA) isomers. The spatial arrangement of PDA molecules within the interlayer, from near-vertical to tilted to disordered packing, governs structural stability, release kinetics, and chloride uptake, providing a molecular-level guide for designing LDHs with tailored properties. Three PDA isomers (2,3-, 2,5-, and 3,4-PDA) were incorporated into ZnAl LDH and characterized by XRD, FTIR, and UV–Vis spectroscopy. Multi-cycle ion exchange tests in NaCl solution provided mechanistic insight into ion-exchange kinetics. ZnAl-2,3PDA LDH showed superior stability and minimal release due to near-vertical alignment and strong electrostatic interactions. ZnAl-2,5PDA LDH achieved the highest chloride uptake while retaining moderate stability via tilted molecular orientation. ZnAl-3,4PDA LDH exhibited rapid release and structural degradation associated with disordered packing. Multi-cycle release confirmed pseudo-second-order kinetics consistent with chemisorption-driven exchange. Density functional theory calculations reproduced the isomer-dependent trends in binding strength and local charge distribution. These findings highlight the critical role of isomer configuration in guiding rational LDH design for controlled release and selective ion capture, enabling advanced functional materials for diverse applications.