Adsorption and Dissociation of Toxic Gas Molecules on Graphene-like BC3: A Search for Highly Sensitive Molecular Sensors and Catalysts

Adsorption and Dissociation of Toxic Gas Molecules on Graphene-like BC3: A Search for Highly Sensitive Molecular Sensors and Catalysts S. M. Aghaei* M. M. Monshi, I. Torres, and I. Calizo Quantum Electronic Structures Technology Lab, Department of Electrical and Computer Engineering, Florida International University, Miami, Florida 33174, United States *E-mail: smehd002@fiu.edu Abstract The adsorption behavior of toxic gas molecules (NO, CO, NO2, and NH3) on graphene-like BC3 are investigated using first-principle density functional theory (DFT). The most stable adsorption configurations, adsorption energies, binding distances, charge transfers, electronic band structures, and the conductance modulations are calculated to deeply understand the impacts of the molecules above on the electronic and transport properties of the BC3 monolayer. The graphene-like BC3 monolayer is a semiconductor with a band gap of 0.733 eV. The semi-metal graphene has a low sensitivity to the abovementioned molecules. However, it is discovered that all the above gas molecules are chemically adsorbed on the BC3 sheet with the adsorption energies less than −1 eV. The NO2 gas molecule is totally dissociated into NO and O species through the adsorption process, while the other gas molecules retain their molecular forms. The amounts of charge transfer upon adsorption of CO and NH3 gas molecules on BC3 are found to be small. Hence, the band gap changes in BC3 as a result of interactions with CO and NH3 are only 4.63% and 16.7%, indicating that the BC3-based sensor has a low and moderate sensitivity to CO and NH3, respectively. Contrariwise, upon adsorption of NO or NO2 on BC3, a significant charge is transferred from the molecules to the BC3 sheet, causing a semiconductor-metal transition. It is found that the BC3-based sensor has high potential for NO detection due to the significant conductance changes, moderate adsorption energy, and short recovery time. More excitingly, the BC3 is a likely catalyst for dissociation of the NO2 gas molecule. Our findings divulge promising potential of the graphene-like BC3 as a highly sensitive molecular sensor for NO and NH3 detection and a catalyst for NO2 dissociation.
Keywords Boron carbide; BC3; Graphene; Gas sensor; Catalyst; DFT 2 | P a g e

1. Introduction The need for miniaturized sensors with high sensitivity, fast response, high selectivity, high reliability, quick recovery, and low cost has motivated the scientists to seek new gas sensing systems based on novel nanomaterials. Graphene, the first discovered two-dimensional (2D) atomic crystal [1, 2], has enticed great interest thanks to its extraordinary properties, for instance, high surface-volume ratio, high carrier mobility, high chemical stability, low electronic temperature noise, high thermal stability, and fast response time. Ergo, it offers promise in the development of ultrasensitive gas sensors with high selectivity, fast recovery, high packing density, and low power consumption [3, 4]. The applicability of graphene in the field of gas sensing has been widely investigated both experimentally [5-7] and theoretically [8-12]. Pristine graphene shows low sensitivity toward common gas molecules such as CO, CO2, CH4, N2, NO2, NH3, H2, and H2O [8, 9, 11] which limits its potential for detection of individual gas molecules [12]. It has been reported that functionalization, introducing dopants, and defects can tune the electronic and magnetic properties of the various nanomaterials [13-19]. It has been reported that the sensitivity of graphene-based gas sensors can be significantly improved by introducing the dopants or defects [9, 11, 18, 20-24]. Zhang et al. discovered strong interactions between B- doped, N-doped, and defective graphene with small gas molecules such as NO2, CO, NO, and NH3 [9]. B-, N-, and Si-doped graphene indicated enhanced interactions with common gases such as N2, NO, NO2, NH3, SO2, CO, CO2, O2, H2, and H2O compared to pristine graphene [11]. In another study, graphene doped with transition metals (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt) exhibited high sensitivity toward O2 adsorption [21]. Borisova et al. discovered that the interactions of H2S with C atoms of defected graphene are much stronger than those of pristine graphene [25]. Density functional theory (DFT) calculations on Eu decorated single- and double- sided graphene sheets showed that each Eu could firmly bind to six hydrogen molecules [22].
   Inspired by the astonishing gas sensing performance of graphene, the sensing capability of other 2D structures such as MoS2 [26, 27], WS2 [28, 29], phosphorene [30, 31], boron nitride [32, 33], silicene [34, 35], and germanene [36] toward various gases have been investigated. Recently, the graphene-like BC3 sheet has been epitaxially grown on the NbB2 (0001) surface [37]. The 2D honeycomb structures of BC3 and graphene are analogous becau

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