Spin Trapping Research Articles

Understanding the Photocatalytic Activity of Sodium Hexatitanate Nanoparticles for Pollutants Degradation: A Spectroscopic Insight

Sodium hexatitanate (Na2Ti6O13) nanoparticles have been synthesized by the hydrothermal method with microwave and conventional heating, after which their photocatalytic properties toward an azo dye pollutant degradation have been investigated. Insights into the dynamics and reactivity of the species involved in the photocatalytic mechanism of the (Na2Ti6O13) samples were precisely investigated, for the first time, by X-band electron paramagnetic resonance (EPR) spectroscopy under different experimental conditions. X-ray diffraction structural analysis revealed that all samples crystallized in a monoclinic C2/m structure, with different short-range structural order according to the employed heating, as indicated by Raman. Field-emission scanning electron microscopy and transmission electron microscopy results revealed the formation of rod- and fiber-like nanoparticles with different diameters and lengths. EPR measurements indicated the presence of different Ti3+ point defects and F centers in the samples. X-ray photoelectron spectroscopy analysis proved the presence of oxygen-related defects, but no Ti3+ was detected on the surface. Spin trapping experiments monitored the generation of hydroxyl (OH·) radicals over UV-irradiation time. Various parameters contribute to the photocatalytic activity of the samples; however, the type of defect and particle morphology appeared as key factors for enhanced efficiency. Our study provides significant information about paramagnetic defects in Na2Ti6O13 materials and their role in photocatalysis to design other Ti-based photocatalysts.

Dietary Magnesium Deficiency in Rats Enhances Free Radical Production in Skeletal Muscle

Recent studies suggest that free radicals may be involved in tissue injuries induced by magnesium deficiency. The aim of the present study was to assess the effect of magnesium deficiency on free radical production of skeletal muscle tissue. Male Wistar rats were pair-fed from weaning for 12 d either control or Mg-deficient diets containing 960 or 40 mg magnesium/kg diet, respectively. In the Mg-deficient rats, hypomagnesemia was accompanied by significantly lower magnesium and greater calcium concentrations in skeletal muscle tissue. Electron microscopy of skeletal muscle tissue revealed ultrastructural changes, including swelling mitochondria and disorganization of the sar-coplasmic reticulum network. Using the spin-trapping technique, we showed that significantly more hydroxyl radicals were generated in muscle homogenates of Mg-deficient rats. Moreover, the amount of spin trap adducts was increased in the presence of exogenous iron in both groups. In agreement with these observations, a greater concentration of thiobarbituric acid-reactive substances and a lower concentration of thiol groups were found in skeletal muscle of the Mg-deficient group compared with controls. These results strongly support the hypothesis that free radical-mediated injury could contribute to skeletal muscle lesions resulting from magnesium deficiency.

Construction of hierarchical core-shell Z-scheme heterojunction FeVO4@ZnIn2S4 for boosted photocatalytic degradation of tetracycline

Constructing core-shell heterojunction and designing hierarchical structures have been considered as efficient strategies for enhancing the activity and stability of photocatalysts. Herein, a novel hierarchical core-shell Z-scheme heterojunction FeOV4@ZnIn2S4 was prepared via the in-situ growth of ZnIn2S4 on the surface of FeVO4 submicron bar with a facile solvothermal method. The formation of the hierarchical core-shell heterostructure between FeVO4 and ZnIn2S4 improved light-harvesting ability and promoted the separation of photoinduced electron-hole pairs. The prepared FeOV4@ZnIn2S4 exhibited superior photocatalytic activity toward tetracycline. The removal efficiency of tetracycline reached up to 90.8% within 120 min. The degradation rate were 5.75 and 2.06 times that of FeVO4 and ZnIn2S4, respectively. Furthermore, Z-Scheme charge transfer mechanism at the interface between FeVO4 and ZnIn2S4 was proposed based on the results obtained from radical trapping test and electron spin resonance (ESR), which revealed that •O2−, •OH and h+ all act as active species in photocatalytic reaction. This work can bring a strategy for the preparing highly efficient heterojunction photocatalysts.

Effects of acetate and nitrate ions on radical and intercalation reactions initiated by CuZn hydroxy double salts

The role of hydroxy double salts (HDS) in the effective removal of organic contaminants from water is still controversial among researchers. In this work HDS materials, copper-zinc hydroxy acetate (CuZn-HA), and copper-zinc hydroxy nitrate (CuZn-HN) were produced and treated with aqueous methyl orange (MO), acid red 44 (AR44), or congo red (CR) under ambient conditions. Evidence from dye removal testing, materials analyses, and spin trapping measurements suggested possible three removal processes, dye sorption, intercalation reactions, and ·OH radicals assisted oxidation for suitable matching between dye and HDS material. Such three processes are responsible for the complete color (from the aqueous 500 ppm MO and AR44) and TOC removal achieved by using the CuZn-HN. The structural stability of the dye and HDS chemical composition play a key role on the oxidative reactivity and the intercalation ability of the dye in HDS structure.

A metal-organic framework (MOF) and graphene oxide (GO) based peroxymonosulfate (PMS) activator applied in pollutant removal

Fenton-like reactions based on the peroxymonosulfate (PMS) can efficiently degrade pollutants and have attracted widespread attention. Herein, we reported a facile strategy to synthesize a heterogeneous PMS activator (Zn/Co-MOF@rGO-600) derived from a cobalt-zinc bimetallic metal-organic framework (MOF). The Zn/Co-MOF@rGO-600 was applied as the catalyst for the effective tetracycline (TC) removal during the PMS activation process. The introduction of Zn and the presence of graphene oxide (GO) not only enhanced the yield of the single-atom cobalt (Co0) in the catalyst through the bimetallic synergy but also had a positive effect on adjusting the morphology of the catalyst. The charge transfer resistance (Rct) of Zn/Co-MOF@rGO-600 decreased by 3.15 times after GO modification. The reaction rate constant (k) increased by 14.88 times in the reaction system with Zn/Co-MOF@rGO-600 as PMS activator, the corresponding efficiencies of TC removal and mineralization increased to 91.66 % and 45.04 %, respectively. Density functional theory (DFT) calculation suggested that the bonding energy (Ebon) between PMS and the Zn-Co atom was low enough to − 2.76 eV so that the Zn/Co-MOF@rGO-600 could act as an effective PMS activator. The quenching experiment and the radical spin trap test showed the main generated reactive species were SO4•-, O2•- and 1O2. The presence of SO4•- was the main driving factor for the generation of other radicals such as 1O2 and •OH during the PMS activation process. This research proposes a new reference to fabricate an effective catalyst for PMS activation, which was derived from a bimetallic (Zn/Co) MOFs.

Thermal degradation of thaumatin at low pH and its prevention using alkyl gallates

Thaumatin, a potent sweet tasting protein extracted from the Katemfe Plant, is emerging as a natural alternative to synthetic non-nutritive sweeteners and flavor enhancer. As a food additive, its stability within the food matrix during thermal processing is of great interest to the food industry. When heated under neutral or basic conditions, thaumatin was found to lose its sweetness due to protein aggregation caused by sulfhydryl catalyzed disulfide bond interchange. At lower pH, while thaumatin was also found to lose sweetness after heating, it does so at a slower rate and shows more resistance to sweetness loss. SDS-PAGE indicated that thaumatin fragmented into multiple smaller pieces under heating in acidic pH. Using BEMPO-3, a lipophilic spin trap, we were able to detect the presence of a free-radical within the hydrophobic region of the protein during heating. Protein carbonyl content, a byproduct of protein oxidation, also increased upon heating, providing additional evidence for protein cleavage by a radical pathway. Hexyl gallate successfully inhibited the radical generation as well as protein carbonyl formation of thaumatin during heating.

Photoinduced Ligand-to-Metal Charge Transfer of Cobaltocene: Radical Release and Catalytic Cyclotrimerization.

Irradiation of cobalt metallocenes at the ligand-to-metal charge transfer energies results in the labilization of the cyclopentadienyl-cobalt bond and radical release. The cyclopentadienyl radical is detected by electron paramagnetic resonance (EPR) spectroscopy using a spin trap and can also be chemically trapped using hydrogen-atom-donating reagents. This reaction presents a new photochemical method of generating new cobalt complexes or of forming cyclopentadienyl cobalt(I) species that are active for catalytic [2 + 2 + 2] cyclotrimerization reactions. More importantly, these results also show that cobaltocene should not be considered as a photostable redox reagent under many conditions, including those relevant to photovoltaics or photocatalysis.

Nanoemulsions of Clove Oil Stabilized with Chitosan Oleate—Antioxidant and Wound-Healing Activity

Clove oil (CO) is a powerful antioxidant essential oil (EO) with anti-inflammatory, anesthetic, and anti-infective properties. It can be therefore considered a good candidate for wound-healing applications, especially for chronic or diabetic wounds or burns, where the balance of reactive oxygen species (ROS) production and detoxification is altered. However, EOs require suitable formulations to be efficiently administered in moist wound environments. Chitosan hydrophobically modified by an ionic interaction with oleic acid (chitosan oleate, CSO) was used in the present work to stabilize CO nanoemulsions (NEs). The dimensions of the NE were maintained at around 300 nm as the volume distribution for up to six months, and the CO content did not decrease to under 80% over 4 months, confirming the good stabilizing properties of CSO. The antioxidant properties of the CO NE were evaluated in vitro by a 2,2-diphenil-2-picrylhydrazyl hydrate (DPPH) assay, and in fibroblast cell lines by electron paramagnetic resonance (EPR) using α-phenyl-N-tert-butyl nitrone (PBN) as a spin trap; a protective effect was obtained comparable to that obtained with α-tocopherol treatment. In a murine burn model, the ability of CO formulations to favor macroscopic wound closure was evidenced, and a histological analysis revealed a positive effect of the CO NE on the reparation of the lesion after 18 days. Samples of wounds at 7 days were subjected to a histological analysis and parallel dosage of lipid peroxidation by means of a thiobarbituric acid-reactive substances (TBARS) assay, confirming the antioxidant and anti-inflammatory activity of the CO NE.

Oxidative damage to βL-crystallin in vitro by iron compounds formed in physiological buffers

βL-crystallin aggregation due to oxidative damage in the presence of H2O2 and ferric chloride was studied in-vitro under conditions close to physiological. It was shown that the protein aggregation characterized by the nucleation time and the aggregation rate significantly depended on the composition of the isoosmotic buffers used, and decreased in the series HEPES buffer > Tris buffer > PBS. Ferric chloride at neutral pH was converted into water-insoluble iron hydroxide III (≡FeIIIOH). According to the data of scanning electron microscopy the ≡FeIIIOH particles formed in HEPES buffer, Tris buffer, and PBS practically did not differ in structure. However, the sizes of ≡FeIIIOH floating particles measured by dynamic light scattering differed significantly and were 44 ± 28 nm, 93 ± 66 nm, 433 ± 316 nm (Zaver ± SD) for HEPES buffer, Tris buffer, and PBS, respectively. It was found by the spin trap method that the ability of ≡FeIIIOH to decompose H2O2 with the formation of a •OH decreases in the series HEPES buffer, Tris buffer, and PBS. The authors suggest that the ability to generate •OH during the decomposition of H2O2 is determined by the total surface area of ≡FeIIIOH particles, which significantly depends on the composition of the buffer in which these particles are formed.

Construction of BiOCl/Ti-MOFs type-II heterojunction photocatalyst for enhanced photocatalytic performance for multiple antibiotics removal.

The increased threats to environmental and human health caused by the widespread use of antibiotics have increased the need for efficient technologies for removing antibiotic remnants from wastewater after production. Photocatalysis, which is non-toxic, highly efficient, and low energy consumption, has played a vital role in wastewater treatment among the aforementioned technologies. Therefore, a MIL-125(Ti)/BiOCl type-II heterojunction photocatalyst was fabricated using solvothermal method. Investigations remarkably revealed that the enhanced photocatalytic performance of the photocatalyst for multiple antibiotics degradation (tetracycline and ofloxacin) was attributed to the construction of a heterojunction, which inhibits carrier recombination and enhances visible-light absorption. Furthermore, the radical trapping experiments and electron spin resonance determined superoxide radicals and holes to be the main species in the photocatalytic process. Finally, we presented a potential photocatalytic mechanism that could account for the observations. Overall, this study offered guidelines for developing more photocatalysts with visible-light responses and removing multiple antibiotics from water more efficiently.

Undiscovered Spin Trapping Artifacts in Persulfate Oxidation Processes: Implications for Identification of Hydroxyl or Sulfate Radicals in Water

Electron paramagnetic resonance (EPR) coupled with the spin trapping technique is widely used to identify radicals and has become a tool that is being heavily relied on to probe the reaction mechanism in advanced oxidation processes (AOPs). However, the unexpected spin trapping artifacts in a highly oxidizing environment may mislead the mechanistic interpretations of AOPs. Here, we report previously unrevealed reactions between peroxydisulfate (PDS) and 5,5-dimethyl-1-pyrroline N-oxide (DMPO) or N-tert-butyl-α-phenylnitrone (PBN). The mainly detectable adducts are attributed to DMPO-OH and PBN-OH. Through radical quenching experiments, the nonradical generation pathways of DMPO-OH and PBN-OH are validated, and the 17O incorporation experiment demonstrates that H2O plays a critical role in DMPO-OH production. The formation routes of the primary artifact signals (DMPO-OH, DMPO-SO4, PBN-OH, and PBN-SO4) are further proposed by applying diverse solvents. PDS may directly oxidize DMPO to generate DMPO-SO4 in acetonitrile or acetone solvent, while DMPO-OH is yielded using H2O as the solvent. The generation of PBN-OH or PBN-SO4 follows the inverted spin trapping mechanism (a combination of one-electron oxidation and nucleophilic addition). These findings manifest the necessity of selecting the proper spin traps and performing careful control tests during exploration of the catalytic oxidation mechanism under highly oxidizing conditions.

Multifunctional photocatalyst of graphitic carbon embedded with Fe2O3/Fe3O4 nanocrystals derived from lichen for efficient photodegradation of tetracycline and methyl blue

ABSTRACT We propose a feasible and economical method of constructing biomass-based multifunctional photocatalysts with excellent adsorption performance and high photodegradation abilities toward tetracycline (TC) and methyl blue (MB) under visible light. A series of novel hybrids of porous graphitic carbon embedded with Fe2O3/Fe3O4 nanocrystals (denoted as Fe2O3/Fe3O4@C) were derived from lichen doped with different dosages of Fe3+ by calcination at 700°C under a N2 atmosphere. The Fe2O3/Fe3O4@C hybrids exhibited nanoflake-like shapes, mesoporous structures, and efficient visible light harvesting, thus indicating enhanced adsorption ability and photoactivity toward pollutants. The formed Fe2O3/Fe3O4 heterojunction improved the separation efficiency and inhibited the recombination of photogenerated carriers, whereas the carbon network improved the transfer of photogenerated electrons. Under optimised conditions, the Fe2O3/Fe3O4@C-1 hybrid demonstrated enhanced photodegradation efficiencies of 96.4% for TC and 100% for MB under visible light. In addition, electron spin resonance and trapping measurements were performed to identify active species and determine the photocatalytic mechanism toward pollutants. •O2 − and •OH were the active species involved, playing critical roles in the TC and MB photodegradation processes. In addition, a bacterium test revealed that the products of TC degradation by Fe2O3/Fe3O4@C-1 showed low biological toxicity. This work provides a promising preparation strategy or biomass-based photocatalysts for application in environmental pollutant treatment.

Construction of Bi/Polyoxometalate doped TiO2 composite with efficient visible-light photocatalytic performance: Mechanism insight, degradation pathway and toxicity evaluation

Exploration of visible-light-responsive, efficient and durable photocatalysts is of great concern for removing organic dyes and antibiotics from the wastewater. Herein, a series of mesoporous TiO2-doped with polyoxometalates [H3PMo12O40] (PMo12) and loaded with Bi nanoparticles (NPs) composites were fabricated through a convenient electrospinning/calcination and hydrothermalmethods, which was labelled as × wt% Bi/PMo12 doped TiO2 (abbr. x% Bi/PT, x = 10, 20 and 30, respectively). In these composites, polyoxometalate PMo12 acts as a dopant to reduce the band gap value of TiO2, effectively expanding its visible light absorption and enhance its photocatalytic redox ability. Moreover, the Schottky junction between Bi NPs and PT further promotes the separation efficiency of the photoinduced carriers. Therefore, these as-prepared catalysts demonstrated outstanding and persistent photocatalytic activity for removing tetracycline (TC), enrofloxacin (EFA) and methylorange (MO) with visible-light (λ > 420 nm) illumination. Especially, 20 % Bi/PT specimen presented the optimal catalytic performance, whose degradation efficiencies for TC, EFA and MO reached 86.0 %, 90.9 % and 92.5 % with k = 0.03019, 0.01275 and 0.01199 min−1, respectively. The superoxide radical (⋅O2–), hydroxyl radical (⋅OH) and holes (h+) were proved to be the dominating active species in contaminants degradation through the trapping tests and electron spin resonance (ESR) measurements. Furthermore, the possible TC degradation pathways were established based on the identification of degradation products by high performance liquid chromatography-mass spectrometry (HPLC-MS). The toxicity of intermediates was also assessed through QSAR prediction. According to the energy band structure analysis, the corresponding photocatalytic mechanism was revealed. The current work provides several new insights for the design and preparation of low cost, efficient, stable and versatile photocatalysts.

Vasorelaxant Effect of Moroccan Cannabis sativa Threshing Residues on Rat Mesenteric Arterial Bed is Endothelium and Muscarinic Receptors Dependent.

Ethanolic fraction of Moroccan Cannabis sativa threshing residues (EFCS) was evaluated for its vasorelaxant activity. The current work aims to identify the active metabolites in the ethanolic fraction of the EFCS and illustrate their mechanism of action. Free radical scavenging capacity of EFCS was assessed using DPPH method. The EFCS vasodilation activities in phenylephrine-precontracted isolated rat mesenteric arterial beds were investigated in presence of L-NAME (nitric oxide synthase inhibitor), indomethacin (cyclooxygenase inhibitor), potassium channel blockers (namely tetraetylamonium, barium chloride, and glibenclamide), and atropine. Nitric oxide vascular release was measured by electron paramagnetic resonance (EPR) using a spin trap in rat aortic rings. EFCS induced dose-dependent vasorelaxation on mesenteric vascular bed. Incubation of the preparations with L-NAME, ODQ (a soluble guanylyl cyclase inhibitor), or potassium channel blockers reduced the fall of perfusion pressure caused by EFCS. Endothelial denudation or atropine abolished the EFCS's vasorelaxant effect, suggesting involvement of muscarinic receptors and endothelium-relaxing factors. The extract induced nitric oxide release in aortic rings in a similar manner as acetylcholine suggesting an effect of EFCS on the muscarinic receptor and the conductance arteries. Chemical investigation of EFCS identified potential active components namely apigenin and derivatives of luteolin skeleton and also additional components such as neophytadiene, squalene, and β-sitosterol. In conclusion, the vasorelaxant effect of EFCS on rat mesenteric arterial bed, which is dependent of muscarinic receptor activation, nitric oxide, and EDHF, can account for potential therapeutic use against high blood pressure related cardiovascular diseases.

Radicals from tributyl phosphate decomposition: a combined electron paramagnetic resonance spectroscopic and computational chemistry investigation.

The radiation- and chemically-induced radicals from tributyl phosphate (TBP) have been characterized by EPR spectroscopy and theoretical calculations. The yield of X-ray-generated TBP radicals measured by a PBN spin trap is 0.22 μmol J-1 (2.1 radicals/100 eV) at room temperature (298 K). The EPR spectra obtained by irradiating TBP with an electron beam at 77 K are in close agreement with literature data for samples irradiated with gamma- and X-rays [https://doi.org/10.1007/BF02165504, https://doi.org/10.1016/1359-0197(89)90319-6]. Possible conformers of alkyl-type, TBP-derived radicals were analyzed by Density Functional Theory calculations. The main contribution to the experimental spectrum at 77 K is shown to be made by a conformer of the CH3˙CHCH2-radical, which contains all carbon atoms of the butyl group in the same plane. The EPR spectra of TBP radicals induced by the OH radical in aqueous solution were measured for the first time using a continuous flow system. The formation of the alkyl-type TBP radicals CH3˙CHCH2-, ˙CH2CH2-, and -CH2˙CHO- in the ratio of 5/4/1 was detected; their spectral assignment was based on quantum chemical calculations with rotational averaging of HFC constants for the corresponding beta- and alpha-protons.

Low-temperature persulfate activation by powdered activated carbon for simultaneous destruction of perfluorinated carboxylic acids and 1,4-dioxane.

Carbonaceous materials have emerged as a method of persulfate activation for remediation. In this study, persulfate activation using powdered activated carbon (PAC) was demonstrated at temperatures relevant to groundwater (5-25°C). At room temperature, increasing doses of PAC (1-20gL-1) led to increased persulfate activation (3.06×10-6s-1 to 2.10×10-4 with 1 and 20gL-1 PAC). Activation slowed at lower temperatures (5 and 11°C); however, substantial (>70 %) persulfate activation was achieved. PAC characterization showed that persulfate is activated at the surface of the PAC, as indicated by an increase in the PAC C:O ratio. Similarly, electron paramagnetic resonance (EPR) spectroscopy studies with a spin trapping agents (5,5-dimethyl-1-pyrroline N-oxide (DMPO)) and 2,2,6,6-tetramethylpiperidine (TEMP) revealed that singlet oxygen was not the main oxidizing species in the reaction. DMPO was oxidized to form 5,5-dimethylpyrrolidone-2(2)-oxyl-(1) (DMPOX), which forms in the presence of strong oxidizers, such as sulfate radicals. The persulfate/PAC system is demonstrated to simultaneously degrade both perfluorooctanoic acid (PFOA) and 1,4-dioxane at room temperature and 11°C. With a 20gL-1 PAC and 75mM persulfate, 80 % and 70 % of the PFOA and 1,4-dioxane, respectively, degraded within 6h at room temperature. At 11°C, the same PAC and persulfate doses led to 57% dioxane degradation and 54 % PFOA degradation within 6h. Coupling PAC with persulfate offers an effective, low-cost treatment for simultaneous destruction of 1,4-dioxane and PFOA.

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.

Spin Trapping Analysis of Radical Intermediates on the Thermo-Oxidative Degradation of Polypropylene.

The purpose of this study is to investigate the thermo-oxidative degradation behavior of polypropylene (PP) by comparing three types of pristine PP granules (consisting of homopolymer, random copolymer, and block copolymer) with their corresponding oxidized analogues. These analogues were intensely oxidized under oxygen at 90 °C for 1000 h by using the electron spin resonance (ESR) spin trapping method that can detect short-lived radical intermediates during the degradation. The degrees of oxidation could be evaluated by chemiluminescence (CL) intensity, which was related to the concentration of hydroperoxide groups generated in the PP chain. In the pristine PP samples, a small amount of hydroperoxides were found to be formed unintentionally, and their homolysis produces alkoxy radicals, RO•, which then undergo β-scission to yield chain-end aldehydes or chain-end ketones. These oxidation products continue to take part in homolysis to produce their respective carbonyl and carbon radicals. On the other hand, in the oxidized PP granules, because of their much higher hydroperoxide concentration, the two-stage cage reaction and the bimolecular decomposition of hydroperoxides are energetically favorable. Carbonyl compounds are formed in both reactions, which are then homolyzed to form the carbonyl radical species, •C(O)-. PP homopolymer produced the largest amount of carbonyl radical spin adduct; thus, it was found that the homopolymer is most sensitive to oxygen attack, and the presence of ethylene units in copolymers enhances the oxidation resistance of PP copolymers.

Integrated adsorption and photodegradation of tetracycline by bismuth oxycarbonate/biochar nanocomposites

Adsorption and photodegradation are two widely studied wastewater treatment technologies. In this work, we have firstly prepared the bismuth oxycarbonate (Bi2O2CO3) and biochar nanocomposites for synergistic adsorption-photodegradation of tetracycline (TC). It was found that Bi2O2CO3 and biochar composites exhibited stronger adsorption capacity and photocatalytic activity compared to Bi2O2CO3. Among them, Bi2O2CO3/2.5 wt% biochar possessed the highest adsorption capacity for TC (173.0 mg/L) and the best combined removal rate of TC (84.7 %) in 60 min by adsorption and photodegradation, which were 1.9 times and 1.5 times that of Bi2O2CO3, respectively. The biochar in the composite increased the specific surface area, promoted the adsorption of TC, facilitated charge transfer capability, thereby enhanced the photocatalytic activity of composites. The effects of experimental parameters (temperature, co-existing ions, and initial pH) on TC degradation were examined. Electron spin resonance (ESR) and trapping experiments of free radical confirmed that 1O2, •O2− and h+ were the main species in photocatalytic degradation. The potential degradation pathways were proposed based on liquid chromatograph mass spectrometer (LC-MS) test of the intermediates of TC degradation. It is hoped that this work not only represents the significantly importance of biochar in photocatalytic wastewater treatment, but also promotes further interests in design synergistic adsorption-photodegradation materials.

Effect of substituents on 1,3,5-triphenylpyrazoline as light-emitting diode-sensitive initiators in photopolymerization

By introducing different substituents at the N1 position, a series of 1,3,5-triphenylpyrazolines were designed and synthesized as photoinitiators (PIs) for cationic and free radical photopolymerization processes. As evaluated through ultraviolet–visible (UV–vis) spectroscopy, fluorescence spectroscopy, theoretical calculations, electrochemistry, and electron spin resonance–spin trapping tests, all PIs show good photoinitiating properties under light-emitting diode (LED) irradiation at 365–425 nm. Their light absorption within the UV–vis range (λmax = 352–390 nm; εmax = 26 000–40 700 M−1 cm−1) is strongly influenced by the substituents on the N1 phenyl ring. Remarkably, the introduction of the carbonyl group redshifts the maximum absorption spectra from 375 nm to 390 nm, which could well match the emission of LEDs in the range of 365–425 nm. The pyrazolines, together with iodonium salt and N-methyldiethanolamine, can generate acid and free radicals under LED irradiation and conduct high-performance LED-induced cationic and free radical photopolymerization processes under 365–425 nm irradiation. Cationic polymerization is enhanced by the introduction of an electron-pushing group, and free radical polymerization is promoted by the introduction of a carbonyl group at the N1 position. These pyrazoline-based photoinitiating systems have promising applications in LED-induced photopolymerization.