Electron Paramagnetic Resonance Spin Trapping Research Articles

New visible-light-driven Bi2MoO6/Cs3Sb2Br9 heterostructure for selective photocatalytic oxidation of toluene to benzaldehyde

Herein, new Bi2MoO6/Cs3Sb2Br9 heterostructure (BiMo/CSB) was investigated for the first time as a visible-light-driven photocatalyst for C(sp3)–H bond activation using molecular oxygen as a green oxidant and toluene as a model substrate. The optimized BiMo/CSB photocatalyst exhibited enhanced toluene oxidation activity (2,346 μmol g-1h−1), which was almost two- and five-fold that of pristine CSB (1,165 μmol g-1h−1) and BiMo (482 μmol g-1h−1), respectively. The improved photocatalytic performance was essentially attributed to the formation of staggered band energy lineup in the BiMo/CSB hybrid, which promoted S-scheme charge transfer across the BiMo/CSB heterointerface as supported by ultraviolet photoelectron spectroscopy (UPS), density functional theoretical (DFT), time-resolve photoluminescence (TRPL), and photoelectrochemical studies. Spin–trapping electron paramagnetic resonance (EPR) and radical scavenging studies revealed that photoinduced hole, molecular oxygen, and superoxide radical are key active species in this photocatalytic system. The developed BiMo/CSB catalyst provided good selectivity toward benzaldehyde product (94–98 %), presumably due to the inhibiting effect of benzyl alcohol on benzaldehyde oxidation. No significant change in structure and morphology was observed for the spent catalyst, however small negative shift of Sb 3d and Bi 4f binding energy was found suggesting partial reduction of Sb3+ and Bi3+. This work not only provides a new visible-light-driven photocatalyst for C(sp3)–H bond activation but also opens the doors for exploitation of the conversion and functionalization of this inert bond toward the production of high value-added organic chemicals.

Triggering “signal-on” photoelectrochemical responses by heterojunction transition for selective detection of copper(II) based on Pd/MoS2@g-C3N4 nanocomposites

Controlling the concentration of copper(II) in aquatic systems is of importance for human health. Numerous traditional technologies to detect Cu2+ may encounter with limitations, such as high signal background and complicated operation. Herein, a highly selective photoelectrochemical (PEC) sensor is proposed for the “signal-on” detection of Cu2+ employing g-C3N4 nanosheets with MoS2 and Pd quantum dots deposited (Pd/MoS2@g-C3N4). Pd/MoS2@g-C3N4 could present the enhanced photocurrents of specific responses to Cu2+ under light irradiation. MoS2 quantum dots on the sensor are agglomerated into MoS2 bulk during sensing Cu2+, forming an efficient Z-scheme heterojunction. The heterojunction transition induced photoelectrons transferring from the bulk MoS2 to g-C3N4, resulting in “signal-on” PEC responses. Such Z-scheme heterojunction has conquered the traditional heterojunction towards “signal-on” mechanism, that was further verified by band structure measurements and DMPO spin trapping ESR analysis. Photocurrent intensities increased gradually with the addition of incremental Cu2+ concentrations, achieving a detection limit of 0.21 μM and a broad linear interval range from 1 μM to 1 mM with high selectivity and stability. This work may open a new door towards the in situ construction of g–C3N4–based Z-scheme heterojunctions for the signal-on PEC sensing platform, providing wide applications in environmental monitoring and food safety.

The photoinitiator of bifunctional α-hydroxy ketone with long-wavelength in photopolymerization under UV-LEDs

α-hydroxy ketone photoinitiators have been widely used in the photopolymerization industry, such as coating, ink and adhesive, for they have high initiating activity, good thermal stability, and yellowing resistance. However, few works have been reported in developing α-hydroxy ketone photoinitiators that match the absorption of long wavelength LEDs. In this work, a new bifunctional α-hydroxy ketone photoinitiator, (1,4-phenylene) bis (4-hydroxy-4-methylpent-1-en-3-one) (B-HMP), was synthesized and characterized. B-HMP exhibited excellent absorption among the wavelength of 300– 400 nm due to the introduction of unsaturated double bonds which could be employed to match 365/405 nm LEDs. From the results of electron spin resonance spin-trapping (EPR-ST) and steady-state photolysis investigations, the mechanism of the generation of radicals of B-HMP may be via not only the cleavage of CC bonds, but also intermolecular hydrogen abstraction. The efficiency of photopolymerization of B-HMP and triethanolamine (TEOA) was better than those of B-HMP alone because of the synergistic effect. Furthermore, the B-HMP/TEOA had a significantly yellowing resistance property.

Peroxymonocarbonate activation via Co nanoparticles confined in metal-organic frameworks for efficient antibiotic degradation in different actual water matrices.

Traditional advanced oxidation processes suffer from low availability of ultrashort lifetime radicals and declining stability of catalysts. Co nanoparticles in hollow bimetallic metal-organic frameworks (Co@MOFs) were synthesized via a solvothermal method. Nanoconfinement and peroxymonocarbonate (PMC) degradation system endows Co@MOFs with high catalytic activity and stability even in the actual water matrices. The nanocomposites exhibited 100-200nm polyhedron structure with irregular nanocavity between the 20nm shell and multicores. Co nanoparticles were completely encapsulated by the FeIII-MOF-5 shell according to the X-ray diffraction and photoelectron spectra. Both 0.8nm micropores and 3.6nm mesopores were proven to be present. The yolk-shell Co@MOFs exhibited higher catalytic performance than that of Co nanoparticles, hollow FeIII-MOF-5 and its core-shell counterpart toward PMC activation during sulfamethoxazole degradation. The catalytic activities of Co@MOFs for the activation of unsymmetrical peroxides (PMC and peroxymonosulfate) were much higher than those for the symmetrical peroxides (H2O2 and persulfate) and the heterogeneous catalysis was dominant in the Co@MOFs activated H2O2 and PMC systems. The MOF stability was the highest and metal leakages were the least in the activated PMC system among the four peroxides because of mild reaction conditions and the alkalescent solution (pH=8.3-8.4). Furthermore, the high removal efficiencies (>94%) and degradation rates could be maintained in the different actual water matrices due to the confinement effects. The contributions of carbonate and hydroxyl radicals were primary for sulfamethoxazole degradation, and superoxide anion and singlet oxygen also played essential roles according to scavenging experiments and time-series spin-trapping electron spin resonance spectra. Six degradation pathways were proposed according to 26 intermediate identification and the pharmacophores of more than 80% intermediates were destroyed, which would benefit subsequent biological treatment. Successful combination of nanoconfinement and PMC might provide a new effective solution for pollution remediation.

Complexation of AAPH (2,2′-azobis(2-methylpropionamidine) dihydrochloride) with cucurbit[7]uril enhances the yield of AAPH-derived radicals

AAPH (2,2′-azobis(2-methylpropionamidine) dihydrochloride), a water-soluble azo compound is widely employed to produce peroxyl radicals for chemical and biological studies. This compound is shown herein to form a stable inclusion complex with cucurbit[7]uril (CB7), a well-established supramolecular host. Competitive binding assays using berberine dye, isothermal titration calorimetry (ITC), and nuclear magnetic resonance (1H NMR) experiments, provided evidence for the inclusion of AAPH inside the CB7 cavity with a binding constant of 2.51 ± 0.76 × 105 M−1 (determined by ITC). Computational analysis at B3LYP-D3BJ/6-311G(d,p) of the complex (AAPH@CB7) showed interactions of the positively-charged amino groups of AAPH with carbonyl functions at the CB7 entrances. Photolysis of AAPH@CB7 by illumination at 365 nm, gave a higher yield of carbon-centered radicals when compared to the absence of CB7, as evidenced by electron paramagnetic resonance spin trapping using α-phenyl-N-t-butylnitrone. Enhanced radical formation was corroborated by increased consumption of pyrogallol red, free Trp and Trp-containing peptides when these were exposed to AAPH@CB7 in the presence of light. The increased yield of radicals generated by AAPH@CB7 is believed to arise from a pull effect of CB7 portals on initial AAPH-derived carbon-centered radicals generated by photolysis. It is proposed that these radicals are exposed and released to the bulk solution and react with O2 to give peroxyl radicals. These results suggest that the AAPH@CB7 complex can be used to generate high yields of peroxyl radicals for their use in studying these species in material, environmental and biomedical sciences amongst others.

Systematical comparison of antibiotic degradation in the activated peroxymonocarbonate and Fenton systems: Kinetics, matrix influence, mechanisms and intermediate toxicities

The degradation of representative antibiotics and their mechanisms in the activated peroxymonocarbonate (PMC) and Fenton systems were systematically investigated and compared in this work. The PMC can exist and be reliable at high ratios for 1 h according to the 13C nuclear magnetic resonance spectra. The activated PMC system was proven to be more efficient than the Fenton system for the degradation of sulfamethoxazole, ciprofloxacin and ceftriaxone under same experiment conditions. The activated PMC system exhibited higher sulfamethoxazole removal performance in different actual water matrices due to the insignificant effect of coexisting substances, while the impurities had an adverse impact on the Fenton system. The pH of the activated PMC system was relatively stable and ranged from 7.8 to 8.2, while the pH of the Fenton system dropped from 5.2 to 4.1. The slight decreases of sulfamethoxazole removal efficiencies were observed after bubbling O2, N2 and CO2 in the Fenton system, while removal rates in the activated PMC system were greatly prohibited and the inhibition ratios increased with gas solubility. The selective 1O2 and CO3− played primary roles in the activated PMC system according to scavenging experiments and time-series spin-trapping electron spin resonance spectra, which resulted in higher removal efficiencies and lower oxidation degree. The non-selective OH contribution was dominant in the Fenton system. The activated PMC system was more suitable for subsequent biological treatment and friendlier to the ecosystem than the Fenton system according to intermediate pharmacophore removal and toxicity comparisons. The activated PMC system showed apparent advantages over the Fenton system in most cases, which might encourage more researchers to devote their interest and time on this promising degradation system.

Molecular mechanism for the activation of the potent hepatotoxin acetylhydrazine: Identification of the initial N-centered radical and the secondary C-centered radical intermediates.

Acetylhydrazine (AcHZ), a major human metabolite of the widely-used anti-tuberculosis drug isoniazid (INH), was considered to be responsible for its serious hepatotoxicity and potentially fatal liver injury. It has been proposed that reactive radical species produced from further metabolic activation of AcHZ might be responsible for its hepatotoxicity. However, the exact nature of such radical species remains not clear. Through complementary applications of ESR spin-trapping and HPLC/MS methods, here we show that the initial N-centered radical intermediate can be detected and identified from AcHZ activated by transition metal ions (Mn(III)Acetate and Mn(III) pyrophosphate) and myeloperoxidase. The exact location of the radical was found to be at the distal-nitrogen of the hydrazine group by 15N-isotope-labeling techniques via using 15N-labeled AcHZ we synthesized. Additionally, the secondary C-centered radical was identified unequivocally as the reactive acetyl radical by complementary applications of ESR spin-trapping and persistent radical TEMPO trapping coupled with HPLC/MS analysis. This study represents the first detection and unequivocal identification of the initial N-centered radical and its exact location, as well as the reactive secondary acetyl radical. These findings should provide new perspectives on the molecular mechanism of AcHZ activation, which may have potential biomedical and toxicological significance for future research on the mechanism of INH-induced hepatotoxicity.

Unveiling singlet oxygen spin trapping in catalytic oxidation processes using in situ kinetic EPR analysis

Singlet oxygen (1O2) plays a pivotal role in numerous catalytic oxidation processes utilized in water purification and chemical synthesis. The spin-trapping method based on electron paramagnetic resonance (EPR) analysis is commonly employed for 1O2 detection. However, it is often limited to time-independent acquisition. Recent studies have raised questions about the reliability of the 1O2 trapper, 2,2,6,6-tetramethylpiperidine (TEMP), in various systems. In this study, we introduce a comprehensive, kinetic examination to monitor the spin-trapping process in EPR analysis. The EPR intensity of the trapping product was used as a quantitative measurement to evaluate the concentration of 1O2 in aqueous systems. This in situ kinetic study was successfully applied to a classical photocatalytic system with exceptional accuracy. Furthermore, we demonstrated the feasibility of our approach in more intricate 1O2-driven catalytic oxidation processes for water decontamination and elucidated the molecular mechanism of direct TEMP oxidation. This method can avoid the false-positive results associated with the conventional 2D 1O2 detection techniques, and provide insights into the reaction mechanisms in 1O2-dominated catalytic oxidation processes. This work underscores the necessity of kinetic studies for spin-trapping EPR analysis, presenting an avenue for a comprehensive exploration of the mechanisms governing catalytic oxidation processes.

Oxidative stability and oxygen permeability of oil-loaded capsules produced by spray-drying or electrospraying measured by electron spin resonance

The oxidative stability and the oxygen permeability of oil-loaded capsules were investigated by Electron Spin Resonance (ESR). The capsules were produced by spray-drying or electrospraying in the monoaxial or coaxial configuration using glucose syrup as the encapsulating agent. ESR-spin trapping results showed that electrosprayed capsules oxidized faster and during the early stages of incubation, irrespective of the emitter configuration (monoaxial or coaxial), when compared to those produced by spray-drying. Furthermore, ESR oximetry showed that oxygen inside the spray-dried capsules reached equilibrium with the surrounding atmosphere significantly slower than the monoaxially electrosprayed capsules (i.e., ∼2h and ∼10 min, respectively). These findings have been attributed to the larger particle size of the spray-dried capsules influencing the oxygen diffusion area (i.e., lower surface-to-volume ratio) and diffusion path (i.e., thicker encapsulating wall for a fixed oil load). Together, the lower oxygen uptake reported for the spray-dried capsules correlated well with their higher oxidative stability.

Efficient removal of organic pollution via photocatalytic degradation over a TiO2@HKUST-1 yolk-shell nanoreactor

Currently, the design and development of yolk-shell nanoreactors for photocatalytic organic pollution removal have received increasing attention because of their unique architecture. In this work, we developed a novel TiO2@HKUST-1 yolk-shell nanoreactor for the removal of tetracycline (TC) and rhodamine B (RhB) under visible light radiation with clearly increased photocatalytic activity and stability. The degradation efficiency of RhB and TC over the TiO2@HKUST-1 composite was significantly higher than that of pure TiO2 and HKUST-1. Within 60 min, the RhB and TC elimination rates reached 95.2% and 92.40%, respectively when exposed to visible light radiation. After the fifth cycle, the photocatalytic TC degradation efficiency by TiO2@HKUST-1 remained at 89.02%. In TiO2@HKUST-1, a yolk-shell nanoreactor structure with intimate interfacial contact significantly increased the carrier density, specified surface area, and separation effect of photogenerated electron-hole pairs, all of which were highly helpful for enhancing the photocatalytic performance. Additionally, by using electron spin resonance (ESR) spin-trap technology, density function theory (DFT) calculations, positive species trapping studies, and other methods, a potential photocatalytic degradation mechanism was proposed. It was discovered that h+ and •OH were the main active species. In view of its excellent gas properties, TiO2@HKUST-1 was used as an adsorbent for Rh B solution. The effect of mixing time and different initial mass concentration on the adsorption effect was investigated, and the adsorption isotherm and kinetic equation were fitted to the experimental results. This work's successful augmentation can effectively remove organic contaminants and has a wide range of potential environmental applications.

Direct observation of the thermo-oxidative degradation of PA66 by spin-trapping ESR analysis

We succeeded in detecting the radical intermediates produced during the thermo-oxidative degradation of polyamide 66 (PA66) in air between 80°C to 240°C, the temperature range for practical applications, using spin-trapping electron spin resonance (ST-ESR) even in the presence of oxygen, which interferes with ESR measurements. As a result, ST-ESR analysis has newly revealed the presence of two more radical intermediates, −•CH−NH− and •(C=O)NH−, under air in addition to the two radical intermediates, •CH2− and −CH2−•CH−CH2−, already found in the previous report, which was examined under oxygen-free conditions. The formation of those four radicals can be explained by hydrogen abstraction and β-scission in the autoxidation mechanism. The onset temperature of the rapid oxidation reaction observed in chemiluminescence (CL) measurement coincides with the one for generating the −•CH−NH− radical, indicating that the initial radical of thermo-oxidative degradation of PA66 is −•CH−NH− radical generated by selective oxygen attack on the NH-adjacent methylene group. This finding strongly supports previous reports that concluded hydrogen abstraction from the NH-adjacent methylene group is the main reaction under air.

Photoreactivity and phototoxicity of experimentally photodegraded hair melanosomes from individuals of different skin phototypes.

Even though melanin is commonly viewed as natural photoprotectant, the pigment demonstrates residual photoreactivity, which under certain conditions could contribute to UVA-dependent melanomagenesis. Skin melanin is constantly exposed to external stressors, including solar radiation, which could induce photodegradation of the pigment. Although photodegradation of melanin pigments was studied in synthetic models and RPE melanosomes, photochemical and photobiological effects of experimental photodegradation of human skin melanin of different chemical composition remain unknown. In this work, melanosomes isolated from hair of individuals of different skin phototypes (I-III, V) were exposed to high-intensity violet light and its impact on physical and chemical properties of the pigments were analyzed using electron paramagnetic resonance (EPR), spectrophotometry and dynamic light scattering (DLS). Photoreactivity of photodegraded melanins was examined by EPR oximetry, EPR spin-trapping and time-resolved singlet oxygen phosphorescence. Antioxidant potential of the pigments was measured using the EPR DPPH assay. Cellular effect of the exposure of melanosome-loaded HaCaT cells to UV-Vis light was determined by MTT assay, JC-10 assay, and iodometric assay. The data revealed that experimental photodegradation increased photoreactivity of natural melanins, while decreasing their antioxidant capacity. Photodegraded melanin was responsible for higher cell death, a decrease in mitochondrial membrane potential and elevated levels of lipid hydroperoxides.

A Physicochemical Study of the Antioxidant Activity of Corn Silk Extracts.

Corn silk (CS) extracts are reported to contain flavonoids (appx. 59.65 mg quercetin/g), polysaccharides (appx. 58.75 w.%), steroids (appx. 38.3 × 10-3 to 368.9 × 10-3 mg/mL), polyphenols (appx. 77.89 mg/GAE/g) and other functional biological substances. This study investigated the antioxidant activity of corn silk extracts related to their functional compounds. The radical scavenging effect of corn silk extracts was evaluated by the spin-trapping electron paramagnetic resonance (EPR) technique, 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulfonate) (ABTS•+) free radical measurement, ferric ion-reducing antioxidant power, and copper ion reductive capacity. It was found that the maturity stage of CS plant materials and the applied extraction procedure of their bioactive compounds have a profound effect on the radical scavenging capacity. Differences in the antioxidant activity of the studied corn silk samples based on their maturity were also confirmed. The strongest DPPH radical scavenging effect was observed for the corn silk mature stage (CS-M)stage (CS-MS) (65.20 ± 0.90)%, followed by the silky stage (CS-S) (59.33 ± 0.61)% and the milky stage (CS-M) (59.20 ± 0.92)%, respectively. In general, the final maturity stage (CS-MS) provided the most potent antioxidant effect, followed by the earliest maturity stage (CS-S) and the second maturity stage (CS-M).

An unprecedented free radical mechanism for the formation of DNA adducts by the carcinogenic N-sulfonated metabolite of aristolochic acids

The carcinogenicity of aristolochic acids (AAs) has been attributed mainly to the formation of stable DNA-aristolactam (DNA-AL) adducts by its reactive N-sulfonated metabolite N-sulfonatooxyaristolactam (N–OSO3--AL). The most accepted mechanism for such DNA-AL adduct formation is via the postulated but never unequivocally-confirmed aristolactam nitrenium ion. Here we found that both sulfate radical and two ALI-derived radicals (N-centered and C-centered spin isomers) were produced by N–OSO3--ALI, which were detected and unequivocally identified by complementary applications of ESR spin-trapping, HPLC-MS coupled with deuterium-exchange methods. Both the formation of the three radical species and DNA-ALI adducts can be significantly inhibited (up to 90%) by several well-known antioxidants, typical radical scavengers, and spin-trapping agents. Taken together, we propose that N–OSO3--ALI decomposes mainly via a new N–O bond homolysis rather than the previously proposed heterolysis pathway, yielding reactive sulfate and ALI-derived radicals, which are together and in concert responsible for forming DNA-ALI adducts. This study presents strong and direct evidence for the production of free radical intermediates during N–OSO3--ALI decomposition, providing an unprecedented free radical perspective and conceptual breakthrough, which can better explain and understand the molecular mechanism for the formation of DNA-AA adducts, the carcinogenicity of AAs and their potential prevention.

Unveiling the Mechanism of Photodamage to Sphingolipid Molecules via Laser Flash Photolysis and EPR.

Sphingolipids are involved in the maintenance of the skin barrier function and regulate cellular processes of keratinocytes. The work reported here is designed to uncover details of the mechanism of damage to such lipids by UV radiation. Our approach employs laser flash photolysis and electron paramagnetic resonance (EPR) spectrometry to explore the mechanism of the decay reactions, and to determine the associated kinetic parameters. To interpret our experiments, we computed both excitation energies and EPR parameters of radicals formed during photolysis. Employing the spin-trap EPR method confirmed the formation of both carbon- and nitrogen-centered radicals. Thus, we can conclude that the photodecomposition of sphingolipids and their analogues proceeds by Norrish type I reactions with the formation of both nitrogen-centered and alkyl radicals.

Carbon Quantum Dots Accelerating Surface Charge Transfer of 3D PbBiO2I Microspheres with Enhanced Broad Spectrum Photocatalytic Activity-Development and Mechanism Insight.

The development of a highly efficient, visible-light responsive catalyst for environment purification has been a long-standing exploit, with obstacles to overcome, including inefficient capture of near-infrared photons, undesirable recombination of photo-generated carriers, and insufficient accessible reaction sites. Hence, novel carbon quantum dots (CQDs) modified PbBiO2I photocatalyst were synthesized for the first time through an in-situ ionic liquid-induced method. The bridging function of 1-butyl-3-methylimidazolium iodide ([Bmim]I) guarantees the even dispersion of CQDs around PbBiO2I surface, for synchronically overcoming the above drawbacks and markedly promoting the degradation efficiency of organic contaminants: (i) CQDs decoration harness solar photons in the near-infrared region; (ii) particular delocalized conjugated construction of CQDs strength via the utilization of photo-induced carriers; (iii) π-π interactions increase the contact between catalyst and organic molecules. Benefiting from these distinguished features, the optimized CQDs/PbBiO2I nanocomposite displays significantly enhanced photocatalytic performance towards the elimination of rhodamine B and ciprofloxacin under visible/near-infrared light irradiation. The spin-trapping ESR analysis demonstrates that CQDs modification can boost the concentration of reactive oxygen species (O2•-). Combined with radicals trapping tests, valence-band spectra, and Mott-Schottky results, a possible photocatalytic mechanism is proposed. This work establishes a significant milestone in constructing CQDs-modified, bismuth-based catalysts for solar energy conversion applications.

Fabrication of 2D/1D Bi2WO6/C3N5 heterojunctions for efficient antibiotics removal

Photocatalysis is a hopeful way to treat antibiotics-containing wastewater, but its practical application is impeded by the lack of high-performance photocatalysts for now. In the present work, a 2D/1D Bi 2 WO 6 /C 3 N 5 heterojunction photocatalyst was fabricated through a hydrothermal route, and applied to the photocatalytic degradation of tetracycline hydrochloride (TCH). The Bi 2 WO 6 /C 3 N 5 nanocomposites showed superior catalytic activity, compared with a single counterpart. The apparent TCH degradation kinetic constant achieved by the optimized Bi 2 WO 6 /C 3 N 5 nanocomposite was 7.7 times that achieved by Bi 2 WO 6 and 262 times that achieved by C 3 N 5 . Moreover, the influences of the dosage of Bi 2 WO 6 /C 3 N 5 , the initial concentration and pH of TCH solution, and the presence of anions on the photocatalytic TCH degradation were investigated. In addition, the TCH degradation pathway was studied. The collaborative results of X-ray photoelectron spectra, band structure determination, active species capturing experiments, and spin-trapping electron paramagnetic resonance spectra revealed a direct Z -scheme photocatalytic mechanism of Bi 2 WO 6 /C 3 N 5 . • 2D/1D Bi 2 WO 6 /C 3 N 5 heterostructures were successfully fabricated for the first time. • The apparent kinetic constant of the optimized sample was greatly enhanced as compared to a single component. • Factors affecting the tetracycline hydrochloride photodegradation were investigated. • The separation of the photoinduced charge carriers was efficiently promoted. • A possible direct Z-scheme photocatalytic mechanism was proposed.

Ionic liquid-induced construction of 0D/3D carbon quantum dots modified PbBiO2Cl/PbBiO2Br microspheres: Boosting molecular oxygen activation for efficient antibiotics degradation

Developing highly efficient heterostructured photocatalysts for contaminants removal has long been studied, which is mainly limited by ineffective capture of visible-light photon, undesirable recombination of photoinduced hole-electron pairs, and insufficient consumption of charge carriers during surface catalytic reactions. Herein, carbon quantum dots (CQDs) modified PbBiO2Cl/PbBiO2Br nanocomposite photocatalyst have been firstly developed through in-situ ionic liquids induced synthesis. The bridge function of ionic liquids guarantees the symmetrical disperse of CQDs around PbBiO2Cl/PbBiO2Br microspheres, for synchronically overcoming the above drawbacks and markedly promoting antibiotics degradation efficiency: (i) CQDs modification harness solar photons from visible to near-infrared region; (ii) tight coupling of PbBiO2Cl and PbBiO2Br endows the heterojunction with enhanced separation efficiency of charge carriers; (iii) particular delocalized conjugated construction of CQDs strength the enrichment and utilization of photogenerated electrons. Benefiting from these distinguished features, the optimized CQDs/PbBiO2Cl/PbBiO2Br nanocomposite displays obviously enhanced photocatalytic activity towards the elimination of ciprofloxacin and tetracycline under visible light irradiation. The spin-trapping ESR spectra and radicals trapping tests demonstrate that superoxide radicals, hydroxyl radicals and holes are the major active species participated in the purification of antibiotics and the conceivable photocatalytic mechanism has been promoted. This research provides new insights into the development of CQDs modified heterostructured photocatalyst for solar energy conversion applications.

Spin-Trapping Analysis of the Thermal Degradation Reaction of Polyamide 66.

The radical mechanisms of the thermal degradation of polyamide 66 (PA66) occurring under a vacuum at a temperature range between 80 °C and 240 °C (which includes the temperature of practical applications) were investigated using a spin-trapping electron spin resonance (ST-ESR) technique, as well as FTIR, TG-DTA, and GPC methods. No significant weight loss and no sign of thermal degradation are observed at this temperature range under oxygen-free conditions, but a slight production of secondary amine groups is confirmed by FTIR. GPC analysis shows a small degradation by the main chain scission. ST-ESR analysis reveals two intermediate radicals which are produced in the thermal degradation of PA66: (a) a ●CH2- radical generated by main chain scission and (b) a -●CH- radical generated by hydrogen abstraction from the methylene group of the main chain. The ST-ESR result does not directly confirm that a -NH-●CH- radical is produced, although this reaction has been previously inferred as the initiation reaction of the thermal degradation of PA; however, the presence of -●CH- radicals strongly suggests the occurrence of this initiation reaction, which takes place on the α-carbon next to the NH group. The ST-ESR analysis reveals very small levels of reaction, which cannot be observed by common analytical methods such as FTIR and NMR.

Benzo[A]Pyrene and Benzo[E]Pyrene: Photoreactivity and Phototoxicity toward Human Keratinocytes.

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds derived mostly from the incomplete combustion of fossil fuels and biomass. Human skin can absorb PAHs and the uptake increases with their molar mass and lipophilicity. Benzopyrene is high molecular weight PAH frequently appearing in ambient pollution. It exists in two isomeric forms: benzo[a]pyrene (BaP) and benzo[e]pyrene (BeP), which exhibit different biological activity. Although certain properties of benzopyrenes suggested photoreactivity of the compounds, no direct measurements were previously conducted to characterize their photochemical activity. In this study, quantum yield and action spectra of singlet oxygen photogeneration by BaP and BeP were measured by time-resolved near-infrared phosphorescence, and the ability of both compounds to photogenerate superoxide anion was assessed by electron paramagnetic resonance (EPR) spin-trapping. The measurements revealed high efficiency of benzopyrenes to photogenerate singlet oxygen and their ability to photogenerate superoxide anion. Using HaCaT cells as single-layer skin model, we demonstrated concentration-dependent and light-dependent cytotoxicity of BaP and BeP. The compounds induced damage to the cell mitochondria and elevated the levels of intracellular reactive oxygen species.