Humidity Sensors Based on Metal–Organic Frameworks

Abstract

Humidity sensors are important in industrial fields and human activities. Metal−organic frameworks (MOFs) and their derivatives are a class of promising humidity−sensing materials with the characteristics of a large specific surface area, high porosity, modifiable frameworks, and high stability. The drawbacks of MOFs, such as poor film formation, low electrical conductivity, and limited hydrophilicity, have been gradually overcome with the development of material science. Currently, it is moving towards a critical development stage of MOF−based humidity sensors from usability to ease of use, of which great challenges remain unsolved. In order to better understand the related challenges and point out the direction for the future development of MOF−based humidity sensors, we reviewed the development of such sensors based on related published work, focusing on six primary types (impedance, capacitive, resistive, fluorescent, quartz crystal microbalance (QCM), and others) and analyzed the sensing mechanism, material design, and sensing performance involved, and presented our thoughts on the possible future research directions.

Oral micro-electronic platform for temperature and humidity monitoring

“…Organic substances, like molecular rectifiers, offer precise humidity data 43 . Metal–organic frameworks and their derivatives also exhibit great potential as materials for humidity sensing, primarily due to their remarkable porosity and stability 49 . Moreover, the development of printed capacitive humidity sensors, featuring stacked parallel-plate electrodes, has yielded sensors that possess high capacitance and sensitivity, all while maintaining an economical cost.…”

A low-cost, swift response, highly sensitive MOF-based dual sensing device enables detection of ultralow humidity levels and solvent polarity changes

“…Depending on different sensing platforms, humidity sensors can be capacitive, resistive, impedance, optical, electrical conductivity, and thermal-based. 29 Out of these, capacitance-based sensors are more attractive than the other listed sensors because they are highly sensitive, operate at low cost, have fast response time, consume less power, and can be operated at room temperature. [30][31][32] Moisture-induced changes in the dielectric properties of humidity-adsorbing materials are the basis for the operation of capacitive humidity sensors.…”

Mullite 3D Printed Humidity Sensors

“…Clay minerals with layered structures have also been also investigated, due to their high specific surface area and their capacity for ion exchange and the hydration process [25][26][27]. More recently, because of new applications such as the Internet of Things (IoT) and human-body monitoring, new sensors based on different materials such as paper [28], sulfides [29], sulfates [30], metal-organic frameworks (MOFs) [31] and other materials [32] have also been proposed.…”