Wavelength-Dependent Photoreactivity of Root Exudates from Aquatic Plants under UV-LED Irradiation

Abstract

Aquatic plants and their root exudates play important roles in the removal of trace organic contaminants in aquatic environments. However, the wavelength-dependent photogeneration of reactive species (RS) and photodegradation of organic contaminants by root exudates are poorly understood. This paper presents the first evidence that the photogeneration of 3DOM*, 1O2, and ·OH by root exudates varied under UV light-emitting diode (UV-LED) irradiation in the wavelength range of 265–400 nm. The quantum yields of 3DOM* and 1O2 of the four plants’ root exudates, including Scindapsus aureus, Pistia stratiotes, Eichhornia crassipes, and Nymphaea tetragona, reached the highest value at an irradiation wavelength of 275 nm and further decreased with increasing wavelength, while the ·OH quantum yield decreased gradually from 3.2–5.5 × 10–4 at 265 nm to 1.4–2.6 × 10–6 at 400 nm. The root exudate of Pistia stratiotes showed higher quantum yields of 3DOM* and 1O2 than that of the other three plants, while the highest ·OH quantum yield was observed in that of Eichhornia crassipes. The excitation wavelength affected the indirect degradation of organic contaminants by altering the photogeneration of RS in root exudate solutions. These findings highlight the wavelength-dependent photoreactivity of root exudates and improve the understanding of their photochemical processes in aquatic environments.

Interaction of Cerium Oxide Nanoparticles and Ionic Cerium with Duckweed (Lemna minor L.): Uptake, Distribution, and Phytotoxicity

“…Root exudates of aquatic plants mainly consist of carbon-containing compounds, such as organic acids, amino acids, carbohydrates, polysaccharides, proteins, tannins, phenolic compounds, etc. [ 46 ]. As we demonstrated, CeO 2 NPs could be reduced to Ce(III) in aquatic plant duckweed with the assistant of organic acids and reducing substances (such as phenols).…”

Effect of UV-LED Wavelength on Reactive Species Photogeneration from Dissolved Organic Matter

“…Irradiation experiments were conducted in a customized quartz beaker featuring a diameter of 3.85 cm, an empty volume of 50 mL, and a working volume of 40 mL, as illustrated in Figure 1. The UV-LED light source (Yonglin Optoelectronics Co., Ltd., Shenzhen, China) was affixed to the outside of the bottom of the beaker, as described in previous literature [20]. The photochemical reactor was placed on a magnetic stirrer that provided a stirring speed of 400 rpm to achieve a homogeneous mixture.…”

Reassessing the Quantum Yield and Reactivity of Triplet-State Dissolved Organic Matter via Global Kinetic Modeling

“…2,4,6-Trimethylphenol (TMP) has been suggested as an ideal chemical probe for 3 DOM* due to its high reactivity with 3 DOM* and its resistance to both direct photolysis and the inhibitory effects from the antioxidant components of DOM. ,− Consequently, TMP probing has found extensive application in numerous studies and has become the most classic method for evaluating the quantum yield (Φ 3 DOM* ) and reactivity of 3 DOM*. ,− However, the reaction rate constant between 3 DOM* and TMP ( k 3 DOM*,TMP ) is not a fixed value but varies greatly with the DOM source in the range of (0.5–2.6) × 10 9 M –1 s –1 . ,,,, For convenience, some studies utilized empirical values of (e.g., 0.8 × 10 9 M –1 s –1 for aquatic DOM, 1.1 × 10 9 M –1 s –1 for dissolved black carbon (DBC)-like DOM, , and 2.6 × 10 9 M –1 s –1 for model sensitizers) to quantify the formation rate of 3 DOM* ( R 3 DOM* ), which was then used to calculate Φ 3 DOM* . In addition, the quantum yield coefficient ( f TMP ) of 3 DOM* has also been recently proposed as a relative measure of 3 DOM*. ,,− Nonetheless, these simplified approaches may introduce significant errors or fail to yield the absolute values of Φ 3 DOM* and k 3 DOM*,TMP , with only qualitative information provided.…”