High-quality single-crystal ZnO nanowire arrays with diameter ranging from 30 to 110 nm were synthesized using a two-step process: (1) synthesis of ZnO thin film by sol–gel technique, which was used as seed layer, and (2) oriented ZnO nanowire arrays were grown on ZnO seed layer using a hydrothermal reaction process at a low temperature of 90 °C. Experimental results reveal an ultrahigh sensitivity of ∼98% to 100 ppm of H2 gas and 93% to 200 ppm of CO gas, an ultrafast recovery of 1 to 2 ms to CO gas with high repeatability. The current transients demonstrate the reversible type sensing to reducing gas (H2 or CO) detection using as-grown ZnO nanowire arrays sensor. The hydrothermally grown ZnO nanowire-array-based gas sensors may have potential application in industry without much modification.

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