Metal-support interactions at the Pt/Co₃O₄(111) interface yield Pt^δ+ species which control the stability of the supported nanoparticles.

Ceria represents a technologically indispensable reducible catalyst support. Besides the general impact on the surface chemistry, the oxygen content of the ceria surface directly influences the dispersion of ceria-supported metal nanoparticles, and the properties of ceria-supported metal catalysts. We investigate the role of oxygen atoms on a CeO₂(111) surface in supporting Pt as smallest metallic Pt clusters or, concurrently, as monodispersed Pt²⁺ ions. We demonstrate that the necessary condition for the formation of Pt²⁺ ions is the availability of lattice O or excess O atoms at surface step edges. Although Pt²⁺ ions can exist on partially reduced surfaces, excess O atoms are required to maximize the capacity of the surface to accommodate Pt²⁺ and to trigger the redispersion of metallic Pt clusters. Our study provides atomic-level understanding and control of the highest dispersions of Pt on the ceria surface for advancing the state-of-the-art Pt/ceria catalysts that are presently identified at the verge of single-atom Pt dispersion.

Hydroxyapatite (HAP) coatings can improve the biocompatibility and bioactivity of titanium alloys, such as Ti6Al4V, commonly used as material for orthopedic prostheses. In this framework, we have studied the surface of HAP coatings enriched with Mg and either Si or Ti deposited by RF magnetron sputtering on Ti6Al4V. HAP coatings have been furtherly functionalized by adsorption of a self-assembling peptide (SAP) on the HAP surface, with the aim of increasing the material bioactivity. The selected SAP (peptide sequence AbuEAbuEAbuKAbuKAbuEAbuEAbuKAbuK) is a self-complementary oligopeptide able to generate extended ordered structures by self-assembling in watery solutions. Samples were prepared by incubation of the HAP coatings in SAP solutions and subsequently analyzed by X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared (FTIR) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopies, in order to determine the amount of adsorbed peptide, the peptide stability and the structure of the peptide overlayer on the HAP coatings as a function of the HAP substrate and of the pH of the mother SAP solution. Experimental data yielded evidence of SAP adsorption on the HAP surface, and peptide overlayers showed ordered structure and molecular orientation. The thickness of the SAP overlayer depends on the composition of the HAP coating.