Electron Spin Resonance Spectrometer Research Articles

High-efficient removal of tetracycline in water via porous magnetic Ce/Fe photocomposite under visible light

Tetracycline is a typical antibiotic commonly used in various industries which is eco-toxic and quickly causes bacterial resistance. Therefore, studying the efficient removal of tetracycline is necessary to protect the water environment. Herein, a novel Ce/Fe nanoparticle composite (1CCFO) was prepared by the sol–gel method and its removal effects of tetracycline under visible light were performed. The relationship between physicochemical properties of catalyst and photocatalytic degradation effects of tetracycline was analyzed based on a series of characterizations data such as X-ray diffraction (XRD), Raman spectroscopy, a vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) method, X-ray photoelectron spectroscopy (XPS), and ultraviolet–visible (UV–Vis) spectroscopy. The results show that Ce/Fe photocatalyst possesses a large specific surface area, good visible light response, abundant oxygen vacancies and excellent redox performance, exhibiting good adsorption capacity, remarkable catalytic performance and stability. The optimal conditions for tetracycline removal were explored through orthogonal experiments. About 88% of tetracycline can be photodegraded in 1 h under optimal conditions. The possible decomposition pathways, main reactive oxygen species and suitable mechanism of the photocatalytic system were studied by liquid chromatography-mass spectrometry (LC-MS), an electron spin resonance (ESR) spectrometer and free radical quenching experiments. The results show that 1CCFO has an efficient degradation effect on tetracycline under visible light, which provides a feasible method to improve the performance of 1CCFO.

The influence of methane on the development of free radical during low-temperature oxidation of coal in gob

Methane dilutes the oxidation environment of coal in the gob, thus affecting the free radical reaction in low-temperature oxidation of coal. To investigate methane’s effects in this process, three coal samples (i.e., anthracite, coking coal, gas-fat coal) were non-isothermally oxidized to different temperatures in methane-containing environments and then analyzed in an electron paramagnetic resonance (EPR) spectrometer. The experimental results demonstrate that the g-factor and free radical concentration were not only related to oxygen but also associated with methane in the oxidation environment. The g-factor grew with the rising methane and the oxidation temperature. With the rising methane, the free radicals of the anthracite changed from carbon-centred radicals to carbon-centred radicals with an adjacent oxygen atom. Besides, the free radical concentration was found to decrease with methane and increase with oxidation temperature. The rising methane restrains the increase of free racial concentration during coal spontaneous combustion. It is inferred that the influence of methane is related to the competitive adsorption of coal on different gases. The results of this study added to our understanding of the role that methane plays in the low-temperature oxidation of coal and can serve as a reference in coal spontaneous combustion prevention in working face gobs with methane emissions.

Reverse dynamic nuclear polarisation for indirect detection of nuclear spins close to unpaired electrons.

Polarisation transfer schemes and indirect detection are central to magnetic resonance. Using the trityl radical OX063 and a pulse electron paramagnetic resonance spectrometer operating in the Q-band (35 GHz, 1.2 T), we show here that it is possible to use pulsed dynamic nuclear polarisation (DNP) to transfer polarisation from electrons to protons and back. The latter is achieved by first saturating the electrons and then simply using a reverse DNP step. A variable mixing time between DNP and reverse DNP allows us to investigate the decay of polarisation on protons in the vicinity of the electrons. We qualitatively investigate the influence of solvent deuteration, temperature, and electron concentration. We expect reverse DNP to be useful in the investigation of nuclear spin diffusion and envisage its use in electron-nuclear double-resonance (ENDOR) experiments.

ИССЛЕДОВАНИЕ ДОЗИМЕТРИЧЕСКИХ ХАРАКТЕРИСТИК ЧЕЛОВЕЧЕСКОГО ВОЛОСА В ЗАВИСИМОСТИ ОТ СОДЕРЖАНИЯ МЕЛАНИНА

Purpose: Investigation of paramagnetic properties of radiation-induced centers that occur when hair samples are irradiated with ionizing radiation, depending on the color of the sample. Material and methods: A Bruker Elexsys E580 electron paramagnetic resonance spectrometer was used. To improve the signal-to-noise ratio, the spectrum was recorded with three accumulations with a constant scan time equal to one minute. Measurements were made using a highly sensitive rectangular Bruker SuperHighQ resonator. For irradiation of samples, the linear electron accelerator UELR-10-10С2 of the innovation and implementation center for radiation sterilization of the Urals Federal University (Institute of Physics and technology) was used. Results: Research of the EPR signal parameters of the melanin in hair samples of different colors (black, brown, red and gray with different degrees of pigmentation) showed that the intensity of the EPR signal varies depending on the hair color. The higher the radiation sensitivity of the hair, the lighter the color of the hair. The melanin signal, which is the background for the radiation-induced signal, increases with increasing intensity of hair color.

Design of S-scheme heterojunction catalyst based on structural defects for photocatalytic oxidative desulfurization application

Carbon nitride (g-C3N4) is promising for many applications, but its photocatalytic activity is limited by weak visible light absorption and photogenerated carrier complexes. Herein, the thermally defective carbon nitride (d-C3N4) has a larger specific surface area and more reactive sites. d-C3N4 helped Ag3PO4 nanoparticles to be uniformly deposited on the surface of it and made it easier for particle dispersion. d-C3N4 and Ag3PO4 form an S-scheme heterojunction, facilitating the transfer and separation of photogenerated electrons and holes, and possessing high redox ability, which results in improved photocatalytic performance. The experimental results showed that the conversion of 10: 1 Ag3PO4/d-C3N4 for photocatalytic oxidative desulfurization (PODS) under visible light was as high as 92.5 % at 3 h, mainly due to the S-scheme heterojunction further promoting the transfer and separation of photogenerated carriers, suppressing the fast complexation and improving the efficiency of photocatalysis. In addition, the conversion mechanism of PODS was demonstrated using radical capture test, electron paramagnetic resonance spectrometer (EPR), and gas chromatography-mass spectrometry (GC–MS). This study helps researchers to understand the S-scheme heterojunctions constructed based on defects and provides new ideas for the design and application of photocatalysts.

Enhanced degradation of carbamazepine in water over SC-modified NiFe2S4 nanocomposites by peroxymonosulfate activation

In this study, novel Semi-coke-modified NiFe2S4 nanocomposites with different mass ratios are successfully prepared by hydrothermal method to activate peroxymonosulfate (PMS) for the degradation of carbamazepine (CBZ) in water. The factors affecting the degradation of CBZ, such as initial solution pH, PMS and catalyst dosage, inorganic anions, and humic acid (HA) are investigated. The possible PMS activation mechanism and CBZ possible degradation pathways are also explored. The results show that the performance of SCNF-0.5/PMS (mass ratio of SC:NiFe2S4 = 1:2) is better than that of monomeric NiFe2S4 and semi-coke (SC). X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectrometer, and free radical quenching experiments show that both non-radical (1O2 and Ov) and free radical pathways (SO4− and OH) may be responsible for the degradation of CBZ, but 1O2 is dominant active species. S2− promotes the Ni2+/Ni3+, Fe2+/Fe3+ cycle to ensure the stable performance of the catalyst, and the oxygen vacancies (Ov) in the SC act synergistically with the catalyst to promote the degradation of CBZ. This study may provide new insights into the degradation of antibiotics in water by modifying stable bimetallic sulfide to activate PMS.

Radical footprinting and regularity revealing during the pyrolysis of technical lignins

Revealing radical-mediated reactions is conducive to illustrate lignin pyrolysis and achieve subsequent regulation. Three technical lignins (hot-water-extracted lignin, kraft lignin, and soda lignin) were selected in this study and pyrolyzed from 400 °C to 700 °C, and their pyrolysis radicals in both chars and bio-oils were monitored with the electron paramagnetic resonance spectrometer. Results showed that spin concentrations of char radicals had a volcanic trend against the pyrolysis temperature, and reached the maximum values at 550–600 °C. However, the contents of bio-oil radicals were low during pyrolysis at low and medium temperature, but their spin concentrations exploded abruptly over 600–650 °C. Meanwhile, the bio-oil yields were found to drop after 550–600 °C, and the three inflection temperatures for char radicals, bio-oil radicals, and bio-oil yields were perfectly matched. These findings systematically elucidated the radical regularity in technical lignin pyrolysis and fundamentally contributed to the development of radical-mediated lignin pyrolysis mechanisms.

Reveal of free radicals in manganese-based catalysts and their roles during selective catalytic reduction of nitrogen oxide

HypothesisManganese-based catalysts attract extensive attentions in low-temperature selective catalytic reduction (SCR) of nitrogen oxide (NOx). However, seldom work focuses on the existence of free radicals and their roles in SCR. ExperimentsIn this work, electron paramagnetic resonance spectrometer and density functional theory are combined to reveal surface characterizations of manganese oxide and Ce/La-doped manganese oxides. FindingsAs a result, superoxide radical (O2*) exists on manganese-oxide surface, produces nitrogen-containing free radical, and functions as electron transfer between NOx and NH3 at 100 °C, resulting in good NOx conversion as well as N2 selectivity at the same time. The O2* is born of accepting electrons on adsorbed oxygen through overlapped orbits of Mn-d and O-p. Additional metal doping increases the percentage of O2* among all oxygen species from 2.9 % to 6.9 % (Ce doping) and 5.1 % (La doping). The order of O2* percentage is consistent with the NOx-conversion order at 100 °C, i.e., Ce doping (91.6 %) > La doping (55.7 %) > catalyst without doping (27.5 %). Above result helps to understand interface behaviors of manganese-based catalyst in SCR. This work is also in favor of developing more effective low-temperature catalysts.

Perspective on Fe0-PS synergetic effect and reaction mechanism in the thallium(I) contaminated water treatment

Due to extreme toxicity of the element of thallium (Tl), increasing aqueous Tl pollution incidents have aroused growing concerns. As the prevalent and stable form, i.e., monovalent Tl, the highly efficient removal methodologies of Tl(I) from (waste)water remains limited and challenging. In this study, an advanced oxidation method, the feasibility of using zero valent iron (Fe0) coupled with persulfate (PS) to treat Tl(I)-containing synthetic wastewater was investigated. Its influence parameters, including reaction time, initial Tl concentration, dosages of PS and Fe0, initial and coagulation pH, temperature, coexisting ions and organic matter (NO3−, SO42−, Cl− and HA) were examined. The results revealed that the system can be applied to a wide range of pH and temperature and the reaction equilibrium can be reached in about 30 min. Favorable Tl(I) removal rate (>98%) was observed in the synthetic wastewater with medium and relatively high Tl(I) concentration (≤0.250 mM). The analyses of characterization results including electron spin resonance spectrometer and X-ray photoelectron spectroscopy indicated that ·OH played a vital role in the removal of Tl(I), which was oxidized and removed by co-precipitation. Fe0 can be served as a stable source of Fe2+ to efficiently catalyze PS. The remaining Fe0 can be easily separated because of its magnetism, assuring the promising reusability of the reactant. The study aims to provide references for treatment of real Tl polluted wastewater.

A design of resonant cavity with an improved coupling-adjusting mechanism for the W-band EPR spectrometer

We report a new design of resonant cavity for a W-band electron paramagnetic resonance (EPR) spectrometer. An improved coupling-adjusting mechanism, which is robust, compact, and suits with both solenoid-type and split-pair magnets, is utilized on the cavity, and thus enables both continuous-wave (CW) and pulsed EPR experiments. It is achieved by a tiny metal cylinder in the iris. The coupling coefficient can be varied from 0.2 to 17.9. Furthermore, two pistons at each end of the cavity allow for adjustment of the resonant frequency. A horizontal TE011 geometry also makes the cavity compatible with the two frequently used types of magnets. The coupling-varying ability has been demonstrated by reflection coefficient (S 11) measurement. CW and pulsed EPR experiments have been conducted. The performance data indicates a prospect of wide applications of the cavity in fields of physics, chemistry and biology.

Underlying mechanisms of promoted formation of haloacetic acids disinfection byproducts after indometacin degradation by non-thermal discharge plasma

Indometacin (IDM), as a kind of non-steroidal anti-inflammatory drugs, has ecological and health risks, which is the potential precursor of chlorination disinfection byproducts (DBPs). Non-thermal discharge plasma was attempted to eliminate IDM and control subsequent DBPs formation. Satisfactory removal performance for IDM was realized by the plasma oxidation; almost 100% of IDM was removed within 2 min. Relatively greater removal efficiency was gained at a higher plasma voltage and a lower pH level. Electron paramagnetic resonance spectrometer revealed that reactive species ·OH, O2·−, and 1O2 were responsible for IDM decomposition. Based on analyses of Fourier transform infrared spectroscopy, two-dimensional correlation spectroscopy, three-dimensional fluorescence spectrum, and gas chromatography-mass spectrometer, attacks of reactive species resulted in sequence breakages in functional groups of IDM, leading to production of small molecular alcohols, acids, and amines. Possible decomposition pathways of IDM were proposed. The produced acetamide and 1H-indol-5-ol were important precursors of DBPs. Formation and toxicity of nitrogen-containing DBPs were dramatically inhibited after IDM degradation; however, those of haloacetic acids were strengthened. The relevant roadmaps among DBPs and degradation intermediates were figured out. This study revealed the underlying mechanisms of IDM degradation by discharge plasma and its potential risks in chlorination disinfection.

Development of Electron Paramagnetic Resonance Magnet System for In Vivo Tooth Dosimetry

As part of a homebuilt continuous wave electron paramagnetic resonance (EPR) spectrometer operating at 1.2 GHz, a magnet system for in vivo tooth dosimetry was developed. The magnet was designed by adopting NdFeB permanent magnet (PM) for the main magnetic field generation. For each pole of the magnet, 32 cylindrical PMs were arranged in 2 axially aligned ring arrays. The pole gap was 18 cm, which was wide enough for a human head breadth. The measured magnetic field was compared with the magnetic field distribution calculated in a finite element method (FEM) simulation. EPR spectra of intact human teeth irradiated 5 and 30 Gy were measured for the performance test with the developed magnet system and spectrometer. The measured mean magnetic flux density was estimated to be 44.45 mT with homogeneity of 1,600 ppm in a 2 cm diameter of the spherical volume of the XY plane, which was comparable to the FEM simulation results. The sweep coefficient of the magnetic field sweep coil was 0.35 mT per Ampere in both the measurement and FEM simulation. With ±9 A current, the sweep range was 5.7 mT, which was sufficiently wide to measure the tooth radiation-induced signal (RIS) and reference material. The peak-to-peak amplitude of the measured modulation field was 0.38 mT at the center of the magnet. With the developed magnet fully integrated into an EPR system, the EPR spectra of 5 and 30 Gy irradiated teeth were successfully acquired. The developed magnet system showed sufficiently acceptable performance in terms of magnetic flux density and homogeneity. The EPR spectrum of tooth RIS could be measured ex vivo. The RIS of 5 and 30 Gy irradiated teeth was clearly distinguishable from intact human teeth.

Effect of thermal damage on pore development and oxidation reaction of coal

AbstractWith the coal entering deep mining, the thermal damage to the destruction of the coal body structure, causing the phenomenon of coal spontaneous combustion is more and more common. To better understand the effect of thermal damage on coal spontaneous combustion, the law of thermal damage on pore structure and free radical of coal was studied by automatic specific surface area analyzer and electron spin resonance spectrometer. It was concluded that 225°C was a key point of thermal damage on coal spontaneous combustion. The pore structure analysis indicates that the specific surface area and pore volume of coal decrease with the increase of thermal damage temperature, while the average pore diameter increases gradually. While the specific surface area of Qianyingzi coal is the lowest at 225°C, which is 67.5% of that of raw coal. The average pore size of Zhaotong coal continues to increase by 18.9%. In addition, the pore structure of coal changes greatly in the thermal damage temperature range of 150–225°C, and the connectivity of coal pore is greatly strengthened at this range. The free radical results show that the free radical concentration in thermally damaged coal soars, compared with that in raw coal, and reaches the maximum value at 225°C, indicating that the active groups in coal are greatly active at this temperature. The g factor value declines firstly, then increases, and finally falls. These investigations may serve to reveal the internal mechanism of thermal damage on coal structure and natural oxidation characteristics and provide experimental basis for the prevention and control of coal spontaneous combustion affected by thermal damage.

Determination of the number of radiation induced alanine radicals by measuring the magnetic moment using SQUID magnetometer

This study proposes a technique for alanine dosimetry using a superconducting quantum interference device (SQUID) magnetometer. Conventional measurements performed using an electron spin resonance spectrometer typically detect the relative amount of stable radicals generated in irradiated alanine using a magnetic field and microwaves. The SQUID magnetometer uses a magnetic field and a pickup coil to measure the total magnetic moment of stable alanine radicals. In this study, we demonstrate the principle of the alanine/SQUID measurement system. SQUID successfully detected the alanine radical at 4.2 K, and the reproducibility test showed that the relative standard deviation were 0.13 % and 0.10 % at the minimum value and averaged value in the measurement with different angles after 11 repetitions. This study shows that calibration curves can be constructed between 0.3 and 101 kGy and that the magnetic moment of alanine radicals can be measured in that dose range. The magnetic moments corresponding to the dose range of the calibration curve were 6.7×10−3 to 1.1×10−1μA⋅m2⋅mg−1. The number of radicals in alanine pellet induced by 101 kGy irradiation was 1.91×1022kg−1, which was determined by measuring the magnetic moment in the range of 80 K–300 K. Radiation chemical yield (G-value) of the alanine derived from the measured radical number was 0.31 μmol⋅J−1.

Highly synergetic effect for norfloxacin degradation by coupling underwater bubble plasma formation with a Fe (III)–S (IV) system

• Coupling plasma with Fe (III)–S (IV) system can efficiently remediate NOR and prolong it during plasma-off. • Underwater bubble plasma accelerates radical chain reactions and improves the transfer efficiency. • Enhanced NOR degradation is attributed to the presence of • OH and SO 4 •− . • • OH and SO 4 •− can be regenerated by chain reactions through plasma-generated effects. • The synergetic degradation mechanism and possible contribution of approaches are proposed. Antibiotics are widely used to treat or prevent infectious diseases in human and veterinary medicine. Excessive residues in the aquatic environment lead to increasingly prominent antibiotic pollution; therefore, it is urgent to develop sustainable strategies for rapidly degrading antibiotics. In this study, a highly synergetic effect for norfloxacin (NOR) remediation is achieved by coupling underwater bubble plasma formation with a Fe (III)–S (IV) system due to the efficient utilization of reactive species in chain reactions. The degradation rate using synergetic approach can reach 76.4% within 50 min discharge, and further increases significantly to 94.4% after 5 h post-discharge. The effects of pulsed peak voltage and Fe (III)/S (IV) dosage on NOR removal are characterized. The existence of hydroxyl radicals ( • OH) and sulfate radicals (SO 4 •− ) are proved by electron spin resonance spectrometer (ESR) during degradation. Furthermore, radical scavenger experiments demonstrate that • OH and SO 4 •− play a crucial role in degradation. Underwater bubble plasma provides the oxic and acidic liquid environment for the Fe (III)–S (IV) system to accelerate the self-perpetuating chain reactions. These reactions not only introduce SO 4 •− and generate more • OH during plasma-on, but also induce their regeneration and further prolong the degradation process during plasma-off through plasma-generated effects. Finally, the degradation intermediates of NOR are identified, and a possible degradation pathway is proposed. The possible contribution weight of each approach on the degradation rate is speculated. These new findings offer promising applications for developing a technology with real potential for the treatment of organic compounds in industrial wastewater treatment.

Maximizing the applicability of continuous wave (CW) Electron Paramagnetic Resonance (EPR): what more can we do after a century?

Electron Paramagnetic Resonance/Electron Spin Resonance (EPR/ESR) spectroscopy is a powerful experimental approach solving challenging problems that are inaccessible to other experimental techniques. While pulsed EPR techniques and their applications have been the central focus of the field nowadays, methodology development and application of continuous wave (CW) EPR have never been undervalued. Although the importance of EPR in research has been recognized in many areas as indicated by the increasing number of EPR research articles published every year, the growth in the number of EPR research teams seems to not match the former, likely caused by the relatively high cost of modern pulsed EPR spectrometers. In this perspective, we aim to discuss the new areas and new directions of the application of CW EPR in combination with spin labeling that are slightly different from the classic/traditional applications of the CW EPR technique. Based on our experience, we show example applications of CW EPR on the interfaces of protein-confinement materials, protein-inorganic crystal lattices, protein-nanoparticles, and protein-polymers. Various structure and dynamics information can be resolved from the data analysis of CW EPR, leading to enhanced understanding of protein biophysics upon interaction with the synthetic nanostructures as well as possible guidance of hybrid materials development based on the combination of proteins and nanostructures. We also discussed the possibilities of even broadening the application spectrum of EPR spectroscopy. The relatively high affordability of CW EPR spectrometers (as compared to the pulsed ones) also facilitates the growth in EPR research groups worldwide.

Mode of inactivation of Staphylococcus aureus and Escherichia coli by heated oyster-shell powder

• HOS is a highly effective disinfectant for the bacterial inactivation. • ROS species verification in HOS revealed the presence of singlet oxygen. • Disparate HOS disinfection rates between S. aureus and E. coli were firstly studied. • FM, TEM, and K + leakage provide early diagnosis of altered membrane permeability. • Biophysical properties and 3D images of inactivated bacteria were firstly identified. Bacterial infection and subsequent disinfection of microorganisms are ongoing issues around the world. Bio-calcium oxide derived from heated oyster-shell (HOS) waste product has been shown to be an effective disinfectant and has the additional advantage of the marketing use of utilizing waste materials that would otherwise contribute to environmental problems; however, its mode of inactivation is unknown. In this research, fluorescence microscopy (FM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and electron spin resonance (ESR) spectrometer techniques were used to characterize the mode of inactivation of S. aureus and E. coli via HOS. This is the first work to provide insight into the three-dimensional morphology and biophysical properties of the inactivated S. aureus and E. coli cells via HOS. Noteworthy, the presence of singlet oxygen in HOS suspension altered bacterial cell permeability, leading to sustained inactivation. The HOS exhibited excellent disinfection capacity and achieved a 5-log-inactivation E. coli within 60 min with a dose of 0.2 g/L, superior to other shell-derived disinfectants. Thus, HOS provides a cost-effective disinfectant for the application of controlling pathogens.

Enhancement of Fenton processes at initial circumneutral pH for the degradation of norfloxacin with Fe@FeS core–shell nanowires

ABSTRACT The disadvantages of narrow working pH range (2.5–4.0), accumulation of iron sludge and incomplete degradation have hindered the practical application of the traditional homogeneous Fenton technique. In this research, Fe@FeS core–shell nanowires were synthesised and the innovative Fe@FeS/Fe2+/H2O2 system was adopted for norfloxacin (NOR) degradation at an initial circumneutral pH. More than 95% NOR has been removed in the Fe@FeS/Fe2+/H2O2 system within 30 min at pH 7. After investigating the concentration change of total iron, Fe2+ and H2O2 during the degradation process, NOR degradation in the Fe@FeS/Fe2+/H2O2 system might be attributed to the combined effect of homogeneous Fenton reaction and heterogeneous Fenton process. Besides that, the added Fe@FeS has accelerated Fe3+/Fe2+ redox cycle with extremely high degree. The generated reactive ●OH has been identified by electron paramagnetic resonance spectrometer results, possible degradation intermediates have also been proposed according to Gas chromatography-mass spectrometry analysis results. Moreover, Fe@FeS core–shell nanowires showed excellent reusability, it is a promising heterogeneous Fenton catalyst that is applicable for practical application.

Effect of controlled temperature and biomass addition on the formed environmental persistent free radicals (EPFRs) in sewage sludge-based biochar from pyrolysis treatment

Sludge-based biochar derived from pyrolysis treatment is often utilized into soil agricultural fertilizer and soil amendment. While recent studies found that a new class of emerging environmental pollutant, environmental persistent free radicals (EPFRs) could be produced in combustion-based particles and airborne particulate matter. This study was aimed to determine if similar radicals were present in biochar derived from the pyrolyzed organic solid waste. The formation of EPFRs in sludge-based biochar during the pyrolysis treatment were in detailed characterized. EPFRs in biochar derived from sewage sludge pyrolysis at 200–600 ℃ and with various biomass addition were identified by using Electron paramagnetic resonance spectrometer. Three types of EPFRs were mainly spotted in the obtained biochar, including oxygen-centered, carbon-centered and F-centered radicals. Results revealed that the spin concentration of EPFRs decreased with temperature, and an increasing pyrolysis temperature could inhibit the formation of EPFRs. Lower pyrolysis temperature (＜400 ℃) favored the production of carbon-centered radicals, whereas higher temperature (＞400 ℃) mainly produced oxygen-centered radicals. Adding biomass also significantly affected the spin concentration and types of EPFRs. The spin concentration of EPFRs reached the highest value when adding 50% of biomass. The g-values of EPFRs in biochar were all less than 2.0030, indicating that carbon-centered and F-centered free radicals had occupied the dominance. In addition, the determination on the half-lives of EPFRs indicated that carbon-centered EPFRs were almost transformed to oxygen-centered EPFRs with storage time increased. The oxygen-centered free radicals became the dominant type of EPFRs after 100 days and even 200 days storage. The obtained findings imply the ecotoxicity of sludge-based biochar and give in-depth insight on the formation EPFRs, thus guiding the innocuous utilization of sludge.

Modified Approach Using Mentha arvensis in the Synthesis of ZnO Nanoparticles—Textural, Structural, and Photocatalytic Properties

Zinc oxide arouses considerable interest since it has many applications—in microelectronics, environmental decontaminations, biomedicine, photocatalysis, corrosion, etc. The present investigation describes the green synthesis of nanosized ZnO particles using a low-cost, ecologically friendly approach compared to the classical methods, which are aimed at limiting their harmful effects on the environment. In this study, ZnO nanoparticles were prepared using an extract of Mentha arvensis (MA) leaves as a stabilizing/reducing agent, followed by hydrothermal treatment at 180 °C. The resulting powder samples were characterized by X-ray diffraction (XRD) phase analysis, infrared spectroscopy (IRS), scanning electron microscopy (SEM), and electron paramagnetic resonance (EPR). The specific surface area and pore size distribution were measured by the Brunauer–Emmett–Taylor (BET) method. Electronic paramagnetic resonance spectra were recorded at room temperature and at 123 K by a JEOL JES-FA 100 EPR spectrometer. The intensity of the bands within the range of 400–1700 cm−1 for biosynthesized ZnO (BS-Zn) powders decreased with the increase in the Mentha arvensis extract concentration. Upon increasing the plant extract concentration, the relative proportion of mesopores in the BS-Zn samples also increased. It was established that the photocatalytic performance of the biosynthesized powders was dependent on the MA concentration in the precursor solution. According to EPR and PL analyses, it was proved that there was a presence of singly ionized oxygen vacancies (V0+) and zinc interstitials (Zni). The use of the plant extract led to changes in the morphology, phase composition, and structure of the ZnO particles, which were responsible for the increased photocatalytic rate of discoloration of Malachite Green dye.