Persistent Free Radicals Research Articles

Oxidative potential, environmentally persistent free radicals and reactive oxygen species of size-resolved ambient particles near highways

Particulate matter (PM) is a group of atmospheric pollutants with an uncertain toxicity, particularly when collected near highways. This study examined the oxidative potential (OP) of, as well as the environmentally persistent free radicals (EPFRs) and reactive oxygen species (ROS) present in PM samples collected near highways in Xiamen, China. Our findings revealed that PM had a relatively high OP, ranging from 3.8 to 18.5 nmol/min/μg, surpassing values reported in previous research. The oxidative potential of the water-insoluble fraction (OPWIS), which accounted for 68% of the total oxidative potential (OPTotal), demonstrated rapid toxicity, whereas the oxidative potential of the water-soluble fraction (OPWS) displayed a steadier toxicity release pattern. The primary free radicals detected in PM were oxygen-centered. The measured concentration of EPFRs was 6.073 × 1014 spins/m3, which is lower than that reported in previous studies, possibly because of the high relative humidity of the road environment in Xiamen. We also investigated the interaction between PM and water near highways and observed the generation of R and OH radicals. Additionally, we analysed the sample composition and evaluated the contributions of the different components to OPTotal. Transition metals (Fe, Cu, and Zn) were identified as the major contributors, accounting for 33.2% of the OPTotal. The positive correlation observed between EPFRs and ROS suggests that EPFRs may be involved in ROS generation. The correlation analysis indicated that the oxidative potential measured using the DTT method (OPDTT) could serve as an indicator of ROS generation. Finally, based on the relationship between OPDTT, EPFRs, and ROS, we propose that reducing the emission of transition metals, particularly Fe, represents an effective control measure for mitigating PM toxicity near highways.

Critical impact of pyrolysis temperatures on biochars for peroxymonosulfate activation: Structural characteristics, degradation performance and mechanism

In order to gain insights into the critical impact of pyrolysis temperatures, a series of pine needle biochars were prepared by one-step pyrolysis method at different temperatures, and were applied for peroxymonosulfate activation to degrade enrofloxacin. Interestingly, with the increase of temperature, the degradation efficiencies increase first, then slightly decrease. BC-700 (biochar synthesized at 700 °C) exhibited best performance, and the degradation rate could reach 97.7 % within 180 min under the optimized conditions. Characterization results demonstrated biochar synthesized at relatively low temperature exhibited more oxygen-containing functional groups and persistent free radicals, while biochar synthesized at high temperature contained more pore structure and higher graphitization degree. Mechanism studies demonstrated that biochar synthesized at relatively low temperature tend to generate transient radicals, while biochar synthesized at high temperature exhibited better electron transfer capability, which might be the key factor of the superior degradation rate of BC-700. In addition, singlet oxygen played an important role in both systems.

Photoaged Polystyrene Nanoplastics Result in Transgenerational Reproductive Toxicity Associated with the Methylation of Histone H3K4 and H3K9 in Caenorhabditis elegans.

Polystyrene nanoplastics (PS-NPs) are emerging environmental contaminants that are ubiquitously detected in various environments and have toxic effects on various organisms. Nevertheless, the transgenerational reproductive toxicity and underlying mechanisms of PS-NPs remain largely unknown, especially for photoaged PS-NPs under ultraviolet irradiation. In this study, only the parental generation (P0) was exposed to virgin and aged PS-NPs at environmentally relevant concentrations (0.1-100 μg/L), and subsequent generations (F1-F4) were cultured under normal conditions. Ultraviolet irradiation induced the generation of environmentally persistent free radicals and reactive oxygen species, which altered the physical and chemical characteristics of PS-NPs. The results of toxicity testing suggested that exposure to aged PS-NPs caused a more severe decrease in brood size, egg ejection rate, number of fertilized eggs, and hatchability than did the virgin PS-NPs in the P0, F1, and F2 generations. Additionally, a single maternal exposure to aged PS-NPs resulted in transgenerational effects on fertility in the F1 and F2 generations. Increased levels of H3K4 and H3K9 methylation were observed in the F1 and F2 generations, which were concomitant with the transgenerational downregulation of the expression of associated genes, such as spr-5, set-17, and met-2. On the basis of correlation analyses, the levels of histone methylation and the expression of these genes were significantly correlated to transgenerational reproductive effects. Further research showed that transgenerational effects on fertility were not observed in spr-5(by134), met-2(n4256), and set-17(n5017) mutants. Overall, maternal exposure to aged PS-NPs induced transgenerational reproductive effects via H3K4 and H3K9 methylation, and the spr-5, met-2, and set-17 genes were involved in the regulation of transgenerational toxicity. This study provides new insights into the potential risks of photoaging PS-NPs in the environment.

Effect of zinc-biochar composite aging on its physicochemical and ecotoxicological properties

The stability of Zn-biochar composites is determined by environmental factors, including the aging processes. This paper focused on the ecotoxicological evaluation of Zn-biochar (Zn-BC) composites subjected to chemical aging. Pristine biochars and composites produced at 500 or 700 °C were incubated at 60 and 90 °C for six months. All biochars were characterized in terms of their physicochemical (elemental composition, Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and porous structure), ecotoxicological properties (tested with Folsomia candida and Aliivibrio fischeri) and contaminant content (polycyclic aromatic hydrocarbons (PAH), heavy metals (HM) and environmentally persistent free radicals (EPFR)). An increase in the number of surface oxygen functional groups and increased hydrophilicity and polarity of all Zn-BC composites were observed due to oxidation during aging. It was also found that Zn-BC aging at 90 °C resulted in a 28–30% decrease in solvent-extractable PAHs (Ʃ16 Ctot PAHs) compared to nonaged composites. The aging process at both temperatures also caused a 104 fold reduction in EPFRs in Zn-BC composites produced at 500 °C. The changes in the physicochemical properties of Zn-BC composites after chemical aging at 90 °C (such as pH and HM content) caused an increase in the toxicity of the composites to Folsomia candida (reproduction inhibition from 19 to 24%) and Aliivibrio fischeri (luminescence inhibition from 96 to 99%). The aging of composites for a long time may increase the adverse environmental impact of BC-Zn composites due to changes in physicochemical properties (itself and its interactions with pollutants) and the release of Zn from the composite.

Persistent free radicals generated from a range of biochars and their physiological effects on wheat seedlings

Biochar is a promising soil conditioner and environmental remediation material. However, the amount, type, and environmental effect and risk of persistent free radicals (PFRs) associated with biochar need to be better understood. Thus, this study characterized PFRs in a range of biochar types and their effects on the growth and oxidative stress of wheat seedlings. Among the biochars prepared by pyrolysis of different types of biomass at 500 °C, the concentrations of PFRs in cow dung and egg shell biochar were the highest and the lowest, respectively. They both increased with artificial weathering treatment but decreased with aging. The dominant types of biochar PFRs were transformed from carbon-centered to oxygen and carbon/oxygen-centered free radicals with weathering. The amount and type of biochar PFRs in mixtures of biochar and soil varied with soil type and biochar dose. After 30 d incubation in different soil-biochar mixtures, measures of wheat plant germination and growth and antioxidant enzyme activity showed increases at lower biochar doses but decreases at higher doses. Catalase activity was 38.1 % greater at 20 g·kg−1 biochar dosage and 25.2 % less at 80 g·kg−1 dosage, on average. In contrast, leaf malondialdehyde content and staining by Evans Blue, both indicators of plant cell membrane damage, generally increased with increasing biochar dosages. Finally, soil hydrolase enzyme activity also displayed an inverted U-shaped dose response. The toxicity indicators showed an increasing trend with higher PFR concentrations in the soil-biochar combinations. While these findings provide evidence for significant potential agricultural and ecological risks associated with the application of biochar due to PFRs damage, it also points to ways that these risks could be mediated such as through biochar dosage restrictions and pre-aging. This study provides new insights into the potential toxicological mechanism and ecological risks associated with the application of biochar in agricultural and environmental settings.

Thermal evolution of biochar in nature: A potential mode to enhance the self-cleaning of environmental DOC

Biochar often undergoes multiple thermal processes. Thermal evolution is described in this study as the process by which biochar in the environment changes again in a thermal environment. In this study, the thermal evolution process of biochar was studied by characterization test. The results showed that the oxygen content in biochar increased after thermal evolution, mainly due to functional groups such as O-H and C-O, while the functional groups of CO did not change significantly. Micro-pores will be generated in biochar after thermal evolution, which will increase the surface area and significantly enhance the adsorption capacity. The biochar was added to natural water to observe how biochar enhanced the removal of dissolved organic carbon (DOC). The concentration of DOC was reduced by about 6.68 mg/L by SB 800, and most of the components were humus, which indicated that the thermal evolution of biochar promoted the removal of DOC. The Electron spin resonance (ESR) test shows that after thermal evolution, biochar has more oxygen-containing carbon center persistent free radicals due to the increase of C-O functional groups in biochar. Under visible light, persistent free radicals in oxygen center are formed by electron transition, which can undergo a variety of reactions with water to form reactive oxygen species.

Insight into the self-driven O2 activation and interfacial electron transfer for micropollutant degradation by boron-doped biochar: Role of boron moieties and persistent free radicals

Advance oxidation process (AOP) is a promising way for micropollutants treatment, but the consumption of chemicals and energies limits its large-scale application. To address this issue, a novel boron-doped biochar (BBC) system was developed for the efficient removal of micropollutants, requiring no external energy or oxidant. Herein we demonstrated that the synthesized BBC could efficiently activate the dissolved oxygen (O2) in the water or oxidize micropollutant directly. The complete sulfamethoxazole (SMX) could be removed within 30 min by the BBC synthesized at 600 °C (BBC-600). The experiments on material characterization and removal performance with quenchers revealed that the introduction of boron into biochar increased the active sites for O2 activation, including persistent free radicals (PFRs) and boron moieties (BC3, BCO2, and BC2O) on the biochar. The generated reactive oxidation species (ROS), mainly O2−, were responsible for the SMX degradation in this BBC system. Different performance of aged experiments in air and N2 conditions indicated that PFRs could also directly oxidize SMX. Density functional theory (DFT) was used to further illustrate the inner mechanism of enhanced electron transfer via boron moieties for O2 activation and SMX degradation. Electrons of the adsorbed micropollutant could be transferred to boron moieties, and then trapped by O2 in water to produce O2− and 1O2 for SMX degradation. This study provided a new insight into the structure–activity relationship of B-doped biochar for the direct and indirect degradation of micropollutant, and opened a new avenue for micropollutant degradation without external energy and oxidant.

Effects of different national standards and driving conditions on pollutants and persistent free radicals in diesel engine exhaust particles

Exhaust pollutants from diesel vehicles constitute an important portion of air pollution. In addition to conventional pollutants such as carbon and nitrogen oxides, persistent free radicals (PFRs) exist on exhaust particles could also pose a health risk by inducing oxidative stress. However, recently there is a dearth of comprehensive studies addressing this concern. In this study, the exhaust particles emitted by tractors adhering to two prominent emission standards, namely GB III and GB I, that currently hold the largest tractor stocks, were collected under various working conditions. For the first time, this study dynamically monitored the characteristics of PFRs in exhaust particles emitted by internal combustion engines using biodiesel as fuel during driving on rural actual roads. Due to the stricter emission standard of GB III, which resulted in lower particle emissions, the concentration of PFRs emitted under the same fuel consumption was ultimately reduced. Noteworthily, while advancements like fuel atomization under engine electronic control unit (ECU) and the utilization of oxidation catalysts with low ignition temperature successfully decreased polycyclic aromatic hydrocarbons (PAHs) emission by altering combustion in the engine, they also resulted in heightened carbon structure defects, leading to a higher concentration of PFRs emitted per unit mass of particles. Additionally, compared to non-plowing driving conditions, localized hypoxia during plowing that could cause excessive fuel injection and uneven formation of fuel-air mixture resulted in the emission of a significant amount of carbon-containing substances with unstable structures. Consequently, this scenario led to an increased concentration of PFRs during plowing conditions. The results of this study demonstrated that the stricter emission standards and optimized technology could better reduce the concentration and types of PFRs in exhaust particles, reducing the environmental risk of exhaust particle, which is also of great significance for the realization of pollution reduction and carbon reduction goals.

Environmentally persistent free radicals on photoaged nanopolystyrene induce neurotoxicity by affecting dopamine, glutamate, serotonin and GABA in Caenorhabditis elegans

Microplastics are widely detected in the environment and induce toxic effects in various organisms. However, the properties and toxicity associated with environmentally persistent free radicals (EPFRs) in photoaged nanopolystyrene (NPS) remain largely unknown. We investigated the generation of EPFRs on photoaged NPS and their neurotoxicity and underlying mechanism in Caenorhabditis elegans. The results suggested that photoaging induces the generation of EPFRs and reactive oxygen species (O2•−, •OH, and 1O2), which altered the physicochemical properties (morphology, crystallinity, and functional groups) of NPS. Acute exposure to 1 μg/L of NPS-60 (NPS with light irradiation time of 60 d) significantly decreased locomotion behaviors and neurotransmitter contents (e.g., glutamate, serotonin, dopamine, and γ-aminobutyric acid). Treatment with N-acetyl-L-cysteine (NAC) by radical quenching test significantly reduced EPFRs levels on the aged NPS, and the toxicity of NAC-quenching NPS was decreased in nematodes compared to those in photoaged NPS. EPFRs also caused dysfunction of neurotransmission-related gene expression in C. elegans. Thus, EPFRs generated on photoaged NPS contributed to neurotoxicity by affecting dopamine, glutamate, serotonin, and γ-aminobutyric acid neurotransmission. The study highlights the potential risks of photoaged NPS and the contributions of EPFRs to toxicity.

Reactivity of aged biochars to the degradation of adsorbed p-nitrophenol: Role of intensity and species of persistent free radicals

Persistent free radicals (PFRs) in biochar have been found to the transformation of organic contaminants in environment. However, there remains insufficient comprehension on the relationship of biochar aging with interfacial reactivity of PFRs to the degradation of phenolic compound in geochemical process. Herein, we studied both sorption and degradation of p-nitrophenol (PNP) on fresh and aged biochars via H2O2 aging under anoxic condition. With increasing aging extent, the enhancive proportion of O-centered radicals was observed progressively as indicated by increased g factors. The aging of PS350 annihilated the presence of PFRs in aged biochars of low-temperature, weakening PFR intensity. But, the aging of PS650 supplied more O-centered radicals for aged biochars of high-temperature, enhancing PFR intensity. This caused the decreased degradation on 5%PS350 and 15%PS350 (37.7–79.6% decline), whereas the increased degradation on 5%PS650 and 15%PS650 (33.3–55.8% increase). At similar intensity and species of PFRs, more adsorbed amount on fresh and aged biochars produced more degradation of PNP. Nevertheless, when PFR intensity of PS650 was much lower than that of PS350, despite high sorption capacity of PS650, the degradation amount of PS350 and PS650 was comparable. The results indicated that the reactivity of C-centered radicals of PS650 was stronger than that of O-centered radicals of PS350 in anoxic system. Overall, the interfacial reactivity of biochars was simultaneously regulated by the sorption capacity of biochars and intensity and species of PFRs. This work provides a deep perspective to the impact of biochar aging on the interfacial reactivity of PRFs to phenolic compound, which will be beneficial to accurately predict the fate of organic contaminant in carbon-rich environment.

Formation and evolution mechanism of persistent free radicals in biochar during biomass pyrolysis: Insights from biochar’s element composition and chemical structure

The persistent free radicals (PFRs) in biochar can play a crucial role during biochar’s utilization, but the formation and evolution mechanism of PFRs in biochar are poorly understood because of biochars’ element specificity and chemical structure complexity. In order to further understand the formation and evolution mechanism of PFRs, the PFRs characteristics, chemical structure and element composition of six types of biomasses were investigated. The results revealed that the changing trend of the PFRs types, concentration and line width with pyrolysis temperature is similar for all six feedstocks. The difference in the feedstocks’ properties just affects the absolute value of PFRs’ characteristic parameters. The arrangement and combination of elements and carbon skeleton structure in biochar determine the evolution of PFRs in the pyrolysis process. Additionally, the (H + O)/C atomic ratio of the biomass feedstock and the content of substitutional groups on aromatic rings were found to influence the types of PFRs in biochar. When biochar has a similar O/C atom ratio, a higher H content can reduce the carbon-centered PFRs in biochar. Besides, the reduction in O element content contributes to a decrease in line width due to the reduction in the effect of heteroatoms. The good correlation between O/C atomic ratio, H/C atomic ratio, chemical structure and PFRs characteristics can be used to predict the PFRs characteristics. Combining the changing characteristics in PFRs concentration and carbon skeleton structure of biochar, a three-stage model of PFRs formation and evolution was constructed.

Photo-enhanced oxidation of arsenite by biochar: The effect of pH, kinetics and mechanisms

The persistent and photo-induced free radicals of biochar play significant roles in the transformation or degradation of inorganic and organic pollutants. However, the redox capacity of biochar for arsenite (As(III)) photochemistry under different pH conditions remains unclear. In this study, we discovered that solar radiation primarily expedited the oxidation of As(III) by biochar by augmenting the production of reactive oxygen species (ROS). Biochar demonstrated a strong pH reliance on the photooxidation of As(III). Under acidic and neutral conditions, solar radiation amplified the generation of •OH (hydroxyl radicals) by BC-P (phenolic −OH of biochar) and semiquinone-type BC-PFRs (persistent free radicals of biochar) by 4.9 and 2.0 times, respectively, resulting in enhanced As(III) oxidation. Under alkaline conditions, BC-P and BC-Q (quinoid CO of biochar) facilitated the production of H2O2 (hydrogen peroxide) by 2.1 times through the spontaneous formation of semiquinone-type BC-PFRs via an anti-disproportionation reaction, promoting approximately 88.2% of As(III) photooxidation. Furthermore, solar radiation elevated around 11.8% As(III) oxidation driven by BC-Q and semiquinone-type BC-PFRs. This study provides a crucial theoretical foundation for using biochar to treat arsenic pollution in aquatic systems and understanding the migration and transformation of arsenic in different environments.

Differential cytotoxicity to human cells in vitro of tire wear particles emitted from typical road friction patterns: The dominant role of environmental persistent free radicals

Tire wear particles (TWPs) have been recognized as one of the major sources of microplastics (MPs), however, effects of initial properties and photochemical behavior of TWPs on cytotoxicity to human cells in vitro have not been reported. Therefore, here, three TWPs generated from typical wear of tires and pavements (i.e., rolling friction (R-TWPs) and sliding friction (S-TWPs)) and cryogenically milled tire tread (C-TWPs), respectively, and their photoaging counterparts were used to study the reasons for their differential cytotoxicity to 16HBE cells in vitro. Results showed in addition to changes of surface structure and morphology, different preparation methods could also induce formation of different concentration levels of environmental persistent free radicals (EPFRs) (from 1.24 to 3.06 × 1017 spins/g with g-factors ranging 2.00307–2.00310) on surfaces of TWPs, which contained 7.3%–65.8% of reactive EPFRs (r-EPFRs). Meanwhile, photoaging for 90 d could strengthen formation of EPFRs (from 4.03 to 4.61 × 1017 spins/g) with containing 74.7%–78.1% r-EPFRs on surfaces of TWPs and improve their g-factor indexes (ranging 2.00309–2.00313). At 100 μg mL−1 level, compared to C-TWPs, both R-TWPs and S-TWPs (whether photoaging or not) carried higher intensity EPFRs could significantly inhibit 16HBE cells proliferation activity, cause more cells oxidative stress and induce more cell apoptosis/necrosis and secretion of inflammatory factor (P < 0.05). However, regardless of how TWPs were prepared, photoaged or not, exposure at a concentration of 1 μg mL−1 appeared to be non-acute cytotoxic. Correlation analysis suggested dominant toxicity of TWPs was attributed to the formation of r-EPFRs on their surfaces, which could promote accumulation of excess reactive oxygen species in cells and the massive deposition of intracellular particles. This study provides direct evidence of TWPs cytotoxicity, and underlining the need for a better understanding of the influences of initial properties and photochemical characteristics on risk assessment of TWPs released into the environment.

Environmentally persistent free radicals in household dust: longitudinal and seasonal trends

Environmentally persistent free radicals in household dust: longitudinal and seasonal trends

Biochar-activated persulfate oxidation of arsenic(III): Nonnegligible roles of environmentally persistent free radicals

The water ecosystem and public health are often threatened by Arsenic (As). The primary type of As in paddy field and ground water is As(III), which is more toxic and mobile than As(V). In this research, biochar prepared from sewage sludge (SBC) through hydrothermal technique was used to activate persulfate (PS) to oxidate As(III), making it less toxic As(V). The developed SBC/PS system could oxidate As(III) effectively in the wide pH values (2−10). Excluding the influence of specific surface area and functional groups, the concentration of environmental persistent free radicals (EPFRs) had a good linear relationship with the oxidation of As(III), reaching above 0.96. According to a mechanism analysis, EPFRs on SBC could transfer electrons to directly activate PS to produce SO4−·, ·OH, O2−·, and 1O2 to improve the oxidation of As(III). These results not only indicated that the biochar/PS system’s application scope can be successfully increased by adjusting the preparation conditions, but also revealed the invaluable role of EPFRs in As(III) oxidation process.

Toxic effects of environmentally persistent free radicals (EPFRs) on the surface of tire wear particles on freshwater biofilms: The alleviating role after sewage-incubation-aging

The aquatic ecological risks posed by the surface-active components of tire wear particles (TWPs) are not fully understood. This study aimed to determine the acute (24 h exposure) aquatic toxicity effects of TWPs on freshwater biofilms in terms of total organic carbon (TOC), chlorophyll-a (Chl-a) abundance, quantum yield (ФM), and adenosine triphosphate (ATP). Three types of TWP were tested: TWPs produced via the typical wear of tires and roads (i.e., rolling friction (R-TWPs) and sliding friction (S-TWPs)) and cryogenically milled tire treads (C-TWPs). The results showed that the surface structural properties of the three TWPs differed significantly in morphology, bare composition, functional groups, and surface-active components (environmental persistent free radicals). The exposure of biofilms to the TWPs increased TOC and ATP at low concentrations (1 mg L−1) but inhibited them at high concentrations (50 mg L−1). All TWP types inhibited biofilm photosynthesis (reduced Chl-a and ФM) and altered the community structure of algae to varying degrees; in addition, the toxicity mechanisms of the TWPs contributed to the accumulation of reactive oxygen species and cell membrane (or cell-wall) fragmentation, leading to lactate dehydrogenase release. S-TWPs were the most toxic because their surface carried the highest environmental persistent free radicals. R-TWPs were the second most toxic, which was attributed to their smaller particle size. The toxicity of all TWPs was tested after sewage incubation aging. The results showed that the toxicity of all TWPs reduced as the sewage covered their surface components and active sites. This process also reduced the differences in toxicity among the TWPs. This study filled a research gap in our understanding of aquatic toxicity caused by the surface structural properties of tire microplastics and has implications for the study of microplastic biotoxicity mechanisms.

Contamination profiles and potential health risks of environmentally persistent free radicals in PM2.5 over typical central Chinese megacity

As one of the most important transportation hubs and industrial bases in China, Zhengzhou has suffered from serious PM2.5 pollution for a long time. However, the investigation of contamination status and possible exposure risks of environmentally persistent free radicals (EPFRs) in PM2.5 from Zhengzhou is rare. In this work, a comprehensive study of pollution levels, seasonal variations, sources, and potential health risks of PM2.5-bound EPFRs in Zhengzhou was conducted for the first time. The atmospheric concentrations of EPFRs in PM2.5 from Zhengzhou ranged from 1.732 × 1012 spin m−3 to 7.182 × 1014 spin m−3 between 2019 and 2020. Relatively serious contamination was noticed in winter and spring. Primary fossil fuel combustion and Fe-mediated secondary formation were apportioned as possible sources of PM2.5-bound EPFRs in Zhengzhou. Moreover, to avert the bias of the toxicity assessment induced by utilization of incompletely extracted EPFRs from sample filter, simulatively generated EPFRs were applied to toxicological evaluations (cell viability and reactive oxygen species assays). Corresponding experimental dosages were based on the estimated adults’ annual exposure amounts of EPFRs in real PM2.5 samples. The results elucidated that EPFRs might cause growth inhibition and oxidative stress of human lung cells, suggesting the possible exposure-induced health concerns for local people in Zhengzhou. This study provides practical information of real contamination status of PM2.5-bound EPFRs in Zhengzhou, which is favorable to local air pollution control and reduction of exposure risks on public health in central China.

Mn-modified biochars for efficient adsorption and degradation of cephalexin: Insight into the enhanced redox reactivity.

Mn-modified biochars (BCs) were developed by pre-treatment of feedstock (MBCs) or post-modification of biochar (BCM), for simultaneous adsorption and degradation of a model pollutant, cephalexin. The apparent removal rates of cephalexin in the presence of MBCs (2.49 - 6.39×10-2 h-1) and BCM (13.3×10-3 h-1) were significantly higher than that in the presence of biochar prepared under similar conditions (4.2×10-3 h-1). While the •OH generated from the activation of dissolved O2 by the persistent free radicals (PFRs) and phenolic -OH on BC could cause degradation of cephalexin, its removal was drastically enhanced through direct oxidation by the MnOx and related Mn species on Mn-modified BCs. The removal of cephalexin by MBCs decreased as the solution pH was raised from 5.0 to 9.0, which supports the critical role played by Mn3O4 in its oxidation. Removal of cephalexin in the presence of MBCs and Mn3O4 was enhanced with the introduction of Mn(II) ions, suggesting that the Mn3O4 present on MBCs facilitates the re-oxidation of Mn(II) to highly reactive Mn(III). While MnO2 anchored on BCM also enhanced the cephalexin oxidation, the active sites of BC and MnO2 were partially destroyed during post-modification of BC, compromising the redox cycling of Mn(II)/Mn(III) and the generation of •OH. As a result, the performance of BCM in oxidizing cephalexin was inferior to that of MBCs. These findings shed new light on the development of environmentally benign sorbents capable of simultaneously adsorbing and oxidizing organic pollutants.

Oxidation 1-methyl naphthalene based on the synergy of environmentally persistent free radicals (EPFRs) and PAHs in particulate matter (PM) surface

Studies of the environmental fate through the interactions of particle-associated polycyclic aromatic hydrocarbons (PAHs) with environmentally persistent free radicals (EPFRs) are presented. The formation of PAHs and EPFRs typically occurs side by side during combustion-processes. The laboratory simulation studies of the model PAH molecule 1-Methylnaphthalene (1-MN) interaction with model EPFRs indicate a transformational synergy between these two pollutants due to mutual and matrix interactions. EPFRs, thorough its redox cycle result in the oxidation of PAHs into oxy-/hydroxy-PAHs. EPFRs have been shown before to produce OH radical during its redox cycle in aqueous media and this study has shown that produced OH radical can transform other PM constituents resulting in alteration of PM chemistry.In model PM, EPFRs driven oxidation process of 1-MN produced 1,4-naphthoquinone, 1-naphthaldehyde, 4-hydroxy-4-methylnaphthalen-1-one, and various isomers of (hydroxymethyl) naphthalene. Differences were observed in oxidation product yields, depending on whether EPFRs and PAHs were cohabiting the same PM or present on separate PM. This effect is attributed to the OH radical concentration gradient as a factor in the oxidation process, further strengthening the hypothesis of EPFRs’ role in the PAH oxidation process.This finding is revealing new environmental role of EPFRs in a natural degradation process of PAHs. Additionally, it points to implications of such PM surface chemistry in the changing mobility of PAHs into an aqueous medium, thus increasing their bioavailability.

Persistent Free Radicals (PFRs) Formed in Pyrolyzed Synthetic CHO-Type Polymers: Novel Raw Material for PFR and Better Understanding for Its Formation

Persistent Free Radicals (PFRs) Formed in Pyrolyzed Synthetic CHO-Type Polymers: Novel Raw Material for PFR and Better Understanding for Its Formation