  First-principles calculations are performed to investigate the interaction of
physisorbed small molecules, including CO, H2, H2O, NH3, NO, NO2, and O2, with
phosphorene, and their energetics, charge transfer, and magnetic moment are
evaluated on the basis of dispersion corrected density functional theory. Our
calculations reveal that CO, H2, H2O and NH3 molecules act as a weak donor,
whereas O2 and NO2 act as a strong acceptor. While NO molecule donates
electrons to graphene, it receives electrons from phosphorene. Among all the
investigated molecules, NO2 has the strongest interaction through hybridizing
its frontier orbitals with the 3p orbital of phosphorene. The nontrivial and
distinct charge transfer occurring between phosphorene and these physisorbed
molecules not only renders phosphorene promising for application as a gas
sensor, but also provides an effective route to modulating the polarity and
density of carriers in phosphorene. In addition, the binding energy of H2 on
phosphorene is found to be 0.13 eV/H2, indicating that phosphorene is suitable
for both stable room-temperature hydrogen storage and its subsequent facile
release.
