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Communication

Evidence of Enhanced Molecular Oxygen Activity Induced by the Synergistic Effect of Oxygen Vacancies and Ag Nanoparticles in Ag3PO4

by
Xu Zhang
1,2,3,†,
Futao Yi
1,†,
Li Zhou
2,*,
Weifeng Xie
4,
Zhenqi Wang
1,
Huaqiang Chu
1,*,
Xuefei Zhou
1 and
Yalei Zhang
1
1
College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China
2
Shanghai Engineering Research Center of Low-Carbon Agriculture, Institute of Eco-Environmental Protection Research, Shanghai Academy of Agricultural Sciences, Shanghai 201403, China
3
Key Laboratory of Urban Water Supply, Water Saving, and Water Environment Governance in the Yangtze River Delta of Ministry of Water Resources, Tongji University, Shanghai 200092, China
4
Shanghai Qingpu District Chonggu Town Agriculture and Rural Service Center, Shanghai 201706, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Catalysts 2025, 15(6), 527; https://doi.org/10.3390/catal15060527
Submission received: 7 April 2025 / Revised: 15 May 2025 / Accepted: 23 May 2025 / Published: 26 May 2025
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Abstract

This study investigates the synergistic enhancement of molecular oxygen activation (MOA) in silver phosphate (Ag3PO4) photocatalysts modified with oxygen vacancies (OVs) and silver nanoparticles (Ag0). The vacuum-calcined Ag3PO4 exhibited a 2.05-fold increase in the degradation efficiency of cylindrospermopsin (CYN), reaching 88.00% within 5 min, compared to its pristine counterpart. This work proposes a novel dual-modification approach—rarely explored in previous MOA studies—by introducing OVs and Ag0 simultaneously. The characterization results confirmed that OVs improved the charge transfer and adsorption of molecular oxygen, while the Ag0 nanoparticles facilitated electron–hole separation and interfacial charge transfer. Reactive oxygen species (ROS) such as ·O2−, 1O2, H2O2, and ·OH were confirmed via ESR analysis and chemical assays. A detailed mechanism was proposed and illustrated, showing how OVs and Ag0 synergistically promote MOA. These findings highlight a cost-effective method for enhancing photocatalysis and environmental remediation.

1. Introduction

Cylindrospermopsin (CYN) is a potent hepatotoxin commonly found in freshwater cyanobacteria blooms, posing significant environmental and public health risks [1]. Due to its resistance to conventional treatment methods, CYN remains persistent in water systems, making it a challenging pollutant to remove [2,3]. The chemical stability of CYN in aquatic environments necessitates the development of advanced degradation technologies to mitigate its harmful effects. Advanced oxidation processes (AOP) have been generally developed as one of the major approaches for environmental remediation over the past several decades [4]. Unlike the conventional AOPs using precursor chemical oxidants and/or energy, the photocatalytic AOP can take effect via oxidizing water molecules and activating O2 molecules to generate reactive oxygen species (ROS) under mild conditions without additional oxidants [5]. Molecular oxygen activation (MOA) plays a pivotal role in ROS generation during the photocatalytic processes. Because MOA has such an important practical effect, extensive regulation strategies have been widely applied to modify photocatalysts to promote MOA [6,7,8].
Recent work has emphasized defect engineering strategies in photocatalytic materials for boosting O2 activation efficiency [9,10,11,12]. Vacancy, as a representative of defect engineering, plays an important role in the energy transfer and charge transfer process of MOA. For instance, oxygen vacancies (OVs) in BiOBr have been shown to improve both pollutant adsorption and O2 activation efficiency [13], while defective TiO2 enhances exciton separation and facilitates the generation of singlet oxygen [14]. Recent studies have also demonstrated that metal oxide semiconductors with OVs significantly enhance the photocatalytic activity of O2 [15,16]. In terms of the most common oxygen vacancy, it can not only reduce the energy barrier of ground-state oxygen molecules exciting to singlet active oxygen [14,17] but also induce excitons dissociated into charge carriers [18,19]. The oxygen vacancy can improve the adsorption of molecular oxygen and promote the reaction of electrons and adsorbed O2 to generate ROS [20,21]. Poor carrier separation efficiency is also an important factor that limits the MOA performance involving the electron transfer process. The metal served as electron mediators that promote the capture and transfer of photogenerated charge carriers [22]. Overall, the OVs and metal could synergistically tailor the charge transfer pathway and enhance the photocatalytic performance significantly.
As a representative of silver-based photocatalysts, silver phosphate (Ag3PO4, APO) has presented with a wide light absorbance [23] and powerful oxidability [24]. Nevertheless, APO inevitably has its inherent defects, namely, the high recombination rate of photogenerated electrons and holes. Therefore, the modification to boost the charge separation could improve the photocatalytic performance of Ag3PO4. Recent advances have demonstrated that the photocatalytic performance of Ag3PO4 can be significantly enhanced by introducing structural modifications such as heterojunction constructions [25], oxygen vacancy engineering [26], and integration with conductive supports [27]. These strategies effectively promote charge separation and suppress electron–hole recombination, thereby improving photocatalytic efficiency under visible light. Focusing on MOA in Ag3PO4 is particularly important due to its inherent high charge recombination rate and the role of O2 as a green oxidant in ROS generation without sacrificial agents. However, these studies are immature, and it is still challenging to find a low-cost and efficient method to improve the performance of MOA and the stability of the APO. This study distinguishes itself by simultaneously engineering defects and metallic sites in Ag3PO4 to synergistically enhance O2 activation.
In this study, oxygen vacancies and Ag metal nanoparticles were simultaneously introduced in situ on the surface of vacuum-calcined Ag3PO4. Compared with pristine Ag3PO4, the vacuum-calcined Ag3PO4 demonstrated a 2.05-fold enhancement in the degradation of cylindrospermopsin (CYN). Further analysis confirmed that the synergistic effects of oxygen vacancies and Ag0 metal nanoparticles played a critical role in activating the MOA process to enhance photocatalytic performance.

2. Result and Discussion

2.1. Characterizations of Photocatalysts

The analogous nanoparticles were observed in APO and APO-200 samples and particle sizes were ~300 nm (as shown in Figure 1a,b). A small number of nanoparticles were observed on the surface of APO-200, as highlighted by yellow circles in Figure 1b. The XRD spectra in Figure 1c confirmed no secondary phase other than Ag3PO4 and metallic Ag. All peaks could be fitted into Ag3PO4 with the typical body-centered cubic structure (JCPDS NO.06-0505) [28]. Crystallite sizes were determined using the Scherrer equation based on XRD data. The results showed that the crystallite size for the APO sample was 107.7 nm, while the APO-100, APO-200, and APO-300 samples had a size of 82.9 nm each, which correlates with the improved photocatalytic activity in the modified samples [29]. Furthermore, the peak around 38.1° could be attributed to the (002) plane of metallic Ag0 in vacuum-calcined samples. The contents of Ag0 [30] in Figure 1f are 4.56%, 20.18%, and 5.34% for samples APO-100, APO-200, and APO-300, respectively. The shifts of XPS spectra observed in the Ag 3d5/2 and Ag 3d3/2 binding energies (from 367.88 eV in APO to 368.00 eV in APO-200 and from 373.88 eV in APO to 374.00 eV in APO-200, respectively) in the XPS spectra suggest an interaction between Ag0 nanoparticles and Ag3PO4. These shifts indicate changes in the chemical environment of Ag0, which may contribute to enhanced charge transfer and improved photocatalytic performance [31]. Meanwhile, a more quantitative analysis was performed on the EPR and XPS spectra. The EPR spectra of vacuum-calcined samples displayed the obvious OVs signal at g = 2.004 [32], and showed a direct correlation with photocatalytic activity. Specifically, APO-200 exhibited the strongest EPR signal among all samples, consistent with its highest degradation efficiency. The XPS peak at 531.50 eV (Figure 1e) is consistent with previous studies [33,34,35] that have identified similar peaks in oxygen-deficient materials, confirming the presence of oxygen vacancies in our samples. The contents of OVs were 13.27%, 16.06%, and 15.16% for samples APO-100, APO-200, and APO-300, respectively. Similarly, XPS analysis of the O 1s spectra revealed that the relative peak area associated with surface defects (531.5 eV) increased in APO-200, confirming the enhanced presence of OVs. The above analysis confirmed the simultaneous production of OVs and Ag0.

2.2. Excitation and Separation of Charges

As shown in Figure 2a, all vacuum-calcined APOs exhibited a red shift in the UV-vis absorbance spectra. According to the Mulk equation [36], the band gap of APO and APO-200 could be calculated as 2.18 eV and 1.90 eV, respectively (Figure 2b). According to the above results and empirical equation [37], the conductive and valence band position of APO-200 could be theoretically predicted as 0.51 V and 2.41 V (vs. NHE). Although the narrow band structure in defective APO conducts the positive shift of the band structure, the conduction band still processes sufficient negative potential to deliver MOA and two electrons reduction processes (E0 (O2/H2O2) = 0.69 V, vs. NHE) [38]. The varying percentages of Ag0 and OVs directly influenced the optical and structural characteristics of the materials [30]. For instance, an increased Ag0 content contributed to the enhancement of interfacial charge transfer and visible light harvesting, while a higher concentration of OVs led to band gap narrowing and extended light absorption into the visible range. These changes are evident from the red-shift observed in UV-vis spectra and the decreased band gap energy in Tauc plots. The observed narrowing of the band gap is likely influenced by both oxygen vacancies and the introduction of metallic Ag0 [14]. Oxygen vacancies create mid-gap states that reduce the energy required for electronic transitions, while the presence of Ag0 can modify the electronic structure at the interface, enhancing visible-light absorption through localized surface plasmon resonance effects.
Among all of the samples, the lowest intensity of PL spectrum in APO-200 indicated the best charge separation property and the order of peak intensity was identical with the rank of photocatalytic performances (Figure 2c and Figure S1). Based on the two-parameter formula [39], the quantum lifetime was fitted in Figure 2d. All vacuum-calcined samples, such as APO-100 (23.46 ns), APO-200 (32.37 ns), and APO-300 (29.89 ns), obtained a longer lifetime than the original APO (18.34 ns). During the photoelectric experiments for charge mobility analysis, APO-200 possessed the smallest arc in the EIS spectra (Figure 2f), indicating the best conductivity among all samples. In agreement with the EIS spectrum, APO-200 also exhibited the strongest current intensity; this result also affirmed the superior conductivity among all catalysts (Figure 2e). Furthermore, aiming to calculate the mobility efficiency of charge carriers quantitatively, H2O2 reacted as the acceptor to quench electrons, this principle could calculate mobility efficiency by the transportation efficiency ( η t r a n s ) based on the ratio of J H 2 O / J H 2 O 2 (where J H 2 O and J H 2 O 2 are the photocurrent density for photoelectrochemical H2O and H2O2 oxidation, respectively) [40]. According to the photocurrent density of different samples in Figure S2, the η t r a n s of APO, APO-100, APO-200, and APO-300 could be accounted for as 17.12%, 20.76%, 27.06%, and 25.56%, respectively. These results demonstrate that the surface charge carrier is rapidly transferred on the surface of vacuum-calcined APO.
As the beginning step of the MOA process, the charge separation could provide sufficient excited electrons as raw materials for MOA. Photo energy might excite charge carriers for later separations, therefore light adsorption is an effective factor for the MOA process [41,42]. In the excitation process, unoccupied orbitals in defects might assist in electron excitation at the middle level. On the recombination side, defects also limited the charge recombination by attracting electrons as Lewis acid sites [43]. On the other hand, the metal Ag0 on the interface enhances electron–hole separation and the interfacial charge transfer, which is also important in the photocatalytic MOA and two electrons reduction process [30]. The efficient charge excitation and transportation due to the synergistic effects of OVs and Ag0 could stimulate later MOA and a two-electron reduction to generate ROSs for degradation.

2.3. Performances of Catalysts

Activated molecular oxygen can be widely used in the oxidation of organic molecules, such as attacking the active sites of organic pollutants to destroy their structure, ultimately achieving the removal of pollutants, and attacking specific atoms to cause cross-coupling reactions and selective oxidation reactions [44,45]. CYN as a model pollutant was utilized to evaluate the photocatalytic performances of samples. As shown in Figure 3a,b, all vacuum-calcined samples revealed better photocatalytic degradation performances than normal APO. Specifically, removal rates were 88.0%, 81.3%, 71.7%, and 64.1%, corresponding to APO-200, APO-300, APO-100, and APO in just 5 min. According to the previous research, the photocatalytic degradation process agreed with the pseudo-first-order reaction model as follows [46]:
ln(C/C0) = −kt
where k (min−1) and t (min) were the kinetic constant and reaction time, and C and C0 represent the initial and immediate concentration of pollutants at t. The kinetic constants (k) and R2 values for the photocatalytic degradation of CYN are summarized in Table 1. The APO-200 sample exhibited the highest kinetic constant (k = 0.41 min−1) and the best fit for the pseudo-first-order reaction model (R2 = 0.99), indicating its superior photocatalytic performance compared to the other samples. Compared with the APO, all vacuum-calcined catalysts revealed a higher constant than AOP and the 2.05 times enhancement could be confirmed in the APO-200. These results indicated that the defective strategy and metal deposition by calcination in a vacuum could activate the photocatalytic activity of APO.

2.4. Products of the MOA

ROSs were determined by trapping experiments and ESR measurements. The degradation ratios were depressed from 88.00% to 76.60%, 48.90%, 44.20%, and 42.70% due to the involvement of IPA, EDTA-2Na, NaN3, and p-BQ, respectively (Figure 4a), indicating the major oxidability forms of h+, 1O2, ·O2−, and ·OH. An ESR measurement also certified the strong signals of 1O2, ·O2−, and ·OH in APO- 200 (Figure 4b), which are the product of MOA and two electrons reduction, which can be expressed as follows [38]:
e − + O 2 → · O 2 −
· O 2 − + e − + 2 H + → H 2 O 2
H 2 O 2 + · O 2 − → · O H + O H − + O 2
H 2 O 2 → 2 · O H
O 2 − + h + → O 2 1
These results both endorsed that ·O2, ·O2−, and ·OH, as products of the MOA process, were the main radicals to mineralize pollutants. According to the above equations, ·O2− and H2O2 were the main immediates of electron reduction. While ESR provides qualitative confirmation of ROS species, it is not suitable for precise quantification. Therefore, we used chemical detection methods by nitroblue tetrazolium and potassium iodide (detailed in the Supplementary Information Section) to measure the concentrations of H2O2 and ·O2−, as shown in Figure 4c,d. These results confirm that APO-200 could form more H2O2 and ·O2− than other samples, which is consistent with the order of photocatalytic activity. The OVs and Ag0 could accelerate the oxygen adsorption and play as the active site for the latter MOA process [47].
To evaluate the structural stability of the photocatalysts, cyclic degradation experiments and XRD analyses before and after photocatalysis were conducted. As shown in Figure S1 in the Supplementary Information Section, the catalyst maintained a high photocatalytic performance over multiple cycles, and no significant changes were observed in its crystalline structure, indicating good structural and operational stability.

2.5. Mechanisms of Photocatalytic MOA Enhancement

To further elucidate the synergistic mechanism of Ag0 and OVs in boosting photocatalytic performances, a schematic illustration is presented in Figure 5. Upon vacuum calcination, the Ag3PO4 surface is modified with surface-deposited Ag nanoparticles and oxygen vacancies. These two components act as electron sinks and catalytic centers, promoting the activation of O2 into ROS. Under light irradiation, photogenerated electrons are preferentially transferred to Ag0 and OVs sites, where adsorbed O2 molecules undergo stepwise reduction to form·O2−, 1O2, H2O2, and ·OH. These ROS species play pivotal roles in degrading the target contaminant CYN (C15H21N5O7S), as shown in the central molecular model. The active species induce oxidative cleavage of the CYN molecule, leading to the formation of small intermediates, including CO2 and H2O. While reactive oxygen species responsible for degradation were comprehensively analyzed, the identification of degradation intermediates of CYN is beyond the scope of this study. A detailed analysis of CYN degradation pathways and by-products has been reported in a separate publication by us [48].

3. Materials and Methods

3.1. Catalysts Preparation Process

Firstly, 4 mL of Na2HPO4 (≥99%) solution (21.25 g/L) was added dropwise to 100 mL of acetic silver (CH3COO-Ag, ≥99%) solution (3 g/L) under stirring. After stirring for 0.5 h, the obtained sample was separated by centrifugation, washed with deionized water and ethanol (≥99.7%), and dried at 60 °C overnight in a vacuum. Secondly, the as-obtained Ag3PO4 (APO) was placed in a quartz boat and calcined in a vacuum (~10−2 Pa) at a heating rate of 4 °C/min for 1 h at 100, 200, and 300 °C, respectively. The final Ag3PO4 photocatalysts were denoted as APO-T, where T refers to the calcination temperature (100, 200, and 300 °C). All reagents used in this process were purchased from Sinopharm Chemical Reagent Co. Ltd., Shanghai, China.

3.2. The Performance of Catalysts

Cylindrospermopsin (CYN, ≥95%, purchased from Enzo Life Sciences AG, Lausen, Switzerland) acted as the model pollutant to evaluate the photocatalytic performance of as-prepared samples. In detail, 0.2g·L−1 catalyst powder was dispersed into the CYN solution (1 mg L−1). After the adsorption equilibrium for 120 min, the suspension was irradiated under an 300 W Xe lamp (PLS-SXE300D, Beijing Perfect Light Technology Co., Ltd., Beijing, China) with a cut filter (λ > 420 nm) at room temperature. The distance from the lamp to the catalyst was maintained at 10 cm, and the light intensity was measured at 36.7 mW/cm2 using a calibrated radiometer. The CYN concentration was quantified by high-performance liquid chromatography (HPLC, (Waters e2695, Milford, MA, USA)) methods and the details have been elaborated on in Text S2 of the Supplementary Information (SI) Section.
The characterization data for the as-prepared photocatalysts, as well as the methods and results for the detection and degradations of pollutants and reactive radicals, are provided in the Supplementary Information Section. Among the detection of photocatalysts, the scanning electron microscope (SEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), Electron spin resonance (ESR), UV-visible absorbance spectra (UV-vis), photoluminescence (PL), Time-resolved photoluminescence (TRPL), photo-current response, and electrochemical impedance spectroscopy (EIS) were conducted. For specific details on the detection methods, instrument models, and manufacturers, please refer to Supplementary Information Text S1.

4. Conclusions

In this work, we demonstrated that the simultaneous incorporation of oxygen vacancies and Ag nanoparticles into Ag3PO4 significantly enhanced molecular oxygen activation, enabling a 2.05-fold improvement in CYN degradation efficiency. The enhanced performance is attributed to improved light absorption, charge separation, and oxygen activation. We also confirmed the generation of ROS (·O2−, 1O2, H2O2, and ·OH) via ESR and chemical assays. This study provides a detailed understanding of the underlying mechanisms of MOA enhancement. Our findings suggest that combining defect engineering with noble metal decoration is a scalable and low-cost approach to improve photocatalysis. However, this study does not address the toxicity or environmental persistence of degradation by-products, which remains a limitation. Future research should extend this strategy to 2D materials or heterojunction architectures, which may further enhance MOA efficiency and operational durability.
Highlights from this study include the following:
➢
An enhanced photocatalytic degradation of cylindrospermopsin by Ag3PO4 with Ag0 and OVs.
➢
Synergistic effects of oxygen vacancies and silver nanoparticles boost molecular oxygen activation.
➢
Improved charge separation and ROS generation for efficient environmental remediation.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal15060527/s1, Figure S1: (a) Recycle experiments of APO-200 in CYN degradation, and (b) the XRD patterns between fresh and used APO-200, Figure S2: The photo-current response of the as-prepared sample with and without H2O2.

Author Contributions

X.Z. (Xu Zhang): Investigation, Validation, Funding acquisition, Data curation, Writing—original draft. F.Y.: Investigation, Validation, Funding acquisition, Data curation, Writing—original draft. L.Z.: Conceptualization, Project administration, Writing—review & editing. W.X.: Formal analysis. Z.W.: Data curation. H.C.: Formal analysis, Conceptualization. X.Z. (Xuefei Zhou): Formal analysis, Conceptualization. Y.Z.: Project administration, Conceptualization. All authors have read and agreed to the published version of the manuscript.

Funding

This research was financially supported by the Shanghai Agriculture Technology Development Program, China (T2024332), and the National Natural Science Foundation of China (42377055).

Data Availability Statement

All data included in this study are available upon request from the corresponding author.

Acknowledgments

We would like to acknowledge the administrative and technical support provided by Guoyan Zou, from Institute of Eco-Environmental Protection Research, Shanghai Academy of Agricultural Sciences, Shanghai, China, who greatly assisted this work.

Conflicts of Interest

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

References

  1. Scarlett, K.R.; Kim, S.; Lovin, L.M.; Chatterjee, S.; Scott, J.T.; Brooks, B.W. Global scanning of cylindrospermopsin: Critical review and analysis of aquatic occurrence, bioaccumulation, toxicity and health hazards. Sci. Total Environ. 2020, 738, 139807. [Google Scholar] [CrossRef] [PubMed]
  2. Abbas, T.; Kajjumba, G.W.; Ejjada, M.; Masrura, S.U.; Marti, E.J.; Khan, E.; Jones-Lepp, T.L. Recent advancements in the removal of cyanotoxins from water using conventional and modified adsorbents—A contemporary review. Water 2020, 12, 2756. [Google Scholar] [CrossRef]
  3. Schneider, M.; Bláha, L. Advanced oxidation processes for the removal of cyanobacterial toxins from drinking water. Envrion. Sci. Eur. 2020, 32, 94. [Google Scholar] [CrossRef]
  4. Peng, Q.; Yu, J.; Pang, Y.; Deng, L.; Tang, J.; Wang, J.; Wu, N.; Tang, L. Prospects of advanced oxidation processes for high-salinity coking wastewater treatment: A strategy to support sustainable management. Resour. Conserv. Recycl. 2025, 212, 107880. [Google Scholar] [CrossRef]
  5. Loeb, S.K.; Alvarez, P.J.J.; Brame, J.A.; Cates, E.L.; Choi, W.; Crittenden, J.; Dionysiou, D.D.; Li, Q.; Li-Puma, G.; Quan, X.; et al. The technology horizon for photocatalytic water treatment: Sunrise or sunset? Environ. Sci. Technol. 2019, 53, 2937–2947. [Google Scholar] [CrossRef]
  6. Zhang, W.; Bian, Z.; Peng, Y.; Tang, H.; Wang, H. Dual-function oxygen vacancy of BiOBr intensifies pollutant adsorption and molecular oxygen activation to remove tetracycline hydrochloride. Chem. Eng. J. 2023, 451, 138731. [Google Scholar] [CrossRef]
  7. Wang, Y.; Wang, M.; Jin, X.; Bohan, A.; Nan, B.; Li, L.; Zhang, L.; Shi, J. Cyclable CuI-Ov-Mn sites accelerate O2 activation to enhance photo-driven catalytic oxidation performance. Appl. Catal. B Environ. Energy 2024, 353, 124110. [Google Scholar] [CrossRef]
  8. Shang, H.; Li, M.; Li, H.; Huang, S.; Mao, C.; Ai, Z.; Zhang, L. Oxygen vacancies promoted the selective photocatalytic removal of NO with blue TiO2 via simultaneous molecular oxygen activation and photogenerated hole annihilation. Environ. Sci. Technol. 2019, 53, 6444–6453. [Google Scholar] [CrossRef]
  9. Boukhvalov, D.W.; Politano, G.G.; D’Olimpio, G.; Politano, A. 2D semiconductor nanostructures for solar-driven photocatalysis: Unveiling challenges and prospects in air purification, sustainable energy harvesting, and water treatment. Adv. Sustain. Syst. 2024, 8, 2400018. [Google Scholar] [CrossRef]
  10. Xu, C.J.; Wang, J.Y.; Wang, D.S.; Qi, H.; Wang, L.B.; Cheng, R.Q.; Ta, N.; Shi, J.H.; Zhang, W.Y.; Chen, J.P.; et al. Defect-engineered CuxO/CeO2 catalysts: Enhanced low-temperature CO preferential oxidation through dual-promotion of CO adsorption and O2 activation. Mol. Catal. 2025, 581, 115148. [Google Scholar] [CrossRef]
  11. Zou, Y.; Li, X.; Zhao, Y.Q.; Liu, X.L.; Xie, S.H.; Liu, F.D.; Zhu, T.Y. Boosting oxygen activation via defect engineering to regulate co oxidation pathway over Pt/TiO2 catalysts. ACS Catal. 2025, 15, 6346–6360. [Google Scholar] [CrossRef]
  12. Zheng, F.; Lu, J.Y.; Zheng, H.X.; Xu, Q.; Jin, Y.J. Acid-etched defect engineering in spinel CoMn2O4: Synergizing oxygen and cation vacancies to unlock high NH3-SCR performance. J. Environ. Manag. 2025, 382, 125392. [Google Scholar] [CrossRef] [PubMed]
  13. Yang, W.J.; Sun, K.L.; Wan, J.; Ma, Y.A.; Wang, Y.; Liu, L.; Zhu, B.C.; Fu, F. Dual-site oxygen activation for enhanced photocatalytic aerobic oxidation by S-scheme Ni2P/Bi3O4Br-OVs heterojunction. Chem. Eng. J. 2023, 452, 139425. [Google Scholar] [CrossRef]
  14. Fattakhova-Rohlfing, D.; Zaleska, A.; Bein, T. Three-dimensional titanium dioxide nanomaterials. Chem. Rev. 2014, 114, 9487–9558. [Google Scholar] [CrossRef]
  15. Wang, X.Y.; Xue, S.K.; Huang, M.R.; Lin, W.; Hou, Y.D.; Yu, Z.Y.; Anpo, M.; Yu, J.C.; Zhang, J.S.; Wang, X.C. Pressure-Induced Engineering of Surface Oxygen Vacancies on Metal Oxides for Heterogeneous Photocatalysis. J. Am. Chem. Soc. 2025, 147, 4945–4951. [Google Scholar] [CrossRef]
  16. Yu, Z.Z.; Yu, D.X.; Wang, X.Y.; Huang, M.R.; Hou, Y.D.; Lin, W.; Anpo, M.; Yu, J.C.; Zhang, J.S.; Wang, X.C. Photoinduced formation of oxygen vacancies on Mo-Incorporated WO3 for direct oxidation of benzene to phenol by air. J. Am. Chem. Soc. 2025, 147, 13885–13892. [Google Scholar] [CrossRef]
  17. Hazari, N.; Melvin, P.R.; Beromi, M.M. Well-defined nickel and palladium precatalysts for cross-coupling. Nat. Rev. Chem. 2017, 1, 0025. [Google Scholar] [CrossRef]
  18. Li, H.; Jiang, F.; Drdova, S.; Shang, H.; Zhang, L.; Wang, J. Dual-function surface hydrogen bonds enable robust O2 activation for deep photocatalytic toluene oxidation. Catal. Sci. Technol. 2021, 11, 319–331. [Google Scholar] [CrossRef]
  19. Vatti, S.K.; Gupta, S.; Raj, R.P.; Selvam, P. Periodic mesoporous titania with anatase and bronze phases—The new generation photocatalyst: Synthesis, characterisation, and application in environmental remediation. New J. Chem. 2020, 44, 16269–16284. [Google Scholar] [CrossRef]
  20. Jin, X.; Lv, C.; Zhou, X.; Zhang, C.; Meng, Q.; Liu, Y.; Chen, G. Molecular adsorption promotes carrier migration: Key step for molecular oxygen activation of defective Bi4O5I2. Appl. Catal. B Environ. 2018, 226, 53–60. [Google Scholar] [CrossRef]
  21. Chen, Q.; Wang, H.; Wang, C.; Guan, R.; Duan, R.; Fang, Y.; Hu, X. Activation of molecular oxygen in selectively photocatalytic organic conversion upon defective TiO2 nanosheets with boosted separation of charge carriers. Appl. Catal. B Environ. 2020, 262, 118258. [Google Scholar] [CrossRef]
  22. Liu, D.J.; Zhang, C.Y.; Shi, J.W.; Li, L.B.; Liu, W.; Liu, M.C.; Su, J.Z.; Liu, J.; Guo, L.J. Constructing asymmetric dual active sites of Ag single atoms and nitrogen defects on carbon nitride for enhanced photocatalytic H2O2 production. J. Mater. Sci. Technol. 2025, 223, 56–65. [Google Scholar] [CrossRef]
  23. Xu, D.; Li, G.; Dong, Y.; Wang, Q.; Zhang, J.; Yang, T.; Pang, S.; Zhang, G.; Lv, L.; Xia, Y.; et al. Photocatalytic O2 activation enhancement and algae inactivation mechanism of BiO2−x/Bi3NbO7 van der Waals heterojunction. Appl. Catal. B Environ. 2022, 312, 121402. [Google Scholar] [CrossRef]
  24. Yang, Z.F.; Xia, X.N.; Shao, L.H.; Wang, L.L.; Liu, Y.T. Efficient photocatalytic degradation of tetracycline under visible light by Z-scheme Ag3PO4/mixed-valence MIL-88A(Fe) heterojunctions: Mechanism insight, degradation pathways and DFT calculation. Chem. Eng. J. 2021, 410, 128454. [Google Scholar] [CrossRef]
  25. Chen, X.; Chen, J.; Li, N.; Li, J.; He, J.; Xu, S.; Zhu, Y.; Yao, L.; Lai, Y.; Zhu, R. Ag3PO4-anchored La2Ti2O7 nanorod as a Z-Scheme heterostructure composite with boosted photogenerated carrier separation and enhanced photocatalytic performance under natural sunlight. Environ. Pollut. 2023, 323, 121322. [Google Scholar] [CrossRef]
  26. Han, H.; Jiang, S.; Zhao, Q.; Jiang, T. Photocatalytic Performance and Degradation Pathways of Z-Scheme BiO2−X-Ag3PO4 Photocatalysts with Oxygen-Deficient Structures. Chemistryselect 2023, 8, e202300957. [Google Scholar] [CrossRef]
  27. Wang, X.; Yuan, S.; Geng, M.; Sun, M.; Zhang, J.; Zhou, A.; Yin, G. Combination of alkali treatment and Ag3PO4 loading effectively improves the photocatalytic activity of TiO2 nanoflowers. New J. Chem. 2024, 48, 6789–6795. [Google Scholar] [CrossRef]
  28. Xiao, Y.W.; Li, H.Y.; Yao, B.; Xiao, K.; Wang, Y.D. Hollow g-C3N4@Ag3PO4 core-shell nanoreactor loaded with Au nanoparticles: Boosting photothermal catalysis in confined space. Small 2024, 20, 2308032. [Google Scholar] [CrossRef]
  29. Anbuvannan, M.; Vinosel, V.M.; Dhatshanamurthi, P.; Rajesh, S.; Ramesh, M.; Kannadasan, N. Investigation of pure TiO2 and BaO-loaded TiO2 nanocomposites with enhanced photocatalytic activities. J. Nanopart. Res. 2025, 27, 49. [Google Scholar] [CrossRef]
  30. Yan, T.; Guan, W.; Xiao, Y.; Tian, J.; Qiao, Z.; Zhai, H.; Li, W.; You, J. Effect of thermal annealing on the microstructures and photocatalytic performance of silver orthophosphate: The synergistic mechanism of Ag vacancies and metallic Ag. Appl. Surf. Sci. 2017, 391, 592–600. [Google Scholar] [CrossRef]
  31. Sasikumar, K.; Theanmozhi, M.; Devaraji, P.; Gopinath, C.S.; Saravanakumar, B.; Michael, R.J.V. Influence of natural carbon template on Ag-ZnO nanocomposites for enhanced supercapacitor, photocatalytic hydrogen production and antifungal activity. Mater. Sci. Semicond. Process. 2025, 193, 109523. [Google Scholar] [CrossRef]
  32. Hao, L.; Huang, H.; Zhang, Y.; Ma, T. Oxygen vacant semiconductor photocatalysts. Adv. Funct. Mater. 2021, 31, 2100919. [Google Scholar] [CrossRef]
  33. Luo, S.; Chen, J.; Huang, Z.; Liu, C.; Fang, M. Controllable synthesis of titania-supported bismuth oxyiodide heterostructured nanofibers with highly exposed (1 1 0) bismuth oxyiodide facets for enhanced photocatalytic activity. ChemCatChem 2016, 8, 3780–3789. [Google Scholar] [CrossRef]
  34. Wang, F.; Yang, H.; Zhang, Y.C. Enhanced photocatalytic performance of CuBi2O4 particles decorated with Ag nanowires. Mater. Sci. Semicond. Process. 2018, 73, 58–66. [Google Scholar] [CrossRef]
  35. Zheng, C.; Yang, H.; Cui, Z.; Zhang, H.; Wang, X. A novel Bi4Ti3O12/Ag3PO4 heterojunction photocatalyst with enhanced photocatalytic performance. Nanoscale Res. Lett. 2017, 12, 608. [Google Scholar] [CrossRef]
  36. Bui, D.P.; Pham, M.T.; Tran, H.H.; Nguyen, T.D.; Cao, T.M.; Pham, V.V. Revisiting the key optical and electrical characteristics in reporting the photocatalysis of semiconductors. ACS Omega 2021, 6, 27379–27386. [Google Scholar] [CrossRef]
  37. Ma, Z.; Yi, Z.; Sun, J.; Wu, K. Electronic and photocatalytic properties of Ag3PC4VI (C = O, S, Se): A systemic hybrid DFT study. J. Phys. Chem. C 2012, 116, 25074–25080. [Google Scholar] [CrossRef]
  38. Jiang, L.B.; Yuan, X.Z.; Zeng, G.M.; Wu, Z.B.; Liang, J.; Chen, X.H.; Leng, L.J.; Wang, H.; Wang, H. Metal-free efficient photocatalyst for stable visible-light photocatalytic degradation of refractory pollutant. Appl. Catal. B Environ. 2018, 221, 715–725. [Google Scholar] [CrossRef]
  39. Lin, Y.; Wu, S.H.; Yang, C.P.; Chen, M.; Li, X. Preparation of size-controlled silver phosphate catalysts and their enhanced photocatalysis performance via synergetic effect with MWCNTs and PANI. Appl. Catal. B Environ. 2019, 245, 71–86. [Google Scholar] [CrossRef]
  40. Zhang, M.M.; Lai, C.; Li, B.S.; Xu, F.H.; Huang, D.L.; Liu, S.Y.; Qin, L.; Fu, Y.K.; Liu, X.G.; Yi, H.; et al. Unravelling the role of dual quantum dots cocatalyst in 0D/2D heterojunction photocatalyst for promoting photocatalytic organic pollutant degradation. Chem. Eng. J. 2020, 396, 125343. [Google Scholar] [CrossRef]
  41. Chen, Y.; Dai, Y.T.; Li, Y.W.; Hou, Z.X.; Gao, B.Y.; Yue, Q.Y.; Li, Q. Oxygen vacancies-mediated CuO@N-doped carbon nanocomposites for non-radical-dominated photothermal catalytic degradation of contaminants. J. Clean. Prod. 2023, 389, 109523. [Google Scholar] [CrossRef]
  42. Xu, X.; Yang, N.; Wang, P.; Wang, S.Y.; Xiang, Y.G.; Zhang, X.H.; Ding, X.; Chen, H. Highly intensified molecular oxygen activation on Bi@Bi2MoO6 via a metallic Bi-coordinated facet-dependent effect. ACS Appl. Mater. Interfaces 2020, 12, 1867–1876. [Google Scholar] [CrossRef] [PubMed]
  43. Wang, Q.; Wang, W.; Zhong, L.L.; Liu, D.M.; Cao, X.Z.; Cui, F.Y. Oxygen vacancy-rich 2D/2D BiOCl-g-C3N4 ultrathin heterostructure nanosheets for enhanced visible-light-driven photocatalytic activity in environmental remediation. Appl. Catal. B Environ. 2018, 220, 290–302. [Google Scholar] [CrossRef]
  44. Huang, J.; Li, D.; Li, R.; Chen, P.; Zhang, Q.; Liu, H.; Lv, W.; Liu, G.; Feng, Y. One-step synthesis of phosphorus/oxygen co-doped g-C3N4/anatase TiO2 Z-scheme photocatalyst for significantly enhanced visible-light photocatalysis degradation of enrofloxacin. J. Hazard. Mater. 2020, 386, 121634. [Google Scholar] [CrossRef]
  45. Wei, L.-Q.; Ye, B.-H. Cyclometalated Ir–Zr metal–organic frameworks as recyclable visible-light photocatalysts for sulfide oxidation into sulfoxide in water. ACS Appl. Mater. Interfaces 2019, 11, 41448–41457. [Google Scholar] [CrossRef]
  46. Jadaa, W.; Prakash, A.; Ray, A.K. Photocatalytic degradation of diazo dye over suspended and immobilized TiO2 catalyst in swirl flow reactor: Kinetic modeling. Processes 2021, 9, 1741. [Google Scholar] [CrossRef]
  47. Li, J.; Wu, X.Y.; Pan, W.F.; Zhang, G.K.; Chen, H. Vacancy-rich monolayer BiO2−x as a highly efficient UV, visible, and near-infrared responsive photocatalyst. Angew. Chem. 2018, 57, 491–495. [Google Scholar] [CrossRef]
  48. Zhang, X.; Zhou, L.; Liu, Y.; Hengchao, E.; Zhao, Z.; Chu, H.; Zhou, X.; Zhang, Y.; Zou, G. Novel synthesis of sulfur-doped Ag3PO4 photocatalyst for efficient degradation of cylindrospermopsin. Chem. Eng. J. 2025, 504, 158462. [Google Scholar] [CrossRef]
Catalysts 15 00527 g001
Figure 1. (a,b) SEM images of APO and APO-200 (Scale bars are included in the micrographs, with a length of 2 μm for (a,b); The observed nanoparticles on the surface of APO-200 were marked with yellow circles in (b)); (c) XRD patterns and (d) EPR spectra of as-prepared samples; XPS spectra of (e) O 1s and (f) Ag 3 d of as-prepared samples.
Figure 1. (a,b) SEM images of APO and APO-200 (Scale bars are included in the micrographs, with a length of 2 μm for (a,b); The observed nanoparticles on the surface of APO-200 were marked with yellow circles in (b)); (c) XRD patterns and (d) EPR spectra of as-prepared samples; XPS spectra of (e) O 1s and (f) Ag 3 d of as-prepared samples.
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Figure 2. (a) UV-vis spectra, (b) Tauc Plot (c) steady and (d) time-dependent PL spectra of as-prepared samples, (e) photo-current response, and (f) electrochemical impedance spectroscopy of samples.
Figure 2. (a) UV-vis spectra, (b) Tauc Plot (c) steady and (d) time-dependent PL spectra of as-prepared samples, (e) photo-current response, and (f) electrochemical impedance spectroscopy of samples.
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Figure 3. (a) CYN degradation performance and (b) pseudo-first-order reaction kinetics plot of as-prepared samples.
Figure 3. (a) CYN degradation performance and (b) pseudo-first-order reaction kinetics plot of as-prepared samples.
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Figure 4. (a) Trapping experiment of CYN degradation in APO-200; (b) ESR measurement of ·O2−, ·O2 and·OH in APO-200; (c) H2O2 and (d) ·O2− measurement within different APO samples.
Figure 4. (a) Trapping experiment of CYN degradation in APO-200; (b) ESR measurement of ·O2−, ·O2 and·OH in APO-200; (c) H2O2 and (d) ·O2− measurement within different APO samples.
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Catalysts 15 00527 g005
Figure 5. Schematic mechanism of photocatalytic MOA enhancement via OVs and Ag0 in Ag3PO4.
Figure 5. Schematic mechanism of photocatalytic MOA enhancement via OVs and Ag0 in Ag3PO4.
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Table 1. Kinetic Constants (k) and R2 Values for the Photocatalytic Degradation of Cylindrospermopsin (CYN) Using APO, APO-100, APO-200, and APO-300 Samples.
Table 1. Kinetic Constants (k) and R2 Values for the Photocatalytic Degradation of Cylindrospermopsin (CYN) Using APO, APO-100, APO-200, and APO-300 Samples.
Samplesk (min−1)R2
APO0.200.99
APO-1000.240.99
APO-2000.410.99
APO-3000.330.99
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Zhang, X.; Yi, F.; Zhou, L.; Xie, W.; Wang, Z.; Chu, H.; Zhou, X.; Zhang, Y. Evidence of Enhanced Molecular Oxygen Activity Induced by the Synergistic Effect of Oxygen Vacancies and Ag Nanoparticles in Ag3PO4. Catalysts 2025, 15, 527. https://doi.org/10.3390/catal15060527

AMA Style

Zhang X, Yi F, Zhou L, Xie W, Wang Z, Chu H, Zhou X, Zhang Y. Evidence of Enhanced Molecular Oxygen Activity Induced by the Synergistic Effect of Oxygen Vacancies and Ag Nanoparticles in Ag3PO4. Catalysts. 2025; 15(6):527. https://doi.org/10.3390/catal15060527

Chicago/Turabian Style

Zhang, Xu, Futao Yi, Li Zhou, Weifeng Xie, Zhenqi Wang, Huaqiang Chu, Xuefei Zhou, and Yalei Zhang. 2025. "Evidence of Enhanced Molecular Oxygen Activity Induced by the Synergistic Effect of Oxygen Vacancies and Ag Nanoparticles in Ag3PO4" Catalysts 15, no. 6: 527. https://doi.org/10.3390/catal15060527

APA Style

Zhang, X., Yi, F., Zhou, L., Xie, W., Wang, Z., Chu, H., Zhou, X., & Zhang, Y. (2025). Evidence of Enhanced Molecular Oxygen Activity Induced by the Synergistic Effect of Oxygen Vacancies and Ag Nanoparticles in Ag3PO4. Catalysts, 15(6), 527. https://doi.org/10.3390/catal15060527

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