Monitoring carbon dioxide (CO2) levels is extremely important in a wide range of applications. Although metal oxide-based chemoresistive sensors have emerged as a promising approach for CO2 detection, the development of efficient CO2 sensors at low temperature remains a challenge. Herein, we report a low temperature hollow nanostructured CeO2-based sensor for CO2 detection. We monitor the changes in the electrical resistance after CO2 pulses in a relative humidity of 70% and show the high performance of the sensor at 100°C. The yolk-shell nanospheres have not only two times higher sensitivity but also significantly increased stability and reversibility, faster response times, and greater CO2 adsorption capacity than commercial ceria nanoparticles. The improvements in the CO2 sensing performance are attributed to hollow and porous structure of the yolk-shell nanoparticles allowing for enhanced gas diffusion and high specific surface area. We present an easy strategy to enhance the electrical and sensing properties of metal oxides at a low operating temperature that is desirable for practical applications of CO2 sensors.

The interference of humidity is a key factor to be considered in metal oxide semiconductors gas sensing performance. However, an efficient gas detection under humid conditions is a challenge. Herein, we report the effect of reduced graphene oxide (RGO) on volatile organic compounds (VOCs) sensing performance of hollow SnO 2 nanoparticles (NPs) under wet atmosphere. For this purpose, RGO-SnO 2 nanocomposite was obtained by a one-pot microwave-assisted solvothermal synthesis. The sensing tests for VOCs were conducted under dry air and at a relative humidity (RH) between 24 and 98%. The samples exhibited better response toward ethanol than to other VOCs such as acetone, benzene, methanol, m-xylene, and toluene, at the optimum operating temperature of 300 • C. Furthermore, RGO-SnO 2 nanocomposite showed an enhanced ethanol response in comparison with pure hollow SnO 2 NPs. Even under 98% of RH, the RGO-SnO 2 nanocomposite showed a response of 43.0 toward 100 ppm of ethanol with a response time of 8 s. The excellent sensor performance is related to the hollow structure of SnO 2 NPs, and the heterojunction between RGO and SnO 2. Therefore, the RGO content can be a promising approach to minimize the humidity effect on SnO 2 ethanol sensing performance.

The sensors based on WO3·0.33H2O, RGO-WO3·0.33H2O, h-WO3, and RGO-h-WO3 showed great VOCs sensing properties at room temperature and 55% relative humidity. The materials exhibited a p-type behavior. RGO improved the acetone sensing response.

Isopropanol sensors on flexible PET substrates presented high-performance at room-temperature in terms of sensitivity, selectivity and mechanical stability.

a b s t r a c tGraphene-based composites have emerged as gas sensor due to the possibility to obtain higher surface area with additional functional groups. In this paper, ZnO nanorods (ZnO-NR) with controlled size and morphology were grown via chemical bath deposition in mild temperature (90 C) over gold interdigital tracks deposited on an alumina substrate. Furthermore, it was also possible to obtain by the same method composites with graphene oxide sheets below ZnO-NR structures (GO/ZnO-NR) or ZnO-NR between GO sheets (GO/ZnO-NR/GO) when GO is placed in the bath during the growth of GO/ZnO-NR. The samples were characterized by Raman spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. These structures were tested as sensors of volatile organic compounds (VOCs), such as acetone, benzene, ethanol and methanol in the concentration range of 10e500 parts per million (ppm). It was found that the optimum working temperature of all sensors was 450 C. The GO/ ZnO-NR/GO composite showed better selectivity due to GO functional groups. In the case of our welldesigned sensors, we found that the dominant oxygen species (O 2-) on ZnO-NR surface were responsible for the sensors response. These findings offer a new viewpoint for further advance of the sensing performance of one-dimensional ZnO/GO nanocomposites VOCs sensors.