Search Results (323)

The state of the art in the thermodynamics of calix[4]resorcinarene derivatives and its metal ion complexes is briefly discussed in the introduction. This is followed by the synthesis and characterization of a recyclable calix[4]resorcinarene amide derivative (L). The 1H NMR analyses in CD3CN and CD3OD showed solvent-dependent conformational changes with a notable downfield chemical shift in the aromatic proton (H-2) in moving from deuterated methanol to acetonitrile, indicating an interaction of the solvent within the ligand cavity as suggested by molecular dynamic simulations. 1H NMR complexation in acetonitrile revealed that L forms relatively strong 1:1 complexes with cations, with selectivity for Ca(II) and, to lesser extent, with Pb(II) over other metal cations. The composition of the complexes is corroborated by conductance measurements. The thermodynamics of these systems indicate that the complexation process is predominantly enthalpy controlled in acetonitrile, while it is entropy controlled in methanol. A remarkable outcome of fundamental studies is found in its application as new material for the removal of Ca(II) from water. The capacity of L to remove Ca(II) from water is 24 mmol/g which exceeds by far the capacity of cation exchange resins. Full article

Selenium (Se) is a natural detoxifier of the heavy metal mercury (Hg), and the interaction between Se and Hg has been widely investigated. However, the ecological response of Hg to Se in Hg-contaminated farmland requires further study, especially the relationship between Se–Hg interactions and soil abiotic and biological properties. Through a field experiment, the effects of different levels of exogenous Se (0, 0.50, 0.75, 1.00, and 2.00 mg kg⁻¹) on Hg and Se transport in maize, soil properties, enzyme activities, and the microbial community in Hg-contaminated farmland were systematically studied. The Se treatments significantly reduced the Hg concentration in maize roots, stems, leaves, and grains and significantly increased the Se concentration in maize tissues. Except for the 0.75 mg kg⁻¹ Se treatment which significantly increased electrical conductivity compared to the control, other Se treatments had non-significant effect on soil physicochemical properties (pH, conductivity, organic matter content, and cation exchange capacity) and oxidoreductase activities (catalase, peroxidase, and ascorbate peroxide). The activities of soil invertase, urease, and alkaline phosphatase increased significantly after Se application, and the highest enzyme activities were observed with a 0.50 mg kg⁻¹ Se treatment. The bacteria and fungi with the highest relative abundance in this study were Proteobacteria (>30.5%) and Ascomycota (>73.4%). The results of a redundancy analysis and predictions of the microbial community showed that there was a significant correlation between the soil nutrient cycle enzyme activity, microbial community composition, and microbial community function. Overall, exogenous Se application was found to be a viable strategy for mitigating the impact of Hg stress on ecosystems. Furthermore, the results provide new insights into the potential for the large-scale application of Se in the remediation of Hg-contaminated farmland. Full article

The information on the seasonal variability of the chemical composition of the Arctic rivers is necessary for the proper assessment of the status of river runoff and the influence of anthropogenic and natural factors. Spring freshet is an especially important period for the Arctic rivers with a sharp maximum of water discharge. The Kolyma River is the least studied large river with a basin located solely in the permafrost zone. The change in the concentration of dissolved organic carbon (DOC), major, trace, and rare earth (RE) elements was studied at the peak and waning of the spring freshet of 2024 in the lower reaches of the Kolyma River. The concentration of elements was determined in filtrates <0.45 μm and in suspended solids > 0.45 μm. The content of coarse colloids (0.05–0.45 μm) was estimated by the intensity of dynamic light scattering (DLS). It was shown that the freshet peak is characterized by a minimal specific conductivity, concentration of major cations, and chemical elements migrating mainly in solution (Li, Sr, and Ba). During the freshet decline, the concentration of these elements increases with dynamics depending on the water exchange. The waters from the Kolyma River main stream have a maximal content of coarse colloids and concentration of <0.45 μm forms of hydrolysates (Al, Ti, Fe, Mn, REEs, Zr, Y, Sc, and Th), DOC, P, and heavy metals (Cu, Ni, Cd, and Co) at the freshet peak. A decrease of 8–10 times for hydrolysates and coarse colloids (0.05–0.45 μm) and of 3–6 times for heavy metals was observed at the freshet waning during the first half of June. This indicates a large-scale accumulation of easy soluble forms of hydrolysates, DOC, and heavy metals in the seasonal thawing topsoil layer on the catchment upstream in the previous summer, with a flush out of these elements at the freshet peak of the current year. In the large floodplain watercourse Panteleikha River, the change in concentration of major cations and REEs, Zr, Y, Sc, and Th at the freshet is less accented compared with the Kolyma River main stream due to a slower water exchange. Yet, <0.45 μm forms of Fe, Mn, Co, As, V, and P show an increase of 4–6 times in the Panteleikha River in the second half of June compared with the freshet peak, which indicates an additional input of these elements from the thawing floodplain landscapes and bottom sediments of floodplain watercourses. The concentration of the majority of chemical elements in suspended matter (>0.45 μm) of the Kolyma River is rather stable during the high-water period. The relative stability in the chemical composition of the suspended solids means that the content of the suspension and not its composition is the key to the share of dissolved and suspended forms of chemical elements in the Kolyma River runoff. Full article

Complex oxides with the general formula Gd₂(Ti_1−xZr_x)₂O₇ are promising candidates for radioactive waste immobilization due to their capacity to withstand radiation by dissipating part of the free energy driving defect creation and phase transitions. In this study, samples with varying zirconium content (xZr = 0.00, 0.15, 0.25, 0.375, 0.56, 0.75, 0.85, 1.00) were synthesized via the sol–gel method and thermally treated at 500 °C to obtain nanosized powders mimicking the defective structure of irradiated materials. Synchrotron-based techniques were employed to investigate their structural properties: High-Resolution X-ray Powder Diffraction (HR-XRPD) was used to assess long-range structure, while Pair Distribution Function (PDF) analysis and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy provided insights into the local structure. HR-XRPD data revealed that samples with low Zr content (xZr ≤ 0.25) are amorphous. Increasing Zr concentration led to the emergence of a crystalline phase identified as defective fluorite (xZr = 0.375, 0.56). Samples with the highest Zr content (xZr ≥ 0.75) were fully crystalline and exhibited only the fluorite phase. The experimental G(r) functions of the fully crystalline samples in the low r range are suitably fitted by the Weberite structure, mapping the relaxations induced by structural disorder in defective fluorite. These structural insights informed the subsequent EXAFS analysis at the Zr-K and Gd-L₃ edges, confirming the splitting of the cation–cation distances associated with different metal species. Moreover, EXAFS provided a local structural description of the amorphous phases, identifying a consistent Gd-O distance across all compositions. Full article

Wastewater contains dyes originating from textile industries, and above a certain concentration, they can become dangerous due to their high toxicity. Divalent and trivalent metal coagulants, usually aluminum- or iron-based, have been studied worldwide. However, tetravalent coagulants, such as tin chloride, have not yet been extensively studied for application in wastewater treatment. Therefore, in this study, three types of coagulants were examined: SnCl₄, Cs, and a hybrid composite (CS@Sn) in two different mass ratios, abbreviated hereafter as CS@Sn_5% and CS@Sn_50%. The formation of the suggested CS@Sn hybrid coagulants was confirmed by applying SEM, XRD, and FTIR techniques. The results showed that the optimum conditions for RB5 removal was the addition of 20 mg Sn/L SnCl₄ (97.8%) and 50 mg Sn/L of CS@Sn_50% (64.8%) at pH 3.0. In addition, SnCl₄ was found to be an effective coagulant for all the examined anionic dyes, but it was not as effective for cationic dyes. Moreover, the coagulants were then tested in two mixed-dye solutions, both anionic dyes (RB5/RR120) and anionic/cationic (RB5/MV), resulting in a synergistic effect in the first one and a competitive effect in the secon. Finally, the proposed coagulants were successfully tested on real wastewater samples from an untreated textile dyeing industry. Therefore, the coagulants presented in this work for the removal of several dyes are also capable of being used for wastewater treatment. Full article

The mineral composition of table salt can be indicative of its origin. This work evaluated the possibility of identifying the origin of salt from four countries: Brazil, Spain, France, and Portugal. Eight metals were quantified through flame atomic absorption/emission spectroscopy (FAAS). The possibility of using portable near-infrared spectroscopy (NIR) as a faster and lower-cost alternative for identifying salt provenance was also evaluated. The content of Ca, Mg, Fe, Mn, and Cu was identified as possible markers to differentiate the salt origin. One-class classifiers using FAAS data and DD-SIMCA could discriminate the salt origin with few misclassifications. For NIR spectroscopy, it was possible to highlight the importance of controlling the humidity and granulometry before the spectra acquisition. After drying and milling the samples, it was possible to discriminate between samples based on the interaction between the water of hydration and the presence of the cations in the sample. The Mg, Mn, and Cu are important in identifying the origin of salt using NIR spectra. The DD-SIMCA model using NIR spectra could classify the origin with the same performance as observed in FAAS. However, it is important to emphasize that NIR spectroscopy requires less sample preparation, is faster, and has low-cost instrumentation. Full article

Conjugated microporous polymers (CMP) are advanced photocatalytic systems for degrading organic dyes. However, their potential and efficiency are often limited by rapid electron–hole pair (e⁻/h⁺) recombination. To overcome this limitation, this study proposes a strategy that involves designing a Mott–Schottky heterojunction and integrating graphene sheets with a near-zero bandgap into the CMP-1 framework, resulting in a non-covalent graphene/CMP (GCMP) heterojunction composite. GCMP serves two main functions: physical adsorption and photocatalytic absorption that uses visible light energy to trigger and degrade the organic dye. GCMP effectively degraded four dyes with both anionic and cationic properties (Rhodamine B; Nile Blue; Congo Red; and Orange II), demonstrating stable recyclability without losing its effectiveness. When exposed to visible light, GCMP generates reactive oxygen species (ROS), primarily singlet oxygen (¹O₂), and superoxide radicals (^•O₂), degrading the dye molecules. These findings highlight GCMP’s potential for real-world applications, offering a metal-free, cost-effective, and environmentally friendly solution for wastewater treatment. Full article

The influence of petroleum hydrocarbons (PHCs) on the transport and transformation of heavy metals may limit bioremediation efficiency. The mechanisms by which PHC degradation intermediates control heavy metal distribution in calcareous soils from karst areas require further exploration. This study systematically investigated how compositional changes in diesel fuel during aging regulated the fate of Cd and Pb in calcareous soils. The results demonstrated that the low-molecular-weight fractions of diesel fuel (C₁₀−C₁₆) were preferentially degraded. This degradation process altered zeta potential, cation exchange capacity (CEC), and pH, thereby promoting Cd stabilization through electrostatic attraction and speciation transformation. Particularly, reducible Cd content showed a strong positive correlation with C₁₆ content (r = 0.88, p < 0.05). Furthermore, the degradation of C₁₀−C₁₆ fractions caused Pb transformation from residual to bioavailable fractions by stimulating microbial activity. Residual Pb content was positively correlated with C₁₀−C₁₆ fractions (r = 0.55, p < 0.05). Notably, dissolved organic matter (DOM) and CaCO₃ content in calcareous soils enhanced Cd and Pb adsorption, thereby weakening the interactions between these metals and C₁₀−C₁₆ fractions. Consequently, multiple linear regression (MLR) models relying exclusively on C₁₀−C₁₆ degradation parameters showed poor fitting coefficients for Cd/Pb mobility. The present work provides scientific guidance for heavy metal bioremediation in calcareous soils. Full article

A novel polyhedron-based anionic Er-MOF with three types of cages and abundant open metal sites (OMSs) and Lewis base sites (LBSs) has been successfully synthesized. The inorganic secondary unit possesses a rarely reported six-connected three-nucleated rare-earth cluster, and the overall framework shows a new (3,3,6)-connected topology. The Er-MOF has good fluorescence selectivity and anti-interference performance with Fe³⁺ and Cu²⁺. In addition, benefiting from the anionic framework, nanoscale cavity and small window size of the Er-MOF, the composite RhB@Er-MOF has been synthesized by in situ encapsulation of the cationic dye Rhodamine B (RhB). It can provide dual-emitting fluorescence that facilitates self-calibration in sensing. The RhB@Er-MOF has higher accuracy than the Er-MOF with regard to the fluorescence-selective and anti-interference performance of Fe³⁺ and quenching coefficient K_sv values of 1.97 × 10⁴ M⁻¹, which are attributed to its self-calibration function that can eliminate environmental interference. The fluorescence quenching mechanism was explained by our experiments and density functional theory (DFT) calculations. Furthermore, RhB@Er-MOF can achieve the visual and rapid selective detection of Fe³⁺ by a smartphone RGB color analysis application, resulting in the dual-signal output performance of the material. Full article

Combinatorial magnetron sputtering and electrical characterization were used to systematically study the impact of compositional changes in the resistive switching of transition metal oxides, specifically the Zr_xTa_1−xO_y system. Current-voltage behavior across a range of temperatures provided insights into the mechanisms that contribute to differences in the electrical conductivity of the pristine Ta₂O₅ and ZrO₂, and mixed Zr_xTa_1−xO_y devices. The underlying conductive mechanism was found to be a mixture of charge trapping and ionic motion, where charge trapping/emission dictated the short-term cycling behavior while ion motion contributed to changes in the conduction with increased cycling number. ToF-SIMS was used to identify the origin of the “wake-up” behavior of the devices, revealing an ionic motion contribution. This understanding of how cation concentration affects conduction in mixed valence systems helps provide a foundation for a new approach toward manipulating resistive switching in these active layer materials. Full article

Soil heavy metal contamination poses critical challenges to ecological sustainability in mining regions, particularly in acidic soils from copper sulfide mines. This study developed a sustainable remediation strategy using a carbonyl iron powder–biochar composite (CIP@BC) derived from agricultural waste (rice husk) and industrial byproducts. The composite was synthesized through an energy-efficient mechanical grinding method at a 10:1 mass ratio of biochar to carbonyl iron powder, aligning with circular economy principles. Material characterization revealed CIP particles uniformly embedded within biochar’s porous structure, synergistically enhancing surface functionality and redox activity. CIP@BC demonstrated exceptional Cu²⁺ immobilization capacity (910.5 mg·g⁻¹), achieved through chemisorption and monolayer adsorption mechanisms. Notably, the remediation process concurrently improved key soil health parameters. Soil incubation trials demonstrated that 6% CIP@BC application elevated soil pH from 4.27 to 6.19, reduced total Cu content by 29.43%, and decreased DTPA-extractable Cu by 67.26%. This treatment effectively transformed Cu speciation from bioavailable to residual fractions. Concurrent improvements in electrical conductivity (EC), cation exchange capacity (CEC), soil organic matter (OM), and soil water content (SWC) collectively highlighted the composite’s multifunctional remediation potential. This study bridges environmental remediation with sustainable land management through an innovative waste-to-resource approach that remediates acidic mine soils. The dual functionality of CIP@BC in contaminant immobilization and soil quality restoration provides a scalable solution. Full article

Porous nanocrystalline lanthanum perovskite La-Fe-O (LaFeO₃) powders were synthesized by the sol–gel self-combustion method, using polyvinyl alcohol as the colloidal medium. The perovskite structure of the material, without secondary phases, was obtained at a calcination temperature of 900 °C for 40 min. The obtained powder was tested for catalytic activity at moderate temperatures (50–550 °C) for ethanol, methanol, acetone, benzene, and Pb-free gasoline vapors. Catalytic combustion begins at quite low temperatures (60–200 °C), compared to normal combustion, and this can be attributed to the nanometric crystallites, the large specific surface area, and the presence of iron cations with different valences, Fe³⁺/Fe²⁺, resulting from the method we used to obtain the material. The degree of conversion reaches values of over 99% for acetone and ethanol vapors at a temperature of 270 °C and 310 °C, respectively, and over 97% for methanol vapors at a temperature of 330 °C. The degree of conversion for Pb-free gasoline and benzene reaches somewhat lower values, over 88% at much higher temperatures, 470 °C and 550 °C, respectively. The lanthanum perovskite catalyst, LaFeO₃, obtained by the presented preparation method, can be recommended for the combustion of acetone, ethanol, and methanol vapors. The performance of this catalyst is remarkable and can be compared to that of a catalyst containing noble metals in its composition. Full article

Polyethylene imine (PEI) is a synthetic water-soluble and nitrogen-rich polymer with an ethylene amine repeating unit. It exists in a linear or branched forms and finds applications in various areas. PEI is often chemically modified by crosslinking reactions using molecular and polymeric crosslinkers (e.g., trichlorotriazine, epichlorohydrin, ethylene glycol diglycidyl ether, poly(ethylene glycol) diglycidyl ether, etc.) to increase its stability and reduce its water solubility. PEI (pristine/crosslinked) has a strong affinity for metal cations (e.g., Cu²⁺, Au³⁺, Pb²⁺, etc.), where the nitrogen atoms interact with the metal ions, and hence is suitable to remove metals from water with high efficiency. A thin film of crosslinked PEI on substrates can be prepared and finds diverse applications such as in removing metals and dyes, and biofouling prevention in the marine environment. The copper ion, as an example, can be stored (adsorbed) in a thin film of crosslinked PEI on a carbon cloth substrate, which can be released to water by passing an electric current through the film or with an acid treatment. It has also been reported that crosslinked PEI and composite materials can be used for the adsorption of dyes and gases such as CO₂ and SO₂ from the environment. The performance of pristine/composite/crosslinked PEI in gas, metal ion, and dye adsorption is affected by several factors. The focus of this review is to discuss the different reactions used to crosslink PEI and review the properties of the crosslinked materials and their applications. Studies have shown that the properties of the crosslinked PEI and hence its success in capturing metal ions, dyes, and CO₂ is dependent not only on the type of crosslinker but also on the degree of crosslinking. Full article

Natural zeolites (NatZ) are widely available, porous, crystalline aluminosilicate minerals that are commonly used as cost-effective adsorbents in water treatment processes. Despite their efficiency in removing various heavy metal ions from wastewater, NatZ show relatively low affinity toward Ni²⁺ and Cr³⁺ ions. This study aimed to develop composite adsorbents based on NatZ and hydroxyapatite using two methods, hydrothermal and mechanochemical, and their adsorption properties for the removal of Ni²⁺ and Cr³⁺ ions from aqueous solutions were investigated. X-ray powder diffraction and scanning electron microscopy analyses confirmed that under hydrothermal conditions, needle-like hydroxyapatite crystals were formed on the surface of NatZ, while the zeolite structure remained unchanged. Compared to the mechanochemically prepared sample, this adsorbent showed higher efficiency, binding 6.91 mg Ni²⁺/g and 16.95 mg Cr³⁺/g. Adsorption kinetics of the tested cations in both cases can be described by a pseudo-second-order model (R² is higher than 0.95 for all adsorbents). It is concluded that the presence of hydroxyapatite on the zeolite surface significantly improves the adsorption performance of NatZ, demonstrating its potential for the removal of heavy metal ions in wastewater treatment. Full article

Heavy metal pollution in surface soils poses significant environmental and health risks, yet the factors driving its spatial distribution remain poorly understood in certain regions. This study investigates the distribution and key influencing factors of heavy metal contamination in surface soils across Zhenjiang and Yangzhou, Jiangsu Province, China. This study analyzed the chemical compositions of 449 soil samples from the study area. Descriptive statistics, stepwise multiple regression, and the random forest (RF) method were employed to identify the key factors affecting the distribution and migration of heavy metals in soils. According to the national standards for soil risk screening values, cadmium (Cd) and mercury (Hg) were identified as the most heavily contaminated heavy metals in the study area. The average concentrations of Cd and Hg were 2.38 and 2.32 times higher than the provincial soil background values, respectively. A substantial proportion of samples exceeded the risk screening thresholds established for agricultural land. Key factors influencing the distribution of heavy metals in surface soils include soil iron oxides, pH, total organic carbon (Corg.), cation exchange capacity (CEC), and weathering intensity, as represented by the Chemical Index of Alteration (CIA). By integrating advanced data analysis techniques, this study provides new insights into the mechanisms governing heavy metal pollution in soils, offering a foundation for targeted soil management and pollution mitigation strategies. Full article