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Photo-assisted electrocatalysis with bimetallic PdCu/TiOx catalysts: Enhancing denitrification and economic viability
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Yuxin Zenga, b, Yan Luoa, Yao Hea, Kaihang Zhangc, Binbin Zhua, Yuanzheng Zhanga, *, Junfeng Niua
Chinese Chemical Letters | 2025, 36(6) : 110514
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Chinese Chemical Letters | 2025, 36(6): 110514
• Communication •
Photo-assisted electrocatalysis with bimetallic PdCu/TiOx catalysts: Enhancing denitrification and economic viability
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Yuxin Zenga, b, Yan Luoa, Yao Hea, Kaihang Zhangc, Binbin Zhua, Yuanzheng Zhanga, *, Junfeng Niua
Affiliations
  • a College of Environmental Science and Engineering, North China Electric Power University, Beijing 102206, China
  • b State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China
  • c Brook Byers Institute of Sustainable Systems and School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332, United States
Published: 2025-06-15 doi: 10.1016/j.cclet.2024.110514
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Electrocatalysis for nitrate (NO3–) removal from wastewater faces the challenge of merging efficient reduction and high selectivity to nitrogen (N2) with economic viability in a durable catalyst. In this study, bimetallic PdCu/TiOx composite catalysts were synthesized with varying Pd and Cu ratios through electrochemical deposition on defective TiOx nanotube arrays. Denitrification experiments demonstrated that the Pd1Cu1/TiOx catalyst exhibited the highest NO3– removal rate (81.2%) and N2 selectivity (67.2%) among all tested catalysts. Leveraging the exceptional light-responsive property of TiOx, the introduction of light energy as an assisting factor in electrocatalysis further augmented the NO3– treatment rate, resulting in a higher NO3– removal rate of 95.1% and N2 selectivity of approximately 90%. Compared to individual electrocatalysis and photocatalysis systems, the overpotential for the catalytic interface active *H formation in the photo-assisted electrocatalysis system was remarkably reduced, thus accelerating electron migration and promoting NO3– reduction kinetics. Economic analysis revealed an energy consumption of 2.74 kWh/mol and a corresponding energy consumption per order (EEO) of 0.79 kWh/m3 for the Pd1Cu1/TiOx catalyst to reduce 25.2 mg/L of NO3–-N in water to N2, showcasing remarkable competitiveness and economic advantages over other water treatment technologies. This study developed the PdCu/TiOx electrocatalysts with high NO3– removal rates and N2 selectivity, particularly when combined with light energy, the efficiency and selectivity were significantly enhanced, offering a competitive and economically viable solution for wastewater treatment.

Nitrate reduction  /  Photo-assisted electrocatalysis  /  PdCu/TiOx composite catalyst  /  Nitrogen selectivity  /  Economic analysis
Yuxin Zeng, Yan Luo, Yao He, Kaihang Zhang, Binbin Zhu, Yuanzheng Zhang, Junfeng Niu. Photo-assisted electrocatalysis with bimetallic PdCu/TiOx catalysts: Enhancing denitrification and economic viability[J]. Chinese Chemical Letters, 2025 , 36 (6) : 110514 - . DOI: 10.1016/j.cclet.2024.110514
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Nitrate (NO3–) contamination of surface and groundwater has emerged as a pressing global concern, predominantly attributed to human activities, such as the excessive application of nitrogen-based fertilizers, improper treatment of domestic and industrial wastewater discharge, leaching from livestock manure, and landfill leachate [1,2]. Elevated levels of NO3– in water can induce eutrophication, trigger red tide, and deplete oxygen levels, resulting in suffocation and mortality of aquatic organisms [3,4]. Trace amounts of NO3– in drinking water can be converted into toxic NO2– within the human body, resulting in cyanosis (methemoglobinemia), fatigue, rapid breathing, cerebral hypoxia, and even fatality [5,6]. Additionally, NO3– in drinking water can also damage the human endocrine system, potentially causing liver damage and cancer [7,8]. Thus, urgent development of treatment processes and technologies for the harmless removal and resource utilization of NO3– in water is imperative.
Electrochemical reduction presents a promising technique for the removal of NO3– from water. Only electrons and active hydrogen (*H) provided through electrical energy are utilized as reducing agents, eliminating the need for additional reducing agents [9]. This approach demonstrates high treatment efficiency, relatively low investment costs, mild operating conditions, and negligible generation of secondary hazardous substances [10]. However, the electrochemical reduction of NO3– entails a complex process that may lead to the formation of various nitrogen-containing species, with typical reaction intermediates and products including nitrite (NO2–), nitric oxide (NO), nitrous oxide (N2O), nitrogen (N2), hydrazine (N2H4), and ammonia (NH3) [10,11], facilitated by adjustable potential/current (Eqs. 1-3) [12]. Hence, achieving efficient removal and highly selective conversion of NO3– in treating surface water, groundwater, or wastewater has long been a paramount objective. Among these products, N2 and NH3 are the most thermodynamically stable states of nitrogen, especially under neutral pH conditions [13]. Therefore, N2 and NH3 are commonly produced as end products in the electrocatalytic reduction of nitrates. Considering NH3 tends to dissolve in water, resulting in the formation of ammonium ions (NH4+) which may also be a potential pollutant, from an environmental perspective, the most desirable approach for NO3– removal with low concentration levels involves selectively reducing it to harmless N2 [14]. Therefore, it is imperative to screen appropriate electrocatalysts to enhance N2 selectivity in the electroreduction of NO3–.
In order to enhance the efficiency of NO3– conversion and N2 selectivity, metal catalysts are widely employed in the *H-driven electrocatalytic reduction of NO3–. Noble metal electrodes, such as Pd, Pt, and Ru, are notable examples due to their good adsorption activation capabilities for *H [15,16]. Transition metals such as Cu, Fe, Co and Ni have also exhibited considerable catalytic activity in the nitrate reduction reaction [17]. The preferential conversion of NO3– to N2 is commonly facilitated by Pd and Pt electrocatalysts, which are recognized as the most selective catalysts for producing N2 [18]. Pd-based materials are favored by researchers due to the relatively higher cost-effectiveness to Pt. However, Pd catalysts may not undergo effective transformation of NO3–, which often restricts the overall production rate. In this regard, a majority of the related studies have investigated the bimetallic multiphase catalysts, which could offer advantages of not only high N2 selectivity but also easily controllable catalytic active sites [5,19,20]. Introducing other metallic or nonmetallic elements through doping or substitution can alter the electronic structure of Pd and induce strain in the Pd lattice, which could significantly contribute to the enhanced electrocatalytic activity and/or stability of the catalyst [21]. For example, PdCu bimetallic catalysts exhibit excellent catalytic activity and N2 selectivity due to Cu enhancing NO3– reduction kinetics and Pd promoting N2 selectivity [22,23].
To address the restriction of high cost associated with noble metal electrodes in practical applications, using inexpensive conductive materials as substrates to prepare composite electrodes is a feasible approach [5]. Much of the current research primarily involves depositing noble metal catalysts on carbon paper through drop-casting. The poor dispersibility of the catalyst on carbon paper and the weak interaction between the catalyst and the substrate may lead to lower catalyst utilization efficiency and poor stability. Highly ordered and photo-responsive TiO2 nanotube arrays, distinguished by their unique nanotube structure and large surface area, as well as outstanding stability, optical, and electronic properties, are regarded as a catalyst support with high application potential [24,25]. Moreover, TiO2 nanotube arrays, directly grown on a Ti substrate without the need for additional conductive additives and binders, offer advantageous for charge transfer. Notably, the properties of TiO2 nanotubes, such as electrical conductivity, surface charge, and band gap, can be precisely controlled by constructing oxygen defects to meet specific requirements [26]. Therefore, it is reasonable to believe that TiO2 nanotube arrays, as a carrier for metal catalysts, can be tailored to exhibit excellent catalytic activity.
Furthermore, despite significant progress in electrocatalytic NO3− reduction technology, its substantial overpotential remains a major obstacle to achieving efficient NO3− conversion [27]. Introducing external energy, such as light, in electrocatalysis is expected to accelerate electrochemical interface reactions and reduce overpotential [28]. Researches have reported that, compared to standalone electrocatalysis, photo-assisted electrocatalysis exhibits high energy efficiency in the activation of small molecules at low overpotential [29-31]. Simultaneously, light irradiation may interfere with the electronic properties of electrocatalysts, such as electron migration, band bending, charge distribution, Fermi level, and intermediate desorption energy. These factors could alter catalytic pathways and performance [32]. Therefore, an in-depth exploration of the performance changes and mechanisms for photo-assisted electrocatalytic NO3– reduction system is required.
In this study, defective TiOx nanotube arrays were utilized as the substrate, and PdCu/TiOx composite catalysts were prepared via electrochemical deposition. The morphology, structure, and PdCu loading of the catalyst were characterized. The NO3– reduction efficiency and N2 selectivity with different Pd-Cu ratios were investigated under both electrocatalysis and photo-assisted electrocatalysis conditions. The mechanism of NO3– reduction in the photo-assisted electrocatalysis system was explored. Finally, the application potential and economic feasibility of the photo-assisted electrocatalytic technology for selectively reducing NO3– to N2 were analyzed and evaluated.
The synthesis and characterization of PdCu/TiOx composite catalysts was stated in detail in the materials and method part in Supporting information. After electrochemical reduction, the color of the electrode changed from silver-gray to deep blue (Fig. S1 in Supporting information), indicating the formation of oxygen vacancy defects on the surface of TiO2 nanotubes [33]. A top-view scanning electron microscopy (SEM) image of the Pd1Cu1/TiOx nanotube arrays (Fig. 1a) showed a highly ordered morphology with open-ended nanotubes, similar to the TiO2 nanotube arrays. The nanotubes had an approximate length of 5 µm as observed in the cross-sectional image (Fig. 1b). Transmission electron microscopy (TEM) images revealed a nanotube diameter of approximately 70–100 nm in the Pd1Cu1/TiOx samples (Figs. 1c and d). However, no PdCu nanoparticles were observed, indicating that PdCu might be loaded on the nanotubes as sub-nanometer clusters or individually dispersed atoms. High-resolution TEM (HRTEM) analysis confirmed the presence of the (101) crystal plane of anatase TiO2 with a lattice fringe spacing of 0.35 nm in the Pd1Cu1/TiOx (Fig. 1e) [34]. High-angle annular dark-field scanning transmission electron microscopy (HADDF-STEM) and energy-dispersive X-ray spectroscopy (EDS) elemental mapping images further verified the successful deposition of Pd and Cu metals, which was evenly distributed on the nanotubes (Figs. 1f–j). The uniform distribution of PdCu on the nanotubes implies an increased exposure of active sites, thus benefiting catalytic reactions [35]. The atomic percentages of Pd and Cu on the Pd1Cu1/TiOx nanotube arrays were determined to be 0.15 at% and 0.17 at%, respectively (Table S1 in Supporting information).
The structure of the catalysts was revealed through X-ray characterization techniques. The X-ray diffraction (XRD) patterns of TiO2 and Pd1Cu1/TiOx nanotube arrays exhibit similar diffraction peaks at around 2θ = 25.5°, 38.1°, 48.2°, 54.2°, 55.2° (Fig. 2a), corresponding to the (101), (004), (200), (105), (211) crystal planes of anatase TiO2 (PDF #75–1537) [36]. Additionally, two additional diffraction peaks at 2θ = 62.5° and 71.6° correspond to the (110) and (103) crystal planes of Ti [37]. Notably, no peaks corresponding to the crystal planes of palladium oxide or copper oxide were detected, indicating the successful incorporation of Pd and Cu ions into the TiO2 lattice. This can be attributed to the presence of oxygen vacancy defects on the surface of the TiOx, which facilitates the capture and stabilization of metal atoms [38]. Electron paramagnetic resonance spectroscopy (EPR) spectra show that the TiOx exhibited a prominent signal peak at a g-value of 2.005 (Fig. 2b), indicating the abundant formation of oxygen defect sites on the surface of the nanotube arrays after electrochemical reduction [39]. The O 1s signals also confirm the presence of oxygen vacancies in TiOx (Fig. S2 in Supporting information). The O 1s peak of TiOx can be deconvoluted into three peaks at 530.29, 530.90 and 532.17 eV, corresponding to lattice oxygen (O-metal), oxygen vacancy (OV) and adsorbed oxygen (Ads. O) [40,41]. Fig. 2c demonstrates the high-resolution X-ray photoelectron spectroscopy (XPS) spectra of TiO2 and Pd1Cu1/TiOx nanotube arrays in the Ti 2p region. The TiO2 nanotube arrays exhibit two characteristic peaks at 458.68 eV and 464.46 eV, corresponding to Ti 2p3/2 and Ti 2p1/2, respectively. In contrast, the Pd1Cu1/TiOx nanotube arrays show a shift in the Ti 2p3/2 and Ti 2p1/2 characteristic peaks towards lower binding energies by 0.25 and 0.27 eV, respectively. This shift is attributed to the presence of Ti3+ and oxygen vacancies on the surface of the sample [34].
The oxidation states of PdCu loaded on nanotubes were investigated using high-resolution XPS analysis in the Pd 3d region and Cu 2p region separately. Fig. 2d shows distinct peaks at 334.8 eV and 340.2 eV, corresponding to Pd 3d5/2 and Pd 3d3/2, respectively [35]. Further peak fitting analysis reveals characteristic peaks of Pd0 at binding energies of 334.7 and 340.2 eV, indicating that the majority of Pd was loaded on the support in the metallic form. Additionally, small signal peaks at binding energies of 336.1 and 342.2 eV correspond to Pd2+, indicating the presence of a small amount of Pd in the form of PdO [42]. Fig. 2e shows the Cu 2p XPS spectrum of Pd1Cu1/TiOx. The oxidation state of Cu is often determined by the position of the Cu 2p3/2 peak [43]. The Cu 2p3/2 spectrum was deconvoluted into signal peaks at 932.2 and 934.5 eV. The peak at 932.2 eV was attributed to Cu0 or Cu1+, while the peak at 934.5 eV was attributed to Cu2+ [44]. In addition, satellite peaks of Cu2+ were observed at 941.1 eV, 943.7 eV, and 962.4 eV, indicating that the deposited Cu species on the nanotubes primarily existed in the form of elemental Cu and its oxides. The atomic percentages of Pd and Cu on the Pd1Cu1/TiOx nanotube arrays obtained from XPS results were 0.17 at% and 0.21 at%, respectively (Table S1), slightly higher than the EDS results. This difference can be attributed to the higher sensitivity of XPS to the sample surface [45]. Fig. 2f shows the ultraviolet–visible spectroscopy (UV–vis) absorption spectra of TiO2 and TiOx nanotube arrays. The reduced TiOx exhibited enhanced light absorption in the 400–600 nm visible range compared to TiO2 nanotubes, which is attributed to the formation of a high concentration of oxygen vacancies on the nanotube surface and the induction of Ti3+ centers through electroreduction treatment. These defects lead to the generation of defect levels below the conduction band, imparting strong visible light absorption capability to the TiOx nanotube arrays [46]. In summary, defective TiOx nanotube arrays were successfully prepared. The abundant oxygen vacancies on the surface served as capture sites for PdCu metal atoms, ensuring their uniform distribution on the nanotube support. Additionally, these defects enhanced the responsiveness to visible light, facilitating catalytic reactions driven by light energy.
To screen for the catalyst with optimal activity, the NO3– electrocatalytic reduction efficiency and product selectivity of TiO2, TiOx, Cu/TiOx, Pd/TiOx, Pd1Cu2/TiOx, Pd1Cu1/TiOx and Pd2Cu1/TiOx nanotube arrays were investigated, respectively (Fig. S3 in Supporting information). Individual TiO2 and TiOx nanotube arrays exhibited weak kinetics for NO3– reduction. However, the introduction of Cu onto the TiOx significantly enhanced the rate of NO3– reduction. Notably, the concentration of NO2– increased visibly during the reaction in the Cu/TiOx system, suggesting that Cu sites primarily facilitate the conversion of NO3– to NO2– [23,47]. On the other hand, the Pd/TiOx nanotube arrays displayed the weakest NO3– reduction performance, indicating that individual Pd is not efficient in promoting the reduction of NO3–. This could be ascribed to the exceptional hydrogen spill-over capabilities of Pd [48,49]. However, when Pd and Cu were simultaneously loaded onto the TiOx nanotube arrays, PdCu/TiOx composite catalysts exhibited faster kinetics of NO3– reduction with minimal generation of NO2– throughout the entire experimental process (<1%). The incorporation of Cu can modify the electronic configuration and the d-band center of Pd, thereby enhancing the catalytic efficacy [50]. As shown in Fig. 3a, after 75 min of reaction, the Pd1Cu1/TiOx catalyst showed the highest NO3– conversion rate (81.2%) and N2 selectivity (67.2%) compared to other catalysts. Therefore, Pd1Cu1/TiOx catalyst was selected for further study on the photo-assisted electrocatalytic reduction of NO3–.
Considering the excellent light-responsive properties of TiOx, the introduction of light holds promise in altering the electronic performance of Pd1Cu1/TiOx catalyst, thereby changing its intrinsic activity and selectivity [28]. Fig. S4 (Supporting information) illustrates the photo-assisted electrocatalytic NO3– reduction performance and product generation of the Pd1Cu1/TiOx catalyst at voltages ranging from –0.35 V to –0.55 V vs. reversible hydrogen electrode (RHE). Similar to the electrocatalytic NO3– reduction, the final products under the photo-assisted electric field still consist mainly of N2 and NH3. It is noteworthy that the introduction of light remarkably improved the removal rate of NO3– and the selectivity for N2. At a voltage of –0.35 V vs. RHE, the photo-assisted electrocatalytic NO3– conversion rate and the N2 selectivity could reach 81.7% and 75.8% respectively (Fig. 3b), which was superior to what is achieved under electrocatalysis at –0.45 V vs. RHE, indicating that introducing light can contribute to reducing the reaction overpotential. At the voltage of –0.45 V vs. RHE, the photo-assisted electrocatalysis (PEC) exhibited the highest NO3– conversion rate of 95.1% and a N2 selectivity of approximately 90%, much better than that under either sole photocatalysis (PC) or electrocatalysis (EC) modes (Fig. 3c). The significantly enhanced NO3– reduction performance indicates that the electron transfer capability and intrinsic activity of Pd1Cu1/TiOx can be improved through photo-assisted methods [51]. In addition to its excellent NO3– reduction activity and N2 selectivity, the Pd1Cu1/TiOx nanotube arrays also demonstrated good durability. In nine repeated PEC tests, the Pd1Cu1/TiOx nanotube arrays did not show any signs of deactivation (Fig. 3d). Further, the XRD patterns and SEM image of Pd1Cu1/TiOx evidenced no significant alterations was found on the structure and surface characteristics of Pd1Cu1/TiOx before and after the durability test, as depicted in Figs. S5 and S6 (Supporting information), respectively.
To investigate the mechanism behind the improved performance of NO3– reduction in PEC system, a photoelectrochemical analysis was conducted. The linear sweep voltammetry (LSV) curve indicates that the current density under PEC conditions was higher than that under EC conditions (Fig. 4a). Furthermore, the current density was further enhanced when NO3– was added to the electrolyte, suggesting the occurrence of a noticeable NO3– reduction reaction on the cathode [52]. The transient photocurrent curve of Pd1Cu1/TiOx exhibited corresponding increases and decreases in photocurrent with the periodic opening and closing of light illumination (Fig. 4b), indicating its excellent photo-responsive capability. Moreover, the photocurrent response was more pronounced with the addition of NO3–, implying the participation of photogenerated electrons in the NO3– reduction reaction. Comparing the electrochemical impedance spectroscopy (EIS) of Pd1Cu1/TiOx under EC and PEC conditions, it is evident that the introduction of an external light field reduced the interfacial charge transfer resistance of the catalyst (Fig. 4c). These results indicate that the introduction of a light field not only significantly reduced the reaction overpotential but also accelerated the electron transfer rate at the catalyst interface, thereby improving the removal efficiency of NO3–.
Research has shown that electrocatalytic reduction of NO3– can primarily proceed through two pathways: direct electron transfer reduction and a *H-mediated indirect reduction pathway [53-55]. The direct electron reduction pathway primarily occurs on non-precious metal catalyst sites, such as Cu and Cu/Ni, due to their strong NO3– adsorption capability [56]. On the other hand, the *H-mediated NO3– reduction pathway is more likely to occur on precious metals, such as Pd, Pt, and Rh, which possess a strong hydrogen adsorption capability, thus inhibiting the occurrence of hydrogen evolution side reactions [7]. To validate the hypothesis, the generation of *H and its involvement in the NO3– reduction process was investigated using EPR spectroscopy. As shown in Fig. 4d, the EPR spectra of Pd1Cu1/TiOx system exhibited nine distinct characteristic signal peaks with intensity ratio approaching 1:1:2:1:2:1:2:1:1 and the calculated hyperfine coupling constants as αN = 16.3 G and αH = 22.5 G, which corresponds to the adduct of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) with atomic *H [53,57]. This suggests that atomic *H generated during the reaction desorbed from the catalyst surface and was captured by DMPO in the reaction solution [57]. To further investigate the contribution of *H in the NO3– reduction, tert-butyl alcohol (TBA) was applied as a radical scavenger [58]. The results showed that increasing the TBA concentration in the reaction solution greatly suppressed NO3– reduction (Fig. 4e). The removal rate of NO3– decreased by approximately 21% when TBA was added at 1 mmol/L, and the removal rate further decreased by 37% when TBA concentration was increased to 10 mmol/L. However, increasing the TBA concentration to 20 mmol/L showed little difference in the NO3– removal rate, indicating that *H in the solution may be almost completely inhibited [7]. It is worth noting that while TBA as a scavenger inhibits the reaction of NO3– and free *H which desorbs from the catalyst into the solution, it may not completely eliminate the *H adsorbed on the surface of the Pd1Cu1/TiOx catalyst. This adsorbed *H still plays a crucial role in the removal of NO3–. Therefore, it is reasonable to speculate that, in the PEC reduction of NO3–, at least 37% of the NO3– reduction occurs through the *H-mediated indirect pathway.
Based on the obtained results and discussions, the reduction mechanisms of NO3– on the Pd1Cu1/TiOx catalyst can be proposed. The Pd active sites dissociate nearby water molecules through the Volmer mechanism to generate *H (Eq. 4), therefore the pH of the solution in the cathode chamber gradually increased from 6.80 to 11.69 as the reaction proceeds (Fig. S7 in Supporting information). Meanwhile, Cu sites, as strong Lewis acid sites, change the electronic structure of the catalyst surface and initially adsorb NO3– ions in the solution [59]. Then the overflow of *H at Pd sites facilitates the reduction of *NO3– to *NO2– (Eq. 5). The high reduction ability of *H (E 0 (H+/H) = –2.31 V vs. SHE) enables the cleavage of the N—O bond in NO2–, leading to the gradual transformation into *N on the Pd surface (Eqs. 6 and 7). Finally, N2 is formed through N—N coupling (Eq. 8) [49,60].
The economic feasibility of the PEC system for selectively reducing NO3– was assessed. High removal efficiency and N2 selectivity make the designed PEC system with the Pd1Cu1/TiOx nanotube arrays as the cathode promising for treating NO3–-containing wastewater due to its superiority over other systems equipped with Pd or Cu-based electrocatalysts (Fig. S8 in Supporting information). Taking into account that in practical applications, light energy can be derived from sunlight, which would be no cost involved, the total energy cost was mainly attributed to the electrical energy cost to achieve the highest efficiency in converting NO3–-N to N2 and the catalyst preparation [61]. Using the formula Eqs. S5 and S6 in Supporting information, the energy consumption required for Pd1Cu1/TiOx nanotube arrays to reduce 25.2 mg/L of NO3–-N in water to N2 was calculated to be 2.74 kWh/mol, with a corresponding EEO of 0.79 kWh/m3, which is comparable to the systems using other electrocatalysts (Fig. S9 in Supporting information). Considering the potential utilization of inexpensive renewable energy sources such as solar or wind power, studies have indicated that the price of wind power in the next 10 years is estimated to be around $0.02 per kilowatt-hour (kWh) [62]. Therefore, the corresponding total electrical energy cost for the Pd1Cu1/TiOx nanotube arrays was $0.0944/m3, presenting a significantly competitive or economically advantageous option compared to other water treatment technologies (Table 1) [8]. Importantly, this reaction system does not necessitate the addition of Cl– to enhance the selectivity of N2, thus reducing water purification costs while eliminating the production of toxic by-products containing Cl.
In order to investigate the efficacy of PdCu/TiOx catalysts in selectively reducing NO3– to N2 in complex real water, the potential impact of alkali metal ions and organic matter present in the water on NO3– reduction must be considered. Consequently, the secondary effluent from a wastewater treatment plant (WWTP) was subjected to treatment using PdCu/TiOx under the PEC mode. The main water quality parameters of this water are shown in Table S3 (Supporting information). For consistency with previous experimental results, suspended solids in the water were initially filtered using a 0.45 µm membrane, and NO3– was added to elevate the concentration to 25.2 mg/L. As shown in Fig. 4f, under the PEC mode, the Pd1Cu1/TiOx catalyst demonstrated commendable treatment performance for the secondary effluent. Following 75 min of reaction, the removal efficiency of NO3– reached 95.3%, with a selectivity for N2 of 83.7%. These results closely resemble those observed in deionized water, indicating minimal impact of the presence of organic matter or inorganic ions in the secondary effluent on NO3– reduction.
The TiOx nanotube arrays feature enriched oxygen defect sites to capture PdCu metals, ensuring uniform dispersion on the carrier surface. Consequently, the Pd1Cu1/TiOx composite catalyst showed optimal electrocatalytic activity, and the catalytic activity was further enhanced when light was introduced due to the remarkably reduced overpotential for the interface active *H formation and accelerating electron migration. The cost-effectiveness of the photo-assisted Pd1Cu1/TiOx electrocatalytic system demonstrated competitiveness and economic advantages compared to other water treatment technologies.
Although with high efficiency and selectivity, electrochemical nitrate reduction is currently still limited to small-scale laboratory experiments and has not yet been adapted for large-scale industrial or commercial uses, nor for practical implementation in real-world aquatic settings. As the stability and cost of the electrocatalysts are highly required in the industrial and commercial applications, it is of greater importance to do longer stability tests on the studied electrocatalysts to make such electrocatalysts more suitable for large-scale industrial utilization. Methods to synthesize electrocatalysts also need to improve for larger-scale usage and lower costs, such as using milder synthesis techniques, designing self-supporting and integrated catalytic materials. In future research, consideration should be given to the investigation of corrosion, leaching, and surface poisoning that may occur during the long-term operation of the catalyst, which may lead to a decrease in reaction activity and potential adverse effects on the environment. Meanwhile, the removal of nitrates in surface and groundwater with low conductivity may require additional electrolyte supplementation, which needs to be overcome in the future. Additionally, for water with more complex qualities, the combined use with other water treatment processes may be necessary to increase practicality.
Declaration of competing interest
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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.
CRediT authorship contribution statement
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Yuxin Zeng: Writing – original draft, Visualization, Formal analysis, Data curation. Yan Luo: Resources, Methodology, Investigation. Yao He: Resources, Methodology, Investigation. Kaihang Zhang: Writing – review & editing, Validation, Conceptualization. Binbin Zhu: Writing – review & editing, Validation, Conceptualization. Yuanzheng Zhang: Writing – review & editing, Supervision, Project administration, Funding acquisition, Conceptualization. Junfeng Niu: Writing – review & editing, Supervision, Project administration.
Acknowledgments
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This work was funded partly by the National Natural Science Foundation of China (No. 52300084), China Postdoctoral Science Foundation (No. 2023M741151), and the Fundamental Research Funds for the Central Universities (No. 2024MS063).
Supplementary materials
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Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2024.110514.
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doi: 10.1016/j.cclet.2024.110514
  • Receive Date：2024-05-06
  • Online Date：2025-10-29
  • Published：2025-06-15
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  • Received：2024-05-06
  • Revised：2024-07-25
  • Accepted：2024-09-27
Affiliations
    a College of Environmental Science and Engineering, North China Electric Power University, Beijing 102206, China
    b State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China
    c Brook Byers Institute of Sustainable Systems and School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332, United States
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表12种不同金属材料的力学参数
科
Family		 属数
Number of
genus		 种数
Number of
species		 占总种数比例
Percentage of
total species (%)		 属
Genus		 种数
Number of
species		 占总种数比例
Percentage of total
species (%)
鹅膏菌科Amanitaceae 2 11 5.26 鹅膏菌属 Amanita 10 4.78
小菇科 Mycenaceae 2 12 5.74 丝盖伞属 Inocybe 5 2.39
多孔菌科 Polyporaceae 8 14 6.70 蜡蘑属 Laccaria 5 2.39
红菇科 Russulaceae 3 23 11.00 小皮伞属 Marasmius 6 2.87
小菇属 Mycena 11 5.26
光柄菇属 Pluteus 5 2.39
红菇属 Russula 17 8.13
栓菌属 Trametes 5 2.39
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