Proficient capture of carbon dioxide (CO) is considered to be a backbone for environment protection through countering the climate change caused by mounting carbon content. Here we present a comprehensive mechanism to design novel functional nanostructures capable of capturing a large amount of CO efficiently. By means of van der Waals corrected density functional theory calculations, we have studied the structural, electronic and CO storage properties of carbon nitride (g-CN) nano sheets functionalized with a range of transition metal (TM) dopants ranging from Sc to Zn. The considered TMs bind strongly to the nano sheets with binding energies exceeding their respective cohesive energies, thus abolishing the possibility of metal cluster formation. Uniformly dispersed TMs change the electronic properties of semiconducting g-CN through the transfer of valence charges from the former to the latter. This leaves all the TM dopants with significant positive charges, which are beneficial for CO adsorption. We have found that each TM's dopants anchor a maximum of four CO molecules with suitable adsorption energies (-0.15 to -1.0 eV) for ambient condition applications. Thus g-CN nano sheets functionalized with selected TMs could serve as an ideal sorbent for CO capture.