Intercalation of Lamellar Mineral Kaolinite with 2-Picolinic Acid: Facile Preparation, Crystal Structure Optimization, and Proton Conductivity

Kaolinite intercalated with 2-picolinic acid was prepared and characterized by scanning electron microscopy, powder X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis. The proton conductivity (σ) of the material is 1.85 × 10^-10 S cm^-1 at 353 K and gradually increases to 1.7 × 10^-7 S cm^-1 at 393 K under N₂ (anhydrous environment) with an activation energy of E_a = 1.93 eV, whereas σ = 1.56 × 10^-7 S cm^-1 under 80 % relative humidity at 353 K with E_a = 0.91 eV. The crystal structure optimized with the Cambridge Sequential Total Energy Package discloses the absence of a dense H-bond network in the layer space of kaolinite, which explains the low proton conductivity and high proton transfer activation energy of the intercalated proton conductor.