Efficient uranous nitrate production using membrane electrolysis

Electrochemical reduction of uranyl nitrate is a green, simple way to make uranous ion. In order to improve the ratio of uranous ion to the total uranium and maintain high current efficiency, an electrolyser with very thin cathodic and anodic compartment, which were separated by a cation exchange membrane, was setup, and its performance was tested. The effects of various parameters on the reduction were also evaluated. The results show that the apparatus is quite positive. It runs well with 120 mA/cm² current density (72 cm² cathode, constant current batch operation). U(IV) yield can achieve 93.1 % (500 mL feed, total uranium 199 g/L) after 180 min electrolysis. It was also shown that when U(IV) yield was below 80 %, very high current efficiency was maintained, and there was almost a linear relationship between uranous ion yield and electrolysis time; under the range of experimental conditions, the concentration of uranyl nitrate, hydrazine, and nitric acid had little effect on the reduction.     

Reduction of uranyl nitrate ions in a continuous flow electrochemical reactor

In a contemporary salt-free flowsheet of nuclear fuel reprocessing, uranous ions are used as a reducing agent to accomplish the separation of uranium and plutonium from each other which is normally produced electrochemically. In the present study, continuous mode electrochemical reduction of uranyl ions in nitric acid medium and in the presence of hydrazine nitrate was carried out in a divided cell at three different feed flow rates and cathodic current densities for the purpose of optimizing the process conditions for better conversion efficiency. A correlation function is described as a mathematical model in which, mass transfer parameter is expressed as a function of current density and flow rate. From the multivariable nonlinear regression of the experimental data, rate parameter was determined. The electro reduction of uranyl ions was not influenced by the initial acidity. The maximum conversion rate of 87 % was obtained for the electro-reduction of 100 g/l U(VI) in 3 M nitric acid with feed flow rate as 0.3 l/h and current density as 15 mA/cm². The results for the reduction of 100 g/l uranyl ions indicate that an optimum flow rate of about 0.5 l/h and 15 mA/cm² as cathodic current density may suffice for the conversion with efficiency better than 60 %. The calculated steady state concentrations for U(IV) were found to be in good agreement with the experimental results.     

Electrochemical degradation of tramadol hydrochloride: Novel use of potentiometric carbon paste electrodes as a tracer

The electrochemical removal of tramadol hydrochloride from aqueous solutions has been investigated under several operating conditions using a Pb/PbO₂ electrode. The optimum conditions of the treatment process are: current density of 1000 mA/cm⁻², pH ≈6, temperature of 10 °C and initial tramadol hydrochloride concentration of 100 mg/L. The time of electrolysis is 25 min for degradation rate of tramadol hydrochloride and chemical oxygen demeaned (COD) removal is 22 h. The results were obtained by UV–Vis spectrophotometer and the presently designed electrode was coincident.     

Degradation of azithromycin using Ti/RuO<Subscript>2</Subscript> anode as catalyst followed by DPV,HPLC–UV and MS analysis

The electrodegradation of azithromycin was studied by its indirect oxidation using dimensionally stable Ti/RuO₂ anode as catalyst in the electrolyte containing methanol, 0.05 M NaHCO₃, sodium chloride and deionized water. The optimal conditions for galvanostatic electrodegradation for the azithromycin concentration of 0.472 mg cm^?3 were found to be NaCl concentration of 7 mg cm^?3 and the applied current of 300 mA. The differential pulse voltammetry using glassy carbon electrode was performed for the first time in the above-mentioned content of electrolyte for the nine concentration of azithromycin (0.075–0.675 mg cm^?3) giving the limits of azithromycin detection and of quantification as: LOD 0.044 mg cm^?3 and LOQ 0.145 mg cm^?3. The calibration curve was constructed enabling the electrolyte analysis during its electrodegradation process. The electrolyte was analyzed by high-performance liquid chromatography and electrospray ionization time-of-flight mass spectrometry. The electrooxidation products were identified and after 180 min there was no azithromycin in the electrolyte while TOC analysis showed that 79% of azithromycin was mineralized. The proposed degradation scheme is presented.     

Vertical crosslinking MoS2/three-dimensional graphene composite towards high performance supercapacitor

The vertical crosslinking MoS₂/three-dimensional graphene composite has been prepared by hydrothermal method, which delivered a superior and stable electrochemical capacitive performance.     

Electrodeposition of zinc oxide nanoparticles on multiwalled carbon nanotube-modified electrode for determination of caffeine in wastewater effluent

We report on the development of an electrochemical sensor based on electrodepositing zinc oxide on multiwalled carbon nanotube-modified glassy carbon electrode for the detection of caffeine in pharmaceutical wastewater effluents. The measurements were carried out using cyclic voltammetry, electrochemical impedance spectroscopy, chronoamperometry and differential pulse voltammetry (DPV). DPV measurements showed a linear relationship between oxidation peak current and concentration of caffeine in 0.1 M HClO₄ (pH 1.0) over the concentration range 0.00388–4.85 mg/L and a detection limit of 0.00194 mg/L. The diffusion coefficient and Langmuir adsorption constant for caffeine were calculated to be 3.25 × 10^?6 cm² s^?1 and 1.10 × 10³ M^?1, respectively. The sensor showed satisfactory results when applied to the detection of caffeine in wastewater effluents.     

Synthesis,characterization, crystal structure,electrochemical properties and electrocatalytic activity of an unexpected nickel(II) Schiff base complex derived from bis(acetylacetonato)nickel(II), acetone and ethylenediamine

The synthesis, crystal structure and electrochemical properties of a Ni(II) Schiff base complex, [Ni(L)]PF₆ (where L is 2,4,9,11,11-pentamethyl-2,3,4 triaza-1-one-4-amine) are reported herein. The complex has been characterized by its electrochemical behavior, X-ray crystallographic structural analysis, physio-chemical methods and spectroscopic techniques. Electrospray mass spectroscopic analysis gives a dominant ion peak with m/z = 296 which corresponds to the {[Ni(L)]PF₆–HPF₆}⁺ fragment. Cyclic voltammograms for [Ni(L)]PF₆, obtained in DMF (0.1 M Bu₄NPF₆) at a glassy carbon electrode with a scan rate of 100 mV s^?1, exhibit reversible ([Ni^II(L)]⁺/[Ni^I(L)]) reduction and chemically irreversible ([Ni^II(L)]⁺/[Ni^III(L)]²⁺→ electroactive product) oxidation processes at ?2.05 and 0.62 V, respectively. The diffusion coefficient, calculated using the Randles–Sevcik relationship, is 9.7 × 10^?6 cm² s^?1. Electrochemical studies reveal that the Ni^I reduced form of the complex is capable of catalyzing CO₂ reduction at a potential that is thermodynamically more favorable than for the reduced [Ni(N,N′-ethylenebis(acetylacetoneiminato)]complex. Spectroelectrochemical analyses following bulk electrolysis of [Ni(L)]PF₆ under CO₂ revealed the formation of oxalate and bicarbonate.     

Automated chromatographic separation coupled on-line to ICP-MS measurements for the quantification of actinides and radiostrontium in soil samples

The uranium (III) ions behaviour in fused 3LiCl–2KCl eutectic versus the Cl^?/Cl₂ reference electrode in the temperature range of 723–823 K on the liquid cadmium electrode by transient electrochemical techniques on the tungsten or molybdenum electrodes was studied. The mechanism of electrochemical reduction on cadmium cathode and the influence of temperature, cathode current density and the duration of electrolysis were studied. The activity coefficients and the base thermodynamic properties of uranium in fused U–Cd/3LiCl–2KCl system were calculated.     

Effect of acid treatment of Corich core–Ptrich shell/C electrocatalyst on oxygen reduction reaction

Co_{rich core}–Pt_{rich shell}/C prepared by thermal decomposition and chemical reduction methods were treated by 20% H₂SO₄ aqueous solution and used as the electrocatalysts for the oxygen reduction reaction (ORR). The particle size range of Co_{rich core}–Pt_{rich shell} (molar ratio of 0.92:1) on carbon powder support decreased from 3–8 to 1–6 nm when the time for the electrocatalysts immersed and treated with 20% H₂SO₄ aqueous solution increased from 0 to 4 h. Using Co_{rich core}–Pt_{rich shell} (molar ratio of 0.92:1)/C treated with 20% H₂SO₄ from 0 to 4 h as the working electrode, the open circuit potential of ORR in 0.5 M HClO₄ aqueous solution increased from 0.9995 to 1.0155 V, and the current density, mass activity, and specific activity at the overpotential of 0.1 V increased from 0.619 mA cm^?2, 6.184 A g^?1, and 18.614 μA cm^?2 to 0.912 mA cm^?2, 15.544 A g^?1, and 23.413 μA cm^?2, respectively.     

Kinetics and optimisation of process parameters for electrochemical generation of uranous ions in nitric acid–hydrazine media

For the quantitative generation of uranous from uranyl ions in the presence of hydrazine in nitric acid medium, electrochemical reduction was carried out in divided and undivided cells. The influence of process conditions, viz. current density, concentration of nitric acid and hydrazine was studied for 50, 100 and 150 g/l of U(VI) solutions. The performance of the cathodes (titanium and platinum) was evaluated by calculating the conversion efficiencies in the reduction process using these electrodes for the reduction of 100 g/l U(VI) at 6 mA/cm² as the cathodic current density. Batch mode experiments using Ti cathode revealed the reduction reaction of U(VI) to follow zero order kinetics and the simultaneous reduction of nitric acid to follow first order kinetics. From the temperature dependence, the activation energy for the reduction of U(VI) was determined to be 4.05 kJ/mol. The chemical stability of U(IV) in nitric acid–hydrazine medium, under ambient conditions of temperature and pressure was established from the amount of U(VI) produced from U(IV) by aerial oxidation over a period of 16 weeks.     

Determination of neptunium in a reprocessing plant by an on-line solid-phase extraction/electrochemical detection system

In this study, a flow-based electrochemical detection system coupled to a solid-phase extraction column was developed for the determination of neptunium in the presence of Pu(IV). Np(V) in the sample solution was completely oxidized to Np(VI) via electrolysis using a column electrode composed of carbon fibers. The column electrode effluent was then loaded onto a TEVA^® column, and subsequently onto a UTEVA^® column using 3 mol L^?1 HNO₃. Pu(IV) was retained on the TEVA column and separated from Np(VI), while Np(VI) was retained on the UTEVA column. Np(VI) was eluted from the UTEVA column with 0.01 mol L^?1 HNO₃ and then introduced directly into a flow-through electrolysis cell. An electrochemical amperometric method with a working potential of +0.1 V (vs. Ag/AgCl) was used to detect Np(VI). The current produced due to the reduction of Np(VI) was continuously monitored and recorded, and the Np concentration was calculated from the peak area. The relative standard deviation of 10 analyses was 2.4 % for an Np solution (0.50 mg L^?1) containing 1.0 μg Np. The detection limit, which was determined to be three times the standard deviation, was 35 μg L^?1 (70 ng Np).     

Effect of surfactant on the morphology and capacitive performance of porous NiCo2O4

A promising nickel cobaltite oxide (NiCo₂O₄) composite electrode material was successfully synthesized by a sol-gel method and followed by a simple sintering process. The microstructure and surface morphology of NiCo₂O₄ modified by hexadecyltrimethylammonium bromide (CTAB) and polyvinyl alcohol were physically characterized by powder X-ray diffraction and scanning electron microscopy. Meanwhile, electrochemical performance was widely investigated in 2 M KOH aqueous electrolyte using cyclic voltammetry, galvanostatic charge-discharge test, and electrochemical impedance spectroscopy. The results show that evident porous microstructure was successfully fabricated by CTAB. The NiCo₂O₄ controlled by CTAB exhibited highly specific capacitance of 1,440 F?g^?1 at a current density of 5 mA?cm^?2. Remarkably, it still displays desirable cycle retention of 94.1 % over 1,000 cycle numbers at a current density of 20 mA?cm^?2. The excellent electrochemical performance suggests its potential application in electrode material for electrochemical capacitors.     

Electrochemical behavior and electrowinning of palladium in nitric acid media

In this study, the electrochemical behavior of Pd(II) in nitric acid media was investigated using various electrochemical techniques. By analyzing the cyclic voltammogram of Pd(II) recorded at Pt electrode, a series of electrochemical reactions associated with palladium were recognized, indicating that Pd(II) undergoes a single step two-electrons irreversible process. Electroreduction reaction of Pd(II) and auto-catalytic reactions of nitrous acid are supposed to play a leading role in low and high concentrations of nitric acid, respectively. Stirring could facilitate the reduction of Pd(II) in relatively low nitric acid concentration (? 3 mol/L). The value of charge transfer coefficient was determined to be 0.18 for the measurements at 298 K. The diffusion coefficient of Pd(II) increased from 1.89 × 10^?8 cm²/s at 288 K to 4.23 × 10^?8 cm²/s at 318 K, and the activation energy was calculated to be 21.5 kJ/mol. In electrowinning experiments, SEM images of palladium obtained by electrolysis reveal the dendrite growth in all cases, which is uniform all over the entire surface of Pt electrode. The recovery ratios of Pd at different nitric acid concentrations are high, and the faradic efficiency of electrolysis decreases with increasing the nitric acid concentration. When stirring was introduced during electrolysis, the electrodeposition rate of Pd increased substantially.     

Removal of pesticide chlorobenzene by anodic degradation: Variable effects and mechanism

The oxidation of chlorobenzene (CB) was studied by electrochemical electrolysis using boron-doped diamond (BDD), PbO₂ or platine (Pt) as anode and graphite bar as cathode. The effect of applied current density, supporting electrolyte and initial pH value were also studied. The results demonstrated that BDD anode had the best effectiveness and accomplishment of electrochemical degradation of CB compared to PbO₂ and Pt anodes. For a current density of 20 mA/cm² and at pH = 3, the elimination of COD and TOC were about 97% and 98%, respectively, after 360 min of electrolysis with the BDD anode. Pseudo-first order kinetics appears to be the most appropriate to describe the degradation of chlorobenzene. The electrochemical mechanism of chlorobenzene on BDD was proposed based on the identified intermediates.     

Electrocatalytic Functionalized Specialty Paper as Low-Cost Porous Transport Layer Material in CO2-Electrolysis

The development of low-cost and efficient electrolyzer components is crucial for practical electrochemical carbon dioxide reduction (ECR). In this study, facile non-woven cellulose-based porous transport layers (PTLs) were developed for high current density CO₂-to-CO conversion. By depositing a cobalt phthalocyanine (CoPc) catalyst-layer over the PTLs, we fabricated ECR-functioning gas-diffusion-electrodes (GDEs) for both flow-cell and zero-gap electrolyzers. Under optimal conditions, the Faradaic efficiency of CO (FE_CO) reached 92 % at a high current density of 200 mA cm⁻². Furthering the architecture of the GDEs, CoPc was incorporated into the initial PTL slurry, forming ECR-active PTLs without the need for an additional catalyst-layer. The new GDE-architecture favored the CoPc-distribution by enhancing the contact and interactions with the carbon substrate and demonstrated a stable electrolysis process for over 50 h in a zero-gap cell at 200 mA cm⁻² with a FE_CO of 80 %.     

Development of 166Ho bleomycin as a possible therapeutic complex

Due to interesting therapeutic properties of ¹⁶⁶Ho and the antineoblastic antibiotic, bleomycin (BLM), ¹⁶⁶Ho-bleomycin (¹⁶⁶Ho-BLM) was developed as a possible therapeutic compound. ¹⁶⁶Ho chloride was obtained by thermal neutron irradiation (1 × 10¹³ n cm^?2 s^?1) of natural Ho(NO₃)₃ samples (specific activity = 3–5 GBq mg^?1), dissolved in acidic media. At optimized conditions (room temperature, 12 h, 0.15–0.3 mg bleomycin for 74 MBq ¹⁶⁶HoCl₃) a radiochemical purity of 94–97% was obtained as shown by ITLC and HPLC (specific activity, 700–740 GBq mmol^?1). Biodistribution studies of ¹⁶⁶Ho chloride and ¹⁶⁶Ho-BLM were performed in wild-type rats. The accumulation of the radiolabeled compound in lungs, liver and spleen demonstrates a similar pattern to the other radiolabeled bleomycins.     

General synthesis of Pt and Ni co-doped porous carbon nanofibers to boost HER performance in both acidic and alkaline solutions

It is essential to develop efficient electrocatalysts to generate hydrogen from water electrolysis for hydrogen economy. In this work, platinum(Pt) and nickel(Ni) co-doped porous carbon nanofibers(Pt/NiPCNFs) with low Pt content were prepared via an electrospinning, carbonization and galvanic replacement reaction. Because of the high electrical conductivity, abundant electrochemical active sites and synergistic effect between Pt and Ni nanoparticles, the optimized Pt/Ni-PCNFs catalyst shows an e...     

Thermoelectric properties of Bi2Te3 films by constant and pulsed electrodeposition

Bi₂Te₃ films have been grown by constant and pulsed electrochemical deposition. The pulsed deposition was carried out by alternating between a constant potential (potentiostatic mode) and an open circuit potential (galvanostatic mode, where current density is fixed at 0 mA/cm²). The Harris texture analysis was performed to determine the degree of preferred orientation. The results showed that the films were strongly oriented along (1?1?0) direction. The morphology and compositions of the films were then analyzed. Finally, their Seebeck coefficient and electrical resistivity were measured and used to determine the thermoelectric Power Factor of the films for a temperature range between 57 and 107 °C.     

Preparation and electrochemical characterization of Ruddlesden–Popper oxide La4Ni3O10 cathode for IT-SOFCs by sol–gel method

La₄Ni₃O₁₀ oxide was synthesized as a cathode material for intermediate-temperature solid oxide fuel cells by a facile sol–gel method using a nonionic surfactant (EO)106(PO)70(EO)106 tri-block copolymer (F127) as the chelating agent. The crystal structure, electrical conductivity, and electrochemical properties of La₄Ni₃O₁₀ were investigated by X-ray diffraction, DC four-probe method, electrochemical impedance spectra, and I–V measurements. The La₄Ni₃O₁₀ cathode showed a significantly low polarization resistance (0.26 Ω cm²) and cathodic overpotential value (0.037 V at the current density of 0.1 A cm^?2) at 750 °C. The results measured suggest that the diffusion process was the rate-limiting step for the oxygen reduction reaction. The La₄Ni₃O₁₀ cathode revealed a high exchange current density value of 62.4 mA cm^?2 at 750 °C. Furthermore, an anode-supported single cell with La₄Ni₃O₁₀ cathode was fabricated and tested from 650 to 800 °C with humidified hydrogen (～3 vol% H₂O) as the fuel and the static air as the oxidant. The maximum power density of 900 mW cm^?2 was achieved at 750 °C.     

Hybrid materials utilizing polyelectrolyte-derivatized carbon nanotubes and vanadium-mixed addenda heteropolytungstate for efficient electrochemical charging and electrocatalysis

Preparation and electrochemical behavior of new hybrid materials composed of multi-walled carbon nanotubes (CNTs) that were derivatized with poly(diallyldimethylammonium) chloride and modified with vanadium-mixed addenda Dawson-type heteropolytungstate, [P₂W₁₇VO₆₂]^8?, is described here. These nanostructured composite systems exhibited fast dynamics of charge propagation. They were characterized by the transport (effectively diffusional) kinetic parameter of approximately 8?×?10^?8 cm^?2 s^?1/2 and the specific capacitance parameter of 82 F g^?1 (at the charging/discharging current of 200 mA g^?1). The latter parameter for bare CNTs was found to be only 50 F g^?1 under analogous conditions. These observations were based on the results of galvanostatic charging–discharging, cyclic voltammetric, and AC impedance spectroscopic measurements. The improved capacitance properties were attributed to the systems’ pseudocapacitive features originating from the fast redox transitions of the [P₂W₁₇VO₆₂]^8? polyanions. In addition to the fast redox conduction, the proposed organic–inorganic hybrid materials exhibited interesting electrocatalytic activity toward reduction of bromate in the broad concentration range (sensitivity, 0.24 mA cm^?2 mmol^?1 dm³).