Studies on promising cell performance with H2SO4 as the catholyte for electrogeneration of Ag2+ from Ag+ in HNO3 anolyte in mediated electrochemical oxidation process

Electrochemical performance of a divided cell with electrogeneration of Ag²⁺ from Ag⁺ in 6 M HNO₃ anolyte has been studied with 6 M HNO₃ or 3 M H₂SO₄ as the catholyte. This work arose because in mediated electrochemical oxidation (MEO) processes with Ag(II)/Ag(I) redox mediator, HNO₃ is generally used as catholyte, which, however, produces NO _x gases in the cathode compartment. The performance of the cell with 6 M HNO₃ or 3 M H₂SO₄ as the catholyte has been compared in terms of (i) the acid concentration in the cathode compartment, (ii) the Ag⁺ to Ag²⁺ conversion efficiency in the anolyte, (iii) the migration of Ag⁺ from anolyte to catholyte across the membrane separator, and (iv) the cell voltage. Studies with various concentrations of H₂SO₄ catholyte have been carried-out, and the cathode surfaces have been analyzed by SEM and EDXA; similarly, the precipitated material collected in the cathode compartment at higher H₂SO₄ concentrations has been analyzed by XRD to understand the underlying processes. The various beneficial effects in using H₂SO₄ as catholyte have been presented. A simple cathode surface renewal method relatively free from Ag deposit has been suggested.     

PHYSICAL ANALOGS AND PERFORMANCE OF A BOX MODEL FOR COMPOSITION AND GROWTH OF H2SO4/H2O AND HNO3/H2SO4/H2O AEROSOL IN THE STRATOSPHERE

A physical box model simulating the aerosol particle evolution along air mass trajectories is developed to provide a tool for interpreting the local observations of stratospheric aerosols (i.e., polar stratospheric clouds). The model calculates the composition and the size distributions of H₂SO₄/H₂O and HNO₃/H₂SO₄/H₂O liquid droplets. The parameterization of the physical processes affecting the dynamics of HNO₃ and H₂SO₄ solid hydrates and ice particle size distributions is also included, but not used. This work is restricted to some speculations about the liquid to solid transition, according to existing theories. The evolution of liquid particles is simulated taking into account nucleation, diffusive condensation/evaporation and coagulation. This paper reports the physical and numerical details of the model, which are discussed within the framework of the current understanding of the stratospheric aerosol physics. Performance and limitations of the model are discussed on the basis of the evolution of particle size, and composition along synthetic air mass thermal histories. Size distributions and size-dependent acid weight fractions of the liquid stratospheric aerosols consisting of HNO₃/H₂SO₄/H₂O are calculated in the cases of air mass thermal histories with different cooling rates and with rapid temperature fluctuations.     

Roughening of atomically flat diamond (111) surfaces by a hot HNO3/H2SO4 solution

A systematic investigation of the roughening of atomically flat diamond (111) surfaces by immersion in a hot mixture of HNO₃/H₂SO₄ acids was performed using atomic force microscopy. Before the immersion the diamond surfaces were atomically flat, with single bilayer steps and terraces; surface roughness increased after the immersion in the hot acid mixture. This result suggests that surface oxidation by the hot acid mixture etches the surface causing surface roughening.     

Flattening of oxidized diamond (111) surfaces with H2SO4/H2O2 solutions

Changes in the topography of a diamond (111) surface with atomically flat and wide terraces, caused by immersion in HNO₃/H₂SO₄ and H₂SO₄/H₂O₂ solutions were investigated by atomic force microscopy. We observed surface roughening from the HNO₃/H₂SO₄ treatment, and flattening of the HNO₃/H₂SO₄ treated surface from the H₂SO₄/H₂O₂ treatment. This suggests that the H₂SO₄/H₂O₂ treatment is an effective wet-process for preparing atomically flat oxidized diamond (111) surfaces.     

Reduction of lean NOx by ethanol over Ag/Al2O3 catalysts in the presence of H2O and SO2

The reduction of lean NOx using ethanol in simulated diesel engine exhaust was carried out over Ag/Al₂O₃ catalysts in the presence of H₂O and SO₂. The Ag/Al₂O₃ catalysts are highly active for the reduction of lean NOx by ethanol but the reaction is accompanied by side reactions to form CH₃CHO, CO along with small amounts of hydrocarbons (C₃H₆, C₂H₄, C₂H₂ and CH₄) and nitrogen compounds such as NH₃ and N₂O. The presence of H₂O enhances the NOx reduction while SO₂ suppresses the reduction. The presence of SO₂ along with H₂O suppresses the formation of acetaldehyde and NH₃. By infrared spectroscopy, it was revealed that the reactivity of NCO species formed in the course of the reaction was greatly enhanced in the presence of H₂O. The NCO species readily reacts with NO in the presence of O₂ and H₂O at room temperature, being converted to N₂ and CO₂ (CO). Addition of SO₂ suppresses the formation of NCO species and lowers the reactivity of the NCO species. However, the reduction of NOx is still kept at high conversion levels in the presence of H₂O and SO₂ over the present catalysts. About 80% of NOx in the simulated diesel engine exhaust was removed at 743 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Absorption of NO by Aqueous Solutions of KMnO4/H2SO4

The absorption of NO in aqueous solutions of KMnO₄ and H₂SO₄ was carried out in a stirred tank reactor under atmosphere pressure. The results indicated that the absorption process was under a fast pseudo-m th reaction regime. The reaction between NO and aqueous solutions of KMnO₄/H₂SO₄ was found to be first-order with respect both to NO and to KMnO₄. The addition of H₂SO₄ to KMnO₄ solutions increased the absorption rate of NO and increasing reaction temperature was also favorable to the absorption of NO.     

Partitioning of U(VI) and Eu(III) between Acidic Aqueous Al(NO3)3 and Tributyl Phosphate in n‐Dodecane

Abstract

The preferred approach to removing Al from Hanford tank sludges, based on aqueous alkaline leaching, often does not achieve complete success. Previous laboratory investigations on the treatment of Hanford tank sludge simulant samples indicate that an acidic scrub can enhance the dissolution of Al from various sludge matrices. If acidic leaching was deployed to enhance removal of tank waste residues, the resulting acidic Al(NO₃)₃ leachate solution could contain measurable amounts of solubilized transuranic elements and so would demand treatment prior to disposal. In this study, a liquid‐liquid extraction system for the decontamination of the HNO₃/Al(NO₃)₃ aqueous leachate by contact with 60% v/v tributyl phosphate (TBP)/n‐dodecane organic solution has been examined. The partitioning of U and Eu between the TBP phase and solutions of varying [HNO₃] and [Al(NO₃)₃] containing small amounts of Cr or ascorbic acid have been investigated._. The results indicate that >99% of both species could be removed from the aqueous phase using such a process.     

Electrochemical performance of the carbon coated Li3V2(PO4)3 cathode material synthesized by a sol-gel method

A carbon coated Li₃V₂(PO₄)₃ cathode material for lithium ion batteries was synthesized by a sol-gel method using V₂O₅, H₂O₂, NH₄H₂PO₄, LiOH and citric acid as starting materials, and its physicochemical properties were investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), transmission electron microscope (TEM), and electrochemical methods. The sample prepared displays a monoclinic structure with a space group of P2₁/n, and its surface is covered with a rough and porous carbon layer. In the voltage range of 3.0-4.3 V, the Li₃V₂(PO₄)₃ electrode displays a large reversible capacity, good rate capability and excellent cyclic stability at both 25 and 55 °C. The largest reversible capacity of 130 mAh g⁻¹ was obtained at 0.1C and 55 °C, nearly equivalent to the reversible cycling of two lithium ions per Li₃V₂(PO₄)₃ formula unit (133 mAh g⁻¹). It was found that the increase in total carbon content can improve the discharge performance of the Li₃V₂(PO₄)₃ electrode. In the voltage range of 3.0-4.8 V, the extraction and reinsertion of the third lithium ion in the carbon coated Li₃V₂(PO₄)₃ host are almost reversible, exhibiting a reversible capacity of 177 mAh g⁻¹ and good cyclic performance. The reasons for the excellent electrochemical performance of the carbon coated Li₃V₂(PO₄)₃ cathode material were also discussed.     

Influence of different concentrations of Al2(SO4)3 and anionic polyelectrolytes on tannery wastewater flocculation

Tanning of hides and skins to convert them into leather can have a considerable environmental impact. Wastewatertreatment technology can successfully purify leather wastewater. The first part of this research investigated the influence of Al₂(SO₄)₃ concentration on the velocity of tannery wastewater settling. The wastewater sample was taken from two of the most polluted wastewater flows after liming and after chrome tanning. These wastewater flows were mixed together in a ratio of 1:1. The second part was carried out with the samples of wastewater mixed together with different concentrations of A1₂(SO₄)₃. The behaviour of settling was investigated after an addition of different concentrations of anionic polyelectrolytes in these samples. The pH, suspended solids mass, volume of sediment, γ(Na₂S), γ(Cr₂O₃), chemical oxygen demand, along with turbidity in the supernatant were determined in the obtained sludge. The results demonstrate the influence of A1₂(SO₄)₃ and anionic polyelectrolyte concentrations on the parameters studied and the improvement of environmental properties.     

Preparation and luminescent properties of Tb3+ doped Y2O2SO4 microflakes

Abstract

Tb³⁺ doped Y₂O₂SO₄ (Y₂O₂SO₄:Tb³⁺) microflakes were prepared by a combination method of electrospinning and calcination. The two-dimensional microflakes had smooth surface and high radial/axial ratio. Crystal structures of the Y₂O₂SO₄:Tb³⁺ microflakes resulted in layer by layer growth in axial direction. A possible formation mechanism was proposed on the basis of experimental results, which indicated that poly(vinyl pyrrolidone) played the role of the nanostructure directing template and revealed the growth priority in radial direction. The microflakes showed a favourable fluorescent property symbolised by the characteristic green emission (541 nm) resulting from the ⁵D₄→⁷F₅ transition of Tb³⁺ ions under 229 nm ultraviolet excitation. The maximum intensity of Tb³⁺ emission of the Y₂O₂SO₄:Tb³⁺ microflakes was 2·3 times stronger than that of the Y₂O₂SO₄:Tb³⁺ bulk powders with the same doping concentration.     

Solid–Liquid Equilibrium (SLE) for Polyhydric Alcohol + Cs2SO4 + H2O Ternary Systems at Different Temperatures

The solubility, density, and refractive index data for 1,2-propanediol + Cs₂SO₄ + H₂O, ethylene glycol + Cs₂SO₄ + H₂O, and glycerin + Cs₂SO₄ + H₂O ternary systems were determined at 15°C, 25°C, and 35°C. In all cases, the solubility of Cs₂SO₄ in aqueous solutions decreased significantly due to the presence of the polyhydric alcohol. The experimental density, refractive index, and solubility data of saturated solutions for these systems were correlated using polynomial equations. Furthermore, the refractive index and density of unsaturated ternary solutions were also determined and correlated with salt concentrations and proportions of polyhydric alcohol in these systems.     

Interpretation of Third Phase Formation in the Th(IV)–HNO3, TBP–n‐Octane System with Baxter's “Sticky Spheres” Model

Abstract

Small‐angle neutron scattering (SANS) data for the tri‐n‐butylphosphate (TBP)–n‐octane, HNO₃–Th(NO₃)₄ solvent extraction system, obtained under a variety of experimental conditions, have been interpreted using two different models. The particle growth model led to unrealistic results. The Baxter model for hard‐spheres with surface adhesion, on the other hand, was more successful. According to this model, the increase in scattering intensity in the low Q range observed when increasing amounts of Th(NO₃)₄ are extracted into the organic phase, has been interpreted as arising from interactions between small reverse micelles containing three TBP molecules. Upon extraction of Th(NO₃)₄, the micelles interact through attractive forces between their polar cores with a potential energy of up to about 2 k_BT. The intermicellar attraction, under suitable conditions, leads to third phase formation. Upon phase splitting, most of the solutes of the original organic phase separate in a continuous phase containing interspersed layers of n‐octane.     

Comparative study of Li(Li1/3Ti5/3)O4 and Li(Ni1/2−xLi2x/3Tix/3)Ti3/2O4 (x = 1/3) anodes for Li rechargeable batteries

A solid solution of spinel (2/3)Li(Li_1/3Ti_5/3)O₄–(1/3)Li(Ni_1/2Ti_3/2)O₄ was prepared, and its structural/electrochemical properties were compared with Li(Li_1/3Ti_5/3)O₄ to identify the effect of doping to the structural invariance of Li(Li_1/3Ti_5/3)O₄. The solid solution retained the zero strain characteristic of Li(Li_1/3Ti_5/3)O₄ during discharge/charge with an excellent cycle stability, while the rate capability was notably improved. However, a reversible broadening of the XRD peak was observed at the end of discharge, indicating some structural changes. XANES measurements showed that the oxidation state of Ti was +4 and that of Ni was +2 in the solid solution.     

Effect of vanadium on the behaviour of unsulfated and sulfated Ti-pillared clay catalysts in the SCR of NO by NH3

Vanadium supported on unsulfated and sulfated Ti-pillared clays are developed for the selective catalytic reduction (SCR) of nitrogen oxide (NO) by ammonia. The unsulfated Ti-pillared clays (TiM-PILC) were prepared by hydrolysis of titanium methoxide (Ti(OCH₃)₄) with HCl. The same procedure was employed using H₂SO₄ in order to obtain the sulfated Ti-pillared clays (STiM-PILC). All the pillared materials were characterized before and after vanadium addition by chemical analysis, XRD, N₂-physisorption, TGA, NH₃-TPD, H₂-TPR and UV–vis. It was found that the sulfation or the addition of a low amount of vanadium into the TiM-PILC reduces the surface area but improves the acidity of the material. The addition of vanadium to the STiM-PILC decreases the surface area, the number of acid sites and the stability of the sulfate species but enhances the redox properties of the material. The STiM-PILC and the V-TiM-PILC exhibit higher NO removal activity at high temperature than the TiM-PILC. The presence of both sulfate and a low amount of vanadium (2 wt.%) in the TiM-PILC leads to an excellent active and selective catalyst for SCR-NO with NH₃.     

Simultaneous removal of SO2, SO3 and H2SO4 mist from the gas after TiO2 calcining

Absorption of SO₂ and SO₃ in the solutions of waste ferrous sulfate (so-called ‘green salt’) and in the spent acid after TiO₂ hydrolysis, at H₂SO₄ concentrations ranging from 0–5 to 15 g/m³ (STP), was studied. The rate of SO₃ absorption has been found to rise linearly with increasing SO₃ concentration in the gas and to be independent on H₂SO₄ concentration in solution. The SO₂ absorption also rises linearly with increasing SO₂ content in the gas, but diminishes as H₂SO₄ concentration increases—an upper limit of 100 g H₂SO₄/kg H₂O is indicated. The initial concentration of the solution must not be higher than 40 g H₂SO₄/kg H₂O.     

First-principles DFT study of SO2 and SO3 adsorption on 2PANI: a model for polyaniline response

Interaction of SO_x (x?=?2,3) molecules on active sites of dianiline (as a model for polyaniline, denoted here as 2PANI) was studied using density functional theory at the BLYP-D/6-31+G(d) level of theory. Natural population analysis was used to find out the charge distribution as well as the net transferred charge of SO_x upon adsorption on 2PANI and the result has been compared with Mulliken charge analysis to evaluate the sensing ability of 2PANI. The computed density of states point to the remarkable orbital hybridization between SO_x and 2PANI during the adsorption process. As a consequence, the results of UV–VIS confirm the sensing ability of 2PANI toward SO₂ and SO₃. Based on our results, it can be found that at proper configuration the SO₂ and SO₃ molecules can be adsorbed on 2PANI with adsorption energies (E_ads) of ?18.2 and ?62.9?kJ/mol (BSSE), respectively.     

UV/H2O2氧化联合Ca(OH)2吸收同时脱硫脱硝

在小型紫外光-鼓泡床反应器中,对UV/H₂O₂氧化联合Ca(OH)₂吸收同时脱除燃煤烟气中NO与SO₂的主要影响因素[H₂O₂浓度、紫外光辐射强度、Ca(OH)₂浓度、NO浓度、溶液温度、烟气流量以及SO₂浓度]进行了考察。采用烟气分析仪和离子色谱仪分别对尾气中的NO₂和液相阴离子作了检测分析。结果显示:在本文所有实验条件下,SO₂均能实现完全脱除。随着H₂O₂浓度、紫外光辐射强度和Ca(OH)₂浓度的增加,NO的脱除效率均呈现先大幅度增加后轻微变化的趋势。NO脱除效率随烟气流量和NO浓度的增加均有大幅度下降。随着溶液温度和SO₂浓度的增加,NO脱除效率仅有微小的下降。离子色谱分析表明,反应产物主要是SO₄^2-和NO₃^-,同时有少量的NO₂^-产生。尾气中未能检测到有害气体NO₂。     

Determination of the promoting effect of nano SiO2 and H3PO4@nano SiO2 in the thiocyanation of N-containing aromatic compounds under solvent-free conditions

Silica nanoparticles/ammonium thiocyanate (nano SiO₂/NH₄SCN) and H₃PO₄ embedded on nano silica (H₃PO₄@nano SiO₂) in the presence of NH₄SCN were found to be effective systems for the thiocyanation of some arylamines and indoles to afford their corresponding thiocyanated adducts at 70°C under solvent-free conditions. The recovery and reusability of nano SiO₂ as a prompting system have been investigated. A simple procedure for the synthesis of H₃PO₄@nano SiO₂ has also been represented. In addition, a plausible mechanism of thiocyanation has also been suggested.     

Synthesis and electrochemical properties of Co-doped Li3V2(PO4)3 cathode materials for lithium-ion batteries

Co-doped Li₃V_2−xCo_x(PO₄)₃/C (x = 0.00, 0.03, 0.05, 0.10, 0.13 or 0.15) compounds were prepared via a solid-state reaction. The Rietveld refinement results indicated that single-phase Li₃V_2−xCo_x(PO₄)₃/C (0 ≤ x ≤ 0.15) with a monoclinic structure was obtained. The X-ray photoelectron spectroscopy (XPS) analysis revealed that the cobalt is present in the +2 oxidation state in Li₃V_2−xCo_x(PO₄)₃. XPS studies also revealed that V⁴⁺ and V³⁺ ions were present in the Co²⁺-doped system. The initial specific capacity decreased as the Co-doping content increased, increasing monotonically with Co content for x > 0.10. Differential capacity curves of Li₃V_2−xCo_x(PO₄)₃/C compounds showed that the voltage peaks associated with the extraction of three Li⁺ ions shifted to higher voltages with an increase in Co content, and when the Co²⁺-doping content reached 0.15, the peak positions returned to those of the unsubstituted Li₃V₂(PO₄)₃ phase. For the Li₃V_1.85Co_0.15(PO₄)₃/C compound, the initial capacity was 163.3 mAh/g (109.4% of the initial capacity of the undoped Li₃V₂(PO₄)₃) and 73.4% capacity retention was observed after 50 cycles at a 0.1 C charge/discharge rate. The doping of Co²⁺into V sites should be favorable for the structural stability of Li₃V_2−xCo_x(PO₄)₃/C compounds and so moderate the volume changes (expansion/contraction) seen during the reversible Li⁺ extraction/insertion, thus resulting in the improvement of cell cycling ability.     

Comparison of AlPO4- and Co3(PO4)2-coated LiNi0.8Co0.2O2 cathode materials for Li-ion battery

Electrochemical and thermal properties of Co₃(PO₄)₂- and AlPO₄-coated LiNi_0.8Co_0.2O₂ cathode materials were compared. AlPO₄-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 170.8 mAh g⁻¹ and had a capacity retention (89.1% of its initial capacity) between 4.35 and 3.0 V after 60 cycles at 150 mA g⁻¹. Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 177.6 mAh g⁻¹ and excellent capacity retention (91.8% of its initial capacity), which was attributed to a lithium-reactive Co₃(PO₄)₂ coating. The Co₃(PO₄)₂ coating material could react with LiOH and Li₂CO₃ impurities during annealing to form an olivine Li_xCoPO₄ phase on the bulk surface, which minimized any side reactions with electrolytes and the dissolution of Ni⁴⁺ ions compared to the AlPO₄-coated cathode. Differential scanning calorimetry results showed Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathode material had a much improved onset temperature of the oxygen evolution of about 218 °C, and a much lower amount of exothermic-heat release compared to the AlPO₄-coated sample.