The feasibility of boron removal from water by capacitive deionization

We report on the possibility of removing boron (in the form of boric acid) from water by electrochemical means. We explore capacitive de-ionization (CDI) processes in which local changes in pH near the surface of high-surface-area activated carbon fiber (ACF) electrodes during charging are utilized, in order to dissociate boric acid into borate ions which can be electro-adsorbed onto the positive electrode in the CDI cells. For this purpose, a special flow-through CDI cell was constructed in which the feed solution flows through the electrodes. Local pH changes near the carbon electrode surface were investigated using a MgCl₂ solution probe in three- (with reference) and two-electrode cells, and described qualitatively. We show that, to a certain extent, boron can indeed be removed from water by CDI.     

Electrospun porous carbon nanofibers/TiO2 composite coated over carbon cloth- A flexible electrode for capacitive deionization

The combination of porous carbon matrix and metal oxide is trending for capacitive deionization (CDI) due to their synergistic electrochemical behaviour and properties. In this research, a flexible electrode based on electrospun porous carbon nanofibers and TiO₂ nanoparticles (particle size ～7 nm) i.e., PCNFs/TiO₂ composite coated over carbon cloth is developed. A facile in-situ activation procedure using sacrificial polymer is adopted over typical chemical activation treatment to synthesize PCNFs/TiO₂ composite. PCNFs/TiO₂ composite is prepared in two steps, possessing a high specific surface area of ～343 m² g^?1 and pore volume of 0.038 cm³ g^?1. Interestingly, CDI unit assembled with PCNFs/TiO₂ composite based flexible electrodes delivers the large salt electrosorption capacity of 204.8 mg g^?1 at voltage 1.2 V in a salt solution of concentration 500 ppm and conductivity 880 μS cm^?1. The excellent adsorption capacity retention of 96.4% up to ten adsorption-regeneration cycles can be a tempting option for future flexible CDI applications.     

活性炭纤维电极的电容去离子脱盐试验研究

以活性炭纤维为电极材料研制液流式电容去离子模块,考察了电压、进水流量、进水浓度对其脱盐性能的影响。结果表明,活性炭纤维电极用于电容去离子脱盐具有吸附效率高、再生性能好的优点。对活性炭纤维进行载钛改性．改性后的电极单位吸附量提高了31．61％。对于电导率为7．31mS／cm的电镀反渗透浓水,在21级电容去离子模块串联作用下．离子去除率高达95．21％。处理后的电导率与自来水相近,说明以活性炭纤维为电极的电容去离子技术具有广阔的应用前景。     

Synthesis and characterization of asymmetric electrochemical capacitive deionization materials using nanoporous silicon dioxide and magnesium doped aluminum oxide

New capacitive deionization (CDI) materials based on using nanoporous silicon dioxide or alumina surface-doped with magnesium were shown to remove a wide range of cations having different valent states and hydrated radii. The use of the asymmetric insulating oxide nanoparticles as CDI materials increased removal rates due to their small size and opposite surface potentials. This system can be regenerated electrochemically by reversing the potential of the electrodes in order to drive the ions off the electrodes. Unique to this system is that ions do not adsorb onto the opposite electrode during regeneration due to the inherent surface potential of the nanoporous oxide which repels the ions under the conditions employed for these tests. As might be expected, the maximum allowable regeneration voltage was directly related to the zeta potential of the nanoporous coating on the working electrode under the specific test conditions.     

Atomic layer deposition of TiO2 on carbon-nanotubes membrane for capacitive deionization removal of chromium from water

Chromium (Cr) is a common heavy metal that has severe impacts on the ecosystem and human health. Capacitive deionization (CDI) is an environment-friendly and energy-efficient electrochemical purification technology to remove Cr from polluted water. The performance of CDI systems relies primarily on the properties of electrodes. Carbon-nanotubes (CNTs) membranes are promising candidates in creating advanced CDI electrodes and processes. However, the low electrosorption capacity and high hydrophobicity of CNTs greatly impede their applications in water systems. In this study, we employ atomic layer deposition (ALD) to deposit TiO₂ nanoparticulates on CNTs membranes for preparing electrodes with hydrophilicity. The TiO₂-deposited CNTs membranes display preferable electrosorption performance and reusability in CDI processes after only 20 ALD cycles deposition. The total Cr and Cr(VI) removal efficiencies are significantly improved to 92.1% and 93.3%, respectively. This work demonstrates that ALD is a highly controllable and simple method to produce advanced CDI electrodes, and broadens the application of metal oxide/carbon composites in the electrochemical processes.     

Preparation of electrodes for hybrid capacitive deionization and its influence on the adsorption behaviour

ABSTRACT

The influence of the ratio of poly(vinyl chloride) in electrode composition into their surface energetics, hybrid capacitive deionization performance as well as adsorption kinetics and isotherms was evaluated. The electrodes were comprised of lithium manganese titanium oxide or activated carbon. Electrodes were tested by used hybrid capacitive deionization. To testing surface energetic the goniometer measurements were applied. It was possible to calculate free surface energy with its components. For investigated the adsorption kinetics the pseudo first order, pseudo second order, Weber–Morris intraparticle diffusion, Elovich models were chosen. While for the detection of adsorption isotherms Temkin and Harkins–Jura models were examined.     

Improvement in the capacitance of a carbon electrode prepared using water-soluble polymer binder for a capacitive deionization application

It is very important to increase the wetted surface area of a carbon electrode for high capacitive deionization performance. To increase the wettability of a carbon electrode, we fabricated carbon electrodes by using water-soluble polymer binder, polyvinyl alcohol (PVA). The electrochemical properties of the PVA-bonded carbon electrode were compared with another that was prepared using hydrophobic binder, polyvinylidene fluoride (PVdF). Electrochemical methods - cyclic voltammetry, chronoamperometry, and electrical impedance spectroscopy - were used to characterize the electrochemical properties of the electrodes. As might be expected, it was confirmed that the PVA-bonded electrode was more wettable than the PVdF-bonded one, based on contact angle measurements. From the cyclic voltammetric analysis, we found that the specific capacitance was 74.4-80.3 Fg⁻¹ for the PVdF-bonded electrode and 89.6-99.8 Fg⁻¹ for the PVA-bonded electrode, depending on the potential, indicating a 13.3-30.1% increase in specific capacitance. It was observed that the ac-signal penetrated micropores of the PVA-bonded carbon electrode more deeply than the PVdF-bonded one, resulting in a higher capacitance. This was attributed to the fact that the ac-signal was able to charge more inner surface sites because micropores in the PVA-bonded electrode could be wetted due to the PVA binder.     

Limitations of charge efficiency in capacitive deionization processes III: The behavior of surface oxidized activated carbon electrodes

In previous papers we reported on attempts to improve the performance of water desalination using capacitive de-ionization (CDI) processes by understanding the ions transport and adsorption/desorption behavior of activated carbon electrodes as a function of the applied potential. We also investigated the charge efficiency in CDI processes of brackish water in symmetrical cells containing identical highly porous activated carbon electrodes. In this work, we study the influence of oxygen-containing surface groups on activated carbon electrodes on the adsorption/desorption behavior of ions in brackish water. A special methodology was developed in order to estimate the charge efficiency of CDI processes which include the ability to prepare various kinds of activated carbon electrodes (ACEs) with controlled porosity and surface groups, measuring the PZC (potential of zero charge) of ACE in solutions and simultaneous adsorption and desorption of ions into/from them. The presence of polar, oxygen containing surface groups on ACE does not affect the electroadsorption behavior of Na⁺ and Cl⁻ ions into porous carbons whose average pore size is greater than 0.58 nm, apart of considerably changing the PZC. This results in a shift of the entire curves of ion adsorption vs. potential. The possible use of ACE with oxidized surfaces in CDI processes is discussed.     

Capacitive deionization of NaCl solution with carbon aerogel-silicagel composite electrodes

Carbon aerogel-silica gel composite materials with different kinds of ratios were used as the electrode-activematerials for a capacitive deionization (CDI) process, which were prepared by a paste rolling method. The electrochemical parameters such as current values, coulombs, specific coulombs and coulombic efficiencies were investigated using a unit cell. The composite electrodes showed good wettability and high mechanical strengths with adequate durability under 1,000 ppm NaCl solution. Also, the composite electrodes showed an effective cycle ability without destroying active materials from the composite electrode, which decreased the manufacturing time by 50%. Additions of silica gel obviously improved coulombic results and led to effective performance of the CDI process.     

Biocomposite based electrode for effective removal of Cr (VI) heavy metal via capacitive deionization

Abstract

This study focuses on the fabrication of biocomposite electrode and removal of Cr (VI) ions from wastewater using a capacitive deionization (CDI) method. The activated carbon (AC) was synthesized from Bael fruit shell (BS). The synthesized AC surface has a macroporous and mesoporous structure with the large specific surface area (617.72?m² g^?1) and high adsorption capacity. The cyclic voltammetry and CDI were performed for the detection and for the removal of chromium (VI) ions, respectively. The lower level of detection of Cr (VI) by a modified electrode was found to be 10 ppt. SEM, BET, and FTIR analyses were performed to explore the surface properties of electrode materials. The removal efficiency was achieved 100% by using biocomposite electrode with an applied potential of 15?V. The highest percent removal mechanism consists of electrosorption and electroreduction due to the affinity between polyvinyl alcohol modified electrode and Cr (VI) ions, under electrochemically faradic process.     

Electro-sorption of ammonium by a modified membrane capacitive deionization unit

A modified membrane capacitive deionization (MCDI) unit with additional flow channels in the anode and cathode chambers was used to study the performance of ammonium ion removal. The influences of operating parameters including initial ammonium concentration, flow rate and applied potential and the effect of flow in the anode and cathode chambers were investigated. Flow through the anode and cathode chambers significantly enhanced the electro-sorption efficiency. The electro-sorption of ammonium at 5 mL/min was about 65% greater than without flow.     

流动电极电容去离子去除铵根离子模型及优化

为了更直观地研究流动电极电容去离子（flow electrode capacitive deionization, FCDI）除氨工艺的机理并进行高效改进,本文构建了FCDI装置去除NH{}_{\mathrm{4}}^{+}的电化学稳态模型,实验结果模拟准确率达到93.8%。利用该模型研究了FCDI除氨工艺在进水流量、电流密度、电极液中活性炭质量分数等工况条件下的能耗和去除效率变化趋势,计算离子选择性和去除速率两个指标,定性阐明操作参数对去除氨的影响机理,筛选出较优化工况。研究结果表明,FCDI除氨工艺在进水流量1.25mL/min、电流密度21.26A/m²、活性炭质量分数为10%时,除氨效率为74.5%,能耗为29.62kWh/kg N,达到较为理想的状态。在优化的工况条件下,讨论了NH{}_{\mathrm{4}}^{+}在FCDI装置内部的微观传输情况,考虑到过长的流道长度会增强电流密度的极化现象,降低装置除氨性能,提出了串联装置的建议。保持流道长度和工况条件不变,串联的装置可以比原装置的去除效率提升32.9%,同时去除单位质量N的能耗降低22.0%,表明装置的改进是有效的。优化后的FCDI除氨工艺比同类处理工艺更有优势,NH{}_{\mathrm{4}}^{+}去除效率更高,能耗更低,具有广泛应用前景。     

水溶性带电聚合物黏结剂修饰炭电极用于增强电容去离子性能

电容去离子技术（capacitive deionization,CDI）是一种基于电吸附原理的新型脱盐技术,具有成本低、无污染、能耗小等优点。采用亲水性的羧甲基纤维素钠（CMC）和聚乙烯醇（PVA）黏结剂及其化学修饰得到的具有更多带电基团的磺化羧甲基纤维素（SCMC）和季铵化聚乙烯醇（QPVA）黏结剂制备活性炭电极,能进一步增强活性炭（AC）电极的亲水性和离子选择性。亲水性带电聚合物黏结剂依靠自身的电荷可以有效抑制阳极氧化的副反应,并增强离子吸附驱动力。在500 mg/L NaCl盐溶液,1.2/0 V电压下,AC-CMC//AC-PVA和AC-SCMC//AC-QPVA可分别获得14.58和17.39 mg/g的脱盐量,且在0.8/0 V电压下循环100圈之后,脱盐量的保持率分别为65.48%和80.53%。     

流动电极电容去离子技术综述：研究进展与未来挑战

随着全球能源危机的加剧和碳中和的提出,污水资源化和能源回收成为近年来的研究热点。电容去离子（CDI）这一新型电化学技术,以节能、无污染等优势受到广泛关注。流动电极电容去离子（FCDI）技术是在CDI技术的基础上,结合离子交换膜及流动电极的新型电化学吸附方法,在保持节能的同时,能够实现连续运行从而不间断地产水。本文重点关注FCDI技术的原理、设计、操作模式、考察指标及在环境领域中的应用（包括污水处理、能源回收及其他新兴应用）,全面概述了这项水处理技术的研究进展和未来前景。此外,还介绍了FCDI系统中常用性能评价指标,以便不同系统、不同条件之间进行对比。最后,提出了FCDI技术在未来全面应用中的主要挑战。     

Membrane-assisted capacitive deionization: Effect of Poly(vinyl alcohol) cross-linking on the properties of ion exchange membranes

Novel composite electrodes were developed for application in membrane capacitive deionization (MCDI). Activated carbon (AC) was dispersed in a solution of poly(vinyl alcohol) (PVA) mixed with polyacrylic acid (PAA) or poly dimethyl diallyl ammonium chloride (PDMDAAC), and cast onto the surface of an AC-based modified graphite electrode, prepared by phase inversion, to form a composite membrane further cross-linked with glutaraldehyde (GA). The effect of the cross-linking on the chemical structure of the PVA-based membranes was determined by attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy. Cyclic voltammetry was conducted to examine the specific capacitance of the composite electrodes. Desalination experiments were then performed with MCDI unit cells to study the effect of cross-linking on the desalination efficiency. It was proved that after optimization, the synthesized composite electrodes exhibited one and a half times higher NaCl removal capacity and three times higher adsorption rate as compared to that of a conventional CDI cell using commercial ion exchange membranes (IEMs) with almost the same energy consumption. The enhanced desalination performance was attributed to the optimized properties of the selected polymers and the improved adhesion of IEMs to the electrodes. This research paves the way for the application of new materials in MCDI processes for improved water desalination.     

石油焦基高比表面积活性炭电吸附脱盐性能的研究

采用石油焦为原料,以KOH为活化剂,制得高比表面积活性炭,比表面和孔容远高于常规活性炭,孔径分布和常规活性炭相似.以高比表面积活性炭作为电吸附电极,考察其在NaCl溶液中的电吸附性能,并对话性炭电极电吸附的影响因素进行研究.结果表明,活性炭电极的电吸附性能主要受比表面积和孔容的影响,高比表面积和大孔容的活性炭单位电吸附...     

聚间苯二胺/碳纳米管复合材料制备及其电容法脱盐研究

采用原位氧化聚合方法制备聚间苯二胺（PmPD）和碳纳米管（CNT）复合电极材料（PmPD@CNT）,考察了PmPD的添加对复合材料亲水性、电化学性能的影响,研究了以PmPD@CNT为电极的电容法脱盐（Capacitive Deionization,CDI）性能。扫描电镜和透射电镜分析表明PmPD的球形形貌保留在复合材料中且均匀包裹在CNT外表面。接触角测试证明,与CNT （107°）相比,PmPD@CNT的接触角（61°）显著降低,亲水性明显提高。X射线衍射和拉曼光谱图的测试结果证明PmPD@CNT相比CNT有更多的缺陷点位,有利于提高离子吸附能力。电化学测试证明,PmPD@CNT （72.5 F·g^-1,0.071 Ω）比CNT （27.4 F·g^-1,0.089 Ω）具有更高的比电容和较低的电阻。将PmPD@CNT制备成固体电极用于CDI组件进行饱和脱盐测试,结果表明以500 mg·L^-1的NaCl溶液为原料液及1.4 V操作电压条件下,该复合电极的盐吸附量为16.64 mg,对应的比吸附量为35.40 mg·g^-1,平均吸附速率为10.11 mg·g^-1·min^-1,PmPD@CNT的比吸附量和平均吸附速率分别是CNT的2.4和1.4倍。PmPD@CNT因其良好的亲水性,优异的电化学性能和脱盐性能,有望成为有竞争力的CDI电极材料。     

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。     

Several basic and practical aspects related to electrochemical deionization of water

We examine water desalination processes based on the electrosorption of ions onto activated carbon electrodes (capacitive deionization, CDI). A flow‐by operation mode was used (solutions flows within channels in the separator, parallel to the electrodes) in both continuous and stopped flow experiments. The different response of solutions containing more than 5000 ppm NaCl and dilute solutions (e.g., 1000 ppm NaCl) to the applied potential is discussed. The electrical current transients on potential steps were faster by two orders of magnitude than the resulting concentration transients due to the dynamics of these deionization processes and the properties of the cells used herein. Guidelines for the practical development of capacitive water deionization processes are discussed herein. It is assumed that for brackish water containing several thousands ppms of NaCl, CDI may be advantageous over competitive methods (e.g., reverse osmosis). © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Electrodialysis, a mature technology with a multitude of new applications

Electrodialysis is a mature process which is applied since more than 50 years on a large industrial scale for the production of potable water from brackish water sources. But more recently electrodialysis in combination with bipolar membranes or with ion-exchange resins has found a large number of new interesting applications in the chemical process industry, in the food and drug industry as well as in waste water treatment and the production of high quality industrial water.In this paper the principle of electrodialysis is described and its advantages and limitations in various applications are pointed out. More recent developments in electrodialysis as well as in related processes such as electrodialytic water dissociation or continuous electrodeionization are discussed and their present and potential future applications are indicated. Research needs for a sustainable growth of electrodialysis and related processes are pointed out.