Electron Paramagnetic Resonance Analysis Research Articles

Perovskite Nanocrystals In Situ Encapsulated in TiO2 Microspheres for Stable CO2 Photoreduction in Water.

Photoreduction of carbon dioxide (CO2) into fuels presents a promising approach to mitigate global warming and energy crises. Halide perovskite nanocrystals (NCs) with prominent optoelectronic properties have triggered substantial attention as photocatalysts but are limited by the charge recombination and instability. Here, we develop stable CsPbBr3/titania microspheres (TMs) by in situ growth of CsPbBr3 NCs inside mesoporous TMs through solid-state sintering, which significantly improves the stability of perovskite NCs, making them applicable in water with efficient CO2 photoreduction performance. Notably, the CsPbBr3/TMs demonstrates a 6.73- and 9.23-fold increase in the rate of CH4 production compared to TMs and CsPbBr3, respectively. The internal electric field facilitates S-scheme charge transfer, enhancing the separation of electron-hole pairs, as evidenced by X-ray photoelectron spectroscopy and electron paramagnetic resonance analysis, which is pivotal for the selective photoreduction of CO2. These insights pave the way for the design of CsPbBr3-based photocatalysts with superior efficiency and stability.

Synthesis, Spectral Characteristics, Sensing Properties and Microbiological Activity of New Water-Soluble 4-Sulfo-1,8-naphthalimides

A new water-soluble polyamidoamine (PAMAM) dendrimer modified with 4-sulfo-1,8-naphthalimide (DSNI) and its monomeric structural analogue (MSDI) were synthesized. Their photophysical properties were investigated in organic solvents of different polarities and aqueous solutions. The effect of pH on fluorescence intensity was determined. It was found that the dendrimer emits blue fluorescence in an acidic medium, which is quenched in an alkaline environment. This phenomenon is due to the possibility of suppression of nonradiative photoinduced electron transfer in acidic media. The influence of different metal ions (Cu2+, Pb2+, Sn2+, Sr2+, Mg2+, Ba2+, Co2+, Hg2+, Zn2+, Ni2+, Fe3+, Al3+) and anions (CN−, S2−, S2O52−, HPO42−, H2PO4−, F−, CH3COO−, NO2−, CO32−, SO42−) on the intensity of the emitted fluorescence was studied. Quenching was only found in the presence of Cu2+. This makes the dendrimer suitable for determining copper ions in water solutions in the presence of other metal ions and anions. Additionally, DSNI was used as a ligand to obtain a stable copper complex, the structure of which was investigated by electron paramagnetic resonance (EPR), infrared spectrum, and elemental analysis. Two copper ions were found to form a complex with one dendrimer. The in vitro microbiological activity of the new compounds against bacteria Pseudomonas aeruginosa and two viruses HRSV-2 and HAdV-5 was investigated. With a view to obtaining antibacterial and anti-viral textiles, cotton fabrics were treated with the three compounds, and then their activity against the same microbial strains was investigated. It was found that the microbiological activity was preserved after the application of the new compounds to the cotton fabrics.

Evaluation of PEGylation efficacy of curcumin-loaded nanoemulsions using complementary methods to assess protein interactions and physicochemical properties

Nanoemulsions (NEs) are frequently used in the food, cosmetics and pharmaceutical industries to deliver nutraceuticals, pharmaceutical or cosmetic active ingredients. When administering NEs parenterally, various stabilisers are added to prevent rapid plasma clearance and to successfully deliver the active ingredient to the target site. For this purpose, PEGylation is often used to prolong the circulation time of the droplets. However, the problem is to determine the optimal concentration of the PEGylating agent – the PEGylation efficacy – that ensures adequate surface protection. This is a particular challenge when the active ingredient is incorporated into the stabilising layer, where any changes could disrupt the stability of the droplet. For this reason, we aimed to determine the optimal concentration of PEG2000-DSPE for surface protection of curcumin-loaded NEs for parenteral administration using electron paramagnetic resonance (EPR) spectroscopy. NEs were prepared using the high pressure homogenisation technique with 0.1 %, 0.3 % or 0.6 % of the PEGylated phospholipid. A droplet size of approximately 100 nm and polydispersity index below 0.25 indicated suitability for parenteral application. EPR analysis showed that PEG2000-DSPE had a stabilising effect on selected NEs, which was most pronounced in the part of the stabilising layer closest to the aqueous phase. To confirm these results, protein interaction studies were carried out using dynamic light scattering, UV–Vis spectroscopy, atomic force microscopy and release studies from protein-enriched media – bovine serum albumin (BSA) or foetal bovine serum (FBS) in phosphate-buffered saline. These analyses confirmed that the addition of PEG2000-DSPE reduced protein binding to the droplets as a function of concentration, with 0.3 % providing the best protection for the droplets. Our conclusions from the EPR spectroscopy study demonstrate the usefulness of EPR in determining the optimal concentrations of PEGylating agents for surface coverage and its usefulness in the formulation development phase.

Simultaneous degradation of pharmaceutical contaminants and sterilization in real hospital wastewater by a highly efficient electrocatalytic ozonation process: Performance, mechanism and application

Herein, this work investigated an electrocatalytic ozonation (ECO) strategy using stainless steel-graphite plates as cathode–anode for the degradation of the pharmaceutical pollutant dexamethasone (DXMS) and the treatment of real hospital wastewater. The reaction kinetic constant of the ECO degradation of DXMS (0.387 min−1) was 4 times higher than that of single ozone (0.087 min−1). The established efficient ECO system successfully degraded pharmaceutical contaminants and had excellent bactericidal effects against pathogenic microorganisms (Escherichia coli). The results of scavenging experiments, chemical probe experiments, and electron paramagnetic resonance (EPR) analysis indicated that the newly generated 1O2 in the ECO system achieved the synergistic effect of the combined EC-ozonation process. More to the point, the ECO system has a high removal rate of chemical oxygen demand (COD) and total organic carbon (TOC) for real hospital wastewater treatment. After 60 min treatment of the ECO system, the COD removal of hospital wastewater ranged from 70 % to 88.91 %, and the TOC removal ranged from 52.05 % to 71.81 %. The ECO system developed in this work has the capacity for simultaneous degradation of pharmaceutical contaminants and sterilization of pathogenic microorganism for hospital wastewater treatment.

Direct Z-scheme charge transfer Bi2O3/UiO-66-NH2 heterojunctions for boosted photocatalytic degradation of tetracycline hydrochloride in different water systems

The development of hybrid heterostructure photocatalysts with enhanced visible light absorption capacity holds significant importance in environmental remediation. However, the challenge persists in exploiting strong visible-light responsive photocatalysts with both high efficiency and stability. Herein, we successfully synthesized a hybrid Z-scheme heterojunction of Bi2O3 and UiO-66-NH2 (Bi2O3/UiO-66-NH2) through a simple hydrothermal route. The visible light photocatalytic performance of Z-scheme Bi2O3/UiO-66-NH2 heterojunction is systematically evaluated for persistent antibiotic tetracycline hydrochloride (TC-HCl) both in the clean and real water matrix. All heterojunction catalysts exhibit superior photodegradation capabilities compared to pristine Bi2O3 and UiO-66-NH2. The optimal ratio of the two components heterojunction (BUN-150), in particular, demonstrates the highest removal efficiencies for TC-HCl (95 %) within a 90-min timeframe. This remarkable photocatalytic performance is credited to the Z-scheme charge transfer occurring at the interface of Bi2O3 and UiO-66-NH2 in Bi2O3/UiO-66-NH2 heterojunction. The active species experiments and electron paramagnetic resonance analyses are conducted to identify the active reactive species during the TC-HCl degradation (·OH, h+, and ·O2−), and a precise photocatalytic degradation mechanism is explained. Additionally, the photodegradation intermediates of TC-HCl are detected using the HPLC-MS analysis to explain the degradation pathways of TC-HCl. This research paves the way for the development of novel Z-scheme Bi2O3-based heterojunction catalysts for outstanding photocatalytic applications.

Constructing 3D sandwich-like structured Ti foam/TiO2−x/SnO2-Sb composite electrodes for the degradation of PPCPs

The fabrication of Sb-doped SnO2 electrode with high catalytic activity and excellent durability for decomposition PPCPs (Pharmaceuticals and personal care products, PPCPs) is challenging. Herein, a Ti3+/Ovs-related TiO2−x is prepared by short-time annealing at low temperature in mixed gas with Zr as a cocatalyst. DFT calculations indicate that the introduction of Ti3+/Ovs defects could promote the formation of more ·OH. Then, the nanoflower rod-like SnO2-Sb catalytic layer supported on dual-defects TiO2−x is successfully synthesized by one-step pulse electrodeposition (PLED) combined with hydrothermal methods (H). This newly pulse electrodeposition technique solves the short lifetime problem of SnO2-Sb nanoflower electrodes current hydrothermal-based methods. 1O2 and ·OH are found to be the primary reactive oxygen species (ROSs) by radical quenching tests and electron paramagnetic resonance analysis. The optimized Ti foam/TiO2−x /SnO2-Sb electrode could degrade over 96.3 % of 20 mg L−1 amoxicillin (AMX) within 30 min, corresponding kinetic constant 0.10228 min−1. This will provide inspiration for the construction of defect engineering and new insights for the development of low-cost and high electrooxidation activity Sb-doped SnO2 electrode.

Bimetallic Ag125Cu8 Nanocluster, Structure Determination, and Nonlinear Optical Properties.

The atomic precision of the subnanometer nanoclusters has provided sound proof on the structural correlation of metal complexes and larger-sized metal nanoparticles. Herein, we report the synthesis, crystallography, structural characterization, electrochemistry, and optical properties of a 133-atom intermetallic nanocluster protected by 57 thiolates (3-methylbenzenethiol, abbreviated as m-MBTH) and 3 chlorides, with the formula of Ag125Cu8(m-MBT)57Cl3. This is the largest Ag-Cu bimetallic cluster ever reported. Crystallographic analysis revealed that the nanocluster has a three-layer concentric core-shell structure, Ag7@Ag47@Ag71Cu8S57Cl3, and the Ag54 metal kernel adopts a D5h symmetry. The nuclei number is between that of the previously reported large silver cluster [Ag136(SR)64Cl3Ag0.45]- and the large silver-rich cluster Au130-xAgx(SR)55 (x = 98). All these three clusters bear a similar metallic core structure, while the main structural difference lies in the shell motif structures. Electron counting revealed an open electron shell with 73 delocalized electrons, which was verified by the electron paramagnetic resonance analysis. The DPV electrochemical measurement indicates a multielectron state quantization double-layer charging shape and single-electron sequential charging and discharging characteristic of the AgCu alloy cluster. In addition, the open-hole Z-scan test reveals the nonlinear optical absorption (2-3 optical absorption in the NIR-II/III region) of Ag125Cu8 nanoclusters.

Highly efficient CdS/SbVO4 composites for visible-light-driven Cr(VI) reduction

Heavy metal contamination is a grave environmental concern due to its severe implications for human health and ecosystems, causing carcinogenic and teratogenic effects. This study addresses this pressing issue by exploring the synthesis and application of CdS/SbVO4 composites as effective photocatalysts. These composites were synthesized by a streamlined two-step hydrothermal method, with investigations conducted on varying molar ratios. The composite with a molar ratio of 0.2:1 demonstrated superior Cr(VI) photoreduction properties under visible light irradiation, exhibiting an efficiency quadruple that of pure SbVO4. This enhancement in photocatalytic activity is credited to the augmented separation of electrons and holes facilitated by the integration of narrow band gap materials within the composite. Electrochemical tests indicated the electron transfer mechanism and identified the primary active centers of the samples. The detailed photocatalytic mechanism of the composite was further discussed, grounded on insights derived from free radical trapping experiments and electron spin resonance analyses.

Optical properties, FTIR, and electron spin resonance analysis on the impact of gamma irradiation on fluorophosphate glasses doped with Iron(III) oxide

In the present investigation, conventional melting techniques were employed to fabricate the fluorophosphate glass composites with a composition of 20NaF–60P2O5–20Na2O–3Fe2O3 (mol.%). An investigation was conducted to analyze the impact of various doses of gamma-ray irradiation on certain optical properties. The alteration in the localized defects caused by gamma irradiation can explain the reduction in the refractive index (n) as the doses of gamma-ray irradiation increase, up to 10 kGy. The results of the solar skin protection factor (SSPF) and solar material protection factor (SMPF) tests demonstrate that the un-irradiated composite offers the highest level of protection against the harmful effects of solar energy on both human skin and materials. Some optical parameters, such as the concentrations of the charge carrier (Nopt), the relaxation time (τ), the optical electronegativity (ηopt), and the optical mobility (μopt) showed gamma dose-dependent. The effects of gamma-ray irradiation on the composites were analyzed using Electron Spin Resonance (ESR) and Fourier Transform Infrared (FTIR) spectroscopic studies, both before and after exposure to 10 and 20 kGy.

Iron coupled with hydroxylamine turns on the “switch” for free radical degradation of organic pollutants under high pH conditions

Reducing iron by hydroxylamine (HA) can promote the generation of reactive oxygen species (ROS) in the Fenton reaction and play a crucial role in the degradation of organic pollutants. However, the performance of this system at wider environmental thresholds is still not sufficiently understood, especially in the highly alkaline environments resulting from human activities. Here, we assessed the impact of solution pH on organic pollutant degradation by goethite with the addition of HA and H2O2. The solid phase variation and ROS generation were analyzed using Mössbauer spectroscopy, X-ray absorption near edge structure spectroscopy, and electron paramagnetic resonance analysis. This study found that under alkaline conditions, the system can continuously scavenge organic pollutants through oxygen-mediated generation of free radicals. At lower pH levels, organic pollutant decomposition, exemplified by the breakdown of bisphenol A (BPA), is primarily driven by the Fenton reaction facilitated by iron. As pH increases, hydroxyl radical (•OH) production decreases, accompanied by decreased BPA removal efficiency. However, the removal efficiency of BPA increased significantly at pH > 9. At pH 12, the removal of BPA exceeded that of the acidic condition after one hour, which is consistent with observations in soil system studies. Unlike the Fenton reaction, which is not sensitive to oxygen content, the removal of BPA under alkaline conditions occurs only under aerobic conditions·H2O2 is hardly involved in the reaction, and the depletion of HA becomes a critical factor in the decomposition of BPA. Importantly, in contrast to acidic conditions, where the dramatic decomposition of BPA occurs mainly in the first 10 min, the decomposition of BPA under alkaline conditions continued to occur over the 2 h of observation until complete removal. For natural systems, the remediation of pollutants depends more on the active time of ROS than on their reactivity. Therefore, this idea can reference pollution remediation strategies in anthropogenically disturbed environments.

S-scheme BiOBr/Bi2WO6 with oxygen vacancies for synergistic photodegradation and hydrogen generation: Mechanisms insight and DFT calculations

An S-type heterojunction photocatalyst Bi2WO6/BiOBr (BWO/BiOBr) with an interlaced band structure and abundant oxygen vacancies (Ov) was synthesized using a hydrothermal method and high-temperature calcination. The surface was modified with carbon quantum dots (CQDs) to create a 0D/2D/2D structure. The resulting photocatalyst exhibited superior performance, with a degradation rate for Norfloxacin (NOR) antibiotics surpassing Bi2WO6 with oxygen vacancies (BWO-Ov) and BiOBr by 6.55 and 3.96 times, respectively. Notably, it achieved a high hydrogen generation rate of 459.49 μmol·g−1·h−1 under visible light. The enhanced carrier transfer and solar absorption were attributed to the synergistic effect of CQDs and S-type heterojunctions. The face-to-face 2D/2D structure provided abundant reaction sites. The influence of initial NOR concentration and photocatalyst dosage on photocatalytic activity was investigated in our study. Incorporating CQDs improved solar absorption, as confirmed by NOR degradation under various wavelengths. Electron spin resonance (ESR) analysis indicated the generation of reactive oxygen species. Density functional theory (DFT) calculations and characterization explored charge transfer mechanisms and degradation pathways. These findings contribute to the design of efficient S-type heterogeneous photocatalysts for sustainable energy and environmental applications.

Ball-milled biochar-modified zero-valent aluminum activates peroxodisulfate for phenol degradation: Enhancement of catalysis by membrane-breaking effect

Zero-valent aluminum (ZVAl) is a potential activator for peroxodisulfate (PDS), yet the dense oxide film on its surface hampers electron transfer for the O−O bond cleavage of PDS. We synthesized zero-valent aluminum-biochar (BM-ZVAl@BC) composites through ball milling, which effectively disrupted the native oxide layer on BM-ZVAl@BC. Within the BM-ZVAl@BC/PDS system, biochar (BC) not only suppressed the rapid oxidation of BM-ZVAl@BC but also enhanced the dispersion and electron transfer rate of ZVAl, thereby improving the overall catalytic efficiency. Consequently, the phenol removal efficacy in the BM-ZVAl@BC/PDS system was notably improved. Optimal catalytic performance of the prepared BM-ZVAl@BC was achieved at a charcoal-to‑aluminum mass ratio of 2:1, resulting in 95.7 % phenol removal after 180 min. Quenching experiments and electron spin resonance (ESR) analysis revealed that both free radicals (SO4•−, •OH, and O2•−) and non-radical species (1O2) contributed to phenol degradation, with SO4•− and •OH playing predominant roles. In summary, the BM-ZVAl@BC/PDS system represents an effective and promising technology for the remediation of phenolic water pollutants.

New insight into wastewater treatment by activation of sulfite with humic acid under visible light irradiation

Sulfite (S(IV)), as an alternative to persulfate, has demonstrated its cost-effectiveness and environmentally friendly nature, garnering increasing attention in Advanced Oxidation Processes (AOPs). Dissolved organic matter (DOM) commonly occurred in diverse environments and was often regarded as an interfering factor in sulfite-based AOPs. However, less attention has been paid to the promotion of the activation of sulfite by excited DOM, which could produce various reactive intermediates. The study focused on the activation of sulfite using visible light (VL) - excited humic acid (HA) to efficiently degrade many common organic pollutants, which was better than peroxydisulfate (PDS) and peroxymonosulfate (PMS) systems. Quenching experiments and electron paramagnetic resonance (EPR) analysis revealed that the triplet states of HA (3HA*) activated sulfite through energy transfer, resulting in the production of SO4•−, O2•−, and 1O2. The most significant active species found in the degradation of roxarsone (ROX) was 1O2, which was a non-radical pathway and exhibits high selectivity for pollutant degradation. This non-radical pathway was not commonly observed in traditional sulfite-based AOPs. Additionally, the coexistence of various inorganic anions, such as NO3−, Cl−, SO42−, CO32−, and PO43−, had little effect on the degradation of ROX. Furthermore, DOM from different natural water demonstrated efficient activation of S(IV) under light conditions, opening up new possibilities for applying sulfite-based advanced oxidation to the remediation of organic pollution in diverse sites and water bodies. In summary, this research offered promising insights into the potential application of sulfite-based AOPs, facilitated by photo-excited HA, as a new strategy for efficiently degrading organic pollutants in various environmental settings.

Photo-assisted natural chalcopyrite activated peracetic acid for efficient micropollutant degradation

The effective activation of natural chalcopyrite (CuFeS2) on peracetic acid (PAA) to remove organic micropollutants was studied under visible light irradiation. Results showed than an effective sulfamethoxazole (SMX) degradation (95.0 %) was achieved under visible light irradiation for 30 min at pH 7.0. Quenching experiments, electron spin resonance analysis, and LC/MS spectrum demonstrated that HO• and CH3C(O)OO• were the main reactive species for SMX degradation, accounting for 43.3 % and 56.7 % of the contributions, respectively. Combined with X-ray photoelectron spectroscopy analysis, the photoelectrons generated on CuFeS2 activated by visible light enhanced the Fe3+/Fe2+ and Cu2+/Cu+ cycles on the surface, thereby activating PAA to generate HO•/CH3C(O)OO•. The removal rate of SMX decreased with the increase in wavelengths, due to the formation of low energy photons at longer wavelengths. Besides, the optimal pH for degradation of SMX by CuFeS2/PAA/Vis-LED process was neutral, which was attributed to the increasing easily activated anionic form of PAA during the increase in pH and the depletion of Fe species at alkaline conditions. Cl−, HCO3−, and HA slightly inhibited SMX degradation because of reactive species being quenched and/or shielding effect. Furthermore, the degradation efficiency of different pollutants by CuFeS2/PAA/Vis-LED was also measured, and the removal efficiency was different owing to the selectivity of CH3C(O)OO•. Finally, the process exhibited good applicability in real waters. Overall, this study provides new insight into visible light-catalyzed activation of PAA and suggests on further exploration of the intrinsic activation mechanism of PAA.

Spectroscopic and dosimetric comparison of tooth enamel separation methods for EPR retrospective dosimetry

Precise estimation of individual radiation dose utilizing biomaterials (fingernail, bone, and tooth) is very challenging due to their complex sample processing. Despite, tooth enamel, the most mineralized tissue of tooth is used for this purpose due to its high radiation sensitivity and ability to produce radiation induced long lived CO2− radicals. However, human teeth are not always available, and invasive nature of sample collection adds to the complexity making dose estimation difficult. In such cases, animal teeth (goat, cow, and moose) can be used as a substitute for human teeth due to comparable enamel sensitivity. Moreover, separation of enamel from dentine is a crucial step towards accurate dose estimation from irradiated teeth. In this work, Indian goat teeth were used as it was readily available to us and the comparison of goat enamel sensitivity to radiation was found to be within ∼7.4 % that of human. The enamel samples were separated following two chemical methods; (1) density separation using sodium polytungstate, (2) alkaline denaturation using NaOH and the quality was compared based on their purity and radiation sensitivity. Combined results of spectroscopic characterization using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Raman analysis authenticated the crystallinity and purity of the separated enamel samples. The radiation sensitivity of separated enamel samples was compared by electron paramagnetic resonance (EPR) analysis as a part of dosimetric characterization. The suitability of both the samples for retrospective dosimetry and epidemiological studies was checked by validating the dose estimated from separated enamel samples with standard alanine/EPR dosimeter.

Effective Degradation of 1,4-Dioxane by UV-Activated Persulfate: Mechanisms, Parameters and Environmental Impacts

There is more and more research focusing on the removal of dioxane by advanced oxidation technology at this stage, and this study investigated the efficacy of an advanced oxidation system with UV-activated persulfate (UV/PDS). This method had the advantages of fast reaction rate, simple equipment and convenient operation. Free radical quenching test and electron paramagnetic resonance (EPR) analysis showed that the main active radicals in the reaction system were SO4− and ·OH. This study also investigated that the optimal parameters were the initial PDS dosage of 3 mM, the UV intensity of 0.190 mM/cm2, the pH between 5 and 7 and the initial dioxane concentration of 50 mg/L. Additionally, after a reaction time of 150 min, the total organic carbon (TOC) content still remained at 83.53%, which revealed that the mineralization degree of organic matter was not fully achieved through UV/PDS treatment. The concentration of SO42− in the reaction system was 74.69 mg·L−1, which complied with the standard concentration specified. Furthermore, the cytotoxicity of the system exhibited an initial increase followed by a subsequent decrease, under the influence of the intermediates. It showed that the technology could efficiently degrade organic pollutants.

Mechanistic insights of PO43− functionalized carbon nitride homojunction hydrogels in photocatalytic-self-Fenton-peroxymonosulfate system for tetracycline degradation

In this study, metal-free PO43− enriched g-C3N4/g-C3N4 (PGCN) homojunction alginate 3D beads were developed for in-situ H2O2 production under visible light. Later, the photocatalytic-self-Fenton system was integrated with peroxymonosulfate for tetracycline degradation. Initially, the PO43− enriched g-C3N4 (PCN) and a homojunction composed of PCN and g-C3N4 (GCN) were prepared via the wet-impregnation method. Later, PGCN homojunction was formulated into 3D alginate beads through the blend-crosslinking method. The comprehensive characterization of the homojunction beads affirmed the closer contact between the semiconductors, alteration of the bandgap, faster channelization of electron-hole pairs, and improved separation of charge carriers that attributed to higher catalytic efficacy. The PGCN beads exhibited a maximum H2O2 production of 535 ± 12 µM under visible light irradiation for 60 min. The homojunction hydrogels displayed 99 ± 0.25 % tetracycline degradation in 20 min in the photocatalytic-self-Fenton-PMS system. The experimental studies also claimed a maximum chemical oxygen demand removal of 81 ± 3.6 % in 20 min with maximum reusability of beads up to 20 cycles. The Z-scheme electron migration mechanism is proposed based on the results aided by scavenger and electron spin resonance analysis. Overall, the as-synthesized alginate-supported homojunction-based photocatalytic-self-Fenton-peroxymonosulfate system is highly versatile and reusable for energy and environmental remediation.

Insights into the generation of multiple reactive species in UV254/PMS/I− system and their roles for degradation of phenolic and non-phenolic pollutants

An innovative technology for the removal of phenolic and non-phenolic organic pollutants from aqueous solution was developed by combining UV254 irradiation, peroxymonosulfate (PMS), and iodide ions (I−). Effects of pH, ratio of [I−]/[PMS], initial concentration of pollutant, dissolved organic matter (DOM) and typical inorganic constituents of environmental water on the degradation of studied pollutants with UV254/PMS/I− system were examined. The results showed that pH and [I−]/[PMS] exhibited significant impact on the degradation of pollutants during UV254/PMS/I− process. As the ratio of [I−]/[PMS] increased from 0.1 to 10.0, the removal efficiencies of phenolic pollutants remarkably increased, but those of non-phenolic pollutants decreased. The DOM at high concentration obviously inhibited the degradation of pollutants during UV254/PMS/I− process. Meanwhile, the occurrence of NO3− can slightly enhance the degradation of pollutants, and SO42−, Cl−, and HCO4− ions had no significant effects on UV254/PMS/I− system. The abundant reactive species including OH, SO4−, and I/I2− during UV254/PMS/I− process were generated based on electron spin resonance, fluorescence spectroscopy and steady-state concentration analysis. Quenching experimental results indicated that I/I2− can selectively degrade phenolic pollutants via one-electron oxidation. This study provided a reference for the application of reactive radicals involved oxidative technique in water purification.

Hypochlorite-mediated degradation and detoxification of sulfathiazole in aqueous solution and soil slurry

Although various activated sodium hypochlorite (NaClO) systems were proven to be promising strategies for recalcitrant organics treatment, the direct interaction between NaClO and pollutants without explicit activation is quite limited. In this work, a revolutionary approach to degrade sulfathiazole (STZ) in aqueous and soil slurry by single NaClO without any activator was proposed. The results demonstrated that 100% and 94.11% of STZ could be degraded by 0.025 mM and 5 mM NaClO in water and soil slurry, respectively. The elimination of STZ was shown to involve superoxide anion (O2•−), chlorine oxygen radical (ClO•), and hydroxyl radical (•OH), according to quenching experiments and the analysis of electron paramagnetic resonance. The addition of Cl−, HCO3−, SO42−, and humic acid (HA) marginally impeded the decomposition of STZ, while NO3−, Fe3+, and Mn2+ facilitated the process. The NaClO process exhibited significant removal effectiveness at a neutral initial pH. Moreover, the NaClO facilitated application in various soil samples and water matrices, and the procedure was also successful in effectively eliminating a range of sulfonamides. The suggested NaClO degradation mechanism of STZ was based on the observed intermediates, and the majority of the products exhibited lower ecotoxicity than STZ. Besides, the experiment results by using X-ray diffraction (XRD) and a fourier transform infrared spectrometer (FTIR) indicated the negligible effects on the composition and structure of soil by the treatment of NaClO. Simultaneously, the experimental results also illustrated that the bioavailability of heavy metals and the physiochemical characteristics of the soil before and after the remediation did not change to a significant extent. Following the remediation of NaClO, the phytotoxicity tests showed reduced toxicity to wheat and cucumber seeds. As a result, treating soil and water contaminated with STZ by using NaClO was a reasonably practical and eco-friendly method.

Effective degradation of recalcitrant naphthenic acids by the Fe(III)/peroxymonosulfate oxidation enhanced by molybdenum disulfide: Degradation performance and mechanisms

In this study, molybdenum disulfide (MoS2) has been investigated as a catalyst to boost the redox cycle of Fe(III)/Fe(II) to activate peroxymonosulfate (PMS) to effectively break down cyclohexanecarboxylic acid (CHA), which is a model naphthenic acid (NA) pollutant. The optimum conditions of pH 3, MoS2 concentration of 0.4 g/L, Fe(III) concentration of 0.3 mmol/L, and PMS concentration of 2 mmol/L has been applied for complete degradation of 0.1 mmol/L CHA in 10 minutes reaction time. Based on results of electron paramagnetic resonance analysis, chemical probe and quenching experiment, it was found that all of •OH, SO4•−, 1O2, and Fe(IV) contributed to the MoS2/Fe(III)/PMS oxidation system. Eighteen CHA byproducts and three primary CHA degradation pathways were revealed according to the results of UHPLC-QTOF-MS analysis. By using XPS, SEM, and XRD to characterize the MoS2 powders before and after the reaction, MoS2 was found with high stability and the oxidation of Mo(IV) on the surface was negligible. The impacts of background anions on CHA degradation were found to be nonimportant, and commercial NAs mixture were verified to be efficiently degraded in current system. Overall results indicate the capacity and potential of MoS2/Fe(III)/PMS system to be utilized for future treatment of authentic oil and gas field wastewater.