Search Results (11)

This study investigates the degradation mechanisms of fiber-reinforced polymer (FRP) matrices in composite insulators under partial discharge (PD) conditions. The degradation products may further cause deterioration of the electrical and chemical resistance (ECR) glass fibers. Using pyrolysis–gas chromatography-mass spectrometry (PY-GC-MS) and high-performance liquid chromatography–tandem mass spectrometry (HPLC-MS-MS), the thermal degradation gas and liquid products of the degraded FRP matrix were analyzed, revealing the presence of organic acids. These acids form when the epoxy resin’s cross-linked bonds break at high temperatures, generating anhydrides that hydrolyze into carboxylic acids in the presence of moisture. The hydrolyzation process is accelerated by hydroxyl radicals produced during PD. The resulting carboxylic acids deteriorate the glass fibers within the FRP matrix by degrading surface coupling agents and reacting with the alkali metal–silica network, leading to the substitution and precipitation of metal ions. Organic acids, particularly carboxylic acids, were found to have a more severe deteriorating effect on glass fibers compared to inorganic acids, with high temperatures exacerbating this process. These findings provide critical insights into the deterioration mechanisms of FRP under operational conditions, offering valuable guidance for optimizing manufacturing processes and enhancing the longevity of composite insulators. Full article

Solid-state electrolytes are currently receiving increasing interest due to their high mechanical strength and chemical stability for safe battery construction. However, their poor ion conduction and unclear conduction mechanism need further improvement and exploration. This study focuses on a hybrid solid-state electrolyte containing MOF-based scaffolds, using metal salts as the conductor. In this paper, we employ an ion substitution strategy to manipulate the scaffold structure at the lattice level by replacing hydrogen with larger alkali cations. The research systematically presents how changes in the lattice affect the physical and chemical properties of MOFs and emphasizes the role of scaffold–salt interactions in the evolution of ion conduction. The results reveal that long range-ordered structural distortion can enhance permittivity at 1 Hz, from 58 ohms to more than 10 M ohms, which can boost ion pairs dissociation and improve the transference number from 4.7% to 22.6%. Defects in the lattice can help stabilize the intermediate state in the charge transfer process and lower the corresponding impedance from 2.6 MΩ to 559 Ω. Full article

The performance optimization of photoluminescent (PL) materials is a hot topic in the field of applied materials research. There are many different crystal defects in photoluminescent materials, which can have a significant impact on their optical properties. The luminescent properties and chemical stability of materials can be effectively improved by adjusting lattice defects in crystals. We systematically studied the effect of doping ions on the energy transfer upconversion mechanism in different defect crystals by changing the matrix alkali metal ions. Meanwhile, the influence mechanism of crystal defect distribution on luminescence performance is explored by adjusting the ratio of Na–Li. The PL spectra indicate that changing the alkaline ions significantly affects the luminescence performance and efficiency of UCNPs. The change in ion radius leads to substitution or gap changes in the main lattice, which may alter the symmetry and strength of the crystal field around doped RE ions, thereby altering the UCL performance. Additionally, we demonstrated the imaging capabilities of the synthesized upconversion nanoparticles (UCNPs) in cellular environments using fluorescence microscopy. The results revealed that Na_0.9Li_0.1LuF₄–Yb, Er nanoparticles exhibited significantly enhanced fluorescence intensity in cell imaging compared to other compositions. We further investigated the mechanism by which structural defects formed by doping ions in UCNPs with different alkali metals affect energy transfer upconversion (ETU). This work emphasizes the importance of defect regulation in the ETU mechanism to improve the limitations of crystal structure on the luminescence performance and promote the future application of upconversion nanomaterials, which will provide important theoretical references for the exploration of high-performance luminescent materials in the future. Full article

A series of red-emitting phosphors, Na_3.6Y_1.8−x(PO₄)₃:xEu³⁺, have been synthesized by a high-temperature solid-phase method. The impact of the partial Li⁺/K⁺ ion substitution on the crystal structure and photoluminescence (PL) performance of Na_3.6Y_1.05(PO₄)₃:0.75Eu³⁺ phosphor have been investigated. Various techniques have been used for characterization of the as-obtained materials. X-ray diffraction (XRD) analysis was utilized to confirm the composites of these samples, and the morphology and element distribution were examined by scanning electron microscope (SEM) and transmission electron microscope (TEM). This study found that the developed Na_3.6Y_1.8−x(PO₄)₃:xEu³⁺ phosphors exhibited a prominent emission peak at ~620 nm when excited at 393 nm, which corresponded to ⁵D₀ → ⁷F₂ transitions of Eu³⁺ ions. Furthermore, the robust emission peak at ~705 nm (⁵D₀ → ⁷F₄) of these phosphors enables a better match with plant pigment absorption. Beyond that, the partial substitution of Li⁺/K⁺ ions probably changed the crystal structure, and reduces the symmetry around Eu³⁺, leading to significantly enhanced luminous intensities by 23.24% and 18.29%, with the highest quantum yields (QYs) reaching 99.85% and 96.29%, respectively. Additionally, the prepared phosphors show non-thermal quenching and superior thermal stability at elevated temperatures from 298 to 473 K. These findings and results suggest that Li⁺/K⁺-substituted Na_3.6Y_1.05(PO₄)₃:0.75Eu³⁺ phosphors can serve as promising red-emitting phosphors for plant lighting applications. Full article

The environment model for the description of the location of carbonate ions in apatites predicts that approximately half of the carbonate occupies the apatite channel. This model relies on the influence of entities surrounding the carbonate on its IR spectrum and can be used to determine how various substituents affect the location and structure of that ion. Careful deconvolution (peak-fitting) of the asymmetric carbonate IR region was used to determine the percentage of A-type (channel) ions, A′-type (channel with either a Ca²⁺ vacancy or substitution of Na⁺ for Ca²⁺) ions, and B-type (substitution for phosphate) ions. In our previous applications of this model, we have looked at the effect of alkali metal ions, such as sodium, lithium, and potassium, the ammonium ion, and the rare earth europium ion. In the present work, we explore the incorporation of the first-row transition metal ions and find that they have little effect on the location of the carbonate ion. Like the un-substituted carbonated apatite, these apatites contain about half of the carbonate in the channel, at least in derivatives that contain up to half a mole of the metal ion per mole of apatite. Attempts to incorporate greater amounts of metal ions by aqueous ion-combination reactions generally lead to lower-resolution XRD patterns and IR spectra that produce greater uncertainties in the peak-fitting modeling. Full article

Geopolymers are inorganic, chemically resistant aluminosilicate-based binding agents, which remove hazardous metal ions from exposed aqueous media. However, the removal efficiency of a given metal ion and the potential ion remobilization have to be assessed for individual geopolymers. Therefore, copper ions (Cu²⁺) were removed by a granulated, metakaolin-based geopolymer (GP) in water matrices. Subsequent ion exchange and leaching tests were used to determine the mineralogical and chemical properties as well as the resistance of the Cu²⁺-bearing GPs to corrosive aquatic environments. Experimental results indicate the pH of the reacted solutions to have a significant impact on the Cu²⁺ uptake systematics: the removal efficiency ranged from 34–91% at pH 4.1–5.7 up to ~100% at pH 11.1–12.4. This is equivalent to Cu²⁺ uptake capacities of up to 193 mg/g and 560 mg/g in acidic versus alkaline media. The uptake mechanism was governed by Cu²⁺-substitution for alkalis in exchangeable GP sites and by co-precipitation of gerhardtite (Cu₂(NO₃)(OH)₃) or tenorite (CuO) and spertiniite (Cu(OH)₂). All Cu-GPs showed excellent resistance to ion exchange (Cu²⁺ release: 0–2.4%) and acid leaching (Cu²⁺ release: 0.2–0.7%), suggesting that tailored GPs have a high potential to immobilize Cu²⁺ ions from aquatic media. Full article

The chemical composition of biominerals is essential for understanding biomineral formation and is regarded as an attractive subject in bio-mineralogical research on human kidney stones (urinary calculi). In order to obtain more geochemically interpreted data on biogenic minerals, mineralogical compositions and major and trace element concentrations of sixty-six kidney stone samples derived from kidney stone removal surgeries were measured. Infrared spectroscopy results showed that calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) were the two main mineral components of kidney stones. Geochemical results indicated that major and trace element concentrations were present in the following order: Ca > Mg > Na > K > Zn > Fe > Pb > Ba > Cu > Ti > Mo > Cd > Cr. With the exception of Ca, Mg was the second-most abundant element. Zn exhibited higher concentrations relative to other trace elements, which suggests a potential substitution of calcium by metal ions with a similar charge and radius rather than by metals in kidney stone formation. Pb appeared in significantly higher concentrations than in previous studies, which indicates Pb enrichment in the environment. In order to discern multi-element relationships within kidney stones, principal component analysis was applied. Three principal components (PCs, eigenvalues >1) were extracted to explain 64.4% of the total variance. The first component exhibited positively correlated Na-Zn-Cr-Mo-Cd-Pb, while the second component exhibited more positively weighted Mg-K-Ba-Ti. Fe-Cu demonstrated a positive correlation in the third component. This study suggests that Ca exhibits a preference for uptake by oxalates during human urinary stone crystallization, while other alkali metals and alkaline earth metals precipitate with phosphate. Full article

Octacalcium phosphate (OCP) is widely used in biomaterial fabrication by virtue of its unique crystal structure and low environmental loading. Although various ion and molecule substitution methods into the OCP unit lattice have been introduced, it remains unclear which factors and mechanisms dominate the substitution process. Experimental studies have indicated that Na alkali metal ions are substituted at the P3 PO₄ conjugated site in acidic to weakly acidic conditions and the P5 PO₄ conjugated site in neutral to weak basic conditions. Ionic species calculation methods have indicated that the pair ratios of Na and HPO₄²⁻ (NaHPO₄⁻) are small in acidic reacting solutions but large under weakly basic conditions. Consequently, the roles played by NaHPO₄⁻ and ionic pair formation processes are thought to dominate ion and molecule substitution into the OCP unit lattice. Such ionic pair formation strongly inhibits dicarboxylic acid substitution into the OCP unit lattice due to the replacement of the Ca ion, which conjugates P5 PO4 as an anchor of dicarboxylic acid. Full article

Silicas chemically modified with a number of sulfur-containing groups (mercaptopropyl, mercaptophenyl, dipropyl disulfide, thiadiazole thiol, dithiocarbamate and thiourea derivatives) were proposed for the separation and preconcentration of precious metals. These adsorbents quantitatively extracted precious metals from 0.5 to 4 M solutions of hydrochloric acid. It allowed their separation from high concentrations of non-ferrous, alkaline earth, alkali and some other related metals. The selectivity of separation of kinetically labile precious metal ions in ligand substitution reactions from kinetically inert ones depended on the nature of sulfur atom within the functional group of adsorbents and increased when passing from thione to thiol sulfur. Approaches for the preconcentration of precious metals using silicas chemically modified with sulfur-containing groups prior to their AAS, ICP-OES, and ICP-MS determination in ores, concentrates and their processing products were proposed. The correctness of the developed methods was confirmed by the analysis of certified reference materials. Full article

Vanadium phosphate positive electrode materials attract great interest in the field of Alkali-ion (Li, Na and K-ion) batteries due to their ability to store several electrons per transition metal. These multi-electron reactions (from V²⁺ to V⁵⁺) combined with the high voltage of corresponding redox couples (e.g., 4.0 V vs. for V³⁺/V⁴⁺ in Na₃V₂(PO₄)₂F₃) could allow the achievement the 1 kWh/kg milestone at the positive electrode level in Alkali-ion batteries. However, a massive divergence in the voltage reported for the V³⁺/V⁴⁺ and V⁴⁺/V⁵⁺ redox couples as a function of crystal structure is noticed. Moreover, vanadium phosphates that operate at high V³⁺/V⁴⁺ voltages are usually unable to reversibly exchange several electrons in a narrow enough voltage range. Here, through the review of redox mechanisms and structural evolutions upon electrochemical operation of selected widely studied materials, we identify the crystallographic origin of this trend: the distribution of PO₄ groups around vanadium octahedra, that allows or prevents the formation of the vanadyl distortion (O^…V⁴⁺=O or O^…V⁵⁺=O). While the vanadyl entity massively lowers the voltage of the V³⁺/V⁴⁺ and V⁴⁺/V⁵⁺ couples, it considerably improves the reversibility of these redox reactions. Therefore, anionic substitutions, mainly O²⁻ by F⁻, have been identified as a strategy allowing for combining the beneficial effect of the vanadyl distortion on the reversibility with the high voltage of vanadium redox couples in fluorine rich environments. Full article

A series of benzoxazine monomer supramolecules with different substituted groups on their benzene ring was prepared with a Mannich reaction and characterized by FTIR, ¹H-NMR and MS. The obtained products were 3,4-dihydro-3-(2’-hydroxyethylene)-6-methyl-2H-benzoxazine (BM1), 3,4-dihydro-3-(2’-hydroxyethylene)-6-ethyl-2H-benz-oxazine (BM2), and 3,4-dihydro-3-(2’-hydroxyethylene)-6-methoxy-2H-benzoxazine (BM3). The efficiency of alkali metal ion extraction from the products was determined with Pedersen’s technique, while the complexation of the Ce(III) ion was confirmed by the Job’s and the mole ratio methods. The evidence of complex formation between benzoxazine monomers and Ce(III) ions was obtained with FTIR and a computational simulation. Single phase ceria (CeO₂) as observed with XRD was successfully prepared by calcinating the Ce(III)-benzoxazine monomer complexes at 600 °C for 2 h. In addition, the geometry of the ceria nanoparticles confirmed by TEM is spherical, with an average diameter of 10‑20 nm. Full article