Recent advances in niobium-based materials for photocatalytic solar fuel production

The search for renewable and clean energy sources is a key aspect for sustainable development as energy consumption has continuously increased over the years concomitantly with environmental concerns caused by the use of fossil fuels. Semiconductor materials have great potential for acting as photocatalysts for solar fuel production, a potential energy source able to solve both energy and environmental concerns. Among the studied semiconductor materials, those based on niobium pentacation are still shallowly explored, although the number of publications and patents on Nb(V)-based photocatalysts has increased in the last years. A large variety of Nb(V)-based materials exhibit suitable electronic/morphological properties for light-driving reactions. Not only the extensive group of Nb2O5 polymorphs is explored, but also many types of layered niobates, mixed oxides, and Nb(V)-doped semiconductors. Therefore, the aim of this manuscript is to provide a review of the latest developments of niobium based photocatalysts for energy conversion into fuels, more specifically, CO2 reduction to hydrocarbons or H2 eVolution from water. Additionally, the main strategies for improving the photocatalytic performance of niobium-based materials are discussed

Application of EPR Spectroscopy in TiO2 and Nb2O5 Photocatalysis

The interaction of light with semiconducting materials becomes the center of a wide range of technologies, such as photocatalysis. This technology has recently attracted increasing attention due to its prospective uses in green energy and environmental remediation. The characterization of the electronic structure of the semiconductors is essential to a deep understanding of the photocatalytic process since they influence and govern the photocatalytic activity by the formation of reactive radical species. Electron paramagnetic resonance (EPR) spectroscopy is a unique analytical tool that can be employed to monitor the photoinduced phenomena occurring in the solid and liquid phases and provides precise insights into the dynamic and reactivity of the photocatalyst under different experimental conditions. This review focus on the application of EPR in the observation of paramagnetic centers formed upon irradiation of titanium dioxide and niobium oxide photocatalysts. TiO2 and Nb2O5 are very well-known semiconductors that have been widely used for photocatalytic applications. A large number of experimental results on both materials offer a reliable platform to illustrate the contribution of the EPR studies on heterogeneous photocatalysis, particularly in monitoring the photogenerated charge carriers, trap states, and surface charge transfer steps. A detailed overview of EPR-spin trapping techniques in mechanistic studies to follow the nature of the photogenerated species in suspension during the photocatalytic process is presented. The role of the electron donors or the electron acceptors and their effect on the photocatalytic process in the solid or the liquid phase are highlighted

Characterization of a highly efficient N-doped TiO 2 photocatalyst prepared via factorial design

The preparation of titanium dioxide nanoparticles doped with nitrogen for application as a photocatalyst in the decomposition of azo dyes was optimized by factorial planning. Five variables were evaluated and the results showed that the stirring method of the reaction medium, the nitrogen source and the calcination temperature are the determining parameters that affect the photocatalytic activity. With this methodology, it was possible to obtain an optimized photocatalyst (K1) with high surface area and high mineralization efficiency (100%) of the dye Ponceau 4R under solar irradiation. K1, its non-doped version and the worst photocatalyst obtained by the factorial planning (K2) were characterized by several techniques to rationalize the different behaviors. The observed mineralization rate constants under artificial UV-A radiation were in the order of 10−2, 10−4 and 10−3 min−1, respectively, for K1, K2 and the non-doped oxide. As shown by N2 sorption isotherms, the powders exhibited large variations in porosity as well as in the specific surface area, with values ranging from 63.03 m2 g−1 for K1 to 12.82 m2 g−1 for K2. Infrared spectra showed that the calcination of the doped oxides between 300 and 500 °C leads to considerable loss of the nitrogen content, which is corroborated by XPS measurements that also indicate the presence of oxygen vacancies on their surfaces. Nanosecond transient absorption measurements show that the electron–hole half-lifetime in K1 is 870 ns, ca. two times longer than that observed for the other photocatalysts. Additionally, dye degradation studies under solar radiation reveal that K1 is ca. 28% faster than the non-doped TiO2 under similar conditions. This higher photoactivity for K1 is attributed to its extended visible light absorption and the optimized morphological and electronic properties.DFG/BA 1137/8-

Charge carrier dynamics and photocatalytic behavior of TiO2 nanopowders submitted to hydrothermal or conventional heat treatment

The sol–gel technique followed by conventional (TiO2-1) and hydrothermal (TiO2-2) thermal treatment was employed to prepare TiO2-based photocatalysts with distinct particle sizes and crystalline structures. The as prepared metal oxides were evaluated as photocatalysts for gaseous HCHO degradation, methanol, and dye oxidation reactions. Additionally, metallic platinum was deposited on the TiO2 surfaces and H2 evolution measurements were performed. The photocatalytic activities were rationalized in terms of morphologic parameters along with the electron/hole dynamics obtained from transient absorption spectroscopy (TAS). TiO2-2 exhibits smaller particle size, poorer crystallinity, and higher surface area than TiO2-1. Moreover the hydrothermal treatment leads to formation of the metastable brookite phase, while TiO2-1 exhibits only the anatase phase. TAS measurements show that the electron/hole recombination of TiO2-2 is faster than that of the latter. Despite that, TiO2-2 exhibits higher photonic efficiencies for photocatalytic oxidation reactions, which is attributed to its larger surface area that compensates for the decrease of the surface charge carrier concentration. For H2 evolution, it was found that the surface area has only a minor effect and the photocatalyst performance is controlled by the efficiency of the electron transfer to the platinum islands. This process is facilitated by the higher crystallinity of TiO2-1, which exhibits higher photonic efficiency for H2 evolution than that observed for TiO2-2. The results found here provide new insights into the correlations between thermal treatment conditions and photocatalytic activity and will be useful for the design of high performance photocatalysts.Fundac˜ao de Amparo `a Pesquisa do Estado de Minas GeraisConselho Nacional de Desenvolvimento Cientif´ıco e Tecnolog´ıcoCoordenac˜ao de Aperfeiçoamento de Pessoal de N´ıvel SuperiorDFG/BA 1137/8-

Rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART): Study protocol for a randomized controlled trial

Background: Acute respiratory distress syndrome (ARDS) is associated with high in-hospital mortality. Alveolar recruitment followed by ventilation at optimal titrated PEEP may reduce ventilator-induced lung injury and improve oxygenation in patients with ARDS, but the effects on mortality and other clinical outcomes remain unknown. This article reports the rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART). Methods/Design: ART is a pragmatic, multicenter, randomized (concealed), controlled trial, which aims to determine if maximum stepwise alveolar recruitment associated with PEEP titration is able to increase 28-day survival in patients with ARDS compared to conventional treatment (ARDSNet strategy). We will enroll adult patients with ARDS of less than 72 h duration. The intervention group will receive an alveolar recruitment maneuver, with stepwise increases of PEEP achieving 45 cmH(2)O and peak pressure of 60 cmH2O, followed by ventilation with optimal PEEP titrated according to the static compliance of the respiratory system. In the control group, mechanical ventilation will follow a conventional protocol (ARDSNet). In both groups, we will use controlled volume mode with low tidal volumes (4 to 6 mL/kg of predicted body weight) and targeting plateau pressure <= 30 cmH2O. The primary outcome is 28-day survival, and the secondary outcomes are: length of ICU stay; length of hospital stay; pneumothorax requiring chest tube during first 7 days; barotrauma during first 7 days; mechanical ventilation-free days from days 1 to 28; ICU, in-hospital, and 6-month survival. ART is an event-guided trial planned to last until 520 events (deaths within 28 days) are observed. These events allow detection of a hazard ratio of 0.75, with 90% power and two-tailed type I error of 5%. All analysis will follow the intention-to-treat principle. Discussion: If the ART strategy with maximum recruitment and PEEP titration improves 28-day survival, this will represent a notable advance to the care of ARDS patients. Conversely, if the ART strategy is similar or inferior to the current evidence-based strategy (ARDSNet), this should also change current practice as many institutions routinely employ recruitment maneuvers and set PEEP levels according to some titration method.Hospital do Coracao (HCor) as part of the Program 'Hospitais de Excelencia a Servico do SUS (PROADI-SUS)'Brazilian Ministry of Healt

A química de coordenação e a produção de combustíveis solares

Life on earth depends on the absorption and conversion of solar energy into chemical bonds, i.e. photosynthesis. In this process, sun light is employed to oxidize water into oxygen and reducing equivalents used to produce fuels. In artificial photosynthesis, the goal is to develop relatively simple systems able to mimic photosynthetic organisms and promote solar-to-chemical conversion. The aim of the present review was to describe recent advances in the application of coordination compounds as catalysts in some key reactions for artificial photosynthesis, such as water splitting and CO2 reduction

Photoswitches and Luminescent Rigidity Sensors Based on fac-[Re(CO)(3)(Me(4)phen)(L)](+)

The fac-[Re(CO)(3)(Me(4)phen)(trans-L)](+) complexes, Me(4)phen = 3,4,7,8-tetramethyl-1,10-phenanthroline and L = 4-styrylpyridine, stpy, or 1,2-bis(4-pyridyl)ethylene, bpe, were synthesized and characterized by their spectroscopic, photochemical, and photophysical properties. The complexes exhibit trans-to-cis isomerization upon 313, 334, 365, and 404 nm irradiation, and the true quantum yields can be efficiently determined by absorption changes combined with (1)H NMR data. For fac-[Re(CO)(3)(Me(4)phen)(trans-bpe)](+) similar quantum yields were determined at all wavelengths investigated. However, a lower value (phi(true) = 0.35) was determined for fac-[Re(CO)(3)(Me(4)phen)(trans-stpy)](+) at 404 nm irradiation, which indicates different pathways for the photoisomerization process. The photoproducts, fac-[Re(CO)(3)(Me(4)phen)(cis-L)](+), exhibit luminescence at room temperature with two maxima ascribed to the (3)IL(Me4phen) and (3)MLCT(Re -> Me4phen) excited states. The luminescence properties were investigated in different media, and the behavior in glassy EPA at 77 K showed that the contribution of each emissive state is dependent on the excitation wavelength. The photochemical and photophysical behavior of the complexes were rationalized in terms of the energy gap of excited states and can be exploited in photoswitchable luminescent rigidity sensors.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP Fundacao de Amparo a Pesquisa do Estado de Sao PauloFAPESPFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CNPq Conselho Nacional de Desenvolvimento Cientifico e TecnologicoConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPqConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Dissociative Ligand Field-Based Photochemistry in Organometallic Compounds

The dissociation of ligands by excitation of coordination complexes with visible and UV light is a field that is now over 100 years old, yet it is increasingly relevant due to the opportunities it provides for applications from photoinduced anionic polymerization and biomedical applications, for example, to release small molecules (CO, NO, etc.) of relevance to signaling or to release/activate drugs. In this chapter we will focus on the release of small molecules (primarily amine, CO and arene) with paradigms of the main classes of photochemically induced ligand dissociation. The discussion will focus on the processes themselves and not applications