Electron Paramagnetic Resonance Analysis Research Articles

Fabrication of magnetic MnFe2O4@HL composites with an in situ Fenton-like reaction for enhancing tetracycline degradation

Novel magnetic MnFe2O4@honey locust-derived carbon (MnFe2O4@HL) composites were synthesized via an in-situ hydrothermal precipitation method, and were characterized as an excellent Fenton-like catalyst for tetracycline (TC) degradation. Results showed that the vast majority of TC was mineralized in hydrogen peroxide (H2O2)/MnFe2O4@HL system after 120 min of reaction time with 92.3% of removal efficiency and the removal of 71.3% of total organic carbon (TOC). Systematic characterization approaches including scanning electron microscope (SEM), energy-dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometry (VSM) were introduced to reveal the microstructure and properties of magnetic MnFe2O4@HL composites. Hydroxyl radicals (•OH) were identified as the major reactive oxygen species (ROS) via the quenching experiments and electron spin resonance (ESR) analysis, while superoxide radicals (·O2−) played a negligible role. The dual cycles of both Fe3+/Fe2+ and Mn3+/Mn2+ were significant enhanced through the bimetallic redox effect and the electron transfer effect of the carbon-based functional group, accelerating the generation of •OH. The removal of TC was still up to 79.3% after five reuses of magnetic composites, demonstrating the MnFe2O4@HL with excellent stability and reuse performance. The influence of various experimental control conditions involving initial pH, catalyst and H2O2 dosage, temperature, as well as common anions (Cl−, NO3−, and HCO3−) on the degradation of TC were finally evaluated. This study provides an efficient in-situ generation method of emerging magnetic materials, and systematically reveals its mechanism of homogeneous Fenton-like catalysis, which shows promising applications for the degradation of environmental contaminants.

Fabrication of OVs enriched BiOCl microflowers doped with Fe3+ for effective destruction of two typical contaminants

ABSTRACT In this study, a one-step solvothermal method was used to fabricate Fe3+ doped BiOCl microflowers with abundant oxygen vacancies (OVs) in the presence of glacial acetic acid. Various analytical techniques were employed to characterize the structural, morphological, and optical properties of the prepared samples. The presence of OVs was confirmed by low temperature electron paramagnetic resonance (EPR) analysis. The photocatalytic results show that Fe3+ doped BiOCl photocatalysts have higher activity than the bare BiOCl, and 10% Fe3+/BiOCl exhibits the highest photocatalytic performance, the photocatalytic efficiency of this sample is 2.3 and 1.1 times higher than that of the blank BiOCl toward photocatalytic degradation of perfluorooctanoic acid (PFOA) and rhodamine B (RhB), respectively. Furthermore, Fe3+ doped BiOCl demonstrates excellent reusability. Based on the experimental observations, an enhancement mechanism for the photocatalytic activity of Fe3+ doped BiOCl was reasonably elucidated.

Fe3O4 derived from the decomposition of siderite as a heterogeneous photocatalyst to degrade 2,4-dichlorophenol via activating PMS

This study showcases the performance of Fe3O4 (S600) derived from the decomposition of siderite in activating peroxymonosulfate (PMS) for the 2,4-dichlorophenol (2,4-DCP) degradation, as well as the enhancement of visible light in the S600/PMS system. With the involvement of visible light, 2 g/L Fe3O4 and 0.5 mM PMS achieved 100 % degradation of 2,4-DCP within 70 min. Singlet oxygen (1O2) and hydroxyl radicals (OH) were the primary reactive species responsible for 2,4-DCP degradation under visible light irradiation based on the scavenging experiments and electron paramagnetic resonance (EPR) analysis. Importantly, compared to the absence of visible light, the visible light boosted 1O2 production and accelerated 2,4-DCP degradation. The effects of various operating parameters on the degradation efficiency were also examined, and the intermediates and possible degradation pathways of 2,4-DCP were identified. This study proves that the integrated utilization of natural siderite derivatives to activate oxidants for pollutant degradation is a promising approach.

Inducing oxygen vacancies in ZnO/Co3O4 via g-C3N4 carrier for enhanced universality and stability in TC degradation

The universality and stability are significant for efficient environmental catalysts. Herein, a series of g-C3N4 supported ZnO/Co3O4 nanocomposites (ZCO-CN) were constructed through the one-pot pyrolysis method. The constructed ZCO-CN composites showed superior properties in peroxymonosulfate (PMS) activation to degrade tetracycline (TC) with remarkable universality and stability. It has been able to accommodate common anions and cations and a wide pH range (3−11) in the real wastewater system with a removal rate of 91% within 5 min. After 5 cycles, the degradation rate can still be maintained at 83.8%. Moreover, ZCO-CN still displayed outstanding catalytic performance for methyl orange and oxytetracycline. The singlet oxygen (1O2) and superoxide radicals (∙O2-) during the TC degradation process are confirmed through quenching experiments and electron paramagnetic resonance (EPR) analysis. The abundant N in the support of g-C3N4 can form interactions with ZnO/Co3O4 (ZCO) facilitating the formation of oxygen vacancies, which promotes the formation of 1O2, inhibits the leaching of metal ions and significantly enhances the stability of the catalyst. This work proposes an immobilized ZnO/Co3O4/g-C3N4 with enhanced catalytic performance, high universality, and stability for PMS activated toward pollution removal.

Highly efficient activation of peroxymonosulfate by ZIF-67 anchored cotton derived for ciprofloxacin degradation

Metal–organic framework (MOF) and MOF-derived materials have attracted extensive research interest as environmental catalysts. In this study, a composite material (ZIF-67/CCot-8) was successfully prepared using cotton fiber as a substrate and growing ZIF-67 in situ. This material exhibited excellent catalytic performance and significantly improved the efficiency of antibiotics degradation. ZIF-67/CCot-8 at a concentration of 0.05 g/L, combined with 0.2 mM peroxymonosulfate (PMS), removed approximately 97% of ciprofloxacin (CIP) and 99% of tetracycline and sulfamethoxazole within 15 min. The high catalytic efficiency of this catalyst is mainly attributed to the uniform distribution of ZIF-67-derived nanoparticles on the surface of the cotton fibers, providing abundant active sites and thereby significantly enhancing the efficiency of antibiotics degradation. Radical quenching experiments and electron paramagnetic resonance (EPR) analyses revealed that sulfate radicals (SO4•-) and singlet oxygen (1O2) were the main active species. Mass spectrometry (MS) was used to elucidate the CIP degradation pathway. The growth of the roots and stems of soybean sprouts in different water environments (tap water, treated water, and untreated water) was also observed. The results demonstrated a significant improvement in the inhibition of plant growth in the post-degradation CIP solution, indicating a substantial reduction in the toxicity of the degraded aqueous solution. To validate the practicality of the ZIF-67/CCot-8/PMS system, a continuous-flow water-treatment device was designed. This system removed 98% of the CIP solution within 180 min, demonstrating its excellent durability. This study presents a potential pathway for effective antibiotics removal using MOF-derived materials.

Mechanistic investigation of the electricity and gallic acid synergistically accelerated Fe(III)/Fe(II) cycle for the degradation of carbamazepine

This study investigated the application of a natural plant polyphenol, gallic acid (GA) to form complex with iron to promote the redox cycle of Fe(III)/Fe(II) under neutral initial pH conditions in the electrochemical (EC) system for activation of peroxymonosulfate (PMS) to efficiently degrade carbamazepine (CBZ). Results demonstrated that the synergistic effects of GA and EC significantly improved the removal efficiency, and the EC/GA/Fe(III)/PMS system effectively removed 100% of CBZ within a wide initial pH range of 3.0–7.0. The optimum stoichiometric ratio of GA to Fe(III) was found as 2:1. Investigations including quenching experiment, chemical probe analysis, and electron paramagnetic resonance (EPR) analysis were conducted to identify the primary reaction radicals as •OH, SO4•−, along with the 1O2 and Fe(IV). In the EC/GA/Fe(III)/PMS system, the synergistic effect of GA and electrochemistry led to a remarkable enhancement in the generation of •OH. Furthermore, the complexation reduction mechanism of GA and Fe(III) was proposed based on experimental and instrumental analyses, which demonstrated that the semi-quinone products of GA were the main substances promoting the Fe(III)/Fe(II) cycle. Mass spectrometry results showed that CBZ generated 27 byproducts during degradation, with formic acid as the main product of GA. The degradation efficiency of the EC/GA/Fe(III)/PMS system remained stable and excellent, exhibiting remarkable performance in the presence of various inorganic anions, including Cl− and NO3−, as well as naturally occurring organic compounds such as fulvic acid (FA). Overall results indicated that the EC/GA/Fe(III)/PMS system can be applied to effectively treat practical wastewater treatment without requirement of pH adjustment.

Superstructure and Correlated Na+ Hopping in a Layered Mg-Substituted Sodium Manganate Battery Cathode are Driven by Local Electroneutrality.

In this work, we present a variable-temperature 23Na NMR and variable-temperature and variable-frequency electron paramagnetic resonance (EPR) analysis of the local structure of a layered P2 Na-ion battery cathode material, Na0.67[Mg0.28Mn0.72]O2 (NMMO). For the first time, we elucidate the superstructure in this material by using synchrotron X-ray diffraction and total neutron scattering and show that this superstructure is consistent with NMR and EPR spectra. To complement our experimental data, we carry out ab initio calculations of the quadrupolar and hyperfine 23Na NMR shifts, the Na+ ion hopping energy barriers, and the EPR g-tensors. We also describe an in-house simulation script for modeling the effects of ionic mobility on variable-temperature NMR spectra and use our simulations to interpret the experimental spectra, available upon request. We find long-zigzag-type Na ordering with two different types of Na sites, one with high mobility and the other with low mobility, and reconcile the tendency toward Na+/vacancy ordering to the preservation of local electroneutrality. The combined magnetic resonance methodology for studying local paramagnetic environments from the perspective of electron and nuclear spins will be useful for examining the local structures of materials for devices.

Enhancement effect of Fe(III) on the degradation of fluoranthene by iron sulfide-activated percarbonate: Performance and mechanism

In the advanced oxidation process for the remediation of organic contaminated water and soil, sodium percarbonate (SPC) is regarded as a potential oxidant. Iron sulfide (FeS) was chosen as an activator in this work for assisting fluoranthene (FLT) removal, with Fe(III) addition overcoming the solution pH constraint on FLT removal in the SPC/FeS process. At the optimal chemical dosages, SPC/FeS (pH = 3.0) and SPC/FeS/Fe(III) (pH = 5.7) processes removed approximately 100% and 92.8% of FLT, respectively. Based on the results of scavenging trials and electron paramagnetic resonance analysis, HO• was the dominant reactive oxygen species in FLT removal by SPC/FeS and SPC/FeS/Fe(III) processes. Dissolved oxygen (DO) played a crucial role in FLT removal, and SPC/FeS/Fe(III) process was more dependent on DO than SPC/FeS process. Both processes overcame the limitation of Cl– on the application of SPC-induced oxidation process. In actual groundwater experiments, 95.5% of FLT was removed in SPC/FeS/Fe(III) process at an initial solution pH of 5.0. In soil slurry trials, 12 h was the optimal reaction time for FLT removal, and the SPC/FeS and SPC/FeS/Fe(III) processes degraded 85.6% and 86.7% of FLT, respectively. In conclusion, the FeS-activated SPC-induced oxidation process offers perspectives for PAHs contaminated field decontamination and contributes to the optimization of modern oxidation methods.

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”.

Performance and mechanism of efficient activation of peroxymonosulfate by Co-Mn-ZIF derived layered double hydroxide for the degradation of enrofloxacin

Due to the uncontrolled synthesis of layered double hydroxides (LDHs), a simple and efficient strategy was needed to construct high-performance LDHs. Herein, Co-Mn-ZIF was used as the sacrificial template to form cobalt-manganese-nickel LDH (M−Co−Mn−Ni LDH) through the process of deconstruction and reconstruction. Due to the sufficient in-situ etching of the Co-Mn-ZIF template, M−Co−Mn−Ni LDH exhibited a larger specific surface area (482.4 m2/g) and pore volume (3.3 × 10−2 cm3/g) as well as easier diffusion and interaction with reaction sites of organic molecules. The prepared M−Co−Mn−Ni LDH showed high catalytic performance for the degradation of enrofloxacin (ENR) by activating peroxymonosulfate (PMS), with the removal rate of 88.5 % within 30 min. The quenching reaction and electron paramagnetic resonance (EPR) analysis results indicated that SO4•− and 1O2 were main active substances in the oxidation process of ENR. In addition, the Co-Mn-Ni LDH/PMS system was stable and almost unaffected by pH values, organic and inorganic substances, and it could achieve high removal efficiency in various pollutant samples. This work provided a convenient and efficient approach for the construction of high-performance MOFs derived LDHs catalysts.

Dual Z-scheme Pr2Sn2O7/P@g-C3N4/SnS2 heterojunctions for the removal of tetracycline antibiotic by persulfate activation: Kinetics, thermodynamic parameters, density functional theory, and toxicity studies

In this study, a Pr2Sn2O7/P@g-C3N4/SnS2 ternary nanocomposite photocatalyst is obtained by hydrothermal synthesis followed by mechanical grinding. By separating electrons and holes (e−/h+) effectively through the dual Z-scheme heterojunction and activating persulfate (PS), the heterojunction demonstrated superior visible light-driven catalytic activity. Tetracycline (TC) was degraded (89.48%) in 60 min using 30 mg/L of ternary composite and 30 mg/L of PS. This system displayed the highest pseudo-first-order kinetic constant (0.0989 min−1 and R2 = 0.969). The electron paramagnetic resonance analysis showed that SO4−, OH, O2−, and 1O2 were involved in TC degradation. TC's vulnerability positions and degradation pathways were analyzed using DFT and gas chromatography-mass spectrometry analysis, while toxicity assessment software was used to determine the toxicity of intermediate products. Thus, Pr2Sn2O7/P@g-C3N4/SnS2 was established to be a promising photocatalyst template for pollutant remediation.

Tuning visible light-driven photocatalytic NO removal: Insights from glucose-derived CQDs/ZnO nanorods composite

The potential of visible light photocatalysis in mitigating environmental pollutants has gained significant attention. In this study, we investigate the photocatalytic NO removal efficiency of oxygen defect-rich zinc oxide nanorods (ZnO NRs), facilitated by the incorporation of carbon quantum dots (CQDs) under mild conditions. The successful integration of CQDs with ZnO NRs represents a novel and sustainable approach for efficient NO removal under visible light irradiation. Notably, the CQDs/ZnO NRs shows a substantial increase in NO removal efficiency (71.9%), low toxicity (2.7%) and durability (only 7.7% efficiency reduction after five cycles). The synergetic effects of CQDs and oxygen defects within the ZnO NRs structure, which broadens the light absorption spectrum, facilitates electron separation, thus enhanced photocatalytic NO removal. Furthermore, photoluminescence, active species trapping experiments, and electron spin resonance analysis have confirmed the generation of hydroxyl radicals (•OH) and superoxide radicals (•O2–) during the excitation of electrons. Finally, the synergetic mechanism of CQDs and oxygen defects in ZnO NRs for amplifying visible-light-driven photocatalytic NO removal was elucidated.

Boosted micropollutant removal over urchin-like structured hydroxyapatite-incorporated nickel magnetite catalyst via peroxydisulfate activation

In this work, urchin-like structured hydroxyapatite-incorporated nickel magnetite (NiFe3O4/UHdA) microspheres were developed for the efficient removal of micropollutants (MPs) via peroxydisulfate (PDS) activation. The prepared NiFe3O4/UHdA degraded 99.0 % of sulfamethoxazole (SMX) after 15 min in 2 mM PDS, having a first-order kinetic rate constant of 0.210 min−1. In addition, NiFe3O4/UHdA outperformed its counterparts, i.e., Fe3O4/UHdA and Ni/UHdA, by giving rise to corresponding 3.6-fold and 8.6-fold enhancements in the SMX removal rate. The outstanding catalytic performance can be ascribed to (1) the urchin-like mesoporous structure with a large specific surface area and (2) the remarkable synergistic effect caused by the redox cycle of Ni3+/Ni2+ and Fe2+/Fe3+ that enhances multipath electron transfers on the surface of NiFe3O4/UHdA to produce more reactive oxygen species. Moreover, the effects of several reaction parameters, in this case the initial solution pH, PDS dosage, SMX concentration, catalyst loading, co-existing MPs and humic acid level on the catalytic performance of the NiFe3O4/UHdA + PDS system were systematically investigated and discussed in detail. The plausible catalytic mechanisms in the NiFe3O4/UHdA + PDS system were revealed via scavenging experiments and electron paramagnetic resonance analysis, which indicated a radical (•OH and SO4•−) as the major pathway and a nonradical (1O2) as the minor pathway for SMX degradation. Furthermore, NiFe3O4/UHdA exhibited fantastic magnetically separation and retained good catalytic activity with a low leached ion concentration during the performance of four cycles. Overall, the prepared NiFe3O4/UHdA with outstanding PDS activation could be a promising choice for the degradation of persistent organic pollutants from wastewater.

Fabrication of easily separated biochar balls and their catalytic mechanism for PMS

In this work, N-doped biochar balls NBC3800 were prepared from waste biomass corn straw. The biochar balls supported by clay have an obvious spherical structure. Clay can enhance the adsorption capacity of the biochar balls to pollutants by its excellent adsorption property. Thus, the clay can speed up the catalytic reaction by strengthening the adsorption function. The biochar balls NBC3800 have the best catalytic performance and the removal rate of NC can reach 100% within 100 min. The electron transfer resistance of NBC3800 is only 36 Ω indicating a lower resistance value and higher conductivity to transfer electrons compared with carbon nanotube. Electron paramagnetic resonance (EPR) and electrochemical analysis show that sulfate radical (SO4•−), hydroxyl radical (·OH), singlet oxygen (1O2), and electron transfer are all involved in the reaction. The removal rate of NC can still be maintained at 83.41% after being reused five times. Besides, it can be further improved to 100% by high temperature regeneration at 800 ℃. Most importantly, the biochar balls can be separated from the solution very easily which not only extremely improves the recyclability but also avoids secondary pollution to the water body.

Pentanuclear iron complex for water oxidation: Spectroscopic analysis of reactive intermediates in solution and catalyst immobilization into the MOF-based photoanode

Photoelectrochemical water splitting can produce green hydrogen for industrial use and CO2-neutral transportation, ensuring the transition from fossil fuels to green, renewable energy sources. The iron-based electrocatalyst [FeII4FeIII(μ-3-O)(μ-L)6]3+ (LH = 3,5-bis(2-pyridyl)pyrazole) (1), discovered in 2016, is one of the fastest molecular water oxidation catalysts (WOC) based on earth-abundant elements. However, its water oxidation reaction (WOR) mechanism has not been yet fully elucidated. Here, we present in situ X-ray spectroscopy and electron paramagnetic resonance (EPR) analysis of electrochemical WOR promoted by (1) in water-acetonitrile solution. We observed transient reactive intermediates during the in situ electrochemical WOR, consistent with a coordination sphere expansion prior to the onset of catalytic current. At a pre-catalytic (∼+1.1 V vs. Ag/AgCl) potential, the distinct g ∼ 2.0 EPR signal assigned to FeIII/FeIV interaction was observed. Prolonged bulk electrolysis at catalytic (∼+1.6 V vs. Ag/AgCl) potential leads to the further oxidation of Fe centers in (1). At the steady state achieved with such electrolysis, the formation of hypervalent FeVO and FeIVO catalytic intermediates was inferred with XANES and EXAFS fitting, detecting a short FeO bond at ∼ 1.6 Å. (1) was embedded into MIL-126 MOF with the formation of a (1)-MIL-126 composite. The latter was tested in photoelectrochemical WOR and demonstrated an increase in electrocatalytic current upon visible light irradiation in acidic (pH = 2) water solution. The presented spectroscopic analysis gives further insight into the catalytic pathways of multinuclear systems and should help the subsequent development of more energy- and cost-effective water-splitting catalysts based on earth-abundant metals. Photoelectrocatalytic activity of (1)-MIL-126 confirms the possibility of creating an assembly of (1) inside a solid support and harnessing solar irradiation towards industrial applications of the catalyst.

Cobalt-loaded carbon nanofibers as magnetic catalyst for tetracycline degradation through peroxydisulfate activation: Non-radical dominated mechanism

Cobalt/carbon nanofibers (Co/CNF) were prepared by electrostatic spinning of CoCl2⋅6H2O and polyacrylonitrile solution and subsequent calcination. The physicochemical properties of Co/CNF were examined by various characterizations. The characterization results show the presence of multivalent cobalt in Co/CNF, the increased oxygen-containing groups on CNF surface, the microporous structure of Co/CNF, and the strong magnetic property. Compared with CNF, Co/CNF demonstrates a superior catalytic activity in activating peroxodisulfate (PDS) for the degradation of tetracycline (TC). The degradation of 89.5 % TC was obtained within 60 min in the Co/CNF/PDS system. The effects of process parameters such as Co/CNF dosage, PDS dosage, TC concentration, pH value, temperature, and common anions are studied on the removal of TC in the catalytic system. Electron paramagnetic resonance (EPR), quenching experiments, and electrochemical analysis confirm that TC degradation in the Co/CNF/PDS system relies on the non-radical pathway dominated by 1O2 and electron transfer. Co/CNF not only activates PDS to generate reactive species, but also acts as an electronic intermediator from TC to the activated PDS surface for reaction. This study provides novel insights into the synthesis of efficient PDS catalysts for wastewater treatment concerning antibiotics.

Electron bridge rGO synergized with Z-scheme ZnTe/WO3 heterojunction for simultaneous and efficient tetracycline degradation and Cu (II) reduction

Z-scheme heterojunction photocatalysts can restrain carriers’ recombination while retaining high redox capacity. Herein, a novel ZnTe/rGO/WO3 (ZRW) Z-scheme heterojunction was constructed for simultaneous removal of TC and Cu (II) from wastewater. The highly conductive rGO served as a bridge connecting the ZnTe and WO3 whereby forming a tight interaction interface, beneficial to carriers transfer and separation. The removals of TC and Cu (II) using the optimized ZRW-10% achieved 90.6% and 89.5% within 150 min of light exposure, which were much higher than those from the ZnTe and WO3. Results of free radical trapping experiments and electron spin resonance analysis suggested that·O2- and·OH were the key active species for TC oxidation while e- dominated Cu (II) reduction. Based on the identified TC degradation intermediates, two possible degradation pathways for TC were proposed, and the ecotoxicity of most intermediates were less than TC. This study can advance research development of designing efficient Z-scheme photocatalyst and elimination of complex pollutants.

Exceptional tribo-catalytic degradation of concentrated methyl orange and methylene blue solutions by DXN-RT30 TiO2 nanoparticles

As tribo-catalysis gains increasing attention to harness mechanical energy for environmental remediation, it is time to explore its application to those organic pollutants that have been challenging to degrade. In this study, four commercial metal oxide nanoparticles, BaTiO3, ZnO, P25 TiO2, and DXN-RT30 TiO2 nanoparticles, were stimulated through magnetic stirring to degrade 20 mg/L methyl orange (MO) and 30 mg/L methylene blue (MB) solutions. While all the other nanoparticles showed rather poor performance, DXN-RT30 TiO2 nanoparticles performed exceptionally well: With Teflon magnetic disks rotating at 400 rpm, 98.2% of MO and 100% of MB were degraded within 330 and 420 min, respectively. DXN-RT30 TiO2 nanoparticles demonstrated a unique absorption for MB molecules, yielding significantly different outcomes in active species trapping experiments between degradation of MO and MB solutions by DXN-RT30 TiO2. Complemented by electron paramagnetic resonance analysis, our findings suggest that for DXN-RT30 TiO2 nanoparticles under magnetic stirring, MO molecules are degraded by h+, ·OH, and e− in solution, while MB molecules are absorbed and degraded via h+ and e− on the surface of DXN-RT30 TiO2 nanoparticles. This study identifies DXN-RT30 TiO2 nanoparticles as a cost-effective, high-performance, and environmentally friendly tribo-catalyst for environmental remediation, stimulating further exploration for more excellent tribo-catalysts.

Visible light-mediated activation of periodate for bisphenol A degradation in the presence of Fe3+ and gallic acid at neutral pH

The current study demonstrates, for the first time, the effectiveness of an innovative visible light (VL) photo-Fenton like system using periodate (PI) mediated by Fe3+ and gallic acid (GA) for bisphenol A (BPA) elimination at neutral pH. The promotion of VL irradiation and GA on the Fe2+/Fe3+ cycle in the system allowed the VL/GA/Fe3+/PI system to exhibit excellent performance for BPA removal. Complete degradation of BPA was carried out in the VL/GA/Fe3+/PI process after 30 min reaction under the optimum conditions (0.10 mM Fe3+, 0.10 mM GA, 1 mM PI, and initial pH 7.0). Electron paramagnetic resonance analysis and quenching tests confirmed that the singlet oxygen, iodate radical, and hydroxyl radical were primarily involved in the elimination of BPA with minor contribution from superoxide anion radical and high-valent iron species (Fe4+ and Fe5+). BPA abatement was slightly inhibited by the addition of Cl−, NO3−, and SO42−, whereas the addition of HCO3− obviously hindered this process. Notably, Huimic acid dramatically expedited BPA decomposition. Besides, the VL/GA/Fe3+/PI process demonstrated remarkable removal efficiency over a broad range of initial pH values (3.01–8.97). Meanwhile, based on the eight identified intermediates, the possible degradation pathways of BPA were predicted. The phytotoxicity test concluded that a decrease in toxicity of the degraded intermediates to the growth of radish seed compared to BPA. In addition, the VL/GA/Fe3+/PI system demonstrated favorable potential for application in different actual water matrices. Moreover, efficient and simultaneous abatement of various organic contaminants by the GA/Fe3+/PI process was success accomplished under natural solar light or VL. Consequently, all results implied that the VL/GA/Fe3+/PI process might be a perspective technique for the treatment of organic contaminants.

Facile synthesis of ball-milling and oxalic acid co-modified sludge biochar to efficiently activate peroxymonosulfate for sulfamethoxazole degradation: 1O2 and surface-bound radicals

A novel approach of ball milling and oxalic acid was employed to modify sludge-based biochar (BOSBC) to boost its activation performance for peroxymonosulfate (PMS) towards efficient degradation of sulfamethoxazole (SMX). 98.6% of SMX was eliminated by PMS/BOSBC system within 60 min. Furthermore, PMS/BOSBC system was capable of maintaining high removal rates for SMX (>88.8%) in a wide pH range from 3 to 9, and displayed a high tolerance to background electrolytes including inorganic ions and humic acid (HA). Quenching experiments, electron paramagnetic resonance (EPR) analysis, in-situ Raman characterization and PMS decomposition experiments confirmed that the non-radicals of 1O2 and surface-bound radicals were the main contributors to SMX degradation by PMS/BOSBC system. The results of ecotoxicity assessment illustrated that all transformed products (TPs) generated in PMS/BOSBC system were less toxic than that of SMX. After five reuse cycles, PMS/BOSBC system still maintained a high removal rate for SMX (77.8%). Additionally, PMS/BOSBC system exhibited excellent degradation performance for SMX in various real waters (Yangtze River water (76.5%), lake water (74.1%), tap water (86.5%), and drinking water (98.1%)). Overall, this study provided novel insights on non-metal modification for sludge-based biochar and non-radical mechanism, and offered a feasible approach for municipal sludge disposal.