高铁酸盐分析方法研究进展

高铁酸盐可以用作超铁电池储能阴极材料,也是新型绿色有机合成氧化剂和水处理药剂.日益广泛的应用需要精准的分析测试方法.综述了高铁酸盐的定性、定量分析方法,包括红外光谱、紫外可见光谱、滴定分析、XRD、穆斯堡尔谱、电化学分析、荧光分析法等,详述了分析方法原理及适用范围.     

Research progress in the electrochemical synthesis of ferrate(VI)

There is renewed interest in the +6 oxidation state of iron, ferrate (VI) (Fe^VIO₄²⁻), because of its potential as a benign oxidant for organic synthesis, as a chemical in developing cleaner (“greener”) technology for remediation processes, and as an alternative for environment-friendly battery cathodes. This interest has led many researchers to focus their attention on the synthesis of ferrate(VI). Of the three synthesis methods, electrochemical, wet chemical and thermal, electrochemical synthesis has received the most attention due to its ease and the high purity of the product. Moreover, electrochemical processes use an electron as a so-called clean chemical, thus avoiding the use of any harmful chemicals to oxidize iron to the +6 oxidation state. This paper reviews the development of electrochemical methods to synthesize ferrate(VI). The approaches chosen by different laboratories to overcome some of the difficulties associated with the electrochemical synthesis of ferrate(VI) are summarized. Special attention is paid to parameters such as temperature, anolyte, and anode material composition. Spectroscopic work to understand the mechanism of ferrate(VI) synthesis is included. Recent advances in two new approaches, the use of an inert electrode and molten hydroxide salts, in the synthesis of ferrate(VI) are also reviewed. Progress made in the commercialization of ferrate(VI) continuous production is briefly discussed as well.     

Chemical and electrochemical considerations on the removal process of hexavalent chromium from aqueous media

Two methods were used to remove Cr(VI) from industrial wastewater. Although both are based in the same general reaction: 3Fe(II)_(aq) + Cr(VI)_(aq) ; 3Fe(III)_(aq) + Cr(III)_(aq) the way in which the required amount of Fe(II) is added to the wastewater is different for each method. In the chemical method, Fe(II)_(aq) is supplied by dissolving FeSO₄ · 7(H₂O)_(s) into the wastewater, while in the electrochemical process Fe(II)_(aq) ions are formed directly in solution by anodic dissolution of an steel electrode. After this reduction process, the resulting Cr(III)_(aq) and Fe(III)_(aq) ions are precipitated as insoluble hydroxide species, in both cases, changing the pH (i.e., adding Ca(OH)_2(s)). Based on the chemical and thermodynamic characteristics of the systems Cr(VI)–Cr(III)–H₂O–e^– and Fe(III)–Fe(II)–H₂O–e^– both processes were optimized. However we show that the electrochemical option, apart from providing a better form of control, generates significantly less sludge as compared with the chemical process. Furthermore, it is also shown that sludge ageing promotes the formation of soluble polynuclear species of Cr(III). Therefore, it is recommended to separate the chromium and iron-bearing phases once they are formed. We propose the optimum hydraulic conditions for the continuous reduction of Cr(VI) present in the aqueous media treated in a plug-flow reactor.     

Influence of Ti and Fe doping on the structural and electrochemical performance of LiCo0.6Ni0.4O2 cathode materials for Li-ion batteries

The combination of lithium cobalt oxide (LCO) and lithium nickel oxide (LNO) property for Li-ion batteries (LIB) brings a very promising cathode material, LiCo_1?xNi_xO₂ with a high specific reversible capacity and good cycling behaviour. Nonetheless, high toxic Co content and an instability of Li⁺/Ni²⁺ interaction in LiCo_1?xNi_xO₂ crystal structure paved the way for some modification for the development of this potential material. In this research, the self-propagating combustion method is used to reduce 40% Co content of LCO by replacing it with 40% Ni content resulting in cathode material with the stoichiometry of LiCo_0.6Ni_0.4O₂ (LCN). To improve the stability of the LiCo_0.6Ni_0.4O₂ structure, 5% of Ti and Fe was substituted at the Co site of the LCN material. The effect of these different cation substitutions (Ti⁴⁺ and Fe³⁺) on the structural and electrochemical performance of layered LiCo_0.6Ni_0.4O₂ cathode materials was investigated. Rietveld refinement revealed that Fe doped material has the longest atomic distance Li–O in the structure that allow better Li⁺ diffusion during intercalation/deintercalation to give an excellent electrochemical performance (138 mAhg^?1). After 50th cycle, it is found that the discharge cycling for Ti and Fe substituted materials were improved by more than 5% compared to pristine material. Both Ti and Fe doped materials were also having less than 13% of capacity fading indicates that the substitution of some Co with Ti and Fe are stable and can retain their electrochemical properties.     

ZrO2包覆对层状氧化物正极材料储钠性能的改善

层状氧化物正极材料具有良好的结构稳定性和较高的充放电比容量,是一类理想的钠离子电池正极材料。本工作研究了层状氧化物正极材料NaNi1/3Fe1/3Mn1/3O2表面修饰对其电化学性能的影响,采用固相球磨法在正极材料表面包覆一层纳米ZrO2,采用形貌、结构、电化学方法等研究了包覆后性能改进机理。研究结果表明,ZrO2在NaNi1/3Fe1/3Mn1/3O2表面形成一层惰性保护层,有效隔开了电解液与正极材料的接触,缓解了电解液的分解速度,抑制了金属离子的溶出速度,从而显著改善了电池的循环性能以及高温性能。在ZrO2包覆修饰后,55℃下正极材料相比于未包覆的正极材料有明显提升,100次循环后容量保持率达到83.6%,高于未包覆的75.2%。此外,包覆后的NaNi1/3Fe1/3Mn1/3O2正极材料在空气环境存储后,稳定性得到明显提高。     

铬污染地下水的PRB修复试验

以铬污染地下水为研究对象,分别用活性炭、零价铁、活性炭+零价铁作为反应介质,设计了渗透反应隔栅(PRB),对PRB治理六价铬污染地下水的可行性和有效性进行了试验研究,试验结果表明,活性炭对Cr(VI)有一定的吸附作用,零价铁对Cr(VI)有较强的还原作用,零价铁与活性炭配合作用时,二者的配比影响Cr(VI)的去除,零价铁所占质量分数越大,去除效果越好。零价铁、活性炭和石英砂质量分数分别为40%,4%和2%时,可以使Cr(VI)的质量浓度从100mg/L降低到0.05mg/L以下,达到《饮用净水水质标准》。采用PRB技术治理Cr(VI)污染地下水是可行的。     

Adsorption Characteristics of Chromium(VI) Ions onto Fe(III)-Coordinated Amino-Functionalized Poly(glycidylmethacrylate)-Grafted TiO2-Densified Cellulose

An investigation was conducted with a newly developed adsorbent, iron(III)- coordinated amino-functionalized poly(glycidylmethacrylate)-grafted TiO₂-densified cellulose (Fe(III)-AM-PGDC) on the removal of chromium(VI) from aqueous solution. Batch experiments were performed under various conditions of time, pH, concentration, dose, ionic strength, and temperature. Adsorption of Cr(VI) on Fe(III)-AM-PGDC was dominated by ion exchange or outer-sphere complexation. The maximum adsorption capacity was found to be 109.76 mg g^?1. Thermodynamic study showed that adsorption of Cr(VI) onto Fe(III)-AM-PGDC is more favored. The complete removal of Cr(VI) from electroplating wastewater was achieved by the adsorbent. The adsorbent did not lose its adsorption capacity even after the fourth regeneration.     

The improvement of boron-doped diamond anode system in electrochemical degradation of p-nitrophenol by zero-valent iron

Boron-doped diamond (BDD) electrodes are promising anode materials in electrochemical treatment of wastewaters containing bio-refractory organic compounds due to their strong oxidation capability and remarkable corrosion stability. In order to further improve the performance of BDD anode system, electrochemical degradation of p-nitrophenol were initially investigated at the BDD anode in the presence of zero-valent iron (ZVI). The results showed that under acidic condition, the performance of BDD anode system containing zero-valent iron (BDD-ZVI system) could be improved with the joint actions of electrochemical oxidation at the BDD anode (39.1%), Fenton's reaction (28.5%), oxidation–reduction at zero-valent iron (17.8%) and coagulation of iron hydroxides (14.6%). Moreover, it was found that under alkaline condition the performance of BDD-ZVI system was significantly enhanced, mainly due to the accelerated release of Fe(II) ions from ZVI and the enhanced oxidation of Fe(II) ions. The dissolved oxygen concentration was significantly reduced by reduction at the cathode, and consequently zero-valent iron corroded to Fe(II) ions in anaerobic highly alkaline environments. Furthermore, the oxidation of released Fe(II) ions to Fe(III) ions and high-valent iron species (e.g., FeO²⁺, FeO₄²⁻) was enhanced by direct electrochemical oxidation at BDD anode.     

Role of Iron and Chromium Complexes in Environmental Self‐cleaning Processes

Abstract

The present research includes solar‐light‐driven photocatalytic cycles based on the photoreductions of Fe(III), Cr(VI), and Cr(III) compounds with EDTA, oxalate and other ligands. Molecular oxygen is needed to close the photocatalytic cycles in which the metal species plays a role of photocatalyst; it affects the reaction mechanism and rate. The photoinduced electron transfer was also investigated in the presence of some external electron donors, such as EDTA, aliphatic alcohols, phenol, and its halogen derivatives, oxalate, nitrate(III), sulfate(IV). The results apply to the removal of such hazardous environmental pollutants as chromate(VI) or phenol derivatives and such recalcitrant pollutants as EDTA.     

A review: Conventional and supercritical hydro/solvothermal synthesis of ultrafine particles as cathode in lithium battery

Olivine LiMPO₄ (M = Mn, Fe, Co and Ni, LMP) materials are considered to be the most promising cathode candidates for high energy storage devices. In this work, the feasibility of the thermodynamics of powder formation is discussed for explaining such a reaction mechanism, as well as the recent progress of conventional and supercritical hydro/solvothermal syntheses, are summarized. The association among synthesis conditions, structure, morphology and electrochemical properties, especially for rate capability and tap density under hydro/solvothermal condition, are highlighted. Notably, this work primarily concentrates on the processes in which additives participate in the hydrothermal synthesis of LMP and considers less the subsequent treatments of synthesized LMP with extra additives. In other words, the modifications during the synthesis process with additives are the primary topic. Recently, supercritical hydro/solvothermal synthesis has been demonstrated to be a promising approach for generating high-crystalline micro-nanoparticles with short reaction times (less than 2 min) and high crystallization rates affected by the specific characteristics in supercritical fluids. Additionally, the smallest powders among the reported LFP nanoparticles (less than 15 nm) had been synthesized via SHS (supercritical hydrothermal synthesis). Inspired by the structure-function relationships that are gained by hydro/solvothermal synthesis, rapid and continuous supercritical hydro/solvothermal synthesis is of interest for the commercial production of high-performance micro/nanocrystals due to its environmental friendliness and easy scale-up.     

黄腐酸和湖泊孔隙水对Fe(Ⅱ)还原Cr(Ⅵ)为Cr(Ⅲ)的影响

考查了缺氧条件下Fe(Ⅱ)-有机质(DOM)的络合物将Cr(Ⅵ)还原为Cr(Ⅲ)的还原能力。研究发现在没有或有萨旺尼河黄腐酸(SRFA)和波尼湖黄腐酸(PLFA)存在的情况下,Fe(Ⅱ)都能够将Cr(Ⅵ)快速地还原(几分钟)。Fe(Ⅱ)-DOM溶液不一定比仅含有Fe(Ⅱ)单一的体系具有更强的还原力。DOM的组成也影响了Cr(Ⅲ)的还原机制,湿地(俄亥俄州老妇人河河口区)沉积物进行缺氧萃取得到的沉积物孔隙水能够将Cr(Ⅵ)更快地还原。这些研究数据表明自然界中富含Fe(Ⅱ)和DOM的缺氧孔隙水对Cr(Ⅵ)的非生物还原反应速率远大于生物还原反应速率,并且这一非生物还原反应是自然环境中Cr(Ⅵ)被还原的主要途径。     

All-solid-state MoS2/WO3 photoelectrodes as high-efficiency catalysts for reductive/sorptive/recycling of hexavalent chromium

Photoelectrocatalysis (PEC) is an effective approach to eliminate carcinogen hexavalent chromium (Cr(VI)) in wastewater, in which high-performance catalysts are crucial. Herein, controlled growth of thin molybdenum disulphide (MoS₂) nanosheets on self-supported tungsten trioxide (WO₃) created an all-solid-state MoS₂/WO₃ heterojunction serving as electrode and catalyst simultaneously for removing Cr(VI). Countless small and thin MoS₂ nanoflakes build in a huge and porous interface for harvesting lights and adsorbing chromium species. And the highly conductive WO₃ substrate facilitates the transfer of those photoexcited-electron and therefore suppresses the recombination between electrons and holes. Furthermore, assisted by bias potential, electron streams from external circuit render an electron-rich interface at the MoS₂/WO₃ cathode, accelerating the Cr(VI) reduction by PEC. At −1.2 V, the PEC reduction efficiency of Cr(VI) reaches 100% within 30 min, surpassing the pristine WO₃ by 2.7 times. The generated Cr(III) ions can be immobilized on the porous MoS₂/WO₃ cathode through electrostatic attraction, enabling removal of total chromium. More importantly, the Cr(III) anchored to the catalyst can be effortlessly recovered by eluting with clean water, which also refreshes the MoS₂/WO₃ cathode. This study provides a new approach to fabricating photoelectrodes for sustainable PEC reduction and treatment of Cr(VI) containing wastewater.     

新一代储能钠离子电池正极材料的改性研究进展

近年来,原料广泛、成本低廉的钠离子电池被公认为新一代综合效能优异的储能电池系统,但较低的能量密度和有限的循环寿命仍然是阻碍其商业化应用的主要挑战。借鉴锂离子电池的开发经验,合理的改性工艺已被证实可以明显提高钠离子电池的电化学性能,尤其是在已建立的正极体系中。本文分析了过渡金属氧化物、聚阴离子化合物、普鲁士蓝类化合物以及有机化合物等钠离子电池正极材料的结构、性能特点,并系统综述了粒径纳米化、表面包覆、元素掺杂等多类改性方法的最新研究成果。未来的研发和设计中,改进合成工艺控制粒径、拓宽包覆物质种类、梯度掺杂协同元素以及寻找不同结构特征的钠离子电池正极材料是研究重点。     

Heterogeneous photocatalytic reduction of Fe(VI) in UV-irradiated titania suspensions: effect of ammonia

Results of the heterogeneous photocatalytic reduction of Fe(VI) in UV-irradiated TiO₂ suspensions in the presence of ammonia are presented. The initial rate of Fe(VI) reduction, R, may be expressed as R = k _Fe(VI)[Fe(VI)]^1.25 where k _Fe(VI) = a[Ammonia]+b), a = 6.0 × 10³ μm ^0.25 s and b = 4.1 × 10⁶ μm ^−1.25s⁻¹. The rate constant, k _Fe(VI), increases with the ammonia concentration. The photocatalytic oxidation of ammonia is enhanced in the presence of Fe(VI). A mechanism involving Fe(V) as a reactive intermediate is presented which explains the faster photocatalytic oxidation of ammonia in the presence of Fe(VI).     

Antimony Remediation Using Ferrate(VI)

This research investigates a remediation technique for antimony involving the adsorption and co-precipitation of aqueous antimony by in-situ formed ferric hydroxide. Flocculation is initiated by the oxidation of iron(II) with potassium ferrate(VI), K₂FeO₄, along with oxidation of the more toxic Sb(III) to Sb(V). A 3/1 mole ratio of Fe(II)/Fe(VI) and a total Fe/Sb mole ratio of 300/1 was needed to achieve total antimony concentrations below the maximum contaminant levels for drinking water (6 μg/l).     

Modeling an electrochemical process to remove Cr(VI) from rinse‐water in a stirred reactor

Experimental studies were developed in a batch reactor (16 dm³), to obtain the kinetic model of Cr(VI) removal by means of an electrochemical process. An overall kinetic model was obtained and experimentally validated in a continuous stirred electrochemical reactor (16 dm³) with synthetic and industrial wastewater. To develop the mathematical model of the continuous reactor in relation to the Cr(VI) and Fe(II) concentration in the solution, a classical mass balance procedure was performed. The Cr(VI) concentration in the electrochemically‐treated waters was less than 0.5 mg dm^?3. In the electrochemical process the Cr(VI) reduction is caused by the Fe(II) released from the anode due to the electric current applied, by the Fe(II) released for the dissolution (corrosion) of the electrodes due to the acidic media, and by reduction at the cathode. During the process, reduction from Fe(III) to Fe(II) occurs. All of these different reactions cause a diminution in the quantity of sludge generated. Finally, it was found that due to the slow rate of reduction of Cr(VI) during the first part of the process it is necessary to develop a method of control to apply the process in a continuous industrial system. © 2003 Society of Chemical Industry     

聚丙烯酸修饰的Fe3O4@C核壳型微球的制备及其在锂离子电池 负极中的电化学性能

锂离子电池作为最有前途的储能技术之一,因具有循环寿命长、能量密度大、自放电率低、热稳定性能好、记忆效应不明显等优势,已成为新型能源领域的研究热点。本工作以聚丙烯酸(PAA)修饰的粒径约250 nm的Fe3O4微球为核,葡萄糖为碳源,通过水热法制备了Fe3O4@C核壳型微球,研究其作为锂离子电池负极材料的电化学特性。通过X射线衍射(XRD)、扫描电镜(SEM)、热重(TGA–DTA)和傅里叶红外光谱(FT-IR)等手段对其表征,并通过循环伏安特性曲线、循环性能曲线、倍率性能曲线,充放电平台曲线和阻抗及其拟合曲线等研究其电化学性能。结果表明,制备的聚丙烯酸(PAA)修饰的Fe3O4@C核壳型微球球状完整,粒径均一,平均尺寸约310 nm,碳层表面光滑,包覆均匀,平均厚度约30 nm。Fe3O4@C的核壳结构有效缓解了恒流充放电过程中的体积膨胀,避免了晶体结构的快速坍塌。PAA中大量的羧基基团对Fe3O4起到表面改性的作用,有效避免了颗粒团聚,保证了良好的分散性。碳的有效包覆可改善Fe3O4材料作为锂离子电池负极材料的离子和电子电导,增加其比容量、库伦效率和循环稳定性。Fe3O4@C核壳型微球在100 mA/g电流密度下,恒流充放电循环370圈后,仍能保持655 mAh/g放电比容量,约为首次放电的50%,具有良好的容量保持率。     

A ternary mechanism for the facilitated transfer of metal ions onto metal–organic frameworks: implications for the ‘‘versatility’’ of these materials as solid sorbents

Although metal–organic frameworks offer a new platform for developing versatile sorption materials, yet coordinating the functionality, structure and component of these materials remains a great challenge. It depends on a comprehensive knowledge of a “real sorption mechanism”. Herein, a ternary mechanism for U(VI) uptake in metal–organic frameworks was reported. Analogous MIL-100s (Al, Fe, Cr) were prepared and studied for their ability to sequestrate U(VI) from aqueous solutions. As a result, MIL-100(Al) performed the best among the tested materials, and MIL-100(Cr) performed the worst. The nuclear magnetic resonance technique combined with energy-dispersive X-ray spectroscopy and zeta potential measurement reveal that U(VI) uptake in the three metal–organic frameworks involves different mechanisms. Specifically, hydrated uranyl ions form outer-sphere complexes in the surface of MIL-100s (Al, Fe) by exchanging with hydrogen ions of terminal hydroxyl groups (Al-OH₂, Fe-OH₂), and/or, hydrated uranyl ions are bound directly to Al(III) center in MIL-100(Al) through a strong inner-sphere coordination. For MIL-100(Cr), however, the U(VI) uptake is attributed to electrostatic attraction. Besides, the sorption mechanism is also pH and ionic strength dependent. The present study suggests that changing metal center of metal–organic frameworks and sorption conditions alters sorption mechanism, which helps to construct effective metal–organic frameworks-based sorbents for water purification.     

Cobalt(III)-mediated oxidative destruction of phenol using divided electrochemical cell

Mediated electrochemical oxidation is one of the suitable processes for the destruction of hazardous organic compounds and the dissolution of nuclear wastes at ambient temperature and pressure. The electrochemical oxidation of Co(II) was carried out in an undivided and divided electrochemical cell. The formation of Co(III) was studied in an divided electrochemical cell by varying conditions such as temperature and concentration of nitric acid in a batch type electrochemical reactor in recirculation mode. It was found that the formation of Co(III) increased with increasing nitric acid concentration and decreased with increasing temperatures. The produced Co(III) oxidant was then used for the destruction of phenol. It was noted that phenol could be mineralized to CO₂ and water by Co(III) in nitric acid under different nitric acid concentrations and temperatures. The evolved CO₂ was continuously measured and used for the calculation of destruction efficiency. The destruction was increased with increasing nitric acid concentration as well as the temperature. The maximum efficiency was observed to be 78% based on CO₂ evolution for 5,000 ppm phenol solution at 60 °C in a continuous feed mode. The destruction efficiency was increased 28% by addition of silver at 25 °C.