G. Cacciato

Surface diffusion coefficient of Au atoms on single layer graphene grown on Cu

A 5 nm thick Au film was deposited on single layer graphene sheets grown on Cu. By thermal processes, the dewetting phenomenon of the Au film on the graphene was induced so to form Au nanoparticles. The mean radius, surface-to-surface distance, and surface density evolution of the nanoparticles on the graphene sheets as a function of the annealing temperature were quantified by scanning electron microscopy analyses. These quantitative data were analyzed within the classical mean-field nucleation theory so to obtain the temperature-dependent Au atoms surface diffusion coefficient on graphene: DS(T)=[(8.2±0.6)×10−8]exp[−(0.31±0.02eVat)/kT] cm2/s.

Laser irradiation in water for the novel, scalable synthesis of black TiOx photocatalyst for environmental remediation

Since 1970, TiO2 photocatalysis has been considered a possible alternative for sustainable water treatment. This is due to its material stability, abundance, nontoxicity and high activity. Unfortunately, its wide band gap (≈3.2 eV) in the UV portion of the spectrum makes it inefficient under solar illumination. Recently, so-called “black TiO2” has been proposed as a candidate to overcome this issue. However, typical synthesis routes require high hydrogen pressure and long annealing treatments. In this work, we present an industrially scalable synthesis of TiO2-based material based on laser irradiation. The resulting black TiOx shows a high activity and adsorbs visible radiation, overcoming the main concerns related to the use of TiO2 under solar irradiation. We employed a commercial high repetition rate green laser in order to synthesize a black TiOx layer and we demonstrate the scalability of the present methodology. The photocatalyst is composed of a nanostructured titanate film (TiOx) synthetized on a titanium foil, directly back-contacted to a layer of Pt nanoparticles (PtNps) deposited on the rear side of the same foil. The result is a monolithic photochemical diode with a stacked, layered structure (TiOx/Ti/PtNps). The resulting high photo-efficiency is ascribed to both the scavenging of electrons by Pt nanoparticles and the presence of trap surface states for holes in an amorphous hydrogenated TiOx layer.

TiO2 Nanostructures and Nanocomposites for Sustainable Photocatalytic Water Purification

Water, together with energy and food, has been addressed as one of the main urgent problems of humanity. The conventional wastewater treatments suffer some limita‐ tions related to the effectiveness in decontamination (mechanical filtration), in the heavy use of chemicals (chlorination), or in elevation of operational costs and energy require‐ ments (desalination and reverse osmosis). In this sense, new materials such as nanocom‐ posites may overcome these issues taking advantage of the peculiar properties of materials at nanoscale. Research on novel nanotechnologies must bring advances in order to contrast and prevent water scarcity and pollution. In order to be effective, these nanotechnolo‐ gies should run at low operational cost, even in places unequipped by strong infrastruc‐ tures and in concert with conventional cheap methodologies. Among the alternative water purification methods, TiO2-based photocatalysis has attracted great attention due to material stability, abundance, non-toxicity and high decontamination efficiency. In this material, electron–hole pairs generated by light absorption separate from each other and migrate to catalytically active sites at the surface of the photocatalyst. Photogenerated carriers are able to induce the decomposition of organic pollutants as well as the deactivation of bacteria and viruses. The main deficien‐ cy of this material, related to its large bandgap, is that only the UV fraction of the solar spectrum which is effective to this purpose. Several approaches have been proposed to overpass this issue and, among them, the use of metal–TiO2 nanocomposites with proper nanostructuration seems very promising for water purification strategies.

Electrical properties modulation of thin film solar cell using gold nanostructures at textured FTO/p–i–n interface

We report about the modulation of the electrical properties of thin film solar cells due to the incorporation of size-selected Au nanostructures (NSs) at a textured FTO/p–i–n interface. By increasing the Au NSs size, the analyses of current-voltage characteristics show lower Schottky barrier heights and the gradual reduction of the open-circuit voltages (VOC). The optical measurements show higher parasitic absorption by larger Au NSs that reduces the amount of radiation transmitted by the transparent to absorber layer. This process decreases the number of photo-generated carriers and may explain the VOC reduction related to the devices with larger Au NSs at the interface. So, the correlation between materials properties and device performances was established.

Sb-Doped Titanium Oxide: A Rationale for Its Photocatalytic Activity for Environmental Remediation

The problem of water purification is one of the most urgent issues in developing countries, where large infrastructures and energy resources are limited. Among the possibilities for a cheap route to clean water, photocatalytic materials in the form of coatings or nanostructures are among the most promising. The most widely studied photocatalytic material is titanium dioxide (TiO2). Here, we investigate the photocatalytic properties of 1.5% Sb-doped TiO2 and laser-irradiated Sb-doped TiOx. Calcined Sb-doped TiO2 was found to adopt the rutile structure, but it turned amorphous after laser irradiation. Photocatalytic tests for Sb-doped TiO2 showed an activity 1 order of magnitude higher than that of an undoped TiO2 control sample under both ultraviolet and visible irradiation. A further sizeable enhancement resulted from laser irradiation. The increased photocatalytic activity is ascribed to both enhanced visible region absorption associated with Sb-induced lone pair surface electronic states and trapping of the holes at the lone pair surface sites, thus inhibiting the recombination of the electrons and holes generated in the initial photoexcitation step. This study shows the first rationalization of the photocatalytic properties of Sb–TiO2 in terms of its electronic structure.