Sergejs Osipovs

The present work describes the characterization of complexes between various metals and three benzanthrone derivatives bearing structurally similar substituents. Within this investigation, the obtained complexes were meticulously examined using spectroscopic techniques. The absorption spectra of solutions of the obtained complexes in the UV-visible region showed a small bathochromic or hypsochromic shift in the visible region compared to the initial compounds. In the emission spectra of these complexes, significant changes in the positions and intensities of the fluorescence bands were observed as a function of the dyes' chemical structures. Interaction with metal ions in the presence of β-lactoglobulin amyloid fibrils showed metal-specific effects, including fluorescence enhancement with Zn²⁺ and pronounced quenching with Cu²⁺, suggesting a combined contribution of dye–metal and fibril–metal interactions. These findings highlight the potential of benzanthrone derivatives, both free and fibril-bound, as sensitive and selective fluorescent probes for heavy metal detection, providing a foundation for the development of hybrid biomaterial-based sensing platforms.

Pyrolysis of refuse-derived fuel (RDF) is a promising waste-to-energy route, but its use in higher-value applications remains limited by tar carryover, benzene, toluene, ethylbenzene, and xylenes (BTEX), heteroatom-containing compounds, and pollutant accumulation in recirculated scrubber water. This study evaluated operating windows for RDF pyrolysis coupled with direct wet scrubbing and closed-loop water reuse, with the aim of identifying regimes suitable for different end-use tiers. A Taguchi L27 design of experiments (DOE), i.e., an orthogonal array comprising 27 experimental runs, was applied to evaluate the effects of pyrolysis temperature, residence time, scrubber liquid-to-gas ratio, and scrubber-water temperature, while sequential reuse of the same scrubber-water inventory was evaluated at 5, 10, and 15 cycles. Cleaned-gas pollutants were quantified by compound-resolved gas chromatography–mass spectrometry (GC–MS) after solid-phase adsorption (SPA) sampling, while phenolics and polycyclic aromatic hydrocarbons (PAHs) in scrubber water were determined by extraction followed by GC–MS. Feasibility within each end-use tier was defined as simultaneous satisfaction of tier-specific cleaned-gas thresholds (C_tar, C_BTEX, I_N, and I_S) and the corresponding water-loop hazard limit (I_tox), using literature-informed engineering screening criteria. The results showed that stronger scrubbing reduced gas-phase tar and BTEX burdens, whereas extended water reuse caused systematic accumulation of phenolics and PAHs and increased the composite water-loop hazard index. Boiler-grade operation remained feasible across a broad operating range, with 23 of the 27 tested conditions remaining robust, whereas internal combustion engine combined heat and power (ICE-CHP) feasibility was restricted to a narrow robust regime, and no robust microturbine-grade condition was identified. These findings show that operating windows for RDF pyrolysis must be defined jointly by gas cleanliness and water-loop management constraints.

Pyrolysis of refuse-derived fuel (RDF) is a promising waste-to-energy route, but its use in higher-value applications remains limited by tar carryover, BTEX, heteroatom-containing compounds, and pollutant accumulation in recirculated scrubber water. This study evaluated operating windows for RDF pyrolysis coupled with direct wet scrubbing and closed-loop water reuse, with the aim of identifying regimes suitable for different end-use tiers. An L27 design of experiments was applied to 27 pyrolysis runs by varying pyrolysis temperature, residence time, scrubber liquid-to-gas ratio, scrubber-water temperature, and sequential reuse of the same scrubber-water inventory over 5, 10, and 15 cycles. Cleaned-gas pollutants were quantified by compound-resolved GC–MS after solid-phase adsorption sampling, while phenolics and PAHs in scrubber water were determined by extraction followed by GC–MS. The results showed that stronger scrubbing reduced gas-phase tar and BTEX burdens, whereas extended water reuse caused systematic accumulation of phenolics and PAHs and increased the composite water-loop hazard index. Boiler-grade operation remained feasible across a broad operating range, whereas ICE-CHP feasibility was restricted to a narrow robust regime and no robust microturbine-grade condition was identified. These findings show that operating windows for RDF pyrolysis must be defined jointly by gas-cleanliness and water-loop management constraints.

The novel benzanthrone derivative, 2-bromo-3-aminobenzo[de]anthracene-7-one (2-Br-3-NH₂BA), was synthesized and extensively characterized to investigate its photophysical behavior in various solvents. It was prepared through selective bromination of 3-aminobenzanthrone using N-bromosuccinimide in dimethylformamide at −20 °C. Featuring a donor–π–acceptor (D–π–A) structure, 2-Br-3-NH₂BA exhibits pronounced solvatochromism due to the intramolecular charge transfer (ICT) between the amino donor and the carbonyl acceptor groups. Optical measurements conducted in eight solvents of varying polarity revealed a significant bathochromic shift in both absorption and fluorescence emission, with emission maxima red-shifting by over 110 nm from non-polar to polar environments. Corresponding reductions in the optical band gap energies, as calculated from Tauc plots, further support solvent-induced electronic state modulation. Additionally, quantum yield analysis showed higher fluorescence efficiency in non-polar solvents, while polar solvents induced twisted intramolecular charge transfer (TICT), leading to emission quenching. These findings demonstrate the sensitivity of 2-Br-3-NH₂BA to environmental polarity, making it a promising candidate for color-tunable luminescent applications in optoelectronics and sensing. However, further studies in the solid state are required to validate its applicability in device architectures such as OLEDs.

In the present study, new fluorophores based on disubstituted benzanthrone derivatives were designed starting from 9-nitro-3-bromobenzanthrone with nucleophilic substitution of the bromine atom with some secondary cyclic amines. It has been found that this reaction is positively affected by the presence of a nitro group in comparison with 3-bromobenzanthrone. The new compounds exhibit intense absorption and pronounced luminescent properties in various organic solvents. In this regard, their photophysical properties were evaluated with an experimental study of the solvatochromic behavior of the obtained compounds in various solvents. It has recently been found that the addition of an electron-withdrawing nitro group to the benzanthrone core increases its first- and second-order hyperpolarizability. Such dyes can be used in the fabrication of optical limiter devices. Therefore, the developed fluorescent molecules have a potential prospect for extensive application in optoelectronics.

The research looks into the potential of generating biogas from waste generated by aquaculture. The EDF-5.4_2 bioreactor, produced by "Biotehniskais centrs" (Latvia), was utilized for the experimental study. Samples of sludge from a fish farm located in Nagļu parish, Rēzekne district were collected and analysed for their moisture and organic matter content before being mixed with crushed reeds to increase the organic matter available for fermentation and biogas extraction.In this study, biogas was produced by mixing different ratios of sludge and reed residue. The yield of biogas varied based on the temperature, with the best results being achieved at 40°C. During the experiment, 2.75 L of biogas containing 37.3% methane was produced from the mixture of 1,200 g of fish farming sludge and 100 g of crushed reeds. Although the highest methane content of 40.16% was recorded at 43°C, the total amount of biogas produced was lower by 15% at this temperature.The least favourable results were recorded at 37°C, in terms of both the amount of biogas produced and the methane content. The experimental studies demonstrate that residues from aquaculture can be used for biogas production.

The present work describes the synthesis of the new benzanthrone dye-3-[4-(2-phenylethyl)piperazin-1-yl]-7H-benzo[de]anthracen-7-one by bromine atom nucleophilic substitution reaction. The structure of the obtained benzanthrone derivative is characterized by NMR spectroscopy, mass spectrometry, and X-ray diffraction analysis. The photophysical properties of the target compound are investigated by means of UV-Vis and fluorescence spectroscopy in various organic solvents.

Pyrolysis converts waste and also produces useful by-products. In this case, gas, liquid, and solid phases are formed. The gas mixture contains tar, among other components. Water scrubbing technology is used to purify pyrolytic gas. The disadvantage of this technology is that the tar components gradually accumulate in the water. The tar compounds most exposed to this process are readily soluble light heterocyclic aromatic and heavy polyaromatic compounds. Some light aromatic tar compounds−the content of which is usually very high in pyrolytic gas−are present in small amounts in the cooling and cleaning water. In the pyrolytic gas purification process, not only does the total amount of tar in the cooling and cleaning water increase as the number of pyrolytic cycles increases but the ratio of the individual tar compounds to each other also changes, especially in relation to the accumulation of heaviest polyaromatic tar compounds. This, in turn, leads to problems, requiring further purification of the cooling and rinsing water used in the process.