The decay of free radicals involved in side reactions is one of the challenges faced by electrochemical degradation of organic pollutants. To this end, a non-radical oxidation process was constructed by a natural air diffusion cathode (ADC) and a RuO2-Ti anode for cathodic hydrogen peroxide activation by anodic chlorine evolution. The ADC fabricated by the carbon black of BP2000 produced a stable concentration of hydrogen peroxide of 339.94 mg/L (current efficiency of 73.4%) without aeration, which was superior to the cathode made by the carbon black of XC72. The flow-by electrochemical system consisted of an ADC and a RuO2-Ti anode showed high selectivity to aniline compared to benzoate. Quenching experiments revealed the main active intermediate responsible for the pollutant degradation was singlet oxygen (1O2), which was also identified by the electron spin resonance (ESR) analysis. Finally, the steady-stable content of 1O2 was quantitatively determined to be 6.25×10− 11 M by the method of furfuryl alcohol (FFA) probe. Our findings provide a fast, low energy consumption and well controlled electrochemical oxidation method for selective degradation of organic pollutants.
Research Article
Singlet oxygen generation for selective oxidation of emerging pollutants in a flow-by electrochemical system based on natural air diffusion cathode
https://doi.org/10.21203/rs.3.rs-1759002/v1
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non-radical oxidation
natural air diffusion cathode
singlet oxygen
hydrogen peroxide activation
emerging pollutants
Non-radical pathways due to their stable oxidative ability receive increasing attention in the field of water and wastewater treatment. Researches show non-radical oxidative pathways exhibit great resistance to certain anions (Duan et al., 2015; Luo et al., 2019). Among them, singlet oxygen (1O2) is the excited state of molecular oxygen molecule, which has higher reactivity than the unexcited state (Stacey & Pope, 2013). It is a non-radical and electrophilic oxidant that selectively reacts with electron-rich moieties of organic compounds(Agnez-Lima et al., 2012). Moreover, singlet oxygen has the anti-interference ability to other coexisting substrates (such as natural organics, inorganic ions) and the characteristic of producing less halogenated disinfection by-products (Huang et al., 2021).
Oxidation of H2O2 by hypochlorite is known to generate 1O2 (Held et al., 1978). Based on this reaction, some electrochemical systems were developed for organic pollutants oxidation (Guo & Liu, 2020; Lu et al., 2022; Tian et al., 2016). For example, Tian et al. utilized in-situ generation of HOCl at an anode of RuO2-Ti and H2O2 at a cathode of activated carbon fiber for singlet oxygen dominated cyanide oxidation (Tian et al., 2016). Lu developed an electrochemical disinfection system by a dimensionally stable anode and a graphite-felt cathode with O2 aeration, where the important role of 1O2 was also verified (Lu et al., 2022). Guo et al. designed a flow-through electrochemical system based on a functional carbon nanotubes cathode filter to generate 1O2 by in situ formed H2O2 with ClO− electrolyte (Guo & Liu, 2020). However, the production of H2O2 in these systems all depends on dissolved oxygen content which limited by the saturation solubility in the electrolyte (Sirés & Brillas, 2021). In addition, extra energy input for the aeration increases the cost of treatment.
To develop a 1O2-mediated electrochemical system for practical applications, an efficient cathode for H2O2 production is critical since it is one of the main reactants for 1O2 generation. In order to elevate the efficiency of H2O2 electrosynthesis, researchers have developed cathodes of various structures and materials (Brillas, 2022a; Luo et al., 2015; Walker et al., 2021; Zhang et al., 2022). The mass transport of O2 to the cathode is essential for the production of hydrogen peroxide (Sirés & Brillas, 2021) Carbonaceous cathodes like carbon sponge, carbon felt, seem the better choices for high mass transport of O2 and low coast (Brillas, 2022b). Zhang et. prepared a cathode of synthesized agarose catalyst using the air-brushing method obtaining a H2O2 yield of 20.3 mM (Zhang et al., 2022). Among them, air diffusion cathodes (ADC) are usually reported for highly efficient production of H2O2 under extensive range of current densities (Liao et al., 2022). Márquez developed a 3D-like air-diffusion cathode to favor the H2O2 production for Fenton’s reaction (Márquez et al., 2020) The special structure of ADC give rise to a three-phase interface for O2 gas, electrolyte and catalyst, which brings fast O2 mass transfer from air (An et al., 2019). Our previous work developed a flow-by electrochemical system where O2 used for H2O2 production is sourced from natural diffusion of air (Jia-xiong & Shi-wei, 2021). Thus, the energy cost by this design was largely decreased. Nevertheless, coupling the natural air diffusion cathode into the electrochemical system is still rarely utilized for 1O2 generation.
In this study, we developed an ADC for highly efficient production of H2O2 without aeration and then constructed a flow-by electrochemical system. The main objective is to explore the generation mechanism of singlet oxygen, leverage the characteristics of 1O2 to overcome the interference of chloride ions and effectively degrade emerging pollutants. Firstly, devoted to choosing the catalyst material for the ADC fabrication, the microscopic properties of the cathodes, as well as hydrogen peroxide production were compared using two different carbon black. Secondly, the oxidation selectivity of the electrochemical system was examined by five individual pollutants and a mixture of four emerging pollutants. Thirdly, the contribution of singlet oxygen to the pollutant oxidation was elucidated by quenching tests and ESR analyses. Finally, the yield of H2O2, ClO−, and steady-state concentration of singlet oxygen in the system was quantitatively measured.
2.1 Materials
Two kinds of carbon black materials (BP2000, XC72) were purchased from Cabot Corporation (US). PTFE emulsion (60%), titanium sulfate (Ti(SO)4), sodium benzoate (BA), tetracycline (TC), sulfamethoxazole (SMX), p-benzoquinone (p-BQ), furfuryl alcohol (FFA), N,N-Diethyl-1,4-phenylenediamine (DPD), were provided by Aladdin, Inc (Shanghai, China). Bisphenol A (BPA), aniline (AN), tert-butyl alcohol (TBA), sodium bicarbonate (NaHCO3), and potassium iodate (KIO3) were obtained from Sinopharm Chemical Reagent Co., Ltd. 4-amino-2,2,6, 6-tetramethylpiperidine (TEMP) was purchased from Dojindo Laboratories (Japan). All chemicals were at least analytic reagents and used as received. Inert electrodes made by RuO2 metal oxide coating on titanium diamond mesh (RuO2-Ti, Shanghai Kaida) were used in the electrolysis experiments. Deionized (DI) water with resistivity of 18.2 MΩ cm− 1 was used for all the experiments
2.2 Fabrication of air diffusion cathode
Air diffusion cathode (ADC) was made by rolling a mixture of conductive carbon black (CB) and PTFE emulsion. Firstly, CB was dispersed in anhydrous ethanol and stirred well. Then PTFE emulsion with a solid content of 60% was added dropwise. The above two steps need to be mixed under ultrasonically stirring for 30 min. The mass ratios of carbon black to PTFE in gas diffusion layer (GDL) and catalytic layer (CL) were 1:3 and 2:1, respectively. The suspension obtained was dried in water bath at 80 ℃ to remove the excess ethanol and to form a dough. Then the dough was pressed into sheet of about 0.2 mm under a roller press. The sheets of GDL and CL were placed a wire mesh of the same size (the collector layer) on both sides and pressed into a sandwich-like ADC. For each type of carbon black material, three cathodes with the same composition were fabricated to verify the reproducibility of the results.
2.3 Experimental approach
Electrolysis experiments were performed at a parallel plate electrochemical device. As shown in Fig. S1, the volume of resin electrochemical cell was 8.0 mL, where the central cross section was a square (1.0 cm × 1.0 cm). The ADC (8.0 cm × 1.0 cm) was assembled tightly between the cell and air chamber (8.0 cm × 1.0 cm) with CL facing to the electrolyte and GDL facing to the air. RuO2-Ti anode was placed parallel to ADC 1 cm away. The relationship of H2O2 and free chlorine with the current intensity were performed in a beaker of 250 ml as shown in Fig. S2. During the experiments, a 1.0 mL min− 1 air was fed to the ADC by an air pump (SB-748, China SEBO)
Constant current was supplied by a DC power supply (GPS-X303/C, Taiwan Goodwill Instrument), and the current intensity was measured by a multimeter (FLUKE F15B+). Water entered the cell through the bottom and outflowed from the top to avoid backwater with hydraulic residence times (θ) of 2 minutes at the flow rate of 4 ml/min by a peristaltic pump (iPump2s, Baoding sinuo Fluid Technology Co., Ltd, China). Source waters were stored in a beaker of 1 L.
In the absence of special instructions, the electrolyte was 0.1 M NaCl or Na2SO4, the initial concentration of the pollutant was 0.1 mM. The initial pH of 10 and current intensity of 200 mA were employed at room temperature. Samples were taken from the outlet at a predetermined time for concentration analysis. All experiments were performed in duplicate.
2.4 Analysis
The concentration of H2O2, was determined by titanium sulfate with a AOE UV-1800 spectrophotometer (Ao Yi Instrument, Shanghai) at 405 nm (Liao et al., 2013). Free chlorine concentration was determined by the DPD method, using a AOE UV-1800 spectrophotometer at 515 nm.
AN, BPA, TC, SMX were the detected by a FL2200 HPLC (Fuli Instruments) equipped with an UV-vis detector and an InertSustain C18 reverse-phase chromatographic column (Shimadzu). A mixture of 70% methanol and 30% water was used as the mobile phase at a flow rate of 1 mL/min and the detection wavelength were 230 nm, 276 nm, 280 nm, and 275 nm for AN, BPA, TC, and SMX separately (Ahmed et al., 2012; Kyotani et al., 1996; Sattler et al., 1994; Zhang et al., 2014). BA was detected with mobile phase containing 30% methanol and 70% water with 0.1% trifluoroacetate at 255 nm (Nicoli et al., 2008). FFA was analyzed with mobile phase of methanol/water (50/50) at 220 nm (Kohn & Nelson, 2007). The pH value of the electrolyte was measured by a portable pH meter (wtw-350i, Germany).
Current efficiency also known as Faraday efficiency was calculated as the Eq. 1 (Liu et al., 2015)
$$CE = \frac{nCqF}{I}$$
1
Where n was the number of electrons transferred from oxygen reduction to hydrogen peroxide (2), F was Faraday's constant (96486 mol L− 1), C represented the concentration of hydrogen peroxide concentration (mol L− 1), q was flow rate (L/s), I was current intensity (A).
The electric energy consumption (EEC, kWh kg− 1) was calculated by Eq. 2 (Zhang et al., 2020)
$$EEC = \frac{1000UI}{Cq}$$
2
where U and I were the applied voltage (V) and current (A), t was the electrolysis time (h), C was the concentration of H2O2 (mg L− 1), and q was flow rate (L/s).
The FFA decay model was assumed to follow the pseudo-first-order kinetics with the rate constant of kobs, FFA. The steady state concentration of singlet oxygen could be calculated as Eq. 3 (Cheng et al., 2017)
Where ks, FFA is the second-order rate constant of singlet oxygen with FFA, which was 1.2×108 M− 1 s− 1 at room temperature(Cheng et al., 2017).
2.5 Characterization
The morphology of ADC was observed under field emission scanning electron microscope (SEM, Zeiss G300). The N2 adsorption analysis of the sample was analyzed at 77 K by a specific surface area and pore size analyzer (SSA-4300 beijing builder electronic technology co., ltd). The specific surface area was measured by the Brunauer-Emmett-Teller (BET) method, and the Barrett-Joyner-Halenda (BJH) method was used to study the porosity and volume distribution of the material. The electronic spinning resonance (ESR) were carried on an electron paramagnetic resonance spectrum (JES-FA200). 4-amino-2,2,6,6-tetramethylpiperidine (TEMP) was used as the spin-trapping agent of 1O2 (Zhang et al., 2020). The trapping agent of 60 mM TEMP was added to electrolyte containing 0.1 M NaCl or 0.1 M Na2SO4 before electrolysis.
3.1 Performance of the ADC
The scanning images of the catalytic layers (CL) were shown in Fig. 1a, b. The images illustrated that honeycomb-like pores distributed evenly on the flat surface, and black-gray carbon particles were attached to the white polytetrafluoroethylene (PTFE) grid for both materials. The images also showed massive micropores, mesopores and micropores co-existed, which composed channels for gas and electron transfer. However, the catalytic layer made by BP2000 had a flatter surface with more micropores and mesopores. For XC72, the macropores and cracks appeared significantly, which may be due to the large difference in the particles of the two carbon black materials.
To further analyze the microscopic structure, N2 adsorption and desorption tests were carried out. Figure 2a-c illustrated that the isotherms of GDL and CL belonged to typical type IV isotherms, which indicated the formation of mesopores and capillary condensation (Li et al., 2021). Furthermore, hysteresis loops were generated in both materials which were in accord with H3-type hysteresis suggesting the existence of micropores (Guo et al., 2020). As shown in Table 1, BET surface area of CL made by BP2000 was 396.044 m2/g, which was about 8 times than that of XC72 (51.542 m2/g). Larger surface area provided more active sites for ORR reactions(An et al., 2019). Besides, CL made by BP2000 had huge pore volume (2.40 cm3/g), smaller average pore size (19.360 nm), indicated higher content of micropores and mesopores. This was consistent with the regular flat and huge surface area of CL fabricated by BP2000. More micropores and mesopores were conducive to the liquid-solid-gas three-phase, which may promote the production of hydrogen peroxide (Guo et al., 2020).
| Material | BET specific surface area (m2/g) | Cumulative total pore volume for BJH adsorption (cm3/g) | BJH adsorption average pore size (nm) |
|---|---|---|---|
| CL(XC72) | 51.542 | 0.475 | 35.220 |
| GDL(XC72) | 27.676 | 0.301 | 40.400 |
| CL(BP2000) | 396.044 | 2.400 | 19.360 |
| GDL(BP2000) | 61.596 | 0.546 | 33.880 |
The electrocatalytic activity of the ADC was examined, as shown in Fig. 2c-d. The yield rate of hydrogen peroxide reached 336.55 mg/L for ADC made by BP2000 after 4 θ, and the stable current efficiency was about 73.4%, which was much higher than XC72 (275.34 mg/L, 62.67%). For each time period, the yield of hydrogen peroxide for ADC made by BP2000 was larger than that of XC72. The results were in line with the BET surface area and pore size distribution of ADCs. To sum up, the BP2000 material was more suitable for making air diffusion cathodes. Therefore, BP2000 will be used as raw material for the following experiments.
In addition, as shown in Fig. S4, the effect of current density, solution pH value, flow rate and electrolyte concentration on the ADC performance was explored. The yield of H2O2 increased from 72.18 to 630.42 mg/L, the CE significantly decreased to 55.4% with the current density increasing to 61.9 mA cm− 2. High current density was generally thought to be harmful for H2O2 production, owing to side reactions such as H2 evolution and H2O2 decomposition (An et al., 2019). While the yield of H2O2 and CE were about 330 mg/L and 70% regardless of the pH value. As reported, poor performance would be caused by H2 evolution and combination of H+ under strong acidic condition (Wang et al., 2020). Even so, the ADC exhibited good performance in a wide pH range. While alkaline solution was in favor of ClO− generation, the pH of 10 was employed in following experiments. The production increased remarkable from 99.38 to 335.27 mg/L as the flow rate increasing from 16 to 4 ml/min but decreased to 298.34 mg/L at 1 ml/min. Lower flow rate facilitated the H2O2 reaction. But limited by GDL area and oxygen mass transfer, H2O2 production did not increase at very low flow rates. The yield increased to 335.27 mg/L when the concentration of electrolyte increased to 0.1 M. However, when the electrolyte concentration continues increasing the yield did not rise. From the economic point of view, the current density of 25.2 mA cm− 2 (current intensity of 200 mA), pH = 10, 4 ml/min, flow rate of 4 ml/min, 0.1 M electrolyte were employed for the following experiments.
Energy consumption for H2O2 via ADC was also compared with that of other gas diffusion cathode. During the electrolysis, an average EEC of 6.7 kWh kg− 1 and 21.1 kWh kg− 1 were obtained for BP2000 and XC72-ADC. Yu et al. fabricated an improved hydrogen peroxide cathode with the CEE of 17.9 kWh kg− 1, while the aeration energy consumption (64.1 kWh kg− 1) was more than three times the electric energy consumption of H2O2 (Yu et al., 2015). Salmerón et al. fabricated a hydrogen peroxide cathode, which caused the aeration energy consumption up to 1077 kWh kg− 1 (Salmerón et al., 2019). The special structure of our ADC give rise to a three-phase interface for O2 gas, electrolyte and catalyst, which brings fast O2 mass transfer from air (An et al., 2019). At a result, the energy cost by this design was largely decreased without aeration.
3.2 Oxidation capacity of the ADC-RuO2 system
In order to verify the oxidation ability of the ADC-RuO2 system, two model pollutants, BA and AN, were selected for oxidation experiments. As shown in Fig. 3a, AN had a degradation efficiency of 97.72% when the reaction reached equilibrium after 1 θ. While BA was hardly oxidized after 2 θ, the degradation efficiency of BA remained around 1.3%. The results may reveal the selectivity for the oxidation of pollutants., which were almost the same as previous studies (Zhu et al., 2018), whose degradation of BA was also low.
There was no selectivity for the hydroxyl radical oxidation pathway, which was obviously inconsistent with the experimental results. Studies have shown that organic substrates with electron-donating groups (such as anilines) can act as electron donors to reactive oxides, such pollutants were more prone to be oxidized by electrophilic reactions through non-radical processes (Lee et al., 2016; Lee et al., 2015). BA was an organic substrate with electron-withdrawing groups, which it was difficult to be oxidized.
Since multi pollutants existed in actual wastewater, it was necessary to evaluate the ability of the system to remove multiple complex pollutants simultaneously (Liu et al., 2002). Therefore, common industrial raw materials bisphenol A (BPA), aniline (AN) and medical antibiotics tetracycline (TC) and sulfamethoxazole (SMX) were added to the water as targets. These substances called emerging pollutants were stable in water, even if with tiny concentration, they may cause harm to the human body (Horikoshi et al., 2008; Kwon et al., 2018; Liu et al., 2002; Zhang et al., 2017). As shown in Fig. 3b, the excellent effect to degrade four kinds of pollutants was observed in ADC-RuO2 system. The degradation efficiency of all the pollutants were more than 90%. After 2 min, residual rates from effluent of BPA, TC, SMX and AN were 8.31%, 0.81%, 3.81% and 2.73%, respectively. Thus, the flow-by electrochemical system exhibited the best oxidation capacity on TC, while the weakest on BPA. Figure 3c showed that the degradation of the four pollutants (BPA, TC, SMX and AN) basically conformed to the first-order kinetics (kobs = 1.23, 2.46, 1.64, and 1.81 min− 1, respectively). The results indicated that the reactive oxides preferentially reacted with TC, followed by AN and SMX, and the worst was BPA.
It could be proved that the ADC-RuO2 system had excellent performance for the degradation of antibiotics and industrial raw materials in the wastewater containing high concentrations of chloride ions. In contrast, radicals-based oxidation processes were weakened by the side reactions with some coexisting organic or inorganic substrates (such as chloride ions, etc.) because of their strong oxidizing and non-selective properties (Duan et al., 2015; Huang et al., 2021; Luo et al., 2019). However, the reactive oxides established in this system exhibited strong anti-interference ability and selective degradation ability. The results suggested that the system may degrade these pollutants through a non-radical process.
3.3 Identification of reactive oxidizing intermediates
ESR and radical scavenging experiments were typical means to analyze the oxidation mechanism. Hydroxyl radicals (•OH), free chlorine, and superoxide radicals (HO2•/O2•−) were considered as the main reactive oxides in the reaction process. TBA, NaHCO3, p-BQ as exclusive scavengers for hydroxyl radicals, free chlorine and superoxide radicals, respectively (Cai et al., 2022; Luna-Trujillo et al., 2020; Yang et al., 2018). Figure 4 showed that the addition of TBA or p-BQ barely inhibited the AN degradation. With 10 mM TBA or p-BQ, the removal efficiency of AN decreased insignificantly from 97.72–96.25% and 97.72–97.36%. And the kobs decreased from 1.94 min− 1 to 1.71 min− 1 and 1.88 min− 1 respectively, which means tiny quantity of the (•OH) and HO2•/O2•−. While in the presence of 10 mM NaHCO3 the removal efficiency of AN decreased from 97.72–86.42% and the kobs reduced from 1.94 min− 1 to 1.01 min− 1, which exhibited free chlorine playing a part as well. In general, it could be concluded that radical process was not the dominant pathway. Studies had
shown that hypochlorous acid can activate hydrogen peroxide to produce singlet oxygen (Guo & Liu, 2020; Lu et al., 2022). Therefore, FFA was commonly used as a quencher of 1O2 (k1O2, FFA = 1.2×108 M− 1s− 1) (Cheng et al., 2017). Figure 5 showed that the degradation efficiency of AN obviously decreased from the 97.75–71.47%, and the kobs was significantly cut down from 1.94 min− 1 to 0.62 min− 1 with 10 mM FFA. When the concentration of FFA was further increased to 50 mM and 100 mM, the degradation efficiency of AN decreased sharply to 53.93% and 26.97% respectively. The quenching experiments indicated that 1O2 may be the dominant reactive oxides for the degradation of AN in the system.
In order to confirm the assumption, the electron spin resonance (ESR) spectroscopy was conducted. The experimental results were shown in Fig. 4d. There was no obvious signal when ADC electrodes or RuO2 electrodes were employed alone. However, in the ADC-RuO2 system, strong peaks with intensity ratio of 1:1:1 were observed, which can be assigned to TEMPO generated by the oxidation of 1O2 (An et al., 2019). Moreover, with increasing the current to 200 mA, the intensity of TEMPO was significantly enhanced, indicating that increasing the current intensity can promote the generation of 1O2. Overall, the radical quenching tests and ESR analysis proved that the system went through a non-radical pathway, and singlet oxygen was the main reactive oxides.
3.4 Quantitative analysis of singlet oxygen generation
In the RuO2-ADC system, ClO− and H2O2 generated 1O2 at a ratio of 1:1:1 (pH = 10) (Wang et al., 2019). Figure 6 illustrated that production increased over time and current intensity. The yield of H2O2 and free chlorine increased from 0.05 to 0.31 mM·min− 1 and 0.05 to 0.35 mM·min− 1 with the current intensity increasing from 50 to 300 mA. Figure 6c the relationship of H2O2 and free chlorine were following monotonic function with current intensity (Eq. 4–5),
[H2O2] = 0.0012·I ‒ 0.0127 (4)
[ClO−] = 0.0011·I ‒ 0.005 (5)
where I was current intensity (mA), [H2O2] and [ClO−] were the yield of H2O2 and ClO− (mM).
It suggested that high current was favorable for the generation of H2O2 and free chlorine. At 200 mA, according to the fitted equation, the instantaneous production of hydrogen peroxide and free chlorine was 0.21 mM/min and 0.23 mM/min. According to the reaction formula (Eq. 6) (Wang et al., 2019), the theoretical production of 1O2 can be preliminarily calculated to be 0.2150 mM/min at a current intensity of 200 mA.
$$OC{{\text{l}}^ - }+{H_2}{O_2} \to {H_2}O+C{{\text{l}}^ - }+{}^{1}{O_2}$$
6
Furfuryl alcohol (FFA) was a common chemical indicator for the detection of singlet oxygen (k FFA = 1.2×108 M− 1 s− 1) (Cheng et al., 2017). 1O2 could be completely scavenged by FFA thus the reduction of FFA concentration was proportional to the amount of singlet oxygen generated. As shown in Fig. 6d, the stable residual rate of FFA was 40.77% with the pseudo-first-order rate constants (kobs, FFA) of 0.45 min− 1. According to the Eq. 3, the steady state concentration of singlet oxygen could be calculated to be 6.25×10− 11 M, which was quite less than the theoretical value of 0.2150 mM/min. A possible explanation for this might be that the short half-life of singlet oxygen (0.2‒2.0 µs) (Salokhiddinov et al., 1981); In addition, because of other substances existed in the measured free chlorine, such as perchlorate, ClO− yield might be overestimated (Shinohara et al., 2006). Moreover, according to relevant studies, the reaction rate between H2O2 and ClO− was affected by the relative molar ratio of each other. When the initial concentration of H2O2 and ClO− was 10 mg/L, it took two minutes to react completely (Agnez-Lima et al., 2012). However, as a reactive intermediate, 1O2 still exhibited significant impact on the pollutant degradation as showed in previous sections.
A novel and efficient non-radical oxidation process was constructed based on a natural air diffusion cathode (ADC) and a RuO2-Ti anode. A self-breathing and high-efficiency hydrogen peroxide-producing cathode was made of BP2000 exhibited great catalytic performance without aeration. Then ClO− from anode activated hydrogen peroxide to generate 1O2 efficiently degrading pollutants by non-radical oxidation process without adding any catalyst. Moreover, the system exhibited excellent degradation effect of multiple emerging pollutants of AN, BPA, TC, SMX. The steady-stable content of 1O2 was quantitatively determined to be 6.25×10− 11 M by the FFA probe. Overall, our findings provided a fast, low energy consumption and well controlled electrochemical oxidation method wishing to provide a new idea for future distributed water treatment technology. However, the intermediates produced in the degradation process need further investigation. And larger scale experiments will be conducted to verify the degradation efficiency of other substances.
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Acknowledge
This work was supported by the National Natural Science Foundation of China (No. 51808415). We would like to thanks Miss Wang and Mr. Wang at the Analytical & Testing Center of Wuhan University of Science and Technology for their help on SEM and BET analysis.
Funding
This work was supported by the National Natural Science Foundation of China (No. 51808415)
Author information
Yi Li, Shiwei Xie, and Jiaxiong Yao contributed equally to this work.
Authors and Affiliations
School of Urban Construction, Wuhan University of Science and Technology, Wuhan 430065, P. R. China
Yi Li, Shiwei Xie, and Jiaxiong Yao
Institute of High Performance Engineering Structure, Wuhan University of Science and Technology, Wuhan 430065, P. R. China
Shiwei Xie
Contributions
All authors contributed to the study conception and design. Material preparation, experiment conduct, data collection and analysis were performed by Yi Li, and Jiaxiong Yao. The first draft of the manuscript was written by Yi Li. Supervision, reviewing editing, and validation were performed by Shiwei Xie and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
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Correspondence to Shiwei Xie.
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Competing interests
The authors declare no competing interests.
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