Formation Of Coordination Complexes Research Articles

Optimization of LiF dissolution with Al2(SO4)3 and its application to lithium extraction by fluorination of α-spodumene

Numerous Li extraction methods from minerals and e-waste have been reported in the literature. Among them, direct fluorination processes appear to be a viable alternative due to their high lithium extraction efficiencies (>90%) as LiF. However, a drawback is the low water solubility of LiF, which requires acids for its separation and to obtain other commercial lithium salts. An interesting alternative for dissolving salts with low solubility is through the formation of coordination complexes. In this case, aluminum forms highly stable soluble complexes with the F− anion, such as AlF2+, AlF2+, AlF3, AlF4−, AlF52−, AlF63−.This study proposes an acid-free LiF dissolution methodology using aluminum sulfate as a leaching agent. The LiF dissolution was modeled and optimized using Response Surface Methodology (RSM). The investigated operating parameters for LiF dissolution were the solid/liquid ratio (A), reaction temperature (B), and leaching time (C). Thus, a predictive mathematical model was successfully optimized (R2 = 0.9445). The results indicated that the S/L ratio negatively influences the dissolution of LiF, while temperature and time have a positive effect. The LiF dissolutions of 90 ± 3% were achieved with a leaching time of 31 min, a S/L ratio of 20 g/mL, and a temperature of 45 °C.

Decoration of phosphoric acid groups onto Ti3C2Tx MXene for enhanced uranium removal

The construction of novel MXene-based composites with superb abilities through functionalization is an effective strategy to enhance the potential of this emerging inorganic lamellar material for environmental adsorption applications. The present work systematically investigated the adsorption performance of Ti3C2Tx MXene modified with phosphate functional groups that facilitate the capture of uranyl ions. After introducing phosphate groups via a two-step modification of 3-aminopropyltriethoxysilane (APTES) and phytic acid (PA), the synthesized Ti3C2-APTES-PA is significantly superior to pristine Ti3C2Tx nanosheets in terms of adsorption capacity, adsorption selectivity and reusability for uranium. The maximum uptake capacity of Ti3C2-APTES-PA at pH = 5 reaches 323 mg/g, which is 2.5 times higher than that of unmodified MXene. Furthermore, the large selectivity coefficient (SU/M > 16.2) declares that Ti3C2-APTES-PA preferentially adsorbs uranium among substantial competing ions. Ti3C2-APTES-PA also shows good cycling performance that its adsorption capacity remained 92.3 % after 6 cycles. When it comes to treating simulated uranium tailings pond leachate and radioactive wastewater from mines, high U(VI) removal rates of 88.9 % and 96.8 % can be achieved by our ternary composite at a dosage of 0.05 g/L. The underlying adsorption mechanism was unraveled by spectroscopic analysis to be the formation of coordination complexes of uranyl ions with phosphate groups on PA and hydroxyl groups on Ti3C2Tx substrate, as well as the reduction of a small amount of adsorbed U(VI) to U(IV) by MXene. The overall results imply that Ti3C2-APTES-PA is an effective uranium chelating scavenger for the treatment of environmental radioactive wastewater.

Photochromic sensing of La3+ and Lu3+ ions using poly(caprolactone) fibers doped with spiropyran dyes

Here, we report three spiropyran derivatives, which were then incorporated into poly(caprolactone) electrospun fibers as a platform for sensing heavy metals. The materials obtained showed distinct colorimetric responses to different ions, especially Lanthanum and Lutetium. We also demonstrated that it is possible to selectively identify and differentiate La3+ and Lu3+ ions by emission and detection by the unaided eye. Further analyses were conducted in solution to study spiropyran interaction with these ions, indicating the formation of complexes at a 2:1 ligand:metal ratio. In addition, emission lifetime showed an increased lifetime of the emissive species with the addition of La3+ or Lu3+ ions, also indicating the formation of coordination complexes. These results showed a promising prospect for a portable sensor for field use that may function as colorimetric sensors of toxic heavy metals. Overall, this study demonstrates the potential of spiropyran derivatives as versatile and tunable materials for surface modifications with various applications.

Simultaneously enhancing the mechanical robustness and conductivity of ionogels by in situ formation of coordination complexes as physical crosslinks

Ionogels with environmental tolerance have recently emerged as promising candidates for use in flexible electronics.

Screening, separation and identification of metal-chelating peptides for nutritional, cosmetics and pharmaceutical applications.

Metal-chelating peptides, which form metal-peptide coordination complexes with various metal ions, can be used as biofunctional ingredients notably to enhance human health and prevent diseases. This review aims to discuss recent insights into food-derived metal-chelating peptides, the strategies set up for their discovery, their study, and identification. After understanding the overall properties of metal-chelating peptides, their production from food-derived protein sources and their potential applications will be discussed, particularly in nutritional, cosmetics and pharmaceutical fields. In addition, the review provides an overview of the last decades of progress in discovering food-derived metal-chelating peptides, addressing several screening, separation and identification methodologies. Furthermore, it emphasizes the methods used to assess peptide-metal interaction, allowing for better understanding of chemical and thermodynamic parameters associated with the formation of peptide-metal coordination complexes, as well as the specific amino acid residues that play important roles in the metal ion coordination.

Schiff Bases, Syntheses, Characterisation and their Application to Heavy Metal Removal: A Review

Schiff bases are compounds resulting from the condensation reaction between an aldehyde or ketone with primary amines. The confirmation of the formation of these compounds involves the use of characterisation techniques which encompasses spectroscopic and thermoanalytical techniques. Recently, Schiff bases have garnered attention because of their wide applications which range from industrial uses to use in remediation of metal ions. Their use in extraction of heavy metal is of particular interest due to rising levels of metal pollution globally. The ability of Schiff bases to form coordination complexes with metal ions makes them suitable for these purposes. This review article outlines the synthesis, characterisation and application of Schiff bases to metal extraction.

Binuclear nitrosyl iron complex with 4-acetamidothiophenolyl: Synthesis and study of its decomposition in a system with glutathione and albumin

In this work, we synthesized a new binuclear nitrosyl iron complex of the family of Roussin's red salt ester [Fe2(C8H8NOS)2(NO)4] (complex 1) with 4-acetamidothiophenol (a structural analog of acetaminophen), which generates NO during hydrolysis and is promising for treatment socially significant diseases. It has been established that solvents have a significant effect on the process of its decomposition: in a buffer solution, complex 1 retains its binuclear structure, while in DMSO it forms mononuclear iron-nitrosyl products. Reduced glutathione does not replace 4-acetamidothiophenol ligands in the structure of complex 1. In addition, complex 1 and its products are not coordinated with the known binding sites of bovine serum albumin, including Cys34. It was found that the studied complex 1 is adsorbed on the protein surface due to weak intermolecular interactions, which leads to a decrease in the rate of decomposition, and, as a result, to a longer generation of NO.Thus, it has been shown for the first time that compound 1 and its decay products do not form coordination complexes with the biosubstrates studied in this work. It can be assumed that glutathione will not participate in the transformation of complex 1 in vivo, while albumin, due to the effective stabilization of the complex on the surface, can act as its carrier to therapeutic targets.

Photophysical, thermal, and DFT studies on a tetraaryl-azadipyrromethene ligand and its zinc(II) complex.

An azadipyrromethene ligand (H1) and homoleptic zinc(II) (H1-Zn) complex were synthesized. The resulting structures were elucidated by NMR, FTIR, and HRMS techniques. The photophysical properties and effects of complexing the zinc(II) atom to azadipyrromethene ligands in solution were studied by means of UV-Vis absorption and fluorescence spectroscopy. Experimental findings were elucidated using density functional theory computations and interfragment charge transfer (IFCT) and electron-hole analyses. The fluorescence features were found to be negligible. The ligand molecule decayed at a rate of 3% while the complex decayed at 2% upon photoirradiation based on photostability experiments. The singlet oxygen quantum yields of the ligand and complex were calculated as 0.127 and 0.233, respectively, signifying low photodynamic activity. The charge transfer transitions were determined between reciprocal ligands responsible for the red shift of the main absorption band by IFCT and electron-hole analysis. Compounds in an inert N2 atmosphere demonstrated high thermal stability. Although the thermogravimetric analysis (TGA) and derivative thermogravimetry curves of the complexes were similar, zinc(II) coordination and homoleptic complex formation reduced the degradation temperatures. These findings suggest that azadipyrromethene and the Zn(II) class of chromophores have beneficial features for use in the development of novel photo- and thermostable materials that combine charge transfer with low energy in the visible and near infrared regions.

CuS/Cellulose acetate nanofiber composite: A study on adsorption and photocatalytic activity for water remediation

This paper addresses the pressing concern of environmental deterioration by investigating innovative solutions for tackling water pollution in aquatic ecosystems. Various hazardous pollutants, such as dyes, pharmaceuticals, heavy metals, and pesticides, pose significant threats to both the environment and human health. To combat these issues, in this work we explored the synthesis of composite nanofibers using copper sulfide (CuS) nanoparticles and cellulose acetate (AC) polymer matrix through a gas-liquid sulfurization process. The resulting nanocomposites were used to fabricate nanofibers by the electrospinning technique. The morphological analyses revealed a transition from ribbon-like structures to cylindrical forms as nanoparticle concentration was increased. Chemical analysis confirmed the presence of CuS nanoparticles within the composite nanofibers. XRD studies indicated a covellite crystal structure of the CuS nanoparticles. TGA analysis revealed a coordination complex formation between nanoparticles and dimethylformamide. Optical properties showed variations in band gap energies, from 1.76 to 1.9 eV, as nanoparticle concentration changed. Photocatalysis studies demonstrated that the composite nanofibers exhibited enhanced adsorption and degradation of methylene blue dye under solar irradiation. Overall, this study contributes to understanding the potential application of CuS/AC composite nanofibers for environmental remediation.

Predictive analytics of conductance and HOMO-LUMO gaps with topological descriptors of porphyrin nanosheets

Porphyrins are planar tetrapyrolic aromatic molecules that serve as a host for the formation of metal coordination complexes, which enable additional capabilities. The 2D porphyrin derivative sheets attracted interest due to their versatility and capacity to interact with other chemicals due to the existence of a core metal ion. Topological descriptors are employed as a predictive technique to determine the physical, chemical, and structural characteristics of molecules by considering the molecular structure of compounds as molecular graphs. This paper investigates the degree and degree sum based descriptors of some potential porphyrin derivative nanosheets, using the edge partition method. We also demonstrate a predictive model for analyzing the electrical conductance of porphyrin derivative nanosheets using degree and degree sum based topological descriptors. Furthermore, the Shannon’s information entropies of these porphyrin derivatives are investigated, and the HOMO-LUMO gap of these nanostructures is predicted using these entropy.

La2O3 modified porous boron nitride for enhanced adsorption and removal of fluoride pollutants from an aqueous solution

AbstractFluorine contamination has caused great harm to humans and the environment. In this study, novel lanthanum modified porous boron nitride (porous BN) composites (BN−La−X) were successfully prepared and applied to remove fluoride from water. The results indicated that lanthanum was present on the surface of BN in the form of amorphous La2O3. BN−La‐4 has excellent adsorption performance, and its removal of fluoride is much more effective than that of porous BN with good cyclic regeneration ability. In addition, the fluoride adsorption by BN−La‐4 could reach adsorption equilibrium within 2 h and the adsorption kinetics was conformed to the pseudo‐second‐order model. The maximum adsorption capacity of BN−La‐4 was calculated from the Langmuir model to be 80.04 mg g−1, which was better than most related adsorbents. Furthermore, the presence of anions and pH values affected the removal of fluoride. The adsorption mechanisms were consisted of electrostatic attraction, ion exchange between hydroxyl and fluorine ions, and the formation of coordination complexes between lanthanide ions and fluoride ions. In summary, La2O3 modified porous boron nitride composite is a promising adsorbent for the removal of fluoride contamination in aquatic environment.

Prediction of arsenic adsorption onto metal organic frameworks and adsorption mechanisms interpretation by machine learning

Metal–organic frameworks (MOFs) are promising adsorbents for the removal of arsenic (As) from wastewater. The As removal efficiency is influenced by several factors, such as the textural properties of MOFs, adsorption conditions, and As species. Examining all of the relevant factors through traditional experiments is challenging. To predict the As adsorption capacities of MOFs toward organic, inorganic, and total As and reveal the adsorption mechanisms, four machine learning-based models were developed, with the adsorption conditions, MOF properties, and characteristics of different As species as inputs. The results demonstrated that the extreme gradient boosting (XGBoost) model exhibited the best predictive performance (test R2 = 0.93–0.96). The validation experiments demonstrated the high accuracy of the inorganic As-based XGBoost model. The feature importance analysis showed that the concentration of As, the surface area of MOFs, and the pH of the solution were the three key factors governing inorganic-As adsorption, while those governing organic-As adsorption were the concentration of As, the pHpzc value of MOFs, and the oxidation state of the metal clusters. The formation of coordination complexes between As and MOFs is possibly the major adsorption mechanism for both inorganic and organic As. However, electrostatic interaction may have a greater effect on organic-As adsorption than on inorganic-As adsorption. Overall, this study provides a new strategy for evaluating As adsorption on MOFs and discovering the underlying decisive factors and adsorption mechanisms, thereby facilitating the investigation of As wastewater treatment.

A Facile Strategy to Fabricate Tough and Adhesive Elastomers by In Situ Formation of Coordination Complexes as Physical Crosslinks

AbstractCoordination bonds with a dynamic nature and wide‐spectrum bond energy have gained great popularity in use for fabricating tough soft materials. However, most existing coordination‐based elastomers are prepared through complicated procedures, usually involving elaborate synthesis of ligand‐containing monomers or polymers, ion diffusion to form coordination complexes, and removal of organic solvent during the synthesis, which are neither easy operation nor environmentally friendly. Here, a facile and effective strategy is demonstrated to fabricate tough metallosupramolecular elastomers by one‐pot polymerization of aqueous precursor solutions containing commercial agents, 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid, 2‐[2‐(2‐methoxyethoxy)ethoxy]ethyl acrylate, and Zr4+ ions. After solvent (i.e. water) evaporation, the obtained elastomers are transparent and extremely tough owing to the presence of sulfonate‐Zr4+ coordination complexes as physical crosslinks. Their mechanical properties are tunable over a wide spectrum by adjusting the composition of copolymers and the density of coordination bonds. This eco‐friendly strategy is further extended to various commercial monomers, manifesting good universality to toughen elastomers. Furthermore, the abundant functional groups of copolymers make the elastomers adhesive to various substrates including themselves, favoring applications such as interfacial adhesion and encapsulations. The easy fabrication, tunable mechanical properties, and adhesion ability endow the elastomers with great potential as the substrate of wearable soft electronics.

Facet-dependent and defect-enhanced vanadate adsorption on Mg(OH)2 surface: A combined study of DFT calculations and batch experiments

Vanadium contamination has gained increasing attention around the world and it is urgent to develop feasible approach to tackle this growing pollution (e.g., vanadate). Herein, density functional theory (DFT) calculations combined with batch experiments were used to systematically evaluate the capacity of Mg(OH)2 to adsorb vanadate, by investigating the impacts of different exposed facet and surface OH defect on the structure configurations, adsorption energy and the efficiency of vanadate adsorption. DFT calculations suggested that although the capacity of vanadate adsorption on the facets of Mg(OH)2 would be obviously influenced by the formation of various coordination complex (e.g., monodentate, bidentate and tridentate) on each facet, the capacity for these facets of Mg(OH)2 towards vanadate adsorption followed the order: (100) > (001). Moreover, such a vanadate adsorption was further enhanced by the presence of surface OH defect, owing to altered densities of states (DOS) of the adsorption site. Batch experiments verified the defect-rich Mg(OH)2 was favorable to adsorb vanadate, and both (001) and (100) facet play the great roles. This molecular-level understanding of the facet-dependent and defect-enhanced adsorption behavior of Mg(OH)2 toward vanadate provides a useful insight into designing and applying effective adsorbents for the removal of heavy metal oxyanions.

Carboxylic acids and light interact to affect nanoceria stability and dissolution in acidic aqueous environments.

Cerium atoms on the surfaces of nanoceria (i.e., cerium oxide in the form of nanoparticles) can store or release oxygen, cycling between Ce3+ and Ce4+; therefore, they can cause or relieve oxidative stress within living systems. Nanoceria dissolution occurs in acidic environments. Nanoceria stabilization is a known problem even during its synthesis; in fact, a carboxylic acid, namely citric acid, is used in many synthesis protocols. Citric acid adsorbs onto nanoceria surfaces, limiting particle formation and creating stable dispersions with extended shelf life. To better understand factors influencing the fate of nanoceria, its dissolution and stabilization have been previously studied in vitro using acidic aqueous environments. Nanoceria agglomerated in the presence of some carboxylic acids over 30 weeks, and degraded in others, at pH 4.5 (i.e., the pH value in phagolysosomes). Plants release carboxylic acids, and cerium carboxylates are found in underground and aerial plant parts. To further test nanoceria stability, suspensions were exposed to light and dark conditions, simulating plant environments and biological systems. Light induced nanoceria agglomeration in the presence of some carboxylic acids. Nanoceria agglomeration did not occur in the dark in the presence of most carboxylic acids. Light initiates free radicals generated by ceria nanoparticles. Nanoceria completely dissolved in the presence of citric, malic, and isocitric acid when exposed to light, attributed to nanoceria dissolution, release of Ce3+ ions, and formation of cerium coordination complexes on the ceria nanoparticle surface that inhibit agglomeration. Key functional groups of carboxylic acids that prevented nanoceria agglomeration were identified. A long carbon chain backbone containing a carboxylic acid group geminal to a hydroxy group in addition to a second carboxylic acid group may optimally complex with nanoceria. The results provide mechanistic insight into the role of carboxylic acids in nanoceria dissolution and its fate in soils, plants, and biological systems.

Nanosized Silk-Magnesium Complexes for Tissue Regeneration.

Metal ions provide multifunctional signals for cell and tissue functions, including regeneration. Inspired by metal-organic frameworks (MOFs), nanosized silk protein aggregates with a high negative charge density are used to form stable silk-magnesium ion complexes. Magnesium ions (Mg ions) are added directly to silk nanoparticle solutions, inducing gelation through the formation of silk-Mg coordination complexes. The Mg ions are released slowly from the nanoparticles through diffusion, with sustained release via tuning the degradation or dissolution of the nanosized silk aggregates. Studies in vitro reveal a dose-dependent influence of Mg ions on angiogenic and anti-inflammatory functions. Silk-Mg ion complexes in the form of hydrogels also stimulate tissue regeneration with a reduced formation of scar tissue in vivo, suggesting potential utility in tissue regeneration.

Organometallic-Organic Hybrid Assemblies Featuring the Diantimony Complex [Cp2Mo2(CO)4(μ,η2-Sb2)], Ag(I) Ions and Ndonor Molecules as Building Blocks.

The reactions of the of the organometallic ligand complex [Cp2Mo2(CO)4(μ,η2-Sb2)] (C) with Ag[TEF] ([TEF]‾ = [Al{OC(CF3)3}4]‾) in the presence of a number of di- or polytopic N-donor molecules (1,6,7,12-tetraazaperylene (L1), 2,2'-bipyrimidine (L2), 4,4'-bipyridine (L3), trans-1,2-di(4-pyridyl)ethylene (L4)) and 1,3-di(4-pyridyl)propane (L5), were studied. These reactions lead, depending on the reaction stoichiometry and choice of linker, to the selective formation of dimeric or tetrameric supramolecular coordination complexes as well as 1D and 2D coordination polymers (CPs). The presented compounds are unique examples of supramolecular complexes incorporating both organometallic Sb-donor and organic N-donor molecules as ligands to stabilize metal ions. Moreover, one of the formed compounds, the CP [Ag4(η2:1-C)4(L4)4]n[TEF]4n, represents an exceptional 1D polymer incorporating both N- and Sb-donor ligands as connectors for metal ions.

Toughening Hydrogels by Forming Robust Hydrazide-Transition Metal Coordination Complexes.

Energy dissipation based on dynamic fracture of metal ligands is an effective way to toughen hydrogels for specific applications in biomedical and engineering fields. Exploration of new kinds of metal-ligand coordinates with robust bonding strength is crucial for the facile synthesis of tough gels. Here a hydrogel toughening strategy based on the formation of robust coordination complexes between the hydrazide ligands and zinc ions is reported. The resultant hydrogels exhibit high strength and toughness at room temperature. Their mechanical properties show temperature dependence due to the dynamic nature of coordination bonds. In addition, the amine group of hydrazides in the gel matrix provides a reactive site for Schiff's base reaction, enabling surface modification without influence on overall mechanical performances of the gel. The hydrazide ligands are easy to synthesize and can coordinate very well with several transition metals. Such a metal-ligand coordination should be suitable to develop tough soft materials with versatile applications.

Rational design of polymeric nanozymes with robust catalytic performance via copper-ligand coordination

Incorporating copper (Cu) ions into polymeric particles can be a straightforward strategy for mimicking copper enzymes, but it is challenging to simultaneously control the structure of the nanozyme and of the active sites. In this report, we present a novel bis-ligand (L2) containing bipyridine groups connected by a tetra-ethylene oxide (4EO) spacer. In phosphate buffer the Cu-L2 mixture forms coordination complexes that (at proper composition) can bind polyacrylic acid (PAA) to produce catalytically active polymeric nanoparticles with well-defined structure and size, which we refer to as ‘nanozymes’. Manipulating the L2/Cu mixing ratio and using phosphate as a co-binding motif, cooperative copper centres are realized that exhibit promoted oxidation activity. The structure and activity of the so-designed nanozymes remain stable upon increasing temperature and over multiple cycles of application. Increasing ionic strength causes enhanced activity, a response also seen for natural tyrosinase. By means of our rational design we obtain nanozymes with optimized structure and active sites that in several respects outperform natural enzymes. This approach therefore demonstrates a novel strategy for developing functional nanozymes, which may well stimulate the application of this class of catalysts.

Charge and size selective thin film composite membranes having tannic acid – Ferric ion network as selective layer

Selective membranes that can distinguish between solutes of different physicochemical properties are highly desirable for membrane applications such as nanofiltration. Rapid coordination complex formation of metals and polyphenols triggered the development of thin film composite membranes in the last decade through a green synthesis procedure, eliminating the use of toxic organic solvents. In this work, thin film composite membranes with high selectivity between organic solutes were prepared. They contain a selective layer based on a metal-polyphenol network (tannic acid – ferric ion (TA-Fe3+)) with a thickness of approximately 10 nm thickness. The thin layer was obtained by coating aqueous solutions of the two components on top of a microporous polyacrylonitrile support in a sequential mode. The morphological, chemical and physical properties of the membranes were investigated. The results demonstrate that hydrophilicity, surface charge, and pore size of the membranes can be fine-tuned by varying the TA/Fe3+ ratio of the casting solutions. The separation performance of the membranes was further analyzed by filtration tests. For instance, selectivities in the range of 3.2–20.6 were achieved between uncharged(0)/(−)charged dyes of comparable molecular size, while exhibiting a good selectivity, reaching up to 3 times, between monovalent to trivalent negatively charged dyes. This work paves a way to eco-friendly membrane synthesis for diverse applications in water and wastewater treatment.