Natural zeolite clinoptilolite for sustainable energy applications: Insights into water affinity and adsorption properties

Recently, natural zeolites have emerged as promising solutions in the renewable energy sector, offering sustainable solutions and finding applications in several areas. Among them, clinoptilolite stands out for its unique physicochemical properties, low cost, and natural abundance. However, its potential in the energy sector remains largely unexplored. In this study, the performance of natural clinoptilolite and its sodium-exchanged form is evaluated for thermal energy storage and release, focusing on their reversible dehydration behavior and the influence of extra-framework cations on water adsorption capacity. To explore this potential, the samples were characterized using complementary physicochemical techniques, including nitrogen physisorption at −196 °C, X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX). Thermal properties were assessed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) to determine mass loss upon heating, enthalpy change, and energy density. Furthermore, FT-IR spectroscopy was employed to gain detailed insights into the interaction of cation-exchanged clinoptilolite with water. Finally, climatic chamber tests were performed to evaluate the water uptake behavior and validate the FT-IR findings. The results indicated that the performance of natural clinoptilolite decreased with increasing sodium content, a trend confirmed by FT-IR spectroscopy and climatic chamber tests. FT-IR spectra revealed variations in peak intensities in both the stretching and bending regions of –OH groups. Clinoptilolite with the highest sodium content (Na/Clino_H) exhibited reduced water affinity, with water desorbing more readily through progressive framework expansion. In contrast, the other samples required thermal activation to achieve desorption, indicating stronger water–zeolite interactions. This behavior is likely related to the elevated sodium content, which appears to hinder water adsorption.