An iron-based photoelectrode

Spinel ZnFe2O4 (ZFO) is a widely studied iron-based semiconductor for application as photoanode material in photoelectrochemical water splitting tandem cells. However, the current benchmark efficiency reported for photoelectrochemical water oxidation at ZFO photoanodes is approximately one order of magnitude smaller than the predicted theoretical maximum. In addition, a large dispersion between the efficiencies reported for ZFO photoanodes prepared by different synthetic approaches, as well as poor reproducibility, become obvious from published data. It has been recently reported that the cation distribution, i.e., the ordering of the Fe3+ and Zn2+ cations within the oxygen lattice, has an impact on the photoelectrochemical activity of the semiconductor. However, the impact of the cation distribution on physicochemical properties directly related to the photoelectrochemical activity was poorly understood. The parameter employed to characterize the cation distribution is the degree of inversion, x, defined as T[Zn1-xFex]O[ZnxFe2-x]O4, with 0 ≤ x ≤ 1 (the superscripts T and O denote tetrahedral and octahedral sites, respectively). In this work, highly pure ZFO samples exhibiting degrees of inversion ranging from x ≈ 0.07 to x ≈ 0.20 were synthesized. The samples exhibited, within the limit of the experimental determination, equal particle size, crystallite size, and crystallinity, as was confirmed by XRD plus Rietveld refinement, Mössbauer spectroscopy, Raman spectroscopy, scanning electron microscopy, and elemental analysis. Oxygen vacancies were not detected. Therefore, the degree of inversion is assumed to be the only independent variable between the different samples. The light absorption, charge carrier transport, and electronic properties were investigated by UV-Vis-NIR reflectivity, impedance spectroscopy, and time-averaged as well as transient photoluminescence spectroscopy, respectively. The photoelectrochemical efficiency for the methanol oxidation reaction under simulated solar irradiation was determined in order to compare the activity of the ZFO samples having different degrees of inversion. VI It was found that the cation distribution does not affect the band gap energy of ZFO but has a large impact on the charge carrier transport and the electronic properties. An increase in the photoelectrochemical activity was observed by increasing the degree of inversion. This impact was mainly ascribed to the enhanced charge carrier transport properties of the samples having higher degrees of inversion. In addition, changes in the probability of the photoinduced electronic transitions of ZFO produced by increasing the degree of inversion were found to additionally contribute, to a lesser extent, to the observed enhancement in the photoelectrochemical activity. This thesis provides a fundamental insight concerning the impact of the degree of inversion on the photoelectrochemical activity of ZFO. Furthermore, the results presented herein contribute to the understanding of some factors limiting the efficiency of ZFO photoanodes

An iron-based photoelectrode

Spinel ZnFe2O4 (ZFO) is a widely studied iron-based semiconductor for application as photoanode material in photoelectrochemical water splitting tandem cells. However, the current benchmark efficiency reported for photoelectrochemical water oxidation at ZFO photoanodes is approximately one order of magnitude smaller than the predicted theoretical maximum. In addition, a large dispersion between the efficiencies reported for ZFO photoanodes prepared by different synthetic approaches, as well as poor reproducibility, become obvious from published data. It has been recently reported that the cation distribution, i.e., the ordering of the Fe3+ and Zn2+ cations within the oxygen lattice, has an impact on the photoelectrochemical activity of the semiconductor. However, the impact of the cation distribution on physicochemical properties directly related to the photoelectrochemical activity was poorly understood. The parameter employed to characterize the cation distribution is the degree of inversion, x, defined as T[Zn1-xFex]O[ZnxFe2-x]O4, with 0 ≤ x ≤ 1 (the superscripts T and O denote tetrahedral and octahedral sites, respectively). In this work, highly pure ZFO samples exhibiting degrees of inversion ranging from x ≈ 0.07 to x ≈ 0.20 were synthesized. The samples exhibited, within the limit of the experimental determination, equal particle size, crystallite size, and crystallinity, as was confirmed by XRD plus Rietveld refinement, Mössbauer spectroscopy, Raman spectroscopy, scanning electron microscopy, and elemental analysis. Oxygen vacancies were not detected. Therefore, the degree of inversion is assumed to be the only independent variable between the different samples. The light absorption, charge carrier transport, and electronic properties were investigated by UV-Vis-NIR reflectivity, impedance spectroscopy, and time-averaged as well as transient photoluminescence spectroscopy, respectively. The photoelectrochemical efficiency for the methanol oxidation reaction under simulated solar irradiation was determined in order to compare the activity of the ZFO samples having different degrees of inversion. VI It was found that the cation distribution does not affect the band gap energy of ZFO but has a large impact on the charge carrier transport and the electronic properties. An increase in the photoelectrochemical activity was observed by increasing the degree of inversion. This impact was mainly ascribed to the enhanced charge carrier transport properties of the samples having higher degrees of inversion. In addition, changes in the probability of the photoinduced electronic transitions of ZFO produced by increasing the degree of inversion were found to additionally contribute, to a lesser extent, to the observed enhancement in the photoelectrochemical activity. This thesis provides a fundamental insight concerning the impact of the degree of inversion on the photoelectrochemical activity of ZFO. Furthermore, the results presented herein contribute to the understanding of some factors limiting the efficiency of ZFO photoanodes

Manganese Defective Clustering: Influence on the Spectroscopic Features of Ceria-Based Nanomaterials

The influence of manganese modification on the spectroscopic features of manganese-doped CeO2 systems synthesized by the microwave-assisted hydrothermal route and their correlation with the presence of O defective structures were verified, focusing on their interaction with poisonous atmospheres. Raman and electron paramagnetic resonance studies confirmed the presence of defective clusters formed by dipoles and/or quadrupoles. The number of paramagnetic species was found to be inversely proportional to the doping concentration, resulting in an increase in the Mn2+ signal, likely due to the reduction of Mn3+ species after the interaction with CO. X-ray photoelectron spectroscopy data showed the pure system with 33% of its cerium species in the Ce3+ configuration, with an abrupt decrease to 19%, after the first modification with Mn, suggesting that 14% of the Ce3+ species are donating one electron to the Mn2+ ions, thus becoming nonparamagnetic Ce4+ species. On the contrary, 58% of the manganese species remain in the Mn2+ configuration with five unpaired electrons, corroborating the paramagnetic feature of the samples seen in the electron paramagnetic resonance study

Argentine squid (Illex argentinus): A source of mycosporine-like amino acids with antioxidant properties

Here we report on the occurrence of mycosporine-like amino acids (MAAs) in the Argentine shortfin squid, Illex argentinus, the second fishery resource mostly exploited in the Argentinean continental shelf. The total content of four MAAs was evaluated by reverse-phase-HPLC in different tissues (eyes, skin, liver, and gonads). Also, the antioxidant activity of crude extracts was assessed by in-vitro determinations: 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), Folin-Ciocalteu, and ferrous ion-chelating capacity assays. The content of MAAs was found to be almost ten times higher in female gonads than in other tissues (11,89 ± 0,56 mg/g dry weight). Extracts from skin, female gonads and eyes, exhibit higher antioxidant activity than the reference compounds ascorbic acid and TROLOX. Overall, Argentine squid waste is a promising potential source of MAAs with antioxidant and UV photoprotective properties, which could bear interest in food, cosmetic and pharmaceutical industries, thus encouraging maximal and sustainable use of fishing resources.Fil: Isla Naveira, Rocío. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Granone, Luis Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Físicas de Mar del Plata. Grupo de Investigación del Departamento de Química de la Unmdp | Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Físicas de Mar del Plata. Grupo de Investigación del Departamento de Química de la Unmdp; ArgentinaFil: Massa, Agueda Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Churio, Maria Sandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Físicas de Mar del Plata. Grupo de Investigación del Departamento de Química de la Unmdp | Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Físicas de Mar del Plata. Grupo de Investigación del Departamento de Química de la Unmdp; Argentin

Iron-based photocatalytic and photoelectrocatalytic nano-structures: Facts, perspectives, and expectations

The increasing demand for clean renewable energy needed for sustainable industrial progress and population growth is the driving force for the scientific community to achieve a continuous development in the field of photocatalysis and photoelectrochemistry. Nanostructures and nanomaterials have contributed significantly to the field of renewable energy due to their new physicochemical properties. Iron-based nanostructures have considerable advantages like small band gaps, allowing to harvest photons in the visible region of the solar spectrum, abundance, and important physical properties like magnetism and ferroelectricity. But they also have many shortcomings and drawbacks related to stability in the different photocatalytic media, low surface area, conductivity, and fast charge carrier recombination. In this review, the focus is placed on important members of the iron-based photocatalyst family such as, hematite, iron oxy-hydroxide, iron-based perovskites, and spinel ferrites. Also, iron doped titanium dioxide as visible light photocatalysts is covered. Various strategies employed for enhancing the photocatalytic and photoelectrocatalytic performance are discussed. Doping, oxygen vacancies, induced defects and formation of solid solutions seem to be a working strategy to address some of the challenges in photocatalysis and photoelectrocatalysis. Finally, photocatalytic and photoelectrocatalytic applications employing iron-based semiconductors are presented.Fil: AlSalka, Yamen. Leibniz Universitat Hannover.; AlemaniaFil: Granone, Luis Ignacio. Leibniz Universitat Hannover.; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Ramadan, Wegdan. Leibniz Universitat Hannover.; Alemania. Alexandria University; EgiptoFil: Hakki, Amer. University of Aberdeen; Reino UnidoFil: Dillert, Ralf. Leibniz Universitat Hannover.; AlemaniaFil: Bahnemann, Detlef W.. Leibniz Universitat Hannover.; Alemania. Saint Petersburg State University; Rusi

Yerba Mate (Ilex paraguariensis) extraction using CO2 and hydrated ethanol as cosolvent

Yerba mate is a plant that grows in subtropical South America that exhibit many healthbeneficial properties. In particular, the bio-extracts obtained from this plant findapplications in the manufacture of functional foods due to their stimulating andantioxidants properties. In this work, extract products were obtained from the extractionof yerba mate (Ilex paraguaryensis) by different high pressure technologies using liquidand supercritical CO2. Extractions were carried out in a high pressure Soxhlet apparatuswith liquid CO2 at 291 K and 55 bar. Also, supercritical CO2 extractions wereperformed at pressures between 175 bar and 260 bar and temperatures between 313 Kand 333 K. Yerba mate was previously impregnated with ethanol or an ethanolicsolution with 30 wt.% water (0.15 g/g to 1 g/g solution/yerba mate) to enhance theextraction of the main active principles. A wide range of global extraction yields(between 0.74 wt.% and 26.14 wt.%) were obtained in the experiments. Also,HPLC/MS-MS analyses of the extract products were performed to assess the selectivityof the different extraction conditions and cosolvents towards components like caffeine,theobromine, theophylline, caffeic acid and chlorogenic acid. Bioactive extractsobtained in this work show a high concentration of methylxanthines and chlorogenicacid, making these products valuable for functional food and nutraceutical applications.Fil: Hegel, Pablo Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Granone, Luis Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Kotnic, P.. University of Maribor; EsloveniaFil: Knez, Z.. University of Maribor; EsloveniaFil: Knez Hrncic, M.. University of Maribor; EsloveniaFil: Pereda, Selva. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaV Iberoamerican Conference on Supercritical Fluids (Prosciba)CampinasBrasilUniversidad Estatal de Campina

Alkaloid-rich vs. antioxidant-rich yerba mate (Ilex paraguariensis) extracts: Exploiting the selectivity of supercritical CO2 using hydrated ethanol as co-solvent

Yerba mate (Ilex paraguariensis A.St-Hil.) is an autochthonous plant species from South America whose leaves exhibit beneficial health properties due to the presence of alkaloids and antioxidants. In the present study, the content of alkaloids and antioxidants in yerba mate extracts obtained by supercritical CO2 extraction was analyzed. Extractions were carried out using ethanol and hydrated ethanol as co-solvents at up to 333 K and 26.0 MPa. Bioactive extracts with a high concentration and yield of alkaloids (11.9 wt% and 5.0 g kg−1 of yerba mate, respectively) were obtained when pure ethanol was used as co-solvent. The alkaloid selectivity decreased and the antioxidants extraction capacity increased to a maximum of 8.4 g kg−1 of yerba mate when hydrated ethanol was loaded as co-solvent. Thus, by controlling the solvent composition and the extraction conditions, extracts rich in alkaloids or antioxidants can be obtained for the development of nutraceutical and functional food products.Fil: Hegel, Pablo Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería Química; ArgentinaFil: Granone, Luis Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería Química; ArgentinaFil: Hrnčič, M. Knez. University of Maribor. Faculty of Chemistry and Chemical Engineering. Laboratory for Separation Processe and Product Design; EsloveniaFil: Pereda, Selva. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería Química; ArgentinaFil: Kotnik, P.. University of Maribor. Faculty of Chemistry and Chemical Engineering. Laboratory for Separation Processe and Product Design; EsloveniaFil: Knez, Z.. University of Maribor. Faculty of Chemistry and Chemical Engineering. Laboratory for Separation Processe and Product Design; Esloveni

Anchoring lead-free halide Cs3Bi2I9 perovskite on UV100–TiO2 for enhanced photocatalytic performance

Halide perovskites have shown great potential in photocatalytic applications. In order to enhance the charge transportation efficiency, the chemical stability, and the light absorption ability, we anchored a lead-free halide perovskite (Cs3Bi2I9) on UV100–TiO2 nanoparticles to build a visible-light active photocatalysts. The as-prepared material exhibited excellent stability and a remarkable yield for photocatalytic oxidation of methanol to formaldehyde under visible light irradiation. The photocatalyst was characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, Brunauer–Emmett–Teller surface area measurement, and photoelectrochemical properties. The analyses confirmed a remarkable improvement of visible-light absorption, a favorable decrease in the recombination of photoinduced charge carriers, and a suitable bandgap for visible-light photocatalytic applications. Recycle experiments showed that the composites still presented significant photocatalytic activity after three successive cycles. A possible underlying mechanism of the composite accounting for the enhanced photocatalytic activity under visible light irradiation was proposed. Our study aims to open new possibilities of using lead-free halide perovskites for photocatalytic applications.Fil: Bresolin, Bianca Maria. Lappeenranta University of Technology; FinlandiaFil: Balayeva, Narmina O.. Leibniz Universitat Hannover; AlemaniaFil: Granone, Luis Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentina. Leibniz Universitat Hannover; AlemaniaFil: Dillert, Ralf. Leibniz Universitat Hannover; Alemania. Gottfried Wilhelm Leibniz Universität Hannover; AlemaniaFil: Bahnemann, Detlef W.. Leibniz Universität Hannover; Alemania. Gottfried Wilhelm Leibniz Universität Hannover; Alemania. Saint-Petersburg State University; RusiaFil: Sillanpää, Mika. Lappeenranta University of Technology; Finlandia. Florida International University; Estados Unido

Tuning the morphology to enhance the catalytic activity of α-Ag2WO4 through V-doping

Here, we present the synthesis of a highly efficient V-doped α-Ag2WO4 catalyst for the oxidation of sulfides to sulfones, exhibiting a high degree of tolerance towards various sensitive functional groups. Remarkably, the catalysts with 0.01% V-doping content exhibited outstanding selectivity towards the oxidation process. Scavenger experiments indicated the direct involvement of electron–hole (e−/h+) pairs, hydroxyl radical (˙OH), and singlet oxygen (1O2) in the catalytic mechanism. Based on the experimental and theoretical results, the higher activity of the V-doped α-Ag2WO4 samples was associated with the preferential formation of the (100) surface in the catalyst morphology.Funding for open access charge: CRUE-Universitat Jaume

Introducing Structural Diversity: Fe-2(MoO4)(3) Immobilized in Chitosan Films as an Efficient Catalyst for the Selective Oxidation of Sulfides to Sulfones

This work reports how the immobilization of Fe2(MoO4)3 in chitosan films affects the oxidation reaction of sulfide derivatives to sulfates in the dark, resulting in good yields and excellent selectivity. As demonstrated, a variety of substituted sulfides were tolerated even in the presence of oxidative-sensitive functional groups, leading to a regioselective application of the catalyst under mild reaction conditions and guaranteeing its reuse for at least 6 cycles without losing its catalytic performance. Specifically, films containing 1 mg of Fe2(MoO4)3 per ml of chitosan showed a yield and selectivity of 99 %. The key success of the selective oxidation was associated with the presence of the hydroxyl radical, ⋅OH, and the Fe3+/Fe2+ Fenton-like process. As a proof of concept, the selective oxidation of sulfides to the corresponding sulfones was performed to demonstrate the synergistic effect between Fe2(MoO4)3 and chitosan. This work offers a design strategy for efficient catalysts that may extend to other semiconductors and oxidation processes