Heterogeneous Catalytic Ozonation Research Articles

Synergetic Manipulation Mechanism of Single-Atom M-N4 and M-OH (M = Mn, Fe, Co, Ni) Sites for Ozone Activation: Theoretical Prediction and Experimental Verification.

Carbon-based single-atom catalysts (SACs) have been gradually introduced in heterogeneous catalytic ozonation (HCO), but the interface mechanism of O3 activation on the catalyst surface is still ambiguous, especially the effect of a surface hydroxyl group (M-OH) at metal sites. Herein, we combined theoretical calculations with experimental verifications to comprehensively investigate the O3 activation mechanisms on a series of conventional SAC structures with N-doped nanocarbon substrates (MN4-NCs, where M = Mn, Fe, Co, Ni). The synergetic manipulation effect of the metal atom and M-OH on O3 activation pathways was paid particular attention. O3 tends to directly interact with the metal atom on MnN4-NC, FeN4-NC, and NiN4-NC catalysts, among which MnN4-NC has the best catalytic activity for its relatively lower activation energy barrier of O3 (0.62 eV) and more active surface-adsorbed oxygen species (Oads). On the CoN4-NC catalyst, direct interaction of O3 with the metal site is energetically infeasible, but O3 can be activated to generate Oads or HO2 species from direct or indirect participation of M-OH sites. The experimental results showed that 90.7 and 82.3% of total organic carbon (TOC) was removed within 40 min during catalytic ozonation of p-hydroxybenzoic acid with MnN4-NC and CoN4-NC catalysts, respectively. Phosphate quenching, catalyst characterization, and EPR measurement further supported the theoretical prediction. This contribution provides fundamental insights into the O3 activation mechanism on SACs, and the methods and ideals could be helpful for future studies of environmental catalysis.

Local microenvironment modulation of Pt0/Pt2+ nano-clusters inducing synchronous mass transfer effect to boost catalytic ozonation

Rational catalyst structure design is expected to solve the low O3 utilization and poor molecular mass transfer efficiency in heterogeneous catalytic ozonation (HCO). Herein, Pt/CMK-3 catalyst with confined space to enhance mass transfer was synthesized and employed for CH3SH removal. Unlike fully free diffusion in 0–2.0 wt% Pt/CMK-3 and bulk phase diffusion in 10.0 wt% Pt/CMK-3, removal efficiency of 5.0 wt% Pt/CMK-3 was significantly improved to 97.0%, which was attributed to the effective interfacial diffusion of O3 and CH3SH through local microenvironment modulation of Pt0/Pt2+ nanoclusters (NCs) inducing synchronous mass transfer. Experimental and DFT calculations confirmed the strong electronic interactions between O3 and Pt0 facilitated charge redistribution and preferential O3 activation. AIMD simulation demonstrated that the synchronous difference in mean-square displacements (MSD) and diffusion coefficient (Dc) of CH3SH (Dc=0.022) and O3 (Dc=0.0046) in the confined Pt/CMK-3 system could facilitate CH3SH migrate to Pt2+ through interfacial diffusion. Especially, the d-orbital electrons of Pt NCs interact sequentially with p-orbital electrons of CH3SH and O3 to maintain redox of Pt0/Pt2+. This study provides novel insights on effective mass transfer and kinetic properties of gaseous reaction between oxidant and pollutant by constructing unique interfacial diffusion behaviors.

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.

N-coordinated single cobalt atoms catalyst triggering concerted radical-nonradical process in catalytic ozonation for efficient water decontamination

Heterogeneous catalytic ozonation (HCO) has been developed as a promising technology for wastewater treatment, while traditional radical-based HCO process still suffers from insufficient mineralization of organic pollutants. Herein, we constructed a N-coordinated single cobalt atoms catalyst (CoSAC-N-C) triggering concerted radical-nonradical process in catalytic ozonation for efficient decontamination of pollutants. Experiments and theoretical calculations proved that mediate O in O3 obtained electrons from electron-rich N sites for hydroxyl radical (·OH) production, and the terminal O in O3 was attracted on electron-deficient Co sites for nonradical *O generation by O-O cleavage. The synergistic oxidation of ·OH and *O enabled excellent pollutants mineralization, surpassing most of conventional HCO catalysts. CoSAC-N-C exhibited excellent treatment performance for the coking wastewater in a continuous-flow reactor with COD reducing from 86 mg/L to less than 50 mg/L. This work provided a viable strategy of developing dual-site HCO catalysts to promote concerted radical-nonradical oxidations for wastewater treatment.

Treatment of pharmaceutical wastewater by a sequential KMnO4/CoFe2O4-mediated catalytic ozonation process

Pharmaceutical compounds, which are of utmost concern, have found their way into natural water bodies, causing numerous problems for both human health and ecosystems. In this study, an integrated system including potassium permanganate (PM) pre-oxidation, followed by a heterogeneous catalytic ozonation process (HCOP) using CoFe2O4 magnetic nanoparticles (CF MNPs), and an activated sludge-based biological treatment (BT) was employed for the first time to treat pharmaceutical wastewater (PWW). In this regard, the effluent from PM pre-oxidation process was used as a batch for the HCOP, and the effluent was used as a batch for the BT process. The results showed that PM pre-treatment of PWW (PM dose = 1264 mg/L and pH = 8.0) reduced the COD content of the PWW from 900 ± 50 to 443 ± 10 mg/L within 120 min of reaction time. The application of HCOP for further treatment of PWW dramatically enhanced COD and TOC removal compared with the single ozonation process (SOP). Under optimum conditions (pH = 10, O3 = 4.0 mg/L, and CF MNPs = 1000 mg/L), HCOP successfully reduced the COD and TOC contents of PWW by 37 % and 46.1 %, respectively, after 120 min of treatment. The consecutive combination of PM pre-treatment followed by HCOP exhibited good potential and reduced COD by over 69 %, resulting in a residual COD of less than 280 mg/L. A biodegradability ratio of over 81 % and residual COD of 54 mg/L for the PWW treated by the PM/HCOP/BT integrated system indicated that biodegradability was enhanced, and a high fraction of refractory organic compounds was effectively removed. In conclusion, the PM/HCOP/BT integrated system is an efficient, synergistic, and easy-to-operate technique for enhancing the biodegradability of PWW.

Florfenicol removal from veterinary pharmaceutical effluents: Tri-metallic zeolite 5A° for electrochemical oxidation and catalytic ceramic membrane separation

Contaminants of emerging concern, including pharmaceuticals, are commonly found in wastewater from households, farms, and healthcare facilities. When active pharmaceutical ingredients enter water sources, they contaminate the waterways and cause potential hazard effects on the aquatic environment and human populations. This concern is especially critical with antibiotics, due to the development of antibiotic-resistant bacterial strains. However, Florfenicol, a bacteriostatic antibiotic widely used in veterinary medicine, poses a significant risk of water pollution when discharged into waterways. In the present study and its practical application, removal of targeted pollutant namely antibiotic florfenicol by ozonation was investigated by measuring chemical oxidation demand (COD), biochemical oxygen demand (BOD), and turbidity for pharmaceutical wastewater in the batch reactor, while optimizing feeding electro flocculation voltage, O3 flow rate, O3 dosage and ceramic membrane filtration. Due to the production of hydroxyl radicals with strong oxidation properties, pollutants in wastewater can be effectively degraded via heterogeneous catalytic ozonation. It was examined whether the regenerated catalyst exhibited good catalytic activity after three cycles of washing with Milli-Q water and ethanol. The results show that the effluent concentration of antibiotic Florfenicol is about 99% alongside residual values for 91%, 79%, and 89% for COD, BOD, and turbidity, respectively (Time: 30 min, pH: 7.5). Meanwhile, the wastewater's degradability capacity (BOD5/COD ratio) increased from 0.37 to 0.53, rendering it more readily biodegradable for further treatment. These results indicate that the process of hybrid electro flocculation and catalytic ozonation with ceramic membrane has a high treatment efficiency for veterinary antibiotics, and a continuous-flow reactor can be utilized more practically for a full-scale industrial application.

Evaluation of Heterogeneous Catalytic Ozonation for Micropollutants Removal from Wastewater: Application of a Pre-Industrial-Scale Unit

The present study evaluates the application of heterogeneous catalytic ozonation for the removal of micropollutants from wastewater effluent in a pre-industrial-scale unit, consisting of a post-filtration, an ozone dilution, a catalytic ozonation, and a final biological stabilization step. The important step of ozone dilution is optimized by the use of a hollow fiber membrane that minimizes the loss of ozone gas due to the transfer of ozone to the liquid phase mainly by diffusion. It is observed that the efficiency of this sub-system is maximized for the dead-end operation of the membrane and the introduction of ozone gas to the shell side and liquid phase to the lumen side of the membrane module. Under these conditions, the concentration of dissolved ozone is directly dependent on the ratio of ozone gas feed to the wastewater flow subjected to post-treatment. Regarding the removal of MPs, part of their degradation already takes place at this stage (i.e., during ozone dilution), while after the post-treatment of wastewater effluent in the catalytic ozonation bed, the MP degradation yield ranges from 35% up to complete removal, depending on the type and properties of the specific MP. The addition of a final biological filtration bed to the overall treatment unit significantly increased its performance, regarding the removal of MPs, enhancing it by an additional removal rate that can reach up to 30%.

Electron transfer in MOF-derived cobalt-magnesium oxide–carbon microsphere composite catalytic ozonation of thiamphenicol

Cobalt-magnesium oxide–carbon microsphere composite (Co-MgO-CMS), Cobalt-carbon nanosheet composite (Co-CNS), and magnesium oxide–carbon nanorod composite (MgO-CNR) were synthesized by the MOFs self-sacrificing template method. And they were used as the catalysts for catalytic ozonation of thiamphenicol (20 mg/L) in water at an initial pH of 7.0. The phase of Co-MgO-CMS is mainly composed of metallic cobalt, magnesium oxide and carbon according to X-ray diffraction and transmission electron microscopy analyses. Thiamphenicol removal efficiency is enhanced through Co-MgO-CMS catalytic ozonation (75.4 %, in 6 min), compared with those in ozonation alone (39.8 %), Co-CNS catalytic ozonation (43.2 %), MgO-CNR catalytic ozonation (65.1 %) and Mg-Co binary oxide (Mg2CoOy) catalytic ozonation (69.0 %). Self-increasing of solution pH, protonated hydroxyl groups and electron transfer on metallic Co and lattice Co2+ are advantageous for the ozone decomposition into reactive oxygen species in Co-MgO-CMS catalytic ozonation. Owing to the metallic Co in Co-MgO-CMS, the electron transfer ability of Co-MgO-CMS is better than that of Mg2CoOy according to the in situ electrochemical test. Moreover, electron transfers directly from metallic Co to ozone. While protonated hydroxyl groups are the key for electron transfer on lattice Co2+. A possible degradation pathway for thiamphenicol in Co-MgO-CMS catalytic ozonation is proposed according to the detected intermediates. This work provides insight into improvement on electron transfer ability of concerted acid-base catalyst in heterogeneous catalytic ozonation.

Enhanced heterogeneous catalytic ozonation to degrade p-nitrophenol by Co-doped Ni3S2/NF nanosheets

In this study, a cobalt-doped nickel disulfide (Co-Ni3S2) catalyst was prepared by a one-step hydrothermal method, which was grown on the surface of firm and dense three-dimensional porous nickel foam (NF). Although researchers have conducted extensive research on heterogeneous catalytic ozonation (HCO) over the past decades, the development of highly efficient, easily separable, stable, and recyclable HCO catalysts is still a bottleneck for practical applications. Taking p-nitrophenol (PNP) as the targeted pollutant, the synergistic effect of Co-Ni3S2/NF composites and ozone was studied. The results show that Co-Ni3S2/NF with different doping ratios can degrade PNP by more than 99% within 40 minutes, showing high activity. At the same time, in the cycle experiment, Co-Ni3S2/NF showed good stability and recyclability compared with the powder catalyst and therefore, the former could reduce water treatment cost. We also found that in the Co-Ni3S2/NF/O3 system, the production rates of 1O2, •OH and O2•- can be greatly improved, and the process of degradation is synergistic with both non-radicals and free radicals.

Performance evaluation and optimization of a suspension-type reactor for use in heterogeneous catalytic ozonation

Packed fixed-bed reactors are traditionally used for heterogeneous catalytic ozonation. However, a high solid-to-liquid requirement, poor ozone dissolution, ineffective utilization of catalyst surface area, and production of large amounts of catalyst waste impede application of such reactors. In this study, we designed a suspension catalytic ozonation reactor and compared the performance of this reactor with that of a traditional fixed-bed catalytic ozonation reactor employing oxalic acid (OA) as the target contaminant. Our results showed that total O3 dissolved into the suspension reactor (117–134 mg.L−1) was much higher compared to that measured in the fixed-bed reactor (53 mg.L−1) due to a higher O3(g) interphase mass transfer rate in the suspension reactor. In accordance with the higher O3(g) interphase mass transfer, we observed a much higher proportional OA removal (32 %) compared to that achieved in the fixed-bed reactor (10%) employing an Fe-oxide catalyst supported on Al2O3 (Fe-oxide@Al2O3) in both reactors. Use of a double-layered Cu-Al hydroxide (Cu-Al LDHs) catalyst in the suspension reactor further enhanced the performance with nearly 90 % OA removal observed. Given the superior performance of the suspension reactor, we investigated the impact of operating conditions (catalyst dosage, hydraulic retention time and ozone dosage) employing Cu-Al LDHs as the catalyst. We also developed a mathematical kinetic model to describe the performance of the suspension reactor and, through use of the kinetic model, showed that O3(g) interphase transfer rate was the rate-limiting step in OA removal. Thus, improvement in ozone gas diffuser design is required to improve the performance of the suspension reactor. Overall, the present study demonstrated that suspension reactors were more effective than fixed-bed reactors for oxidation of surface-active organic compounds such as OA due to the higher ozone interphase mass transfer rate and effective utilization of the catalyst surface area that can be achieved. As such, further research on suspension reactor design and development of catalysts suitable for use in suspension reactors should facilitate large-scale application of catalytic ozonation processes by the wastewater treatment industry.

Catalytic ozonation with carbon-coated copper-based core-shell catalysts (C/Cu-Al2O3) for the treatment of high-salt petrochemical wastewater

High-salt petrochemical wastewater requires advanced treatment for water reuse due to its high salinity and the presence of refractory organic compounds. Heterogeneous catalytic ozonation is an effective advanced treatment method, with the key to its success lying in the preparation of catalysts. A novel carbon-coated copper-based core-shell catalyst (C/Cu-Al2O3) was successfully prepared. In this work, Al2O3 was used as a carrier and copper as an active component to construct a catalyst with levodopa (L-DOPA) shell and embedded copper sites through the self-polymerization of L-DOPA. The active groups in L-DOPA molecules such as amine and carboxyl groups can be introduced into catalyst and L-DOPA also served as carbon source to reduce Cu(II) to more reactive Cu(I) and Cu(0). Under optimal conditions, its chemical oxygen demand (COD) removal rate for high-salt petrochemical wastewater reached 62.5%. After 20 cycles, its COD removal rate was maintained at above 53%. Electron paramagnetic resonance (EPR) investigations, quenching tests, and degradation experiments of oxalic acid revealed that the generation of embedded copper sites (Cu-O, Cu-N) and the construction of the carbon shell provided the catalyst with rich surface hydroxyl groups and Lewis acid sites, which promoted the decomposition of ozone into hydroxyl radicals (•OH), superoxide radicals (•O2-), and singlet oxygen (1O2) and achieved efficient degradation of organic compounds.

Preparation of catalyst of cobalt‐ and/or iron‐doped strontium zirconate and its performance in removal of m‐cresol using ozone as oxidant

AbstractBACKGROUNDWastewater containing m‐cresol has become a global water environmental problem because its degradation is difficult, and it is highly toxic to plants, animals, and humans. The heterogeneous catalytic ozonation process has been widely used in the treatment of environmental pollution, so it is very important to study efficient catalysts. Perovskite catalysts have been widely investigated and applied in catalytic ozonation processes. Among them, strontium zirconate is a promising perovskite catalyst owing to its high oxidation efficiency and environmental friendliness.RESULTSStrontium zirconate was successfully synthesized via the co‐precipitation method. To improve strontium zirconate catalytic performance, some methods such as changing the doping ratio of cobalt and iron, changing the amount of polyethylene glycol added, changing the calcination temperature, and changing the aging time were carried out during the synthesis process. Finally, the optimal conditions were determined. 0.4 g L−1 Sr2Co0.4Fe0.6ZrO6 prepared under the optimal conditions was used for catalytic ozonation of 100 ppm m‐cresol, which achieved the optimum degradation (0.136 min−1), m‐cresol conversion rate (92.2%) and total organic carbon removal rate (12.1%) within 20 min.CONCLUSIONThis work provides the best preparation conditions. The Sr2Co0.4Fe0.6ZrO6 catalyst, as prepared, is the optimal catalyst for catalytic ozonation of m‐cresol among the investigated Sr2CoxFe1−xZrO6 catalysts. © 2024 Society of Chemical Industry (SCI).

Pilot test of Mn-Fe/Al2O3 catalytic ozonation in tertiary wastewater treatment

Heterogeneous catalytic ozonation has received increasing popularity in wastewater treatment across China. However, some challenges, such as metal leaching from catalysts, still exist. Meanwhile, it is lesser known about its removal efficiency of dissolved organic carbon and impact on biological toxicity in pilot-scale applications. Here we synthesized an Al-based catalyst (Mn-Fe/Al2O3) for catalytic ozonation in pilot-scale. Results of characterization show that Mn and Fe were effectively supported on porous alumina and formed chemical bonds. The catalytic ozonation process could generate hydroxyl radical, superoxide radical and singlet oxygen for the deep degradation of dissolved organic carbon. Its chemical oxygen demand removal efficiency (average removal of 14.5 mg/L) could meet the requirement of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002) in China with acceptable metal leaching. The process also effectively removed dissolved organic carbon, especially the hydrophobic fractions (99 % removal). In toxicogenomics assay, the total transcriptional effect level index value for the effluent (1.40) was ≤ 1.50, indicating there was no obvious toxic effect for ecosystem. Based on economical estimation, the operational cost of the catalytic ozonation was 0.09 $/m3, much less than previous reported cases. This study provides convincing evidence for the effectiveness of Mn-Fe/Al2O3 catalytic ozonation in future wastewater treatment.

Pentachlorophenol degradation in the heterogeneous catalytic ozonation process using Al2O3 as a catalyst agent

Pentachlorophenol degradation in the heterogeneous catalytic ozonation process using Al2O3 as a catalyst agent

Electric field-enhanced heterogeneous catalytic ozonation (EHCO) process for sulfadiazine removal: The role of cathodic reduction

In this work, an electric field-enhanced heterogeneous catalytic ozonation (EHCO) was systematically investigated using a prepared FeOx/PAC catalyst. The EHCO process exhibited high sulfadiazine (SDZ) and TOC removal efficiency compared with electrocatalysis (EC) and heterogeneous catalytic ozonation (HCO) process. Almost 100% of SDZ was removed within 2 min, and the TOC removal reached approximately 85% within 60 min. Quenching experiments and EPR analysis suggested that the prominent SDZ and TOC removal performance is supported by the enhanced ·OH generation ability. Further study proved that H2O2 formed by O2 electrochemical reduction, peroxone reaction and electrochemical reduction of ozone contributed to improving ·OH generation. Furthermore, the EHCO system showed satisfactory stability and recyclability compared to conventional HCO systems, and the SDZ and TOC removal rates were maintained at ≥95% and ≥70% in 16 consecutive recycles, respectively. Meanwhile, XPS analysis and Boehm's titration for the FeOx/PAC catalyst used in HCO and EHCO process confirmed that the external electron supply could restrain the oxidation of surface functional groups of PAC and maintain a balance of the Fe(II)/Fe(III) ratio, which proved the critical role of cathode reduction in catalyst in situ regeneration during long consecutive recycles. In addition, the EHCO system could achieve more than 80% SDZ removal within 2 min in different water matrices. These results confirmed that the EHCO process has a wide application perspective for refractory organics removal in actual wastewater.

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.

Preparation of metal organic frame derived MgO-porous carbon composite and its high catalytic activity in ozonation with excellent stability

BackgroundOzone-based advanced oxidation technology has been extensively studied so far, but is hardly successfully used in treating actual wastewater. Preparation of a catalyst with high activity and stability, and insensitivity to quencher is still a big challenge in this field. MethodThe calcination of MOF-74 in inert gas resulted in a composite of the MgO-porous carbon, in which 2 nm MgO nanoparticles were uniformly distributed in porous carbon. Significant findingsThe specific surface area of MgO-PC composite (531.16 m²/g) was about 15 times that of MgO. The results of MgO-PC catalytic ozonation indicated it had not only high activity in ozonation of different organic but also excellent stability. The constant rate of p-CBA degradation in O3/MgO-PC only decreased from 11.63 × 10−2 min−1 to 9.36 × 10−2 min−1 after consecutive 15 cycles of the catalyst owing to the coating of porous carbon on nano particles of MgO. The most important thing is that O3/MgO-PC is a little insensitive to the free radical quenchers, which is an amazing result in progress of heterogeneous catalytic ozonation.

Enhanced dual synergistic mechanism of adsorption and ozone triggering via biochar-derived zero-valent bimetal sites for water purification

Novel zero-valent iron (ZVI) and zero-valent zinc (ZVZ) bimetal-supported biochar (ZF@BC) was developed for heterogeneous catalytic ozonation (HCO), which demonstrated the unique dual synergistic adsorption and catalysis-induced effective O3 triggering and interfacial decontamination. ZF@BC exhibited impressive catalytic and structure stabilities for 2-methyl-4-chlorophenoxyacetic acid (MCPA) degradation during long-lasting HCO, which can resist interference from a complex water quality background. Abundant electron-rich oxygen-containing functional groups and defects on BC contributed to the adsorption of MCPA and O3, respectively, while the introduced ZVZ was anticipated to expedite O3 decomposition by facilitating single-electron transfer reduction of O2 and establishing a robust connection with ZVI. Continuous efficacy of bimetal in three stages enhanced the efficiency of O3 utilization and hydroxyl radicals (•OH) yield, thereby safely mitigating the associated toxicity of MCPA after treatment. The development of O3/ZF@BC introduced a sustainable, long-term decontamination strategy and provided valuable insights for the advancement of HCO.

Enhanced 2, 6-dimethylpyrazine removal by catalytic ozonation with legumes biochar: The roles of oxygen- and nitrogen-containing functional groups

Designing efficient and environmentally friendly catalysts is essential to activating ozonation for wastewater remediation. This study prepared soybean biochar (SB), adzuki beans biochar (AB), and mung beans biochar (MB) catalysts using moldy legumes as precursors. The biochars were characterized to investigate the surface characters’ effect on ozone activation toward 2, 6-dimethylpyrazine (2,6-DMP) degradation. All prepared samples drastically facilitated the degradation more than with sole ozonation. It was found that at pH 7 with 10 mg L−1 catalysts, the removal rates of 5 μM 2,6-DMP were 88.3 %, 90.7 %, and 87.3 % by SB, MB, and AB at 30 min, respectively. The surface-area-normalized reaction rate constants (kobs/SBET) showed that AB exhibited the best catalytic activity with the rate of 1.5 × 10−2 mg·m2·min−1, which is 2.3- and 23.1-fold higher than that of SB and MB, respectively. Further characterization confirmed that oxygen- (C–O/C = O and –OH) and nitrogen-containing groups (pyridine N and pyrrole N) were crucial to the catalytic degradation, as electron transfer was promoted to form more ROS. In addition, the quenching test and electron paramagnetic resonance (EPR) revealed OH, O2−, and 1O2 as the main reactive oxygen species (ROS) during the heterogeneous catalytic ozonation (HCO), indicating that 2,6-DMP degradation followed the radical and non-radical oxidation pathways. Overall, this study helped to understand the relationship between surface functional groups and intrinsic activity. It also provided a new direction for utilizing agricultural waste.

MgAl2O4 incorporated catalytic ceramic membrane for catalytic ozonation of organic pollutants

Heterogeneous catalytic ozonation (HCO) is a promising technology for organic pollutants removal in wastewater treatment owing to the generation of powerful but short-lived hydroxyl radicals (HO·). Herein, we incorporate MgAl2O4 catalysts on the surface of ceramic membrane pores (MgAl membrane) to enhance HO· utilization and promote pollutant degradation under spatial confinement. The MgAl catalytic membrane achieved a removal efficiency of 74.0% for ibuprofen (5 mg/L) with 68.8% total organic carbon (TOC) removal, and the pollutant removal efficiency maintained over 67% in 25 h. Electron paramagnetic resonance (EPR) and scavenging experiments revealed that HO· played the dominant role in pollutant degradation. The catalyst surface hydroxyl groups were identified as active sites to effectively generate HO· via ozone decomposition. This work provides a viable strategy to achieve efficient pollutant degradation in wastewater treatment under spatial confinement in a membrane configuration.