Using density functional theory, we investigated the adsorption of different gases, including CO, CO2, H2S, NO2, and SO2, on decorated phosphorene with various alkali metals such as Li, Na, K, Rb, and Cs. Gas molecules are physisorbed on phosphorene and, according to calculations, alkali metal decoration significantly improves the adsorption of gas molecules by phosphorene due to the reinforcement of interface interactions. Based on the stability criterion (ΔEads), the preference for choosing the best decorated phosphorene system for adsorbing different gases can be arranged as follows: Li > Na > K > Rb > Cs. Li-phosphorene is the most stable decorated system, and due to its higher binding energy in complexation with CO, CO2, H2S, NO2, and SO2, Li-decorated phosphorene shows greater potential in absorbing these gases. Donor-acceptor interactions analysis has confirmed that the origin of stability can be attributed to molecular orbital interactions between these metals and the phosphorene surface (201.69 kcal mol-1). Based on the calculated adsorption energies, Li-decoration on black phosphorene has the most significant adsorption value for CO (2.48 eV). Finally, Li has been suggested as the most suitable phosphorene decorator for enhanced gas molecule adsorption or detection.

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