Synthesis and characterization of novel nanocomposite membrane of sodium titanate/Nafion

Novel nanocomposite membrane of sodium titanate/Nafion based on sodium titanate nanotubes with Nafion^® were prepared by solvent casting techniques. Nanotubes of sodium titanate were synthesized by hydrothermal method. TEM, XRD, and FTIR were employed to characterize the crystal phase, microstructure, and other physicochemical properties of the membrane and the nanotube samples. FTIR results showed us that the nanotube material of Na₂Ti₃O₇ has existed in the nanocomposite membrane of Na₂Ti₃O₇/Nafion. The existence of sodium titanate nanotubes in Nafion^® improves the methanol crossover and makes promising practical value of blocking methanol in direct methanol fuel cells.     

Effect of sulfate ions and associated cation type on the pore solution chemistry in chloride-contaminated plain and blended cements

This paper presents the results of a study conducted to evaluate the effect of chloride and sulfate contamination on the pore solution chemistry in plain and blended cements. The cement paste specimens were admixed with a fixed quantity of sodium chloride and varying quantities of sodium sulfate or magnesium sulfate. The pore solution was extracted from these specimens and analyzed to determine OH⁻, Cl⁻ and SO₄²⁻ concentrations. The OH⁻ concentration of the pore solution in both the plain and blended cements increased with increasing concentration of sodium sulfate while no increase was noted in the specimens admixed with sodium chloride plus magnesium sulfate. The chloride concentration in the pore solution in plain and blended cements increased with increasing sodium sulfate concentration. In the specimens admixed with magnesium sulfate, the increase was noted up to 1% SO₄²⁻, beyond which no change was noted. The SO₄²⁻ concentration also increased with increasing quantity of sulfate contamination in the specimens admixed with both sodium and magnesium sulfate. The sulfate concentration in the cements admixed with sodium chloride plus sodium sulfate was more than that in the specimens admixed with sodium chloride or sodium chloride plus magnesium sulfate. The alkalinity of the pore solution influenced both chloride- and sulfate-binding capacity of cements.     

Barium borosilicate glass as a matrix for the uptake of dyes

Barium borosilicate (BBS) and sodium borosilicate (SBS) glass samples, prepared by the conventional melt-quench method, were used for the uptake of Rhodamine 6G dye from aqueous solution. The experimental conditions were optimized to get maximum uptake and was found to be 0.4 mg of dye per gram of BBS glass sample. For the same network former to modifier ratio, barium borosilicate glasses are found to have improved extent of uptake for the dye molecules from aqueous solutions compared to sodium borosilicate glasses. Based on ²⁹Si MAS NMR studies on these glasses, it is inferred that significantly higher number of non-bridging oxygen atoms present in barium borosilicate glasses compared to sodium borosilicate glasses is responsible for its improved uptake of Rhodamine 6G dye. ¹¹B MAS NMR studies have confirmed the simultaneous existence of boron in BO₃ and BO₄ configurations in both barium borosilicate and sodium borosilicate glasses. The luminescence studies have established that the dye molecule is incorporated into the glass matrix through ion exchange mechanism by replacing the exchangeable ions like Na⁺/Ba²⁺ attached with the non-bridging oxygen atoms present in the glass.     

Mechanically Robust Gel Polymer Electrolyte for an Ultrastable Sodium Metal Battery

Sodium dendrite growth is responsible for short circuiting and fire hazard of metal batteries, which limits the potential application of sodium metal anode. Sodium dendrite can be effectively suppressed by applying mechanically robust electrolyte in battery systems. Herein, a composite gel polymer electrolyte (GPE) is designed and fabricated, mainly consisting of graphene oxide (GO) and polyvinylidene fluoride‐hexafluoropropylene (PVDF‐HFP). With the addition of an appropriate amount of GO content, the compressive Young's modulus of 2 wt% GO+PVDF‐HFP (2‐GPH) composite GPE is greatly enhanced by a factor of 10, reaching 2.5 GPa, which is crucial in the suppression of sodium dendrite growth. As a result, uniform sodium deposition and ultralong reversible sodium plating/stripping (over 400 h) at high current density (5 mA cm^?2) are achieved. Furthermore, as evidenced by molecular dynamics simulation, the GO content facilitates the sodium ion transportation, giving a high ionic conductivity of 2.3 × 10^?3 S cm^?1. When coupled with Na₃V₂(PO₄)₃ cathode in a full sodium metal battery, a high initial capacity of 107 mA h g^?1 at 1 C (1 C = 117 mA g^?1) is recorded, with an excellent capacity retention rate of 93.5% and high coulombic efficiency of 99.8% after 1100 cycles.     

Determination of radiochemical and radionuclide purity of a <Superscript>131</Superscript>I preparation

The radiochemical purity of a ¹³¹I preparation (the iodide fraction) was determined by ascending paper chromatography using a mixture of sodium iodide, sodium iodate, and sodium carbonate as a carrier and aqueous methanol as an eluent. The chromatogram was developed with a scanning β-ray spectrometer. The radiochemical purity of ¹³¹I determined by this procedure was 99.98%. The radionuclide purity of the ¹³¹I preparation was measured on a γ-ray spectrometer with an ultrapure Ge detector. The content of radionuclide impurities estimated from their detection limits in the ¹³¹I preparation isolated from TeO₂ in 3–4 days after its irradiation in a reactor was no more than 0.03%. The ⁷⁵Se content in the preparation aged for 6–7 months (which corresponds to a decrease in the ¹³¹I activity by a factor of 10⁶–10⁷ owing to decay) corresponds to 2 × 10^?6% of the activity by the end of irradiation.     

S-character of Cd+ centre in γ-irradiated alkali silicate glasses

The s-character of Cd⁺ centres and its fluctuation in -irradiated alkali silicate glasses were investigated using ESR spectroscopy. With increasing alkali content, the s-characters of Cd⁺ centres in sodium and potassium silicate glasses decrease monotonically whereas the s-character in lithium silicate glasses shows a maximum and then decreases. The temperature effect on compositional dependence of the s-character of a Cd⁺ centre is rarely observed in lithium silicate glasses. On the other hand, the temperature effect is clearly observed in sodium and it is suggested that local structures around Cd⁺ centres in sodium and potassium silicate glasses is relaxed by annealing at room temperature.     

cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX), its properties and initiation reactivity

Pre-treatment of simulated industrial wastewaters (SIM1, SIM2 and SIM3) containing organic and inorganic compounds (1,2-dichloroethane, sodium formate, sodium hydrogen carbonate, sodium carbonate and sodium chloride) by oxidative degradation using homogeneous Fenton type processes (Fe²⁺/H₂O₂ and Fe³⁺/H₂O₂) has been evaluated. The effects of initial Fe²⁺ and Fe³⁺ concentrations, [Fe^2+/3+], type of iron salt (ferrous sulfate vs. ferric chloride), initial hydrogen peroxide concentration, [H₂O₂], on mineralization extent, i.e., total organic content (TOC) removal, were studied. Response surface methodology (RSM), particularly Box–Behnken design (BBD) was used as modelling tool, and obtained predictive function was used to optimize the overall process by the means of desirability function approach (DFA). Up to 94% of initial TOC was removed after 120 min. Ferrous sulfate was found to be the most appropriate reagent, and the optimal doses of Fe²⁺ and H₂O₂ for reducing the pollutant content, in terms of final TOC and sludge production were assessed.     

Reduction of sodium-accelerated oxidation of silicon nitride ceramics by aluminium implantation

Norton NBD 200 silicon nitride ceramics were implanted with sodium to a dose of 7.0×10¹⁵cm^-2 at 72 keV (1 at% peak sodium content at 100 nm). The sodium-implanted samples were further implanted with aluminium to 7.3×10¹⁵cm^-2 at 87 keV (1 at% peak aluminium content at 100 nm). The implanted and unimplanted samples were oxidized in 1 atm dry oxygen at 1100 and 1300°C for 2–6 h. Profilometry and scanning electron microscopy measurements indicated that sodium implantation led to up to a two-fold increase in the oxidation rate of silicon nitride. The sodium effect was effectively neutralized when aluminium was co-implanted. The opposite effects of sodium and aluminium on the oxidation resistance of silicon nitride can be attributed to their different roles in modifying the structure and properties of the oxide formed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Hydrothermal synthesis of phosphate-mediated ZnO nanosheets

ZnO nanosheets were obtained via a simple hydrothermal synthesis in the presence of sodium tripolyphosphate. The formation mechanism and effect of sodium tripolyphosphate concentration on the morphology of ZnO nanosheets have also been reported. Field emission scanning electron microscopy, transmission electron microscopy and fourier transform infrared spectroscopy were used to characterize the structure features and chemical compositions. The results show that the replacement of OH^? dangling bond on ZnO positive polar faces (0001) by PO₄^3? hinders splicing growth of [Zn(OH)₄]^2? growth units along the [0001] direction, which results in the formation of ZnO nanosheets.     

Interaction of sodium with simple glasses

The interactions of binary and ternary silicates with sodium were found to be similar to that of vitreous silica in that the number of Si-O^– bonds was observed to increase at the expense of the Si-O bonds as the temperature of exposure to sodium is raised. From the model developed for vitreous silica [1], it was argued that Si-O^– bonds are more stable than Si-O bonds in the presence of sodium. Using this concept, the discoloration behaviour of these binary and ternary silicates could be explained. The more general problem of selecting materials compatible with sodium is also dealt with by collecting a set of criteria based on equilibrium thermodynamics, and the shortcomings of these criteria are discussed.     

Novel Structural Design and Adsorption/Insertion Coordinating Quasi-Metallic Na Storage Mechanism toward High-performance Hard Carbon Anode Derived from Carboxymethyl Cellulose

Hard Carbon have become the most promising anode candidates for sodium-ion batteries, but the poor rate performance and cycle life remain key issues. In this work, N-doped hard carbon with abundant defects and expanded interlayer spacing is constructed by using carboxymethyl cellulose sodium as precursor with the assistance of graphitic carbon nitride. The formation of N-doped nanosheet structure is realized by the C N• or C C• radicals generated through the conversion of nitrile intermediates in the pyrolysis process. This greatly enhances the rate capability (192.8 mAh g⁻¹ at 5.0 A g⁻¹) and ultra-long cycle stability (233.3 mAh g⁻¹ after 2000 cycles at 0.5 A g⁻¹). In situ Raman spectroscopy, ex situ X-ray diffraction and X-ray photoelectron spectroscopy analysis in combination with comprehensive electrochemical characterizations, reveal that the interlayer insertion coordinated quasi-metallic sodium storage in the low potential plateau region and adsorption storage in the high potential sloping region. The first-principles density functional theory calculations further demonstrate strong coordination effect on nitrogen defect sites to capture sodium, especially with pyrrolic N, uncovering the formation mechanism of quasi-metallic bond in the sodium storage. This work provides new insights into the sodium storage mechanism of high-performance carbonaceous materials, and offers new opportunities for better design of hard carbon anode.     

Soft Magnetic Properties and Electrochemical Behavior of Nanocrystalline CoFeCu Thin Films Electrodeposited from Citrate-Added Baths

CoFeCu thin films were electrodeposited from baths with natural pH (instead of pH～2.8 used in conventional baths) and containing different sodium citrate dosages. ChemEQL V.3.0 software was employed to study speciation diagrams of citrate-added CoFeCu bath with natural pH. At low sodium citrate dosage, Co⁺⁺, Fe⁺⁺, and Cu⁺⁺ species were dominant in CoFeCu bath with natural pH (around 5.2). However, as dosage of sodium citrate in the bath increased, the concentration of complexed species (especially Co(C₆H₅O₇)^?, Fe(C₆H₅O₇)^?, and Cu(OHC₆H₅O₇)^2?) significantly raised. Cyclic voltammetry (CV) studies showed that the formation of complexed species in the bath shifted reduction potential of metals towards more negative potentials. Moreover, in order to deposit cobalt and iron simultaneously with copper, it was necessary to increase the reverse potential (E _λ ) value gradually with sodium citrate dosage, otherwise, only copper would have deposited from citrate-added CoFeCu bath. Scanning electron micrographs illustrated that using natural pH (about 5.2) remarkably decreased the number of microvoids in the deposited films compared with the film deposited from conventional baths with pH level of 2.8. EDS, XRD, and VSM were also used for characterization of the deposited films. All deposited films exhibited nanocrystalline structures, and increasing sodium citrate into the baths led to reduction in grain sizes (D) and coercivity (H _c) of the CoFeCu thin films. Plotting log(H _c) versus log(D ⁶) demonstrated that films coercivity followed the “D ⁶ law”. There were only two phase structures (FCC (Co) or BCC (Fe)) observed in the X-ray diffraction patterns of the films. In addition, films with double-phase structures (FCC+BCC) showed finer grain sizes and therefore exhibited lower coercivity in comparison with single-phase (FCC or BCC) films. CoFeCu thin films deposited at higher dosages of sodium citrate (>20 g/L) were poor in diamagnetic copper and consequently showed higher saturation magnetizations.     

Superhydrophobic sodium silicate based silica aerogel prepared by ambient pressure drying

The superhydrophobic silica aerogel was prepared by using less expensive sodium silicate as a main silica source through a cost-effective and simple route via ambient pressure drying. The sodium impurity was first eliminated by mixing sodium silicate with a co-precursor methyltriethoxysilane (MTES) followed by ion exchange process. The hydrogel was formed by gelation and the alcogel was further obtained by alcoholization of the hydrogel. The surface of alcogel was modified by reacting with trimethylchlorosilane (TMCS) diluted in n-hexane. It was suggested that MTES accelerated water expelling from the hydrogel, while TMCS modified the surface of silica network by replacing Si–OH with Si–C. As a result, the obtained silica aerogel exhibited excellent physical properties with less than 10% volume shrinkage. The density, surface area and cumulative pore volume were 0.12 g cm⁻³, 684.44 m² g⁻¹, and 3.55 cm³ g⁻¹, respectively. The optical transmission reached 82.8% with the water contact angle of 146°.     

Effect of metal clusters on the absorption and emission spectra of high-density sodium vapors

The optical absorption spectra of high-density (10¹⁶–10¹⁹ cm⁻³) sodium vapors were studied in a broad spectral range (0.35–1.1 μm). The intensity of thermal radiation from sodium vapors was measured in the 2–3 μm wavelength interval. It is established that the effect of metal clusters can account neither for the observed structure of absorption spectra nor for the increased intensity of emission in the near-IR range reported in some works (in particular, for the emission spectra of high-pressure gas-discharge sodium lamps).     

A Heterostructure Coupling of Bioinspired,Adhesive Polydopamine,and Porous Prussian Blue Nanocubics as Cathode for High‐Performance Sodium‐Ion Battery

Prussian blue (PB) and its analogues are recognized as promising cathodes for rechargeable batteries intended for application in low‐cost and large‐scale electric energy storage. With respect to PB cathodes, however, their intrinsic crystal regularity, vacancies, and coordinated water will lead to low specific capacity and poor rate performance, impeding their application. Herein, nanocubic porous Na_xFeFe(CN)₆ coated with polydopamine (PDA) as a coupling layer to improve its electrochemical performance is reported, inspired by the excellent adhesive property of PDA. As a cathode for sodium‐ion batteries, the Na_xFeFe(CN)₆ electrode coupled with PDA delivers a reversible capacity of 93.8 mA h g^?1 after 500 cycles at 0.2 A g^?1, and a discharge capacity of 72.6 mA h g^?1 at 5.0 A g^?1. The sodium storage mechanism of this Na_xFeFe(CN)₆ coupled with PDA is revealed via in situ Raman spectroscopy. The first‐principles computational results indicate that Fe^II sites in PB prefer to couple with the robust PDA layer to stabilize the PB structure. Moreover, the sodium‐ion migration in the PB structure is enhanced after coating with PDA, thus improving the sodium storage properties. Both experiments and computational simulations present guidelines for the rational design of nanomaterials as electrodes for energy storage devices.     

Dual Mechanism for Sodium based Energy Storage

A dual-mechanism energy storage strategy is proposed, involving the electrochemical process of sodium ion battery (SIB) and sodium metal battery (SMB). This strategy is expected to achieve a higher capacity than SIB, and obtain dendrite-free growth of SMB with a well-designed anode. Here, self-constructed bismuth with “sodiophilic” framework and rapid ion transmission characteristics is employed as the sodium host (anode) integrating alloy/de-alloy and plating/stripping process that suppresses the dendrite growth and overcomes the limited capacity of traditional anode. Benefited from this, the capacity (capacity contributed by alloy and plating of sodium in total) of 2000 mAh g⁻¹ can be reached, which can retain up to 800 h at 1 A g⁻¹. Also, the capacity of 3100 mAh g⁻¹ can be achieved that is ≈7.7 times than that of alloyed-bismuth (Bi). This work proposes a dual-mechanism strategy to tackle the dilemma of high-performance sodium (Na) storage devices, which opens a new avenue for the development of next-generation energy storage device.     

Phase modification induced drying shrinkage reduction on Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> activated slag by incorporating Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>

This paper aims to study the phase modification, reaction kinetics, mechanical properties and drying shrinkage of sodium carbonate activated slag by incorporating sodium sulfate in the activator. The results show that the reaction process is firstly controlled by CO₃ ^2? anions, and later runs similar to that of sodium sulfate activation. Besides, the relatively unstable phase gaylussite, commonly found in the sodium carbonate activation, is not observed in the reaction products upon hybrid activation, and monosulfoaluminate rather than ettringite is identified, probably caused by the reduced aluminate-to-sulfate ratio and increased pH value. The drying shrinkage is considerably reduced by up to 41% when replacing 50 wt% sodium carbonate by sodium sulfate, most possibly attributed to the induced phase modification. Furthermore, the relationships between the phase modification and drying shrinkage, and the potentially involved chemical reaction are discussed.     

Antibacterial activity of silver-modified natural clinoptilolite

The aim of the present work was to estimate the bactericidal activity and efficacy of silver pre-treated clinoptilolite-rich tuff from Marsid (Romania) in solid media (agar plates) against Gram-negative Escherichia coli ATCC 25922 and Gram-positive Staphylococcus aureus ATCC 25923. Two samples of natural clinoptilolite-rich tuff was first pre-treated with oxalic acid and sodium hydroxide solutions, respectively. The sample treated with oxalic acid was then exchanged with sodium chloride solution to obtain sodium form. Finally, both samples were exchanged with silver nitrate solution at room temperature for 24 h to obtain silver forms (P1-Ag⁺ and P2-Ag⁺) of clinoptilolite. The structure, morphology, and elemental composition of the pre-treated clinoptilolite samples were characterized by XRD, infrared (ATR-IR), SEM, and EDX analysis. The antibacterial activity was investigated by exposing E. coli and S. aureus in nutritive agar to the silver-clinoptilolite samples. Microorganisms were completely inhibited at 2 mg Ag⁺-clinoptilolite/mL nutritiv medium after 24 h of incubation at 37 °C. The silver-clinoptilolite sample derived from natural clinoptilolite pre-treated with oxalic acid (P1-Ag⁺) exhibit a stronger antibacterial effect in the presence of E. coli and the sample derived from natural clinoptilolite pre-treated with sodium hydroxide (P2-Ag⁺) in the presence of S. aureus.     

A High-Kinetics Sulfur Cathode with a Highly Efficient Mechanism for Superior Room-Temperature Na–S Batteries

Applications of room-temperature–sodium sulfur (RT-Na/S) batteries are currently impeded by the insulating nature of sulfur, the slow redox kinetics of sulfur with sodium, and the dissolution and migration of sodium polysulfides. Herein, a novel micrometer-sized hierarchical S cathode supported by FeS₂ electrocatalyst, which is grown in situ in well-confined carbon nanocage assemblies, is presented. The hierarchical carbon matrix can provide multiple physical entrapment to polysulfides, and the FeS₂ nanograins exhibit a low Na-ion diffusion barrier, strong binding energy, and high affinity for sodium polysulfides. Their combination makes it an ideal sulfur host to immobilize the polysulfides and achieve reversible conversion of polysulfides toward Na₂S. Importantly, the hierarchical S cathode is suitable for large-scale production via the inexpensive and green spray-drying method. The porous hierarchical S cathode offers a high sulfur content of 65.5 wt%, and can deliver high reversible capacity (524 mAh g⁻¹ over 300 cycles at 0.1 A g⁻¹) and outstanding rate capability (395 mAh g⁻¹ at 1 A g⁻¹ for 850 cycles), holding great promise for both scientific research and real application.     

Depth profiles of aluminum and sodium near surfaces: Nuclear resonance method

Depth profiles of aluminum and sodium implanted into silicon carbide, silicon and silicon dioxide have been measured by means of sharp resonances in the reactions ²⁷Al(p,γ)²⁸Si and ²³Na(p,γ)²⁴Mg. The absolute number of impurity atoms has been determined and compared with that indicated by charge integration during implantation. Adjacent areas of some specimens have been measured by the Cameca ion-beam mass spectrometer and the nuclear resonance method; results are compared. A depth resolution of less than 20 Å has been demonstrated for Al very near the surface of SiC. Information concerning the migration of sodium in SiO₂ under ion bombardment is presented. Depth profiles are extracted from gamma-ray yield curves taking into account the beam energy distribution, the resonance shape, the average proton energy loss in the sample and the energy loss straggling.