Catalyst For Catalytic Ozonation Research Articles

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

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

Precisely constructing orbital coupling-modulated iron dinuclear site for enhanced catalytic ozonation performance

The advancement of atomically precise dinuclear heterogeneous catalysts holds great potential in achieving efficient catalytic ozonation performance and contributes to the understanding of synergy mechanisms during reaction conditions. Herein, we demonstrate a "ship-in-a-bottle and pyrolysis" strategy that utilizes Fe2(CO)9 dinuclear-cluster to precisely construct Fe2 site, consisting of two Fe1-N3 units connected by Fe-Fe bonds and firmly bonded to N-doped carbon. Systematic characterizations and theoretical modeling reveal that the Fe-Fe coordination motif markedly reduced the devotion of the antibonding state in the Fe-O bond because of the strong orbital coupling interaction of dual Fe d-d orbitals. This facilitates O-O covalent bond cleavage of O3 and enhances binding strength with reaction intermediates (atomic oxygen species; *O and *OO), thus boosting catalytic ozonation performance. As a result, Fe dinuclear site catalyst exhibits 100% ozonation efficiency for CH3SH elimination, outperforming commercial MnO2 catalysts by 1,200-fold. This research provides insights into the atomic-level structure-activity relationship of ozonation catalysts and extends the use of dinuclear catalysts in catalytic ozonation and beyond.

Construction of highly dispersed iron active sites for efficient catalytic ozonation of bisphenol A

The essential factor of catalytic ozonation technology relies on an efficient and stable catalyst. The construction of highly dispersed active sites on heterogeneous catalysts is an ideal strategy to combine the merits of homogeneous and heterogeneous catalysis with high activity and stability. Herein, an iron-containing mesoporous silica material (Fe-SBA15) with sufficient iron site exposure and enhanced intrinsic activity of active sites was employed to activate ozone for bisphenol A (BPA) degradation. Approximately 100% of BPA and 36.6% of total organic carbon (TOC) removal were realized by the Fe-SBA15 catalytic ozonation strategy with a reaction constant of 0.076 min−1, well beyond the performance of FeOx/SBA15 mixture and Fe2O3. Radical quenching experiments and electron paramagnetic resonance (EPR) analysis demonstrated that the hydroxyl radicals (HO•) and superoxide radicals (O2•−) played an important role in the degradation process. The iron sites with recyclable Fe(III)/Fe(II) pairs act as both the electron donors and active sites for catalytic ozonation. The mesoporous framework of SBA15 in Fe-SBA15 stabilizes the iron sites that enhance its stability. With high catalytic performance and high reusability for catalytic ozonation of BPA, the Fe-SBA15 is expected to be a promising catalyst in catalytic ozonation for wastewater treatment.

Preparation and application of Ag–Ce–O composite metal oxide catalyst in catalytic ozonation for elimination of Reactive Black 5 dye from aqueous media

It is necessary to treat textile effluents before discharging them into natural water bodies as they harm the environment. Compared to conventional treatment methods, catalytic ozonation has gained attention due to its effectiveness in removing refractory organic pollutants. In this study, the coprecipitation method was used to synthesize a composite metal oxide of silver and cerium oxide, and the synthesized catalyst was used to eliminate the Reactive Black 5 (RB5) dye. X-ray diffraction, scanning electron microscopic, and Brunauer–Emmett–Teller surface area analyses were performed to characterize the synthesized catalyst. Afterwards, relevant experimental parameters, such as pH, ozone and catalyst dosages, and initial dye concentration, were investigated. The experiments revealed that the optimal experimental conditions were a pH value of 10, a catalyst dosage of 0.7 g/L, and an ozone dosage of 60 L/h. In these optimized conditions, the RB5 dye was entirely removed, and a chemical oxygen demand removal efficiency of 88% was achieved within a reaction time of 80 min. Furthermore, the recycling potential of the catalyst was tested for three cycles, and no deterioration in its activity was observed. Additionally, studies were conducted using a hydroxyl radical scavenger in order to understand the reaction pathway of the system. As a result, the indirect pathway was more dominant than the direct pathway in the system.

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.

The special mechanisms of quasi-complexation and enhanced effect of “·OH action zone” in activated carbon combined ozonation

Activated carbon (AC) is an excellent adsorbent and is widely employed as a catalyst in catalytic ozonation. However, the massive change in surface oxygen groups on AC before and after ozonation in this research indicated that AC was not a real catalyst. Moreover, the lower oxalic acid removal effect and the observed hydroxyl radicals (·OH) accumulative amount of pre-oxidative AC combined ozonation confirmed that AC functioned as an activator. We investigated the removal trend of oxalic acid in AC-activated ozonation under different pH, and it was consistent with its adsorption via adjusting the oxalic acid adsorbed on AC. Despite the accumulation concentration of ·OH reaching the highest value at pH = 4.7, the activated ozonation did not perform best. Considering the extremely short life of ·OH in an aqueous solution, an “action zone” existed, which was the effective region for ·OH to react with organics. This result proved that the AC adsorption would concentrate organics in the “action zone”, thus improving the degradation of organic contaminants. The solution containing oxalic acid had a higher accumulative concentration of ·OH than without oxalic acid, which meant a previously neglected pathway existed to produce ·OH. In addition, C2O4·- was reported in the solution containing AC, oxalic acid, and oxygen. Thus, the quasi-complexation reaction might occur between AC, oxalic acid, and oxygen. Overall, this study disclosed distinct mechanisms due to AC adsorption in the AC combined ozonation system.

Manipulating Selectivity of Hydroxyl Radical Generation by Single-Atom Catalysts in Catalytic Ozonation: Surface or Solution.

Hydroxyl radical-dominated oxidation in catalytic ozonation is, in particular, important in water treatment scenarios for removing organic contaminants, but the mechanism about ozone-based radical oxidation processes is still unclear. Here, we prepared a series of transitional metal (Co, Mn, Ni) single-atom catalysts (SACs) anchored on graphitic carbon nitride to accelerate ozone decomposition and produce highly reactive ·OH for oxidative destruction of a water pollutant, oxalic acid (OA). We experimentally observed that, depending on the metal type, OA oxidation occurred dominantly either in the bulk phase, which was the case for the Mn catalyst, or via a combination of the bulk phase and surface reaction, which was the case for the Co catalyst. We further performed density functional theory simulations and in situ X-ray absorption spectroscopy to propose that the ozone activation pathway differs depending on the oxygen binding energy of metal, primarily due to differential adsorption of O3 onto metal sites and differential coordination configuration of a key intermediate species, *OO, which is collectively responsible for the observed differences in oxidation mechanisms and kinetics.

Accelerated catalytic ozonation for aqueous nitrobenzene degradation over Ce-loaded silicas: Active sites and pathways

Cerium oxides loaded silica catalysts were synthesized by an impregnation method by simply mixing Ce precursor with silica spherule (Ce/SS) and ordered MCM-41 zeolites (Ce/MCM-41), followed by a mild calcination. Compared with pure SS and MCM-41, Ce modified Ce/SS and Ce/MCM-41 demonstrate much improved catalytic ozonation activities for mineralization of recalcitrant nitrobenzene (NB). At solution pH of 6, 86 and 97% TOC mineralization rates were achieved within 60 min for Ce/MCM-41 and Ce/SS, respectively. Characterization results suggest that Ce loading significantly increases the surface Lewis acidic sites, which would synergize with Ce3+/Ce4+ redox cycle for the activity improvement. With the aid of in situ electron paramagnetic resonance (EPR) spectra and quenching tests, hydroxyl radical (·OH), superoxide radical (O2•–), and singlet oxygen (1O2) are identified as the O3 catalytic decomposition products, while ·OH mainly accounts for NB mineralization. The detailed degradation route of NB was further investigated by the multi-chromatography analysis. NB is firstly oxidized into polyhydroxy compounds, followed by small molecular organic acids, and finally being mineralized into CO2 and H2O. This study established a facile strategy to synthesize highly active and stable Ce/SiO2 catalysts for catalytic ozonation, and elucidated the in-depth mechanisms for the activity origins of the Ce loaded silica-based materials in catalytic ozonation processes (COP).

Catalytic ozonation for metoprolol and ibuprofen removal over different MnO2 nanocrystals: Efficiency, transformation and mechanism

Manganese dioxide has been widely recognized as catalyst in catalytic ozonation for organic pollutants removal from wastewater in recent decades. However, few studies focus on the structure-activity relationship of MnO2 and catalytic ozonation mechanism in water. In the present study, the oxidative reactivity of three different crystal phases of MnO2 corresponding to α-MnO2, β-MnO2 and γ-MnO2 towards metoprolol (MET) and ibuprofen (IBU) were evaluated. α-MnO2 was found to contain the most abundant oxygen vacancy and readily reducible surface adsorbed oxygen (O2−, O−, OH−), which facilitated an increase of ozone utilization and the highest catalytic performance with 99% degradation efficiency for IBU and MET. α-MnO2 was then selected to investigate the optimum key operating parameters with a result of catalyst dosage 0.1 g/L, ozone dosage 1 mg/min and an initial pH 7. The introduction of α-MnO2 promoted reactive oxygen species (O2−, O−, OH−) generation which played significant roles in IBU degradation. Probable degradation pathways of MET and IBU were proposed according to the organic intermediates identified and the reaction sites based on density function theory (DFT) calculations. The present study deepened our understanding on the MnO2 catalyzed ozonation and provided reference to enhance the process efficiency.

Enhanced ozonation of pollutants by MgO nanoclusters/sewage sludge-derived hierarchical porous carbon: experimental and theoretical study

MgO nanoclusters stabilized by modified sewage sludge-derived hierarchical porous carbon were prepared and used as an efficient catalyst in catalytic ozonation of refractory pollutants.

In-situ growing protective Cr-substituted goethite film on iron shavings (Fe0) as efficient catalytic ozonation catalysts: A comparative study

Abstract H2O2-modified iron shavings (HMI) with surface γ-FeOOH film were effective as a catalyst in catalytic ozonation, but the iron leaching and loss of surface component limited its application. In this study, Cr-modified iron shavings (CrMI) was developed by introducing Cr3+ to promote Cr-substituted goethite (α-Fe(Cr3+)OOH) film formation on iron shavings. The variety in stability and catalytic performance between CrMI and HMI were compared. The α-Fe(Cr3+)OOH film was compact while the γ-FeOOH film contained abundant voids and microcracks as observed from SEM. After long-time ozonation, α-Fe(Cr3+)OOH film was thin and homogeneous whereas γ-FeOOH film grew thicker through inner iron layer corrosion as indicated by XPS etching. The α-Fe(Cr3+)OOH film has 63% reduction in corrosion current densities (22.95 μA) and 96% reduction of donor densities (3.40 × 1020 cm−3) as well as 9 times increase in polarization resistance (4399.0 Ω cm2), which verified that it was more stable and less defective. Owing to the protective properties of α-Fe(Cr3+)OOH film, iron leaching of CrMI were reduced for 85% with only 4.1 mg L−1 of total iron concentration detected in solution, and surface loss of CrMI were reduced for 91% with only 5.8 NTU of turbidity left in the solution after catalytic ozonation. Moreover, the addition of CrMI as catalyst in ozonation led to slightly higher mineralization rate of 79% for organic pollutants as the results of higher surface acid sites density and more hydroxyl radicals generation. It also presented excellent reusability based on 20 h successive run with unnoticeable performance decay and metal release. These results revealed that, with excellent stability and high catalytic performance, CrMI was highly competitive for long-term application in wastewater treatment.

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

CoFe2O4 (Cobalt ferrite, CF) nanoparticles were prepared, well characterized and applied as efficient solid catalyst in catalytic ozonation, named CF/O3 process, for the removal of emerging organic contaminants (EOCs). The degradation and mineralization of clofibric acid (CA) in CF/O3 process were dramatically enhanced in comparison with those under the O3 system. Surface hydroxyl groups (HGs) were considered as an important factor for ozone decomposition and the reactive oxygen species (ROS) on the catalyst surface were mainly responsible for CA elimination. The contribution and formation of ROS, including hydroxyl radicals (•OH), especially superoxide radicals (O2•−), singlet oxygen (1O2), and hydrogen peroxide (H2O2) were evaluated, and a rational mechanism was elucidated accordingly. Probable degradation pathway of CA was proposed according to the organic intermediates identified. The acute toxicity of the treated solution increased during the first 15 min and then declined rapidly and nearly disappeared as the reaction proceeded. In addition, acceptable catalytic performance of CF/O3 can be obtained for the treatment of other EOCs and the treatment of natural surface water spiked with CA. This work presents an efficient and promising catalytic ozonation technique for the elimination of EOCs in complex water matrices.

Catalytic ozonation of NH4+-N in wastewater over composite metal oxide catalyst

Large amounts of water containing-ammonium nitrogen (NH4+-N) have attracted increasing attention. Catalytic ozonation technology, involving the generation of hydroxyl radical (·OH) with strong oxidation ability, was originally utilized to degrade organic-containing wastewater. In this paper, Ce/MnOx composite metal oxide catalysts prepared with different preparation conditions were used to degrade wastewater containing inorganic pollutant (NH4+-N). The as-prepared catalyst features were characterized using X-ray diffraction (XRD), Brunauer–Emmett–Teller method (BET), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and H2-temperature programmed reduction (H2-TPR) techniques. The results show that the catalyst, prepared by conditions with precipitant Na2CO3 and Ce/Mn molar ratio 1:2 calcined at 400 °C for 3 h in pH 11.0, displays the optimal performance, with the removal rate of NH4+-N and selectivity to gaseous nitrogen, 88.14 wt% and 53.67 wt%, respectively. The effects of several operating factors including solution pH, initial NH4+-N concentrations and scavengers were evaluated. In addition, XRD patterns of catalyst with the best performance and the comparative study on decontamination of NH4+-N by various processes (O3, catalyst and catalyst/O3) show that the primary metal oxides are CeO2 and MnO2 in Ce/MnOx composite metal oxide catalysts, which have a synergistic effect on the catalytic ozonation of NH4+-N, and the new phase MnO2 plays a great role. After 5 consecutive use cycles, the degradation efficiency is declined slightly, and can still achieve better than 70 wt% over 1 h reaction. Additionally, the application of catalytic ozonation for actual wastewater on the removal rate of NH4+-N was investigated. Possible mechanism and degradation pathway of NH4+-N were also proposed. In a word, the application of CeO2–MnO2 composite metal oxide catalysts in catalytic ozonation can be regarded as an effective, feasible and promising method for the treatment of NH4+-N.

Catalytic ozonation treatment of biochemically treated leachate from municipal waste solid using Ti–Mn oxide‐coated stainless steel mesh catalyst

AbstractBACKGROUNDLandfill leachate is a kind of complex organic wastewater, the discharge standard of which is difficult to meet after traditional biochemical treatment. In this work, a Ti–Mn stainless steel corrugated wire mesh (SSCWM) catalyst was prepared by the sol–gel method, which was used for the catalytic ozonation of biochemically treated leachate.RESULTSThe catalyst was characterized using scanning electron microscopy, energy dispersive X‐ray spectroscopy, X‐ray diffraction and X‐ray photoelectron spectroscopy techniques. The data showed that the chemical oxygen demand (COD) removal efficiency of the leachate by ozone alone, SSCWM/O3, Ti–SSCWM/O3 and Ti–Mn/SSCWM/O3 system reached 55.06%, 64.44%, 68.97% and 78.43%, respectively. The catalytic effect of different layers of Ti–Mn oxide‐coated SSCWM catalyst showed that two catalytic layers had the best activity of COD removal efficiency, reaching 87.17%, and the final COD reached the national emission standard (<100 mg L−1). At the same time, the results of fluorescence spectrum and gas chromatography–mass spectrometry (GC‐MS) analysis confirmed this point. The stability of the catalyst decreased with the increase in usage times, and the final COD removal efficiency was 73.91% after six cycles of use. To understand the reason for catalyst deactivation, the adsorbed organic matter on the catalyst surface was determined by GC‐MS analysis. In addition, COD removal of the catalyst can be increased to 80.55% after in situ regeneration of the mesh catalyst by a sequential cleaning process consisting of alkali–acid–hydrogen peroxide–ethanol–water.CONCLUSIONIn short, application of the mesh catalyst in catalytic ozonation can be considered as a promising method for wastewater treatment, because of avoidance of solid–liquid separation and easy regeneration of catalytic activity. © 2020 Society of Chemical Industry

Two advanced oxidation pathways of modified iron-shavings participation in ozonation

In this study, the performance of ozonation, catalytic ozonation and activation of molecular oxygen (AMO) process was examined with oxalate as the target refractory organics. Modified iron-shavings was used as catalyst for catalytic ozonation in degradation of oxalate at ambient temperature (25 ± 2 °C). Under catalytic ozonation, the removal of oxalate was as high as 90%, which was much better than ozone alone. Initial pH was a key factor affecting the mechanisms of oxalate degradation. In AMO process, with the existence of Fe (II) there occurred an inner-Fenton reaction, hydrogen peroxide (H2O2) was produced at initial pH2.27 and its concentration ranged from 120 to 200 μmol/L. Heterogeneous catalytic ozonation occurred in alkaline solution with hydroxyl radicals (·OH) production, which was indirectly oxidation instead of inner-Fenton reaction. Carbonate would be produced in alkaline solution during catalytic ozonation of oxalate which would in turn inhibit the process. Lepidocrocite (γ-FeOOH) was formed through the dissolved iron ions precipitation and considered as the main component of catalyst, which was confirmed via field emission scanning electron microscope with energy-dispersive spectrometer (SEM-EDS), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Hydroxyl radicals produced via different paths were detected out by electron paramagnetic resonance (EPR) and were considered as strong oxidant in catalytic ozonation and AMO process.

Role of Si[sbnd]F groups in enhancing interfacial reaction of Fe-MCM-41 for pollutant removal with ozone

Heterogeneous catalytic ozonation had met the bottlenecks when treating low concentration but high toxic pollutants: (i) the low mass transfer efficiency of ozone and pollutants to hydrophilic catalyst; (ii) the negative impact of coexisted water matrixes. Herein, to enhance the mass transfer efficiency of reactants toward hydrophilic Fe-MCM-41 as well as enhance the interfacial reaction, the fluoride planting Fe-MCM-41 (F-Fe-MCM-41) was synthesized and employed as catalyst in catalytic ozonation for nitrobenzene (NB). Both NB and TOC removal were promoted in F-Fe-MCM-41/O3 with 99.0 % NB removal in 60 min and 88.6 % TOC removal in 120 min, which were superior to the degradation efficiency by O3 and Fe-MCM-41/O3. FTIR, EPR, Mössbauer spectra, 29Si NMR, 19F NMR et al verified that the replacement of non-reactive silanols (-Si−OH) of Fe-MCM-41 with SiF groups could enhance its hydrophobicity, Lewis acidity and mass transfer effect. Comparative characterizations, experiments and theoretical calculations verified that interfacial reaction played the major role over liquid phase reaction for NB degradation in F-Fe-MCM-41/O3. Moreover, the strengthened interfacial reaction also reduced the OH scavenging effect of water matrix, such as humic acid and carbonate. The interfacial adjustment method proposed in this study provided a novel insight into catalyst design and water treatment process.

Catalytic Ozonation by Manganese, Iron and Cerium Oxides on γ-Al2O3 Pellets for the Degradation of Organic Pollutants in Continuous Fixed-Bed Reactor

ABSTRACTHeterogeneous catalytic ozonation is an efficient technology for degrading refractory organic pollutants in water. However, most studied heterogeneous catalysts for catalytic ozonation were powders, which were not practically available for continuous fixed-bed reactor in water treatment. In this work, manganese, iron and cerium oxides on γ-Al2O3 pellets were synthesized and used as heterogeneous catalysts for catalytic ozonation in a continuous fixed-bed reactor. Results showed that all the prepared metal oxides on γ-Al2O3 pellets exhibited facilitated catalytic ozonation for degrading refractory contaminates compared with ozonation alone and catalytic ozonation on pure γ-Al2O3 pellets. The cerium oxides supported on γ-Al2O3 pellets (CeO2/γ-Al2O3) performed best catalytic performance with the COD removal efficiency of 64.3% and TOC removal efficiency of 41.7%. Moreover, the catalytic activity was further enhanced by the synergistic effect of the bimetallic oxides on γ-Al2O3 pellets (CeO2-Fe2O3/γ-Al2O3). This study is expected to help to encourage further research and applications in AOPs based on the success of this work in designing heterogeneous catalysts available for continuous fixed-bed reactor.

Catalytic ozonation benefit from the enhancement of electron transfer by the coupling of g-C3N4 and LaCoO3: Discussion on catalyst fabrication and electron transfer pathway

In this study, the novel design approach of catalyst in catalytic ozonation was proposed to enhance electron transfer in catalytic ozonation, achieving a better performance on micro-pollutants degradation and bromate elimination. The combination of perovskite oxide (LaCoO3, LCO) and graphitic carbon nitride (g-C3N4, CN) was studied to overcome some significant drawbacks of catalytic ozonation with metal oxides catalysts, such as the rate-limiting step between Men+ and Me(n+m)+. Additionally, the in-depth analysis of electron transfer pathway in CN/LCO catalytic ozonation was provided, which provided new insight into the design of highly efficient catalysts for facilitating micro-pollutants degradation and bromate inhibition. CN/LCO was successfully prepared and connected by the formation of -C-O-Co linkages, which exhibited a high activity in the catalytic ozonation for the synchronous degradation of benzotriazole (BZA) and elimination of bromate. Interestingly, being different with the general mechanism of catalytic ozonation, nitrogen vacancies and -C-O-Co bonds were the main active sites in CN/LCO rather than the surface hydroxyl group. With the largest amount of -C-O-Co and more nitrogen defects, CN/LCO exhibited a fast charge transfer along the in-plane direction. Additionally, the fast reduction of Co3+ to Co2+ was found to be initialized by O2•− and single electrons in catalytic ozonation, which resulted in more formation of H2O2 and good inhibition efficiency of bromate. This study not only present the good catalytic ozonation ability for refractory organic micro-pollutants and elimination of bromate using CN/LCO, but also provided insight into electron transfer pathway in the interlayers of CN/LCO, which will be significant for the design of catalyst and to promote charge transfer in catalytic ozonation.

Insights into Heteroatom-Doped Graphene for Catalytic Ozonation: Active Centers, Reactive Oxygen Species Evolution, and Catalytic Mechanism.

To guide the design of novel graphene-based catalysts in catalytic ozonation for micropollutant degradation, the mechanism of catalytic ozonation with heteroatom-doped graphene was clarified. Reduced graphene oxide doped with nitrogen, phosphorus, boron, and sulfur atoms (N-, P-, B-, and S-rGO) were synthesized, and their catalytic ozonation performances were evaluated in the degradation of refractory organics and bromate elimination simultaneously. Doping with heteroatoms, except sulfur, significantly improved the catalytic ozonation activity of graphene. Introducing sulfur atoms destroyed the stability of graphene during ozonation, with the observed partial performance improvement caused by surface adsorption. Degradation pathways for selected refractory organics were proposed based on the intermediates identified using high-resolution Orbitrap mass spectroscopy and gas chromatographic-mass spectroscopy. Three and six new unopened intermediates were identified in benzotriazole and p-chlorobenzoic acid degradation, respectively. Roles of chemical functional groups, doped atoms, free electron, and delocalized π electron of heteroatom-doped graphene in catalytic ozonation were identified, and contributions of these active centers to the formation of reactive oxygen species (ROS), including hydroxyl radicals, superoxide radicals, singlet oxygen, and H2O2, were evaluated. A mechanism for catalytic ozonation by heteroatom-doped graphene was proposed for the first time.

Application of Heterogeneous Catalytic Ozonation for Refractory Organics in Wastewater

Catalytic ozonation is believed to belong to advanced oxidation processes (AOPs). Over the past decades, heterogeneous catalytic ozonation has received remarkable attention as an effective process for the degradation of refractory organics in wastewater, which can overcome some disadvantages of ozonation alone. Metal oxides, metals, and metal oxides supported on oxides, minerals modified with metals, and carbon materials are widely used as catalysts in heterogeneous catalytic ozonation processes due to their excellent catalytic ability. An understanding of the application can provide theoretical support for selecting suitable catalysts aimed at different kinds of wastewater to obtain higher pollutant removal efficiency. Therefore, the main objective of this review article is to provide a summary of the accomplishments concerning catalytic ozonation to point to the major directions for choosing the catalysts in catalytic ozonation in the future.