LEEIXS and XPS studies of reactive unbalanced magnetron sputtered chromium oxynitride thin films with air

Chromium oxynitride thin films were deposited onto polished carbon substrates by an unbalanced magnetron sputtering in a reactive atmosphere of argon and air with different relative humidities (concentrations of water vapor). The composition and thickness of chromium oxynitride thin films were measured by ion beam techniques such as: Rutherford backscattering spectroscopy (RBS) and resonant nuclear reaction analysis (RNRA). The nitrogen and hydrogen profiles were determined by RNRA and Tof-SIMS, the chemical bond analysis was carried out by low energy electron induced X-ray spectroscopy (LEEIXS) and X-ray photoemission spectroscopy (XPS). The LEEIX spectroscopic studies analysis have shown that, during metallic sputtering mode, the composition of Cr---N---O can be fitted only by Cr2O3 with low content of CrN and CrO2, and in the compound sputtering mode the CrO2 stoichiometry predominates in the presence of low content of CrN. XPS results have also indicated the existence of another compound with (CrO2)3'N stoichiometry

Study of the Partial Substitution of Pb by Sn in Cs–Pb–Sn–Br Nanocrystals Owing to Obtaining Stable Nanoparticles with Excellent Optical Properties

Halide perovskites are revolutionizing the photovoltaic and optoelectronic fields with outstanding performances obtained in a remarkably short time. However, two major challenges remain: the long-term stability and the Pb content, due to its toxicity. Despite the great effort carried out to substitute the Pb by a less hazardous element, lead-free perovskite still remains more unstable than lead-containing perovskites and presents lower performance as well. In this work, we demonstrate the colloidal preparation of Cs–Pb–Sn–Br nanoparticles (NPs) where Sn is incorporated up to 18.8%. Significantly, we have demonstrated that the partial substitution of Pb by Sn does not produce a deleterious effect in their optical performance in terms of photoluminescence quantum yield (PLQY). We observed for the first time a positive effect in terms of enhancement of PLQY when Sn partially substitutes Pb in a considerable amount (i.e., higher than 5%). PLQYs as high as 73.4% have been obtained with a partial Pb replacement of 7% by Sn. We present a systematic study of the synthesis process in terms of different growth parameters (i.e., precursor concentration, time, and temperature of reaction) and how they influence the Sn incorporation and the PLQY. This high performance and long-term stability is based on a significant stabilization of Sn2+ in the NPs for several months, as determined by XPS analysis, and opens an interesting way to obtain less Pb-containing perovskite NPs with excellent optoelectronic properties

Ecofriendly Perovskites with Giant Self-Defocusing Optical Response

[EN] The full optical control of light using sustainable green technologies is one of the incipient challenges of the Photonics community. There are, however, few optical materials able to provide a significant nonlinear refractive index change under small enough intensities (< 1 GW cm(-2)), and, more importantly, allowing the external control of the magnitude and sign of their nonlinear response. This manuscript demonstrates that Cs2SnI6 lead-free nanocrystals (NCs) present an extraordinary self-defocusing response not yet observed up to now in any material. Despite its complex structural form, these NCs are fully characterized here, both experimentally and theoretically, revealing a giant negative refractive change Delta n = -0.05 under proper illumination conditions. The nonlinear response is tuned with the intensity, concentration of NCs in the solvent, and propagation distance leading to a crossover where the media transforms to self-focusing with Delta n = +0.002. These results can provide fascinating opportunities in sensing and light-matter interactions for a future ecofriendly photonic technology.This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 862656 (project DROP-IT) and by the Spanish MICINN through project no. PID2020-120484RB-I00 and by Generalitat Valenciana PROMETEO/2021/082.Suárez, I.; Martinez-Pastor, JP.; Oszajca, MF.; Lüchinger, NA.; Graves, B.; Agouram, S.; Milián Enrique, C.... (2022). Ecofriendly Perovskites with Giant Self-Defocusing Optical Response. Advanced Optical Materials. https://doi.org/10.1002/adom.20220212

Enhanced NiO Dispersion on a High Surface Area Pillared Heterostructure Covered by Niobium Leads to Optimal Behaviour in the Oxidative Dehydrogenation of Ethane

This is the peer reviewed version of the following article: E. Rodríguez-Castellón, D. Delgado, A. Dejoz, I. Vázquez, S. Agouram, J. A. Cecilia, B. Solsona, J. M. López Nieto, Chem. Eur. J. 2020, 26, 9371, which has been published in final form at https://doi.org/10.1002/chem.202000832. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.[EN] A Nb-containing siliceous porous clay heterostructure (PCH) with Nb contents from 0 to 30 wt %) was prepared from a bentonite and used as support in the preparation of supported NiO catalysts with NiO loading from 15 to 80 wt %. Supports and NiO-containing catalysts were characterised by several physicochemical techniques and tested in the oxidative dehydrogenation (ODH) of ethane. The characterisation studies on Nb-containing supports showed the presence of well-anchored Nb(5+)species without the formation of Nb(2)O(5)crystals. High dispersion of nickel oxide with low crystallinity was observed for the Nb-containing PCH supports. In addition, when NiO is supported on these Nb-containing porous clays, it is more effective in the ODH of ethane (ethylene selectivity of ca. 90 %) than NiO supported on the corresponding Nb-free siliceous PCH or on Nb2O5(ethylene selectivities of ca. 30 and 60 %, respectively). Factors such as the NiO-Nb(5+)interaction, the NiO particle size and the properties of surface Ni(n+)species were shown to determine the catalytic performance.The authors would like to acknowledge the Ministerio de Ciencia, Innovacion y Universidades of Spain (CRTl2018-099668-B-C21, RTl2018-099668-B-C22 and MAT2017-84118-C2-1-R projects). Authors from ITQ also thank Project SEV-2016-0683 for supporting this research. D.D. thanks MINECO and Severo Ochoa Excellence Program for his fellowship (SVP-2014-068669).Rodríguez-Castellón, E.; Delgado-Muñoz, D.; Dejoz, A.; Vázquez, I.; Agouram, S.; Cecilia, JA.; Solsona, B.... (2020). Enhanced NiO Dispersion on a High Surface Area Pillared Heterostructure Covered by Niobium Leads to Optimal Behaviour in the Oxidative Dehydrogenation of Ethane. Chemistry - A European Journal. 26(42):9371-9381. https://doi.org/10.1002/chem.202000832S937193812642L. Nichols Industry Perspectives: Global petrochemical sector to see robust growth to 2020 Hydrocarbon Processing 2017.Hermabessiere, L., Dehaut, A., Paul-Pont, I., Lacroix, C., Jezequel, R., Soudant, P., & Duflos, G. (2017). Occurrence and effects of plastic additives on marine environments and organisms: A review. Chemosphere, 182, 781-793. doi:10.1016/j.chemosphere.2017.05.096Jia, L., Evans, S., & Linden, S. van der. (2019). Motivating actions to mitigate plastic pollution. 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Study by electrical conductivity measurements of semiconductive and redox properties of M-doped NiO (M = Li, Mg, Al, Ga, Ti, Nb) catalysts for the oxidative dehydrogenation of ethane. Physical Chemistry Chemical Physics, 16(10), 4962. doi:10.1039/c3cp54817aPopescu, I., Skoufa, Z., Heracleous, E., Lemonidou, A., & Marcu, I.-C. (2015). A study by electrical conductivity measurements of the semiconductive and redox properties of Nb-doped NiO catalysts in correlation with the oxidative dehydrogenation of ethane. Physical Chemistry Chemical Physics, 17(12), 8138-8147. doi:10.1039/c5cp00392jLópez Nieto, J. M., Solsona, B., Grasselli, R. K., & Concepción, P. (2014). Promoted NiO Catalysts for the Oxidative Dehydrogenation of Ethane. Topics in Catalysis, 57(14-16), 1248-1255. doi:10.1007/s11244-014-0288-2Delgado, D., Solsona, B., Ykrelef, A., Rodríguez-Gómez, A., Caballero, A., Rodríguez-Aguado, E., … López Nieto, J. M. (2017). 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White light emission from lead-free mixed-cation doped Cs2SnCl6 nanocrystals

We have designed a synthesis procedure to obtain Cs2SnCl6 nanocrystals (NCs) doped with metal ion(s) to emit visible light. Cs2SnCl6 NCs doped with Bi3+, Te4+ and Sb3+ ions emitted blue, yellow and red light, respectively. In addition, NCs simultaneously doped with Bi3+ and Te4+ ions were synthesized in a single run. Combination of both dopant ions together gives rise to the white emission. The photoluminescence quantum yields of the blue, yellow and white emissions are up to 26.5, 28, and 16.6%, respectively under excitation at 350, 390, and 370 nm. Pure white-light emission with CIE chromaticity coordinates of (0.32, 0.33) and (0.32, 0.32) at 340 and 370 nm excitation wavelength, respectively, was obtained. The as-prepared NCs were found to demonstrate a long-time stability, resistance to humidity, and an ability to be well-dispersed in polar solvents without property degradation due to their hydrophilicity, which could be of significant interest for wide application purposes

Tungsten-titanium mixed oxide bronzes: Synthesis, characterization and catalytic behavior in methanol transformation

[EN] Tungsten oxide bronze-based materials show extremely adaptive structural and compositional features that make them suitable for functional properties modulation. Herein we report the preparation of a series of Ti-containing tungsten oxide catalysts presenting a hexagonal tungsten bronze-type structure. The insertion of Ti4+ within the structure (likely in the octahedral framework of the hexagonal tungsten bronze) leads to an increase in the number of strong acid sites, and the disappearance of W5+ surface species found in the undoped tungsten oxide. With the aim of studying the acid-redox properties of the titled catalysts, the catalytic transformation of methanol has been carried out in the presence and the absence of O-2 in the feed. Both catalytic activity and the acid-redox properties of these catalysts are highly dependent on catalyst composition and reaction conditions applied (i.e. in the presence or in the absence O-2 in the feed). Aerobic experiments show the depletion of the redox functionality (i.e. no formaldehyde detected in the products) when Ti4+ is incorporated in the framework (i.e. 100% selectivity to dimethyl ether). On the other hand, all the catalysts show the loss of the redox function and a decrease in the catalytic activity when anaerobic conditions are used. In the absence of oxygen, the catalysts are still active in the dehydration of methanol to dimethyl ether, i.e. they maintain their acid functionality even when oxygen is not present in the feed. The results are discussed in terms of the available surface active sites present in each case.Authors would like to thank DGICYT in Spain for RTI2018-099668-B-C21, CTQ2015-68951-C3-1-R and MAT2017-84118-C2-1-R projects. Authors from ITQ also thank Project SEV-2016-0683 for supporting this research. D.D. thanks MINECO and Severo Ochoa Excellence Program for his fellowship (SVP-2014-068669). Finally, authors thank the Electron Microscopy Service of SCSIE of Universitat de Valencia for their support.Delgado-Muñoz, D.; Soriano Rodríguez, MD.; Solsona Espriu, BE.; Zamora Blanco, S.; Agouram, S.; Concepción Heydorn, P.; López Nieto, JM. (2019). Tungsten-titanium mixed oxide bronzes: Synthesis, characterization and catalytic behavior in methanol transformation. Applied Catalysis A General. 582:1-10. https://doi.org/10.1016/j.apcata.2019.05.026S11058

The prevalence of surface oxygen vacancies over the mobility of bulk oxygen in nanostructured ceria for the total toluene oxidation

AbstractThis paper reveals the key importance of surface oxygen defects in the oxidation catalytic activity of nanostructured ceria. A series of nanostructured rods and cubes with different physico–chemical properties have been synthesized, characterized and tested in the total toluene oxidation. The variation of the temperature and base concentration during the hydrothermal syntheses of nanostructured ceria leads not only to different ceria morphologies with high shape purity, but also to structures with tuneable surface areas and defect concentrations. Ceria nanorods present a higher surface area and a higher concentration of bulk and surface defects than nanocubes associated with their exposed crystal planes, leading to high oxidation activities. However, for a given morphology, the catalytic activity for toluene oxidation is directly related to the concentration of surface oxygen defects and not the overall concentration of oxygen vacancies as previously believed