Individual iron(iii) glycerolate: synthesis and characterisation

Iron(ii) and iron(iii) salts of strong acids form iron glycerolates on heating at 180 °C with glycerol in the presence of an equivalent amount of alkali. Individual iron(iii) glycerolate was obtained for the first time. When Fe₃O₄ magnetic nanoparticles were heated with glycerol, an iron(iii) glycerolate shell was formed on their surface.

Individual iron(iii) glycerolate was obtained and characterized; a method for the preparation of an iron(iii) glycerolate shell on the surface of Fe₃O₄ MNPs was proposed.

Currently, glycerolates of various metals (Ti, Co, Fe, Zn, etc.) are used as catalytic systems^1,2 or as precursors to obtain nanoparticles, including iron oxide magnetic nanoparticles (MNPs),³ and nanostructure materials for technical and biomedical applications.^4–8Glycerolates of biogenic elements (Si, Zn, B and Ti) are of particular interest because of their biological activity. They are used as biocompatible precursors in the sol–gel synthesis of pharmacologically active hydrogels with reparative, regenerative, antioxidant, immunotropic and antimicrobial effects.^8–10 In this regard, glycerolate of the biogenic iron element can be considered as an innovative biocompatible precursor in the sol–gel synthesis of composite bioactive hydrogels possessing a haemostatic effect characteristic of various iron compounds.¹¹A promising trend in biomedicine is the core–shell modification of Fe₃O₄ MNPs for MRI diagnostics or magnetic hyperthermia of tumors.^12–14 So, the development of an iron glycerolate shell on the surface of Fe₃O₄ MNPs¹⁵ and studying an opportunity of using modified nanoparticles in magnetic hyperthermia is of particular interest. In addition, the antibacterial activity of Fe₃O₄ MNPs with glycerol adsorbed on the surface was also demonstrated.^16,17In the literature, individual iron(ii) and iron(iii) glycerolates have not so far been described. At the same time, the synthesis of individual forms is extremely important for biomedical purposes in order to determine bioavailability parameters. The available literature data concern only mixed iron(ii,iii) glycerolate that is usually formed as a result of the interaction of di- or trivalent iron oxides, hydroxides or salts (mainly oxalates) with glycerol at elevated temperatures (up to 245 °C).^15,18–20 It is worth noting that all attempts to synthesize iron glycerolates from chlorides and sulfates of ferrous or ferric irons proved to be unsuccessful.²⁰ At the same time, iron glycerolate was obtained from iron(iii) nitrate in boiling glycerol under reflux (280 °C);³ however, contents of iron(iii) and iron(ii) were not determined in that product.Regardless of the iron valence state in the starting compound, Fe(ii) and Fe(iii) are present in the resulting glycerolate in all cases. It should be noted that the possible pathways of the redox process for obtaining mixed iron(ii,iii) glycerolate are not discussed in the literature. The quantitative Fe(ii)/Fe(iii) ratio is usually determined by the Mössbauer spectroscopy²¹ or the colorimetric method.¹⁹ The composition of iron(ii,iii) glycerolate is mainly described by the following formulas: Fe₂C₆H₁₁O₆ (powder diffraction file JCPDSD-ICDD PDF 2, card [23-1731])¹⁸ and Fe₃⁺²Fe₂⁺³(C₃H₅O₃)₄.^19–21 It was not possible to obtain single crystals of iron glycerolate and calculate the unit cell parameters.^4,18We have found that the reactions of iron(ii) or iron(iii) chlorides and sulfates with glycerol proved to proceed only in the presence of an equivalent amount of alkali to give glycerolates of various chemical compositions. Thus, for the first time, individual iron(iii) glycerolate FeC₃H₅O₃ (1) was obtained in 91% yield on heating iron(iii) chloride hexahydrate FeCl₃·6H₂O with sodium hydroxide in an excess of glycerol C₃H₈O₃ at 180 °C for 18 h (Scheme 1) (see ESI^†).Open in a separate windowScheme 1Synthesis of iron(iii) glycerolate 1.The resulting product 1 is a light green powder insoluble in water and organic solvents, thus indicating a probable polymeric structure. It should be noted that the reaction temperature (180 °C) and duration (18 h) appear to be optimal taking into account a high yield of the product and its purity.Heating iron(ii) sulfate heptahydrate FeSO₄·7H₂O in glycerol in the presence of an equivalent amount of NaOH under the same conditions (180 °C, 18 h) resulted in mixed iron(ii,iii) glycerolate Fe₃⁺²Fe₅⁺³(C₃H₅O₃)₇ (2) in 83% yield (see ESI^†). The resulting product is a dark green powder that is poorly soluble in water and organic solvents.Iron glycerolates 1 and 2 were formed as colored powders; they are storage stable with no change in structure and no noticeable change in color; they do not melt to decomposition temperature. Dilute acids or hot water caused decomposition with the production of glycerol and iron (hydroxy)oxides or salts, as it was noted earlier.¹⁸ Plausible pathways for the formation of iron glycerolate 1, as well as iron glycerolate 2 (Scheme 2) and the features of the process are discussed below.Open in a separate windowScheme 2Formation of iron(ii,iii) glycerolate 2.Magnetic materials based on Fe₃O₄ nanoparticles with a biologically compatible coating are of great interest for biology and medicine.^12–14 Previously, we were the first to demonstrate the possibility of forming a shell of iron glycerolate on the surface of Fe₃O₄ MNPs by a simple and reproducible method, namely, by interacting Fe₃O₄ MNPs with glycerol at 220 °C for 40 h.¹⁵ In this work, we optimized the synthetic procedure and chose the optimum conditions (180 °C, 18 h) (see ESI^†). The composition of the resulting shell was found to correspond to iron glycerolate 1.To determine the Fe(ii)/Fe(iii) ratio in the obtained products, we used the Mössbauer spectroscopy. Fig. 1 shows the Mössbauer spectra of iron glycerolates 1 (a and c) and 2 (b). The samples were prepared by deposition of the powder onto aluminum foil with a diameter of 22 mm (see ESI^†).Open in a separate windowFig. 1 ⁵⁷Fe Mössbauer spectra at 295 K of (a) iron(iii) glycerolate 1, (b) iron(ii,iii) glycerolate 2, and (c) iron(iii) glycerolate 1 from Fe₃O₄ MNPs. The doublets of Fe³⁺ and Fe²⁺ ions are marked in red and blue, respectively. The black line represents the sum of these lines. Sodium nitroprusside C₅FeN₆Na₂O was taken as reference.The Mössbauer spectrum of iron glycerolate 1 (Fig. 1a) contains only one doublet (red line) with quadrupole splitting value of 0.48 mm s⁻¹ (iii) positions,21 at the same time there are no signals typical for Fe(ii). The Mössbauer spectrum of iron glycerolate 2 (Fig. 1b) contains two doublets (red and blue lines) with quadrupole splitting Q_s values of 0.46 and 2.29 mm s⁻¹ (iii) and Fe(ii) positions, respectively.21 In this case, the content of Fe(ii) was 38%; Fe(iii), 62%.Fitting parameters of ⁵⁷Fe Mössbauer spectra (Fig. 1) for iron glycerolates

Preparation of polymethacrylate monolith modified with cysteine for the determination of Cr(iii) ions

In this study, a simple and rapid polymer monolith microextraction procedure was developed for the determination of Cr(iii) ions by inductively coupled plasma-atomic emission spectrometry. A monolithic column modified with cysteine was synthesized and characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermal gravimetric analysis, specific surface area analysis and pore size distribution analysis. The influences of analytical parameters such as sample pH, adsorption time, eluent type, and coexisting ions were examined. The limit of detection (LOD) and limit of quantification (LOQ) for Cr(iii) ions were 0.005 μg mL⁻¹ and 0.017 μg mL⁻¹, and the relative standard deviation (RSD) was 7.4% (n = 5). The prepared cysteine functionalized monolithic column displayed good enrichment capacity and was successfully applied to the determination of Cr(iii) ions in real samples.

In this study, a simple and rapid polymer monolith microextraction procedure was developed for the determination of Cr(iii) ions by inductively coupled plasma-atomic emission spectrometry.     

Effect of Ti-doping on the electrochemical performance of sodium vanadium(iii) phosphate

Na₃V_2−xTi_x(PO₄)₃ (x = 0.00, 0.05, 0.10, and 0.15) was successfully synthesized by a conventional solid-state route. The XRD results show that Ti is incorporated in the lattice of Na₃V₂(PO₄)₃ and the tetragonal structure has not been changed after doping. Among all the composites, the Na₃V_1.9Ti_0.1(PO₄)₃ composite delivers the highest discharge capacity of 114.87 mA h g⁻¹ at 0.1C and possesses a capacity retention of 96.23% after 20 cycles at 0.1C, demonstrating the better rate performance and cycle stability in the potential range of 2.0–3.8 V. Electrochemical impedance spectroscopy (EIS) results reveal that the Na₃V_1.9Ti_0.1(PO₄)₃ composite has a lower charge transfer resistance and a higher Na-ion diffusion coefficient compared to other composites. The results indicate that Ti-doping in Na₃V₂(PO₄)₃ can effectively enhance the electrochemical performance of this tetragonal compound, especially at a high charge/discharge rate.

Na₃V_2−xTi_x(PO₄)₃ (x = 0.00, 0.05, 0.10, 0.15) was synthesized by a conventional solid-state route. Ti doping can effectively enhance the electrochemical performance of this tetragonal compound, especially under high charge–discharge rates.     

Towards ferroelectricity-inducing chains of halogenoantimonates(iii) and halogenobismuthates(iii)

In halogenoantimonate(iii) and halogenobismuthate(iii) organic–inorganic hybrids, chains of trans-connected octahedra, trans-[MX₅]_∞, are considered attractive anionic structures for inducing ferroelectricity. The latter is realized by displacing the bridging halogen atoms along the chain direction – the process that changes the polarity of the whole unit. Advances in the identification of such materials have been hindered, however, by substantial difficulty in obtaining such structures. Here we investigate structural and dielectric properties of three families of compounds based on 2-mercaptopyrimidinium, 2-aminopyrimidinium, and 2-amino-4-methylpyrimidinium cations in which 8 out of 12 compounds show trans-[MX₅]_∞ chains in their crystal structures. Two of the compounds adopt a polar P2₁ space group and are potentially ferroelectric. We perform a detailed structural analysis of all compounds with trans-[MX₅]_∞ chains discovered by far to understand the factors that lead to the chains'' formation. We reveal that the size of a cation predominantly defines the accessibility of structures with this anionic form and we provide rules for designing hybrids with trans-[MX₅]_∞ chains to help guide future efforts to engineer materials with interesting non-linear electrical properties.

A discovered abundance of structures with rare and highly-desired anionic chains is examined to identify structural factors leading to the chains'' formation.     

Enhanced phosphate sequestration by Fe(iii) modified biochar derived from coconut shell

In this work, a novel Fe-modified coconut shell biochar (Fe-CSB) was synthesized and utilized to remove phosphate from aqueous solution. Characterization results confirmed that the iron in the Fe(iii)-impregnated CSB existed mainly in the amorphous phase, as ferrihydrite and amorphous hydroxide, which substantially enhanced the phosphate adsorption. Batch experiments indicated that phosphate adsorption on the Fe-CSB was highly dependent on the pH, the humic acid, and temperature, while it was less affected by the nitrate. Phosphate adsorption by the CSB and Fe-CSB could be well described by the pseudo n-th order and Langmuir–Freundlich models. The fitting of the experimental data with the intra-particle diffusion model revealed that surface adsorption and inner-sphere diffusion were involved in the phosphate adsorption process, and that the latter was the rate-controlling step. Batch adsorption experiments and post-adsorption characterization results revealed that the phosphate adsorption by Fe-CSB was primarily governed by four mechanisms: ligand exchange, electrostatic attraction, chemical precipitation, and inner-sphere complexation. This work demonstrated that the modified Fe-CSB is an environmentally friendly and cost-effective bioretention medium and could open up new pathways for the removal of phosphorus from stormwater, as well as solve the problem of waste biomass pollution.

In this work, a novel Fe-modified coconut shell biochar (Fe-CSB) was synthesized and utilized to remove phosphate from aqueous solution.     

Tinospora cordifolia derived biomass functionalized ZnO particles for effective removal of lead(ii), iron(iii), phosphate and arsenic(iii) from water

Owing to the vast diversity in functional groups and cost effectiveness, biomass can be used for various applications. In the present study, biomass from Tinospora cordifolia (TnC) was prepared and grafted onto the surface of ZnO particles following a simple method. The TnC functionalized ZnO particles (ZnO@TnC) were characterized and exhibited excellent adsorption properties towards Pb²⁺ (506 mg g⁻¹), Fe³⁺ (358 mg g⁻¹) and PO₄³⁻ (1606 mg g⁻¹) and the Fe³⁺ adsorbed ZnO@TnC adsorbs AsO₂¹⁻ (189 mg g⁻¹); the metal ions and anions were analyzed by ICP and IC. For reuse of ZnO@TnC, a desorption study was successfully carried out using NaOH and EDTA for PO₄³⁻ and Pb²⁺, respectively; Fe³⁺ was further used for adsorption of As(iii). The adsorption fits well with the Langmuir adsorption isotherm model and the adsorption kinetic data are best fitted with a pseudo-second-order equation. The system developed may be useful for treatment of waste water and industrial effluents.

Owing to the vast diversity in functional groups and cost effectiveness, biomass can be used for various applications.     

Synthesis,spectroscopic, thermal,antimicrobial and electrochemical characterization of some novel Ru(iii), Pt(iv) and Ir(iii) complexes of pipemidic acid

Three new solid complexes of pipemidic acid (Pip–H) with Ru³⁺, Pt⁴⁺ and Ir³⁺ were synthesized and characterized. Pipemidic acid acts as a uni-dentate chelator through the nitrogen atom of the –NH piperazyl ring. The spectroscopic data revealed that the general formulas of Pip–H complexes are [M(L)_n(Cl)_x]·yH₂O ((1) M = Ru³⁺, L: Pip–H, n = 3, x = 3, y = 6; (2) M = Pt⁴⁺, L: Pip–NH₄, n = 2, x = 4, y = 0 and (3) M = Ir³⁺, L: Pip–H, n = 3, x = 3, y = 6). The number of water molecules with their locations inside or outside the coordination sphere were assigned via thermal analyses (TG, DTG). The DTG curves refer to 2–3 thermal decomposition steps where the first decomposition step at a lower temperature corresponds to the loss of uncoordinated water molecules followed by the decomposition of Pip–H molecules at higher temperatures. Thermodynamic parameters (E*, ΔS*, ΔH* and ΔG*) were calculated from the TG curves using Coats–Redfern and Horowitz–Metzeger non-isothermal models. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques were carefully used to assign properly the particle sizes of the prepared Pip–H complexes. The biological enhancement of Pip–H complexes rather than free chelate were assessed in vitro against four kinds of bacteria G(+) (Staphylococcus epidermidis and Staphylococcus aureus) and G(−) (Klebsiella and Escherichia coli) as well as against the human breast cancer (MCF-7) tumor cell line.

Three new solid complexes of pipemidic acid (Pip–H) with Ru³⁺, Pt⁴⁺ and Ir³⁺ were synthesized and characterized. Pipemidic acid acts as a uni-dentate chelator through the nitrogen atom of the –NH piperazyl ring.     

Fe(iii) and Cr(vi) ions' removal using AgNPs/GO/chitosan nanocomposite as an adsorbent for wastewater treatment

Heavy metal ions in water refer to significant risks to the biological system due to their high toxicity. Therefore, the decontamination of water polluted by heavy metal ions attracts significant interest of researchers. Adsorption by nanomaterials has been a widely used technique for removing heavy metal ions from water. Chitosan was extracted from shrimp shellfish and mixed with laboratory-prepared AgNPs/GO in the ratio of 3 : 1. A series of tests evaluates the best condition of pH, amount of adsorbent, retention time, stirring speed, temp, and initial concentration. The research was conducted under various conditions. Langmuir, Freundlich, Tempkin, and Dubinin–Radushkevich isotherms were also tested. Also, the column adsorption experiment was carried out on industrial wastewater at different flow rates and column bed heights. The optimal values of the contact time, pH, and adsorbent dose of Cr(vi) were found to be 80 min, 4, and 0.1 g 100 mL⁻¹, respectively, at room temperature (30 °C), agitation at 150 rpm, and initial concentration of 50 ppm. On the other hand, the optimal value of contact time, pH, and adsorbent dose of Fe(iii) were found to be 30 min, 6, and 0.02 g 100 mL⁻¹, respectively, at room temp (30 °C) with a stirring speed of 250 rpm and an initial concentration of 40 ppm. For Cr(vi) and Fe(iii), equilibrium studies show that the data fit the Freundlich isotherm well (correlation coefficient, R² = 0.98) (III). A link between the pseudo-second order active model and data fitting the pseudo-first order active models were made. Within the intraparticle diffusion model, there are four stages that the mechanism must go through before it is at equilibrium. The adsorbent was tested in an industrial adsorbent column. This test proves that the nanocomposite''s adsorption capacity can be restored by washing it with 0.1 M HCl, as shown by the periodicity test. After four cycles, the amount of Cr(vi) adsorbed on AgNPs/GO/chitosan was just 20%, which is insufficient for further adsorption experiments. Cr(vi) removal rates (%R) decreased slightly.

Steps of AgNPs/GO/chitosan nanocomposite preparation.     

Fabrication of a low-cost adsorbent supported zero-valent iron by using red mud for removing Pb(ii) and Cr(vi) from aqueous solutions

In this study, a granular red mud supported zero-valent iron (ZVI@GRM) was successfully prepared and was used to remove Pb(ii) and Cr(vi) from aqueous solution. Zero-valent iron (ZVI) was synthesized by direct reduction of iron oxide in red mud by maize straw as a reductant at 900 °C in an anoxic atmosphere. The technical characterization (SEM, EDS, XRD, FTIR and BET) revealed that ZVI@GRM was loaded with zero-valent iron and contained different size pores. The factors of adsorption experiments include initial concentration, contact time, pH and temperature. The Pb(ii) and Cr(vi) removal by ZVI@GRM well fitted the pseudo-second-order kinetics model and the removal of heavy metals was an endothermic process. Essentially, Pb(ii) was transformed to precipitate forms (Pb⁰, Pb (OH)₂, or 2PbCO₃·Pb (OH)₂) and Cr(vi) was converted to Cr (OH)₃ or Cr³⁺/Fe³⁺ hydroxides. The maximum removal capacity for Pb(ii) and Cr(vi) by ZVI@GRM was 149.42 and 37.14 mg g⁻¹. ZVI@GRM was a low-cost material and had outstanding performance and great potential in wastewater treatment.

In this study, a granular red mud supported zero-valent iron (ZVI@GRM) was successfully prepared and was used to remove Pb(ii) and Cr(vi) from aqueous solution.     

Novel electroblowing synthesis of tin dioxide and composite tin dioxide/silicon dioxide submicron fibers for cobalt(ii) uptake

Nanoscale SnO₂ has many important properties ranging from sorption of metal ions to gas sensing. Using a novel electroblowing method followed by calcination, we synthesized SnO₂ and composite SnO₂/SiO₂ submicron fibers with a Sn : Si molar ratio of 3 : 1. Different calcination temperatures and heating rates produced fibers with varying structures and morphologies. In all the fibers SnO₂ was detected by XRD indicating the SnO₂/SiO₂ fibers to be composite instead of complete mixtures. We studied the Co²⁺ separation ability of the fibers, since ⁶⁰Co is a problematic contaminant in nuclear power plant wastewaters. Both SnO₂ and SnO₂/SiO₂ fibers had an excellent Co²⁺ uptake with their highest uptake/K_d values being 99.82%/281 000 mL g⁻¹ and 99.79%/234 000 mL g⁻¹, respectively. Compared to the bare SnO₂ fibers, the SiO₂ component improved the elasticity and mechanical strength of the composite fibers which is advantageous in dynamic column operation.

Calcination temperature and heating rate markedly affected the structure and morphology of electroblown SnO₂/SiO₂ composite fibers. Compared with bare SnO₂ fibers, the SiO₂ component improved the mechanical strength but slightly weakened Co²⁺ uptake.     

Thermodynamic investigation with chemical kinetic analysis on the reoxidation phenomenon of the Cr(iii) in air

In this paper, the reoxidation behaviours of CrOOH and Cr(OH)₃ are investigated as the major reduction products of Cr(vi). The atmosphere oxidation of Cr(iii) is studied in the environment of soil without manganese and hydrogen peroxide. The influence of temperature and pH value on the oxidation rate of Cr(iii) is examined by Experiment methods in details. According to the experimental results, the oxidation of Cr(iii) is promoted in the environment with high pH value, however, the oxidation process is stable with temperature. The oxidation process of CrOOH and Cr(OH)₃ are theoretically researched by thermodynamic calculation and density functional theory (DFT) simulation. The results of DFT indicate that both CrOOH and Cr(OH)₃ are oxidized during the chemical adsorption process of O₂ in alkaline environment. With the transformation from Cr(iii) to Cr(vi), the Cr–O covalent bond forms in the adsorption process. The crystal structure difference between CrOOH and Cr(OH)₃ leads to the different oxidation reaction between O₂ and Cr(iii). The significant alteration of oxidation process in (110), (310), (321) crystal planes is also observed indicating the crystal orientation dependence. Based on the chemical reaction kinetics, the chemical equivalent constant K of CrOOH is higher than Cr(OH)₃, illustrating higher chemical stability in air. In summary, both experimental study and theoretical analysis on the reoxidation phenomenon of Cr(iii) reduced from Cr(vi) in natural environment demonstrate that not only the external factors such as temperature and pH value but also the crystal structure of Cr(iii) compound have dramatic influence on the oxidation process.

In this paper, the reoxidation behaviours of CrOOH and Cr(OH)₃ are investigated as the major reduction products of Cr(vi).     

Experimental and theoretical studies on the extraction behavior of Cf(iii) by NTAamide(C8) ligand and the separation of Cf(iii)/Cm(iii)

In this work we studied the extraction behaviors of Cf(iii) by NTAamide (N,N,N′,N′,N′′,N′′-hexaocactyl-nitrilotriacetamide, C8) in nitric acid medium. Influencing factors such as contact time, concentration of NTAamide(C8), HNO₃ and NO₃⁻ as well as temperature were considered. The slope analysis showed that Cf(iii) should be coordinated in the form of neutral molecules, and the extraction complex should be Cf(NO₃)₃·2L (L = NTAamide(C8)), which can achieve better extraction effect under the low acidity condition. When the concentration of HNO₃ was 0.1 mol L⁻¹, the separation factor (SF_Cf/Cm) was 3.34. The extractant has application prospect to differentiate the trivalent Cf(iii) and Cm(iii) when the concentration of nitric acid is low. On the other hand, density functional theory (DFT) calculations were conducted to explore the coordination mechanism of NTAamide(C8) ligands with Cf/Cm cations. The NTAamide(C8) complexes of Cf(iii)/Cm(iii) have similar geometric structures, and An(iii) is more likely to form a complex with 1 : 2 stoichiometry (metal ion/ligands). In addition, bonding property and thermodynamics analyses showed that NTAamide(C8) ligands had stronger coordination ability with Cf(iii) over Cm(iii). Our work provides meaningful information with regard to the in-group separation of An(iii) in practical systems.

We performed basic chemical studies on Cf using NTAamide extractant. The results of experiments and DFT calculations show that NTAamide has a good coordination ability to Cf/Cm and is expected to be applied to Cf/Cm separation.     

Cerium(iii) complexes with azolyl-substituted thiophenolate ligands: synthesis,structure and red luminescence

In order to obtain molecular Ce(iii) complexes which emit red light by f–d transitions the azolyl-substituted thiophenolates were used as the ligands. The thiophenolate Ce(iii) complexes were synthesized by the reaction of Ce[N(SiMe₃)₂]₃ with respective thiophenols 2-(2′-mercaptophenyl)benzimidazole (H(NSN)), 2-(2′-mercaptophenyl)benzoxazole (H(OSN)) and 2-(2′-mercaptophenyl)benzothiazole (H(SSN)) in DME media. The structures of the benzimidazolate (Ce(NSN)₃(DME)) and benzothiazolate (Ce(SSN)₃(DME)) derivatives were determined by X-ray analysis which revealed that the cerium ion in the molecules is coordinated by one DME and three anionic thiophenolate ligands. The lanthanum complex La(OSN)₃(DME) has been synthesized similarly and structurally characterized. It was found that the solids of Ce(SSN)₃(DME) and Ce(OSN)₃(DME) exhibit a broad band photoluminescence peaking at 620 nm which disappears upon solvatation. With an example of OSN derivatives it was proposed that this behaviour is caused by the blue shift of the f–d transition of Ce³⁺ ions.

Novel Ce(iii) complexes with azolyl-substituted thiolate ligands have been synthesized. Some of them exhibit red PL.     

Recent developments in alginate-based adsorbents for removing phosphate ions from wastewater: a review

The huge development of the industrial sector has resulted in the release of large quantities of phosphate anions which adversely affect the environment, human health, and aquatic ecosystems. Naturally occurring biopolymers have attracted considerable attention as efficient adsorbents for phosphate anions due to their biocompatibility, biodegradability, environmentally-friendly nature, low-cost production, availability in nature, and ease of modification. Amongst them, alginate-based adsorbents are considered one of the most effective adsorbents for removing various types of pollutants from industrial wastewater. The presence of active COOH and OH⁻ groups along the alginate backbone facilitate its physical and chemical modifications and participate in various possible adsorption mechanisms of phosphate anions. Herein, we focus our attention on presenting a comprehensive overview of recent advances in phosphate removal by alginate-based adsorbents. Modification of alginate by various materials, including clays, magnetic materials, layered double hydroxides, carbon materials, and multivalent metals, is addressed. The adsorption potentials of these modified forms for removing phosphate anions, in addition to their adsorption mechanisms are clearly discussed. It is concluded that ion exchange, complexation, precipitation, Lewis acid–base interaction and electrostatic interaction are the most common adsorption mechanisms of phosphate removal by alginate-based adsorbents. Pseudo-2^nd order and Freundlich isotherms were figured out to be the major kinetic and isotherm models for the removal process of phosphate. The research findings revealed that some issues, including the high cost of production, leaching, and low efficiency of recyclability of alginate-based adsorbents still need to be resolved. Future trends that could inspire further studies to find the best solutions for removing phosphate anions from aquatic systems are also elaborated, such as the synthesis of magnetic-based alginate and various-shaped alginate nanocomposites that are capable of preventing the leaching of the active materials.

The huge development of the industrial sector has resulted in the release of large quantities of phosphate anions which adversely affect the environment, human health, and aquatic ecosystems.     

Tb(iii)-doped nanosheets as a fluorescent probe for the detection of dipicolinic acid

A new fluorescent probe based on terbium(iii)-doped nanosheets was designed for detecting low-levels of dipicolinic acid (DPA), a biomarker of bacterial spores. The ability to detect ultra-low concentrations of DPA is therefore of great significance. First, Tb(iii)-doped ytterbium hydroxide nanosheets were obtained by mechanical exfoliation from layered rare-earth hydroxide (LRH) materials. The morphology of the as-synthesized nanosheets was studied by transmission electron microscopy and atomic force microscopy. The Tb(iii)-doped nanosheets are demonstrated to be highly sensitive to DPA, which remarkably enhances Tb(iii) luminescence intensities at a wavelength of 544 nm. Furthermore, Tb(iii) emission increases linearly with DPA concentration. Selectivity studies were conducted by adding different competing aromatic ligands to the sensing solution; however, their fluorescence responses were observed to be negligibly small in comparison with that of DPA. Our findings provide a basis for the application of Tb(iii)-doped nanosheets for accurate, sensitive, and selective monitoring of DPA as a biomarker of anthrax.

A new fluorescent probe based on terbium(iii)-doped nanosheets was designed for detecting low-levels of dipicolinic acid (DPA), a biomarker of bacterial spores.     

Furan oxidation by Mn(iii)/Co(ii) catalysts – application to benzofuran synthesis

Furans containing a β-ketoester group at 2-position undergo oxidative ring-opening by Mn(iii)/Co(ii) catalysts under an O₂ atmosphere to produce 1,4-dicarbonyl moieties through an endoperoxide intermediate, which consecutively cyclized with the β-ketoester unit to afford 4-hydroxy-2-cyclohexen-1-ones. This oxidation/cyclization products were efficiently transformed into versatile benzofuran derivatives after consecutive aromatization and Paal–Knorr reaction.

Catalytic oxidation of furan containing β-ketoester at 2-position by Mn^III/Co^II produced 4-hydroxy-2-cyclohexen-1-ones, which can be transformed into versatile benzofuran derivatives.

Furan is a hetero-aromatic compound, ready to react with various oxidants or reactive electrophiles to serve as versatile C₄ building blocks in organic synthesis.¹ Furan can produce a conjugated 1,4-dicarbonyl unit by singlet oxygen through an endoperoxide intermediate,² which may be trapped by a nearby internal hydroxy group to generate a pyranose structure as was reported by Achmatowicz.³ This oxidative conversion may also be attained through the epoxide intermediate by other oxidants including dioxiranes, metal oxides, N-bromosuccinimide, H₂O₂, peroxy acids etc.⁴ Lallemand et al. demonstrated that the furan oxidation product by MCPBA would be trapped by a nearby enolic carbon of β-ketoester leading to a polyoxygenated decalin system (Scheme 1).⁵Open in a separate windowScheme 1Furan as versatile C₄ building blocks for pyranose and cyclohexenone by oxidation.We recently reported that the Mn^III-mediated peroxy radical in β-ketoester A induced oxidation of the acetyl group to α-ketoester C through the dioxetane intermediate B, which was eventually transformed into bichalcophen D by hetero-aromatization (Paal–Knorr reaction).^6a In the present work, we want to report that β-ketoester 2a containing a proximal furan moiety undergoes the furan oxidation to the conjugated 1,4-dicarbonyl intermediate E under the same reaction conditions, and is trapped by the active α-methinyl carbon radical of β-ketoester to produce 4-hydroxy-2-cyclohexen-1-ones 3a-1 and 3a-2 (Scheme 2). Whereas the distal electron-deficient furan ring in A was not affected, the proximal furan ring in 2a was smoothly oxidized by Mn^III/Co^II catalysts under aerobic condition. Cyclohexenones 3a-1 and 3a-2, stereoisomers at the α-carbon of β-ketoester with both hydroxy and benzoyl substituents in equatorial positions (vide infra), were produced in equal amounts, which would be perfect substates for the conversion into versatile benzofuran derivative 4a after decarbonylative aromatization and Paal–Knorr reaction.Open in a separate windowScheme 2Disparate reactivity of β-ketoesters A and 2a under the Mn^III/Co^II catalyzed oxidation.We herein delineated the optimal condition for the furan oxidation of β-ketoester 2a to produce 4-hydroxy-2-cyclohexen-1-ones 3a-(1/2). Generality of the furan oxidation was demonstrated for β-ketoesters 2 with various aroyl substituents. Finally, the transformation of the above oxidative cyclization products 3 into versatile benzofuran derivatives 4 was described.The substrate 2a for furan oxidation was prepared by conjugate addition of ethyl acetoacetate to chalcone derivative 1a containing a furan-2-yl group at β-position. Ethyl acetoacetate was utilized as reagent and solvent at 60 °C under CeCl₃ and NaI catalysts (10 mol% each).⁷ The Michael adduct 2a was obtained in 58% yield as a 1 : 1 diastereomeric mixture, which was utilized for the oxidation reaction without separation. The typical condition for the previous oxidative deacetylation of chalcone derivative A under Mn(OAc)₃ and CoCl₂ catalysts (10 mol% each) in AcOH was utilized as a standard condition for the optimization study of the furan oxidation of 2a (6aOptimization study for the oxidation of 2a to 3a-(1/2) under Mn^III/Co^II catalysts^a

Introduction of a trinuclear manganese(iii) catalyst on the surface of magnetic cellulose as an eco-benign,efficient and reusable novel heterogeneous catalyst for the multi-component synthesis of new derivatives of xanthene

In this work, the new trinuclear manganese catalyst defined as Fe₃O₄@NFC@NNSM-Mn(iii) was successfully manufactured and fully characterized by different techniques, including FT-IR, XRD, TEM, SEM, EDX, VSM, and ICP analysis. There have been reports of the use of magnetic catalysts for the synthesis of xanthine derivatives. The critical potential interest in the present method include short reaction time, high yields, recyclability of the catalyst, easy workup, and the ability to sustain a variety of functional groups, which give economical as well as ecological rewards. Also, the synthesized catalyst was used as a recyclable trinuclear catalyst in alcohol oxidation reactions at 40 °C. The magnetic catalyst activity of Fe₃O₄@NFC@NNSM-Mn(iii) could be attributed to the synergistic effects of the catalyst Fe₃O₄@NFC@NNS-Mn(iii) with melamine. Employing a sustainable and safe low temperature, using an eco-friendly solvent, no need to use any additive, and long-term stability and magnetic recyclability of the catalyst for at least six successive runs are the advantages of the current protocol towards green chemistry. This protocol is a benign, environmentally friendly method for heterocycle synthesis.

In this work, the new trinuclear manganese catalyst defined as Fe₃O₄@NFC@NNSM-Mn(iii) was successfully manufactured and fully characterized by different techniques, including FT-IR, XRD, TEM, SEM, EDX, VSM, and ICP analysis.     

Modulation of a coordination structure in a europium(iii)-based metallo-supramolecular polymer for high proton conduction

Developing high proton conducting solid materials is significant in the field of fuel cells. A europium(iii)-based metallo-supramolecular polymer with uncoordinated carboxylic acids (PolyEu-H) was successfully synthesized by modifying the synthesis conditions. The proton conductivity was enhanced with increasing the relative humidity (RH) from 30 to 95% RH. PolyEu-H showed about 10⁴ times higher proton conductivity than the polymer with coordinated carboxylic acids (PolyEu) and about 400 times higher than the polymer without carboxylic acids (PolyEu-2). The proton conductivity of PolyEu-H reached 4.45 × 10⁻² S cm⁻¹ at 95% RH and 25 °C and 5.6 × 10⁻² S cm⁻¹ at 75 °C. The activation energy, E_a was ultralow (0.04 eV), which indicates proton conduction based on the Grotthuss mechanism. The results indicate that efficient proton conduction occurs through proton channels formed by moisture in PolyEu-H.

Developing high proton conducting solid materials is significant in the field of fuel cells. We firstly synthesized europium(iii)-based metallo-supramolecular polymer with uncoordinated carboxylic acids (PolyEu-H), for high proton conduction.     

Qualitative colorimetric analysis of a Ir(iii)/Eu(iii) dyad in the presence of chemical warfare agents and simulants on a paper matrix

The addition of G- and V-series organophosphorus chemical warfare agents and simulants to a paper-based assay of a dual-luminescent Ir(iii)/Eu(iii) dyad generated different emissive responses between the classes and compound types. The emission responses are complex and based not only on altering the balance between red Eu(iii)-based and blue Ir(iii)-based luminescent components, but also incorporate other factors such as analyte volatility, concentration and UV absorption. The extent of this emission colour change was analysed colorimetrically and related to the change in RGB output over time.

A dual emissive Ir(iii)/Eu(iii) dyad in a paper-based luminescence assay for liquid chemical warfare agents demonstrated clear visual responses.

The traditional organophosphorus chemical warfare agents (OP CWAs) comprise two main series of agents: the G- and V-series (examples GB and VX respectively, Fig. 1). Although the G- and V-series OP CWAs display differing structural and physico-chemical properties (e.g. volatility), these chemicals are all fast-acting and potent acetylcholinesterase inhibitors that can cause incapacitation or death rapidly upon exposure.¹ Thus, fast and reliable chemical sensing methods are required to inform and protect military and national security first responders and the general public.Open in a separate windowFig. 1The chemical structures of the G and V-series chemical warfare agents VX (2-diisopropylaminoethyl ethyl methylphosphonothiolate) and GB (Sarin, isopropyl methylphosphonofluoridate) and simulants TEP (triethyl phosphate), VO (2-diisopropylaminoethyl ethyl methylphosphonate) and DMMP (dimethyl methylphosphonate) utilised in this investigation.Trivalent lanthanide [Ln(iii)] complexes that display characteristic strong luminescence in the visible region are being increasingly exploited for the luminescence-based sensing of OP CWAs due to their known ability to form coordinative bonds with phosphonyl and phosphoryl moieties.² In addition, the trivalent lanthanide complexes display high intensity and narrow emission bands, long excited state lifetimes and substantial Stokes shifts which provide attractive foundations for luminescence-based sensing systems.³Previously we reported the solution-state emissive behaviour of an Ir(iii)/Eu(iii) dyad (denoted Ir·L·Eu, Fig. 2) as the basis of a ratiometric sensor for the V-series simulant 2-diisopropylaminoethyl ethyl methylphosphonate (VO).⁴ Upon excitation of this Ir·L·Eu dyad, photoinduced energy transfer from the ³MLCT/³LC excited-state of the Ir(iii) complex to the lower-lying ⁵D₀ excited state of the Eu(iii) ion results in the sensitised red luminescence from the Eu(iii) centre with concomitant partial quenching of the Ir(iii) blue emission.⁵ Titration of VO aliquots into a solution of Ir·L·Eu resulted in a sequential colour change of the emission from red through to blue (ESI Fig. S1(a)^†).⁴ This emission colour ‘switch’ is the result of both static and dynamic luminescence quenching of the Eu(iii) complex arising from the presence of VO. In particular, bidentate chelating coordination of VO to the Eu(iii) ion displaces the {Eu(hfac)₃} unit from the Ir·L·Eu dyad (Fig. 2). This resulted in the loss of sensitised Eu(iii)-based emission and restoration of the blue Ir(iii)-based emission.^4,6 Additional quenching of any residual Eu(iii)-based emission occurs by photoinduced electron transfer from the tertiary amine unit of either chelated VO, or by collision with excess VO in solution (Scheme 1).^4,6Open in a separate windowFig. 2Comparison of the agent, simulant and potential interferent results over time using neat samples of analyte under 254 nm UV irradiation (one drop of each concentration added). Note the acetone 1 minute image is actually from the 30 second time point.Open in a separate windowScheme 1Interaction of the V-series simulant VO with the dyad sensor Ir·L·Eu.There are numerous other literature examples of lanthanide-based sensors for the detection of OP CWAs, simulants, pesticides and toxic industrial chemicals.^2,6–14 Whilst many of these systems have displayed positive results and properties in solution-based studies, only a few have been applied to solid state or matrix loaded assays such as polymers, films or silica. The translation of detection properties to solid state or matrix loaded systems is often imperative for application into electronic detection systems. However, there is also a need for simple presumptive systems such as colorimetric kits, disclosure sprays and detection papers which have the potential to be carried by numerous personnel (low burden and low cost) and utilised quickly and easily. These types of system generally work with high concentrations of analyte to give presumptive results indicative of exposure and contamination and to direct sampling activities.Herein we investigate the use of qualitative luminescent paper-based assays of the Ir·L·Eu dyad for the detection and differentiation of different chemical warfare agents, simulants and potential interferents. Warning: the organophosphorus chemical warfare agents VX and GB are extremely potent acetylcholinesterase inhibitors that can cause incapacitation and death at extremely low concentrations. All of the work reported here has been performed by highly trained personnel in specialised facilities designed for the safe handling and experimentation with highly toxic chemicals. VX and GB are Schedule 1 chemicals under the Chemical Weapons Convention and their synthesis, use and experimentation is tightly controlled under national laws with international oversight form the Organisation for the Prohibition of Chemical Weapons in The Hauge.The Ir·L·Eu dyad paper assays were prepared on Whatman 1 filter paper as described in the ESI.^† One drop of a neat analyte was then placed on a test strip and images of the emissive colour response were taken with the test strip assays under 254 nm under UV irradiation at multiple time points (blank, immediate response, 30, 60, 120, 180, 240, 300 seconds and 60 minutes). This procedure was repeated for all CWAs, simulants and interferents studied. All CWAs and simulants were also tested at varied concentrations in MeCN (0.1 M, 0.05 M, 0.01 M and 0.001 M).Two modes of visual comparison were performed to generate qualitative results: (i) a general comparison of all neat CWAs, simulants and interferents at varied time points to understand which systems would result in a visual change (Fig. 2); and (ii) a targeted comparison of the agent and simulant data at varied concentrations at a time point more suitable for in field testing (Fig. 3). The visual comparison of agent and simulant response over time using neat compounds (Fig. 2) generated some unexpected results in comparison to the solution studies with VO.⁴ VX and its simulant VO gave a very dark blue-black response that correlated well with each other over all time points. GB, however, displayed minimal colorimetric changes up to 5 minutes with the bright blue Ir(iii) luminescence seen only at the 1 hour time point (Fig. 2). This increased time of detection was initially attributed to a reactive pathway that can occur with the G-series CWAs only (hydrolysis of the P–F bond and subsequent detection of F⁻).^2,8 However, when the similar (neat) results of the non-reactive G-series simulant DMMP (which does not contain a P–F bond) are considered this pathway is called into question. Whilst some competitive binding (Scheme 1) likely occurs with VX, VO, GB and DMMP at early time points, the excess analyte also absorbs the UV-light.¹⁵ Over time the excess of the more volatile analytes is lost via evaporation leaving the light blue Ir(iii)-based emission seen with GB and DMMP. With VX and VO evaporation does not occur and a dark blue colour persists; a similar result was also observed with the simulant TEP. This contrast (between the V- and G-series results) is likely the result of a combination of factors including differing volatilities of the CWAs (affecting UV Vis absorbance of excess analyte and test strip dampness), the presence of additional luminescence modulating moieties (i.e. amine in VX and VO) and the loss of luminescence via other pathways. The amine simulant TEA and the P(iii) simulant TEPhosphite did not generate a comparable result to the V- or G-series agents. Both generated near-reversible responses (TEA by 4 minutes and TEPhosphite at 1 hour) as a result of their volatilities and inability to form strong coordinative bonds to the Eu(iii) centre. The difference in emission intensity of the TEPhosphite assay compared to the other analytes at 1 minute and 4 minutes indicates that the system could be utilised to help distinguish between different classes of OP compounds.Open in a separate windowFig. 3Comparison of the agent and simulant luminescence results at varied concentrations in MeCN (one drop of each concentration added) 4 minutes after exposure, under 254 nm UV irradiation.The interferents tested were selected to cover a range of functional groups and volatilities as well as ubiquitous chemicals including common solvents and agent precursors (such as isopropanol). Numerous potential interferents either gave little to no response (e.g. water, hexane and DCM) or a rapid regenerative response as a result of the volatility of the analyte (ethanol, isopropanol, triethyl amine, diethyl ether and ethyl acetate). Toluene, acetonitrile and acetone, whilst resulting in a reversible darkening of the test assay upon application did not yield a change towards blue emission and were not considered to generate an ‘interferent like’ response. The major positive interferents identified were dimethyl formamide (DMF) and the alcohols. DMF displayed results that could be visually confused with both V- and G-series results (depending on the time point) with the initial dark colouration associated with the V-series results and the development over time of the bright blue luminescence similar to that noted with the G-series.One of the main complications in using lanthanide complexes as sensors is the known interference of OH oscillators such as water and alcohols which efficiently provide non-radiative deactivation of the excited states of trivalent lanthanide complexes.¹⁶ The addition of ethanol and isopropanol generated a change from the initial red to purple/blue emission that almost completely visually reversed over time as a result of evaporation (Fig. 2). When water was tested a droplet formed on the surface of the test assay that left an emissive blue ring on absorption. Ultimately evaporation of the water yielded only a slight reduction in the visually observable red emission (Fig. 2). This lack of interference is especially favourable for presumptive tests to be used in operational environments where water is commonly encountered.Presumptive tests taking 1 hour are well outside of operational requirements in the field. However, the time to detection could be lowered in this assay by decreasing the concentration of the analyte or via the application of heat or airflow to facilitate evaporation of excess analyte. The use of such processes to accelerate the development of the results is not unprecedented in analytical chemistry (e.g. TLC plate development) and with this in mind we focused on sample dilution and performed the visual comparison on the images taken 4 minutes after exposure (Fig. 3). This timeframe was selected to allow any residual solvent from the diluted samples to evaporate and to allow for the development of emission changes whilst still falling within the operational requirements for fast detection (where time for detection should be no longer than 4 minutes).^2,17 The comparison of agent response versus concentration at 4 minutes (Fig. 3) demonstrates that the detection limit for visually interpretable responses is quite high (10–50 mM) which implies that the system is best suited for presumptive testing of high concentration or undiluted suspect liquid samples. Across all the concentrations tested, the differences in assay emission between the G and V-series agents was again noted. The VX and VO results were visually consistent (with each other) over neat, 0.1 M and 0.05 M tests even though the amount of analyte was reduced indicating that other factors rather than excess analyte contribute to the loss of luminescence. The bright blue Ir(iii) based emission generated with GB at 0.1 M and 0.05 M was not observed in the experiment using neat GB at 4 minutes. This blue emission is at least partially due the absence of the large excess of (neat) analyte. The results of the diluted G-series simulants DMMP and TEP are quite different to those obtained with GB and supports earlier observations that there may be a reactive component to the GB colour change mechanism (i.e. P–F hydrolysis and detection of F⁻). This means that at 0.1 M and 0.05 M GB can be readily differentiated from compounds that are sufficiently structurally similar to be used as simulants. TEA and TEPhosphite only generated luminescence colour changes when used neat, and not with dilute solutions, which is likely the result of poor binding affinity to Eu(iii) and (in the case of TEA) rapid evaporation.Whist many of the analytes gave emission changes that can be observed with the naked eye (under UV light illumination); many of the responses are variations of the blue emission which may be too subtle to allow visual differentiation between OP compounds and other analytes. Thus interpretation of the results of these systems can be subjective and/or rely upon visual acuity in high stress situations. To combat this we analysed the photographic results to generate RGB colorimetric data for potential application into colour reading technologies to facilitate the reliable, fast and accurate interpretation of results in the field and to differentiate between the outputs obtained with various analytes. The images were processed as outlined in the ESI^† and loaded into the colorimetric program Spot Finder 1.13 (iSense).¹⁸ An area in the centre of the spot formed upon liquid application with the most even colouration was selected for analysis and the averaged RGB data generated. The percentage change in intensity over time (300 seconds) for each RGB colour element at each concentration point was plotted to give a visual representation of the colorimetric changes occurring over the experiment. Fig. 4 demonstrates the RGB plots of the luminescence responses for the application of neat VX, VO, GB and DMMP over 5 minutes (300 seconds). From this analysis it can be seen that VX and VO generate greater colorimetric differences in the blue component compared to GB and DMMP. VX results in near complete loss of the red and green components of the dyad and majority (∼85% loss) of the blue component with no recovery of any colour component over the experiment time; whilst VO only demonstrates complete loss of the red component with significant recovery of the blue component after approximately 60 seconds. It should be noted that increases in the blue component are observable in VX and VO down to 0.01 M (ESI Fig. S4 and S8^†). When looking at the G-series results, GB displays partial loss of the red component with a substantial increase in the blue component which is a trend observable down to 0.05 M (Fig. 4). DMMP however, displayed less significant increases in the blue component observed with GB at neat concentrations but demonstrated more when diluted (ESI Fig. S10^†). This is again most likely due to the reduced amounts of excess analyte present at the lower concentrations.Open in a separate windowFig. 4Colorimetric time response profiles (smoothed data) over 300 seconds by percentage change in each of the R, G and B colour components for neat and 0.05 M VX, VO, GB and DMMP.     

Mechanism of the Fe(iii)-catalyzed synthesis of hexahydropyrimidine with α-phenylstyrene: a DFT study

It is very important to develop multiple C–H substitution reactions of simple alkenes to obtain complex unsaturated components. The present study focuses on a theoretical investigation of the plausible mechanism in the Fe(OTf)₃-catalyzed tandem amidomethylative reactions of α-phenylstyrene. Bis(tosylamido)methane is activated by Fe(OTf)₃ to form tosylformaldimine and its Fe(OTf)₃-adduct. The Fe(OTf)₃-adduct undergoes an intermolecular aza-Prins reaction with α-phenylstyrene to form allylamide. The DFT data support the formation of the hexahydropyrimidine derivative from allylamide, and “condensation/iminium homologation/intramolecular aza-Prins” is the optimal reaction path. At the same time, a possible reaction pathway for the conversion of the hydrolysate 1,3-diamide derivative to the hexahydropyrimidine (HHP) derivative is given. This work is thus instructive for understanding Fe(iii)-based tandem catalysis for the amidomethylative multiple-substitution reactions of alkenes.

It is very important to develop multiple C–H substitution reactions of simple alkenes to obtain complex unsaturated components.