| Summary: | We used a grand canonical Monte Carlo simulation to study the influence of impurities including water vapor, SO<sub>2</sub>, and O<sub>2</sub> in the flue gas on the adsorption of CO<sub>2</sub>/N<sub>2</sub> mixture in carbon nanotubes (CNTs) and carboxyl doped CNT arrays. In the presence of single impure gas, SO<sub>2</sub> yielded the most inhibitions on CO<sub>2</sub> adsorption, while the influence of water only occurred at low pressure limit (0.1 bar), where a one-dimensional chain of hydrogen-bonded molecules was formed. Further, O<sub>2</sub> was found to hardly affect the adsorption and separation of CO<sub>2</sub>. With three impurities in flue gas, SO<sub>2</sub> still played a major role to suppress the adsorption of CO<sub>2</sub> by reducing the adsorption amount significantly. This was mainly because SO<sub>2</sub> had a stronger interaction with carbon walls in comparison with CO<sub>2</sub>. The presence of three impurities in flue gas enhanced the adsorption complexity due to the interactions between different species. Modified by hydrophilic carboxyl groups, a large amount of H<sub>2</sub>O occupied the adsorption space outside the tube in the carbon nanotube arrays, and SO<sub>2</sub> produced competitive adsorption for CO<sub>2</sub> in the tube. Both of the two effects inhibited the adsorption of CO<sub>2</sub>, but improved the selectivity of CO<sub>2</sub>/N<sub>2</sub>, and the competition between the two determined the adsorption distribution of CO<sub>2</sub> inside and outside the tube. In addition, it was found that (7, 7) CNT always maintained the best CO<sub>2</sub>/N<sub>2</sub> adsorption and separation performance in the presence of impurity gas, for both the cases of single CNT and CNT array.
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