Mechanism of Ag-enhanced Bi2Fe4O9 photocatalytic Fenton system for inactivation of marine microorganisms

Mechanism of Ag-enhanced Bi2Fe4O9 photocatalytic Fenton system for inactivation of marine microorganisms | 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 Mechanism of Ag-enhanced Bi2Fe4O9 photocatalytic Fenton system for inactivation of marine microorganisms Yulin Song, Haoyang Ma, Jiayu An, Su Zhan, Wenjun Jiang, Feng Zhou This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4825782/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 20 Dec, 2024 Read the published version in Research on Chemical Intermediates → Version 1 posted 11 You are reading this latest preprint version Abstract In this work, Ag was loaded on the surface of Bi 2 Fe 4 O 9 to constitute a composite photocatalyst by a photo-reduction method. Under visible light irradiation and accompanied by a small amount of H 2 O 2 assisted to constitute a photocatalytic-Fenton coupling system, the highest sterilization rate of BFO-Ag-1 was obtained through sterilization experiments, and the sterilization rate after 30 min light irradiation reached 90.8%. This was mainly due to the fact that the silver loading not only improved the Fe(III)/Fe(II) cycle and H 2 O 2 utilization efficiency, but also resulted in a positive shift of the valence band potential of the photocatalyst and an increase in the charge separation efficiency. Comprehensive radical trapping experiments showed that •OH and holes were the main active substances for inactivating marine microorganisms. In this work, by loading Ag nanoparticles on the surface of Bi 2 Fe 4 O 9 , the efficiency of the effective conversion of H 2 O 2 to •OH was improved, which provided a new idea for the development of photocatalytic-Fenton coupling technology and ballast water treatment. Visible photocatalysis Ag/Bi2Fe4O9 Inactivation Photocatalysis-Fenton coupling Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Highlights The Ag/Bi 2 Fe 4 O 9 composite photocatalyst was successfully prepared. Ag modification significantly enhanced the inactivation of Bi 2 Fe 4 O 9 against marine bacteria. The mechanism of photocatalytic sterilization of Ag/Bi 2 Fe 4 O 9 was identified. 1. Introduction Cargo ships are loaded with ballast water to ensure their stability and operational safety during their voyage. Between 100 and 300 billion tons of ballast water are drained from ships around the world annually, carrying various biological communities. These non-indigenous aquatic species can cause severe ecological damage and economic losses when introduced into new natural environments. Therefore, there was an urgent need for the development of technologies and materials that were both environmentally friendly and effective against bacteria[ 1 – 4 ]. At present, photocatalysts have shown great potential in deactivating marine microorganisms due to their rapid deactivation rate, lack of toxicity, and absence of secondary pollution[ 5 – 7 ]. Bi 2 Fe 4 O 9 was widely regarded as a promising photocatalytic functional material because of its narrow bandgap that is responsive under visible light, and its advantages of high stability, environmental protection, non-toxicity, and low-cost raw materials[ 8 – 12 ]. However, in the current research, the photocatalytic performance of Bi 2 Fe 4 O 9 was not high, and there were problems of insufficient photoresponse and low photoreaction quantum efficiency. Therefore, it had to be modified to improve its photocatalytic activity. Noble metal deposition has been used as one of the most effective ways to improve the photocatalytic activity of semiconductors. After metal deposition on the semiconductor surface, a space charge region is established at the contact interface due to electron transfer, which is known as the Schottky barrier[ 13 – 15 ]. The formation of the space charge region can promote the separation of photogenerated carriers, which in turn improves the photoelectric conversion efficiency and catalyst activity of the catalyst. Among these, the noble metal Ag is widely used due to its relatively low toxicity and low cost[ 16 – 19 ]. Hu et al. loaded Ag onto the surface of bismuth ferrate by photo reduction and found that the degradation rate of MB by Ag/Bi 2 Fe 4 O 9 under visible light irradiation was increased by 8% compared to Bi 2 Fe 4 O 9 [ 16 ]. Wang et al. successfully prepared Ag uniformly distributed on the surface of Bi 2 Fe 4 O 9 by glycine combustion and visible light irradiation. The decomposition rate of Ag/ Bi 2 Fe 4 O 9 in visible light for methyl orange was increased compared to Bi 2 Fe 4 O 9 [ 18 ]. Although bismuth-ferrite loaded Ag can indeed improve its carrier separation efficiency when the electron-hole pairs migrate to the catalyst surface, the improvement of its photocatalytic activity with noble metal deposition is not obvious because the slow Fe(III)/Fe(II) conversion makes Fe(III) less electron-rich and the carrier complexation efficiency is higher than the separation efficiency. Based on the above considerations, in this paper, an appropriate amount of H 2 O 2 was added after bismuth ferrate-loaded silver to form a photofenton under visible light irradiation, and the addition of H 2 O 2 could promote the cycling of Fe(III)/Fe(II), improve the electron utilization of the separated electrons, reduce the carrier complexes, and greatly improve the activity of this composite photocatalyst. The redox peaks shown in the test results of the CV cycling curves also further proved the cycling rate between Fe(III)/Fe(II). In this work, monolithic silver is loaded onto the surface of bismuth ferrate by photoreduction to improve the photogenerated carrier separation efficiency. The optimal silver loading and the specific sterilization mechanism of this composite photocatalyst are also investigated through sterilization experiments and a battery of features. This work combines the advantages of photocatalytic technology and Fenton technology, and markedly amplifies the activity of the composite against marine microorganisms by adding trace amounts of hydrogen peroxide and cycling between Fe(III)/Fe(II), providing a new idea for the development of photocatalytic-Fenton coupling technology and ballast water treatment. 2. Experimental section 2.1. Materials The chemical reagents used in this study were all analytical grade. Iron nitrate non-ahydrate (Fe(NO 3 ) 3 ·9H 2 O), bismuth nitrate pentahydrate (Bi(NO 3 ) 3 ·5H 2 O), silver nitrate (AgNO 3 ) and sodium hydroxide were purchased from Tianjin Chemical Reagent Co., Ltd. (Tianjin, China). Carbon paper was purchased from Suzhou Shengnuo Technology Co., Ltd. (Jiangsu, China). Hydrogen peroxide 30% (H 2 O 2 , Kermel, China). 2.2. Synthesis of Bi 2 Fe 4 O 9 sample Fe(NO 3 ) 3 ·9H 2 O was dissolved in 10 ml of dilute nitric acid solution at a concentration of 1 mol/L with a strong magnetic stirrer for at least 30 minutes, then Bi(NO 3 ) 3 ·5H 2 O was added and further stirred for 30 min to form a well-mixed solution in which the molar ratio of Fe(NO 3 ) 3 ·9H 2 O to Bi(NO 3 ) 3 ·5H 2 O was 2:1. NaOH solution at a concentration of 12 mol/L was then added dropwise to the solution, and 2 ml ethanol as a morphological modifier was added and stirred continuously for 2 h. The well-mixed solution was transferred to the inner liner of a polytetrafluoroethylene reactor. The autoclave was capped and placed in a flash-drying oven and heated at 180°C during 12 hours. After cooling to ambient temperature, the products were rinsed several times with deionized water and anhydrous ethanol and dried at 80°C throughout 24 hours. 2.3. Synthesis of Ag/Bi 2 Fe 4 O 9 sample A certain amount of AgNO 3 was weighed and an AgNO 3 solution was prepared with 10 ml of deionized water. 0.1 g of Bi 2 Fe 4 O 9 sample was dispersed with 40 ml of deionized water, 5 ml of methanol was added as a sacrificial agent, the configured AgNO 3 solution was dropped into the suspension, then the Bi 2 Fe 4 O 9 suspension containing AgNO 3 was placed in a dark place with magnetic stirring for 30 min and the xenon lamp was turned on for photoreaction with continuous stirring for 1 h. The samples thus obtained were washed with de-ionized water and ethanol a number of times, and the final sample was dried in an oven at 80°C for 12 hours. The samples were named BFO-Ag-0.1, BFO-Ag-0.5, BFO-Ag-1, BFO-Ag-1.5, and BFO-Ag-2 with different silver loading of 0.1 g, 0.5 g, 1 g, 1.5 g, and 2 g respectively. The photocatalyst carbon paper, the electrode preparation, and the method used to study and characterize the photocatalytic sterilization have been included in the Supplementary Materials. 3. Results and discussion 3.1. Characterization of photocatalysts 3.1.1. XRD phase analysis The physical phase and crystallinity of the specimens prepared were investigated via XRD. The results are shown in Fig. S1 , where it will be on display that the XRD spectra of BFO-Ag-0.1, BFO-Ag-0.5, BFO-Ag-1, BFO-Ag-1.5, and BFO-Ag-2 were consistent with those of the unloaded silver-loaded BFO. Further comparison of the prepared samples with the standardized card (JCPDS No. 25–0090) also showed good agreement, indicating that the manufactured photocatalyst was of high pureness with no other peaks generated[ 20 ]. In comparison with the standard PDF map (JCPDS NO.41-1402), the diffraction peaks of Ag were also not found in the complex photocatalysts. The possible reason for this was that the loading concentration of Ag was low and the diffraction peaks were weak and could not be captured by the X-ray diffractometer. When the Ag content was increased, the diffraction peaks of the composite photocatalyst were still highly consistent with the BFO standard PDF map (JCPDS No. 25–0090) without any shift. 3.1.2. Infrared spectral analysis As shown in Fig.S2, this IR spectrum revealed that the characteristic peaks of Bi 2 Fe 4 O 9 were located at 449 cm − 1 (Fe-O stretching vibration in the FeO 6 octahedron), 495 cm − 1 and 524 cm − 1 (O-Fe-O bending vibration in the FeO 4 tetrahedron). 639 cm − 1 (Fe-O bending mode was part the FeO 4 tetrahedron, and the Fe-O-Fe bending and stretching occurred at two different positions within the FeO 4 octahedron, whereas the Bi-O vibrations in the BiO 6 tetrahedron showed broad peaks) and 813 cm − 1 (Fe-O bending mode of the FeO 4 tetrahedron)[ 21 , 22 ]. By analyzing the signal maps of the IR spectra from 2000 − 400 cm − 1 , we observed that the peak intensities of the photoreduced samples loaded with different silver contents showed almost no change in the functional groups of Bi 2 Fe 4 O 9 compared to the initial Bi 2 Fe 4 O 9 . Infrared absorption spectroscopy further confirmed that the silver was bound to the surface of Bi 2 Fe 4 O 9 as a single substance. 3.1.3. Analysis of the physical state of the photocatalyst (XPS) In order to confirm the existence of silver in more detail, the photocatalysts BFO and BFO-Ag-1 have been studied by means of X-ray photoelectron spectroscopy (XPS) in order to determine their elementary-chemical state. The photoelectron spectra of BFO and BFO-Ag-1 are plotted in Fig.S3. It was observed as the BFO sample mainly consisted of three elements: Fe, Bi, and O, and the BFO-Ag-1 specimen was mainly made out of four elements: Fe, Bi, O, and Ag. The XPS spectra of Fe 2p were shown in Fig. 1 a, and the bonds at 711.12 eV and 724.57 eV could match the peaks of Fe 2p 3/2 and Fe 2p 1/2 , respectively[ 23 ]. Two satellite peaks related to Fe(III) ion were noted at positions 718.40 eV (Sat. 1) and 732.04 eV (Sat. 2). A very sharp XPS spectrum of Bi 4f can be seen in Fig. 1 b. The two characteristic peaks located at 158.96 eV and 164.26 eV in the sample represent Bi 4f 7/2 and Bi 4f 5/2 respectively, which were prominent signatures of Bi(III). Highly resolved spectra of O 1s, shown in Fig. 1 c, revealed binding energy spiking at 529.79 eV and 531.40 eV, assigned to hydroxyl oxygen and superficially adsorbed oxygen, individually. In the high temporal resolved spectrum of sample BFO-Ag-1, shown in Fig. 1 d, there were significant peaks with binding energies of 368.26 eV and 374.26 eV, which were characteristic peaks of Ag, were attributed to Ag 3d 5/2 and Ag 3d 3/2 , respectively, indicating that Ag could be introduced by photoreduction, and it was verified that the valence of the Ag element was 0, indicating that the composite photocatalysts were not Ag ions present with the compound photocatalyst, and Ag was present in the solid form. 3.1.4. Morphology and microstructure The deposition of monolithic Ag on the BFO surface was further understood by SEM characterization. As can be seen in Fig.S4b-f, different concentrations of Ag were loaded on the Bi 2 Fe 4 O 9 cubic blocks and the Ag appears to be gradually agglomerated with increasing Ag loading. The occurrence of Ag nanoparticles and the distribution of each element was further determined using EDS, and the BFO-Ag-1 scan was selected to obtain the EDS patterns. The elemental mapping of BFO-Ag-1 is shown in Fig.S4g-j. Bi, Fe, O, and Ag were all detected with uniform distribution. It was demonstrated that Ag is loaded on the cubic block of the BFO. To further determine the attachment of Ag nanoparticles to Bi 2 Fe 4 O 9 , BFO-Ag-1 was selected for TEM observation, and it can be seen from Fig. 2 a that Ag nanoparticles effectively were loaded onto the surface area of the BFO photocatalyst, and Fig. 2 c-d were partial enlargements of Fig. 2 b, respectively, in which the lattices of pure Bi 2 Fe 4 O 9 and Ag can be clearly seen as stripes. The crystallinity of the pure Bi 2 Fe 4 O 9 photocatalyst was confirmed by the measurements. It can be concluded that the BFO was grown along the (001) plane with a dot matrix stripe with a spacing of 0.591 nm, and the lattice stripe of Ag nanoparticles with a lattice spacing of 0.250 nm corresponded to the crystal plane of Ag (100). The TEM characterization further confirmed that the photo-reduced method had successfully loaded the monolithic silver in Bi 2 Fe 4 O 9 . 3.2. Photocatalytic performance test The effectiveness of the photocatalytic sterilization of BFO, BFO-Ag-0.1, BFO-Ag-0.5, BFO-Ag-1, BFO-Ag-1.5, and BFO-Ag-2 photocatalysts were investigated under simulated sunlight. Under the irradiation of a 300 W xenon lamp, Fig. 3 a has shown the comparison of BFO and its five composite photocatalysts with different amounts of Ag supported on them with or without the addition of H 2 O 2 to form a Fenton-like reaction. It can be clearly inferred as shown in the figure that the sterilization degree of the sterilization group with the addition of H 2 O 2 was significantly higher than that of the group without the introduction of H 2 O 2 , which indicated that the addition of a suitable amount of H 2 O 2 to form a Fenton-like reaction can greatly enhance the sterilization activity of composite photocatalysts. Figure 3 b has depicted the test of the sterilization performance of BFO and its five composite photocatalysts with different amounts of Ag supported thereon under different illumination times with the addition of 3×10 − 4 mol/L H 2 O 2 . As can be seen from Fig. 3 b, the sterilization performance of 30 min illumination was better. In conclusion, the bactericidal effect of BFO-Ag-1 loaded with Ag content of 1g under 300W xenon lamp for 30 min was the highest, up to 90.8%. By the comparison of the sterilization rates of BFO, BFO-Ag-0.1, BFO-Ag-0.5, BFO-Ag-1, BFO-Ag-1.5, and BFO-Ag-2, the sterilization rate of the composite photocatalyst first increased and later declined with the increase of Ag content, which may be because excessive Ag loading resulted in the decrease of h + and e − generation, which were not conducive to the decomposition of Fe(III) to Fe(II)[ 24 ]. In order to further explore the sterilization stability of BFO-Ag-1, five cycle sterilization tests were carried out. It can be seen from the figure that the sterilization level of BFO-Ag-1 has slightly decreased, as shown in Fig. 3 c, it has remained at a high level. It can be concluded that BFO-Ag-1 had a high environmental stability. 3.3. Photocatalytic performance enhancement mechanistic discussion 3.3.1. Optical properties analysis The effect of Ag loading on the light absorption properties as well as the forbidden band of Bi 2 Fe 4 O 9 was investigated using a UV-visible spectrometer, and the results are shown in Fig. 4 . The BFO samples exhibited good light harvesting ability in the visible region, with the two main absorption edges around 600 nm and 800 nm, respectively, with 2.081 eV narrow band gap, indicating that the BFOs can be used as a visible-assisted catalytic catalyst[ 25 ]. Accompanied with the increase in Ag loading, a red shift in absorption was exhibited, indicating that all the composite photocatalysts had a higher degree of light harvesting than pure BFO in the visible region, suggesting that the incorporation of Ag could improve the photoresponsivity of BFO in the visible region. The forbidden bandwidths for the compound photocatalysts were all narrower than that of BFO, and the narrowest forbidden bandwidth was that of the BFO-Ag-1 compound photocatalyst with a forbidden bandwidth of 1.828 eV, which was 0.253 eV narrower than that of BFO. To further investigate the effect of Ag loading on the conduction band of the photocatalytic materials and their valence band potentials, Mott-Schottky tests were performed on pure BFO and BFO-Ag-1. The slopes of both were positive as shown in Fig. 4 c-d, indicating that both BFO and BFO-Ag-1 were n-type semiconductors. Taking the intercepts of their positive slopes with the horizontal coordinates, the flat potential E fb for BFO and BFO-Ag-1 samples were found to be -1.08 V and − 0.74 V, respectively. Flat-band potentials were 0.1 V higher than conduction band potentials (vs. Ag/AgCl). E (RHE) = E (Ag/AgCl) + 0.197 + 0.0591 * pH as -0.51 V (against RHE) and − 0.17 V (against RHE) respectively. The valence band potentials of BFO and BFO-Ag-1 were 1.57 V and 1.66 V, respectively, indicating that the valence band potentials of BFO were positively shifted by the addition of Ag. The valence band potential is positively shifted after the addition of Ag, this positive displacement of the valence band can facilitate the generation of photogenerated electrons, which in turn improves the separation efficiency of photogenerated radicals, and the effect of the improved separation efficiency on the photocatalytic performance will be studied further by the radical trapping experiments. 3.3.2. Electrochemical testing and analysis of samples When a material is excited by light, the sequestration and migration ability for the light-generated electrons and holes are important factors affecting the activity of the photocatalyst. In other words, disinfecting performance associated with photocatalysts is mainly related to the separation and transfer efficiency of photogenerated charges and particles. Therefore, in order a further investigation of the photogenerated rate of charge separation and transfer efficiency of some of the samples mentioned above, we performed the trickle photocurrent response test and the electrochemical impedance test. Transient photocurrent response is performed at a uniform time interval of 50 seconds and photocurrent measurements are shown in Fig. 5 a after four repetitions. It can be seen from the figure that the BFO-Ag-1 composite sample with the strongest photocurrent exhibited the most pronounced current density undulation as the light source was turned on and off. The current density undulations were, in order from strongest to weakest, BFO-Ag-1, BFO-Ag-1.5, BFO-Ag-0.5, BFO-Ag-2, BFO-Ag-0.1, and BFO catalyst. Based on the above, it can be concluded the loading of Ag monomers facilitated the photogenerated electron-hole pairs of the samples to undergo separation, and the BFO-Ag-1 catalyst composite fabricated had the greatest charge separation rate, the strongest wandering ability and the highest photocatalytic capacity. In Fig. 5 b, the separation process of photogenerated carriers of six catalysts was investigated by EIS test. The larger radius of the hemispherical arc represented the larger interfacial resistivity value and the slower electron migration ability, on the contrary, the smaller radius of the hemispherical arc represented the smaller interfacial resistivity value and the faster electron negotiation ability. From the observation of the curve direction of each hemispherical arc in the Nyquist plot, it was found that the BFO-Ag-1 composite catalyst had the minimum arc radius, which suggested that it could effectively promote the interfacial charge transfer and the photocatalytic efficiency was much higher when compared with that of the pure-phase BFO. To investigate the redox process of BFO and BFO-Ag-1 materials, we measured the cyclic voltammetry (CV) curves of the modified electrodes of BFO and BFO-Ag-1 materials. As shown in Fig. 5 c, both BFO and BFO-Ag-1 showed reduction peaks around − 0.8 V, and BFO-Ag-1 had a higher reduction current. This indicated that the BFO-Ag-1 material had an excellent Fe(III)/Fe(II) redox efficiency, which could accelerate the conversion of Fe(III) to Fe(II), and thus effectively activate and decompose H 2 O 2 , resulting in more sterilization of hydroxyl radicals[ 24 ]. Figure 5 . a Transient photocurrent response images of pure BFO and Ag/BFO; b Electrochemical impedance spectra (EIS) of pure BFO and Ag/BFO; c Cyclic voltammetric curves of pure BFO and Ag/BFO. 3.3.3. Samples Free Radical Capture Radical trapping was performed to validate the photocatalytic sterilization mechanism and to quantify the active species in the reaction. Ethylenediaminetetraacetic acid (EDTA) was used as a scavenger for photogenerated holes, tertiary butyl alcohol (TBA) as a scavenger for hydroxyl radicals, p-benzoquinone (BQ) as a scavenger for superoxide radicals, and BFO-Ag-1 carbon paper, which had the highest photocatalytic sterilization rate, was used for testing. Fig.S5 showed the sterilization rate of BFO-Ag-1 carbon paper by different scavengers, which can be observed after the addition of a certain amount of TBA, EDTA and BQ, respectively. After adding TBA, the sterilization rate of the composite photocatalyst coating decreased gradually from 90.8–25.0%, and the silver loading could promote the decomposition of H 2 O 2 to be further converted into hydroxyl radicals, which indicated that hydroxyl radicals were the primary active substances involved in photocatalytic sterilization, and the BFO-Ag-1 had the excellent performance of converting H 2 O 2 into hydroxyl radicals. The sterilization rate decreased by 30.8% after the addition of EDTA, indicating that holes were implicated in the sterilization reaction. In conjunction with the combined results of the DRS and Mott-Schottky experiments, the composite catalyst BFO-Ag-1 had a more positive valence band potential and enhanced hole oxidation ability compared to BFO, which further improved the sterilization rate of the catalyst. The addition of BQ resulted in a sterilization rate of 83.0%, indicating that the superoxide radicals had almost no effect on the sterilization performance. 3.3.4. Photocatalytic sterilization mechanism On the basis of the above-mentioned experimental results and analyses, we have proposed a rational mechanism for photocatalytic Fenton inactivation of microorganisms, as shown in Fig. 6. In the presence of H 2 O 2 , irradiation of BFO-Ag-1 with visible light can be excited to form •OH for photocatalytic Fenton oxidation, which excited electrons from VB to CB to produce electron and hole pairs, and the electron-hole pairs are separated and transferred to the collector surface, and the holes undergo a redox reaction with the molecules adsorbed on the collector surface, thereby achieving photocatalytic inactivation of microbes. And Ag simple is coated to the photocatalyst surface, by the SPR effect, metal Ag 0 is stimulated to produce photogenerated electrons and holes. Due to the sufficient energy of the excited hot electrons, the photogenerated electrons from the Ag 0 nanoparticles are emitted into the CB of BFO-Ag-1. The holes were left in the VB of Ag 0 to oxidize the microorganisms into products such as CO 2 , H 2 O, etc. The large number of photoelectrons accumulated on the CB of BFO-Ag-1 promoted the conversion of Fe(III) to Fe(II), which then reacted with H 2 O 2 to produce hydroxyl radicals to inactivate the microorganisms. At the same time, Fe(II) was converted to Fe(III)[ 26 – 28 ]. The visible light was used to run the Fe(III)/Fe(II) cycle continuously and the process significantly reduced the consumption of H 2 O 2 , which resulted in a much higher H 2 O 2 consumption efficiency and a considerable improvement in photofenton output. 4. Conclusion In summary, in this work, different contents of Ag were loaded onto the surface of BFO in the form of monomers by photoreduction method. Compared with pure Bi 2 Fe 4 O 9 , the composite photocatalyst exhibited better photocatalytic activity and higher sterilization performance. Combined with DRS and electrochemical analyses, the BFO-Ag-1 composite photocatalyst showed the best spectral utilization and photogenerated carrier efficiency, which could maximize the Fe(III)/Fe(II) cycle and H 2 O 2 utilization efficiency. Free radical quenching experiments identified •OH as the main active site of the photocatalytic bactericidal reaction, and a photocatalytic Fenton reaction mechanism was proposed for the efficient bactericidal inactivation of seawater microorganisms by Ag/Bi 2 Fe 4 O 9 . This study showed that the coupled system had strong activity and excellent stability, which not only provided a new idea for improving the activity of photocatalysts, but also inspired us to design new multiphase advanced oxidation systems for inactivating marine microorganisms in practical applications. Declarations Author contributions YS participated in the overall conception and the whole experiment, HM and JA participated in the conception of part of the experiment and part of the data analysis. SZ and WJ participated in part of the data analysis. FZ supervised the experimental process and received financial support. All authors reviewed of the manuscript. Funding The authors acknowledge the financial support from the National Natural Science Foundation of China (No.52271340, 51879018). Competing interests The authors declare no competing interests. Conflict of interest The authors declare that they have no competing interests to influence the work reported in this paper. Ethical approval Not applicable. Availability of data and materials All the data have been obtained from our laboratory experiment and analysis. References M. Bai, Z. Zhang, N. Zhang, Y. Tian, C. Chen, X. Meng. Plasma Chem. Plasma Process. 32, 693–702 (2012) J. Guilbaud, Y. Wyart, P. Moulin. J. Mar. Sci. 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Supplementary Files SuppementaryMaterial.docx Cite Share Download PDF Status: Published Journal Publication published 20 Dec, 2024 Read the published version in Research on Chemical Intermediates → Version 1 posted Editorial decision: Revision requested 01 Oct, 2024 Reviews received at journal 01 Oct, 2024 Reviewers agreed at journal 21 Sep, 2024 Reviews received at journal 14 Sep, 2024 Reviewers agreed at journal 05 Sep, 2024 Reviewers agreed at journal 31 Aug, 2024 Reviewers agreed at journal 19 Aug, 2024 Reviewers invited by journal 16 Aug, 2024 Editor assigned by journal 30 Jul, 2024 Submission checks completed at journal 30 Jul, 2024 First submitted to journal 30 Jul, 2024 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. 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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-4825782","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":345330178,"identity":"f45225cd-b131-4098-81b3-a6baff67f32b","order_by":0,"name":"Yulin Song","email":"","orcid":"","institution":"Dalian Maritime University","correspondingAuthor":false,"prefix":"","firstName":"Yulin","middleName":"","lastName":"Song","suffix":""},{"id":345330179,"identity":"424bbe7b-4165-4f66-a45f-4336c3b2f485","order_by":1,"name":"Haoyang Ma","email":"","orcid":"","institution":"Dalian Maritime University","correspondingAuthor":false,"prefix":"","firstName":"Haoyang","middleName":"","lastName":"Ma","suffix":""},{"id":345330180,"identity":"b35989b7-54e0-42e4-8b27-5051f65fc722","order_by":2,"name":"Jiayu An","email":"","orcid":"","institution":"Dalian Maritime University","correspondingAuthor":false,"prefix":"","firstName":"Jiayu","middleName":"","lastName":"An","suffix":""},{"id":345330181,"identity":"70990c59-49e7-4705-9f4c-eae665fdd49e","order_by":3,"name":"Su Zhan","email":"","orcid":"","institution":"Dalian Maritime University","correspondingAuthor":false,"prefix":"","firstName":"Su","middleName":"","lastName":"Zhan","suffix":""},{"id":345330183,"identity":"1eccf773-c731-42b6-ac47-a336d6d8e2da","order_by":4,"name":"Wenjun Jiang","email":"","orcid":"","institution":"Dalian Maritime University","correspondingAuthor":false,"prefix":"","firstName":"Wenjun","middleName":"","lastName":"Jiang","suffix":""},{"id":345330185,"identity":"78cc1447-3ea5-4ca6-97c1-a720cd1172d7","order_by":5,"name":"Feng Zhou","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA4ElEQVRIiWNgGAWjYDACCSCuAGJ+huQGEJ+xgSgtZ4BYsiGRVC0GB4jVIj+7+ZjEgYo7dpuPJ7Zu5mGwkd1wgPnZA3xaGOccS5M4cOZZ8rYzD9tu8zCkGW84wGZugE8Ls0SOmfTHtsPJZjcSQVoOJ244wMMmgU8LG1CLxMF/h5ONZ4C1/CeshQespeGwnYEEWMsBwlokJNKSLQ4cO5wgAfTLzTkGycYzD7OZ4dUiPyP54I0DNYft+duTj914U2En23e8+RleLTAAiRQGUFAxE6MeCOyJVDcKRsEoGAUjEQAA+5lQA2iT+1oAAAAASUVORK5CYII=","orcid":"","institution":"Dalian Maritime University","correspondingAuthor":true,"prefix":"","firstName":"Feng","middleName":"","lastName":"Zhou","suffix":""}],"badges":[],"createdAt":"2024-07-30 05:21:52","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4825782/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4825782/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11164-024-05475-3","type":"published","date":"2024-12-20T15:58:38+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":63401158,"identity":"f5b6b407-fc7f-4afa-8ab8-62241c060458","added_by":"auto","created_at":"2024-08-27 18:37:33","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":79817,"visible":true,"origin":"","legend":"\u003cp\u003ea Fe 2p spectra; b Bi 4f spectra; c O 1s spectra; d Ag 3d spectra.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4825782/v1/a11b30569bb585d984245c66.png"},{"id":63401159,"identity":"77a92c5f-01e3-4ab6-975e-be81ed524b83","added_by":"auto","created_at":"2024-08-27 18:37:33","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":787279,"visible":true,"origin":"","legend":"\u003cp\u003eTEM images of BFO-Ag-1.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4825782/v1/d9444e315cf0ff769c9d3726.png"},{"id":63401156,"identity":"eedae48c-b3b2-4444-bc2f-52ac31bb08bd","added_by":"auto","created_at":"2024-08-27 18:37:32","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":42081,"visible":true,"origin":"","legend":"\u003cp\u003ea Sterilization rate of BFO, BFO-Ag-0.1, BFO-Ag-0.5, BFO-Ag-1, BFO-Ag-1.5, and BFO-Ag-2 photocatalyst with and without H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e; b Sterilization rate of BFO, BFO-Ag-0.1, BFO-Ag-0.5, BFO-Ag-1, BFO-Ag-1.5, and BFO-Ag-2 photocatalyst with H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e added at different light exposure times; c The sterilization rate of BFO-Ag-1 photocatalyst after 5 cycles of durability test.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4825782/v1/c1c38d93af0ab5f4f5bb39b8.png"},{"id":63399694,"identity":"60da70ca-43a2-4ab6-b431-7098ff0107d4","added_by":"auto","created_at":"2024-08-27 18:29:32","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":83337,"visible":true,"origin":"","legend":"\u003cp\u003ea-b DRS images of pure BFO and Ag/BFO; c-d Mott-Schottky images of BFO, BFO-Ag-1.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4825782/v1/c29f718f4bd8b4eeaf01556a.png"},{"id":63401157,"identity":"695f500e-6400-4155-8184-0327d2a8ac10","added_by":"auto","created_at":"2024-08-27 18:37:32","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":60888,"visible":true,"origin":"","legend":"\u003cp\u003ea Transient photocurrent response images of pure BFO and Ag/BFO; b Electrochemical impedance spectra (EIS) of pure BFO and Ag/BFO; c Cyclic voltammetric curves of pure BFO and Ag/BFO.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4825782/v1/2b3050eabe9a2e06c663f5bf.png"},{"id":63399692,"identity":"8a39cb68-5492-4530-aaff-584502e6558e","added_by":"auto","created_at":"2024-08-27 18:29:32","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":156374,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of catalytic mechanism of Ag/ BFO composite photocatalysts.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-4825782/v1/95c3862ea3b1dc5198965cc2.png"},{"id":72202021,"identity":"040fb870-d508-4256-825f-fbe1d4c39eca","added_by":"auto","created_at":"2024-12-23 16:13:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1911636,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4825782/v1/ac4f0c85-895e-4b5c-ada7-21fb88065242.pdf"},{"id":63399696,"identity":"470e102d-a16f-49b7-aa12-fd232283dfea","added_by":"auto","created_at":"2024-08-27 18:29:33","extension":"docx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":1342257,"visible":true,"origin":"","legend":"","description":"","filename":"SuppementaryMaterial.docx","url":"https://assets-eu.researchsquare.com/files/rs-4825782/v1/305e5ac11bc8349352c770e9.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Mechanism of Ag-enhanced Bi2Fe4O9 photocatalytic Fenton system for inactivation of marine microorganisms","fulltext":[{"header":"Highlights","content":"\u003col\u003e\n\u003cli\u003eThe Ag/Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e composite photocatalyst was successfully prepared.\u003c/li\u003e\n\u003cli\u003eAg modification significantly enhanced the inactivation of Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e against marine bacteria.\u003c/li\u003e\n\u003cli\u003eThe mechanism of photocatalytic sterilization of Ag/Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e was identified.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"1. Introduction","content":"\u003cp\u003eCargo ships are loaded with ballast water to ensure their stability and operational safety during their voyage. Between 100 and 300\u0026nbsp;billion tons of ballast water are drained from ships around the world annually, carrying various biological communities. These non-indigenous aquatic species can cause severe ecological damage and economic losses when introduced into new natural environments. Therefore, there was an urgent need for the development of technologies and materials that were both environmentally friendly and effective against bacteria[\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. At present, photocatalysts have shown great potential in deactivating marine microorganisms due to their rapid deactivation rate, lack of toxicity, and absence of secondary pollution[\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eBi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e was widely regarded as a promising photocatalytic functional material because of its narrow bandgap that is responsive under visible light, and its advantages of high stability, environmental protection, non-toxicity, and low-cost raw materials[\u003cspan additionalcitationids=\"CR9 CR10 CR11\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. However, in the current research, the photocatalytic performance of Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e was not high, and there were problems of insufficient photoresponse and low photoreaction quantum efficiency. Therefore, it had to be modified to improve its photocatalytic activity.\u003c/p\u003e \u003cp\u003eNoble metal deposition has been used as one of the most effective ways to improve the photocatalytic activity of semiconductors. After metal deposition on the semiconductor surface, a space charge region is established at the contact interface due to electron transfer, which is known as the Schottky barrier[\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The formation of the space charge region can promote the separation of photogenerated carriers, which in turn improves the photoelectric conversion efficiency and catalyst activity of the catalyst. Among these, the noble metal Ag is widely used due to its relatively low toxicity and low cost[\u003cspan additionalcitationids=\"CR17 CR18\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Hu et al. loaded Ag onto the surface of bismuth ferrate by photo reduction and found that the degradation rate of MB by Ag/Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e under visible light irradiation was increased by 8% compared to Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Wang et al. successfully prepared Ag uniformly distributed on the surface of Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e by glycine combustion and visible light irradiation. The decomposition rate of Ag/ Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e in visible light for methyl orange was increased compared to Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Although bismuth-ferrite loaded Ag can indeed improve its carrier separation efficiency when the electron-hole pairs migrate to the catalyst surface, the improvement of its photocatalytic activity with noble metal deposition is not obvious because the slow Fe(III)/Fe(II) conversion makes Fe(III) less electron-rich and the carrier complexation efficiency is higher than the separation efficiency.\u003c/p\u003e \u003cp\u003eBased on the above considerations, in this paper, an appropriate amount of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e was added after bismuth ferrate-loaded silver to form a photofenton under visible light irradiation, and the addition of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e could promote the cycling of Fe(III)/Fe(II), improve the electron utilization of the separated electrons, reduce the carrier complexes, and greatly improve the activity of this composite photocatalyst. The redox peaks shown in the test results of the CV cycling curves also further proved the cycling rate between Fe(III)/Fe(II). In this work, monolithic silver is loaded onto the surface of bismuth ferrate by photoreduction to improve the photogenerated carrier separation efficiency. The optimal silver loading and the specific sterilization mechanism of this composite photocatalyst are also investigated through sterilization experiments and a battery of features. This work combines the advantages of photocatalytic technology and Fenton technology, and markedly amplifies the activity of the composite against marine microorganisms by adding trace amounts of hydrogen peroxide and cycling between Fe(III)/Fe(II), providing a new idea for the development of photocatalytic-Fenton coupling technology and ballast water treatment.\u003c/p\u003e"},{"header":"2. Experimental section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Materials\u003c/h2\u003e \u003cp\u003eThe chemical reagents used in this study were all analytical grade. Iron nitrate non-ahydrate (Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;9H\u003csub\u003e2\u003c/sub\u003eO), bismuth nitrate pentahydrate (Bi(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;5H\u003csub\u003e2\u003c/sub\u003eO), silver nitrate (AgNO\u003csub\u003e3\u003c/sub\u003e) and sodium hydroxide were purchased from Tianjin Chemical Reagent Co., Ltd. (Tianjin, China). Carbon paper was purchased from Suzhou Shengnuo Technology Co., Ltd. (Jiangsu, China). Hydrogen peroxide 30% (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, Kermel, China).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Synthesis of Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e sample\u003c/h2\u003e \u003cp\u003eFe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;9H\u003csub\u003e2\u003c/sub\u003eO was dissolved in 10 ml of dilute nitric acid solution at a concentration of 1 mol/L with a strong magnetic stirrer for at least 30 minutes, then Bi(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;5H\u003csub\u003e2\u003c/sub\u003eO was added and further stirred for 30 min to form a well-mixed solution in which the molar ratio of Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;9H\u003csub\u003e2\u003c/sub\u003eO to Bi(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;5H\u003csub\u003e2\u003c/sub\u003eO was 2:1. NaOH solution at a concentration of 12 mol/L was then added dropwise to the solution, and 2 ml ethanol as a morphological modifier was added and stirred continuously for 2 h. The well-mixed solution was transferred to the inner liner of a polytetrafluoroethylene reactor. The autoclave was capped and placed in a flash-drying oven and heated at 180\u0026deg;C during 12 hours. After cooling to ambient temperature, the products were rinsed several times with deionized water and anhydrous ethanol and dried at 80\u0026deg;C throughout 24 hours.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Synthesis of Ag/Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e sample\u003c/h2\u003e \u003cp\u003eA certain amount of AgNO\u003csub\u003e3\u003c/sub\u003e was weighed and an AgNO\u003csub\u003e3\u003c/sub\u003e solution was prepared with 10 ml of deionized water. 0.1 g of Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e sample was dispersed with 40 ml of deionized water, 5 ml of methanol was added as a sacrificial agent, the configured AgNO\u003csub\u003e3\u003c/sub\u003e solution was dropped into the suspension, then the Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e suspension containing AgNO\u003csub\u003e3\u003c/sub\u003e was placed in a dark place with magnetic stirring for 30 min and the xenon lamp was turned on for photoreaction with continuous stirring for 1 h. The samples thus obtained were washed with de-ionized water and ethanol a number of times, and the final sample was dried in an oven at 80\u0026deg;C for 12 hours. The samples were named BFO-Ag-0.1, BFO-Ag-0.5, BFO-Ag-1, BFO-Ag-1.5, and BFO-Ag-2 with different silver loading of 0.1 g, 0.5 g, 1 g, 1.5 g, and 2 g respectively. The photocatalyst carbon paper, the electrode preparation, and the method used to study and characterize the photocatalytic sterilization have been included in the Supplementary Materials.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Characterization of photocatalysts\u003c/h2\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e3.1.1. XRD phase analysis\u003c/h2\u003e \u003cp\u003eThe physical phase and crystallinity of the specimens prepared were investigated via XRD. The results are shown in Fig.\u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e, where it will be on display that the XRD spectra of BFO-Ag-0.1, BFO-Ag-0.5, BFO-Ag-1, BFO-Ag-1.5, and BFO-Ag-2 were consistent with those of the unloaded silver-loaded BFO. Further comparison of the prepared samples with the standardized card (JCPDS No. 25\u0026ndash;0090) also showed good agreement, indicating that the manufactured photocatalyst was of high pureness with no other peaks generated[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. In comparison with the standard PDF map (JCPDS NO.41-1402), the diffraction peaks of Ag were also not found in the complex photocatalysts. The possible reason for this was that the loading concentration of Ag was low and the diffraction peaks were weak and could not be captured by the X-ray diffractometer. When the Ag content was increased, the diffraction peaks of the composite photocatalyst were still highly consistent with the BFO standard PDF map (JCPDS No. 25\u0026ndash;0090) without any shift.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e3.1.2. Infrared spectral analysis\u003c/h2\u003e \u003cp\u003eAs shown in Fig.S2, this IR spectrum revealed that the characteristic peaks of Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e were located at 449 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fe-O stretching vibration in the FeO\u003csub\u003e6\u003c/sub\u003e octahedron), 495 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 524 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (O-Fe-O bending vibration in the FeO\u003csub\u003e4\u003c/sub\u003e tetrahedron). 639 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fe-O bending mode was part the FeO\u003csub\u003e4\u003c/sub\u003e tetrahedron, and the Fe-O-Fe bending and stretching occurred at two different positions within the FeO\u003csub\u003e4\u003c/sub\u003e octahedron, whereas the Bi-O vibrations in the BiO\u003csub\u003e6\u003c/sub\u003e tetrahedron showed broad peaks) and 813 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fe-O bending mode of the FeO\u003csub\u003e4\u003c/sub\u003e tetrahedron)[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. By analyzing the signal maps of the IR spectra from 2000\u0026thinsp;\u0026minus;\u0026thinsp;400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, we observed that the peak intensities of the photoreduced samples loaded with different silver contents showed almost no change in the functional groups of Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e compared to the initial Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e. Infrared absorption spectroscopy further confirmed that the silver was bound to the surface of Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e as a single substance.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e3.1.3. Analysis of the physical state of the photocatalyst (XPS)\u003c/h2\u003e \u003cp\u003eIn order to confirm the existence of silver in more detail, the photocatalysts BFO and BFO-Ag-1 have been studied by means of X-ray photoelectron spectroscopy (XPS) in order to determine their elementary-chemical state. The photoelectron spectra of BFO and BFO-Ag-1 are plotted in Fig.S3. It was observed as the BFO sample mainly consisted of three elements: Fe, Bi, and O, and the BFO-Ag-1 specimen was mainly made out of four elements: Fe, Bi, O, and Ag. The XPS spectra of Fe 2p were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, and the bonds at 711.12 eV and 724.57 eV could match the peaks of Fe 2p\u003csub\u003e3/2\u003c/sub\u003e and Fe 2p\u003csub\u003e1/2\u003c/sub\u003e, respectively[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Two satellite peaks related to Fe(III) ion were noted at positions 718.40 eV (Sat. 1) and 732.04 eV (Sat. 2). A very sharp XPS spectrum of Bi 4f can be seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb. The two characteristic peaks located at 158.96 eV and 164.26 eV in the sample represent Bi 4f\u003csub\u003e7/2\u003c/sub\u003e and Bi 4f\u003csub\u003e5/2\u003c/sub\u003e respectively, which were prominent signatures of Bi(III). Highly resolved spectra of O 1s, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec, revealed binding energy spiking at 529.79 eV and 531.40 eV, assigned to hydroxyl oxygen and superficially adsorbed oxygen, individually. In the high temporal resolved spectrum of sample BFO-Ag-1, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed, there were significant peaks with binding energies of 368.26 eV and 374.26 eV, which were characteristic peaks of Ag, were attributed to Ag 3d\u003csub\u003e5/2\u003c/sub\u003e and Ag 3d\u003csub\u003e3/2\u003c/sub\u003e, respectively, indicating that Ag could be introduced by photoreduction, and it was verified that the valence of the Ag element was 0, indicating that the composite photocatalysts were not Ag ions present with the compound photocatalyst, and Ag was present in the solid form.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e3.1.4. Morphology and microstructure\u003c/h2\u003e \u003cp\u003eThe deposition of monolithic Ag on the BFO surface was further understood by SEM characterization. As can be seen in Fig.S4b-f, different concentrations of Ag were loaded on the Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e cubic blocks and the Ag appears to be gradually agglomerated with increasing Ag loading. The occurrence of Ag nanoparticles and the distribution of each element was further determined using EDS, and the BFO-Ag-1 scan was selected to obtain the EDS patterns. The elemental mapping of BFO-Ag-1 is shown in Fig.S4g-j. Bi, Fe, O, and Ag were all detected with uniform distribution. It was demonstrated that Ag is loaded on the cubic block of the BFO.\u003c/p\u003e \u003cp\u003eTo further determine the attachment of Ag nanoparticles to Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e, BFO-Ag-1 was selected for TEM observation, and it can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea that Ag nanoparticles effectively were loaded onto the surface area of the BFO photocatalyst, and Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec-d were partial enlargements of Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, respectively, in which the lattices of pure Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e and Ag can be clearly seen as stripes. The crystallinity of the pure Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e photocatalyst was confirmed by the measurements. It can be concluded that the BFO was grown along the (001) plane with a dot matrix stripe with a spacing of 0.591 nm, and the lattice stripe of Ag nanoparticles with a lattice spacing of 0.250 nm corresponded to the crystal plane of Ag (100). The TEM characterization further confirmed that the photo-reduced method had successfully loaded the monolithic silver in Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Photocatalytic performance test\u003c/h2\u003e \u003cp\u003eThe effectiveness of the photocatalytic sterilization of BFO, BFO-Ag-0.1, BFO-Ag-0.5, BFO-Ag-1, BFO-Ag-1.5, and BFO-Ag-2 photocatalysts were investigated under simulated sunlight. Under the irradiation of a 300 W xenon lamp, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea has shown the comparison of BFO and its five composite photocatalysts with different amounts of Ag supported on them with or without the addition of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e to form a Fenton-like reaction. It can be clearly inferred as shown in the figure that the sterilization degree of the sterilization group with the addition of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e was significantly higher than that of the group without the introduction of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, which indicated that the addition of a suitable amount of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e to form a Fenton-like reaction can greatly enhance the sterilization activity of composite photocatalysts. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb has depicted the test of the sterilization performance of BFO and its five composite photocatalysts with different amounts of Ag supported thereon under different illumination times with the addition of 3\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e mol/L H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. As can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb, the sterilization performance of 30 min illumination was better. In conclusion, the bactericidal effect of BFO-Ag-1 loaded with Ag content of 1g under 300W xenon lamp for 30 min was the highest, up to 90.8%. By the comparison of the sterilization rates of BFO, BFO-Ag-0.1, BFO-Ag-0.5, BFO-Ag-1, BFO-Ag-1.5, and BFO-Ag-2, the sterilization rate of the composite photocatalyst first increased and later declined with the increase of Ag content, which may be because excessive Ag loading resulted in the decrease of h\u003csup\u003e+\u003c/sup\u003e and e\u003csup\u003e\u0026minus;\u003c/sup\u003e generation, which were not conducive to the decomposition of Fe(III) to Fe(II)[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn order to further explore the sterilization stability of BFO-Ag-1, five cycle sterilization tests were carried out. It can be seen from the figure that the sterilization level of BFO-Ag-1 has slightly decreased, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, it has remained at a high level. It can be concluded that BFO-Ag-1 had a high environmental stability.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Photocatalytic performance enhancement mechanistic discussion\u003c/h2\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e3.3.1. Optical properties analysis\u003c/h2\u003e \u003cp\u003eThe effect of Ag loading on the light absorption properties as well as the forbidden band of Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e was investigated using a UV-visible spectrometer, and the results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The BFO samples exhibited good light harvesting ability in the visible region, with the two main absorption edges around 600 nm and 800 nm, respectively, with 2.081 eV narrow band gap, indicating that the BFOs can be used as a visible-assisted catalytic catalyst[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Accompanied with the increase in Ag loading, a red shift in absorption was exhibited, indicating that all the composite photocatalysts had a higher degree of light harvesting than pure BFO in the visible region, suggesting that the incorporation of Ag could improve the photoresponsivity of BFO in the visible region. The forbidden bandwidths for the compound photocatalysts were all narrower than that of BFO, and the narrowest forbidden bandwidth was that of the BFO-Ag-1 compound photocatalyst with a forbidden bandwidth of 1.828 eV, which was 0.253 eV narrower than that of BFO.\u003c/p\u003e \u003cp\u003eTo further investigate the effect of Ag loading on the conduction band of the photocatalytic materials and their valence band potentials, Mott-Schottky tests were performed on pure BFO and BFO-Ag-1. The slopes of both were positive as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec-d, indicating that both BFO and BFO-Ag-1 were n-type semiconductors. Taking the intercepts of their positive slopes with the horizontal coordinates, the flat potential E\u003csub\u003efb\u003c/sub\u003e for BFO and BFO-Ag-1 samples were found to be -1.08 V and \u0026minus;\u0026thinsp;0.74 V, respectively. Flat-band potentials were 0.1 V higher than conduction band potentials (vs. Ag/AgCl). E (RHE)\u0026thinsp;=\u0026thinsp;E (Ag/AgCl)\u0026thinsp;+\u0026thinsp;0.197\u0026thinsp;+\u0026thinsp;0.0591 * pH as -0.51 V (against RHE) and \u0026minus;\u0026thinsp;0.17 V (against RHE) respectively. The valence band potentials of BFO and BFO-Ag-1 were 1.57 V and 1.66 V, respectively, indicating that the valence band potentials of BFO were positively shifted by the addition of Ag. The valence band potential is positively shifted after the addition of Ag, this positive displacement of the valence band can facilitate the generation of photogenerated electrons, which in turn improves the separation efficiency of photogenerated radicals, and the effect of the improved separation efficiency on the photocatalytic performance will be studied further by the radical trapping experiments.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e3.3.2. Electrochemical testing and analysis of samples\u003c/h2\u003e \u003cp\u003eWhen a material is excited by light, the sequestration and migration ability for the light-generated electrons and holes are important factors affecting the activity of the photocatalyst. In other words, disinfecting performance associated with photocatalysts is mainly related to the separation and transfer efficiency of photogenerated charges and particles. Therefore, in order a further investigation of the photogenerated rate of charge separation and transfer efficiency of some of the samples mentioned above, we performed the trickle photocurrent response test and the electrochemical impedance test. Transient photocurrent response is performed at a uniform time interval of 50 seconds and photocurrent measurements are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea after four repetitions. It can be seen from the figure that the BFO-Ag-1 composite sample with the strongest photocurrent exhibited the most pronounced current density undulation as the light source was turned on and off. The current density undulations were, in order from strongest to weakest, BFO-Ag-1, BFO-Ag-1.5, BFO-Ag-0.5, BFO-Ag-2, BFO-Ag-0.1, and BFO catalyst. Based on the above, it can be concluded the loading of Ag monomers facilitated the photogenerated electron-hole pairs of the samples to undergo separation, and the BFO-Ag-1 catalyst composite fabricated had the greatest charge separation rate, the strongest wandering ability and the highest photocatalytic capacity. In Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb, the separation process of photogenerated carriers of six catalysts was investigated by EIS test. The larger radius of the hemispherical arc represented the larger interfacial resistivity value and the slower electron migration ability, on the contrary, the smaller radius of the hemispherical arc represented the smaller interfacial resistivity value and the faster electron negotiation ability. From the observation of the curve direction of each hemispherical arc in the Nyquist plot, it was found that the BFO-Ag-1 composite catalyst had the minimum arc radius, which suggested that it could effectively promote the interfacial charge transfer and the photocatalytic efficiency was much higher when compared with that of the pure-phase BFO.\u003c/p\u003e \u003cp\u003eTo investigate the redox process of BFO and BFO-Ag-1 materials, we measured the cyclic voltammetry (CV) curves of the modified electrodes of BFO and BFO-Ag-1 materials. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec, both BFO and BFO-Ag-1 showed reduction peaks around \u0026minus;\u0026thinsp;0.8 V, and BFO-Ag-1 had a higher reduction current. This indicated that the BFO-Ag-1 material had an excellent Fe(III)/Fe(II) redox efficiency, which could accelerate the conversion of Fe(III) to Fe(II), and thus effectively activate and decompose H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, resulting in more sterilization of hydroxyl radicals[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. a Transient photocurrent response images of pure BFO and Ag/BFO; b Electrochemical impedance spectra (EIS) of pure BFO and Ag/BFO;\u003c/p\u003e \u003cp\u003ec Cyclic voltammetric curves of pure BFO and Ag/BFO.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e3.3.3. Samples Free Radical Capture\u003c/h2\u003e \u003cp\u003eRadical trapping was performed to validate the photocatalytic sterilization mechanism and to quantify the active species in the reaction. Ethylenediaminetetraacetic acid (EDTA) was used as a scavenger for photogenerated holes, tertiary butyl alcohol (TBA) as a scavenger for hydroxyl radicals, p-benzoquinone (BQ) as a scavenger for superoxide radicals, and BFO-Ag-1 carbon paper, which had the highest photocatalytic sterilization rate, was used for testing. Fig.S5 showed the sterilization rate of BFO-Ag-1 carbon paper by different scavengers, which can be observed after the addition of a certain amount of TBA, EDTA and BQ, respectively. After adding TBA, the sterilization rate of the composite photocatalyst coating decreased gradually from 90.8\u0026ndash;25.0%, and the silver loading could promote the decomposition of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e to be further converted into hydroxyl radicals, which indicated that hydroxyl radicals were the primary active substances involved in photocatalytic sterilization, and the BFO-Ag-1 had the excellent performance of converting H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e into hydroxyl radicals. The sterilization rate decreased by 30.8% after the addition of EDTA, indicating that holes were implicated in the sterilization reaction. In conjunction with the combined results of the DRS and Mott-Schottky experiments, the composite catalyst BFO-Ag-1 had a more positive valence band potential and enhanced hole oxidation ability compared to BFO, which further improved the sterilization rate of the catalyst. The addition of BQ resulted in a sterilization rate of 83.0%, indicating that the superoxide radicals had almost no effect on the sterilization performance.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003e3.3.4. Photocatalytic sterilization mechanism\u003c/h2\u003e \u003cp\u003eOn the basis of the above-mentioned experimental results and analyses, we have proposed a rational mechanism for photocatalytic Fenton inactivation of microorganisms, as shown in Fig.\u0026nbsp;6. In the presence of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, irradiation of BFO-Ag-1 with visible light can be excited to form \u0026bull;OH for photocatalytic Fenton oxidation, which excited electrons from VB to CB to produce electron and hole pairs, and the electron-hole pairs are separated and transferred to the collector surface, and the holes undergo a redox reaction with the molecules adsorbed on the collector surface, thereby achieving photocatalytic inactivation of microbes. And Ag simple is coated to the photocatalyst surface, by the SPR effect, metal Ag\u003csup\u003e0\u003c/sup\u003e is stimulated to produce photogenerated electrons and holes. Due to the sufficient energy of the excited hot electrons, the photogenerated electrons from the Ag\u003csup\u003e0\u003c/sup\u003e nanoparticles are emitted into the CB of BFO-Ag-1. The holes were left in the VB of Ag\u003csup\u003e0\u003c/sup\u003e to oxidize the microorganisms into products such as CO\u003csub\u003e2\u003c/sub\u003e, H\u003csub\u003e2\u003c/sub\u003eO, etc. The large number of photoelectrons accumulated on the CB of BFO-Ag-1 promoted the conversion of Fe(III) to Fe(II), which then reacted with H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e to produce hydroxyl radicals to inactivate the microorganisms. At the same time, Fe(II) was converted to Fe(III)[\u003cspan additionalcitationids=\"CR27\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. The visible light was used to run the Fe(III)/Fe(II) cycle continuously and the process significantly reduced the consumption of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, which resulted in a much higher H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e consumption efficiency and a considerable improvement in photofenton output.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn summary, in this work, different contents of Ag were loaded onto the surface of BFO in the form of monomers by photoreduction method. Compared with pure Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e, the composite photocatalyst exhibited better photocatalytic activity and higher sterilization performance. Combined with DRS and electrochemical analyses, the BFO-Ag-1 composite photocatalyst showed the best spectral utilization and photogenerated carrier efficiency, which could maximize the Fe(III)/Fe(II) cycle and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e utilization efficiency. Free radical quenching experiments identified \u0026bull;OH as the main active site of the photocatalytic bactericidal reaction, and a photocatalytic Fenton reaction mechanism was proposed for the efficient bactericidal inactivation of seawater microorganisms by Ag/Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e. This study showed that the coupled system had strong activity and excellent stability, which not only provided a new idea for improving the activity of photocatalysts, but also inspired us to design new multiphase advanced oxidation systems for inactivating marine microorganisms in practical applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor contributions \u0026nbsp;\u003c/strong\u003eYS participated in the overall conception and the whole experiment, HM and JA participated in the conception of part of the experiment and part of the data analysis. SZ and WJ participated in part of the data analysis. FZ supervised the experimental process and received financial support. All authors reviewed of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding \u0026nbsp;\u0026nbsp;\u003c/strong\u003eThe authors acknowledge the financial support from the National Natural Science Foundation of China (No.52271340, 51879018).\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\u003eConflict of interest \u0026nbsp;\u003c/strong\u003eThe authors declare that they have no competing interests to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval\u003c/strong\u003e\u0026nbsp; Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u0026nbsp; All the data have been obtained from our laboratory experiment and analysis.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eM. 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Chem. 89, 1289\u0026ndash;1296 (2011) \u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"research-on-chemical-intermediates","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"rint","sideBox":"Learn more about [Research on Chemical Intermediates](http://link.springer.com/journal/11164)","snPcode":"11164","submissionUrl":"https://submission.nature.com/new-submission/11164/3","title":"Research on Chemical Intermediates","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Visible photocatalysis, Ag/Bi2Fe4O9, Inactivation, Photocatalysis-Fenton coupling","lastPublishedDoi":"10.21203/rs.3.rs-4825782/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4825782/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this work, Ag was loaded on the surface of Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e to constitute a composite photocatalyst by a photo-reduction method. Under visible light irradiation and accompanied by a small amount of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e assisted to constitute a photocatalytic-Fenton coupling system, the highest sterilization rate of BFO-Ag-1 was obtained through sterilization experiments, and the sterilization rate after 30 min light irradiation reached 90.8%. This was mainly due to the fact that the silver loading not only improved the Fe(III)/Fe(II) cycle and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e utilization efficiency, but also resulted in a positive shift of the valence band potential of the photocatalyst and an increase in the charge separation efficiency. Comprehensive radical trapping experiments showed that \u0026bull;OH and holes were the main active substances for inactivating marine microorganisms. In this work, by loading Ag nanoparticles on the surface of Bi\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e9\u003c/sub\u003e, the efficiency of the effective conversion of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e to \u0026bull;OH was improved, which provided a new idea for the development of photocatalytic-Fenton coupling technology and ballast water treatment.\u003c/p\u003e","manuscriptTitle":"Mechanism of Ag-enhanced Bi2Fe4O9 photocatalytic Fenton system for inactivation of marine microorganisms","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-08-27 18:29:27","doi":"10.21203/rs.3.rs-4825782/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-10-02T01:48:32+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-10-01T19:22:21+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"325990443740941229950664476068924344028","date":"2024-09-21T16:33:04+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-09-14T22:05:30+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"82737227410108497543177814564763577855","date":"2024-09-05T13:17:13+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"22063476379607106687468418505313042304","date":"2024-08-31T22:40:08+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"83559585402077206796652113053031114539","date":"2024-08-19T04:21:23+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-08-16T09:17:24+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-07-31T03:45:50+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-07-31T03:45:49+00:00","index":"","fulltext":""},{"type":"submitted","content":"Research on Chemical Intermediates","date":"2024-07-30T05:20:27+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"research-on-chemical-intermediates","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"rint","sideBox":"Learn more about [Research on Chemical Intermediates](http://link.springer.com/journal/11164)","snPcode":"11164","submissionUrl":"https://submission.nature.com/new-submission/11164/3","title":"Research on Chemical Intermediates","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"6c642779-e294-4615-ab50-99896e1e6d89","owner":[],"postedDate":"August 27th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-12-23T16:06:10+00:00","versionOfRecord":{"articleIdentity":"rs-4825782","link":"https://doi.org/10.1007/s11164-024-05475-3","journal":{"identity":"research-on-chemical-intermediates","isVorOnly":false,"title":"Research on Chemical Intermediates"},"publishedOn":"2024-12-20 15:58:38","publishedOnDateReadable":"December 20th, 2024"},"versionCreatedAt":"2024-08-27 18:29:27","video":"","vorDoi":"10.1007/s11164-024-05475-3","vorDoiUrl":"https://doi.org/10.1007/s11164-024-05475-3","workflowStages":[]},"version":"v1","identity":"rs-4825782","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4825782","identity":"rs-4825782","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}