Dimensional transition of rigid MOF induced by dynamic dihydrogen phosphate anion coordination for enhanced acetone sensing

Metal organic frameworks (MOFs) with a two-dimensional (2D) morphology exhibit more accessible active sites and efficient charge transfer for enhanced sensing performance. Herein, this work introduces a top-down dihydrogen phosphate (H₂PO₄⁻) anion coordination blocking strategy to achieve dimensionality reduction of three-dimensional (3D) rigid MOFs. The reported strategy involves the substitution of partial ligands by H₂PO₄⁻ anions in the 3D Cu-BTC (3DCuM) framework to form an axial Cu-O-P chemical bond and an intramolecular hydrogen bond within Cu₂(COO)₄⁻ units, triggering a structural dimensional transition to 2D Cu-BTC nanoflakes (2DCuM) for the first time. Benefiting from the optimized electronic structure, a narrower bandgap, and shorter 2D in-plane charge transfer distance, the 2DCuM-4:1 sensor obtained from a 4:1 M ratio of pristine 3D Cu-BTC (3DCuM) to H₂PO₄⁻ showcases excellent acetone sensing performance with good sensitivity, rapid response, and full recoverability at low temperature. Notably, the acetone sensor also exhibits excellent humidity resistance (i.e., only 3.6 % decrease with the increasing relative humidity from 25 % to 85 %) and long-term stability over 20 weeks, which is attributed to the occupancy effect of H₂PO₄⁻ ions to effectively prevent water from coordinating with the open Cu sites. The current work provides a new strategy for achieving dimensionality reduction of rigid 3D MOFs, unleashing the potential to design different morphologies in MOF-based functional materials and enhance sensing performance parameters.