Introducing Single Pd Atoms into a Two-Dimensional Metal–Organic Framework for Enhanced Benzene Vapor Detection

We report the design and synthesis of a two-dimensional porphyrinic metal–organic framework (MOF), Al-TCPP-Pd, which incorporates atomically dispersed palladium sites for ultrasensitive benzene vapor detection. Compared with pristine Al-TCPP and Al-TCPP-Al analogs, Al-TCPP-Pd exhibits superior performance with an actual detection limit of 1 ppb (logic LOD is 0.48 ppb) and a response value that is four times higher than Al-TCPP at 1 ppm benzene concentration. This remarkable sensitivity is attributed to a synergistic mechanism involving geometric confinement within the MOF's rectangular pores and π-electron channel enhancement induced by Pd coordination. The sensor also shows excellent selectivity against aromatic and nonaromatic interfering gases, strong resistance to humidity, and long-term operational stability over 180 days. Through in situ Raman, quasi-in situ XPS, and Grand Canonical Monte Carlo simulations, it is revealed that the superior detection performances are attributed to the increased adsorption energies and preferential benzene localization in Pd-activated pores. These results underscore the effectiveness of noble metal single-atom functionalization in enhancing MOF-based sensor performance and offer a modular framework for designing.