Nitrate-citrate Method Research Articles

A study on the structural, magnetic, and electromagnetic wave absorption properties of CoFe2O4@MWCNT nanocomposites

Because of their low density, high electrical conductivity, and distinctive structure, magnetic nanoparticles have been used in conjunction with dielectric materials like carbon nanotubes in a number of studies on electromagnetic wave absorption. This paper describes the preparation of cobalt ferrite-multi-walled carbon nanotube (CoFe2O4@MWCNT) nanocomposites (NCs) at varying weight ratios for use in X and Ku-band electromagnetic wave (EMW) absorbing coatings. Investigations were also conducted on their structural, magnetic, and dielectric properties. Using the nitrate-citrate method, cobalt ferrite nanoparticles (NPs) having the chemical formula CoFe2O4 (CF) were first successfully produced. Then, carbon nanotubes (MWCNT) were mixed with cobalt ferrite NPs under different weight ratios to form CF@MWCNT NCs. The following are the methods used to determine the crystal structure of the samples: X-ray diffraction (XRD) measurements; scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) attached; Fourier transform infrared spectroscopy (FT-IR); magnetic properties determined by vibrating sample magnetometer (VSM); and room temperature dielectric properties investigated by vector network analyzer (VNA). CF@MWCNT NCs were extensively described and prepared in five distinct weight ratios. Under the thickness of d = 2.18 mm, sample EM5 exhibited the best reflection loss (RL) under the X band of all the samples, measuring −54.29 dB. Under the Ku band, sample EM5, which has a thickness of d = 1.18 mm, exhibited the best RL, measuring −53.42 dB. A method for creating magnetic @dielectric NCs with adjustable parameters and electromagnetic wave characteristics is presented in this work.

Effects of Co-Substitution of Layered Perovskite Lsfo on Oer Activity in Alkaline Media

Introduction Oxygen evolution reaction (OER) is the fundamental processes for water splitting and rechargeable metal-air batteries in alkaline media. Ir-based catalysts are regarded as one of the promising active OER catalysts, however the use of such noble metal-based materials leads to high cost. Perovskite metal oxide has been attracted much attention as the alternative low cost materials. Among them, the layered perovskite, LaSr3Fe3O10 (LSFO) shows enhanced ORR activity thus is expected as a bifunctional catalyst for ORR and OER1). Moreover, ABxB’1−xO3 structure shows improved OER activity compared to the simple perovskites 2). In this study, we prepared the layered perovskite LaSr3Fe3-x Co x O10-δ (x = 0, 0.15, 0.3, 0.6, 1.5, 3.0). Their OER activity and performance as a cathode catalyst for Zn-air batteries were studied. Experimental Synthesis of LaSr3Fe3-x Co x O10-δ was carried out by a nitrate-citrate method. Stoichiometric metal nitrates and citric acid were dissolved in water (metal : citric acid = 1 : 1 mol) and the solution was concentrated at 120 oC for several hours, followed by drying at 450°C for 1 hour. After drying, the obtained powders were pelletized into a disk, then calcined in air at 1400 oC for 20 hours. LaSr3Fe3-x Co x O10-δ electrode was fabricated by pressing the calcined pellet at 15 MPa for 10 minutes and sintering at 900 oC for 10 hours. H type-cell consisted of the prepared LaSr3Fe3-x Co x O10-δ as a cathode, platinum plate as an anode, 4.0 mol dm-3 KOH as an electrolyte, and Celgard #3401 as the separator was used for OER measurement under air atomosphere. For zinc-air battery tests under O2 atmosphere, zinc foil and ZnO saturated 4.0 mol dm-3 KOH were instead used as anode electrode and electrolyte, respectively. Results and Discussion For choronoamperometry tests, the LaSr3Fe3-x Co x O10-δ electrode showed higher OER activity than the Pt/C and Ir/C electrodes. As shown in Figure 1(a), the OER activity of LaSr3Fe3-x Co x O10-δ electrodes is sensitive to the amount of Co substitution. This result suggests that Co substitution into Fe-occupied site is effective in improvement of the OER activity of LSFO. The LaSr3Fe3-x Co x O10-δ electrode also shows superior charge/discharge energy efficiency than the Pt/C electrode in zinc-air battery cycling. Moreover, it is found that Co substitution to LSFO unfortunately led to decrease in ORR activity while somewhat effective on OER activity improvement under O2 atmosphere. The catalytic behavior of LaSr3Fe3-x Co x O10-δ is highly complicated, however the valence of B-site elements probably has a significant effect on determining OER and ORR activity. References 1) T. Takeguchi, et al., J. Am. Chem. Soc., 135, 11125 (2013). 2) A. Vignesh, et al., ACS Appl. Mater. Interfaces, 8, 6019 (2016). Acknowledgement This work is partly supported by NEDO. Fig.1. (a) Current density of LaSr3Fe3-x Co x O10-δ electrodes as a function of the amount of Co substitution (x). Current densities were recorded at 10 hours after applying potential at 1.55 V vs. RHE. (b) Charge/discharge curves of Pt/C and LaSr3Fe3-x Co x O10-δ (x = 1.5) electrodes in zinc-air battery. Current density of 0.1 mA cm-2 for 12 hours each. Figure 1

Crystal structure of Ca2Zn2(V4O14) and Pb2Cd2(V3O10)(VO4) double vanadates

Polycrystalline samples of Ca2Zn2(V4O14) (I) and Pb2Cd2(V3O10)(VO4) (II) were synthesized using the nitrate–citrate method (I) and conventional solid state reaction (II). The structural refinement based on X-ray powder diffraction data showed that the crystal structure of (I) is characterized by monoclinic symmetry with unit-cell parameters a = 6.8044(1) Å, b = 14.4876(3) Å, c = 11.2367(2) Å, β = 99.647(1)° [space group P21/c (No. 14), Z = 4], and the crystal structure of (II) is triclinic with unit-cell parameters a = 7.03813(6) Å, b = 12.9085(1) Å, c = 6.99961(5) Å, α = 90.7265(5)°, β = 96.3789(5)°, γ = 94.9530(6)°, V = 629.470(8) Å3 [space group P$\bar 1$ (No. 2), Z = 2].

Preparation and crystal structure of garnet-type calcium zirconium germanate Ca4ZrGe3O12

A polycrystalline sample of Ca4ZrGe3O12was synthesized using the nitrate–citrate method and heated at 850–1100 °C. Structural refinement based on X-ray powder diffraction data showed that the crystal structure is of the garnet type with a cubic unit-cell parameter [a= 12.71299(3) Å] and the space groupIa$\bar 3$d. The structural formula is presented as Ca3[CaZr]octa[Ge]tetraO12.

Features of Mg(Fe0.8Ga0.2)2O4 synthesis by glycine-nitrate method

A finely dispersed powder of composition Mg(Fe0.8Ga0.2)2O4 was prepared by glycine-nitrate method. The use of glycine as a reducing agent allows preparation of the product without carbon-containing admixtures with unimodal particle size distribution and lower crystallization temperature (as compared with nitrate-citrate method of Mg(Fe0.8Ga0.2)2O4 synthesis) immediately after reaction completion.

ChemInform Abstract: Synthesis and Crystal Structures of New Oxyapatites BiCa4‐xLax(VO4)3‐x (GeO4)xO, x = 1—3.

AbstractThe new compounds BiCa3La(VO4)2(GeO4)O, BiCa2La2(VO4) (GeO4)2O, and BiCaLa3(GeO4)3O are synthesized by the nitrate—citrate method and characterized by powder XRD, IR, and Raman spectroscopy.

Synthesis and crystal structures of new oxyapatites BiCa4−xLax(VO4)3−x(GeO4)xO, x=1–3

New germanate–vanadates with the general formula BiCa4−xLax(VO4)3−x(GeO4)xO, x=1−3, have been synthesized by the nitrate–citrate method and characterized. Structural refinement based on X-ray powder diffraction data showed that these compounds are isostructural with BiCa4(VO4)3O (space group P63/m (N 176), Z=2, а=9.8327–9.8755(3), and с=7.1203–7.2133(2)). They may be viewed as continuous series of solid solutions where Ca2+ and V5+ cations in the crystal lattice of vanadate BiCa4(VO4)3O are replaced by La3+ and Ge4+ cations. In the process of substitution, the La3+ cations occupy mainly the 4f lattice sites of the germanate–vanadate oxyapatites, but the filling of the 4f and 6h lattice sites in the germanate BiCaLa3(GeO4)3 is equivalent. IR and Raman spectra were studied. The Raman spectra clearly show a two-mode behavior: the lines of GeO4 and VO4 are separated from each other, and the (V/Ge)O4 tetrahedra exhibit a quasi-independent behavior.

Mössbauer study of iron-based perovskite-type materials as potential catalysts for ethyl acetate oxidation

La-Sr-Fe perovskite-type oxides were prepared by the nitrate-citrate method. The basic object of this study is layered Ruddlesden-Popper phase LaSr3Fe3O10. The phase composition and structural properties of the obtained materials are investigated by Mössbauer spectroscopy, X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and temperature programmed reduction (TPR). The preliminary catalytic tests show a high potential of these materials for volatile organic compounds (VOCs) elimination as they possess high conversion ability and selectivity to total oxidation of ethyl acetate. Catalytic performance of LaSr3Fe3O10 is depended on the stability of structure and Fe4+-oxidation state.