Ab initio study of NO compounds adsorption on SnO2 surface

Abstract

Abstract:An ab initio study of the adsorption processes on NO x compounds on (110) SnO 2 surface is presented with the aim of providing theoretical hints for the development of improved NO x gas sensors.From first principles calculations (DFT-GGA approximation), the most relevant NO and NO 2 adsorption processes are analyzed by means of the estimation of their adsorption energies. The resulting values and the developed model are also corroborated with experimental desorption temperatures for NO and NO 2 , allowing us to explain the temperature-programmed desorption experiments. The interference of the SO 2 poisoning agent on the studied processes is discussed and the blocking adsorption site consequences on sensing response are analyzed. Key words:AB INITIO, SnO 2 , GAS SENSOR, NO, NO 2 , SO 2 , POISONING Manuscript 2 1.-Introduction:Developing new solid state gas sensors with improved properties carries with it an obvious close relationship between the sensing performance of the active materials and their surface chemical activity.The theoretical study of such surface-absorbate interactions provides a valuable tool to get superior performances that are unattainable using only a trial-and-error approach together with a powerful analytic methodology to explain the experimental data.Tin dioxide (SnO 2 ) plays a key role as one of the more representative sensing materials in solid state gas sensors [1], presenting a significant surface reactivity with many important reducing (CO, NO) and oxidizing gases (O 2 , NO 2 ) [2,3]. The present article deals with sensing mechanisms and processes concerning the detection of NO x using SnO 2 . Detection of NO x is clearly important because it is a wellknown environmental pollutant with harmful consequences for human health [4]. However, to explain the sensing behavior it is necessary to keep in mind that there exist interfering processes poisoning the surface [5] and that these can dramatically change the effective adsorptions of the target species and, therefore, their eventual detection. In the case of the SnO 2 surface, SO 2 is one of the more relevant poison specimens [6]. Thus, in the present analysis, its effects have also been studied in order to point up the consequences of the poisoning process on the sensing mechanisms.Nowadays, first-principles methodologies based on density functional theory (DFT) can provide precise calculations of the energetic and vibrational properties of the adsorption [7]. Moreover, faster codes and new computational facilities allow dealing with numbers of surface-absorbate configurations in moderate computing times.In this context, the aim of the present work is to provide theoretical hints for the development of improved NO x gas sensors using SnO 2 as the base sensing material. The surface orientation relevance is discussed, and the most significant adsorption sites of NO x are identified. Regarding SO 2 as poisoning specimen, its adsorption sites are located and the dependence of the poisoning effect with technologically accessible p...

Ab initio thermodynamic study of the SnO2(110) surface in an O2 and NO environment: a fundamental understanding of the gas sensing mechanism for NO and NO2

“…The results agree with previous work for NO x adsorption on SnO 2 (110) surface [10,41,42], where preferred adsorption sites for NO and NO 2 are bridging oxygen atom and bridgingoxygen vacancies respectively [41,42], and Epifani et al [10] also emphasize the role of bridging oxygen vacancies for NO 2 adsorption from an experimental and computational point of view. When compared with Al 2 O 3 surface, NO adsorbate had also N-down orientation [65].…”

“…Prades et al, [41,42] revealed using DFT calculations that NO and NO 2 molecules are adsorbed on bridging oxygen sites and bridging oxygen vacancy sites at the SnO 2 (110) surface.…”

“…However, the preceding NO x /SnO 2 (110) studies have either focused on surface adsorption without consideration of surrounding gas effect [41,42], or used only oxygen chemical potential to get the energetically lowest surface in contact with oxygen gas [10]. Therefore, these studies could not investigate the effect of ambient NO gas on NO x gas sensing of SnO 2 -based gas sensor, and the suggested mechanisms could be limited.…”

Shrinkage Effects of the Conduction Zone in the Electrical Properties of Metal Oxide Nanocrystals: The Basis for Room Temperature Conductometric Gas Sensor

“…According to previously reported models [25], UV illumination desorbs NO 2 molecules and oxygens from the metal oxide surface leading to partially reduced surfaces [26,27]. In this situation, NO 2 molecules and oxygens in air compete for the same adsorption sites (which are light-induced surface oxygen vacancies, according to first principles calculations [28][29][30]). The higher efficiency of NO 2 molecules to refill the light-emptied sites explains the effective response.…”

A theoretical study on CO sensing mechanism of In-doped SnO2 (110) surface

“…Due to its unique optical, catalytic and electrical properties, it has been applied in solar cells, catalysis, transparent electrodes, and particularly in gas sensor devices [1][2][3][4][5][6]. Theoretically, the density functional theory (DFT) method has been successfully used to investigate the surface electronic structures [7][8][9][10] and the mechanism of adsorption on the surfaces [11][12][13][14][15][16][17][18][19]. The electronic structure of the CO adsorption on the SnO 2 (110) surface has been studied, and the result showed that the band structure and the order of the electronic levels were modified because of the CO adsorption [13].…”