Search Results (41)

The focus in microplastic research has shifted from marine ecosystems towards freshwater ecosystems. Still, most studies are based on small sample numbers, both spatially and temporally. Little is known about the spatiotemporal variability of microplastics (MPs) in large river systems such as the Rhine River, Germany. Within our study, we performed four cross-sectional sampling campaigns at two sites in the Rhine River, at Koblenz and Emmerich, involving depth-distributed sampling over a particle size range from 10 µm to 25 mm. For plastic particle analysis, we used both optical and thermoanalytical approaches to determine mass-based polymer concentrations. Our results show that MP variability within the water column is complex, but mostly follows the particles density: the ratio between superficial MPs concentration and mean concentration of the verticals was >1 for lighter polymers with a density below 1.04 g/cm³ and <1 for polymers with a density above 1.04 g/cm³ among all size classes with only a few exceptions, even though the Rouse theory would indicate a more homogeneous distribution for small particle sizes. Large sampling volumes are essential, particularly for larger MP particles, as the coefficient of variation rises with particle size. At our study sites, no significant lateral variation was apparent, while during a flood event, MP concentrations were significantly higher than during low and mean water stages. This study is the first to (i) gain insights into cross-sectional MPs distribution in the Rhine River and (ii) account for particle mass concentrations, and thus lays the foundation for potential future MPs flux monitoring. Full article

A new complex, tetrakis(1,10-phenanthroline)-bis(succinate)-(µ₂-oxo)-bis(iron(III)) nonahydrate, [Fe₂(Phen)₄(Succinate)₂(μ-O)](H₂O)₉, was synthesized using the slow evaporation method. This study provides a comprehensive characterization of this coordination compound, focusing on its structural, spectroscopic, and thermal properties, which are relevant for applications in catalysis, material science, and chemical engineering processes. Single-crystal X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared (FT-IR), ultraviolet-visible (UV-Vis) spectroscopy, and thermoanalytical analyses were employed to investigate the material properties. Intermolecular interactions were further explored through Hirshfeld surface analysis. XRD results revealed a monoclinic crystal system with the C2/c space group, lattice parameters: a = 12.7772(10) Å, b = 23.0786(15) Å, c = 18.9982(13) Å, β = 93.047(2)°, V = 5594.27(7) ų, and four formulas per unit cell (Z = 4). The crystal packing is stabilized by C–H⋯O, C–O⋯H, C–H⋯π, and π⋯π intermolecular interactions, as confirmed by vibrational spectroscopy. The heteroleptic coordination environment, combining weak- and strong-field ligands, results in a low-spin state with an estimated crystal field stabilization energy of −4.73 eV. Electronic properties indicate direct allowed transitions (γ = 2) with a maximum optical band gap of 2.66 eV, suggesting potential applications in optoelectronics and photochemical processes. Thermal analysis demonstrated good stability within the 25–136 °C range, with three main stages of thermal decomposition, highlighting its potential for use in high-temperature processes. These findings contribute to the understanding of Fe(III)-based complexes and their prospects in advanced material design, catalytic systems, and process optimization. Full article

Carvedilol (CARV) is a nonselective beta and alpha-1 adrenoceptor antagonist commonly indicated for chronic heart failure and hypertension. Its clinical potential is limited by its low aqueous solubility, resulting in poor bioavailability. Encapsulation of CARV by cyclodextrins (CDs) was performed to exceed its solubility-related barriers. This study examines the impact of the CD type and ethanol, as a co-solvent used in the preparation step, on the complexation of CARV with two β-CD derivatives. The inclusion complexes (ICs) were prepared employing the kneading method and investigated using different analytical techniques, including thermoanalytical methods, powder X-ray diffractometry (PXRD), universal attenuated total reflectance Fourier transform infrared (UATR-FTIR) spectroscopy, UV spectroscopy and saturation solubility studies. The binary products of CARV with heptakis(2,6-di-O-methyl)-β-cyclodextrin (DM-β-CD) and randomly methylated β-cyclodextrin (RM-β-CD) exhibit different thermal behavior, different FTIR spectral and diffractometric profiles from those of the parent compounds, emphasizing the interaction between the components and the IC formation. CARV solubility increased 1.78 to 3.32 times as a result of drug complexation with CDs. Analytical data indicate a significant influence of both solvent systems and CD type on the IC solubility, highlighting the CARV/DM-β-CD IC as a promising entity for further research to obtain new formulations containing CARV with improved bioavailability. Full article

Background: Olmesartan medoxomil (OLM) is the prodrug of olmesartan, an angiotensin II type 1 receptor blocker that has antihypertensive and antioxidant activities and renal protective properties. It exhibits low water solubility, which leads to poor bioavailability and limits its clinical potential. To improve the solubility of OLM, a host–guest inclusion complex (IC) between heptakis(2,6-di-O-methyl)-β-cyclodextrin (DMβCD) and the drug substance was obtained. Along with active substances, excipients play a crucial role in the quality, safety, and efficacy of pharmaceutical formulations. Therefore, the compatibility of OLM/DMβCD IC with several pharmaceutical excipients was evaluated. Methods: IC was characterized in both solid and liquid states, employing thermoanalytical techniques, universal-attenuated total reflectance Fourier-transform infrared spectroscopy, powder X-ray diffractometry, UV spectroscopy, and saturation solubility studies. Compatibility studies were carried out using thermal and spectroscopic methods to assess potential physical and chemical interactions. Results: The 1:1 OLM:DMβCD stoichiometry ratio and the value of the apparent stability constant were determined by means of the phase solubility method that revealed an A_L-type diagram. The binary system showed different physicochemical characteristics from those of the parent entities, supporting IC formation. The geometry of the IC was thoroughly investigated using molecular modeling. Compatibility studies revealed a lack of interaction between the IC and all studied excipients at ambient conditions and the thermally induced incompatibility of IC with magnesium stearate and α-lactose monohydrate. Conclusions: The results of this study emphasize that OLM/DMβCD IC stands out as a valuable candidate for future research in the development of new pharmaceutical formulations, in which precautions should be considered in choosing magnesium stearate and α-lactose monohydrate as excipients if the manufacture stage requires temperatures above 100 °C. Full article

Angiotensin II receptor antagonists are tetrazole derivatives used in the treatment of high blood pressure, and are also indicated for the treatment of heart failure (NYHA class II-IV). They are used alone or in combination with other classes of antihypertensives or diuretics for the effective management of high blood pressure. In this study, we aim to evaluate the thermal stability and degradation kinetics for the principal compounds used in therapy from this class, namely telmisartan, valsartan, olmesartan medoxomil, and losartan potassium. To obtain the thermoanalytical data for the kinetic investigations, the TG and DTG curves were registered at five different heating rates (β = 2, 4, 6, 8, and 10 °C min⁻¹). The kinetic methods used were a preliminary ASTM E698 method and two isoconversional methods: Flynn–Wall–Ozawa and Friedman. For each molecule, the results showed complex decomposition processes consisting of complex reaction sequences. Full article

The development of a methodological approach to detecting the presence of flame retardants in building materials and products and finding their concentration is an essential part of the performance evaluation of flame retardants for timber. The above issue is a relevant constituent of supervision over fire safety compliance at construction facilities. Thermal analysis was used in this research project to (1) detect the presence of flame retardants in timber, and (2) identify methods of their application. Comparative experiments were conducted to detect the presence and effectiveness of flame retardants applied to the surface and inner layers of specimens of timber planken (façade board) at a construction facility. Relevant values, characterizing the thermal decomposition of timber specimens, enable predicting the heat flux rate that triggers ignition. A quick test, conducted to check the flammability of specimens, confirmed the authors’ hypothesis. The study revealed principal (relevant) thermo-analytical criteria for the fire resistance of timber impregnated with combustion retardants using different methods of impregnation. A methodological approach to studying relevant thermo-analytical characteristics was developed to evaluate the efficiency of (1) fire resistance of timber products and (2) fireproofing techniques. Flammability and combustibility of timber impregnated with fire retardants was prognosticated. It was revealed that the proposed methodology can monitor the efficiency of fireproofing applied to façade structures made of pine timber. Full article

Tutton salts have received considerable attention due to their potential applications in thermochemical energy storage (TCHS) systems. This technology requires high-purity materials that exhibit reversible dehydration reactions, significant variations in dehydration enthalpy, and high-temperature melting points. In this study, K₂Cu(SO₄)₂(H₂O)₆ Tutton salt in the form of single crystals was grown using the slow solvent evaporation method. Their structural, morphological, and thermal characteristics are presented and discussed, as well as temperature-induced phase transformations. At room temperature, the salt crystallizes in a monoclinic structure belonging to the P2₁/a space group, which is typical for Tutton salts. The lack of precise control over the solvent evaporation rate during crystal growth introduced structural disorder, resulting in defects on the crystal surface, including layer discontinuities, occlusions, and pores. Thermoanalytical analyses revealed two stages of mass loss, corresponding to the release of 4 + 2 coordinated H₂O molecules—four weakly coordinated and two strongly coordinated to the copper. The estimated dehydration enthalpy was ≈ 80.8 kJ/mol per mole of H₂O. Powder X-ray diffraction measurements as a function of temperature showed two phase transformations associated with the complete dehydration of the starting salt occurring between 28 and 160 °C, further corroborating the thermal results. The total dehydration up to ≈ 160 °C, high enthalpy associated with this process, and high melting point temperature make K₂Cu(SO₄)₂(H₂O)₆ a promising candidate for TCHS applications. Full article

Emerging pharmaceutical pollutants like ciprofloxacin (CIP) and ibuprofen (IBU) are frequently detected in aquatic environments, posing risks to ecosystems and human health. Since pollutants rarely exist alone in the environment, understanding the thermal stability and degradation kinetics of these compounds, especially in mixtures, is crucial for developing effective removal strategies. This study therefore investigates the thermal stability and degradation kinetics of CIP and IBU, under different heating rates. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were employed to examine the thermal behavior of these compounds individually and in mixture (CIP + IBU) at heating rates of 10, 20, and 30 °C/min. The kinetics of thermal degradation were analyzed using both model-fitting (Coats–Redfern (CR)) and model-free (Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), and Friedman (FR)) methods. The results showed distinct degradation patterns, with CIP decomposing between 280 and 550 °C and IBU between 152 and 350 °C, while the mixture exhibited multistep decomposition in the 157–500 °C range. The CR model indicated first-order kinetics as a better fit for the degradation (except for IBU). Furthermore, CIP exhibits higher thermal stability and activation energy compared to IBU, with the KAS model yielding activation energies of 58.09 kJ/mol for CIP, 11.37 kJ/mol for IBU, and 41.09 kJ/mol for CIP + IBU mixture. The CIP + IBU mixture generally showed intermediate thermal properties, suggesting synergistic and antagonistic interactions between the compounds. Thermodynamic parameters (ΔH°, ΔG°, ΔS°) were calculated, revealing non-spontaneous, endothermic processes for all samples (except in the FWO method) with a decrease in molecular disorder and positive ΔG° values across all models and heating rates. The study found that higher heating rates led to less thermodynamically favorable conditions for degradation. These findings provide important information concerning the thermal behavior of these pharmaceutical pollutants, which can inform strategies for their removal from the environment and the development of more effective waste-treatment processes. Full article

An effective type of polymer heat-insulating material (foams) based on reactive oligomers is casting epoxy foams with high technological and operational parameters. However, polyepoxide foams are highly flammable, which significantly restrains their application in the construction industry. The aim of this work was to develop effective methods for reducing the flammability of filling epoxy foams. In order to achieve the objective, the following objectives were addressed: determining the influence of the chemical nature and content of additive and reactive bromine- and phosphorus-containing compounds on the thermal stability, flammability and operational properties of filling epoxy foams, and the development of polyepoxy foams of reduced flammability with high-quality physical and mechanical characteristics. When estimating the flammability of epoxy foams, we used both state-approved methods and the methods described in scientific and technical literature. The thermal properties of epoxy foams were studied with the help of multimodular thermoanalytical complex DuPont-9900. The data on the influence of the apparent density of foams and oxygen concentration in the oxidant flow on the flame propagation speed on the horizontal surface of polyepoxy foams are presented. It was revealed that the chemical nature of amine hardeners does not affect the thermal stability and flammability of epoxy foams. It was established that phosphate plasticizers are ineffective flame retardants of foamed epoxy resin, and the chemical structure of additive organobromic flame retardants insignificantly affects their efficiency. It was shown that microencapsulated flame retardants are inferior in flame retardant efficiency to additive flame retardants. It was found that effective flame retardants for casting polyepoxy foams are phosphorus-containing oligoether methacrylate and epoxidized waste from the production of tetrabromodiphenylpropane. The results of this research will form the basis for the production of an experimental industrial batch of samples of pouring epoxy foams of reduced flammability. Full article

Olmesartan medoxomil (OLM) is a selective angiotensin II receptor antagonist used in the treatment of hypertension. Its therapeutic potential is limited by its poor water solubility, leading to poor bioavailability. Encapsulation of the drug substance by two methylated cyclodextrins, namely randomly methylated β-cyclodextrin (RM-β-CD) and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TM-β-CD), was carried out to overcome the limitation related to OLM solubility, which, in turn, is expected to result in an improved biopharmaceutical profile. Supramolecular entities were evaluated by means of thermoanalytical techniques (TG—thermogravimetry; DTG—derivative thermogravimetry), spectroscopic methods including powder X-ray diffractometry (PXRD), universal-attenuated total reflectance Fourier-transform infrared (UATR-FTIR) and UV spectroscopy, saturation solubility studies, and by a theoretical approach using molecular modeling. The phase solubility method reveals an A_L-type diagram for both inclusion complexes, indicating a stoichiometry ratio of 1:1. The values of the apparent stability constant indicate the higher stability of the host–guest system OLM/RM-β-CD. The physicochemical properties of the binary systems are different from those of the parent compounds, emphasizing the formation of inclusion complexes between the drug and CDs when the kneading method was used. The molecular encapsulation of OLM in RM-β-CD led to an increase in drug solubility, thus the supramolecular adduct can be the subject of further research to design a new pharmaceutical formulation containing OLM, with improved bioavailability. Full article

The processes of structural relaxation, crystal growth, and thermal decomposition were studied for amorphous griseofulvin (GSF) by means of thermo-analytical, microscopic, spectroscopic, and diffraction techniques. The activation energy of ~395 kJ·mol⁻¹ can be attributed to the structural relaxation motions described in terms of the Tool–Narayanaswamy–Moynihan model. Whereas the bulk amorphous GSF is very stable, the presence of mechanical defects and micro-cracks results in partial crystallization initiated by the transition from the glassy to the under-cooled liquid state (at ~80 °C). A key aspect of this crystal growth mode is the presence of a sufficiently nucleated vicinity of the disrupted amorphous phase; the crystal growth itself is a rate-determining step. The main macroscopic (calorimetrically observed) crystallization process occurs in amorphous GSF at 115–135 °C. In both cases, the common polymorph I is dominantly formed. Whereas the macroscopic crystallization of coarse GSF powder exhibits similar activation energy (~235 kJ·mol⁻¹) as that of microscopically observed growth in bulk material, the activation energy of the fine GSF powder macroscopic crystallization gradually changes (as temperature and/or heating rate increase) from the activation energy of microscopic surface growth (~105 kJ·mol⁻¹) to that observed for the growth in bulk GSF. The macroscopic crystal growth kinetics can be accurately described in terms of the complex mechanism, utilizing two independent autocatalytic Šesták–Berggren processes. Thermal decomposition of GSF proceeds identically in N₂ and in air atmospheres with the activation energy of ~105 kJ·mol⁻¹. The coincidence of the GSF melting temperature and the onset of decomposition (both at 200 °C) indicates that evaporation may initiate or compete with the decomposition process. Full article

Five trifluoroacetylacetonate (tfaa⁻) complexes [Tm(tfaa)₃(H₂O)]₂, [Tm(tfaa)₃(H₂O)₂], [Tm(tfaa)₃(H₂O)₂] · diglyme, [Tm(tfaa)₃(DME)] (DME = 1,2-dimethoxyethane) and [TmCl₂(tfaa)(diglyme)] (diglyme = bis(2-methoxyethyl) ether) of thulium have been synthesized and characterized by X-ray single-crystal structure analysis and spectroscopic techniques. Thermoanalytical studies at elevated temperatures provide information about their volatility. The results are compared with the hexafluoroacetylacetonate (hfaa⁻) complexes of thulium known in the literature, which were reported as volatile precursors for CVD application. The reported high volatility of [Tm(hfaa)₃(DME)] was confirmed and compared with those of the aqueous complexes which show a lower transport rate. In addition, the new crystal structures of the hexafluoroacetylacetonate complexes [Tm(hfaa)₃(H₂O)₂], [Tm(hfaa)₂(tfa)(H₂O)₂]₂ (tfa⁻ = trifluoroacetate), [Tm(hfaa)₃(DME)NaCl]₂ and Na[Tm(hfaa)₄] are presented. Full article

Increasing demand to store intermittent renewable electricity from, e.g., photovoltaic and wind energy, has led to much research and development in large-scale stationary energy storage, for example, ZEBRA batteries (Na-NiCl₂ solid electrolyte batteries). Replacing Ni with abundant and low-cost Zn makes the ZEBRA battery more cost-effective. However, few studies were performed on this next-generation ZEBRA (Na-ZnCl₂) battery system, particularly on its AlCl₃-NaCl-ZnCl₂ secondary electrolyte. Its properties such as phase diagrams and vapor pressures are vital for the cell design and optimization. In our previous work, a simulation-assisted method for molten salt electrolyte selection has shown its successful application in development of molten salt batteries. The same method is used here to in-depth study the AlCl₃-NaCl-ZnCl₂ salt electrolyte in terms of its phase diagrams and vapor pressures via FactSage^TM and thermo-analytical techniques (Differential Scanning Calorimetry (DSC) and OptiMelt^TM), and their effects on battery performance such as operation safety and charging/discharging reaction mechanism. The DSC and OptiMelt results show that the experimental data such as melting temperatures and phase changes agree well with the simulated phase diagrams. Moreover, the FactSage^TM simulation shows that the salt vapor pressure increases significantly with increasing temperature and molar fraction of AlCl₃. The obtained phase diagrams and vapor pressures will be used in the secondary electrolyte selection, cell design and battery operation. Full article

Plant oils contain a high content of unsaturated fatty acids. Studies of food products have revealed a considerable disproportion in the ratio of ω6 to ω3. This article presents information on the healthful qualities of eight new oil blends that contain a beneficial proportion of ω6 to ω3 fatty acids (5:1), as well as their degradation during heating at 170 and 200 °C. The fatty acid profile was analyzed by gas chromatography (GC), content of polar compounds and polymers of triacylglycerols by liquid chromatography (LC), water content was measured by the Karl Fischer method, and oxidative stability was measured by differential scanning calorimetry (DSC) and low-field nuclear magnetic resonance (LF NMR) methods. The results showed that during heating, the polar fraction content increased in samples heated at both analyzed temperatures compared to unheated oils. This was mainly due to the polymerization of triacylglycerols forming dimers. In some samples that were heated, particularly those heated to 200 °C, trimers were detected, however, even with the changes that were observed, the polar fraction content of the blends did not go beyond the limit. Despite the high content of unsaturated fatty acids, the analyzed blends of oils are characterized by high oxidative stability, confirmed by thermoanalytical and nuclear magnetic resonance methods. The high nutritional value as well as the oxidative stability of the developed oil blends allow them to be used in the production of food, in particular products that ensure an adequate supply of ω3 fatty acids. Full article

The limiting content of combustibles to spread/suppress the fire in the minestone of the coal tailing dump (gangue) was studied. This knowledge appears crucial mainly when deciding on the possible usage of minestone as fireproof material for engineering purposes. Theoretical analysis, laboratory experiments as well as scale (in situ) considerations were performed. In the laboratory, a model series of coal–mineral matter mixtures and six representative minestone samples of coal tailing dump (gangue) were investigated. The thermoanalytical (TG/DSC) method was used to evaluate the content of combustibles with their energetic equivalent, EEC (%). The EEC has been suggested as a proper way to quantify the content of combustibles in the samples. Based on the original combustion calorimetric test, an EEC value of 7–9% was found to be a limit between fireproof and fire spreading minestone in a laboratory, while only 2% of combustibles resulted as the limit from the theoretical analysis. On the other hand, respecting real conditions of thermally active dump (Heřmanice tailing coal dump), the laboratory limit of 7–9% of EEC was then assessed to shift to the value of about 10 ± 1% for practice. Full article