Catalytic Ozonation for Phenol Removal over Cobalt-doped α-MnO2 Catalyst: Performance and Mechanism

doi:10.21203/rs.3.rs-1194666/v1

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 in terms of catalytic ability and mechanism. Results showed that that Co doped on 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. In order to investigate the effect of Co doping on the physicochemical properties of the catalysts, the synthesized α-MnO₂ and Co-α-MnO₂ (2% Co/Mn doping ratio) catalysts were characterized by XRD, TEM, BET and XPS techniques, including the phase, morphology, structural properties and dispersity of the surface active species. The larger specific surface area and pore volume, more crystal defect and oxygen vacancy, higher relative content of Mn³⁺and adsorbed oxygen (O_ads) as well as surface hydroxyl were obtained after Co doping on α-MnO₂, which could result in higher catalytic oxidation performance of Co-α-MnO₂. The influence of masking agent showed that surface hydroxyl group and active free radicals (•OH and •O^2-) 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 (ROS) on phenol removal in Co-α-MnO₂ systems.

Phenol

Catalytic Ozonation

Co Doping

α-MnO2

Advanced Oxidation Process

Catalyst Structure

Ozonation has been widely undertaken in industrial wastewater treatment because ozone poses the outstanding oxidation potential on a large number of organic pollutants (Chen et al., 2017; Wang and Chen, 2020). However, single ozonation commonly presented a low removal rate on organic compounds degradation (Hu and Xia, 2018). To overcome the limitation of this process, ozonation coupled with catalyst have been attracted much attention. Heterogeneous catalytic ozonation can enhance the oxidation of ozone by selecting appropriate solid catalysts. This method can promote ozone decomposition, which will generate more reactive oxygen species (ROS) and further enhance the degradation of organic compounds (Peng et al., 2018; Zhang et al., 2020).

Metal oxides (e.g., MnO₂, Fe oxides, CoFe₂O₄, TiO₂) have been widely used as the catalysts in heterogeneous catalytic ozonation (Du et al., 2020; Liu et al., 2019; Oliveira et al., 2019; Yang et al., 2014). Among these metal oxides, MnO₂ showed the excellent catalytic performance on benzene series degradation due to its strong redox coples of Mn²⁺/Mn³⁺ and Mn³⁺/Mn⁴⁺ on the surface of catalysts, diverse and crystallographic structure (Niu et al., 2019; Zhang et al., 2020). MnO₂ has great structural flexibility and crystallographic polymorphs (e.g., α-, β-, γ-, and δ-MnO₂) because the basic structural MnO₆ units can be linked in different manners forming tunnels (Wang et al., 2016). α-MnO₂ has been extensively studied due to its structural characteristics and excellent activity for ozone decomposition and catalytic ozonation (Wang et al., 2015; Zhu et al., 2017). Moreover, recent studies have showed that metal doping can improve the catalytic performance by modifying α-MnO₂ structure. Wang et al. synthesized Zr⁴⁺ doped α-MnO₂ nanowires, and observed that Zr⁴⁺ ions originally occupied the positions belonging to elemental manganese in the crystal structure and resulted in a mutual action between Zr⁴⁺ ions and Mn³⁺ ions, thus improving the catalytic performance of α-MnO₂ (Wang et al., 2018). Uematsu et al. reported that the morphology of α-MnO₂ was changed by doping with Mo⁶⁺, leading to an increase in its specific surface area and the number of catalytically active surface positions, which in turn improved the catalytic performance of the catalyst (Uematsu et al., 2016).

As a kind of transition metal, Co has a strong Co²⁺/Co³⁺ redox cycle which can also promote electron transfer and thus improve catalytic oxidation efficiency (Anfar et al., 2021). Lv et al. reported that Co doping on Fe₃O₄ increased the catalytic activity and stability of Fe₃O₄ (Lv et al., 2012). Li et al. observed that an interface synergistic effect between the doped metal Co and cerium oxide on catalyst Co-Ce-MCM-48 improved the interface electronic behavior and promoted the production of ROS (Li et al., 2019). Faleh et al. developed a new heterogeneous cobalt (Co) catalyst supported on activated carbon (Co/AC) and found the doping of Co improved the surface adsorption capacity of activated carbon which enhanced the degradation efficiency of oxalic acid in catalytic ozonation process (Faleh et al., 2019). Additionally, some studies have showed that the synergistic role can be well presented when the radius of doped metal ions is close to that of metal ions in the catalyst (Kang et al., 2013). Therefore, due to the close ionic radius between Co²⁺ and Mn²⁺, the catalyst with Co doping on the α-MnO₂ might have a better catalytic activity than that of the sole α-MnO₂ catalyst. However, it is not clear how influence cobalt doping on its structure and physical and chemical properties.

In this article, α-MnO₂ catalyst doped with Co²⁺ was prepared by hydrothermal method, and then investigate the catalytic ozonation activities on phenol removal. BET, XRD, XPS and FTIR were used to analyze the phase, morphology and structural properties of the synthesized catalysts. The catalytic ozonation mechanism of Co-doped α-MnO₂ catalyst on phenol removal was explored in depth by the masking experiment of free radicals combining with catalyst structure characteristics.

2.1 Materials and reagents

Potassium permanganate (KMnO₄, ≥99%), Manganese sulphate (MnSO₄·H₂O, ≥98%), Cobalt Sulfate (CoSO₄·7H₂O, ≥98%) were purchased from Sinopharm Chemical Reagent Co., Ltd. Deionized water was obtained from a Millipore Q water purification system. All reagents and chemicals were of analytical grade.

2.2 Synthesis of Catalysts

Co-doped α-MnO₂ were synthesized using a modified hydrothermal method, which was showed in Fig. 1. Co-doped α-MnO₂ were synthesized via a one-step hydrothermal method according to a previous report (Hu et al., 2020). 36 mmol of MnSO₄·H₂O and certain molar of CoSO₄·7H₂O were dissolved in 50 mL of deionized water under stirring, and then the above mixed solution was added into 50 mL Potassium homologate solution (KMnO₄ was 20 mmol) dropwise, followed by stirring magnetically for about 30 min until the solution became homogeneous. After that, it was transferred into a 200 mL Teflon-lined stainless-steel autoclave. The autoclave was kept at 160°C for 16 h in an oven and then cooled to room temperature, and then, the product was collected by filtration and fully rinsed several times with deionized water to remove K⁺, followed by drying at 105℃ for 8 h. In order to determine the optimal doping ratio, we prepared catalysts with different initial molar ratio of Co and Mn (0.1, 0.2, 0.3, 0.4 and 0.5 respectively). The sample with Co/Mn = 0.2 had the highest catalytic ozonation of phenol (Fig S1). Therefore, catalysts with Co/Mn = 0.2 named Co-α-MnO₂ was the materials synthesized. The synthetic procedures for α-MnO₂ was similar to that for Co-doped α-MnO₂ with the exception of adding CoSO₄·7H₂O to the initial solution.

2.3 Catalysts characterization

The catalyst was purged 5 h at 120 ℃ under nitrogen atmosphere protection and then determined the BET surface area and pore-size distribution on a Micromeritics ASAP2020 analyser when the sample was cooled. Powder X-ray diffraction (XRD) analysis was carried out on a Bruker D8 ADVANCE Phaser using Cu Ka radiation (k = 0.15418 nm) with a LYNXEYE detector at 40 kV and 30 mA. X-ray photoelectron spectroscopy (XPS) was performed with an ESCALAB250 system equipped with an Al Kα excitation source and operated at 15 kW and 1486.6 eV. Fourier transformed infrared (FTIR) analyses were carried out using a NicoletiS10 FT-IR plus spectrophotometer in a wavelength range of 4000-400 cm⁻¹.

2.4 Catalytic ozonation activities

In this study, phenol was selected as the aim pollutant because it is one of the most common industrial wastewater contaminates and would cause serious ecological and environmental problems (Saputra et al., 2017). The phenol degradated by catalytic ozonation was performed in a self-regulating quartz reaction with 1 L aqueous solution showed in Fig. 2. The concentration of ozone was adjusted via controlling the current and flow rate of the ozone generator and measured by ozone detector. When the ozone concentration was stable and then bubbled into the integrated adsorption-catalytic ozonation reactor to start the reaction. The pneumatic panel was adopted to ensure that gaseous ozone was completely mixed with aqueous solution. During the reaction, ozone concentration and flow rate were set at 3.0 mg/L and 3.0 L/min, respectively. The tail gas was absorbed by potassium iodide solution. 2 g catalyst was mixed with 1 L phenol wastewater (initial concentration was 400 mg/L; pH = 10; 293 ± 1 K) in the reaction system. The residual phenol concentration and COD concentration of water samples were measured to evaluate removal performance.

3.1 Catalytic degradation of phenol

The phenol removal investigated by adsorption, ozonation and catalytic ozonation are indicated in Fig. 3. It is clear to Fig out that the phenol removal efficiencies achieved by adsorption (showed in red and black line in Fig. 3) are all less than 5%. So, the contribution of catalyst adsorption on phenol removal could be neglectable. The phenol removal efficiencies during 40 min are in order of Co-α-MnO₂ (97.47%) > α-MnO₂ (81.01%) > single ozonation (58.55%). Phenol removals were also described with pseudo zero-order, first order and second order kinetics, and the kinetic models were expressed as Eq. (1), Eq. (2) and Eq. (3).

C₀-C_t = K₁t (1)

-Ln(C_t/C₀)=K₁t (2)

1/C_t - 1/C₀ = K₂t (3)

Where K₁, K₂, K₃ are the pseudo zero-order, first-order and second-order rate constant, respectively (min⁻¹); t represents the reaction time; C₀ and C_t stand for the phenol concentration at 0 min and t min, respectively.

The reaction rate constants in different processes are showed in Table 1. The removal efficiency of catalytic ozonation on phenol well accords with the first-order reaction kinetics, while that of single ozonation accords with the zero-order reaction kinetics. Based on first-order kinetic fitting, Co-α-MnO₂ achieved the highest reaction rate constant for phenol removal (0.092 min⁻¹), which was 2.09 and 4 times higher than that in α-MnO₂ (0.044 min⁻¹) and O₃ (0.023 min⁻¹), respectively. It can be further verified that the doping of Co on α-MnO₂ efficiently improved the catalytic activities. The results might be attributed to the changes of catalyst construction, elementary composition and surface properties, et al., which will be detailly discussed in the following section.

Table 1

Parameters of Kinetic Fitting for the Removal Phenol
order	Zero-order		First-order		Second-order
System	K₁(min⁻¹)	R²	K₂(min⁻¹)	R²	K₃(min⁻¹)	R²
O₃	6.172	0.996	0.023	0.987	8.862×10⁻⁵	0.951
O₃/α-MnO₂	8.386	0.945	0.044	0.991	2.763×10⁻⁴	0.936
O₃/Co-α-MnO₂	10.303	0.909	0.092	0.975	1.986×10⁻³	0.708

3.2 Specific surface and pore size distribution

The calculated results of specific surface area and pore volume of α-MnO₂ and Co-α-MnO₂ are showed in Table 2. It can be seen that Co-α-MnO₂ catalyst has a bigger of specific surface area (79.496 m²/g) and pore volume (0.0396 cm³/g) than that of α-MnO_2。 The specific surface area and pore volume are more, the better catalytic activity can be obtained. The reason is that the large specific surface area and pore volume can promote the mass transfer rate between solid-liquid-gas (Ghuge and Saroha 2018). So, catalytic activity of Co-α-MnO₂ is more great than that of α-MnO₂. N₂ adsorption-desorption isotherm showed that two kinds of catalysts belong to typically Ⅲ type (as showed in Fig. 4) (Zhai and Hao 2017), indicating that the interaction between catalysts and adsorbate is weak. The surface of the catalysts generally adsorbs small molecules such as H₂O molecules, which decomposed to generate hydroxyl radicals to promote the catalytic ozonation (Zhao et al., 2009).

3.3 Crystal phase

The XRD results of α-MnO₂ and Co-α-MnO₂ catalysts are showed in Fig. 5. All patterns of the prepared α-MnO₂ and Co-α-MnO₂ catalyst samples can be indexed to body-centered tetragonal, which are same as that of the standard α-MnO₂ (JCPDS NO.44-0141). There are no additional peaks in XRD patterns be identified after Co doping, which indicates that the crystal structure of the preparation of test samples was the same as that of α-MnO₂. This shows that Co doping enters the MnO₂ skeleton structure by replacing Mn or is embedded in the pore structure of the catalyst tunnel, rather than existing on the catalyst surface in the form of cobalt oxide with similar ionic radius to CO²⁺ and Mn²⁺. However, the Co doping on α-MnO₂ would cause the deformation of α-MnO₂ lattice, which make the grain diameter decrease and the parameters a, b and c increase (as showed in Table 2) and show a distortion in the lattice cell, thus further promotes the migration of adsorbed oxygen to decompose and oxidize organic matter (Yu et al., 2020; Peña et al., 2004).

Table 2

Specific surface area, pore volume, Lattice Parameters and Grain Diameters of α-MnO₂ and Co-α-MnO₂
Catalysts	Specific surface area(m²/g)	Pore volume(cm³/g)	Lattice parameter			Grain diameter (Å)
Catalysts	Specific surface area(m²/g)	Pore volume(cm³/g)	a (Å)	b (Å)	c(Å)	Grain diameter (Å)
α-MnO₂	51.166	0.0250	9.7681	9.7681	2.8529	320
Co-α-MnO₂	79.496	0.0396	9.7822	9.7822	2.8534	287

3.4 Surface chemical compositions

In order to further investigate the elemental valence on the catalyst surface, Mn 2P, O1s and Co2p of both α-MnO₂ and Co-α-MnO₂ characterized by XPS were presented in Fig. 5(b), Fig. 5(c) and Fig. 5(d), respectively. Fig. 6(b) shows that the XPS spectrum of Mn 2p contains two main peaks at binding energies of 657.5 ± 7.5 and 642.5 ± 2.5eV, which could be attributed to Mn2P_1/2 and Mn2p_3/2. The binder energy of the peak at 641.6 eV, 642.5 eV and 643.4 eV are found in Mn2p_3/2, which can be attributed to Mn³⁺ and Mn⁴⁺ (Zhou et al., 2018; Li et al., 2018), respectively. As showed in Table 3, the relative content of Mn³⁺ of Co-α-MnO₂ increases from 8.42–41.16% and the ratio of Mn³⁺/Mn⁴⁺ increases from 0.092 to 0.70 compared with α-MnO₂. According to the results of the Table 5, the main valence state of Co in the catalyst is Co³⁺, which indicates that the doped Co²⁺ has a redox reaction in the catalyst preparation process, and promotes the increase of the ratio of Mn³⁺/Mn⁴⁺ in Co-α-MnO₂. The higher ratio of Mn³⁺/Mn⁴⁺ in Co-α-MnO₂ is an important reason for the occurrence of more oxygen vacancy, which would promote the generation of reactive oxygen species and facilitate the migration and transformation of oxygen species (Liu et al., 2019; Liu et al., 2009). In addition, Mn³⁺ and other unsaturated metal ions behave as Lewis acid in the aqueous phase, which is easy to coordinate with water molecules and undergo chemical adsorption to form the surface hydroxyl group. Furthermore, the XPS spectrums of O1s for α-MnO₂ and Co-α-MnO₂ are showed in Fig. 5(c). The binding energy energies at the peak position 530.1 eV and 531.5 eV in the O1s spectrum, corresponding to the lattice oxygen and the adsorbed oxygen respectively (Ge et al. 2017). Oxygen presenting form and relative content of oxygen calculated are showed in Table 4. Compared with α-MnO₂, the ratio of adsorbed oxygen (O_ads)/ lattice oxygen (O_latt) of Co-α-MnO₂ increases from 0.15 to 0.23, indicating that more O_latt would combine with H₂O to produce surface hydroxyl, which is the active site for the catalyst to adsorb and decompose ozone to produce reactive oxygen, and then improve the efficiency of catalytic ozone oxidation. Surface hydroxyl group is well confirmed by the results of the following FT-IR analysis.

Table 3

Relative element content of α-MnO₂ and Co-α-MnO₂
Catalysts	Mn (%)	O (%)	Co (%)	Mn/O	Co/Mn	Co/O
α-MnO₂	27.77	56.59	-	0.491	-	-
Co-α-MnO₂	23.21	55.64	4.27	0.417	0.184	0.076

Table 4

XPS energy spectra analysis of α-MnO₂ and Co-α-MnO₂
Catalysts	Mn³⁺ (%)	Mn⁴⁺ (%)	Mn³⁺/Mn⁴⁺	Co²⁺	Co³⁺	Co²⁺/Co³⁺	O_ads (%)	O_latt (%)	O_ads/O_latt
α-MnO₂	8.42	91.58	0.092	-	-	-	13.32	86.68	0.15
Co-α-MnO₂	41.16	58.84	0.70	20.67	79.33	0.26	18.99	81.01	0.23

3.5 Surface functional groups properties

In order to expose the influence of doping Co on surface functional groups of α-MnO₂, the catalysts were characterized with FT-IR, and the results are present in Fig. 7. Although the position is slightly shifted, the intensities of stretching vibration of Mn-O and Mn-O-Mn bonds (467cm⁻¹, 524 cm⁻¹ and 719 cm⁻¹) (Mishrap et al., 2016; Abdel-Latif et al., 2015) are greatly improved, which is caused by the microstructure regulation due to the doping of Co on α-MnO₂, and has been verified by the results of XRD. The characteristic peak of Mn-OH presents at the wavelength of 1042 cm⁻¹, which is constructed by adsorbing water molecules on the catalyst surface and shedding hydrogen ions (Han et al., 2010). Compared with the α-MnO₂, the peak intensity of Mn-OH in Co-α-MnO₂ increases obviously, indicating that the adsorption capacity of α-MnO₂ is improved by Co doping. The new peaks appeared at 879cm⁻¹, 1387cm⁻¹ corresponding to the stretching vibration of Co-O (Fu et al., 2017), further confirm the XRD results of Co replacing Mn into the structure of α-MnO₂. The other three new peaks appeared at 1611cm⁻¹, 2969cm⁻¹and 3320cm⁻¹ corresponded to the stretching vibration of the surface hydroxyl (O-H) (Kim et al., 2009), which are produced by flexural and telescopic vibration of adsorbed water on the catalyst surface. Therefore, in the Co-α-MnO₂ catalytic ozonation system, more surface hydroxyl were generated, and they were showed as acidic or alkaline groups through proton exchange with aqueous solution, which promotes electron transfer and produces reactive oxygen species contributing to higher catalytic ozonation efficiency (Maehida et al., 2000; Lu et al., 2016).

3.6 Mechanisms of catalytic ozonation

3.6.1 Surface hydroxylation and ROS

In order to further recognize the role of surface hydroxyl of the catalysts, HPO₄²⁻ was introduced and employed to occupy surface hydroxyl to deactivate the catalytic performance (Nawaz et al., 2015). The results of masking experiments were showed in Fig. 8. In comparison to the experiments without masking agent, the phenol removal rates were much decreased because HPO₄²⁻ was added to deactivate surface hydroxyl of catalyst. The removal rate of phenol obtained by single ozonation, O₃/α-MnO₂ and O₃/Co-α-MnO₂ were 52.74%, 57.62% and 64.58%, respectively, which are reduced by 5.81%, 23.39% and 32.89%, respectively. So, surface hydroxyl played a key role in these catalytic ozonation systems.

The surface hydroxyl group might be the main active cite for catalyst to absorb and further decomposed ozone to produce •OH. •OH and •O²⁻ were active free radicals produced in the process of catalytic ozonation, which played an important role in the degradation of organic compounds. Tert-butanol and p-benzoquinone were introduced and employed to occupy •OH and •O²⁻ in O₃, O₃/α-MnO₂ and O₃/Co-α-MnO₂ systems, respectively. The results of masking experiments were showed in Fig. 9 and Fig. 10. After the addition of TBA or PBQ as masking agent, the removal rates of phenol decreased by 13.28%, 31.88%, 40.33% and 9.63%, 18.46% and 35.63%, respectively, which indicated that both •OH and •O₂⁻ were active oxygen influencing the degradation of phenol by catalytic ozonation. The addition of the catalyst promotes the decomposition of O₃ to generate •OH and •O²⁻, while the doping of Co enhanced the catalytic activity of the catalyst.

3.6.2 Analysis of the catalytic mechanism

The masking experiment results demonstrated that the presence of surface hydroxyl group and reactive oxygen species promoted the degradation efficiency of phenol. Therefore, the mechanism of catalytic ozonation of phenol by α-MnO₂ and Co-α-MnO₂ was analyzed from the surface of polyphase catalysis (as showed in Fig. 11).

According to the adsorption-desorption isotherm of the catalyst, the interaction between the adsorption material and the adsorption gas is relatively weak, indicating that the interaction between the catalyst and the adsorbent is relatively weak (as showed in Fig. 4). The surface of the catalyst generally absorbs small molecules, so H₂O molecules are preferentially adsorbed than O₃ molecules (Zhao et al., 2009(a)). When introduced into an aqueous solution, H₂O molecules will be strongly adsorbed on the surface of catalyst. The adsorbed H₂O molecules will always dissociate into OH⁻ and H⁺ (Zhao et al., 2009(a)), and form the surface hydroxyl group with the surface cation and oxygen anion respectively. The released HO₃• will further decompose and release O₂ and produce •OH. Then, the doping of Co could promote the generation of more surface hydroxyl groups, which promoted the catalytic ozonation process.

The surface hydroxyl group reacts with O₃ to form a surface five-member ring, which will further decompose to release O₂ and form surface HO₂⁻. Surface HO₂⁻ on the one hand reacts further with O₃ to form HO₃⁻, then releases O₂ to form •OH, and produces O₃⁻ at the same time. On the other hand, HO₂⁻ can further produce •O₂⁻ by releasing H⁺. Under the action of O₃ molecule, the surface •O₂⁻ will form the surface cation, and the surface cation will absorb H₂O molecule to form the surface hydration cation (H₂O⁺). With the release of HO₃⁻, the •OH will be generated, while the surface H₂O⁺ will be converted to the surface hydroxyl group (Zhao et al., 2009(b); Wang et al., 2016; Zhu et al., 2017). Therefore, the catalyst completed the surface hydroxyl regeneration and initiated the free radical chain reaction.

Co-doped α-MnO₂ was prepared by hydrothermal method to be as the catalyst for phenol removal. The removal performance and mechanism by catalytic ozonation was obtained. The results showed that Co doping played a great role in promoting the efficiency of phenol removal by catalytic ozonation over Co-α-MnO₂. After 40 min catalytic ozonation, the phenol removal rates by Co-α-MnO₂ reached 97.47%, which was 16.46%, 38.92% higher than that of α-MnO₂ catalytic ozonation and pure O₃ without catalyst respectively. The kinetic rate of Co-α-MnO₂ on phenol ozonation reaching 0.092min⁻¹, which was 2.09 times and 4 times of α-MnO₂ and ozonation without catalyst respectively. The higher catalytic activity of Co-α-MnO₂ catalyst could be attributed to a series of better properties in comparison with α-MnO₂ catalyst. Compared with α-MnO₂, the doping of Co made Co-α-MnO₂ had much larger specific surface area and pore volume, more crystal defect and oxygen vacancy, higher relative content of Mn³⁺ and adsorbed oxygen (O_ads) and more surface hydroxyl. The combined action of these factors finally improved the catalytic ozonation performance of Co-α-MnO₂. Masking experiments had showed that surface hydroxyl group and active free radicals (·OH and ·O²⁻ ) were involved in the catalytic ozonation of phenol. Furthermore, the primary reaction mechanism was proposed. The catalyst achieved the regeneration of surface hydroxyl group and the initiation of free radical chain reaction. The doping of Co promoted these reactions by producing more surface hydroxyl groups, which promoted the catalytic ozonation process.

Acknowledgements

Thanks for the Fundamental Research Funds for the Central Universities (2019XKQYMS78), the Open Sharing Fund for the Large-scale Instruments and Equipments of China University of Mining and Technology (CUMT) and Postgraduate Research & Practice Innovation Program of Jiangsu Province (SJCX21_1020)’s support.

Funding

This work was supported by the Fundamental Research Funds for the Central Universities (2019XKQYMS78).

Competing Interests

The authors have no relevant financial or non-financial interests to disclose.

Author Contributions

D.B. (M.D. student), Z.X.C. (M.D. student) and H.Y. (M.D. student) conducted all the experiments and wrote the manuscript. Z.J. (Associate Professor) and H.S.L. (Professor) wrote and revised the manuscript. G.S.J. (Associate Professor) peformed data analysis and interpretation as well as revised the manuscript.

Ethical Approval

Not applicable

Consent to Participate

Not applicable

Consent to Publish

Not applicable

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SupplmentaryMaterial.docx

Catalytic Ozonation for Phenol Removal over Cobalt-doped α-MnO₂Catalyst: Performance and Mechanism

Status:

Version 1

Abstract

Figures

1. Introduction

2. Experimental

2.1 Materials and reagents

2.2 Synthesis of Catalysts

2.3 Catalysts characterization

2.4 Catalytic ozonation activities

3. Results And Discussions

3.1 Catalytic degradation of phenol

3.2 Specific surface and pore size distribution

3.3 Crystal phase

3.4 Surface chemical compositions

3.5 Surface functional groups properties

3.6 Mechanisms of catalytic ozonation

3.6.1 Surface hydroxylation and ROS

3.6.2 Analysis of the catalytic mechanism

4. Conclusion

Declarations

References

Supplementary Files

Status:

Version 1