Surface Functionalized Sensors for Humidity‐Independent Gas Detection

Abstract

Semiconducting metal oxides (SMOXs) are used widely for gas sensors. However, the effect of ambient humidity on the baseline and sensitivity of the chemiresistors is still a largely unsolved problem, reducing sensor accuracy and causing complications for sensor calibrations. Presented here is a general strategy to overcome water‐sensitivity issues by coating SMOXs with a hydrophobic polymer separated by a metal–organic framework (MOF) layer that preserves the SMOX surface and serves a gas‐selective function. Sensor devices using these nanoparticles display near‐constant responses even when humidity is varied across a wide range [0–90 % relative humidity (RH)]. Furthermore, the sensor delivers notable performance below 20 % RH whereas other water‐resistance strategies typically fail. Selectivity enhancement and humidity‐independent sensitivity are concomitantly achieved using this approach. The reported tandem coating strategy is expected to be relevant for a wide range of SMOXs, leading to a new generation of gas sensors with excellent humidity‐resistant performance.

Humidity-Tolerant Room-Temperature Selective Dual Sensing and Discrimination of NH3 and NO Using a WS2/MWCNT Composite

“…But, the design of a material or composite that can consistently detect and discriminate ppb levels of these gases has always remained a challenging task. − At room-temperature, two requirements must be satisfied by a sensing surface: (i) low electrical noise with strong sensing signal and (ii) high performance in natural humid conditions. For example, a water vapor concentration for a high humidity (RH) range of 80% at 1 atmospheric pressure and 25 °C is equivalent to 25 000 ppm (ppm), which is clearly much higher than the conventional concentration range (ppm or ppb) of analytes of interest in environmental air or human exhaled breath . This makes the gas detection at higher RH levels even more difficult.…”

“…For example, a water vapor concentration for a high humidity (RH) range of 80% at 1 atmospheric pressure and 25 °C is equivalent to 25 000 ppm (ppm), which is clearly much higher than the conventional concentration range (ppm or ppb) of analytes of interest in environmental air or human exhaled breath. 9 This makes the gas detection at higher RH levels even more difficult. A tradeoff between sensitivity and robustness (tolerance to humidity or other interferents) is typical of most existing gas sensors.…”

Recent Development of Hierarchical Metal Oxides Based Gas Sensors: From Gas Sensing Performance to Applications

“…Though many literatures have reported the humidity independent response to H 2 S, few of them elaborated the mechanism in detail. [144,145] Yang and co-workers [145] demonstrated a dualshell coating strategy to overcome the water-sensitive issue of the metal oxides based sensing materials. First, to obtain the sensing material CoSnO 3 , the CoSn(OH) 6 nanocubes prepared by hydrothermal reaction were calcinated in Ar.…”

Humidity-Independent Artificial Olfactory Array Enabled by Hydrophobic Core–Shell Dye/MOFs@COFs Composites for Plant Disease Diagnosis

“…Metal–organic frameworks (MOFs) composed of metal ions and organic linkers are a new class of porous materials. , The high surface area and porosity make MOFs as excellent supports or hosts for loading dyes uniformly, effectively avoiding the agglomeration of dyes. , Moreover, MOFs featuring high specific surface area and the potential active sites (such as, unsaturated open metal sites and terminated functional groups) are conducive to preconcentrating the VOCs molecules, − further enhancing the sensitivity. Surface hydrophobic modification of MOF materials is considered as a useful approach to improve the water-resistance performance of MOFs. − Covalent organic frameworks (COFs) with porous structure construct from organic building blocks through covalent bonds, − and some kinds of COFs with the excellent hydrophobic characteristic are ideal hydrophobic modification materials. For example, hydrophobic core–shell structured MOFs@COFs composites, such as NH 2 -MIL-101­(Fe)@NTU-COF and Ti-MOFs@DM-LZU1 have been successfully synthesized and applied to elevate the catalysis efficiency.…”