1O2 Concentration Research Articles

Polydopamine-Based Multifunctional Antitumor Nanoagent for Phototherapy and Photodiagnosis by Regulating Redox Balance.

The development of multifunctional nanoagents for the simultaneous achievement of high diagnostic and therapeutic performances is significant for precise cancer treatment. Herein, we report on a polydopamine (PDA)-based multifunctional nanoagent, PML, in which the methylene blue (MB) photosensitizer (PS) and l-arginine (l-Arg) tumor-targeting species are equipped. After selectively accumulating in tumor sites, glutathione (GSH)-responsive PML degradation can controllably release loaded MB to produce singlet oxygen (1O2) under near-infrared (NIR) photoirradiation. This GSH-depleted PS release process can not only weaken the body's antioxidant defence ability but also synergistically increase the 1O2 concentration. Therefore, GSH depletion-enhanced photodynamic therapy (PDT) efficiency is logically achieved by regulating the intracellular redox balance. In addition, our nanoagent can guide photoacoustic/NIR thermal dual-modal imaging and convert light into heat for cooperative cancer phototherapy because of the inherent photothermal conversion nature of PDA. As a result, excellent in vivo antitumor phototherapy (PDT + PTT) is achieved under the precise guidance of dual-modal imaging. This work not only realizes the integration of cancer diagnosis and treatment through PDA-based nanocarriers but also delivers dimensions in designing the next generation of multifunctional antitumor nanoagents for enhanced phototherapy and photodiagnosis by regulating the redox balance.

Rational Design of Self-Assembled Cationic Porphyrin-Based Nanoparticles for Efficient Photodynamic Inactivation of Bacteria.

Bacterial infection has become an urgent health problem in the world. Especially, the evolving resistance of bacteria to antibiotics makes the issue more challenging, and thus new treatments to fight these infections are needed. Antibacterial photodynamic therapy (aPDT) is recognized as a novel and promising method to inactivate a wide range of bacteria with few possibilities to develop drug resistance. However, the photosensitizers (PSs) are not effective against Gram-negative bacteria in many cases. Herein, we use conjugated meso-tetra(4-carboxyphenyl)porphine (TCPP) and triaminoguanidinium chloride (TG) to construct self-assembled cationic TCPP-TG nanoparticles (NPs) for efficient bacterial inactivation under visible light illumination. The TCPP-TG NPs can rapidly adhere to both Gram-negative and Gram-positive bacteria and display promoted singlet oxygen (1O2) generation compared with TCPP under light irradiation. The high local positive charge density of TCPP-TG NPs facilitates the interaction between the NPs and bacteria. Consequently, the TCPP-TG NPs produce an elevated concentration of local 1O2 under light irradiation, resulting in an extraordinarily high antibacterial efficiency (99.9999% inactivation of the representative bacteria within 4 min). Furthermore, the TCPP-TG NPs show excellent water dispersity and stability during 4 months of storage. Therefore, the rationally designed TCPP-TG NPs are a promising antibacterial agent for effective aPDT.

Tunable S doping from Co3O4 to Co9S8 for peroxymonosulfate activation: Distinguished Radical/Nonradical species and generation pathways

The introduction of non-metal heteroatoms is an effective way to improve the catalytic properties of heterogeneous catalysts to peroxymonosulfate. Unfortunately, the influence of foreign elements on the catalytic process has not been deeply revealed. Herein, we reported a series of Co9S8 nanorods catalysts from Co3O4 precursor with different S doping ratios. S doping effectively enhanced the catalytic properties, and the catalytic process gradually switched from non-radical (1O2) into radical (SO4−) with the increase of S doping ratio. Moreover, quenching experiments, EPR, XPS, and radicals quantification indicated that the concentration of 1O2 exhibited a linear relationship with ΔOL. Indicating that 1O2 was derived from the reaction between PMS and OL. S doping also altered the valency of cobalt. In Co3O4/PMS, ROS was generated through Co3+/Co2+ catalytic circle. However, in Co9S8/PMS, Co3+/Co2+/Co0 were all involved and accounted for the generation of ROS due to the low redox potential of S2-. Our work may provide some new clues and strategies for studying the influence of foreign elements on the catalytic process in PMS-based heterogeneous catalytic system.

Synergistic mediation of metallic bismuth and oxygen vacancy in Bi/Bi2WO6-x to promote 1O2 production for the photodegradation of bisphenol A and its analogues in water matrix

Bi/Bi2WO6-x heterostructures has been successfully prepared by a facile one-step hydrothermal method. By maneuvering reaction time and Bi/W molar ratio of the precursors, we have been able to selectively introduce oxygen vacancy and metallic Bi into Bi2WO6 nanostructures. The obtained Bi/Bi2WO6-x heterostructures with more oxygen vacancy and moderate metallic Bi exhibit significantly improved photocatalytic activity for the photodegradation of bisphenol A (BPA) and its analogues due to its great ability for the generation of singlet oxygen (1O2), which has proven to work as the main reactive oxygen species during photocatalysis. It is also found the 1O2 concentration is highly depended on and modulated by the content of oxygen vacancy and metallic bismuth. Besides, we also demonstrate that the obtained Bi/Bi2WO6-x products display efficient photocatalytic performance toward BPA derivatives degradation and enhanced stability to resist the interferences in the water matrix.

A novel peroxymonosulfate activation process by periclase for efficient singlet oxygen-mediated degradation of organic pollutants

In this study, a novel peroxymonosulfate (PMS) activator, periclase (MgO) was applied to the activation of PMS for the degradation of organic contaminants in aqueous solution. It was found that MgO exerts an excellent and stable catalytic performance for PMS activation to degrade a wide range of pollutants including bisphenol A (BPA), phenol, chlorophenol, and dye, with degradation efficiencies of 100%, 100%, 41%, and 59%, respectively. Results from a combination of electron spin resonance (ESR), free radical quenching, chemical probe and isotope labeling investigations confirm that singlet oxygen (1O2) was the dominant reactive species generated in the PMS/MgO system and accounted for BPA degradation. The steady-state concentration of 1O2 was 13.2 × 10−13 M. Further evidence from X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) spectroscopy, and density functional theory (DFT) suggested that 1O2 was generated by the self-decomposition of PMS induced by surface hydroxyl groups on MgO. In addition, the degradation of BPA was hardly affected by anions and humic acid (HA) that commonly existed in the environmental matrices. The naturally occurring periclase also has high catalytic ability for PMS activation and BPA degradation. Compared with other transition metals-based radical pathways and carbonaceous materials-based non-radical pathways of PMS activation, MgO exerts a comparable catalytic performance but less potential risk and cheaper. This study developed a novel environmentally friendly catalyst with low cost and high efficiency for the selective degradation of organic pollutants in wastewater treatment.

Fundamental Studies of the Singlet Oxygen Reactions with the Potent Marine Toxin Domoic Acid.

Domoic acid (DA), a potent marine toxin, is readily oxidized upon reaction with singlet oxygen (1O2). Detailed product studies revealed that the major singlet oxygenation reaction pathways were the [2 + 2] cycloaddition (60.2%) and ene reactions (39.8%) occurring at the Z double bond. Diene isomerization and [4 + 2] cycloaddition, common for conjugated diene systems, were not observed during the singlet oxygenation of DA. The bimolecular rate constant for the DA reaction with 1O2 determined by competition kinetics was 5.1 × 105 M-1 s-1. Based on the rate constant and steady-state concentrations of 1O2 in surface waters, the environmental half-life of DA due to singlet oxygen-induced transformations is between 5 and 63 days. The 1O2 reaction product mixture of DA did not exhibit significant biological activity based on ELISA studies, indicating that singlet oxygenation could be an important natural detoxification process. The characteristic oxidation products can provide valuable markers for the risk assessment of DA-contaminated natural waters.

Secondary organic aerosol formation from 3C⁎-initiated oxidation of 4-ethylguaiacol in atmospheric aqueous-phase

In this study, we investigated aqueous-phase triplet excited states (3C⁎)-induced photo-degradation of 4-ethylguaiacol (EG) under both simulated sunlight and ultraviolet (UV) light irradiations. Through quencher experiments, the relative contributions of reactive oxygen species (ROS, such as 1O2/O2−/·OH) and 3C⁎ were calculated and results showed three reactive species, e.g., 3C⁎, 1O2 and O2−, all seemed to play important roles in the photo-degradation of EG, but contribution from ·OH was relatively minor. High steady-state 1O2 concentration after 1 h irradiation further revealed the major contribution of 1O2 to photo-degradation under Xe light irradiation. The degradation experiment under three saturated gases (air, O2 and N2) showed that the degradation rate in air-saturated condition was the largest owing to synergistic effect of 1O2 and 3C⁎. Oxidative capacity of aqueous secondary organic aerosol (aqSOA) increased with reaction time by monitoring oxygen-to‑carbon (O/C) ratio and carbon oxidation state (OSc) via an aerodyne soot particle aerosol mass spectrometer (SP-AMS). Moreover, aqSOA mass yields were calculated via SP-AMS data. The UV–vis spectral change suggested formation of light-absorbing organics at first stage under simulated sunlight irradiation. Based on the identified products and the reactive intermediates, we postulated that 3C⁎-induced oxidation might be attributed to direct reactions by 3C⁎ and 1O2, chemical reaction by ROS, as well as oligomerization via H-abstraction. To the best of our knowledge, this is the first time to explore systematically reaction pathways of 4-ethylguaiacol under 3C∗ radical on the basis of thorough analysis of products and reactive species. Our findings highlight the impacts of aqSOA from biomass burning emissions on air quality and climate change.

Inactivation of Escherichia coli and MS2 coliphage via singlet oxygen generated by homogeneous photosensitization

The inactivation kinetics of E. coli and MS2 coliphage by singlet oxygen (1O2) were investigated in a homogeneous photosensitization system using Rose Bengal (RB) and visible light illumination (the Vis/RB system). The inactivation of E. coli and MS2 in the Vis/RB system was monitored over time with variations of several parameters such as pH, light intensity, concentration of RB, and the presence of dissolved oxygen. In addition, the concentration of 1O2 generated by the Vis/RB system was quantified using furfuryl alcohol under each microbial inactivation conditions. Based on the obtained results, the degree of microbial inactivation was quantitatively correlated with 1O2 exposure using the (delayed) Chick-Watson model. The Ct (concentration-time product) values of 1O2 required for 2 log microbial inactivation were found to be 1.3×10−4 mg·min/L for E. coli and 1.9×10−5 mg·min/L for MS2, respectively. The inactivation of E. coli exhibited an initial lag phase until 0.5×10−4 mg·min/L of Ct.

Reactive Oxygen Species Production from Secondary Organic Aerosols: The Importance of Singlet Oxygen.

Organic aerosols are subjected to atmospheric processes driven by sunlight, including the production of reactive oxygen species (ROS) capable of transforming their physicochemical properties. In this study, secondary organic aerosols (SOA) generated from aromatic precursors were found to sensitize singlet oxygen (1O2), an arguably underappreciated atmospheric ROS. Specifically, we quantified 1O2, OH radical, and H2O2 quantum yields within photoirradiated solutions of laboratory-generated SOA from toluene, biphenyl, naphthalene, and 1,8-dimethylnaphthalene. At 5 mgC L-1 of SOA extracts, the average steady-state concentrations of 1O2 and of OH radicals in irradiated solutions were 3 ± 1 × 10-14 M and 3.6 ± 0.9 × 10-17 M, respectively. Furthermore, ROS quantum yields of irradiated ambient PM10 extracts were comparable to those from laboratory-generated SOA, suggesting a similarity in ROS production from both types of samples. Finally, by using our measured ROS concentrations, we predict that certain organic compounds found in aerosols, such as amino acids, organo-nitrogen compounds, and phenolic compounds have shortened lifetimes by more than a factor of 2 when 1O2 is considered as an additional sink. Overall, our findings highlight the importance of SOA as a source of 1O2 and its potential as a competitive ROS species in photooxidation processes.

Effects of Ozone on the Photochemical and Photophysical Properties of Dissolved Organic Matter.

This study focused on the effects of ozonation on the photochemical and photophysical properties of dissolved organic matter (DOM). Upon ozonation, a decrease in DOM absorbance was observed in parallel with an increase in singlet oxygen (1O2) and fluorescence quantum yields (Φ1O2 and ΦF). The increase in Φ1O2 was attributed to the formation of quinone-like moieties during ozonation of the phenolic moieties of DOM, while the increase in ΦF can be explained by a significant decrease in the internal conversion rate of the first excited singlet state of the DOM (1DOM*). It is a consequence of an increase in the average energy of the first electronic transition (S1 → S0) that was assessed using the wavelength of maximum fluorescence emission (λF,max). Furthermore, ozonation did not affect the ratio of the apparent steady-state concentrations of excited triplet DOM (3DOM*) and 1O2, indicating that ozonation does not affect the efficiency of 1O2 production from 3DOM*. The consequences of these changes for the phototransformation rates of micropollutants in surface waters were examined using photochemical model calculations. The decrease in DOM absorbance caused by ozonation leads to an enhancement of direct photolysis rates due to the increased transparency of the water. Rates of indirect photooxidation induced by 1O2 and 3DOM* slightly decrease after ozonation.

A new pathway of monomethylmercury photodegradation mediated by singlet oxygen on the interface of sediment soil and water

Photodegradation is an important pathway for monomethylmercury (MeHg) degradation in aquatic ecosystems. In this process, dissolved organic matter (DOM) plays an essential role. However, little information is available regarding the photo-transformation of MeHg in shallow aquatic environments, where a significant portion of MeHg is associated with soil suspensions. In this study, 14 soils sampled from different sites in China were used to simulate these conditions. Our results clearly demonstrated that soil organic matter (SOM) was the most important factor controlling the MeHg photodegradation in suspension. Degradation in this heterogeneous aqueous system was shown to be mediated by the 1O2 produced by organic matter on the surface of the soil particles rather than by DOM. This was confirmed by the strong correlation between the kinetics rate constant of MeHg degradation and steady state concentrations of 1O2 (R2 = 0.81). Our results propose a new pathway of MeHg induced by sediment soils under sunlight irradiation. Identification of this pathway may improve the estimates of potential ecological risk of Hg in shallow field ecosystems.

Mechanistic Study on the Role of Soluble Microbial Products in Sulfate Radical-Mediated Degradation of Pharmaceuticals.

The role of soluble microbial products (SMP), the most important component of effluent organic matter from municipal wastewater treatment plants, in sulfate radical (SO4•-)-based advanced oxidation technologies (AOTs) remains substantially unclear. In this study, we first utilized a suite of macro- and microanalytical techniques to characterize the SMP from a membrane bioreactor for its fundamental molecular, spectroscopic, and reactivity properties. The degradation kinetics of three representative pharmaceuticals (i.e., naproxen, gemfibrozil, and sulfadiazine) in the presence of SMP was significantly reduced as compared to in its absence. Possible mechanisms for the interference by SMP in degrading these target compounds (TCs) were investigated. The low percentage of bound TCs to SMP ruled out the cage effect. The measurement of steady-state 1O2 concentration indicated that formation of 1O2 upon UV irradiation on SMP was not primarily responsible for the degradation of TCs. However, the comparative and quenching results reveal that SMP absorbs UV light acting as an inner filter toward the TCs, and meanwhile scavenges SO4•- with a high second-order rate constant of 2.48 × 108 MC-1 s-1.

Promoted peroxymonosulfate activation into singlet oxygen over perovskite for ofloxacin degradation by controlling the oxygen defect concentration

Recently, perovskite is becoming a promising alternative as peroxymonosulfate (PMS) activator for the remediation of organic pollutants in water. But the factor determining PMS activation efficiency of perovskite and the evolution of reactive oxygen species (ROS) remain equivocal and elusive. In this study, we proposed an oxygen defect dependent PMS activation mechanism over perovskite with the singlet oxygen (1O2) as the dominant ROS. Among the tested four perovskites, ofloxacin (OFX) degradation efficiency increased with the following order: LaFeO3 < LaZnO3 < LaMnO3 < LaNiO3, which agreed well with their oxygen defect amounts based on X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) analysis. The results clearly demonstrated a good relationship among oxygen defects in LaBO3, OFX degradation efficiency and 1O2 concentration. Moreover, 1O2 evolution mechanism over perovskite by decreasing the activation energy of PMS self-decomposition was proposed. The 1O2 mediated OFX degradation pathway was further studied by HPLC-MS technique and three-dimensional excitation–emission matrix fluorescence spectroscopy (3D EEMs). This work provides a new insight into PMS activation by perovskites and favors its application in actual water treatment.

Dissolved organic matter processing and photoreactivity in a wastewater treatment constructed wetland

Constructed wetlands have the capacity to degrade a host of contaminants of emerging concern through photodegradation via sunlight produced reactive oxygen species. Dissolved organic matter (DOM) is a critical intermediary in photodegradation as it influences the production of reactive oxygen species. In this study, the photochemical behavior of DOM of wastewater treated in constructed wetlands was characterized. Whole water samples and fractionated DOM were characterized using SUVA254, spectral slope ratios, excitation emission matrix fluorescence spectroscopy (EEMs), and proton nuclear magnetic resonance (1H NMR). Photoreactivity was assessed by measuring formation rates and steady state concentrations of hydroxyl radical (•OH), singlet oxygen (1O2), and the triplet excited states of DOM (3DOM⁎). The effluent was observed to transition from a microbially sourced protein-like DOM to a terrestrial DOM with higher aromaticity. Size exclusion chromatography revealed an 18% increase in larger molecular weight fractions of vegetated wetland effluent DOM. Additionally, wetland effluent DOM was observed to have a 32% increase in the aromatic region of 1H NMR spectra as compared to untreated wastewater. 1H NMR analysis also indicated an increase in the complexity of wetland effluent DOM. Fluorescence intensity fraction of the protein-like Peak T (Ex/Em:278/342 nm) of EEMs decreased by 16% from the untreated wastewater to wetland effluent. A negative correlation between the percent fluorescence of Peak T (Ex/Em:278/342 nm) and Peaks A (Ex/Em:245/460 nm), C (Ex/Em:336/435 nm), and M (Ex/Em:312/400 nm) of the excitation emission spectra confirmed the transition from a spectrum of pure wastewater to a spectrum characteristic of terrestrially derived DOM. Microbial uptake of bio-labile DOM and leaching of humic like substances from vegetated wetland cells were the predominant processes involved in this transition. This transition coincided with an increase in the formation rates of 1O2 and 3DOM⁎ and in the steady state concentration of 1O2.

Copper Inhibition of Triplet-Induced Reactions Involving Natural Organic Matter.

The triplet excited state of natural organic matter (3NOM*) is an important reactive intermediate in sensitizing transformation of a wide range of environmentally relevant organic compounds, but the impact of trace metals on the fate and reactivity of 3NOM* is poorly understood. In this study, we investigate the effect of low concentrations of copper on 3NOM*-mediated oxidation (electron transfer) and energy transfer reactions. The oxidative efficiency of 3NOM* from Suwannee River NOM (SRNOM) and the widely used model triplet sensitizer 4-carboxybenzophenone were determined by measuring the photooxidation of 2,4,6-trimethylphenol (TMP). The pseudo-first-order photooxidation rate constants of TMP decreased markedly in the presence of trace amounts of Cu(II) (25-500 nM) with the decrease associated with the continuous reduction of the oxidation intermediates of TMP (i.e., TMP•(-H)) by the photochemically produced Cu(I). A kinetic model is developed that adequately describes the Cu inhibition effect in TMP photooxidation in irradiated SRNOM solutions. The 3NOM* energy transfer ability was assessed by measuring the isomerization of sorbic acid with the rate of this process markedly retarded in the presence of significantly higher (micromolar) concentrations of Cu(II) than previously used. This result is attributed to (i) decreased formation of high energy 3NOM* due to formation of Cu-NOM complexes and (ii) increased loss of 3NOM* as a result of quenching by Cu. Since 3NOM* is the precursor to singlet oxygen (1O2) formation, the steady-state concentrations of 1O2 also decreased in the presence of micromolar concentrations of Cu(II) with the quenching rate constant of 3NOM* by Cu calculated to be 1.08 × 1010 M-1 s-1.

Photochemical Production of Singlet Oxygen by Urban Road Dust

Road dust resuspension is a major source of particulate matter in many urban centers, especially those in which traction materials are applied to roadways in winter. Although many studies have investigated the composition and toxicity of road dust, nothing is currently known regarding its photochemical reactivity. Here, we show for the first time that road dust is photochemically active: in particular, we use a molecular probe technique to show that the illumination of aqueous road dust suspensions leads to the production of singlet oxygen (1O2), an important environmental oxidant. In experiments conducted using size-fractionated road dust, we found that the surface area-normalized steady-state 1O2 concentration ([1O2]ss) increased with decreasing particle size. We also observed correlations between [1O2]ss and the dissolved organic carbon content and ultraviolet absorbance properties of dust extracts, which suggests the involvement of chromophoric water-soluble organic carbon in the observed photochemist...

Interaction between air plasma-produced aqueous 1O2 and the spin trap DMPO in electron spin resonance

A series of electron spin resonance (ESR) experiments is done to quantitatively measure the concentrations of aqueous 1O2 and ̇OH produced by a surface micro-discharge air plasma device. 1O2 is tested to be existed in the plasma treated solution by using the spin trap of TEMP. However, the unexpected DMPOX spectrum is observed in measuring ̇OH by the spin trap of 5,5-Dimethyl-1-Pyrroline-N-Oxide (DMPO). With more chemical scavenger experiments, it is found that removal of aqueous 1O2 leads to the disappearance of DMPOX in ESR. Therefore, the generation of DMPOX is directly related to the oxidation of DMPO by plasma-produced aqueous 1O2. This oxidation process and interactions between DMPO and chemical scavengers used in experiments can all be well explained by a proposed reaction mechanism. The revelation of interactions between aqueous 1O2 and the spin trap DMPO shows that the observation of spectra of DMPOX in the ESR measurement can be regarded as a marker of high concentrations of plasma-produced 1O2 in liquid. These results also prove the existence of interactions between spin traps and non-targeted plasma-produced reactive species in ESR experiments. Also, these results have offered a better understanding of the use of spin traps such as DMPO in the plasma-induced highly oxidative aqueous environment.

Time-gated luminescence imaging of singlet oxygen photoinduced by fluoroquinolones and functionalized graphenes in Daphnia magna

Singlet oxygen (1O2) can be photogenerated by photoactive xenobiotics and is capable of causing adverse effects due to its electrophilicity and its high reactivity with biological molecules. Detection of the production and distribution of 1O2 in living organisms is therefore of great importance. In this study, a luminescent probe ATTA-Eu3+ combined with time-gated luminescence imaging was adopted to detect the distribution and temporal variation of 1O2 photoinduced by fluoroquinolone antibiotics and carboxylated/aminated graphenes in Daphnia magna. Results show that the xenobiotics generate 1O2 in living daphnids under simulated sunlight irradiation (SSR). The photogeneration of 1O2 by carboxylated/aminated graphenes was also confirmed by electron paramagnetic resonance spectroscopy. The strongest luminescence signals of 1O2 were observed in the hindgut of daphnids, and the signals in different areas of the daphnids (gut, thoracic legs and post-abdominal claw) displayed a similar trend of enhancement over irradiation time. Mean 1O2 concentrations at different regions of daphnids within one hour of SSR irradiation were estimated to be in the range of 0.5∼4.8μM. This study presented an efficient method for visualizing and quantifying the temporal and spatial distribution of 1O2 photogenerated by xenobiotics in living organisms, which can be employed for phototoxicity evaluation of xenobiotics.

Light absorption and the photoformation of hydroxyl radical and singlet oxygen in fog waters

The atmospheric aqueous-phase is a rich medium for chemical transformations of organic compounds, in part via photooxidants generated within the drops. Here we measure light absorption, photoformation rates and steady-state concentrations of two photooxidants – hydroxyl radical (•OH) and singlet molecular oxygen (1O2*) – in 8 illuminated fog waters from Davis, California and Baton Rouge, Louisiana. Mass absorption coefficients for dissolved organic compounds (MACDOC) in the samples are large, with typical values of 10,000–15,000 cm2 g-C−1 at 300 nm, and absorption extends to wavelengths as long as 450–600 nm. While nitrite and nitrate together account for an average of only 1% of light absorption, they account for an average of 70% of •OH photoproduction. Mean •OH photoproduction rates in fogs at the two locations are very similar, with an overall mean of 1.2 (±0.7) μM h−1 under Davis winter sunlight. The mean (±1σ) lifetime of •OH is 1.6 (±0.6) μs, likely controlled by dissolved organic compounds. Including calculated gas-to-drop partitioning of •OH, the average aqueous concentration of •OH is approximately 2 × 10−15 M (midday during Davis winter), with aqueous reactions providing approximately one-third of the hydroxyl radical source. At this concentration, calculated lifetimes of aqueous organics are on the order of 10 h for compounds with •OH rate constants of 1 × 1010 M−1 s−1 or higher (e.g., substituted phenols such as syringol (6.4 h) and guaiacol (8.4 h)), and on the order of 100 h for compounds with rate constants near 1 × 109 M−1 s−1 (e.g., isoprene oxidation products such as glyoxal (152 h), glyoxylic acid (58 h), and pyruvic acid (239 h)). Steady-state concentrations of 1O2* are approximately 100 times higher than those of •OH, in the range of (0.1–3.0) × 10−13 M. Since 1O2* is a more selective oxidant than •OH, it will only react appreciably with electron-rich species such as dimethyl furan (lifetime of 2.0 h) and substituted polycyclic aromatic hydrocarbons (e.g., 9,10-dimethylbenz[a]anthracene with a lifetime of 0.7 h). Comparing our current Davis samples with Davis fogs collected in the late 1990s shows a decrease in dissolved organic carbon content, similar mass absorption coefficients, lower •OH concentrations, but very similar 1O2* concentrations.

Sustainable process for functional group introduction onto HOPG by exposing [rad]OH and 1O2 using a radical vapor reactor (RVR) without any chemical reagents

Efficient generation of reactive oxygen species (high concentrations of 1O2 and OH) was successfully performed using a radical vapor reactor (RVR) at ordinary temperature and atmospheric pressure without using any chemical reagent. In this study, we successfully introduced modified functional groups onto highly oriented pyrolytic graphite (HOPG) by a sustainable process using an RVR. Although the introduction of a functional group onto HOPG is difficult because of the presence of strong CC bonds in HOPG, the RVR can easily modify it because reactive oxygen species have high energy and high reactivity. Moreover, the RVR process does not require any chemical reagent; it also does not produce any exhaust, except for air and water. The RVR-treated HOPG was analyzed by contact angle measurement (CAM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), and scanning tunneling microscopy (STM). These analyses revealed that the HOPG surface became hydrophilic and it showed different physical property owing to the modification caused by the introduced oxygen element.