Enhanced CO₂ adsorption on doped Au₃₂ gold nanocages: A density functional approach

The properties of Au₃₂ clusters through selective doping with Si, Ge and Cu atoms and its interaction with CO₂ molecule are reported in this work. The relative stabilities of the clusters compared on the basis of average binding energy per atom indicated that Cu₁₂Au₂₀ is stable with a binding energy of −86.085 kcal mol⁻¹/atom. A charge density-based analysis of the doped clusters is also presented. The highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gap of M₁₂Au₂₀ cluster (M denotes dopants) is much smaller, compared to that of the Au₃₂ cluster, implying higher reactivity. Molecular electrostatic potential (MESP) and its analysis gave guidelines to the various possible sites for the adsorption of CO₂ molecule. The most favourable dopant for CO₂ adsorption was found to be Cu amongst all the others. Calculated Infrared (IR) frequencies indicate that Cu-doped gold clusters give maximally intense peaks for CO₂ stretching. Absorption spectra of the nanocages are also presented using time-dependent density functional theory (TDDFT). This has maximum change in wavelength for Si-doped cluster on CO₂ adsorption. The structural and band gap changes are manifested in the catalytic properties with the result that the doped cages showed strong adsorption for CO₂ as compared to pristine Au₃₂ cluster, with Cu being the best doping agent. (paper)