[en] Formaldehyde is a well-known indoor air pollutant that is regulated by authorities worldwide. Formaldehyde has adverse health effects in humans, especially as a sensory irritant to the eyes and to the upper air way, and more importantly, it is a known carcinogen. Adsorption by carbon adsorbents is an old, but indispensable cleaning technology for combating indoor formaldehyde. In this study, we report isotherms and 2D-density distributions by conducting comprehensive Monte Carlo simulation. The effects of the functional group and pore size were investigated. We found that formaldehyde has a different response when the number of functional group and pore size change from that of water. Therefore, by tuning pore size and functionalities it may be feasible to produce real materials that retain effective capture of formaldehyde but which avoid pore blocking by water based on the differences in adsorption properties between water and formaldehyde. (paper)