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Bismuth vanadate (BiVO4) has surface states that give rise to defect levels that mediate electron-hole recombination. In order to minimize the inefficiencies, an ultrathin Al overlayer was deposited on the BiVO4electrodes. A 54 % improvement on the photocurrent density was obtained using the Al-modified BiVO4electrode, accompanied by a 15 % increase in stability over 7.5 h of continuous irradiation. Moreover, surface capacitance measurements showed that the Al overlayer was indeed passivating the surface states. We also shed light on the deposition of an Al overlayer on the surface of BiVO4, by investigating the process on model BiVO4powders. This study presents useful, previously unreported information about the surface chemistry of BiVO4based on experimental methods and gives unique insights on the characterization of the BiVO4surface. The existence of surface reactive sites on BiVO4was confirmed and quantified (1.5 reactive sites/nm2) via chemical titration

Ammonia production from N2 and H2 by the high-temperature and high-pressure catalytic Haber-Bosch process is among the largest and the most energy intensive industrial process. This large environmental footprint is strongly linked to the current, mostly-fossil origin of dihydrogen. The room temperature and ambient pressure photo reduction of N2, which is what some microorganisms obtain overall with ATP-fueled N2 reduction by nitrogenase enzymes, would circumvent such need for (fossil) H2 and hence could provide a sustainable route to NH3. This chapter reviews the current state-of-the-art process for ammonia photocatalysts, providing representative examples for the various classes of active materials reported so far (titania, metal sulfides, bismuth, and carbon-based materials).

The behaviour of photoanodes based on TiO2 nanotubes (TNTs) grown on Ti gauze (80 mesh) by controlled anodic oxidation was studied in a compact photo-electrocatalytic (PECa) device for H2 production by water photo-electrolysis. The 3D-type structured TNTs-Ti meshes evidenced: i) a mesoporosity due to the presence of highly ordered TiO2 nanotube arrays grown on the round surface of the regularly woven wires of the Ti gauze and ii) a macroporosity due to the open area (36%) of the mesh. The resulting hierarchical porous 3D structure allowed the TNTs-Ti meshes to act both as photoactive materials for efficient light absorption and as porous substrates for fast mass diffusion of protons. The synthesis of TNTs was investigated by varying the applied voltage (in the range 40–60 V) and the anodization time (from 20 min to 7 h). Results showed that two main opposite aspects influenced their performances in the PECa cell: i) the inner diameter and ii) the length of TNTs. While the increase of the inner diameter with the anodization time should favour H2 productivity, longer nanotubes negatively influence the catalytic activity due to increasing charge recombination phenomena. The result is an initial decreasing profile of H2 evolution vs. anodization time, reaching a minimum at 3 h and then increasing again for the 5 h-anodized sample (H2 production rate: 1.4 L m−2 h−1). The maximum photoconversion efficiency (0.7%) was obtained, instead, for the 20 min-anodized sample. It is to remark that tests of water splitting were performed with no applied bias and without adding sacrificial donors, opening the route for a sustainable use of these 3D-type meso/macro porous structured photoanodes in the production of solar fuels.

The addition of a CO

The addition of a CO2 adsorption component (substituted imidazolate-based SIM-1 crystals) to a gas diffusion layer (GDL) type catalytic electrode allows to enhance the activity and especially the selectivity to >C1 carbon chain products (ethanol, acetone and isopropanol) of a Pt-based electrocatalyst that is not able to form products of CO2 reduction involving C-C bond formation under conventional (liquid-phase) conditions. This indicates that the increase of the CO2 effective concentration at the electrode active surface is the factor controlling the formation of >C1 products rather than only the intrinsic properties of the electrocatalyst.

Biologically and pharmaceutically relevant arylated quinones (Quin-Ar) have been synthesized via direct CH arylation of a variety of phenols using arylboronic acids. An inexpensive, environmentally friendly iron catalyst, ferric sulphate, Fe-2(SO4)(3), was employed in this operationally simple and efficient method.

A detailed study of the gold-catalyzed tandem 1,3-carboxy migration/allene-enyne cycloisomerization was undertaken. It was found that after the initial allene formation the selectivity of the reaction is strongly influenced by the polarization of the remaining alkyne. Depending on the substitution pattern of the starting diynes, either a Schmittel- or a Myers-Saito-type cyclization was triggered. The 6-endo-dig Myers-Saito-type cyclization gave access to benzo[b]fluorenes, while the Schmittel pathway (5-exo-dig) delivered benzofulvenes as final products. In special cases a yet unknown pathway was opened by the ambiphilic nature of the allene moiety. In these cases completely different products were obtained by the nucleophilic attack of the alkyne moiety onto the allene that can also act as an electrophile. Mechanistic studies revealed that diradical pathways can be ruled out for this type of tandem cyclization reactions and it is shown that both steps of the reaction cascade are catalyzed by the gold complex.

Nitroolefins are usually synthesized using the Henry reaction. Here we report an alternative metal-free decarboxylative nitration protocol for the preparation of the nitroolefins from alpha,beta-unsaturated carboxylic acids using t-butylnitrite (t-BuONO) and TEMPO. alpha,beta-Unsaturated carboxylic acids bearing beta-aromatic and beta-heteroaromatic substituents gave (E)-nitroolefins exclusively under mild conditions. A radical based pathway has been proposed for this decarboxylative nitration reaction.