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Understanding the effect of copper oxide (CuO)–decorated zinc oxide nanotube on carbon monoxide (CO) adsorption is crucial for designing a high-performance CO gas sensor. In this work, CO sensing properties of copper oxide–decorated zinc oxide (CuO-ZnO) nanotube are studied theoretically by employing first-principles density functional theory for the first time. The stability, adsorption mechanism, density of states, and change in electrical conductivity are studied. The results of calculating the adsorption energy show strong chemical adsorption of CO on CuO-ZnO nanotubes. The adsorption energy of CO on CuO-ZnO nanotube is calculated as 7.5 times higher than that on ZnO nanotube. The results of the Mulliken charge analysis reveal that electron transfer occurs from CO molecules to CuO-ZnO nanotubes. Additionally, the electrical conductivity of CuO-ZnO nanotubes significantly changes after adsorption of CO at room temperature. According to these studies, CuO-ZnO nanotube sensors can be used for the detection of CO gas. The results are in excellent agreement with the reported experimental results. [ABSTRACT FROM AUTHOR]

Reliable, sensitive and selective ammonia gas sensing at room temperature is very important for monitoring the environment for hazardous pollutants. In this study, ammonia (NH3) gas sensor is proposed based on polyaniline/three-dimensional reduced graphene oxide (PANI/3D-RGO) hybrid samples, which are loaded on glass substrates by electrochemical polymerization method. The PANI/3D-RGO hybrid samples with different weight percentages of 3D-RGO (weight% =0.05, 0.2, 0.5 and 1) are characterized by field emission-scanning electron microscopy, Fourier transform infrared and X-ray diffraction. The specific surface area is analyzed by the Brunauer-Emmett-Teller (BET) equation. The gas-sensing performances of the fabricated sensors indicate that PANI/3D-RGO (0.2wt. %) exhibits the best response for 50 ppm NH3 gas at room temperature, this sensor response to lower concentrations of NH3 (5ppm, 10 ppm and 25 ppm) too. The PANI/3D-RGO (0.2wt. %) hybrid sensor shows represent response values of about 3.72 and acceptable response and recovery times (98 s and 288 s) to 50 ppm NH3 which is about 4.27 fold higher than that of pure PANI in 50 ppm NH3 gas. The excellent sensing performance of the developed gas sensor can be attributed to the synergetic effects of PANI and 3D-RGO, $\pi -\pi $ interaction between the two components, efficient increase in hole-like carriers and substantial increase in active sites. [ABSTRACT FROM AUTHOR]