Visible-Light-Activated Type II Heterojunction in Cu(3)(hexahydroxytriphenylene)(2)/Fe(2)O(3) Hybrids for Reversible NO(2) Sensing: Critical Role of π–π* Transition

[Image: see text] Metal–organic frameworks (MOFs) with high surface area, tunable porosity, and diverse structures are promising platforms for chemiresistors; however, they often exhibit low sensitivity, poor selectivity, and irreversibility in gas sensing, hindering their practical applications. Herein, we report that hybrids of Cu(3)(HHTP)(2) (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) nanoflakes and Fe(2)O(3) nanoparticles exhibit highly sensitive, selective, and reversible detection of NO(2) at 20 °C. The key parameters to determine their response, selectivity, and recovery are discussed in terms of the size of the Cu(3)(HHTP)(2) nanoflakes, the interaction between the MOFs and NO(2), and an increase in the concentration and lifetime of holes facilitated by visible-light photoactivation and charge-separating energy band alignment of the hybrids. These photoactivated MOF–oxide hybrids suggest a new strategy for designing high-performance MOF-based gas sensors.