Efficient degradation of clofibric acid by heterogeneous catalytic ozonation using CoFe2O4 catalyst in water

High-efficient M-NC single-atom catalysts for catalytic ozonation in water purification: Performance and mechanisms

Heterogeneous catalytic ozonation (HCO) holds promise in water purification but suffers from limited accessible metal sites, metal leaching, and unclear structure-activity relationships. This work reported M-NC (M=Co, Ni, Fe, and Mn) single-atom catalysts (SACs) with high atomic efficiency and minimal metal release. The new HCO systems, especially the Co-based system, exhibited impressive performance in various refractory contaminant removal, involving various reactive species generation, such as •OHads, •OHfree, *O, and 1O2. For sulfamethoxazole removal, the normalized kobs for Co-NC, Ni-NC, Fe-NC, and Mn-NC were determined as 13.53, 3.94, 3.55, and 4.13 min-1·mMmetal-1·g·m-2 correspondingly, attributed to the abundant acid sites, faster electron transfer, and lower energy required for O3 decomposition and conversion. The metal atoms and hydroxyl groups, individually serving as Lewis and Bronsted acid sites (LAS and BAS), were the primary centers for •OH generation and O3 adsorption. The relationships between active sites and both O3 utilization and •OH generation were found. LAS and BAS were responsible for O3 adsorption, while strong LAS facilitated O3 conversion into •OH. Theoretical calculations revealed the catalytic mechanisms involved O3→ *O→ *OO→ O3•-→ •OH. This work highlights the significance of SAC design for HCO and advances the understanding of atomic-level HCO behavior.

MnFe2O4/MoS2 catalyst used for ozonation: optimization and mechanism analysis of phenolic wastewater treatment

The performance of catalytic ability of MFe2O4/MoS2 in the ozonation process was investigated in this work. The synthesized MnFe2O4/MoS2 was optimize prepared and then characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photo-electron spectroscopy, and magnetic saturation strength. The results showed that when Cphenol = 200 mg/L, initial pH = 9.0, Q = 0.10 L/min, and CMnFe2O4/MoS2 = 0.10 g/L, MnFe2O4/MoS2 addition improved the degradation efficiency of phenol by 20.0%. The effects of pH, catalyst dosage, and inorganic ions on the phenol removal by the MnFe2O4/MoS2 catalytic ozonation were investigated. Five cycle experiments proved that MnFe2O4/MoS2 had good recyclability and stability. MnFe2O4/MoS2 also showed good catalytic performance in the treatment of coal chemical wastewater pesticide wastewater. The MnFe2O4 doped with MoS2 could provide abundant surface active sites for ozone and promote the stable cycle of Mn2+/Mn3+and Fe2+/Fe3+, thus generating large amounts of •OH and improving the degradation of phenol by ozonation. The MnFe2O4/MoS2/ozonation treatment system provides a technical reference and theoretical basis for industrial wastewater treatment.

Multi-level FeCo/N-doped carbon nanosheet for peroxymonosulfate oxidation and sterilization inactivation

Magnetic carbon-based catalysts with environmental friendliness have exhibited prominent effects on advanced oxidation processes. Herein, a multi-level FeCo/N-doped carbon nanosheet (FeCo/CNS) was synthesized by facile impregnation iron-cobalt salt onto cotton and followed by confined pyrolysis. We identified excellent advantages of the modified FeCo/CNS materials: (i) The convenience of the synthesis method and (ii) The dual effect of sterilization and contaminant degradation achieved through the FeCo/CNS-activated Peroxymonosulfate (PMS). The comparative experimental showed that FeCo/CNS could provide favorable catalytic performance, completely removing bisphenol A (BPA) and tetracycline (TC) within 5 min. Moreover, the potent sterilization properties against Staphylococcus aureus and Escherichia coli were also verified. Analysis of the degradation pathway confirmed the existence of intermediates, and toxicological research demonstrated that the toxicity of the degradation intermediates of BPA gradually decreased over time. Our research provided an excellent application of FeCo/CNS in PMS oxidation and sterilization inactivation.

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.

Enhancing water purification through F and Zn-modified Fe-MCM-41 catalytic ozonation

Due to its low interfacial electron migration ability and highly hydrophilic, Fe-MCM-41 (FeM) had poor activity and stability during catalytic ozonation. To this end, the secondary metal Zn and Si-F group were introduced into the framework of FeM to create surface potential difference and hydrophobic sites. Comparative characterizations showed that there existed rich acid sites with great potential difference on F-Fe-Zn-MCM-41 (FFeZnM). Additionally, because of the existence of hydrophobic and electron-withdrawing Si-F unit, the electron migration ability, hydrophobicity and acidity of FFeZnM were enhanced. The greater O3 mass transfer was induced by Si-F group and O3 was directly activated at Fe and Zn Lewis acid sites into •OH, •O2- and 1O2. With •OH acting as main species, FFeZnM/O3 achieved the superior IBP removal (93.4%, 30 min) and TOC removal (46.6%, 120 min) over those of sole O3 and F-FeM/O3 processes, respectively. HCO3-, Cl-, NO3- and SO42- hindered IBP degradation by FFeZnM/O3, but high concentration humic acid (HA) exhibited promotion by forming HA-IBP complex. IBP degradation by FFeZnM/O3 was enhanced with tap water, river water, and effluent from the secondary sedimentation tank of the sewage plant acting as medium. This study proposed an innovative approach to catalyst design for catalytic ozonation.

Oxygen doped graphite carbon nitride as efficient metal-free catalyst for peroxymonosulfate activation: Performance, mechanism and theoretical calculation

In this study, oxygen-doped graphitic carbon nitride (g-C3N4), named O-g-C3N4, was successfully fabricated and characterized, and its performance in activating peroxymonosulfate (PMS, HSO5-) for the removal of phenol, 2,4-dichlorophenol (2,4-DCP), bisphenol A (BPA), rhodamine B (RhB), reactive brilliant blue (RBB) and acid orange 7 (AO7) was evaluated. The catalytic performance of O-g-C3N4 for AO7 removal increased by 14 times compared to g-C3N4. In the presence of 0.2 g L-1 O-g-C3N4, 3.5 mM PMS at natural pH 5.8, 96.4% of AO7 could be removed in 60 min, reduced toxicity of the treated AO7 solution was obtained, and the mineralization efficiency was 47.2% within 120 min. Density functional theory (DFT) calculations showed that the charge distribution changed after oxygen doping, and PMS was more readily adsorbed by O-g-C3N4 with the adsorption energy (Eads) of -0.855 kcal/mol than that of the pristine g-C3N4 (Eads: -0.305 kcal/mol). Mechanism investigation implied that AO7 was primarily removed by the sulfate radicals (SO4•-) and hydroxyl radicals (•OH) on the surface of O-g-C3N4, but the role of singlet oxygen (1O2) to AO7 elimination was negligible. The results of cyclic experiments and catalyst characterization after reaction confirmed the favorable catalytic activity and structural stability of O-g-C3N4 particles. Furthermore, the O-g-C3N4/PMS system was very resistant to most of the environmental impacts, and AO7 removal was still acceptable in natural water environment. This study may provide an efficient metal-free carbonaceous activator with low dosage for PMS activation to remove recalcitrant organic pollutants (ROPs).

Coating CoFe2O4 shell on Fe particles to increase the utilization efficiencies of Fe and peroxymonosulfate for low-cost Fenton-like reactions

Bimetallic composites (Fe@CoFe2O4) with zero-valent Fe as the core encapsulated by CoFe2O4 layers are synthesized by a coprecipitation-calcination method, which are applied to activate PMS for the degradation of bisphenol A (BPA). Enhanced activity of Fe@CoFe2O4 is achieved with very fast degradation rate (kobs = 0.5737 min-1). In the fixed-bed reactor, the catalyst lifetime (tul) of Fe@CoFe2O4 is determined to be 22 h compared to 11 h of Fe, and the deactivation rate constant (kd) for Fe@CoFe2O4 is 0.0083 mg·L-1·h-1, only ∼1/10 of Fe (0.0731). The XPS results indicate that the core-shell structure of Fe@CoFe2O4 could promote the redox cycles of Co3+/Co2+ and Fe3+/Fe2+. It is proved that the coating of CoFe2O4 shell on Fe0 can protect the Fe0 core from being oxidized by PMS to form passivation layer. The electrons of Fe0 can therefore be used effectively for activating PMS to produce ROSs via the CoFe2O4 shell. This modification method of Fe0 would decrease the cost of PMS based wastewater remediation greatly, thus should have great potential on an industrial scale.

Degradation of Sodium Acetate by Catalytic Ozonation Coupled with a Mn-Functionalized Fly Ash: Reaction Parameters and Mechanism

Supported ozone catalysts usually take alumina, activated carbon, mesoporous molecular sieve, graphene, etc. as the carrier for loading metal oxide via the impregnation method, sol-gel method and precipitation method. In this work, a Mn-modified fly ash catalyst was synthesized to reduce the consumption and high unit price of traditional catalyst carriers like alumina. As a solid waste discharged from coal-fired power plants fueled by coal, fly ash also has porous spherical fine particles with constant surface area and activity, abd is expected to be applied as the main component in the synthesis of ozone catalyst. After the pretreatment process and modification with MnOx, the obtained Mn-modified fly ash exhibited stronger specific surface area and porosity combined with considerable ozone catalytic performance. We used sodium acetate as the contaminant probe, which is difficult to directly decompose with ozone as the end product of ozone oxidation, to evaluate the performance of this Mn-modified fly. It was found that ozone molecules can be transformed to generate ·OH, ·O2- and 1O2 for the further oxidation of sodium acetate. The oxygen vacancy produced via Mn modification plays a crucial role in the adsorption and excitation of ozone. This work demonstrates that fly ash, as an industrial waste, can be synthesized as a potential industrial catalyst with stable physical and chemical properties, a simple preparation method and low costs.

Performance, community structure, metabolic pathway, and mechanism in a three-dimensional electrocatalytic biofilter (3DEBF) for the degradation of multiple concentrations of clofibric acid (CA)

A three-dimensional electrocatalytic biofilter (3DEBF) was constructed to remove clofibric acid (CA). This study compared the effectiveness of 3DEBF and biological aerated filter (BAF) in the removal of refractory CA, examined the effects of influent CA concentrations (0.1, 0.3, 0.5, 0.7, and 1.0 mg/L) on microbial community, and proposed a possible 3DEBF degradation mechanism. Results indicated that the average removal efficiency of 3DEBF reached a peak (76.09%) at 0.7 mg/L, which was 14.43% higher than that of BAF. Based on the microbial community analysis, the significant enrichment of Rhodobacter, Mycobacterium, and Sphingopyxis in 3DEBF was associated with the effect of the CA concentration and the electric field. The degradation pathway indicated that xenobiotics biodegradation and metabolism, membrane transport and replication and repair related genes were upregulated in 3DEBAF. Moreover, CA degradation is based on a combination of adsorption, electrochemical oxidation, and biodegradation.

Metal ion endogenous cycles of CoFe2O4-x induced boosted photocatalytic/PMS degradation toward polycyclic aromatic hydrocarbons

The rational design of photocatalytic nanomaterials with unique structures is critical for remediating environmental problems and thus reducing ecological risks. In this work, we employed H₂ temperature-programmed reduction to modify MFe₂O₄ (M = Co, Cu, and Zn) photocatalysts for obtaining additional oxygen vacancies. After activation of PMS, naphthalene and phenanthrene degradation rates in the soil phase were increased by 3.24-fold and 1.39-fold, respectively, and 1.38-fold for naphthalene in the aqueous phase by H-CoFe₂O_4-x. The extraordinary photocatalytic activity is attributed to the oxygen vacancies on the H-CoFe₂O_4-x surface, which promote electron transfer and thus enhance the redox cycle from Co(III)/Fe(III) to Co(II)/Fe(II). In addition, oxygen vacancies are used as electron traps to hinder the recombination of photogenerated carriers and accelerate the generation of hydroxyl and superoxide radicals. Quenching tests showed that the addition of p-benzoquinone resulted in the greatest decrease in the degradation rate of naphthalene (inhibition of about 85.5%), demonstrating that O₂˙^- radicals are the main active species in the photocatalytic degradation of naphthalene. H-CoFe₂O_4-x showed improved degradation performance in synergy with PMS (82.0%, k_app = 0.00714 min^-1) while maintaining excellent stability and reusability. Hence, this work provides a promising approach for the design of efficient photocatalysts to degrade persistent organic pollutants in soil and aqueous environments.

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.

Artificial intelligence-aided preparation of perovskite SrFexZr1-xO3-δ catalysts for ozonation degradation of organic pollutant concentrated water after membrane treatment

Membrane technology has been widely used to treat wastewater from a variety of industries, but it also results in a large amount of concentrated wastewater containing organic pollutants after membrane treatment, which is challenging to decompose. Here in this work, a series of perovskite SrFe_xZr_1-xO_3-δ catalysts were prepared via a modified co-precipitation method and evaluated for catalytic ozone oxidative degradation of m-cresol. An artificial neural intelligence networks (ANN) model was employed to train the experimental data to optimize the preparation parameters of catalysts, with SrFe_0.13Zr_0.87O_3-δ being the optimal catalysts. The resultant catalysts before and after reduction were then thoroughly characterized and tested for m-cresol degradation. It was found that the co-doping of Fe and Zr at the B-site and the improvement of oxygen vacancies and oxygen active species by reduction dramatically increased TOC removal rates up to 5 times compared with ozone alone, with the conversion rate of m-cresol reaching 100%. We also proposed a possible mechanism for m-cresol degradation via investigating the intermediates using GC-MS, and confirmed the good versatility of the reduced SrFe_0.13Zr_0.87O_3-δ catalyst to remove other common organic pollutants in concentrated wastewater. This work demonstrates new prospects for the use of perovskite materials in wastewater treatment.

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.

Efficient catalytic ozonation via Mn-loaded C-SiO2 Framework for advanced wastewater treatment: Reactive oxygen species evolution and catalytic mechanism

Heterogeneous catalytic ozonation (HCO) is attractive for water decontamination and catalyst is a core element. However, it is difficult to maintain high efficiency and stability of catalysts under stern conditions. In this study, we proposed Mn-loaded C-SiO₂-Framework (Mn-CSF) which contained stable silica core and robust carbon shell for efficient catalytic ozonation. The pseudo-first-order kinetic rate constant for oxalic acid removal of Mn-CSF catalytic ozonation was 160 % and 875 % higher than those of Mn-SiO₂ and pristine CSF, respectively. Mn-CSF was also proven effective in gasification wastewater treatment, where the COD was decreased to 46 mg·L^-1, 37 % lower than that of Mn-SiO₂. These results indicated that the graphitization carbon layer and Mn significantly enhanced the activity of the catalyst. Furthermore, a fulvic-like component and a protein-like component were recognized through 3D-EEM in coal gasification wastewater. It was proven that Mn-CSF catalytic ozonation exhibited higher fulvic-like component and protein-like component removal compared with ozonation. Moreover, O₂^- and ¹O₂ were identified to be responsible for organic degradation in this research. Sufficient external specific surface area and porous structure were important for complex wastewater treatment. Specifically, external specific surface area could enhance the degradation of macromolecular organics while porous structures were vital for smaller molecular pollutant removal. The results highlighted that Mn-CSF was a promising HCO catalyst for advanced wastewater treatment, and this study provided evidence of relationship between structure of catalysts and HCO efficiency.

Bicarbonate enhanced heterogeneous activation of peroxymonosulfate by copper ferrite nanoparticles for the efficient degradation of refractory organic contaminants in water

Nowadays, the treatment of residual refractory organic contaminants (ROCs) is a huge challenge for environmental remediation. In this study, a potential process is provided by copper ferrite catalyst (CuFe₂O₄) activated peroxymonosulfate (PMS, HSO₅^-) in the bicarbonate (HCO₃^-) enhanced system for efficient removal of Acid Orange 7 (AO7), 2,4-dichlorophenol, phenol and methyl orange (MO) in water. The impact of key reaction parameters, water quality components, main reactive oxygen species (ROS), probable degradation mechanism, rational degradation pathways and catalyst stability were systematically investigated. A 95.0% AO7 (C₀ = 100 mg L^-1) removal was achieved at initial pH (pH₀) of 5.9 ± 0.1 (natural pH), CuFe₂O₄ dosage of 0.15 g L^-1, PMS concentration of 0.98 mM, HCO₃^- concentration of 2 mM, and reaction time of 30 min. Both sulfate radical (SO₄^-•) and hydroxyl radical (^•OH) on the surface of catalyst were proved as the predominant radical species through radical quenching experiments and electron paramagnetic resonance (EPR) analysis. The buffer nature of HCO₃^- was partially contributed for the enhanced degradation of AO7 under CuFe₂O₄/PMS/HCO₃^- system. Importantly, according to ¹³C nuclear magnetic resonance (NMR) and EPR analysis, the positive effect of bicarbonate may be mainly attributed to the formation of peroxymonocarbonate (HCO₄^-), which may enhance the generation of ^•OH. The magnetic CuFe₂O₄ particles can be well recycled and the leaching concentration of Cu was acceptable (<1 mg L^-1). Considering the widespread presence of bicarbonate in water environment, this work may provide a safe, efficient, and sustainable technique for the elimination of ROCs from practical complex wastewater.

Catalytic ozonation mechanisms of Norfloxacin using Cu-CuFe2O4

As an easily recoverable, environmentally friendly and cost-effective catalyst, CuFe₂O₄ is a promising candidate for the catalytic ozonation of antibiotics in wastewater. However, its catalytic activity is restricted due to its limited active sites and low electron transfer efficiency. In this study, cetyl trimethyl ammonium bromide (CTAB) and Cu⁰ were doped with CuFe₂O₄ to introduce more O_V, providing more active sites and improving electron transfer efficiency. Experimental results show that the optimum removal efficiency of the catalytic ozonation of Norfloxacin (NOR, a widely used antibiotic) using CTAB doped with Cu-CuFe₂O₄ as the catalyst is 81.58% with a first-order reaction kinetics constant of 0.03967 min^-1. The associated O₃ and catalyst dosages are 2.72 mg·L^-1 and 0.1 g·L^-1, respectively, which are 1.63 times and 2.22 times higher than those in an equivalent O₃ system. O_V can provide generation sites for surface hydroxyl groups and trigger ·O₂^- and ¹O₂ as the main active oxygen species. The synergistic redox cycles of Fe²⁺/Fe³⁺ and Cu⁰/Cu²⁺ accelerate electron transfer efficiency. The possible degradation pathways of NOR are identified as defluorination, naphthyridine ring-opening and piperazine ring-opening. In summary, this work proposes a new strategy for the modification of CuFe₂O₄ catalysts and provides new insights into the catalytic ozonation mechanisms for NOR removal.

Catalytic ozonation of phenol by ZnFe2O4/ZnNCN: performance and mechanism

A novel magnetic catalyst was synthesized and applied in heterogeneous catalytic ozonation process. The ZnFe₂O₄/ZnNCN material was synthesized by hydrothermal and high-temperature calcination method and characterized by XPS, XRD, FTIR, VSM, and SEM techniques. In the system of O₃/ZnFe₂O₄/ZnNCN, the removal rates of phenol and chemical oxygen demand (COD) reached 93% and 43% at 60 min. Further analysis shows that ZnFe₂O₄/ZnNCN has a significant catalytic effect on O₃, which is demonstrated by the first-order kinetic constant being 1.93 times than O₃ alone. The catalyst exhibits excellent cycling stability during repeated catalytic ozonation process and can be fully recycled under an applied magnetic field. The role of hydrogen peroxide (H₂O₂) and surface hydroxyl groups was investigated, and a mechanism for catalytic ozonation was proposed. This work not only builds an efficient catalytic ozonation system, but also provides a potential modification strategy for spinel oxides.

Impact of water matrices on oxidation effects and mechanisms of pharmaceuticals by ultraviolet-based advanced oxidation technologies: A review

The binding between water components (dissolved organic matters, anions and cations) and pharmaceuticals influences the migration and transformation of pollutants. Herein, the impact of water matrices on drug degradation, as well as the electrical energy demands during UV, UV/catalysts, UV/O₃, UV/H₂O₂-based, UV/persulfate and UV/chlorine processes were systemically evaluated. The enhancement effects of water constituents are due to the powerful reactive species formation, the recombination reduction of electrons and holes of catalyst and the catalyst regeneration; the inhibition results from the light attenuation, quenching effects of the excited states of target pollutants and reactive species, the stable complexations generation and the catalyst deactivation. The transformation pathways of the same pollutant in various AOPs have high similarities. At the same time, each oxidant also can act as a special nucleophile or electrophile, depending on the functional groups of the target compound. The electrical energy per order (EEO) of drugs degradation may follow the order of EEO_UV > EEO_UV/catalyst > EEO_UV/H2O2 > EEO_UV/PS > EEO_UV/chlorine or EEO_UV/O3. Meanwhile, it is crucial to balance the cost-benefit assessment and toxic by-products formation, and the comparison of the contaminant degradation pathways and productions in the presence of different water matrices is still lacking.

Prediction of pharmaceutical and personal care products elimination during heterogeneous catalytic ozonation via chemical kinetic model

Prediction of the removal of pollutants is important for the process design and optimization of wastewater treatment. In this study, the heterogeneous catalytic ozonation chemical kinetic model based on reaction kinetic constants between O₃ (and •OH) and pollutants, and pseudo-first order rate constants for pollutant adsorption was established. The model parameters were obtained via O₃ and p-chlorobenzonic acid decay curves, and adsorption kinetic experiments, respectively. Higher •OH exposures were obtained at the expense of lower O₃ exposures during catalytic ozonation compared to simple ozonation. Importantly, the experimentally measured and model-predicted removal ratios correlated well in all reaction systems, with correlation coefficients above 0.950 in synthetic solution and 0.893-0.979 in secondary effluent. Furthermore, the model revealed that pollutants were degraded mainly by O₃ and/or •OH oxidation during catalytic ozonation, while adsorption of pollutants on catalysts contributed negligibly. Hence, the degradation ratios of pollutants could be satisfactorily predicted using the simplified model based only on the O₃ and •OH exposures in the heterogeneous catalytic ozonation systems with low adsorption capacity catalysts.

Recent Developments in Activated Carbon Catalysts Based on Pore Size Regulation in the Application of Catalytic Ozonation

Due to its highly developed pore structure and large specific surface area, activated carbon is often used as a catalyst or catalyst carrier in catalytic ozonation. Although the pore structure of activated carbon plays a significant role in the treatment of wastewater and the mass transfer of ozone molecules, the effect is complicated and unclear. Because different application scenarios require catalysts with different pore structures, catalysts with appropriate pore structure characteristics should be developed. In this review, we systematically summarized the current adjustment methods for the pore structure of activated carbon, including raw material, carbonization, activation, modification, and loading. Then, based on the brief introduction of the application of activated carbon in catalytic ozonation, the effects of pore structure on catalytic ozonation and mass transfer are reviewed. Furthermore, we proposed that the effect of pore structure is mainly to provide catalytic active sites, promote free radical generation, and reduce mass transfer resistance. Therefore, large external surface area and reasonable pore size distribution are conducive to catalytic ozonation and mass transfer.

ZnO-Zn2TiO4 heterostructure for highly efficient photocatalytic degradation of pharmaceuticals

In this study, ZnO-Zn₂TiO₄ (ZTM) material was prepared through a novel synthesis method based on a ultrasound-assisted polyol-mediated process followed by calcination at a different temperature. Physical features of the samples were studied by using various analysis techniques including XRD, FT-IR, SEM/EDX, pH_PZC, and UV-Vis DRS. Subsequently, the materials were employed as catalysts for the photocatalytic degradation of clofibric acid as a model pharmaceutical contaminant. The photocatalytic performance was evaluated under different conditions of calcination temperature, catalyst dosage, starting concentration, and initial pH of clofibric acid solution. The finding results revealed that hexagonal-tetragonal phases of ZnO-Zn₂TiO₄ calcined at 600 °C (ZTM-600) with an average crystallite size of 97.8 Å exhibited the best degradation efficiency (99%). The primary bands characteristic of ZnO and Zn₂TiO₄ were displayed by FT-IR analysis and the UV-visible DRS confirms the larger absorption capacity in UV-visible regions. The photogenerated electrons are the powerful reactive species involved in clofibric acid photodegradation process. This study shows a promising photocatalyst and provides new sight to rational design the facets of photocatalysis process for enhanced photocatalytic performances and effective wastewater treatment.

Catalytic ozone decomposition and adsorptive VOCs removal in bimetallic metal-organic frameworks

Atmospheric ozone has long been a threat to human health, however, rational design of high-performance O₃-decomposition catalysts remains challenging. Herein, we demonstrate the great potential of a series of isomorphous bimetallic MOFs denoted as PCN-250(Fe₂M) (M = Co²⁺, Ni²⁺, Mn²⁺) in catalytic O₃ decomposition. Particularly, PCN-250(Fe₂Co) showed 100% O₃ removal efficiency for a continuous air flow containing 1 ppm O₃ over a wide humidity range (0 ‒ 80% RH) at room temperature. Mechanism studies suggested that the high catalytic performance originated from the introduction of open Co(II) sites as well as its porous structure. Additionally, at low pressures around 10 Pa, PCN-250(Fe₂Co) exhibited high adsorption capacities (89 ‒ 241 mg g^-1) for most VOCs, which are not only a class of hazardous air pollutants but also the precursor of O₃. This work opens up a new avenue to develop advanced air purification materials for O₃ and VOCs removal in one.

Challenges and pitfalls in the investigation of the catalytic ozonation mechanism: A critical review

Catalytic ozonation is a promising technology for pollutant abatement in water and wastewater treatment. However, there are many controversies and contradictions regarding the mechanisms of catalytic ozonation in literature, which has seriously confounded the development of the technology towards industrial applications. Herein, a critical review of literature is conducted to reveal possible underlying causes of the controversies and contradictions, and several common pitfalls in the experimental design and data interpretation are identified, e.g., the fundamentally flawed quenching method popularly used for evaluating the role of reactive oxygen species for pollutant abatement in catalytic ozonation and the neglect of monitoring ozone transfer doses in lab-scale experiments. Based on the identified pitfalls, several measures are suggested to improve the experimental design and data interpretation of catalytic ozonation studies. In addition, recent advances in mechanistic understanding of catalytic ozonation by principle-based modelling approaches are described. Finally, additional works that are needed to shrink the gap between academic research and practical applications and the prospect of catalytic ozonation in future water and wastewater treatment systems are analyzed.

Kinetic and mechanistic insights into the degradation of clofibric acid in saline wastewater by Co2+/PMS process: a modeling and theoretical study

Recently, the degradation of non-chlorinated organic pollutants in saline pharmaceutical wastewater by SO₄˙⁻-based advanced oxidation processes (AOPs) has received widespread attention. However, little is known about the oxidation of chlorinated compounds in SO₄˙⁻-based AOPs. This study chose clofibric acid (CA) as a chlorinated pollutant model; the oxidation kinetics and mechanistic pathway were explored in the Co²⁺/peroxymonosulfate (PMS) system. Notably, a high removal efficiency (81.0%) but low mineralization rate (9.15%) of CA within 120 min were observed at pH 3.0 during Co²⁺/PMS treatment. Exogenic Cl⁻ had a dual effect (inhibitory then promoting) on CA degradation. Several undesirable chlorinated by-products were formed in the Co²⁺/PMS system. This demonstrated endogenic chlorine and exogenic Cl⁻ both reacted with SO₄˙⁻ to generate chlorine radicals, which participated in the dechlorination and rechlorination of CA and its by-products. Furthermore, SO₄˙⁻ was the dominant species responsible for CA degradation at low Cl⁻ concentrations (≤1 mM), whereas Cl₂˙⁻ was the predominant radical at [Cl⁻]₀ > 1 mM. A possible degradation pathway of CA was proposed. Our findings suggested that chlorinated compounds in highly saline pharmaceutical wastewater will be more resistant and deserve more attention.

Recently, the degradation of non-chlorinated organic pollutants in saline pharmaceutical wastewater by SO₄˙⁻-based advanced oxidation processes (AOPs) has received widespread attention.

Enhancing catalytic ozonation activity of MCM-41 via one-step incorporating fluorine and iron: The interfacial reaction induced by hydrophobic sites and Lewis acid sites

Fe-MCM-41 had been widely used as ozonation catalyst, however, the existence of large amount of hydrophilic silanol hindered its interfacial reaction with O₃ and pollutants. To solve this problem, F-Fe-MCM-41 was synthesized by co-doping F and Fe into the framework of MCM-41 to replace silanol with Si-F groups through a one-step hydrothermal method. F introduced hydrophobic sites which contributed to more ibuprofen (IBP) chemisorption on the surface of F-Fe-MCM-41. Moreover, doping F also enhanced the acidity, which accelerated O₃ decomposition into •OH. F-Fe-MCM-41/O₃ exhibited notably activity with 96.6% IBP removal efficiency within 120 min, while only 78.5% and 80.9% in O₃ alone and Fe-MCM-41/O₃, respectively. Surface Lewis acid sites and metal hydroxyl groups were considered as important factors for O₃ activation and •OH generation. F-Fe-MCM-41 exhibited excellent catalytic performance under acidic and alkaline conditions. Comparative experiments revealed that F doping improved the interfacial reaction, especially the interfacial electron transfer, which resulted in the high catalytic activity of F-Fe-MCM-41. F-Fe-MCM-41 possessed good stability and reusability, with only 5.7% decline for IBP removal in five successive cycles. Furthermore, the possible degradation path of IBP was proposed according to DFT calculation and GC-MS analysis.

Catalytic ozonation of chloramphenicol with manganese-copper oxides/maghemite in solution: Empirical kinetics model, degradation pathway, catalytic mechanism, and antibacterial activity

The composite material of manganese-copper oxide/maghemite (Mn_xCu_yO_z/γ-Fe₂O₃) was synthesized by the co-precipitation-calcination method. With the initial concentration of 0.2 g/L Mn_xCu_yO_z/γ-Fe₂O₃ and 10 mg/L O₃, the chloramphenicol (CAP, 10 mg/L) could be completely degraded, which was about 2.22 times of that treated with ozonation alone. The contribution of O₃ and hydroxyl radical (•OH) for CAP degradation in the catalytic process was 6.9% and 93.1%, respectively. According to the effects of catalyst dosage, ozone dosage, and pH on the catalytic performance of Mn_xCu_yO_z/γ-Fe₂O₃, a predictive empirical model was developed for the ozonation with the Mn_xCu_yO_z/γ-Fe₂O₃ system. The HCO₃^-/CO₃^2- and phosphates in solution could inhibit the degradation of CAP with the inhibition ratios 8.45% and 13.8%, respectively. The HCO₃^-/CO₃^2- could compete with CAP and react with •OH, and the phosphates were considered as poisons for catalysts by blocking the surface active sites to inhibit ozone decomposition. The intermediates and possible degradation pathways were detected and proposed. The catalytic ozonation could effectively control the toxicity of the treated solution, but the toxicity was still not negligible. Furthermore, Mn_xCu_yO_z/γ-Fe₂O₃ could be easily and efficiently separated from the reaction system with an external magnet, and it possessed excellent reusability and stability.

An Isopolymolybdate-Incorporated Metal-Organic Framework with Sulfite Oxidase-Mimicking Activity for Photocatalytic Oxidation of Sulfides Utilizing In Situ-Generated Singlet Oxygen

Developing new photocatalysts for sulfide oxidation utilizing in situ-generated 1O2 is very significant. Inspired by natural enzymatic processes, we synthesized a mimic sulfite oxidase (SO), {[Co(Mo4O13)(TPT)2]} (CoMo-TPT), by incorporating an isopolymolybdate anion [Mo4O13]2- into a 2,4,6-tri(4-pyridyl)-1,3,5-triazine (TPT)-based metal-organic framework under mild hydrothermal conditions. In this structure, {Mo4O13} units with intrinsic SO-like catalytic sites are beneficial for the selective oxidation of sulfite and thioether. The ultraviolet-visible spectra of CoMo-TPT exhibited strong absorption from 250 to 650 nm and potential application in the utilization of solar energy. Mott-Schottky measurements indicated that CoMo-TPT is an n-type semiconductor with a LUMO value of -0.70 V (vs NHE) and a HOMO value of 1.39 V. The transient photocurrent responses with strong current density cycles with visible light indicated CoMo-TPT has a high photochemical activity. The lower resistance indicated that CoMo-TPT has a higher efficiency of photoinduced electron and hole separation. CoMo-TPT displayed a high efficiency of 99% and a selectivity of 97.3% in photocatalytic oxidation of sulfides by utilizing in situ-generated 1O2 through a tandem process of formation of H2O2 from O2 followed by catalyzed disproportionation of H2O2.