Molecular-level insights into the temperature-dependent formation dynamics and mechanism of water-soluble dissolved organic carbon derived from biomass pyrolysis smoke.

Water soluble organic carbon (WSOC) derived from biomass pyrolytic smoke is deposited through atmospheric aerosols, negatively affecting aquatic ecological quality and safety. However, the temperature-dependent molecular diversity and dynamic formation of smoke-derived WSOC remain poorly understood in water. Herein, we explored the molecular-level formation mechanism of pyrolytic smoke-derived WSOC in water to explain the evolution, heterogeneous correlations, and sequential responses of molecules and functional groups to increasing pyrolysis temperature. Two-dimensional correlation spectroscopy was used to innovatively establish the characteristic correlations between spectroscopy and Fourier transform-ion cyclotron resonance mass spectrometry. Temperature-dependent formation of WSOC exhibited diversity in absorbance/fluorescent components, unique/common molecules, and their chemical parameters, showing the simultaneous formation and degradation reactions. The common WSOC molecules with lower and higher degrees of oxidation showed significant positive and negative correlations with the fluorescent components, respectively. The primary sequential response of WSOC molecules to increasing pyrolysis temperature (lignin-like molecules â†’ unsaturated hydrocarbons, condensed aromatic molecules â†’ lipid-like/aliphatic-/peptide-like molecules) corresponded to the temperature response of functional groups (carboxylic/alcoholic â†’ polysaccharides â†’ aromatics/amides/phenolic/aliphatic groups), demonstrating well synergistic relationships between them. These novel findings will contribute to the comprehensive understanding and assessments of potential environmental behavior or risks of WSOC in aquatic ecosystems.

Molecular-level insights into the heterogeneous variations and dynamic formation mechanism of leached dissolved organic matter during the photoaging of polystyrene microplastics.

Microplastics (MPs) and their derivatives have received worldwide attention owing to their adverse effects on ecosystems. However, molecular diversity and dynamic formation of dissolved organic matter (DOM) during the photoaging of MPs remain unclear. Herein, we explored a molecular‒level formation mechanism for polystyrene MP (MPPS)‒derived DOM (PSDOM) during the photoaging of MPs to explain the evolution, heterogeneity, and sequential response of molecules to irradiation. Two‒dimensional correlation spectroscopy was applied to correlate the variations of PSDOM molecules detected by Fourier transform-ion cyclotron resonance mass spectrometry with those of MPPS functional groups detected by Fourier transform infrared spectroscopy. Irradiation‒induced PSDOM contained the most highly unsaturated structures with oxygen, but showed fewer aromatic structures than natural aquatic DOM. Photochemical transformations occurred between saturated‒reduced and oxidized molecules during PSDOM leaching, with the low‒oxidized and high‒oxidized molecules undergoing considerable changes in the normal carbon oxidation state and molecular number, respectively. The primary sequential response of PSDOM molecules to increasing irradiation time [low‒oxidized/high‒weight (450

Temperature-Dependent Molecular Evolution of Biochar-Derived Dissolved Black Carbon and Its Interaction Mechanism with Polyvinyl Chloride Microplastics.

Biochar-derived dissolved black carbon (DBC) molecules are dependent on the BC formation temperature and affect the fate of emerging contaminants in waters, such as polyvinyl chloride microplastic (MPPVC). However, the temperature-dependent evolution and MPPVC-interaction of DBC molecules remain unclear. Herein, we propose a novel DBC-MPPVC interaction mechanism by systematically interpreting heterogeneous correlations, sequential responses, and synergistic relationships of thousands of molecules and their linking functional groups. Two-dimensional correlation spectroscopy was proposed to combine Fourier transform-ion cyclotron resonance mass spectrometry and spectroscopic datasets. Increased temperature caused diverse DBC molecules and fluorophores, accompanied by molecular transformation from saturation/reduction to unsaturation/oxidation with high carbon oxidation states, especially for molecules with acidic functional groups. The temperature response of DBC molecules detected via negative-/positive-ion electrospray ionization sequentially occurred in unsaturated hydrocarbons → lignin-like → condensed aromatic → lipid-/aliphatic-/peptide-like → tannin-like → carbohydrate-like molecules. DBC molecular changes induced by temperature and MPPVC interaction were closely coordinated, with lignin-like molecules contributing the most to the interaction. Functional groups in DBC molecules with m/z < 500 showed a sequential MPPVC-interaction response of phenol/aromatic ether C-O, alkene C═C/amide C═O → polysaccharides C-O → alcohol/ether/carbohydrate C-O groups. These findings help to elucidate the critical role of DBCs in MP environmental behaviors.