Flexible, non-contact and multifunctional humidity sensors based on two-dimensional phytic acid doped co-metal organic frameworks nanosheets.

Abstract The development of high-performance humidity sensors is of great significance to explore their practical applications in the fields of environment, energy saving and safety monitoring. Herein, a flexible, non-contact and multifunctional humidity sensor based on two-dimensional Co-metal organic frameworks (Co-MOF) nanosheets is proposed, which is fabricated by simple bottom-up synthesis method. Furthermore, environmentally friendly, renewable and abundant biomass phytic acid (PA) is modified on the surface of Co-MOF nanosheets, which releases free protons being capable of etching the framework of MOF to improve the hydrophilicity and conductivity of MOF. Compared with Co-MOF-based sensor, the Co-MOF@PA-based sensor exhibits significantly enhanced sensitivity and broadened response range within 23–95% relative humidity (RH). The humidity sensor has an excellent humidity sensing response over 2 × 103. The Co-MOF@PA-based sensor shows good flexibility and humidity sensing properties, endowing it with multifunctional applications in real-time facial respiration monitoring, skin humidity perception, cosmetic moisturizing evaluation and fruit freshness testing. Four respiration patterns, including slow breath, deep breath, normal breath and fast breath are wirelessly monitored in real time by Co-MOF@PA-based sensor and recorded by mobile phone software. The research work presents potential applications in human–machine interactions (HMI) devices in future.