Salt Flux Method Research Articles

EuSi7P10: An Inorganic Supramolecular Nonlinear Optical Crystal Exhibiting Strong Second-Harmonic Generation Response.

Inorganic supramolecular compounds are the emergent class of infrared (IR) nonlinear optical (NLO) materials. However, the reported inorganic supramolecular IR NLO pnictides are still scarce. In this work, a new inorganic supramolecular IR NLO phosphide, EuSi7P10, has been synthesized using the metal salt flux method. The structure of EuSi7P10 features an anionic host framework containing the oriented [Si7P16] dual-T2 supertetrahedra with the guest Eu2+ cations filling in the intervals. Additionally, EuSi7P10 exhibits strong phase-matched (PM) second-harmonic generation (SHG) (4.0 × AgGaS2), large birefringence (0.087 @2050 nm), and wide infrared transparency. This study highlights the potential of inorganic supramolecular pnictides for exploring high-performance IR NLO crystals.

Incorporation of palladium into pyrite: Insights from X-ray absorption spectroscopy analysis and modelling

Pyrite (FeS2) often accommodates elevated concentrations of platinum-group elements in ores of magmatic and hydrothermal origin. In order to elucidate the role of pyrite in concentrating Pd, Pd-doped synthetic crystals were studied via X-ray absorption spectroscopy (XAS). Crystals were obtained by salt-flux method in the system saturated with respect to Pd at the temperature of 580 °C and sulphur fugacity of log f (S2) = −0.4. Scanning electron microscopy, electron probe microanalysis, and laser ablation inductively coupled plasma mass spectrometry studies demonstrated a uniform distribution of Pd within the pyrite crystals. The median and average values of Pd content of ∼0.7 ± 0.1 wt% were measured. Comparison of the Pd K-edge X-ray absorption near edge structure (XANES) spectra with the spectra of standards revealed that the formal oxidation state of Pd was close to +2. Fitting of the extended X-ray absorption fine structure (EXAFS) and Finite Difference Method for Near-Edge Structure (FDMNES) theoretical simulations of XANES spectra showed that Pd substituted for Fe in the crystal structure of pyrite. The isomorphous Pd in pyrite was octahedrally coordinated by S atoms at ∼2.385 Å. The PdS interatomic distance was 5.6 % larger than that of FeS due to the difference in their covalent radii of ∼5.3 %. The expansion caused by the incorporation of Pd into the pyrite structure disappeared at the distance of R > 3 Å. The information on the state of Pd in pyrite, including the local atomic environment and formal oxidation state, is essential for scientific and industrial purposes, e.g. physical-chemical modelling and improvement of leaching and extraction processing respectively.

The formation mechanism of NaLiTi3O7 and its effect on Li4Ti5O12 prepared by the NaCl molten salt flux method

Octahedral single-crystal Li4Ti5O12 materials with {111} crystalline surfaces exposed are prepared in NaCl flux, but the presence of NaLiTi3O7 in the product deteriorates the electrochemical performance of Li4Ti5O12 materials. Herein, the formation mechanism of NaLiTi3O7 in the product was discussed, and it was suggested that the impurity content is affected by the diffusion of the raw materials in the NaCl molten salt flux. The more NaCl is present, the more NaLiTi3O7 is generated. Because Li2O and TiO2 are separated by the salt, and both reactants should diffuse a much longer distance to react. Once the ratio of Li2O and TiO2 reaches 1:3, NaLiTi3O7 will form immediately; otherwise, if the ratio reaches 2:5, Li4Ti5O12 forms. Based on this hypothesis, NaLiTi3O7 will form because there is not enough Li2O to react with TiO2 to form Li4Ti5O12. Therefore, the content of Li2CO3 in the material preparation process was increased, allowing more Li2O to come into contact with TiO2 in the NaCl flux, thereby increasing the probability of Li4Ti5O12 formation and reducing the generation of NaLiTi3O7. Two modification strategies have been proposed to inhibit the generation of impurities. It was found that increasing the amount of Li2CO3 to 15 wt % in excess can reduce impurities of NaLiTi3O7, and further increasing its amount will cause the occurrence of new impurities. Adding a small amount of LiCl to the precursor mixtures can also inhibit NaLiTi3O7 generation in the prepared LTO materials and improve their electrochemical performances.

Two-Dimensional Violet Phosphorus P11: A Large Band Gap Phosphorus Allotrope.

The discovery of novel large band gap two-dimensional (2D) materials with good stability and high carrier mobility will innovate the next generation of electronics and optoelectronics. A new allotrope of 2D violet phosphorus P11 was synthesized via a salt flux method in the presence of bismuth. Millimeter-sized crystals of violet-P11 were collected after removing the salt flux with DI water. From single-crystal X-ray diffraction, the crystal structure of violet-P11 was determined to be in the monoclinic space group C2/c (no. 15) with unit cell parameters of a = 9.166(6) Å, b = 9.121(6) Å, c = 21.803(14)Å, β = 97.638(17)°, and a unit cell volume of 1807(2) Å3. The structure differences between violet-P11, violet-P21, and fibrous-P21 are discussed. The violet-P11 crystals can be mechanically exfoliated down to a few layers (∼6 nm). Photoluminescence and Raman measurements reveal the thickness-dependent nature of violet-P11, and exfoliated violet-P11 flakes were stable in ambient air for at least 1 h, exhibiting moderate ambient stability. The bulk violet-P11 crystals exhibit excellent stability, being stable in ambient air for many days. The optical band gap of violet-P11 bulk crystals is 2.0(1) eV measured by UV-Vis and electron energy-loss spectroscopy measurements, in agreement with density functional theory calculations which predict that violet-P11 is a direct band gap semiconductor with band gaps of 1.8 and 1.9 eV for bulk and monolayer, respectively, and with a high carrier mobility. This band gap is the largest among the known single-element 2D layered bulk crystals and thus attractive for various optoelectronic devices.

Ba4X][In19S32] (X = Cl, Br): two quaternary metal chalcohalides exhibiting remarkable photocurrent responses.

Inorganic metal chalcohalides, as significant semiconductor materials, have emerged as promising candidates for photoelectric applications. Herein, a new type of quaternary chalcohalide, [Ba4X][In19S32] (X = Cl, Br), has been discovered using the high-temperature halide salt flux method. Single-crystal X-ray diffraction analysis reveals that they are isostructural and crystallize in the tetragonal space group I41/amd (no. 141) featuring the octahedral hole formed by six [InS4]5- tetrahedra filled with a [ClBa4]7+ polycation, surrounded by a three-dimensional covalent framework formed by interconnecting [InS6]9- octahedra through corner-sharing and edge-sharing. Moreover, [Ba4Cl][In19S32] and [Ba4Br][In19S32] exhibit wide optical bandgaps of 2.70 eV and 2.46 eV, respectively, and moderate birefringences (0.044 @ 2100 nm and 0.042 @ 2100 nm, respectively). Specifically, [Ba4X][In19S32] (X = Cl, Br) display remarkable photocurrent responses under simulated solar-light illumination, implying their potential for photocatalytic applications. Theoretical calculations were employed to understand the interrelationship between the optical properties and electronic structure. The study on the synthesis and structure-property relationship analysis of inorganic metal chalcohalides provides new insight into the exploration of promising photoelectric materials.

The state of gold in phases of the Cu-Fe-S system: In situ X-ray absorption spectroscopy study

Chalcopyrite and bornite are the main Au-bearing minerals at Cu porphyry deposits, volcanogenic massive sulfide (VMS) deposits, Cu-Ni deposits of the mafic magmatic complexes, and ores of submarine sulfide edifices. Bornite and intermediate solid solutions with wide compositional variations (bnss and iss – high-temperature chalcopyrite, correspondingly), which can scavenge economic concentrations of Au, appear in the Cu-Fe-S system at ore-forming conditions. However, the state of Au in bnss and iss is yet unknown. To solve this conundrum, we synthesized samples with net chemical composition of bnss and iss, studied them by in situ X–ray absorption spectroscopy (XAS), and used the experimental data to explain the Au distribution among natural ore-forming minerals. The sulfide samples were obtained at 495–700 °C in Au-saturated system by means of salt flux method. The bnss contained ∼1.2–1.6 log units more Au than iss: up to 18 wt.% Au in bnss vs 0.4 wt.% Au in iss at 700 °C. An increase of temperature resulted in the sharp increase of Au concentration in both phases, ∼1 log unit per 100 °C at f(S2) close to S(l) saturation. Analysis of Au L3-edge spectra recorded at 25–675 °C revealed that at 25 °C Au exists mainly in the metallic state. At t > 500 °C the spectral features of Au° disappear, and “chemically bound” Au predominates. The Au form of occurrence in the iss field is interpreted as Au-bearing clusters with a stromeyerite-like (CuAgS) structure. Digenite Cu2–xS and bnss contain Au in a mixture of stromeyerite-like and petrovskaite-like (Au0.8Ag1.2S) clusters. The chemical composition of both forms is close to CuAuS, where the nearest Au neighbors are two S atoms at RAu-S = 2.34–2.36 Å. Results of the present study allow to determine the state of Au and its concentration in the main Cu-bearing minerals of sulfide ores as a function of the T-f(S2)-compositional parameters. Due to the sharp increase of the CuAuS clusters stability with increasing temperature, in high-temperature ores formed at t > 350 °C Au enriches Cu-bearing minerals in comparison with Cu-free or Cu-deficient ones. As a result, in these ores native gold, being a product of decomposition of the Au-bearing clusters, is associated with Cu-rich minerals – chalcopyrite, bornite, digenite, chalcocite.

Single crystal growth of superconducting UTe2 by molten salt flux method

The molten salt flux method is applied as a synthetic route for the single crystals of the spin-triplet superconductor ${\mathrm{UTe}}_{2}$. The single crystals under an optimized growth condition with excess uranium exhibit a superconducting transition at ${T}_{\mathrm{c}}=2.1\phantom{\rule{4pt}{0ex}}\mathrm{K}$, which is the highest ${T}_{\mathrm{c}}$ reported for this compound. The obtained crystals show a remarkably large residual resistivity ratio with respect to the room temperature value and a small residual electronic contribution in specific heat well below ${T}_{\mathrm{c}}$. These results indicate that the increase of ${T}_{\mathrm{c}}$ in ${\mathrm{UTe}}_{2}$ can be achieved by reducing the disorder associated with uranium vacancies. The excess uranium in the molten salt acts as a reducing agent, preventing tetravalent uranium from becoming pentavalent and suppressing creation of uranium vacancies. At the same time, the relatively low growth temperature can suppress Te volatilization.

Ba6(CuxZy)Sn4S16 (Z = Mg, Mn, Zn, Cd, In, Bi, Sn): High Chemical Flexibility Resulting in Good Nonlinear-Optical Properties.

Seven acentric sulfides Ba6(CuxZy)Sn4S16 (Z = Mg, Mn, Zn, Cd, In, Bi, Sn) were grown by a high-temperature salt flux method. The crystal structures of the Ba6(CuxZy)Sn4S16 (Z = Mg, Mn, Zn, Cd, In, Bi, Sn) compounds were determined by single-crystal X-ray diffraction with the aid of solid-state NMR spectroscopy. The Ba6(CuxZy)Sn4S16 (Z = Mg, Mn, Zn, Cd, In, Bi) compounds are isostructural and crystallize in the Ba6Ag4Sn4S16 structure type. The Sn-containing compound exhibits high structural similarity to Ba6(CuxZy)Sn4S16 (Z = Mg, Mn, Zn, Cd, In, Bi) with the presence of an interstitial atomic position partially occupied by Sn atoms. The chemical bonding characteristics of Ba6(Cu2.9Sn0.4)Sn4S16 were understood with electron localization function calculations coupled with crystal orbital Hamilton population calculations. The Ba-S and Cu-S interactions are dominantly ionic, but the Sn-S interactions consist of strong covalent bonding characteristics in Ba6(Cu2.9Sn0.4)Sn4S16. The monovalent Cu atoms, mixed with certain metals with various oxidation states, significantly shift the optical properties of the Ba6(CuxZy)Sn4S16 (Z = Mg, Mn, Zn, Cd, In, Bi) compounds. This results in a good balance between the second-harmonic-generation (SHG) response and laser damage threshold (LDT). Ba6(Cu1.9Zn1.1)Sn4S16 possesses a high SHG response and a high LDT of 2.8 × AGS and 3 × AGS, respectively. A density functional theory calculation revealed that CuS4 and SnS4 tetrahedra significantly contribute to the SHG response in Ba6(Cu2Mg)Sn4S16, which also confirmed that CuS4 tetrahedra are crucial for the stability and optical properties of the Ba6(CuxZy)Sn4S16 (Z = Mg, Mn, Zn, Cd, In, Bi, Sn) compounds revealed by electronic structure analysis.

AIn4S6Cl (A = Rb and Cs) and Pb5Sn3Q10Cl2 (Q = S and Se): quaternary chalcohalides with mixed anionic coordination exhibit photocurrent responses.

Mixed-anionic compounds have caught considerable attention due to their flexible coordination manners and abundant physical properties. Four new chalcohalides RbIn4S6Cl (1), CsIn4S6Cl (2), Pb5Sn3S10Cl2 (3) and Pb5Sn3Se10Cl2 (4) were successfully obtained by the high-temperature halide salt flux method. Compounds 1 and 2 have layered structures that consist of octahedral InS6 and aliovalent-anionic InS3Cl units. Compounds 3 and 4 feature 3-D structural frameworks built by [Pb4SnQ8Cl4]6- and [PbSn2Q6]2- (Q = S and Se) polyhedral chains, in which partial Pb2+ cations are coordinated by Q2- and Cl- anions. Compounds 1-4 have optical band gaps close to the wavelength range of visible light and exhibit significant photocurrent responses of 28.75 nA cm-2, 55.12 nA cm-2, 19.58 mA cm-2, and 36.12 μA cm-2 with on/off ratios 30.0, 2.5, 15.7 and 2.6, respectively, implying their potential for photovoltaic applications. To the best of our knowledge, compound 3 has the largest photocurrent response among all non-oxides. In addition, the activation energies of 1-4 are well below 0.3 eV, which makes these compounds interesting for potential applications in electrochemical devices. This work sheds light on the exploration of promising photocurrent response materials in the mixed-anionic compound system.

Photocurrent, humidity sensitivity and proton conductivity properties of a new sulfide semiconductor CsCuS4.

Copper chalcogenides have drawn considerable attention due to their prominent semiconducting properties. A new Cu-containing semiconductor, namely, CsCuS4 (1), was obtained by a halide salt flux method. Its structure featured 1D infinite ∞1[CuS4] - chains, where the polysulfide anion S42- was relatively rare in Cu chalcogenides. The compound was multifunctional and exhibited significant photocurrent, humidity sensitivity, and proton conductivity properties. Specifically, it exhibits an "on" state photocurrent response of 0.95 μA cm-2 and an "off" state photocurrent response of 0.55 μA cm-2 with good reversibility. The humidity-sensitive resistance in dry air (10% RH) could reach up to six orders of magnitude higher than that in wet air (100% RH). Compound 1 showed an activation energy of 0.19 eV and may have potential electrochemical applications.

Synthesis, Crystal Growth, Electronic Properties and Optical Properties of Y6IV2.5S14 (IV=Si, Ge)

AbstractTwo isostructural ternary acentric sulfides, Y6Si2.5S14 (1) and Y6Ge2.5S14 (2) were re‐investigated to understand the origin of the chemical flexibility of RE6BxCyCh14(RE=Y, La−Lu; B=Si, Ge, Sn, Al, Ga; C=monovalent M+ (Ag, Na, Li, etc.), divalent M2+ (Mg, Cr, Ni, Zn, etc.), trivalent M3+ (Al, In, Ga, etc.), tetravalent M4+ (Si, Ge, Sn) and pentavalent M5+ (Sb), Ch=S, Se), which consists of ∼444 isostructural compounds. Y6IV2.5S14 (IV=Si, Ge) were synthesized by a high‐temperature salt flux method. The crystal structures of Y6IV2.5S14 (IV=Si, Ge) are constructed by [YS8] polyhedra, [Si1S6] octahedra, and [Si2S4] tetrahedra. The Si1 atom displaces from the center of [Si1S6] octahedra with partial occupancy, which can be replaced by various metals, and mainly accounts for the chemical flexibility of the RE6BxCyCh14 family. The bonding pictures of Y6Si2.5S14 were studied by electron localization function (ELF) and crystal orbital Hamilton population (COHP) calculations. Y6Si2.5S14 is evaluated as an indirect semiconductor with a bandgap of 2.4(1) eV measured by UV‐Vis. The indirect bandgap of Y6Ge2.5S14 is 1.7(1) eV. Y6IV2.5S14 (IV=Si, Ge) are not type‐I phase‐matchable materials. For samples of 47 μm particle size, Y6Si2.5S14 and Y6Ge2.5S14 own good second harmonic generation (SHG) responses of ∼3.0×AGS and ∼2.8×AGS respectively. Y6Si2.5S14 and Y6Ge2.5S14 possess high laser damage threshold (LDT) of ∼5.5×AGS and ∼5.2×AGS respectively.

The chemical state of Hg in synthetic crystals of zinc and mercury sulfides studied by XAFS spectroscopy

In this study, a series of synthetic mercury-bearing sphalerite and zinc-bearing metacinnabar crystals was grown using the salt flux method at 605-650 ​°C at the hot and cold ends of the ampoule, respectively, in a composition range from 2 to 82 ​mol.% of the HgS component. According to the XAFS (X-ray Absorption Fine Structure) measurements, mercury in the sphalerite-metacinnabar crystals exists in the form of a solid solution. The EXAFS (Extended X-ray Absorption Fine Structure) spectra confirm the increase in the ionic radius of all coordination shells in the crystal structure of the Hg-sphalerite and Zn-metacinnabar on 0.14–0.28 ​Å, depending on the calculated model compared to the distances in pure sphalerite. However, the crystal structure does not change. The established nominal oxidation state of mercury in the (Zn, Hg)S is 2+.

Synthesis, crystal structure and Na+ transport in Na3La(AsO4)2

Much of the research effort in the past decade has been closely focused on finding suitable solid electrolytes with high ionic conductivity for various applications. In this context, the compound Na3La(AsO4)2 was synthesized using the molten salt (flux) method and its structure was solved from the single-crystal X-ray diffraction data for the first time. Na3La(AsO4)2 crystallizes in the monoclinic space group P21/c (#14) with a ​= ​19.451(4)Å; b ​= ​5.554(1)Å; c ​= ​14.365(3)Å; β ​= ​90.035(2)°. Its crystal structure consists of an open 3D network built of [LaO8] polyhedra sharing oxygen corners and edges with neighboring [AsO4] tetrahedra. Tunnels in the [010] direction accommodate Na+ cations. The ionic conductivity was investigated experimentally and computationally. High-temperature ac-conductivity measurements yielded the highest ionic conductivity of 1.93 ​× ​10−4 ​S ​cm−1 ​at 700 ​°C with the apparent activation energy Ea ​= ​0.85eV. A complementary analysis through the bond valence site energy calculation (BVSE), revealed that the structure of Na3La(AsO4)2 favors a 3D ionic diffusion pathway with the empirical activation energy of 1.061 ​eV for the long-range migration of Na+ ions.

LaSiP3 and LaSi2P6: Two Excellent Rare‐Earth Pnictides with Strong SHG Responses as Mid‐ and Far‐Infrared Nonlinear Optical Crystals

AbstractTwo rare‐earth pnictide‐based infrared (IR) nonlinear optical (NLO) crystals, LaSiP3 and LaSi2P6, are successfully synthesized by metal salt flux method, which are the first two cases for rare‐earth pnictides as IR NLO crystals. LaSiP3 (Pna21) features 2D structure consisting of alternately stacked SiP4 tetrahedra layers and isolated PP chains. LaSi2P6 (Cmc21) has a 3D structure composed of two types of SiP4 tetrahedra layers and diversiform phosphorous polyanions. Particularly, LaSi2P6 exhibits the largest second‐order NLO coefficient (d33 = 98.5 pm V−1) among the known IR NLO phosphides. Besides, LaSiP3 and LaSi2P6 both can achieve phase matching, cover wide IR transparent regions, and own large birefringence (0.24 and 0.25 @2050 nm for LaSiP3 and LaSi2P6, respectively). The studies on LaSiP3 and LaSi2P indicate that they are potentially applied in the middle‐ and far‐IR regions. In addition, more importantly, the theoretical calculations uncover the second‐harmonic‐generation enhancement mechanisms for PP bonds in different forms, which highlight that either PP chains or phosphorous polyanions will be excellent NLO‐active units for constructing high‐performance IR NLO crystals.

Synthesis, crystal structure, and thermoelectric properties of ternary phosphide BaCu5P3

A new copper-phosphide, BaCu5P3, was synthesized by a high-temperature solid-state route and salt flux method. The crystal structure of BaCu5P3 was determined using single crystal X-ray diffraction. BaCu5P3 crystallizes in the orthorhombic space group Pnnm (No. 58) with unit cell parameters of a ​= ​12.018 (1) Å, b ​= ​23.762 (2) Å, and c ​= ​3.984 (1) Å with Z ​= ​8. BaCu5P3 crystallizes in a new structure type. A complicated three-dimensional framework built by Cu–Cu and Cu–P interactions hosts Ba cations in BaCu5P3. According to differential scanning calorimetry, BaCu5P3 decomposes to BaCu2P4 and BaCu8P4 around 1180 (5)K. Theory calculation and thermoelectric measurements confirm the metallic nature of BaCu5P3. The experimentally measured moderate thermal conductivity of BaCu5P3 is mainly originated from its complex crystal structure. The Seebeck coefficient of BaCu5P3 is positive and low, ranging from 10 ​K to 400 ​K.

Fabrication of VN/TaC Composites with Dual Functions of VN as a Catalyst Support and a Cocatalyst for Improved PEMFC Performance

Tantalum carbide (TaC) was prepared by a salt flux method, and vanadium nitride (VN) and VN/TaC composites (with 2.5, 5.0, and 10.0 wt % VN) were prepared by a sol–gel method. Pt nanoparticles were...

Enhanced Band Gap, Optical and Near-Infra-Red Reflecting Properties of Environmentally Benign Synthesized Nanocrystalline Gd₂Ti₂O7 Pyrochlore Materials.

The recent trend of reflecting the NIR rays with cool and color pigments to reduce the transfer of heat inside the buildings is highly encouraged. In this work, the pyrochlore-type Gd₂Ti₂O7 nanomaterials were synthesized through a hybrid process comprising planetary ball milling and chloride salt flux method. Different combination of alkali metal chloride fluxes was used to enhance the phase formation and purity. In order to investigate the phase formation, purity, particle size, optical property, morphology and elemental composition of the prepared samples, many characterization techniques including XRD, RAMAN, FT-IR, UV-vis, NIR, PL, and HRSEM-EDX were carried out. The XRD patterns revealed that the annealed materials crystallized in cubic structure with lattice parameter, a = 1.019(1) nm, and the ball milled product annealed with LiCl:NaCl and LiCl:CsCl flux crystallized in a single cubic phase with high purity. The FT-IR analysis confirmed the presence of metal oxide bonds (Gd-O vibration and Ti-O-Ti bending vibration) in the wavenumber regions 400 cm-1 and 500 cm-1. The band gap of the Gd₂Ti₂O7 powder is enhanced from 2.77 eV to 3.27 eV through the addition of LiCl:CsCl flux. The PL emission property of Gd₂Ti₂O7 is enhanced by annealing with flux under the excitation wavelength of 230 nm. Further, the band gap and NIR reflectivity of the nanomaterials are enhanced by the conditions employed in the synthesis method.

Effect of High-Energy Ball Milling on Molten Salt Synthesized Barium Hexaferrite Powder

M-type hexagonal ferrite powder was prepared by the molten salt flux method calcined at a relatively low temperature (850 °C) with a product yield of 99.87%. The synthesized sample was then milled for 3 h by high-energy ball milling in toluene suspension to obtain ultrafine nanoparticles. The structural, morphological, and magnetic properties of the particles were investigated to observe the effect of milling on the molten salt synthesized powder. The analyses reveal the presence of barium hexaferrite (BaFe12O19) as the main phase with less impurities. Average crystallite size, determined by X-ray diffraction (XRD), decreased from 81 ± 20 nm to 52 ± 5 nm after ball milling. The Fourier transform infrared (FTIR) spectra ensure the tetrahedral and octahedral positions in barium hexaferrite structure with an increase in the intensity of absorption bands after milling. The electron paramagnetic resonance (EPR) signal shows a broad line that demonstrates a decrease in the amplitude of the milled sample. Furthermore, remanence measured by vibrating sample magnetometer (VSM) increases from 8.5 to 25 emu/g. A 72% increase in coercivity and 84% increase in magnetic saturation is observed for the milled samples compared to that of pure BaFe12O19 (unmilled). The variations of the magnetic properties are thus attributed to the reduction in crystalline size and lattice parameters after milling.

Optimized synthesis of Bi4NbO8Cl perovskite nanosheets for enhanced visible light assisted photocatalytic degradation of tetracycline antibiotics

A novel 3D architecture of perovskite Bi4NbO8Cl (BNOC) nanosheet was synthesized by molten salt flux method and was employed in the photocatalytic degradation of tetracycline hydrochloride (TCH) and oxytetracycline (OTC), under visible Light Emitting Diode (LED) irradiation. A multivariate approach using response surface methodology (RSM) coupled with face-centered central composite design was performed to model and optimize the synthesis process parameters (solute concentration, temperature, and duration of calcination) targeting the enhancement of degradation efficiency. The significant role of these parameters in the present study was exhibited from the wide variation of degradation efficiencies ranging from 28.53 to 80.12 % for OTC and from 25.46 to 78.36 % for TCH, respectively. The physicochemical properties of BNOC prepared at various synthesis conditions were explored using XRD, FESEM, BET, FTIR, DRS, and PL spectroscopy to delineate the influence of several conditions of the preparation process. A pronounced variation in the crystal structures, morphologies, surface area, and optical properties of the photocatalysts further confirmed the significant influence of synthesis process condition. The maximum degradation of OTC and TCH was 82.07 % and 79.28 %, respectively, when the optimum values of calcination temperature, duration, and solute concentration were 500.1 °C, 10.44 h, and 1.3 mol %, respectively. The catalyst efficiently mineralized 30.4 % OTC in 60 min and was also stable up to four cycles of degradation experiments. Despite having a wide bandgap, the visible light response shown by the BNOC nanosheet photocatalyst evoked its promising future in the field of photocatalysis.

The State of Platinum in Pyrite Studied by X-Ray Absorption Spectroscopy of Synthetic Crystals

Abstract Pyrite (FeS2) is a typical container of Pt in ores of magmatic and hydrothermal origin and in some carbonrich ores of sedimentary-diagenetic origin. Knowledge of the state of Pt disseminated in the matrix of pyrite, including local atomic environment (type of atoms in the nearest and distant coordination shells, coordination numbers, interatomic distances) and oxidation state, is necessary for physical-chemical modeling of platinum group element mineralization and for the improvement of Pt ore extraction and processing technologies. Here we report results of an investigation of local atomic structure of synthetic Pt-bearing pyrites by means of X-ray absorption spectroscopy (XAS). Synthesis experiments, performed at 580° and 590°C in a Pt-saturated system by means of salt-flux method, yielded crystals of pyrite with concentrations of Pt up to 4 wt %. Scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) showed that the distribution of Pt within the pyrite grains is of zonal character, but within the distinct zones Pt is distributed homogeneously. Negative correlation between the concentrations of Pt and Fe was observed in the synthesized pyrite grains. The slope of the correlation line corresponds to the formation of the solid solution in the Pt-Fe-S system and/or to the formation of PtS2. The XAS experiments revealed the existence of two forms of Pt in pyrite. The main form is the solid solution Pt(IV), which isomorphically substitutes for Fe. The Pt-S distance in pyrite is ~0.1 Å longer than that of Fe-S in pure pyrite. The distortion of the pyrite crystal structure disappears at R >2.5 Å. The second Pt-rich form was identified by means of high-resolution transmission electron microscopy (HRTEM) as nanosized inclusions of PtS2. Heating experiments with in situ registration of X-ray absorption spectra resulted in partial decomposition (dissolution) of PtS2 nanosized inclusions with the formation of the solid solution (Fe1–xPtx)S2. Therefore, the PtS2 nanosized particles can be considered as a quench product. Our data demonstrate that both Pt solid solution and PtS2 nanosized inclusions (at high Pt content) can exist in natural Pt-bearing pyrites.