Alkali-treated straw and insoluble straw xanthate as low cost adsorbents for heavy metal removal – preparation,characterization and application

Heavy metal removal using alkali-treated straw (ATS) and insoluble straw xanthate (ISX) is reported. Insoluble straw xanthate consisting of 4.1% total sulfur is also applied for the removal of various metal ions simultaneously. Potentiometric data of alkali-treated straw and xanthated straw indicated polyfunctionality of these materials. Diffuse Reflectance IR (DRIFT) spectra of ISX exhibited peaks characteristic of xanthate groups on straw. Removal of Cr³⁺ from aqueous solutions using ATS and ISX followed the Langmuir adsorption model and both the materials have shown significant chromium removal efficiencies (>80%). In the case of chromate and dichromate, pore adsorption preceded the surface adsorption. Detailed spectroscopic (DRIFT & EPR) and sodium release studies conducted using ISX suggest that Cr³⁺ is removed through the adsorption-exchange mechanism involving alkoxide or xanthate groups. Xanthate groups bind Cr³⁺ aqua complex through unidentate monosulfur chelation.     

A metal‐chelate affinity reverse micellar system for protein extraction

A new nonionic reverse micellar system is developed by blending two nonionic surfactants, Triton X‐45 and Span 80. At total surfactant concentrations lower than 60 mmol/L and molar fractions of Triton X‐45 less than 0.6, thermodynamically stable reverse micelles of water content (W₀) up to 30 are formed. Di(2‐ethylhexyl) phosphoric acid (HDEHP; 1–2 mmol/L) is introduced into the system for chelating transition metal ions that have binding affinity for histidine‐rich proteins. HDEHP exists in a dimeric form in organic solvents and a dimer associated with one transition metal ion, including copper, zinc, and nickel. The copper‐chelate reverse micelles (Cu‐RM) are characterized for their W₀, hydrodynamic radius (R_h), and aggregation number (N_ag). Similar with reverse micelles of bis‐2‐ethylhexyl sodium sulfosuccinate (AOT), R_h of the Cu‐RM is also linearly related to W₀. However, N_ag is determined to be 30–90 at W₀ of 5–30, only quarter to half of the AOT reverse micelles. Then, selective metal‐chelate extraction of histidine‐rich protein (myoglobin) by the Cu‐RM is successfully performed with pure and mixed protein systems (myoglobin and lysozyme). The solubilized protein can be recovered by stripping with imidazole or ethylinediaminetetraacetic acid (EDTA) solution. Because various transition metal ions can be chelated to the reverse micelles, it is convinced that the system would be useful for application in protein purification as well as simultaneous isolation and refolding of recombinant histidine‐tagged proteins expressed as inclusion bodies. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

Comparison of the Heavy Metal Biosorption Capacity of Active,Heat‐Inactivated and NaOH‐Treated Phanerochaete chrysosporium Biosorbents

Three different kinds of Phanerochaete chrysosporium (NaOH‐treated, heat‐inactivated and active) biosorbent were used for the removal of Cd(II) and Hg(II) ions from aquatic systems. The biosorption of Cd(II) and Hg(II) ions on three different forms of Phanerochaete chrysosporium was studied in aqueous solutions in the concentration range of 50–700 mg/L. Maximum biosorption capacities of NaOH‐treated, heat‐inactivated and active Phanerochaete chrysosporium biomass were found to be 148.37 mg/g, 78.68 mg/g and 68.56 mg/g for Cd(II) as well as 224.67 mg/g, 122.37 mg/g and 88.26 mg/g for Hg(II), respectively. For Cd(II) and Hg(II) ions, the order of affinity of the biosorbents was arranged as NaOH‐treated > heat‐inactivated > active. The order of the amount of metal ions adsorbed was established as Hg(II) > Cd(II) on a weight basis, and as Cd(II) > Hg(II) on a molar basis. Biosorption equilibriums were established in about 60 min. The effect of the pH was also investigated, and maximum rates of biosorption of metal ions on the three different forms of Phanerochaete chrysosporium were observed at pH 6.0. The reusability experiments and synthetic wastewater studies were carried out with the most effective form, i.e., the NaOH‐treated Phanerochaete chrysosporium biomass. It was observed that the biosorbent could be regenerated using 10 mM HCl solution, with a recovery of up to 98%, and it could be reused in five biosorption‐desorption cycles without any considerable loss in biosorption capacity. The alkali‐treated Phanerochaete chrysosporium removed 73% of Cd(II) and 81% of Hg(II) ions from synthetic wastewater.     

Generating “Tide” in Pilot‐Scale Constructed Wetlands to Enhance Agricultural Wastewater Treatment

The operation of tidal flow was studied using a pilot‐scale system treating high strength piggery wastewater. Located on a farm in Staffordshire, UK, the system consisted of five wetland treatment stages vegetated with common reeds of Phragmites australis. Wastewater samples were collected from the inlet and outlet of each stage and analyzed for BOD₅, COD, NH₄‐N, NO₃‐N, NO₂‐N, SS, PO₄‐P and pH. Average hydraulic and organic loadings on the system were 0.12 m³/m² d and 240 g BOD/m² d, respectively, which is considerably higher than the typical loadings on conventional subsurface flow systems. On average, BOD₅ and COD were reduced by 82 % and 80 % from initial concentrations of 2000 mg/L and 2750 mg/L, respectively, across the whole system. The first‐order kinetics constant for BOD₅ removal (K_BOD in m/d) in this tidal flow system is approximately 2.5 times the rate constant obtainable in a typical horizontal flow system, demonstrating a more efficient removal of organic matter in tidal flow wetlands. The overall efficiency of the system was found to increase with time before stabilizing towards the end of a start‐up period. Straight‐line correlations were established between the loading and removal of BOD₅ and COD. Contributions by individual stages to the overall treatment were analyzed. SEM images of wetland media demonstrated the formation of biofilms and microbial activities inside the matrices of the wetland system, which accounted for the degradations of organic pollutants.     

Tolerance of a ruminant ciliate <Emphasis Type="Italic">Entodinium caudatum</Emphasis> against mercury,copper and chromium

The effects of three heavy metal cations, mercury (II), copper (II), and chromium (VI), on the growth of the rumen ciliate Entodinium caudatum in vitro culture was studied. The E. caudatum culture was challenged by HgCl₂, CuCl₂, and K₂Cr₂O₇ for a period of 4 days. The tested concentrations of mercury (II) and copper (II) were 1, 5, 10, 20, 50 mg/L and 2, 10, 20, 40 mg/L for chromium (VI) at single dose with either untreated or inhibited bacterial co-culture population. Effective metal concentrations required to reduce ciliate growth by 50% (EC₅₀) for mercury (II), copper (II), and chromium (VI) either with untreated or inhibited bacterial co-culture population after 24 h of metal application were 24, 20, and 21 or 15, 20, and 19 mg/L, respectively. After 4 days of metal application, corresponding EC₅₀ values for mercury (II), copper (II), and chromium (VI) were 16, 20, and 17 (with untreated bacterial population) or not determinable, 20, and 15 mg/L, respectively (with inhibited bacterial population). Increased sensitivity of E. caudatum to tested heavy metals with inhibited bacterial co-culture population indicate that the ciliate resistance to the heavy metal tested depends on detoxification abilities of rumen bacterial population.     

Role of various parameters in synthesis of insoluble agrobased xanthates for removal of copper from wastewater

The research identifies and studies the parameters involved in the synthesis of two types of insoluble agrobased xanthates, named insoluble baggase xanthate (IBX) and insoluble wood xanthate (IWX) and their ability to remove heavy metals from wastewater. Copper was selected as the model metal and the metal removal capacity of IBX and IWX were expressed by copper loading (mg of copper removed/g of IBX or IWX). It was observed that contact times of 3 h and alkali strengths of 4 mol/L were necessary during alkalization. The maximum base material to alkali ratio (w/w) was 1.125 without sacrificing proper mixing of the base material alkali mixture. Optimum contact time during xanthation was 4h with a carbon-disulfide to base material ratio (w/w) of 1.25. Only strong bases like NaOH, KOH contributed high copper loadings and the starting liquor was reused twice without sacrificing the copper removal capacity of IBX and IWX. Maximum copper loadings achieved with IBX and IWX were 26.9+/-0.15 and 27.8+/-0.39 mg/g, respectively.     

Effective bioremoval of reactive dye and heavy metals by Aspergillus versicolor

In this study, bioaccumulation of heavy metal and dye by Aspergillus versicolor was investigated. Optimum pH values of the maximum heavy metal bioaccumulation was found as 6 for 50 mg/L Cr(VI), Ni(II) and 5 for Cu(II) ions with the 99.89%, 30.05% and 29.06% removal yield, respectively. The bioremoval of the dye up to 800 mg/L at pH 5 and 6 was investigated and 27.15% and 28.95% removal rates were measured respectively. The presence of Cr(VI) with dye, decreased the uptake yield for both pollutants. In the medium with Cu(II) and dye, dye removal was not affected by Cu(II), but Cu(II) removal rate increased from 29.06% to 37.91% by the existence of the dye. When Ni(II) and dye were combined, neither pollutant affected the other’s removal yield. These results indicate that the isolated A. versicolor strain deserves attention as a promising bioaccumulator of heavy metal ions and reactive dyes in wastewater effluents.     

Effects of metal quantity and quality to the removal of zinc and copper by two common green microalgae (Chlorophyceae) species

Appearance of metals as pollutants in the environment is an increasing global problem. Microalgae as subjects of biological remediation methods may provide a cost‐effective and environmentally friendly alternative to the removal of metals during wastewater treatment. Despite the high number of data in the topic, there is still little information on how the type and the concentration of the metal affect the process of removal. In this study, correlations among the algal species, quality and quantity of metals and characteristics of metal removal mechanism were investigated at lower metal concentrations (0.2–5.0 mg L^?1) during zinc and copper removal of the green algae Desmodesmus communis and Monoraphidium pusillum. Analyses of the results proved that there is a statistically significant interaction (P < 0.05) between algal species and quality and concentration of the metals, that is, they have a significant effect on the mode and extent of removal. Both metals were mainly extracellularly bound, but at concentrations of 0.2–1.4 mg L^?1, intracellular proportion could exceed the extracellular adsorption. Although there were differences between the two algae, generally copper appeared in a higher intracellular proportion than zinc in the whole studied concentration range. Overall, the quality and initial concentration of the metal is decisive for the way of removal, the knowledge of which is useful for planning post treatment retention times or post treatment processes of the used biomass during wastewater treatment.     

Understanding the 7‐Cys module amplification of C. neoformans metallothioneins: how high capacity Cu‐binding polypeptides are built to neutralize host nutritional immunity

Cryptococcus neoformans metallothioneins (MTs), CnMT1 and CnMT2, have been identified as essential infectivity and virulence factors of this pathogen. Both MTs are unusually long Cu‐thioneins, exhibiting protein architecture and metal‐binding abilities compatible with the hypothesis of resulting from three and five tandem repetitions of 7‐Cys motives, respectively, each of them folding into Cu₅‐clusters. Through the study of the Zn(II)‐ and Cu(I)‐binding capabilities of several CnMT1 truncated mutants, we show that a 7‐Cys segment of CnMT1 folds into Cu₅‐species, of additive capacity when joined in tandem. All the obtained Cu‐complexes share practically similar architectural features, if judging by their almost equivalent CD fingerprints, and they also share their capacity to restore copper tolerance in MT‐devoid yeast cells. Besides the analysis of the modular composition of these long fungal MTs, we evaluate the features of the Cys‐rich stretch spacer and flanking sequences that allow the construction of stable metal clusters by adjacent union of binding modules. Overall, our data support a mechanism by which some microbial MTs may have evolved to enlarge their original metal co‐ordination capacity under the specific selective pressure of counteracting the Cu‐based immunity mechanisms evolved by the infected hosts.     

Distinct functions of serial metal‐binding domains in the Escherichia coli P1B‐ATPase CopA

P_1B‐ATPases are among the most common resistance factors to metal‐induced stress. Belonging to the superfamily of P‐type ATPases, they are capable of exporting transition metal ions at the expense of adenosine triphosphate (ATP) hydrolysis. P_1B‐ATPases share a conserved structure of three cytoplasmic domains linked by a transmembrane domain. In addition, they possess a unique class of domains located at the N‐terminus. In bacteria, these domains are primarily associated with metal binding and either occur individually or as serial copies of each other. Within this study, the roles of the two adjacent metal‐binding domains (MBDs) of CopA, the copper export ATPase of Escherichia coli were investigated. From biochemical and physiological data, we deciphered the protein‐internal pathway of copper and demonstrate the distal N‐terminal MBD to possess a function analogous to the metallochaperones of related prokaryotic copper resistance systems, that is its involvement in the copper transfer to the membrane‐integral ion‐binding sites of CopA. In contrast, the proximal domain MBD2 has a regulatory role by suppressing the catalytic activity of CopA in absence of copper. Furthermore, we propose a general functional divergence of tandem MBDs in P_1B‐ATPases, which is governed by the length of the inter‐domain linker.     

Treatment of Process Water Containing Heavy Metals with a Two‐Stage Electrolysis Procedure in a Membrane Electrolysis Cell

The capability of a two‐stage electrochemical treatment for the regeneration of acidic heavy‐metal containing process water was examined. The process water came from sediment bioleaching and was characterized by a wide spectrum of dissolved metals, a high sulfate content, and a pH of about 3. In the modular laboratory model cell used, the anode chamber and the cathode chamber were separated by a central chamber fitted with an ion exchanger membrane on either side. The experiments were carried out applying a platinum anode and a graphite cathode at a current density of 0.1 A/cm². The circulation flow of the process water in the batch process amounted to 35 L/h, the electrolysis duration was 5.5 h at maximum and the total electrolysis current was about 1 A. In the first stage, the acidic process water containing metals passed through the cathode chamber. In the second stage, the cathodically pretreated process water was electrolyzed anodically. In the cathode chamber the main load of dissolved Cu, Zn, Cr and Pb was eliminated. The sulfuric acid surplus of 3–4 g/L decreased to about 1 g/L, the pH rose from initially 3.0 to 4–5, but the desired pH of 9–10 was not achieved. Precipitation in the proximity to the cathode evidently takes place at a higher pH than farther away. The dominant process in the anode chamber was the precipitation of amorphous MnO₂ owing to the oxidation of dissolved Mn(II). The further depletion of the remaining heavy metals in the cathodically pretreated process water by subsequent anodic treatment was nearly exhaustive, more than 99 % of Cd, Cr, Cu, Mn, Ni, Pb, and Zn were removed from the leachate. The high depletion of heavy metals might be due to both the sorption on MnO₂ precipitates and/or basic ferrous sulfate formed anodically, and the migration of metal ions through the cation exchanger membrane via the middle chamber into the cathode chamber. In the anode chamber, the sulfuric acid content increased to 6–7 g/L and the pH sank to 1.7. All heavy metals contained, with the exception of Zn, were removed to levels below the German limits for discharging industrial wastewaters into the receiving water. Moreover, the metal‐depleted and acid‐enriched process waters could be returned to the leaching process, hence reducing the output of wastewater. The results indicated that heavy metals could be removed from acidic process waters by two‐stage electrochemical treatment to a large extent. However, to improve the efficiency of metal removal and to establish the electrochemical treatment in practice, further work is necessary to optimize the operation of the process with respect to current density, energy consumption, discharging of metal precipitates deposited in the electrode chambers and preventing membrane clogging.     

One‐Step Controllable Synthesis of Catalytic Ni4Mo/MoOx/Cu Nanointerfaces for Highly Efficient Water Reduction

Currently, in addition to the electroactive non‐noble metal water‐splitting electrocatalysts, a scalable synthetic route and simple activity enhancement strategy is also urgently needed. In particular, the well‐controlled synthesis of the well‐recognized metal–metal nanointer face in a single step remains a key challenge. Here, the synthesis of Cu‐supported Ni₄Mo nanodots on MoO_x nanosheets (Ni₄Mo/MoO_x) with controllable Ni₄Mo particle size and d‐band structure is reported via a facile one‐step electrodeposition process. Density functional theory (DFT) calculations reveal that the active open‐shell effect from Ni‐3d‐band optimizes the electronic configuration. The Cu‐substrate enables the surface Ni–Mo alloy dots to be more electron‐rich, forming a local connected electron‐rich network, which boosts the charge transfer for effective binding of O‐related species and proton–electron charge exchange in the hydrogen evolution reaction. The Cu‐supported Ni₄Mo/MoO_x shows an ultralow overpotential of 16 mV at a current density of 10 mA cm^?2 in 1 m KOH, demonstrating the smallest overpotential, at loadings as low as 0.27 mg cm^?2, among all non‐noble metal catalysts reported to date. Moreover, an overpotential of 105 mV allows it to achieve a current density of 250 mA cm^?2 in 70 °C 30% KOH, a remarkable performance for alkaline hydrogen evolution with competitive potential for applications.     

Assessment of the metal removal capability of two capsulated cyanobacteria, Cyanospira capsulata and Nostoc PCC7936

Two capsulated, exopolysaccharide-producing cyanobacteria, Cyanospira capsulata and Nostoc PCC7936, were tested with regard to their metal removal capability by using copper as model metal. The experiments, carried out with the sole cyanobacterial biomass suspended in distilled water and confined into small dialysis tubings, showed that C. capsulata biomass is characterized by the best efficiency in metal removal, with a q_max (maximum amount of copper removed per biomass unit) of 96 ± 2 mg Cu(II) removed per g of protein in comparison with the value of 79 ± 3 of Nostoc PCC7936 biomass. The experimental data obtained with both cyanobacterial biomass best fit the Langmuir sorption isotherm. The sorption of copper started from the first minutes of contact with the metal and attained the equilibrium state, when no more copper removal was evident, after 5 and 6 hours, for C. capsulata and Nostoc PCC7936, respectively. The best efficiency in Cu(II) removal was obtained at pH 6.1–6.2, while the presence of Mg²⁺ or Ca²⁺ reduced copper removal capability of both species to 60–70% of their q_max. The results showed that the biomass of C. capsulata and Nostoc PCC7936 possesses a high affinity and a high specific uptake for copper, comparable with the best performances shown by other microbial biomass, and suggest the possibility to use the capsulated trichomes of the two cyanobacteria for the bioremoval of heavy metals from polluted water bodies.     

Redox Dynamics of Arsenic Species in the Root‐Near Environment of Juncus effusus Investigated in a Macro‐Gradient‐Free Rooted Gravel Bed Reactor

In the framework of investigating the dynamics of As species within the planted soil beds of treatment wetlands, the redox dynamics of As species particularly in the root‐near environment of the rhizosphere were investigated. For this purpose, long‐term experiments were carried out using a specially designed macro‐gradient‐free rooted gravel bed reactor, planted with Juncus effusus to treat an artificial wastewater containing As (200 μg As/L). The exceptional quality of the biofilm processes at the helophyte root‐surfaces in treatment wetlands were of special importance in this investigation. The results showed that under C‐deficient conditions, a highly efficient As immobilization (> 85 %), obviously due to adsorption and/or co‐precipitation, was attained. The addition of organic carbon immediately caused an elevated As concentration and enrichment of As(III) (nearly 80 % of total As) in the reactor. Increasing the SO₄^2– concentration in the artificial wastewater inflow facilitated a high As immobilization (> 82 %) under sulfate reducing condition. In principle, a highly efficient microbial dissimilatory sulfate reduction contributed to S^2– formation and a greater As immobilization (most likely as As₂S₃) under C surplus and reducing conditions. Significant differences in As immobilization were observed by varying the inflow of the SO₄^2– concentration (0.2, 5, 10, 25 S/L) under C surplus conditions. More As(III) precipitates (15 % less in the outflow) when the inflow of the SO₄^2– concentration was decreased from 25 mg S/L to 10 mg S/L. Immobilized As showed greater instability by releasing As(V) (up to 85 % of total As) due to changes in the dynamic redox conditions inside the reactor. Re‐oxidation of reduced sulfur into other S species (e.g. S⁰, SO₄^2–) due to plant‐root mediated O₂ release probably caused an oxidative dissolution of already precipitated insoluble As (e.g. As₂S₃) and as a consequent As remobilization. The findings of this study highlighted the significance of SO₄^2– in relation to organic C supply in planted soil beds treating As‐contaminated wastewater under constructed wetland conditions.     

Antibacterial,antifungal and in vitro antileukaemia activity of metal complexes with thiosemicarbazones

1‐phenyl‐3‐methyl‐4‐benzoyl‐5‐pyrazolone 4‐ethyl‐thiosemicarbazone (HL) and its copper(II), vanadium(V) and nickel(II) complexes: [Cu(L)(Cl)]·C₂H₅OH·( 1 ), [Cu(L)₂]·H₂O ( 2 ), [Cu(L)(Br)]·H₂O·CH₃OH ( 3 ), [Cu(L)(NO₃)]·2C₂H₅OH ( 4 ), [VO₂(L)]·2H₂O ( 5 ), [Ni(L)₂]·H₂O ( 6 ), were synthesized and characterized. The ligand has been characterized by elemental analyses, IR, ¹H NMR and ¹³C NMR spectroscopy. The tridentate nature of the ligand is evident from the IR spectra. The copper(II), vanadium(V) and nickel(II) complexes have been characterized by different physico‐chemical techniques such as molar conductivity, magnetic susceptibility measurements and electronic, infrared and electron paramagnetic resonance spectral studies. The structures of the ligand and its copper(II) ( 2 , 4 ), and vanadium(V) ( 5 ) complexes have been determined by single‐crystal X‐ray diffraction. The composition of the coordination polyhedron of the central atom in 2 , 4 and 5 is different. The tetrahedral coordination geometry of Cu was found in complex 2 while in complex 4 , it is square planar, in complex 5 the coordination polyhedron of the central ion is distorted square pyramid. The in vitro antibacterial activity of the complexes against Escherichia coli, Salmonella abony, Staphylococcus aureus, Bacillus cereus and the antifungal activity against Candida albicans strains was higher for the metal complexes than for free ligand. The effect of the free ligand and its metal complexes on the proliferation of HL‐60 cells was tested.     

Isolation of highly copper‐tolerant fungi from the smelter of the Naganobori copper mine,an historic mine in Japan

Aims: Copper is a critical metal of modern industry, and is the most widespread heavy metal contaminant in wastewater. Therefore, isolation of copper‐tolerant microbes having the potential as biosorbent is fascinating not only from an environmental microbiology, but also from a biotechnology view point. In this study, we attempted to isolate highly copper‐tolerant microbes from soil samples of the Nabanobori copper mine, the oldest mine in Japan. Methods and Results: As a result of an enrichment culture, two fungal strains were isolated from soil of the smelter remains. The isolates could grow in a maximum of 200 mmol l^?l Cu²⁺, and grew under a wide pH range. The Cu²⁺‐binding capacity of nontreated biomass of the isolates was around 35 mg Cu²⁺ g^?1‐biomass. Analysis of 18S rDNA suggested that the isolates belong to the Aspergillus/Penicillium clade, but they represented a distinct lineage against known neighbours. Conclusion: The isolates were highly copper‐tolerant, and their Cu²⁺‐binding capacity was comparable to well‐studied fungal sorbents. The isolates were implied as novel species. Soil of the historic old mine under weather‐beaten conditions might be a suitable source for metal‐tolerant microbes. Significance and Impact of the Study: The present results advance our understanding of metal‐tolerant microbes, and offer a new tool for both environmental control and metal recovery operations.     

Galvanic Corrosion of Lithium‐Powder‐Based Electrodes

Lithium metal is considered to be the most promising anode for the next generation of batteries if the issues related to safety and low coulombic efficiency can be overcome. It is known that the initial morphology of the lithium metal anode has a great influence on the cycling characteristics of a lithium metal battery (LMB). Lithium‐powder‐based electrodes (Li_p‐electrodes) are reported to diminish the occurrence of high surface area lithium deposits. Usually, ultra‐thin lithium foils (<50 µm) and Li_p‐electrodes are prepared on a copper substrate, thus a metal–metal contact area is generated. The combination of these two metals in the presence of an electrolyte, however, can lead to galvanic corrosion. Herein, the corrosion behavior of Li_p‐electrodes is studied. The porosity of such electrodes leads to a high amount of accessible Cu surface in contact with electrolyte. As a consequence, Li_p‐electrodes aged for 1 week in the electrolyte show spontaneous lithium dissolution near the junction to copper and void formation on the lithium‐powder particles. This corrosion process affects the delivered capacity of Li_p‐electrodes and increases the overvoltage of the lithium electrodissolution process. The occurrence of corrosion at the Cu|Li_p interface raises concerns about the practicality of multi‐metallic component systems for LMBs.     

Facile Patterning of Laser‐Induced Graphene with Tailored Li Nucleation Kinetics for Stable Lithium‐Metal Batteries

A facile and scalable approach is reported to stabilize the lithium‐metal anode by regulating the Li nucleation and deposition kinetics with laser‐induced graphene (LIG). By processing polyimide (PI) films on copper foils with a laser, a 3D‐hierarchical composite material is constructed, consisting of a highly conductive copper substrate, a pillared array of flexible PI, and most importantly, porous LIG on the walls of the PI pillars. The high number of defects and heteroatoms present in LIG significantly lowers the Li nucleation barrier compared to the copper foil. An overpotential‐free Li nucleation process is identified at current densities lower than 0.2 mA cm^?2. Theoretical computations reveal that the defects serve as nucleation centers during the heterogeneous nucleation of lithium. By adopting such composites, ultrastable lithium‐metal anodes are obtained with high Coulombic efficiencies of ≈99%. Full lithium‐metal cells based on LiFePO₄ cathodes with a material loading of ≈15 mg cm^?2 and a negative/positive ratio of 5/1 could be cycled over 250 times with a capacity loss of less than 10%. The current work highlights the importance of nucleation kinetics on the stability of metallic anodes and demonstrates a practical method toward long lasting Li‐metal batteries.     

Separation of Tryptophan Enantiomers by Ligand‐Exchange Chromatography With Novel Chiral Ionic Liquids Ligand

Chiral ionic liquids (CILs) with amino acids as cations have been applied as novel chiral ligands coordinated with Cu²⁺ to separate tryptophan enantiomers in ligand exchange chromatography. Four kinds of amino acid ionic liquids, including [L‐Pro][CF₃COO], [L‐Pro][NO₃], [L‐Pro]₂[SO₄], and [L‐Phe][CF₃COO] were successfully synthesized and used for separation of tryptophan enantiomers. To optimize the separation conditions, [L‐Pro][CF₃COO] was selected as the model ligand. Some factors influencing the efficiency of chiral separation, such as copper ion concentration, CILs concentration, methanol ratio (methanol/H₂O, v/v), and pH, were investigated. The obtained optimal separation conditions were as follows: 8.0 mmol/L Cu(OAc)₂, 4.0 mmol/L [L‐Pro][CF₃COO] ,and 20% (v/v) methanol at pH 3.6. Under the optimum conditions, acceptable enantioseparation of tryptophan enantiomers could be observed with a resolution of 1.89. The results demonstrate the good applicability of CILs with amino acids as cations for chiral separation. Furthermore, a comparative study was also conducted for exploring the mechanism of the CILs as new ligands in ligand exchange chromatography. Chirality 26:160–165, 2014. © 2014 Wiley Periodicals, Inc.