Enhancement of removal efficiency of heavy metal ions by polyaniline deposition on electrospun polyacrylonitrile membranes

This paper describes the preparation of a membrane of polyacrylonitrile(PAN)and its corresponding membrane coated with polyaniline(PANI)for the adsorption of heavy metal ions.Scanning electron microscopy micrographs revealed that all the membranes exhibited nanofibrous morphology.The prepared membranes were characterized by Fourier transform infrared spectroscopy(FTIR).The prepared membranes were used as an adsorbent for hazardous heavy metal ions Pb^(2+) and Cr_(2)O^(2-)_(7).The adsorption capacity and the removal efficiency of the membranes were examined as function of the initial adsorbate concentration and pH of the medium.Coated membranes with PANI showed better adsorption performance and their direct current(DC)conductivities were correlated to heavy metal ion concentrations.Adsorption isotherms were also performed,and the adsorption process was tested according to the Langmuir and Freundlich models.The regeneration and reuse of the prepared membranes to re-adsorb heavy metal ions were also investigated.The enhancement in adsorption performance and reusability of PANI-coated membranes in comparison with non-coated ones is fully discussed.The results show that the maximum adsorption capacities of lead and chromate ions on the PANI-coated membranes are 290.12 and 1202.53 mg/g,respectively.

Ultrafiltration recovery of alginate: Membrane fouling mitigation by multivalent metal ions and properties of recycled materials

Recovery of alginate extracted from aerobic granular sludge(AGS)has given rise to a novel research direction.However,these extracted alginate solutions have a water content of nearly 100%.Alternately,ultrafiltration(UF)is generally used for concentration of polymers.Furthermore,the introduction of multivalent metal ions into alginate may provide a promising method for the development of novel nanomaterials.In this study,membrane fouling mitigation by multivalent metal ions,both individually and in combination,and properties of recycled materials were investigated for UF recovery of sodium alginate(SA).The filtration resistance showed a significantly negative correlation with the concentration of metal ions,arranged in the order of Mg^2+<Ca^2+<Fe^3+<Al^3+(filtration resistance mitigation),and the moisture content of recycled filter cake showed a marked decrease.For Ca^2+,Mg^2+,Fe^3+,and Ca^2++Fe^3+,the filtration resistances were almost the same when the total charge concentration was less than 5 mmol·L^–1.However,when the total charge concentration was greater than 5 mmol·L^–1,membrane fouling mitigation increased significantly in the presence of Ca^2+or Fe^3+and remained constant for Mg^2+with the increase of total charge concentration.The filtration resistance mitigation was arranged in the order of Fe^3+>Fe^3++Ca^2+>Ca^2+>Mg^2+.Three mechanisms were proposed in the presence of Fe^3+,such as the decrease of SA concentration,change in p H,and production of hydroxide iron colloids from hydrolysis.The properties of recycled materials(filter cake)were investigated via optical microscope observation,dynamic light scattering,Fourier transform infrared,X-ray photoelectron spectroscopy(XPS),and scanning electron microscopy.The results provide further insight into UF recoveries of alginate extracted from AGS.

Transport of yttrium metal ions through fibers supported liquid membrane solvent extraction

A novel idea of transport of yttrium(Ⅲ) metal ions through fibers supported liquid membrane in two stage processes namely source to membrane and membrane to receiving phase has been proposed.The fibers supported liquid membrane was impregnated with different concentrations carrier.The experimental variables explored were concentration of yttrium(Ⅲ) ions,pH of source phase,PC-88A concentration in membrane phase,acid concentration in receiving phase and stirring speed.The pre-concentration of yttrium(Ⅲ) ions ...

Enhanced Pervaporative Separation of Thiophene/n-Heptane Using Metal Loaded PEBAX/PAN Membranes

The mass transfer of thiophene through pervaporation（PV） membranes could be facilitated by certain transitional metal ions like Ag+, Mn2+, and Cr3+ thanks to their p complexation with thiophene. In this study, Ag+, Mn2+, and Cr3+ ions were loaded onto the polyether block amide（PEBAX）/PAN composite membranes and were tested on the performance for separation of thiophene/n-heptane mixture. Pervaporation test results showed that the pervaporative separation index increased significantly to 73.1%, 75.5%, and 97.2% at 30 oC for the Ag+-, Mn2+-, Cr3+-loaded PEBAX membranes, respectively,as compared to the pristine PEBAX/PAN composite membrane.

Transport of Indium, Gallium and Thallium Metal Ions Through Chromatographic Fiber Supported Solid Membrane in Acetylacetone Containing Mixed Solvents

The transport of metal ions of indium, gallium and thallium from source solution to receiving phase through the chromatographic fiber supported solid membrane in the acetylacetone （HAA） containing mixed solvent system has been explored. The fibers supported solid membranes were prepared with chemical synthesis from cellulose fibers and citric acid with the carboxylic acid ion exchange groups introduced. The experimental variables, such as concentration of metal ions （10^-2 to 10^-4 mol.L^-1） in the source solution, mixed solvent composition [for exampl, e, acetylacetone, （2,4-pentanedione）, （HAA） 20% （by volume）, 1,4-dioxane 10% to 60% and HC1 0.25 to 2 mol.L^-1] in the receiving phase and stirring speed （50-130 r.min ） of the bulk source and receiving phase, were explored. The efficiency of mixed solvents for the transport of metal ions from the source to receiving phase through the fiber supported solid membrane was evaluated. The combined ion exchange solvent extraction （CIESE） was observed effective for the selective transport of thallium, indium and gallium metal ions through fiber supported solid membrane in mixed solvents. The oxonium salt formation in the receiving phase enhances thallium, indium and gallium metal ion transport through solid membrane phase. The selective transport of thallium metal ions from source phase was observed from indium and gallium metal ions in the presence of hydrochloric acid in organic solvents in receiving phase. The separation of thallium metal ions from the binary mixtures of Be（II）, Ti（IV）, AI（III） Ca（II）, Mg（II）, K （I）, La（III） and Y（III） was carried out in the mixed solvent system using cellulose fiber supported solid membrane.

Measurement of free heavy metal ion concentrations in soils using Donnan membrane technique

In natural systems heavy metals are present in very low concentrations (less than micro-molar), so precise measurement of the free metal ions is difficult. Recently, a new method has been developed called the Donnan membrane technique (DMT). Several heavy metals could be measured simultaneously using this method. Furthermore, all the metals did not interfere with each other, and the balance between the measured system and the surrounding condition could not be disturbed. Improvements were made according to the internal condition. The free heavy metal ion concentrations were measured in different systems using the improved method, and satisfied results have been obtained.

Gas permeation properties of a metallic ion-cross-linked PIM-1 thin-film composite membrane supported on a UV-cross-linked porous substrate

Metallic ion-cross-linked polymer of intrinsic microporosity(PIM-1) thin-film composite(TFC) membranes supported on an ultraviolet(UV)-cross-linked porous substrate were fabricated. The UV-cross-linked porous substrate was prepared via polymerization-induced phase separation. The PIM-1 TFC membranes were fabricated via a dip-coating procedure. Metallic ion-cross-linked PIM-1 TFC membranes were fabricated by hydrolyzing the PIM-1 TFC membrane in an alkali solution and then cross-linking it in a multivalent metallic ion solution. The pore size and porous structures were evaluated by low-temperature N_2 adsorption–desorption analysis. The membrane structure was investigated by field-emission scanning electron microscopy. The effects of heat treatment and pore-forming additives on the gas permeance of the UV-cross-linked porous substrate are reported. The effects of different pre-coating treatments on the gas permeance of the metallic ion-cross-linked PIM-1 TFC membrane are also discussed. The metallic ion-crosslinked PIM-1 TFC membrane displayed high CO_2/N_2 selectivity(23) and good CO_2 permeance(1058 GPU).

Engineering Leaf-Like UiO-66-SO3H Membranes for Selective Transport of Cations

Metal–organic frameworks(MOFs)with angstrom-sized pores are promising functional nanomaterials for the fabrication of cation permselective membranes(MOF-CPMs).However,only a few research reports show successful preparation of the MOF-CPMs with good cation separation performance due to several inherent problems in MOFs,such as arduous selfassembly,poor water resistance,and tedious fabrication strategies.Besides,low cation permeation flux due to the absence of the cation permeation assisting functionalities in MOFs is another big issue,which limits their widespread use in membrane technology.Therefore,it is necessary to fabricate functional MOF-CPMs using simplistic strategies to improve cation permeation.In this context,we report a facile in situ smart growth strategy to successfully produce ultrathin(<600 nm)and leaflike UiO-66-SO3H membranes at the surface of anodic alumina oxide.The physicochemical characterizations confirm that sulfonated angstrom-sized ion transport channels exist in the as-prepared UiO-66-SO3H membranes,which accelerate the cation permeation(~3×faster than non-functionalized UiO-66 membrane)and achieve a high ion selectivity(Na^+/Mg^2+>140).The outstanding cation separation performance validates the importance of introducing sulfonic acid groups in MOF-CPMs.

Reconstructing proton channels via Zr-MOFs realizes highly ion-selective and proton-conductive SPEEK-based hybrid membrane for vanadium flow battery

There is an urgent need to break through the trade-off between proton conductivity and ion selectivity of proton exchange membrane(PEM)in vanadium flow battery(VFB).Proton channels in PEM are the key to controlling the ion sieving and proton conductivity in VFB.Herein,two types of proton channels are reconstructed in the hybrid membrane via introducing modified Zr-MOFs(IM-UIO-66-AS)into SPEEK matrix.Internal proton channels in IM-UIO-66-AS and interfacial proton channels between grafted imidazole groups on Zr-MOFs and SPEEK greatly improve the conductivity of the IM-UIO-66-AS/SPEEK hybrid membrane.More importantly,both reconstructed proton channels block the vanadium-ion permeation to realize enhanced ion selectivity according to the size sieving and Donnan exclusion effects,respectively.Moreover,the hybrid membrane exhibits good mechanical property and dimensional stability.Benefiting from such rational design,a VFB loading with the optimized membrane exhibits enhanced voltage efficiency of 79.9%and outstanding energy efficiency of 79.6%at 200 m A cm^(-2),and keeps a notable cycle stability for 300 cycles in the long-term cycling test.Therefore,this study provides inspiration for preparing next-generation PEMs with high ion selectivity and proton conductivity for VFB application.

Chemodynamics of heavy metals in long-term contaminated soils:Metal speciation in soil solution

The concentration and speciation of heavy metals in soil solution isolated from long-term contaminated soils were investigated. The soil solution was extracted at 70% maximum water holding capacity （MWHC） after equilibration for 24 h. The free metal concentrations （Cd^2＋, Cu^2＋, Pb^2＋, and Zn^2＋） in soil solution were determined using the Donnan membrane technique （DMT）. Initially the DMT was validated using artificial solutions where the percentage of free metal ions were significantly correlated with the percentages predicted using MINTEQA2. However, there was a significant difference between the absolute free ion concentrations predicted by MINTEQA2 and the values determined by the DMT. This was due to the significant metal adsorption onto the cation exchange membrane used in the DMT with 20%, 28%, 44%, and 8% mass loss of the initial total concentration of Cd, Cu, Pb, and Zn in solution, respectively. This could result in a significant error in the determination of free metal ions when using DMT if no allowance for membrane cation adsorption was made. Relative to the total soluble metal concentrations the amounts of free Cd^2＋ （3%-52%） and Zn^2＋ （11%-72%） in soil solutions were generally higher than those of Cu^2＋ （0.2%-30%） and Pb^2＋ （0.6%-10%）. Among the key soil solution properties, dissolved heavy metal concentrations were the most significant factor governing free metal ion concentrations. Soil solution pH showed only a weak relationship with free metal ion partitioning coefficients （Kp） and dissolved organic carbon did not show any significant influence on Kp.

多离子印迹膜的制备及其吸附性能研究

以Zn^(2+)、Co^(2+)、Cr^(3+)和Pb^(2+)为混合模板,双硫腙为螯合剂,APTES为功能单体,TEOS为交联剂,PVDF为基膜,采用凝胶溶胶法成功合成了对模板离子有高吸附量和良好特异性识别能力的多离子印迹膜(MIIM)。采用SEM对材料的形貌进行了表征,并以多离子印迹聚合物(MIIP)为对比评价了MIIM的吸附性能。结果表明,MIIM对Zn^(2+)、Co^(2+)、Cr^(3+)和Pb^(2+)的吸附量分别是MIIP的1.71、1.43、1.60和9.03倍,最大吸附量分别为21.32、11.21、12.72和25.97 mg·g^(-1)。在竞争离子(Cu^(2+)、Ni^(2+)、Fe^(2+))存在的情况下具有良好的吸附选择性,MIIM的4种模板离子对Ni^(2+)和Fe^(2+)的特异性因子(SP)值在4.86~8.34之间,对Cu^(2+)的SP值在3.58~3.92之间。同时,MIIM可以多次再生,而不会明显降低吸附能力,在废水处理和样品前处理领域具有很好的应用前景。

MOFs膜在离子分离中的应用研究进展

金属有机框架(MOFs)材料在膜技术领域受到的关注日益增长,其规则且高度可调的亚纳米尺寸孔道结构、高孔隙率以及官能化修饰的灵活性,使MOFs膜在精细化离子筛分方面表现出良好的应用潜力。近年来,离子在MOFs多晶膜、MOFs混合基质膜和MOFs通道膜体系内的选择性传输行为相继被报道,基于MOFs材料的结构-性能关系,通过可控设计以优化膜的选择性和稳定性取得了诸多进展。系统地梳理了上述MOFs膜的制备、离子选择性分离机理和优化思路,对比分析了其各自的特点和实际应用面临的挑战,基于此,提出MOFs膜在离子分离领域的潜在发展方向。

PES/改性UiO⁃66复合膜的制备及其重金属离子分离性能研究

制备了锆1,4⁃羧基苯(UiO⁃66)系列金属有机骨架(MOF)材料,对比了不同MOF材料对重金属离子的吸附性能,并制备了聚醚砜/聚醚酰亚胺/改性MOF(PES/PEI/MOF)复合膜,对比了MOF添加量对膜重金属离子吸附和渗透性能的影响。结果表明,在UiO⁃66系列MOF材料中,UiO⁃66⁃NH2对重金属离子的吸附性能最好;在其负载量为15%(质量分数,下同)时,复合膜对重金属离子的截留性能最好。

MOF/COF膜在重金属分离和脱盐领域的研究进展

特定结构的金属/共价有机框架(MOF/COF)及其高效渗透性在分离和脱盐领域引起广泛关注。目前纳米材料与化学结构的研究,促进了具有独特原子厚度、有效支撑和优异机械性能的MOF/COF膜的发展。文章介绍了MOF基膜和COF基膜的设计策略、性能和在环境领域的应用,特别是膜在去除重金属离子和海水淡化领域应用。同时提出了MOF膜和COF膜及膜分离技术在未来发展中遇到的机遇和挑战,为膜材料的合理设计和应用研究提供了未来的方向。

金属离子-腐殖酸对超滤膜污染的研究进展

膜污染是限制超滤技术在饮用水生产方面大规模应用的一大障碍。以腐殖酸(Humic Acid,HA)为代表的大分子天然有机物吸附或沉积在膜表面是引起超滤膜污染的主要原因之一。广泛存在于水环境中的金属离子几乎不会造成膜污染,但金属离子会通过电荷屏蔽、电荷中和、络合和架桥等作用对超滤膜HA产生影响,引起有机、无机以及复合膜污染问题。本文参考国内外研究成果,系统分析了一价(Na^(+)、K^(+))、二价(Ca^(2+)、Mg^(2+))和三价(Fe^(3+)、Al^(3+))金属离子对超滤膜HA污染的影响机理,为缓解HA引起的超滤膜污染问题提供了新的见解。

面向一/二价离子分离的金属有机骨架膜研究进展

膜分离技术因操作简单、效率高、环境友好等特点,被誉为最具发展潜力的分离技术之一。金属有机骨架是一种新兴的分离膜材料,其可调变的孔道微结构、高孔隙率、拓扑结构多样性,使其在一/二价离子分离方面具有良好潜力。回顾了近二十年金属有机骨架膜在一/二价离子分离的研究进展并深入探讨了其传递机理,此外,也系统总结了金属有机骨架膜的制备方法,探讨了金属有机骨架膜在一/二价离子分离领域面临的挑战及未来研究方向。

MOF膜对金属离子的去除性能及机理研究进展

金属有机骨架材料(Metal organic frameworks,MOFs)具备高渗透性、高选择性、孔径可调及拓扑结构等特点,在金属离子的吸附、还原方面展现出极大优势,因此被广泛应用于MOF膜合成.本文综述了MOF膜的合成方法及其对金属离子的去除性能,重点探讨了MOF负载量、温度、pH值、膜通量及膜孔径等因素对MOF膜去除金属离子的影响,在此基础上归纳了MOF膜对金属离子的吸附和过滤机理,并对MOF膜在金属离子去除方面的应用前景进行了展望,以期为MOF膜的工程化应用提供参考.

AOPAN/PU复合膜的制备及其金属离子吸附性能研究

采用聚乙烯吡咯烷酮(PVP)和聚乙二醇(PEG)对聚丙烯腈/聚氨酯(PAN/PU)涂层微孔进行调控。通过扫描电镜分析和水通量截留率测试发现,PVP含量为6%、PEG含量为4%时,平板膜涂层性能最佳。以无纺布作为基底,采用浸轧涂覆的方法将最优参数的铸膜液涂覆在无纺布上,通过化学改性制备胺肟化聚丙烯腈/聚氨酯(AOPAN/PU)复合膜,探究复合膜通量变化和金属离子截留性能。研究表明,改性后制备的AOPAN/PU熔喷复合膜水通量由349L/(m^(2)·h)增长到435L/(m^(2)·h),在对100mg/L的Cu^(2+)、Fe^(3+)、Zn^(2+)混合金属溶液3次吸附循环测试后发现,最终滤液中金属离子截留率均在90%以上。

聚四氟乙烯膜的亲水改性及其性能研究

采用紫外光固化技术将2-羟乙基甲基丙烯酸酯磷酸酯(HEMAP)负载于聚四氟乙烯(PTFE)膜表面,进而制备得到亲水的PTFE膜。研究结果表明,随着HEMAP用量的增加,PTFE膜的亲水性提高,表面润湿性越好。纯水通量测试表明,随着HEMAP用量的增加,纯水通量增加,当HEMAP用量继续增加,PTFE膜中纤维间的空隙被HEMAP填充,纯水通量反而下降。此外,HEMAP亲水改性的PTFE膜在弱酸环境下可吸附Fe(Ⅲ)离子。研究结果可为PTFE膜的亲水改性及其在酸性环境下对重金属离子的吸附规律提供一定的参考。

金属-有机骨架离子凝胶膜的制备及其在C_(3)H_(6)/C_(3)H_(8)分离中的应用

通过调节反应时间合成出3种不同颗粒大小金属-有机骨架(ZIF-8),并将其与离子液体1-丙基-3-甲基咪唑双三氟甲磺酰亚胺盐(PmimTf_(2)N)和聚醚共聚酰胺(Pebax 1657)混合制得ZIF-8/IL/Pebax离子凝胶膜,用于对丙烯/丙烷混气体系的分离.通过ZIF-8颗粒与离子液体在Pebax膜中的协同作用,实现了金属-有机骨架(MOF)填料在聚合物基质中高达70%的质量掺杂量,C_(3)H_(6)/C_(3)H_(8)体系的气体分离性能也得到明显提升.研究表明,ZIF-8/IL/Pebax离子凝胶膜相比于Pebax纯膜,C_(3)H_(6)渗透通量提高了385%,达到了227.1 Barrer;同时,C_(3)H_(6)/C_(3)H_(8)的选择性也从3.04提高到了25.11.此外,在不同温度和压力条件下(10~40℃,0.15~0.3 MPa),ZIF-8/IL/Pebax离子凝胶膜均表现出优异的气体分离性能,并表现出了良好的应用前景.