Formation Of Reactive Radicals Research Articles

Activation of peroxymonosulfate by sludge-derived magnetic biochar for pollutant removal: Performance, applicability, and synergetic mechanism of iron species and carboxylated biochar

Developing eco-friendly, economical, and efficient catalytic systems for pollutant removal has become an imperative orientation in water treatment. Conversion of municipal sludge into multifunctional biochar has been considered as a feasible strategy for dual applicability in water treatment and sludge management. Herein, municipal biological and ferric sludge were recycled to synthesize an iron-based biochar (Fe4SBC1-800) with great magnetic separation performance (Ms = 29.96 emu g−1). The mixed sludge-derived biochar (Fe4SBC1-800) engaged as an efficient catalyst of peroxymonosulfate (PMS), which efficiently promoted the pollutants elimination including typical azo dye and several antibiotics and anti-inflammatory drugs. The enhanced degradation performance primarily originated from the formation of reactive radicals and non-radical species. The respective and synergetic mechanisms of biochar and supported iron species on PMS activation were verified based on experimental results and theoretical computations. The carboxyl groups served as the major active sites of biochar that donated electrons to PMS for •OH and SO4•− formation. The supported FeO species further boosted the activation capability: (i) the enhanced formation of radicals and FeIV = O via heterogeneous Fenton-like reactions; (ii) the promoted oxygen reduction for O2•− formation by promoting electron transfer from PMS to the FeO species through high sp2-hybridized biochar. Overall, this study innovatively proposed a sustainable and efficient activation system for PMS by iron-based magnetic biochar, which systematically probed the activation mechanism and reconsidered the role of the supported iron species in the iron-based biochar/PMS system.

Two‐dimensional β‐ketoenamine linked azo covalent organic frameworks as heterogeneous catalysts for photo‐induced RCMP

AbstractPhoto‐induced reversible complexation‐mediated polymerization (RCMP) is a green and economical method to prepare polymers with precise molecular weights, narrow molecular weight distributions and functionally active chain ends. Covalent organic frameworks (COFs) are a promising heterogeneous photocatalyst for mediating RCMP due to their adjustable structure, band gap, and porosity. In this work, 1,3,5‐triformylphloroglucinol (Tp) and p‐azoaniline (Azo) were selected to construct 2D β‐ketoenamine linked Tp‐Azo‐COF as a heterogeneous photocatalyst to trigger RCMP under white light irradiation. A series of polymers with controllable molecular weight and narrow molecular weight distribution were successfully prepared by using Tp‐Azo‐COF as photocatalysis. On/off light experiments confirmed the good spatiotemporal control feature, and chain expansion experiments demonstrated the high “activity” of polymer chain ends. Furthermore, the mechanistic research elucidated that electron transfer between Tp‐Azo‐COF and initiator occurred, allowing the formation of reactive radicals to mediate RCMP. Density functional theory calculations revealed that the coordination of iodine on the initiator to catalyst obviously reduced the bond dissociation energy, leading to enhance in the polymerization rate. This work provides a platform for constructing heterogeneous photocatalysts with more efficient and stable to mediate RCMP.

Visible light photocatalytic NOx removal with suppressed poisonous NO2 byproduct generation over simply synthesized triangular silver nanoparticles coupled with tin dioxide.

The treatment or conversion of air pollutants with a low generation of secondary toxic substances has become a hot topic in indoor air pollution abatement. Herein, we used triangle-shaped Ag nanoparticles coupled with SnO2 for efficient photocatalytic NO removal. Ag triangular nanoparticles (TNPs) were synthesized by the photoreduction method and SnO2 was coupled by a simple chemical impregnation process. The photocatalytic NO removal activity results show that the modification with Ag TNPs significantly boosted the removal performance up to 3.4 times higher than pristine SnO2. The underlying roles of Ag TNPs in NO removal activity improvement are due to some advantages of Ag TNPs. Moreover, the Ag TNPs contributed photogenerated holes as the main active species toward enhancing the NO oxidation reaction. In particular, the selectivity toward green products significantly improved from 52.78% (SnO2) to 86.99% (Ag TNPs/SnO2). The formation of reactive radicals under light irradiation was also verified by DMPO spin-trapping experiments. This work provides a potential candidate for visible-light photocatalytic NO removal with low toxic byproduct generation.

THE ROLE OF VITAMIN E AS AN ANTIOXIDANT AND PREVENTING DAMAGE CAUSED BY FREE RADICALS

Vitamin E is one of the four fat-soluble vitamins that is made naturally in plants. It is one of the necessary vitamins for humans and animals, and the body needs it because it cannot manufacture it. It works to preserve polyunsaturated fatty acids (PUSFA) outside and inside cells in the body and prevents free radical formation reactions resulting from respiratory and respiratory processes and through exposure to toxic external factors such as pollutants. Its deficiency leads to many, Vitamin E comes from plant elements that are in the form of tocopherols, which are compounds that possess the activity of vitamin E. They are in the form of yellow fats that do not dissolve in water, but they do dissolve in organic solvents. The name (Tocopherol) is derived from a Greek word, where “Tocos” means childbirth and Phero from Bear. These words mean the producer of offspring or offspring and are linked to his main role in reproduction in various types of animals. The OL from alcohol is evidence that it is an alcoholic substance.

TiO2-Based Mortars for Rendering Building Envelopes: A Review of the Surface Finishing for Sustainability

Building envelopes coated with TiO2-based mortars benefit from depolluting, antibiological and self-cleaning effects. Therefore, photocatalytic renders are allies in the quest for sustainability in the built environment, potentially combatting atmospheric pollution, enhancing durability and reducing maintenance needs. Surface finishing characteristics of the renders influence their photocatalytic efficiency and esthetic and functional properties. In this context, this study reviews the existing literature, focusing on proven surface-affecting parameters, the surface and color of TiO2-based mortars, to explore their impacts on photoactive behavior. The incorporation of TiO2 within an additional surface layer and its mixture into the mortar in bulk were observed for surface roughness. Mainly the addition of TiO2 during casting was identified in colored mortars. Generally, a moderate surface roughness led to better photoactivity; microroughness affected self-cleaning by facilitating dirt deposition. The interaction between the surface roughness and the photocatalytic layer affected the water contact angle, regarding superhydrophilicity or superhydrophobicity. The photoactivity of colored mortars with TiO2 depended on the color and amount of the added pigments, which influenced electron–hole recombination, physically occupied active sites or, on the other hand, led to a higher formation of reactive radicals. Surface finishing can thus be designed to enhance the photoactivity of TiO2-based mortars, which is fundamental for current climate concerns and emphasizes the need for life cycle assessments and environmental protection.

Accelerated degradation of micro-pollutant by combined UV and chlorine dioxide: Unexpected inhibition of chlorite formation

UV/chlorine dioxide (ClO2) process can be intentionally or accidently conducted and is potentially effective in micro-pollutants degradation. UV irradiation can promote ClO2 decay and subsequently result in the formation of reactive radicals. Hence, the co-exposure of ClO2 and UV exhibited a synergetic effect on metribuzin (MET) degradation. The MET degradation was promoted by UV/ClO2 with a rate of 0.089 min−1 at pH 7.5, which was around 2.4 folds the total of rates caused by single ClO2 (0.004 min−1) and single UV (0.033 min−1). Reactive radicals mainly HO• and reactive chlorine species were involved in the acceleration effect, and contributed to 59%–67% of the total degradation rate of MET during UV/ClO2 under pHs 5.5–7.5. Among them, HO• was the predominant contributor and the contribution rate gradually rose under higher pH. Chlorite (ClO2−) and chlorate (ClO3−) formation has been the major concern of ClO2 oxidation. However, a comparison of their formation during UV/ClO2 and ClO2 oxidation is rarely reported. Herein, during MET degradation by ClO2, only ClO2− was identified with the highest amount of 1.17 mg L−1. Conversely, during MET degradation by UV/ClO2, only ClO3− was identified with the highest amount of 0.68 mg L−1, showing an upward trend with prolonging treatment time. Furthermore, organic halogenated DBPs formation after 24 h post-chlorination with UV/ClO2 and ClO2 pre-treatments was comparatively evaluated. Organic DBPs formation after post-chlorination was higher with UV/ClO2 pre-treatment compared to ClO2 pre-treatment. The overall concentration of DBPs produced with 30 min UV/ClO2 pre-treatment was about 4.5 times that with 1min UV/ClO2 pre-treatment. This study provided useful reference for the application of UV/ClO2 in micro-pollutants degradation.

Iron nanoparticles decorated TiO2 hollow microspheres for boosting degradation of tetracycline in a photo-Fenton catalytic system

The problem of water pollution caused by antibiotic contamination is essential for human health and the ecological environment. In this study, Fe-doped TiO2 (FT-2) photocatalyst with a hollow microsphere structure was fabricated for efficient photocatalytic-Fenton removal of tetracycline (TC) under visible light irradiation. The unique hollow microsphere structure of FT-2, iron doping and oxygen vacancies enhance the photo-Fenton activity and stability of the material. The results showed that the degradation rate of tetracycline in the FT-2 photo-Fenton system at 60 min was 98.18%, with a degradation efficiency of mostly 90% after five successful reuses. The efficient TC degradation activity should be mainly ascribed to the structure of hollow microspheres and oxygen vacancies, resulting in the extended optical light absorption in the visible light region, reduced compound efficiency of electron cavitation pairs, and accelerated separation and migration of photogenerated carriers. In addition, this highly benefits the formation of reactive radicals·O2- and h+ play a key role in the TC degradation in a photo-Fenton reaction system and thus lead to great improvement in TC removal according to the capture experiments and EPR. This study provides an idea for the construction of semiconductor catalysts with oxygen vacancy and doped with transition metal elements for the effective photocatalytic remediation of wastewater containing antibiotic contaminants.

Comparative study of UV/chlorine and VUV/chlorine as ultrafiltration membrane pretreatment techniques: Performance, mechanisms and DBPs formation

Membrane fouling, primarily resulting from natural organic matter (NOM) widely existing in water sources, has always been a chief hindrance for the prevalent application of ultrafiltration (UF). Thus, vacuum ultraviolet (VUV)/chlorine process was proposed as a strategy for UF membrane fouling control and ultraviolet (UV)/chlorine process was used for comparison. VUV/chlorine process exhibited more excellent performance on NOM removal than UV/chlorine process. [HO•]ss and [Cl•]ss were calculated as 1.26 × 10−13 and 3.06 × 10−14 M, respectively, and ClO• might not exist under the conditions of 0.08 mM chlorine and 30 min VUV irradiation. [HO•]ss, [Cl•]ss and [ClO•]ss were not available and the formation of reactive radicals was unsustainable in UV/chlorine system. Moreover, VUV/chlorine pretreatment also showed better performance on the reversible and irreversible membrane fouling control than UV/chlorine pretreatment. The dominated fouling mechanism in the final stage of filtration was cake filtration. Additionally, the amount of detected disinfection by-products (DBPs) in VUV/chlorine system was significantly lower than that in UV/chlorine system. During subsequent chlorination disinfection, the yield of DBPs with VUV/chorine pretreatment was higher than that with UV/chlorine pretreatment. VUV/chlorine pretreatment could effectively control DBPs formation when the pretreatment time was extended to 120 min. In summary, VUV/chlorine system presented a most excellent performance on membrane fouling control, NOM degradation and DBPs control.

Tuning the ZnO/GaN heterojunction for atmospheric NO abatement

Photocatalysis was a green and sustainable strategy for environmental remediation as it could accelerate the degradation/oxidation of pollutants using the widely available solar energy as the driving force. The efficacy of photocatalysis could be improved by the formation of a heterojunction and microstructure optimization of the semiconducting catalysts to manipulate the transfer of hot charge carriers. The re-oxidation of a visible light photocatalyst, (Ga, Zn)(N, O) (ZGN), was used for the in-situ production of ZnO/GaN(O) heterojunction with different surface properties for efficient NO oxidation. Re-oxidation at different temperatures imparted the new state of the surface oxide of the substrate (ZGN) anion redistribution by the mode strain between the oxide and the nitride, leading to the transformation of material properties. The ZGN-550 (ZnO/GaN(O)) showed a significantly higher oxidation efficiency (90.2%) than the pristine ZGN (62.3%) under visible light insolation, because the nanoscale discrete ZnO over the oxynitride matrix promoted the separation of charge carriers and the formation of reactive radicals (•OH and •O2–). The ZGN-550 heterojunction obtained a high apparent quantum efficiency of about 6.64% at photons around 400 nm. ZnO/GaN(O) heterojunction has great potential for sustainable and efficient degradation of air pollutants.

FexO4-enhanced degradation of bisphenol A in visible light/peroxydisulfate system: production of singlet state oxygen

In this study, ferrous composites (FexO4) were prepared by microreactor to activate peroxydisulfate (PDS) for the degradation of bisphenol A (BPA) with visible (Vis) light irradiation. X-ray diffraction (XRD), energy-dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM) were used to characterize the morphology and crystal phase of FeXO4. Photoluminescence (PL) spectroscopy combined with amperometric tests were used to determine the role of PDS on the performance of photocatalytic reaction. The main reactive species and intermediates for BPA removal were determined by electron paramagnetic resonance (EPR) measurement and quenching experiments. The result indicated that singlet state oxygen (1O2) contributed more to the BPA degradation than that of other reactive radicals (·OH, SO4·- and ·O2-); these reactive radicals and 1O2 formed by the reaction between photo-generated electrons (e-) and holes (h+) of FexO4 and PDS. During this process, the consumption of e- and h+ also improved their separation efficiency and thus enhanced the degradation of BPA. In addition, the photocatalytic activity of FexO4 in Vis/FexO4/PDS system was 3.2-fold and 6.6-fold higher than that of single FexO4 and PDS under Vis light, respectively. The Fe2+/Fe3+ cycle could effectively drive the photocatalytic activation of PDS through indirect electron transfer and the formation of reactive radicals. This work illustrated that the degradation of BPA was rapidly in Vis/FexO4/PDS system mainly through 1O2, which further improve our understanding on the efficient removal of organic contaminants in the environment.

Tannic Acid as a Versatile Template for Silica Monoliths Engineering with Catalytic Gold and Silver Nanoparticles.

Tannic acid in alkaline solutions in which sol-gel synthesis is usually performed with tetraethoxysilane is susceptible to various modifications, including formation of reactive radicals, oxidation under the action of atmospheric oxygen, self-association, and self-polymerization. Here, a precursor with ethylene glycol residues instead of ethanol was used, which made it possible to synthesize bionanocomposites of tannic acid and silica in one stage in neutral media under normal conditions without the addition of acid/alkali and organic solvents. Silica was fabricated in the form of optically transparent monoliths of various shapes with 2-4 nm pores, the radius of which well correlated with the size of a tannic acid macromolecule in a non-aggregated state. Polyphenol, which was remained in pores of silica matrix, served then as reducing agent to synthesize in situ gold and silver nanoparticles. As shown, these Au@SiO2 and Ag@SiO2 nanocomposites possessed localized surface plasmon resonance and high catalytic activity.

Improving plasma sterilization by constructing a plasma photocatalytic system with a needle array corona discharge and Au plasmonic nanocatalyst

Efficient sterilization by a plasma photocatalytic system (PPS) requires strong synergy between plasma and photocatalyst to inactivate microorganisms while suppressing the formation of secondary pollutants. Here, we report that a PPS constructed from a needle array corona discharge and Au/TiO2 plasmonic nanocatalyst could remarkably improve the sterilization of Escherichia coli (E. coli) and alleviate formation of the discharge pollutant O3. At 6 kV, the combination of corona discharge and Au/TiO2 achieves sterilization efficiency of 100% within an exposure time of 5 min. At 5 kV and an exposure time of 8 min, the presence of Au/TiO2 improves sterilization efficiency of the corona discharge from 73% to 91% and reduces the O3 concentration from 0.38 to 0.04 ppm, whereas the presence of TiO2 reduces the sterilization efficiency and O3 concentration to 66% and 0.17 ppm, respectively. The Au/TiO2 in the PPS enables a uniform corona discharge, enhances the interaction between plasma, E. coli and nanocatalysts, and suppresses the formation of O3. Further, the Au/TiO2 can be excited by ultraviolet–visible light emitted from the plasma to generate electron–hole pairs, and thus contributes to the formation of reactive radicals and the oxidative inactivation of E. coli. The PPS constructed from a needle array corona discharge and Au-based plasmonic nanocatalyst provides a promising approach for developing high-efficiency sterilization techniques.

A biophotoelectrocatalytic system for pollutant removal based on carbon fiber cloth supported TiO2 photoanode with oxygen vacancy defects and CuO/g-C3N4 photocathode

As an advanced oxidation technology, photoelectrocatalysis (PEC) has been widely explored to degrade refractory contaminants in the environment. Meanwhile, enzymatic biodegradation provides an effective approach to removal of organic pollutants under mild conditions. Herein, we developed a biophotoelectrocatalytic system to remove bisphenol A (BPA) based on the combination of PEC and enzymatic biodegradation. We utilized carbon fiber cloth (CFC) as substrate to construct a dual-photoelectrode biophotoelectrocatalytic system based on three dimensional (3D) nanostructured TiO2 photoanode with oxygen vacancy defects (Ov-TiO2/CFC) and enzyme-coupled CuO/g-C3N4/CFC photocathode. The excellent PEC performance of Ov-TiO2/CFC photoanode significantly promoted the formation of reactive radicals for the degradation reaction, ascribed to efficient separation and migration of photogenerated carriers. The proposed system displayed good synergistic effect between PEC and enzymatic catalysis for BPA removal, with more than 99% degradation efficiency after 90-min treatment. This work demonstrates CFC as a useful substrate material for constructing highly efficient biophotoelectrocatalytic degradation system for organic pollutant removal.

UV/Sodium percarbonate for bisphenol A treatment in water: Impact of water quality parameters on the formation of reactive radicals

Reported herein is an investigation of the impact of water quality parameters on the formation of carbonate radical anion (CO3•−) and hydroxyl radical (HO•) in UV/sodium percarbonate (UV/SPC) system versus in UV/hydrogen peroxide (UV/H2O2) system for bisphenol A (BPA) degradation in water. Pathways of CO3•− oxidation of BPA were proposed in this study based on the evolution of direct transformation products of BPA. Observed in this study, the degradation of BPA in the UV/SPC system was slower than that in the UV/H2O2 system in the secondary effluents collected from a local wastewater treatment plant due to the significant impact of coexisting constituents in the matrices on the former system. Single water quality parameter (e.g., solution pH, common anion, or natural organic matter) affected radical formations and BPA degradation in the UV/SPC system in a way similar to that in the UV/H2O2 system. Namely, the rise of solution pH decreased the steady state concentration of HO• resulting in a decrease in the observed pseudo first-order rate constant of BPA (kobs). Chloride anion and sulfate anion played a negligible role over the examined concentrations; nitrate anion slightly suppressed the reaction at the concentration of 20 mM; bicarbonate anion decreased the steady state concentrations of both CO3•− and HO• exerting significant inhibition on BPA degradation. Different extents of HO• scavenging were observed for different types of natural organic matter in the order of fulvic acid > mixed NOM > humic acid. However, the impact was generally less pronounced on BPA degradation in the UV/SPC system than that in the UV/H2O2 system due to the existence of CO3•−. The results of this study provide new insights into the mechanism of CO3•− based oxidation and new scientific information regarding the impact of water quality parameters on BPA degradation in the sytems of UV/SPC and UV/H2O2 from the aspect of reactive radical formation, which have reference value for UV/SPC application in wastewater treatment.

Insight into the degradation of ciprofloxacin by medium-pressure UV-activated monochloramine process

The degradation efficiency and mechanisms of ciprofloxacin (CIP), a typical antibiotic, by a medium-pressure ultraviolet/chloramine (MPUV/NH2Cl) treatment were investigated. The results showed that CIP degradation by MPUV/NH2Cl was significantly higher than that by NH2Cl oxidation and MPUV photolysis, and that this degradation processes were consistent with pseudo-first-order kinetics. The initial CIP concentration (7.5–30.2 μM) and the presence of HCO3− (0.5–10 mM) significantly inhibited CIP degradation with kobs,CIP 0.0090–0.0069 and 0.0078–0.0048 cm2/mJ. In contrast, NO3− (50–500 μM) and Br− (0.5–10 mM) significantly promoted the degradation with kobs,CIP 0.0078–0.0102 and 0.0078–0.0124 cm2/mJ. The effect of Cl− (0.5–10 mM) and natural organic matter (1–5 mg/L) were negligible. The NH2Cl dosage (30–60 μM) presented a dual effect, in which its increase within the optimal concentration range (30–40 μM) accelerated CIP degradation due to the formation of reactive radicals, whereas an excessive increase (40–60 μM) quenched the free radicals, ultimately quenching the free radicals and inhibiting the degradation. The optimum pH for CIP degradation under MPUV/NH2Cl treatment was 7.0. The contribution of reactive halogen species (i.e., reactive chlorine species and reactive nitrogen species) to CIP degradation was substantially greater than that of hydroxyl radicals under acidic or neutral conditions. We identified the degradation products of CIP and proposed degradation pathways, which included defluorination and cracking of the piperazine ring, with the latter being dominant. Compared to haloacetic acid (HAA) and nitrogenous disinfection byproducts (N-DBPs), MPUV/NH2Cl significantly reduced trihalomethane (THM) production and theoretical cytotoxicity by 80.1% and 78.4% respectively, compared to the background experiment in natural water at a UV dose of 300 mJ/cm2.

A novel Sm doped Cr2O3 sesquioxide-decorated MWCNTs heterostructured Fenton-like with sonophotocatalytic activities under visible light irradiation

Novel Sm doped Cr2O3 decorated MWCNTs nanocomposite photocatalyst was successfully prepared by a facile hydrothermal method for metoprolol (MET) degradation. A heterogeneous photo -Fenton like system was formed with the addition of H2O2 for ultrasonic irradiation (US), visible light irradiation (Vis) and dual irradiation (US/Vis) systems. The intrinsic characteristics of Sm doped Cr2O3 decorated MWCNTs nanocomposite was comprehensively performed using state-of-art characterization tools. Optical studies confirmed that Sm doping shifted the absorbance of Cr2O3 towards the visible-light region, further enhanced by MWCNTs incorporation. In this study, degradation of metoprolol (MET) was investigated in the presence of Cr2O3 nanoparticles, Sm doped Cr2O3 and Sm doped Cr2O3 decorated MWCNTs nanocomposites using sonocatalysis and photocatalysis and simultaneously. Several different experimental parameters, including irradiation time, H2O2 concentration, catalyst amount, initial concentration, and pH value, were optimized. The remarkably enhanced sonophotocatalytic activity of Sm doped Cr2O3 decorated MWCNTs could be attributed to the more formation of reactive radicals and the excellent electronical property of Sm doping and MWCNTs. The rate constant of degradation using sonophotocatalytic system was even higher than the sum of rates of individual systems due to its synergistic performance based on the kinetic data. A plausible mechanism for the degradation of MET over Sm-Cr2O3/MWCNTs is also demonstrated by using active species scavenger studies and EPR spectroscopy. Our findings imply that (•OH), (h+) and (•O2−) were the reactive species responsible for the degradation of MET based on the special three-way Fenton-like mechanism and the dissociation of H2O2. The durability and stability of the nanocomposite were also performed, and the obtained results revealed that the catalysts can endure the harsh sonophotocatalytic conditions even after fifth cycles. Mineralization experiments using the optimized parameters were evaluated as well. The kinetics and the reaction mechanism with the possible reasons for the synergistic effect were presented. Identification of degraded intermediates also investigated.

Effects of initial mixture temperature and pressure on laminar burning velocity and Markstein length of ammonia/air premixed laminar flames

Ammonia is attractive not only as a hydrogen energy carrier but also as a carbon-free fuel. The goal of the present work is to study the laminar burning velocities and Markstein lengths of ammonia/air under a broad range of conditions including high-temperature and high-pressure because high-temperature and high-pressure conditions are relevant in internal combustion engines. The experiments were conducted in a constant volume chamber for equivalence ratios ranging from 0.8 to 1.2, initial mixture temperatures of 400 and 500 K, and initial mixture pressures ranging from 0.1 to 0.5 MPa. The temperature and pressure exponents were experimentally obtained, and it was clarified that the temperature exponents of the ammonia/air flame were larger than those of the methane/air flame. To evaluate the temperature and pressure effects on ammonia/air flames, these effects were compared with the effects on methane/air flames. Numerical simulations using the detailed reaction mechanisms showed that the effect of the initial mixture temperature on the reaction rate of H + O2 = O + OH was larger for ammonia/air flames than that for methane/air flames. This could be related to the difference in the effects of initial mixture temperature on the H2 and H radical formation reactions. The results also show that the pressure exponent of the ammonia/air flame was closer to zero compared with that of the methane/air flame. This observation can be explained from the standpoint of the effects of pressure on the reaction path of ammonia flames.

Plasma-assisted catalysis for ammonia synthesis in a dielectric barrier discharge reactor: key surface reaction steps and potential causes of low energy yield

Ammonia synthesis experiments were carried out in a coaxial dielectric barrier discharge (DBD) reactor packed with several different supports and metal catalysts. There was a marked increase in the reaction rate, over that obtained in an empty DBD plasma reactor, upon introduction of a packed bed of γ-Al2O3, Ru/γ-Al2O3, or SiO2 particles. The difference in the reaction rates over γ-Al2O3 and Ru/γ-Al2O3 was minimal. Complementary zero-dimensional plasma kinetic model analysis was also performed using inputs from experimental data. This kinetic analysis allowed for gas phase reactions, Eley–Rideal (E–R) reactions, and direct adsorption of radical species on the γ-Al2O3 surface. On the metal surface, dissociative adsorption of N2 and H2, and Langmuir–Hinshelwood reactions were also included. This analysis revealed that, under the conditions of our experiments, ammonia synthesis proceeds principally by the formation of reactive radicals in the gas phase, which then adsorb and participate in E–R reactions on both the metal and support material surfaces. This finding illustrates a challenge for substantially increasing the energy yield for plasma-assisted ammonia synthesis in typical DBD reactors containing packed catalyst beads.

Degradation and transformation of norfloxacin in medium-pressure ultraviolet/peracetic acid process: An investigation of the role of pH

Given that fluoroquinolone antibiotics (FQs) are frequently detected in aquatic environments, there is an urgent need for the development of efficient water treatment technologies for their removal. Peracetic acid (PAA)-based advanced oxidation processes (AOPs) have increasingly attracted attention as promising technologies for water decontamination in this regard. In this study, a novel PAA-based AOP (the medium-pressure ultraviolet (MPUV)/PAA process) was employed to degrade norfloxacin (NOR), which is an extensively applied FQ that is widely present in water. Mechanistic and kinetic aspects of the role of pH on this NOR degradation process were investigated. The results obtained showed that the MPUV/PAA process could effectively degrade NOR (pH = 5–9), and the degradation efficiency was significantly enhanced at pH 7 and 9 compared with that at pH 5. This observation could be attributed to the effect of pH on the ionic forms of NOR and the generation of reactive oxygen species (ROS). Further, the rate of PAA photolysis, which resulted in the formation of reactive radicals, increased with pH, as evidenced by the observed increase in the molar absorption coefficient of PAA (εPAA). Electron paramagnetic resonance (EPR) tests also indicated that the generation of ROS was significantly enhanced when the pH increased from 5 to 7, and at pH 9, a large amount of •OH were possibly consumed by PAA to form organic radicals, leading to a decrease in the •OH signal. Furthermore, it was observed that •OH is primarily responsible for NOR degradation in the MPUV/PAA process at pH 5, whereas organic radicals were primarily responsible for the degradation at pH 7 and 9. The identification of the transformation products (TPs) led to the observation of different NOR transformation pathways owing to the MPUV/PAA process under different pH conditions. Overall, this study provides a comprehensive understanding of the role of pH on the MPUV/PAA degradation behavior of FQs.

Activity of free radical oxidation processes in rats with paracetamol hepatitis and correction with shiitake mushrooms thick extract

The antioxidant defense system controls and inhibits all stages of free radical formation reactions, which start from their initiation and end with the formation of hydroperoxides and malonic dialdehyde. Disorders of the body's antioxidant defense system can be caused by both endogenous and exogenous factors and can lead to the oxidative stress development. For the purpose of the negative impact minimizing and correction of the existing disorders, both natural and synthetic origin antioxidants are used. Preference is given to antioxidants of natural origin, due to their mild action and minimal side effects.
 Shiitake mushrooms are known in China and Japan as a product that has nutritional and medicinal value, for thousands of years. They contain an extremely rich complex of various biologically active substances that can have antioxidant, hepatoprotective effect and influence on the liver diseases pathogenesis.
 The aim of the work was to investigate the effect of shiitake mushrooms thick extract on the activity of free radical processes and indicators of the antioxidant system under the conditions of paracetamol hepatitis in rats.
 The experimental work was being conducted on the white male rats, which were divided into 10 groups of 6 animals each. Acute hepatitis was simulated by intragastric administration of paracetamol in a dose of 1 250 mg/kg 1 time per day (for 2 days) as a suspension in 2% starch gel solution. We investigated the effect of shiitake mushrooms thick extract on the induced pathology, which was administered intragastrically 2 hours before the paracetamol introduction and daily after the lesion in a dose of 150 mg/kg of the rat’s body weight. Silibor was selected as the comparison drug, which was administered according to the same scheme like the investigated extract in a dose of 20 mg/kg of the animal’s body weight. Euthanasia was conducted on the 3rd, 7th and 10th day after the onset of the lesion. Liver homogenate and animal serum were examined. The effectiveness of shiitake mushrooms thick extract was evaluated under the conditions of the caused pathology by superoxide dismutase and catalase activity, as well as by the content of TBA-active and proteins oxidative modification products.
 An increasing of the TBA-active products content and the products of proteins oxidative modification in the serum and liver of animals after the toxic paracetamol exposure testifies to the liver damage and the development of acute hepatitis in rats. Decreased activity of antioxidant enzymes such as catalase and superoxide dismutase was also noted.
 An investigation, which was conducted by us, allowed us to reveal a positive effect of shiitake mushrooms thick extract on the activity of lipoperoxidation and oxidative modification of proteins under the conditions of white rats paracetamol lesion.