Free Radical Reactions Research Articles

Cobalt Encapsulated in Nitrogen-Doped Graphite-like Shells as Efficient Catalyst for Selective Oxidation of Arylalkanes.

Selective oxidation of ethylbenzene to acetophenne is an important process in both organic synthesis and fine chemicals diligence. The cobalt-based catalysts combined with nitrogen-doped carbon have received great attention in ethylbenzene (EB) oxidation. Here, a series of cobalt catalysts with metallic cobalt nanoparticles (NPs) encapsulated in nitrogen-doped graphite-like carbon shells (Co@NC) have been constructed through the one-pot pyrolysis method in the presence of different nitrogen-containing compounds (urea, dicyandiamide and melamine), and their catalytic performance in solvent-free oxidation of EB with tert-butyl hydrogen peroxide (TBHP) as an oxidant was investigated. Under optimized conditions, the UCo@NC (urea as nitrogen source) could afford 95.2% conversion of EB and 96.0% selectivity to acetophenone, and the substrate scalability was remarkable. Kinetics show that UCo@NC contributes to EB oxidation with an apparent activation energy of 32.3 kJ/mol. The synergistic effect between metallic cobalt NPs and nitrogen-doped graphite-like carbon layers was obviously observed and, especially, the graphitic N species plays a key role during the oxidation reaction. The structure-performance relationship illustrated that EB oxidation was a free radical reaction through 1-phenylethanol as an intermediate, and the possible reaction mechanistic has been proposed.

Construction of copper-manganese based aminoclays with significant laccase-like activity and its prominent degradation performance towards bisphenol A

In recent years, nanozymes have become promising alternatives to natural enzymes owing to their high catalytic efficiency, substrate specificity, and mild reaction conditions. The catalytic performance of nanozymes can be further improved by doping heterogeneous metals to provide high redox potentials. However, nanozymes for the degradation of endocrine-disrupting chemicals (EDCs) have been scarcely studied, and the degradation mechanisms remain unclear. Herein, a series of aminoclays (ACs) containing various metal dopants were prepared and employed for the degradation of phenolic compounds. The as-synthesized ACs with a Cu-Mn molar ratio of 1:7 (CuMnAC-1–7) showed excellent stability and superior activity for oxidizing bisphenol A (BPA) than natural laccases owing to the electron transport between Cu2+/Cu+ and Mn4+/Mn3+ in the nanozyme. The catalytic oxidation process of BPA consists of a non-free radical pathway mediated by Mn3+, as well as a free radical pathway facilitated by superoxide radicals (O2·-) and singlet oxygen (1O2). Specifically, Mn3+ deprived the electrons of the BPA benzene ring to form phenolic hydroxyl radicals, which were then polymerized to BPA dimers. Cu+ in the structure reduced Mn4+ to Mn3+, accelerating the electron deprivation of BPA and promoting the polymerization reaction. Finally, the high-charge-density region on the dimeric benzene ring tended to lose electrons and form free radicals, facilitating the polymerization into trimers and tetramers. The CuMnAC-1–7 could remove 95% of BPA at a concentration of 200 mg/L within 1 h under acidic conditions. This study provides a new strategy to design high-performance laccase nanozymes for EDCs degradation.

DPPH Scavenging Activity, Reducing Power, and Metal Chelating Capacity of Compound 1-(2,5-dihydroxyphenyl)-3-pyridine-2-yl-propenone

Background: The excessive free radicals in the body could stimulate oxidative stress which has been implicated in several diseases such as cancer, inflammation, aging, and cardiovascular diseases. The presence of antioxidants can diminish the reactivity of free radicals. The antioxidant defense system in the body may be insufficient thus intake of dietary antioxidants is recommended. Natural flavonoid such as chalcone has been known to exert several biological activities, especially antioxidant activity. Compound 1-(2,5-dihydroxyphenyl)-3-pyridine-2-yl-propenone was successfully synthesized using microwave radiation and several studies reported its biological activities such as antiinflammation, anticancer, and antibacterial activities. Those activities are thought to be related to antioxidant mechanisms. Therefore, this study aimed to evaluate its antioxidant activity. Methods: The antioxidant activities were performed with three different methods: DPPH scavenging activity, ferric reducing power, and metal chelating capacity. Results: 1-(2,5-dihydroxyphenyl)-3-pyridine-2-yl-propenone showed DPPH scavenging activity, ferric reducing power, and metal chelating capacity with IC50S values of 4,471 ± 0,052 μg/mL; 156.56 ± 4.42μg/mL; and 6,273 ± 0,025 μg/mL, respectively. Conclusions: Our results found that 1-(2,5-dihydroxyphenyl)-3-pyridine-2-yl-propenone had quite potent antioxidant activity.

Test the Antioxidant Effectiveness of Oyster Mushroom (Pleurotus ostreatus) Ethyl Acetate Fraction Cream Formula using FRAP (Ferric Reducing Antioxidant Power) and ABTS (2,2'-azino-bis (3-3) ethylbenzothiazoline-6-sulphonic acid) Methods)

molecules due to chemical reactions and metabolic events in the body. Phenolic compounds work to reduce the reaction of increasing the oxidation number, and are able to reduce highly reactive free radicals, lipid peroxidation processes, and metal oxides that can be obtained from oyster mushrooms. This study aims to make an antioxidant cream preparation and measure the IC50 value by conducting an antioxidant test of the ethyl acetate fraction of oyster mushroom (Pleurotus ostreotus) cream using FRAP (ferric reducing antioxidant power) and ABTS (2.2'-azino-bis (3-3) ethylbenzothiazoline-6-sulphonic acid) methods. Oyster mushrooms go through a liquid-liquid partition process and are made into cream preparations with a concentration of 2%, 4%, and 6% formulas, then the antioxidant activity is seen. Based on the measurement results of the three cream formulas, the IC50 value using the FRAP method was 110.12 in the medium category and the IC50 value with ABTS method was 84.61 in the strong category.
 
 Keywords: antioxidants; free radicals; oyster mushroom; frap; abts.

Enhancing lipid peroxidation via radical chain transfer reaction for MRI guided and effective cancer therapy in mice

Lipid peroxidation (LPO), the process of membrane lipid oxidation, is a potential new form of cell death for cancer treatment. However, the radical chain reaction involved in LPO is comprised of the initiation, propagation (the slowest step), and termination stages, limiting its effectiveness in vivo. To address this limitation, we introduce the radical chain transfer reaction into the LPO process to target the propagation step and overcome the sluggish rate of lipid peroxidation, thereby promoting endogenous lipid peroxidation and enhancing therapeutic outcomes. Firstly, radical chain transfer agent (CTA-1)/Fe nanoparticles (CTA-Fe NPs-1) was synthesized. Notably, CTA-1 convert low activity peroxyl radicals (ROO·) into high activity alkoxyl radicals (RO·), creating the cycle of free radical oxidation and increasing the propagation of lipid peroxidation. Additionally, CTA-1/Fe ions enhance reactive oxygen species (ROS) generation, consume glutathione (GSH), and thereby inactivate GPX-4, promoting the initiation stage and reducing termination of free radical reaction. CTA-Fe NPs-1 induce a higher level of peroxidation of polyunsaturated fatty acids in lipid membranes, leading to highly effective treatment in cancer cells. In addition, CTA-Fe NPs-1 could be enriched in tumors inducing potent tumor inhibition and exhibit activatable T1-MRI contrast of magnetic resonance imaging (MRI). In summary, CTA-Fe NPs-1 can enhance intracellular lipid peroxidation by accelerating initiation, propagation, and inhibiting termination step, promoting the cycle of free radical reaction, resulting in effective anticancer outcomes in tumor-bearing mice.

A light-driven enzymatic enantioselective radical acylation.

Enzymes are recognized as exceptional catalysts for achieving high stereoselectivities1-3, but their ability to control the reactivity and stereoinduction of free radicals lags behind that of chemical catalysts4. Thiamine diphosphate (ThDP)-dependent enzymes5 are well-characterized systems that inspired the development of N-heterocyclic carbenes (NHCs)6-8 but have not yet been proved viable in asymmetric radical transformations. There is a lack of a biocompatible and general radical-generation mechanism, as nature prefers to avoid radicals that may be harmful to biological systems9. Here we repurpose a ThDP-dependent lyase as a stereoselective radical acyl transferase (RAT) through protein engineering and combination with organophotoredox catalysis10. Enzyme-bound ThDP-derived ketyl radicals are selectively generated through single-electron oxidation by a photoexcited organic dye and then cross-coupled with prochiral alkyl radicals with high enantioselectivity. Diverse chiral ketones are prepared from aldehydes and redox-active esters (35 examples, up to 97% enantiomeric excess (e.e.)) by this method. Mechanistic studies reveal that this previously elusive dual-enzyme catalysis/photocatalysis directs radicals with the unique ThDP cofactor and evolvable active site. This work not only expands the repertoire of biocatalysis but also provides a unique strategy for controlling radicals with enzymes, complementing existing chemical tools.

Chemical waste treatment based on hydrogen energy (II): Aqueous methyl orange solution under the oxyhydrogen flame

The oxyhydrogen flame (OHF) can generate temperatures as high as 2800 K and a jet flow of highly reactive free radicals including H, OH, HO2 and O. Therefore, it could serve as an effective means for treating various chemical wastes, particularly organic wastes. Building upon our previous research on metal chlorides, we present here a study on the degradation mechanism of aqueous methyl orange (MO) solution under OHF. Although the decolorization of MO solution is rapid, complete degradation is a slow and intricate process. Initially, MO solution undergoes decolorization by breaking the azo bond followed by oxidation processes that convert aminobenzene compounds to benzoquinone and break down the benzene ring until ultimately being fully converted into CO2 and H2O.

Copper‐Catalyzed Stepwise Aerobic Oxidation/N‐Arylation from Benzothiazole

AbstractWe report herein an efficient synthesis of 3‐arylbenzothiazolin‐2‐one compounds. First, substituted benzothiazoles can be smoothly oxidized to benzothiazolin‐2‐one derivatives in the presence of CuCl2 and trifluoroacetic anhydride. Secondly, the Cu2S‐catalyzed N‐arylation of benzothiazolin‐2‐one with arylboronic acids yields a series of novel 3‐aryl benzothiazolin‐2‐one derivatives. The method provides good yields for a variety of substrates and shows good compatibility with functional groups. The usefulness of the skeleton was further illustrated by the derivatization of 3‐aryl‐benzothiazolin‐2‐one. Mechanistic studies suggest that the oxidation of benzothiazole may undergo a free radical reaction process.

Highly graphitized biochar as nonmetallic catalyst to activate peroxymonosulfate for persistent quinclorac removal in soil through both free and non-free radical pathways

To explore highly effective and nonmetallic advanced oxidation process system to alleviate the persistent herbicides contamination in agricultural soils is of great importance. In this study, a significantly graphitized biochar with abundant C = O structure is prepared as non-metallic catalyst (WCGBC800). Different from other traditional amorphous pristine biochar, WCGBC800 can accelerate the electron transfer in the system and then effectively activate peroxymonosulfate (PMS) to produce free (OH, O2–, SO4−, etc.) and non-free radicals (1O2, electron transfer, etc.). Consequently, WCGBC800 can degrade 100 % the persistent organic herbicide quinclorac (QNC, with a content of 50 mg·kg−1) in soil within 20 min after PMS addition. The T.E.S.T-QSAR software simulation evidence that the toxicity of degradation intermediates is much lower than QNC. The stress of QNC on rice seedlings was directly described through rice cultivation experiment. The stress of rice seedlings was relieved after WCGBC800 + PMS treatment. The growth experiment of rice seedlings also shows that with an original QNC concentration of 7 mg·kg−1 in soil, the root length, root surface area, leaf length, leaf area, and leaves perimeter of rice increase of 255.30 %, 148.38 %, 207.64 %, 204.19 %, and 63.69 % respectively after detoxification by WCGBC800 + PMS system. This functional material and the WCGBC800 + PMS system provide new solutions for solving the problem of herbicide residues in soil with promising safety.

Cocamidopropyl betaine - a potential source of nitrogen-containing disinfection by-products in pool water.

Water treatment for most public pools involves disinfection with active chlorine leading to the formation of disinfection by-products (DBPs). Among them, nitrogen-containing compounds (N-DBPs) having increased toxicity and adverse effects on human health are of the greatest concern. Being the major component of various body washers for swimmers, cocamidopropyl betaine (CAPB) represents a potential and still underestimated anthropogenic precursor of N-DBPs in pool water. The purpose of this study was to investigate CAPB transformation pathways and mechanisms under the aqueous chlorination conditions. High-performance liquid and two-dimensional gas chromatography hyphenated with high-resolution mass spectrometry were used for the search and tentative identification of the primary and final CAPB transformation products. A wide range of DBPs containing up to five chlorine atoms including these in combination with hydroxyl and additional carbonyl groups has been revealed in model chlorination experiments for the first time. The proposed mechanism of their formation involves nucleophilic substitution of the secondary amide hydrogen atom at the first stage with subsequent free radical and electrophilic addition reactions resulting in non-selective introduction of halogen atoms and hydroxyl groups in the alkyl chain. The deep transformation products include short-chain chlorinated hydrocarbons and their oxidation products as well as dimethylcarbamoyl chloride possessing high toxicity and carcinogenic properties. Targeted analysis of real swimming pool water samples confirmed the results of model experiments enabling semi-quantitative determination of CAPB (0.8µg L-1) and 18 primary DBPs, including 10 chlorine-containing compounds with the total concentration of 0.1µg L-1. Among them, monochloro (50%) and hydroxydichloro (25%) derivatives predominate. The toxicity and health of the main DBPs has been estimated using QSAR/QSTR approach. Thus, the possibility of formation of new classes of potentially toxic chlorine-containing DBPs associated with the widespread use of detergents and cosmetics was shown.

Peroxymonosulfate activation by microplastics coagulated sludge-derived iron-carbon composite for effective degradation of tetracycline hydrochloride: Performance and mechanism

A simple one-step pyrolysis method was adopted to prepare microplastics (MPs) coagulated sludge into an iron-carbon composite (Fe-PSMPC), which was used to activate peroxymonosulfate (PMS) for the degradation of tetracycline hydrochloride (TC). The iron species in coagulated sludge were thermally reduced by carbon at 800 °C to produce abundant Fe0, which was successfully loaded on the surface of carbon derived from MPs. Then, the effects such as Fe-PSMPC dosage, PMS dosage, initial pH, and pollutant concentration on TC degradation were further investigated. The results showed that the Fe-PSMPC/PMS system was able to degrade TC effectively over a wide pH range. Under the optimal process conditions, the removal rate of TC could reach 87.5 % within 16 min. In addition, quenching experiments, electron paramagnetic resonance, electrochemical measurements, and X-ray photoelectron spectroscopy analyses indicated that the non-free radical (1O2 and electron transfer) pathway was dominant in the TC degradation system, and the free radical (•OH and SO4• −) pathway also showed significant contribution. Fe0 on Fe-PSMPC was the main active site, and the keto group (C = O) also acted as an active site to facilitate the generation of 1O2. Furthermore, three possible degradation pathways of TC were elaborated based on the 17 intermediates detected by liquid chromatography-mass spectrometry. This work provides an economical and convenient recycling strategy for the MPs coagulated sludge, which can be converted into an effective catalyst to activate PMS for the degradation of organic pollutants, thus realizing “treating waste with waste”.

Water Microdroplets-Initiated Methane Oxidation.

The special redox reactivity of water microdroplets causes "mild ignition" of methane gas to form methane oxygenates. The C(sp3)-H bond of methane can be activated by the hydroxyl radical (OH·) or the hydrogen radical (H·) across the air-water interface (AWI) of microdroplets to generate the methyl radical (CH3·). Once CH3· is formed, it undergoes free-radical reactions with O2 in the air, excessive OH· and H· across the AWI, and H2O2 present at the AWI and generated CH3· itself to produce methanol and other species. Production of the methanol and other oxygenates was confirmed by gas chromatography, mass spectrometry, and 1H- and 13C-nuclear magnetic resonance. Formic acid, acetic acid, ethanol, carbon dioxide, and methyl peroxide were also detected as methane oxidation byproducts. This water microdroplet-initiated oxidation process can be further enhanced under ultrasonication to yield 2.66 ± 0.77 mM methanol conversion from the methane gas in a single spray run for 30 min, with a selectivity of 19.2% compared with all other oxygenated species.

Research status and prospect of nano silver (Ag)-modified photocatalytic materials for degradation of organic pollutants.

Nano silver (Ag) was metallic Ag monomers with particle size to the nanoscale. Photocatalyst was a kind of semiconductor material with photocatalytic function. Loading precious metal Ag onto semiconductor surfaces by microwave, laser-induced, solvent-thermal and hydrothermal methods could capture photogenerated electrons, reduced the compounding rate of holes and photogenerated electrons during the photocatalytic process, thereby improving the electron transfer efficiency of photocatalysis and enhancing the absorption of visible light by silver nanoparticles through the plasma resonance effect. The highly reactive free radicals produced by photocatalysts were used in the organic degradation process to degrade organic matter into inorganic matter and was a faster, more efficient and less polluting method of pollutant degradation, which has attracted a lot of attention from researchers. This review discussed the modification of various types of photocatalysts by nano Ag through different methods. The photocatalytic degradation of dyes, antibiotics and persistent organic pollutants by different modified composites was also analyzed. This review covered the several ways and means in which nano Ag has modified diverse photocatalytic materials as well as the photocatalytic degradation of dyes, antibiotics and persistent organic pollutants. This review identified the drawbacks of the existing nano Ag-modified photocatalytic materials, including their low yield and lack of recyclability, and it also offered suggestions for potential future directions for their improvement. The purpose of this review was to further research on the technology of nano Ag-modified photocatalytic materials and to encourage the creation of new modified photocatalytic nanomaterials for the treatment of organic pollutant degradation.

Dentoalveolar anomalies and modern views on the mechanisms of local stress-modeling effect of orthodontic appliances on the periodontal tissues (a literature review)

The aim of the study was to highlight the results of modern scientific developments in tracing the mechanisms of local stress-modeling effect of orthodontic appliances on the oral cavity and periodontal tissues during the active period of orthodontic treatment. Materials and methods. The research methodology was implemented in the collection and analysis of scientific results on the stress-modeling effect of orthodontic appliances in patients with dentoalveolar anomalies obtained from the processed sources – published full-text articles of original and fundamental research by national and foreign authors based on the evidential databases MEDLINE / PubMed, PMC, Scopus, Web of Science, Cochrane, Google Scholar, ResearchGate and other scientific and practical resources. Results. The main components of the stress-modeling effect of fixed orthodontic appliances on the oral cavity, and particularly on the periodontal tissues, were analyzed. The proportion of various complications is quite high and ranges from 32.7 % to 50.0 % of all cases. The development of oxidative stress during orthodontic treatment is potentiated by microcirculatory disorders and hypoxia of the periodontal tissues. The peculiarities of the periodontal cellular complex reaction, which has the ability to bear stress generated in the actin cytoskeleton by direct mechanical stimulation, to extracellular matrix proteins, affecting the three-dimensional organization of the extracellular matrix and its remodeling, have been traced. The role of lipid peroxidation, antioxidant system and enzymatic reaction of oral and crevicular fluids was also defined. Conclusions. The development of oxidative stress during orthodontic treatment can be caused by local and systemic exposure to metals, corrosion processes in particular; by inflammation of periodontal tissues due to poor oral hygiene and activation of periodontal pathogenic microflora; by aseptic inflammation in the periodontal ligament due to the use of mechanical force. Certain enzymes of the oral fluid, in particular lactate dehydrogenase, can act as a sensitive marker of changes in the periodontal ligament metabolism during orthodontic teeth movement. The localization and nature of free radical pathology are largely caused by the nature of an exogenous inducer of lipid peroxidation and the genotypic characteristics of antioxidant system. It is this ratio that determines the initiation and further chain branching of free radical reactions. Without normalization of all pathogenetic links, successful treatment of inflammatory and dystrophic-inflammatory diseases of the periodontal tissues, in particular in orthodontic patients, is impossible.

Approaches to Help Older Women in ART

Ancient Chinese emperors sent messengers to the whole country and explored an elixir of life. Determent of aging has been an ultimate hope for humans for a long period. In the modern era, aging become a hot topic to be solved according to longevity. Equality of both sexes in society contributed to the late marriage and start of making children. There happen adverse effects to being conceived in the aged ovaries. The quality and quantity become impaired by the ovarian aging process. In the artificial reproductive treatment, the obtained number of oocytes in ovarian hyperstimulation diminishes in aged women. The aging impairs quality both in the nucleus and cytoplasm. Chromosomal and genetic abnormalities increase lower implantation and higher abortion. In aged women, PGT-A may be effective to effective treatment. On the other hand, aging affects organelles in the cytoplasm of oocytes by protein metabolic dysregulations. Especially it induces mitochondria dysfunction. Mitochondria are called a “powerhouse” and have an essential role in oogenesis and embryogenesis. There exist 200,000-40,000 mitochondria DNA copies in the mature oocytes. Mitochondria dysfunction causes maturation arrest of oocytes, fertilization failure, late cleavage, and fragmented embryos. We have two strategies to solve this problem by enhancement of mitochondrial function. One is the holistic approach. Reactive oxygen species (ROS) or free radicals impair mitochondrial function. Also, mitochondria themselves are known to produce ROS. We measure Diacron-Reactive Oxygen Metabolites (d-Rom) and biological antioxidant potential (BAP) that are predictors of systemic ROS level and antioxidant competence, respectively. Another method is a cell-engineering approach. We have conducted autologous mitochondria transfer into mature oocytes. The quality of the oocytes and embryos were dramatically improved by this method, and we obtained 13 healthy children.

Sustained Release of Voriconazole Using 3D-Crosslinked Hydrogel Rings and Rods for Use in Corneal Drug Delivery.

Corneal disorders and diseases are prevalent in the field of clinical ophthalmology. Fungal keratitis, one of the major factors leading to visual impairment and blindness worldwide, presents significant challenges for traditional topical eye drop treatments. The objective of this study was to create biocompatible 3D-crosslinked hydrogels for drug delivery to the cornea, intending to enhance the bioavailability of ophthalmic drugs. Firstly, a series of flexible and porous hydrogels were synthesized (free-radical polymerization), characterized, and evaluated. The materials were prepared by the free-radical polymerization reaction of 1-vinyl-2-pyrrolidinone (also known as N-vinylpyrrolidone or NVP) and 1,6-hexanediol dimethacrylate (crosslinker) in the presence of polyethylene glycol 1000 (PEG-1000) as the porogen. After the physicochemical characterization of these materials, the chosen hydrogel demonstrated outstanding cytocompatibility in vitro. Subsequently, the selected porous hydrogels could be loaded with voriconazole, an antifungal medication. The procedure was adapted to realize a loading of 175 mg voriconazole per ring, which slightly exceeds the amount of voriconazole that is instilled into the eye via drop therapy (a single eye drop corresponds with approximately 100 mg voriconazole). The voriconazole-loaded rings exhibited a stable zero-order release pattern over the first two hours, which points to a significantly improved bioavailability of the drug. Ex vivo experiments using the established porcine eye model provided confirmation of a 10-fold increase in drug penetration into the cornea (after 2 h of application of the hydrogel ring, 35.8 ± 3.2% of the original dose is retrieved from the cornea, which compares with 3.9 ± 1% of the original dose in the case of eye drop therapy). These innovative hydrogel rods and rings show great potential for improving the bioavailability of ophthalmic drugs, which could potentially lead to reduced hospitalization durations and treatment expenses.

Novel heterogeneous Fenton catalysts for promoting carbon iron electron transfer by one-step hydrothermal synthesization

Carbon materials play a crucial role in promoting the Fe(III)/Fe(II) redox cycle in heterogeneous Fenton reactions. However, the electron transfer efficiency between carbon and iron is typically low. In this study, we prepared a novel heterogeneous Fenton catalyst, humboldtine/hydrothermal carbon (Hum/HTC), using a one-step hydrothermal method and achieved about 100 % reduction in Fe(III) during synthesis. Moreover, the HTC continuously provided electrons to promote Fe(II) regeneration during the Fenton reaction. Electron paramagnetic resonance (EPR) and quenching experiments showed that Hum/HTC completely oxidized As(III) to As(V) via free radical and non-free radical pathways. Attenuated total reflectance Fourier-transform infrared (ATR-FTIR) and two-dimensional correlation spectroscopy (2D-COS) analyses revealed that monodentate mononuclear (MM) and bidentate binuclear (BB) structures were the dominant bonding methods for As(V) immobilization. 40 %Hum/HTC exhibited a maximum As(III) adsorption capacity of 167 mg/g, which was higher than that of most reported adsorbents. This study provides a novel strategy for the efficient reduction of Fe(III) during catalyst synthesis and demonstrates that HTC can continuously accelerate Fe(II) regeneration in heterogeneous Fenton reactions.

Unraveling kinetic and synergistic effects during ultrasound-enhanced carbocatalysis for water remediation as a function of ultrasonic frequency

The ability of the ultrasound (US) combined with peroxymonosulfate (PMS), and a carbonaceous material (BC) was evaluated in the degradation of a model pollutant (acetaminophen, ACE). The US/BC/PMS system was compared with other possible systems (US, oxidation by PMS, BC adsorption, BC/PMS, US/PMS, and US/BC. The effect of the ultrasonic frequency (40, 375, and 1135 kHz) on the kinetics and synergy of the ACE removal was evaluated. In the US system, kinetics was favored at 375 kHz due to the increased production of hydroxyl radicals (HO•), but this did not improve in the US/PMS and US/BC systems. However, synergistic and antagonistic effects were observed at the low and high frequencies where the production of radicals is less efficient but there is an activation of PMS through mechanical effects. US/BC/PMS at 40 kHz was the most efficient system obtaining ∼95% ACE removal (40 μM) in the first 10 min of treatment, and high synergy (S = 10.30). This was promoted by disaggregation of the carbonaceous material, increasing the availability of catalytic sites where PMS is activated. The coexistence of free-radical and non-radical pathways was analyzed. Singlet oxygen (1O2) played the dominant role in degradation, while HO• and sulfate radicals (SO4•–), scarcely generated at low frequency, play a minimum role. Performance in hospital wastewater (HWW), urine, and seawater (SW) evidenced the competition of organic matter by BC active sites and reactive species and the removal enhancement when Cl− is present. Besides, toxicity decreased by ∼20% after treatment, being the system effective after three cycles of reuse.

The impact of dissolved organic matter on the photodegradation of tetracycline in the presence of microplastics

Microplastics (MPs), an emerging class of pollutants, significantly impact the photoconversion dynamics of tetracycline (TC). But the effect of prevalent dissolved organic matter (DOM) on TC photodegradation in the presence of MPs remains a gap in current research. In this study, the photoconversion behavior and mechanism of TC under simulated sunlight conditions were systematically investigated, both in the presence of DOM and in combination with polystyrene (PS) MPs. The results demonstrated that both DOM and MPs enhanced the photodegradation of TC when compared to its direct degradation. However, DOM, particularly humic acid (HA, 10 mg/L), exhibited a more pronounced enhancing effect on TC photodegradation within 1 h reaction, regardless of the presence or absence of MPs, reaching up to 80%. In reaction systems involving TC-HA and TC-HA-PS, the primary contributors to TC degradation were direct photolysis and HA photosensitization (free radical reactions). Conversely, photosensitization effects were not significant in the presence of fulvic acid (FA). Furthermore, even under dark reaction conditions, HA exhibited a 10% degradation effect on TC. Quenching experiments and electron spin resonance (ESR) results indicate that dark reaction processes involve free radical reactions. Additionally, toxicity test results showed a reduction in the acute toxicity of TC photodegradation products, yet the long-term cumulative risks to organisms deserved attention. In general, this investigation significantly advances our understanding of the intricate photoconversion behavior of TC in the presence of coexisting chemical components.

Enhancing the mechanical and dielectric properties of high thermally stable polyimides via a crosslinkable bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride monomer

Polyimides (PIs) have attracted great attention because of their excellent properties and applications in areas such as flexible display substrates, microelectronics, and integrated circuits. The effects of crosslinking on the thermal, mechanical, and dielectric properties of PIs, however, still require further investigation. In this work, we introduce a crosslinkable monomer, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride (BTA), which contains double bonds, into the system consisting of cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA) and 4,4′-oxydianiline (ODA) for the synthesis of PI films. The obtained PIs are further crosslinked by free radical reactions using a crosslinking agent, 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TAIC) to form three crosslinked PI materials, PI-TAIC-5%, PI-TAIC-10%, and PI-TAIC-15%. The resulting all three crosslinked PI films exhibit excellent thermal properties with their glass transition temperatures (Tg) higher than 400 °C. For the mechanical properties, the formation of the rigid network structure leads to an improvement in their tensile strengths and Young's moduli. The introduction of 10 mol% TAIC in the PI (PI-TAIC-10%) shows the highest tensile strength (114.77 MPa), representing an 18.6% enhancement in comparison with that of the original PI material. In terms of dielectric properties, the crosslinking reactions effectively increase the free volumes between the polymer chains and reduce the molecular dipole moments. As a result, PI-TAIC-15% significantly reduces the dielectric properties, resulting in a decrease in the dielectric constant (Dk, from 3.42 to 3.15) and the dielectric loss (Df, from 3.67 × 10−2 to 2.58 × 10−2) under 10 GHz frequency. As far as the coefficient of thermal expansion (CTE) results, the formation of the network structure in PI-TAIC-15% restricts the movement of the polymer chains, leading to a 15% reduction in the CTE value than that of the non-crosslinked PI film. Overall, this work provides a promising strategy to optimize the mechanical and dielectric properties of high thermally stable PIs via crosslinking reactions.