Radical Probe Research Articles

Oxyanion-Sensitive Catalytic Activity of Ni(II)/Oxyanion Systems for Heterogeneous Organic Degradation: Differential Oxidizing Capacity of Ni(III) and Ni(IV) as High-Valent Intermediates.

This study demonstrated that NiO and Ni(OH)2 as Ni(II) catalysts exhibited significant activity for organic oxidation in the presence of various oxyanions, such as hypochlorous acid (HOCl), peroxymonosulfate (PMS), and peroxydisulfate (PDS), which markedly contrasted with Co-based counterparts exclusively activating PMS to yield sulfate radicals. The oxidizing capacity of the Ni catalyst/oxyanion varied depending on the oxyanion type. Ni catalyst/PMS (or HOCl) degraded a broad spectrum of organics, whereas PDS enabled selective phenol oxidation. This stemmed from the differential reactivity of two high-valent Ni intermediates, Ni(III) and Ni(IV). A high similarity with Ni(III)OOH in a substrate-specific reactivity indicated the role of Ni(III) as the primary oxidant of Ni-activated PDS. With the minor progress of redox reactions with radical probes and multiple spectroscopic evidence on moderate Ni(III) accumulation, the significant elimination of non-phenolic contaminants by NiOOH/PMS (or HOCl) suggested the involvement of Ni(IV) in the substrate-insensitive treatment capability of Ni catalyst/PMS (or HOCl). Since the electron-transfer oxidation of organics by high-valent Ni species involved Ni(II) regeneration, the loss of the treatment efficiency of Ni/oxyanion was marginal over multiple catalytic cycles.

Reutilization of pyrite tailings in peracetic acid-based advanced oxidation process for water purification

Iron-based heterogeneous catalysts in peracetic acid (PAA)-based advanced oxidation technologies are currently a considerable interest, yet the sluggish reduction from Fe(III) to Fe(II) impedes the efficiency of PAA activation. Pyrite tailings (PRT) still contains a certain amount of FeS2 composition, and its reducing sulfur species have the ability of electron-donating for Fe(III) reduction. Therefore, from the view of resource utilization and environmental protection, we applied PRT to activate PAA for removing sulfamethoxazole (SMX) in this work. In-situ Raman spectra verified the activation of PAA by PRT, and 93.67 % of SMX (5 mg/L) can be removed after 50 min in near-neutral circumstance (pH 5.8), which could be mainly attributed to the activation of PAA through the leached Fe ions from PRT. Radical scavenging and probe tests testified that hydroxyl and acetylperoxy radicals are responsible for SMX decomposition. A series of spectroscopic characterizations and theory calculation confirmed that the ability of sulfur sites to donate electrons, thereby boosting Fe(II) regeneration on PRT. The continuous catalytic test proved the sustainable utilization capacity of PRT. This study presented PRT as an effective catalyst with potential uses for PAA-based wastewater treatment process.

Removal of cyanide by peroxydisulfate activated by copper ions inherently present in the electroplating wastewater

Cyanide is widely used in electroplating processes to ensure the quality of metal plating. Alkaline chlorination process is commonly employed to remove cyanide from electroplating wastewater. However, several drawbacks exist, including the formation of toxic intermediates, high consumption of chemical reagents, and low removal efficiency of metal-cyanide complexes. In this study, persulfate advanced oxidation process was explored for the removal of cyanide from electroplating wastewater. The metal ions typically present in the electroplating wastewater, including Cu2+, Zn2+, Fe2+, Ag+ and Ni2+, may activate peroxydisulfate (PDS) to oxidize cyanide. Among these metal ions, cyanide can be most effectively removed in the presence of Cu2+ and PDS, likely due to the activation of PDS by Cu2+ and Cu(II)-cyanide complex. The results of lab studies indicated that 99 % removal of cyanide (4 mM) could be achieved in the presence of 10 mM PDS and 1 mM Cu2+ within 20 min. The results of radical scavenging experiments, radical probe tests and electron paramagnetic resonance (EPR) studies showed that sulfate radical (SO4•−) and hydroxyl radical (OH•) were primarily responsible for cyanide removal and the complexation of cyanide and Cu2+ significantly enhanced the formation of SO4•−. Cyanate and nitrite were the main by-products detected. For real electroplating wastewater, the addition of 40 mM PDS could almost completely remove cyanide (19.5 mM) in 20 min.

A Rationally Designed Iron(II) Catalyst for C(sp3)−C(sp2) and C(sp3)−C(sp3) Suzuki–Miyaura Cross‐Coupling

AbstractDespite the paramount importance of the Suzuki–Miyaura coupling (SMC) in academia and industry, and the great promise of iron to offer sustainable catalysis, iron‐catalyzed SMC involving sp3‐hybridized partners is still in its infancy. We herein report the development of a versatile, well‐defined electron‐deficient anilido‐aldimine iron(II) catalyst. This catalyst effectively performed C(sp3)−C(sp2) and C(sp3)−C(sp3) SMC of alkyl halide electrophiles and (hetero)aryl boronic ester and alkyl borane nucleophiles respectively, in the presence of a lithium amide base. These couplings operated under mild reaction conditions and displayed wide functional group compatibility including various medicinally relevant N‐, O‐ and S‐based heterocycles. They also tolerated primary, secondary and tertiary alkyl halides (Br, Cl, I), electron‐neutral, ‐rich and ‐poor boronic esters and primary and secondary alkyl boranes. Our methodology could be directly and efficiently applied to synthesize key intermediates relevant to pharmaceuticals and a potential drug candidate. For C(sp3)−C(sp2) couplings, radical probe experiments militated in favor of a carbon‐centered radical derived from the electrophile. At the same time, reactions run with a pre‐formed activated boron nucleophile coupled to competition experiments supported the involvement of neutral, rather than an anionic, (hetero)aryl boronic ester in the key transmetalation step.

A Rationally Designed Iron(II) Catalyst for C(sp3)-C(sp2) and C(sp3)-C(sp3) Suzuki-Miyaura Cross-Coupling.

Despite the paramount importance of the Suzuki-Miyaura coupling (SMC) in academia and industry, and the great promise of iron to offer sustainable catalysis, iron-catalyzed SMC involving sp3-hybridized partners is still in its infancy. We herein report the development of a versatile, well-defined electron-deficient anilido-aldimine iron(II) catalyst. This catalyst effectively performed C(sp3)-C(sp2) and C(sp3)-C(sp3) SMC of alkyl halide electrophiles and (hetero)aryl boronic ester and alkyl borane nucleophiles respectively, in the presence of a lithium amide base. These couplings operated under mild reaction conditions and displayed wide functional group compatibility including various medicinally relevant N-, O- and S-based heterocycles. They also tolerated primary, secondary and tertiary alkyl halides (Br, Cl, I), electron-neutral, -rich and -poor boronic esters and primary and secondary alkyl boranes. Our methodology could be directly and efficiently applied to synthesize key intermediates relevant to pharmaceuticals and a potential drug candidate. For C(sp3)-C(sp2) couplings, radical probe experiments militated in favor of a carbon-centered radical derived from the electrophile. At the same time, reactions run with a pre-formed activated boron nucleophile coupled to competition experiments supported the involvement of neutral, rather than an anionic, (hetero)aryl boronic ester in the key transmetalation step.

Replacement of Tyrosines by Unnatural Amino Acid Aminophenylalanine Leads to Metal-Mediated Aniline Free Radical Formation in a Copper Amine Oxidase.

Copper amine oxidases (CAOs) catalyze the oxidative deamination of primary amines to aldehyde, ammonia, and hydrogen peroxide as products and are widely distributed in bacteria, plants, and eukaryotes. These enzymes initiate the single turnover, post-translational conversion of an active site tyrosine to the redox cofactor 2,4,5-trihydroxyphenylalanine quinone (TPQ), subsequently employing TPQ to catalyze steady-state amine oxidation. The mechanisms of TPQ biogenesis and steady-state amine oxidation have been studied extensively, with consensus mechanisms proposed for both reactions. One unresolved issue has been whether the Cu2+ center must undergo formal reduction to Cu1+ in the course of the reaction. Herein, we investigate the properties of the active site of a yeast (Hansenula polymorpha) amine oxidase (HPAO) that has undergone site-specific insertion of a para-aminophenylalanine (pAF) into the position of either the precursor tyrosine to TPQ (Y405) or the two strictly conserved neighboring tyrosines (Y305 and Y407). While our original intention was to interrogate cofactor biogenesis using a precursor unnatural amino acid (UAA) of altered redox potential and pKa, we instead observe an unanticipated reaction assigned to an intramolecular electron transfer from pAF to the active site copper ion. We establish the generality of the observed active site chemistry using exogenously added, aniline-containing substrates under conditions that prevent side chain amine oxidation. The results support previous proposals that the activation of the TPQ precursor occurs in the absence of a formal valence change at the active site copper site. The described reaction of pAFs with the active site redox Cu2+ center of HPAO provides a prototype for either the engineering of the enzymatic oxidation of exogenous anilines or the insertion of site-specific free radical probes within proteins.

Nanoscale detection and real-time monitoring of free radicals in a single living cell under the stimulation of targeting moieties using a nanodiamond quantum sensor

Intracellular radicals play important roles in cell signaling and regulation of growth factors, cytokines, transcription, apoptosis, and immunomodulation, among others. To gain a more comprehensive understanding of their biological functions from a spatio-temporal pers­pective, there is a great need for nanoscale sensitive tools that allow real-time detection of these reactive species. Currently, intracellular radical probes are based on chemical reactions that could significantly alter radical levels during detection. Due to the excellent bio­compatibility and favorable photophysical properties of nitrogen-vacancy (NV–) centers in fluorescent nanodiamonds (fNDs), the fNDs can serve as a powerful and chemically inert nanotool for intracellular radical detection. In this study, a positively charged nanogel (NG) coating was prepared to prevent the precipitation of fNDs and promote cellular internalization. After internalization of nanodiamond-nanogels (fND-NGs), different stimulators, namely somatostatin (SST), triphenylphosphonium (TPP), and trans-activator of transcription (TAT) peptide, which are widely used cell- or organelle-targeting ligands in medicine, drug delivery, and diagnostics, were applied to stimulate the cells. In parallel, the intracellular radical changes under stimulation of SST, TPP, and TAT ligands were monitored by fND-NGs in a home-built optically detected magnetic resonance (ODMR) microscope. Our method allows for detecting intracellular radicals in-situ and monitoring their real-time changes during incubation with the targeting ligands in a single living cell. We believe that our method will provide insights into the generation of radical stress in cells, which could improve our fundamental understanding of the pharmacology and signaling pathways of widely used cell- and organelle-targeting ligands associated with free radicals.

Activation of peroxymonosulfate with natural pyrite-biochar composite for sulfamethoxazole degradation in soil: Organic matter effects and free radical conversion

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) represent an effective method for the remediation of antibiotic-contaminated soils. In this study, a natural pyrite-biochar composite material (FBCx) was developed, demonstrating superior activation performance and achieving a 76% removal rate of SMX from soil within 120 min. There existed different degradation mechanisms for SMX in aqueous and soil solutions, respectively. The production of 1O2 and inherent active species produced by soil slurry played an important role in the degradation process. The combination of electron paramagnetic resonance (EPR) and free radical probe experiments confirmed the presence of free radical transformation processes in soil. Wherein, the·OH and SO4·− generated in soil slurry did not directly involve in the degradation process, but rather preferentially reacted with soil organic matter (SOM) to form alkyl-like radicals (R·), thereby maintaining a high concentration of reactive species in the system. Furthermore, germination and growth promotion of mung bean seeds observed in the toxicity test indicated the environmental compatibility of this remediation method. This study revealed the influence mechanism of SOM in the remediation process of contaminated soil comprehensively, which possessed enormous potential for application in practical environments.

Characterization of elastomer degradation in O2/Ar plasma via mass and surface morphology changes

The degradation of fluoroelastomer, perfluoroelastomer (FFKM), and fluorosilicone materials were compared between three O2/Ar plasma conditions: full plasma (ions plus radicals), radical only, and ion only. These elastomer materials are used extensively in plasma processing equipment used to manufacture semiconductors, and understanding the plasma environments that enhance degradation will inform material choice and further material development. Langmuir probe measurements were made to quantify the electron temperature and plasma density; radical probe measurements were made to quantify the oxygen radical density. The results suggested that plasma radicals were required to drive significant mass loss rates, with ions speeding up the mass loss rate further in the full plasma case. Additionally, it was determined that plasma radicals were the main driver of surface changes of the elastomer, with similar surface roughening in plasma versus radical only conditions and less significant roughening in ion-only conditions. The O2/Ar plasma discharge had an electron temperature of 4.6 ± 0.1 eV and a plasma density of 2.9 ± 0.07 × 1016 m−3. It was observed that the fluorosilicone material had the lowest mass loss rate, the unfilled FFKM had the highest mass loss rate, and the silica-filled FFKM had the lowest mass loss rate among the FFKMs tested. The presence of oxygen radicals during exposure conditions significantly changed surface roughness.

A novel fluidized electrode electrolysis system activated ferrate (VI) oxidation promoting sludge solubilization: Performance and mechanism

Energy and resource recovery is a viable and sustainable solution for sludge treatment and disposal, while sludge solubilization is one of the most critical issues hindering sludge conversion to valuable products. Although ferrate (VI) was considered a green sludge pretreatment approach, the poor stability of ferrate (VI) hindered the effective utilization of its oxidative potential. This study demonstrated that an innovative electrochemical system with granular activated carbon (GAC) as the fluidized electrode activated potassium ferrate (PF) oxidation could effectively catalyze the destruction of sludge structure, thereby promoting the release of organic matter and improving sludge solubilization. The results showed that the electro- granular activated carbon- potassium ferrate (E-GAC-PF) process achieved a sludge solubilization of 30.9 % within 15 min, resulting in a reduction in sludge volume by 33.9 %. In comparison, the sludge solubilization rate under PF oxidation alone was 11.5 %, with corresponding in sludge volume reduction of 13.0 %. The radical scavenging experiment and probe compound (sulfoxide) oxidation experiment revealed that the E-GAC-PF system was responsible for the production of a higher quantity of Fe (V) and Fe (IV), which significantly contributed to the sludge decomposition. Additionally, XPS and XRD analysis discovered that Fe3O4 was present as a byproduct, which opened up a new route for iron recycling during the pretreatment. Hence, E-GAC-PF system held promise as a pioneering and efficient alternative for catalytically activating PF, thereby facilitating environmentally friendly and highly efficient pretreatment of sludge.

Fluoranthene degradation in a persulfate system activated by sulfidated nano zero-valent iron (S-nZVI): performance and mechanisms.

Fluoranthene (FLT) has received mounting focus due to its hazardous properties and frequent occurrence in groundwater. In this study, sulfidated nano zero-valent iron (S-nZVI) was selected as an efficient catalyst for activating persulfate (PS) to degrade FLT. The effects of reagent doses, various water conditions (pH, anions, and humic acid), and the presence of surfactants on FLT degradation were investigated. Radical probe experiments, electron paramagnetic resonance (EPR) spectrum detection, and scavenging tests were performed to identify the major reactive oxygen species (ROS) in the system. The results showed that in the PS/S-nZVI system, 96.2% of FLT was removed within 120 min at the optimal dose of PS = 0.07 mM and S-nZVI = 0.0072 g L-1. S(-II) in the S-nZVI surface layer promoted Fe(II) regeneration. Furthermore, HO• and SO4-• were identified as the main contributors to FLT degradation. The intermediates of FLT degradation were detected by gas chromatograph-mass spectrometry (GC-MS) and a possible FLT degradation pathway was proposed. Finally, the effective degradation of two other common polycyclic aromatic hydrocarbons (PAHs) (naphthalene and phenanthrene) demonstrated the broad-spectrum reactivity of the PS/S-nZVI process. In conclusion, these findings strongly demonstrate that the PS/S-nZVI process is a promising alternative for the remediation of PAH-contaminated groundwater.

The Radical Feminist Interpretation of the Jilting of Granny Weatherall

The Jilting of Granny Weatherall is one of the classic short stories of the famous American writer Katherine Anne Porter. The short story expresses womens liberation through the protagonist Granny Weatheralls attitude in the face of frustration. Some scholars focus more on analyzing the techniques used in the stream of consciousness used in the short story; some compare it to other similar works, while others provide a broader interpretation from a feminist perspective. However, this essay tends to make a tentative analysis of the interpretation of the masculinity displayed by the protagonist from the perspective of radical feminism and probe into the relationship between sex and gender temperament in a patriarchal society. In this way, it is shown that under the patriarchy, women are able to choose whether they show masculinity or not of their own free will. Furthermore, they will be more conscious of the significance of improving their self-awareness as economic, social, and ideological growth continues.

Mechanistic Elucidation of a Radical‐Promoted Hydrogenation Relevant to Borrowing Hydrogen Catalysis

AbstractIn the borrowing hydrogen catalysis, hydrogenation of an in situ generated imine or olefinic bond is a crucial step. There is a growing body of literature in olefinic hydrogenation promoted by metal hydride of Earth‐abundant metals, where radical mechanism is followed. This report presents a thorough study of the mechanistic details of a nickel catalyzed α‐alkylation of ketones with secondary alcohols and showcases that the olefinic hydrogenation of an enone happens, completely bypassing the involvement of a metal hydride. This pathway is radical promoted, where a single electron reduction of the substrate olefin and a subsequent hydrogen atom transfer step are most critical. A series of control reactions, detection of critical reaction intermediates, and radical probe experiments provide compelling proofs for such radical‐promoted olefinic hydrogenation. The experimental clues, further aided by DFT calculations altogether suggest the precise one‐electron chemistry where the involvement of metal‐hydride is not required. Notably, the redox non‐innocence of the azophenolate backbone, as well as imposed noninnocence of the substrate olefin, when bound to the catalyst molecule makes such mechanism feasible.

New Insights into the Phototoxicity of Anthracene-Based Chromophores: The Chloride Salt Effect†.

Unraveling the causes underlying polycyclic aromatic hydrocarbon phototoxicity is an essential step in understanding the harmful effects of these compounds in nature. Toward this end, we have studied the DNA interactions and photochemistry of N1-(anthracen-9-ylmethyl)ethane-1,2-diaminium dichloride in the presence and absence of NaF, KF, NaCl, KCl, NaBr, KBr, NaI, and KI (350 nm hν, pH 7.0). Exposing pUC19 plasmid to UV light in solutions containing 400 mM KCl formed significantly more direct strand breaks in DNA compared to no-salt control reactions. In contrast, NaCl increased DNA damage moderately, while the sodium(I) and potassium(I) fluoride, bromide, and iodide salts generally inhibited cleavage (I- > Br- > F-). A halide anion-induced heavy-atom effect was indicated by monitoring anthracene photodegradation and by employing the hydroxyl radical (•OH) probe hydroxyphenyl fluorescein (HPF). These studies revealed that among no-salt controls and the eight halide salts, only NaCl and KCl enabled the anthracene to photosensitize the production of high levels of DNA-damaging reactive oxygen species (ROS). Pre-irradiation of N1-(anthracen-9-ylmethyl)ethane-1,2-diaminium dichloride at 350 nm increased the amounts of chloride salt-induced •OH detected by HPF in subsequent anthracene photoactivation experiments. Taking into consideration that •OH and other highly reactive ROS are extremely short-lived, this result suggests that the pre-irradiation step might lead to the formation of oxidized anthracene photoproducts that are exceedingly redox-active. The fluorometric probes HPF and Singlet Oxygen Sensor Green revealed that KCl concentrations ranging from 150 to 400 mM and from 100 to 400 mM, respectively, enhanced N1-(anthracen-9-ylmethyl)ethane-1,2-diaminium dichloride photosensitized •OH and singlet oxygen (1O2) production over no-salt controls. Considering the relatively high levels of Na+, K+, and Cl- ions that exist in the environment and in living organisms, our findings may be relevant to the phototoxic effects exhibited by anthracenes and other polycyclic hydrocarbons in vivo.

Degradation of Perfluorooctanoic Acid by Chlorine Radical Triggered Electrochemical Oxidation System.

Electrochemical oxidation (EO) has been shown to have the unique ability to degrade perfluorooctanoic acid (PFOA), although the radical chemistry involved in this degradation is unclear, particularly in the presence of chloride ions (Cl-). In this study, reaction kinetics, free radical quenching, electron spin resonance, and radical probes were used to examine the roles of ·OH and reactive chlorine species (RCS, including Cl·, Cl2•-, and ClO·) in the EO of PFOA. Using EO in the presence of NaCl, PFOA degradation rates of 89.4%-94.9% and defluorination rates of 38.7%-44.1% were achieved after 480 min with PFOA concentrations ranging from 2.4 to 240 μM. The degradation occurred via the synergistic effect of ·OH and Cl· rather than through direct anodic oxidation. The degradation products and density functional theory (DFT) calculations revealed that Cl· triggered the first step of the reaction, thus the initial direct electron transfer was not the rate-limiting step of PFOA degradation. The change in Gibbs free energy of the reaction caused by Cl· was 65.57 kJ mol-1, which was more than two times lower than that triggered by ·OH. However, ·OH was involved in the subsequent degradation of PFOA. The synergistic effect of Cl· and ·OH in PFOA degradation is demonstrated for the first time in this study, which is promising for the development of electrochemical technology to remove perfluorinated alkyl substances from the environment.

Cost-Effective FeIVO2+ Generation for Antibiotics Removal in Electrochlorination of Mariculture Wastewater

Organic decontamination in saline wastewater was limited in the·OH-dominated oxidation processes due to the inevitable emergence of chlorinated byproducts, and the electrochlorination process could degrade the contaminants utilizing the inherent Cl– ions but shared the same problem. To solve this problem, an iron electrode was integrated to the electrochlorination system as a second anode, and 100% organic pollutant removal can be achieved. In the iron-modified electrochlorination (IMEC) process, Fe2+ from the iron anode could react with the electrogenerated HClO, inducing the steady generation of iron-oxo (FeIVO2+) by a radical scavenger, probe experiments, and DFT calculation analyses. In comparison to the·OH-dominated processes, the majority of intermediates was biodegradable and moderately toxic for different aquatic organisms in the IMEC process, as indicated by in silico prediction. Furthermore, the coagulation mechanism could contribute to 23.3% removal of the total organic carbon in the pH adjustment process to the circumneutral level, and the coagulant aids further enhanced the coagulation efficiency to 41.4%. Finally, the system was found to be excellent for antibiotics removal in mariculture wastewater and costed an order of magnitude less than the most reported ferrate-based processes. Overall, the research pioneers an electrochemical FeIVO2+-dominated technology for efficient purification of saline water, and the ecofriendly and cost-effective properties endow it with a huge application potential in the saline wastewater.

A study on photodegradation of trichloroethylene using an optical fiber coated with different photocatalysts

In this research, optical fiber photocatalytic technology was used to treat trichloroethylene (TCE) in simulated groundwater. The study investigated the effects of various conditions on TCE treatment, including the type and modification method of photocatalyst, pH value of the solution, and pollutant concentration on the photocatalytic reaction rate and hydroxyl radical conversion rate (ROH,UV). The objective was to improve the transmission and extension of light energy using the high light-conducting properties of optical fibers. This technique is particularly useful in areas where light transmission is obstructed and can address the issues associated with traditional photocatalytic treatment methods, such as photocatalyst recovery. Soil reaction flasks were used as containers, and a LED as the experimental light source. The coated photocatalysts were analyzed for their basic characteristics using SEM/EDS, UV–Vis DRS, and XRD. In addition, p-chlorobenzoic acid (pCBA) as a hydroxyl radical (･OH) probe for kinetic study and calculation of ROH,UV. The results show that N-doped TiO2 (NT) with the addition of 10 mL NH4OH improved TCE removal efficiency at sampling point A from about 20% to 49.6%, while Ag-doped TiO2 (AT) was increased to 53.8% with the addition of 0.5 g AgNO3. These two dosages had the highest hydroxyl radical generation efficiency compared to other higher dosage conditions. However, excessive dosage can inhibit crystal formation. The study also conducted reaction rates under different pH solution environments, showing that NT had the highest reaction rate (kapp) at pH 7 and AT at pH 10. Overall, this research highlights the potential of optical fiber photocatalytic technology for TCE treatment in groundwater and provides insights into the factors that affect its efficiency.

Fluorescent switch-on probe for carbon-centered radicals and real-time assessment of toluene degradation efficacy

Carbon-centered radicals derived from parent compounds are primary radical intermediates involved in the degradation of organic pollutants. This study presents a bifunctional probe with a fluorescent "switch-on" and radical capture functions for in situ trapping and specific detection of carbon-centered radicals. Carbon-centered radicals can be quickly trapped and they can notably turn on the 11-fold fluorescence, which enables the monitoring of unstable and short-lived carbon-centered radicals generated during toluene degradation. The proposed system was applied to assess the toluene degradation efficacy in real time. The fluorescence response was similar to that of the toluene degradation efficiency measured using high-performance liquid chromatography (HPLC). In addition, the benzyl radical was identified as the primary carbon-centered radical intermediate by high-resolution liquid chromatography-mass spectrometry (LC-MS), which provides direct evidence for the toluene degradation mechanism by thermally activated persulfate.

Urea removal for ultrapure water production by VUV/UV/chlorine under acidic aqueous conditions: Facile elimination and efficient denitrification

Urea in the ultrapure water production process threatens semiconductor manufacturing. This work proposed a urea removal strategy involving the VUV/UV/chlorine process in an acidic solution to achieve high-efficiency urea removal. VUV/UV/chlorine could thoroughly remove urea of 2 mg/L within 9 min at pH 3. A TN removal rate of 70% and a dissolved organic carbon removal rate of 84% were achieved in the urea degradation process. The decrease in pH and the increase in oxidant dosage could improve urea removal efficiency. The presence of chloride anion could improve urea removal by 55–85%. Based on the radical probe and quenching experiments, free radicals accounted for more than 90% of urea removal. •Cl2− and •OH were calculated to contribute approximately 36% and 22%, respectively, to urea removal. •Cl and •ClO together contributed less than 32%. The chlorination of urea was responsible for less than 10% of urea removal. Nitrogen in urea was transformed efficiently into inorganic nitrogen (N2, ammonium, and nitrate with a rough ratio of 6:1:1.1). Organic chlorine products formed in the urea degradation process took up less than 3% in all chlorine element and was converted into chloride anion finally.

Fluorine-free MXene activate peroxymonosulfate to remove tetracyclic antibiotics

The most typical synthesis method for MXene is to etch the Al layer from its MAX phase using an acidic solution containing fluorine. However, etching with fluorine-containing reagents can lead to environmental contamination and experimental safety issues. Herein, fluorine-free Ti3C2Tx (Ff-Ti3C2Tx) was successfully prepared by using a safer and more environmentally friendly tetramethylammonium hydroxide solution (TMAOH) at a controlled temperature of 40 °C and reacting continuously for one week. Based on the characterization results, we demonstrated that the prepared Ff-Ti3C2Tx exhibits outstanding hydrophilicity and exposes more active sites on the surface, which is beneficial towards activating peroxymonosulfate (PMS). The catalyst exhibited superior degradation of tetracycline hydrochloride (TC) than Fluorine-Ti3C2Tx (F-Ti3C2Tx). The effects of catalyst dosage, optimum concentration of PMS, initial pH, common coexisting ions (Cl−, SO42−, HCO3− and humic acid) and different real water environments on TC degradation were systematically investigated in the Ff-Ti3C2Tx/PMS system. Meanwhile, the degradation effects of both Doxycycline (DC) and Oxytetracycline (OTC) reached more than 89.7%. In addition, Ff-Ti3C2Tx exhibited excellent reusability with a mineralization efficiency of 49.7%. Based on the electron paramagnetic resonance (EPR) test, quenching experience, radical probe experiments, electrochemical measurements and XPS characterization, a possible activation mechanism was proposed. The contribution of reactive oxygen species (ROS) was calculated, 1O2 (45.3%) and ·O2− (30.2%) play a major role in the degradation of TC. Furthermore, a possible degradation pathway was proposed by liquid chromatography-mass spectrometry (LC-MS) with a decreasing trend in the toxicity of TC intermediates. This work not only demonstrates a novel strategy for preparing fluorine-free MXene via simple TMAOH etching, but it also provides new insight into the use of MXene as a catalyst directly in the activation of PMS.