Abstract. Light-absorbing organic carbon, collectively known as brown carbon (BrC), significantly influences climate and air quality, particularly in urban environments like Dhaka, Bangladesh. Despite their significance, the contributions and transformation pathways of phenolic compounds – major precursors of brown carbon (BrC) – are still insufficiently understood in the South Asian megacities. This study addresses this gap by investigating the surface morphology of PM2.5, quantifying seven phenolic BrC precursors, and exploring the aqueous-phase formation pathway of nitrophenols at two urban sites (Dhaka South and Dhaka North) from July 2023 to January 2024. Phenolic compounds, including phenol, methylphenols, methoxyphenol, hydroxyphenol, and nitrophenol were identified and quantified using gas chromatography–flame ionization detector (GC-FID). PM2.5 surface morphology and elemental composition were analyzed via Field Emission Scanning Electron Microscopy – Energy Dispersive X-ray Spectroscopy (FESEM-EDX), and functional groups were characterized using Attenuated Total Reflectance – Fourier Transform Infrared Spectroscopy (ATR-FTIR). Results revealed that PM2.5 particles were predominantly spherical or chain-like with carbonaceous elements (C, O, N, S), mineral dust, and trace metals. The dominant functional groups included aromatic conjugate double bond, carbonyl, and nitro group. Aqueous-phase nitration of 2-hydroxyphenol under acidic conditions, analyzed via UV-Vis spectroscopy, demonstrated an alternative nitrophenol formation pathway. Among the detected compounds, 2-hydroxyphenol and 4-nitrophenol showed the highest average concentrations (2.31 ± 1.39 and 2.20 ± 1.21 µg m−3, respectively). Seasonal variations showed elevated nitrophenol levels during winter, especially in Dhaka South (4.54 ± 2.94 µg m−3). These findings highlight the quantification of phenolic precursors and the role of aqueous-phase reactions in BrC formation, providing valuable insights for future atmospheric modeling and air quality management strategies in South Asia.

PurposeThis study aims to develop synthetic ester lubricating oil using renewable sinapic acid as raw material, to explore the structural design and selection of raw materials for green, high-performance synthetic ester oils.Design/methodology/approachA series of the sinapate ester oils were synthesized through esterification and alkoxylation reactions using renewable source sinapic acid as the raw material. The molecular structures of the oils were characterized by nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy spectroscopy and elemental analysis. The oils were evaluated for safety, viscosity-temperature properties, thermal and oxidative stability, as well as friction reducing and anti-wear characteristics.FindingsCompared to commercial base oil tris (2-ethylhexyl) trimellitate (Phe-3Ci8), the bio-lubricant exhibits superior antifriction and anti-wear properties. Notably, the JCi8-C12 sample performed exceptionally well, reducing the friction coefficient by 11.42% and wear volume (WV) by 54.44% in steel/steel tribo-pairs. In steel/aluminum tribo-pairs, the friction coefficient decreased by 27.48%, while WV was reduced by 85.81%. Mechanistic studies reveal that the introduction of short-chain methoxy groups and stable conjugated systems (aromatic rings and double bonds) inhibit oxidation and decomposition at elevated temperatures. The p-p stacking effect enables lubricant molecules to arrange stably on friction surfaces, forming a durable lubricating film.Originality/valueThe utilization of biomass resources to develop green synthetic lubricating oil with excellent performance not only enhances the added value of waste from agricultural processing but also offers significant benefits in terms of both economic and environmental sustainability.

Zea mays bracts extract as an eco-friendly corrosion inhibitor for steel in HCl pickling solution: Experimental and simulation studies

There is need to have cost-effective treatment strategy by using medicinal plant that have therapeutic potentials against varieties of disease due to presence of bioactive compound. The study aimed to characterize the bioactive compounds from the aqueous layer of Guiera senegalensis leaf extracts. Aqueous layer extracts from Guiera senegalensis leaf were prepared and analyzed using FTIR and GCMS. The GCMS result of the plant extract reveals the presence of Carboxylic acid and its derivatives and other compounds such as n-Propyl 11-octadecenoate , Aspidospermidin-17-ol, 1-acetyl-19,21-epoxy-15,16-dimethoxy- . The results of the study have justified therapeutic potential of Guiera senegalensis plant extract. FTIR result indicate a signal at 3205 cm-1which is a vigorous intensity which is attributed to carboxylic acid, a strong signal was observed at 2926 cm-1which is attributed to C-H stretch (alkane),carbon-oxygen (C-O) band was observed at 1200 cm-1 which is attributed to ester, carboxylic acid or ether and aromatic functional carbon-carbon double bond at 1442 cm1, a strong intensity was observed at 1602 cm-1, which is attributed to N-H bend of primary amine, aromatic ring stretch at 1457 cm-1 was also observed with medium intensity. Alkane bend vibration was observed at 1375cm-1, and a strong signal was observed at 1162cm-1, which is attributed to C-N (Amine).

Background: Reduction is one of the major chemical processes that takes place in life and laboratory as observed in photosynthesis (carbohydrates) and addition of hydrogen atoms to unsaturated compounds (alkenes, alkynes and carbonyls) respectively. Objectives: A reaction mechanism is proposed for a new variant of “selective” reduction using sodium borohydride (NaBH4) and iodine (I2). Methodology: Three compounds namely, gallic acid, vanillin and caffeic acid were separately reduced by sodium borohydride in iodine and the obtained products identified. Results: The identities of the reduced products had been revealed to be 3, 4, 5-trihydoxycyclohexyl methanol, o-methoxy-p-methyl cyclohexan-1-ol and 1-(3, 4-dihydroxy phenyl)-2-propen-3-ol (3, 4-benzenediol-2-propen-3-ol respectively in previously documented studies. Expectedly, the first two start-up compounds had their carbonyls (-C= O) groups reduced. In addition, the aromatic endocyclic double bonds (-Ar-C= C) were similarly reduced which introduced a new twist (variant) to this particular reduction hence the essence of the proposed reaction mechanism. However, the third compound had only its -C= O reduced while the double bonds (endocyclic and exocyclic) were left unreduced. Conclusion: The reaction mechanism for this variant of reduction shows that the associated electromeric and hyper-conjugation effects are resonance- stabilized in the transfer of electrons and or bonds over the carbon atom positions in the gallic acid which also serves as a reference for vanillin. This reaction mechanism is given trivial appellation- Olawale reduction mechanism.

Shaping sustainable pathways: Enhancing mechanical properties of biocomposite through tannic acid treatment of flax fabrics

Reported herein is a Paternò-Büchi reaction of aromatic double bonds with quinones under visible light irradiation. The reactions of aromatics with quinones exposed to blue LED irradiation yielded oxetanes at -78 °C, which was attributed to both the activation of double bonds in aromatics and the stabilization of oxetanes by thiadiazole, oxadiazole, or selenadiazole groups. The addition of Cu(OTf)2 to the reaction system at room temperature resulted in the formation of diaryl ethers via the copper-catalyzed ring opening of oxetanes in situ. Notably, the substrate scope was extended to general aromatics.

Reaction kinetic modelling of tar cracking in a non-thermal plasma reactor: Model evaluation and reaction mechanism investigation

Stilbenes are a compelling class of organic photoswitches with a high degree of tunability that sensitively depend on their environment. In this study, we investigate the adsorption properties of 4-(N,N-dimethylamino)-4'-nitrostilbene (DANS), a push-pull stilbene, on amorphous silica glass. Plane-wave density functional theory (DFT) calculations are used to understand how the trans and cis isomers of DANS interact with the amorphous surface and which are the most preferred modes of adsorption. Our calculations revealed that the O-H···O hydrogen bonds between the nitro group and hydroxyl groups of the silica surface dominate the intramolecular interaction. In addition to hydrogen bonding, O-H···π interactions with the aromatic ring and double bond play a critical role in adsorption, whereas C-H···O interactions are present, but contribute little. Therefore, both isomers of DANS favor parallel orientations such that not only the functional groups but also the aromatic parts can strongly interact with the glass surface.

Abstract Indoles, benzofurans and benzothiophenes substituted by a cyano group at positions 2 or 3 are shown to behave differently toward azomethine ylide 1,3‐dipole 1 , in (3+2) cycloadditions. While the C2=C3 aromatic double bond of 3‐cyanoheteroarene reacts as dipolarophile to generate the corresponding dearomatized cycloadducts, the C≡N bond of 2‐cyanobenzofuran reveals more reactive and imidazoline are obtained in this case. 2‐Cyanoindole substituted by an electron‐withdrawing triflyl group on the nitrogen atom allows the formation of the bis‐cycloadduct where the C=C and C≡N moieties both reacted. The C≡N vs C=C reactivity is nicely supported by DFT computations.

Plasma-mediated aging process of different microplastics: Release of dissolved organic matter and formation of disinfection by-products

Elements from groups 14–18 and periods 3–6 commonly behave as Lewis acids, which are involved in directional noncovalent interactions (NCI) with electron-rich species (lone pair donors), π systems (aromatic rings, triple and double bonds) as well as nonnucleophilic anions (BF4−, PF6−, ClO4−, etc.). Moreover, elements of groups 15 to 17 are also able to act as Lewis bases (from one to three available lone pairs, respectively), thus presenting a dual character. These emerging NCIs where the main group element behaves as Lewis base, belong to the σ–hole family of interactions. Particularly (i) tetrel bonding for elements belonging to group 14, (ii) pnictogen bonding for group 15, (iii) chalcogen bonding for group 16, (iv) halogen bonding for group 17, and (v) noble gas bondings for group 18. In general, σ–hole interactions exhibit different features when moving along the same group (offering larger and more positive σ–holes) or the same row (presenting a different number of available σ–holes and directionality) of the periodic table. This is illustrated in this review by using several examples retrieved from the Cambridge Structural Database (CSD), especially focused on σ–hole interactions, complemented with molecular electrostatic potential surfaces of model systems.

Deeper understanding of all aspect of biomass thermochemical conversion is necessary as researchers pursue multiple avenues for energy and environmental sustainability. In this paper, the agglomerative accumulation of soot observed, captured on the inner surface of the exhaust pipe, during the operation of a top-lit updraft biomass gasification system was evaluated to understand its nature and qualities. The soot was evaluated using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy with Energy Dispersion Spectroscopy (SEM-EDS) and Brunauer–Emmett–Teller (BET) analyses. The combustion fuels were bamboo (Bambusa vulgaris) stalk and stem of African balsam (Daniellia olivieri). FTIR analysis revealed the presence of hydroxyl, aromatic double bond, aldehyde, thyiol and carbonyl functional groups. EDS analysis revealed that the elemental carbon content of the soot was found to be 75.05% carbon with 15.13% oxygen. SEM analysis revealed that the soot has a hollow morphology and a lustrous appearance with white tiny grit grains of carbon nano-spheres. The BET analysis revealed that the specific surface area of the soot was 500 m2/g while the pore volume and pore diameter were measured to be 0.218 cc/g and 2.113 nm respectively. The material can find use in water purification purposes, and as an additive in lubricating oils

The screening and studying the lignite solubilization/degradation capacities of indigenous microorganisms are key to exploring the in-situ biotransformation of lignite. Herein, a fungus was isolated from in-situ lignite samples and identified as Fusarium sp. NF01. This isolate was then cultured on four different carbon sources to evaluate its lignite-transformation capacity. When cultured on a solid agar medium containing sodium gluconate or sodium glutamate, Fusarium sp. NF01 completely liquefied 0.5 g of lignite within 6 days, and when cultured in a liquid medium containing sodium gluconate, the weight of lignite decreased by 28.4% within 7 days. Elemental analysis showed that the rate of lignite biodegradation was inversely proportional to the C:O ratio of the residual lignite samples. Additionally, a 5.9% biodesulfurization rate was achieved when Fusarium sp. NF01 was cultured in the presence of sodium gluconate. Finally, Fourier-transform infrared analysis of the residual lignite samples revealed relatively weak signal intensities of the signature peaks representing the following: aromatic ring side chains; ether, ester, and alcohol bonds; aromatic ring carbon-carbon double bonds; and aliphatic methyl and methylene. The results show that Fusarium sp. NF01 degrades lignite in a carbon-dependent manner and could be thus used for the bioconversion of subsurface coalbeds.

Oxidative degradation of Bisphenol A in aqueous solution using cobalt ion-activated peroxymonosulfate

Distribution and removal of fluorescent dissolved organic matter in 15 municipal wastewater treatment plants in China

Abstract We present the instance of two aromatic double bonds and an imine double bond involved thermal 6π‐azaelectrocyclization and, on this basis, a one‐step synthesis of triazacoronenes (TACs) from triphenylene‐1,5,9‐triamines and aldehydes under nonacidic conditions. This method has several advantages such as simplicity, high yields, and extensive substrate scope. A plausible reaction mechanism has been proposed with several experimental supports. A typical derivative shows a unique dimer holding together via a π‐π interaction and six H‐bonds and a zigzag superstructure stabilized by three centered H‐bonds and Br ⋅⋅⋅ π interaction between the adjacent dimers.magnified image

Decomplexation of Cu(II)-natural organic matter complex by non-thermal plasma oxidation: Process and mechanisms

Aged microplastics polyvinyl chloride interact with copper and cause oxidative stress towards microalgae Chlorella vulgaris

Abstract A diastereoselective dearomative carboiodination reaction is reported. We report a novel metal‐catalyzed approach to install reactive secondary benzylic iodides. Utilizing the unique reactivity of nickel, we have expanded the carboiodination reaction to non‐activated aromatic double bonds forming a previously unattainable class of iodides. We also report a broadly applicable method to avoid the use of a metallic reducing agent by utilizing an alkyl phosphite as the ligand. The reaction is thought to proceed through a syn intramolecular carbonickelation across a 2‐substituted indole followed by a diastereoretentive reductive elimination of the carbon−iodine bond. The complex iodinated indolines generated in the reaction were obtained in moderate to good yields and good to excellent diastereoselectivity. The products were easily functionalized by a variety of synthetic methods.