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Article

Construction and Application of a Novel Three-Dimensional Electrocatalytic Ozonation System for Micropollutant Removal

by
Yang Zhang
1,
Xian Zhang
2,
Shiyi Wang
3,
Jiafeng Huang
3,
Yuxiao Zhang
3,
Yang Guo
3,
Chunrong Wang
1,* and
Tao Yu
4,*
1
School of Chemical and Environmental Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
2
Research Institute for Regional Situation Studies, Inner Mongolia University of Technology, Hohhot 010051, China
3
School of Environment, Tsinghua University, Beijing 100084, China
4
College of Resources and Environmental Engineering, Guizhou Institute of Technology, Guiyang 550025, China
*
Authors to whom correspondence should be addressed.
Catalysts 2025, 15(11), 1026; https://doi.org/10.3390/catal15111026
Submission received: 1 October 2025 / Revised: 16 October 2025 / Accepted: 28 October 2025 / Published: 31 October 2025
(This article belongs to the Special Issue Nanocatalysts for Contaminant Degradation)
Browse Figures
Versions Notes

Abstract

Conventional two-dimensional (2D) electrocatalytic ozonation faces challenges such as low mass transfer efficiency, limited hydroxyl radical (•OH) yield, and insufficient pollutant degradation rates. To address these limitations, this study developed a novel three-dimensional electrocatalytic ozonation system using a 316 stainless-steel skeleton as the cathode. By systematically comparing the ozone decay kinetics, •OH yield, imidacloprid degradation efficiency, and ozone mass transfer characteristics among the 3D electrocatalytic ozonation system, 2D electrocatalytic ozonation system, and conventional ozonation system, combined with electrode interface reaction analysis and structural simulation, the core mechanism by which the 3D structure enhances the electrocatalytic ozonation reaction was revealed. The results showed that the 3D electrocatalytic ozonation technology primarily promotes ozone decay and •OH generation through a reaction pathway dominated by the reduction of ozone at the cathode, while simultaneously enhancing pollutant removal efficiency. The pseudo-first-order kinetic constant for ozone decay in the 3D system reached 1.0 min−1, which was five times that of the 2D system (0.2 min−1). The •OH yield increased to 38%, significantly higher than that of the 2D system (15%) and conventional ozonation (10%). The complete degradation of imidacloprid was achieved within 5 min, and the degradation rate (2.14 min−1) was 10 times that of the 2D system. The high specific surface area (75 cm2/g, 30–90 times that of the 2D flat electrode) and 70% porosity of the 3D framework overcame the mass transfer limitation of the 2D structure, exhibiting excellent reaction activity. The ozone mass transfer amount was approximately 1.5 times that of the 2D electrode and 2 times that of conventional ozonation. This study provides theoretical support and technical basis for the engineering application of 3D electrocatalytic ozonation technology in the field of micro-pollutant control.

Graphical Abstract

1. Introduction

The increasing occurrence of micropollutants, such as pesticides and antibiotics, in aquatic environments poses a significant threat to ecological security and human health. Their low concentrations, persistent structures, and potential for bioaccumulation make them difficult to remove using conventional water treatment processes [1,2]. Imidacloprid (IMI), a widely used neonicotinoid pesticide, is frequently detected in water bodies and exhibits high toxicity to non-target aquatic organisms [3,4]. Consequently, developing efficient and stable technologies for micropollutant removal is a critical research focus in environmental engineering.
Advanced oxidation processes (AOPs) generate highly oxidizing hydroxyl radicals (•OH), which can non-selectively degrade persistent organic pollutants, making them a core technology for micropollutant control [5,6]. Electrocatalytic ozonation, an important AOP, combines electrochemical processes with ozone oxidation. It enhances •OH production by catalyzing ozone reduction at the cathode [7], improving pollutant mineralization efficiency by 40–60% compared to ozonation alone [8,9]. Conventional electrocatalytic ozonation systems typically use two-dimensional (2D) plate electrodes [10,11,12]. However, their limited specific surface area results in insufficient active sites, and the presence of a mass transfer boundary layer restricts the efficiency of ozone and •OH transport [13]. These limitations lead to low ozone utilization and high energy consumption, hindering practical application [14,15,16].
Three-dimensional (3D) electrode technology offers a solution by providing a larger surface area and enhanced mass transfer. This is achieved by filling the space between 2D electrodes with porous conductive materials like granular activated carbon or metal oxides, increasing the specific surface area to 500–1500 m2/g and reducing diffusion distances to the micrometer scale [17,18,19,20]. Recent studies integrating 3D structures with electrocatalytic ozonation have shown that optimizing the electric field and flow dynamics can further enhance ozone reduction and •OH generation at the cathode. Research has shown that three-dimensional electrodes offer considerably higher treatment efficiency for antibiotic wastewater than their two-dimensional counterparts [21]. Other studies have indicated that the combination of 3D electrodes with ozonation can significantly enhance •OH production and organic pollutant degradation efficiency [22]. In addition, a study employing microscale zero-valent iron particles as the three-dimensional cathode demonstrated a remarkable synergistic effect in the degradation of nitrobenzene, indicating that the 3D configuration effectively improved both mass transfer and reaction efficiency [23]. Furthermore, other researchers have developed structured three-dimensional electrode modules and systematically investigated their superior mass transfer and hydrodynamic behaviors during the electrocatalytic oxidation process, thereby reinforcing the notion that 3D electrodes possess inherent advantages in electrocatalytic applications [24]. Despite these advances, research has primarily focused on carbon-based or metal oxide materials filled between the electrodes [25,26,27,28], with limited attention given to low-cost, stable alternatives like stainless-steel. Key questions regarding the interface reaction mechanisms, mass transfer regulation by pore structure, and synergistic degradation effects for stainless-steel 3D cathodes remain unanswered.
316 stainless-steel, a Fe-Cr-Ni-Mo alloy, forms a protective Cr2O3 passive film, offering excellent corrosion resistance and electrochemical stability at a cost approximately 1/20th that of noble metal catalysts. These properties make it particularly suitable for harsh environments involving ozone and high salinity [29,30]. Compared to metal materials such as titanium, nickel, and copper, 316 stainless steel offers the most cost-effective solution across key dimensions including cost, stability, mechanical properties, and environmental compatibility [31,32,33]. Fabricating 316 stainless-steel into a 3D skeleton structure could combine material durability with enhanced mass transfer, potentially leading to an efficient and economical electrocatalytic ozonation system. This study constructed both 2D plate and 3D skeleton electrode electrocatalytic ozonation systems using 316 stainless-steel cathodes. We investigated the effects of electrode structure on ozone decay kinetics, •OH yield, imidacloprid degradation, and ozone mass transfer. The interface reaction mechanism and mass transfer enhancement were analyzed using linear sweep voltammetry (LSV) and COMSOL Multiphysics 5.6 simulations. Our findings provide a theoretical and technical foundation for applying 3D electrocatalytic ozonation in micropollutant control. To achieve this, the electrochemical properties, reaction kinetics, and mass transfer efficiencies of the 2D and 3D electrocatalytic ozonation systems were systematically compared and analyzed.

2. Results and Discussion

2.1. Electrode Structure and Interface Reaction Characteristics

2.1.1. Specific Surface Area and Porosity

The geometric specific surface area of the 316 SS skeleton electrode was approximately 75 cm2/g, about 30 times higher than that of the 2D plate electrode (2.5 cm2/g). When surface roughness was considered, the effective surface area increased to 225 cm2/g (i.e., nearly 90 times that of the 2D plate electrode), thereby providing substantially more active sites for electrochemical reactions. The porosity of the skeleton, determined by the water displacement method (see Supplementary Materials Text S3), was approximately 70%. This porous architecture forms 3D reaction channels that markedly enhance mass transfer and interfacial contact among ozone, target pollutants, and the electrode surface [34,35].

2.1.2. LSV Analysis

The electrolyte was aerated with ozone (O3/O2) for approximately 15 min, resulting in an O3 concentration of about 10 mg/L in the solution, after which linear sweep voltammetry (LSV) tests were conducted. As shown in Figure 1a, almost no current response was observed at the initial scanning potential of +0.2 V (vs. SCE). With the decrease in potential, when the cathode potential reached 0 V (vs. SCE), both the 2D cathode and 3D cathode (both made of 316 stainless-steel) exhibited current responses, indicating that the ozone reduction reaction was initiated at this potential. For the 3D electrode, the current response gradually increased as the potential continued to decrease, and when the potential was scanned to −1.2 V (vs. SCE), the current reached approximately 125 mA/cm2. In contrast, the current of the 2D electrode began to increase at −0.5 V (vs. SCE), rising from 1 mA/cm2 to 5 mA/cm2; thereafter, as the potential decreased further, the increasing trend of the current slowed down significantly. The 3D cathode maintained a continuously high reduction current, which demonstrated that its porous structure could overcome mass transfer limitations and allow the ozone reduction reaction to proceed continuously (Equations (1)–(3)) [36,37]. It can be concluded that the 3D stainless-steel cathode exhibits a significant ozone reduction reaction in the O3 solution. Although the 2D stainless-steel cathode initially undergoes O3 reduction on its surface, as the surface O3 is completely consumed, O3 cannot be replenished to the electrode surface in a timely manner under mass transfer-limited conditions, leading to changes in the chemical reactions on the electrode surface.
To further confirm the reaction process on the surface of the 2D cathode, the electrolyte was aerated with N2 for approximately 30 min to reach saturation (while keeping other conditions unchanged), followed by a second LSV test. As shown in Figure 1b, the current response of the N2-saturated solution increased significantly when the cathode potential decreased to −1.2 V (vs. SCE), which is attributed to the hydrogen evolution reaction (HER) occurring on the electrode surface (Equation (4)). In the O3 environment, a significant increase in current response was also observed when the potential dropped to −1.2 V (vs. SCE). This phenomenon indicates that at this stage, O3 on the surface of the 2D cathode was depleted due to the ozone reduction reaction; however, under mass transfer limitations, O3 could not be continuously replenished to the electrode surface, leading to the occurrence of HER on the electrode surface thereafter. Consistent with this observation, electrocatalytic ozonation technology has been shown in multiple studies to exhibit accelerated oxidation kinetics with increasing current/charge. Research focusing on 4-chlorobenzoic acid (p-CBA) and 1,4-dioxane as target pollutants has demonstrated that the electrocatalytic ozonation process can significantly enhance the degradation rate while reducing energy consumption/cell voltage, highlighting the core role of O3 reduction at the cathode in the “synergistic effect” [38]. The results of this study quantitatively extend this trend and further confirm that the 3D cathode structure can amplify the synergistic effect.
O 3 − + e − → O 3 −
O 3 − + H 2 O → ∙ O H + O 2 + O H −
O 3 − + 2 e − + H 2 O → O 2 + 2 O H −
2 H 2 O + 2 e − → H 2 + 2 O H −

2.2. Ozone Decay and •OH Yield

2.2.1. Ozone Decay Kinetics

Under the condition that tert-butanol (TBA) inhibits the •OH chain reaction, the ozone decay patterns of different systems are shown in Figure 2. Due to the addition of excess TBA, which effectively terminates the ozone chain reaction, the O3 decay in the conventional ozonation system is relatively slow, requiring approximately 30 min for complete decay, with a pseudo-first-order kinetic constant of 0.1208 min−1. In the electrocatalytic ozonation systems, the O3 decay rate is significantly accelerated. For the 2D electrocatalytic ozonation system, although complete O3 decay still takes about 30 min, the decay rate constant increases to 0.2 min−1, which is 1.7 times higher than that of the conventional ozonation system. When the 3D stainless-steel cathode is used, complete O3 decay is achieved in only 5 min, with a kinetic constant of 1.0 min−1—this is 5 times higher than that of the 2D electrocatalytic ozonation system and nearly 8.3 times higher than that of the conventional ozonation system. These results indicate that the introduction of the electrochemical process greatly accelerates ozone decay, and the cathode structure has a particularly significant impact on this process.

2.2.2. •OH Yield Comparison

The •OH yields of different systems are presented in Figure 3. In the conventional ozonation system, the generation of •OH mainly originates from the self-decay of O3, with a yield of approximately 10%. The 2D electrocatalytic ozonation system can promote •OH generation to a certain extent, increasing the •OH yield to 15%. When the 3D stainless-steel cathode is adopted, the •OH yield is further significantly improved, reaching 38%—nearly 4 times that of the conventional ozonation system. This indicates that the generation pathway of •OH in the electrocatalytic ozonation system has undergone a fundamental transformation. Different from the pathway dominated by traditional ozonation processes (e.g., spontaneous decomposition of O3), the •OH in this system is mainly derived from the direct 1-electron reduction reaction of dissolved O3 on the cathode surface (Equations (1) and (2)). This electrocatalytic reduction process serves as the main contributor to •OH generation, significantly increasing the generation rate of •OH and thereby enhancing the oxidation efficiency of the entire system. Relevant studies have shown [9,38] that the 1-electron reduction of ozone on the surface of metal cathodes is the primary source of •OH in electrocatalytic ozonation systems, and it represents the most critical and effective mechanism for •OH generation in this technology.
Although the 2D and 3D cathodes have the same projected area, their structural differences lead to significant disparities in electrochemical behavior. The 2D electrode only has a limited surface in contact with the solution, resulting in insufficient catalytic active sites and being subject to mass transfer limitations. These factors cause the replenishment rate of O3 to be lower than its consumption rate, thereby inhibiting further improvements in the O3 decay rate and •OH yield. In contrast, due to its large specific surface area and porous structure, the 3D electrode not only significantly enhances the directional migration of O3 to the electrode surface and the probability of interfacial reactions, but also provides more catalytic active sites, improves current distribution, and overcomes the mass transfer limitations of traditional 2D structures. Ultimately, this effectively promotes the rapid decay of O3 and the efficient generation of •OH [39]. It should be noted that the •OH yield is not only controlled by current density and cathode material but also depends on mass transfer and phase processes. By expanding the interface through structure (3D cathode), shortening diffusion distance, and increasing the interphase mass transfer coefficient, the efficiency of O3 conversion to •OH can be systematically improved. As a result, higher radical utilization efficiency and pollutant removal rate can be achieved under the same O3 dosage [40], which is consistent with the conclusions of this study.

2.3. Imidacloprid Degradation Performance

2.3.1. Degradation Efficiency and Kinetics

To further elucidate the degradation efficiency of various ozonation technologies toward micro-pollutants, imidacloprid (IMI) was selected as the model contaminant in this study. Experiments were conducted under controlled conditions, with a current intensity of 100 mA, an ozone aeration concentration of 14 mg/L, and an aeration flow rate of 0.25 L/min. The corresponding results are illustrated in Figure 4.
In terms of degradation efficiency, all three technical systems can achieve complete removal of IMI in Figure 4a, but there are significant differences in their degradation rates. In the conventional ozonation system, 20 min are required for the complete degradation of IMI. Although the 2D cathode-based electrocatalytic ozonation system also enables complete IMI degradation within 20 min, its degradation process is faster: 70% of IMI is degraded at the 5 min mark, compared to only 45% degradation by conventional ozonation alone at the same time point. The 3D cathode-based electrocatalytic ozonation system exhibits the most prominent advantage—it can achieve complete IMI removal in just 3 min, with a substantial improvement in degradation rate.
From a kinetic perspective, combined with the pseudo-first-order reaction kinetic fitting results in Figure 4b, it can be seen that there are significant differences in the degradation kinetic constants among the three systems. The pseudo-first-order kinetic constant of the conventional ozonation system is approximately 0.18 min−1, while that of the 2D cathode-based electrocatalytic ozonation system is 0.21 min−1. In contrast, the kinetic constant of the 3D cathode-based electrocatalytic ozonation system increases significantly to 2.14 min−1, which is about 10 times higher than that of the 2D cathode-based electrocatalytic ozonation system. This further confirms the significant optimization effect of the 3D cathode structure on degradation kinetics. Additionally, relevant studies have shown that the 3D electrocatalytic ozonation technology using a titanium-based electrode as the cathode achieves a thiamethoxam removal rate of over 70%, exhibiting higher degradation efficiency than the single ozonation process [41].

2.3.2. Analysis of Degradation Mechanism

The differences in IMI degradation performance among the three ozonation systems essentially stem from variations in their degradation mechanisms, and the optimization of the cathode structure is the key factor driving the transformation of mechanisms and the improvement of efficiency. In the conventional ozonation system, ozone mainly generates •OH through self-decomposition to achieve IMI degradation; however, the low efficiency of the self-decomposition process results in a relatively slow overall degradation rate [42]. When the 2D cathode-based electrocatalytic ozonation system is introduced, the electrochemical effect alters the conversion pathway of ozone. This shifts the ozone conversion in the system from the traditional self-decomposition-induced •OH generation to a mechanism dominated by electrocatalytic •OH production [43]. Since the efficiency of electrocatalytic •OH generation is higher than that of ozone self-decomposition, the IMI degradation performance is improved. The 3D cathode-based electrocatalytic ozonation system exhibits superior degradation performance, with the core reason lying in the 3D cathode’s larger specific surface area, which provides more abundant catalytic active sites. During the reaction, more ozone molecules can contact and attach to the cathode surface at the same instant. Through catalyzing the O3 reduction reaction, the production amount and rate of •OH are significantly enhanced, ultimately achieving the rapid degradation of IMI. This also fully confirms that the 3D cathode structure can significantly improve the effective utilization rate of ozone in the degradation system and optimize the overall degradation mechanism.

2.4. Ozone Mass Transfer Efficiency

2.4.1. Ozone Concentration Dynamics

(1)
Variation in Gas-Phase Ozone Concentration
In the first 3 min of the reaction, the differences in the outlet gas-phase ozone concentration among the three technologies were small (Figure 5a). As the reaction proceeded, the variation trends began to diverge. For the conventional ozonation technology, the outlet gas-phase ozone concentration increased rapidly and tended to stabilize at approximately 10 min, remaining at 12 mg/L until the end of the reaction. In contrast, the outlet gas-phase ozone concentration of the 2D cathode-based electrocatalytic ozonation technology was generally lower, reaching a stable value of about 10 mg/L. The 3D cathode-based electrocatalytic ozonation technology exhibited the lowest outlet gas-phase ozone concentration, which was only around 8 mg/L at the end of the reaction. This phenomenon indicates that under the conditions of the 3D system, more gas-phase ozone is transferred to the liquid phase.
(2)
Variation in Liquid-Phase Ozone Concentration
In terms of the liquid-phase ozone concentrations of the three technologies (Figure 5b, the ozone concentrations in the solution were all relatively low within the first 5 min of the reaction. The main reason is that at the initial stage of the reaction, the concentration of organic matter in the solution was relatively high, leading to the rapid consumption of ozone. Particularly in the electrocatalytic ozonation technologies, ozone on the electrode surface could be rapidly reduced to •OH at the cathode. After 5 min, the liquid-phase ozone concentration of the conventional ozonation technology increased rapidly, reaching approximately 2.3 mg/L at the end of the reaction. The liquid-phase ozone concentration of the 2D cathode-based electrocatalytic ozonation technology also showed an upward trend, reaching 1.7 mg/L at 20 min, but it remained lower than that of the conventional ozonation technology throughout the process. For the 3D cathode-based electrocatalytic ozonation technology, the liquid-phase ozone concentration was maintained within a relatively low range (approximately 0.3 mg/L) during the entire reaction. This indicates that the 3D electrocatalytic ozonation system improves the utilization efficiency of O3.

2.4.2. Mass Transfer Flux and Efficiency

Ozone mass transfer amount and mass transfer efficiency are the core factors affecting the degradation performance of the system. The results in Figure 5c,d reveal the differences in ozone mass transfer among the three technologies, explaining the variation patterns of gas-phase and liquid-phase ozone concentrations. In terms of mass transfer amount, as the reaction proceeded, the ozone mass transfer amount of all three systems increased continuously, but the final gaps were significant. At the end of the reaction, the mass transfer amount of the conventional ozonation technology was 31 mg/L; the mass transfer amount of the 2D cathode-based electrocatalytic ozonation technology was approximately 1.5 times that of the conventional technology, demonstrating the preliminary enhancement of mass transfer by electrocatalysis. In contrast, the mass transfer amount of the 3D cathode-based electrocatalytic ozonation technology reached nearly 65.61 mg/L, which was about twice that of the conventional technology—this highlights the significant promotion effect of the 3D cathode on ozone mass transfer. Regarding mass transfer efficiency, the 3D cathode-based electrocatalytic ozonation technology was also significantly higher than the other two technologies. This indicates that electrocatalytic ozonation technology (especially the 3D cathode configuration) can enhance the dissolution of ozone into the solution and improve gas–liquid mass transfer efficiency, allowing more gas-phase ozone to enter the liquid phase and convert into •OH. This provides sufficient active species for the efficient removal of pollutants, which is also consistent with the result that the 3D system maintains a stable low liquid-phase ozone concentration. These findings confirm the advantage of the 3D system in the synergistic enhancement of mass transfer and reaction.
In addition, this study evaluated the energy consumption (EEO) under the condition of 90% organic removal across different systems. The calculated EEO values were 0.24 kWh/m3 for the three-dimensional (3D) electrocatalytic ozonation system, which is lower than those of the two-dimensional (2D) electrocatalytic ozonation system (0.91 kWh/m3) and the conventional ozonation process (1.11 kWh/m3). These results indicate that although electrochemistry is introduced into the ozone system, it enhances both the mass transfer and decomposition of O3, leading to accelerated pollutant degradation within a shorter time frame and thereby reducing overall energy consumption. Detailed calculation methods are provided in the Supplementary Materials (Text S3: Analytical Methods).

2.5. Numerical Simulation Analysis

To clarify the differences in the catalytic ozonation reactions on the surfaces of different electrode structures, this study compared the product concentration distribution characteristics of the three systems through COMSOL simulation. (model: Supplementary Materials Figure S3).
The simulation results (Figure 6 and Figure 7) show that the electrode type has a significant impact on the O3 catalytic reaction and product distribution. The O3 reaction products of the flat stainless-steel electrode (2D electrode) are distributed in a uniform thin layer on the surface, with the concentration peak located on the side of the fluid near the outlet. Restricted by the smooth surface, a stable boundary layer is formed between the reaction interface and the flow field, which inhibits the liquid phase from rapidly reaching the interface to participate in the reaction. In contrast, the porous stainless-steel framework electrode (3D electrode) exhibits a higher internal product concentration peak, and the high-concentration region extends to the internal pores of the electrode. Its pore structure can induce local backflow, enhance the internal circulation of the liquid, shorten the mass diffusion path, result in a more dispersed and three-dimensional product concentration distribution, and achieve more sufficient contact at the reaction interface.
This difference stems from the larger specific surface area of the porous framework electrode and the optimization of the mass transfer boundary layer by its micro-pore structure. On one hand, it increases the flux of O3 to the reaction sites; on the other hand, it enhances the mass renewal at the reaction interface through micro-scale flow disturbance, thereby reducing concentration polarization. As shown in Figure 7, the product concentration on the surface of the 3D cathode is approximately 5–6 times higher than that on the 2D cathode. Additionally, more •OH is observed in the experiment, indicating that O3 can be rapidly consumed and converted. The simulation results are highly consistent with the experimental conclusions.

3. Materials and Methods

The electrocatalytic ozonation reactor consisted of a cylindrical plexiglass vessel (φ7 cm × 15 cm) with an effective volume of 400 mL (Figure 8). The electrode system included a fixed dimensionally stable anode (DSA; Ti/RuO2-IrO2, 4 cm × 5 cm) and two interchangeable cathodes: a 316 SS plate electrode (4 cm × 5 cm) for the 2D system and a 316 SS skeleton electrode (diameter 5 cm, mass 5 g) for the 3D system. All electrodes were cleaned and activated before use (see Supplementary Materials Text S1).
Ozone was generated from high-purity oxygen using an ozone generator (preheated for 30 min) and introduced into the reactor via a microporous diffuser (pore size: 5–10 μm). The gaseous ozone concentration was controlled by adjusting the generator power and monitored online with an ozone analyzer (BMT964, BMT Messtechnik GmbH, Stahnsdorf, Germany). Dissolved ozone concentration was measured using the indigo colorimetric method [44].
Different experimental configurations were used based on the objective:
(1)
Linear Sweep Voltammetry (LSV): A three-electrode system with an electrochemical workstation (CS1350, Cortest Instruments, Wuhan, China), under continuous ozone aeration.
(2)
Ozone decay kinetics and •OH yield: A two-electrode system powered by a DC supply, initiated by adding pre-saturated ozone water (see Supplementary Materials Text S2).
(3)
Micropollutant degradation and ozone mass transfer: A two-electrode system with DC power, under continuous ozone aeration.
(4)
The primary experiments involved simultaneous application of DC power and ozone gas (electrocatalytic ozonation process). Control experiments included: (a) ozonation alone (no electrodes, no field), (b) 2D electrocatalytic ozonation, and (c) 3D electrocatalytic ozonation.
(5)
Experiments used deionized water spiked with imidacloprid (500 μg/L; 98%, Sigma-Aldrich, Saint Louis, MO, USA) and 0.05 M Na2SO4 as the electrolyte. Tert-butanol (20 mM) was added to quench •OH chains during yield measurements [45].
A comprehensive description of the analytical methods is provided in the Supplementary Materials.

4. Conclusions

This study comprehensively constructed and evaluated the performance of a novel 3D electrocatalytic ozonation system employing a 316 stainless-steel skeleton cathode, in comparison to conventional 2D electrocatalytic ozonation and ozonation systems. The results unequivocally demonstrate that the 3D electrode structure profoundly enhances ozone utilization, hydroxyl radical generation, and pollutant degradation by optimizing mass transfer and electrochemical reactions. The main findings are summarized as follows:
(1)
The 316 stainless-steel framework 3D cathode exhibits significantly superior specific surface area (75 cm2/g) and porosity (70%) compared to the 2D flat electrode. Its LSV curve shows a higher ozone reduction current. The 3D porous structure can overcome mass transfer limitations, provide sufficient active sites for the ozone reduction reaction, and ensure continuous reactant supply. This addresses the bottlenecks of the 2D electrode, such as insufficient active sites and a thick mass transfer boundary layer.
(2)
The 3D electrocatalytic ozonation system significantly enhances ozone decay in the solution. The ozone decay rate (1.0 min−1), •OH yield (38%), and IMI degradation rate (2.14 min−1) of the 3D system are 5 times, 2.1 times, and 10 times those of the 2D system, respectively. In the 3D system, the •OH generation pathway shifts from being dominated by conventional ozone self-decomposition to being dominated by the 1-electron reduction reaction of ozone on the cathode surface. The high specific surface area and three-dimensional porous structure greatly improve the efficiency of this reduction reaction, providing sufficient strong oxidizing species for pollutant degradation.
(3)
Using imidacloprid (a typical neonicotinoid pesticide) as the target pollutant, the 3D electrocatalytic ozonation system demonstrates excellent degradation performance. Although the 2D system degrades 70% of imidacloprid within 5 min (outperforming the 45% degradation rate of conventional ozonation), it is still limited by mass transfer. In contrast, the 3D system achieves an optimization of the degradation mechanism and an order-of-magnitude breakthrough in degradation rate by doubling the number of active sites and improving the reactant contact efficiency.
(4)
The 3D electrocatalytic ozonation system significantly improves the mass transfer efficiency of O3 from the gas phase to the liquid phase. At the end of the reaction, the ozone mass transfer amount of the 3D system is approximately 1.4 times that of the 2D electrocatalytic ozonation system and 2 times that of the conventional ozonation technology. Meanwhile, the three-dimensional porous structure shortens the diffusion distance through flow field disturbance, notably improving the cross-interface mass transfer efficiency of ozone and achieving synergistic enhancement of mass transfer and reaction.
(5)
COMSOL simulations confirm the advantages of the 3D structure in mass transfer enhancement and reaction interface optimization from the perspectives of micro-scale flow field, electric field, and substance distribution. These simulation results are highly consistent with the experimental results, providing theoretical support for the structural design of 3D electrocatalytic ozonation reactors.
In summary, the 3D electrocatalytic ozonation system with a 316 stainless-steel framework constructed in this study optimizes the ozone mass transfer process and electric field distribution through structural innovation. It achieves the synergistic improvement of mass transfer efficiency, •OH yield, and micro-pollutant degradation rate, providing a key technical pathway and theoretical basis for the engineering application of advanced oxidation technologies in the field of aquatic environment micro-pollutant control.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal15111026/s1. Refs. [21,44,46,47,48,49,50,51,52,53,54,55,56] are cited in the Supplementary Materials.

Author Contributions

Conceptualization, Y.Z. (Yang Zhang) and C.W.; methodology, Y.Z. (Yang Zhang) and X.Z.; software, Y.Z. (Yuxiao Zhang); validation, Y.Z. (Yang Zhang), S.W. and J.H.; formal analysis, Y.Z. (Yang Zhang); investigation, S.W. and J.H.; resources, Y.G.; data curation, Y.Z. (Yang Zhang); writing—original draft preparation, Y.Z. (Yang Zhang); writing—review and editing, C.W. and T.Y.; visualization, Y.Z. (Yang Zhang); supervision, C.W. and T.Y.; project administration, X.Z.; funding acquisition, T.Y., Y.G. and X.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was financially supported by the Guizhou Institute of Technology high level talents research start-up funding (grant number XJGC20190964), the National Natural Science Foundation of China (grant number 52160007) and the Fundamental Research Program of Shanxi Province (grant number 202303021212012).

Data Availability Statement

The original contributions presented in this study are included in the article and Supplementary Materials. Further inquiries can be directed to the corresponding authors.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Figure 1. LSV curves of the 3D and 2D cathodes in (a) O3-saturated solution; (b) N2 and O3-saturated solutions.
Figure 1. LSV curves of the 3D and 2D cathodes in (a) O3-saturated solution; (b) N2 and O3-saturated solutions.
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Figure 2. Ozone decay kinetics for the different systems.
Figure 2. Ozone decay kinetics for the different systems.
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Figure 3. •OH yields for the different systems.
Figure 3. •OH yields for the different systems.
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Figure 4. (a) Imidacloprid degradation profiles. (b) Corresponding pseudo-first-order kinetics plots.
Figure 4. (a) Imidacloprid degradation profiles. (b) Corresponding pseudo-first-order kinetics plots.
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Figure 5. (a) Gaseous and (b) aqueous ozone concentrations, (c) ozone mass transfer flux, and (d) mass transfer efficiency for the different systems.
Figure 5. (a) Gaseous and (b) aqueous ozone concentrations, (c) ozone mass transfer flux, and (d) mass transfer efficiency for the different systems.
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Figure 6. Simulation results for the 3D cathode (a–c) and 2D cathode (d–f). (a,d) Electric field distribution; (b,e) Pressure distribution; (c,f) Product concentration distribution.
Figure 6. Simulation results for the 3D cathode (a–c) and 2D cathode (d–f). (a,d) Electric field distribution; (b,e) Pressure distribution; (c,f) Product concentration distribution.
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Figure 7. Comparison of maximum surface flow velocity and product concentration between the 3D and 2D cathodes.
Figure 7. Comparison of maximum surface flow velocity and product concentration between the 3D and 2D cathodes.
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Figure 8. Schematic of the electrocatalytic ozonation reactor. 1. Cathode, 2. Anode, 3. Diffuser, 4. Magnetic stirrer.
Figure 8. Schematic of the electrocatalytic ozonation reactor. 1. Cathode, 2. Anode, 3. Diffuser, 4. Magnetic stirrer.
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Zhang, Y.; Zhang, X.; Wang, S.; Huang, J.; Zhang, Y.; Guo, Y.; Wang, C.; Yu, T. Construction and Application of a Novel Three-Dimensional Electrocatalytic Ozonation System for Micropollutant Removal. Catalysts 2025, 15, 1026. https://doi.org/10.3390/catal15111026

AMA Style

Zhang Y, Zhang X, Wang S, Huang J, Zhang Y, Guo Y, Wang C, Yu T. Construction and Application of a Novel Three-Dimensional Electrocatalytic Ozonation System for Micropollutant Removal. Catalysts. 2025; 15(11):1026. https://doi.org/10.3390/catal15111026

Chicago/Turabian Style

Zhang, Yang, Xian Zhang, Shiyi Wang, Jiafeng Huang, Yuxiao Zhang, Yang Guo, Chunrong Wang, and Tao Yu. 2025. "Construction and Application of a Novel Three-Dimensional Electrocatalytic Ozonation System for Micropollutant Removal" Catalysts 15, no. 11: 1026. https://doi.org/10.3390/catal15111026

APA Style

Zhang, Y., Zhang, X., Wang, S., Huang, J., Zhang, Y., Guo, Y., Wang, C., & Yu, T. (2025). Construction and Application of a Novel Three-Dimensional Electrocatalytic Ozonation System for Micropollutant Removal. Catalysts, 15(11), 1026. https://doi.org/10.3390/catal15111026

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