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Covalent organic frameworks (COFs) consist nanochannels that are fundamentally important for their application. Up to now, the effect of gas phase on COF nanochannels are hard to explore. Here, TAPB-PDA-COFs (triphenylbenzene-terephthaldehyde-COFs) was synthesized in situ at the tip of a theta micropipette. The COF-covered theta micropipette (CTP) create a stable gas-liquid interface inside the COF nanochannels, through which the humidity-modulated ion mass transfer in the COF nanochannels can be recorded by recording the current across the two channels of the theta micropipette. Results show that the humid air changes the mobility of the ions inside the COF nanochannels, which leads to the change of ionic current. Humid air showed different effects on the ion transfer depending on the solvent polarity index and vapor pressure. Current decreases linearly with the increase of relative humidity (RH) from 11% to 98%. The CTP was also mounted on the scanning electrochemical microscopy as a probe electrode for mapping micrometer-scale humidity distribution.

Layered/two-dimensional covalent organic frameworks (2D COF) are crystalline porous materials composed of light elements linked by strong covalent bonds. Interlayer force is one of the main factors directing the formation of a stacked layer structure, which plays a vital role in the stability, crystallinity, and porosity of layered COFs. The as-developed new way to modulate the interlayer force of imine-linked 2D TAPB-PDA-COF (TAPB = 1,3,5-tris(4-aminophenyl)benzene, PDA = terephthaldehyde) by only adjusting the pH of the solution. At alkaline and neutral pH, the pore size of the COF decreases from 34 Å due to the turbostratic effect. Under highly acidic conditions (pH 1), TAPB-PDA-COF shows a faster and stronger turbostratic effect, thus causing the 2D structure to exfoliate. This yields bulk quantities of an exfoliated few/single-layer 2D COF, which was well dispersed and displayed a clear Tyndall effect (TE). Furthermore, nanopipette-based electrochemical testing also confirms the slipping of layers with increase towards acidic pH. A model of pH-dependent layer slipping of TAPB-PDA-COF was proposed. This controllable pH-dependent change in the layer structure may open a new door for potential applications in controlled gas adsorption/desorption and drug loading/releasing.