Electronic structure engineering of phosphorene through transition metal functionalization for toxic gas detection

Designing sensitive, selective, and recyclable materials for toxic gas detection is crucial for environmental monitoring and public safety. In this study, density functional theory calculations are employed to systematically investigate the adsorption behavior, electronic structure modulation, charge transfer, optical response, and sensing performance of CO, CO₂, H₂S, and SO₂ on cobalt-doped and cobalt-adsorbed phosphorene. Cobalt doping transforms pristine phosphorene from a direct-bandgap semiconductor (1.06 eV) into an indirect-bandgap semiconductor with a reduced bandgap of 0.83 eV, while cobalt adsorption further narrows the bandgap to 0.42 eV. Across all target gases and studied temperatures, the Co-doped configuration exhibits stronger adsorption and moderate charge transfer, which govern the observed bandgap modulation and sensing response, while the Co-adsorbed system shows excessive charge transfer, leading to near-irreversible adsorption. Among the investigated gases, SO₂ and CO show the highest sensing responses, whereas CO₂ interacts weakly with both surfaces. Based on literature trends, Co-modified phosphorene is expected to exhibit selective responses toward other common gases, such as NH₃ and NO₂, with minimal interference from H₂O. Recovery-time analysis indicates rapid and reversible desorption under visible-light irradiation for the Co-doped system. In contrast, the Co-adsorbed system exhibits pronounced charge transfer, leading to strongly bound adsorption that is nearly irreversible. These results suggest that Co-doped phosphorene is a promising candidate for gas sensing based on computational predictions.