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This work reports an FTIR study of the NO_x adsorption/desorption cycles on tin oxide nanosized particles under the operating conditions of real sensors (150℃,in presence of O_2).The chemical reactions are monitored in situ and correlated with the variations of the SnO_2 electrical conductivity.On the basis of the FTIR spectra,two contributing mechanisms for the NO_x detection are suggested.The first one presents the formation of bridged nitrate groups bound to the SnO_2 surface via oxygen vacancies acting as electron donor sites.The second mechanism also involves surface oxygen vacancies in the coordination of NO_x,but this time the formation of NO_x anionic species is considered.Both mechanisms lead to the decrease of the electrical conductivity under NO_x adsorption.However,the bridged nitrate groups are not reversible under gas desorption and thus irreversibly contaminate the surface after the first NO_x adsorption.On the contrary,the nitrosyl anionic species are reversible and,from the second NO_x adsorption/desorption cycle,ensure the reproducibility of the sensor response.
This work reports an FTIR study of the NO x adsorption / desorption cycles on tin oxide nanosized particles under the operating conditions of real sensors (150 ° C. in presence of O 2). The chemical reactions are monitored in situ and correlated with the variations of the SnO 2 electrical conductivity. On the basis of the FTIR spectra, two contributing mechanisms for the NO_x detection are suggested. first of presents the formation of bridged nitrate groups bound to the SnO_2 surface via oxygen vacancies acting as electron donor sites. second mechanism also involves surface oxygen vacancies in the coordination of NO_x, but this time the formation of NO_x anionic species is considered.Both mechanisms lead to the decrease of the electrical conductivity under NO_x adsorption. However, the bridged nitrate groups are not reversible under gas desorption and thus irreversibly contaminate the surface after the first NO x adsorption. On the contrary, the nitrosyl anionic species are reversible and, from the second NO x adsorption / desorption cycle, ensure the reproducibility of the sensor response.