Ozonation Of Phenol Research Articles

CeMnOX catalysts for enhanced ozonation of phenol: Performance evaluation and mechanism investigation

CeMnOX catalysts for enhanced ozonation of phenol: Performance evaluation and mechanism investigation

Degradation of phenol with Mn-CoOX/γ-Al2O3 catalytic ozonation enhanced by high gravity technology

In this study, Mn-CoOX/γ-Al2O3 (MCA) was prepared by impregnation for catalytic ozonation of phenol in a rotating packed bed (RPB), and the effects of high gravity factor (β), liquid flow rate (QL), initial solution pH and gaseous ozone concentration (CO3) on the mineralization of phenol were explored. The results show that the degradation rate of phenol (ηphenol) reaches 100% at 9 min and the mineralization rate (ηTOC) reaches 95.01% at 45 min under conditions of β = 104, CO3= 80 mg L-1, QL = 80 L/h, and pH = 6. Compared with the bubbling reactor (BR)/MCA/O3 and O3/RPB systems, the ηTOC of the MCA/O3/RPB system is increased by 25.81% and 40.85%, respectively. The electron paramagnetic resonance (EPR) results reveal that hydroxyl radical (·OH) plays a critical role in the degradation of phenol by MCA catalyzed ozonation. The quenching experiment using tertiary butyl alcohol (TBA) as a scavenger of ·OH reveals that the ratio of direct and indirect degradation of phenol is 16:9. The intermediates generated during the degradation of phenol were detected by gas chromatography-mass spectrometry (GC–MS), and possible degradation pathways were proposed. In conclusion, MCA-catalyzed ozonation and RPB have a synergistic effect on ·OH initiation and improve the degradation and mineralization of phenol. This study provides a new perspective for the degradation of phenol.

Analysis of Reaction Kinetics of the Ozonation of Phenolic Compounds and Assessment of the Role of Mass Transfer in the Overall Rate

The ozonation technique for biorefractory phenolic wastewater is preferred as a clean technology. However, its effectiveness and successful implementation on the commercial scale is crucial. The understanding of the rate-determining step and reliable reaction kinetics is the essence to the design and scale-up of ozonation reactors. In the case of phenolic wastewater, it is found that both mass transfer and chemical reaction contribute to the overall reaction rates. However, the mass transfer resistance is often significant in studies that determine the ozonation rate constant. This has resulted in discrepancies in the reported values of the intrinsic reaction kinetic parameters, and such apparent rate constants cannot be useful for suitable reactor design. The aim of this work is to analyze past works on the reaction kinetics of the ozonation of phenol, chlorophenols, and nitrophenols and determine the role of mass transfer steps in the overall reaction rate. The value of the volumetric liquid-side mass transfer coefficient (kLa) is estimated from the overall observed rates using the theory of mass transfer with chemical reaction, and these are found to be appropriate for the reactor geometry used in the respective works. In this way, our appraisal of the literature has provided key insights, which are yet unfamiliar, and renders useful the large body of data published in the literature, which otherwise remains unutilized.

Hydrogen Peroxide Formation during Ozonation of Olefins and Phenol: Mechanistic Insights from Oxygen Isotope Signatures.

Mitigation of undesired byproducts from ozonation of dissolved organic matter (DOM) such as aldehydes and ketones is currently hampered by limited knowledge of their precursors and formation pathways. Here, the stable oxygen isotope composition of H2O2 formed simultaneously with these byproducts was studied to determine if it can reveal this missing information. A newly developed procedure, which quantitatively transforms H2O2 to O2 for subsequent 18O/16O ratio analysis, was used to determine the δ18O of H2O2 generated from ozonated model compounds (olefins and phenol, pH 3-8). A constant enrichment of 18O in H2O2 with a δ18O value of ∼59‰ implies that 16O-16O bonds are cleaved preferentially in the intermediate Criegee ozonide, which is commonly formed from olefins. H2O2 from the ozonation of acrylic acid and phenol at pH 7 resulted in lower 18O enrichment (δ18O = 47-49‰). For acrylic acid, enhancement of one of the two pathways followed by a carbonyl-H2O2 equilibrium was responsible for the smaller δ18O of H2O2. During phenol ozonation at pH 7, various competing reactions leading to H2O2 via an intermediate ozone adduct are hypothesized to cause lower δ18O in H2O2. These insights provide a first step toward supporting pH-dependent H2O2 precursor elucidation in DOM.

Heterogeneous catalytic ozonation for highly efficient mineralization of phenol with La-modified Ce/γ-Al<sub>2</sub>O<sub>3</sub>

In this study, La-Ce/γ-Al<sub>2</sub>O<sub>3</sub> materials for the catalytic ozonation of phenol were prepared by impregnation. In order to analyze the physicochemical properties, BET, SEM, XRD, XPS, and FTIR were used to characterize the catalysts. The removal performance of phenol under different reactive conditions (catalyst dosage, initial pH value, initial phenol concentration, and ozone concentration) was investigated, and the possible catalytic oxidation mechanism and conversion pathway of phenol were proposed through the analysis of ROS and intermediates in solution. The results indicated that the conversion rate of 2.5% La-Ce/γ-Al<sub>2</sub>O<sub>3</sub> increased by 20.53% within 20 min compared with ozonation alone. Moreover, the CO<sub>2</sub> mineralization rate was more than twice that of ozonation alone within 250 min, reaching 92.53%, and superior CO<sub>2</sub> mineralization was maintained after repeated use. The CO<sub>2</sub> mineralization rate of phenol after adding 3 g/L 2.5% La-Ce/γ-Al<sub>2</sub>O<sub>3</sub> catalyst reached almost 100%, and could be maintained in a solution with a wide pH range of 3~9.5. From the characterization results, it could be seen that the 2.5% La-Ce/γ-Al<sub>2</sub>O<sub>3</sub> catalyst obtained higher adsorbed oxygen and hydroxyl species content than γ-Al<sub>2</sub>O<sub>3</sub> and Ce/γ-Al<sub>2</sub>O<sub>3</sub>. In the process of phenol catalyzed ozonation, the •O<sub>2</sub>ˉ species in the solution were deduced to be the key ROS.

Catalytic ozonation of phenol by magnetic Mn0.7Ce0.3Ox/CNT@Fe3C

A high-efficient and stable catalyst is highly desired to catalyze ozone for refractory organic pollutants removal. In this work, Mn-Ce bimetallic oxide loaded CNT@Fe3C (Mn0.7Ce0.3Ox/CNT@Fe3C) was synthesized with Mn0.7Ce0.3Ox as the active component and magnetic CNT@Fe3C as the support. The catalytic performance of Mn0.7Ce0.3Ox/CNT@Fe3C towards catalytic ozonation was evaluated. The TOC removal efficiency of phenol degradation after 45 min of reaction was 98%, which was 1.5 times and 1.8 times that of monometallic CeO2/CNT@Fe3C (65%) and MnxOy/CNT@Fe3C (54%), respectively. The synthesized-Mn0.7Ce0.3Ox/CNT@Fe3C possessed good reusability during five successive cycles and remained efficient over a wide range of pH 4.2–8.3. The results of EPR measurements and quenching experiments demonstrated that hydroxyl radicals (·OH) were the dominant reactive oxidation species (ROS) for phenol mineralization in the Mn0.7Ce0.3Ox/CNT@Fe3C/O3 system. Moreover, the magnetic Mn0.7Ce0.3Ox/CNT@Fe3C is easily recovered and reused.

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.

Preparation of SnOx-MnOx@Al2O3 for Catalytic Ozonation of Phenol in Hypersaline Wastewater

ABSTRACT The catalytic ozonation process (COP) is an effective and advanced oxidation technology for the treatment of organic wastewater. However, high salinity has a negative impact on catalytic ozonation performance. In this work, tin oxide (SnOx) and manganese oxide (MnOx) doped γ-Al2O3 catalysts (SnOx-MnOx@Al2O3) were prepared by the incipient wetness impregnation method and characterized by SEM, XRD, BET, XRT, XPS and FT-IR techniques. The SnOx-MnOx@Al2O3 catalyst was applied to the catalytic ozonation of phenol in hypersaline wastewater, and the catalytic performance was evaluated by COD removal efficiency. When the mass ratio of MnOx to SnOx was 1:3, the pH was 7, the catalyst dosage was 40 g/L, the ozone dosage was 6 mg/(L·min), the NaCl concentration was 15 g/L and the COD removal efficiency of hypersaline phenol wastewater reached 93.8% after 240 min of catalytic ozonation treatment. Compared with the single ozonation process (SOP), the introduction of SnOx-MnOx@Al2O3 catalyst improved the COD removal efficiency by 32.3%. Cl− may quench surface •OH species and ozone to form Cl• and Cl2•− with low activity and high selectivity, resulting in the reduction of catalytic ozonation efficiency. The catalytic activity of the SnOx-MnOx@Al2O3 catalyst remained high after eight cycles. In conclusion, the SnOx-MnOx@Al2O3 catalytic ozonation system exhibits efficient and stable mineralization performance and is a promising strategy for the treatment of hypersaline organic wastewater.

Phenol Removal Performance and Mechanism Using Catalytic Ozonation with the Catalyst of Cobalt-doped α-MnO2

In this paper, Cobalt-doped α-MnO2 (i.e., Co-α-MnO2) were synthesized through hydrothermal method. Phenol was employed as targeted pollutants to investigate the catalytic ozonation performance of Co-α-MnO2. Results showed that Co-α-MnO2 significantly improved the phenol removal increased to 97.47 % after 40 min, which was 16.46 %, 38.92 % higher than that of α-MnO2 catalytic ozonation and single ozonation without catalyst. Additionally, the physicochemical properties of α-MnO2 and Co-α-MnO2 were analyzed using technologies such as XRD, TEM, BET and XPS. Compared to α-MnO2, Co-α-MnO2 has larger specific surface area (79.496 m2/g) and pore volume (0.0396 cm3/g), higher Mn3+ relative content (41.16 %) and adsorbed oxygen content (18.99 %). Also, the oxygen vacancy content, lattice defect content and surface hydroxyl content of Co-α-MnO2 are higher than that of α-MnO2, which could result in higher catalytic oxidation performance of Co-α-MnO2. The influence of masking agent showed that surface hydroxyl group, •OH and •O2- were involved in the catalytic ozonation of phenol. This study could help recognize the role of surface hydroxyl groups and active free radicals and demonstrate the contribution of reactive oxygen species on phenol removal in Co-α-MnO2 systems.

Ozonation of phenol in the presence of biochar and carbonaceous materials: The effect of surface functional groups and graphitic structure on the formation of reactive oxygen species

To develop a novel oxidation process using ozone and carbonaceous materials for water treatment and groundwater remediation, the effect of carbonaceous materials on the ozonation of phenol was investigated via batch experiments. Anode carbonaceous material (ACM) recovered from spent Li-ion batteries, graphite, granular activated carbon (GAC), and rice straw-derived biochar were evaluated as catalysts to enhance the ozonation of phenol. Compared with direct ozonation (28% removal in 2 h), the addition of carbonaceous materials enhanced the oxidation of phenol by ozone, showing 47%, 45%, 81%, and 74% removal with ACM, graphite, GAC, and biochar, respectively. According to the quenching experiments with chemical reagents and electron paramagnetic resonance analysis, reactive oxygen species, such as hydroxyl radicals (·OH), superoxide radicals (O2·-), and singlet oxygen (1O2), as well as electron transfer in the mediated-reaction, are included in the ozonation of phenol in the presence of carbonaceous materials. The oxygen-containing surface functional groups and graphitic structure are responsible for the reactive oxygen species and electron transfer reactions, respectively. Our results suggest that carbonaceous materials may be effectively used as catalysts to promote the ozonation of recalcitrant contaminants in water.

Ozonation of phenol and substituted phenols: Dependency of the reaction rate constant on the molecular structure

AbstractOzonation is a prospective method for the treatment of phenol‐contaminated wastewaters. In the present work, the reaction of ozone with 10 different substituted phenols was studied at acidic pH in two model gas–liquid contactors to investigate the dependency of the ozonation rate constant on the molecular structure of the phenolic compound. While three phenols were attached to electron‐donating functional groups, seven were characterized by the presence of electron‐accepting groups in their structure. In a stirred cell reactor (with flat‐cell interface) and mechanically agitated contactor, reaction kinetics for these two types of phenols were studied in the fast pseudo‐first order and chemical reaction controlled regime, correspondingly at T = 30°C. The effect of the electron‐donating or electron‐accepting functional group attached to the phenolic ring on the reactivity was studied and the linear dependence of the relative oxidation rate constant (with respect to phenol) on the Hammett substituent constant was proven in a Hammett plot. The values of susceptibility factor for the Hammett plots of phenols with electron‐donating and electron‐accepting substituents were −7.89 and −1.25, respectively. This work is useful to establish the ozonation pathway and predict the reaction rate constant from the molecular structure of the phenolic compound.

Heterogeneous Catalytic Ozonation of Phenol by a Novel Binary Catalyst of Fe-Ni/MAC

Iron-nickel supported on modified active carbon (Fe-Ni/MAC) was prepared and characterized by XRD, SEM, XPS and EDS, followed by evaluating the practicability of Fe-Ni/MAC in treating real wastewater with a high concentration of phenol. Results showed that the optimal conditions for catalytic ozonation obtained by response surface methodology (RSM) were catalyst 10 g/L, ozone 68 mg/L, pH 9 and reaction time 90 min. Fe-Ni alloy and NiFe2O4 were demonstrated to be the dominant active species involved in catalytic reaction. The Fe-Ni/MAC catalyst can be reused six times with a satisfactory performance and little leaching of metal ions. Although some radicals like ·OH and ·O2− functioned well, singlet oxygen (1O2) was regarded as the most important radical in the Fe-Ni/MAC process. Most noticeably, the fluorescence excitation emission matrices (EEMs) certified that as much as 1243 mg/L phenol in the real wastewater was completely degraded, which made Fe-Ni/MAC a fairly practical catalyst.

γ-Al2O3 doped with cerium to enhance electron transfer in catalytic ozonation of phenol

Ozone decomposition into free radicals, which can be facilitated by enhancing electron transfer between ozone and catalyst, is an important segment in catalytic ozonation. We doped cerium uniformly on γ-Al2O3 with an impregnation–calcination method to enhance electron transfer in catalytic ozonation of phenol in aqueous solution. The removal efficiency of phenol is raised from 39.7% by ozonation alone to 46.3% by catalytic ozonation with Ce/Al2O3 in 50 min reaction. A higher Ce3+/Ce4+ ratio in Ce/Al2O3 witnesses a higher electron transfer rate in catalytic ozonation and thus a higher degradation efficiency of phenol, illustrating that the activity of Ce/Al2O3 depends on the valence state of Ce. The electron transfer cycle is formed by the electron donation from Ce3+ to ozone molecule and the electron acceptance of Ce4+ from adjacent lattice oxygen. After getting the electron, the ozone molecule is decomposed to generate free radical of ·OH on the surface of Ce/Al2O3. The continuous flow experiments exhibit a stable and high catalytic activity of Ce/Al2O3 for catalytic ozonation, implying the feasibility in practical application.

Efficient degradation of phenol in aqueous solution by catalytic ozonation over MgO/AC

Phenol is one of the most common and poisonous water pollutants. Treating phenol-containing wastewater has been a challenge in recent years. MgO/Activated Carbon (AC) composites were prepared by the equal volume impregnation method for catalytic ozonation of phenol in water. MgO/AC composites were characterized by ICP, IR, XRD, SEM, TEM, BET and XPS analysis. MgO incorporated in the form of nano-crystal particles on the surface of AC. Prepared MgO/AC shows good catalytic performance for the removal of phenol and COD. Catalyst loading, pH and initial concentration of phenol solution on catalytic ozonation performance were studied. The catalytic performance of AC was significantly improved by the modification with a few amount of MgO. The results showed MgO provides additional active sites for the generation of hydroxyl radicals which is favorable for degradation of organic contaminants. The intermediate products were determined and the possible degradation pathway was put forward. MgO/AC shows a promising way to prepare efficient catalysts for the catalytic ozonation of organic polluted water.

Catalytic ozonation of phenol enhanced by mesoporous MnO2 prepared through nanocasting method with SBA-15 as template

Abstract A mesoporous MnO2 (M-MnO2) was prepared by nanocasting method with SBA-15 as the hard template, and was investigated as an ozonation catalyst. The composition and morphology of the as-prepared MnO2 were characterized using X-ray diffraction analysis, transmission electron microscopy and surface area analysis. The ordered nanorods with high surface area (100 m2g−1) helped the mass transport and the active sites exposed, and thus enhanced the efficiency of catalytic ozonation. The adsorption capacity of M-MnO2 on phenol was about 8 times as high as that of the control MnO2 (C-MnO2) calculated by the Langmuir adsorption model(10.47 mgg−1vs 1.20 mgg−1). Hydroxyl radical was identified as the main reactive oxygen species, and the hydroxyl radical yield from M-MnO2 is about 2-fold enhanced compared with that from C-MnO2. Benefiting from the high mass transport and abundant active sites exposed, the TOC removal of phenol catalyzed by M-MnO2 (35%) was much better than that by C-MnO2(27%)in 30 minutes.

Heterogeneous Catalytic Ozonation of Phenol over Iron-based Catalysts in a Trickle Bed Reactor

The use of continuous reactors for heterogeneous catalytic ozonation is yet to be investigated in order to develop a viable technology for industrial applications. This paper presents hydrodynamic and degradation studies on the use of a co-current down flow trickle bed reactor for heterogeneous catalytic ozonation of phenol (as model pollutant) over Fe-Diatomite pellets and Fe-coated glass beads. It was found that the reactor can operate under trickle or pulsing flow regimes, promoting mass transfer augmentation. Residence time distribution data, fitted with n-CSTR and axial dispersion (ADM) models, showed low axial dispersion and high flow distribution. Just the Fe-diatomite pellets showed important phenol adsorption (16 %). Degradation experiments demonstrated that phenol conversion was substantial when using both catalysts, up to 19,7 % pollutant conversion with liquid-phase space times of just 6 s. Compared to direct ozonation, the use of the Fe-diatomite pellets and Fe-coated glass beads enhanced the reactor performance by 48 % and 23 %, respectively. It was confirmed that mass transfer is an important factor that restricts this reaction system performance; consequently, further improvement in mass transport rate is necessary for system optimization.

Analysis of the effect of the operational conditions in a combined adsorption–ozonation process with granular activated carbon for the treatment of phenol wastewater

Analysis of phenol ozonation using a G–L–S model: through mass transfer, chemical reaction and adsorption parameters.

Enhanced Photocatalytic Ozonation of Phenol by Ag/ZnO Nanocomposites

Ag/ZnO nanocomposites were synthesized and applied in the photocatalytic ozonation of phenol. Their crystal, textural, morphological, optical, and electrochemical properties were investigated by XRD, Raman, SEM, TEM, UV–Vis diffuse reflectance spectroscopy (DRS), X-ray photoemission spectroscopy (XPS), and photoluminescence (PL) techniques in detail. The results indicated that silver nanoparticles were well dispersed on the surface of porous ZnO and the intimate contacts were formed at the Ag/ZnO interfaces. This prominently favored the separation and transfer of photoinduced electrons from ZnO to Ag nanoparticles for the activation of ozone to produce •OH and •O2−. As a result, a significant enhancement in photocatalytic ozonation of phenol was achieved over Ag/ZnO catalysts. It also showed a synergistic effect between photocatalysis and ozonation.

Degradation Pathway of Ozone Oxidation of Phenols and Chlorophenols as Followed by LC-MS-TOF

ABSTRACT This contribution summarizes the temporal intermediates produced during the ozonation of phenol, 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol, as followed by liquid chromatography coupled to a time of flight mass spectrometer (LC-MS-TOF). A 2 × 10−3 M solution of the phenolic compounds was ozonated in a sintered glass reactor at an ozone dose of 0.14 mg/min (O2/O3 flow 10 mL/min). Identified intermediates showed that catechol pathway was the predominant route for phenol oxidation with acrylic acid being the end product. Hydroxylative dechlorination of 2-chlorophenol also gave catechol, and the reaction products were similar to that of phenol. Hydroxylation and ring opening via the 4-chlorocatechol pathways were the predominant route for the ozonation of 4-chlorophenol, while 2,4-dichlorophenol followed both hydroxylation and hydroxylative dechlorination mechanism. Several novel intermediates and coupling products were identified and reaction schemes leading to breakdown products are provided for each phenolic compound.

Ozonation catalyzed by iron- and/or manganese-supported granular activated carbons for the treatment of phenol

Iron- and/or manganese-supported catalysts on granular activated carbons (Fe and/or Mn/GACs) were prepared, and their catalytic activities were evaluated by using them to treat phenol and secondary petrochemical effluent via ozonation. The presence of Fe and/or Mn/GACs significantly improved the degradation and degree of phenol mineralization. Changes in dissolved ozone concentrations and the effects of carbonate and tert-butyl alcohol (TBA) indicated that the prepared catalyst enhanced the decomposition of ozone into hydroxyl radicals (·OH), which was determined to be a key factor in catalyzing the ozonation of phenol. Typical intermediate products were identified by GC-MS and HPLC analysis, and a possible degradation pathway of phenol via catalytic ozonation was proposed. The results of XPS, CV, and other experimental data indicated that introducing Fe and/or Mn increased the rate of ozone decomposition into ·OH, and also enhanced the interfacial electron transfer by Fe2+-Fe3+ and Mn2+-Mn3+-Mn4+ redox cycles, resulting in higher catalytic activity. However, the Fe-Mn/GAC surface was shown to undergo galvanic corrosion between Fe3O4 and MnO2, decreasing the catalytic activity. In addition, catalytic ozonation was used to treat secondary petrochemical effluent. The results demonstrated that the Mn/GAC/O3 system significantly improved the quality of phenol-containing wastewater in terms of its COD, TOC, NH4+-N, water color, and ecotoxicity. This study gives a better understanding of the phenol treatment by catalytic ozonation using Fe and/or Mn/GAC.