Effects of titanium dioxide (TiO 2 ) nanoparticles on the photodissolution of particulate organic matter: Insights from fluorescence spectroscopy and environmental implications.

Widely used titanium dioxide (TiO ₂ ) nanoparticles are likely to accumulate ultimately in sediments and potentially pose a risk to water ecosystems. This study evaluated the effect of TiO ₂ nanoparticles on the photodissolution of particulate organic matter (POM) through fluorescence spectroscopy. Excitation-emission matrices and parallel factor analyses revealed that the fluorescent characteristics of produced dissolved organic matter (DOM) during photodissolution of suspended sediment and synthetic particulate organic matter (SPOM) were primarily humic-like. SPOM particles appeared to simulate well the photodissolution of suspended sediment. Quasi-complete increases in fluorescence intensity and chromophoric DOM (CDOM) abundance were reached after 90, 60, and 50 min irradiation for TiO ₂ concentrations of 0, 2, and 5 mg L ^-1 , respectively. The faster increment of fluorescence intensity and CDOM abundance indicated the photocatalytic dissolution of SPOM, as opposite charges between TiO ₂ and SPOM at pH = 4 favored the adsorption of TiO ₂ onto SPOM. For sediments, the CDOM abundance and fluorescence intensity decreased with increasing TiO ₂ concentration, resulting from the photocatalytic degradation of photoproduced DOM from sediments. These results demonstrated that pH plays an important role in the photocatalytic dissolution of POM by TiO ₂ . Therefore, appropriate pH controls should be implemented when TiO ₂ are used to treat sediments contaminated with organic pollutants. Finally, with increasing use of TiO ₂ , its accumulation in sediments may affect the fate of carbon, nutrients, and heavy metals in shallow-water ecosystems.
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