Ab initio calculations of NO2 and SO2 chemisorption onto non-polar ZnO surfaces

The authors present an ab initio study of NO2 and SO2 chemisorption onto non-polar ZnO ( 1   0   1 ¯   0 ) and ZnO ( 1   1   2 ¯   0 ) surfaces with the aim of providing theoretical hints for further developments in gas sensors. From first principles calculations (DFT-GGA approximation), the most relevant surface reduction scenarios are analyzed and, subsequently, considered in the chemisorption study. First, calculations indicate that NO2 adsorbs avidly onto Zn surface atoms. This is compatible with the oxidizing character of NO2. Second, results also explain the sensor poisoning by SO2 adsorption (since this molecule competes with NO2 for the same adsorption sites) and indicate that poisoning can only be reverted at typical operation temperatures (T ≤ 700 °C) in the case of stoichiometric ZnO ( 1   0   1 ¯   0 ) surfaces.