Degradation of norfloxacin by hydroxylamine enhanced fenton system: Kinetics, mechanism and degradation pathway

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.

Monitoring Photo-Fenton and Photo-Electro-Fenton process of contaminants emerging concern by a gas diffusion electrode using Ca10-xFex-yWy(PO4)6(OH)2 nanoparticles as heterogeneous catalyst

The catalytic performance of modified hydroxyapatite nanoparticles, Ca10-xFex-yWy(PO4)6(OH)2, was applied for the degradation of methylene blue (MB), fast green FCF (FG) and norfloxacin (NOR). XPS analysis pointed to the successful partial replacement of Ca by Fe. Under photo-electro-Fenton process, the catalyst Ca4FeII1·92W0·08FeIII4(PO4)6(OH)2 was combined with UVC radiation and electrogenerated H2O2 in a Printex L6 carbon-based gas diffusion electrode. The application of only 10 mA cm-2 resulted in 100% discoloration of MB and FG dyes in 50 min of treatment at pH 2.5, 7.0 and 9.0. The proposed treatment mechanism yielded maximum TOC removal of ∼80% and high mineralization current efficiency of ∼64%. Complete degradation of NOR was obtained in 40 min, and high mineralization of ∼86% was recorded after 240 min of treatment. Responses obtained from LC-ESI-MS/MS are in line with the theoretical Fukui indices and the ECOSAR data. The study enabled us to predict the main degradation route and the acute and chronic toxicity of the by-products formed during the contaminants degradation.

Optical Bioassays Based on the Signal Amplification of Redox Cycling

Optical bioassays are challenged by the growing requirements of sensitivity and simplicity. Recent developments in the combination of redox cycling with different optical methods for signal amplification have proven to have tremendous potential for improving analytical performances. In this review, we summarized the advances in optical bioassays based on the signal amplification of redox cycling, including colorimetry, fluorescence, surface-enhanced Raman scattering, chemiluminescence, and electrochemiluminescence. Furthermore, this review highlighted the general principles to effectively couple redox cycling with optical bioassays, and particular attention was focused on current challenges and future opportunities.

Recent advances in ultrasound-Fenton/Fenton-like technology for degradation of aqueous organic pollutants

Organic pollutants in water are a serious problem because of their widespread presence, harming the ecosystem and human health. Of the commonly used advanced oxidation processes, a hybrid of ultrasound and the Fenton/Fenton-like technology has received increasing attention in treatment of aqueous organic pollutants. This hybrid is effective in degradation of organic pollutants, but its application has not been summarised. Herein, first, the application and influencing factors of this hybrid technology for organic pollutants degradation are introduced. Second, the mechanism of its action is discussed. Third, the current challenges and future perspectives associated with this technology are proposed. This review provides valuable information regarding this technology, deepens the understanding of its mechanisms of organic pollutants degradation and provides a reference for its use in treatment of aquatic environments.

Removal of ofloxacin using a porous carbon microfiltration membrane based on in-situ generated •OH

This study investigated the removal performance of ofloxacin (OFL) by a novel electro-Fenton enhanced microfiltration membrane. The membranes used in this study consisted of metal-organic framework derived porous carbon, carbon nanotubes and Fe2+, which were able to produce hydroxyl radicals (•OH) in-situ via reducing O2 to hydrogen peroxide. Herein, membrane filtration with bias not only concentrated the pollutants to the level that could be efficiently treated by electro-Fenton but also confined/retained the toxic intermediates within the membrane to ensure a prolonged contact time with the oxidants. After validated by experiments, the applied bias of -1.0 V, pH of 3 and electrolyte concentration of 0.1 M were the relatively optimum conditions for OFL degradation. Under these conditions, the average OFL removal rate could be reach 75% with merely 5% membrane flux loss after 4 cycles operation by filtrating 1 mg/L OFL. Via decarboxylation reaction, piperazinyl ring opening, dealkylation and ipso substitution reaction, etc., OFL could be gradually and efficiently degraded to intermediate products and even to CO2 by •OH. Moreover, the oxidation reaction was preferred to following first-order reaction kinetics. This research verified a possibility for antibiotic removal by electro-enhanced microfiltration membrane.

Harnessing the power of natural minerals: A comprehensive review of their application as heterogeneous catalysts in advanced oxidation processes for organic pollutant degradation

The release of untreated wastewater into water bodies has become a significant environmental concern, resulting in the accumulation of refractory organic pollutants that pose risks to human health and ecosystems. Wastewater treatment methods, including biological, physical, and chemical techniques, have limitations in achieving complete removal of the refractory pollutants. Chemical methods, particularly advanced oxidation processes (AOPs), have gained special attention for their strong oxidation capacity and minimal secondary pollution. Among the various catalysts used in AOPs, natural minerals offer distinct advantages, such as low cost, abundant resources, and environmental friendliness. Currently, the utilization of natural minerals as catalysts in AOPs lacks thorough investigation and review. This work addresses the need for a comprehensive review of natural minerals as catalysts in AOPs. The structural characteristics and catalytic performance of different natural minerals are discussed, emphasizing their specific roles in AOPs. Furthermore, the review analyzes the influence of process factors, including catalyst dosage, oxidant addition, pH value, and temperature, on the catalytic performance of natural minerals. Strategies for enhancing the catalytic efficiency of AOPs mediated by natural minerals are explored, mainly including physical fields, reductant addition, and cocatalyst utilization. The review also examines the practical application prospects and main challenges associated with the use of natural minerals as heterogeneous catalysts in AOPs. This work contributes to the development of sustainable and efficient approaches for organic pollutant degradation in wastewater.

Selective Determination of Norfloxacin in Pharmaceutical Formulations and Human Urine Samples Using Poly(8-aminonaphthaline-2-sulfonic Acid)-Modified Glassy Carbon Electrodes

In this study, a glassy carbon electrode was modified potentiodynamically with poly(8-aminonaphthaline-2-sulfonic acid) [poly(ANSA)/GCE] for the detection of norfloxacin (NFN) in tablet formulations and human urine samples. Improvement of the effective surface area of the modified electrode and decreased charge-transfer resistance confirmed surface modification of the GCE by a conductive poly(ANSA) film. The appearance of an oxidative peak without a reductive peak in the reverse scan direction showed the irreversibility of the electrochemical oxidation of NFN in both the bare GCE and poly(ANSA)/GCE. A better coefficient of determination for the peak current on the square root of the scan rate (R² = 0.99514) than the scan rate (R² = 0.97109), indicating the oxidation of NFN at the poly(ANSA)/GCE, was predominantly diffusion mass transport-controlled. Under optimized pH and square wave parameters, the voltammetric current response of NFN at the poly(ANSA)/GCE showed linear dependence on the concentration, ranging from 1.0 × 10^-8 to 4.0 × 10^-4 M with a limit of detection of 4.1 × 10^-10. The NFN level in the studied tablet brands was in the range of 90.30-103.3% of their labeled values. Recovery results in tablet and urine samples ranged from 98.35 to 101.20% and 97.75 to 99.60%, respectively, and interference recovery results were less than 2.13% error in the presence of ampicillin, chloroquine phosphate, and cloxacillin. The present method had a better performance for the determination of NFN in tablet formulations and urine samples as compared with recently reported voltammetric methods due to its requirement of a simple electrode modification step, which provides the least limit of detection and a reasonably wider linear dynamic range.

Advancements in electrochemical technologies for the removal of fluoroquinolone antibiotics in wastewater: A review

In recent times, the need to make water safer and cleaner through the elimination of recalcitrant pharmaceutical residues has been the aim of many studies. Fluoroquinolone antibiotics such as ciprofloxacin, norfloxacin, enrofloxacin, and levofloxacin are among the commonly detected pharmaceuticals in wastewater. Since the presence of these pharmaceuticals in water bodies poses serious risks to living organisms, it is vital to adopt effective wastewater treatment techniques for their complete removal. Electrochemical technologies such as photoelectrocatalysis, electro-Fenton, electrocoagulation, and electrochemical oxidation have been established as techniques capable of the complete removal of organics including pharmaceuticals from wastewater. Hence, this review presents discussions on the recent progress (literature within 2018-2022) in the applications of common electrochemical processes for the degradation of fluoroquinolone antibiotics from wastewater. The fundamentals of these processes are highlighted while the results obtained using the processes are critically discussed. Furthermore, the inherent advantages and limitations of these processes in the mineralization of fluoroquinolone antibiotics are clearly emphasized. Additionally, appropriate recommendations are made toward improving electrochemical technologies for the complete removal of these pharmaceuticals with minimal energy consumption. Therefore, this review will serve as a bedrock for future researchers concerned with wastewater treatments to make informed decisions in the selection of suitable electrochemical techniques for the removal of pharmaceuticals from wastewater.

Hydroxylamine facilitated catalytic degradation of methylene blue in a Fenton-like system for heat-treatment modified drinking water treatment residues

Rational treatment of drinking water treatment residues (WTR) has become an environmental and social issue due to the risk of secondary contamination. WTR has been commonly used to prepare adsorbents because of its clay-like pore structure, but then requires further treatment. In this study, a Fenton-like system of H-WTR/HA/H₂O₂ was constructed to degrade organic pollutants in water. Specifically, WTR was modified by heat treatment to increase its adsorption active site, and to accelerate Fe(III)/Fe(II) cycling on the catalyst surface by the addition of hydroxylamine (HA). Moreover, the effects of pH, HA and H₂O₂ dosage on the degradation were discussed with methylene blue (MB) as the target pollutant. The mechanism of the action of HA was analyzed and the reactive oxygen species in the reaction system were determined. Combined with the reusability and stability experiments, the removal efficiency of MB remained 65.36% after 5 cycles. Consequently, this study may provide new insights into the resource utilization of WTR.

Construction of Co3O4 anchored on Bi2MoO6 microspheres for highly efficient photocatalytic peroxymonosulfate activation towards degradation of norfloxacin

Dissolved antibiotics have been a research subject due to their widespread presence and potential threats in drinking water treatment. To enhance the photocatalytic activity of Bi₂MoO₆ for the degradation of norfloxacin (NOR), the heterostructured Co₃O₄/Bi₂MoO₆ (CoBM) composites were synthesized by employing ZIF-67-derived Co₃O₄ on Bi₂MoO₆ microspheres. The as-synthesized resultant material 3-CoBM by 300 °C calcination was characterized by XRD, SEM, XPS, transient photocurrent techniques, and EIS. The photocatalytic performance was evaluated by monitoring different concentrations, NOR removal from aqueous solution. Compared with Bi₂MoO₆, 3-CoBM exhibited the better adsorption and elimination capacity of NOR due to the combined effect between peroxymonosulfate activation and photocatalytic reaction. The influences of catalyst dosage, PMS dosage, various interfering ions (Cl^-, NO₃^-, HCO₃^-, and SO₄^2-), pH value, and type of antibiotics for application removal were also invested. By activating PMS under visible-light irradiation, 84.95% of metronidazole (MNZ) can be degraded within 40 min, and NOR and tetracycline (TC) can be completely degraded using 3-CoBM. Degradation mechanism was elucidated by quenching tests in combination with EPR measurement, and the degree of activity of the active groups from strong to weak is h⁺, SO₄^-•, and •OH, respectively. The degradation products and conceivable degradation pathways of NOR were speculated by LC-MS. In combination of excellent peroxymonosulfate activation and highly enhanced photocatalytic performance, this newly Co₃O₄/Bi₂MoO₆ catalyst might be a promising candidate for degrading emerging antibiotic contamination in wastewater.

From Fenton and ORR 2e−-Type Catalysts to Bifunctional Electrodes for Environmental Remediation Using the Electro-Fenton Process

Currently, the presence of emerging contaminants in water sources has raised concerns worldwide due to low rates of mineralization, and in some cases, zero levels of degradation through conventional treatment methods. For these reasons, researchers in the field are focused on the use of advanced oxidation processes (AOPs) as a powerful tool for the degradation of persistent pollutants. These AOPs are based mainly on the in-situ production of hydroxyl radicals (OH•) generated from an oxidizing agent (H2O2 or O2) in the presence of a catalyst. Among the most studied AOPs, the Fenton reaction stands out due to its operational simplicity and good levels of degradation for a wide range of emerging contaminants. However, it has some limitations such as the storage and handling of H2O2. Therefore, the use of the electro-Fenton (EF) process has been proposed in which H2O2 is generated in situ by the action of the oxygen reduction reaction (ORR). However, it is important to mention that the ORR is given by two routes, by two or four electrons, which results in the products of H2O2 and H2O, respectively. For this reason, current efforts seek to increase the selectivity of ORR catalysts toward the 2e− route and thus improve the performance of the EF process. This work reviews catalysts for the Fenton reaction, ORR 2e− catalysts, and presents a short review of some proposed catalysts with bifunctional activity for ORR 2e− and Fenton processes. Finally, the most important factors for electro-Fenton dual catalysts to obtain high catalytic activity in both Fenton and ORR 2e− processes are summarized.

Insight into advanced oxidation processes for the degradation of fluoroquinolone antibiotics: Removal, mechanism, and influencing factors

The enrichment and transport of antibiotics in the environments pose many potential hazards to aquatic animals and humans, which has become one of the public health challenges worldwide. As a widely used class of antibiotics, fluoroquinolones (FQs) generally accumulated in the environments as traditional sewage treatment plants cannot completely remove them. Advanced oxidation processes (AOPs) have been shown to be a promising method for the abatement of antibiotic contamination. In this review, influencing factors and relevant mechanisms of FQs removal by various AOPs were summarized. Compared with other AOPs, photocatalytic ozone may be considered as a cost-effective method for degrading FQs. Finally, the benefits and application restrictions of AOPs were discussed, along with proposed research directions to provide new insights into the control of FQs pollutant via AOPs in practical applications.

Chemical Cyclic Amplification: Hydroxylamine Boosts the Fenton Reaction for Versatile and Scalable Biosensing

Nucleic acid detection is undoubtedly one of the most important research fields to meet the medical needs of genetic disease diagnosis, cancer treatment, and infectious disease prevention. However, the practical detection methods based on biological amplification are complex and time-consuming and require highly trained operators. Herein, we report a simple, rapid, and sensitive method for the nucleic acid assay by fluorescence or naked eye using chemical cyclic amplification. The addition of hydroxylamine (HA) during the Fenton reaction can continuously generate hydroxyl radicals (^•OH) via Fe³⁺/Fe²⁺ cycle, termed as "hydroxylamine boosts the Fenton reaction (Fenton-HA system)". Meanwhile, the reducing substances, such as terephthalic acid or o-phenylenediamine, react with ^•OH to generate oxidized substances that can be recognized by the naked eye or detected by fluorescence so as to realize the detection of Fe³⁺. The concentration of Fe³⁺ has a good linear relationship with fluorescence intensity in the range of 0.1 to 100 nM, and the limit of detection is calculated to be 0.03 nM (S/N = 3). Subsequently, Fe was introduced into the nucleic acid hybridization system after the Fe source was transformed into Fe³⁺, and the nucleic acids were indirectly determined by this method. This Fenton-HA system was used for sensing HIV-DNA and miRNA-21 to verify the validity of this method in nucleic acid detection. The detection limits were as low as 2.5 pM for HIV-DNA and 3 pM for miRNA-21. We believe that our work has unlocked an efficient signal amplification strategy, which is expected to develop a new generation of highly sensitive chemical biosensors.

N-Doped TiO2 Coupled with Manganese-Substituted Phosphomolybdic Acid Composites As Efficient Photocatalysis-Fenton Catalysts for the Degradation of Rhodamine B

The effectiveness of photocatalytic and Fenton reactions in the synergistic treatment of water pollution problems has become indisputable. In this paper, nitrogen-doped TiO₂ was selected as the catalyst for the photocatalytic reaction and manganese-substituted phosphomolybdic acid was used as the Fenton reagent, the two of which were combined together by acid impregnation to construct a binary photocatalysis-Fenton composite catalyst. The degradation experiments of the composite catalyst on RhB indicated that under UV-vis irradiation, the composite catalyst could degrade RhB almost completely within 8 min, and the degradation rate was 19.7 times higher than that of N-TiO₂, exhibiting a superior degradation ability. Simultaneously, a series of characterization methods were employed to analyze the structure, morphology, and optical properties of the catalysts. The results demonstrated that the nitrogen doping not only expanded the photo response range of TiO₂ but reduced the work function of TiO₂, which facilitated the transfer of electrons to the loaded Mn-HPMo side and further promoted the electron-hole separation efficiency. In addition, the introduction of Mn-HPMo provided three pathways for the activation of hydrogen peroxide, which enhanced the degradation activity. This study provides novel insights into the construction of binary and efficient catalysts with multiple hydroxyl radical generation pathways.

Activated Carbon Assisted Fenton-like Treatment of Wastewater Containing Acid Red G

The Fenton reaction as an effective advanced oxidation technology has been widely used in wastewater treatment for its stable effluent quality, simple operation, mild condition, and higher organic degradation with non-selectivity. However, the traditional Fenton reaction is limited by the sluggish regeneration of Fe2+, resulting in a slower reaction rate, and it is necessary to further increase the dosage of Fe2+, which will increase the production of iron sludge. Activated carbon (AC) has a strong adsorption property, and it cannot be ignored that it also can reduce Fe3+. In this study, the degradation of acid red G (ARG) by adding AC to the Fe3+/H2O2 system, the role of the reducing ability, and the reason why AC can reduce Fe3+ were studied. By adding three kinds of ACs, including coconut shell-activated carbon (CSPAC), wood-activated carbon (WPAC), and coal-activated carbon (CPAC), the ability of ACs to assist the Fe3+/H2O2 Fenton-like system to degrade ARG was clarified. Through the final treatment effect and the ability to reduce Fe3+, the type of AC with the best promotion effect was CSPAC. The different influence factors of particle size, the concentration of CSPAC, concentration of H2O2, concentration of Fe3+, and pH value were further observed. The best reaction conditions were determined as CSPAC powder with a particle size of 75 μm and dosage of 0.6 g/L, initial H2O2 concentration of 0.4 mmol/L, Fe3+ concentration of 0.1 mmol/L, and pH = 3. By reducing the adsorption effect of CSPAC, it was further observed that CSPAC could accelerate the early reaction rate of the degradation process of ARG by the Fe3+/H2O2 system. FT-IR and XPS confirmed that the C-O-H group on the surface of CSPAC could reduce Fe3+ to Fe2+. This study can improve the understanding and role of AC in the Fenton reaction, and further promote the application of the Fenton reaction in sewage treatment.

Hydrolysis of norfloxacin in the hyporheic zone: kinetics and pathways

Understanding the hydrolysis behavior and pathway of norfloxacin (NOR) in the hyporheic zone (HZ) is important for predicting its environmental persistence. Therefore, the effects of different environmental factors on NOR hydrolysis were investigated, and the hydrolysis pathway of NOR in the HZ was determined by DFT calculations and UPLC/TOF-MS. The hydrolysis process of NOR was consistent with the first-order kinetic. The experiment of environmental factors showed that DO was an important factor to affect NOR hydrolysis, and its hydrolysis rate was positively correlated with DO concentration. The superoxide radical (·O2-) was the main active species for NOR hydrolysis. The hydrolysis rates of NOR under neutral and alkaline conditions were higher than that under acidic conditions in both aerobic and anoxic environments. The ions of Ca2+, Mg2+, HCO3-, CO32-, and NO3- in simulated water samples inhibited the hydrolysis of NOR, while Cl- promoted its hydrolysis. In addition, the electronegativity of NOR was determined by DFT calculations, and it was speculated that the active sites of NOR hydrolysis were mainly located in the piperazine ring and quinolone ring. The main hydrolysis pathway of NOR in aerobic environment was piperazine ring cracking and quinolone ring decomposition, and that in anoxic environment was piperazine ring cracking. The results are of great significance to evaluate the environmental fate of NOR in the HZ and provide a theoretical basis for further understanding the degradation and governance of fluoroquinolones in water environment.

Two novel and efficient plant composites for the degradation of oxytetracycline: nanoscale ferrous sulphide supported on rape straw waste

As a biomass waste, rape straw shows a good application prospect in heterogeneous catalyst preparation due to its low-cost and stable structure. In this study, FeS-modified rape straw (RS-FeS) and its biochar (RSBC-FeS) were firstly synthesized to remove oxytetracycline (OTC). The highest OTC removal capacities observed for RS-FeS and RSBC-FeS were 635.66 and 827.80 mg g^-1. When compared with the adsorption process, the degradation ratios of the total OTC removal capacity observed in the RS-FeS/H₂O₂ and RSBC-FeS/H₂O₂ systems were 70.14 and 79.35%. Degradation was the dominant process observed during the removal of OTC. Both radical (SO₄^•-, ^•OH, and O₂^•-) and non-radical (¹O₂ and Ov) pathways were involved in the degradation process. OTC was degraded into smaller molecules via hydroxylation, dehydration, quinonization, demethylation, decarbonylation, alcohol oxidation, and ring cleavage reaction, indicating two catalysts could efficiently mineralize organic pollutants. The highest total organic carbon removal efficiencies of observed for RS-FeS and RSBC-FeS in swine wastewater were 88.93 and 96.81%, respectively. In addition, OTC removal efficiency of RS-FeS was more than 80% in successive experiments, further suggesting the feasibility of rape straw to Fenton-like catalysts. In this study, FeS nanoparticles were directly loaded on rape straw for the first time. Compared with biochar, FeS-modified rape straw can also degrade OTC efficiently, which provides an eco-friendly, high-efficient, and sustainable strategy for the preparation of catalyst.

Food By-Product Valorization by Using Plant-Based Coagulants Combined with AOPs for Agro-Industrial Wastewater Treatment

Re-using and adding value to by-products is one of the current focuses of the agri-food industry, following the Sustainable Development Goals of United Nations. In this work, the by-products of four plants, namely chestnut burr, acorn peel, olive leaf, and grape stem were used as coagulants to treat elderberry wastewater (EW), a problematic liquid effluent. EW pre-treatment using these natural coagulants showed promising results after pH and coagulant dosage optimization. However, the decrease in total organic carbon (TOC) was not significant, due to the addition of the plant-based natural coagulants which contain carbon content. After this pre-treatment, the photo-Fenton advanced oxidation process was selected, after preliminary assays, to improve the global performance of the EW treatment. Photo-Fenton was also optimized for the parameters of pH, H₂O₂, Fe²⁺, and irradiance power, and the best conditions were applied to the EW treatment. Under the best operational conditions defined in the parametric study, the combined results of coagulation–flocculation–decantation (CFD) and photo-Fenton for chestnut burr, acorn peel, olive leaf, and grape stem were, respectively, 90.2, 89.5, 91.5, and 88.7% for TOC removal; 88.7, 82.0, 90.2 and 93.1%, respectively, for turbidity removal; and finally, 40.6, 42.2, 45.3, and 39.1%, respectively, for TSS removal. As a final remark, it is possible to suggest that plant-based coagulants, combined with photo-Fenton, can be a promising strategy for EW treatment that simultaneously enables valorization by adding value back to food by-products.

Lattice B-doping evolved ferromagnetic perovskite-like catalyst for enhancing persulfate-based degradation of norfloxacin

Series of B-doped perovskite-like materials CeCu_0.5Co_0.5O₃ (B-C³O) were fabricated with unique ferromagnetic property due to partial substitution of non-magnetic 2p-impurities boron in the lattice. Then, B-C³O was used for activating peroxymonosulfate (PMS) for the degradation of norfloxacin (NOR), one kind of emerging pollutants with the concentration level up to mg/L in wastewaters. The results indicated that 5.0% B-C³O exhibited stable catalytic ability at pH 3.0-9.0 and high degradation efficiency in co-existing inorganic Cl^-, SO₄^2-, NO₃^-, H₂PO₄^- and organic humic acid. Non-radical ¹O₂, radicals •OH and SO₄^•-, as well as ClO^- were detected with synergy effect for NOR degradation. By quantifying free radicals, •OH with 0.52 µM and SO₄^•- with 10.91 µM were obtained at 180 min, verifying the leading role of SO₄^•-. The degradation process involved the defluorination and decarboxylation, as well as opening of quinolone and piperazinyl rings. Adopting alfalfa as the model plant, the toxicity effect before and after NOR degradation was finally evaluated with seed germination rate and chlorophyll content as the physiological indicators. In summary, non-metal B-doping not only provides a creative strategy for the development of ferromagnetic perovskite-like materials, but also affords excellent catalysts for aiding the advanced oxidation technology for removal of emerging pollutants in wastewaters.

Efficient decontamination of ciprofloxacin at neutral pH via visible light assisted Fenton-like process mediated by Fe(III)-GLDA complexation

This work demonstrated a novel N,N-bis(carboxymethyl)glutamic acid (GLDA) modified visible (vis) light assisted Fenton-like system which could effectively removal ciprofloxacin (CIP) at neutral pH. The removal rate of CIP in the GLDA/Fe(III)/H₂O₂/vis system was 97.9% within 120 min and was approximately twice as high as that in the Fe(III)/H₂O₂/vis system. GLDA could significantly accelerate the Fe(III)/Fe(II) cycle under visible light irradiation. Radical scavenging experiments demonstrated that 74.2% of the Fe(II) in the GLDA/Fe(III)/H₂O₂/vis system originated from the ligand-to-metal charge transfer reaction between Fe(III) and GLDA. The hydroxyl radical was the dominant species for CIP degradation. H₂O₂ utilization kinetic modeling exhibited that 90.1% of H₂O₂ was used for CIP mineralization. The effects of experimental parameters and coexisting substances on the removal of CIP in the Fe(III)/GLDA/H₂O₂/vis system were investigated in detail. The intermediate products of CIP were explored via the high-performance liquid chromatography-mass spectrometry.

High-efficiency oxidation of fluoroquinolones by the synergistic activation of peroxymonosulfate via vacuum ultraviolet and ferrous iron

Fluoroquinolones in aquatic environments have caused worldwide concern due to the negative effects on human health and ecological environment. So far, the performance and mechanism for fluoroquinolones removal by the synergistic activation of peroxymonosulfate (PMS) via vacuum UV (VUV) irradiation and Fe²⁺ are still blank. Herein, compared with its sub-processes, VUV/Fe²⁺/PMS process significantly improved the degradation and mineralization efficiencies of three fluoroquinolones. Effect mechanisms of typical parameters (Fe²⁺ and PMS doses, initial pH) on norfloxacin (NOR) removal by VUV/Fe²⁺/PMS were elaborated and VUV/Fe²⁺/PMS showed excellent performance at wide initial pH (3-10). The results of fluorescence molecular probe and radical trapping experiments proved that hydroxyl radical, singlet oxygen, and sulfate radical were primary reactive oxygen species in VUV/Fe²⁺/PMS. The degradation pathways of NOR in VUV/Fe²⁺/PMS were mainly defluorination, piperazine ring transformation and quinolone group transformation, and its main inorganic by-products were F^-, NO₃^-, and NH₄⁺. Besides, the synergistic reaction pathways in integrated VUV/Fe²⁺/PMS process were elaborated. Furthermore, inorganic anions (such as Cl^-, NO₃^-, SO₄^2-, CO₃^2-) hardly affected NOR removal by VUV/Fe²⁺/PMS, while dissolved organic matter showed slight inhibition. Finally, well-pleasing results of fluoroquinolones removal by VUV/Fe²⁺/PMS in actual waters highlighted its superiority in the advanced treatment of secondary effluent.

Cobalt-Enhanced Mass Transfer and Catalytic Production of Sulfate Radicals in MOF-Derived CeO2 • Co3 O4 Nanoflowers for Efficient Degradation of Antibiotics

Antibiotics discharge has been a critical issue as the abuse in clinical disease treatment and aquaculture industry. Advanced oxidation process (AOPs) is regarded as a promising approach to degrade organic pollutants from wastewater, however, the catalysts for AOPs always present low activities, and uncontrollable porosities, thus hindering their further wider applications. In this work, an aliovalent-substitution strategy is employed in metal-organic framework (MOF) precursors assembly, aiming to introduce Co(II/III) into Ce-O clusters which could modify the structure of the clusters, then change the crystallization, enlarge the surface area, and regulate the morphology. The introduction of Co(II/III) also enlarges the pore size for mass transfer and enriches the active sites for the production of sulfate radicals (SO₄^• - ) in MOF-derived catalysts, leading to excellent performance in antibiotics removal. Significantly, the CeO₂ •Co₃ O₄ nanoflowers could efficiently enhance the generation of sulfate radical SO₄^• - and promote the norfloxacin removal efficiency to 99% within 20 min. The CeO₂ •Co₃ O₄ nanoflowers also present remarkable universality toward various antibiotics and organic pollutants. The aliovalent-substitution strategy is anticipated to find wide use in the exploration of high-performance MOF-derived catalysts for various applications.

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

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

Rapid degradation of norfloxacin by VUV/Fe2+/H2O2 over a wide initial pH: Process parameters, synergistic mechanism, and influencing factors

Vacuum UV (VUV) technology has attracted much attention because it effectively splits water to generate reactive oxygen species (ROS) in situ and has the advantages of UV. So far, the synergistic mechanisms, formation pathways and contributions of ROS in VUV/Fe²⁺/H₂O₂ process have not been extensively studied. Herein, complete removal (at 4 min) and 63.3% mineralization (at 8 min) of 45 μM norfloxacin (NOR) were achieved at neutral pH by VUV/Fe²⁺/H₂O₂ (90 μM Fe²⁺ and 3 mM H₂O₂). Compared with its subsystems, VUV/Fe²⁺/H₂O₂ can not only increase the pseudo-first-order reaction rate constant of NOR removal by 2.3-14.9 times and increase the mineralization by 20.4-59.4%, but also reduce the residual ratio of H₂O₂ by 19.9-70.1% and reduce total cost by 20.0-68.0%. The synergy factor of VUV/Fe²⁺/H₂O₂ was 3.97, which was attributed to the VUV irradiation promoting iron redox cycle and H₂O₂ decomposition. Moreover, hydroxyl radical and superoxide radical, which were identified as the main ROS, contributed 79.07% and 18.47% to NOR removal, respectively. Degradation pathways of NOR were proposed. Furthermore, effects of coexisting ions and dissolved organic matter were investigated. As an energy-saving and efficient process, the satisfactory results of VUV/Fe²⁺/H₂O₂ applied in real waters also highlight its application potential.