Mechanism Of Catalytic Ozonation Research Articles

Preparation of Mn-Ce oxide-loaded Al2O3 by citric acid-assisted impregnation for enhanced catalytic ozonation degradation of dye wastewater

The performance of supported catalysts is significantly affected by the dispersion degree of the active components on the support. In this study, citric acid (CA) was used as a modifier to prepare Al2O3 supported Mn-Ce oxides (Mn-Ce/CA-Al2O3) by the impregnation-calcination method. The characterization results showed that adding citric acid enhanced the dispersion of Mn-Ce oxides on the support, rendering Mn-Ce/CA-Al2O3 with a larger specific surface area and abundant surface hydroxyl groups, thereby providing more reaction sites for catalytic ozonation. The Mn-Ce/CA-Al2O3 exhibited excellent catalytic ozonation performance in degrading Reactive Black 5 (RB5) dye. It achieved nearly complete decolorization of RB5 within 60 min, with a COD removal efficiency of 60%, which was superior to the sole ozonation (30%). Furthermore, the Mn-Ce/CA-Al2O3 system demonstrated significant degradation of RB5 over a wide pH range of 3 to 11. Based on the XPS and EPR analysis results, a preliminary mechanism of catalytic ozonation over the Mn-Ce/CA-Al2O3 was proposed. The redox cycle of Mn3+/Mn4+ and Ce3+/Ce4+ effectively accelerated the electron transfer process, thus promoting the generation of reactive oxygen species (ROS) and improving the degradation of RB5. Meanwhile, the Mn-Ce/CA-Al2O3 exhibited superior catalytic stability and effective treatment capabilities for real dye wastewater.

Treatment of landfill leachate in the MBR and catalytic ozonation coupled system based on Mn[sbnd]Ni catalyst: Efficiency and bio/chemical mechanism

Complex organic matters and high concentrations of ammonia nitrogen in landfill leachate required deep treatment before discharge. In this study, a catalytic ozonation-membrane bioreactor (MBR) process equipped with MnNi composite loaded carbon felt catalysts (Mn-Ni@CF) was proposed for landfill leachate treatment. The mechanism of catalytic ozonation was analyzed in focus. The abundant valence of manganese and nickel loaded on Mn-Ni@CF could promote the electron transfer and form the Mn4+ - O2 - Ni2+ redox couples. The redox reactions occurred in bimetallic enhanced transformation of active sites and generation of OH and O2−. It was found that the removal of humic acid substances by Mn-Ni@CF catalysts achieved 85.5 % after 2 h of catalytic ozonation reaction. Coupling with MBR, the removal efficiencies of chemical oxygen demand (COD) and NH4+-N for 25 L of landfill leachate were 99.8 % and 91.4 % after 13 days of operation, respectively. Proteobacteria and Actinobacteriota were effective to promote the nitrification-denitrification reaction. Thauera and Truepera could degrade organic matter. This study provided a new strategy for the efficient treatment of landfill leachate.

Efficient catalytic ozonation for hexazinone degradation by Fe/Ce-doped MOF derivatives

High catalytic efficiency and strong anti-interference catalyst for refractory pollutants removal remains a challenge for the catalytic ozonation. Metal-organic framework (MOF) have shown excellent performance in catalysis filed, but there is a risk of metal ion leaching. Designing MOF derivatives by high temperature modulation is considered to be an effective way to enhance the performance and reduce leaching risk of MOFs. In this paper, Fe/Ce bimetallic metal–organic framework (FeCe-MOF) was synthesized and three MOF derivatives were prepared by calcination at different temperatures. The performance of MOF derivatives in the degradation of hexazinone via catalytic ozonation and the effects were investigated. The mechanism of catalytic ozonation by FeCe@C-600 was also elucidated by the analysis of structural characterization of the fresh and used FeCe@C-600, electron paramagnetic resonance (EPR) and quenching experiment. FeCe@C-600/O3 system achieved 78.78 % removal of hexazinone and 42.37 % degradation of TOC within 20 min. During the catalytic ozonation, FeCe@C-600 has high structural stability and avoiding the release of metal ions. FeCe@C-600 showed excellent performance to degrade and mineralize of hexazinone, and it is more stable and has wider pH applicability. The electron transfer and redox cycling of Mn+/Mn+1 were promoted along with the conversion of lattice oxygen to oxygen vacancies. The degradation of hexazinone was mainly attributed to the generation of reactive oxygen species (•OH, •O2–, 1O2) during catalytic ozonation. MOF derivatives exhibited good adsorption capacity during the degradation of hexazinone. FeCe@C-600 effectively reduces metal leaching while retaining high catalytic activity, providing new ideas for the development of new efficient and environmentally friendly ozone catalysts.

Catalytic Ozonation of Ethyl Acetate with Assistance of MMn2O4 (M = Cu, Co, Ni and Mg) Catalysts through In Situ DRIFTS Experiments and Density Functional Theory Calculations

Catalytic ozonation, with enhanced efficiency and reduced byproduct formation at lower temperatures, proved to be efficient in ethyl acetate (EA) degradation. In this work, MMn2O4 (M = Cu, Co, Ni, Mg) catalysts were prepared via a redox-precipitation method to explore the catalytic ozonation mechanism of EA. Among all the catalysts, CuMn exhibited superior catalytic activity at 120 °C, achieving nearly 100% EA conversion and above 90% CO2 selectivity with an O3/EA molar ratio of 10. Many characterizations were conducted, such as SEM, BET and XPS, for revealing the properties of the catalysts. Plentiful active sites, abundant oxygen vacancies, more acid sites and higher reduction ability contributed to the excellent performance of CuMn. Moreover, the addition of NO induced a degree of inhibition to EA conversion due to its competition for ozone. H2O had little effect on the catalytic ozonation of CuMn, as the conversion of EA could reach a stable platform at ~89% even with 5.0 vol.% of H2O. The presence of SO2 usually caused catalyst deactivation. However, the conversion could gradually recover once SO2 was discontinued due to the reactivation of ozone. A detailed reaction mechanism for catalytic ozonation was proposed via in situ DRIFTS measurements and DFT calculations.

Catalytic ozonation mechanism over M1-N3C1 active sites

The structure-activity relationship in catalytic ozonation remains unclear, hindering the understanding of activity origins. Here, we report activity trends in catalytic ozonation using a series of single-atom catalysts with well-defined M1-N3C1 (M: manganese, ferrum, cobalt, and nickel) active sites. The M1-N3C1 units induce locally polarized M − C bonds to capture ozone molecules onto M atoms and serve as electron shuttles for catalytic ozonation, exhibiting excellent catalytic activities (at least 527 times higher than commercial manganese dioxide). The combined in situ characterization and theoretical calculations reveal single metal atom-dependent catalytic activity, with surface atomic oxygen reactivity identified as a descriptor for the structure-activity relationship in catalytic ozonation. Additionally, the dissociation barrier of surface peroxide species is proposed as a descriptor for the structure-activity relationship in ozone decomposition. These findings provide guidelines for designing high-performance catalytic ozonation catalysts and enhance the atomic-level mechanistic understanding of the integral control of ozone and methyl mercaptan.

Catalytic ozonation of p-xylene over Mn/Ce oxide nanorods treated by vacuum deoxidation

Xylene with high photochemical activity is commonly used as a raw material and organic solvent. The treatment of waste gases containing xylene is a necessary measure to ensure the air quality. Mn/Ce oxide nanorods were prepared using SBA-15 as a template and subjected to vacuum deoxidation for catalytic ozonation of p-xylene. Hydrothermal demolding conduced to detach the nanorods to improve the surface area and porosity, providing massive active sites for catalytic ozonation. The results indicated that numerous Mn-O-Ce solid solution structures formed in Mn/Ce composite oxides, especially Mn0.5Ce0.5Ox, to enhance weak- and medium-acid sites and oxygen vacancies (OVs) on the catalysts. Vacuum deoxidation effectively and facilely raised OVs for the catalysts. Vacuum-deoxidated Mn0.5Ce0.5Ox with the most Mn-O-Ce structures achieved the highest removal rate of p-xylene and CO2 selectivity since the most OVs and weak- and medium-acid sites appeared in it compared with the other catalysts. The mechanism of catalytic ozonation may be that p-xylene adsorbed on the acid site of vacuum-deoxidized Mn0.5Ce0.5Ox is attacked by the reactive oxygen species (ROS) generated by the dissociation of O3 on OVs. The degraded p-xylene and its intermediate are finally oxidized by ROS to CO2 and H2O.

The efficiency and mechanism of excess sludge-based biochar catalyst in catalytic ozonation of landfill leachate

In this study, biochar was produced based on dehydrated excess sludge from the municipal wastewater treatment plant, which was used for catalytic ozonation of pollutants derived from landfill leachate. The necessary catalytic sites in the structure of biochar were originated from the inorganic metals and organic matters in the sludge, which included a large number of functional groups (e.g., C-C, CO, etc.), adsorbed oxygen (Oads accounted for 44.82%) and electron defects (ID/IG=1.01). These active sites could promote the generation of reactive oxygen species (ROS) (e.g., ·OH,·O2-, etc.). The synergistic interaction between the microorganisms in the activated sludge also facilitated the removal rates of pollutants. Proteobacteria, Bacteroidetes, and Deinococcu-Thermus were crucial in the bioreactor. In 16 days of reaction, the removal ratios of NH+4-N and COD were 98.95 ± 0.11% and 90.89 ± 0.47%, respectively. This study not only explains the mechanism of catalytic ozonation of biochar, but also provides a new way of the practical treatment of landfill leachate.

Catalytic ozonation performance of graphene quantum dot doped MnOOH nanorod for effective treatment of ciprofloxacin and bromate formation control in water

A catalyst GQDs@MnOOH was successfully synthesized by attaching graphene quantum dots (GQDs) on the surface of MnOOH nanorods to boost catalytic ozonation of antibiotic, exemplified by ciprofloxacin (CIP). The result demonstrated that the GQDs@MnOOH/O3 system had the greatest CIP removal effectiveness, followed by that of MnOOH/O3 and O3 only. The 0.02 mM CIP was degraded with 99.9% efficiency in 30 min in the presence 9.6 mg L-1 of O3 catalyzed by 12.5 mg L-1 of GQDs@MnOOH. The kinetic rate constants ​​were in the order: GQDs@MnOOH/O3 (0.161 min−1) > MnOOH/O3 (0.079 min−1) > O3 (0.055 min−1). The GQDs@MnOOH could enhance CIP degradation and inhibit BrO3- formation in different water sources. Results of scavenger and electron paramagnetic resonance (EPR) experiments demonstrated that oxygen radical (O2•-), singlet oxygen (1O2), and hydroxyl radicals (•OH) were involved in CIP degradation by the GQDs@MnOOH/O3 system. Accordingly, the degradation pathways of CIP and mechanism of catalytic ozonation over GQDs@MnOOH were investigated and proposed. This research is expected to shed light on the connection between carbonaceous material and metal hydroxide in catalytic ozonation.

Mechanism of catalytic ozonation in different surface acid sites of oxide aqueous suspensions

Proposed mechanism of catalytic ozonation in different surface acid sites of oxide aqueous suspensions.

Highly effective mineralization of acetic acid wastewater via catalytic ozonation over the promising MnO2/γ-Al2O3 catalyst

The complete mineralization of acetic acid in wastewater through a biodegradation process is difficult due to the α-position methyl coordinated with the carboxyl group, and this work explored the oxidation performance of acetic acid by catalytic ozonation with metal oxides supported on γ-Al2O3. It was found that MnO2/γ-Al2O3 catalyst achieved superior mineralization performance to Co/Fe/CeOx supported on γ-Al2O3 for acetic acid wastewater treatment. The effects of MnO2 loading, catalyst dosage, acetic acid concentration, O3 concentration, ozonation temperature, and initial pH value of the acetic acid solution were investigated. Typically, the mineralization of acetic acid over 1.0 wt.% MnO2/γ-Al2O3 catalyst was as high as 88.4% after 300 min ozonation of 1.0 g·L‒1 acetic acid at 25 °C with the highest energy efficiency around 15 g·kWh‒1. By contrast, the mineralization of acetic acid could only reach 43.2% in the absence of the catalyst, with an energy efficiency of 5.1 g·kWh−1. Radical quenchers and indicated that ·OH radical, O2− species originated from ozone played an important role in the catalytic ozonation of acetic acid into CO2 and H2O. Besides, the catalytic ozonation mechanism of acetic acid over MnO2/γ-Al2O3 was carefully proposed based on the in situ DRIFTS results.

Treatment of Phenol-Containing Coal Chemical Biochemical Tailwater by Catalytic Ozonation Using Mn-Ce/γ-Al2O3

In this study, a Mn-Ce/γ-Al2O3 catalyst with multiple active components was prepared through the doping–calcination method for advanced treatment of coal chemical biochemical treatment effluent and characterized by X-ray diffraction, X-ray fluorescence spectroscopy, scanning electron microscopy, and BET analysis. In addition, preparation and catalytic ozonation conditions were optimized, and the mechanism of catalytic ozonation was discussed. The Mn-Ce/γ-Al2O3 catalyst significantly enhanced COD and total phenol removal in reaction with ozone. The characterization results suggested that the pore structure of the optimized Mn-Ce/γ-Al2O3 catalyst was significantly improved. After calcination, the metallic elements Mn and Ce existed in the form of the oxides MnO2 and CeO2. The best operating conditions in the study were as follows: (1) reaction time of 30 min, (2) initial pH of 9, (3) ozone dosage of 3.0 g/h, and (4) catalyst dosage of 30 g/L. The removal efficiency of COD and total phenol from coal chemical biochemical tail water was reduced with the addition of tert-butanol, which proves that hydroxyl radicals (•OH) played a leading role in the Mn-Ce/γ-Al2O3 catalytic ozonation treatment process of biochemical tailwater. Ultraviolet absorption spectroscopy analysis indicated that some conjugated structures and benzene ring structures of organics in coal chemical biochemical tail water were destroyed. This work proposes the utilization of the easily available Mn-Ce/γ-Al2O3 catalyst and exhibits application prospects for the advanced treatment of coal chemical biochemical tailwater.

Mechanism of One-Step Hydrothermally Synthesized Titanate Catalysts for Ozonation.

A titanate nanotube catalyst for ozonation was synthesized with a simple one-step NaOH hydrothermal treatment without energy-consuming calcination. The synthesized titania catalysts were characterized by X-ray diffraction (XRD), Raman, porosimetry analysis, high-resolution transmission electron microscopy (HR-TEM), Fourier transformed infrared (FTIR), and electron paramagnetic resonance (EPR) analysis. The catalyst treated with a higher concentration of NaOH was found to be more catalytically active for phenol removal due to its higher titanate content that would facilitate more OH groups on its surface. Furthermore, the main active oxidizing species of the catalytic ozonation process were recognized as singlet oxygen and superoxide radical, while the hydroxyl radical may only play a minor role. This work provides further support for the correlation between the properties of titania and catalytic performance, which is significant for understanding the mechanism of catalytic ozonation with titania-based materials.

Landfill leachate treatment in-depth by bio-chemical strategy: microbial activation and catalytic ozonation mechanism

The combination of activated sludge process and catalytic ozonation technology was used to treat the landfill leachate as bio-chemical strategy in this study. The technology of activated sludge pretreatment and catalytic ozonation post-treatment coupled with baffled membrane bioreactor (MBR) system was proposed. The COD, ammonia nitrogen and phosphate were removed in anaerobic and aerobic environments. At the same time, catalytic ozonation could significantly remove COD, colority, UV254, ammonia nitrogen, 3D fluorescence peak value, and fluorescence regional integration (FRI) of organic pollutants from landfill leachate. Ultimately, the maximum removal efficiencies of COD, ammonia nitrogen and phosphate were 98.46 ± 0.28%, 99.92 ± 0.01%, and 79.71 ± 1.62%, respectively. The heavy metal contents met the emission standards after treatment with this strategy. The removal of pollutants in landfill leachate could be attributed to the positive effect of microorganism in sludge and catalyst in ozonation: (1) The microorganism found in sludge all played different roles, Proteobacteria and Bacteroidetes accounted for the most, they could degrade organisms and even refractory organic matters. Though the number of Thauera, Acinetobacter, Nitrospira and Nitrosomonas was small, they played an important role on denitrification. (2) During catalytic ozonation, the hydroxyl radical (OH) produced by ozone would combine with oxygen to generate hydrogen peroxide radical (OOH) during the reaction, while unpaired electrons were trapped by surface adsorbed oxygen on the catalysts to produce superoxide radical (O2–). In addition, the active metal components, such as Ce4+/Ce3+ redox pair, Mn2+, Mn3+ and Mn4+ on the catalyst surface were able to transform synergistically, which was able to maintain the catalyst activity and realize the removal of contaminants.

Can the commonly used quenching method really evaluate the role of reactive oxygen species in pollutant abatement during catalytic ozonation?

Reactive oxygen species (ROS) such as hydroxyl radicals (•OH), superoxide radicals (O2•−), and singlet oxygen (1O2) have often been suggested to play a role in ozone-resistant pollutant abatement during catalytic ozonation. However, there are significant controversies regarding their relative importance in literature. Currently, the role of ROS in pollutant abatement is commonly evaluated by the quenching method based on the assumption that the added ROS quenchers (e.g., tert-butanol (TBA) and para-benzoquinone (pBQ)) quench only the target ROS, but do not considerably influence other reaction mechanisms of catalytic ozonation. However, we hypothesized that this assumption is possibly unrealistic and a main cause for the controversies reported in literature. To test this hypothesis, this study evaluated the effects of six commonly used ROS quenchers (TBA, pBQ, methanol (MeOH), 4-chloro-7-nitrobenzo-2-oxa-1,3-dizole (NBD-Cl), furfuryl alcohol (FFA), and sodium azide (NaN3)) on the mechanism of catalytic ozonation with manganese dioxide. The results show that rather than only quenching their target ROS, these quenchers can profoundly change the catalytic ozonation system through various mechanisms, e.g., interrupting the radical chain reaction of O3 decomposition, blocking the active sites of catalysts, and consuming O3 in the system. Due to the significant confounding effects of ROS quenchers on the reaction mechanism, the quenching method actually cannot reveal the role of ROS in pollutant abatement and often misinterpreted the catalytic ozonation mechanism. The results indicate that the commonly used quenching method is probably not an appropriate way to investigate the role of ROS in pollutant abatement during catalytic ozonation, and many previously reported mechanisms obtained with the quenching method may need a revisit.

Mechanism of ozone adsorption and activation on B-, N-, P-, and Si-doped graphene: A DFT study

• Detailed evolution mechanism of O 3 into ROS on the doped graphene was revealed. • O ads produced from O 3 decomposition was a vital intermediate to generate other ROS. • Types and efficiency of the formed ROS from O ads depended on the doped heteroatoms. • CDD was a useful descriptor for carbonaceous catalyst design based on QSAR model. The detailed evolution mechanism of O 3 into Reactive oxygen species (ROS) is of paramount importance but remains elusive in catalytic ozonation. Herein, we report a density functional theory study to comprehensively reveal the specific evolution processes of O 3 into ROS on the B-, N-, P-, and Si-doped graphene, including the adsorption, decomposition and ROS generation. In contrast to some previous reports that O 3 would directly decompose into effective ROS on catalysts, our results indicate that after O 3 adsorption, the decomposition products are ground state O 2 and the adsorbed oxygen species (O ads ). The O ads is more likely to act as a crucial intermediate for generating other ROS instead of directly attacking the organics. The type of the ROS and generation efficiency vary with the doped heteroatoms, and the heteroatoms of B, P and Si, or the neighboring C of N, would serve as active sites for O 3 adsorption and decomposition. The N- and P-doped graphene are predicted to have the superior performance in ROS generation and catalytic stability. Finally, twenty representative descriptors were adopted to build the quantitative structure–activity relationship (QSAR) with the activation energy barrier of O 3 decomposition. The result indicates that condensed dual descriptor (CDD) could be useful for preliminarily selecting the modified graphene catalysts, since it shows a very good linear relation with the activation energy barrier. This contribution provides an alternative way to gain fundamental insights into the mechanism of catalytic ozonation at the molecular level, and could be helpful for designing more-efficient catalysts in environmental remediation.

Insights into mechanism of catalytic ozonation of cinnamyl alcohol over core–shell Fe3O4@SiO2@La2O3 catalyst

In this study, a magnetic Fe3O4@SiO2@La2O3 nano-catalyst with a core–shell structure was synthesized to improve the efficiency of catalytic ozonation of cinnamyl alcohol. The structure, morphology, and elemental composition of the catalyst were analyzed with the help of catalyst characterization methods. The mechanism of strengthened degradation efficiency and mineralization of cinnamyl alcohol in catalytic ozonation system in the existence of the catalyst were further discussed according to the analysis results. The results showed that the Fe3O4@SiO2@La2O3 catalyst can not only greatly improve the degradation of cinnamyl alcohol, but also has good reusability and stability. And its economic efficiency is relatively good. The degradation rate of cinnamyl alcohol could reach up to 99.8% at 30 min, and the COD could be removed by 28.5% at 60 min with the help of the catalyst. The degradation efficiency of cinnamyl alcohol by ozone oxidation alone was only 52.1% at 30 min, and the COD removal rate was only 24.2% at 60 min in the same experimental conditions. Besides, the possible degradation pathway and degradation mechanism of cinnamyl alcohol were proposed according to the intermediate products detected by gas chromatography-mass spectrometry.

Catalytic Ozonation for Effective Degradation of Coal Chemical Biochemical Tail Water by Mn/Ce@RM Catalyst

An Mn/Ce@red mud (RM) catalyst was prepared from RM via a doping–calcination method. Scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used to characterize the surface morphology, crystal morphology, and elemental composition of the Mn/Ce@RM catalyst, respectively. In addition, preparation and catalytic ozonation conditions were optimized, and the mechanism of catalytic ozonation was discussed. Lastly, a fuzzy analytic hierarchy process (FAHP) was adopted to evaluate the degradation of coal chemical biochemical tail water. The best preparation conditions for the Mn/Ce@RM catalyst were found to be as follows: (1) active component loading of 3%, (2) Mn/Ce doping ratio of 2:1, (3) calcination temperature of 550 °C, (4) calcination time of 240 min, and (5) fly ash floating bead doping of 10%. The chemical oxygen demand (COD) removal rate was 76.58% under this preparation condition. The characterization results suggested that the pore structure of the optimized Mn/Ce@RM catalyst was significantly improved. Mn and Ce were successfully loaded on the catalyst in the form of MnO2 and CeO2. The best operating conditions in the study were as follows: (1) reaction time of 80 min, (2) initial pH of 9, (3) ozone dosage of 2.0 g/h, (4) catalyst dosage of 62.5 g/L, and (5) COD removal rate of 84.96%. Mechanism analysis results showed that hydroxyl radicals (•OH) played a leading role in degrading organics in the biochemical tail water, and adsorption of RM and direct oxidation of ozone played a secondary role. FAHP was established on the basis of environmental impact, economic benefit, and energy consumption. Comprehensive evaluation by FAHP demonstrated that D3 (with an ozone dosage of 2.0 g/H, a catalyst dosage of 62.5 g/L, initial pH of 9, reaction time of 80 min, and a COD removal rate of 84.96%) was the best operating condition.

Catalytic Ozonation Mechanism of Norfloxacin Wastewater Using Cu-Cufe2o4: Oxygen Vacancies Initiate Free Radical and Non-Free Radical Coupling Reactions

Catalytic Ozonation Mechanism of Norfloxacin Wastewater Using Cu-Cufe2o4: Oxygen Vacancies Initiate Free Radical and Non-Free Radical Coupling Reactions

Fischer–Tropsch synthetic wastewater treatment with Fe/Mn@CH: Catalytic ozonation and process evaluation

• Fe-Mn@CH with high catalytic activity was prepared. • The organic matter is transformed into protein-like and tryptophan-like substances. • Ozone catalytic oxidation process is closer to the secondary reaction kinetics. • A multi-level-gray relational evaluation model is established. In this study, the honeycomb ceramic catalyst Fe/Mn@CH with high catalytic activity was prepared. The effect of preparation conditions on the catalytic performance of Fe/Mn@CH was systematically studied. Scanning electron microscope; X-ray energy spectrum analysis; X-ray diffraction; specific surface area, pore distribution and adsorption performance analysis; X-ray fluorescence spectroscopy; and X-ray photoelectron spectroscopy were performed to analyze the structural characteristics of the catalyst. The optimal working conditions of the catalytic ozonation system for the degradation of Fischer–Tropsch synthesis wastewater were also studied. The metal elements Fe and Mn were successfully loaded on the surface of the honeycomb ceramic carrier in the form of α-MnO 2 and α-Fe 2 O 3 oxides. The optimal COD removal rate could reach 64.37% at pH of 9, ozone dosage of 6 g/h, Fe/Mn@CH dosage of 50 g/300 mL, and reaction time of 60 min. The specific mechanism of catalytic ozonation in the presence of tert -butanol was explored through ultraviolet absorption spectroscopy and three-dimensional fluorescence spectroscopy. The COD removal efficiency for Fischer–Tropsch synthesis wastewater was analyzed on the basis of catalytic oxidation reaction kinetics. Finally, a multilevel gray correlation evaluation model was established for the quantitative evaluation of the ozonation catalytic oxidation of Fischer–Tropsch wastewater.

Mechanism of catalytic ozonation for elimination of methyldopa with Fe3 O4 @SiO2 @CeO2 catalyst.

In this study, a magnetic nanocatalyst (Fe3 O4 @SiO2 @CeO2 ) was prepared and applied in the catalytic ozonation of methyldopa (MD). The effects of operational parameters on catalytic ozonation performance were investigated, including ozone dosage, catalyst dosage, initial MD concentration, and pH. The removal of MD was 45.2% in ozonation, whereas the efficiency was achieved to 83.0% with the addition of Fe3 O4 @SiO2 @CeO2 . The results showed that Fe3 O4 @SiO2 @CeO2 could significantly improve the catalytic ozonation performance. And the enhanced mechanism study showed that it was attributed to promotion of ozone decomposition to generate hydroxyl radical. The reaction model was explored, and the reaction rates were calculated for the MD degradation in catalytic ozonation. A higher degradation efficiency of MD in catalytic ozonation was attributed to the enhanced surface effect of the catalysts, which was confirmed by using TBA, PO4 3- , and p-BQ as scavengers of hydroxyl radical, surface reaction, and superoxide radical. The hydroxyl radical and superoxide radical played an important role in the degradation of MD. The mechanism of catalytic ozonation by Fe3 O4 @SiO2 @CeO2 was discussed via X-ray photoelectron spectroscopy (XPS) spectra and experimental data.