Photogeneration Of Reactive Species Research Articles

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

The photogeneration of reactive species from dissolved organic matter (DOM) plays a crucial role in the photochemical and photobiochemical processes in natural aquatic systems. However, the impact of the ultraviolet (UV) wavelength on the photogeneration of reactive species by different sources of DOM remains unclear. In this study, UV light at four wavelengths (365 nm, 310 nm, 280 nm, and 260 nm) provided by UV-LEDs were irradiated onto three types of DOM: humic acid (HA), fulvic acid (FA), and effluent organic matter (EfOM). Three reactive species produced by DOM, including excited triplet-state DOM (3DOM*), singlet oxygen (1O2), and hydroxyl radicals (•OH), were determined. UV365 proved to be the most efficient wavelength for generating 1O2 and •OH, with formation rates of 3.47 × 10−6 M s−1 and 1.67 × 10−8 M s−1, respectively, with the addition of FA and EfOM. The highest steady-state concentrations of all three reactive species were also generated under UV365, reaching 3.00 × 10−13 M (3DOM*) and 1.64 × 10−11 M (1O2) with the FA addition, and 1.44 × 10−10 M (•OH) with the EfOM. Across the different DOM sources, UV365 obtained the maximum quantum yields of reactive species, indicating the stronger effect of UV365 on inducing the photosensitization of DOM compared to the other shorter wavelengths. This study expands our understanding of the photochemistry of DOM in aquatic environments.

Photogeneration of Reactive Species from Biochar-Derived Dissolved Black Carbon for the Degradation of Amine and Phenolic Pollutants.

Due to agricultural waste combustion and large-scale biochar application, biochar-derived dissolved black carbon (DBC) is largely released into surface waters. The photogeneration of reactive species (RS) from DBC plays an important role in organic pollutant degradation. However, the mechanistic interactions between RS and pollutants are poorly understood. Here, we investigated the formation of DBC triplet states (3DBC*), singlet oxygen (1O2), and hydroxyl radical (•OH) in straw biochar-derived DBC solutions and photodegradation of typical pharmaceuticals and personal care products (PPCPs). Laser flash photolysis and electron spin resonance spectrometry showed that DBC exhibited higher RS quantum yields than some well-studied dissolved organic matter. The RS caused rapid degradation of atenolol, diphenhydramine, and propylparaben, selected as target PPCPs in this study. The 3DBC* contributed primarily to the oxidation of selected PPCPs via one-electron-transfer interaction, with average reaction rate constants of 1.15 × 109, 1.41 × 109, and 0.51 × 109 M-1 s-1, respectively. •OH also participated in the degradation and accounted for approximately 2.7, 2.5, and 18.0% of the total removal of atenolol, diphenhydramine, and propylparaben, respectively. Moreover, the photodegradation products were identified using high-resolution mass spectrometry, which further confirmed the electron transfer and •OH oxidation mechanisms. These findings suggest that DBC from the combustion process of agricultural biomass can efficiently induce the photodegradation of organic pollutants under sunlight in aquatic environments.

Exploring hierarchical porous silica-supported Ag3PO4 as high-efficient and environmental-friendly photocatalytic disinfectant

Silver orthophosphate (Ag3PO4) is an attractive photocatalytic catalyst for disinfection and degradation, but its instability arising from silver release generates significant environmental issue. Aiming to develop a highly efficient and environmental-friendly catalyst, we synthesized Ag3PO4 nanoparticle incorporated hierarchical porous silica (Ag3PO4@h-SiO2) as a novel high-performance photocatalytic catalyst without observed silver release. Brain-like hierarchical porous SiO2 (h-SiO2) brings a scaffold support with high surface areas, and the h-SiO2 surface modified thiols are able to anchor in situ formed 10 nm Ag3PO4 to eliminate silver release. Systematic investigations revealed that because of its structural advantages, Ag3PO4@h-SiO2 show excellent disinfection and degradation ability under visible-light irradiation and stable characteristics without obviously observed silver leaching during photo-oxidation operation. In-depth scavenger study reveals Ag3PO4@h-SiO2 as an effective semiconducting photocatalyst stimulates the production of photo-generated reactive species, which dominate its distinguished disinfection performance via photo-oxidation.Graphical abstractAg3PO4 are anchored to thiol modified hierarchical porous SiO2 to produce a visible-light responsive photocatalyst of Ag3PO4@h-SiO2. The enhanced catalytic sites and surface areas promote pathogen disinfection, and the structure advantages minimize silver release to environment. Both H2O2 and holes being generated in photocatalysis dominate overall disinfection activity.

Facile synthesis of binary metal substituted copper oxide as a solar light driven photocatalyst and antibacterial substitute

This work presents the synthesis of Cu0.95Mn0.05O (CMO), Cu0.95Ag0.05O (CAO), and Cu0.9Mn0.05Ag0.05O (CMAO) samples via wet chemical route for photocatalytic and antibacterial applications. The phase, morphology, chemical composition, and absorption range of the transition metal substituted CuO samples were investigated using various techniques such as PXRD, FESEM, EDX, and UV/Visible spectroscopy . The photocatalytic and antibacterial aptitude of all the synthesized samples was tested using methylene blue (MB) and bacterial strains. The results of application studies showed that the CMAO sample has a greater potential for dye degradation and bacterial strain destruction because of its long-lived photo-generated reactive species. More precisely, among all the synthesized samples, the CMAO sample showed excellent photocatalytic activity and degraded 83.9% dye at a higher rate constant value (0.0127 min−1). Moreover, the CMAO sample also showed better bactericidal activity against Gram-positive (S. aureus) and Gram-negative bacterial strains (E. coli). Actually, components of the bacterial cell membrane are also organic like organic dyes, so they are likely to degrade by photo-generated species. The results revealed that binary metal substituted CuO (CMAO) has an excellent ability to kill bacteria and eliminate toxic dyes from industrial effluents.

Superior photodegradation and antibacterial activity of r-GO supported ternary nanocomposite of doped transition metal compounds

In this research, we have fabricated cerium-doped nickel ferrite (NiCe0.04Fe1.96O4, C.NFO) and iron-doped cerium oxide (Ce0.96Fe0.04O2, F.CO) via a simple co-precipitation approach. The doped samples were supported with r-GO nanosheets via facile ultra-sonication methodology to develop ternary nanocomposite (C.NFO/F.CO/r-GO). The fabricated samples were characterized and their photodegradation and bactericidal aptitude were examined by using model organic chemicals (methylene blue (MB), SF-dyes, and Rhodamine-B (Rh–B)) and bacterial strains (Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus)), respectively. The results of the application studies revealed that fabricated C.NFO/F.CO/r-GO ternary nanocomposite exhibited excellent potential towards the photodegradation and bactericidal activities due to its photo-generated reactive species (HO⋅,O‾2⋅&H2O2). Distinctively, as-synthesized ternary nanocomposite, after 1.5 h of visible light irradiation, decomposed 99.12% MB-dye, 72.78% SF-dye, and 77.9% Rh–B dye. The reusability tests of C.NFO/F.CO/r-GO photocatalyst over MB dye revealed that it has excellent stability and can be reused four times with only ~5% loss in the photocatalytic efficiency. Furthermore, the fabricated ternary nanocomposite also showed outstanding bactericidal activity towards the gram-positive (S. aureus) and gram-negative bacterial strains (E. coli). In fact, like organic dyes, the main constituents of the bacterial cell wall are also organic molecules and are liable to decompose via redox reaction driven by photo-generated reactive species. Our fabricated ternary nanocomposite has an excellent aptitude to eliminate the toxic dyes and kill the bacteria present in the industrial effluents.

Enhanced photodegradation of applied dithianon fungicides on plant leaves by dissolved substances in atmosphere under simulated sunlight

Photolysis of pesticides has been widely investigated for evaluating their environmental behavior and agricultural effectiveness after crop spraying. However, little information about the effects of the water-soluble substances in atmosphere on photodegradation of pesticides is available. In current study, we found that photolysis of applied dithianon fungicides on real plant leaves was much faster than that in sealed stock aqueous suspensions under simulated sunlight. To simulate the natural conditions, for the first time, photodegradation of dithianon in air-saturated solutions containing typical dissolved atmospheric substances (DAS) including CO2 (HCO3−/CO32−), NO2 (NO3−), Fe3+ (Fe3+-complexes), and humic-like substances (HULIS) exposed to simulated solar irradiations were carried out in lab-scale. Fulvic acid (FA) was used as a surrogate for atmospheric HULIS in this study. The dithianon photodegradation was significantly enhanced in the presence of DAS and the photo-generated reactive species such as ·OH, 1O2, CO3·- and 3FA∗ play important roles according to the results of reactive species quenching, electron spin resonance spectroscopy, and laser flash photolysis experiments. Moreover, the photodegraded intermediates and final products of dithianon on plant leaves have been identified by HPLC-MS analysis, and its possible photodegradation pathways were proposed. This work indicated that, except for direct photolysis, indirect photosensitive degradation induced by the dissolved photo-active substances in atmosphere should be considered for evaluating the degradation of the applied pesticides on crops.

Mechanistic Insight into the Effect of Metal Ions on Photogeneration of Reactive Species from Dissolved Organic Matter.

The photogeneration of reactive species (RS) from dissolved organic matter (DOM) exhibits a great impact on the attenuation of pollutants in natural waters. However, the effect of metal ions on the photogeneration of excited triplet-state DOM (3DOM*), singlet oxygen (1O2), and hydroxyl radical (•OH) by effluent organic matter (EfOM), fulvic acid (FA), and humic acid (HA) is poorly understood. Here, we provided the first evidence that the quenching of 3DOM* was positively correlated with the complexation capacity of metal ions with DOM. Generally, the paramagnetic metal ions (Cr3+, Mn2+, Fe3+, and Cu2+) exhibited higher conditional stability constants (log KML) with DOM and stronger inhibition for RS than the others (Mg2+, Ca2+, Al3+, and Zn2+). For DOM of different sources, the metal binding capacity increased in the order of EfOM < HA < FA and the humic substances were more susceptible to metal ions. The inhibition was attributed to both static and dynamic quenching of 3DOM* by metal ions. The dynamic quenching rate constants of metal ions for 3DOM* were estimated as ∼109 M-1 s-1, which was positively related to the corresponding log KML. These findings highlight crucial links between metal-DOM complexation and 3DOM* quenching and, consequently, the inhibition of RS.

Constructing magnetic and high-efficiency AgI/CuFe2O4 photocatalysts for inactivation of Escherichia coli and Staphylococcus aureus under visible light: Inactivation performance and mechanism analysis

Magnetic materials usually exhibit advanced performance in many areas for their easy separating and recycle ability. In this study, silver iodide/copper ferrite (AgI/CuFe2O4) catalysts with excellent magnetic property were successfully synthesized and characterized by a series of techniques. Two typical bacteria Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were applied to estimate the photocatalytic inactivation performance of obtained AgI/CuFe2O4 catalysts. Results revealed that the AgI/CuFe2O4 (12.5% AgI) composite could absolutely inactivate 3 × 109 CFU/mL E. coli and 2.7 × 108 CFU/mL S. aureus cells severally in 50 min and 40 min under visible light irradiation, which showed a much higher photo-disinfection activity than monomers. Transmission electron microscopy was used to study the biocidal action of this nanocatalyst, the results confirmed that the treated E. coli cells were damaged, the nanocatalyst permeated into cells and resulting in death of cells. Besides, it was found that the destruction of bacterial membrane together with substantial leaked potassium ion (K+) which caused by the photo-generated reactive species superoxide radical (O2−) and holes (h+) could be the direct disinfection principles. For a deep insight into practical applications, the influences of different catalyst concentrations and reaction pH were also taken into discussion in details. The overall results indicated the novel photocatalyst with strong redox capacity and outstanding reusability can be widely employed in bacteria elimination.

Photogeneration and interactive reactions of three reactive species in the Seto Inland Sea, Japan

Environmental contextPhotogenerated reactive species play important roles in the degradation of dissolved organic pollutants. Photogeneration and concerted measurements of hydroxyl (·OH), nitric oxide (NO·) and superoxide (O2·−) radicals in samples from the Seto Inland Sea suggest that their interactive reactions could yield peroxynitrite (ONOO−), a secondary reactive species. These results reveal how discrete photochemical reactions synergise to influence the variety and fates of reactive species in a marine environment. AbstractPhotochemically generated reactive species are involved in photodegradation of dissolved organic pollutants in natural waters. However, there is a dearth of empirical evidence, from each batch of water samples collected, to predict the influence of interactive reactions among several photogenerated reactive species on their variety and fates in natural waters. Concerted photogeneration and measurement of hydroxyl (·OH), nitric oxide (NO·) and superoxide (O2·−) radicals were carried out on water samples obtained during two consecutive summers in 2016 and 2017 from the Seto Inland Sea, Japan. Photogeneration rates of ·OH are (6.98–35.27) × 10−12 M s−1, and those of NO· are (1.20–58.25) × 10−12 M s−1. Compared with these generation rates, that for O2·− ((4.54–18.20) × 10−10 M s−1) was the highest, which suggests that O2·− is a very important photochemically generated reactive species in coastal seawater. The average steady-state concentrations of the three reactive species are ·OH, 7.23 × 10−18 M; O2·−, 3.79 × 10−12 M; and NO·, 1.39 × 10−10 M. Estimated mutual consumption or sink percentages via interactive reactions between O2·− and NO· radicals are five to nine orders of magnitude higher than any other radical pair considered in this study. Hence, we predict that the reaction between photochemical O2·− and NO· could dominate to form ONOO−, a powerful oxidant and nitrating agent, in the coastal marine environment.

Facile fabrication of micro-floriated AgBr/Bi2O3 as highly efficient visible-light photocatalyst

Semiconductor with photocatalytic property is the potential solution to solve the problem about water pollution. Novel floriated AgBr/Bi2O3 fabricated through a facile simple two-step hydrothermal method is an efficient photocatalyst. The eminent performance for degradation of methyl orange (MO) was evaluated under visible light irradiation. Many characterization methods, including XPS, XRD, FT-IR, SEM, TEM and UV–vis diffuse reflection spectroscopy, were used to investigate the structure, elemental composition, morphology and catalytic activity. Broad contact between AgBr and Bi2O3 interface enabled hybrid materials possess superior efficiency for the decomposition of MO under visible light irradiation. The optimum photocatalytic activity of samples was approximately 11.7 times higher than pure Bi2O3. In addition, the photo-generated reactive species were identified based on free radicals trapping experiments, which revealed that superoxide radical is the key factor to the photocatalytic process.

Probing the intracellular organic matters released from the photocatalytic inactivation of bacteria using fractionation procedure and excitation-emission-matrix fluorescence

Photocatalysis provides a “green” and effective strategy for water disinfection. During the photocatalytic disinfection process, intracellular organic matter (IOM) from bacterial cells may be released into the bulk solution. In this study, the role of released IOM in the photocatalytic bacterial inactivation was investigated by fractionation procedure and fluorescence excitation-emission-matrix (EEM) combined with parallel factor analysis (PARAFAC) approaches. The normal bacterial cells treated by TiO2-UVA in the presence and absence with fractionated IOM results implied that the released IOM would be either absorbed on the surface of the photocatalysts or reacted by the photo-generated reactive species, and thereby affecting the kinetics of photocatalytic bacterial inactivation. Fluorescence EEM-PARAFAC results showed that two components (C1 and C3) associated with tryptophan- and tyrosine-like proteins were released. While another two components (C2 and C4) were the oxidation products, and their intensities were found to negatively correlate with those of C1 and C3, respectively. Microtox® test results indicated that toxicity occurred during the photocatalytic bacterial inactivation process. The toxicity was found to decrease after the bacteria were completely inactivated, and completely removed if provided a sufficient reaction time. Of particular interest is that a significant high linear correlation was observed between the toxicity and the maximum fluorescence intensity of C4. The results and information obtained in this study will be important for further developing photocatalysis in water/wastewater disinfection.

Photodegradation of avobenzone: Stabilization effect of antioxidants

Avobenzone is one of the most common UVA-filters in sunscreens, and is known to be photounstable. Some of the strategies used to stabilize this filter present some drawbacks like photosensitization reactions. Antioxidants are widely used as cosmetic ingredients that prevent photoageing and complement the photoprotection offered by the UV-filters preventing or reducing photogenerated reactive species. The purpose of this work was to study the effect of antioxidants in the photostabilization of avobenzone. The filter dissolved in dimethyl sulfoxide or incorporated in a sunscreen formulation was irradiated with simulated solar radiation (750W/m2). The tested antioxidants were vitamin C, vitamin E, and ubiquinone. The area under the curve of the absorption spectrum for UVA range and the sun protection factor (SPF) were calculated. Vitamin E (1:2), vitamin C (1:0.5) and ubiquinone (1:0.5) were the more effective concentrations increasing the photostability of avobenzone. In sunscreen formulations, the most effective photostabilizer was ubiquinone which also promoted an increase in SPF.This knowledge is important to improve effectiveness of sunscreen formulation. Antioxidants can be valuable ingredients for sunscreens with a triple activity of filter stabilization, SPF boosting and photoageing prevention.

The degradation mechanism of methyl orange under photo-catalysis of TiO2

The properties of photo-generated reactive species, holes and electrons in bulk TiO(2) (anatase) film and nano-sized TiO(2) were studied and their effects towards decomposing pollutant dye methyl orange (MO) were compared by transient absorption spectroscopies. The recombination of holes and electrons in nano-sized TiO(2) was found to be on the microsecond time scale consistent with previous reports in the literature. However, in bulk TiO(2) film, the holes and electrons were found to be on the order of picoseconds due to ultra fast free electrons. The time-correlated single-photon counting (TCSPC) technique combined with confocal fluorescence microscopy revealed that the fluorescence intensity of MO is at first enhanced noticeably by TiO(2) under UV excitation and soon afterwards weakened dramatically, with the lifetime prolonged. Photo-generated holes in nano-sized TiO(2) can directly oxidize MO on the time scale of nanoseconds, while free electrons photo-generated in bulk TiO(2) film can directly inject into MO on the order of picoseconds. Through cyclic voltammetry measurements, it was found that MO can be reduced at -0.28 V and oxidized at 1.4 V (vs. SCE) and this provides thermodynamic evidence for MO to be degraded by electrons and holes in TiO(2). Through comparison of the hole-scavenging effect of MO and water, it was found that in polluted water when MO is above 1.6 × 10(-4) M, the degradation is mainly due to a direct hole oxidation process, while below 1.6 × 10(-4) M, hydroxyl oxidation competes strongly and might exceed the hole oxidation.

Enhanced effect of vacuum-deposited SiO2 overlayer on photo-induced hydrophilicity of TiO2 film

Photo-induced hydrophilicity of SiO2/TiO2 multilayer film prepared by using the vacuum deposition method was investigated by means of water contact angle measurement. Using black light irradiation of the films centering at a wavelength of 365 nm, an extreme photo-induced hydrophilicity was achieved when the TiO2 film was covered by SiO2 overlayer ranging from 10 to 20 nm in thickness. These multilayer films exhibited much more extreme hydrophilicity than the TiO2 film without SiO2 overlayer. The surface analyses revealed that the enhanced photo-induced hydrophilic surface of the multilayer films exhibited an improved photo-catalytic activity towards decomposition of organic substances on their surfaces. It was found that significant growth of the SiOH group occurred in the uppermost surface of the SiO2 overlayer of the multilayer films through the depth profile measurement of TOF-SIMS. This result suggests that the photo-generated reactive species such as hole created in the TiO2 film may transmit the SiO2 layer to reach the surface. The enhanced photo-induced hydrophilicity of the films can be explained by a synergetic effect of the improved photo-catalytic activity of the multilayer film and the stable hydrophilicity of SiO2 itself.

Quantitation of cutaneous inflammation induced by reactive species generated by UV-visible irradiation of Rose bengal

The present studies were undertaken to quantitate the initial inflammatory response produced by the photo-generated reactive species in rabbit skin. Rose bengal (RB), a photosensitizer dye, was injected into the skin sites at various concentrations and exposed to UV-visible light for 30-120 min. The increase in vascular permeability and the accumulation of PMNs were investigated using 125I-labeled albumin and 51Cr-labeled PMNs. RB at a concentration of 1 nmol with 120-min exposure to light enhanced vascular permeability by 3.7 times and accumulation of PMNs by 3.3 times. As low as 0.01 nmol of RB produced discernible effects. beta-Carotene (0.1 nmole) inhibited the inflammatory response by 75-100%, suggesting that the reactive species involved in this response was predominantly singlet oxygen. The increase in vascular permeability was inhibited by 48-70% by 25 micrograms of chlorpheniramine maleate. It is therefore suggested that histamine plays a major role in the initial vascular response. The studies demonstrate that this rabbit model is suitable for the quantitation of photoinduced inflammatory response which is not observable by gross anatomic procedures.