Voltammetric determination of vitamin B<Subscript>6</Subscript> (pyridoxine) at a graphite screen-printed electrode modified with graphene oxide/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> nanocomposite

The preparation and study of electrochemical properties of a graphite screen-printed electrode (SPE) modified with the GO/Fe₃O₄@SiO₂ (GO is graphene oxide) nanocomposites are described. The morphologies of the GO/Fe₃O₄@SiO₂ nanocomposites were examined by scanning electron microscopy. The electrochemical oxidation of vitamin B₆ (pyridoxine) on SPE modified with the GO/Fe₃O₄@SiO₂ nanocomposite was investigated by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. Under optimum conditions (pH 7.0), the vitamin B₆ oxidation at the surface of the modified SPE occurs at a potential about 190 mV less positive than that at the unmodified SPE. A linear voltammetric response for vitamin B₆ was obtained in the concentration range 1.0?10 ⁶—9.0?10 ⁴ mol L^–1 with a detection limit of 5.2?10 ⁷ mol L^–1 using differential pulse voltammetry. The developed sensor was also successfully applied for determination of trace level of vitamin B₆ in both the standard vitamin B₆ sample and biological samples (urine).     

Electrochemical behavior of α-Keggin-type nanoparticles,Co(en)<Subscript>3</Subscript>(PMo<Subscript>12</Subscript>O<Subscript>40</Subscript>), in polyethylene glycol

The electrochemical behavior of α-Keggin-type nanoparticles, Co(en)₃(PMo₁₂O₄₀) (abbreviated as PMo₁₂-Co), have been studied in poly(ethylene glycol) for four different molecular weights (PEG, average MW 400, 600, 1000, and 2000 g mol^–1) and containing LiClO₄ (O/Li=100/1) supporting electrolyte. The diffusion coefficients of the PMo₁₂-Co nanoparticles were determined using a microelectrode by chronoamperometry for PEG of different molecular weights that were used to describe the diffusion behavior of PMo₁₂-Co nanoparticles in different phase states. Moreover, the conductivity of the composite system increases upon addition of PMo₁₂-Co nanoparticles, which was measured by an a.c. impedance technique. FT-IR spectra and DSC were used to follow the interactions of PEG-LiClO₄-PMo₁₂-Co, and well described the reason that the PMo₁₂-Co nanoparticles could promote the conductivity of the PEG-LiClO₄-PMo₁₂-Co system. Electronic Publication     

Electrodeposition of thin Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> films

The electrochemical behavior of copper(II), zinc(II), and thiosulfate (S₂O₃ ^2-) ions on the molybdenum electrode in individual 0.2 М sodium sulfate solutions (рН 6.7) and with addition of either 0.1 М tartaric acid (рН 4.6) or 0.1 М citric acid (рН 4.7) is studied. A one-step electrochemical method is developed for the deposition of thin Cu₂ZnSnS₄ films, which is carried out on the molybdenum electrode at a constant potential in sodium sulfate solutions containing tartaric acid. The effect of the concentration of electrolyte components on the chemical composition of Cu₂ZnSnS₄ films is determined. The phase composition is confirmed by the Raman spectroscopy data. The surface morphology of synthesized films is studied by means of scanning-electron and atomic-force microscopes. The photoelectrochemical characteristics of Cu₂ZnSnS₄ films are determined. Samples of these coatings on the Mo electrode are found to be highly photosensitive.     

LaNi<Subscript>0.5</Subscript>Ti<Subscript>0.5</Subscript>O<Subscript>3</Subscript>/CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>-based sensor for sensitive determination of paracetamol

A novel electrochemical sensor based on LaNi_0.5Ti_0.5O₃/CoFe₂O₄ nanoparticle-modified electrode (LNT–CFO/GCE) for sensitive determination of paracetamol (PAR) was presented. Experimental conditions such as the concentration of LNT–CFO, pH value, and applied potential were investigated. Under the optimum conditions, the electrochemical performances of LNT–CFO/GCE have been researched on the oxidation of PAR. The electrochemical behaviors of PAR on LNT–CFO/GCE were investigated by cyclic voltammetry. The results showed that LNT–CFO/GCE exhibited excellent promotion to the oxidation of PAR. The over-potential of PAR decreased significantly on the modified electrode compared with that on bare GCE. Furthermore, the sensor exhibits good reproducibility, stability, and selectivity in PAR determination. Linear response was obtained in the range of 0.5 to 901 μM with a detection limit of 0.19 μM for PAR.     

Electrochemical performance of novel Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> glass-ceramic nanocomposites as electrodes for energy storage devices

The novel Li₃V₂(PO₄)₃ glass-ceramic nanocomposites were synthesized and investigated as electrodes for energy storage devices. They were fabricated by heat treatment (HT) of 37.5Li₂O–25V₂O₅–37.5P₂O₅?mol% glass at 450 °C for different times in the air. XRD, SEM, and electrochemical methods were used to study the effect of HT time on the nanostructure and electrochemical performance for Li₃V₂(PO₄)₃ glass-ceramic nanocomposites electrodes. XRD patterns showed forming Li₃V₂(PO₄)₃ NASICON type with monoclinic structure. The crystalline sizes were found to be in the range of 32–56 nm. SEM morphologies exhibited non-uniform grains and changed with variation of HT time. The electrochemical performance of Li₃V₂(PO₄)₃ glass-ceramic nanocomposites was investigated by using galvanostatic charge/discharge methods, cyclic voltammetry, and electrochemical impedance spectroscopy in 1 M H₂SO₄ aqueous electrolyte. The glass-ceramic nanocomposites annealed for 4 h, which had a lower crystalline size, exhibited the best electrochemical performance with a specific capacity of 116.4 F g^?1 at 0.5 A g^?1. Small crystalline size supported the lithium ion mobility in the electrode by decreasing the ion diffusion pathway. Therefore, the Li₃V₂(PO₄)₃ glass-ceramic nanocomposites can be promising candidates for large-scale industrial applications in high-performance energy storage devices.     

Layered LiNi<Subscript>0.80</Subscript>Co<Subscript>0.15</Subscript>Al<Subscript>0.05</Subscript>O<Subscript>2</Subscript> as cathode material for hybrid Li<Superscript>+</Superscript>/Na<Superscript>+</Superscript> batteries

LiNi_0.80Co_0.15Al_0.05O₂ (NCA) is explored to be applied in a hybrid Li⁺/Na⁺ battery for the first time. The cell is constructed with NCA as the positive electrode, sodium metal as the negative electrode, and 1 M NaClO₄ solution as the electrolyte. It is found that during electrochemical cycling both Na⁺ and Li⁺ ions are reversibly intercalated into/de-intercalated from NCA crystal lattice. The detailed electrochemical process is systematically investigated by inductively coupled plasma-optical emission spectrometry, ex situ X-ray diffraction, scanning electron microscopy, cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy. The NCA cathode can deliver initially a high capacity up to 174 mAh g^?1 and 95% coulombic efficiency under 0.1 C (1 C?=?120 mA g^?1) current rate between 1.5–4.1 V. It also shows excellent rate capability that reaches 92 mAh g^?1 at 10 C. Furthermore, this hybrid battery displays superior long-term cycle life with a capacity retention of 81% after 300 cycles in the voltage range from 2.0 to 4.0 V, offering a promising application in energy storage.     

A Novel V<Subscript>2</Subscript>AlC Electrode Material for Supercapacitors

A novel V₂AlC electrode material for supercapacitors was investigated in this study. The structure and surface morphology were examined using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The formation of irregularly shaped V₂AlC with different particle size distribution was confirmed by XRD and FESEM. The electrochemical measurements were performed by cyclic voltammetry (CV), galvanostatic charge discharge and electrochemical impedance spectroscopy (EIS). V₂AlC electrode exhibited 27.6 F g^–1 of specific capacitance at the current density of 0.5 A g^–1. The specific capacitance of V₂AlC electrode remained 93.8% of the first cycle after 2000 cycles. V₂AlC has great potential for application in supercapacitors.     

Carbon paste electrode modified with Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles and BMI.PF<Subscript>6</Subscript> ionic liquid for determination of estrone by square-wave voltammetry

A carbon paste electrode (CPE) modified with Fe₃O₄ nanoparticles (Fe₃O₄ NP) and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (IL BMI.PF₆) was employed for the electroanalytical determination of estrone (E1) by square-wave voltammetry (SWV). At the modified electrode, cyclic voltammograms of E1 in B–R buffer (pH 12.0) showed an adsorption-controlled irreversible oxidation peak at around +0.365 V. The anodic current increased by a factor of five times and the peak potential shifted 65 mV to less positive values compared with the unmodified CPE. Under optimized conditions, the calibration curve obtained showed two linear ranges: from 4.0 to 9.0 μmol L^?1 and from 9.0 to 100.0 μmol L^?1. The limits of detection (LOD) and quantification (LOQ) attained were 0.47 and 4.0 μmol L^?1, respectively. The proposed modified electrode was applied to the determination of E1 in pork meat samples. Data provided by the proposed modified electrode were compared with data obtained by UV–vis spectroscopy. The outstanding performance of the electrochemical device indicates that Fe₃O₄ NP and the IL BMI.PF₆ are promising materials for the preparation of chemically modified electrodes for the determination of E1.     

Voltammetric determination of B<Subscript>1</Subscript> and B<Subscript>6</Subscript> vitamins using a pencil graphite electrode

Due to the importance of B₁ and B₆ vitamins for human health it is useful to develop new cheap and rapid methods for their determination. Voltammetric behavior of these vitamins on a pencil graphite electrode was investigated using cyclic voltammetry in different media. Direct quantitative determination of the two vitamins, one in the presence of the other, was done by differential pulse voltammetry. Vitamin B₁ was electroactive only in a NaOH solution generating two irreversible oxidation peaks; the first peak obtained at 250 mV is well-defined and was used in quantitative determinations. In case of vitamin B₆, a well-defined oxidation peak was observed in all investigated supporting electrolytes except for HCl. The linear concentration ranges were 10^?5–10^?3 M for vitamin B₁ in a NaOH solution and 5 × 10^?6–10^?3 M for vitamin B₆ in an acetate buffer solution. The obtained detection limits were 5.34 × 10^?6 M and 2.81 × 10^?6 M for vitamin B₁ and vitamin B₆, respectively. The developed method is simple and rapid and it was successfully applied in the determination of the two vitamins in pharmaceuticals.     

Effects of Mg,Al Co-doping into Mn site on electrochemical performance of LiNi<Subscript>0.5</Subscript>Co<Subscript>0.2</Subscript>Mn<Subscript>0.3</Subscript>O<Subscript>2</Subscript>

In order to study the influence of multiple ions doping into single-site on the structure and electrochemical properties of Ni-rich layered-structure cathode material LiNi_0.5Co_0.2Mn_0.3O₂, the coprecipitation of hydroxides was applied to synthesize Mg, Al co-doped cathode material LiNi_0.5Co_0.2Mn_0.3–x Mg_1/2x Al_1/2x O₂ (x = 0.00, 0.01, 0.02, 0.04) in this paper. Morphology and structure, kinetic parameter, impedance and electrochemical performance of the material were respectively characterized by SEM, XRD, CV, EIS and galvanostatic charge/discharge test. The results of comprehensive analysis showed that the properties of material were improved obviously when the amount of doping was 0.02. At this amount of doping, the corresponding material has smaller cation mixing, higher hexagonal ordering of layered-structure, larger Li⁺ ion diffusion coefficients which are 2.444 × 10^–10 and 4.186 × 10^–10 cm² s^–1 for Li+ intercalation and deintercalation respectively, smaller impedance which is 33.93 Ω, higher specific capacity of first-discharge which is 168.01 mA h g^–1 and higher capacity retention rate which is up to 95.06% after 20 cycles at 0.5 C (100 mA g^–1).     

Glycine-assisted combustion synthesis and electrochemical behavior of LiNi<Subscript>0.5</Subscript>Mn<Subscript>0.5</Subscript>O<Subscript>2</Subscript> nanoparticles under microwave irradiation

Layered LiNi_0.5Mn_0.5O₂ nanoparticles have been successfully prepared by the glycine-assisted combustion method under microwave irradiation. The exothermic reaction can generate a large quantity of heat rapidly leading to the formation and crystallization of LiNi_0.5Mn_0.5O₂. From the X-ray diffraction and scanning electronic microscopy results, the resulting powders have a well-developed layered structure and average particle-size is about 80 nm. The chemical composition analysis and electrochemical characteristics of the obtained LiNi_0.5Mn_0.5O₂ nanoparticles as cathode material for rechargeable lithium-ion battery were also investigated. The improved electrochemical performances of the layered LiNi_0.5Mn_0.5O₂ nanoparticles might be ascribed to the nanostructure of the powders and the unique combustion synthesis under microwave irradiation.     

Magnetic solid-phase extraction of imatinib and doxorubicin as cytostatic drugs by Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/graphene oxide nanocomposite

Magnetic solid-phase extraction based on Fe₃O₄/graphene oxide nanocomposites was investigated for the separation, preconcentration and determination of imatinib and doxorubicin in aqueous solutions. Synthesis of Fe₃O₄/graphene oxide was characterized by transmission electron microscopy, energy-dispersive X-ray analyzer and vibrating sample magnetometer. After optimizing the conditions, optimal experimental conditions including sample pH, the amount of the magnetic nanoparticles, the effect of salt concentration and other chemotherapy medications, eluent type and extraction time were studied and established. The method showed good linearity for the determination of doxorubicin and imatinib in the concentration range of 0.01–100 μg mL^?1 in aqueous solutions with limit of detection 1.8 ng mL^?1 for doxorubicin and 1.9 ng mL^?1 for imatinib. The relative recoveries of doxorubicin and imatinib levels were 96.7 and 88.4%, respectively. The results indicate that the present procedure is a suitable method for extraction of imatinib and doxorubicin from environmental water samples.     

Supercapacitive performance of homogeneous Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> nanotube arrays enhanced by carbon layer and oxygen vacancies

Self-supported and binder-free electrodes based on homogeneous Co₃O₄/TiO₂ nanotube arrays enhanced by carbon layer and oxygen vacancies (Co₃O₄/co-modified TiO₂ nanotube arrays (m-TNAs)) are prepared via a simple and cost-effective method in this paper. The highly ordered TNAs offer direct pathways for electron and ion transport and can be used as 3D substrate for the decoration of electroactive materials without any binders. Then, by a facile one-step calcination process, the electrochemical performance of the as-obtained carbon layer and oxygen vacancy m-TNAs is approximately 83 times higher than that of pristine TNAs. In addition, Co₃O₄ nanoparticles are uniformly deposited onto the m-TNAs by a universal chemical bath deposition (CBD) process to further improve the supercapacitive performance. Due to the synergistic effect of m-TNAs and Co₃O₄ nanoparticles, a maximum specific capacitance of 662.7 F g^?1 can be achieved, which is much higher than that of Co₃O₄ decorated on pristine TNAs (Co₃O₄/TNAs; 166.2 F g^?1). Furthermore, the specific capacitance retains 86.0 % of the initial capacitance after 4000 cycles under a high current density of 10 A g^?1, revealing the excellent long-term electrochemical cycling stability of Co₃O₄/m-TNAs. Thus, this kind of heterostructured Co₃O₄/m-TNAs could be considered as promising candidates for high-performance supercapacitor electrodes.     

Nanofibers of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/C@MWCNTs as the cathode material for lithium-ion batteries

Vanadium pentoxide (V₂O₅) nanofibers (NFs) with a thin carbon layer of 3–5 nm, which wrapped on V₂O₅ nanoparticles, and integrated multiwalled carbon nanotubes (MWCNTs) have been fabricated via simple electrospinning followed by carbonization process and post-sintering treatment. The obtained composite displays a NF structure with V₂O₅ nanoparticles connected to each other, and good electrochemical performance: delivering initial capacity of 320 mAh g^?1 (between 2.0 and 4.0 V vs. Li/Li⁺), good cycling stability (223 mAh g^?1 after 50 cycles), and good rate performance (~?150 mAh g^?1 at 2 A g^?1). This can attribute to the carbon wrapped on the V₂O₅ nanoparticles which can not only enhance the electric conductivity to decrease the impendence of the cathode materials but also maintain the structural stability to protect the nanostructure from the corruption of electrolyte and the strain stress due to the Li-ion intercalation/deintercalation during the charge/discharge process. And, the added MWCNTs play the role of framework of the unique V₂O₅ coated by carbon layer and composited with MWCNT NFs (V₂O₅/C@MWCNT NFs) to ensure the material is more stable.     

Synthesis and electrochemical performance of the Li-rich cathode material Li<Subscript>1.17</Subscript>Ni<Subscript>0.12</Subscript>Co<Subscript>0.13</Subscript>Mn<Subscript>0.58</Subscript>O<Subscript>2</Subscript> for lithium-ion batteries

Lithium-riched cathode material for lithium-ion batteries, Li_1.17Ni_0.12Co_0.13Mn_0.58O₂, was synthesized via crystallization from a solution of metal acetates, followed by a thermal treatment of the material obtained as a powder. The phase, elemental, and granulometric compositions of the material were examined, as well as the morphology of the powder particles obtained. The discharge capacity of the material in relation to the charging voltage was found from the results of electrochemical tests, and endurance tests were performed. The discharge capacity upon 85 charge/discharge cycles at voltages in the range 2.8–4.8 and a current of 0.1C was about 180 mA h g^–1.     

Preparation and characterization of the Ti/IrO<Subscript>2</Subscript>/WO<Subscript>3</Subscript> as supercapacitor electrode materials

WO₃ films have been prepared onto IrO₂-coated Ti substrate by electro-deposition, and as-deposited and annealed films have been characterized by using Raman spectroscopy. It was found that the asdeposited film consists of orthorhombic WO₃ · H₂O phase, which transforms to amorphous WO₃ by annealing at 250°C and to monoclinic phase by annealing at and above 350°C. All electrochemical experiments were carried on Ti/IrO₂/WO₃ annealed at 450°C. The open-circuit potential could change significantly due to the hydration of the coating film. However this process is fairly slow. Reproducible voltammograms could be obtained quickly, further revealing high electrochemical stability of the Ti/IrO₂/WO₃ electrode. And the shapes of CV show the approximate rectangular mirror image, showing the typical characteristic of capacitive behavior. The specific capacitance obtained at a scan rate of 50 mV s⁻¹ is 46 F g⁻¹.     

Cellulose scaffolds modulated synthesis of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals: preparation,characterization and properties

Magnetic Co₃O₄ nanoparticles were prepared by using microporous regenerated cellulose films as sacrificial scaffolds. The cellulose macromolecules and the porous structure of the films made them used as spatially confined reacting sites where Co(OH)₂ nanoparticles could be synthesized in situ. When the cellulose matrix was removed by sintering at 500 °C, Co₃O₄ nanoparticles were obtained. XRD and XPS indicated that the prepared nanoparticles were pure Co₃O₄ without any impurity. TEM and SEM images revealed that the particle size of the nanoparticles was smaller than 100 nm. The nanoparticles had weak ferromagnetic properties at 25 °C. Furthermore, the pronounced quantum confinement effects of the synthesized nanoparticles have been observed, the optical bandgap energies determined were about 1.92 ~ 2.12 and 2.74 ~ 2.76 eV for O²⁻ → Co³⁺ and O²⁻ → Co²⁺ charge-transfer processes, respectively. Furthermore, the resulted Co₃O₄ nanoparticles behaved stable electrochemical performance with promising applications in the electrode for lithium ion battery.     

Hydrogen sorption and electrochemical properties of intermetallic compounds La<Subscript>2</Subscript>MgNi<Subscript>9</Subscript> and La<Subscript>1.9</Subscript>Mg<Subscript>1.1</Subscript>Ni<Subscript>9</Subscript>

Intermetallic compounds La_3–xMg_xNi₉ (x = 1.0, 1.1) were synthesized and their hydrogen sorption and electrochemical properties were studied. The maximum hydrogen storage capacities for La₂MgNi₉ and La_1.9Mg_1.1Ni₉ were shown to be 1.6±0.1 and 1.5±0.1 wt.%, respectively, and the unit cell volume increased by 24% and 16%, respectively, upon the hydrogenation of the alloys. The maximum specific capacity of the electrodes with the La_1.9Mg_1.1Ni₉ and La₂MgNi₉ alloys is 390 mA h g^–1 at a discharge current density of 60 mA g^–1, which is 24% higher as compared to the similar data for the LaNi₅ alloy (315 mA h g^–1). The electrodes demonstrate high specific capacity and performance at high current densities, as well as good cyclic stability.     

Synthesis and electrochemical properties of yttrium-doped LiMn<Subscript>0.98</Subscript>Y<Subscript>0.02</Subscript>O<Subscript>2</Subscript> for lithium secondary batteries

Yttrium-doped lithium manganese oxide (LiMn_0.98Y_0.02O₂) was prepared by ion exchange of lithium for sodium in NaMn_0.98Y_0.02O₂ precursors obtained by using rheological phase reaction method. This material had small particle size, which was composed of grain size of about 100 nm. Especially, LiMn_0.98Y_0.02O₂ delivered the initial discharge capacity of about 191 mA h g⁻¹ at room temperature when cycled between 2.0 and 4.4 V vs Li/Li⁺. Moreover, it showed an excellent cycling behavior, its specific capacity remained above 173 mA h g⁻¹ after 20 cycles, and the material did not transform into spinel structure during the electrochemical cycling according to the cyclic voltammograms and X-ray powder diffraction. The electrochemical results revealed that the doping of Y³⁺ improved the performance of LiMnO₂ considerably.     

Electrochemical determination of <Emphasis Type="Italic">p</Emphasis>-cresol using mesoporous TiO<Subscript>2</Subscript>-modified carbon paste electrode

A mesoporous TiO₂ (meso-TiO₂) was synthesized, and used to prepare modified carbon paste electrode (CPE). The electrochemical sensing properties were characterized using K₃[Fe(CN)₆], showing that meso-TiO₂ modified CPE possesses larger surface area and higher electron transfer rate. The electrochemical behavior of p-cresol was investigated. At the meso-TiO₂ modified CPE, the oxidation peak current of p-cresol remarkably increases, and the oxidation peak potential shifts negatively, suggesting that meso- TiO₂ exhibits highly efficient catalytic activity to the oxidation of p-cresol. Based on this, a sensitive, rapid and convenient electrochemical method was developed for the detection of p-cresol. The linear range is from 1.5 × 10⁻⁷ and 2.0 × 10⁻⁵ mol l⁻¹, and the limit of detection is as low as 8.0 × 10⁻⁸ mol l⁻¹. Finally, the new method was successfully used to determine p-cresol in water samples.