High Sample Throughput LED Reactor for Facile Characterization of the Quantum Yield Spectrum of Photochemically Produced Reactive Intermediates

Abstract

Photochemically produced reactive intermediates (PPRIs) by natural photosensitizers such as chromophoric dissolved organic matter (CDOM) play numerous key roles in aquatic biogeochemical processes. PPRI productions rely on both the intensity and the spectrum of incident sunlight. While the impacts of sunlight intensity on PPRI productions are well-studied, there remains insufficient understanding of the spectrum-dependence of PPRI productions. Here we designed a high sample throughput reactor equipped with monochromatic LED lights for systematic assessments of wavelength-dependent productions of four important PPRI species, i.e., triplet-state excited CDOM (3CDOM*), singlet oxygen (1O2), hydrogen peroxide (H2O2), and hydroxyl radical (•OH), in CDOM solutions. The quantum yields of PPRIs followed the order: 3CDOM* > 1O2 ≫ H2O2 > •OH. Moreover, PPRI quantum yields decreased with the light wavelength increasing from 375 to 490 nm and sharply decreased to zero above 490 nm, while the shapes of quantum yield spectra differed among PPRI species. Simulations on PPRI productions under varying season, latitude, altitude, and cloud cover conditions show that the sunlight spectrum plays a role as equally important as intensity in determining PPRI productions and PPRI-mediated transformations of aquatic nutrients and micropollutants. Therefore, incorporating the spectrum dependence of PPRI productions will advance our understandings of PPRI-driven biogeochemical processes and pollutant dynamics under varying spatial-temporal and climatic conditions. Regarding this, the high sample throughput LED reactor sheds light on a new approach for the facile characterization of PPRI quantum yield spectrum.

Tide-Triggered Production of Reactive Oxygen Species in Coastal Soils

“…We note that the tidal ROS production efficiency is dependent on hydrological conditions, microbial activity, and soil properties. In the meantime, the incident sunlight intensity may profoundly vary depending on numerous factors (e.g., cloud cover, atmospheric gases, and particles), which can affect photochemical ROS productions . Therefore, the relative importance of tidal and photochemical ROS productions in coastal biogeochemical processes may vary depending on environmental conditions.…”

“…Dipotassium terephthalate (TPA) was applied as a chemical probe to quantitatively detect • OH production. 30 An excessive amount of TPA probe (1 mM) was added into the reduced coastal soils, and • OH production was assessed by measuring the formation of hydroxyterephthalate (hTPA) through • OHmediated hydroxylation of TPA. Adsorption control shows minor adsorption of hTPA (<10%) on soils (Figure S3).…”

Photo-Reactivity and Photo-Transformation of Algal Dissolved Organic Matter Unraveled by Optical Spectroscopy and High-Resolution Mass Spectrometry Analysis

“…Prior to irradiation, all DOM concentrations were diluted to 5 mg C L –1 in air-saturated ultrapure water and the solutions were adjusted to pH 7 ± 0.2 by adding 10 mM phosphoric acid and dipotassium hydrogen phosphate. 2,4,6-trimethylphenol (TMP), furfuryl alcohol (FFA), and benzene (BZ) were used as molecular probes for 3 DOM*, 1 O 2 , and • OH, respectively. ,, The initial concentrations of the probes were [TMP] 0 = 100 μM, [FFA] 0 = 10 μM, and [BZ] 0 = 5 mM . Different probe compounds were added separately to measure different reactive intermediates individually.…”

“…2,4,6-trimethylphenol (TMP), furfuryl alcohol (FFA), and benzene (BZ) were used as molecular probes for 3 DOM*, 1 O 2 , and • OH, respectively. 18,37,38 The initial concentrations of the probes were [TMP] 0 = 100 μM, 39 [FFA] 0 = 10 μM, 40 and [BZ] 0 = 5 mM. 18 Different probe compounds were added separately to measure different reactive intermediates individually.…”

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

“…Most interestingly, UV-LEDs provide versatility in emitting light at any designated wavelength . It has been reported that the excitation wavelength significantly impacted the photoreactivity of DOM. − For example, an approximately linear decrease of 1 O 2 quantum yield with a longer excitation wavelength in the range of 300–560 nm was observed for DOM irradiated with pulsed laser light . The quantum yields of RS by lake DOM were also found to decrease with irradiation wavelength in the order of UVB > UVA > blue using mercury lamps .…”