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Article

Ozone Catalysis Degradation of Sodium Acetate via Vacancy-Driven Radical Oxidation over Fe-Modified Fly Ash

by
Yaoji Chen
1,
Ruifu Chen
2,
Xinglan Chang
1,
Jingying Yan
1,
Yajie Gu
1,
Shuang Xi
1,
Pengfei Sun
2,* and
Xiaoping Dong
2
1
Zhejiang Tiandi Environmental Protection Technology Co., Ltd., 2159-1 Yuhangtang Road, Hangzhou 311199, China
2
Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, School of Chemistry and Chemical Engineering, Zhejiang Sci-Tech University, 928 Second Avenue, Xiasha Higher Education Zone, Hangzhou 310018, China
*
Author to whom correspondence should be addressed.
Water 2023, 15(21), 3801; https://doi.org/10.3390/w15213801
Submission received: 11 September 2023 / Revised: 14 October 2023 / Accepted: 16 October 2023 / Published: 30 October 2023
(This article belongs to the Special Issue Advances in Wastewater Resourcezation)
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Abstract

:
In order to realize the high value-added reuse of coal fly ash, a reusable Fe-modified fly ash catalyst was synthesized for ozone catalysis degradation of chemical oxygen demand (COD) in wastewater. Through enhancement of the pretreatment procedure and FeOx modification, the resulting fly ash with Fe modification demonstrated increased specific surface area and porosity. The presence of Fe loading significantly enhances the reactivity of surface oxidizing reactive species, particularly oxygen vacancy, leading to improved adsorption and activation properties towards ozone molecules. Sodium acetate is chosen as a probe for contaminants due to its status as a small organic substance that remains resistant to further direct oxidation by ozone. This makes it suitable for evaluating the catalyst’s effectiveness in degrading chemical oxygen demand (COD). The quantitative detection of free radicals revealed the generation of •O2− was nearly 10 times that of •OH and dominated the reaction. This study showcases the potential of fly ash, an industrial byproduct, to be utilized as a cost-effective and easily prepared catalyst with consistent physical and chemical characteristics.

1. Introduction

Fly ash is a pozzolanic mixture resulting from the combustion of coal at temperatures between 650 and 800 °C [1,2]. The significant buildup of fly ash in prominent power plants has emerged as a concern for the nearby ecosystem and public well-being. In order to reduce the problems caused by its storage, fly ash has been intensively investigated as a starting material in different fields of research. In recent years, some environmentally functional materials modified by fly ash have received increasing attention. Particular attention has been given to the development of effective adsorption materials, oxidizing catalysts, and novel advanced oxidation processes (AOP) technology using fly ash-modified materials for addressing water pollutants such as organic dyes, antibiotics, heavy metals, nitrogen, and phosphorus contaminants [3,4].
Fly ash is mainly composed of microspheres containing SiO2 and Al2O3, accounting for 60~80% of the total composition [5]. While the surface of fly ash has already undergone passivation to form mullite and quartz at high temperatures, there is still potential for further exploration of its physical and chemical properties to enhance modification [6]. For instance, treating fly ash with NaOH has been found to increase its specific surface area, resulting in improved adsorption performance for cadmium in water. The maximum recorded adsorption capacities ranged from 9.18 mg/g to 48.5 mg/g [7]. Additionally, utilizing pretreated fly ash as a source of silicon and aluminum has garnered attention for catalyst synthesis, offering a means to reduce fly ash disposal by transforming it into valuable products. For instance, fly ash was utilized as a carrier for the incorporation of CoFe2O4 to form a nanocomposite. This composite exhibited exceptional efficiency as a Fenton-like catalyst in treating wastewater from polymer-flooding processes [8]. Through meticulous optimization of reaction conditions, an impressive removal rate of 70.3% for polyacrylamide was attained. Fe3O4 was also deposited on fly ash and used as a catalyst for the Fenton reaction in the treatment of stabilized landfill leachate [9]. It was witnessed that fly ash-augmented Fe3O4 exhibited 84.7% of COD degradation at optimum pH 3, 0.05 M H2O2 and 1000 mg/L of catalyst and also showed 68% of total organic carbon (TOC) removal and good increment in biodegradability. In addition, different kinds of mesoporous zeolites can also be synthesized with fly ash as the silicon and aluminum source [10,11]. Some heterogeneous catalysts were prepared with the use of high-cost commercial zeolites, like SBA-15, MCM-41, or ZSM-5, as the supports and applied in a variety of wastewater treatment processes [12,13,14]. By using fly ash to synthesize molecular sieves and introducing some metal oxides as catalytic active centers, the cost of the water treatment reaction can be greatly reduced.
Catalytic ozone oxidation is a typical AOP that has received increasing attention in recent decades [15,16]. Different kinds of metal catalyst, including MnO2, Fe2O3, Al2O3 and MgO, for catalytic ozonation have been reported to display both catalytic activity and superb degradation efficiency for organic pollutants in water [17,18,19,20]. However, due to their low specific surface areas and adsorption capacity, their catalytic efficiency and decontamination effectiveness were inevitably disturbed in practical application. In the course of ozone catalytic oxidation, pollutants are eliminated through the direct oxidation of ozone in water, as well as via the oxidation process triggered by reactive oxygen species (ROS) generated from ozone activation at the catalyst’s active site [21]. Consequently, incorporating metal oxide as the active component in supported ozone catalysts imparts not only superior activity and stability but also cost-effectiveness.
In order to optimize the utilization of fly ash generated from power plants, this study investigates the modification of fly ash and its preparation as a catalytic material for environmental wastewater treatment. A series of catalysts loaded with iron oxide were synthesized using fly ash as the support material to investigate the process of ozone-catalyzed oxidation. To evaluate the effectiveness of the catalyst in degrading chemical oxygen demand (COD), CH3COONa was chosen as a contaminant probe. This is because CH3COONa is difficult to direct decomposition by ozone, and it is one of the end products of ozone oxidation of most organic pollutants [22]. The structural properties of pretreated fly ash and Fe-modified samples were characterized using techniques such as SEM, XRD, XPS, ESR, ICP, and TEM. Different reaction parameters were adjusted to evaluate their effects on ozone catalytic performance. This study showcases the potential of repurposing fly ash, an industrial waste, as a reliable and effective catalyst for ozone generation. This finding presents a novel avenue for further exploration in the field of wastewater treatment.

2. Experimental

2.1. Pretreatment of Fly Ash

The fly ash was sourced from the Zhoushan Power Plant of China’s National Energy Group. Initially, it underwent immersion in a 1.2 mol/L HCl solution and agitation at a temperature of 85 °C for a duration of 2 h. Subsequently, it was rinsed with deionized water until neutralization occurred. Following drying at 50 °C, the resulting sample underwent thermal treatment at 90 °C using a hydrothermal kettle containing a 5 mol/L NaOH solution for a period of 15 h and was designated as CFA.

2.2. Synthesis of Fe-Modified Fly Ash

The CFA was impregnated with iron oxide (at mass ratios of 4%, 8%, and 12%) using a commonly reported wet impregnation method [23]. Ferric nitrate (purchased from Aladdin Biochemical Technology Co., Ltd., Shanghai, China) and CFA were accurately measured, mixed in deionized water, and continuously stirred for 5 h. The mixture was then dried at 90 °C for 10 h and calcinated at 400 °C. The resulting catalysts were labeled as Fex/CFA, where x represented the respective values of 0.04, 0.08, and 0.12.

2.3. Characterization

An X-ray powder diffractometer (XRD, Haoyuan DX-2700, Dandong, China) with Cu Ka radiation (35 kV, 25 mA) was utilized to measure the wide-angle X-Ray Diffraction patterns of various CFA samples. A scanning electron microscope (SEM, Hitachi SU-8100, Tokyo, Japan) was employed for observing and recording the morphology. Additionally, the microstructure of the Fex/CFA surface was further examined using a transmission electron microscope (TEM, JEM 2100, Tokyo, Japan). Nitrogen adsorption–desorption isotherms were analyzed using an ASAP 2020 analyzer (Micromeritics, Norcross, GA, USA). The specific surface area and pore size distribution were determined through the application of Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) methods. A Kratos AXIS Ultra DLD spectrometer equipped with Al Ka X-rays was used for measuring X-ray photoelectron spectroscopy (XPS). Inductively Coupled Plasma Emission Spectra (ICP-OES) were obtained by employing an iCAP PRO XP ICP-OES emission spectrometer from Thermo Scientific (Waltham, MA, USA). Electron paramagnetic resonance spectroscopy measurements were conducted utilizing a A300 EPR spectrometer (Bruker, Karlsruhe, Germany).

2.4. Catalytic Ozonation Reaction

Ozone was produced from oxygen with a high level of purity at 99.9% using an ozone generator (M-1000, Tonglin, Beijing, China) in the laboratory. The ozone was introduced into a specially designed reactor through a porous titanium aerator at a concentration of 24~60 mg/L, and its concentration was determined using the sodium indigo disulphonate method. A solution of CH3COONa (100~250 mg/L), measuring 600 mL, was added to the reactor along with a catalyst dosage ranging from 1 to 5 g/L. The pH level was adjusted by adding either NaOH or HCl solution at a concentration of 0.1 mol/L. During the catalytic ozonation process, samples were collected at specific time intervals totaling 4.0 mL each and subsequently filtered using an inorganic filter membrane that had a thickness of 0.45 μm. To immediately neutralize any remaining ozone, a solution containing Na2S2O3 at a concentration of 0.01 mol/L was added. The elimination rate of sodium acetate was determined by employing a chemical oxygen demand (COD) tester (COD-571, Leici, Shanghai, China).

2.5. Reactive Species Detection

Nitro blue tetrazolium chloride (NBT) can react with •O2−, and the formation of •O2− is detected by ultraviolet visible spectrophotometry. The specific steps are as follows: add 1.8 g of catalyst to NBT solution (4.2 × 10−5 mol/L), stir in oxygen for 60 min to achieve adsorption equilibrium, and then inject ozone. Take 4.0 mL of liquid at regular intervals and take the upper clear liquid after centrifugation. Use the ultraviolet visible spectrophotometer Sodnm (Shimadzu UV-2600, Tokyo, Japan) to record the change in its concentration at 259 nm.
Terephthalic acid (TA) can react with •OH to generate 2-hydroxyterephthalic acid (TAOH) with high fluorescence intensity. With 315 nm as the excitation wavelength, the generation of TAOH can be detected by fluorescence spectrophotometry, so that the generation of •OH in solution can be monitored. The specific operation steps were as follows: 1.8 g of catalyst was dispersed in 600 mL of solution containing 2.0 mmol/L NaOH and 2.0 mmol/L TA, the solution was stirred under oxygen for 60 min to achieve adsorption equilibrium, ozone was injected, 4.0 mL liquid was extracted at intervals, and the upper clear liquid was taken after centrifugation. A fluorescence spectrophotometer (HORIBA Fluorax-4, Tokyo, Japan) was used to measure the fluorescence intensity. Fluorescence conditions were excitation wavelength 315 nm and slit width 2 nm.

3. Results and Discussion

3.1. Enhancing the Degradation of CH3COONa through Catalytic Ozonation

CH3COONa is one of the end products of ozone oxidation of most organic pollutants [22], and has been used as a contaminant probe to evaluate the application prospects of fly ash-modified catalyst in ozone-catalyzed oxidative degradation of COD. Figure 1 exhibits the catalytic ozonation performance of CH3COONa degradation over different Fe modified fly ash catalysts. A certain reduction in CH3COONa is observed under conditions with only fly ash and ozone, which could be caused by the adsorption effect over the fly ash surface as proved by the SBET, Vtotal, and pore size of pretreated fly ash being 59.64 m2/g, 0.13 cm3/g, and 12.76 nm, respectively (see Table 1). When only ozone and CH3COONa were present in the reaction process, the elimination efficiency of acetic acid was inconspicuous, indicating that CH3COONa, the end product of ozone oxidation, was resistant to further direct decomposition by ozone. After addition of different Fe-modified fly ashes as catalysts, the removal rate of CH3COONa could be improved by a maximum of 53.3% over the Fe0.08/CFA catalyst.

3.2. Structure Characterization of Fe-Modified Fly Ash

The XRD patterns of pretreated fly ash and different Fe-modified fly ash catalysts are shown in Figure 2 and all display the characteristic peaks of mullite (2 theta at 16.4°, 20.8°, 25.9°, 30.7°, 33.0°, 35.2°, 40.8°, 42.4°, and 60.6°) and quartz (2 theta at 26.1° 39.2°, 53.5°, 56.8°, and 63.7°) [9]. For catalysts Fe0.04/CFA, Fe0.08/CFA, and Fe0.12/CFA, 2 theta at 29.7° can be attributed to the (122) crystal plane of η-Fe2O3 (JCPDS No. 21-0920) [24]. Only one iron oxide diffraction peak appears, which should be due to the small loading and highly dispersed iron oxide. As observed in Figure 3’s EDX-mapping, the sample of Fe0.08/CFA reveals the uniform dispersion of Fe element consistent with that of Si, Al, and Na elements, proving that iron oxide has been successfully loaded over the surface and irregular pore structure of fly ash.
TEM was also conducted fto investigate the surface structure of the loaded iron oxide. As depicted in Figure 4, the absence of iron oxide agglomeration suggests its effective dispersion throughout the fly ash. The observed lattice spacing values of 0.324 nm and 0.272 nm were identified as corresponding to the (022) and (024) crystal planes of Fe2O3 [25,26], indicating the presence of amorphous iron oxide formation. All of the iron-loaded fly ash samples were also tested for their actual iron content by ICP. As listed in Table 1, there is little difference between the actual iron content and the theoretical iron content, which means the above synthetic method is feasible. In addition, the fly ash itself (CFA) also has a number of impurities, which derive from metal impurities, including Ca, Mg, Fe, etc. The contents of these impurities were greatly weakened by pretreatment of fly ash by acidification and alkalinization.
XPS analyses were also conducted to investigate the surface element state over different Fe-modified samples. As shown in Figure 5A, all of the Fe-modified samples exhibit a peak at a binding energy of ca.720 eV ascribed to Fe 2p compared with the CFA sample [24], indicating the existence of surface iron oxide. In Figure 5B,C, the Fe 2p and O 1s spectra were subjected to deconvolution using a Gaussian peaks fitting technique following Shirley background subtraction. For spectra of Fe 2p, the peaks of Fe 2p3/2 and Fe 2p1/2 were located at 711 eV and 725 eV, respectively, and the binding energy peaks at 711.1 eV and 713.0 were attributed to Fe(II) and Fe(III) species [24,25,26]. The O 1s spectra can be divided into three peaks at ranges of 529.8~530.3 eV, 530.8~531.3 eV, and 532.0~532.5 eV, ascribed to lattice oxygen (Olat) [27], surface chemisorbed oxygen (Osur)-like OH−, O2−, CO32−, oxygen vacancy (OV) [28], and the surface-adsorbed oxygen-like adsorbed water species [29], respectively.
It can be judged from Table 1, that the change in Fe2+/Fe3+ and Osur is consistent with the increase in Fe content. When the Fe content increased from 4 wt% to 8 wt%, the ratio of Fe2+/Fe3+ also increased from 0.85 to 0.88. As reported in a previous study [30], Fe2+ could provide electrons for the decomposition of O3 and be transformed into Fe3+. A higher redox reaction of Fe2+/Fe3+ could maintain the electrostatic equilibrium of the catalyst surface and improve the performance of ozone catalytic oxidation [31,32]. At this time, we can also find that the Fe0.08/CFA sample has the maximum amount of Osur. During the ozone catalysis process, the oxygen vacancy derived from Osur plays an important role in converting the absorbed O3 into •O2− and •OH [28], which then further decompose the organic content of water. The ESR spectra in Figure 6 confirm that the Fe0.08/CFA sample exhibits the strongest oxygen vacancy strength among all of the Fe-modified catalysts, with a pair of steep peaks in accordance with g = 2.002, an indication of electron trapping at oxygen vacancies [33]. Thus, the better CH3COONa degradation performance of Fe0.08/CFA exhibited in Figure 1 could be mainly due to the above two reasons.
For the Fe0.12/CFA sample, the change in Fe2+/Fe3+ and Osur began to decrease with a further increase in Fe content. However, there was a certain degree of improvement in Olat. This could be caused by excessive Fe loading, leading to particle clustering and decreased dispersion over the surface of fly ash, which thus caused more bulk phase lattice oxygen to be produced at the surface due to metal clusters. The significantly decreased SBET and pore size of Fe0.12/CFA compared with that of Fe0.04/CFA and Fe0.08/CFA also implies that a large number of iron oxide clusters may accumulate in the surface channel of CFA.

3.3. Effect of Reaction Parameters on the Degradation Efficiency of CH3COONa

The Fe0.08/CFA was selected as the best catalyst for ozone-catalyzed oxidation of CH3COONa to investigate the effects of different reaction parameters on performance. As shown in Figure 7A, the CH3COONa removal efficiencies obtained after 60 min at ozone dosages of 24, 37, 50, and 60 mg/L were equal to 45.2%, 49.8%, 53.3%, and 53.1%, respectively. It can be found that the CH3COONa-removal efficiency of Fe0.08/CFA increases with an increase in the ozone dosage from 24 to 50 mg/L and then stabilizes at an ozone dosage of 60 mg/L. The degradation of CH3COONa required ozone adsorption onto the catalyst surface and further activation to form effective free radicals to decompose CH3COONa [34]. When the ozone concentration was increased to 60 mg/L, the ozone adsorption and deionization over the surface of Fe0.08/CFA could be considered to reach dynamic equilibrium, and the oxidation-active species formed from ozone for the oxidation of CH3COONa would not increase further. Therefore, the ozone concentration of 50 mg/L was selected to further investigate the influence of Fe0.08/CFA dosage. Figure 7B reveals that the catalyst Fe0.08/CFA, at a concentration of 3.0 g/L, has a CH3COONa-removal efficiency of 53.3% in 60 min, much higher than Fe0.08/CFA at a concentration of 1.0 g/L. When the ozone-oxidizing agent was sufficient, increasing the catalyst dosage could increase the number of catalytic active sites, resulting in the generation of more oxidation-active species and improved CH3COONa-removal efficiency. However, when the Fe0.08/CFA dosage exceeded the optimal value, the extra active sites to be reacted are invalid. Thus, Fe0.08/CFA at a dosage of 5.0 g/L did not result in better CH3COONa-removal efficiency.
The influence of different initial CH3COONa concentrations on the performance of Fe0.08/CFA was also studied. As shown in Figure 7C, the removal efficiencies of CH3COONa achieved after 60 min at initial concentrations of 100, 150, 200, and 250 mg/L are equal to 58.1%, 53.3%, 45.3%, and 36.5%, respectively. The higher removal rates observed at lower CH3COONa concentrations are due to higher ratios of oxidation-active species (like •O2− or •OH) to CH3COONa molecules (that is, the probability of collision of each CH3COONa molecule with •O2− or •OH species is increased with decreasing CH3COONa content) [24]. On the other hand, the increased CH3COONa concentration will also result in competitive adsorption with the dissolved ozone, which thus limits the generation of oxidation-active species and restricts the degradation of CH3COONa [35].
The solution’s pH is regarded as a crucial element that impacts the ozone catalytic process, exerting a significant influence on the routes of ozone reaction. As shown in Figure 7D, the performance of Fe0.08/CFA is obviously suppressed in acidic and alkaline circumstances. The removal efficiency of CH3COONa decreased to 26.7% and 42.2% with pH values at 5.0 and 11.0, respectively. In an acidic environment, ozone molecules have a tendency to react selectively with organic matter containing specific functional groups, such as electrophilic groups, nucleophilic groups, and to take part in dipolar addition reactions in acid solution [36]. This will affect the adsorption efficiency of ozone on the catalyst surface and its further dissociation to form active free radicals such as •O2− or •OH [37]. On the contrary, the suppressed performance of Fe0.08/CFA at pH = 11.0 also suggests that the excess hydroxide in solution will cause insoluble iron hydroxide formation from the loaded Fe ions [9,24], which covers the catalyst surface and reduces the number of active sites. When the pH value was 7 or 9, that the degradation efficiency of CH3COONa was not significantly affected, indicating that the synthesized Fe0.08/CFA has good applicability over a wide pH range on either side of the neutral condition.

3.4. Reaction Mechanism Study

The main active species for oxidation of CH3COONa over Fe0.08/CFA was revealed by adding different scavengers. As shown in Figure S1, p-benzoquinone (p-BQ), tert-butyl alcohol (TBA), and L-histidine (L-HIS) were used to quench •O2−, •OH, and singlet oxygen (1O2), respectively [25]. After quenching 1O2, the removal efficiency of CH3COONa was slightly decreased; however, it was greatly suppressed without •O2− and •OH. This result suggests the main active species for CH3COONa degradation over Fe0.08/CFA were •O2− and •OH. The generation of reactive oxygen species was also characterized by EPR technology, where 5,5-dimethyl-1-pyrroline N-oxide (DMPO) can trap •O2− and •OH to form adducts that have 1:1:1:1 and 1:2:2:1 EPR signals [38]. Figure 8(A1,B1) shows that the corresponding peaks can be only produced with the existence of Fe0.08/CFA, suggesting that ozone was stimulated to form related free radicals after adsorption over the catalyst surface.
The produced •O2− and •OH over catalyst Fe0.08/CFA were also quantified by chemical titration. As shown in Figure 8(A2), TA could be oxidized to 2-hydroxyterephthalic acid (TAOH), which had a characteristic photoluminescence (PL) signal centered at 425 nm [39]. With the extension of reaction time, the amount of •OH was also gradually increased, and the final •OH concentration could be achieved at 0.015 mmol/L within 14 min (see Figure 8(A3)). We also demonstrated •O2− production by the NBT method. After the NBT had reacted with •O2−, and the absorbance of NBT at 259 nm (Figure 8(B2)) gradually decreased with the extension of reaction time, suggesting the steady generation of •O2− in solution [40]. The maximum amount of generated •O2− could be achieved at 0.16 mmol/L within 12 min (see Figure 8(B3)). Obviously, the production concentration of •O2− is nearly 10 times that of •OH, which indicates that •O2− plays a more dominant role in the oxidation of CH3COONa. This result is also consistent with the experimental results exhibited in Figure S1: after quenching of •O2− by p-BQ, the degradation efficiency of CH3COONa would be seriously affected.

4. Conclusions

We developed a supported ozone catalyst by utilizing fly ash as a carrier and incorporating iron oxide as the active phase. The structural characteristics of pretreated fly ash and Fe-modified samples were assessed using various techniques such as SEM, XRD, TEM, ICP, XPS, ESR, etc. The SBET of fly ash samples could reach 59.6 m2/g, which provided better surface circumstances for loading of iron oxide. CH3COONa was selected as a targeted pollutant for assessing the ozone catalysis performance of Fe-modified samples, and the best removal rate of CH3COONa was obtained at 53.3% over Fe0.08/CFA catalyst. A higher ratio of Fe2+/Fe3+ over Fe0.08/CFA improved the formation of O(V), which had an impact on converting the absorbed O3 into •O2− and •OH. The effect of pH on reaction performance was also verified. Under neutral conditions, Fe0.08/CFA could obtain the best performance for removal of CH3COONa, excluding the formation of ferric hydroxide under alkaline conditions and the inhibition of ozone adsorption under acidic conditions. The generation of •O2− and •OH over oxygen vacancy with the existence of ozone were further investigated in detail, revealing that the generation of •O2− was nearly 10 times that of •OH and dominated the reaction. According to current reports [32], this large amount of produced •O2− could be due to the mechanism of O(V) + H2O → Surface–OH2+, Surface–OH2+ + O3 → Surface–•O2− + •OH3 and •OH3 → O2 + •OH. In summary, this work confirms effective COD degradation by modified fly ash, which expands the vision of increasing the added value of fly ash and the new technology for the wastewater treatment of CH3COONa could be seriously affected.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/w15213801/s1, Figure S1: Removal rate of CH3COONa over Fe0.08/CFA under the condition of scavengers added (concentration of CH3COONa: 150 mg/L, concentration of O3: 50 mg/L, temperature: 25 °C, pH: 7.5, catalyst dosage: 3 g/L).

Author Contributions

Conceptualization, Y.C. and R.C.; methodology, Y.C. and R.C.; validation, X.C., J.Y. and X.D.; investigation, Y.C. and X.D.; writing—original draft preparation, Y.C.; writing—review and editing, R.C. and P.S.; supervision, Y.G., P.S. and S.X.; funding acquisition, Y.C., X.D. and P.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received financial support from the R&D Program of Zhejiang Tiandi Environmental Protection Technology Co., Ltd., China (Project Code: ZNKJ-2022-06; TD-KJ-22-006) and was also funded through preferential grants for Postdoctoral Research Projects in Zhejiang Province, China (Grant Number: ZJ2021052).

Data Availability Statement

Data is available through the author.

Conflicts of Interest

The authors declare no conflict of interest.

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Water 15 03801 g001
Figure 1. The degradation performance of CH3COONa over different Fe-modified fly ash catalysts (concentration of CH3COONa: 150 mg/L; concentration of O3: 50 mg/L; temperature: 25 °C; pH: 7.5; catalyst dosage: 3 g/L).
Figure 1. The degradation performance of CH3COONa over different Fe-modified fly ash catalysts (concentration of CH3COONa: 150 mg/L; concentration of O3: 50 mg/L; temperature: 25 °C; pH: 7.5; catalyst dosage: 3 g/L).
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Figure 2. The XRD patterns of pretreated fly ash and different Fe-modified fly ash catalysts.
Figure 2. The XRD patterns of pretreated fly ash and different Fe-modified fly ash catalysts.
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Figure 3. (A1–A3) SEM images of Fe0.08/CFA; (B) EDX-mapping of Fe0.08/CFA.
Figure 3. (A1–A3) SEM images of Fe0.08/CFA; (B) EDX-mapping of Fe0.08/CFA.
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Figure 4. HR-TEM images of Fe0.08/CFA.
Figure 4. HR-TEM images of Fe0.08/CFA.
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Figure 5. XPS spectra of CFA and different Fe- modified CFAs: (A) survey; (B) Fe 2p; and (C) O 1s.
Figure 5. XPS spectra of CFA and different Fe- modified CFAs: (A) survey; (B) Fe 2p; and (C) O 1s.
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Figure 6. ESR spectra of CFA and different Fe-modified CFAs.
Figure 6. ESR spectra of CFA and different Fe-modified CFAs.
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Figure 7. (A) Effect of initial ozone concentration on removal efficiency of CH3COONa. (B) Effect of initial catalyst dosage on removal efficiency of CH3COONa. (C) Effect of initial CH3COONa concentration on performance of Fe0.08/CFA. (D) Effect of pH value on removal efficiency of CH3COON.
Figure 7. (A) Effect of initial ozone concentration on removal efficiency of CH3COONa. (B) Effect of initial catalyst dosage on removal efficiency of CH3COONa. (C) Effect of initial CH3COONa concentration on performance of Fe0.08/CFA. (D) Effect of pH value on removal efficiency of CH3COON.
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Figure 8. EPR spectra of DMPO−•OH (A1) and DMPO-•O2− (B1). Absorption spectra of NBT solution (A2) and PL spectra of TA solution (B2) with Fe0.08/CFA. The quantitative concentration of •OH (A3) and •O2− (B3) via PL spectra of TA and absorption spectra of NBT at different times.
Figure 8. EPR spectra of DMPO−•OH (A1) and DMPO-•O2− (B1). Absorption spectra of NBT solution (A2) and PL spectra of TA solution (B2) with Fe0.08/CFA. The quantitative concentration of •OH (A3) and •O2− (B3) via PL spectra of TA and absorption spectra of NBT at different times.
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Table 1. Specific surface area, porous parameters, and XPS analysis of different Fe-modified CFAs.
Table 1. Specific surface area, porous parameters, and XPS analysis of different Fe-modified CFAs.
SamplesSBET
(m2/g)		Vtotal
(cm3/g)		Pore Size
(nm)		XPS AnalysisICP Test of Fe Element (g/g)
Fe2+/Fe3+OadsOsurOlatTheoreticalActual
CFA59.640.1312.76/0.560.390.05/0.0098
Fe0.04/CFA39.140.1111.460.850.450.420.130.040.034
Fe0.08/CFA20.260.0813.440.880.330.520.150.080.061
Fe0.12/CFA16.370.068.470.830.400.390.210.120.087
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MDPI and ACS Style

Chen, Y.; Chen, R.; Chang, X.; Yan, J.; Gu, Y.; Xi, S.; Sun, P.; Dong, X. Ozone Catalysis Degradation of Sodium Acetate via Vacancy-Driven Radical Oxidation over Fe-Modified Fly Ash. Water 2023, 15, 3801. https://doi.org/10.3390/w15213801

AMA Style

Chen Y, Chen R, Chang X, Yan J, Gu Y, Xi S, Sun P, Dong X. Ozone Catalysis Degradation of Sodium Acetate via Vacancy-Driven Radical Oxidation over Fe-Modified Fly Ash. Water. 2023; 15(21):3801. https://doi.org/10.3390/w15213801

Chicago/Turabian Style

Chen, Yaoji, Ruifu Chen, Xinglan Chang, Jingying Yan, Yajie Gu, Shuang Xi, Pengfei Sun, and Xiaoping Dong. 2023. "Ozone Catalysis Degradation of Sodium Acetate via Vacancy-Driven Radical Oxidation over Fe-Modified Fly Ash" Water 15, no. 21: 3801. https://doi.org/10.3390/w15213801

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