Reaction Mechanism of Hydrogen Generation and Nitrogen Fixation at Carbon Nitride/Double Perovskite Heterojunctions

Photocatalytically active heterojunctions based on metal halide perovskites (MHPs) are drawing significant interest for their chameleon ability to foster several redox reactions. The lack of mechanistic insights into their performance, however, limits the ability of engineering novel and optimized materials. Herein, a report is made on a composite system including a double perovskite, Cs2AgBiCl6/g-C3N4, used in parallel for solar-driven hydrogen generation and nitrogen reduction, quantified by a rigorous analytical approach. The composite efficiently promotes the two reactions, but its activity strongly depends on the perovskite/carbon nitride relative amounts. Through advanced spectroscopic investigation and density function theory (DFT) modeling the H2 and NH3 production reaction mechanisms are studied, finding perovskite halide vacancies as the primary reactive sites for hydrogen generation together with a positive contribution of low loaded g-C3N4 in reducing carrier recombination. For nitrogen reduction, instead, the active sites are g-C3N4 nitrogen vacancies, and the heterojunction best performs at low perovskites loadings where the composites maximize light absorption and reduce carrier losses. It is believed that these insights are important add-ons toward universal exploitation of MHPs in contemporary photocatalysis

Marine and Coastal Hazard Assessment for Three Coastal Oil Rigs

A forecasting and hazard assessment system for oil dispersion from Italian oil rigs was set up within the framework of a national research project. The system is based on 3D hydrodynamic, mesoscale resolving models providing forcing fields for a Lagrangian module of oil dispersion and slick evolution (oil transport and transformation). The tool provides,daily, the outputs of numerical simulations of possible oil spills from extraction platform sites. In this work we present the results for the 3 platforms closest to the Italian coast. Aside the operational usage, the numerical outputs are also stored and adopted to compute statistics of the slick distributions in the coastal and marine areas of interest. The hazard was assessed by means of two different indices (Hazard Index and Occurrence Index) based on the operational system outputs, for the estimation of the hazard at sea (marine hazard or aerial hazard). As short forecasts (2 days long) often do not allow the oil to reach the coast, an extra set of long-period simulations has been performed in order to compute a third Hazard Index (Coastal Hazard Index) suitable to estimate the hazard along the shorelines. The adopted methodology allowed, as a whole, to assess both coastal and marine oil spill hazard due to oil spill extraction activities. The indices constitute a basic informative layer on which the environmental risk could be also evaluated, once opportunely combined with coastal vulnerability and sensitivity layers

Bismuth-Based Halide Perovskites for Photocatalytic H2 Evolution Application

Metal halide perovskites (MHPs), in particular lead-based perovskites, have earned recognized fame in several fields for their outstanding optoelectronic properties, including direct generation of free charge carriers, optimal ambipolar charge carrier transport properties, high absorption coefficient, point-defect tolerance, and compositional versatility. Nowadays, this class of materials represents a real and promising alternative to silicon for photovoltaic technologies. This worthy success led to a growing interest in the exploration of MHPs in other hot research fields, such as solar-driven photocatalytic water splitting towards hydrogen production. Nevertheless, many of these perovskites show air and moisture instability problems that considerably hinder their practical application for photocatalytic water splitting. Moreover, if chemical instability is a problem that can be in part mitigated by the optimization of the chemical composition and crystal structure, the presence of lead represents a real problem for the practical application of MHPs in commercial devices due to environmental and healthcare issues. To successfully overcome these problems, lead-free metal halide perovskites (LFMHPs) have gained increasing interest thanks to their optoelectronic properties, comparable to lead-based materials, and their more eco-friendly nature. Among all the lead-free perovskite alternatives, this mini-review considers bismuth-based perovskites and perovskite derivatives with a specific focus on solar-driven photocatalysis application for H-2 evolution. Special attention is dedicated to the structure and composition of the different materials and to the advantage of heterojunction engineering and the relative impact on the photocatalytic process

Bismuth-Based Halide Perovskites for Photocatalytic H2 Evolution Application

Metal halide perovskites (MHPs), in particular lead-based perovskites, have earned recognized fame in several fields for their outstanding optoelectronic properties, including direct generation of free charge carriers, optimal ambipolar charge carrier transport properties, high absorption coefficient, point-defect tolerance, and compositional versatility. Nowadays, this class of materials represents a real and promising alternative to silicon for photovoltaic technologies. This worthy success led to a growing interest in the exploration of MHPs in other hot research fields, such as solar-driven photocatalytic water splitting towards hydrogen production. Nevertheless, many of these perovskites show air and moisture instability problems that considerably hinder their practical application for photocatalytic water splitting. Moreover, if chemical instability is a problem that can be in part mitigated by the optimization of the chemical composition and crystal structure, the presence of lead represents a real problem for the practical application of MHPs in commercial devices due to environmental and healthcare issues. To successfully overcome these problems, lead-free metal halide perovskites (LFMHPs) have gained increasing interest thanks to their optoelectronic properties, comparable to lead-based materials, and their more eco-friendly nature. Among all the lead-free perovskite alternatives, this mini-review considers bismuth-based perovskites and perovskite derivatives with a specific focus on solar-driven photocatalysis application for H2 evolution. Special attention is dedicated to the structure and composition of the different materials and to the advantage of heterojunction engineering and the relative impact on the photocatalytic process

Caratterizzazione idrodinamica del Golfo di Cagliari mediante misure lagrangiane

In data 9 settembre 2014 il gruppo di oceanografia dell’Istituto per l’Ambiente Marino Costiero (IAMC) di Torregrande (Oristano), del Consiglio Nazionale delle Ricerche (CNR), ha partecipato alla esercitazione di Search and Rescue (SAR) denominata “Squalo 2014”. L’esercitazione è stata organizzata e coordinata dalla Direzione Marittima della Guardia Costiera di Cagliari e ha visto la partecipazione di numerosi enti (civili e militari) preposti alle operazioni di salvataggio e/o di supporto logistico. La partecipazione del CNR ha visto come obiettivo specifico la caratterizzazione idrodinamica dell’area di studio utilizzando osservazioni Lagrangiane e modelli numerici di simulazione. L’obiettivo a lungo termine è la ideazione e la realizzazione di un sistema di supporto alle decisioni (Decisional Support System) capace di determinare l'area di ricerca ottimale (area di probabilità). Questo sarà possibile unendo tecniche di simulazione numerica di tipo deterministico (modelli idrodinamici costieri e moduli di dispersione Lagrangiana) con metodi statistici per la stima dell’errore ed il calcolo delle probabilità. Compatibilmente con le risorse disponibili (finanziarie, computazionali ed umane), l’intenzione è di proseguire la ricerca iniziata nel corso della esercitazione, testando un modello SAR denominato “Leeway” che ha le potenzialità per consentire lo sviluppo del suddetto DSS Questa attività è stata finanziata nell’ambito del progetto bandiera RITMARE (SP3-WP4-AZ6 e SP5-WP4-AZ3)

Halide alloying and role of central atom on the structural and optical properties of decylammonium germanium 2D perovskites

We report here a novel series of halide alloyed Ge-containing 2D perovskites including decylammonium as organic spacer, namely DA2Ge(Br1−xIx)4. This system forms a continuous solid solution on the halide site with a modulation of the bandgap from 2.74 to 2.17 eV with a rapid decrease up to x = 0.5 followed by a plateau. Iodide-rich compositions show enhanced broad room temperature (RT) photoluminescence (PL) that narrows at low temperature with maximum quantum yields for mixed compositions. The replacement of Ge with Pb and Sn in DA2GeBr4 and DA2GeI4 provides a tuning of the bandgap in the whole visible spectrum with a marked blue-shift when lead is present and, opposite, a red-shift for Sn replacement. The RT PL progressively broadens moving from Pb to Sn and to Ge covering an emission range from 400 to 800 nm. Finally, the air stability of lead-free 2D perovskites of this work has been determined indicating its improvement by increasing the hardness of the halide