Ag₇Au₆ Cluster as a Potential Gas Sensor for CO, HCN, and NO Detection

Abstract

Ag−Au bimetallic clusters have demonstrated extreme sensitivity, which can be theoretically explained by the conductivity change of the clusters induced by the absorption process, to molecules such as CO, H 2 S, and so forth. Recently, a 13-atom alloy quantum cluster (Ag 7 Au 6 ) has been experimentally synthesized and characterized. Here, the adsorption of CO, HCN, and NO on the Ag 7 Au 6 cluster was investigated using density functional theory calculations in terms of geometric, energetic, and electronic properties to exploit its potential applications as gas sensors. It is found that the CO, HCN, and NO molecules can be chemisorbed on the Ag 7 Au 6 cluster with exothermic adsorption energy (−0.474 ∼ −1.039 eV) and can lead to finite charge transfer. The electronic properties of the Ag 7 Au 6 cluster present dramatic changes after the adsorption of the CO, HCN, and NO molecules, especially its electric conductivity. Thus, the Ag 7 Au 6 cluster is expected to be a promising gas sensor for CO, HCN, and NO detection. ■ INTRODUCTIONThe environmental gas monitoring and controlling is now recognized as an important issue for our safety and health. Much research has been focused on the development of suitable gas-sensitive materials for continuous monitoring and setting off alarms for hazardous chemical vapors present beyond specified levels. 1−4 Chemical gases such as CO, HCN, and NO are highly toxic to human beings and animals as they inhibit the consumption of oxygen by body tissues. They are colorless, odorless, and tasteless, and thus human beings do not have timely alertness to their presence. For example, exposure levels of 100 ppm of HCN which would result in death are about 1 h or less in some cases, while exposure levels of 500 ppm of HCN are within 15 min. 5 Higher concentration levels will result in faster onset of symptoms or death. Therefore, effective methods for sensing these three toxic gases are highly desired.Bimetallic nanoclusters (also called "nanoalloys" 6 ) are of great interest from both the fundamental and the technological points of view not only because of their new degrees of freedom for understanding their electronic and geometric properties of clusters but also because of their potential applications in catalysis, 7−11 optics, 12−14 nanoelectronics, 15 and sensing. 16 In particular, silver−gold (Ag−Au) clusters have been investigated extensively from a computational point of view 17−27 as well as experimentally. 28−37 Their unique physicochemical properties depend on the shape and structure of the clusters, the surface segregation of the clusters, and the alloying extent or atomic distribution in nanoclusters. Recently, Ag−Au clusters are investigated as potential catalysts or sensors for removal and detection of toxic molecules. In this regard, adsorption of toxic molecules on Ag−Au clusters has attracted several theoretical and experimental studies. 38−45 Experimental investigations on CO adsorption on Au n Ag m (n = 10−45, m = 0, 1, 2) clusters at 140 K indicate that the CO molecule a...

Theoretical insights into the structural, relative stable, electronic, and gas sensing properties of PbnAun (n = 2–12) clusters: a DFT study

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Design and Electrochemical Study of Platinum-Based Nanomaterials for Sensitive Detection of Nitric Oxide in Biomedical Applications

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