Increasing demand for timely and accurate environmental pollution monitoring and control requires new sensing techniques with outstanding performance, i.e., high sensitivity, high selectivity, and reliability. Metal–organic frameworks (MOFs), also known as porous coordination polymers, are a fascinating class of highly ordered crystalline coordination polymers formed by the coordination of metal ions/clusters and organic bridging linkers/ligands.
Owing to their unique structures and properties, i.e., high surface area, tailorable pore size, high density of active sites, and high catalytic activity, various MOF-based sensing platforms have been reported for environmental contaminant detection including anions, heavy metal ions, organic compounds, and gases. In this review, recent progress in MOF-based environmental sensors is introduced with a focus on optical, electrochemical, and field-effect transistor sensors. The sensors have shown unique and promising performance in water and gas contaminant sensing. Moreover, by incorporation with other functional materials, MOF-based composites can greatly improve the sensor performance. The current limitations and future directions of MOF-based sensors are also discussed.
Monolayer
MoS2 (ML-MoS2) with various polymorphic
phases attracts growing interests for device applications in recent
years. Herein, a field-effect transistor (FET) gas sensor is developed
on the basis of monolayer MoS2 with a heterophase of a
1T metallic phase and a 2H semiconducting phase. Lithium-exfoliated
MoS2 nanosheets own a monolayer structure with rich active
sites for gas adsorption. With thermal annealing from 50 to 300 °C,
the initial lithium-exfoliated 1T-phase MoS2 gradually
transforms into the 2H phase, during which the 1T and 2H heterophases
can be modulated. The 1T/2H heterophase MoS2 shows p-type
semiconducting properties and prominent adsorption capability for
NO2 molecules. The highest response is observed for 100
°C annealed MoS2 of a 40% 1T phase and a 60% 2H phase,
which shows a sensitivity up to 25% toward 2 ppm NO2 at
room temperature in a very short time (10 s) and a lower limit of
detection down to 25 ppb. This study demonstrates that the gas detection
capability of ML-MoS2 could be boosted with the heterophase
construction, which brings new insights into transition-metal dichalcogenide
gas sensors.
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