Inorganics

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10 pages, 2775 KiB

Open AccessArticle

Molecularly Engineered Lithium–Chromium Alkoxide for Selective Synthesis of LiCrO₂ and Li₂CrO₄ Nanomaterials

by Olusola Ojelere, David Graf and Sanjay Mathur

Inorganics 2019, 7(2), 22; https://doi.org/10.3390/inorganics7020022 - 14 Feb 2019

Cited by 7 | Viewed by 5217

Achieving control over the phase-selective synthesis of mixed metal oxide materials remains a challenge to the synthetic chemist due to diffusion-driven growth, which necessitates the search for new compounds with pre-existent chemical bonds between the phase-forming elements. We report here a simple solvothermal [...] Read more.

Achieving control over the phase-selective synthesis of mixed metal oxide materials remains a challenge to the synthetic chemist due to diffusion-driven growth, which necessitates the search for new compounds with pre-existent chemical bonds between the phase-forming elements. We report here a simple solvothermal process to fabricate LiCrO₂ and Li₂CrO₄ nanoparticles from bimetallic single-source precursors, demonstrating the distinctive influence of molecular design and calcination conditions on the resulting nanomaterials. The chemical identity of [Li₂Cr(O^tBu)₄Cl(THF)₂] (1) and [LiCr(O^tBu)₂(PyCH=COCF₃)₂(THF)₂] (2) was unambiguously established in the solid state by single-crystal X-ray diffraction, revealing the formation of a coordination polymeric chain in compound 1, whereas electron paramagnetic resonance spectroscopy (EPR) studies revealed a monomeric structure in solution. TEM analysis of synthesized LiCrO₂ nanoparticles showed nearly uniform particles size of approximately 20 nm. The sensitivity of the LiCrO₂ phase towards oxidation was investigated by X-ray diffraction, revealing the formation of the stable Li₂CrO₄ after calcination in air. Full article

(This article belongs to the Special Issue Mixed Metal Oxides)

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12 pages, 28552 KiB

Open AccessArticle

Investigation of the Reduction of a Molybdenum/Iron Molecular Nanocluster Single Source Precursor

by Gibran L. Esquenazi and Andrew R. Barron

Inorganics 2018, 6(4), 104; https://doi.org/10.3390/inorganics6040104 - 27 Sep 2018

Viewed by 4523

Abstract

The thermolysis of the polyoxometalate cluster [H_xPMo₁₂O₄₀⊂H₄Mo₇₂Fe₃₀(O₂CMe)₁₅O₂₅₄(H₂O)_90−y(EtOH)_y] (1) under air, argon, and reducing conditions (5%, 10%, [...] Read more.

The thermolysis of the polyoxometalate cluster [H_xPMo₁₂O₄₀⊂H₄Mo₇₂Fe₃₀(O₂CMe)₁₅O₂₅₄(H₂O)_90−y(EtOH)_y] (1) under air, argon, and reducing conditions (5%, 10%, 50% H₂ with Ar balance) has been investigated. The resulting products have been characterized by XRD, SEM, and EDX analysis. Thermolysis in air at 1100 °C yields predominantly Fe₂O₃, due to sublimation of the molybdenum component; however, under Ar atmosphere, the mixed metal oxide (Fe₂Mo₃O₈) is formed along with Mo and MoO₂. Introduction of 5% H₂ (1100 °C) results in the alloy Fe₂Mo₃ in addition to Fe₂Mo₃O₈ and Mo; in contrast, reduction at a lower temperature (900 °C) yields the carbide (Fe₃Mo₃C) and the analogous oxide (Fe₃Mo₃O), suggesting that these are direct precursors of Fe₂Mo₃. Increasing the H₂ concentration (10%) promotes carbide rather than oxide formation (Fe₃Mo₃C and Mo₂C), until alloy formation (Fe_7.92Mo_5.08) predominates under 50% H₂ at 1200 °C. The effect of temperature and H₂ concentration on the composition, grain size, and morphology has been investigated by EDX, SEM, and XRD. The relationship of the composition of 1 (i.e., Fe:Mo = 30:84) with the product distribution is discussed. Full article

(This article belongs to the Special Issue Mixed Metal Oxides)

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16 pages, 2455 KiB

Open AccessArticle

Botanically Templated Monolithic Macrostructured Zinc Oxide Materials for Photocatalysis

by Nathan M. Black, David S. Ciota and Edward G. Gillan

Inorganics 2018, 6(4), 103; https://doi.org/10.3390/inorganics6040103 - 25 Sep 2018

Cited by 2 | Viewed by 3813

Abstract

With an increased focus on light energy to facilitate catalytic processes, photocatalysts have been intensively studied for a wide range of energy and environmental applications. In this report, we describe the use of chemically dehydrated leaves as sacrificial foam-like templates for the growth [...] Read more.

With an increased focus on light energy to facilitate catalytic processes, photocatalysts have been intensively studied for a wide range of energy and environmental applications. In this report, we describe the use of chemically dehydrated leaves as sacrificial foam-like templates for the growth of monolithic macrostructured semiconducting zinc oxide and nickel or cobalt doped zinc oxide materials. The composition and structure of these templated zinc oxides were characterized using X-ray powder diffraction, scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. Optical properties were examined using solid-state UV–vis diffuse reflectance spectroscopy. The metal-doped ZnO materials have enhanced visible absorption and lower band gaps as compared to ZnO. The botanically templated ZnO materials retain the macroscopic cellular form of the leaf template with fused nanoparticle walls. Their UV photocatalytic oxidative abilities were investigated using methylene blue dye degradation in air. The leaf templated zinc oxides degrade ~85% of methylene blue dye with 30 min of UV illumination. Nickel and cobalt doped zinc oxides showed varying degrees of decreased UV and visible light photocatalytic activity, possibly due to metal-mediated charge recombination. The mild chemical dehydration process here allows complex soft botanical structures to be easily utilized for templating materials. Full article

(This article belongs to the Special Issue Mixed Metal Oxides)

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10 pages, 2497 KiB

Open AccessArticle

Synthesis of NiFe₂O₄-LDH Composites with High Adsorption and Photocatalytic Activity for Methyl Orange Degradation

by Cristian D. Valencia-Lopez, Mario Zafra-Calvo, María José Martín de Vidales, Verónica Blanco-Gutierrez, Evangelina Atanes-Sanchez, Noemí Merayo, Francisco Fernandez-Martinez, Antonio Nieto-Marquez and Antonio J. Dos santos-Garcia

Inorganics 2018, 6(3), 98; https://doi.org/10.3390/inorganics6030098 - 12 Sep 2018

Cited by 19 | Viewed by 4947

Abstract

The presence of hazardous chemicals in wastewater produced by industrial activities and human metropoles is threating the availability of safe drinking water. The development of a multifunctional material coupling adsorption and photocatalytic activity is hereby particularly promising for the removal of pollutants. We [...] Read more.

The presence of hazardous chemicals in wastewater produced by industrial activities and human metropoles is threating the availability of safe drinking water. The development of a multifunctional material coupling adsorption and photocatalytic activity is hereby particularly promising for the removal of pollutants. We have proved the adsorption and catalytic activity of NiFe₂O₄-layered double hydroxide (LDH) composite through the degradation of methyl orange (MO) at room temperature under visible light. This degradation is enhanced by using a set of small light-emitting diodes (LEDs) providing a uniform 405 nm UV light. The remediation process is based on a first-step rapid adsorption of MO molecules by the LDH structures followed by the photocatalytic oxidation of the pollutant by the (·OH) radicals produced by the NiFe₂O₄ semiconductor nanoparticles (NPs). The magnetic properties of the ferrite NPs allow a facile separation of the composite from the liquid media via a simple magnet. NiFe₂O₄-LDH composite could find wide application as a highly effective adsorbent/oxidizing catalyst operating under visible or near UV light. Full article

(This article belongs to the Special Issue Mixed Metal Oxides)

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13 pages, 4166 KiB

Open AccessArticle

New Mixed Y_0.5R_0.5VO₄ and RVO₄:Bi Materials: Synthesis, Crystal Structure and Some Luminescence Properties

by Leonid Vasylechko, Andrii Tupys, Vasyl Hreb, Volodymyr Tsiumra, Iryna Lutsiuk and Yaroslav Zhydachevskyy

Inorganics 2018, 6(3), 94; https://doi.org/10.3390/inorganics6030094 - 10 Sep 2018

Cited by 10 | Viewed by 4466

Abstract

The results are reported on a precise crystal structure and microstructure determination of new mixed YVO₄-based orthovanadates of Y_0.5R_0.5VO₄ (R = Sm, Tb, Dy, Ho, Tm, Yb, Lu) as well as some Bi³⁺-doped [...] Read more.

The results are reported on a precise crystal structure and microstructure determination of new mixed YVO₄-based orthovanadates of Y_0.5R_0.5VO₄ (R = Sm, Tb, Dy, Ho, Tm, Yb, Lu) as well as some Bi³⁺-doped RVO₄ (R = La, Gd, Y, Lu) nano- (submicro-) materials. The formation of continuous solid solutions in the YVO₄–RVO₄ pseudo-binary systems (R = Sm, Tb, Dy, Ho, Tm, Yb, Lu) has been proved. The lattice constants and unit cell volumes of the new mixed orthovanadates were analyzed as a function of R³⁺ cation radius. The impact of crystal structure parameters on the energy band gap of the materials was studied by means of photoluminescence studies of the Bi³⁺-doped compounds. Full article

(This article belongs to the Special Issue Mixed Metal Oxides)

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10 pages, 2841 KiB

Open AccessArticle

Assembly of ZnO Nanoparticles on SiO₂@α-Fe₂O₃ Nanocomposites for an Efficient Photo-Fenton Reaction

by Kasimayan Uma, Sridharan Balu, Guan-Ting Pan and Thomas C.-K. Yang

Inorganics 2018, 6(3), 90; https://doi.org/10.3390/inorganics6030090 - 3 Sep 2018

Cited by 14 | Viewed by 5329

Abstract

The SiO₂@α-Fe₂O₃/ZnO metal oxide nanocomposites employed in this study were obtained using the sol-gel method. Their photocatalytic activities were enhanced by photo-Fenton reactions. The metal oxide composite of ZnO and α-Fe₂O₃ nanoparticles were deposited [...] Read more.

The SiO₂@α-Fe₂O₃/ZnO metal oxide nanocomposites employed in this study were obtained using the sol-gel method. Their photocatalytic activities were enhanced by photo-Fenton reactions. The metal oxide composite of ZnO and α-Fe₂O₃ nanoparticles were deposited on the SiO₂ nanospheres intended for visible light photocatalysis. Further, the as-synthesized SiO₂@α-Fe₂O₃/ZnO nanocomposites exhibited a robust crystallinity and a high adsorption of dye molecules when compared to SiO₂@ZnO and SiO₂@α-Fe₂O₃ nanocomposites, respectively. The experimental results demonstrated a rapid Methylene Blue (MB) degradation among these catalysts within short intervals of time with the addition of α-Fe₂O₃/ZnO mixed metal oxide catalysts on the SiO₂ nanospheres. Finally, a photo-Fenton reaction was implemented to confirm the presence of the hydroxyl (OH) radicals, which are powerful agents used for the degradation of organic pollutants. Full article

(This article belongs to the Special Issue Mixed Metal Oxides)

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16 pages, 2857 KiB

Open AccessArticle

Crystal Structure and Coordination of B-Cations in the Ruddlesden–Popper Phases Sr_3−xPr_x(Fe_1.25Ni_0.75)O_7−δ (0 ≤ x ≤ 0.4)

by Gunnar Svensson, Louise Samain, Jordi Jacas Biendicho, Abdelfattah Mahmoud, Raphaël P. Hermann, Sergey Ya. Istomin and Jekabs Grins

Inorganics 2018, 6(3), 89; https://doi.org/10.3390/inorganics6030089 - 31 Aug 2018

Cited by 3 | Viewed by 7396

Abstract

Compounds Sr_3−xPr_xFe_1.25Ni_0.75O_7−δ with 0 ≤ x ≤ 0.4 and Ruddlesden–Popper n = 2 type structures were synthesized and investigated by X-ray and neutron powder diffraction, thermogravimetry, and Mössbauer spectroscopy. Both samples, prepared at [...] Read more.

Compounds Sr_3−xPr_xFe_1.25Ni_0.75O_7−δ with 0 ≤ x ≤ 0.4 and Ruddlesden–Popper n = 2 type structures were synthesized and investigated by X-ray and neutron powder diffraction, thermogravimetry, and Mössbauer spectroscopy. Both samples, prepared at 1300 °C under N₂(g) flow and samples subsequently air-annealed at 900 °C, were studied. The structures contained oxygen vacancies in the perovskite layers, and the Fe/Ni cations had an average coordination number less than six. The oxygen content was considerably higher for air-annealed samples than for samples prepared under N₂, 7 − δ = ~6.6 and ~5.6 per formula unit, respectively. Mössbauer data collected at 7 K, below magnetic ordering temperatures, were consistent with X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) results. The electrical conductivity was considerably higher for the air-annealed samples and was for x = 0.1~30 S·cm⁻¹ at 500 °C. The thermal expansion coefficients were measured in air between room temperature and 900 °C and was found to be 20–24 ppm·K⁻¹ overall. Full article

(This article belongs to the Special Issue Mixed Metal Oxides)

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13 pages, 4693 KiB

Open AccessArticle

Gd₃Li₃Te₂O₁₂:U⁶⁺,Eu³⁺: A Tunable Red Emitting Garnet Showing Efficient U⁶⁺ to Eu³⁺ Energy Transfer at Room Temperature

by David Böhnisch, Juri Rosenboom, Thomas Jansen and Thomas Jüstel

Inorganics 2018, 6(3), 84; https://doi.org/10.3390/inorganics6030084 - 23 Aug 2018

Cited by 3 | Viewed by 3744

Abstract

Since the invention of fluorescent light sources, there is strong interest in Eu³⁺ activated phosphors as they are able to provide a high color rendering index (CRI) and luminous efficacy, which will also hold for phosphor converted light emitting diodes. Due to [...] Read more.

Since the invention of fluorescent light sources, there is strong interest in Eu³⁺ activated phosphors as they are able to provide a high color rendering index (CRI) and luminous efficacy, which will also hold for phosphor converted light emitting diodes. Due to an efficient U⁶⁺ to Eu³⁺ energy transfer in Gd₃Li₃Te₂O₁₂:U⁶⁺,Eu³⁺, this inorganic composition shows red photoluminescence peaking at 611 nm. That means Eu³⁺ photoluminescence can be nicely sensitized via excitation into the U⁶⁺ excitation bands. Therefore, photoluminescence properties, such as temperature dependent emission and emission lifetime measurements, are presented. Charge transfer bands were investigated in detail. Additionally, density functional theory calculations reveal the band structure of the pure, i.e., non-doped host material. Obtained theoretical results were evaluated experimentally by the aid of diffuse UV reflectance spectroscopy. Full article

(This article belongs to the Special Issue Mixed Metal Oxides)

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14 pages, 3857 KiB

Open AccessArticle

High-Performance La_0.5Ba_0.5Co_1/3Mn_1/3Fe_1/3O_3−δ-BaZr_1−zY_zO_3−δ Cathode Composites via an Exsolution Mechanism for Protonic Ceramic Fuel Cells

by Laura Rioja-Monllor, Sandrine Ricote, Carlos Bernuy-Lopez, Tor Grande, Ryan O’Hayre and Mari-Ann Einarsrud

Inorganics 2018, 6(3), 83; https://doi.org/10.3390/inorganics6030083 - 23 Aug 2018

Cited by 15 | Viewed by 4751

Abstract

A novel exsolution process was used to fabricate complex all-oxide nanocomposite cathodes for Protonic Ceramic Fuel Cells (PCFCs). The nanocomposite cathodes with La_0.5Ba_0.5Co_1/3Mn_1/3Fe_1/3O_3−δ-BaZr_1−zY_zO_3−δ nominal composition [...] Read more.

A novel exsolution process was used to fabricate complex all-oxide nanocomposite cathodes for Protonic Ceramic Fuel Cells (PCFCs). The nanocomposite cathodes with La_0.5Ba_0.5Co_1/3Mn_1/3Fe_1/3O_3−δ-BaZr_1−zY_zO_3−δ nominal composition were prepared from a single-phase precursor via an oxidation-driven exsolution mechanism. The exsolution process results in a highly nanostructured and intimately interconnected percolating network of the two final phases, one proton conducting (BaZr_1−zY_zO_3−δ) and one mixed oxygen ion and electron conducting (La_0.5Ba_0.5Co_1/3Mn_1/3Fe_1/3O_3−δ), yielding excellent cathode performance. The cathode powder is synthesized as a single-phase cubic precursor by a modified Pechini route followed by annealing at 700 °C in N₂. The precursor phase is exsolved into two cubic perovskite phases by further heat treatment in air. The phase composition and chemical composition of the two phases were confirmed by Rietveld refinement. The electrical conductivity of the composites was measured and the electrochemical performance was determined by impedance spectroscopy of symmetrical cells using BaZr_0.9Y_0.1O_2.95 as electrolyte. Our results establish the potential of this exsolution method where a large number of different cations can be used to design composite cathodes. The La_0.5Ba_0.5Co_1/3Mn_1/3Fe_1/3O_3−δ-BaZr_0.9Y_0.1O_2.95 composite cathode shows the best performance of 0.44 Ω·cm² at 600 °C in 3% moist synthetic air. Full article

(This article belongs to the Special Issue Mixed Metal Oxides)

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8 pages, 11702 KiB

Open AccessArticle

Single Crystal Growth of Sillén–Aurivillius Perovskite Oxyhalides Bi₄NbO₈X (X = Cl, Br)

by Chengchao Zhong, Daichi Kato, Fumitaka Takeiri, Kotaro Fujii, Masatomo Yashima, Emily Nishiwaki, Yasuhiro Fujii, Akitoshi Koreeda, Cédric Tassel, Ryu Abe and Hiroshi Kageyama

Inorganics 2018, 6(2), 41; https://doi.org/10.3390/inorganics6020041 - 16 Apr 2018

Cited by 11 | Viewed by 7416

Abstract

Sillén–Aurivillius perovskite Bi₄NbO₈X (X = Cl, Br) is a promising photocatalyst for water splitting under visible light, as well as a potential ferroelectric material. In this work, we investigate the crystal growth conditions by mainly varying soak temperature, soak [...] Read more.

Sillén–Aurivillius perovskite Bi₄NbO₈X (X = Cl, Br) is a promising photocatalyst for water splitting under visible light, as well as a potential ferroelectric material. In this work, we investigate the crystal growth conditions by mainly varying soak temperature, soak time and cooling rate. Under the optimal conditions, we successfully obtained yellow platelet single crystals with an in-plane distance of several hundred microns. As opposed to conventional crystal growth, a moderate cooling is essential to suppress an evaporation of the Bi–O–Cl species from a melt zone. The single crystals of Bi₄NbO₈Br were also grown using a similar condition. We suggest that the knowledge obtained in this study can be generally applied to other Sillén–Aurivillius phases and related oxyhalides. Full article

(This article belongs to the Special Issue Mixed Metal Oxides)

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