NaCl Flux Research Articles

Deoxidation of Titanium Utilizing Thulium and Halide Flux

AbstractDevelopment of an efficient deoxidation method for titanium (Ti) is desired to recycle oxygen (O)-contaminated Ti scrap. In this study, the utilization of thulium (Tm) as a deoxidant for Ti in various halide fluxes was investigated. Tm is a rare-earth metal, which is a by-product of other rare-earth metals with high demand and has limited industrial uses. When NaCl or KCl flux was installed in the deoxidation experiments, the impurity oxygen in Ti was removed to the concentrations of 140–590 mass ppm O, which are lower than that achieved under the equilibrium between Tm and Tm2O3 (290–530 mass ppm O). The results show that the nominal activity of the deoxidation product (Tm2O3) was lowered by the presence of halide fluxes in the reaction systems. The combination of Tm and halide fluxes in a new deoxidation technique holds promising potential for both accelerating the Ti recycling and exploring novel applications for Tm. Graphical Abstract

Advanced electrochemical and mechanical performance of a LiNi0.91Co0.06Mn0.03O2 cathode via use of a NaCl flux agent

We fabricated single-crystalline LiNi0.91Co0.006Mn0.03O2 (SC-NCM) by the NaCl flux method, which improves the overall structural stability. SC-NCM shows better cycle capability than conventional poly-crystalline NCM.

NaCl flux growth of non-polar m-plane ZnO epitaxial thin film on c-plane sapphire substrate

We have developed a technique to fabricate non-polar m-plane ZnO thin films: the post NaCl flux treatment of Zn-containing precursors, such as amorphous zinc carbonate hydroxide, Zn5(CO3)2(OH)6. Conventionally, single-crystal m-plane sapphire or MgO (001) substrates have been utilized to fabricate m-plane ZnO thin films. In contrast, this method facilitates the growth of m-plane ZnO thin films on various substrates, such as sapphire and quartz glass, despite its c-plane growth habit. Furthermore, the m-plane ZnO thin film was demonstrated to epitaxially grow even on a c-plane sapphire substrate. Owing to the good lattice matching with the substrate, the m-plane ZnO epitaxial film had high crystallinity comparable to a c-plane ZnO epitaxial film that was created using a conventional pulsed laser deposition method, and exhibited similar photocatalytic activity to the c-plane ZnO film. This research offers valuable insights into the fundamental mechanisms of flux growth orientation control, which can be beneficial in designing ZnO-based electronic devices and photocatalysts.

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.

Polymeric PDI-based photocatalytic nanoarchitectures promoting the performance of thin film composite membrane for forward osmosis water purification

Exploring versatile membrane with photodegradation capability provides a promising approach to overcome the fouling dilemma of membrane technologies, while the utilization of photocatalysts in the realm of forward osmosis encounters challenges, primarily due to the propensity of the potent oxidizing species produced during photocatalysis to cause substantial harm to the delicate nano-selective layer present within forward osmosis membrane. In this study, we demonstrate a multi-functional polymeric membrane with good stability for water purification via forward osmosis separation. Organic perylene diimide supermolecule was employed to construct a heterostructured catalytic layer for abating the attached pollutants under visible light irradiation. The interfacial polymerization of polyamide layer on the other side of polyethersulfone substrates allows the selective separation function. The synergistic effect of catalytic layer and selective layer simultaneously improved the separation performance and anti-fouling capability, endowing the Janus membrane with a reduced reverse NaCl flux, 83% lower, and a suppressed membrane fouling, 81% lower than the original membrane. This work provides a new strategy for the design of multi-functional composite membrane for high-efficiency water purification.

Improved Performance of Cation Exchange Membranes Coated with Chitosan

Desalination with electrodialysis is used to obtain fresh water from saltwater brines. However, removal of the salt can be inefficient at low ionic concentrations because of the drastic increase of voltage required under those conditions, leading to limited adoption of this process. In this study, a commercially available cation exchange membrane was successfully coated with chitosan with different degrees of deacetylation. Higher degrees of deacetylation led to increased hydrophilicity of the membrane surfaces and possibly improved the wetting of the surface with the salt solutions. The base membrane and membranes coated with varying degrees of deacetylation were tested to determine how standard electrodialysis metrics such as limiting current density (LCD), ionic flux, and current utilization were affected to evaluate the effects of membrane hydrophilicity. Higher hydrophilicity improved the NaCl flux, current efficiency, and voltage requirements at low NaCl concentrations. Our strategy provides a simple method to control the membrane hydrophilicity, leading to improved performance.

Development of ceramic membranes for resource recovery from brine through percrystallization

Availability of efficient methods to fractionate a solution into its solid and liquid components is the key to recycling and reuse of industrial effluents. Percrystallization is a novel membrane process where a thin film of warm permeate present at the membrane surface is evaporated through vacuum to crystalize the soluble compounds. Thus, the process separates a solution into crystalline solute and solvent in a single-step and can partly be operated with sustainable sources of energy such as solar and geothermal heat. Since the process is at early stage of exploration, there is no sufficient knowledge about the suitable membrane features for the percrystallization which hampers its further development and potential progress towards commercialization. This work performs a systematic and groundbreaking investigation to identify and develop suitable membranes for percrystallization applications. The study has been carried out by using silicon carbide (Si-C) and polymeric membranes with different porosities and thicknesses. The effect of pore size and surface hydrophobicity on the process operation was investigated by coating the surface of Si-C membranes with methylated silica particles of different sizes. Inherent hydrophobicity of the polymeric membranes was also modified to test their suitability for the percrystallization applications. All the membranes were tested for separation of NaCl crystals from solution by using different concentrations (3.5, 10 and 17.5 wt%) of NaCl at operating temperatures of 50 °C, 55 °C and 60 °C. It was observed that the membranes with the rate of permeation comparable with the rate of evaporation under the applied vacuum are crucial to operate the process. Thus, only less porous and thick Si-C membranes with liquid entry pressure approaching to 1 bar were suitable for percrystallization. The developed membranes yielded water and NaCl flux in the range of 9.43±2 and 1.2 kg/m2.h, respectively. The process outperformed state-of-the-art membrane processes in terms of productivity and simplicity.

Photocatalytic thin film composite forward osmosis membrane for mitigating organic fouling in active layer facing draw solution mode

As a high-flux operation mode of thin film composite-forward osmosis (TFC-FO) membrane, active layer facing draw solution (AL-DS) mode suffers from the severe membrane fouling tendency, which is not addressed well. Here, we introduced a photocatalyst (Anatase titanium dioxide, A-TiO2) onto the support layer of TFC-FO membrane via the bonding of polydopamine (PDA) and polytetrafluoroethylene (PTFE), and prepared two photocatalytic membranes, A-TiO2/PDA@TFC and A-TiO2/PTFE@TFC. Compared with the pristine TFC-FO membrane, both A-TiO2/PDA @TFC and A-TiO2/PTFE@TFC had an improved water permeability (10.5 L m−2h−1 and 9.5 L m−2 h−1, respectively) and reduced reverse NaCl flux salt (0.8 g m−2 h−1 and 0.7 g m−2 h−1, respectively) in the AL-DS mode using 1 mol/L NaCl as draw solution and pure water as feed solution. Moreover, in the 16 h fouling experiment using 200 ppm bovine serum albumin (BSA) solution as a representative pollutant, the flux decline rate of both photocatalytic membranes was dramatically alleviated from 39.7% and 21.7% in the darkness to 8.5% and 9.7% under UV irradiation, respectively, indicating a significant anti-fouling capacity of photocatalytic effect. In all, the presence of A-TiO2 endowed membrane with high permeability, high rejection efficiency and excellent anti-fouling capacity under UV spotlight. As bonding agent, PTFE provided the modified membrane with a high photocatalytic effect and high self-cleaning capacity, while PDA increased the membrane permeability and protected membrane against photocatalytic damage. This work provides a simple and feasible method to improve the anti-fouling capacity of TFC-FO membrane in AL-DS mode.

La4Ga2Se6O3: A Rare-Earth Oxyselenide Built from One-Dimensional Strips.

The oxyselenide La4Ga2Se6O3 was obtained by reaction in NaCl flux. Its monoclinic crystal structure (space group C2/c, a = 21.2832(13) Å, b = 11.6272(7) Å, c = 6.0006(4) Å, β = 106.3430(10)°, Z = 4), which is a new type, consists of strips of edge-sharing OLa4 tetrahedra and zigzag chains of corner-sharing GaSe4 tetrahedra. The separation into distinct structural blocks with mostly ionic vs covalent bonding character was supported by analysis of the electron localization function and crystal orbital bond index. An experimental band gap of 1.8 eV was extracted from optical diffuse reflectance spectra. First-principles calculations suggest that the thermoelectric power factor of this compound would be enhanced by n-doping.

Photoluminescence and thermoluminescence studies in BaSO4:Eu

BaSO4: Eu2+ made with EuCl3 dopant along with MgCl2 and NaCl flux using solid state reaction exhibit high thermoluminescent (TL) sensitivity. Efficient Charge Transfer (CT) transitions between PO43− ions (hole traps) and adjacent anion vacancies (electron traps) offers a clue in the development ultra high sensitive TL phosphor based on BaSO4:Eu,P. However, BaSO4: Eu made with Eu2O3 dopant along with (NH4)2SO4 and Na2SO4 flux is suited for scintillation and X-ray image intensifying screens as it exhibits intense violet (375 nm) fluorescence emission with negligible afterglow up to 125 °C on X-ray irradiation while commercial BaFBr:Eu image intensifying phosphor exhibits intense afterglow at temperatures ≥100 °C. The reduced afterglow of BaSO4:Eu is attributed to the elimination of chlorine ion interstitials and anion vacancies responsible for TL production.

Flux syntheses and single-crystal structures of CsNa10 M 4(AsO4)9 (M = Zr, Hf).

The isostructural compounds caesium deca-sodium tetra-zirconium nona-arsenate, CsNa10Zr4(AsO4)9, and caesium deca-sodium tetra-hafnium nona-arsenate, CsNa10Hf4(AsO4)9, arose as unexpected single-crystal products from the reactions of Na2CO3, MO2 (M = Zr, Hf) and As2O5 in a eutectic flux of NaCl and CsCl. They consist of MO6 octa-hedra and AsO4 tetra-hedra sharing vertices to generate three-dimensional polyhedral networks encapsulating the caesium and sodium ions. The MO6 groups share all their vertices with adjacent As atoms but the As atoms have one or two 'terminal' O atoms not bonded to Zr or Hf. The Cs+ ion adopts a squashed octa-hedral geometry and the coordination polyhedra of the partially occupied sodium ions are variously trigonal bipyramidal, tetra-hedral, square pyramidal and trigonal pyramidal. Site symmetries: Cs ; M 3; As 1 and 2; O 1; Na 1, 2 and 3. The M = Zr crystal was refined as an obverse/reverse rhombohedral twin.

Effects of water matrix on the rejection of neutral pharmaceutically active compound by thin-film composite nanofiltration and reverse osmosis membranes

Thin-film composite (TFC) nanofiltration (NF) and reverse osmosis (RO) membranes have been widely used to remove pharmaceutically active compounds (PhACs) from water and wastewater. However, limited information is available to present the rejection of neutral PhACs under complex water matrices. In this study, we used acetaminophen (AAP) as a representative neutral pollutant to study the effects of feedwater matrices on the rejection of neutral PhACs by NF and RO membranes. The results showed that the permeation of solutes and water through NF and RO membranes followed the classical solution-diffusion model. The corresponding permeability coefficients of AAP for the RO membrane showed good consistency, with average values ranging between (6.19–7.56) × 10−6 μm s−1 in fresh and brackish feedwater. Meanwhile, the NF membrane exhibited stable AAP and NaCl fluxes as the applied pressure increased from 4.8 to 7.6 bar, suggesting an insignificant influence of convection on solute transport. In addition, a 10-fold increase in NaCl concentration reduced the average AAP permeability coefficient of the NF membrane by 57% (i.e. from 2.8 × 10−5 m s−1 to 1.2 × 10−5 m s−1), highlighting the relevance of co-existing ions to AAP transport. Furthermore, organic fouling resulted in enhanced AAP rejection by both NF and RO membranes at neutral pH level and medium applied pressure (i.e. 5.8 bar). Overall, this study provided important insights into the separation mechanism of TFC membranes for neutral PhACs, as well as the complex effects of the water matrix on the solute permeation processes.

CeO2-stabilised ZrO2 nanoparticles with excellent sintering performances synthesized by sol-gel-flux method

ZrO2 nanoparticles (NPs) stabilised by 12 mol% CeO2 (12Ce-ZrO2) with high sintering ability were prepared using a novel sol-gel-flux method (SGFM) for the first time, where NaCl flux was introduced into a citric acid-based sol-gel system. The microstructure and sintering performances of the as-prepared NPs were compared with those of the product synthesised using the traditional citric acid-based sol-gel method (SGM). The effect of the calcination temperature on the phase compositions and micromorphologies of the as-prepared 12Ce-ZrO2 products was investigated. The results showed that the optimum calcination temperature for the SGFM was 800 °C, and the corresponding 12Ce-ZrO2 product (SGFM-800) was composed of well-dispersed 20–40 nm t-ZrO2 NPs with homogenous micromorphology, while the 12Ce-ZrO2 NPs synthesised using the SGM (SGM-800) were severely agglomerated. The SGM-800 NPs could not be fully densified up to the sintering temperature of 1450 °C owing to severe agglomeration. However, the SGFM-800 NPs exhibited good sintering ability, and a relative density of 99.67 % could be achieved at 1150 °C for 4 h. The fully dense 12Ce-TZP ceramics prepared with SGFM-800 had an average grain size of 0.46 μm. To the best of our knowledge, such a fine grain size has not been reported to date for 12Ce-TZP ceramics obtained by single-step pressless sintering.

An enhancement of thermoelectric performance in Na/Cd co-doped β-Zn4Sb3 prepared by NaCl flux

In this paper, Cd-doped β-Zn4Sb3 crystal with space group R3¯c was prepared using the NaCl-flux method according to the stoichiometric ratio of Zn4.1Sb3(NaCl)7Cdx (x ​= ​0, 0.05, 0.1, 0.15). Electron probe microanalysis results showed that Cd and Na atoms were introduced into samples. The transmission electron microscopy and the corresponding area electron diffraction showed that the β-Zn4Sb3 samples prepared by NaCl flux method were of high quality and density. X-ray photoelectron spectroscopy results showed that the valence states of Zn, Cd, and Na were +2, +2, and +1, respectively. All the samples were p-type semiconductors with carrier concentration ranges from 18.61 ​× ​1019 to 9.04 ​× ​1019 ​cm−3. The thermal conductivity (κ) of the sample decreased with the increase of Cd content. Eventually, the maximum dimensionless figure of merit(ZT) value obtained 1.51 ​at 690 ​K for the β-Zn4.1Sb3(NaCl)7Cd0.1 sample, which is higher than that of the Bi-doped β-Zn4Sb3 samples(∼ 1.09 ​at 673 ​K) and Te-doped β-Zn4Sb3 samples(∼ 1.08 ​at 680 ​K). The findings provide a feasible insight toward understanding the effect of the Cd atom on the crystal structure and thermoelectric properties of β-Zn4Sb3.

Influence of post‐synthesis NaCl flux treatment on the magnetic properties of jet‐milled SrFe12O19 powders

AbstractA post‐synthesis NaCl flux treatment was carried out on jet‐milled strontium hexaferrite, SrFe12O19 powders prepared by conventional high‐temperature solidstate reaction starting from SrCO3 and Fe2O3. Microstructural studies reveal that the adverse effects of jet‐milling on the particle morphology like jagged edges and ruptured surfaces have been effectively mitigated by annealing at elevated temperatures in the presence of molten NaCl flux. The coercivity values obtained from angle‐dependent M versus H measurements revealed that the coercivity mechanism in the jet‐milled powders is dominated by reverse nucleation due to the strain induced during milling. Annealing the powders in presence of NaCl flux changes the coercivity mechanism to exclusively domain rotation. This results in a dramatic increase of coercivity from 1.6 kOe for the jet‐milled powders to a maximum of 5.3 kOe for the flux‐annealed powders. XPS studies show that the NaCl flux treatment has not altered the chemical state of Fe.

Sandwich layered double hydroxides with graphene oxide for enhanced water desalination

Layered double hydroxides (LDHs) are a class of two-dimensional (2D) clay compounds that consist of positively charged host layers and exchangeable interlayer anions. The stability of their assemblies in aqueous environment is a challenge due to the extremely high hydrophilicity, which limits their use in membrane-based technologies. Here, we propose a graphene oxide (GO) armour protection strategy to substantially improve the stability of LDH membranes in aqueous solution. The sandwich structured GO/LDH/GO membranes (GLGMs) possess a negative-positive-negative charge heterojunction in the vertical direction that effectively blocks the transport of both cations and anions, i.e., NaCl, but allows the permeation of water molecules. Following this mechanism, the GLGMs are used for desalination in a forward osmosis mode. A high rejection rate of over 95.2% for NaCl and water flux of over 2.1 L m−2 h−1 are achieved with simulated seawater.

Screening cost effectiveness and salinity build up control in osmotic membrane bioreactors for refinery wastewater treatment: A draw solute with lower diffusivity and ultrafiltration implementation

Two strategies were investigated for salinity build up prevention in osmotic membrane bioreactors (OMBR) treating a real refinery wastewater. Firstly, a solute with lower diffusivity (MgCl2, for 102 days) was used. The impact on the microbiological activity was lower, which favored the recalcitrant compounds degradation. However, without salinity relief, the mixed liquor (ML) salinity increased, impacting the forward osmosis (FO) flux (0.18 L/m2h). Secondly, an ultrafiltration (UF) membrane was submerged within the ML and the draw solution (DS) replaced to NaCl. The ML conductivity was stable along 330 days without a severe flux decay (1.07 L/m2h). Nonetheless, the reverse NaCl flux had a higher impact on the microbiological activity and the concentration of dissolved organic carbon and ammoniacal nitrogen started to increase in the UF permeate. Due to the lower permeate flux, the OMBR had a higher membrane area requirement which represented the main contributor for the total operating costs.

Preparation and Characterization of Polyamide Thin Film Composite Nanofiltration Membrane Based on Polyurethane Nanofibrous Support

Polyurethane nanofibers recognized to perform as a sub-layer were employed herein as a medial-layer of high porosity in the fabrication of a novel class of thin-film nanofiltration membranes. In line with the primary aim of high throughput production of PU electrospun nanofibrous membranes (ENMs) with different fiber sizes and proper morphologies, the needle-free electrospinning technique was employed. An interfacial polymerization procedure was also utilized to conveniently coat a polyamide (PA) thin film on the polyurethane ENMs. The effects of the nanofibrous interconnecting network, fiber size, pore size, and morphology on the NF performance were investigated. The nanofiltration performance including the separation of various salts, water flux, and the MWCO test were performed. The results implied that the fiber size decrement, nanofibers interconnection increment, as well as nanofibrous membrane pore size decrement, and the nanofibrous layer increment (with different fiber size) would lead the interfacial polymerization to perfection and obtaining a uniform PA thin layer. The salts rejection and water flux of Na2SO4, MgSO4, MgCl2 and NaCl were (~ 99 ± 0.5 %, 37 ± 2.7 L/m2h), (~ 98 ± 1 %, 40 ± 1.5 L/m2h), (~ 95 ± 2 %, 33 ± 2 L/m2h) and (~ 52 ± 1 %, 30 ± 3 L/m2h), respectively. In the final analysis, a comparison of filtration performance between PU nanofibrous NF membranes with other well-known nanofibrous NF membranes was conducted.

Thermal stability and thermoelectric properties of Cd-doped nano-layered Cu2Se prepared using NaCl flux method* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61864012 and 21701140) and the Program for Innovative Research Team (in Science and Technology) in University of Yunnan Province, China.

Cu2Se is a promising “phonon liquid–electron crystal” thermoelectric material with excellent thermoelectric performance. In this work, Cd-doped Cu2–x SeCd x (x = 0, 0.0075, 0.01, and 0.02) samples were prepared using NaCl flux method. The solubility of Cd in Cu2Se at room temperature was less than 6%, and a second phase of CdSe was found in the samples with large initial Cd content (x = 0.01 and 0.02). Field-emission scanning electron microscopic image showed that the arranged lamellae formed a large-scale layered structure with an average thickness of approximately 100 nm. Transmission electron microscopy demonstrated that doping of Cd atoms did not destroy the crystal integrity of Cu2Se. A small amount of Cd in Cu2Se could reduce the electrical and thermal conductivities of the material, thus significantly enhancing its thermoelectric performance. With the increase in Cd content in the sample, the carrier concentration decreased and the mobility increased gradually. Thermogravimetric differential thermal analysis showed that no weight loss occurred below the melting point. Excessive Cd doping led to the emergence of the second phase of CdSe in the sample, thus significantly increasing the thermal conductivity of the material. A maximum ZT value of 1.67 at 700 K was obtained in the Cu1.9925SeCd0.0075 sample.

Plugging nanoscale imperfections in the polyamide active layer of thin-film composite reverse osmosis membrane to inhibit advective solute transport

The objective of this study is to inhibit advective solute passage through reverse osmosis (RO) membranes by filtering a small volume of polyvinyl alcohol (PVA) aqueous solution for 1 min at 0.1 MPa to selectively plug nanoscale imperfections. The PVA plugging the nanoscale imperfections was stabilized by cross-linking with glutaraldehyde. Experimental data showed that PVA treatment with PVA concentrations of up to 20 ppm did not decrease the water permeability, but it improved the solute removal efficiencies significantly. Specifically, at an applied pressure of 2.0 MPa, the NaCl and Rhodamine-WT rejection improved from 97.4% to 98.8% (a 67% decrease in NaCl flux) and 99.74% to 99.96% (a 85% decrease in Rhodamine-WT flux), respectively. Modeling analysis using a solution-diffusion model coupled with unhindered advection through nanoscale imperfections demonstrated that these improvements in solute rejection were due to selective plugging of nanoscale imperfections by PVA without building up an additional resistive layer on the polyamide active layer. Experimental data also showed that the cross-linked PVA plugging the nanoscale imperfections was stable under repeated exposure to citric acid, sodium hydroxide, and ethylenediaminetetraacetic acid.