Water-Mediated Hydrogen Bonding Enables Precise Pore-Size Engineering in Hydrogen-Bonded Organic Frameworks for...

Hydrogen-bonded organic frameworks (HOFs) provide an ideal green and sustainable material platform for the efficient removal of thorium (Th(IV)). However, traditional solvent-mediated HOFs exhibit poor structural stability and hydrophobicity in aqueous media. In this study, water (H₂O), featuring well-defined molecular geometry and directional hydrogen-bonding capability, was employed as a structural modulator to enable controlled assembly of two 2,7-bis(4H-1,2,4-triazole-4-yl)benzo[lmn][3,8]phenol-1,3,6,8(2H,7H)-tetraketone (NDIT)-based HOFs, NDIT-HOF-1 and NDIT-HOF-2, which exhibit distinct hydrogen-bond topologies and pore dimensions (4.86 Å and 1.80 Å, respectively). The concentration of water governs hydrogen-bonding kinetics: at low concentrations, water acts as a directional bridging unit that strengthens intermolecular coupling, at elevated concentrations, it undergoes preferential self-aggregation, thereby diminishing the efficacy of interframework hydrogen-bonding connections and leading to pronounced differences in pore aperture and surface polarity. Owing to its size-complementary architecture and enhanced hydrophilicity, NDIT-HOF-1 demonstrates a 2.7-fold higher Th(IV) uptake capacity and a 10-fold faster adsorption kinetics rate compared with NDIT-HOF-2. Collectively, this work establishes water as a programmable, atomic-scale structure modulator in HOF design and provides direct experimental evidence that precise control over framework structure regulation is critical for optimizing actinide ion capture performance.