Revisiting triplet state dissolved organic matter (3DOM*): Advances in probes, photoreactivity, and environmental implications

Triplet-state dissolved organic matter ((DOM)-D-3*) plays a critical role in the photodegradation of organic pollutants in aquatic environments. This review offers a comprehensive overview of (DOM)-D-3*, focusing on monitoring methods using various probes, formation mechanisms, and photoreactivity. Traditional probes, such as 2,4,6-trimethylphenol (TMP) and sorbic acid, are widely used, while novel probes promise improved accuracy and sensitivity. The E-2:E-3 ratio emerges as a promising indicator for (DOM)-D-3* due to its simplicity and correlation with photoreactivity, though further validation is needed to confirm its broader applicability. This review highlights the higher photoreactivity of DOM with low molecular weight, low aromaticity, and autochthonous sources, although DOM with contrasting features can also show significant photoreactivity. The presence of inorganic ions and nanomaterials significantly influences (DOM)-D-3*'s degradation capacity, demonstrating complex interactions with surrounding species. Additionally, the review underscores the importance of various environmental factors, including light source and DOM concentration, in affecting the photodegradation rates of contaminants. Recent literature suggests that future research should focus on developing new probes to capture different aspects of (DOM)-D-3*, exploring the synergistic effects of plastic leachate, and investigating the role of co-existing ions and nanomaterials on (DOM)-D-3* activity. Employing machine learning (ML) techniques to predict (DOM)-D-3*-related parameters from easily measurable DOM descriptors presents an exciting research avenue. Enhanced understanding of (DOM)-D-3* can lead to more effective strategies in wastewater treatment and environmental remediation.