Synergetic effect of defects rich MoS2 and Ti3C2 MXene as cocatalysts for enhanced photocatalytic H2 production activity of TiO2

Here we report a hierarchical flower-like SnO/SnO2 gas sensing material for detecting formaldehyde vapor at a low temperature. It was rationally designed and successfully synthesized via a one-step hydrothermal route. The crystal phase, defects, element composition and morphology of the obtained samples were characterized in detail by XRD, FESEM, TEM, Raman, PL, and XPS. The characterized results reveal that hierarchical SnO/SnO2 nano-flowers are assembled from ultrathin nanosheets with about 9–11 nm in thickness. Gas sensing performance shows that the sensor based on SnO/SnO2 nano-flowers has crucial advantages for formaldehyde detection, such as low operating temperature (120 °C), excellent selectivity, short response time (7 s), high response value (80.9) and low detection limitation (8.15 ppb). The excellent gas responses of the sensor can be attributed to its unique hierarchical microstructure (for decrease of Rg and increase of Ra) and p-n junction between SnO and SnO2 (for increase of Ra). Finally, the sensing mechanism of the prepared was proposed in detail.

A low temperature formaldehyde gas sensor based on hierarchical SnO/SnO2 nano-flowers assembled from ultrathin nanosheets: Synthesis, sensing performance and mechanism

Review of ZnO-based nanomaterials in gas sensors

Hierarchical structures (HSs) of metal oxide semiconductor (MOS) have stimulated tremendous research attentions owing to their fascinating properties. Here, a HS of ZnO/ZnCo2O4 with varied ZnO contents (0–8 wt%) has been successfully prepared via a surfactant-free hydrothermal method combined with subsequent calcination. The prepared ZnO/ZnCo2O4 HS features an ordered assembly of two dimensional (2D) porous nanosheets with the thickness about 15 nm and evenly distributed ZnCo2O4-ZnO p-n junctions. The gas sensing properties of the ZnO/ZnCo2O4 HS were investigated and compared with pure ZnCo2O4 with similar morphology. It was found that after decorating with ZnO, the gas sensing properties of ZnCo2O4 to triethylamine (TEA) were remarkably improved, such as lowered optimum working temperature (decreased from 260 to 220 °C), faster response/recover speed, and higher sensitivity (0.0377/ppm) within a linear concentration range of 5–300 ppm. The improved gas sensing properties can be attributed to the sensitization effect of n-type ZnO on p-type ZnCo2O4 as well as the unique porous nanosheets-assembled hierarchical structure.

Synthesis of porous nanosheets-assembled ZnO/ZnCo2O4 hierarchical structure for TEA detection

Plasma-induced oxygen vacancies enabled ultrathin ZnO films for highly sensitive detection of triethylamine.

Bimetallic nanoparticles (NPs) usually exhibit some novel properties due to the synergistic effects of the two distinct metals, which is expected to play an important role in the field of gas sensing. PdPt bimetal NPs with Pd-rich shell and Pt-rich core were successfully synthesized and used to modify SnO2 nanosheets. The 1P-PdPt/SnO2-A sensor obtained by self-assemblies of PdPt NPs exhibited temperature-dependent dual selectivity to CO at 100 °C and CH4 at 320 °C. Furthermore, the sensor possessed good long term stability and antihumidity interference. The activation energy of adsorption for CO and CH4 were estimated by the temperature-dependent response process modeled using Langmuir adsorption kinetics, which proved that the lower activation energy of adsorption corresponded to better sensing performance. The gas-sensing mechanism based on the diffusion depth of the tested gas in the sensing layer was discussed. The dramatically improved sensing performance could be ascribed to the high catalytic activity of PdPt bimetal, the electron sensitization of PdO, and Schottky barrier-type junctions at the interface between SnO2 and PdPt NPs. Our present results demonstrate that bimetal NPs with special structure and components can significantly improve the gas-sensing performance of metal oxide semiconductor and the obtained sensor has great potential in monitoring coal mine gas.

PdPt Bimetal-Functionalized SnO2 Nanosheets: Controllable Synthesis and its Dual Selectivity for Detection of Carbon Monoxide and Methane.

Building an effective way for finding the role of surface defects in gas sensing property remains a big challenge. In the present work, we synthesized the ZnO nanodishes (NDs) and first explored the formation process of rich electron donor surface defects by means of studying mechanism for the ZnO NDs synthesis. The test results revealed that ZnO-6, added by 6 mmol Zn powder, had the best gas-sensing properties with the excellent selectivity to ethanol than the others. Specially, the ZnO-6 sensor exhibited the best response (about 49) to 100 ppm ethanol at 230 °C among four as-synthesized samples, while noncustomized ZnO was only 28. It was mainly caused by the following two reasons: the exposure of target (0001) crystal facet and rich electron donor surface defects zinc interstitial (Zni) and oxygen vacancy (VO). As a guide, the formation process of surface defects was revealed by an ideal defect model. By the small-angle XRD and TEM patterns, we could conclude that ZnO NDs, changing stoichiometric ratio, increased the content of Zni by adding Zn powder, while excessive Zn powder promoted the growth of c axis of ZnO NDs in the self-assembly engineering. Besides, a depletion model has been provided to explain how the surface defects work on the sensors and the complex mechanism of gas sensing performance. These findings will develop the application of ZnO-based gas sensor in health and security.

Controllable Evolution of Dual Defect Zni and VO Associate-Rich ZnO Nanodishes with (0001) Exposed Facet and Its Multiple Sensitization Effect for Ethanol Detection

Xiaohong Wang

Papers

PdPt Bimetal-Functionalized SnO2 Nanosheets: Controllable Synthesis and its Dual Selectivity for Detection of Carbon Monoxide and Methane.

Controllable Evolution of Dual Defect Zni and VO Associate-Rich ZnO Nanodishes with (0001) Exposed Facet and Its Multiple Sensitization Effect for Ethanol Detection