Optical Hydrogen Sensing Properties of e-Beam WO3 Films Decorated with Gold Nanoparticles.

Tungsten oxide thin films with different thicknesses, crystallinity and morphology were synthesized by e-beam deposition followed by thermal treatment and acid boiling. The films with different surface morphologies were coated with gold nanoparticles and tested as optical sensing materials towards hydrogen. X-ray diffraction, scanning electron microscopy, ellipsometry and UV-VIS spectroscopy were employed to characterize the structural, morphological and optical properties of the film. We demonstrated a good response towards hydrogen in air, reaching a good selectivity among other common reducing gases, such as ammonia and carbon monoxide. The sensitivity has been proven to be highly dependent on the thickness and crystallinity of the samples.

Photoelectrochemical C-H Activation Through a Quinacridone Dye Enabling Proton-Coupled Electron Transfer.

Dye-sensitized photoanodes for C-H activation in organic substrates are assembled by vacuum sublimation of a commercially available quinacridone (QNC) dye in the form of nanosized rods onto fluorine-doped tin oxide (FTO), TiO2 , and SnO2 slides. The photoanodes display extended absorption in the visible range (450-600 nm) and ultrafast photoinduced electron injection (<1 ps, as revealed by transient absorption spectroscopy) of the QNC dye into the semiconductor. The proton-coupled electron-transfer reactivity of QNC is exploited for generating a nitrogen-based radical as its oxidized form, which is competent in C-H bond activation. The key reactivity parameter is the bond-dissociation free energy (BDFE) associated with the N⋅/N-H couple in QNC of 80.5±2.3 kcal mol-1 , which enables hydrogen atom abstraction from allylic or benzylic C-H moieties. A photoelectrochemical response is indeed observed for organic substrates characterized by C-H bonds with BDFE below the 80.5 kcal mol-1 threshold, such as γ-terpinene, xanthene, or dihydroanthracene. This work provides a rational, mechanistically oriented route to the design of dye-sensitized photoelectrodes for selective organic transformations.

Enhancing Tungsten Oxide Gasochromism with Noble Metal Nanoparticles: The Importance of the Interface.

Crystalline tungsten trioxide (WO3 ) thin films covered by noble metal (gold and platinum) nanoparticles are synthesized via wet chemistry and used as optical sensors for gaseous hydrogen. Sensing performances are strongly influenced by the catalyst used, with platinum (Pt) resulting as best. Surprisingly, it is found that gold (Au) can provide remarkable sensing activity that tuned out to be strongly dependent on the nanoparticle size: devices sensitized with smaller nanoparticles display better H2 sensing performance. Computational insight based on density functional theory calculations suggested that this can be related to processes occurring specifically at the Au nanoparticle-WO3 interface (whose extent is in fact dependent on the nanoparticle size), where the hydrogen dissociative adsorption turns out to be possible. While both experiments and calculations single out Pt as better than Au for sensing, the present work reveals how an exquisitely nanoscopic effect can yield unexpected sensing performance for Au on WO3 , and how these performances can be tuned by controlling the nanoscale features of the system.

Artificial photosynthesis: photoanodes based on polyquinoid dyes onto mesoporous tin oxide surface.

Dye-sensitized photoelectrochemical cells represent an appealing solution for artificial photosynthesis, aimed at the conversion of solar light into fuels or commodity chemicals. Extensive efforts have been directed towards the development of photoelectrodes combining semiconductor materials and organic dyes; the use of molecular components allows to tune the absorption and redox properties of the material. Recently, we have reported the use of a class of pentacyclic quinoid organic dyes (KuQuinone) chemisorbed onto semiconducting tin oxide as photoanodes for water oxidation. In this work, we investigate the effect of the SnO2 semiconductor thickness and morphology and of the dye-anchoring group on the photoelectrochemical performance of the electrodes. The optimized materials are mesoporous SnO2 layers with 2.5 µm film thickness combined with a KuQuinone dye with a 3-carboxylpropyl-anchoring chain: these electrodes achieve light-harvesting efficiency of 93% at the maximum absorption wavelength of 533 nm, and photocurrent density J up to 350 µA/cm2 in the photoelectrochemical oxidation of ascorbate, although with a limited incident photon-to-current efficiency of 0.075%. Calculations based on the density functional theory (DFT) support the role of the reduced species of the KuQuinone dye via a proton-coupled electron transfer as the competent species involved in the electron transfer to the tin oxide semiconductor. Finally, a preliminary investigation of the photoelectrodes towards benzyl alcohol oxidation is presented, achieving photocurrent density up to 90 µA/cm2 in acetonitrile in the presence of N-hydroxysuccinimide and pyridine as redox mediator and base, respectively. These results support the possibility of using molecular-based materials in synthetic photoelectrochemistry.

Up-Cycling of LCD Glass by Additive Manufacturing of Porous Translucent Glass Scaffolds.

Additive manufacturing technologies, compared to conventional shaping methods, offer great opportunities in design versatility, for the manufacturing of highly porous ceramic components. However, the application to glass powders, later subjected to viscous flow sintering, involves significant challenges, especially in shape retention and in the achievement of a substantial degree of translucency in the final products. The present paper disclosed the potential of glass recovered from liquid crystal displays (LCD) for the manufacturing of highly porous scaffolds by direct ink writing and masked stereolithography of fine powders mixed with suitable organic additives, and sintered at 950 °C, for 1-1.5 h, in air. The specific glass, featuring a relatively high transition temperature (Tg~700 °C), allowed for the complete burn-out of organics before viscous flow sintering could take place; in addition, translucency was favored by the successful removal of porosity in the struts and by the resistance of the used glass to crystallization.

SILAR Deposition of Metal Oxide Nanostructured Films.

Methods for the fabrication of thin films with well controlled structure and properties are of great importance for the development of functional devices for a large range of applications. SILAR, the acronym for Successive Ionic Layer Adsorption and Reaction, is an evolution and combination of two other deposition methods, the Atomic Layer Deposition and Chemical Bath Deposition. Due to a relative simplicity and low cost, this method has gained increasing interest in the scientific community. There are, however, several aspects related to the influence of the many parameters involved, which deserve further deepening. In this review article, the basis of the method, its application to the fabrication of thin films, the importance of experimental parameters, and some recent advances in the application of oxide films are reviewed. At first the fundamental theoretical bases and experimental concepts of SILAR are discussed. Then, the fabrication of chalcogenides and metal oxides is reviewed, with special emphasis to metal oxides, trying to extract general information on the effect of experimental parameters on structural, morphological and functional properties. Finally, recent advances in the application of oxide films prepared by SILAR are described, focusing on supercapacitors, transparent electrodes, solar cells, and photoelectrochemical devices.

Titanate Fibroin Nanocomposites: A Novel Approach for the Removal of Heavy-Metal Ions from water.

In this study, we report the fabrication of nanocomposites made of titanate nanosheets immobilized in a solid matrix of regenerated silk fibroin as novel heavy-metal-ion removal systems. The capacity of these nanocomposite films to remove lead, mercury, and copper cations from water was investigated, and as shown by the elemental quantitative analysis performed, their removal capacity is 73 mmol/g for all of the ions tested. We demonstrate that the nanocomposites can efficiently retain the adsorbed ions, with no release of titanate nanosheets occurring even after several exposure cycles to ionic solutions, eliminating the risk of release of potentially hazardous nanosubstances to the environment. We also prove that the introduction of sodium ions in the nanocomposite formulation makes the materials highly selective toward the lead ions. The developed biopolymer nanocomposites can be potentially used for the efficient removal of heavy-metal-ion pollutants from water and, thanks to their physical and optical characteristics, offer the possibility to be used in sensor applications.