Singly and multiply doped graphene oxide quantum dots have been synthesized by a simple electrochemical method using water as solvent. The obtained materials have been characterized by photoemission spectroscopy and scanning tunneling microscopy, in order to get a detailed picture of their chemical and structural properties. The electrochemical activity toward the oxygen reduction reaction of the doped graphene oxide quantum dots has been investigated by cyclic voltammetry and rotating disk electrode measurements, showing a clear decrease of the overpotential as a function of the dopant according to the sequence: N ∼ B > B,N. Moreover, assisted by density functional calculations of the Gibbs free energy associated with every electron transfer, we demonstrate that the selectivity of the reaction is controlled by the oxidation states of the dopants: as-prepared graphene oxide quantum dots follow a two-electron reduction path that leads to the formation of hydrogen peroxide, whereas after the reduction with NaBH4, the same materials favor a four-electron reduction of oxygen to wate

TiO 2 nanoparticles are fundamental building blocks of many TiO 2 -based technologies. However, most of the computational studies simulate either bulk or surface titania. Structural and electronic properties of nanoparticles are expected to differ much from extended systems. Moreover, nanoparticles of different size and shape may also present peculiar features. In this study we compare nanocrystals and nanospheres of various sizes (up to a diameter of 3 nm) in order to highlight analogies and differences. In particular, we focus the attention on the surface-to-bulk sites ratio, on the surface sites coordination distribution, on the atomic distortions or curvature and on the surface energies, from the structural point of view. Regarding the electronic properties, we investigate the difference between Kohn-Sham and fundamental gaps of these finite-sized systems, the frontiers orbitals space distribution, ionization potentials and electron affinities and finally the densities of states projected on the various coordination sites present in the nanoparticles. This detailed analysis proves that faceted and spherical nanoparticles present different structural and electronic properties which make each of them better suited for different uses and applications.

Heterogeneous photocatalysis is vital in solving energy and environmental issues that this society is confronted with. Although photocatalysts are often operated in the presence of water, it has not been yet clarified how the interaction with water itself affects charge dynamics in photocatalysts. Using water-coverage-controlled steady and transient infrared absorption spectroscopy and large-model (∼800 atoms) ab initio calculations, we clarify that water enhances hole trapping at the surface of TiO2 nanospheres but not of well-faceted nanoparticles. This water-assisted effect unique to the nanospheres originates from water adsorption as a ligand at a low-coordinated Ti–OH site or through robust hydrogen bonding directly to the terminal OH at the highly curved nanosphere surface. Thus, the interaction with water at the surface of nanospheres can promote photocatalytic reactions of both oxidation and reduction by elongating photogenerated carrier lifetimes. This morphology-dependent water-assisted effect provides a novel and rational basis for designing and engineering nanophotocatalyst morphology to improve photocatalytic performances.

Boron-doped graphene was reported to be the best non-metal doped graphene electrocatalyst for the oxygen reduction reaction (ORR) working at an onset potential of 0.035 V [JACS 136 (2014)

TiO nanoparticles (NPs) are nowadays considered fundamental building blocks for many technological applications. Morphology is found to play a key role with spherical NPs presenting higher binding properties and chemical activity. From the experimental point of view, the characterization of these nano-objects is extremely complex, opening a large room for computational investigations. In this work, TiO spherical NPs of different sizes (from 300 to 4000 atoms) have been studied with a two-scale computational approach. Global optimization to obtain stable and equilibrated nanospheres was performed with a self-consistent charge density functional tight-binding (SCC-DFTB) simulated annealing process, causing a considerable atomic rearrangement within the nanospheres. Those SCC-DFTB relaxed structures have been then optimized at the DFT(B3LYP) level of theory. We present a systematic and comparative SCC-DFTB vs DFT(B3LYP) study of the structural properties, with particular emphasis on the surface-to-bulk sites ratio, coordination distribution of surface sites, and surface energy. From the electronic point of view, we compare HOMO-LUMO and Kohn-Sham gaps, total and projected density of states. Overall, the comparisons between DFTB and hybrid density functional theory show that DFTB provides a rather accurate geometrical and electronic description of these nanospheres of realistic size (up to a diameter of 4.4 nm) at an extremely reduced computational cost. This opens for new challenges in simulations of very large systems and more extended molecular dynamics.