Electrically accelerated removal of organic pollutants by a three‐dimensional graphene aerogel

Fast and effective methods for the removal of pollutants are crucial for the development of new sustainable water treatment technologies. In this work, we have reported the electrically accelerated removal of some typical organic pollutants by a three‐dimensional graphene aerogel (3DG). The porous 3DG was fabricated by chemical reduction of graphene oxide. The morphology and structure of 3DG were characterized by microscopic and spectroscopic approaches. The experiments indicated that 3DG‐based electrosorption could accelerate the removal of positively and negatively charged pollutants, such as Acid Red 88, Orange II, and Methylene Blue, as well as enhance the maximum adsorption capacity toward these contaminants. The interaction mechanisms between these organic pollutants and 3DG surface were further elucidated by Dispersion corrected Density Functional Theory (DFT‐D) calculations. This 3DG‐based system offers a potentially effective method for the rapid removal of organic pollutants and provides a new sustainable approach for water and wastewater treatment. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2154–2162, 2016     

生物质碳气凝胶/MnO2复合电极对 Rb+、Cs+的电吸附行为

以柚子皮为主要原料,采用低温水热碳化-真空冷冻干燥-高温碳化相结合的方法,制备了生物质碳气凝胶（PCA）,并将其用于制备PCA单一和PCA@MnO2（MPCA）复合电吸附电极,利用SEM、XRD、FT-IR、BET及电化学工作站对电极材料的形貌、结构和电化学性质进行了表征,并考察了两种电极对Rb+、Cs+的电吸附行为。结果表明,自制PCA为三维多孔结构,利于吸附质扩散;电极比电容大,循环性能好。电极的组成对电吸附行为具有较大的影响,二氧化锰的加入改变了电极对离子的吸附选择性,MPCA［m（二氧化锰）∶m（PCA）=4∶1］复合电极对铷的吸附量明显优于铯,平衡吸附量分别可以达到85 μmol/g和64 μmol/g,优于PCA电极,且具有良好的循环再生性能。     

电吸附法处理模拟含镍废水的研究

采用电吸附法对模拟含镍废水进行处理。考察了电压、极板间距、pH值、原水的质量浓度及进水流量对Ni~(2+)去除率的影响,并在最优条件下进行循环电吸附/脱附实验。结果表明:在电压1.6V、极板间距0.8cm、pH值7.0、原水的质量浓度40mg/L及进水流量20mL/min的条件下,Ni~(2+)的去除率可以达到96.89%;经过5次电吸附循环后,Ni~(2+)的吸附性能依旧显著,Ni~(2+)的去除率保持在81.23%。     

不同模式电场增强活性炭电吸附钴(Ⅱ)的研究

自制活性炭电极,施加不同模式电场,探讨其对Co2+电增强吸附行为的影响。考察因素主要包括电压、溶液pH和离子强度。活性炭电极在阴极极化的条件下,交流伏安和方波伏安电场显著提高活性炭的吸附量,而恒电位和常规脉冲极谱无明显增强效果。溶液pH为5～7时,有利于活性炭对Co2+的电吸附。恒电位、常规脉冲极谱和恒电流电场适用于低盐溶液Co2+的吸附,而方波伏安电场适用于去除高盐溶液的Co2+。5种电场对活性炭的电脱附率均大于60%。     

TiO2改性石墨烯电极电吸附去除污水中NH4+

通过水热法制备得到TiO₂改性石墨烯复合材料（RGO/TiO₂）,考察了其形貌结构和电化学性能。将其组装成电极,对比未改性石墨烯（RGO）电极和RGO/TiO₂电极的电吸附NH₄⁺性能。重点考察外加电压、循环流速、初始浓度等工艺参数对RGO/TiO₂电极电吸附NH₄⁺的影响,并对其电吸附NH₄⁺特性和对模拟实际含NH₄⁺废水深度脱NH₄⁺效果进行研究。结果表明：RGO/TiO₂复合材料具有三维孔洞结构,比表面积为382.08 m²·g^-1,比电容量在扫速为0.01 V·s^-1时达到325.80 F·g^-1,优于RGO材料。RGO/TiO₂电极的初次电吸附量较RGO电极提升了28.3%,循环再生吸附10次后,RGO/TiO₂电极的NH₄⁺吸附量仅降低了5.87%,循环再生吸附性能优于RGO电极。外加电压2.0 V、循环流速35 ml·min^-1和NH₄⁺初始浓度1.0 mmol·L^-1为RGO/TiO₂电极的最佳NH₄⁺电吸附条件。RGO和RGO/TiO₂电极电吸附NH₄⁺过程符合准一级动力学模型和Freundlich等温吸附模型,电吸附NH₄⁺为非均匀表面的多层吸附行为,以物理吸附为主。RGO/TiO₂电极4级串联时对模拟实际含NH₄⁺炼油净化水的去除率达到86.84%。     

Electro-enhanced adsorption of As(V) by activated carbon in three-dimensional electrode reactor

This study focused on As(V) removal by electrosorption in a self-made three-dimensional electrode reactor, in which granular activated carbon (GAC) was used as the particle electrode. Under the optimal conditions, the removal efficiency of As(V) was 84%, and its residual concentration in solution was 0.08 mg/L. From kinetic investigation, the rate determining steps of the entire process may involve more than two processes: membrane diffusion, material diffusion and physical/chemical adsorption processes. During the desorption process, As(V) can be desorbed from GAC, and the GAC was able to electro-adsorb As(V) again after desorption, which means that the electrode has good cycling performance.     

Structure and Potential-Dependent Selectivity in Redox-Metallopolymers: Electrochemically Mediated Multicomponent Metal Separations

Electro-responsive functional materials can play a critical role in selective metal recovery and recycling due to the need for molecular differentiation between transition metals in complex mixtures. Redox-active metallopolymers are a promising platform for electrochemical separations, offering versatile structural tuning and fast electron transfer. First, through a judicious selection of polymer structure between a main-chain metallopolymer (polyferrocenylsilane) and a pendant-group metallopolymer (polyvinylferrocene), charge-transfer interactions and binding strength toward competing metal ions are tuned, which as a result, dictate selectivity. For example, almost an order of magnitude increase in separation factor between chromate and meta-vanadate can be achieved, depending on polymer structure. Second, these metallopolymer electrodes exhibit potential-dependent selectivity that can even flip ion preference, based solely on electrical means—indicating a control parameter that is orthogonal to structural modifications. Finally, this work presents a framework for evaluating electrochemical separations in multicomponent ion mixtures and elucidates the underlying charge-transfer mechanisms resulting in molecular selectivity through a combination of spectroscopy and electronic structure calculations. The findings demonstrate the applicability of redox-metallopolymers in tailored electrochemical separations for environmental remediation, value-added metal recovery, waste recycling, and even mining processing.     

Removal of ammonium ions in wastewater by electrosorption with TiO2 modified graphene electrode

In this study, the TiO₂ modified graphene composite material (RGO/ TiO₂) was prepared by hydrothermal method, and its morphological structure and electrochemical properties were investigated. Then RGO/TiO₂ material was assembled into electrode, and NH₄⁺ ions electrosorption efficiencies of unmodified graphene (RGO) electrode and the RGO/TiO₂ electrode were compared. The effects of applied voltage, circulating velocity and initial concentration on NH₄⁺ ions electrosorption by RGO/TiO₂ electrode were investigated. The characteristics of NH₄⁺ ions electrosorption and the effect of advanced NH₄⁺ ions removal from simulated actual wastewater containing NH₄⁺ ions were also studied. The results showed that the RGO/TiO₂ composite material had a three-dimensional pore structure with specific surface area of 382.08 m²·g^-1 and specific capacitance of 325.80 F·g^-1 at a scan rate of 0.01 V·s^-1, which were better than those of the RGO material. The initial adsorption capacity of RGO/TiO₂ electrode was 28.3% higher than that of RGO electrode. After 10 cycles of regeneration adsorption, the adsorption capacity of NH₄⁺ ions of RGO/TiO₂ electrode only decreased 5.87%, and its cyclic regeneration adsorption property was better than that of RGO electrode. In addition, the applied voltage 2.0 V, circulating velocity 35 ml·min^-1 and initial concentration 1.0 mmol·L^-1 were the optimal NH₄⁺ ions electrosorption conditions for RGO/TiO₂ electrode. The electrosorption process of NH₄⁺ ions by RGO and RGO/TiO₂ electrodes was in accordance with the quasi-first-order kinetic model and the Freundlich isothermal adsorption model. The electrosorption of NH₄⁺ ions was a multi-layer adsorption behavior on heterogeneous surface and physical adsorption was the dominant. When the RGO/TiO₂ electrode was connected in 4-stage series, the removal efficiency of simulated actual NH₄⁺ refining purified water reached 86.84%.     

The bromine electrode Part II: reaction kinetics at polycrystalline Pt

The kinetics of bromide oxidation and Br₃^– reduction were studied at polycrystalline Pt electrodes in acidic media. The electrochemical behavior of equimolar Br₃^– and Br^– solutions was investigated, in a concentration range of the electroactive species between 0.1 and 1.0 M. E–log j plots did not exhibit linear segments, most probably because of extensive adsorption of bromine radicals. Further analysis supported the hypothesis of a Volmer–Tafel mechanism, with the chemical recombination step as rate determining. Electrosorption isotherms for Br radicals were found to be of the Frumkin type. The kinetics of Br₃^– reduction was controlled by the surface dissociation of the Br₂ molecules.