Study of Intermolecular Reconfiguration of Flexible COF‐5 Film and Its Ultra‐high Chemiresistive Humidity Sensitivity

Abstract

Recently, abundant active materials are developed to achieve the wearable detection of human body humidity. However, the limited response signal and sensitivity restrict further application due to their moderate affinity to water. Herein, we propose a flexible COF‐5 film synthesized by a brief vapor‐assisted method at room temperature. Intermediates are calculated by DFT simulation to investigate the interaction between COF‐5 and water. The adsorption and desorption of water molecule result in a reversible deformation of COF layers while creating new conductive path by π–π stacking. The as‐prepared COF‐5 films are applied to the flexible humidity sensors, exhibiting a resistance change in 4 orders of magnitude with remarkable linear relation between log function of resistance and relative humidity (RH) in 11 %–98 % RH range. Applications including respiratory monitoring and non‐contact switch are tested, providing a promising prospect for the detection of human body humidity.

Passivation of 2D Cs2PbI2Cl2 Nanosheets for Efficient and Stable CsPbI3 Quantum Dot Solar Cells

“…Figures a and S8 display the hydrophobic property of CsPbI 3 PQD films without and with Cs 2 PbI 2 Cl 2 NS modification. With the increasing Cs 2 PbI 2 Cl 2 NS concentration, the contact angle of the PQD film increases from 84.3° (hydrophilic) to 100.8° (hydrophobic), confirming the enhanced hydrophobicity of the PQD film surface due to the modification of Cs 2 PbI 2 Cl 2 NSs. , As H 2 O and O 2 in the atmosphere could easily combine with ionic vacancies on the PQD surface, a series of reactions occur under light stimulation, resulting in the phase transition and degradation of PQDs . The excessive vacancy on the PQD surface and the poor hydrophobicity of the PQD solid film will accelerate the occurrence of this adverse reaction.…”

“…Figures 5a and S8 NSs. 51,52 As H 2 O and O 2 in the atmosphere could easily combine with ionic vacancies on the PQD surface, a series of reactions occur under light stimulation, resulting in the phase transition and degradation of PQDs. 53 The excessive vacancy on the PQD surface and the poor hydrophobicity of the PQD solid film will accelerate the occurrence of this adverse reaction.…”

Porous materials as effective chemiresistive gas sensors

“…Fathoming this need for the COF-based chemiresistive gas sensors, Mei et al fabricated a flexible and robust COF-5 film on a polyimide (PI) substrate and employed it for humidity sensing. 325…”

Opportunity and Challenge of Emerging COFs in Chemiresistive Sensing for Gas and Humidity

“…[34] By combination the active sites and large surface area, impedance type humidity sensors based on COFs have been fabricated basing on the Grotthuss chain reaction [35] and ion transport. [36] The most recent studies demonstrated the reversible protonated tautomerism mechanism [29] and the intermolecular reconfiguration feature [37] in the humidity sensing behavior, promoting a significant humidity sensitivity in the resistance type sensors. [37] In terms of gas sensing process, the sensitivity to analyte molecules is highly related to the organic building units and linkage of COFs.…”