Metal Anions Research Articles

High-Efficiency Mono-Cyclopentadienyl Titanium and Rare-Earth Metal Catalysts for the Production of Syndiotactic Polystyrene.

Syndiotactic polystyrene (SPS) refers to a type of thermoplastic material with phenyl substituents that are alternately chirally attached on both sides of an aliphatic macromolecular main chain. Owing to its excellent physical and mechanical properties, as well as its chemical stability, high transparency, and electrical insulation characteristics, SPS is used in a wide variety of technical fields. SPS is commonly produced via the stereoselective transition metal-catalyzed coordination polymerization method mediated by stereospecific catalysts, which consists of anionic mono-cyclopentadienyl derivative η5-coordinated single active metal centers (referred to as "mono-Cp'-M"), with active center metals involving Group 4 transition metals (with an emphasis on titanium) and rare-earth (RE) metals of the periodic table. In this context, the use of mono-cyclopentadienyl titanocene (mono-Cp'Ti) catalysts and mono-cyclopentadienyl rare-earth metal (mono-Cp'RE) metallocene catalysts for the syndiospecific polymerization of styrene is discussed. The effects of the mono-cyclopentadienyl ligand structure, cationic active metal types, and cocatalysts on the activity and syndiospecificity of mono-Cp' metallocene catalysts are briefly surveyed.

Dual thiols-decorated metal–organic framework for efficient separation and recovery of gold

The selective adsorption and recovery of gold (Au) from water is highly necessary due to its shortage and large value. Herein, we anchored meso-2,3-dimercaptosuccinic acid (DMSA) in metal–organic framework (MOF) to obtain a novel adsorbent, MOF-808-DMSA. Benefited from highly dispersed and dense thiol groups, MOF-808-DMSA exhibits a high adsorption capacity of 2008.4 mg g−1 with an equilibrium time of 60 min, superior to most of MOF-based adsorbents. Common metal cations and anions have negligible effects on the capture of Au(III) ion, and effective adsorption (>99.0%) is feasible under a wide acidic pH range of 1.0–6.0. Based on that, the selective capture of Au(III) ion from a real electronic wastewater was achieved successfully. Furthermore, via using hydrochloric acid-thiourea aqueous solution as the eluent, Au(III)-adsorbed adsorbent can be well regenerated. Combining density functional theory calculations and experimental analysis, the strong chemical affinity of Au(III) ion and the active groups with dispersed distribution was verified.

Late-stage Ligand Modification After Coordination Strengthens Stereoselectively Self-Assembled Hemiaminal Ether Complexes.

Fragile hemiaminal ether linkages present in the backbone of koneramines (LR OR'), tridentate ligands, bound to copper(II) in stereoselectively self-assembled syn-[Cu(LR OR')X2 ] complexes were transformed into sturdy methylene linkages to make corresponding rac-[Cu(LR H)Cl2 ] complexes by late-stage ligand modification after coordination with the retention of coordination sphere. The generality of stereoselective self-assembly of koneramine complexes is shown by utilising a number of metal ions, anions, amines, alcohols and thiols with complete characterisations.

Bandgap engineering approach for synthesising photoactive novel Ag/HAp/SnS2 for removing toxic anti-fungal pharmaceutical from aqueous environment

The present work shed light on synthesising a novel ternary Z-scheme Ag/HAp/SnS2 (AHS) nano photocatalyst to degrade metronidazole (MTZ) in wastewater through H2O2-assisted AOP under natural sunlight. HAp extracted from the fish scales of rohu fish through alkaline treatment was decorated with Ag nanoparticles using ascorbic acid as a bio-reductant. Tin disulphide (SnS2) was anchored over Ag/HAp to prevent agglomeration and enhance photocatalytic activity by delaying the electron-hole recombination rate. After 45 min of irradiation, a degradation efficiency of 98.85 ± 1.86% for 15 ppm MTZ could be achieved. The performance of the prepared photocatalyst in real wastewater was investigated by introducing several metal cations and anions in the photodegradation process. The degradation products were identified by HRLCMS analysis, and the breakdown mechanism of MTZ was proposed. The present study enlightens the importance of SnS2-based photocatalysts for organic pollutant degradation under natural sunlight through an advanced oxidation process. The characterization results showed that the enhanced photodegradation efficiency of AHS is attributed to the formation of an all-solid-state Z-scheme heterojunction with Ag nanoparticles acting as charge transfer medium and as electron accumulators helping in delaying charge recombination.

A Cationic Metal Glue Strategy for Expanding Paramagnetic Hetero-Multinuclear Metal-Oxo Clusters within Polyoxometalate Ligands.

Precise structural design of large hetero-multinuclear metal-oxo clusters is crucial for controlling their large spin ground states and multielectron redox properties for application as a single-molecule magnet (SMM), molecular magnetic refrigeration, and efficient redox catalyst. However, it is difficult to synthesize large hetero-multinuclear metal oxo clusters as designed because the final structures are unpredictable when employing conventional one-step condensation reaction of metal cations and ligands. Herein, we report a "cationic metal glue strategy" for increasing the size and nuclearity of hetero-multinuclear metal-oxo clusters by using lacunary-type anionic molecular metal oxides (polyoxometalates, POMs) as rigid multidentate ligands. The employed method enabled the synthesis of {(FeMn4 )Mn2 Ln2 (FeMn4 )} oxo clusters (Ln=Gd, Tb, Dy, and Lu), which are the largest among previously reported paramagnetic hetero-multinuclear metal-oxo clusters in POMs and showed unique SMM properties. These clusters were synthesized by conjugating {FeMn4 } oxo clusters with Mn and Ln cations as glues in a predictable way, indicating that the "cationic metal glue strategy" would be a powerful tool to construct desired large hetero-multinuclear metal clusters precisely and effectively.

A Cationic Metal Glue Strategy for Expanding Paramagnetic Hetero‐Multinuclear Metal‐Oxo Clusters within Polyoxometalate Ligands

AbstractPrecise structural design of large hetero‐multinuclear metal‐oxo clusters is crucial for controlling their large spin ground states and multielectron redox properties for application as a single‐molecule magnet (SMM), molecular magnetic refrigeration, and efficient redox catalyst. However, it is difficult to synthesize large hetero‐multinuclear metal oxo clusters as designed because the final structures are unpredictable when employing conventional one‐step condensation reaction of metal cations and ligands. Herein, we report a “cationic metal glue strategy” for increasing the size and nuclearity of hetero‐multinuclear metal‐oxo clusters by using lacunary‐type anionic molecular metal oxides (polyoxometalates, POMs) as rigid multidentate ligands. The employed method enabled the synthesis of {(FeMn4)Mn2Ln2(FeMn4)} oxo clusters (Ln=Gd, Tb, Dy, and Lu), which are the largest among previously reported paramagnetic hetero‐multinuclear metal‐oxo clusters in POMs and showed unique SMM properties. These clusters were synthesized by conjugating {FeMn4} oxo clusters with Mn and Ln cations as glues in a predictable way, indicating that the “cationic metal glue strategy” would be a powerful tool to construct desired large hetero‐multinuclear metal clusters precisely and effectively.

Dendrimer functionalized spinel ferrite for robust sorption of precious metals from strongly acidic medium

The separation of noble metal ions from strongly acidic solutions is considered to be a challenging task due to the significantly low pH of these solutions. Spinel ferrites possess unique physicochemical properties, such as excellent magnetic properties, high specific surface area, high chemical stability, active surface sites, and easy modification or functionalization, making them suitable for various applications. In this study, we have introduced a facile method for synthesizing polyamidoamine (PAMAM) dendrimer-functionalized spinel ferrite (DFSF) with a particle size of approximately 10 nm. The prepared DFSF materials have investigated its ability to adsorb Pt(IV) and Pd(II) anions (PtCl62− and PdCl42−) from strongly acidic solutions. The results indicate that the adsorption kinetics and isotherm studies of synthesized materials have a rapid and high adsorption capacity for Pt(IV) and Pd(II) with simple solid-liquid separation. The data analysis suggests an anion exchange interaction between the adsorbate and the adsorbent, specifically the electrostatic interaction between the protonated amine group (–NH3+) and the noble metal anions (PtCl62–and PdCl42−). The Pseudo second-order rate model fitting suggests that the adsorption of noble metals by DFSF is a function of valence. The excellent superparamagnetic properties (0.346 emu g−1) of DFSF make it a promising candidate for large-scale applications, as it exhibited good reusability with a short recovery time (25 s) and high recovery efficiency through the adsorption-reduction-precipitation route. This study suggests that DFSF can be a potential sorbent for noble metal ions in various applications.

Terra Rossa Soil as an Adsorbent to Remove Hexavalent Chromium in Aqueous Solutions

Kaolinite is a phyllosilicate clay of type 1:1 which is usually associated with iron oxides in nature. The clay is abundant in Terra Rossa soils which is located in the Gunungkidul, karst area. Based on the structure and nature of it’s the charge, it has the potential to adsorb anionic heavy metals, especially hexavalent chromium. Heavy metal chromium in the form of hexavalent is very dangerous for human health and the metal is mostly produced from the waste of leather tanning factories that are widely available in Yogyakarta. The purpose of this study was to investigate the possibility of using Terra Rossa soil as an adsorbent to remove heavy metal Cr (VI) from aqueous solution. The experiment was carried out by mixing the adsorbent with a dose of: 1 – 4.5 grams of fine soil, Φ 0.5 mm into a 50 ml solution containing 10 ppm chromium with pH 5 and 3. Stirred at 200 rpm for 2 hours, then centrifuged 3500 rpm for 20 minutes. The filtrate was given phosphoric acid and diphenyl carbazide and then measured using a spectrophotometer with a wavelength of 540 nm. The results showed that the average percentage of chromium removal at pH 5 = 30%, while pH 3 = 49%. The adsorbent absorption (mg/g) decreased in line with increasing adsorbent dose. Absorption graphs of Freundlich and Langmuir models in pH3 solution show R2=0.9264 and 0.9361 respectively, while in pH5 solution the R2 values are 0.3752 and 0.3461, respectively. Adsorption capacity according to Freundlich = 1.7331 mg/g, while according to Langmuir = 5.28 mg/g with adsorption site affinity 0.1894 L/mol.

Fast synthesis of Hcy-modified Au nanoclusters under microwave-assisted irradiation and their response to Cu (II) ions

In this work, Cu (II) ion was chosen as an analyte because it is an important trace element in the human body to maintain organism health. AuNCs (gold nanoclusters) with a mean diameter of ∼2 nm were prepared by a microwave-assisted method, using homocysteine (Hcy) as a reducer and stabilizer. The optimal sample showed a red emission peaking at 624 nm with an emission quantum yield of 17.1%, which was assigned as a ligand to metal nanoparticle core charge transfer (LMNCT). This red emission was effectively quenched by Cu (II) but immune to competing metal cations and anions, showing good selectivity. The quenching mechanism was found as the Cu (II) quenching on the LMNCT procedure to AuNCs. The primary advantage of Hcy-modified AuNCs was the easy and quick synthetic procedure, along with acceptable sensing performance, including good selectivity, linear response, and wide working region.

Coupling of N2 and O2 in the Gas Phase to Synthesize Nitric Oxide at Room Temperature: A Zeldovich-Like Strategy.

Dinitrogen (N2) activation and its chemical transformations are some of the most challenging topics in chemistry. Herein, we report that heteronuclear metal anions AuNbBO- can mediate the direct coupling of N2 and O2 to generate NO molecules. N2 first forms the nondissociative adsorption product AuNbBON2- on AuNbBO-. In the following reactions with two O2 molecules, two NO molecules are gradually released, with the formation of AuNbBO2N- and AuNbBO3-. In the reaction with the first O2, the generated nitrene radical (N••-) originating from the dissociated N2, induces the activation of O2. Subsequently, the second O2 is anchored and forms a superoxide radical (O2•-); this radical attacks the other N atom to form an N-O bond, releasing the second NO. The N••- and O2•- radicals play key roles in the reactions. The mechanism adopted in this direct oxidation of N2 by O2 to NO can be labeled as a Zeldovich-like mechanism.

Zn(II) Metal–Organic Frameworks with a Long Spacer Ligand and a Tricarboxylate Coligand

The preparations and structural characteristics of three-dimensional Zn(II) metal-organic frameworks (MOFs) with dipyridyl-olefin and tricarboxylate are reported. The solvothermal reactions of zinc(II) nitrate hexahydrate, 1,4-bis [2-(4-pyridyl)ethenyl]benzene (bpeb), and 4,4′,4″,-benzene-1,3,5-triyl-tris(benzoic acid) (H3btb) furnished three Zn(II) MOFs (1–3) with new topologies. Depending on the temperature or mole-ratio variations, self-interpenetrated [Zn2(bpeb)(btb)(OH)]·DMF·H2O (1), noninterpenetrated [Zn3(btb)2(bpeb)]·xSolvent (2), and fourfold interpenetrated [Zn2(Hbtb)2(bpeb)][Zn2(Hbtb)2(bpeb)][Zn4(Hbtb)4(bpeb)2] (3) structures were generated with different molecular building blocks. It is interesting that although all three MOFs contain the same metal cation, anion, and spacer ligand, they show different emissions due to structure and connectivity.

Removal of Cationic and Anionic Heavy Metal Ions From Aqueous Phase by a HGMS and Magnetized Zeolite

A magnetic separation study was conducted employing magnetized zeolite and a high gradient magnetic separation system (HGMS) for removal of both cationic and anionic heavy metals. Magnetized zeolite Y was prepared with variable iron contents ranged from 1.2-22.8% based on surface concentration. The magnetized zeolite showed decreased adsorption capacity for cations while the adsorption capacity of the adsorbent for anion increased and the adsorption capacity was proportional to the iron contents. The captured rate of dispersed adsorbents after use for removal of contaminants is a very important factor in water treatment processes. The magnetic separation system recovered more than 98% of magnetized zeolite at 3 T of magnetic field. Current result indicates the combination of magnetized zeolite and HGMS separation could be an efficient alternative for simultaneous removal of cationic and anionic heavy metal from water phase.

Chiral cholesteric molecular tweezer artificial receptors 7a for the rapid detection of tryptophan and the chiral resolution of D-/-tryptophan

A cholesteric chiral molecular tweezer 7a was synthesized using deoxycholic acid as the raw material. The effects of various amino acids on the fluorescence spectra of molecular tweezer 7a were investigated. The chiral molecular tweezer 7a exhibited a specific recognition ability for tryptophan in Ethanol/Tris (1:1, v/v, pH 7.0) buffer, with a low detection limit of 0.17 μmol/L. In addition, the interference behavior of common metal cations and anions on compound 7a recognition of tryptophan was investigated. After eliminating the interference of anions and cations, a new method for the rapid determination of tryptophan in food samples was established. The recoveries of the method ranged from 97.53% to 107.35%, and the relative standard deviation ranged from 0.204% to 0.825%, according to the new method, the tryptophan content in infant milk powder, wheat flour and chicken meat were 2.029 mg/g, 1.844 mg/g and 3.306 mg/g, respectively, which were close to the reference value, indicating that the new method was accurate and reliable. Concurrently, molecular tweezer 7a was used for the chiral resolution of D-/L-tryptophan enantiomers. Baseline separation of D-/L-tryptophan enantiomers was realized by high performance liquid chromatography (HPLC) with a methanol solution (86.5/13.5, V/V) of cholesteric molecular tweezer 7a as the mobile phase. Data will be made available on request.

Autonomous enrichment and deep removal of heavy metals by salt-tolerant gradient polyelectrolyte hydrogels

The integration of nanostructured materials into hydrogel matrix with chemical gradient holds great promise in gathering the pollutants and enhancing their adsorption or photocatalytic performance. However, the electric potentials rooting in the common gradient polyelectrolyte hydrogel are almost completely shielded by the co-existing counter-ions. In this study, a salt-tolerant gradient polycationic electrolyte hydrogel was fabricated by free radical copolymerization under the induction of unilateral UV illumination, which was used as nanofillers matrix. The cation-π interactions between the adjacent cations and aromatic rings endow the gradient polycationic electrolyte hydrogels deserving the salt-tolerant properties. Thus, the build-in electric potentials are still reactive on enrichment of the anionic heavy metals in highly concentrated salt solutions, altering the defects of the common gradient polyelectrolyte hydrogel. Using Sb(V) adsorption and Cr(VI) photocatalytic reduction as target reactions, the gradient composite hydrogels always display fast and high removal capacities towards these anionic pollutants in the saline solutions of 500 mM, as well as good stability and reusability. This salt-tolerant hydrogel matrix provides a smart material platform with self-driven forces in the fields of pollutant enrichment and removal.

Polyoxometalate‐Incorporated CuI‐Resorcin[4]arene Metal‐Organic Complexes as Heterogeneous Catalysts for Catalytic Oxidation of Mustard Gas Simulant

AbstractExploring efficient heterogeneous catalysts for catalytic oxidation of chemical warfare agents (CWAs) is highly desired. As a class of discrete anionic metal oxide clusters, polyoxometalates (POMs) provide abundant catalytic active sites, thus resulting their rich redox properties. Here, a family of known POM‐incorporated CuI‐resorcin[4]arene metal‐organic complexes, namely, [Cu4(TPTR4A)2][PW12O40](OH) ⋅ 0.5DMA ⋅ 5H2O (Cu‐PW), [Cu4(TPTR4 A)2][PMo12O40](OH) ⋅ 2DMA ⋅ H2O (Cu‐PMo) and [Cu4(TPTR4A)2][SiW12O40] ⋅ 2.5DMA (Cu‐SiW) were utilized as catalysts to promote the oxidation of 2‐chloroethyl ethyl sulfide (CEES). Strikingly, compared to the novel compound [Cu3Cl6(TPTR4A)(DMA)] ⋅ CH3CH2OH (defined as Cu‐T), the three complexes exhibited excellent stability, indicating that the integration of POMs and metal–organic units could improve the stability of the compounds. Moreover, Cu‐PMo and Cu‐PW showed higher activities for the catalytic oxidation of CEES to CEESO with selectivities both of 99 %.

Three-coordinate monoanions of rhodium(1–) and iridium(1–): Isolable examples of coordinatively-unsaturated metalate anions

Metalate complexes – those that possess metal centers in formally negative oxidation states – are typically coordinatively and electronically saturated organometallic species. The reduced nature of the metal centers within these complexes is well understood to be responsible for their high reactivity as metal-based nucleophiles. While the chemistry of such complexes is extensive, there are very few examples where coordinative or electronic unsaturation accompanies highly-reduced d-orbital manifolds as a means to augment reactivity. Reported here is the isolation of the 16e–, d10 rhodium and iridium metalate anions, [M(CNArDipp2)3]–, where coordinative unsaturation is achieved through the use of encumbering m-terphenyl isocyanide ligands. Reactivity studies with electrophiles demonstrate that the Rh and Ir centers in these metalates retain significant nucleophilic character, which enables the formation of unusual metal/main-group-element species on account of low coordination numbers.

Development of colorimetric probe for the selective detection of HgII

A selective sensing technique for HgII ions has been developed utilizing an amino acid based probe. The design, synthesis and efficacy of the chemosensor have been described. The probe (SALTYR) was successfully synthesized from a naturally occurring amino acid after sequential functional group modifications. Recognition studies were performed against a wide variety of metal cations and anions including real water samples. All the analyses were carried out utilizing UV–vis and fluorescence techniques with micromolar concentrations of the probe in HEPES buffer. The selectivity of the probe was found to be very specific for HgII with quenching of the fluorescence in a turn-off mechanism. The detection limit of the probe SALTYR was calculated and found to be 5.9 × 10−6 M. Quantum chemical calculations demonstrated the stability of the HgII complex in the context of binding energy. Furthermore, the change of the pattern of emission spectra has been rationalized with a logic gate model.

Obtaining and study of physical-chemical properties of porous materials based on kaolin

The object of research is kaolin from the Hlukhovetsky deposit (Ukraine). On its basis, granulated sorbent materials were obtained with the addition of various amounts of cellulose as a pore former. After forming the samples, they were dried and fired at a temperature of 800 °C. The obtained granules with a size of 8–9 mm were modified with zero-valent iron. The physicochemical, including sorption properties of granular composites were studied. Using scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), the morphology of the obtained samples was investigated and the presence of zero-valent iron particles on the surface and in the pores of the sorbents was confirmed. Based on desorption experiments, it was determined by chemical analysis that the Fe0 content in modified samples with increased pore former content increases from 0.01 g/g of granules for a sample containing 1% cellulose to 0.016 g/g for a carrier with 3 % pore former. The specific surface area and pore volume of the samples were determined by the method of low-temperature adsorption-desorption of nitrogen. Thus, with an increase in the content of the pore former in the ceramic mass, the specific surface of both unmodified and modified samples slightly decreases. Thus, with a cellulose content of 1 %, it is 20 m2/g and 17 m2/g, respectively. When the pore former is increased to 3%, these values are 15 m2/g and 12 m2/g. After applying a layer of zero-valent iron on porous granules, the volume of pores decreases, which is due to the formation of agglomerates of iron particles during synthesis. The study of the sorption capacity of the obtained sorbents with respect to Cr(VI) from model solutions containing a mixture of metal cations (copper, cadmium, cobalt, zinc) showed that granular materials exhibit sorption capacity for metal anions, even in the presence of cations. The amount of chromium sorption naturally increases for modified samples with an increase in the cellulose content in them. However, for model solutions that do not additionally contain metal cations, the sorption value is somewhat higher. Thus, for a sample with a 3 % pore former content, the sorption value is 0.7 mg/g and 0.9 mg/g, respectively, at an initial chromium(VI) concentration of 10 mg/g. The obtained experimental data indicate that the obtained porous granular sorbents based on kaolin can be used in the further treatment of wastewater from electroplating enterprises, which contain a mixture of pollutants in both anionic and cationic forms.

Removal of Cr(VI) from tanning wastewater using chitosan-SDS complexes in PEUF: Optimization and analysis via response surface methodology

In this study, we addressed the removal of hexavalent chromium (Cr(VI)), a highly toxic and soluble anionic heavy metal, using enhanced ultrafiltration (UF). The objective was to eliminate Cr(VI) species with molecular weights beyond the retention capability of standard UF membranes and achieve their retention through the incorporation of polymers and polymer-surfactant complexes within the UF membrane. Chitosan, a cationic polymer, and sodium lauryl sulfate (SDS), an anionic surfactant, were used in this context. The Cr(VI) solution was subjected to ultrafiltration in a laboratory-scale membrane cell, and its removal was assessed spectrophotometrically. Polymer and surfactant structures were characterized using turbidity, electrical conductivity, SEM-EDX, and FTIR analyses. Experimental studies were conducted using the face-centered central composite design (CCD) of the response surface methodology (RSM) to determine optimal removal and permeate flux values, as well as to unveil the relationships between the studied factors and the resulting responses.The results revealed that 100 % of the Cr(VI) species were removed from wastewater in the chitosan-based polymer-enhanced ultrafiltration (PEUF) study. With the chitosan-SDS complex, a removal efficiency of 98.33 % was achieved in synthetic wastewater. The PEUF study employing chitosan and the chitosan-SDS complex yielded permeate flux values of 30.73 L/h/m2 and 53.89 L/h/m2, respectively. The optimized conditions obtained from the models were then applied to real wastewater obtained from a leather industry tanning process. In the case of chitosan and the chitosan-SDS complex, the Cr(VI) removal efficiencies in the real wastewater were 4.40 % and 98.33 %, respectively.

Plasmonic nanoparticle's anti-aggregation application in sensor development for water and wastewater analysis.

Colorimetric sensors have emerged as a powerful tool in the detection of water pollutants. Plasmonic nanoparticles use localized surface plasmon resonance (LSPR)-based colorimetric sensing. LSPR-based sensing can be accomplished through different strategies such as etching, growth, aggregation, and anti-aggregation. Based on these strategies, various sensors have been developed. This review focuses on the newly developed anti-aggregation-based strategy of plasmonic nanoparticles. Sensors based on this strategy have attracted increasing interest because of their exciting properties of high sensitivity, selectivity, and applicability. This review highlights LSPR-based anti-aggregation sensors, their classification, and role of plasmonic nanoparticles in these sensors for the detection of water pollutants. The anti-aggregation based sensing of major water pollutants such as heavy metal ions, anions, and small organic molecules has been summarized herein. This review also provides some personal insights into current challenges associated with anti-aggregation strategy of LSPR-based colorimetric sensors and proposes future research directions.