Confined Synthesis of Two-Dimensional Covalent Organic Framework Thin Films within Superspreading Water Layer

The confined synthesis of two-dimensional covalent organic framework (2D COF) thin films was developed by using thin superspreading water on the hydrogel immersed under oil as reactor. Through loading two monomers into oil and hydrogel, respectively, COF thin films are synthesized at the oil/water/hydrogel interface. This strategy provides a new way for synthesis of freestanding 2D COF thin films. Detailed characterizations of the COF thin films reveal homogeneous topography, large area, controllable thickness from 4 to 150 nm, and crystallinity with certain orientation. Young's modulus of COF film is measured by AFM indentation as 25.9 ± 0.6 GPa, showing good mechanical properties. On the basis of the freestanding COF films, a nanofilter membrane and photoelectrochemical sensors for Ru³⁺ were successfully developed. Moreover, the strategy was extended to the synthesis of crystalline zeolitic imidazolate framework-8 thin film, which exhibited high application potential.