NH₃ Sensing Mechanism Investigation of CuBr: Different Complex Interactions of the Cu⁺ Ion with NH₃ and O₂ Molecules

Abstract

Copper(I) bromide (CuBr) was considered to be a good gas sensing material with a high sensitivity and selectivity to ammonia (NH3) at ambient temperature. The NH3 sensing mechanism was generally considered to be a result of the strong interaction between NH3 molecules and Cu+ ions. When CuBr-coated quartz-crystal microbalance (QCM), a typical gravimetric transducer, was exposed to NH3, the device displayed a decrease rather than an increase in total mass. This was an unusual phenomenon. In situ diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) was employed to examine the reasons of this total mass decrease. Probing of species formed on the CuBr surface revealed that a complex form between the Cu+ ions and the O2 molecules in air existed. Consequently, O2 gas with a higher molecular weight than NH3 was substituted by NH3 gas, inducing the decrease in mass. The band at 1123 cm−1 of the DRIFT spectrum of CuBr corresponding to the complex formed between O2 molecules and Cu+ ions was identified. The intensity of this band which decreased with the formation of NH3 complex was also observed. The observation was a result of the substitution process for O2 adsorption instead of NH3.

Flexible Room-Temperature NH3 Sensor for Ultrasensitive, Selective, and Humidity-Independent Gas Detection

“…Among all of the reported sensors, five of them − ,, were tested in humid conditions, and their gas responses shifted substantially when tested in a humid atmosphere. Compared to other CuBr sensors in early works, − the NH 3 response in the present work is significantly higher. It should be noted that the CuBr sensors reported previously were mostly synthesized using a wet chemical method, in which copper metal reacts with a CuBr 2 aqueous solution. , As water molecules have a high affinity to CuBr, Cu­(H 2 O) n + is easily formed in the wet chemical product, which in turn decreases the gas response.…”

“…A survey of the available literature shows that the highest response to NH 3 reported thus far was achieved with metal oxide chemiresistors, which operated at elevated temperatures . Note that the NH 3 responses of the present CuBr sensor coated with a 100 nm-thick CeO 2 are among the highest values in the literature (Table − ,− ,− and Figure b). Other room-temperature NH 3 sensors based on TMDCs, conducting polymers, and carbon-related materials − exhibit responses significantly lower than ours.…”

“…The humidity-independent NH 3 sensing characteristics are also mandatory because ambient humidity changes dynamically according to the variation of location, season, day and night, and weather. Although earlier studies have ever demonstrated the possibility of CuBr as ammonia-sensing materials, − the studies neither investigated the humidity dependence of gas-sensing behaviors , nor achieved the humidity-independent gas-sensing characteristics. , Moreover, no flexible CuBr-based ammonia sensor was reported. For medical diagnosis, trace concentrations of NH 3 in exhaled breath should be measured in highly humid atmospheres (>80% relative humidity (RH)), and the humidity-independent ammonia sensor can simplify the sensor system significantly because the preconditioning of exhaled gas through the dehumification process can be neglected .…”

Efficient NH3 Detection Based on MOS Sensors Coupled with Catalytic Conversion

“…Extensive efforts have been carried out to develop gas sensors or detectors to monitor and forewarning NH 3 , such as electrochemical and chemiresistive gas sensors, surface acoustic wave sensors, gas chromatography, optical adsorption spectroscopy, and photoacoustic spectroscopy. − Among them, gas sensor-based metal oxide semiconductors (MOS) have been greatly investigated for NH 3 detection because of their low cost, small size, and simple structure . Metal oxides based on WO 3 , SnO 2 , ZnO, , TiO 2 , and In 2 O 3 have been reported to be a promising sensing material.…”

2-Methyl-2,4-pentanediol gas sensor properties of nano-SnO2 flat-type coplanar gas sensing arrays at low detection limit

“…Obviously, the nano-SnO 2 gas sensor arrays have a better selectivity to MPD in comparison to other interference gases. The similar method for assessment of the selectivity of a sensor was developed by Zhang [47] and Chen [48].…”