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•Synthesis of ZnO hollow spheres via a microwave-assisted solvothermal method.•Preparation of a new heterostructure based on NiS nanosheets and ZnO hollow sphere.•ZnO hollow sphere ...has an excellent sensitivity to butanone.•NiS/ZnO heterostructure presents an outstanding selectivity to butanone.•Reduction of the negative effect of humidity for the NiS/ZnO heterostructure.
Developing a device or material to detect volatile organic compounds (VOC) is no longer a challenge, despite its great interest. The difficulty is linked to developing a material that does not suffer from interferences, such as humidity, other gases, or volatiles present in the analyzes. In this sense, we present a new way to modify zinc oxide (ZnO) hollow spheres with nickel (II) sulfide (NiS) nanosheets, a barely studied material in the literature, to increase the butanone selectivity and to reduce the negative effect of humidity in the final response of the sensor. The ZnO hollow sphere (H-ZnO) was synthesized via a microwave-assisted solvothermal method followed by calcination. The NiS-H-ZnO heterostructures were produced by the deposition of NiS nanosheets on H-ZnO using thioacetamide and nickel (II) acetate tetrahydrate as NiS precursors. Under dry conditions, pure H-ZnO presents the best sensing response of 705.3 to 100 ppm of butanone followed by the 5%-NiS-H-ZnO heterostructure with a response of 123.8. However, the selectivity of 5%-NiS-H-ZnO improves and reaches a value of 12.92, which is more than four times higher than the selectivity of pure H-ZnO (3.12). Furthermore, the performance under humidity atmospheres shows that NiS heterostructures suffer less effect of the humidity. The responses to 100 ppm of butanone under 55% of relative humidity were 40.2 and 23.7 for 5%-NiS-H-ZnO and pure H-ZnO, respectively. Therefore, the developed butanone sensor demonstrated excellent response, selectivity, and a promising possibility for its practical use in sensing devices under real conditions of humidity.
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•RGO-SnO2 nanocomposite was obtained by a one-pot microwave-assisted solvothermal method.•Nanocomposite showed an enhanced ethanol response than pure SnO2 under dry and humid ...conditions.•Excellent performance was due to the RGO/SnO2 junction and hollow nature of SnO2.•RGO-SnO2 nanocomposite could be used for ethanol detection under humid conditions.
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 SnO2 nanoparticles (NPs) under wet atmosphere. For this purpose, RGO-SnO2 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-SnO2 nanocomposite showed an enhanced ethanol response in comparison with pure hollow SnO2 NPs. Even under 98% of RH, the RGO-SnO2 nanocomposite showed a response of 43.0 toward 100ppm of ethanol with a response time of 8s. The excellent sensor performance is related to the hollow structure of SnO2 NPs, and the heterojunction between RGO and SnO2. Therefore, the RGO content can be a promising approach to minimize the humidity effect on SnO2 ethanol sensing performance.
Abstract
Understanding morphological changes of nanoparticles in solution is essential to tailor the functionality of devices used in energy generation and storage. However, we lack experimental ...methods that can visualize these processes in solution, or in electrolyte, and provide three-dimensional information. Here, we show how X-ray ptychography enables in situ nano-imaging of the formation and hollowing of nanoparticles in solution at 155 °C. We simultaneously image the growth of about 100 nanocubes with a spatial resolution of 66 nm. The quantitative phase images give access to the third dimension, allowing to additionally study particle thickness. We reveal that the substrate hinders their out-of-plane growth, thus the nanocubes are in fact nanocuboids. Moreover, we observe that the reduction of Cu
2
O to Cu triggers the hollowing of the nanocuboids. We critically assess the interaction of X-rays with the liquid sample. Our method enables detailed in-solution imaging for a wide range of reaction conditions.
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•ZnSnO3 was fabricated by a microwave-assisted hydrothermal method and calcination.•ZnSnO3 presented a nanocubic and porous structure.•Porous ZnSnO3 nanocubes presented sensitivity ...and selectivity to triethylamine.•High response and fast response time toward triethylamine detection were attained.•The sensor showed a low detection limit (∼0.6 ppm) to triethylamine detection.
Triethylamine (TEA), a volatile organic compound (VOC), is present in several industrial processes and is harmful to human health. Therefore, the development of highly sensitive TEA sensors is desirable. Semiconductor metal oxides (SMOx) have been widely used for VOCs detection due to their efficiency and feasibility. Herein, we report the template-free synthesis of zinc stannate nanocubes (NC-ZnSnO3) by the microwave-assisted hydrothermal method followed by a calcination step. The sample's sensing properties were investigated for different VOCs (methanol, ethanol, isopropanol, acetic acid, acetone, 2-butanone, acetaldehyde, benzene, toluene, m-xylene, and TEA). The sensor presented an improved selectivity toward TEA, showing the highest response of 57.5 to 100 ppm of TEA with a fast response time of 4 s at the optimum operating temperature of 350 °C. The NC-ZnSnO3 also showed a low detection limit for TEA of about 0.6 ppm. In summary, this work described an efficient method for producing NC-ZnSnO3 and demonstrated that this material has high selectivity and sensitivity for TEA detection.
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 2 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 key to fabricating complex, hierarchical materials is the control of chemical reactions at various length scales. To this end, the classical model of nucleation and growth fails to provide ...sufficient information. Here, we illustrate how modern X-ray spectroscopic and scattering in situ studies bridge the molecular- and macro- length scales for assemblies of polyhedrally shaped CoO nanocrystals. Utilizing high energy-resolution fluorescence-detected X-ray absorption spectroscopy, we directly access the molecular level of the nanomaterial synthesis. We reveal that initially Co(acac)
rapidly reduces to square-planar Co(acac)
and coordinates to two solvent molecules. Combining atomic pair distribution functions and small-angle X-ray scattering we observe that, unlike a classical nucleation and growth mechanism, nuclei as small as 2 nm assemble into superstructures of 20 nm. The individual nanoparticles and assemblies continue growing at a similar pace. The final spherical assemblies are smaller than 100 nm, while the nanoparticles reach a size of 6 nm and adopt various polyhedral, edgy shapes. Our work thus provides a comprehensive perspective on the emergence of nano-assemblies in solution.
Graphene-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 10–500 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 well-designed sensors, we found that the dominant oxygen species (O2-) 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.
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•ZnO nanorods and composites with graphene oxide were successfully prepared by chemical bath deposition.•The sensors were more sensitive to acetone.•O2− as dominant oxygen species were responsible for the volatile organic compounds sensing.•Graphene oxide on ZnO nanorods surface greatly improved the sensor selectivity.
The development of highly sensitive and selective gas sensors is essential for the detection of harmful compounds. However, the gas-sensing performance presents some challenging issues such as the ...requirement of high operating temperatures and the negative impact of humidity. Herein, we have prepared porous CeO2 nanospheres (NS) using a simple microwave-assisted solvothermal method, followed by calcination, and demonstrated the triethylamine (TEA) sensing performance of the NS at room temperature and a relative humidity of 98%. The sensor showed enhanced sensing properties towards TEA compared to other volatile organic compounds. Significantly, the CeO2 NS exhibited a response of 4.67 to 100 ppm of TEA with a fast response time of 13 s. Furthermore, the sensor was able to detect low TEA concentrations (5 ppm) and presented excellent repeatability. The outstanding sensing properties are attributed to the high specific surface area, the porous structure of CeO2 NS (which allows a great gas diffusion), and the increased number of active sites for TEA oxidation due to the formation of hydroxyl groups on the CeO2 surface from high humidity conditions. Thus, the use of CeO2 NS is a promising approach by which to fabricate TEA sensors that operate at room temperature and high humidity levels.
Sensors of volatile organic compounds (VOCs) are of great importance for environmental monitoring. Nevertheless, it is a great challenge to develop highly sensitive and selective sensors. In this ...sense, we report the synthesis of ZnO twin-rods
via
a combination of the ultrasonic spray nozzle and microwave-assisted hydrothermal methods, which were then loaded with platinum (Pt) nanoparticles (NPs) to obtain Pt/ZnO heterostructures. The VOC detection tests revealed that the 2% Pt/ZnO heterostructure was the best composition, which showed an improved response of 35.2 to 100 ppm of butanone at 450 °C, with high sensitivity to detect low concentrations of butanone (5 ppm) as well as high selectivity and stability. X-ray absorption spectroscopy studies revealed the presence of oxidized Pt species (PtO
x
) under optimal operating conditions. Thus, the enhanced sensitivity of 2% Pt/ZnO can be attributed to the p-n junction at the PtO
x
/ZnO interface.
ZnO twin-rods were synthesized using a combination of the ultrasonic spray nozzle and microwave-assisted hydrothermal methods. The VOC detection test revealed that the decoration with 2% of Pt provides a more sensitive and selective butanone sensor.
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•RGO-CuO composite was obtained by a one-pot microwave-assisted hydrothermal method.•RGO-CuO composite could be used for ethanol detection under high humid conditions.•The enhanced ...ethanol response can be attributed to the RGO/CuO interface.
Semiconductor metal oxides have been used for detecting volatile organic compounds (VOCs). However, these materials present a poor performance in humidity. Here, we report the effect of reduced graphene oxide (RGO) on the ethanol-sensing of CuO under dry and in the relative humidity range of 36–90%. For this purpose, RGO-CuO composites and CuO were synthesized by a one-step microwave-assisted synthesis. The VOCs sensing were performed at the range of 150–350 °C to acetone, benzene, ethanol, methanol, and m-xylene. The RGO-CuO composites exhibited enhanced ethanol sensing when compared with pure CuO at the optimal operating temperature of 250 °C. In addition, the optimal RGO content resulted in an enhanced selectivity and high sensitivity compared to pure CuO. The enhanced ethanol sensing performance of RGO-CuO was attributed to the RGO/CuO heterojunction. Thus, the combination of RGO and p-type CuO semiconductor can be a promising for VOCs detection under wet conditions.
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