Using naturally available and low-cost materials for the removal of toxic metals from contaminated waters has long been recognized as a promising and sustainable approach. This study evaluates the potential of calcite-rich natural limestone from the "Šuplja Stijena" stone deposit (Pljevlja, Montenegro) for Pb(II) removal from aqueous solutions and acid mine drainage. Batch experiments demonstrated that Pb(II) removal is strongly influenced by the solid-to-liquid ratio, particle size, pH, and initial metal concentration. The highest experimental uptake reached 310 mg/g at an initial Pb(II) concentration of 900 mg/L, with a removal efficiency of 86%. Kinetic analysis revealed two distinct removal stages, indicating that a single adsorption mechanism cannot adequately describe the overall process. Time-resolved ex-situ Fourier transform infrared and X-ray diffraction analyses showed that the transition between these kinetic stages is accompanied by the structural evolution of the sorbent, involving initial surface interactions followed by partial calcite dissolution, Ca2+/Pb2+ ion exchange and progressive cerussite (PbCO3) formation. Although the Langmuir and Freundlich models yielded high correlation coefficients, the obtained parameters lacked physical significance, suggesting that classical equilibrium adsorption isotherms provide only a limited description of this complex removal process. Experiments performed with real acid mine drainage further confirmed the applicability of the investigated limestone under environmentally relevant conditions. These findings demonstrate that locally available calcite-rich limestone overburden is an effective and inexpensive material for Pb(II) removal while providing mechanistic insight into the coupled processes governing metal immobilization.
Basal stem rot, mainly caused by Ganoderma boninense, is a major disease affecting oil palm (Elaeis guineensis) and can lead to reduced productivity and plant mortality. This study characterized metabolic changes associated with different levels of G. boninense infection in oil palm stem tissue using untargeted gas chromatography–mass spectrometry metabolomics. Stem samples representing healthy, low, moderate, and high infection categories were analyzed, and the resulting metabolic features were processed using multivariate and univariate statistical approaches. A total of 14 features were retained after data processing and filtering. Principal component analysis and partial least squares discriminant analysis showed differences in the overall metabolic profiles among infection categories, while variable importance in projection analysis identified features contributing to group discrimination. However, permutation testing did not provide significant evidence for a classification model beyond chance (ANOVA p-value = 0.121), indicating that 121 of 1,000 permuted models achieved an accuracy at least as high as that of the observed model. None of the detected features remained significant after false discovery rate correction. Several fatty acid-related features, including methyl decanoate, methyl myristate, methyl oleate, methyl stearate, and methyl ricinoleate, were prioritized based on their multivariate contribution, abundance patterns, and library-based annotation. These compounds are therefore considered candidate metabolites associated with disease severity rather than validated biomarkers. The findings provide a preliminary view of metabolic variation in oil palm stems associated with G. boninense infection and identify candidate features for further validation using larger and independent sample sets.
Acid mine drainage (AMD) is a major environmental concern characterized by low pH and elevated concentrations of heavy metals such as iron and manganese, requiring effective and sustainable treatment methods. This study investigates the use of industrial fly ash waste as a low-cost adsorbent, enhanced through alkali-leaching modification to produce a zeolite-like material with improved adsorption performance. The novelty of this work lies in the application of alkali-leached fly ash to simultaneously enhance adsorption capacity and neutralization ability for AMD treatment. Adsorbent characterization was conducted using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) analyses. BET results showed that modification significantly increased the specific surface area (14 m2/g) and pore volume (0.025 cm3/g). SEM-EDX results revealed a predominantly spherical morphology and changes in elemental composition following modification. XRD analysis showed partial dissolution of minor phases during alkali leaching, resulting in increased dominance of the quartz (SiO2) phase with a main peak at 2θ = 26.59°. Batch adsorption experiments were performed under varying adsorbent dosages (10–100 g) to evaluate metal removal and pH improvement. The results demonstrated that modified fly ash increased AMD pH from 3.45 to 7.21 and achieved high removal efficiency of Mn, reducing its concentration to 0.05 mg/L (removal efficiency > 95%). Compared to untreated fly ash, the modified adsorbent exhibited significantly enhanced performance. The treated AMD met Indonesian Class I water quality standards. These findings highlight the potential of alkali-leached fly ash as an effective and sustainable adsorbent for AMD remediation.
This study investigates the impact of a novel copper(II)-based flame retardant on the combustibility and fire risk of epoxy composites. The flame retardant is a chelate-type coordination compound of copper(II) chloride and diethylenetriamine (deta) – [Cu(deta)2]Cl2 – and was synthesized through the direct reaction of CuCl2 and polyethylenepolyamine (pepa). When incorporated into epoxy resin, the synthesized coordination compound exhibites bifunctional properties, acting as both a flame retardant and a curing agent. Epoxy composites containing [Cu(deta)2]Cl2 are significantly less combustible, as demonstrated by a decrease in the maximum temperature of the gaseous combustion products and the mass loss of composite samples due to combustion. The flammability of the synthesized composition was evaluated using the vertical burning method in accordance with the UL 94 standard, and the composition met the criteria for the V-1 class. Incorporating the synthesized flame retardant-hardener into the epoxy resin reduces smoke emission intensity during burning and smoldering. The increased fire resistance of the modified compositions is due to the formation of Cu–N coordination bonds in the polymer matrix and the catalytic effect of copper-containing centers on carbonization and oxidation processes. This is in addition to the formation of a dense, carbonized protective layer during thermal decomposition. These results confirm the potential of using copper(II) chelate coordination compounds as multifunctional components in epoxy systems that combine the roles of curing agent and flame retardant. This opens up opportunities for creating a new generation of polymer materials with enhanced fire safety for various applications.
The biocatalytic kinetic resolution of three racemic cyclic β‑amino esters (±)-ethyl cis‑2‑aminocyclopent‑3‑enecarboxylate (±)-1a, (±)-ethyl cis‑2‑aminocyclohex‑3‑enecarboxylate (±)-1b, and (±)-ethyl trans‑6‑aminocyclohex‑3‑enecarboxylate (±)-1c was investigated using lipase B from Candida antarctica immobilized on magnetic nanoparticles with three different acylating agents (E, C, M). Among the substrates examined, (±)-1a underwent a highly enantioselective N‑acylation, displaying the characteristic profile of a classical kinetic resolution with conversions ~50% and excellent enantiomeric excess of the (R)-amide product (ee(R)-2aE > 99.9%). The reaction showed notable robustness across a wide substrate concentration range, highlighting its potential for larger‑scale preparation of enantiomerically pure compounds. In contrast, substrates (±)-1b and (±)-1c were not resolved at preparative scale due to the low selectivity of the biocatalyst in kinetic resolution (for (±)-1b) or insufficient chromatographic separation of the corresponding racemic amide (±)-2cE). The three novel racemic amides [(±)-2a–cE] and enantiopure (R)-2aE and (S)-1a were isolated and properly characterized.
