Molecular Layer Deposition of an Aluminum Formate Metal–Organic Framework for Selective Carbon Dioxide Capture

The urgent need for compact, high-performance CO2 sorbents has spurred the development of vapor-deposited ultrathin films. Here, we construct aluminum formate metal–organic framework (ALF-MOF) films via molecular layer deposition (MLD) and vapor-phase activation. Self-limiting growth is achieved at 150 °C via alternating 0.8 s pulses of trimethylaluminum and 1.5 s pulses of formic acid, yielding 3.6 Å per cycle, as confirmed by quartz crystal microbalance and atomic force microscopy. Subsequent exposure to 55 °C formic-acid vapor transforms the amorphous film into a crystalline ALF-MOF, and X-ray diffraction reveals that the onset of crystallization begins within 30 min and ends after 48 h. Mass spectrometry confirms the framework connectivity, and scanning electron microscopy shows the conformal coverage. Crystalline films show Type I CO2 isotherms (3.95 mmol·g–1, 25 °C) with negligible N2 uptake at 77 K, matching bulk ALF. Deposition on submicron features position ALF-MOF MLD as a scalable route for embedding selective CO2 capture in next-generation separation devices.