Quaternized biomass as an anion exchanger for the removal of nitrate and other anions from water

Dried Chinese Reed (Miscanthus sinensis), a fast growing plant, was used as a model biomass for the development of anion exchangers using a quaternization agent, N‐(3‐chloro‐2‐hydroxypropyl)trimethylammonium chloride (CHMAC), and a cross‐linking agent, epichlorohydrin. Anions studied include nitrate, phosphate, perchlorate and sulfate. Batch mode adsorption studies were conducted using aqueous solutions of anions. Detailed kinetics were studied for nitrate removal. Parameters studied included anion concentration, agitation time, adsorbent dose, and pH. Adsorption equilibrium occurred in 10 min for all the anions studied. Equilibrium adsorption data followed both Langmuir and Freundlich isotherms. The presence of phosphate, perchlorate, fluoride and sulfate lowered the adsorption significantly. The effects of pH on adsorption and desorption show that ion exchange is involved in the adsorption process. The adsorption capacity of the cross‐linked and quaternized Chinese Reed for nitrate, sulfate, phosphate and perchlorate was found to be 7.55, 13.25, 16.61 and 10.07 mg of anion per g of the anion exchanger, respectively. Copyright © 2004 Society of Chemical Industry     

Liquid-Liquid Extraction of Acids by a Malonamide: II-Anion Specific Effects in the Aggregate-Enhanced Extraction Isotherms

Non-electrostatic ion-specific effects are strong for anions when water is involved. We study here the thermodynamic equilibrium of a water-in-oil microemulsion stabilized by a surface-active extractant in a Winsor-II regime. Acid extraction isotherms for different anions located differently in the Hofmeister series have been investigated. A Langmuir like model was written for the specific case of acids treated as electrolytes, describing acid extraction as the adsorption of extracted electrolytes on the polar/apolar interface of the aggregates. Except for sulfate, isotherms can be described at first approximation as simple Langmuir-type isotherms when plotted as a function of the acid activity in the aqueous phase. The validity of the model being hence demonstrated, acid extraction free energies could be derived and compared, taking into account the effect of the anion position in the Hofmeister series. The case of phosphate, chloride, and sulfate as kosmotropes can be distinguished. They are significantly extracted, only above a threshold since the sphere-to-rod transition of the reverse aggregates has to be triggered by high chemical potential of the acid required to compensate anion dehydration.     

Zr4+掺杂对Mg/Al水滑石磷吸附行为的影响

采用共沉淀法制备了系列不同Zr4+含量的Mg/Al/Zr三元类水滑石材料，研究了其对废水中磷酸根离子的吸附性能。采用XRD、DRIFTS、氮气吸脱附实验等手段对材料的结构及织构性质进行了表征，并研究了溶液初始pH以及竞争阴离子对磷吸附量的影响。结果表明：掺杂Zr4+能提高类水滑石层板正电荷密度以及增大层间距，有利于磷酸根阴离子的吸附；Mg/Al/Zr类水滑石对磷的吸附过程符合准二级动力学模型，吸附等温线符合Langmuir模型，当n(Zr4+)/(Al3++Zr4+)为0.3时，理论饱和吸附量最大，达到76.6 mg/g，比Mg/Al水滑石高出28.7%；酸性环境有利于磷酸根的吸附，而二价阴离子的竞争吸附作用会显著降低磷吸附效果。Mg/Al/Zr类水滑石对磷的吸附机理为静电吸引和阴离子交换协同作用。     

Adsorption of phosphate species on poly-oriented Pt and Pt(1 1 1) electrodes over a wide range of pH

The adsorption of phosphate anions from phosphate solutions at poly-oriented and single-crystal platinum electrodes, primarily Pt(1 1 1), was studied over a wide range of pH by cyclic voltammetry. The features observed at the poly-oriented Pt electrode in phosphate solution may be related to the different crystalline facets, the (1 1 1) orientation presenting the most significant behavior in terms of phosphate adsorption. On the reversible hydrogen electrode (RHE) scale, the phosphate adsorption strength decreases with increasing alkalinity of the solution. Qualitatively, three different pH regions can be distinguished. At pH < 6 only a broad reversible peak is observed, corresponding to the adsorption of H₂PO₄⁻ and further deprotonation to adsorbed HPO₄⁻. For 6 < pH < 11 a butterfly feature followed by one or two anodic peaks (depending on scan rate) is observed, ascribed to the adsorption of HPO₄⁻ followed by its subsequent deprotonation to adsorbed PO₄³⁻. The splitting into two or three voltammetric features, and the irreversibility of the two features at more positive potential, is ascribed to the deprotonation reaction leading to a surface species (i.e. phosphate) which needs to change its surface coordination. At pH > 11 a reversible pre-wave and a sharp spike are observed, ascribed to the co-adsorption of phosphate and hydroxide.     

一种新的氨基硫脲类阴离子受体的合成及其性质研究

合成了一种新的阴离子受体化合物PySN,通过1H NMR对其进行了表征。受体分子结合不同阴离子的紫外-可见光谱和荧光发射光谱变化表明:在非质子性溶剂中,PySN可选择性识别和传感氟离子、醋酸根及磷酸二氢根离子。     

二维层状双金属氢氧化物在去除磷酸盐中的应用

层状双金属氢氧化物（LDH）是磷酸盐去除的良好吸附剂，具有表面易改性、电荷可调、层间距可控、吸附能力强和吸附速度快的特点，能够有效解决水体富营养化问题。本文从LDH除磷性能的优化出发，综述了LDH的结构特征、除磷机理、制备方法、剥离方法的前沿理论和应用案例；基于目前LDH用作磷酸盐吸附剂面临着易团聚、胶体溶液不稳定、性能受控于pH以及难回收等问题，分析了磁性LDH、生物炭/LDH、GO(rGO)/LDH等复合材料的复合方法和性能改进方案，指出了LDH复合改性和LDH膜材料的研究新趋势，以及主要研究重点与热点。希望本文能够为LDH在水处理领域的研究提供新思路，为深入优化LDH吸附和膜分离性能提供理论支持和方向引导。     

Graphite intercalation compounds as positive electrodes in galvanic cells

A systematic investigation of the anodic intercalation of the anions HSO^?₄, ClO^?₄ and BF^?₄ into natural graphite (as composite electrodes “CPP” with polypropylene binder) and its cathodic redissolution is presented. Slow cyclic voltammetry (1 mV/s) is the method used. The anions were provided as aqueous acid solutions in the concentration range of 0.1–12 M.At a critical potential of intercalation E_K, which decreases linearly with anion concentration (60 Vcm³/mol), an anodic intercalation current rises steeply. Current limitation occurs due to a diffusion process into the bulk of the electrode. From potentiostatic transients, a diffusion coefficient of about 4.10^?9 cm²/s is derived. In a potential range of only about 200 mV, the different intercalation stages up to C₂₄A are represented as anodic peaks, which are refound as cathodic peaks of low overvoltage (<50 mV) upon redissolution. Current efficiencies up to 100 per cent are found in spite of the high water concentration.A new model of electrochemical intercalation, based on anion adsorption on the graphite electrode, is presented.Due to the very positive potentials (up to 1.9 V vs nhe) and the high reversibility, the electrodes should be useful as positives in galvanic cells.     

Electrolyte effects on oxygen reduction kinetics at platinum: A rotating ring-disc electrode analysis

A comparative study of the electrode kinetics of oxygen reduction of platinum in perchloric, phosphoric, sulfuric, trifluoromethanesulfonic acids (all at pH = 0) and in potassium hydroxide (pH = 14) was made at 25°C using rotatating ring-disc electrode techniques. The platinum electrode was first characterised in these electrolytes using the cyclic voltammetric method. The results showed that in the potential region from 0.8 to 0.6 V/rhe, the kinetics of oxygen reduction in these electrolytes decreases in the order KOH > H₂SO₄ ～ CF₃SO₃H > H₃PO₄ > HClO₄. This order of activity is reflected in the effects of the electrolytes, in respect to specific adsorption of anions, on the platinum oxide formation reaction. The role of anion adsorption is also apparent in the dependence of the rate constant for oxygen reduction to water or to hydrogen peroxide and of hydrogen peroxide reduction to water on potential. The superior behavior of oxygen reduction in KOH is due to minimal adsorption of the OH^? ion. The more complex adsorption behavior of the oxyanions in the investigated acid electrolytes than that of simple anions like the halide ions presents difficulties in drawing detailed correlations between oxygen reduction kinetics and adsorption behavior of oxyanions of platinum.     

Electron Transfer Reactions in Pulping Systems (II): Electrochemistry of Anthraquinone/Lignin Model Quinonemethides

Abstract

Electron transfer reactions have been observed during the electrolyses of solutions containing anthraquinone and 8-aryl ether lignin model quinonemethides. In dry acetonitrile at a reduction potential of -0.9V (vs. Ag/AgCl) electrons are transferred from the electrode to anthraquinone (AQ) to form stable anthrahydroquinone radical anions (AHQ^?). The lignin model quinonemethides are not reduced directly at the electrode at this potential but are reduced by AHQ^? to give quinonemethide radical anions (QM^?) and AQ. The QM^? species rapidly fragment at their β-aryl ether bond to give phenolate ions and radicals; the latter further reduces to another phenolate ion. For example, the β-methyl lignin model QM 1 gives guaiacol and isoeugenol upon electrolysis at -0.9V in the presence of AQ. In wet acetonitrile, reduction of AQ at -0.9V leads to both anthrahydroquinone radical anion and dianion; the dianion is formed by direct electrolysis of the radical anion and by disproportlonation of the radical anion. Under all conditions and substrates examined, electron transfer reactions proceeded in preference to bond formation reactions which would generate “adducts.” The implication of these results Is that it should be possible to delignlfy wood by electron transfer reactions and that anthraquinone probably functions this way.     

Spectroelectrochemical study of the adsorption of acetate anions at gold single crystal and thin-film electrodes

Acetate adsorption at gold electrodes is studied in perchloric acid solutions by cyclic voltammetry and in-situ infrared spectroscopy. External reflection measurements, performed with gold single crystal electrodes, are combined with Surface Enhanced Infrared Reflection Absorption Spectroscopy experiments under attenuated total reflection conditions (ATR-SEIRAS) carried out with sputtered gold thin-film electrodes. Theoretical harmonic IR frequencies of acetate species adsorbed with different geometries on Au clusters with (1 1 1), (1 0 0) and (1 1 0) orientations have been obtained from B3LYP/LANL2DZ, 6-31 + G* calculations. The theoretical and experimental results confirm that, irrespective of the surface crystallographic orientation, bonding of acetate to the surface involves the two oxygen atoms of the carboxylate group, with the OCO plane perpendicular to the metal surface. DFT calculations reveal also that the total charge of the metal cluster-acetate supermolecule has small effect on the vibrational frequencies of adsorbed acetate species. Both the external and the internal reflection measurements show the co-adsorption of acetate and perchlorate anions. Step-scan measurements carried out with the gold thin-film electrodes have allowed the monitoring of the time-dependent behaviour of perchlorate, acetate and water bands in potential step experiments. Acetate adsorption under those conditions is shown to involve perchlorate desorption and to follow a Langmuir-type kinetics. The step-scan spectra also show the rise and decay of transient water structures with parallel time-dependent shifts of the background intensity in the infrared spectra.     

Surface-enhanced Raman spectroscopy and electrochemistry of 2,2′-bipyridine adsorbed at copper electrode

The adsorption of 2,2′-bipyridine (22BPY) on the surface of polycrystalline copper electrode was studied by means of surface-enhanced Raman spectroscopy (SERS) and cyclic voltammetry in a wide range of electrode potential. Experiments were carried out in both acidic and neutral solutions, as well as in presence of two kinds of supporting electrolyte (KCl and LiClO₄) in order to examine the influence of molecule protonation and specifically adsorbed anions. It was found that a molecule orientation with respect to the surface changes from perpendicular to more tilted in the neutral perchlorate solution followed by the conformation change from cis to trans in strongly negative potentials. This conformational transition occurs gradually, probably through a series of intermediate states. The SERS features due to trans conformers are uniquely observed in presence of perchlorate anions. In the presence of chloride the molecular plane is at least slightly inclined towards the surface in the whole potential range. In acidic solutions the SERS results indicate that 22BPY adsorbs in non-protonated form independent on the present anion with the molecular plane tilted although it becomes more perpendicular with respect to the surface at negative potentials. The cyclic voltammetry measurements revealed that the hydrogen evolution is inhibited in presence of 22BPY in both neutral and acidic solutions. It suggests strong adsorption of this molecule in a wide range of electrode potentials.     

微生物燃料电池的研究进展

介绍了微生物燃料电池的工作原理。列举了微生物燃料电池的3个实例模型。概括了微生物燃料电池目前存在的问题和解决方法。展望了微生物燃料电池的应用前景。     

Effect of anions and pH on the ethanol electro-oxidation at a platinum electrode

The electro-oxidation of ethanol and its inhibition by adsorbed chloride ions have been studied by cyclic voltammetry in 0.64 M HNO₃, 0.64 M HClO₄, 0.64 M NaNO₃, 0.64 M NaClO₄, 0.43 M NaNO₃/0.072 M Na₂SO₄ and 0.43 M NaClO₄/0.072 M Na₂SO₄ solutions at 25°C. The results show that these anions and the pH influence the peak current and potential for all three anodic waves. The anion effect is more pronounced in acidic solutions than in neutral solutions. The magnitude of the effect in the absence of chloride indicates that the surface coverage of these anions increases in the order perchlorate, sulfate, nitrate. The chloride inhibition is dependent on the anions and is smallest in sulfate solutions. Mechanisms proposed in an earlier study are found to be consistent with these results. It is also suggested that the ethanol system may be useful as a probe in studies of anion adsorption properties and platinum surface states.     

胶原纤维固载Fe(Ⅲ)对磷酸根的吸附特性

将Fe（Ⅲ）固载在胶原纤维上制备吸附材料，研究了该吸附材料对磷酸根的吸附性能。结果表明，当温度为303 K，溶液的初始浓度为62.0 mg P·L-1时，胶原纤维固载Fe（Ⅲ）(FeICF)对磷酸根的吸附容量为32.69 mg P·g-1。在pH为3.0～6.0范围内平衡吸附量较大，即当磷酸根在溶液中以H2PO-4的形式存在时有利于吸附。吸附等温线符合Langmuir方程，吸附容量随温度和Fe（Ⅲ）的固载量的增加而增加。FeICF对磷酸根的吸附动力学符合拟二级速度方程。溶液中存在的Cl-、NO-3、SO2-4及CO2-3对磷酸根的吸附没有影响，表明FeICF对磷酸根有较强的选择吸附能力。     

Effect of CO2, HCO3 and CO3 on oxygen reduction in anion exchange membrane fuel cells

The effect of carbonate and bicarbonate anions on the oxygen reduction reaction was investigated in four alkaline solutions (pH ∼ 14) on a Pt disk type electrode with varying concentrations of carbonate and bicarbonate. The addition of carbonate and bicarbonate had two primary effects on the observed voltammetric behavior: i) The Tafel slope shifts positive with increasing carbonate/bicarbonate concentration, indicating that the carbonate anions may compete for surface adsorption sites; and ii) The dissolved oxygen concentration and diffusion coefficient are depressed with increasing anion concentration. Finally, adding CO₂ to the cathode stream of an anion exchange membrane fuel cell caused an improvement in the device performance under fully hydrated conditions, suggesting that the fuel cell was operating at least partially under the carbonate cycle.     

Adsorption stages and interfacial orientations of cytidine sulphate at the mercury/electrolyte interface

The adsorption and interfacial orientations of cytidine sulphate were studied by out-of-phase ac voltammetry. The adsorption equilibrium and its attainment have been investigated as a function of various parameters such as pH, adsorption potential, adsorption time, temperature and the bulk concentration of cytidine sulphate. The time dependence of the electrode impedance indicates that the formation of a compact film controlled by nucleation/growth mechanism and the data were analysed according to the Avrami equation. Moreover, the role of the anions of the indifferent supporting electrolyte in the formation of the condensed film of the adsorbed molecules has been elucidated. The stacking interactions between adsorbed molecules are affected by the nature of the anions of the supporting electrolyte and are hindered by their specific adsorption. The adsorption parameters of cytidine sulphate has been computed at various pHs and for various anions in the supporting electrolyte.     

膜法电容去离子技术用于水溶液中单/多价阴离子的分离

将电容去离子技术（CDI）与单价阴离子选择性交换膜结合构建新型膜法电容去离子膜堆（PSMCDI）,并探索其在单/多价阴离子分离中的应用。采用自制的测试装置,以Cl^-/SO₄^2-水溶液为模拟体系,并选择现有的两种商业化单价阴离子选择性交换膜（ASV和ACS）作为膜元件,系统地研究了各参数（PSMCDI种类、阴离子组成和浓度、pH、操作时间、电压和流速）对单价离子选择性的影响。结果表明,总阴离子去除量随着阴离子浓度的增加而增加,但是对于单价离子（Cl^-）选择性降低。随着操作时间的增加,单价离子（Cl^-）选择性也降低。对于ASV膜,在1.2 V的直流电压、10 min吸附时间和30 ml·min^-1进料流速的条件下得到1.6的单价阴离子去除选择性。同时,在相同条件下,ACS膜的单价阴离子去除选择性为1.4。     

Thermodynamic studies of phosphate adsorption on Pt(1 1 1) electrode surfaces in perchloric acid solutions

The thermodynamics of the so-called perfectly polarizable electrode was employed to analyze the total charge densities for a nearly defect-free Pt(1 1 1) electrode in a series of NaH₂PO₄ solutions with an excess of inert electrolyte (0.1 M HClO₄) at constant ionic strength and pH. Thermodynamic analysis using both electrode potential and charge density as independent electrical variables is described. The Gibbs excess, Gibbs energy of adsorption and charge numbers both at constant electrode potential and constant chemical potential for anion adsorption at the Pt(1 1 1) surface have been determined. The calculated electrosorption valencies and charge numbers at constant chemical potential are close to two electrons per adsorbed anion, suggesting that in the absence of co-adsorbed species, HPO₄²⁻ is the predominant adsorbed species. The maximum Gibbs excess of adsorbed hydrogenphosphate attains a value of ≈3.2 × 10¹⁴ ions cm⁻² which corresponds to a coverage of ≈0.22 ML.     

Adsorption of camphor and 2,2′-bipyridine on Bi(1 1 1) electrode surface

Impedance spectroscopy and in situ STM methods have been used for investigation of the camphor and 2,2′-bipyridine (2,2′-BP) adsorption at the electrochemically polished Bi(1 1 1) electrode from weakly acidified Na₂SO₄ supporting electrolyte solution. The influence of electrode potential on the adsorption kinetics of camphor and 2,2′-BP on Bi(1 1 1) has been demonstrated. In the region of maximal adsorption, i.e. capacitance pit in the differential capacitance versus electrode potential curve, the heterogeneous adsorption and diffusion steps are the rate determining stages for camphor and 2,2′-BP adsorption at the Bi(1 1 1) electrode. It was found that for camphor | Bi(1 1 1) interface the stable adsorbate adlayer detectable by using the in situ STM method has been observed only at the positively charged electrode surface, where the weak co-adsorption of SO₄²⁻ anions and camphor molecules is possible. At the weakly negatively charged Bi(1 1 1) electrode surface there are only physically adsorbed camphor molecules forming the compact adsorption layer. The in situ STM data in a good agreement with impedance data indicate that a very well detectable 2,2′-BP adsorption layer is formed at Bi(1 1 1) electrode in the wide region of charge densities around the zero charge potential.     

Comparative study of microbial fuel cell performance using poly ether ether ketone-based anion and cation exchange membranes

In this report, poly ether ether ketone (PEEK)-based anion and cation exchange membranes were assembled separately in two identical and compact microbial fuel cells (MFCs) without water and gas trapping between membrane and the electrode. We examined the use of these two membranes with the same electrode surface area as well as anode and cathode volumes. A maximum power density of 603 and 458 mW m^?2 with a columbic efficiency of 76 and 61% were observed for quaternized poly ether ether ketone (QPEEK) and sulfonated poly ether ether ketone (SPEEK), respectively. A few solution chemistry parameters, which are leading factors behind the cell performance, such as variation in conductivity and solution pH in the two chambers were observed. In addition, the mobility of anions and cations (other than protons and hydroxyl ions in the case of cation and anion exchange membranes, respectively) under the inoculated conditions was also investigated. Further, the membrane charge-based biofilm growth was also analyzed by SEM and impedance spectroscopy to find its influence on the MFC performance.