Decoding MOF surfaces: Insights from inverse gas chromatography and photoelectrochemistry

Metal-organic frameworks (MOFs) are widely studied for their tunable structures and high surface areas, which enable superior performance in surface-driven applications governed by electronic and adsorption properties. Accordingly, establishing robust analytical strategies for studying MOF surface characteristics is of great importance. Recently, Photoelectrochemistry (PEC) has been widely investigated to probe charge transfer dynamics, electronic band structure and interfacial processes at MOF surfaces under illumination. Similarly, chromatographic techniques, especially, inverse gas chromatography (IGC) is an effective surface sensitive tool for evaluating surface energy, acid-base interactions, adsorption thermodynamics, surface polarity and hostguest interactions. Hence, highlighting significant role of surface characteristics in governing photoelectrochemical behavior of MOF based materials is crucial for surface-property-performance correlation. This review primarily focused on the IGC analysis techniques and then discussed different PEC analysis systems. The role of IGC in studying adsorption mechanisms, molecular selectivity and surface interactions in MOF materials is systematically reviewed. Subsequently, the MOF-based photoelectrochemical systems are summarized including Z-scheme, dual Z-scheme, S-scheme, and dual S-scheme with an emphasis on charge transport mechanisms, photocurrent response and interfacial catalytic processes. The scope of the IGC, in synergy with PEC analysis is largely dictated by adsorption behavior and the extensive surface area of materials. Thus, a new pathway of discussion that combined both IGC and PEC for surface analysis of MOF based materials presented here will achieve a complete picture regarding atomic level and molecular level contribution to the surface properties. Finally, current challenges and future perspectives are addressed regarding rational design and optimization of MOFs' surface characteristics for sustainable energy conversion and environmental remediation applications using surface-sensitive IGC technique and PEC analysis.