Ab initio design of light absorption through silver atomic cluster decoration of TiO₂

Abstract

A first-principles study of the stability and optical response of subnanometer silver clusters Agn (n ≤ 5) on a TiO2(110) surface is presented. First, the adequacy of the vdW-corrected DFT-D3 approach is assessed using the domain-based pair natural orbital correlation DLPNO-CCSD(T) calculations along with the Symmetry-Adapted Perturbation Theory [SAPT(DFT)] applied to a cluster model. Next, using the DFT-D3 treatment with a periodic slab model, we analyze the interaction energies of the atomic silver clusters with the TiO2(110) surface. Finally, the hybrid HSE06 functional and a reduced density matrix treatment are applied to obtain the projected electronic density of states and photo-absorption spectra of the TiO2(110) surface, with and without adsorbed silver clusters. Our results show the stability of the supported clusters, the enhanced light absorbance intensity of the material upon their deposition, and the appearance of intense secondary broad peaks in the near-infrared and the visible regions of the spectrum, with positions depending on the size and shape of the supported clusters. The secondary peaks arise from the photo-induced transfer of electrons from intra-band valence 5s orbitals of the noble-metal cluster to 3d Ti band states of the supporting material.

Exploring the properties of Ag5–TiO2 interfaces: stable surface polaron formation, UV-Vis optical response, and CO2 photoactivation

“…Both structures are highly stable, with adsorption energies (À4.53 eV for the pyramidal-shaped geometry at the PBE-D3(BJ)/U level) being of the same order of magnitude as in previous studies. 20,21 Next, we used the wavefunctions calculated at the PBE-D3(BJ)/U level in a follow-up HSE06 calculation at the relaxed geometries. It was thus found that the Ag 5 cluster donates its unpaired electron to the TiO 2 surface and loses its magnetic moment in either pyramidal-and trapezoidal-shaped structures.…”

“…AQCs made of a few silver atoms seem to display better chemical and physical properties. The stability of Ag n clusters (n # 5) on the rutile surface has also been theoretically analysed, 20 predicting an enhanced light absorbance intensity of the material upon their deposition, as well as the appearance of secondary broad peaks with positions depending on the size and shape of the supported clusters. In particular, intense peaks have been identied in the visible region of the spectrum for the specic case of the Ag 5 AQC.…”

“…In particular, intense peaks have been identied in the visible region of the spectrum for the specic case of the Ag 5 AQC. 20 In this work, for completeness, the visible spectrum of Ag 5 -modied TiO 2 surfaces is experimentally determined using diffuse reectance spectroscopy. Theoretically, the following relevant aspects are addressed: (1) the existence of surface polarons on TiO 2 through surface activation with Ag 5 AQCs; (2) the stability of the resulting polaronic states as compared to non-polaronic ones as previously reported; [20][21][22] and (3) the UV-Vis optical absorption spectrum of the polaronic states.…”

“…We chose a DFT-D3 ansatz 41,42 on the basis of its excellent performance in describing the adsorption of the Ag 2 cluster on the rutile TiO 2 (110) surface. 20 For an appropriate determination of the electronic structure, we employed the HSE06 hybrid functional of Heyd, Scuseria and Ernzerhof 43,44 on top of the structures optimized via the DFT-D3 approach instead. It has been previously shown that the HSE06 functional allows description of localized midgap states below the conduction band which are associated with polarons in reduced TiO 2 (ref.…”

“…This combination of RDM and DFT, proposed by Micha and collaborators, [47][48][49] has been successfully applied to silver 20,50-52 and copper 15,19 clusters on semiconductor TiO 2 and silicon surfaces. 15,19,20,[50][51][52][53] The results from our computational calculations and spectroscopy (diffuse reectance and X-ray absorption) measurements are presented and discussed in Section 2. This section is split in several subsections in order to emphasize at each step the importance of the presence of polarons and, in the last subsection, the prediction of CO 2 photo-activation is briey described.…”