La-doped Ti/Sb-SnO2 electrode enhanced removal of microplastics by advanced electrocatalysis oxidation process (AEOP) strategy

La-doped Ti/Sb-SnO2 electrode enhanced removal of microplastics by advanced electrocatalysis oxidation process (AEOP) strategy | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article La-doped Ti/Sb-SnO 2 electrode enhanced removal of microplastics by advanced electrocatalysis oxidation process (AEOP) strategy Weikang Zheng, Boyan Wang, Zhenzhong Liu, Hongwei Yang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4416872/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Microplastics (MPs) in the aqueous environments has attracted widespread attention because of its potential risk to human health .Its high stability makes it difficult to be degraded and long term presence in the environment. Therefore, it is crucial to find an efficient and clean technology to remove microplastics in water. The advanced electrocatalysis oxidation process (AEOP) shows great potential for application. In this work, We focused on preparing Ti/Sb-SnO 2 electrodes doped with different rare earth elements (La, Ce, Sm or Nd) as active layer by sol-gel method. The electrooxidation system has efficiently degraded MPs in aqueous solution. The optimal parameters for the removal of MPs were electrode spacing of 1.5 cm, current density of 46.67 mA cm -2 , Na 2 SO 4 electrolyte concentration of 0.22 mol·L -1 , and initial solution pH of 7. After 3 h, MPs removal rate by Ti/La-Sb-SnO 2 system reached 28.3 %, which was higher than the Ti/Ce-Sb-SnO 2 , Ti/Sm-Sb-SnO 2 , Ti/Nd-Sb-SnO 2 and Ti/Sb-SnO 2 electrode, the removal rates were increased by 8.23 %, 10.13 %, 16.28 % and 77 %, respectively. Electrochemical performance tests and •OH (Hydroxyl radicals) generation results indicated that the surface of Ti/La-Sb-SnO 2 electrode had abundant active sites, which promoted the formation of •OH to degrade microplastics effectively. In summary, the rare earth element-doped Ti/Sb-SnO 2 electrode provides crucial technological support for the electrooxidative removal of microplastics from water. Microplastics AEOP strategy Ti/La-Sb-SnO2 electrode rare earth elements electrocatalytic activity. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Highlights La-doped Ti/Sb-SnO 2 electrode was synthesized by sol-gel method The electrocatalytic activity of Ti/La-Sb-SnO 2 electrode was effectively improved La-doped Ti/Sb-SnO 2 electrode showed superior polystyrene microplastics removal AEOP is a potential strategy for the removal of microplastics in water 1 Introduction As an emerging environmental pollutant, microplastics have attracted much attention in recent years (Ji et al., 2024 ) and become a focal point of water pollution research (Rodrigues et al., 2024 ; Zheng et al., 2024a). They are ubiquitous in our daily lives and pose a great threat to the ecological environment and human health (Duan et al., 2021 ). The hazards of microplastics primarily stem from three aspects. The microplastics themselves and their monomers, the additives present in plastics (Andrady, 2017 ), and the toxic substances adsorbed onto microplastics (Rodriguez-Narvaez et al., 2021 ). Due to their high molecular weight and strong durability, microplastics can persist in the environment for decades or even centuries (Shen et al., 2022 ). Consequently, the removal of microplastics in water presents significant challenges. In recent years, researchers have investigated various water treatment methods (Ma et al., 2019 ) to eliminate microplastics (Zheng et al., 2024b ). These methods comprise coagulation-flocculation (XIANGXiao-fang, 2024), biological treatment (Dai et al., 2024 ), filtration (Talvitie et al., 2017 ), magnetic separation (Grbic et al., 2019 ), photocatalysis (Uheida et al., 2021 ), and electrochemistry (Kiendrebeogo et al., 2021 ). Of these methods, advanced electrocatalysis oxidation process (AEOP) (Ning et al., 2023 ) has demonstrated significant benefits in degrading microplastic pollutants due to its high efficiency (Yan et al., 2023 ), operational simplicity, and environmental friendliness (Ma et al., 2023 ). Electrode materials' properties directly impact the efficiency of AEOP water treatment (Dolatabadi et al., 2023 ). As a result, improving the activity and stability of electrode materials through modification and development has become a crucial and popular topic in electrochemical water treatment research. Currently, research on the electrocatalytic oxidation about microplastics removal is limited. Most of the studies concentrated on using boron-doped diamond (BDD) electrodes (Mukherjee et al., 2023 ), which were expensive and challenging to apply widely. The Ti/Sb-SnO 2 electrode demonstrates excellent electrocatalytic performance, mainly relying on an indirect oxidation process that generates free radicals. The Ti/Sb-SnO 2 electrode costs only one-sixth of the BDD electrode (Zheng et al., 2024b ). Nevertheless, Ti/Sb-SnO 2 electrode is unstable due to the structural differences between the substrate and the active layer. In the AEOP, the reactive oxygen species generated may diffuse to the substrate's surface, resulting in a high-resistance TiO 2 insulating layer formation and significantly reducing the electrode's conductivity, leading to decrease in the electrocatalytic activity (Hu et al., 2021 ). Ti/Sb-SnO 2 electrode modification enhances the electrocatalytic performance and removal efficiency of microplastics, significantly reducing the cost of AEOP and facilitating its industrial application. Rare earth elements have unique structures (Xue et al., 2018 ), both electronically and physicochemically. Doping these elements into the active layer of stable anodes can alter the electrocatalytic performance of the electrode (Ma et al., 2024 ). Based on this premise, we aim to prepare Ti-based metal oxide electrodes for the study of microplastic removal. Different rare earth elements (La, Sm, Nd, or Ce) were doped. Polystyrene (PS) microplastics were used as target pollutants. We focused on the optimal preparation of the electrode, including the coating preparation method, coating layers, heat treatment temperature, and rare earth doping amount. We also investigated the factors affecting the catalytic oxidation and removal of PS microplastics with this electrode, including electrolysis time, current density, electrode spacing, electrolyte types, electrolyte concentration, and initial pH in the solution. The goal was to improve the performance of AEOP for the removal of PS microplastics. We aim to provide new insights into removing microplastics from real water bodies. 2 Experimental 2.1 Materials and chemical reagents Pure Ti mesh was obtained from Suzhou Shuer Tai industrial Technology Co., Ltd. SnCl 5 ·5H 2 O and Sb 2 O 3 were bought form Shanghai Aladdin Biochemical Technology Co., Ltd. La(NO 3 ) 3 ·6H 2 O, Ce(NO 3 ) 3 ·6H 2 O, Nd(NO 3 ) 3 ·6H 2 O, and Sm(NO 3 ) 3 ·6H 2 O were provided from Sinopharm Chemical Reagent Co., Ltd. Other chemical reagents, such as sodium sulfate, sodium carbonate, hydrochloric acid, sodium hydroxide, methanol, sodium nitrate, salicylic acid, anhydrous oxalic acid, polyethylene glycol 2000 were all analytical grade AR. 2.2 Preparation of Ti/La-Sb-SnO 2 electrode The Ti substrate underwent a pre-treatment process by polishing it with 120, 240, and 600 grit sandpaper consecutively, with the aim of removing impurities and oxide films from its surface. Afterward, Ti substrate was immersed in 15 wt% NaOH and underwent constant temperature water bath heating at 90 ℃ for 1 h, aiming to remove any oil residue on its surface. Subsequently, the Ti substrate was immersed in 10 wt% oxalic acid and heated to keep it under micro-boiling conditions for 2 h, achieving etching of the surface, which led to the formation of uneven gray pitted surfaces and loss of its metallic luster. The main objective is to improve the specific surface area of the Ti substrate and enhance its adhesion with metal oxide active coating. Lastly, the Ti substrate were immersed in 3 wt% oxalic acid and stored for future use. The surface morphology of Ti substrate before and after acid etching was shown in Fig. S1 . In this work, Sol-gel method was prepared for the Ti/La-Sb-SnO 2 electrode (Wang et al., 2019 ). (1) Methods for preparing sols For this experiment, we prepared a sol with a concentration ratio of Sn:Sb of 100:10 and a Sn concentration of 1 mol·L − 1 . The following steps were performed: ① To prepare solution A, SnCl 4 ·5H 2 O should be dissolved in anhydrous ethanol.. ② For solution B, Sb 2 O 3 should be dissolved in 2 mL of concentrated hydrochloric acid. ③ Pour solution B into solution A and stir well. Then add polyethylene glycol 2000 (2 g) to the solution. Heat the solution at 60°C while stirring for 1 h to form the sol solution. ④ Take a certain amount of the sol solution and add La rare earth salts according to the respective proportions. Stir the solution in a water bath at 60°C until complete dissolution, then let it stand for at least 120 minutes for aging. (2) Impregnation and heat treatment: ① Immerse the pre-treated Ti substrate in the sol solution for 2 minutes. Slowly lift it out, allowing the excess sol on the surface to drip dry, forming a uniform coating on the substrate surface. ② Place the electrode in an oven and dry at 120°C for 20 minutes to form a gel. Then transfer the electrode to the muffle furnace at 450°C and sinter for 10 minutes. ③ Repeat steps ①-② for a total of 10 times. For the final cycle, perform a high-temperature heat treatment in the muffle furnace for 2 h. The Ti/La-Sb-SnO 2 electrode can be obtained after cooling for further use. Ti/Ce-Sb-SnO 2 , Ti/Sm-Sb-SnO 2 , Ti/Nd-Sb-SnO 2 were obtained by the same method. 2.3 Characterization and Performance Test Electrochemical measurements were tested by PARSTAT 6000 electrochemical workstation (Fig. 1 ). The prepared electrode served as the working electrode, pure platinum electrode as the auxiliary electrode, and saturated calomel electrode as the reference electrode. The conditions for the Linear Sweep Voltammetry (LSV) test were a scan rate of 1.0 mV·s -1 , a range of 0 to 2.5 V, and conducted in H 2 SO 4 solution of 0.5 mol·L -1 (Doumbi et al., 2023; Rathinavelu et al., 2023 ). Conditions for the Cyclic Voltammetry (CV) test were a scan rate of 20 mV·s -1 , a range of 0.5 V to 2 V, and conducted in H 2 SO 4 solution of 0.22 mol·L -1 . Conditions for the Electrochemical Impedance Spectroscopy (EIS) test were a perturbation amplitude of 5 mV, a frequency range of 100 kHz to 10 mHz, a testing potential of 1.2 V, and H 2 SO 4 solution of 0.22 mol·L -1 . Impedance parameters were fitted by Zview software (Sun et al., 2020 ). Surface morphology of the electrode was observed by scanning electron microscope (SEM) (SIGMA500), and the crystal structure of the electrode surface was analyzed by X-ray diffractometer (XRD) (Empyrean 03030502) (Liu et al., 2023 ). The generation of •OH was indirectly determined by high-performance liquid chromatography (HPLC) (Doumbi et al., 2023). 2.4 AEOP removal of PS microplastics 2.4.1 Experimental procedures As shown in Fig. 2 . PS microplastics of 1 g·L − 1 (100 mesh) were added into electrolyte cell. Ti/La-Sb-SnO 2 electrode was used as the anode (in the form of 50×30×1 mm) and Ti electrode was used as the cathode. Constant current electrolysis was controlled with a DC stabilized power supply and simultaneously record the cell voltage. We filtered the solution to collect remaining microplastics after the reaction. In order to minimize experimental errors, we obtained the average of two parallel experiments as the final result. 2.4.2 Removal rate computation PS microplastics removal rate were calculated by the weighing method and using the following Eqs. (1):. PS Removal rate= \({\text{W}}_{\text{0}}\text{-}{\text{W}}_{\text{t}}\text{}{\text{W}}_{\text{0}}\text{×100%}\) (1) Where W 0 and W t represented the mass of PS microplastics at time 0 and t after after filtration and drying. 3 Results and discussion 3.1 Electrocatalytic performance analysis In the Fig. 3 a, LSV curves were shown for the five electrodes, the oxygen evolution potentials of Ti/La-Sb-SnO 2 , Ti/Sb-SnO 2 , Ti/Sm-Sb-SnO 2 , Ti/Ce-Sb-SnO 2 , and Ti/Nd-Sb-SnO 2 electrodes were 2.23 V, 1.92 V, 2.06 V, 2.11 V and 2.14 V, and respectively. As a result of the higher oxygen evolution potentials of Ti/La-Sb-SnO 2 electrode, the electrode's electrocatalytic activity was enhanced to suppress the side reaction of oxygen evolution on its surface and reduce electrode loss. Based on the LSV curves of four electrodes doped with rare earth elements, the Ti/La-Sb-SnO 2 electrode had the highest oxygen evolution potential, which could mostly improve the generation of reactive species and efficient oxidation of pollutants (Wai et al., 2021 ). Figure 3 b showed the CV curves of the five electrodes. All the rare earth-doped electrodes exhibited distinct oxidation peaks at a potential range from 0.8 ~ 1.6 V. CV curves revealed that the oxidation peak current density of the Ti/Sb-SnO 2 electrodes significantly increased after doping with rare earth elements. This enhancement was attributed to the denser structure of the surface oxide layer on the rare earth-doped Ti/Sb-SnO 2 electrodes, which improved the electrochemical capacity (Fang et al., 2011 ). By comparing the peak potentials and peak currents of the rare earth-doped Ti/Sb-SnO 2 electrodes, La-doped electrode (Ti/La-Sb-SnO 2 ) had the highest peak oxidation current (2.4 mA·cm − 2 ). The electrocatalytic oxidation capacity of the modified electrodes for PS microplastics could be ranked as follows: La > Ce > Sm > Nd, indicating that the La-doped electrode exhibited the optimal electrocatalytic performance. Figure 3 c showed the EIS curves of the five electrodes, with the left and right sides representing the high-frequency and low-frequency regions, respectively. The low-frequency region indicated the charge transfer resistance at the interface between the active layer and the solution. A lower impedance value indicated faster reaction rates, stronger generation of •OH, and higher electrocatalytic oxidation ability, resulting in higher degradation efficiency of PS Microplastics in water. The electrocatalytic oxidation performance of the modified electrodes can be ranked as follows: La > Nd > Sm > Ce > undoped. To provide a detailed description of the electrode's electrochemical reactions, an equivalent circuit model (Fig. 4 ) was used to simulate the electrode reaction process. Rare earth doping increased the resistance (R 2 ) between Ti substrate and the active layer while decreasing the reaction resistance (R 3 ). The spread of reactive oxygen species during electrochemical reaction, non-conductive TiO 2 was formed on surface of the Ti substrate, indicating a decrease in the dissolution of the electrode surface active layer and an enhancement of the electrochemical generation of •OH. According to the EIS fitting results in Table 1 , La-doped Ti/Sb-SnO 2 electrode had the lowest resistance between the Ti substrate and the active layer (R 2 = 5.77 Ω) and the lowest faradaic charge transfer resistance (R 3 = 48.3 Ω) among the five electrodes. This indicated that it had more active sites, resulting in the highest electrocatalytic oxidation performance. Additionally, rare earth elements-doped, especially La, increased the double-layer capacitance (C 2 and C 3 ). A higher capacitance value corresponds to higher electrode activity, because rare earths doped can enhance the concentration of oxygen vacancies on the electrode surface, which means that the electrode carrier concentration is higher, resulting in an increase in the amount of active charges and an improvement in the electrocatalytic activity. Table 1 EIS fitting results of rare earth elements doped Ti/Sb-SnO 2 electrode Electrode R 1 (Ω) R 2 (Ω) C 2 (F) R 3 (Ω) C 3 (F) Ti/Sb-SnO 2 0.19 4.89 1.75×10 − 5 336.1 2.49×10 − 5 Ti/La-Sb-SnO 2 0.43 5.17 1.09×10 − 5 48.3 3.27×10 − 4 Ti/Nd-Sb-SnO 2 0.38 5.84 1.02×10 − 4 67.6 3.08×10 − 4 Ti/Ce-Sb-SnO 2 0.74 13.15 3.24×10 − 5 89.9 6.92×10 − 5 Ti/Sm-Sb-SnO 2 0.56 9.74 8.46×10 − 5 119.5 1.38×10 − 4 3.2 Production of hydroxyl radical Oxidation is the main indirect pathway for Ti/Sb-SnO 2 electrode to degrade PS in water, and •OH is the most important oxidant for indirect electrocatalytic oxidation, and its production directly affects the performance of PS microplastics removal (Qiu et al., 2024). To further investigate the electrocatalytic activity of the modified electrodes, 4-hydroxybenzoic acid (4-HBA) was used as a •OH scavenger to produce the hydroxylated product, 3,4-dihydroxybenzoic acid (3,4-DHBA). The concentration of 3,4-DHBA (Fig. S2 ) was then measured using high-performance liquid chromatography (HPLC) to determine the concentration of •OH. The •OH production was shown in Fig. 5 , doping of all four rare earth elements could enhance the production of •OH in the AEOP. The •OH production was consistent with the performance of AEOP by these electrodes. The surface-modified electrodes exhibited greater electrocatalytic activity, more •OH production on the electrode, and better catalytic removal effect on PS microplastics in water. 3.3 Morphology and Structure Characterization 3.3.1 SEM and EDS analysis Cracks could be observed on the surfaces of both electrodes from the SEM images (Fig. 6 a ~ 6b and 6c ~ 6d). The cracks on the surface of the Ti/Sb-SnO 2 electrode were deep, and the surface particle sizes were large and uneven. Therefore, the coating might be more prone to detachment during the AEOP, leading to the exposure of the Ti substrate in the solution to form non-conductive TiO 2 , which ultimately reduced the electrocatalytic activity and lifespan of the electrode. In contrast, the Ti/La-Sb-SnO 2 electrode could exhibited shallower cracks in the active layer, providing better protection for the substrate (Wang et al., 2021 ). Additionally, the surface particle size was smaller and the structure was more compact, which increased the electrode's specific surface area and enhanced the amount of active sites, thereby promoting the electrocatalytic activity (Song et al., 2021 ). Energy Dispersive Spectroscopy (EDS) analysis of the Ti/Sb-SnO 2 and Ti/La-Sb-SnO 2 electrodes were shown in Table 2 . Both Sn and Sb metal elements were detected on the Ti/Sb-SnO 2 electrode. However, the measured content of Sb was significantly higher than the theoretical value for the doping ratio during sol-gel preparation. The discrepancy might be attributed to the fact that different infiltration rates of metal atoms during the preparation process due to their different boiling points. Three metallic elements, Sn, Sb, and La were detected on the Ti/La-Sb-SnO 2 electrode, indicating the La was successfully doped into the active layer of the electrode. The actual ratio of Sn, Sb, and La (100:25.9:3.2) was higher compared to the theoretical ratio (100:10:3) during sol-gel preparation. This suggested that La-doped led to a higher enrichment of Sb on the electrode surface, thereby improving the conductivity of the electrode. Table 2 EDS analysis of Ti/Sb-SnO 2 electrodes doped with different rare earth elements Relative content(%) Element Ti/Sb-SnO 2 Ti/La-Sb-SnO 2 Theoretical value Actual value Theoretical value Actual value Sn 100 100 100 100 Sb 10 18.7304 10 25.9361 La 0 0 3 3.1573 3.3.2 XRD analysis X-ray diffraction (XRD) was showed in Fig. 7 . The diffraction peaks observed at 2θ = 26.4°, 34.1°, and 51.9° correspond to the (110), (101), and (211) crystal planes of tetragonal rutile SnO 2 , indicating that the electrode coatings was mainly composed of SnO 2 crystal phase. The diffraction peaks of La-doped modified electrode coating were observed to shift to lower angles and have broader peaks compared to the undoped electrode. The broadening of the diffraction peaks indicated a reduction in grain size, which was a result of the solid solution formation between Sb, La, and SnO 2 . The dispersion of rare earth elements within the SnO 2 lattice increased the electron attraction capability of the electrode, resulting in improved conductivity and catalytic activity. 3.4 Removal Performance The PS removal curves of different rare earth-doped Ti/Sb-SnO 2 electrodes were depicted in Fig. 8a. Doping of the rare earth elements significantly could enhance the PS microplastics removal rate, especially for La-doped elements, which exhibitd a removal rate approximately twice that of the Ti/SnO 2 electrode and a 45% improvement compared to the Ti/Sb-SnO 2 electrode. It was attributed to the unique electronic structure of rare earth elements, which improved the electronic structure of SnO 2 crystal lattice, enhanced the active sites on the electrode, and promoted the production of •OH, thereby accelerating the removal of PS microplastics in water (Song et al., 2023 ). From the voltage variation curves (Fig. 6 b), it could be observed that the Ti/SnO 2 electrode had the fastest voltage increasing rates, while doping of rare earth elements led to more stable voltage profiles, especially for La-doped elements, which exhibited the slowest voltage increase, Almost a quarter of the Ti/Sb-SnO 2 electrode. Small voltage variation is beneficial for electrode stability and lifespan. This indicated that doping of La as an active layer not only increased the electrode lifespan but also improved the degradation performance of the electrode. Figure 8. (a) PS removal ratio curves of all electrodes. (b) Variation curves of cell voltage of all electrodes. We also investigated the effects of preparation methods on Ti/La-Sb-SnO 2 electrodes. From the Fig. S3 a, it could be seen that the electrode prepared by impregnation method had the lowest removal rate. Because the sol-gel method and electrodeposition method had higher uniformity in preparation process of the electrodes, the uniformity of each component could reach the atomic or molecular level. Compared with impregnation method and electrodeposition method, Sol-gel method for preparation of the electrodes had the slowest rise in cell voltage (Fig. S3 b) and was more stable in the reaction process. Different coating layers also had an impact on electrocatalytic performance when using the sol-gel method. The coating layers of the electrodes had little impact on the removal of PS microplastics (Fig. S4 a). However, the cell voltage with 10 coating layers only increased by 2.2 V (Fig. S4 b) after 4 h, which was the most stable among the three electrodes. The temperature (Fig. S5a) and the La-doped ratios (Fig. S5b) had a considerable impact on the lattice structure and grain size of the electrode coating. Through optimization experiments, it could be known that the preparation under heat treatment of 450 ℃ and ratios of Sn:La = 100:3 had the best PS microplastics removal with the Ti/La-Sb-SnO 2 electrode. 3.5 Effect of experimental parameters for PS microplastics removal 3.5.1 Effect of electrolysis time As shown in Fig. 9 a, the highest PS microplastics removal rate was up to 24.6% at 3 h by AEOP with Ti/La-Sb-SnO 2 electrode. At 6 h, the PS microplastics removal rate was only 2% greater than at 3 h. Furthermore, between 3 to 6 h, the removal rate increased by only 2.5%. These changes occur because the temperature of the reaction system increased as the degradation rate increased. The catalytic activity gradually decreased as the temperature of the reaction system increased. In addition, in the later phase of the reaction, the concentration of electrolyte or PS microplastics in the solution decreased, reducing the opportunity for interaction with the electrode and leading to a decrease in the efficiency of PS microplastics removal. Based on economic and energy considerations, an electrolysis time of 3 h was considered optimal. 3.5.2 Effect of electrode spacing Both the removal rate and the energy consumption of the reaction were affected by the electrode spacing (Dai et al., 2022 ). The removal curves at different electrode spacing were shown in Fig. 9 b, It could be revealed that the PS microplastics removal rate increases initially as the electrode spacing increased and then decreased. Figure 10 illustrated the variation in cell voltage corresponding to different electrode spacings, an increase in electrode spacing resulted in an increase in cell voltage, indicating higher electrode-electrolyte resistance within the electrochemical system. The higher electrode-electrolyte resistance produced greater mass transfer resistance in the solution, resulting in reduced charge quantity per unit volume of the electrolyte, decreased current density within the solution, lower generation of hydroxyl radicals, and a less efficient removal of PS microplastics. Furthermore, larger electrode spacing resulted in higher energy consumption. When the distance between the anode and cathode was too small (less than 1.5 cm), the •OH generated by the anode would be directly reduced by the cathode before it had time to fully react with the PS microplastics. It would be directly reduced by the cathode, reducing the utilization rate of •OH and resulting in a lower removal rate of PS microplastics. Small spacing also affected the mixing of solutions in the reaction system, reducing the probability of collision between PS microplastics and •OH, affecting indirect electrocatalytic oxidation, and reducing the chance of contact between PS microplastics and electrodes. When the electrode spacing is too large, it will cause an increase in the cell voltage and an increase in oxygen evolution side reactions, thereby reducing the removal rate of PS microplastics. Therefore, the optimal reaction electrode spacing in the electrocatalytic oxidation system of this study was set to 1.5 cm. 3.5.3 Effect of current density The removal efficiency of PS microplastics increased gradually with an increase of the current density (Fig. 9 c). Under the current density of 46.67 mA cm − 2 , the PS microplastics removal rate reached its maximum. However, if the current density exceeded 46.67 mA cm − 2 , the removal rate started decreasing. Increasing the current density accelerated the movement of charged particles within the solution, which led to an increased collision probability between PS microplastics and •OH in the reaction system. As a result, the rate of indirect electrocatalytic oxidation was enhanced. In addition, a higher current density implied a faster electron transfer between the electrode and PS microplastics, thus accelerating the rate of direct electrocatalytic oxidation. Nevertheless, when the current density became too high, oxygen evolution reactions occurred within the electrocatalytic system, which competed with the electrocatalytic removal of PS microplastics, resulting in the removal decrease (Wei et al., 2021 ). Additionally, excessive current density could elevate the temperature of the electrocatalytic system, and the ohmic thermal resistance of the electrode material could reduce the catalytic activity of the electrode. This ultimately resulted in the decrease of PS Microplastics removal (Wang et al., 2019 ).Thus, the current density of 46.67 mA cm − 2 was choiced for optimal current density. 3.3.4 Effect of electrolyte type Electrolyte type in the reaction system has a significant impact on the efficiency of electrocatalytic oxidation due to the presence of different anions. The PS Microplastics removal with different electrolytes was depicted in Fig. 9 d. Among the four tested electrolytes, the PS Microplastics removal rate was 28% higher when Na 2 SO 4 electrolyte was used compared to Na 2 CO 3 and NaNO 3 . When Na 2 SO 4 electrolyte was used during the AEOP, sulfate radical anions (SO 4 • − ) might be generated through the activation of a portion of SO 4 2− , HSO 4 − , and H 2 SO 4 present in the solution. Sulfate radical anions (SO 4 • − ) have an oxidation ability similar to hydroxyl radicals (•OH), as demonstrated in Eq. ( 2 )–( 4 ). Therefore, Na 2 SO 4 as the electrolyte for electrocatalytic oxidation resulted in a supreme removal efficiency for PS Microplastics. Thus, the optimal electrolyte type for this study was determined to be Na 2 SO 4 . $${\text{SO}}_{\text{4}}^{\text{2-}}\text{→}{\text{SO}}_{\text{4}}^{\text{-}}\text{•+}{\text{e}}^{\text{-}}$$ 2 $${\text{HSO}}_{\text{4}}^{\text{-}}\text{+•OH→}{\text{SO}}_{\text{4}}^{\text{-}}\text{•+}{\text{H}}_{\text{2}}\text{O}$$ 3 $${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}\text{+•OH→}{\text{SO}}_{\text{4}}^{\text{-}}\text{•+}{\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$$ 4 3.3.5 Effect of electrolyte concentration Electrolyte concentration determined the conductivity of the solution in the AEOP system. This in turn affected the current utilization rate, cell voltage, PS Microplastics removal rate, and energy consumption of the system. Figure 9 e showd the removal curves of PS Microplastics under the different Na 2 SO 4 concentrations. At electrolyte concentrations lower than 0.22 mol·L − 1 , it revealed that an increase in Na 2 SO 4 concentration resulted in higher PS Microplastics removal rate. The increase in conductivity of the solution accelerated the transfer rate of electrons on the surface of the electrodes. In addition, the increased collision frequency between •OH and PS Microplastics could also accelerate the removal rate. Additionally, SO 4 2− ions minght oxidize to persulfate (S 2 O 8 − ) (Hu et al., 2016 ; Rodrigo et al., 2001 ). The following mechanisms (Eq. ( 5 )–( 7 ) ) might produce S 2 O 8 − at higher current density (Araujo et al., 2018 ; Bezerra Rocha et al., 2012 ). $$\text{2S}{\text{O}}_{\text{4}}^{\text{2-}}\text{→}{\text{S}}_{\text{2}}{\text{O}}_{\text{8}}^{\text{2-}}\text{+2}{\text{e}}^{\text{-}}$$ 5 $$\text{•}\text{OH+S}{\text{O}}_{\text{4}}^{\text{2-}}\text{→}{\text{SO}}_{\text{4}}^{\text{-}}\text{•}\text{+2}{\text{HO}}^{\text{-}}$$ 6 $${\text{SO}}_{\text{4}}^{\text{-}}\text{•}\text{+S}{\text{O}}_{\text{4}}^{\text{2-}}\text{→}{\text{S}}_{\text{2}}{\text{O}}_{\text{8}}^{\text{2-}}\text{+}{\text{e}}^{\text{-}}$$ 7 S 2 O 8 − is a more stable oxidizing agent that can persist in the electrolytic solution for an extended period of time. It facilitated the sustained breakdown of pollutants into SO 4 • − . Raising the concentration of electrolytes amplifies the levels of free radicals generated during electrolysis. Therefore, it promoted the degradation of microplastics (Davis et al., 2014 ). In high electrolyte concentrations, boosting Na 2 SO 4 concentrations did not result in the incremental increase of PS Microplastics removal rate. At this point, the mass transfer was no longer the factor that limited the rate of the reaction. The PS Microplastics removal rate was not accelerated by increasing the concentration of Na 2 SO 4 . Instead, its decrease due to excessive SO 4 2− adsorption on the active layer, which occupied the active sites. As a result, it reduced the production of •OH and impeded the effective interaction between the photosensitizer and the electrode. When the electrolyte concentration was high, the ionic bonding force became stronger, causing more energy consumption of the system (Zhang et al., 2022 ). Thus, the study determined that the optimal concentration of Na 2 SO 4 electrolyte was 0.22 mol·L − 1 . 3.3.6 Effect of initial pH The PS microplastics removal rate varied with the initial pH of the solution (Fig. 9 f). The most efficient removal rate occurred when the initial pH was equal to 7. At low pH values, the electrode was prone to corrosion, and the Ti matrix surface could undergo oxidation, affecting the activity and electrocatalytic performance of the coating. Thus, there was a decline in the activity and electrocatalytic performance of the coating. In a weak acid (pH of 5), the removal efficiency was close to a neutral environment, because H + in acidic environment can inhibit the occurrence of oxygen evolution side reactions (Xiao et al., 2023 ). The active sites on the electrode surface would adsorb OH − when initial pH was too high, and the metal ions dissolved from the electrode would precipitate with OH − , leading to electrode passivation and reducing the production of •OH and the interaction between active sites and PS microplastics (Maharaja et al., 2016 ). Therefore, weak acid or neutal initial environment was considered to be done at our work. 4 Conclusion In this study, Ti/La-Sb-SnO 2 electrode were successfully prepared as the active layer to enhance the electrocatalytic activity and improving the •OH production rate during the AEOP, which achieved a PS removal rate of 28.3% after 3 h, compared to the 16% achieved in Ti/Sb-SnO 2 electrode. The optimal electrolysis conditions for PS removal were current density of 46.67 mA·cm − 2 , electrode spacing of 1.5 cm, Na 2 SO 4 electrolyte concentration of 0.22 mol·L − 1 , initial pH of 7, and electrolysis duration of 3 h. This study provides a strategy to prepare the active electrodes for electrocatalytic oxidation reactions, presenting valuable insights into the electrocatalytic removal of microplastics and offering potential applications in water treatment and environmental remediation. Declarations Declaration of interests 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. Author contribution Weikang Zheng: Data curation, Investigation, Formal analysis, Writing – original draft preparation. Boyan Wang: Formal analysis, Writing - review & editing. Zhenzhong Liu: Methodology, Writing – review & editing, Formal analysis, Funding acquisition. Hongwei Yang: Methodology, Formal analysis, Funding acquisition. Data availability All relevant data are included in the text or its Supplementary Information. Ethical approval Not applicable. Consent to participate Not applicable. Consent for publication All authors listed agree to publish this work. Competing interests The authors declare no competing interests. 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Huan jing ke xue= Huanjing kexue 2024a; 45: 1210-1221.https://dx.doi.org/10.13227/j.hjkx.202303232 Zheng W, Liu Z, Wang B, Tao M, Ji H, Xiang X, et al. Effective degradation of polystyrene microplastics by Ti/La/Co-Sb-SnO2 anodes: Enhanced electrocatalytic stability and electrode lifespan. Science of The Total Environment 2024b: 171002 Supplementary Files GraphicalAbstract.emf SupportingMaterials.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4416872","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":313373786,"identity":"292fbfd9-d54e-4adc-b44e-6ef070fa9f5b","order_by":0,"name":"Weikang Zheng","email":"","orcid":"","institution":"Nanchang University School of Resources Environmental and Chemical Engineering","correspondingAuthor":false,"prefix":"","firstName":"Weikang","middleName":"","lastName":"Zheng","suffix":""},{"id":313373787,"identity":"cc5b2052-1a4d-442c-8c09-124978c2c821","order_by":1,"name":"Boyan Wang","email":"","orcid":"","institution":"Nanchang University School of Resources Environmental and Chemical Engineering","correspondingAuthor":false,"prefix":"","firstName":"Boyan","middleName":"","lastName":"Wang","suffix":""},{"id":313373788,"identity":"0f28a442-90a1-41f7-b3ee-11e000ea49a6","order_by":2,"name":"Zhenzhong Liu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAArUlEQVRIiWNgGAWjYBACA2YgwfjPRo6NvfkACVoY2NKM+XiOJRCpBUyyHU6cJ5GjQKQWdh7jjz94Dqe3MeQwMPyo2EaMw3gMDCQk0nPbGM4eYOw5c5s4LQkGBta5bYx9CcyMbURqOZCQwJzOBmQQrcWw4cAB5wQ2NuK1sBUzNjakGbbxsCUcJMov9v2HN3/82WAjLz//8cEHPyqI0IICDpCofhSMglEwCkYBLgAAAGszHfjJ5OwAAAAASUVORK5CYII=","orcid":"","institution":"Nanchang daxue ziyuan yu huanjing xueyuan: Nanchang University School of Resources Environmental and Chemical Engineering","correspondingAuthor":true,"prefix":"","firstName":"Zhenzhong","middleName":"","lastName":"Liu","suffix":""},{"id":313373789,"identity":"d6adfbcb-c129-4d3c-b9a2-ab594f7d244f","order_by":3,"name":"Hongwei Yang","email":"","orcid":"","institution":"Nanchang University School of Resources Environmental and Chemical Engineering","correspondingAuthor":false,"prefix":"","firstName":"Hongwei","middleName":"","lastName":"Yang","suffix":""}],"badges":[],"createdAt":"2024-05-14 06:25:35","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4416872/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4416872/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":59187226,"identity":"567a9261-8480-4077-ba73-a2521f34da2d","added_by":"auto","created_at":"2024-06-27 12:19:39","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":40035,"visible":true,"origin":"","legend":"\u003cp\u003eElectrochemical performance test device.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4416872/v1/51ee23d2c3dbe9af135b83f2.jpg"},{"id":59187815,"identity":"595ba246-b2d9-407e-88a3-57a7342a9c24","added_by":"auto","created_at":"2024-06-27 12:27:39","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":45913,"visible":true,"origin":"","legend":"\u003cp\u003eExperimental device diagram of PS removal.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4416872/v1/b1b41e09c33966c99570bb3e.jpg"},{"id":59187220,"identity":"82aed9dd-6205-4cba-b829-9b0d7d1ce453","added_by":"auto","created_at":"2024-06-27 12:19:39","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":83378,"visible":true,"origin":"","legend":"\u003cp\u003e(a) LSV curves of Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrodes with different rare earth elements doped. (b) CV curves.(c) EIS plots.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4416872/v1/02cea7a05d5dda36e2cfda71.jpg"},{"id":59187222,"identity":"3898a0f6-149a-46c5-a1b8-c318d7dd6703","added_by":"auto","created_at":"2024-06-27 12:19:39","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":20686,"visible":true,"origin":"","legend":"\u003cp\u003eFitting equivalent circuit diagram\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4416872/v1/bdff79f7e3d178fec0ac49fe.jpg"},{"id":59187221,"identity":"130f7c1e-2604-41d2-a0ef-0c94f1b15902","added_by":"auto","created_at":"2024-06-27 12:19:39","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":69832,"visible":true,"origin":"","legend":"\u003cp\u003eOH production of all prepared electrodes\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4416872/v1/d13341e76a76aa66fc8d7e17.jpg"},{"id":59187229,"identity":"93b44698-a168-4384-883f-630d3a7f1a31","added_by":"auto","created_at":"2024-06-27 12:19:39","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":103210,"visible":true,"origin":"","legend":"\u003cp\u003eSEM pictures of (a~b) Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode. (c~d) Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4416872/v1/f716042f1129992bf64fd2e4.jpg"},{"id":59187813,"identity":"4c5eaa6a-c087-483b-9d55-0e1fe0b7eed9","added_by":"auto","created_at":"2024-06-27 12:27:39","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":48426,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e and Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrodes\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4416872/v1/ad25400e0b18a76b3bbca000.jpg"},{"id":59187227,"identity":"172fc26f-e529-48b4-ba43-c9569074ab99","added_by":"auto","created_at":"2024-06-27 12:19:39","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":90124,"visible":true,"origin":"","legend":"\u003cp\u003e(a) PS removal ratio curves of all electrodes. (b) Variation curves of cell voltage of all electrodes.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4416872/v1/fd326479e9c0488a2b9c672a.jpg"},{"id":59187225,"identity":"5b90a19c-4500-4394-9e96-bb10e34a198a","added_by":"auto","created_at":"2024-06-27 12:19:39","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":110507,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Effect of the electrolysis time . (b) Effect of the electrode spacing. (c) Effect of the current density. (d) Effect of the electrolyte types . (e) Effect of the electrolyte concentration. (f) Effect of the initial pH.\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4416872/v1/3e104892688840f612e5e746.jpg"},{"id":59188405,"identity":"ba7921f8-1241-485d-8b92-9de95ebeafc8","added_by":"auto","created_at":"2024-06-27 12:35:39","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":34835,"visible":true,"origin":"","legend":"\u003cp\u003eThe cell voltage variation curves under different electrode spacing\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4416872/v1/6c4a112f74dcf18020de6292.jpg"},{"id":67603587,"identity":"d1512bac-e56e-4478-ad82-c98eb7c03c3b","added_by":"auto","created_at":"2024-10-28 04:03:13","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1389554,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4416872/v1/d0aee41a-ebc7-4f88-a5fe-f0eb960c67ae.pdf"},{"id":59187231,"identity":"081bcc7d-9b7b-4587-8370-fc437ff4be11","added_by":"auto","created_at":"2024-06-27 12:19:40","extension":"emf","order_by":6,"title":"","display":"","copyAsset":false,"role":"supplement","size":49743356,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstract.emf","url":"https://assets-eu.researchsquare.com/files/rs-4416872/v1/9badcfc83404025fbc5b425c.emf"},{"id":59187230,"identity":"ae2eba6d-c7c6-4a70-8a3b-fa3cf8a050f3","added_by":"auto","created_at":"2024-06-27 12:19:40","extension":"docx","order_by":8,"title":"","display":"","copyAsset":false,"role":"supplement","size":2144662,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingMaterials.docx","url":"https://assets-eu.researchsquare.com/files/rs-4416872/v1/bde3e62c88cfb5489f50aa56.docx"}],"financialInterests":"","formattedTitle":"\u003cp\u003eLa-doped Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode enhanced removal of microplastics by advanced electrocatalysis oxidation process (AEOP) strategy\u003c/p\u003e","fulltext":[{"header":"Highlights","content":"\u003cul\u003e\n \u003cli\u003eLa-doped Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode was synthesized by sol-gel method\u003c/li\u003e\n \u003cli\u003eThe electrocatalytic activity of Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode was effectively improved\u003c/li\u003e\n \u003cli\u003eLa-doped Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode showed superior polystyrene microplastics removal\u003c/li\u003e\n \u003cli\u003eAEOP is a potential strategy for the removal of microplastics in water \u003c/li\u003e\n\u003c/ul\u003e"},{"header":"1 Introduction","content":"\u003cp\u003eAs an emerging environmental pollutant, microplastics have attracted much attention in recent years (Ji et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) and become a focal point of water pollution research (Rodrigues et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Zheng et al., 2024a). They are ubiquitous in our daily lives and pose a great threat to the ecological environment and human health (Duan et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The hazards of microplastics primarily stem from three aspects. The microplastics themselves and their monomers, the additives present in plastics (Andrady, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), and the toxic substances adsorbed onto microplastics (Rodriguez-Narvaez et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Due to their high molecular weight and strong durability, microplastics can persist in the environment for decades or even centuries (Shen et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Consequently, the removal of microplastics in water presents significant challenges.\u003c/p\u003e \u003cp\u003eIn recent years, researchers have investigated various water treatment methods (Ma et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) to eliminate microplastics (Zheng et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2024b\u003c/span\u003e). These methods comprise coagulation-flocculation (XIANGXiao-fang, 2024), biological treatment (Dai et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), filtration (Talvitie et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), magnetic separation (Grbic et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), photocatalysis (Uheida et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), and electrochemistry (Kiendrebeogo et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Of these methods, advanced electrocatalysis oxidation process (AEOP) (Ning et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) has demonstrated significant benefits in degrading microplastic pollutants due to its high efficiency (Yan et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), operational simplicity, and environmental friendliness (Ma et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eElectrode materials' properties directly impact the efficiency of AEOP water treatment (Dolatabadi et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). As a result, improving the activity and stability of electrode materials through modification and development has become a crucial and popular topic in electrochemical water treatment research. Currently, research on the electrocatalytic oxidation about microplastics removal is limited. Most of the studies concentrated on using boron-doped diamond (BDD) electrodes (Mukherjee et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), which were expensive and challenging to apply widely. The Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode demonstrates excellent electrocatalytic performance, mainly relying on an indirect oxidation process that generates free radicals. The Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode costs only one-sixth of the BDD electrode (Zheng et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2024b\u003c/span\u003e). Nevertheless, Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode is unstable due to the structural differences between the substrate and the active layer. In the AEOP, the reactive oxygen species generated may diffuse to the substrate's surface, resulting in a high-resistance TiO\u003csub\u003e2\u003c/sub\u003e insulating layer formation and significantly reducing the electrode's conductivity, leading to decrease in the electrocatalytic activity (Hu et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode modification enhances the electrocatalytic performance and removal efficiency of microplastics, significantly reducing the cost of AEOP and facilitating its industrial application.\u003c/p\u003e \u003cp\u003eRare earth elements have unique structures (Xue et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), both electronically and physicochemically. Doping these elements into the active layer of stable anodes can alter the electrocatalytic performance of the electrode (Ma et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Based on this premise, we aim to prepare Ti-based metal oxide electrodes for the study of microplastic removal. Different rare earth elements (La, Sm, Nd, or Ce) were doped. Polystyrene (PS) microplastics were used as target pollutants. We focused on the optimal preparation of the electrode, including the coating preparation method, coating layers, heat treatment temperature, and rare earth doping amount. We also investigated the factors affecting the catalytic oxidation and removal of PS microplastics with this electrode, including electrolysis time, current density, electrode spacing, electrolyte types, electrolyte concentration, and initial pH in the solution. The goal was to improve the performance of AEOP for the removal of PS microplastics. We aim to provide new insights into removing microplastics from real water bodies.\u003c/p\u003e"},{"header":"2 Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials and chemical reagents\u003c/h2\u003e \u003cp\u003ePure Ti mesh was obtained from Suzhou Shuer Tai industrial Technology Co., Ltd. SnCl\u003csub\u003e5\u003c/sub\u003e\u0026middot;5H\u003csub\u003e2\u003c/sub\u003eO and Sb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e were bought form Shanghai Aladdin Biochemical Technology Co., Ltd. La(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO, Ce(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO, Nd(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO, and Sm(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO were provided from Sinopharm Chemical Reagent Co., Ltd. Other chemical reagents, such as sodium sulfate, sodium carbonate, hydrochloric acid, sodium hydroxide, methanol, sodium nitrate, salicylic acid, anhydrous oxalic acid, polyethylene glycol 2000 were all analytical grade AR.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Preparation of Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode\u003c/h2\u003e \u003cp\u003eThe Ti substrate underwent a pre-treatment process by polishing it with 120, 240, and 600 grit sandpaper consecutively, with the aim of removing impurities and oxide films from its surface. Afterward, Ti substrate was immersed in 15 wt% NaOH and underwent constant temperature water bath heating at 90 ℃ for 1 h, aiming to remove any oil residue on its surface. Subsequently, the Ti substrate was immersed in 10 wt% oxalic acid and heated to keep it under micro-boiling conditions for 2 h, achieving etching of the surface, which led to the formation of uneven gray pitted surfaces and loss of its metallic luster. The main objective is to improve the specific surface area of the Ti substrate and enhance its adhesion with metal oxide active coating. Lastly, the Ti substrate were immersed in 3 wt% oxalic acid and stored for future use. The surface morphology of Ti substrate before and after acid etching was shown in Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eIn this work, Sol-gel method was prepared for the Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode (Wang et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e(1) Methods for preparing sols\u003c/p\u003e \u003cp\u003eFor this experiment, we prepared a sol with a concentration ratio of Sn:Sb of 100:10 and a Sn concentration of 1 mol\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The following steps were performed:\u003c/p\u003e \u003cp\u003e① To prepare solution A, SnCl\u003csub\u003e4\u003c/sub\u003e\u0026middot;5H\u003csub\u003e2\u003c/sub\u003eO should be dissolved in anhydrous ethanol..\u003c/p\u003e \u003cp\u003e② For solution B, Sb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e should be dissolved in 2 mL of concentrated hydrochloric acid.\u003c/p\u003e \u003cp\u003e③ Pour solution B into solution A and stir well. Then add polyethylene glycol 2000 (2 g) to the solution. Heat the solution at 60\u0026deg;C while stirring for 1 h to form the sol solution.\u003c/p\u003e \u003cp\u003e④ Take a certain amount of the sol solution and add La rare earth salts according to the respective proportions. Stir the solution in a water bath at 60\u0026deg;C until complete dissolution, then let it stand for at least 120 minutes for aging.\u003c/p\u003e \u003cp\u003e(2) Impregnation and heat treatment:\u003c/p\u003e \u003cp\u003e① Immerse the pre-treated Ti substrate in the sol solution for 2 minutes. Slowly lift it out, allowing the excess sol on the surface to drip dry, forming a uniform coating on the substrate surface.\u003c/p\u003e \u003cp\u003e② Place the electrode in an oven and dry at 120\u0026deg;C for 20 minutes to form a gel. Then transfer the electrode to the muffle furnace at 450\u0026deg;C and sinter for 10 minutes.\u003c/p\u003e \u003cp\u003e③ Repeat steps ①-② for a total of 10 times. For the final cycle, perform a high-temperature heat treatment in the muffle furnace for 2 h. The Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode can be obtained after cooling for further use. Ti/Ce-Sb-SnO\u003csub\u003e2\u003c/sub\u003e, Ti/Sm-Sb-SnO\u003csub\u003e2\u003c/sub\u003e, Ti/Nd-Sb-SnO\u003csub\u003e2\u003c/sub\u003e were obtained by the same method.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Characterization and Performance Test\u003c/h2\u003e \u003cp\u003eElectrochemical measurements were tested by PARSTAT 6000 electrochemical workstation (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The prepared electrode served as the working electrode, pure platinum electrode as the auxiliary electrode, and saturated calomel electrode as the reference electrode. The conditions for the Linear Sweep Voltammetry (LSV) test were a scan rate of 1.0 mV\u0026middot;s\u003csup\u003e-1\u003c/sup\u003e, a range of 0 to 2.5 V, and conducted in H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e solution of 0.5 mol\u0026middot;L\u003csup\u003e-1\u003c/sup\u003e (Doumbi et al., 2023; Rathinavelu et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Conditions for the Cyclic Voltammetry (CV) test were a scan rate of 20 mV\u0026middot;s\u003csup\u003e-1\u003c/sup\u003e, a range of 0.5 V to 2 V, and conducted in H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e solution of 0.22 mol\u0026middot;L\u003csup\u003e-1\u003c/sup\u003e. Conditions for the Electrochemical Impedance Spectroscopy (EIS) test were a perturbation amplitude of 5 mV, a frequency range of 100 kHz to 10 mHz, a testing potential of 1.2 V, and H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e solution of 0.22 mol\u0026middot;L\u003csup\u003e-1\u003c/sup\u003e. Impedance parameters were fitted by Zview software (Sun et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Surface morphology of the electrode was observed by scanning electron microscope (SEM) (SIGMA500), and the crystal structure of the electrode surface was analyzed by X-ray diffractometer (XRD) (Empyrean 03030502) (Liu et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The generation of \u0026bull;OH was indirectly determined by high-performance liquid chromatography (HPLC) (Doumbi et al., 2023).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 AEOP removal of PS microplastics\u003c/h2\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.4.1 Experimental procedures\u003c/h2\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. PS microplastics of 1 g\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (100 mesh) were added into electrolyte cell. Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode was used as the anode (in the form of 50\u0026times;30\u0026times;1 mm) and Ti electrode was used as the cathode. Constant current electrolysis was controlled with a DC stabilized power supply and simultaneously record the cell voltage. We filtered the solution to collect remaining microplastics after the reaction. In order to minimize experimental errors, we obtained the average of two parallel experiments as the final result.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.4.2 Removal rate computation\u003c/h2\u003e \u003cp\u003ePS microplastics removal rate were calculated by the weighing method and using the following Eqs.\u0026nbsp;(1):.\u003c/p\u003e \u003cp\u003ePS Removal rate= \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\text{W}}_{\\text{0}}\\text{-}{\\text{W}}_{\\text{t}}\\text{}{\\text{W}}_{\\text{0}}\\text{\u0026times;100%}\\)\u003c/span\u003e\u003c/span\u003e (1)\u003c/p\u003e \u003cp\u003eWhere W\u003csub\u003e0\u003c/sub\u003e and W\u003csub\u003et\u003c/sub\u003e represented the mass of PS microplastics at time 0 and \u003cem\u003et\u003c/em\u003e after after filtration and drying.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Electrocatalytic performance analysis\u003c/h2\u003e \u003cp\u003eIn the Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, LSV curves were shown for the five electrodes, the oxygen evolution potentials of Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e, Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e, Ti/Sm-Sb-SnO\u003csub\u003e2\u003c/sub\u003e, Ti/Ce-Sb-SnO\u003csub\u003e2\u003c/sub\u003e, and Ti/Nd-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrodes were 2.23 V, 1.92 V, 2.06 V, 2.11 V and 2.14 V, and respectively. As a result of the higher oxygen evolution potentials of Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode, the electrode's electrocatalytic activity was enhanced to suppress the side reaction of oxygen evolution on its surface and reduce electrode loss. Based on the LSV curves of four electrodes doped with rare earth elements, the Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode had the highest oxygen evolution potential, which could mostly improve the generation of reactive species and efficient oxidation of pollutants (Wai et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb showed the CV curves of the five electrodes. All the rare earth-doped electrodes exhibited distinct oxidation peaks at a potential range from 0.8\u0026thinsp;~\u0026thinsp;1.6 V. CV curves revealed that the oxidation peak current density of the Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrodes significantly increased after doping with rare earth elements. This enhancement was attributed to the denser structure of the surface oxide layer on the rare earth-doped Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrodes, which improved the electrochemical capacity (Fang et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). By comparing the peak potentials and peak currents of the rare earth-doped Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrodes, La-doped electrode (Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e) had the highest peak oxidation current (2.4 mA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e). The electrocatalytic oxidation capacity of the modified electrodes for PS microplastics could be ranked as follows: La\u0026thinsp;\u0026gt;\u0026thinsp;Ce\u0026thinsp;\u0026gt;\u0026thinsp;Sm\u0026thinsp;\u0026gt;\u0026thinsp;Nd, indicating that the La-doped electrode exhibited the optimal electrocatalytic performance.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec showed the EIS curves of the five electrodes, with the left and right sides representing the high-frequency and low-frequency regions, respectively. The low-frequency region indicated the charge transfer resistance at the interface between the active layer and the solution. A lower impedance value indicated faster reaction rates, stronger generation of \u0026bull;OH, and higher electrocatalytic oxidation ability, resulting in higher degradation efficiency of PS Microplastics in water. The electrocatalytic oxidation performance of the modified electrodes can be ranked as follows: La\u0026thinsp;\u0026gt;\u0026thinsp;Nd\u0026thinsp;\u0026gt;\u0026thinsp;Sm\u0026thinsp;\u0026gt;\u0026thinsp;Ce\u0026thinsp;\u0026gt;\u0026thinsp;undoped.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo provide a detailed description of the electrode's electrochemical reactions, an equivalent circuit model (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) was used to simulate the electrode reaction process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eRare earth doping increased the resistance (R\u003csub\u003e2\u003c/sub\u003e) between Ti substrate and the active layer while decreasing the reaction resistance (R\u003csub\u003e3\u003c/sub\u003e). The spread of reactive oxygen species during electrochemical reaction, non-conductive TiO\u003csub\u003e2\u003c/sub\u003e was formed on surface of the Ti substrate, indicating a decrease in the dissolution of the electrode surface active layer and an enhancement of the electrochemical generation of \u0026bull;OH. According to the EIS fitting results in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, La-doped Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode had the lowest resistance between the Ti substrate and the active layer (R\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;5.77 Ω) and the lowest faradaic charge transfer resistance (R\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;48.3 Ω) among the five electrodes. This indicated that it had more active sites, resulting in the highest electrocatalytic oxidation performance. Additionally, rare earth elements-doped, especially La, increased the double-layer capacitance (C\u003csub\u003e2\u003c/sub\u003e and C\u003csub\u003e3\u003c/sub\u003e). A higher capacitance value corresponds to higher electrode activity, because rare earths doped can enhance the concentration of oxygen vacancies on the electrode surface, which means that the electrode carrier concentration is higher, resulting in an increase in the amount of active charges and an improvement in the electrocatalytic activity.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEIS fitting results of rare earth elements doped Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026times;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026times;\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElectrode\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e(Ω)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e(Ω)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eC\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e(F)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003e3\u003c/sub\u003e(Ω)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cem\u003eC\u003c/em\u003e\u003csub\u003e3\u003c/sub\u003e(F)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTi/Sb-SnO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c4\"\u003e \u003cp\u003e1.75\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e336.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c6\"\u003e \u003cp\u003e2.49\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTi/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c4\"\u003e \u003cp\u003e1.09\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e48.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c6\"\u003e \u003cp\u003e3.27\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTi/Nd-Sb-SnO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c4\"\u003e \u003cp\u003e1.02\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e67.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c6\"\u003e \u003cp\u003e3.08\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTi/Ce-Sb-SnO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e13.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c4\"\u003e \u003cp\u003e3.24\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e89.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c6\"\u003e \u003cp\u003e6.92\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTi/Sm-Sb-SnO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e9.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c4\"\u003e \u003cp\u003e8.46\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e119.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c6\"\u003e \u003cp\u003e1.38\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Production of hydroxyl radical\u003c/h2\u003e \u003cp\u003eOxidation is the main indirect pathway for Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode to degrade PS in water, and \u0026bull;OH is the most important oxidant for indirect electrocatalytic oxidation, and its production directly affects the performance of PS microplastics removal (Qiu et al., 2024). To further investigate the electrocatalytic activity of the modified electrodes, 4-hydroxybenzoic acid (4-HBA) was used as a \u0026bull;OH scavenger to produce the hydroxylated product, 3,4-dihydroxybenzoic acid (3,4-DHBA). The concentration of 3,4-DHBA (Fig. \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e) was then measured using high-performance liquid chromatography (HPLC) to determine the concentration of \u0026bull;OH. The \u0026bull;OH production was shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, doping of all four rare earth elements could enhance the production of \u0026bull;OH in the AEOP. The \u0026bull;OH production was consistent with the performance of AEOP by these electrodes. The surface-modified electrodes exhibited greater electrocatalytic activity, more \u0026bull;OH production on the electrode, and better catalytic removal effect on PS microplastics in water.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Morphology and Structure Characterization\u003c/h2\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.3.1 SEM and EDS analysis\u003c/h2\u003e \u003cp\u003eCracks could be observed on the surfaces of both electrodes from the SEM images (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea\u0026thinsp;~\u0026thinsp;6b and 6c\u0026thinsp;~\u0026thinsp;6d). The cracks on the surface of the Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode were deep, and the surface particle sizes were large and uneven. Therefore, the coating might be more prone to detachment during the AEOP, leading to the exposure of the Ti substrate in the solution to form non-conductive TiO\u003csub\u003e2\u003c/sub\u003e, which ultimately reduced the electrocatalytic activity and lifespan of the electrode. In contrast, the Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode could exhibited shallower cracks in the active layer, providing better protection for the substrate (Wang et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Additionally, the surface particle size was smaller and the structure was more compact, which increased the electrode's specific surface area and enhanced the amount of active sites, thereby promoting the electrocatalytic activity (Song et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eEnergy Dispersive Spectroscopy (EDS) analysis of the Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e and Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrodes were shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Both Sn and Sb metal elements were detected on the Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode. However, the measured content of Sb was significantly higher than the theoretical value for the doping ratio during sol-gel preparation. The discrepancy might be attributed to the fact that different infiltration rates of metal atoms during the preparation process due to their different boiling points. Three metallic elements, Sn, Sb, and La were detected on the Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode, indicating the La was successfully doped into the active layer of the electrode. The actual ratio of Sn, Sb, and La (100:25.9:3.2) was higher compared to the theoretical ratio (100:10:3) during sol-gel preparation. This suggested that La-doped led to a higher enrichment of Sb on the electrode surface, thereby improving the conductivity of the electrode.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEDS analysis of Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrodes doped with different rare earth elements\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003eRelative content(%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElement\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eTi/Sb-SnO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eTi/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTheoretical value\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eActual value\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTheoretical value\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eActual value\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18.7304\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.9361\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.1573\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e3.3.2 XRD analysis\u003c/h2\u003e \u003cp\u003eX-ray diffraction (XRD) was showed in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The diffraction peaks observed at 2θ\u0026thinsp;=\u0026thinsp;26.4\u0026deg;, 34.1\u0026deg;, and 51.9\u0026deg; correspond to the (110), (101), and (211) crystal planes of tetragonal rutile SnO\u003csub\u003e2\u003c/sub\u003e, indicating that the electrode coatings was mainly composed of SnO\u003csub\u003e2\u003c/sub\u003e crystal phase.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe diffraction peaks of La-doped modified electrode coating were observed to shift to lower angles and have broader peaks compared to the undoped electrode. The broadening of the diffraction peaks indicated a reduction in grain size, which was a result of the solid solution formation between Sb, La, and SnO\u003csub\u003e2\u003c/sub\u003e. The dispersion of rare earth elements within the SnO\u003csub\u003e2\u003c/sub\u003e lattice increased the electron attraction capability of the electrode, resulting in improved conductivity and catalytic activity.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Removal Performance\u003c/h2\u003e \u003cp\u003eThe PS removal curves of different rare earth-doped Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrodes were depicted in Fig.\u0026nbsp;8a. Doping of the rare earth elements significantly could enhance the PS microplastics removal rate, especially for La-doped elements, which exhibitd a removal rate approximately twice that of the Ti/SnO\u003csub\u003e2\u003c/sub\u003e electrode and a 45% improvement compared to the Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode. It was attributed to the unique electronic structure of rare earth elements, which improved the electronic structure of SnO\u003csub\u003e2\u003c/sub\u003e crystal lattice, enhanced the active sites on the electrode, and promoted the production of \u0026bull;OH, thereby accelerating the removal of PS microplastics in water (Song et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). From the voltage variation curves (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb), it could be observed that the Ti/SnO\u003csub\u003e2\u003c/sub\u003e electrode had the fastest voltage increasing rates, while doping of rare earth elements led to more stable voltage profiles, especially for La-doped elements, which exhibited the slowest voltage increase, Almost a quarter of the Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode. Small voltage variation is beneficial for electrode stability and lifespan. This indicated that doping of La as an active layer not only increased the electrode lifespan but also improved the degradation performance of the electrode.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;8. (a) PS removal ratio curves of all electrodes. (b) Variation curves of cell voltage of all electrodes.\u003c/p\u003e \u003cp\u003eWe also investigated the effects of preparation methods on Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrodes. From the Fig. \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003ea, it could be seen that the electrode prepared by impregnation method had the lowest removal rate. Because the sol-gel method and electrodeposition method had higher uniformity in preparation process of the electrodes, the uniformity of each component could reach the atomic or molecular level. Compared with impregnation method and electrodeposition method, Sol-gel method for preparation of the electrodes had the slowest rise in cell voltage (Fig. \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003eb) and was more stable in the reaction process. Different coating layers also had an impact on electrocatalytic performance when using the sol-gel method. The coating layers of the electrodes had little impact on the removal of PS microplastics (Fig. \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003ea). However, the cell voltage with 10 coating layers only increased by 2.2 V (Fig. \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003eb) after 4 h, which was the most stable among the three electrodes. The temperature (Fig. S5a) and the La-doped ratios (Fig. S5b) had a considerable impact on the lattice structure and grain size of the electrode coating. Through optimization experiments, it could be known that the preparation under heat treatment of 450 ℃ and ratios of Sn:La\u0026thinsp;=\u0026thinsp;100:3 had the best PS microplastics removal with the Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Effect of experimental parameters for PS microplastics removal\u003c/h2\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003e3.5.1 Effect of electrolysis time\u003c/h2\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003ea, the highest PS microplastics removal rate was up to 24.6% at 3 h by AEOP with Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode. At 6 h, the PS microplastics removal rate was only 2% greater than at 3 h. Furthermore, between 3 to 6 h, the removal rate increased by only 2.5%.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThese changes occur because the temperature of the reaction system increased as the degradation rate increased. The catalytic activity gradually decreased as the temperature of the reaction system increased. In addition, in the later phase of the reaction, the concentration of electrolyte or PS microplastics in the solution decreased, reducing the opportunity for interaction with the electrode and leading to a decrease in the efficiency of PS microplastics removal. Based on economic and energy considerations, an electrolysis time of 3 h was considered optimal.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e \u003ch2\u003e3.5.2 Effect of electrode spacing\u003c/h2\u003e \u003cp\u003eBoth the removal rate and the energy consumption of the reaction were affected by the electrode spacing (Dai et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The removal curves at different electrode spacing were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003eb, It could be revealed that the PS microplastics removal rate increases initially as the electrode spacing increased and then decreased. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e10\u003c/span\u003e illustrated the variation in cell voltage corresponding to different electrode spacings, an increase in electrode spacing resulted in an increase in cell voltage, indicating higher electrode-electrolyte resistance within the electrochemical system. The higher electrode-electrolyte resistance produced greater mass transfer resistance in the solution, resulting in reduced charge quantity per unit volume of the electrolyte, decreased current density within the solution, lower generation of hydroxyl radicals, and a less efficient removal of PS microplastics. Furthermore, larger electrode spacing resulted in higher energy consumption.\u003c/p\u003e \u003cp\u003eWhen the distance between the anode and cathode was too small (less than 1.5 cm), the \u0026bull;OH generated by the anode would be directly reduced by the cathode before it had time to fully react with the PS microplastics. It would be directly reduced by the cathode, reducing the utilization rate of \u0026bull;OH and resulting in a lower removal rate of PS microplastics. Small spacing also affected the mixing of solutions in the reaction system, reducing the probability of collision between PS microplastics and \u0026bull;OH, affecting indirect electrocatalytic oxidation, and reducing the chance of contact between PS microplastics and electrodes. When the electrode spacing is too large, it will cause an increase in the cell voltage and an increase in oxygen evolution side reactions, thereby reducing the removal rate of PS microplastics. Therefore, the optimal reaction electrode spacing in the electrocatalytic oxidation system of this study was set to 1.5 cm.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section3\"\u003e \u003ch2\u003e3.5.3 Effect of current density\u003c/h2\u003e \u003cp\u003eThe removal efficiency of PS microplastics increased gradually with an increase of the current density (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003ec). Under the current density of 46.67 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, the PS microplastics removal rate reached its maximum. However, if the current density exceeded 46.67 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, the removal rate started decreasing.\u003c/p\u003e \u003cp\u003eIncreasing the current density accelerated the movement of charged particles within the solution, which led to an increased collision probability between PS microplastics and \u0026bull;OH in the reaction system. As a result, the rate of indirect electrocatalytic oxidation was enhanced. In addition, a higher current density implied a faster electron transfer between the electrode and PS microplastics, thus accelerating the rate of direct electrocatalytic oxidation. Nevertheless, when the current density became too high, oxygen evolution reactions occurred within the electrocatalytic system, which competed with the electrocatalytic removal of PS microplastics, resulting in the removal decrease (Wei et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Additionally, excessive current density could elevate the temperature of the electrocatalytic system, and the ohmic thermal resistance of the electrode material could reduce the catalytic activity of the electrode. This ultimately resulted in the decrease of PS Microplastics removal (Wang et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).Thus, the current density of 46.67 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e was choiced for optimal current density.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section3\"\u003e \u003ch2\u003e3.3.4 Effect of electrolyte type\u003c/h2\u003e \u003cp\u003eElectrolyte type in the reaction system has a significant impact on the efficiency of electrocatalytic oxidation due to the presence of different anions. The PS Microplastics removal with different electrolytes was depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003ed. Among the four tested electrolytes, the PS Microplastics removal rate was 28% higher when Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e electrolyte was used compared to Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e and NaNO\u003csub\u003e3\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eWhen Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e electrolyte was used during the AEOP, sulfate radical anions (SO\u003csub\u003e4\u003c/sub\u003e\u0026bull;\u003csup\u003e\u0026minus;\u003c/sup\u003e) might be generated through the activation of a portion of SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e, HSO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, and H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e present in the solution. Sulfate radical anions (SO\u003csub\u003e4\u003c/sub\u003e\u0026bull;\u003csup\u003e\u0026minus;\u003c/sup\u003e) have an oxidation ability similar to hydroxyl radicals (\u0026bull;OH), as demonstrated in Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e2\u003c/span\u003e)\u0026ndash;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Therefore, Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e as the electrolyte for electrocatalytic oxidation resulted in a supreme removal efficiency for PS Microplastics.\u003c/p\u003e \u003cp\u003eThus, the optimal electrolyte type for this study was determined to be Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e.\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$${\\text{SO}}_{\\text{4}}^{\\text{2-}}\\text{\u0026rarr;}{\\text{SO}}_{\\text{4}}^{\\text{-}}\\text{\u0026bull;+}{\\text{e}}^{\\text{-}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$${\\text{HSO}}_{\\text{4}}^{\\text{-}}\\text{+\u0026bull;OH\u0026rarr;}{\\text{SO}}_{\\text{4}}^{\\text{-}}\\text{\u0026bull;+}{\\text{H}}_{\\text{2}}\\text{O}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$${\\text{H}}_{\\text{2}}{\\text{SO}}_{\\text{4}}\\text{+\u0026bull;OH\u0026rarr;}{\\text{SO}}_{\\text{4}}^{\\text{-}}\\text{\u0026bull;+}{\\text{H}}_{\\text{3}}{\\text{O}}^{\\text{+}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section3\"\u003e \u003ch2\u003e3.3.5 Effect of electrolyte concentration\u003c/h2\u003e \u003cp\u003eElectrolyte concentration determined the conductivity of the solution in the AEOP system. This in turn affected the current utilization rate, cell voltage, PS Microplastics removal rate, and energy consumption of the system. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003ee showd the removal curves of PS Microplastics under the different Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e concentrations. At electrolyte concentrations lower than 0.22 mol\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, it revealed that an increase in Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e concentration resulted in higher PS Microplastics removal rate. The increase in conductivity of the solution accelerated the transfer rate of electrons on the surface of the electrodes. In addition, the increased collision frequency between \u0026bull;OH and PS Microplastics could also accelerate the removal rate. Additionally, SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e ions minght oxidize to persulfate (S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e) (Hu et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Rodrigo et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). The following mechanisms (Eq.\u0026nbsp;(\u003cspan refid=\"Equ4\" class=\"InternalRef\"\u003e5\u003c/span\u003e)\u0026ndash;(\u003cspan refid=\"Equ6\" class=\"InternalRef\"\u003e7\u003c/span\u003e) ) might produce S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e at higher current density (Araujo et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Bezerra Rocha et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\text{2S}{\\text{O}}_{\\text{4}}^{\\text{2-}}\\text{\u0026rarr;}{\\text{S}}_{\\text{2}}{\\text{O}}_{\\text{8}}^{\\text{2-}}\\text{+2}{\\text{e}}^{\\text{-}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$$\\text{\u0026bull;}\\text{OH+S}{\\text{O}}_{\\text{4}}^{\\text{2-}}\\text{\u0026rarr;}{\\text{SO}}_{\\text{4}}^{\\text{-}}\\text{\u0026bull;}\\text{+2}{\\text{HO}}^{\\text{-}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ6\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ6\" name=\"EquationSource\"\u003e\n$${\\text{SO}}_{\\text{4}}^{\\text{-}}\\text{\u0026bull;}\\text{+S}{\\text{O}}_{\\text{4}}^{\\text{2-}}\\text{\u0026rarr;}{\\text{S}}_{\\text{2}}{\\text{O}}_{\\text{8}}^{\\text{2-}}\\text{+}{\\text{e}}^{\\text{-}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e7\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e is a more stable oxidizing agent that can persist in the electrolytic solution for an extended period of time. It facilitated the sustained breakdown of pollutants into SO\u003csub\u003e4\u003c/sub\u003e\u0026bull;\u003csup\u003e\u0026minus;\u003c/sup\u003e. Raising the concentration of electrolytes amplifies the levels of free radicals generated during electrolysis. Therefore, it promoted the degradation of microplastics (Davis et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In high electrolyte concentrations, boosting Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e concentrations did not result in the incremental increase of PS Microplastics removal rate. At this point, the mass transfer was no longer the factor that limited the rate of the reaction. The PS Microplastics removal rate was not accelerated by increasing the concentration of Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. Instead, its decrease due to excessive SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e adsorption on the active layer, which occupied the active sites. As a result, it reduced the production of \u0026bull;OH and impeded the effective interaction between the photosensitizer and the electrode. When the electrolyte concentration was high, the ionic bonding force became stronger, causing more energy consumption of the system (Zhang et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Thus, the study determined that the optimal concentration of Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e electrolyte was 0.22 mol\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section3\"\u003e \u003ch2\u003e3.3.6 Effect of initial pH\u003c/h2\u003e \u003cp\u003eThe PS microplastics removal rate varied with the initial pH of the solution (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003ef). The most efficient removal rate occurred when the initial pH was equal to 7. At low pH values, the electrode was prone to corrosion, and the Ti matrix surface could undergo oxidation, affecting the activity and electrocatalytic performance of the coating. Thus, there was a decline in the activity and electrocatalytic performance of the coating.\u003c/p\u003e \u003cp\u003eIn a weak acid (pH of 5), the removal efficiency was close to a neutral environment, because H\u003csup\u003e+\u003c/sup\u003e in acidic environment can inhibit the occurrence of oxygen evolution side reactions (Xiao et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The active sites on the electrode surface would adsorb OH\u003csup\u003e\u0026minus;\u003c/sup\u003e when initial pH was too high, and the metal ions dissolved from the electrode would precipitate with OH\u003csup\u003e\u0026minus;\u003c/sup\u003e, leading to electrode passivation and reducing the production of \u0026bull;OH and the interaction between active sites and PS microplastics (Maharaja et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Therefore, weak acid or neutal initial environment was considered to be done at our work.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eIn this study, Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode were successfully prepared as the active layer to enhance the electrocatalytic activity and improving the \u0026bull;OH production rate during the AEOP, which achieved a PS removal rate of 28.3% after 3 h, compared to the 16% achieved in Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode. The optimal electrolysis conditions for PS removal were current density of 46.67 mA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, electrode spacing of 1.5 cm, Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e electrolyte concentration of 0.22 mol\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, initial pH of 7, and electrolysis duration of 3 h. This study provides a strategy to prepare the active electrodes for electrocatalytic oxidation reactions, presenting valuable insights into the electrocatalytic removal of microplastics and offering potential applications in water treatment and environmental remediation.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eDeclaration of interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe 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.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contribution\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eWeikang Zheng:\u0026nbsp;\u003c/strong\u003eData curation, Investigation, Formal analysis, Writing \u0026ndash; original draft preparation.\u003cstrong\u003e\u0026nbsp;Boyan Wang:\u0026nbsp;\u003c/strong\u003eFormal analysis, Writing - review \u0026amp; editing. \u003cstrong\u003eZhenzhong Liu:\u003c/strong\u003eMethodology, Writing \u0026ndash; review \u0026amp; editing,\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eFormal analysis, Funding acquisition. \u003cstrong\u003eHongwei Yang:\u0026nbsp;\u003c/strong\u003eMethodology, Formal analysis, Funding acquisition.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability \u0026nbsp;\u003c/strong\u003eAll relevant data are included in the text or its Supplementary Information.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval \u0026nbsp;\u003c/strong\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate \u0026nbsp;\u003c/strong\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication \u0026nbsp;\u003c/strong\u003eAll authors listed agree to publish this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests \u0026nbsp;\u003c/strong\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe sincerely appreciate the the Open Fund for Key Laboratory of Poyang Lake Environment and Resource Utilization of Ministry of Education, Nanchang University (Project No. 2022Y04) for financial support.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAndrady AL. 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Science of The Total Environment 2024b: 171002\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Microplastics, AEOP strategy, Ti/La-Sb-SnO2 electrode, rare earth elements, electrocatalytic activity. ","lastPublishedDoi":"10.21203/rs.3.rs-4416872/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4416872/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eMicroplastics (MPs) in the aqueous environments has attracted widespread attention because of its potential risk to human health .Its high stability makes it difficult to be degraded and long term presence in the environment. Therefore, it is crucial to find an efficient and clean technology to remove microplastics in water. The advanced electrocatalysis oxidation process (AEOP) shows great potential for application. In this work, We focused on preparing Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrodes doped with different rare earth elements (La, Ce, Sm or Nd) as active layer by sol-gel method. The electrooxidation system has efficiently degraded MPs in aqueous solution. The optimal parameters for the removal of MPs were electrode spacing of 1.5 cm, current density of 46.67 mA cm\u003csup\u003e-2\u003c/sup\u003e, Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e electrolyte concentration of 0.22 mol·L\u003csup\u003e-1\u003c/sup\u003e, and initial solution pH of 7. After 3 h, MPs removal rate by Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e system reached 28.3 %, which was higher than the Ti/Ce-Sb-SnO\u003csub\u003e2\u003c/sub\u003e, Ti/Sm-Sb-SnO\u003csub\u003e2\u003c/sub\u003e, Ti/Nd-Sb-SnO\u003csub\u003e2\u003c/sub\u003e and Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode, the removal rates were increased by 8.23 %, 10.13 %, 16.28 % and 77 %, respectively. Electrochemical performance tests and •OH (Hydroxyl radicals) generation results indicated that the surface of Ti/La-Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode had abundant active sites, which promoted the formation of •OH to degrade microplastics effectively. In summary, the rare earth element-doped Ti/Sb-SnO\u003csub\u003e2\u003c/sub\u003e electrode provides crucial technological support for the electrooxidative removal of microplastics from water.\u003c/p\u003e","manuscriptTitle":"La-doped Ti/Sb-SnO2 electrode enhanced removal of microplastics by advanced electrocatalysis oxidation process (AEOP) strategy","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-27 12:19:34","doi":"10.21203/rs.3.rs-4416872/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"165fb103-cfcd-4908-b2ca-ff6d5451926d","owner":[],"postedDate":"June 27th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-10-28T03:55:05+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-27 12:19:34","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4416872","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4416872","identity":"rs-4416872","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}