Hierarchical Co 3 O 4 @NiMoO 4 core-shell nanowires (NWs) were synthesized utilizing a two-step hydrothermal method. The NWs show a high chemiresistive response (at a temperature of 255 °C) to xylene, with an R gas /R air ratio of 24.6 at 100 ppm xylene, while the response towards toluene, benzene, ethanol, and acetone, CO, H 2 S and NO 2 is much weaker. In contrast, pure Co 3 O 4 nanowires exhibit weak responses to all the vapors/gases and poor selectivity. The new NW sensor displays an almost linear response (1–100 ppm) to xylene and a lower detection limit of 424 ppb. The remarkable gas sensing characteristics are attributed to the synergistic catalytic effect and the formation of a heterostructure between Co 3 O 4 and NiMoO 4 .
Schematic presentation of a xylene vapor chemiresistive sensor based on Co3O4@NiMoO4 core-shell nanowires. The Co3O4@NiMoO4 core-shell nanowires-based sensor exhibits a high response (24.6) to 100 ppm xylene at 255 °C and high response/recovery speed (13–15 and 25–29 s).
Yu Lu,Yilian Li,Danqing Liu,Yu Ning,Sen Yang,Zhe Yang
Benzene, as the representative compound in volatile organic chemicals (VOCs), widely exists in contaminated sites. Adsorption performance of clay minerals can retard the transport of VOCs gas phase to some extent. Static adsorption experiments were conducted to investigate the adsorption capacity of benzene vapor on natural silicate clay minerals (smectite, illite, chlorite and kaolinite) under different temperatures, moisture contents and mineral mixtures. The results of adsorption isotherms for oven-dried clay minerals implied that the distinct adsorption capacity for benzene was mainly attributed to the specific surface areas and pore volume of clay minerals. The amount of adsorption benzene reduced to the minimum, and then gradually increased as the moisture content raised. The existences of water molecule competed the adsorption sites with benzene on the surface of clay minerals at the low moisture content, whereas the dissolutions of benzene molecule in the adsorbed water and the gravitational water could facilitate the adsorption process of clay minerals its adsorption with a saturated water content . Except for the mixture of smectite-kaolinite samples which showed obstruction of pores and declined the adsorption amount of benzene vapor, the experimentally observed adsorption values of benzene on binary mineral mixtures were equal to the theoretically linear sum of the contributions of each individual minerals.
Yang Du,Shi-Qi Yang,Yun-Jie Li,Zhi-Bin Wang,Xing-Bao Wang,Zhen-Yi Du,Wen-Ying Li
Nickel-based catalysts have been broadly studied for the steam reforming of coal/biomass tar due to their inexpensiveness and good activity. Nevertheless, their industrial application has long been restricted by the deactivation induced by carbon deposition and Ni sintering in the reforming process. Herein, ordered mesoporous nickel-alumina catalysts with varying K contents were prepared. Their performance in steam reforming of toluene as a model compound of tar was evaluated to reveal the effects of K doping. Among them, the catalyst with 2 wt% K loading displayed the best catalytic activity and stability. Experimental and theoretical calculation results suggested that K doping enhances the water adsorption capability of the catalysts, which thereby reduces the amount and graphitization degree of carbon deposits. Moreover, the K doping reduces the acid amount of the support and thereby inhibits the formation of carbon deposits as well. However, K doping does not affect the reaction pathway of the catalysts in toluene steam reforming, and the main reaction intermediates detected with in-situ DRIFTS remain the carbonate groups. Furthermore, the confinement effects of the ordered mesoporous structures inhibit the sintering of Ni particles and the formation of carbon deposits. In addition, the influence of different spatial positions of K on the catalysts was explored. It was found that the K introduction via the one-pot solvent evaporation induced self-assembly method can suppress the loss of K from the catalysts.
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