Gas-sensing characteristics of ZnO and copper-impregnated ZnO

Abstract

The gas-sensing characteristics of ZnO(I) obtained commercially, as well as of ZnO(II) prepared by the dehydration of the hydroxide have been investigated by employing ESR spectroscopy and electrical conductivity measurements. Pellets of both ZnO(I) and (II) sintered at 870 K detect ethanol and H₂ down to ≈1 ppm, unlike those sintered at 1270 K. ZnO(II) pellets sintered at 1270 K are marginally sensitive to diethyl ether and acetone (≈10 ppm), but ZnO(I) pellets sintered at 1270 K exhibit negligible sensitivity to all gases and vapours. ZnO doped with 0.05% Al and sintered at 870 K shows a sensitivity to H₂ and ethanol similar to that of pure ZnO; higher Al doping decreases the sensitivity. ZnO impregnated with 1% copper shows high sensitivity to CO (≈1 ppm) at 650 K, while ZnO impregnated with 0.1% copper shows sensitivity to diethyl ether (≈1ppm) at 600 K. The sensitivity of 1% Cu/ZnO for CO (at 650 K) is higher than that of the CuO/ZnO hetero-contact (at 540 K) and comparable to that of SnO₂ (at 640 K). The hetero-contact YBa₂Cu₃O₇/ZnO shows marginal sensitivity (≈100 ppm) to ethanol and H₂.