Chemija

Title

Lietuvos mokslų akademija — 2026-09-18

Prof. Habil. Dr. JUOZAS VIDAS GRAŽULEVIČIUS: From a Scientific Calling to Interna- tional Recognition

Jūratė Simokaitienė — 2026-09-18

Electrochemical study of the corrosion behaviour of steel rebar in a chloride-containing alkaline environment and the passive-film influence mechanism of Xanthium extract

Yu-chen Zhang — 2026-09-18

To develop a green corrosion inhibitor suitable for chloride-containing alkaline environments in reinforced concrete, Xanthium extract was investigated in a simulated concrete pore solution (saturated Ca(OH)₂ + 3.5 wt% NaCl). Open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarisation were employed to systematically evaluate its effect on the corrosion behaviour of carbon steel electrodes. The results show that the extract exhibits a pronounced concentration dependence. The solution containing 700 mg/L Xanthium extract shows the best performance in terms of overall impedance, Faradaic resistance, total electrode-process resistance, and long-term polarisation behaviour, followed by 1000 mg/L, whereas 200 mg/L provides the poorest overall protection. EIS analysis indicates that the extract influences steel corrosion by regulating the dielectric response of the composite film, the electrochemical reaction process, and the restricted transport process. Combined with the passive-film mechanism in alkaline media and the adsorption-film mechanism of inhibitor molecules, the effect of the extract is not simply to promote film thickening. Instead, at suitable concentrations, it stabilises the passive-film structure through surface adsorption, suppresses passive-film defect evolution, and reduces interfacial charge transfer, thereby enhancing the corrosion resistance of steel rebar in chloride-containing alkaline environments. This concentration-dependent synergy governs the final protection efficiency under the present conditions.

Electrochemical detection of ibuprofen at a graphene–chitosan modified glassy carbon electrode: integrating differential pulse voltammetry with machine learning calibration

Islam Hassan — 2026-09-18

A graphene–chitosan modified glassy carbon electrode (Gr-Chit/GCE) was evaluated for the differential pulse voltammetric (DPV) determination of ibuprofen (IBF) and paired with a transparent machine learning (ML) calibration audit. In a 0.1 M phosphate-based electrolyte (PBE, pH 7.5), the modified electrode gave a linear DPV response from 100 to 488 µmol/L after background subtraction, following I_p = 0.0828 + 0.0275C (R² = 0.9970). The recalculated limit of detection (LOD) and the limit of quantification (LOQ) were 22.27 and 74.25 µM, respectively. Cyclic voltammetric characterisation with [Fe(CN)₆]^3–/4– showed a diffusion-controlled behaviour and a 4.2-fold increase in the electroactive surface area after Gr-Chit deposition. Interference tests indicated that ascorbic acid was resolved at lower potential, while acetaminophen contributed in the IBF potential region without masking the analyte response. The leave-one-out cross-validation of six calibration models showed that the ordinary least-squares inverse calibration gave the lowest prediction error (root-mean-square error, RMSE = 12.11 µmol/L), whereas more complex nonlinear models showed a poorer generalisation for the five-point calibration set. The study therefore positions ML not as a black-box replacement for electroanalytical calibration, but as an auditable model-selection layer for small voltammetric datasets.

Core planarisation suppresses delayed fluorescence in narrowband deep-blue tetraboron MR-TADF emitters

Giedrius Puidokas — 2026-09-18

Narrowband blue multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitters are promising for high-colour-purity OLEDs, but structural modifications that preserve spectral purity can compromise delayed fluorescence. Here, two closely related tetraboron MR-TADF emitters, BO-4B and c-BO-4B, were designed to examine the effect of central-core planarisation on blue emission and triplet harvesting. The compounds were found to retain narrowband deep-blue fluorescence in dilute toluene, with emission maxima at 449 and 444 nm and full widths at half maximum of 14 and 19 nm, respectively. Quantum-chemical calculations indicate similar bright MR-type S1 states but a larger singlet-triplet gap (ΔEST) for planarised c-BO-4B. Low-temperature fluorescence and phosphorescence measurements of PMMA films containing 1 wt% emitter show that core planarisation leaves the S1 energy nearly unchanged while lowering T1, thereby increasing ΔEST from 95 to 165 meV. Time-resolved fluorescence reveals an identical prompt fluorescence quantum yield of 33%, whereas the delayed fluorescence yield decreases from 45 to 3%. Within a simplified kinetic model, this corresponds to a two-order-of-magnitude decrease in a reverse intersystem crossing rate. These findings suggest that core planarisation preserves a narrow prompt emission but strongly suppresses a delayed fluorescence by unfavourably shifting triplet-state energetics.

Adsorption properties of synthetic mayenite substituted with Si4+ ions

Jolanta Donėlienė — 2026-09-18

This work aims to determine the influence of amorphous SiO₂ on the formation of katoite, on the formation of mayenite, and on its adsorption capacity for Cu²⁺ ions. Katoite was synthesised under hydrothermal conditions (130°C; 4 h) in the primary mixture, which consisted of amorphous SiO₂, aluminium oxide and calcium oxide. It has been found that, at 350°C in the pure system, katoite completely recrystallised into a mixture of mayenite and portlandite. Moreover, in the presence of the SiO₂ additive, calcination at 350°C yielded the same products once calcium monocarboaluminate and katoite substituted with Si⁴⁺ ions had fully decomposed. It was also observed that MA-Si3 exhibited slightly better adsorption properties for Cu²⁺ ions than MA3: after 60 min, its adsorption capacities were 196.3 and 194.5 mg/g, respectively. It was determined that in the MA1 sample, a similar intensity of calcite, vaterite and aragonite was formed. Additionally, traces of calcium monocarboaluminate, rouaite and gibbsite were identified in the XRD patterns. Also, more intensive diffraction peaks of calcite were formed in the MA3 sample than in the MA1 and MA-Si1 samples. Moreover, higher intensity diffraction peaks characteristic of katoite formed in the MA-Si3 sample.

Stereolithography-derived boron nitride-based 3D photocatalysts with controlled architectures for water treatment

Petras Rauka — 2026-09-18

A novel boron nitride (BN) containing composite photoresin was developed and used to fabricate BN-based three-dimensional (3D) photocatalysts with controlled geometries via stereolithography (SLA), followed by pyrolysis. Three architectures – gyroid, honeycomb and cubic lattice structures with different structural periodicities – were produced and characterised. The influence of 3D architecture on structural integrity and photocatalytic performance was evaluated through the degradation of Rhodamine B (RhB) under halogen lamp irradiation. The photocatalytic performance strongly depended on the architecture, with increasing structural periodicity leading to a higher density of fabrication defects, a reduced solution permeability, and a lower accessible active surface area. Among all investigated structures, the 2 × 2 cubic lattice exhibited the highest photocatalytic performance, achieving 88.44% RhB degradation after 150 min of halogen lamp irradiation and the highest surface area-normalised efficiency of 259.9 mg/m2. These findings demonstrate that additive manufacturing enables the fabrication of efficient, reusable, self-supporting h-BN-based photocatalysts.

Hydrothermal synthesis and luminescence of Eu3+-doped Gd1–xLaxPO4 phosphates

Monika Rimkienė — 2026-09-18

Eu3+-doped gadolinium, lanthanum and mixed gadolinium–lanthanum phosphates were synthesised by a hydrothermal method and investigated as luminescent phosphate materials. The target compositions included GdPO₄, LaPO₄ and Gd_1–xLa_xPO₄ doped with 15 mol% Eu³⁺; selected GdPO₄:Eu³⁺ samples were also prepared in the presence of sodium lauryl sulfate as a surfactant. X-ray diffraction showed the formation of hydrated phosphate phases. GdPO₄·H₂O:Eu³⁺ samples crystallised in a hexagonal hydrated phase, whereas increasing La content promoted mixtures of hexagonal and monoclinic phases. Photoluminescence measurements confirmed Eu3+-related excitation and emission transitions, with orange–red emission under near–UV excitation. The strongest emission was observed for GdPO₄·H₂O:Eu³⁺, while increasing surfactant content and increasing La substitution reduced emission intensity. Scanning electron microscopy revealed that agglomerated fine particles and partially elongated particles were formed. Thermal analysis indicated dehydration below approximately 500°C and suggested structural transformation at higher temperatures. The results show that hydrothermal synthesis yields luminescent Eu3+-doped hydrated phosphate materials, but further optimisation is required to obtain phase-pure monoclinic products and controlled morphology.

Triazole-containing electroactive compounds in organic light-emitting devices: A review

Mariia Stanitska — 2026-09-18

Organic light-emitting diodes (OLEDs) represent a rapidly developing class of optoelectronic devices widely employed in display and lighting technologies. The continuous improvement of OLED performance critically depends on the development of organic materials capable of efficient charge transport, effective exciton utilisation, and long-term operational stability. Among nitrogen-containing heterocyclic compounds, triazoles have emerged as versatile scaffolds in materials science due to their exceptional electron-transporting properties. Structurally, triazoles are classified as 1,2,3-triazoles and 1,2,4-triazoles, both of which can accommodate diverse substituents around the core, enabling fine-tuning of their electronic and photophysical characteristics. These features make triazole derivatives and their derivatives highly suitable as electron-transporting materials, hosts and emitters in optoelectronic applications, including OLEDs, photovoltaics and sensors. The incorporation of triazole units allows for efficient charge transfer, enhanced thermal and chemical stability, and improved device performance. This review highlights the structural aspects and functional roles of triazole-based compounds in electron-transporting systems. The application of triazole-based compounds as hosts and emitters provides a comprehensive perspective on their potential for next-generation optoelectronic devices.

Synthesis of pH-responsive brush copolymers by raft polymerisation and click chemistry reactions

Jūratė Jonikaitė-Švėgždienė — 2026-09-18

In this study, anionic brush copolymers were synthesised by grafting onto strategy, combining radical addition fragmentation chain transfer (RAFT) polymerisation and two click chemistry reactions, namely, epoxy–thiol and azide–alkyne. The backbone of the prospective brush copolymers with multiple epoxy groups and the nearly equimolar composition of the monomeric units was synthesised by RAFT copolymerisation of butyl methacrylate (BMA) and glycidyl methacrylate (GMA). Poly(tert-butyl methacrylate) (p(t-BMA) as a precursor for the side chains was synthesised by RAFT polymerisation and, subject to the structure of the chain transfer agent, contained terminal thiol or alkyne groups. The course of the click reactions was monitored by DLS. Anionic brush copolymers containing carboxyl groups were obtained via acidic hydrolysis of t-BMA units.
Aqueous solutions of the anionic brush copolymers were studied by potentiometric and turbidimetric titration, and by DLS. Both anionic brush copolymers, irrespective of the type of click chemistry reaction, were weak polyacids. Anionic brush copolymers, synthesised by the epoxy–thiol click reaction, form rather compact aggregates, whereas those, synthesised by the azide–alkyne click reaction, assemble into larger microgel-like aggregates. In the synthesis of brush copolymers, the method of epoxy–thiol click chemistry has some advantages because of simpler experimental procedures and higher grafting density in the products.