Optimal Composition of ZnO/WO3 Composite Nanoparticle Gas Sensors

Herein, the effect of the ZnO/WO3 molar ratio on the response of ZnO/WO3 composite nanoparticle (NP) sensors to CO is reported. For this purpose, NP samples with ZnO/WO3 molar ratios of 2:8, 4:6, 5:5, 6:4, and 8:2 are prepared using wet chemical methods. The strongest response to 200 ppm CO is obtained by the 6:4 ZnO/WO3 composite NP sensor, which differs from previous reports, in which a ZnO/WO3 composite NP sensor with a molar ratio of 5:5 shows the strongest response to gases. The origin of this difference is explained in detail. The response of the 6:4 ZnO/WO3 composite NP sensor to 200 ppm of CO is approximate to 30 times stronger than that of the 8:2 ZnO/WO3 composite NP sensor. The 6:4 ZnO/WO3 composite NP sensor also shows the shortest response and recovery time among the five ZnO/WO3 composite NP sensors with different molar ratios. The underlying mechanism for the enhanced response of the ZnO/WO3 composite NP sensors to CO compared with that of the pure ZnO NP sensor is also discussed in detail.