Selective and sensitive detection of trimethylamine using ZnO-In ₂O₃ composite nanofibers

Three different compositions of ZnO-In₂O₃ composite nanofibers were prepared by electrospinning, and their gas sensing characteristics were compared to those of pure ZnO and In₂O ₃ nanofibers. All ZnO-In₂O₃ composite nanofibers showed high response to trimethylamine (TMA), relatively low cross-response to C₂H₅OH, and negligible cross-responses to CO and H₂; pure ZnO or In₂O₃ nanofibers did not show selective detection of TMA. The maximum responses to 5 ppm TMA of the ZnO-In₂O₃ composite nanofibers with the compositions of [Zn]:[In] = 67:33, 50:50, and 33:67 by at% were 133.9 at 300 °C, 82.9 at 350 °C, and 119.4 at 375 °C, respectively. Considering all the sensing characteristics such as gas response, selectivity, and sensing/recovering kinetics together, the operation of the ZnO-In₂O₃ nanofiber sensor with the composition of [Zn]:[In] = 33:67 by at% at 375 °C was determined to be in optimal condition to detect TMA. The significant enhancement of gas response and selectivity by the formation of composite nanofibers is discussed in relation to the variation of particle size, the formation of hetero-interfaces between ZnO and In₂O₃, and the combination of two sensing materials with different catalytic properties, gas adsorption behaviors, and acid-base properties.