Dual sensitization of MWCNTs by co-decoration with p- and n-type metal oxide nanoparticles

We present a dual sensitization gas sensor for selective detection of either H₂S or C₂H₅OH gases, based on ZnO/CuO nanoparticle (NP)-decorated MWCNTs. First, Cu-Zn layers of three different thickness (3, 6, 9 nm) were successfully deposited on the surfaces of CNTs by a sputtering process and subsequently converted to their corresponding oxides by thermal annealing. The gas sensing characteristics of metal oxide decorated-MWCNTs were studied in the presence of three gases, namely NO₂, H₂S, and C₂H₅OH. The best sensing properties were obtained when the Cu-Zn deposition layer was 6 nm thick. The optimized sensor showed extraordinary responses to both H₂S and C₂H₅OH gases at working temperatures of 100 °C and 200 °C, respectively. Therefore, selectivity was tuned by selection of the working temperature. The sensing mechanisms of the metal oxide-decorated CNTs sensors are discussed in detail. The approach described, namely co-decoration of the surfaces of MWCNTs with different metal oxides, will be of great utility to researchers who wish to fabricate dual sensitive gas sensors.