Investigation of amphoteric polybenzimidazole (PBI) nanofiltration hollow fiber membrane for both cation and anions removal

The removal of both anions (phosphate, arsenate, arsenite and borate ions) and cations (copper ions) has been investigated by employing a lab-developed amphoteric polybenzimidazole (PBI) nanofiltration (NF) hollow fiber membrane. The amphoteric characteristics are due to the imidazole group within PBI molecules that makes the PBI NF membrane have an isoelectric point near pH 7.0 and show different charge signs based on the media pH. Investigations on the rejection capability of typical anions, e.g. phosphate, arsenate, arsenite, borate anions and typical heavy metal cations, e.g. copper ions, reveal that the PBI NF membrane exhibits impressive rejection performance for various ions removal. However, their rejections are strongly dependent on the chemical nature of electrolytes, solution pHs and the feed concentrations. The experimental results are analyzed by using the Spiegler–Kedem model with the transport parameters of the reflection coefficient (σ) and the solute permeability (P). The PBI NF membrane may have potential to be used in industrial removal of various environmentally unfriendly ion species.     

Recent progress in functionalized layered double hydroxides and their application in efficient electrocatalytic water oxidation

Layered double hydroxides(LDHs), a class of anionic clays consisting of brucite-like host layers and interlayer anions, have been widely investigated in the last decade due to their promising applications in many areas such as catalysis, ion separation and adsorption. Owing to the highly tunable composition and uniform distribution of metal cations in the brucite-like layers, as well as the facile exchangeability of intercalated anions, LDHs can be modified and functionalized to form various nanostructures/composites through versatile processes such as anion intercalation and exfoliation, decoration of nanoparticles, selfassembly with other two-dimensional(2D) materials, and controlled growth on conductive supports(e.g.,nanowire arrays, nanotubes, 3D foams). In this article, we briefly review the recent advances on both the LDH nanostructures and functionalized composites toward the applications in energy conversion, especially for water oxidation.     

Effect of various factors influencing the delamination behavior of surfactant intercalated layered double hydroxides

The delamination-restacking behavior of a number of layered double hydroxides (LDHs) differing in [M(II)]/[M(III)] ratio, constituent metal ions and intercalated surfactant anions in different organic solvents has been studied. Colloidal dispersion due to delamination and the stability of the colloid obtained have been found to be not affected much by the nature of the constituent metal ions but increase with increase in the size of the surfactant anion. LDHs with low [M(II)]/[M(III)] ratio delaminate better than the ones with high [M(II)]/[M(III)] ratio. Delamination is best in alcohols such as 1-butanol, 1-hexanol, 1-octanol and 1-decanol, while a little delamination occurs in nonpolar solvents such as hexane. In all the cases, the original layered solid could be obtained through restacking of layers from the colloidal dispersion.     

阴离子层状材料的可控制备

LDHs (layered double hydroxides)是一类具有相同结构、不同物理化学性质的阴离子层状无机功能材料,作为催化剂、催化剂载体和催化剂前驱体在催化领域得到了广泛的关注. 本文综述了LDHs制备技术的最新发展,并从粒径控制、结晶度控制、形貌控制、含贵金属LDHs以及原位固载化等方面详细讨论了LDHs的可控制备技术.     

A Prospect for Environmental Remediation of Perchlorate via Cost-Effective Pinus Leaves and Dandelion Flower Powder-based Layer Double Hydride (LDH) Sorbents

In this study, pine leaves powder (PiP) and dandelion flower powder (DFP) were repurposed to synthesize layered double hydroxides (LDHs) to form a base for sorbents used in perchlorate remediation from wastewater. The effects of the adsorbent dose, pH, thermodynamics, and coexisting ions were evaluated in batch experiments. The results revealed that 0.1 g adsorbent (PiP-LDH and DFP-LDH) removed 97% and 93% of perchlorate contaminants, respectively. In this study, the correlation coefficient of pseudo-second-order was higher than pseudo-first-order for all the LDHs. The kinetic and isotherm studies showed the best uptake of perchlorate in the short time was by PiP-LDH, followed by DFP-LDH (20 min and 40 min, respectively). The calculated and experimental values of adsorption at the equilibrium state also concurred with the pseudo-second-order model. The prepared LDHs were mesoporous. The surface area of PiP-LDH provided more adsorption sites, rendering it more suitable for perchlorate adsorption compared with the other two LDHs. The model suggests Physico-chemical interactions behind the sorption of perchlorate by LDHs. The adsorption was more influenced by anions i.e, PO₄³⁻ > SO₄²⁻ > NO₃ than monovalent anions due to the increase in the charge radius values. The prepared LDHs could be of great benefit to the environmental remediation of wastewater bodies.     

Layered-double-hydroxide-modified electrodes: electroanalytical applications

Two-dimensional inorganic solids, such as layered double hydroxides (LDHs), also defined as anionic clays, have open structures and unique anion-exchange properties which make them very appropriate materials for the immobilization of anions and biomolecules that often bear an overall negative charge. This review aims to describe the important aspects and new developments of electrochemical sensors and biosensors based on LDHs, evidencing the research from our own laboratory and other groups. It is intended to provide an overview of the various types of chemically modified electrodes that have been developed with these 2D layered materials, along with the significant advances made over the last several years. In particular, we report the main methods used for the deposition of LDH films on different substrates, the conductive properties of these materials, the possibility to use them in the development of membranes for potentiometric anion analysis, the early analytical applications of chemically modified electrodes based on the ability of LDHs to preconcentrate redox-active anions and finally the most recent applications exploiting their electrocatalytic properties. Another promising application field of LDHs, when they are employed as host structures for enzymes, is biosensing, which is described considering glucose as an example.

Solar light assisted degradation of dyes and adsorption of heavy metal ions from water by CuO–ZnO tetrapodal hybrid nanocomposite

We report a facile and economic hydrothermal process for multifunctionally engineered copper oxide/zinc oxide-tetrapods (CuO/ZnO-T) nanocomposite for wastewater treatment. The resultant CuO/ZnO-T nanocomposite possesses high porosity, large surface area, and low band gap. All these properties are advantageous for photocatalyst and adsorbent for dyes and heavy metal ions removal. The morphology of synthesized nanocomposite was characterized using X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller, Fourier-transform infrared spectroscopy, and UV–Visible absorption spectroscopy. The results confirmed the attachment of CuO on the ZnO-T surface, forming a hybrid nanocomposite. The concentration of heavy metal ions was monitored using the atomic absorption spectroscopy technique. The synthesized CuO/ZnO-T nanocomposite was investigated for the decontamination of anionic and cationic dyes, Reactive yellow-145 (RY-145) and Basic violet-3 (BV-3) and heavy metal ions (Chromium (VI) and Lead (II)). The CuO/ZnO-T nanocomposite exhibited superior photocatalytic efficiency (80% RY-145 dye removal and 86% BV-3 dye removal) and adsorption capacity (99% Chromium (VI) removal and 97% Lead (II) removal) as compared to pristine ZnO-T. The mechanism for the reduction of dyes and heavy metal ions was discussed by different kinetics and isotherm models. The current study inferred that CuO/ZnO-T nanocomposite is a potential candidate as a proficient photocatalyst/adsorbent for the removal of various wastewater contaminants.     

Adsorption of Cr(VI) and Se(IV) from their aqueous solutions onto Zr4+-substituted ZnAl/MgAl-layered double hydroxides: effect of Zr4+ substitution in the layer

Hydrotalcite-like compounds (layered double hydroxides, LDHs) containing varying amounts of Al(3+), Zr(4+), and Zn(2+) or Mg(2+) in the metal hydroxide layer have been synthesized and characterized by various physicochemical methods. The adsorption behavior of uncalcined (as-synthesized) and calcined LDHs have been investigated for Cr(2)O(7)(2-) and SeO(3)(2-). The mixed oxides, obtained on calcination at 450 degrees C, exhibit high adsorption capacities for Cr(2)O(7)(2-) (1.6-2.7 meq/g) and SeO(3)(2-) (1.1-1.5 meq/g), where adsorption occurs through rehydration. Substitution of Zr(4+) in the LDHs, for either M(2+) or Al(3+) ions, increases the adsorption capacity up to 20%, thus providing an alternative way to enhance the adsorption capacity of this type of material. The high adsorption capacity of these materials could be successfully used for removal of undesirable anions from water and also for synthesis of intercalated materials with tailored acidobasicity.     

Synthesis of Nordstrandite and Nordstrandite-Derived Layered Double Hydroxides of Li and Al: A Comparative Study with the Bayerite Counterpart

The layered double hydroxides (LDHs) of Li and Al can be synthesized from the four polymorphs of Al(OH)₃, namely gibbsite, bayerite, nordstrandite, and doyleite. The crystal structure of this class of compounds depends on the type of the precursor used due to their topotactic reaction mechanism. While the LDHs derived from gibbsite and bayerite yield different crystal structures, the incorporation of Li into nordstrandite was expected to yield new LDH structures different from those derived from gibbsite and bayerite. The structure of nordstrandite derived LDHs were however identical to that derived from the bayerite counterpart. The absence of symmetry in the interlayer of nordstrandite (C₁) makes it unsuitable to accommodate the intercalating anions with different molecular symmetries. To make the interlayer gallery suitable for the anions, the metal hydroxide layers of the nordstrandite translate, transforming nordstrandite to bayerite. The bayerite with site symmetries O_h and C₂ stabilizes the anions in the interlayer by hydrogen bonding. The transformation of nordstrandite to bayerite, when soaked in lithium salt solution is, therefore, a manifestation of the intercalating anions.     

金属有机框架材料对Cr(Ⅵ)离子的吸附去除研究进展

重金属离子污染问题一直备受关注.开发利用多孔材料吸附去除水中重金属离子一直是材料、环境等相关学科领域的研究热点之一.金属有机框架材料(metal-organic frameworks,MOFs)是一类新型的多孔材料,具有结构多样、比表面积大、孔径可调、孔表面特征易设计调控等特点,在气体分离、催化、传感等领域表现出极大的...     

Electrostatic charging due to separation of ions at interfaces: contact electrification of ionic electrets

This Review discusses ionic electrets: their preparation, their mechanisms of formation, tools for their characterization, and their applications. An electret is a material that has a permanent, macroscopic electric field at its surface; this field can arise from a net orientation of polar groups in the material, or from a net, macroscopic electrostatic charge on the material. An ionic electret is a material that has a net electrostatic charge due to a difference in the number of cationic and anionic charges in the material. Any material that has ions at its surface, or accessible in its interior, has the potential to become an ionic electret. When such a material is brought into contact with some other material, ions can transfer between them. If the anions and cations have different propensities to transfer, the unequal transfer of these ions can result in a net transfer of charge between the two materials. This Review focuses on the experimental evidence and theoretical models for the formation of ionic electrets through this ion-transfer mechanism, and proposes--as a still-unproved hypothesis--that this ion-transfer mechanism may also explain the ubiquitous contact electrification ("static electricity") of materials, such as organic polymers, that do not explicitly have ions at their surface.     

Gas-phase anionic complexes of alkali metal ions and peptides: Structure and collision activated decompositions

Alkali metal ions and anionic peptides can be desorbed into the gas phase to give metal-bound peptides and bis(peptide) complexes bearing a ? 1 charge. Although amide nitrogens of peptide bonds are deprotonated in the gas phase by alkali metal ions, this reacion does not occur in solution. Metal-bound dipeptide anions exist as a single structure, whereas those of tripeptide complexes have three structures as revealed by tandem mass spectrometric studies. Ions of bis(peptide) complexes of alkali metals decompose upon collisional activation principally to form deprotonated peptides, in contrast to bis(peptide) complexes of alkaline earth metal ions, which undergo elimination of a neutral peptide.     

纳米零价铁去除水中重金属离子的研究进展

重金属离子危害严重.本文综述了近几年纳米零价铁去除水中重金属离子的研究,总结了纳米零价铁去除水中重金属离子的机理,主要包括:纳米零价铁的表面吸附-配合、还原、吸附-还原,并对纳米零价铁在这一领域的应用进行了展望.     

Gas-phase ion/ion reactions of multiply protonated polypeptides with metal containing anions

Gas-phase reactions of multiply protonated polypeptides and metal containing anions represent a new methodology for manipulating the cationizing agent composition of polypeptides. This approach affords greater flexibility in forming metal containing ions than commonly used methods, such as electrospray ionization of a metal salt/peptide mixture and matrix-assisted laser desorption. Here, the effects of properties of the polypeptide and anionic reactant on the nature of the reaction products are investigated. For a given metal, the identity of the ligand in the metal containing anion is the dominant factor in determining product distributions. For a given polypeptide ion, the difference between the metal ion affinity and the proton affinity of the negatively charged ligand in the anionic reactant is of predictive value in anticipating the relative contributions of proton transfer and metal ion transfer. Furthermore, the binding strength of the ligand anion to charge sites in the polypeptide correlates with the extent of observed cluster ion formation. Polypeptide composition, sequence, and charge state can also play a notable role in determining the distribution of products. In addition to their usefulness in gas-phase ion synthesis strategies, the reactions of protonated polypeptides and metal containing anions represent an example of a gas-phase ion/ion reaction that is sensitive to polypeptide structure. These observations are noteworthy in that they allude to the possibility of obtaining information, without requiring fragmentation of the peptide backbone, about ion structure as well as the relative ion affinities associated with the reactants.     

Chalcogels: porous metal-chalcogenide networks from main-group metal ions. Effect of surface polarizability on selectivity in gas separation

We report the synthesis of metal-chalcogenide gels and aerogels from anionic chalcogenide clusters and linking metal ions. Metal ions such as Sb(3+) and Sn(2+), respectively chelated with tartrate and acetate ligands, react in solution with the chalcogenide clusters to form extended polymeric networks that exhibit gelation phenomena. Chalcogenide cluster anions with different charge densities, such as [Sn(2)S(6)](4-) and [SnS(4)](4-), were employed. In situ rheological measurements during gelation showed that a higher charge density on the chalcogenide cluster favors formation of a rigid gel network. Aerogels obtained from the gels after supercritical drying have BET surface areas from 114 to 368 m(2)/g. Electron microscopy images coupled with nitrogen adsorption measurements showed the pores are micro (below 2 nm), meso (2-50 nm), and macro (above 50 nm) regions. These chalcogels possess band gaps in the range of 1.00-2.00 eV and selectively adsorb polarizable gases. A 2-fold increase in selectivity toward CO(2)/C(2)H(6) over H(2) was observed for the Pt/Sb/Ge(4)Se(10)-containing aerogel compared to aerogel containing Pt(2)Ge(4)S(10). The experimental results suggest that high selectivity in gas adsorption is achievable with high-surface-area chalcogenide materials containing heavy polarizable elements.     

Complexation ion chromatography —an overview of developments and trends in trace metal analysis

Complexation ion chromatography (IC), including all ion chromatographic modes in which complexation is exploited for the separation and detection of metal ions in different ways, is now a widely accepted method of trace metal analysis. Some of the significant advances in the theoretical aspects and practical applications of complexation IC modifications (non-suppressed cation chromatography with complex- forming mobile phases, coordination chromatography with chelate-forming bonded phases, ion-exchange and ion-pair chromatography of anionic metal chelates) recently developed in the authors' laboratories are reviewed. The retention behaviour and separation mechanism of non-complexed and completed metal analytes are discussed from the point of view of basic coordination chemistry (stability of metal complexes, effective charge of metal atom, ligand completing ability, etc.). Comparisons and contrasts between various metal complexation IC techniques and their common features and advantages relative to other methods used in analyses for transition and heavy metal ions are evaluated.     

层状复合金属氢氧化物：结构、性质及其应用

本文评述层状复合金属氢氧化物(layered double hydroxides，LDHs)的化学及其应用。层状复合金属氢氧化物具有结合紧密的氢氧化物层和处于层间的阴离子，其比较突出的化学性质是可逆的阴离子交换和热分解性质。不过，因为受到氢氧化物层的局限，处于层间的阴离子表现出的特殊化学性质近年来也越来越受到重视。利用上述三个方面的性质，人们发掘了层状复合金属氢氧化物在材料(包括有机无机复合材料)制备、离子交换与有害阴离子脱除、异构体化学分离、化学反应控制、阻燃材料、活性分子储存与缓释、局部化学反应合成、催化剂及催化剂载体等方面的应用。     

Effect of Different Counterions of the Manganese Salt as Catalyst on the Kinetics of Resorcinol‐Based Belousov–Zhabotinsky Reaction

Kinetic studies on the Belousov–Zhabotinsky (BZ) system with various metal ions as catalysts have been carried out for a long time, but the effect of counteranions associated with the metal ion solution used as the catalyst in the BZ reaction has not been explored. Thus, we have chosen some metal salts as catalysts having the metal ion (Mnⁿ⁺) but with various anions to study the role of different anionic moieties of catalyst on the oscillatory behavior of the resorcinol‐based BZ reaction system. It is found that organic‐type anionic moieties marginalize the role of organic substrates in the reaction system. On the other hand, the inorganic counterions of the catalyst show salting out effects, thereby increasing the ionic strength, which affects the mobility (diffusion) of the ions in our system performed under batch conditions.     

Study of a heavy metal biosorption onto raw and chemically modified Sargassum sp. via spectroscopic and modeling analysis

In this study, raw and formaldehyde-modified Sargassum sp. are used for heavy metal removal. A series of experiments shows that the chemical modification by formaldehyde improves biosorption capacity by approximately 20%. Solution pH plays an important role in the metal uptake. According to X-ray photoelectron spectroscopic and Fourier transform infrared spectroscopic analysis, the possible organic functional groups in the metal binding include carboxyl, ether, alcoholic, hydroxyl, and amino functional groups. A new model that includes a series of coordination reactions among a generalized functional group, alkaline earth metal ions and heavy metal ions, is developed for simulation of biosorption process. The model well describes the single- and multiple-species metal biosorption process under different conditions such as pH. The biosorption of heavy metals is due to the ion exchange between the heavy metals and alkaline earth metals and their adsorption onto the free sites of the seaweeds. Slightly more than half of the metal uptake is due to ion exchange. The metal affinity for the functional groups follows a descending order of lead > copper > alkaline earth metal.     

投影寻踪和神经网络方法研究金属离子水解规律

对金属离子水解常数pK1的线性模型的局限性进行了讨论,并采用投影寻踪技术对pK1数据结构进行研究。非线性建模可能是更适宜的方法。采用函数连接型神经网络(FLN),以金属离子的电荷、半径、价电子结构、电负性及空价轨道数等作为描述变量,对60种金属离子水解常数pK1数据进行建模,获得了满意的结果,并对10种金属离子的pK1作出了预测。