Nowadays, climate problems caused by greenhouse gases are becoming more and more serious. Motivated by reducing carbon dioxide emissions from fossil fuel power generation, scientists are devoting themselves to developing novel materials or technologies for capturing carbon dioxide. Nanostructure materials, which show great potential for this application, have come to the attention of scientists. Herein, the effects of doping an aluminum atom (replacing one boron atom by one aluminum one) on the adsorption of carbon dioxide on boron nitride nanosheets are theoretically investigated through computational analysis based on density functional theory. The results show that the binding between oxygen and aluminum atoms, which comes from classical Lewis base (CO₂)–Lewis acid (Al) interactions, can provide a considerable gain to the mutual effect between the carbon dioxide molecule and the doped substrate. Compared with pristine boron nitride nanosheets, the adsorption energy value of the carbon dioxide molecule is markedly increased to 0.4784 eV (about 2.5-fold) after the doping process, which is in the range of the ideal adsorption energy of 0.415–0.829 eV. More importantly, the essence of physisorption signifies that carbon dioxide can be released by means of specific physical desorption, and, sequentially, this is more conducive for achieving reversible adsorption.