Confined fluid phase behavior in nanoporous materials: A critical review of implications for energy and environmental applications.

Understanding the phase behavior of fluids confined in nanoporous materials is critical for advancing environmental and energy applications, including gas separation, carbon capture and storage, and energy storage and recovery in natural and artificial porous systems. Unlike their bulk counterparts, fluids under nanoconfinement exhibit unique thermodynamic properties, such as capillary condensation, phase transition hysteresis, and compositional selectivity in multicomponent mixtures. These phenomena are governed by complex interactions between fluid molecules and pore surfaces, strongly influenced by pore size, geometry, and surface chemistry. This review provides a comprehensive overview of the fundamental principles governing confined phase behavior in a wide range of nanoporous systems, such as zeolites, metal-organic frameworks, nanoporous silicates, and carbon-based nanoporous materials. We also highlight how confinement affects key applications, from gas separation processes to carbon capture using solid sorbents and energy storage systems. By bridging nanoscale phenomena with macroscopic performance, this review outlines recent breakthroughs, current challenges, and future directions in designing nanoporous materials for next-generation energy and environmental applications.