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

Copper(I) bromide (CuBr) was considered to be a good gas sensing material with a high sensitivity and selectivity to ammonia (NH 3 ) at ambient temperature. The NH 3 sensing mechanism was generally considered to be a result of the strong interaction between NH 3 molecules and Cu + ions. When CuBr-coated quartz-crystal microbalance (QCM), a typical gravimetric transducer, was exposed to NH 3, 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 O 2 molecules in air existed. Consequently, O 2 gas with a higher molecular weight than NH 3 was substituted by NH 3 gas, inducing the decrease in mass. The band at 1123 cm −1 of the DRIFT spectrum of CuBr corresponding to the complex formed between O 2 molecules and Cu + ions was identified. The intensity of this band which decreased with the formation of NH 3 complex was also observed. The observation was a result of the substitution process for O 2 adsorption instead of NH 3 .