In the current investigation, the CO2 capture capacity of the fabricated B3O3 monolayer was assessed via a periodic DFT study. The present study results show that pristine B3O3 nanosheets can take up five CO2 molecules with a CO2 capture capacity of 57.76 wt%. The average adsorption energy of adsorbed CO2 on the studied adsorbent falls in the range from −0.248 to −0.429 eV/CO2. The calculated CO2 capture capacity of the desired B3O3 monolayer in the present study is high; therefore, it can be recognized as an emerging material for efficient CO2 capture.