This is the submitted version of the following article: Alonso, A. et al. Critical review of existing nanomaterial adsorbents to capture carbon dioxide and methane in Science of the total environment, vol. 595 (Oct. 2017), pp. 51-62, which has been published in final form at DOI 10.1016/j.scitotenv.2017.03.229 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/