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.