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Metal oxides are versatile substrates for the design of a wide range of SAM-based organic-inorganic materials among which ZnO nanostructures modified with phosphonic SAM are promising semiconducting systems for applications in technological fields such as biosensing, photonics, and field-effect transistors (FET). Despite previous studies reported on various successful grafting approaches, issues regarding preferred anchoring modes of phosphonic acids and the role of a second reactive group (i.e., a carboxylic group) are still a matter of controversial interpretations. This paper reports on an experimental and theoretical study on the functionalization of ZnO nanorods with monofunctional alkylphosphonic and bifunctional carboxyalkylphosphonic acids. X-ray photoelectron and infrared spectroscopies have been combined with DFT modeling to explain and understand the interactions that drive the surface anchoring of phosphonic acids on ZnO surface. It was found that both monofunctional and bifunctional acids anchor on ZnO through a multidentate bonding which involves both P=O and P-O moieties of the phosphonic group. Moreover, anchored bifunctional acids bend to the surface, promoting a further interaction between surface hydroxyl groups and carboxylic terminations. This secondary interaction can be limited by increasing the surface density of the anchored molecules.

The relative stability of nine different well defined CeO2 surfaces has been studied by periodic density functional calculations using GGA + U and B3LYP exchange-correlation functional. Both methods consistently predict that CeO2(111) is the most stable surface and also provide a consistent picture of the most stable surfaces which indeed are in agreement with previous studies based on empirical interatomic potentials. The facility of ceria surfaces to undergo a redox process has been investigated by forcing spin-polarized solutions, which lead to the occupancy of Ce 4f orbitals. These calculations provide evidence that surfaces with low-coordinated Ce cations are likely to be reduced more easily than regular low-index Miller surfaces. Fil: Branda, Maria Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Ferullo, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Causá, Mauro. Università degli Studi di Napoli Federico II; Italia Fil: Illas, Francesc. Universidad de Barcelona; España

Surface hydroxy groups are known to play a significant role in the photocatalytic behavior of TiO2. The molecular or dissociative character of H2O adsorption on titania is strongly affected by the local surface structure, but dissociation, producing −OH, should prevail on surface sites with a high degree of coordinative unsaturation. Here we report an IR investigation of hydroxy groups on low coordination sites of TiO2 P25 (Degussa), a commercial titania powder considered a staple in the field of heterogeneous photocatalysis. The presence of coordinatively defective surface terminations well agrees with the roughness of the border of TiO2 particles observed by high resolution transmission electron microscopy. Furthermore, IR spectra of adsorbed CO were used to probe the Lewis acidity of surface Ti4+ ions exposed after the removal of water molecules and hydroxy groups. Evidence for two additional types of surface cationic sites with respect those reported in the literature was found.

The vibrational properties of adsorbed carbonyls on heterogeneous Pd/oxide systems (SiO2−Al2O3, Al2O3, and MgO) are compared and discussed. On the basis of the surface science literature, the complex IR spectra of carbonyls formed on Pd particles are interpreted in terms of what occurs on well-defined Pd(111) and Pd(100) faces and on edge/corner defects, typical of metal nanoparticles, thus bridging the gap between single crystals and high surface area systems. Furthermore, the influence of the electronic properties of the support (i.e., surface acidity/basicity) in determining the spectral features of carbonyls formed on Pd particles is clearly demonstrated.