Abstract: To enhance the adsorption capacity of biochar and prepare efficient adsorbents, elemental analysis was conducted on corn stalks, rice husks, and Chlorella. Chlorella, with the highest nitrogen content (8.85%), was selected as the raw material. Nitrogen-rich biochar was prepared using a one-step activation method, and metal-doped nitrogen-rich biochar adsorbents were fabricated by impregnating metal salts onto it. The effects of different metals coupled with nitrogen-doped biochar on CO₂ adsorption were investigated. SEM-EDS characterization tests indicated that metals were successfully incorporated into the surface of nitrogen-rich biochar and were evenly distributed. XPS test results showed that the nitrogen-containing groups underwent migration and transformation before and after metal doping, but pyrrolic nitrogen (N-5) remained the dominant form. Experimental results revealed that the specific surface areas of nitrogen-rich biochar, Zn-doped nitrogen-rich biochar, and Na-doped nitrogen-rich biochar were 1394.13, 1334.70, and 1185.98 m²/g, respectively, and their micropore rates were 37.11%, 36.70%, and 35.52%, respectively. Compared with nitrogen-rich biochar, the specific surface areas of Zn-doped and Na-doped nitrogen-rich biochar decreased by 59.43 and 208.15 m²/g, respectively, and their micropore rates decreased by 0.41% and 1.59%, respectively. Metal doping facilitated the chemical adsorption of CO₂ by nitrogen-rich biochar, and Na-doped nitrogen-rich biochar exhibited the highest CO₂ adsorption capacity, which was 42.9% and 16.7% higher than that of nitrogen-rich biochar and Zn-doped nitrogen-rich biochar, respectively. Molecular mechanism studies on the adsorption of CO₂ by Na and Zn coupled with N-5 were conducted from the perspective of quantum chemical theory. The theoretical calculation results indicated that the adsorption energy of CO₂ on the surface of CN5@Na₂O (pyrrolic biochar coupled with Na₂O) was 24.98 kJ/mol higher than that of CN5@ZnO (pyrrolic biochar coupled with ZnO), suggesting that metal doping promoted CO₂ adsorption, and the promoting effect of Na was superior to that of Zn. This study not only provides theoretical support for the preparation of nitrogen-containing groups in biochar and metal-doped nitrogen-rich biochar but also offers an important reference for achieving low-cost and high-efficiency CO₂ capture technology.