High-field EPR Study of the Effect of Chloride on Mn2+ Ions in Frozen Aqueous Solutions

The effect of chloride concentration on Mn²⁺ (S = 5/2, I = 5/2) ions in frozen aqueous solutions is studied by high-field high-frequency electron paramagnetic resonance (HFEPR). The usually six sharp lines characteristic of Mn²⁺ ions, arising from the m _s  = ?1/2 → 1/2 transition, is modified by the addition of Cl^? anions and the six resonances become much broader and more complex. This new feature likely arises from the ligation of one Cl^? anion to a hydrated Mn²⁺ ion forming a [Mn(H₂O)₅Cl]^? complex. This complex increases linearly with Cl^? concentration with an association constant of K _{a, apparent} = 61 M^?1. The structure of the putative chloride complex was studied using density functional theory calculations and the expected zero-field interaction of such a manganese center was calculated using the superposition model. The predicted values were similar to those determined from the simulation of the spectrum of the m _s  = ?5/3 → ?3/2 transition of the chloride complex. This effect of Cl^? anions occurs at biologically relevant concentration and can be used to probe the Mn²⁺ ions in cellular and protein environments.     

Preparation and characterization of Y-Fe alloy nanowires by template-assisted electrodeposition from aqueous solution

In this study, a method was proposed for the preparation of Y-Fe alloy nanowires by PC membrane template-assisted electrodeposition from aqueous solution. Citric acid  acted as complexing agent was used into the solution to fabricate Y-Fe alloy nanowires. The electrolyte solution consisted of 5 g L^?1 YCl₃, 12.5 g L^?1 FeSO·6H₂O, different concentrations of citric acid , 25 g L^?1 boric acid in deionized water. The energy dispersive spectroscopy (EDS) found that the content of Y in the nanowires can be controlled by citric acid concentration and the current intensity, and the content of Y could reach up to 33.16 wt%. Scanning electron microscopy (SEM), BET specific surface area (BET), and X-ray diffraction (XRD) showed that there was a shift in the structure of nanowires from semicrystalline to amorphous due to the change of Y content, and their shapes were approximately 100 nm in diameter and 6 μm in length; the surface areas of nanowires were about 3.97 m²/g. Fourier transform infrared (FTIR) spectroscopy, UV–Vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy (XPS) indicated the formation of Y-Fe alloy, Y₂O₃ and Fe₂O₃   existed  in the outer layer of nanowires. The magnetic field applied both parallel and perpendicular to the nanowires by alternating gradient magnetometer (AGM) showed small magnetic anisotropy and low coercivity with easy axis of magnetization perpendicular to the nanowires. In addition, the magneto-optic Kerr effect (MOKE) was investigated, and a Kerr rotation angle of 29 mdeg was obtained.     

Promising nitrogen-doped porous nanosheets carbon derived from pomegranate husk as advanced electrode materials for supercapacitors

Nitrogen-doped porous activated carbons (N-PHACs) have been successfully synthesized using pomegranate husk as carbon precursor via ZnCl₂-activation carbonization and subsequent urea-assisted hydrothermal nitrogen-doping method. The obtained N-PHACs possesses abundant mesoporous structure, high specific surface area (up to 1754.8 m² g^?1), pore volume (1.05 cm³ g^?1), and nitrogen-doping content (4.51 wt%). Besides, the N-PHACs-based material showed a high specific capacitance of 254 F g^?1 at a current density of 0.5 A g^?1 and excellent rate performance (73% capacitance retention ratio even at 20 A g^?1) in 2 M KOH aqueous electrolyte, which is attributed to the contribution of double-layer capacitance and pseudocapacitance. The assembled N-PHACs-based symmetric capacitor with a wide operating voltage range of 0–1.8 V exhibits a maximum energy density of 15.3 Wh kg^?1 at a power density of 225 W kg^?1 and superior cycle stability (only 6% loss after 5000 cycles) in 0.5 M Na₂SO₄ aqueous electrolyte. These exciting results suggest that the novel N-doping porous carbon material prepared by a green and low-cost design strategy has a potential application as high-performance electrode materials for supercapacitors.     

Aerosol characterization and lung deposition of synthesized TiO2 nanoparticles for murine inhalation studies

This study presents a novel exposure protocol for synthesized nanoparticles (NPs). NPs were synthesized in gas phase by thermal decomposition of metal alkoxide vapors in a laminar flow reactor. The exposure protocol was used to estimate the deposition fraction of titanium dioxide (TiO₂) NPs to mice lung. The experiments were conducted at aerosol mass concentrations of 0.8, 7.2, 10.0, and 28.5 mg m^?3. The means of aerosol geometric mobility diameter and aerodynamic diameter were 80 and 124 nm, and the geometric standard deviations were 1.8 and 1.7, respectively. The effective density of the particles was approximately from 1.5 to 1.7 g cm^?3. Particle concentration varied from 4 × 10⁵ cm^?3 at mass concentrations of 0.8 mg m^?3 to 12 × 10⁶ cm^?3 at 28.5 mg m^?3. Particle phase structures were 74% of anatase and 26% of brookite with respective crystallite sized of 41 and 6 nm. The brookite crystallites were approximately 100 times the size of the anatase crystallites. The TiO₂ particles were porous and highly agglomerated, with a mean primary particle size of 21 nm. The specific surface area of TiO₂ powder was 61 m² g^?1. We defined mice respiratory minute volume (RMV) value during exposure to TiO₂ aerosol. Both TiO₂ particulate matter and gaseous by-products affected respiratory parameters. The RMV values were used to quantify the deposition fraction of TiO₂ matter by using two different methods. According to individual samples, the deposition fraction was 8% on an average, and when defined from aerosol mass concentration series, it was 7%. These results show that the exposure protocol can be used to study toxicological effects of synthesized NPs.     

Fluorescence and Nonlinear Optical Properties of Alizarin Red S in Solvents and Droplet

The enhancement of the nonlinear properties of materials is an interesting topic since it has many applications in optical devices and medicines. The Z-scan technique was used to study the values of the two-photon absorption (β), second-order molecular hyperpolarizability (γ_R), third-order susceptibility (χ_R), and nonlinear refractive index (n₂) of Alizarin Red S in different media using a continuous-wave diode-pump laser radiation at 532 nm. For Alizarin Red S in a droplet, the β, n₂, χ_R, and γ_R were estimated at the order of 10^?7 cm²/W and 10^?12 cm/W, 10^?3 m³ W^?1 s^?1 and 10^?24 m⁶ W^?1 s^?1, respectively. The results indicated that the values of β and n₂ reduced, whereas the values of χ_R and γ_R were enhanced when the solvent was changed from droplet to water, DMF, and dimethyl sulfoxide due to the change in the solvent’s dielectric constant (ε). Moreover, the values of β were enhanced by an increase in the concentration of the surfactant in the aqueous solution. The absorption spectra of Alizarin Red S in the aqueous solution was observed at 428 nm, and a few red shifts in the absorption spectra were observed with a reduction in the dielectric constant of the medium. The same effect was observed in the absorption spectra of Alizarin Red S in the droplet when the bulk dielectric constant reduced. The dielectric constant can affect the fluorescence spectra of Alizarin Red S when the solution is changed from water to dimethyl sulfoxide. The dipole moments of Alizarin Red S in the different media were studied using the quantum perturbation theory.     

Controlling the defect density to improve the output power of InGaN/GaN-based vertical light-emitting diodes by using substrates patterned with SiO2 lenses

In this study, we investigated the effect of SiO₂ lenses on the output power of InGaN/GaN-based vertical light-emitting diodes (VLEDs; wavelength = 445 nm) and compared the results to those of reference VLEDs without the SiO₂ lenses (planar samples). Arrays of SiO₂ lenses (pitch = 3 μm, width = 2.5 μm, height = 1.0 μm) were formed on c-plane sapphire substrates. The external quantum efficiency (EQE) of the packaged VLEDs with planar and patterned substrates was characterised. At 5 mA, the EQE of the patterned samples was 150% higher than that of the planar samples. A patterned, N-polar, n-GaN sample contained far fewer nanopipes (approximately 2.2 × 10⁵ cm^?2) than a planar n-GaN sample (approximately 2.4 × 10⁶ cm^?2). Furthermore, the patterned samples contained far fewer threading dislocations (approximately 1.0 × 10⁸ cm^?2) than the planar samples (approximately 5.0 × 10⁸ cm^?2). Scanning electron microscopy (SEM) images showed that the photoelectrochemical (PEC)-etched patterned samples contained cones that were 150% larger than that of the PEC-etched planar samples. In addition, SEM images, cathode luminescence measurements and finite-difference time-domain simulations were used to characterise the improved light output of the patterned samples.     

Novel synthesis and characterization of ZnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoflakes grown on nickel foam as efficient electrode materials for electrochemical supercapacitors

ZnCo₂O₄ nanoflakes were directly grown on Ni foam via a two-step facile strategy, involving cathodic electrolytic electrodeposition (ELD) method and followed by a thermal annealing treatment step. The results of physical characterizations exhibit that the mesoporous ZnCo₂O₄ nanoflakes have large electroactive surface areas (138.8 m² g^?1) and acceptable physical stability with the Ni foam, providing fast electron and ion transport sites. The ZnCo₂O₄ nanoflakes on Ni foam were directly used as integrated electrodes for supercapacitors and their electrochemical properties were measured in 2 M KOH aqueous solution. The ZnCo₂O₄ nanoflake electrode exhibits a high capacitance of 1781.7 F g^?1 at a current density of 5 A g^?1 and good rate capability (62% capacity retention at 50 A g^?1). Also, an excellent cycling ability at various current densities from 5 to 50 A g^?1 was obtained and 92% of the initial capacitance maintained after 4000 cycles. The results demonstrate that the proposed synthesis route is cost-effective and facile and can be developed for preparation of electrode materials in other electrochemical supercapacitors.     

V<Subscript>2</Subscript>O<Subscript>5</Subscript>-SiO<Subscript>2</Subscript> hybrid as anode material for aqueous rechargeable lithium batteries

V₂O₅-SiO₂ hybrid material was fabricated by heat-treating a mixture of H₂SiO₃ and V₂O₅. SEM, TEM, XRD, and N₂ isotherm analyses were performed to characterize the morphology and structure details of the as-prepared V₂O₅-SiO₂. The possibility of using the as-prepared V₂O₅-SiO₂ as anode material for aqueous lithium-ion batteries was investigated. Potentiostatic and galvanostatic results indicated that the intercalation/de-intercalation of Li⁺ in this material in aqueous electrolyte was quasi-reversible. It was also found that a discharge capacity of up to 199.1 mAh g^?1 was obtained at a current density of 50 mA g^?1 in aqueous solution of 1 M Li₂SO₄, a value which is much higher than the available reported capacities of vanadium (+5) oxides in aqueous electrolytes.     

Synthesis of LiCoO<Subscript>2</Subscript> via sol-gel method for aqueous rechargeable lithium batteries

A crystalline structure of LiCoO₂ sample was synthesized at different stirring times via sol-gel method. This was followed by the electrochemical characterization of LiCoO₂ in 5 M LiNO₃ aqueous electrolyte. The hexagonal LiCoO₂ was stirred for 30 h produced the highest peak intensity and smallest particle size. A morphological analysis showed the particle size distribution within the range of 0.32–0.47 μm. At lower scan rates of cyclic voltammetry, three pairs of redox peaks at E_SCE = 0.81/0.65, 0.89/0.83 and 1.01/0.95 V were observed. The peak separation was proportionally consistent with Li⁺ diffusion coefficients of 7.42 × 10^?8 cm² s^?1 (anodic) and 3.59 × 10^?8 cm² s^?1 (cathodic). For specific capacity, the LiCoO₂ demonstrated a higher initial specific capacity (115.49 mA h g^?1). A small difference (1.92 Ω) in the charge transfer resistance before and after a charge discharge analysis indicated that the Li⁺ ions had been well-diffused during the intercalation/de-intercalation process.     

Synthesis and characterisation of the Fe(II–III) hydroxy-formate green rust

A new methodology was envisioned in order to prepare green rust compounds build on organic anions that could intervene in microbiologically influenced corrosion processes of iron and steel. The formate ion was chosen as an example. The formation of rust was simulated by the oxidation of aqueous suspensions of Fe(OH)₂ precipitated from Fe(II) lactate and sodium hydroxide, in the presence of sodium formate to promote the formation of the corresponding green rust. The evolution of the precipitate with time was followed by transmission Mössbauer spectroscopy at 15 K. It was observed that the initial hydroxide was transformed into a new GR compound. Its spectrum is composed of three quadrupole doublets, D ₁ (δ?=?1.28 mm s^?1, Δ?=?2.75 mm s^?1) and D ₂ (δ?=?1.28 mm s^?1, Δ?=?2.48 mm s^?1) that correspond to Fe(II) and D ₃ (δ?=?0.49 mm s^?1, Δ?=?0.37 mm s^?1) that corresponds to Fe(III). The relative area of D ₃, close to the proportion of Fe(III) in the GR, was found at 28.5?±?1.5% (～2/7). Raman spectroscopy confirmed that the intermediate compound was a Fe(II–III) hydroxy-formate, GR(HCOO^?).     

Nitrogen-doped multi-walled carbon nanotubes for paracetamol sensing

A novel sensor consisting of nitrogen-doped multi-walled carbon nanotubes was fabricated by means of chemical vapor deposition technique with decomposition of acetonitrile onto oxidized silicon wafer using ferrocene as catalyst. The electrochemical response of carbon nanotubes-based sensor towards oxidation of paracetamol to N-acetyl-p-quinone imine was investigated in phosphate buffer solution (pH 7.0) by means of standard electrochemical techniques. A quasi-reversible response for oxidation of paracetamol was identified on carbon nanotubes-based sensor with detection limit and sensitivity of 0.485 μM and 0.8406 A M^?1 cm^?2, respectively. It was found that the nitrogen doping in carbon nanotubes enhances the sensor's detection ability. Namely, electrochemical studies performed on film consisting of pristine carbon nanotubes reveal as well quasi-reversible response towards oxidation of paracetamol but nevertheless poorer detection ability and sensitivity (0.950 μM; 0.601 A M^?1 cm^?2). The findings strongly suggest the application of nitrogen-doped carbon nanotubes in biosensing.     

A facile synthesis about amorphous CoS<Subscript>2</Subscript> combined with first principle analysis for supercapacitor materials

The structure and electrochemical properties of amorphous CoS₂ and crystalline CoS₂ have been studied with both experimental characterization and theoretical calculations. In the field of experimental characterization, a facile chemical precipitation method is used to synthesize amorphous and crystalline CoS₂ samples with calcining temperatures of 200 and 280 °C, respectively. Comparing with crystalline CoS₂, amorphous structure of CoS₂ manifests great electron conductivity, effective porous structure, and exhibit a high specific capacitance of 996.16 F g^?1 at current density of 0.5 A g^?1, excellent rate capability of 89.8% retention with the current density ranging from 0.5 to 5 A g^?1, and a great cycling stability of 97.6% retention after 10,000 cycles at 2 A g^?1 in 6 mol L^?1 KOH aqueous electrolyte. In the area of theoretical calculation, we used the first principle and obtained the band structure with band gap of 0.00369 eV and DOSs with high locality of D-orbital from 69.88689 electrons/eV main peak, in the CoS₂ amorphous. The result confirms that amorphous CoS₂ have higher conductivity than crystalline CoS₂ in theory. In addition, the as-assembled asymmetric supercapacitor of Co-S-200//AC also exhibits the maximum specific capacitance of 104 F g^?1 within a cell voltage from 0 to 1.5 V at current density of 0.5 A g^?1 and indicates a great cycling stability of 95.68% and excellent capacitance behavior. All results demonstrate a great potential of amorphous CoS₂ active material for supercapacitors.     

Synthesis and characterization of nanostructure hydrous iron–titanium binary mixed oxide for arsenic sorption

Synthesis of nanostructure hydrous iron–titanium binary mixed oxide (NHITBMO) had been reported by a simple method, and characterized by the X-ray diffraction (XRD), thermal analysis, transmission electron microscope (TEM), Föurier Transform Infrared (FTIR), surface area, and zero surface charge pH (pHzpc). The synthetic oxide was hydrated and microcrystalline with 77.8 m² g^?1 BET surface area. The particle size (nm) calculated using XRD peak table and TEM image was ~10–13 and 6–8, respectively. The pH_zpc value was 6.0 (±0.05) for the oxide. The NHITBMO showed pH dependent good sorption affinity for arsenic from the aqueous solution and, the Langmuir monolayer capacity (mg g^?1) was 80.0 and 14.6, respectively, for the As(III) and As(V). The pseudo-second order equation described the room temperature arsenic sorption kinetic data well. The minimum dose required was 1.6 g NHITBMO per L of water (As_total = 0.24 mg L^?1) to reduce the arsenic level below 0.01 mg L^?1 in batch treatment process.     

Facile synthesis and characterization of high-performance NiMoO<Subscript>4</Subscript> · <Emphasis Type="Italic">x</Emphasis>H<Subscript>2</Subscript>O nanorods electrode material for supercapacitors

One-dimensional NiMoO₄ · xH₂O nanorods were synthesized by a facile template-free hydrothermal method as a potential electrode material for supercapacitors. The influences of reaction temperature, reaction time, and nickel source on the properties of resultant samples were investigated. Electrochemical data reveal that the as-synthesized one-dimensional NiMoO₄ · xH₂O nanorod superstructures can deliver a remarkable specific capacitance (SC) of 1131 F g^?1 at a current density of 1 A g^?1 and remain as high as 914 F g^?1 at 10 A g^?1 in a 6 M KOH aqueous solution. Moreover, there is only 6.2 % loss of the maximum SC after 1000 continuous charge–discharge cycles at the high current density of 10 A g^?1. Such outstanding electrochemical performance may be owing to the unique one-dimensional hierarchical structures, which can facilitate the electrolyte ions and electrons to easily contact the NiMoO₄ nanorod building blocks and then allow for sufficient faradaic reactions to take place, even at high current densities.     

Solvothermal synthesis of mesoporous NiCo2O4 spinel oxide nanostructure for high-performance electrochemical capacitor electrode

NiCo₂O₄ nanostructure was successfully synthesized via a d-glucose-assisted solvothermal process. Spinel-type cubic phase and mesoporous microstructure of the sample for different calcination temperatures were confirmed by X-ray diffraction and transmission electron microscopy. Typical pseudocapacitance feature of the NiCo₂O₄ treated at different temperatures was then evaluated in aqueous 6 M KOH electrolyte solution. Electrochemical measurements showed that the spinel nickel cobaltite nanostructure heated at 300 °C exhibits maximum specific capacitances of 524 F g^?1 at 0.5 A g^?1 and 419 F g^?1 at 10 A g^?1 with excellent cycle stability and only ~9 % of capacitance loss after 2,500 cycles. This demonstrates the potential application of the material for supercapacitors. The attractive pseudocapacitive performance of NiCo₂O₄ is mainly attributed to the redox contribution of the Ni and Co metal species, high surface area, and their desired mesoporous nanostructure.     

A novel synthesis of size-controllable mesoporous NiMoO<Subscript>4</Subscript> nanospheres for supercapacitor applications

A novel hydrothermal emulsion method is proposed to synthesize mesoporous NiMoO₄ nanosphere electrode material. The size of sphere-shaped NiMoO₄ nanostructure is controlled by the mass ratio of water and oil phases. Nickel acetate tetrahydrate and ammonium heptamolybdate were used as nickel and molybdate precursors, respectively. The resultant mesoporous NiMoO₄ nanospheres were characterized by X-ray diffraction, N₂ adsorption and desorption, scanning electron microscopy, and transmission electron microscopy. The electrochemical performances were evaluated by cyclic voltammetry (CV), cyclic chronopotentiometry (CP), and electrochemical impedance spectroscopy (EIS) in 6 M KOH solution. The typical mesoporous NiMoO₄ nanospheres exhibit the large specific surface area of 113 m² g^?1 and high specific capacitance of 1443 F g^?1 at 1 A g^?1, an outstanding cyclic stability with a capacitance retention of 90 % after 3000 cycles of charge-discharge at a current density of 10 A g^?1, and a low resistance.     

A new application of nickel-boron amorphous alloy nanoparticles: anode-catalyzed direct borohydride fuel cell

In this work, an amorphous Ni-B alloy was synthesized by chemical reduction and used in a direct borohydride fuel cell (DBFC). Characterization of the catalyst structure, composition, and morphology was performed by XRD, EDX, TEM, and SEM. In addition, the results showed that Ni-B presents as amorphous nanoparticles. The particle diameters ranged from 22 to 25 nm. The cyclic voltammetry (CV) and chronoamperometry (CA) tests proved that Ni-B has better electrocatalytic activity and higher stability towards KBH₄ oxidation compared to a pure Ni catalyst. A single cell was assembled with a Ni-B anode and a LaNi_0.9Ru_0.1O₃ cathode. A peak power density of 180 mW cm^?2 was achieved at room temperature. In addition, the fuel utilization rate was approximately 41% at a constant current density of 200 mA cm^?2, illustrating that some BH₄ ^? hydrolysis occurs on the Ni-B surface. Finally, the cell had no attenuation after 180 h test, showing good stability.     

Nanocrystalline Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> electrodes for supercapattery application

Nanocrystalline Li₂TiO₃ was successfully synthesized using solid-state reaction method. The microstructural and electrochemical properties of the prepared material are systematically characterized. The X-ray diffraction pattern of the prepared material exhibits predominant (002) orientation related to the monoclinic structure with C2/c space group. HRTEM images and SAED analysis reveal the well-developed nanostructured particles with average size of ～40 nm. The electrochemical properties of the prepared sample are carried out using cyclic voltammetry (CV) and chronopotentiometry (CP) using Pt//Li₂TiO₃ cell in 1 mol L^?1 Li₂SO₄ aqueous electrolyte. The Li₂TiO₃ electrode exhibits a specific discharge capacity of 122 mAh g^?1; it can be used as anode in Li battery within the potential window 0.0–1.0 V, while investigated as a supercapacitor electrode, it delivers a specific capacitance of 317 F g^?1 at a current density of 1 mA g^?1 within the potential range ?0.4 to +0.4 V. The demonstration of both anodic and supercapacitor behavior concludes that the nanocrystalline Li₂TiO₃ is a suitable electrode material for supercapattery application.     

The intercalation/deintercalation kinetic studies on the structure-integrated cathode material 0.5Li2MnO3 0.5LiNi0.5Mn0.5O2

A cathode material, 0.5Li₂MnO₃ 0.5LiNi_0.5Mn_0.5O₂, was prepared by citric acid-assisted sol–gel method and its electrochemical performance was investigated. It delivered a charge capacity of 270 mAh g^?1 and a discharge capacity of 189 mAh g^?1 in the first cycle. With the increase of current density from 14 to 28 mA g^?1, the discharge capacity dropped severely to 130 mA g^?1. Obviously, the rate capability of the material was inferior to most of the oxide cathode materials. The diffusion coefficient of this material was calculated to be 6.04?×?10^?12 cm² s^?1 from the results of cyclic voltammetry measurements. Moreover, diffusion coefficients between 3.13?×?10^?12 and 1.22?×?10^?10 cm² s^?1 in the voltage range of 3.8–4.7 V were obtained by capacity intermittent titration technique. This, together with the localized Li₂MnO₃ domains in the crystal structure, may validate the poor rate capability.