Optical imaging of the intrinsic adsorption kinetics in single zeolite nanoparticles.

The confinement effect is increasingly recognized as a critical factor influencing guest-framework interactions in molecular sieves, yet its impact on adsorption kinetics remains largely unexplored. Conventional ensemble measurements on milligram-scale particle assemblies yield apparent adsorption kinetics that conflate dynamic molecular interactions with macroscopic mass transport. Here, we present an optical imaging approach that quantitatively monitors interaction-dominated adsorption by reducing the sample size to the single-nanoparticle level (sub-picogram scale). The results enable the determination of intrinsic rate constants and activation energy barriers for elementary adsorption and desorption steps. A confinement-induced reversal of adsorption kinetics, relative to proton affinities, is observed among homologous light olefins on the same ZSM-5 nanoparticle. This finding reveals that confinement-rather than interaction strength-primarily governs adsorption kinetics at the single-nanoparticle level and provides a general platform for probing and rationally designing molecular sieves for diverse applications.