Oxidation of Cysteinate Anions Immobilized in the Interlamellar Space of CaAl-Layered Double Hydroxide.

L-Cysteinate-intercalated CaAl-layered double hydroxide (LDH) was prepared by the co-precipitation method producing highly crystalline hydrocalumite phase with a well-pillared interlayer gallery. The obtained materials were characterized by X-ray diffractometry, IR as well as Raman spectroscopies. By performing interlamellar oxidation reactions with peracetic acid as oxidant, oxidation of cysteinate to cystinate in aqueous and cysteinate sulfenic acid in acetonic suspensions occurred.

Catalytic antioxidant nanocomposites based on sequential adsorption of redox active metal complexes and polyelectrolytes on nanoclay particles.

An antioxidant nanocomposite was prepared by successive adsorption of redox active metal complexes (copper(ii)-bipyridyl and iron(iii)-citrate) and polyelectrolytes (poly(styrene sulfonate) and poly(diallyldimethyl ammonium)) on layered double hydroxide nanoclay. The experimental conditions were optimized in each preparation step and thus, the final composite formed highly stable colloids, i.e.

Differential Precipitation of Mg(OH) from CaSO·2HO Using Citrate as Inhibitor-A Promising Concept for Reagent Recovery from MgSO Waste Streams.

In hydrometallurgical processing and acidic wastewater treatment, one of the neutralizing agents employed is MgO or Mg(OH). At the end of this process, the resulting solution, which is rich in SO and Mg is treated with lime to remove (or minimize the amount) of these ions via the precipitation of Mg(OH) and CaSO·2HO (gypsum). In our work, an attempt was made to separate the two solids by increasing the induction time of the gypsum precipitation, thus regenerating relatively pure Mg(OH) which could be reused in wastewater treatments or hydrometallurgical processing circuits, and in this way, significantly enhancing the economic viability of the process.

Equilibria and Dynamics of Sodium Citrate Aqueous Solutions: The Hydration of Citrate and Formation of the NaCit Ion Aggregate.

Sodium citrate (NaCit) has a crucial role in many biological and industrial processes. Yet, quantitative information on its hydration and the ion association between Na and Cit ions in a broad range of salt concentrations is still lacking. In this work, we study both ion association equilibria and relaxation dynamics of sodium citrate solutions by combining potentiometry, spectrophotometry, and dielectric spectroscopy.

The Structure and Thermal Properties of Solid Ternary Compounds Forming with Ca, Al and Heptagluconate Ions.

In the present work, the structure and thermal stability of Ca-Al mixed-metal compounds, relevant in the Bayer process as intermediates, have been investigated. X-ray diffraction (XRD) measurements revealed the amorphous morphology of the compounds, which was corroborated by SEM-EDX measurements. The results of ICP-OES and UV-Vis experiments suggested the formation of three possible ternary calcium aluminum heptagluconate (Ca-Al-Hpgl) compounds, with the formulae of CaAlHpgl(OH), CaAlHpgl(OH) and CaAlHpgl(OH).

A colloid chemistry route for the preparation of hierarchically ordered mesoporous layered double hydroxides using surfactants as sacrificial templates.

An efficient synthetic route was developed to prepare hierarchically ordered mesoporous layered double hydroxide (LDH) materials. Sodium dodecyl sulfate (SDS) was used as a sacrificial template to tune the interfacial properties of the LDH materials during the synthetic process. The SDS dose was optimized to obtain stable dispersions of the SDS-LDH composites, which were calcined, then rehydrated to prepare the desired LDH structures.

Ultrasound-Assisted Hydrazine Reduction Method for the Preparation of Nickel Nanoparticles, Physicochemical Characterization and Catalytic Application in Suzuki-Miyaura Cross-Coupling Reaction.

In the experimental work leading to this contribution, the parameters of the ultrasound treatment (temperature, output power, emission periodicity) were varied to learn about the effects of the sonication on the crystallization of Ni nanoparticles during the hydrazine reduction technique. The solids were studied in detail by X-ray diffractometry, dynamic light scattering, thermogravimetry, specific surface area, pore size analysis, temperature-programmed CO/NH desorption and scanning electron microscopy. It was found that the thermal behaviour, specific surface area, total pore volume and the acid-base character of the solids were mainly determined by the amount of the nickel hydroxide residues.

Magnesium(II) d-Gluconate Complexes Relevant to Radioactive Waste Disposals: Metal-Ion-Induced Ligand Deprotonation or Ligand-Promoted Metal-Ion Hydrolysis?

The complexation equilibria between Mg and d-gluconate (Gluc) ions are of particular importance in modeling the chemical speciation in low- and intermediate-level radioactive waste repositories. NMR measurements and potentiometric titrations conducted at 25 °C and 4 M ionic strength revealed the formation of the MgGluc, MgGlucOH, MgGluc(OH), and MgGluc(OH) complexes. The trinuclear species provides indirect evidence for the existence of multinuclear magnesium(II) hydroxido complexes, whose formation was proposed earlier but has not been confirmed yet.

Effects of ultrasonic irradiation on the synthesis, crystallization, thermal and dissolution behaviour of chloride-intercalated, co-precipitated CaFe-layered double hydroxide.

The output power (30-150 W) and the periodicity (20-100%) of ultrasound emission were varied in a wide range to regulate and improve the crystallization process in the commonly used co-precipitation technique of chloride-intercalated CaFe-layered double hydroxides. The influence of ultrasound irradiation on the as-prepared materials was studied by X-ray diffractometry, dynamic light scattering, UV-Vis-NIR diffuse reflectance spectroscopy, specific surface area measurement, pore size analysis, ion-selective electrode potentiometric investigations and thermogravimetry. Additionally, structural alterations due to heat treatment at various temperatures were followed in detail by Fourier-transform infrared and X-ray absorption spectroscopies as well as scanning electron microscopy.

Effect of Polyelectrolyte Mono- and Bilayer Formation on the Colloidal Stability of Layered Double Hydroxide Nanoparticles.

Sequential adsorption of polyelectrolytes on nanoparticles is a popular method to obtain thin films after deposition. However, the effect of polyelectrolyte multilayer formation on the colloidal stability of the nanoparticles has not been studied in detail. In the present work, layered double hydroxides (LDH) were synthesized and interaction with oppositely and like-charged polyelectrolytes was investigated.

The Synthesis and Use of Nano Nickel Catalysts.

The hydrazine reduction method was applied for the synthesis of nickel nanoparticles without using inert atmosphere and added surface active agents. The effect of the preparation temperature and the chemical quality of the metal sources as well as the solvents were studied. The generation of nanoparticles were studied primarily by X-ray diffractometry, but scanning and transmission electron microscopies as well as dynamic light scattering measurements were also used for the better understanding of the nanoparticles behaviour.

Ball Milling of Copper Powder Under Dry and Surfactant-Assisted Conditions-On the Way Towards Cu/Cu₂O Nanocatalyst.

Samples of copper powder was milled with varied grinding frequencies in the presence of various organic agents (oleylamine, ethylene glycol or dimethyl sulfoxide) or without additives. The effects of experimental conditions were investigated by X-ray diffractometry, scanning electron microscopy and dynamic light scattering measurements. The aggregation of particles were supressed by added organics.

The acidity and self-catalyzed lactonization of l-gulonic acid: Thermodynamic, kinetic and computational study.

Lactonization and proton dissociation of sugar acids take place simultaneously in acidic aqueous solutions. The protonation-deprotonation processes are always fast, whilst the formation and hydrolysis of γ- and δ-lactones are usually slower. Thus, both thermodynamic and kinetic information are required for the complete understanding of these reactions.

Configuration-dependent complex formation between Ca(II) and sugar carboxylate ligands in alkaline medium: Comparison of L-gulonate with D-gluconate and D-heptaguconate.

The calcium sugar carboxylate interactions in hyperalkaline solutions are of relevance in radioactive waste repositories and in certain industrial processes. The complex formation between L-gulonate and Ca ions was studied in strongly alkaline medium at 25 °C and 1 M ionic strength and was compared with previous results reported for D-gluconate and D-heptagluconate. The deprotonation of the ligand was confirmed by potentiometric and C NMR spectroscopic measurements.

Ultrasonically-enhanced preparation, characterization of CaFe-layered double hydroxides with various interlayer halide, azide and oxo anions (CO, NO, ClO).

An ultrasonically-enhanced mechanochemical method was developed to synthesize CaFe-layered double hydroxides (LDHs) with various interlayer anions (CO, NO, ClO, N, F, Cl, Br and I). The duration of pre-milling and ultrasonic irradiation and the variation of synthesis temperature in the wet chemical step were investigated to obtain the optimal parameters of preparation. The main method to characterize the products was X-ray diffractometry, but infrared and synchrotron-based X-ray absorption spectroscopies as well as thermogravimetric measurements were also used to learn about fine structural details.

Formation of mono- and binuclear neodymium(iii)-gluconate complexes in aqueous solutions in the pH range of 2-8.

The complex formation between Nd(iii) and d-gluconate (Gluc) is of relevance in modelling the chemical equilibria of radioactive waste repositories. In the present work, the formation of NdGlucH complexes at 25 °C and pH = 2-8 was studied via spectrophotometry, potentiometry, freezing point depression, conductometry and NMR spectroscopy. In addition to the four mononuclear complexes (pq-r = 110, 120, 130 and 11-2), the formation of two binuclear, so far unknown complexes (pq-r = 23-2 and 24-2) was revealed.

ML and ML complex formation between Ca(ii) and d-glucose derivatives in aqueous solutions.

The complex formation equilibria between Ca ions and six carbohydrate derivatives related to d-glucose was quantitatively characterized by potentiometry, freezing point depression and polarimetry. Complexation could not be observed for d-glucose, while weak association was deduced for d-sorbitol and d-mannitol. Stronger complexes are formed with d-gluconate and d-heptagluconate due to the presence of the carboxylate group.

Calcium complexation and acid-base properties of l-gulonate, a diastereomer of d-gluconate.

The Ca(ii)-complexation and acid-base properties of l-gulonic acid (HGul), a diastereomer of d-gluconic acid (HGluc) differing only in the configurations of C2 and C5 have been investigated viaH and C NMR spectroscopies, Ca-ISE- and pH-potentiometry, polarimetry and freezing point depression. Data obtained for Gul/HGul have been compared with those of Gluc/HGluc. It was found that some properties (acid dissociation constant, the stoichiometry and formation constants of the Ca(ii)-complexes) were insensitive to the difference in the configuration.

Calcium l-tartrate complex formation in neutral and in hyperalkaline aqueous solutions.

The complex formation reaction between the l-tartrate (Tar) and calcium ions taking place in neutral and in hyperalkaline (pH > 13) aqueous solutions has been investigated. It was demonstrated that upon NaOH addition the solubility of the CaTar precipitate significantly increases. Conductometric and freezing point depression measurements further confirmed that in this process water soluble species are formed as a result of a reaction between the CaTar and the hydroxide ion (or, conversely, between Ca(OH) and the Tar ion).

Synthesis of high-quality, well-characterized CaAlFe-layered triple hydroxide with the combination of dry-milling and ultrasonic irradiation in aqueous solution at elevated temperature.

The combination of mechanochemical and ultrasonic treatment was applied to synthesize CaAlFe-layered triple hydroxides with carbonate or chloride anions in the interlamellar space. The optimal parameters of the preparation were explored by altering the initial ratio of the metal ions and the temperature of ultrasonic irradiation. The resulting triple hydroxides were characterized by X-ray diffractometry, infrared and X-ray absorption spectroscopies, thermogravimetric analysis and scanning electron microscopy.

Ultrasonically-enhanced mechanochemical synthesis of CaAl-layered double hydroxides intercalated by a variety of inorganic anions.

CaAl-layered double hydroxides (CaAl-LDHs) were synthesised with various interlayer anions (CO3(2-), F(-), Cl(-), Br(-) and I(-)) by mechanochemical pre-treatment followed by ultrasonic irradiation in aqueous media. The parameters of the syntheses (duration of pre-milling and sonication, quality of the aqueous media, temperature) were altered in order to optimise the procedure and to understand the formation of LDH and other secondary products. The products were characterised by X-ray diffractometry (XRD) and scanning electron microscopy (SEM).

Diterpene Constituents of Euphorbia exigua L. and Multidrug Resistance Reversing Activity of the Isolated Diterpenes.

Phytochemical investigation of the MeOH extract obtained from the aerial parts of the annual weed Euphorbia exigua L. resulted in the isolation of two novel (1, 2) and one known (3) jatrophane diterpenes. Their structures were established by extensive 1D- and 2D-NMR spectroscopy and HR-ESI-MS.

Spherical LDH-Ag°-montmorillonite heterocoagulated system with a pH-dependent sol-gel structure for controlled accessibility of AgNPs immobilized on the clay lamellae.

Aqueous suspensions of spherical ZnMgAl-layered double hydroxides [LDH(sph)] and antibacterial silver nanoparticles (AgNPs) deposited on the lamellae of montmorillonite were used for the synthesis of composites, which behave like coherent gels at low pH (≲4.5) and incoherent sols at higher pH (≳4.5).

Speciation and structure of tin(II) in hyper-alkaline aqueous solution.

The identity of the predominating tin(ii)-hydroxide complex formed in hyper-alkaline aqueous solutions (0.2 ≤CNaOH≤ 12 mol dm(-3)) is determined by potentiometric titrations, Raman, Mössbauer and XANES spectroscopy, supplemented by quantum chemical calculations. Thermodynamic studies using a H2/Pt electrode up to free hydroxide concentrations of 1 mol dm(-3) showed the presence of a single monomeric complex with a tin(II) : hydroxide ratio of 1 : 3.