Adsorption of small molecules on helical gold nanorods: A relativistic density functional study

Abstract

We study the adsorption of a variety of small molecules on helical gold nanorods using relativistic density functional theory. We focus on Au40 which consists of a central linear strand of five gold atoms with seven helical strands of five gold atoms on a coaxial tube. All molecules preferentially adsorb at a single low-coordinated gold atom on the coaxial tube at an end of Au40. In most cases, there is significant charge transfer (CT) between Au40 and the adsorbate, for CO and NO2, there is CT from the Au40 to adsorbate while for all other molecules there is CT from the adsorbate to Au40. Thus, Au40-adsorbate can be described as a donor-accepter complex and we use charge decomposition analysis to better understand the adsorption process. We determine the adsorption energy order to be C5H5N >NO2 > CO > NH3 > CH2=CH2 > CH2=CH-CHO > NO > HC≡CH > H2S > SO2 > HCN > CH3OH > H2C=O > O2 > H2O > CH4 > N2. We find that the Au-C, Au-N, Au-S, and Au-O bonds are surprisingly strong, with clear implications for reactivity enhancement of the adsorbate. The Au-H bond is relatively weak but, for interactions via an H atom that is bonded to a carbon atom (e.g., CH4), we find that there is large charge polarization of the Au-H-C moiety and partial activation of the inert C-H bond. Although the Au-S and Au-O bonds are generally weaker than the Au-C and Au-N bonds, we find that adsorption of H2S or H2O causes greater distortion of Au40 in the binding region. However, the degree of distortion is small and the helical structure is retained, demonstrating the stability of the helical Au40 nanorod under perturbations.

O2Activation by Metal Surfaces: Implications for Bonding and Reactivity on Heterogeneous Catalysts

“…Adsorption of O 2 onto small, unsupported Au n q (with n = 1–55 and q = −1,0,1) clusters has been extensively studied using DFT. ,,− Although the adsorption strength as well as the geometry depend on the calculation details, such as the employed exchange-correlation functional, several trends can be extracted.…”

Helical Gold Nanorods as Chiral Recognition Nanostructures: A Relativistic Density Functional Theory Study

“…In our DFT calculations, the exchange-correlation functional within the generalized gradient approximation (GGA) was employed. Specifically, we use the Becke exchange functional with the Perdew correlation functional (BP86) that was used in our previous studies. , We note that some GGA exchange-correlation functionals, and B3LYP in particular, can be problematic for gold clusters because they tend to favor planar geometries and electron affinities are not well reproduced . However, recent results for neutral gold clusters have shown that the BP86 functional gives excellent results for geometries and adsorption energies, and is sufficiently accurate for the neutral gold clusters we consider in this study .…”

“…However, recent results for neutral gold clusters have shown that the BP86 functional gives excellent results for geometries and adsorption energies, and is sufficiently accurate for the neutral gold clusters we consider in this study . As in our previous studies, , we use the Los Alamos small-core pseudopotential of Hay and Wadt together with the corresponding double-ζ basis set. It is well established that small-core pseudopotentials of this sort can accurately describe relativistic and electron correlation effects in atoms and molecules. , In addition, vibrational frequencies, infrared spectra, and VCD spectra for the optimized structures are calculated.…”

“…As discussed in that study, other isomers of Au 40 are also stable but, in this paper, we exclusively consider the helical Au 40 nanorod. We recently examined the adsorption of a variety of small molecules on the helical Au 40 nanorod . Although the Au–S and Au–O bonds are generally weaker than the Au–C and Au–N bonds, we found that adsorption of H 2 S or H 2 O caused greater distortion of Au 40 in the binding region than adsorption of CO or NH 3 .…”

Emergence of a Low-Energy Peak in the Smoothed Absolute Value Circular Dichroism Spectra of Small Helical Gold Nanorods

“…In a density functional theory (DFT) study, we showed that segments of the (7, 3) single-walled nanotube with a central linear strand, Au 24 , Au 32 , and Au 40 , are stable as free-standing structures and represent atomic cluster analogues of the helical gold wires . That is, they are local minima on the potential energy surface which are robust in the sense that they remain stable when a variety of species are adsorbed on them. , However, they have undercoordinated gold atoms at their ends and, at room temperature, ab initio molecular dynamics calculations indicate that they transform to compact core–shell structures . In this study, we extend these nanorods to include Au 48 and Au 56 and focus on their optical properties.…”