MOF-derived Co3O4-C@FeOOH as an efficient catalyst for catalytic ozonation of norfloxacin

Degradation of Methylene Blue by Ozone Oxidation Catalyzed by the Magnetic MnFe2O4@Co3S4 Nanocomposite

In this study, the MnFe2O4@Co3S4 magnetic nanocomposite was prepared by a two-step hydrothermal method and used to catalyze the ozone oxidation degradation of methylene blue. It was characterized by XRD, EDS, SEM, FT-IR, and XPS. The results showed that the introduction of Co3S4 made MnFe2O4 grow uniformly on Co3S4 nanosheets, which effectively prevented the agglomeration of MnFe2O4. Moreover, MnFe2O4 provided active sites and Mn3+/Mn2+ and Fe3+/Fe2+ cycles for the ozone oxidation process. Not only did Co3S4 provide the active site (Co2+/Co3+) for the ozone oxidation process but also its derived S2-/S22- accelerated the electron transfer rate on the surface of the material, thus improving the efficiency of catalytic ozone oxidation degradation of methylene blue. When the molar ratio of MnFe2O4 to Co3S4 was 6:3 (MnFe2O4@Co3S4-3), the catalytic ozone degradation efficiency of methylene blue was the best, which reached 93.55% in 12 min. The reactive oxygen species in catalytic ozonation degradation of MB were 1O2, O2.-, and ·OH. The MnFe2O4@Co3S4 magnetic nanocomposite is an efficient and stable O3 activator, which maintains high catalytic activity and low metal ion leaching after five cycles, indicating that it has a good application prospect in catalyzing ozone oxidation to degrade organic pollutants.

Clay-catalyzed ozonation of Norfloxacin - Effects of metal cation and degradation rate on aqueous media toxicity towards Lemna minor

Norfloxacin was ozonized in aqueous montmorillonite suspensions and the resulting toxicity on Lemna minor was investigated for understanding the impact of natural partial oxidation of antibiotics on clay-containing ecosystems. Ion-exchanged montmorillonites (Mt) were used as catalysts because of their large occurrence in soils and aquatic media, while Lemna minor, an aquatic macrophyte is regarded as a bioindicator highly responsive to ecotoxicity change in the environment. NOF solutions exhibit intrinsic toxicity on L. minor expressed in terms of fresh mass, frond number, chlorophyll content and production of reactive oxygen species. This toxicity was found to trigger through oxidative stress and was enhanced by ozonation. UV-Vis spectrophotometry and liquid chromatography coupled to mass spectrometry (LC-MS) showed that the toxicity specifically evolves in time according to the clay exchangeable cations, oxidation advancement and derivatives distribution, and confirmed the unavoidable formation of hydroxylated and acidic intermediates. The cleavage of the phenyl and pyridinyl groups appear to occur even in non-catalytic ozonation and generate potentially more toxic derivatives than the parent molecule with excessive oxidative stress and changes in the distribution of the photosynthetic pigments. Addition of Fe(II)Mt and Cu(II)Mt induced a more effective ozonation with, but with much less toxicity with Fe2+ exchanged Mt catalyst. This research provides valuable insights into the environmental fate of antibiotics under aerobic conditions, and allows understanding their impact evolution on biodiversity, envisaging strategies targeting optimized water treatments with complete mineralization of organic pollutants.

MnO2/porous spontaneously polarized ceramic with self-powered electric field and superior charge transfer to catalyze ozonation for efficient demulsification

Ozone (O3) demulsification shows great potential in emulsion wastewater treatment due to its strong oxidative properties. However, the low mass transfer efficiency and oxidation selectivity of O3 cannot be ignored. Herein, a MnO2/porous spontaneously polarized ceramic (MnO2/PSPC) composite with strong interfacial interactions and self-powered electric field was prepared for heterogeneous catalytic ozonation (HCO) to achieve efficient demulsification. Excellent remanent polarization (0.00858 μC/cm2) together with systematic electrochemical characterizations of MnO2/PSPC demonstrated its significant charge transfer capability, which is essential for the subsequent reduction of Mn4+ in the HCO demulsification process. O3- MnO2/PSPC exhibited excellent demulsification performance with 99 % demulsification rate of cetyltrimethylammonium bromide-stabilized emulsion within 30 min, outperforming O3 (130 min), O3-MnO2 (60 min), and O3-PSPC (90 min). O3-MnO2/PSPC showed effective demulsification of non-/anionic surfactant stabilized emulsions and excellent stability after 5 cycles. Density functional theory calculations together with characterizations illustrate that potential difference-induced rapid electron transfer and water flow-induced self-powered electric field were the fundamental motivation for the fast Mn3+/Mn4+ cycle and O3 adsorption/decomposition to generate reactive oxygen species (ROS). Notably, the oxidation of surfactants by ROS led to the coalescence of the oil droplets. This study provides an efficient, sustainable, and energy-efficient method to improve the O3 demulsification performance.

Inhibition of the Germination of Root Parasitic Plants by Zeolitic Imidazolate Framework-8

Crystalline ZIF-8 (C-ZIF-8) and amorphous ZIF-8 (Am-ZIF-8) were prepared and investigated to control the germination of Striga hermonthica, a root parasitic plant, which threatens cereal crops production particularly in sub-Saharan Africa. We have demonstrated that Am-ZIF-8 shows a better performance than C-ZIF-8 in inhibiting Striga seeds germination. This efficient performance of Am-ZIF-8 materials can be attributed to the incomplete deprotonation of 2 methylimidazole (2MIM) during amorphization, leading to the presence of unsaturated Zn-N coordination with the uncoordinated -NH groups available to undergo hydrogen bonding with the strigolactone analog GR24 forming a more stable Am-ZIF-8⋅⋅⋅GR24 hydrogen bonded network. We further established that application of ZIF-8 materials generally has no adverse effects on the growth and quality of rice crops.

Degradation of UV328 by ozone/peroxymonosulfate system: Performance and mechanisms

2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (UV328) is an emerging persistent organic pollutant ubiquitously found in environmental matrices. Though some advanced oxidation processes have been tested to degrade UV328 in waste streams, the degradation mechanisms are largely unknown. In this study, the degradation of UV328 by ozone (O3) and peroxymonosulfate (PMS) was systemically investigated. At neutral pH, 97.0% UV328 was removed in 5 min with 6.4 mg/min O3 and 2 mM PMS, and the degradation rate was positively correlated with the concentration of oxidants. Hydroxyl radical (•OH), sulfate radical (SO4•-) and singlet oxygen (1O2) participated in the degradation of UV328, in which 1O2 played a key role. Based on the identified transformation intermediates and density functional theory simulations, three degradation pathways of dehydrogenation, cycloaddition and hydroxylation were proposed. •OH and SO4•- radicals could attack UV328 through hydrogen atom abstraction channel. 1O2-mediated cycloaddition reaction is favorable, and •OH could react with UV328 via radical adduct formation pathway. Toxicity assessment indicated that O3/PMS treatment mitigated the ecological risks of UV328.

Novel amorphous FeOOH-modified Co9S8 nanosheets with enhanced catalytic activity in oxygen evolution reaction

Efficient oxygen evolution reaction (OER) is vital for water electrolysis and advanced hydrogen energy production. However, the sluggish kinetics of this reaction require significant overpotentials, leading to high energy consumption. Therefore, developing OER electrocatalysts with exceptional performance and long-term durability is crucial for enhancing the energy efficiency and cost-effectiveness of the hydrogen production process. In this research, novel FeOOH/Co9S8 catalysts were prepared through a two-step hydrothermal reaction followed by one-step electrodeposition on nickel foam for an alkaline OER. The as-obtained catalysts possessed abundant non-homogeneous interfaces between FeOOH and Co9S8 nanosheets, conducive to optimized coordination environments of Fe and Co sites by redistributing interfacial charges. This synergy strengthened the chemisorption of oxygenated intermediates, leading to accelerated reaction kinetics, abundant active sites, and enhanced OER performance. The optimized electrocatalyst FeOOH/Co9S8-15 achieved a current density of 10 mA cm-2 at an overpotential of 248 mV and good stability for over 140 h. This study presents a novel approach for producing compelling and durable alkaline dielectric OER electrocatalysts, which will be helpful in the future manufacturing of advanced energy devices.

As(V) adsorption by FeOOH@coal gangue composite from aqueous solution: performance and mechanisms

Arsenic (As) pollution in water poses a significant threat to the ecological environment and human health. Meanwhile, the resource utilisation of coal gangue is of utmost importance in ecologically sustainable development. Thus, the FeOOH@coal gangue composite (FeOOH@CG) was synthesised for As(V) adsorption in this study. The results showed that α-FeOOH, β-FeOOH and Schwertmannite loaded on the surface of FeOOH@CG. Moreover, the adsorption behaviour of As(V) by FeOOH@CG was investigated under different reaction conditions, such as pH, contact time, initial concentration and co-existing anions. The optimum adsorption conditions were as follows: initial As(V) concentration of 60 mg/L, pH of 3.0 and adsorption time of 180-240 h. The adsorption capacity of FeOOH@CG for As(V) was pH-dependent and the maximum adsorption capacity was 185.94 mg/g. The presence of anions (H 2 PO 4 - , HCO 3 - and C l - ) decreased the adsorption efficiency of FeOOH@CG for As(V). The adsorption process of FeOOH@CG for As(V) could be well-described by the pseudo-second-order model and Langmuir model, indicating that the adsorption process mainly depended on chemical adsorption. The thermodynamic analysis suggested that the adsorption was a spontaneous and endothermic process. In addition, according to the analyses of XRD, FTIR and XPS, the dominant mechanisms of As(V) adsorption by FeOOH@CG were electrostatic attraction, complexation and precipitation. In conclusion, FeOOH@CG has great potential as an efficient and environmentally friendly adsorbent for As(V) adsorption from aqueous solution.

Electro-Fenton degradation of pefloxacin using MOFs derived Cu, N co-doped carbon as a nanocomposite catalyst

Electro-Fenton (EF) can in-situ produce H2O2 and effectively activate H2O2 to generate powerful reactive species for the destruction of contaminants under acidic conditions, however, the production of iron-containing sludge and requirement of low working pH significantly hinder its practical application. Herein, a novel Cu, N co-doped carbon (Cu-N@C) with metal organic framework (MOF) as a precursor was constructed and adopted for the elimination of pefloxacin (PEF) in the heterogeneous electro-Fenton (HEF) process. PEF could be almost completely removed within 1 h and total organic carbon (TOC) removal efficiency was 48.57% within 6 h. Meanwhile, Cu-N@C had good repeatability and environmental adaptability, it can still maintain excellent catalytic performance after 10 cycles, and it exhibited satisfactory remediation performance in simulated water matrix. In addition, the HEF process catalyzed by Cu-N@C also showed satisfactory degradation effect on other organic pollutants including atrazine, methylene blue, and chlorotetracycline. Under the action of impressed current, the HEF system could generate H2O2 in-situ, and the active species could be generated in the redox cycle of Cu0/Cu1+/Cu2+. Electron paramagnetic resonance and quenching experiments confirmed that •OH was the dominant active species in the degradation of organic compounds. The degradation process of PEF was studied by mass spectrometry analysis of intermediate products. This study provided a simple method to prepare MOF-based electrocatalyst, which exhibits promising application potential for treatment wastewater.

In-situ growth of Mn-Ni3S2 on nickel foam for catalytic ozonation of p-nitrophenol

In this study, a new catalyst for catalytic ozonation was obtained by in-situ growth of Mn-Ni3S2 nanosheets on the surface of nickel foam (NF). The full degradation of p-nitrophenol (PNP) was accomplished under optimal conditions in 40 min. The effects of material dosage, ozone dosage, pH and the presence of inorganic anions on the degradation efficiency of PNP were investigated. ESR analysis showed that singlet oxygen (1O2) and superoxide radical (O2•-) are the main contributors of PNP degradation. This study offers a new combination of supported catalysts with high efficiency and easy recovery, which provides a new idea for wastewater treatment.

Regulating the interface electron distribution of iron-based MOFs through ligand functionalization enables efficient peroxymonosulfate utilization and catalytic performance

Ligand functionalization is an effective way to endow Metal-organic frameworks (MOF) with versatility for multiple applications by introducing or displaying substituents without changing the origin framework. In this work, the original MIL-101(Fe) was modified by functional groups, including -NH2, -NO2, -CH3, and -Cl substituents. The Bader charge results and electron localization function (ELF) quantitatively indicated that the functional ligands with different properties can regulate the electron structure of transition-metal centers through interface-charge redistribution. Accompanying the higher adsorption and utilization rate of peroxymonosulfate (PMS), more than 96% of acetaminophen (APAP) was degraded with a mineralization rate of 40.17% under the NH2-BDC/PMS system. In terms of mechanism, the amino group not only accelerated the regeneration of Fe(II) via the NCFe electron-transfer path, but also stimulated the appearance of high-valent Fe species. Meanwhile, the degradation pathways of APAP were proposed by integrating the results of liquid chromatograph-mass spectrometry (LC-MS) and Frontier molecular-orbital theory. Finally, the NH2-BDC/PMS system reveals long-term stability, nonselectivity, low biotoxicity as well as secondary pollution for pollutant degradation, which is a considered candidate for further environmental applications.

Tailored Metal-Organic Frameworks for Water Purification: Perfluorinated Fe-MOFs for Enhanced Heterogeneous Catalytic Ozonation

An industrially viable catalyst for heterogeneous catalytic ozonation (HCO) in water purification requires the characteristics of good dispersion of active species on its surface, efficient electron transfer for ozone decay, and maximum active species utilization. While metal-organic frameworks (MOFs) represent an attractive platform for HCO, the metal nodes in the unmodified MOFs exhibit low catalytic activity. Herein, we present a perfluorinated Fe-MOF catalyst by substituting H atoms on the metalated ligands with F atoms (termed 4F-MIL-88B) to induce structure evolution. The Lewis acidity of 4F-MIL-88B was enhanced via the formation of Fe nodes, tailoring the electron distribution on the catalyst surface. As a result of catalyst modification, the rate constant for degradation of the target compounds examined increased by ∼700% compared with that observed for the unmodified catalyst. Experimental evidence and theoretical calculations showed that the modulated polarity and the enhanced electron transfer between the catalyst and ozone molecules contributed to the adsorption and transformation of O3 to •OH on the catalyst surface. Overall, the results of this study highlight the significance of tailoring the metalated ligands to develop highly efficient and stable MOF catalysts for HCO and provide an in-depth mechanistic understanding of their structure-function evolution, which is expected to facilitate the applications of nanomaterial-based processes in water purification.

Enhanced ozonation of vanillin catalyzed by highly efficient magnetic MnFe2O4/ZIF-67 catalysts: Synergistic effects and mechanism insights

In this study, we synthesized magnetic MnFe2O4/ZIF-67 composite catalysts using a straightforward method, yielding catalysts that exhibited outstanding performance in catalyzing the ozonation of vanillin. This exceptional catalytic efficiency arose from the synergistic interplay between MnFe2O4 and ZIF-67. Comprehensive characterization via x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR), Brunauer-Emmett-Teller (BET), field emission scanning electron microscopy (FE-SEM), and energy dispersive spectroscopy (EDS) confirmed that the incorporation of MnFe2O4 promoted the creation of oxygen vacancies, resulting in an increased presence of l adsorbed oxygen (Oads) and the generation of additional ·OH groups on the catalyst surface. Utilizing ZIF-67 as the carrier markedly enhanced the specific surface area of the catalyst, augmenting the exposure of active sites, thus improving the degradation efficiency and reducing the energy consumption. The effects of different experimental parameters (catalyst type, initial vanillin concentration, ozone dosage, initial pH value, and catalyst dosage) were also investigated, and the optimal experimental parameters (300 mg/L1.0-MnFe2O4/ZIF-67, vanillin concentration = 250 mg/L, O3 concentration = 12 mg/min, pH = 7) were obtained. The vanillin removal efficiency of MnFe2O4/ZIF-67 was increased from 74.95% to 99.54% after 30 min of reaction, and the magnetic separation of MnFe2O4/ZIF-67 was easy to be recycled and stable, and the vanillin removal efficiency of MnFe2O4/ZIF-67 was only decreased by about 8.92% after 5 cycles. Additionally, we delved into the synergistic effects and catalytic mechanism of the catalysts through kinetic fitting, reactive oxygen quenching experiments, and electron transfer analysis. This multifaceted approach provides a comprehensive understanding of the enhanced ozonation process catalyzed by MnFe2O4/ZIF-67 composite catalysts, shedding light on their potential applications in advanced oxidation processes. PRACTITIONER POINTS: A stable and recyclable magnetic composite MnFe2O4/ZIF-67 catalyst was synthesized through a simple method. The synergistic effect and catalytic mechanism of the MnFe2O4/ZIF-67 catalyst were comprehensively analyzed and discussed. A kinetic model for the catalytic ozone oxidation of vanillin was introduced, providing valuable insights into the reaction dynamics.

Chitosan derived N-doped carbon anchored Co3O4-doped MoS2 nanosheets as an efficient peroxymonosulfate activator for degradation of dyes

Peroxymonosulfate (PMS), which is dominated by non-free radical pathway, has a good removal effect on organic pollutants in complex water matrices. In this article, a biodegradable cobalt-based catalyst (Co3O4/MoS2@NCS) was synthesized by a simple hydrothermal method with chitosan (CS) as nitrogen‑carbon precursor and doped with Cobaltic‑cobaltous oxide (Co3O4) and Molybdenum disulfide (MoS2), and was used to activate PMS to degrade dye wastewater. Electrochemical tests showed that Co3O4/MoS2@NCS exhibited higher current density and cycling area than MoS2@NCS and MoS2. In the Co3O4/MoS2@NCS/PMS system, the degradation rate of 30 mg·L-1 rhodamine B (RhB) reached 97.75 % within 5 min, and kept as high as 94.34 % after 5 cycles. Its rate constant was 1.91 and 8.37 times that of MoS2@NCS/PMS and MoS2/PMS, respectively. It had good complex background matrices and acid-base anti-interference ability, and had good universality and reusability. The degradation rate of methyl orange (MO) and methylene blue (MB) were more than 91 % within 5 min at pH 4.8. The experimental results demonstrated that MoS2-modified CS as a carrier exposed a large number of active sites, which not only dispersed Co3O4 nanoparticles and improved the stability of the catalyst, but also provided abundant electron rich groups, and promoted the activation of PMS and the production of reactive oxygen species (ROS). PMS was effectively activated by catalytic sites (Co3+/Co2+, Mo4+/Mo5+/Mo6+, CO, pyridine N, pyrrole N, hydroxyl group and unsaturated sulfur), producing a large number of radicals that attack RhB molecules, causing chromophore cleavage, ring opening, and mineralization. Among them, non-free radical 1O2 was the main ROS for RhB degradation. This work is expected to provide a new idea for the design and synthesis of environmentally friendly and efficient MoS2-modified cobalt-based catalysts.

Defluorination of perfluorooctanoic acid and perfluorooctane sulfonic acid by heterogeneous catalytic system of Fe-Al2O3/O3: Synergistic oxidation effects and defluorination mechanism

In this study, catalytic ozonation by Fe-Al2O3 was used to investigate the defluorination of PFOA and PFOS, assessing the effects of different experimental conditions on the defluorination efficiency of the system. The oxidation mechanism of the Fe-Al2O3/O3 system and the specific degradation and defluorination mechanisms for PFOA and PFOS were determined. Results showed that compared to the single O3 system, the defluorination rates of PFOA and PFOS increased by 2.32- and 5.92-fold using the Fe-Al2O3/O3 system under optimal experimental conditions. Mechanistic analysis indicated that in Fe-Al2O3, the variable valence iron (Fe) and functional groups containing C and O served as important reaction sites during the catalytic process. The co-existence of 1O2, OH, O2- and high-valence Fe(IV) constituted a synergistic oxidation system consisting of free radicals and non-radicals, promoting the degradation and defluorination of PFOA and PFOS. DFT theoretical calculations and the analysis of intermediate degradation products suggested that the degradation pathways of PFOA and PFOS involved Kolbe decarboxylation, desulfonation, alcoholization and intramolecular cyclization reactions. The degradation and defluorination pathways of PFOA and PFOS consisted of the stepwise removal of -CF2-, with PFOS exhibiting a higher defluorination rate than PFOA due to its susceptibility to electrophilic attack. This study provides a theoretical basis for the development of heterogeneous catalytic ozonation systems for PFOA and PFOS treatment.

Progress on mechanism and efficacy of heterogeneous photocatalysis coupled oxidant activation as an advanced oxidation process for water decontamination

The rising debate on the dilemma of photocatalytic water treatment technologies has driven researchers to revisit its prospects in water decontamination. Nowadays, heterogeneous photocatalysis coupled oxidant activation techniques are intensively studied due to their dual advantages of high mineralization and high oxidation efficiency in pollutant degradation. This paved a new way for the development of solar-driven oxidation technologies. Previous reviews focused on the advances in one specific coupling technique, such as photocatalytic persulfate activation and photocatalytic ozonation, but lack a consolidated understanding of the synergy between photocatalytic oxidation and oxidant activation. The synergy involves the migration of photogenerated carriers, radical reaction, and the increase in oxidation rate and mineralization. This review systematically summarizes the fundamentals of activation mechanism, advanced characterization techniques and synergistic effects of coupling techniques for water decontamination. Besides, specific cases that lead researchers astray in revealing mechanisms and assessing synergy are critically discussed. Finally, the prospects and challenges are put forward to further deepen the research on heterogeneous photocatalytic activation of oxidants. This work provides a consolidated view of the existing heterogeneous photocatalysis coupled oxidant activation techniques and inspires researchers to develop more promising solar-driven technologies for water decontamination.

Advanced treatment of coking wastewater: Recent advances and prospects

Advanced treatment of refractory industrial wastewater is still a challenge. Coking wastewater is one of coal chemical wastewater, which contains various refractory organic pollutants. To meet the more and more rigorous discharge standard and increase the reuse ratio of coking wastewater, advanced treatment process must be set for treating the biologically treated coking wastewater. To date, several advanced oxidation processes (AOPs), including Fenton, ozone, persulfate-based oxidation, and iron-carbon micro-electrolysis, have been applied for the advanced treatment of coking wastewater. However, the performance of different advanced treatment processes changed greatly, depending on the components of coking wastewater and the unique characteristics of advanced treatment processes. In this review article, the state-of-the-art advanced treatment process of coking wastewater was systematically summarized and analyzed. Firstly, the major organic pollutants in the secondary effluents of coking wastewater was briefly introduced, to better understand the characteristics of the biologically treated coking wastewater. Then, the performance of various advanced treatment processes, including physiochemical methods, biological methods, advanced oxidation methods and combined methods were discussed for the advanced treatment of coking wastewater in detail. Finally, the conclusions and remarks were provided. This review will be helpful for the proper selection of advanced treatment processes and promote the development of advanced treatment processes for coking wastewater.

Effects of operating conditions on iron (hydr)oxides evolution and ciprofloxacin degradation in potassium ferrate-ozone stepwise oxidation system

In this study, a stepwise oxidation system of potassium ferrate (K2FeO4) combined with ozone (O3) was used to degrade ciprofloxacin (CIP). The effects of pH and pre-oxidation time of K2FeO4 on the evolution of K2FeO4 reduction products (iron (hydr)oxides) and CIP degradation were investigated. It was found that in addition to its own oxidation capacity, K2FeO4 can also influence the treatment effect of CIP by changing the catalyst content. The presence of iron (hydr)oxides effectively enhanced the mineralization rate of CIP by catalyzing ozonation. The pH value can influence the content and types of the components with catalytic ozonation effect in iron (hydr)oxides. The K2FeO4 pre-oxidation stage can produce more iron (hydr)oxides with catalytic components for subsequent ozonation, but the evolution of iron (hydr)oxides components was influenced by O3 treatment. It can also avoid the waste of oxidation capacity owing to the oxidation of iron (hydr)oxides by O3 and free radicals. The intermediate degradation products were identified by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Besides, the degradation pathways were proposed. Among the degradation products of CIP, the product with broken quinolone ring structure only appeared in the stepwise oxidation system.

Composite material derived from ZIF-67 and biochar promotes ozonation of 4-nitrophenol

Cobalt 2-methylimidazole (ZIF-67) have abundant nitrogen and cobalt elements, which can be used as an excellent precursor for catalyst synthesis. In this study, a new Co, N co-doped carbon-based catalyst (Co-N-BC) was synthesized from ZIF-67 and biochar, which can significantly improve the degradation of 4-nitrophenol (4-NP) in catalytic ozonation. The mineralization rate of 4-NP achieves 65.8% within 60 min. The catalyst showed high recycling stability in the four cycles of reuse experiment. Different operating parameters, such as solution pH, the concentration of O3 and 4-NP, have been studied in the Co-N-BC catalytic ozonation. O3, O2-· and ·OH are determined as the main reactive species for 4-NP degradation, and ·OH is especially responsibly for 4-NP mineralization. The existence of inorganic ions, such as Cl-, NO2-, CO32- and PO43-, all significantly inhibited the degradation of 4-NP to different extend, respectively. The effect of substituent on a series of organics with similar structure of 4-NP was also investigated in Co-N-BC catalytic ozonation. This study provides a new composite material for heterogeneous catalytic ozonation, which is very promising in 4-NP contained complex wastewater treatment.

Synergistic enhanced activation of peroxymonosulfate by heterojunction Co3O4-CuO@CN for removal of oxytetracycline: Performance, mechanism, and stability

Metal-organic frameworks (MOFs) as precursors for catalysts has drawn growing attentions. In this study, heterojunction Co3O4-CuO doped carbon materials (noted as Co3O4-CuO@CN) were prepared by direct carbonization of CuCo-MOF in air. It was found that the Co3O4-CuO@CN-2 exhibited excellent catalytic activity with the highest Oxytetracycline (OTC) degradation rate of 0.0902 min-1 at 50 mg/L of Co3O4-CuO@CN-2 dosage, 2.0 mM of PMS and 20 mg/L of OTC, which was 4.25 and 4.96 times that of CuO@CN and Co3O4@CN, respectively. Furthermore, Co3O4-CuO@CN-2 was efficient over a wide pH range (pH 1.9-8.4), and possessed good stability and reusability without OTC degradation decrease after five consecutive uses at pH 7.0. In a comprehensive analysis, the rapid regeneration of Cu(II) and Co(II) is responsible for their excellent catalytic performance, and the p-p heterojunction structure formed between Co3O4 and CuO acts as an intermediary of electron transfer to accelerate PMS decomposition. Moreover, it was interesting to find that Cu rather than Co species played a vital role in the PMS activation. The quenching experiments and electron paramagnetic resonance demonstrated that .OH, SO4•-, and 1O2 were the reactive species responsible for oxidation of OTC and the non-radical pathway triggered by 1O2 was dominant.

Synthesis of FeOOH-Loaded Aminated Polyacrylonitrile Fiber for Simultaneous Removal of Phenylphosphonic Acid and Phosphate from Aqueous Solution

Phosphorus is one of the important metabolic elements for living organisms, but excess phosphorus in water can lead to eutrophication. At present, the removal of phosphorus in water bodies mainly focuses on inorganic phosphorus, while there is still a lack of research on the removal of organic phosphorus (OP). Therefore, the degradation of OP and synchronous recovery of the produced inorganic phosphorus has important significance for the reuse of OP resources and the prevention of water eutrophication. Herein, a novel FeOOH-loaded aminated polyacrylonitrile fiber (PAN_AF-FeOOH) was constructed to enhance the removal of OP and phosphate. Taking phenylphosphonic acid (PPOA) as an example, the results indicated that modification of the aminated fiber was beneficial to FeOOH fixation, and the PAN_AF-FeOOH prepared with 0.3 mol L^-1 Fe(OH)₃ colloid had the best performance for OP degradation. The PAN_AF-FeOOH efficiently activated peroxydisulfate (PDS) for the degradation of PPOA with a removal efficiency of 99%. Moreover, the PAN_AF-FeOOH maintained high removal capacity for OP over five cycles as well as strong anti-interference in a coexisting ion system. In addition, the removal mechanism of PPOA by the PAN_AF-FeOOH was mainly attributed to the enrichment effect of PPOA adsorption on the fiber surface's special microenvironment, which was more conducive to contact with SO₄•^- and •OH generated by PDS activation. Furthermore, the PAN_AF-FeOOH prepared with 0.2 mol L^-1 Fe(OH)₃ colloid possessed excellent phosphate removal capacity with a maximal adsorption quantity of 9.92 mg P g^-1. The adsorption kinetics and isotherms of the PAN_AF-FeOOH for phosphate were best depicted by pseudo-quadratic kinetics and a Langmuir isotherm model, showing a monolayer chemisorption procedure. Additionally, the phosphate removal mechanism was mainly due to the strong binding force of iron and the electrostatic force of protonated amine on the PAN_AF-FeOOH. In conclusion, this study provides evidence for PAN_AF-FeOOH as a potential material for the degradation of OP and simultaneous recovery of phosphate.

Application, mechanism and prospects of Fe-based/ Fe-biochar catalysts in heterogenous ozonation process: A review

A growing number of novel organic contaminants have escalated the demands and challenges for water treatment technology. Advanced oxidation processes based on ozone have the advantage of strong oxidative capacity and higher efficiency, which have promising application prospects in the treatment of refractory organic contaminants. Biochar has attracted a lot of interest in recent years in wastewater treatment owing to its porous structure, portable preparation and outstanding stability. Moreover, iron species are widely used in catalytic ozonation owing to their magnetic polarization, vast abundance and low price. Despite a plethora of research on Fe-based catalysts in ozonation process, the heterogeneous catalytic ozonation with Fe-loaded biochar lacks a comprehensive compendium. This review intends to introduce the research progress on Fe-based catalysts and Fe-loaded biochar in heterogeneous catalytic ozonation progress, summarize and further explore the mechanisms and detection techniques of various active components in catalytic ozonation, as well as providing fresh insights for future research.

Rape Straw Supported FeS Nanoparticles with Encapsulated Structure as Peroxymonosulfate and Hydrogen Peroxide Activators for Enhanced Oxytetracycline Degradation

Iron-based catalysts with high load content of iron sulfide (FeS) were commonly peroxymonosulfate (PMS) and hydrogen peroxide (H₂O₂) activators to degrade organic pollutants but limited catalytic efficiency and increased risk of ferrous ion leaching restricted their use. Meanwhile, various biomass materials such as straw, peel, and branch have been extensively prepared into biochar for mechanical support for iron-based catalysts; however, the preparation process of biochar was energy-intensive. In this study, FeS nanoparticles modified rape straw composites (RS-FeS) encapsulated with ethylenediaminetetraacetic acid (RS-EDTA-FeS) were successfully presented by in-situ synthesis method for efficiently activating PMS and H₂O₂ to degrade oxytetracycline (OTC), which was economical and environmentally friendly. The results showed that the modified rape straw can remove OTC efficiently, and the addition of EDTA also significantly enhanced the stability and the reusability of the catalyst. In addition, EDTA also promoted the activation of H₂O₂ at neutral pH. The OTC degradation efficiency of the two catalysts by PMS was faster than that of H₂O₂, but H₂O₂ had a stronger ability to remove OTC than PMS. The highest OTC removal efficiency of RS-FeS and RS-EDTA-FeS were 87.51 and 81.15%. O₂^•- and ¹O₂ were the major reactive oxidative species (ROS) in the PMS system. Furthermore, compared with RS-FeS, the addition of EDTA inhabited the generation of O₂^•- in the PMS system. Instead, O₂^•- and ^•OH were the major ROS in the H₂O₂ system, but ¹O₂ was also identified in RS-FeS/H₂O₂ system. RS-EDTA-FeS showed a trend of rising first and then decreasing in recycle test. Instead, the removal rate of OTC by RS-FeS decreased significantly with the increase in reuse times. In the actual wastewater test, the TOC removal of two catalysts active by H₂O₂ was better than PMS, which was consistent with the test results of OTC, indicating that the two catalysts have application value in the removal of organic pollutants in actual wastewater. This study directly used plant materials as catalysts and omits the preparation process of biochar, greatly reduces the preparation cost and secondary pollution of catalysts, and provides theoretical support for the deepening of advanced oxidation technology.

Electron transfer enhancing the Mn(II)/Mn(III) cycle in MnO/CN towards catalytic ozonation of atrazine via a synergistic effect between MnO and CN

In this study, manganese oxide (MnO) dispersed on CN (Mn-nCN) was fabricated as a catalyst in heterogeneous catalytic ozonation (HCO), achieving excellent catalytic performance on refractory organic pollutant degradation via the synergistic effects between MnO and CN. The study demonstrated that the C-N-Mn and C-O-Mn bonds constructed in the catalyst linking MnO and CN created the synergistic effects which could overcome typical problems, such as metal leaching etc. The C-N-Mn and C-O-Mn bonds could promote electron transfer from cation-π reactions to form electron-rich Mn(II) sites and electron-poor CN sites. The electron-rich Mn(II) sites as active sites supplied electrons to ozone which then further evolved into reactive oxygen species (ROS). The electron-poor CN sites captured electrons from the pollutant intermediate radicals to electron-rich Mn(II) sites via cation-π reactions with the help of C-N-Mn and C-O-Mn bonds, which promote the redox reactions of Mn. The surface hydroxyl groups also participated in ozone decomposition and ROS production. Additionally, ^•OH was the dominant ROS of the Mn-nCN HCO processes. This study presents the excellent HCO performance of Mn-nCN, as well as provides views on the electron transfer route between the catalyst, pollutant and ozone, which is crucial for the design of the catalyst.

A comprehensive review on metal based active sites and their interaction with O3 during heterogeneous catalytic ozonation process: Types, regulation and authentication

Heterogeneous catalytic ozonation (HCO) was a promising water purification technology. Designing novel metal-based catalysts and exploring their structural-activity relationship continued to be a hot topic in HCO. Herein, we reviewed the recent development of metal-based catalysts (including monometallic and polymetallic catalysts) in HCO. Regulation of metal based active sites (surface hydroxyl groups, Lewis acid sites, metal redox cycle and surface defect) and their key roles in activating O₃ were explored. Advantage and disadvantage of conventional characterization techniques on monitoring metal active sites were claimed. In situ electrochemical characterization and DFT simulation were recommended as supplement to reveal the metal active species. Though the ambiguous interfacial behaviors of O₃ at these active sites, the existence of interfacial electron migration was beyond doubt. The reported metal-based catalysts mainly served as electron donator for O₃, which resulted in the accumulation of oxidized metal and reduced their activity. Design of polymetallic catalysts could accelerate the interfacial electron migration, but they still faced with the dilemma of sluggish Me^(n+m)+/Meⁿ⁺ redox cycle. Alternative strategies like coupling active metal species with mesoporous silicon materials, regulating surface hydrophobic/hydrophilic properties, polaring surface electron distribution, coupling HCO process with photocatalysis and H₂O₂ were proposed for future research.

State of Art and Perspectives in Catalytic Ozonation for Removal of Organic Pollutants in Water: Influence of Process and Operational Parameters

The number of organic pollutants detected in water and wastewater is continuously increasing thus causing additional concerns about their impact on public and environmental health. Therefore, catalytic processes have gained interest as they can produce radicals able to degrade recalcitrant micropollutants. Specifically, catalytic ozonation has received considerable attention due to its ability to achieve advanced treatment performances at reduced ozone doses. This study surveys and summarizes the application of catalytic ozonation in water and wastewater treatment, paying attention to both homogeneous and heterogeneous catalysts. This review integrates bibliometric analysis using VOS viewer with systematic paper reviews, to obtain detailed summary tables where process and operational parameters relevant to catalytic ozonation are reported. New insights emerging from heterogeneous and homogenous catalytic ozonation applied to water and wastewater treatment for the removal of organic pollutants in water have emerged and are discussed in this paper. Finally, the activities of a variety of heterogeneous catalysts have been assessed using their chemical–physical parameters such as point of zero charge (PZC), pKa, and pH, which can determine the effect of the catalysts (positive or negative) on catalytic ozonation processes.

Removal of pharmaceutical and personal care products (PPCPs) by MOF-derived carbons: A review

Nowadays, the increasing demand for pharmaceuticals and personal care products (PPCPs) has resulted in the uncontrolled release of large amounts of PPCPs into the environment, which poses a great challenge to the existing wastewater treatment technologies. Therefore, novel materials for efficient treatment of PPCPs need to be developed urgently. MOF-derived carbons (MDCs), have many advantages such as high mechanical strength, excellent water stability, large specific surface area, excellent electron transfer capability, and environmental friendliness. These advantages give MDCs an excellent ability to remove PPCPs. In this review, the effects of different substances on the properties and functions of MDCs are discussed. In addition, representative applications of MDCs and composites for the removal of PPCPs in the field of adsorption and catalysis are summarized. Finally, the future challenges of MDCs and composites are foreseen.

Catalytic ozonation of real food wastewater using catalyst synthesized from waste

ABSTRACTIn the present study, complex wastewater from the food industry was used to study the effect of ozonation and catalysed ozonation for chemical oxygen demand (COD) removal. The catalysts used were synthesized from agro-waste, activated carbon (AC) and plastic waste, multiwalled carbon nanotubes (MWCNTs)(MWCNT). The effect of various operating parameters, like ozone dosage, catalyst dosage, pH, on COD removal of food industry wastewater was investigated. The maximum COD removal was observed at ozone dose of 2gm/hr. MWCNTs(MWCNT) catalysed ozonation removes 85% COD and 48% total organic carbon (TOC) removal within 180 min at pH 9 and 74% COD and 36% TOC removal was observed for activated carbon catalysed ozonation for the same experimental conditions. A significant inhibition of COD removal was observed in the presence of tertiary-butyl alcohol. Using para-chlorobenzoic acid (p-CBA) as a probe compound, the hydroxyl radical exposure was determined for AC and MWCNT catalysed ozonation. The hydroxyl radical exposure was measured to understand the mechanism of catalytic ozonation and compare the performance of two different catalysts in terms of hydroxyl radical generation. It was found that hydroxyl radical exposure increases with increasing catalyst dose, which confirms the hydroxyl radical (OH.) pathway for COD reduction. The kinetic studies showed a 5.5time increment in rate for MWCNT catalysed ozonation and a 4 time increment for activated carbon catalysed ozonation when compared with standalone ozonation. The synergistic factor for MWCNTs and ozone was found to be 1.83 and for activated carbon and ozone, 1.5.Highlights Catalysts used were synthesized from waste.Application of activated carbon and multiwalled carbon nanotubes for catalytic ozonation of real food wastewater was investigated.Effectiveness of standalone ozonation and catalytic ozonation was identified and compared.A multiwalled carbon nanotube presents higher catalytic performance than activated carbon for ozonation of real food wastewater.Hydroxyl radical mechanism of catalytic ozonation was confirmed by using p-CBA as a probe compound.

Covalent organic frameworks@ZIF-67 derived novel nanocomposite catalyst effectively activated peroxymonosulfate to degrade organic pollutants

Metal organic frameworks-Covalent organic frameworks (MOFs-COFs) nanocomposites could improve the catalytic performance. Herein, a novel nanocomposite catalyst (CC@Co₃O₄) derived from MOFs-COFs (COF@ZIF-67) was prepared on peroxymonosulfate (PMS) activation for bisphenol A (BPA) and rhodamine B (RhB) degradation. Owing to the Co species, oxygen vacancy (O_V), surface hydroxyl (-OH), graphite N and ketone groups (C=O), the CC@Co₃O₄ exhibited higher catalytic degradation performance and total organic carbon (TOC) for BPA (93.8% and 22.3%) and RhB (98.2% and 82.5%) with a small quantity of catalyst (0.10 g/L) and low concentration of PMS (0.20 g/L) even without pH adjustment. Sulfate radicals (•SO₄^-), hydroxyl radicals (•OH), single oxygen (¹O₂), superoxide radicals (•O₂^-) and electron transfer process were all involved in the degradation of BPA and RhB. Among them, the degradation of BPA and RhB mainly depended on •O₂^- and ¹O₂, respectively. Meanwhile, the degradation pathways of BPA and RhB were proposed, and the biotoxicity of the degradation products was evaluated by freshwater chlorella. The results illustrated that the degradation products were environmentally friendly to organisms. In addition, the role of COF in the nanocomposites was also studied. The addition of COF remarkably improved the catalytic performance of CC@Co₃O₄ due to the faster electron transfer, more graphite N and C=O. Overall, this work may open the door to the development of COF-based catalysts in the field of water pollutant remediation.

Catalytic Ozonation of Norfloxacin Using Co-Mn/CeO2 as a Multi-Component Composite Catalyst

In this study, a Co-Mn/CeO2 composite was prepared through a facile sol-gel method and used as an efficient catalyst for the ozonation of norfloxacin (NOR). The Co-Mn/CeO2 composite was characterized via XRD, SEM, BET and XPS analysis. The catalytic ozonation of NOR by Co-Mn/CeO2 under different conditions was systematically investigated, including the effect of the initial solution’s pH, Co-Mn/CeO2 composite dose, O3 dose and NOR concentration on degradation kinetics. Only about 3.33% of total organic carbon (TOC) and 72.17% of NOR could be removed within 150 min by single ozonation under the conditions of 60 mg/L of NOR and 200 mL/min of O3 at pH= 7 and room temperature, whereas in the presence of 0.60 g/L of the Co-Mn/CeO2 composite under the same conditions, 87.24% NOR removal was obtained through the catalytic ozonation process. The results showed that catalytic ozonation with the Co-Mn/CeO2 composite could effectively enhance the degradation and mineralization of NOR compared to a single ozonation system alone. The catalytic performance of CeO2 was significantly improved by the modification with Mn and Co. Co-Mn/CeO2 represents a promising way to prepare efficient catalysts for the catalytic ozonation of organic polluted water. The removal efficiency of NOR in five cycles indicates that Co-Mn/CeO2 is stable and recyclable for catalytic ozonation in water treatment.

Techniques for remediation of pharmaceutical pollutants using metal organic framework - Review on toxicology, applications, and mechanism

Treatment of recalcitrant and xenobiotic pharmaceutical compounds in polluted waters have gained significant attention of the environmental scientists. Antibiotics are diffused into the environment widely owing to their high usages, very particularly in the last two years due to over consumption during covid 19 pandemic worldwide. Quinolones are very effective antibiotics, but do not get completely metabolized due to which they pose severe health hazards if discharged without proper treatment. The commonly reported treatment methods for quinolones are adsorption and advanced oxidation methods. In both the treatment methods, metal organic frameworks (MOF) have been proved to be promising materials used as stand-alone or combined technique. Many composite MOF materials synthesized from renewable, natural, and harmless materials by eco-friendly techniques have been reported to be effective in the treatment of quinolones. In the present article, special focus is given on the abatement of norfloxacin and ofloxacin contaminated wastewater using MOFs by adsorption, oxidation/ozonation, photocatalytic degradation, electro-fenton methods, etc. However, integration of adsorption with any advanced oxidation methods was found to be best remediation technique. Of various MOFs reported by several researchers, the MIL-101(Cr)-SO₃H composite was able to give 99% removal of norfloxacin by adsorption. The MIL - 88A(Fe) composite and Fe LDH carbon felt cathode were reported to yield 100% degradation of ofloxacin by photo-Fenton and electro-fenton methods respectively. The synthesis methods and mechanism of action of MOFs towards the treatment of norfloxacin and ofloxacin as reported by several investigation reports are also presented.

Facet Dependent Activity of Fe(III) Species Modified TiO2 for Simulated Sunlight Driven Fenton-like Reactions

TiO₂ crystals with different exposed facets are synthesized and modified facilely by depositing Fe(III) species. With more (101) facets exposed, the photoactivity of Fe-TiO₂ is obviously enhanced with peroxymonosulfate (PMS) as oxidant. The degradation rate for 20 ppm Bisphenol A (BPA) on Fe-TiO₂ (101) can achieve 0.219 min^-1, ∼8.5 times faster than that of pure TiO₂ under simulated sunlight irradiation. Photoelectrochemical measurements and density functional theory (DFT) calculations confirm that the interfacial charge transfer (IFCT) on Fe-TiO₂ (101) is stronger than that on Fe-TiO₂ (001) and a faster Fe(III)/Fe(II) transformation rate can be therefore achieved. As a result, the generation of ·OH and ¹O₂ will be accelerated with more (101) facets exposed, thus obtaining better photoactivity. Under the Fe-TiO₂/PMS/Light system, BPA can be effectively degraded in a wide pH range or in the presence of multiple inorganic anions. After five cycles, 100% BPA can still be degraded within 60 min. The study provides new photocatalysts design strategy based on Fe(III)/Fe(II) redox for PMS based photocatalytic oxidation.

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.

Ultrasonically synthesized MOFs for modification of polymeric membranes: A critical review

Metal-organic framework (MOF) membranes hold the promise for energy-efficient separation processes. These nanocrystalline compounds can effectively separate materials with different sizes and shapes at a molecular level. Furthermore, MOFs are excellent candidates for improving membrane permeability and/or selectivity due to their unique properties, such as high specific area and special wettability. Generally, MOFs can be used as fillers in mixed matrix membranes (MMMs) or incorporated onto the membrane surface to modify the top layer. Characteristics of the MOFs, and correspondingly, the properties of the MOF-based membranes, are majorly affected by their production technique. This critical review discusses the sonication technique for MOF production and the opportunities and challenges of using MOF for making membranes. Effective parameters on the characteristics of the synthesized MOFs, such as sonication time and power, were discussed in detail. Although the ultrasonically synthesized MOFs have shown great potential in the fabrication/modification of membranes for gas and liquid separation/purification, so far, no comprehensive and critical review has been published to clarify such accomplishments and technological gaps for the future research direction. This paper aims to review the most recent research conducted on ultrasonically synthesized MOF for the modification of polymeric membranes. Recommendations are provided with the intent of identifying the potential future works to explore the influential sonication parameters.

Double Z-scheme Co3O4/Bi4O7/Bi2O3 composite activated peroxymonosulfate to efficiently degrade tetracycline under visible light

Co₃O₄/Bi₄O₇/Bi₂O₃ (CBB) composites were prepared, in which Co₃O₄ was synthesized from Co-MOF as precursor. The peroxymonosulfate (PMS) activated by CBB catalyst under visible light was used to degrade tetracycline (TC). Owing to the synergistic effect of photocatalysis and PMS activation, 98.4% of TC was removed within 60 min. The optimal loading of Co₃O₄ was determined, and the influence of PMS dosage, initial pH, and disturbing anions on the degradation effect were investigated. The "CBB + Vis + PMS" system showed good reusability, and the degradation was only reduced by 1.7% after 5 cycles. This system also had a good degradation of other five pollutants. The quenching experiment showed that holes (h⁺), superoxide radicals (·O₂^-), and singlet oxygen (¹O₂) were the main active species. The degradation products of TC were determined by liquid chromatography-mass spectrometry, and the degradation pathway was proposed. Finally, a double Z-scheme degradation mechanism was proposed in the "CBB + Vis + PMS" system. The peroxymonosulfate activated by CBB under visible light to degrade organic pollutants has widespread application prospects in environmental remediation.

Synthesis of Bimetallic FeCu-MOF and Its Performance as Catalyst of Peroxymonosulfate for Degradation of Methylene Blue

Bimetallic MOFs have recently emerged as promising materials for wastewater treatment based on advanced oxidation processes. Herein, a new bimetallic MOF (FeCu-MOF) was fabricated by hydrothermal process. The structural, morphological, compositional and physicochemical properties of the as-synthesized bimetallic FeCu-MOF were characterized by XRD, FT-IR, SEM, TEM, BET, and XPS. TEM and XPS confirmed the homogeneous distribution of CuO₂ nanoparticles in the as-synthesized materials. The result of wastewater treatment indicated that 100% of MB was removed by 6.0 mM PMS activated with 0.6 g/L of FeCu-MOF in 30 min. The high catalytic performance of FeCu-MOF was probably due to the accelerated electron and mass transfer resulting from the existence of a homogeneous distribution of unsaturated metal sites and an abundant mesoporous structure. The obtained results from the competitive quenching tests demonstrated that sulfate radicals (SO₄^•-) were the major species responsible for MB oxidation. In addition, hydroxyl (·OH) and singlet oxygen (¹O₂) also had a nonnegligible role in the MB removal. Interestingly, the addition of acetate ion (CHCOO^-) promoted the removal of MB while other anions (including NO₂^-, H₂PO₄^-, SO₄^2-, HPO₄^2-, and HCO₃^-) inhibited the MB removal. Furthermore, a possible mechanism based on both heterogeneous and homogeneous activation of PMS was proposed, along with the MB degradation mechanism.

Unraveling timescale-dependent Fe-MOFs crystal evolution for catalytic ozonation reactivity modulation

Iron-based metal-organic frameworks (Fe-MOFs) have been considered competitive catalyst candidates for the effective degradation of organic pollutants via advanced oxidation processes (AOPs) due to their unique porous architecture and tunable active site structure. However, little is known about the role of synergetic relationship between porous architecture and active site exposure of Fe-MOFs on catalysis for AOPs yet. Here, we demonstrated an overlooked compromise over these two features on modulating the catalytic ozonation reactivity of MIL-53(Fe) through a timescale-dependent crystal evolution. Enabled by intramolecular hydrogen bonds, the MIL-53(Fe) was subjected to six evolution steps in terms of crystal morphology, leading to a volcano plot of catalytic ozonation reactivity for Rhodamine B (RhB) degradation versus the crystallization time. Evidence suggested that the surface area of MIL-53(Fe) decreased dramatically, while the density of accessible active site increased when prolonging crystallization time, allowing for the facile modulation of catalytic ozonation reactivity of MIL-53(Fe). Electron paramagnetic resonance and fluorescence quantification tests verified that the screened MIL-53(Fe)s had a much better capacity for ∙OH generation than benchmark ozonation catalyst α-MnO₂ and α-FeOOH. Moreover, the MIL-53(Fe) with the highest reactivity (i.e., MIL-53(Fe)-18H) could effectively destruct a broad spectrum of emerging and refractory organic pollutants and allow the thorough purification of secondary effluents discharged from textile dyeing & finishing industry for in situ reuse. Therefore, our study advances the understanding of the compromise effect between porous architecture and active site on catalysis reactivity of Fe-MOFs and promotes the rational design of more effective Fe-MOFs as well as their derivatives for environmental applications.

Fe-zeolite catalyst for ozonation of pulp and paper wastewater for sustainable water resources

The pulp and paper industry consumes enormous quality of freshwater, leading to wastewater. It must be treated to remove pollutants, particularly residual dyestuffs, before releasing them to water bodies to avoid adverse environmental effects. The traditional wastewater treatment methods used for the pulp and paper industry are less efficient in colour and chemical oxygen demand (COD) removal. The current study is aimed at developing a novel catalyst for the catalytic ozonation of pulp and paper wastewater with better colour and COD removal for sustainable resources of clean water. The proposed catalyst is impregnated by iron on natural zeolites. Various parameters such as catalyst dose, pH, ozone dose, initial COD concentration, and reaction time are studied and optimized. The performance was evaluated by comparing the results with the single ozonation process (SOP) and catalytic ozonation process (COP). The highest COD and colour reduction efficiencies have been achieved, i.e., 71%, and 88% at a natural pH of 6.8. The proposed process achieved higher COD and colour efficiencies than the single ozonation process and catalytic ozonation process using raw zeolites. The improvement in efficiencies are 23% and 29% for SOP and 17% and 19% for COP, respectively. Hence, the results proposed the sustainability and applicability of COP to treat paper and pulp sector effluent.