1O2 Concentration Research Articles

Nanozyme Decorated Metal-Organic Framework Nanosheet for Enhanced Photodynamic Therapy Against Hypoxic Tumor.

Photodynamic therapy (PDT) has attracted increasing attention in the clinical treatment of epidermal and luminal tumors. However, the PDT efficacy in practice is severely impeded by tumor hypoxia and the adverse factors associated with hydrophobic photosensitizers (PSs), including low delivery capacity, poor photoactivity and limited ROS diffusion. In this study, Pt nanozymes decorated two-dimensional (2D) porphyrin metal-organic framework (MOF) nanosheets (PMOF@HA) were fabricated and investigated to conquer the obstacles of PDT against hypoxic tumors. PMOF@HA was synthesized by the coordination of transition metal iron (Zr4+) and PS (TCPP), in situ generation of Pt nanozyme and surface modification with hyaluronic acid (HA). The abilities of hypoxic relief and ROS generation were evaluated by detecting the changes of O2 and 1O2 concentration. The cellular uptake was investigated using flow cytometry and confocal laser scanning microscopy. The SMMC-7721 cells and the subcutaneous tumor-bearing mice were used to demonstrate the PDT efficacy of PMOF@HA in vitro and in vivo, respectively. Benefiting from the 2D structure and inherent properties of MOF materials, the prepared PMOF@HA could not only serve as nano-PS with high PS loading but also ensure the rational distance between PS molecules to avoid aggregation-induced quenching, enhance the photosensitive activity and promote the rapid diffusion of generated radical oxide species (ROS). Meanwhile, Pt nanozymes with catalase-like activity effectively catalyzed intratumoral overproduced H2O2 into O2 to alleviate tumor hypoxia. Additionally, PMOF@HA, with the help of externally coated HA, significantly improved the stability and increased the cell uptake by CD44 overexpressed tumor cells to strengthen O2 self-supply and PDT efficacy. This study provided a new strategy of integrating 2D porphyrin MOF nanosheets with nanozymes to conquer the obstacles of PDT against hypoxic tumors.

Solar Photodegradation of a Novel des-F(6)-Fluoroquinolone, Garenoxacin, and Ecotoxicity of Its Phototransformation Products.

Garenoxacin (GRNX) is a novel des-F(6)-fluoroquinolone on the horizon; thus, its fate and risk in the aquatic environment deserve attention. This study systematically investigated, for the first time, the phototransformation of GRNX under simulated and natural sunlight and assessed the ecotoxicity of its photodegradation products. Phototransformation of GRNX was observed to depend strongly on its ionization state, with direct photolysis and self-sensitized photolysis having comparable contributions for the cationic and zwitterionic species, while the latter dominated for the anionic species. Singlet oxygen generated via the self-sensitized photolysis of GRNX was the major reactive oxygen species in its photodegradation. Phototransformation of GRNX in different ionization states followed distinct pathways, with defluorination of the difluoromethyl group occurring only for the zwitterionic and anionic species. GRNX photodegradation in natural water could be described by a simple kinetic model based on the measured steady-state concentrations of 1O2 and ·OH. Toxicity tests with Vibrio fischeri and Chlorella vulgaris consistently indicate that the generation of hydroxylation and decarboxylation products during photodegradation of GRNX increased the acute toxicity. These findings not only provide insights into the fate of GRNX in sunlit surface water but also reveal the potentially significant risk of its photodegradation products to the aquatic ecosystem.

Investigation of singlet-oxygen-responsive genes in the cyanobacterium Synechocystis PCC 6803.

Singlet oxygen (1O2) is an important reactive oxygen species whose formation by the type-II, light-dependent, photodynamic reaction is inevitable during photosynthetic processes. In the last decades, the recognition that 1O2 is not only a damaging agent, but can also affect gene expression and participates in signal transduction pathways has received increasing attention. However, contrary to several other taxa, 1O2-responsive genes have not been identified in the important cyanobacterial model organism Synechocystis PCC 6803. By using global transcript analysis we have identified a large set of Synechocystis genes, whose transcript levels were either enhanced or repressed in the presence of 1O2. Characteristic 1O2 responses were observed in several light-inducible genes of Synechocystis, especially in the hli (or scp) family encoding HLIP/SCP proteins involved in photoprotection. Other important 1O2-induced genes include components of the Photosystem II repair machinery (psbA2 and ftsH2, ftsH3), iron homeostasis genes isiA and idiA, the group 2 sigma factor sigD, some components of the transcriptomes induced by salt-, hyperosmotic and cold-stress, as well as several genes of unknown function. The most pronounced 1O2-induced upregulation was observed for the hliB and the co-transcribed lilA genes, whose deletion induced enhanced sensitivity against 1O2-mediated light damage. A bioreporter Synechocystis strain was created by fusing the hliB promoter to the bacterial luciferase (lux), which showed its utility for continuous monitoring of 1O2 concentrations inside the cell.

Piezoelectric field-modulated peroxymonosulfate nonradical oxidation of bisphenol A via Bio-MOF-1: The dominant contribution of singlet oxygen

Bisphenol A (BPA) has raised worldwide concern owing to its ecological risks, highlighting the urgent need to develop efficient removal strategies in wastewater treatment. Ametal–organic framework (Bio-MOF-1) piezoelectrically activating peroxymonosulfate (PMS) process (Bio-MOF-1/PMS/US) was developed to remove BPA at 98.5%, which was 3.5 times higher than the Bio-MOF-1/US process. Further analysis confirmed that the piezoelectric field initiated by Bio-MOF-1 could reduce the activation energy of PMS and then promote the reaction of PMS with holes and electrons to convert into 1O2 and OH. The steady-state concentration of 1O2 was 4 orders of magnitude higher than OH, indicating the dominant contribution of 1O2 for BPA removal, which resulted in the efficient BPA removal from a variety of anions, organics, and municipal wastewater through a low-risk manner. This work provides new perspectives for the application of MOF-based materials in the field of piezoelectric catalysis and promising applications in wastewater remediation.

EPR Spin-Trapping for Monitoring Temporal Dynamics of Singlet Oxygen during Photoprotection in Photosynthesis.

A central goal of photoprotective energy dissipation processes is the regulation of singlet oxygen (1O2*) and reactive oxygen species in the photosynthetic apparatus. Despite the involvement of 1O2* in photodamage and cell signaling, few studies directly correlate 1O2* formation to nonphotochemical quenching (NPQ) or lack thereof. Here, we combine spin-trapping electron paramagnetic resonance (EPR) and time-resolved fluorescence spectroscopies to track in real time the involvement of 1O2* during photoprotection in plant thylakoid membranes. The EPR spin-trapping method for detection of 1O2* was first optimized for photosensitization in dye-based chemical systems and then used to establish methods for monitoring the temporal dynamics of 1O2* in chlorophyll-containing photosynthetic membranes. We find that the apparent 1O2* concentration in membranes changes throughout a 1 h period of continuous illumination. During an initial response to high light intensity, the concentration of 1O2* decreased in parallel with a decrease in the chlorophyll fluorescence lifetime via NPQ. Treatment of membranes with nigericin, an uncoupler of the transmembrane proton gradient, delayed the activation of NPQ and the associated quenching of 1O2* during high light. Upon saturation of NPQ, the concentration of 1O2* increased in both untreated and nigericin-treated membranes, reflecting the utility of excess energy dissipation in mitigating photooxidative stress in the short term (i.e., the initial ∼10 min of high light).

2D Cobalt-carbon–nitrogen loaded 3D Prussian blue analogues enhances peroxymonosulfate activation for bisphenol A Degradation: Singlet oxygen dominated nonradical pathway

Singlet oxygen (1O2) dominated peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) is an effective technology for the removal of electron-rich organic contaminants. However, the highly selective generation of 1O2 is limited by the development of catalysts. Herein, a two-dimensional (2D) cobalt-carbon–nitrogen loaded three-dimensional (3D) Prussian blue analogue (CoCN@PBA-P) material was synthesized by the one-step method using hematite with different morphologies as the precursor. The two atomically dispersed Co sites in three CoCN@PBA-P were demonstrated that could effectively activate PMS to degrade bisphenol A (BPA) in different and complex environmental backgrounds. The quenching, probe quantitative, and EPR results indicated the dominant role of 1O2 in CoCN@PBA-P/PMS system, and the steady-state concentration of 1O2 can achieve 4.0 × 10-9-1.3 × 10-8 M. Importantly, the role of Co as the active site was verified by screening experiments, and the mechanism of CoCN@PBA-P activate PMS was revealed by experimentally and theoretically, and the pathway to generate 1O2 is *HSO5→*SO4+OH–→*SO4+*OH→*O→1O2 (* represents that the species is bound to the active site). Finally, the analysis of degradation intermediates and their toxicity showed that the whole process is harmless to the environment. This work provides a new perspective to the design of 2D@3D materials and their application in PMS-based AOPs.

Gas Evolution Kinetics in Overlithiated Positive Electrodes and its Impact on Electrode Design.

Increasing lithium contents within the lattice of positive electrode materials is projected in pursuit of high-energy-density batteries. However, it intensifies the release of lattice oxygen and subsequent gas evolution during operations. This poses significant challenges for managing internal pressure of batteries, particularly in terms of the management of gas evolution in composite electrodes-an area that remains largely unexplored. Conventional assumptions postulate that the total gas evolution is estimated by multiplying the total particle count by the quantities of gas products from an individual particle. Contrarily, this investigation on overlithiated materials-a system known to release the lattice oxygen-demonstrates that loading densities and inter-particle spacing in electrodes significantly govern gas evolution rates, leading to distinct extents of gas formation despite of an equivalent quantity of released lattice oxygen. Remarkably, this study discoveres that O2 and CO2 evolution rates are proportional to 1O2 concentration by the factor of second and first-order, respectively. This indicates an exceptionally greater change in the evolution rate of O2 compared to CO2 depending on local 1O2 concentration. These insights pave new routes for more sophisticated approaches to manage gas evolution within high-energy-density batteries.

Sulfur Vacancies in Pyrite Trigger the Path to Nonradical Singlet Oxygen and Spontaneous Sulfamethoxazole Degradation: Unveiling the Hidden Potential in Sediments.

Pharmaceutical residues in sediments are concerning as ubiquitous emerging contaminants. Pyrite is the most abundant sulfide minerals in the estuarine and coastal sediments, making it a major sink for pharmaceutical pollutants such as sulfamethoxazole (SMX). However, research on the adsorption and redox behaviors of SMX on the pyrite surface is limited. Here, we investigated the impact of the nonphotochemical process of pyrite on the fate of coexisting SMX. Remarkably, sulfur vacancies (SVs) on pyrite promoted the generation of nonradical species (hydrogen peroxide, H2O2 and singlet oxygen, 1O2), thereby exhibiting prominent SMX degradation performance under darkness. Nonradical 1O2 contributed approximately 73.1% of the total SMX degradation. The SVs with high surrounding electron density showed an advanced affinity for adsorbing O2 and then initiated redox reactions in the sediment electron-storing geobattery pyrite, resulting in the extensive generation of H2O2 through a two-electron oxygen reduction pathway. Surface Fe(III) (hydro)oxides on pyrite facilitated the decomposition of H2O2 to 1O2 generation. Distinct nonradical products were observed in all investigated estuarine and coastal samples with the concentrations of H2O2 ranging from 1.96 to 2.94 μM, while the concentrations of 1O2 ranged from 4.63 × 10-15 to 8.93 × 10-15 M. This dark-redox pathway outperformed traditional photochemical routes for pollutant degradation, broadening the possibilities for nonradical species use in estuarine and coastal sediments. Our study highlighted the SV-triggered process as a ubiquitous yet previously overlooked source of nonradical species, which offered fresh insights into geochemical processes and the dynamics of pollutants in regions of frequent redox oscillations and sulfur-rich sediments.

Methyl contributes to the directed phosphorus doping of g-C3N4: pH-dependent selective reactive oxygen species enable customized degradation of organic pollutants

In the photocatalytic degradation process, constructing a controllable composite oxidation system with radicals and nonradicals to meet the requirement for efficient and selective degradation of diverse pollutants is significant. Herein, a methylated and phosphorus-doped g-C3N4 (NPEA) can exhibit selective radical and nonradical species formation depending on the pH values. The NPEA can spontaneously switch the production of active species according to the pH value of the reaction system, exhibiting steady-state concentrations of ·O2− for 11.83 × 10−2 µmol L−1 s−1 (with 92.7 % selectivity) under alkaline conditions (pH = 11), and steady-state concentrations of 1O2 for 5.18 × 10−2 µmol L−1 s−1 (with 88.7 % selectivity) under acidic conditions (pH = 3). The NPEA exhibits stability and universality in the degradation of pollutants with rate constant for sulfamethazine (k = 0.261 min−1) and atrazine (k = 0.222 min−1). Moreover, the LC-MS and Fukui function demonstrated that the NPEA can tailor degradation pathways for pollutants, achieving selective degradation. This study offers a comprehensive insight into the mechanism of the photocatalytic oxidation system, elucidating the intricate interplay between pollutants and reactive oxygen species.

Dynamically Securing the Data by 1O2 Sensitization of Fluorescent Composites with a High Latency and Uncrackable Features

Comprehensive SummaryDynamic fluorescent materials play a crucial role in secure inks for data encryption; however, they are still plagued by issues such as photodegradation, poor latency, and susceptibility to unauthorized access. Herein, we propose a photochemically modulated dynamic fluorescent encryption system based on 1O2 sensitization of fluorescent composites, comprising a 1O2‐sensitive fluorophore (F2) and non‐emissive polymers. After UV irradiation, in‐situ generated 1O2 from the polymer effectively binds with F2 to form endoperoxides (F2EPO), resulting in a significant redshift in emission, up to 150 nm. The 1O2 concentration is closely related to the irradiation time, rendering different fluorescent colors in a time‐gated fashion. Moreover, the emission of F2EPO can be regulated by polymer chemical structure, molecular weight, and crosslinking density. Relying on these merits, we develop a dynamic data encryption method with various non‐emissive polymers as the data storage media, UV light irradiation as the data encoder, and F2 as the data decoder. UV light irradiation of diverse polymer solutions generates 1O2 at different concentrations, effectively encoding the data, which remains invisible under both UV and natural lights. The addition of F2 to these irradiated polymer solutions produces different redshifted fluorescence, enabling secure data decryption. Attributing to the non‐emissive nature of the polymers, time‐gated readout fashion, excellent latency of 1O2, and subtle interactions between 1O2 and F2, this data encryption is nearly undecipherable. This work offers an advantage data encryption approach beyond the reach of conventional fluorophores.

Ni/Fe Bimetallic Atom Cluster Activate PMS To Promote 1O2 Production To Efficiently Remove BPA

AbstractThe advanced oxidation process based on peroxymonosulfate (PMS) is a new water purification strategy. In this work, Ni/Fe bimetallic atom cluster composite catalyst is prepared by a hydrothermal synthesis to stimulate PMS to produce high concentration singlet oxygen (1O2) and efficiently remove bisphenol A (BPA) from aqueous solution. The experimental data show that in a broad pH range (pH=3–11), the removal rate of BPA by the non‐free radical pathway induced by 1O2 is close to 100 %, and the catalyst still has high stability after 5 cycles. The mechanism of BPA removal in NiFe−BC/PMS/BPA catalytic degradation system is investigated by quenching experiment. It is found that 1O2 in the system is the most important active component in the degradation process of BPA, and a high concentration of 1O2 could promote the rapid degradation of BPA in solution. In this paper, the high catalytic activity and selectivity of bimetallic atomic cluster catalysts can provide new insights for the treatment of phenolic wastewater.

A Kinetic Study of a Photo-Oxidation Reaction between α-Terpinene and Singlet Oxygen in a Novel Oscillatory Baffled Photo Reactor

By planting LEDs on the surfaces of orifice baffles, a novel batch oscillatory baffled photoreactor (OBPR) together with polymer-supported Rose Bengal (Ps-RB) beads are here used to investigate the reaction kinetics of a photo-oxidation reaction between α-terpinene and singlet oxygen (1O2). In the mode of NMR data analysis that is widely used for this reaction, α-terpinene and ascaridole are treated as a reaction pair, assuming kinetically singlet oxygen is in excess or constant. We have, for the first time, here examined the validity of the method, discovered that increasing α-terpinene initially leads to an increase in ascaridole, indicating that the supply of singlet oxygen is in excess. Applying a kinetic analysis, a pseudo-first-order reaction kinetics is confirmed, supporting this assumption. We have subsequently initiated a methodology of estimating the 1O2 concentrations based on the proportionality of ascaridole concentrations with respect to its maximum under these conditions. With the help of the estimated singlet oxygen data, the efficiency of 1O2 utilization and the photo efficiency of converting molecular oxygen to 1O2 are further proposed and evaluated. We have also identified conditions under which a further increase in α-terpinene has caused decreases in ascaridole, implying kinetically that 1O2 has now become a limiting reagent, and the method of treating α-terpinene and ascaridole as a reaction pair in the data analysis would no longer be valid under those conditions.

Effect of dissolved organic matter on the inactivation of bacteriophage MS2 by graphitic carbon nitride - based photocatalysis

Waterborne pathogenic bacteria and viruses are of great concern to environmental and public health. This study focused on the impact of dissolved organic matter (DOM) on photocatalytic inactivation of bacteriophage MS2 by utilizing a visible-light-responded photocatalyst composed of rGO-supported g-C3N4 (7.5%GCN). The results showed that the inactivation rate of MS2 by 7.5%GCN photocatalysis was 3.20 log at λ > 400 nm and 3.27 log at λ > 305 nm within 120 min. The presence of humic acid (HA) in the water matrix led to a decline in the inactivation rate of 2.19 log at λ > 400 nm and 2.08 log at λ > 305 nm, representing a reduction of 31.56% and 36.4%. During an 8 h inactivation process in ultrapure water using 7.5%GCN photocatalysis under λ > 400 nm, steady-state concentrations of 1O2, •OH, •O2- and H2O2 were measured to be 5.67 × 10-13, 8.56 × 10-7, 1.21 × 10-5 and 7.08 × 10-5 mol/L, respectively; When in presence of HA, the concentrations of ROSs were inhibited except for 1O2. The order of ROS steady-state concentration was found to be H2O2 > •O2-> •OH> 1O2 during 7.5%GCN photocatalysis, both within and without HA. Transmission electron microscopy (TEM) analysis revealed that the distortion in the morphology of MS2, potentially leading to the disclosure of RNA. Furthermore, protein analysis indicated that the protein structure was damaged, resulting in a decrease of approximately 90% in its concentration. This study may shed light on the impact of DOM during solar light-driven photocatalysis, offering a green, environment-friendly, and sustainable water treatment process.

Different bactericidal abilities of plasma-activated saline with various reactive species prepared by surface plasma-activated air and plasma jet combinations

Plasma-activated water (PAW), as an extended form of cold atmospheric-pressure plasma, greatly expands the application of plasma-based technology. The biological effects of PAW are closely related to the aqueous reactive species, which can be regulated by the activation process. In this study, surface plasma-activated air (SAA) and a He + O2 plasma jet (Jet) were parallelly combined (the SAA + Jet combination) or sequentially combined (the SAA → Jet combination and the Jet → SAA combination) to prepare plasma-activated saline (PAS). The PAS activated by the combinations exhibited stronger bactericidal effects than that activated by the SAA or the Jet alone. The concentrations of H2O2 and were higher in the PAS activated by the Jet → SAA combination, while ONOO− concentrations were close in the three kinds of PAS and 1O2 concentrations were higher in the PAS activated by the SAA + Jet combination. The analysis of scavengers also demonstrated that H2O2, 1O2, and ONOO‒ in the PAS activated by the SAA + Jet combination, and 1O2 in the PAS activated by the Jet → SAA combination played critical roles in bactericidal effects. Further, the effective placement time of the three PAS varied, and the PAS activated by the Jet → SAA combination could also inactivate 2.6-log10 of MRSA cells after placement for more than 60 min. The regulation of reactive species in plasma-activated water via different combinations of plasma devices could improve the directional application of plasma-activated water in the biomedical field.

Singlet Oxygen Quantum Yields of Pyrogenic Dissolved Organic Matter from Lab-Prepared and Wildfire Chars.

Wildfires or prescribed fires release pyrogenic dissolved organic matter (pyDOM) into the environment, which can photochemically produce singlet oxygen (1O2) in sun-lit surface waters. 1O2 quantum yields (ΦΔ) are well-studied for non-pyrogenic DOM, but little is understood about the 1O2 generation from pyDOM, especially the ΦΔ values from real wildfire samples and their wavelength dependence. In this study, time-resolved 1O2 phosphorescence was used to determine the wavelength-dependent ΦΔ values for pyDOM generated from wildfire char and a series of lab-prepared chars produced by combusting oak and pine wood. Wildfire and most lab-prepared pyDOM generally had similar ΦΔ values (2.1-2.7%) at 365 nm compared to the reference Suwannee River Natural Organic Matter (SRNOM) isolate (2.4%). Interestingly, pyDOM from the highest combustion temperature char was found to possess extremely low ΦΔ values compared to SRNOM and other pyDOM at all excitation wavelengths. In addition, it was revealed that the predicted steady-state concentration of 1O2 from pyDOM was similar to that from SRNOM, indicating that the addition of pyDOM from wood chars may not strongly impact surface water photochemistry.

Stationary concentration of 1O2 over 1O2 quantum yield: Next level of photoactivity analysis

The investigation of the activity of photosensitizers is a multivariate challenge for their further application in photocatalysis. Porphyrins are attractive photoactive molecules for chemical and biochemical applications, while their observed photocatalytic efficiency is a function of a variety of characteristics. In the present work the influence of porphyrin substituents on their photoactivity and photostability along with the solvent effect were studied and discussed in details. Series of experiments with 9,10-diphenylanthracene (DPA) as a selective 1O2 trap allowed to develop the approach for direct measurement of [1O2] and quantitatively evaluate the influence of various factors onto it. The processes of 1O2 relaxation, as well as its chemical and physical quenching were separated and analyzed individually. A kinetic scheme for the photosensitization process was treated with steady-state approximation to develop a mathematical apparatus, where a non-linear dependence between photosensitizer and singlet oxygen concentration was found. The general character of the derived non-linear dependence was proved experimentally for each studied porphyrin. Physical and chemical quenching rate constants of the studied porphyrins were calculated. DFT calculations allowed to find an empirical correlation between HOMO energies and observed rate constants. A plausible reaction mechanism between TPP and 1O2 was examined with Fast-NEB-TS method.

Seasonal variations in the production of singlet oxygen and organic triplet excited states in aqueous PM2.5 in Hong Kong SAR, South China

Abstract. Photooxidants drive many atmospheric chemical processes. The photoexcitation of light-absorbing organic compounds (i.e., brown carbon, BrC) in atmospheric waters can lead to the generation of reactive organic triplet excited states (3C∗), which can undergo further reactions to produce other photooxidants such as singlet oxygen (1O2∗). To determine the importance of these aqueous photooxidants in secondary organic aerosol (SOA) formation and transformation, we must know their steady-state concentrations and quantum yields. However, there have been limited measurements of aqueous 3C∗ and 1O2∗ in atmospheric samples outside of North America and Europe. In this work, we report the first measurements of the steady-state concentrations and quantum yields of 3C∗ and 1O2∗ produced in aerosols in South China. We quantified the production of 3C∗ and 1O2∗ in illuminated aqueous extracts of PM2.5 collected in different seasons at two urban sites and one coastal semi-rural site during a year-round study conducted in Hong Kong SAR, South China. The mass absorption coefficients at 300 nm for BrC in the aqueous PM2.5 extracts ranged from 0.49 to 2.01 m2 g-C−1 for the three sites. Both 1O2∗ and 3C∗ were produced year-round. The steady-state concentrations of 1O2∗ ([1O2∗]ss) in the illuminated aqueous extracts ranged from 1.56×10-14 to 1.35×10-12 M, with a study average of (4.02±3.52)×10-13 M. At nearly 2 orders of magnitude lower than [1O2∗]ss, the steady-state concentrations of 3C∗ ([3C∗]ss) ranged from 2.93×10-16 to 8.08×10-14 M, with a study average of (1.09±1.39)×10-14 M. The quantum yields of 1O2∗ and 3C∗ also spanned wide ranges across samples, with a range of 1.19 % to 13.74 % and an average of (5.19±2.63) % for 1O2∗ and a range of 0.05 % to 3.24 % and an average of (0.56±0.66) % for 3C∗. The [1O2∗]ss and [3C∗]ss correlated with the concentration and absorbance of BrC, thus implying that the amount of BrC drives the steady-state concentrations of these photooxidants. The locations (urban vs. semi-rural) did not have a significant effect on [3C∗]ss and [1O2∗]ss, which indicated that BrC from local sources did not have a significant influence on the year-round 3C∗ and 1O2∗ production. 3C∗ and 1O2∗ production were found to be the highest in winter and the lowest in summer for all three sites. The observed seasonal trends of 1O2∗ and 3C∗ production could be attributed to the seasonal variations in the long-range air mass transport. Our analysis highlighted the key role that regional sources play in influencing the composition and concentrations of water-soluble BrC in winter PM2.5 in Hong Kong SAR, which contributed to their highest 3C∗ and 1O2∗ production. The current results will be useful for modeling seasonal aqueous organic aerosol photochemistry in the South China region.

DOM optical parameters as a tool to understand degradation of phenolic contaminants of emerging concern

Composition and source of dissolved organic matter (DOM) in water influence the rate of production of reactive intermediates (RIs), affecting the photodegradation of phenolic contaminants of emerging concern (PhCECs). However, this relationship has not been fully quantified. Here, for the first time, we propose a mechanism for photodegradation of a surrogate of PhCECs, p-cresol, in different DOM standard solutions under simulated sunlight irradiation. More importantly, the correlation of DOM optical parameters and p-cresol photodegradation kinetic parameters was determined by Pearson correlation. Results showed that indirect photodegradation was the only degradation pathway for p-cresol, mainly through reaction with excited triplet state of dissolved organic matter (3DOM*). Singlet oxygen (1O2) and hydroxyl radical (•OH) hindered degradation of p-cresol by decreasing the steady state concentration of 3DOM*. Moreover, less aromatic and smaller molecular size DOM showed higher steady-state concentration and quantum yield of 1O2, and 3DOM*, resulting in faster p-cresol photodegradation. Finally, 7 out of 8 optical parameters showed strong correlation with the p-cresol photodegradation rate constant. The mechanism and correlations found are a potential tool to predict PhCECs photodegradation in water using DOM optical parameters.

Clarification of the role of singlet oxygen for pollutant abatement during persulfate-based advanced oxidation processes: Co3O4@CNTs activated peroxymonosulfate as an example

Singlet oxygen (1O2) has often been identified by the popularly used quenching method as a more important reactive species (RS) than sulfate radicals (SO4•−) and hydroxyl radicals (•OH) for pollutant abatement during persulfate-based advanced oxidation processes (PS-AOPs), especially those activated by carbon-based catalysts. However, latest studies have demonstrated that the quenching method actually can often mislead the interpretations of the role of RS for pollutant abatement during AOPs due to various confounding effects caused by adding high-concentration quenchers in the system. To clarify the role of 1O2 in PS-AOPs, this study developed a probe compound-based experimental and kinetic model to quantify the concentrations and exposures of 1O2, SO4•−, and •OH, as well as their relative contributions to pollutant abatement during a cobalt oxide incorporated carbon nanotubes activated peroxymonosulfate (Co3O4@CNTs/PMS) process. Results show that during the Co3O4@CNTs/PMS process, the exposures and transient concentrations of 1O2 were about 19.6 and 41.3 times higher than those of SO4•− and •OH, respectively. However, the relative contribution of 1O2 to the abatement of most pollutants tested in this study (e.g., sulfisoxazole, sulfamethoxyprazine, trimethoprim, and metoprolol) is generally negligible (f1O2 ≤ 8%) compared to that of SO4•− and •OH (fSO4•− = 15%−98% and f•OH = 2%−78%) because of the significantly lower reactivity of 1O2 with these compounds than that of SO4•− and •OH. Reasons for misidentifying 1O2 as the dominant RS for pollutant abatement by the quenching method were then analyzed based on reaction kinetics principles. The results of this study highlight that while 1O2 can be generated in significant amounts and be present at higher concentrations than SO4•− and •OH in PS-AOP systems, 1O2 is unlikely to be the dominant RS for the abatement of most pollutants during the PS-AOPs because of its weak and selective oxidation capacity, and caution should be taken when using the quenching method to evaluate the role of RS for pollutant abatement by the PS-AOPs.

Efficient Degradation of Intracellular Antibiotic Resistance Genes by Photosensitized Erythrosine-Produced 1O2.

Intracellular antibiotic resistance genes (iARGs) constitute the important part of wastewater ARGs and need to be efficiently removed. However, due to the dual protection of intracellular DNA by bacterial membranes and the cytoplasm, present disinfection technologies are largely inefficient in iARG degradation. Herein, we for the first time found that erythrosine (ERY, an edible dye) could efficiently degrade iARGs by producing abundant 1O2 under visible light. Seven log antibiotic-resistant bacteria were inactivated within only 1.5 min, and 6 log iARGs were completely degraded within 40 min by photosensitized ERY (5.0 mg/L). A linear relationship was established between ARG degradation rate constants and 1O2 concentrations in the ERY photosensitizing system. Surprisingly, a 3.2-fold faster degradation of iARGs than extracellular ARGs was observed, which was attributed to the unique indirect oxidation of iARGs induced by 1O2. Furthermore, ERY photosensitizing was effective for iARG degradation in real wastewater and other photosensitizers (including Rose Bengal and Phloxine B) of high 1O2 yields could also achieve efficient iARG degradation. The findings increase our knowledge of the iARG degradation preference by 1O2 and provide a new strategy of developing technologies with high 1O2 yield, like ERY photosensitizing, for efficient iARG removal.