English

• Endocrine-disrupting chemicals (EDCs) are emerging contaminants that can affect the endocrine systems of humans and animals, harming organisms and their offspring [1,2]. Bisphenol AF (BPAF) is an analog of BPA, which has been widely adopted in many fields such as fluororubber and food processing. Concentrations of BPAF in wastewater treatment plants are as high as 16.5 ng/L [3]. Noticeably, BPAF is an EDC with higher estrogenic activity and developmental toxicity than BPA [4]. Consequently, the development of effective treatment methods for removing BPAF is a worthwhile pursuit.

  So far, some studies have been published on the removal of BPAF from water using various technologies, but the results are not satisfactory. Advanced oxidation processes (AOPs), particularly sulfate radical-based AOPs, have become an effective technology for organic pollutants degradation in water bodies due to their long half-life (30–40 μs) and high redox potential [5,6]. Moreover, as an environmentally friendly technology, photocatalysis is considered a promising method for EDC elimination due to its high degradation efficiency and low cost [7,8]. Research has shown that peroxymonosulfate (PMS) can serve as an electron acceptor to inhibit photogenerated carrier recombination during photocatalysis, resulting in more reactive oxidants (ROS) [9,10]. Therefore, designing rational photocatalysts to construct PMS-assisted photocatalytic systems has attracted much attention.

  Bismuth-based photocatalysts have superior photocatalytic properties due to their valence band composed of the hybridization of O 2p and Bi 6s [11,12]. In particular, as an oxygen-enriched BiOX material, Bi₅O₇I has been extensively applied in many fields. However, the weak photoresponse and slow charge transfer of pristine Bi₅O₇I hinder its photocatalytic activity. To overcome these shortcomings, some methods have been explored. Among them, the most widely adopted method is to introduce heterojunctions to form Bi₅O₇I hybrids, including g-C₃N₄/Bi₅O₇I [13], Ag₂O/Bi₅O₇I [14], and BiOI/Bi₅O₇I [15]. MXenes, a new type of 2D metal carbides, have attracted increasing attention since 2011 [16,17]. Pristine MXenes have submetallic characteristics and can generate Schottky junctions when combined with semiconductors [18]. The Schottky barrier not only inhibits electron and hole recombination in the semiconductor but also limits electron backflow from the metal to the semiconductor [19].

  Inspired by the above studies, a novel 2D MXene(Ti₃C₂)/1D Bi₅O₇I Schottky junction was constructed by a hydrothermal method and activated with PMS to degrade BPAF under visible light. Please see the Supporting Information for details on synthesis, characterization, photocatalytic activity experiments, and DFT calculations.

  The construction of the 2D MXene/1D Bi₅O₇I Schottky junction consisted of two steps (Fig. S1 in Supporting information). A series of MXene/Bi₅O₇I Schottky junctions containing different mass ratios of MXene to Bi₅O₇I were obtained by adjusting the preparation conditions, as shown in Figs. S2a–d (Supporting information).

  The field emission scanning electron microscopy (FESEM) (Fig. 1a) image fully demonstrates the laminar structure of MXene. The microscopic morphology of Bi₅O₇I (Fig. 1b) and 8-MXene/Bi₅O₇I (Fig. 1c) is observed by FESEM, indicating that Bi₅O₇I rods of ~5 μm in length are adhered to the surface of 2D MXene. Moreover, the transmission electron microscope (TEM) image (Fig. 1d) clearly shows the formation of a 2D/1D microstructure in MXene/Bi₅O₇I, and a clear boundary between the two materials is observed, suggesting that the Bi₅O₇I rods tightly adhere to the MXene to fabricate this 2D/1D microstructure. The HR-TEM image (Fig. 1e) shows two lattices with spacings of 0.22 and 0.28 nm, representing the MXene (104) and Bi₅O₇I (004) crystal planes, respectively. The obvious heterojunction boundary and the coexistence of the two lattices in MXene/Bi₅O₇I reveal that a heterojunction with a tight interface and strong adhesion is generated, favoring carrier migration and transfer. Elemental mapping (Figs. 1f and g) also confirms this result. The homogeneous distribution of elements Bi, O, I, Ti, and C in MXene/Bi₅O₇I indicates that the two materials are tightly bound. Obviously, a 2D/1D MXene/Bi₅O₇I junction has been successfully prepared.

  Figure 1

  

  Figure 1.  FESEM images of (a) MXene nanosheets, (b) Bi₅O₇I nanorods, (c) 8-MXene/Bi₅O₇I. (d) TEM image, (e) HRTEM image, and (f, g) elemental mapping of 8-MXene/Bi₅O₇I.

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  Nitrogen adsorption-desorption isotherm tests (Fig. S3a in Supporting information) show that all adsorption isotherms are of type Ⅳ, suggesting the presence of mesopores [20]. From Fig. S3b and Table S1 (Supporting information), the pore sizes of the samples are 2–4 nm. Compared with the pristine Bi₅O₇I, the larger BET surface area, pore size, and pore volume of the MXene/Bi₅O₇I heterojunction can offer increased active sites, thereby enhancing the mass transfer and catalytic performance of the system.

  The X-ray diffraction (XRD) pattern (Fig. S4 in Supporting information) shows that the MAX phase exhibits strong diffraction peaks, consistent with the Ti₃AlC₂ crystal (JCPDS No. 52-0875). After etching, the diffraction peaks of (002) and (004) are shifted to a lower angle, and the strongest diffraction peak of (104) at 39.0° disappears, demonstrating that the Al element is removed from Ti₃AlC₂. In Fig. S3c, the diffraction peaks of Bi₅O₇I match the standard card for Bi₅O₇I (JCPDS no 40-0583) [21]. The intensity of all the MXene/Bi₅O₇I junction diffraction peaks is weakened, probably because the growth of Bi₅O₇I crystals is inhibited by the growth-limiting effect of MXene [22]. In the FT-IR spectra (Fig. S3d), no distinct peaks are observed in MXene, and the peaks in the MXene/Bi₅O₇I junctions are similar to those of Bi₅O₇I. These XRD and FTIR tests further confirm the successfully synthesized MXene/Bi₅O₇I junction.

  In X-ray photoelectron spectroscopy (XPS) survey spectra (Fig. S5a in Supporting information), 8-MXene/Bi₅O₇I contains all elements in Bi₅O₇I and MXene. In C 1s spectra (Fig. S5b in Supporting information), the peak at 286.2 eV in 8-MXene/Bi₅O₇I corresponds to C–O originating from adsorbed organic matter [22]. Meanwhile, the XPS peak at 281.6 eV belongs to C-Ti. Both C-Ti and C–O binding energies of 8-MXene/Bi₅O₇I show a 0.2 eV decrease compared with MXene. Similarly, in the Ti 2p spectra (Fig. S5c in Supporting information), the Ti-C (455.0 and 460.8 eV) and Ti-O (458.5 and 464.3 eV) binding energies of 8-MXene/Bi₅O₇I are both negatively shifted by 0.3 eV compared with MXene. Conversely, the Bi 4f spectra (Fig. S5d in Supporting information) of 8-MXene/Bi₅O₇I and MXene exhibit opposite trends. Additionally, the O 1s (Fig. S5e in Supporting information) and I 3d (Fig. S5f in Supporting information) spectra of 8-MXene/Bi₅O₇I display a similar trend with positive shifts of 0.3 and 0.2 eV, respectively.

  Another piece of information obtained from XPS spectra is the internal electric field (IEF). The binding energies of all Ti elements in the MXene/Bi₅O₇I heterojunction display negative migration compared with MXene. Meanwhile, the MXene/Bi₅O₇I heterojunction exhibits higher binding energies for Bi, O, and I than Bi₅O₇I, demonstrating a decrease of electrons on Bi₅O₇I in the MXene/Bi₅O₇I heterojunction. Therefore, when the two materials are coupled to each other to form a heterojunction, electrons are transferred from Bi₅O₇I to MXene to form an electron-withdrawal layer, i.e., (-) MXene/(+) Bi₅O₇I - IEF.

  To further investigate the IEF, the average potential was obtained according to density-functional theory (DFT). In Figs. 2a and b, the work function (Ф) of MXene and Bi₅O₇I is 5.48 and 4.98 eV, respectively. MXene shows a larger Ф and lower Fermi energy level (E_Fermi) than Bi₅O₇I, implying the electrons in Bi₅O₇I are more likely to escape. When they contact each other, the electrons in Bi₅O₇I tend to transfer to MXene, while the energy band of Bi₅O₇I produces an upward bending to form a Schottky barrier (Fig. 2c) [23]. The Schottky barrier from the Schottky junction inhibits the photogenerated electron-hole complexation.

  Figure 2

  

  Figure 2.  Average potential profile along the Z-axis direction for (a) MXene and (b) Bi₅O₇I. (c) Schematic illustration of the Schottky junction on the interface between MXene and Bi₅O₇I. Calculated density of states (DOS) for (d) MXene and (e) Bi₅O₇I. (f) Electron density distribution in the interface between MXene and Bi₅O₇I.

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  The density of states (DOS) is calculated for MXene and Bi₅O₇I, respectively. MXene (Fig. 2d) exhibits a continuum of electronic states throughout the energy levels, highlighting its excellent conductivity and confirming its submetallic nature. In the DOS of Bi₅O₇I (Fig. 2e), the highest part of the valence band consists mainly of O 2p, I 5p, and Bi 6p orbitals. In Fig. 2f, the simulated isosurfaces with different charge densities indicate that the electron migration between MXene and Bi₅O₇I leads to a strong coupling at the heterojunction interface. Further, MXene shows a negative charge at the heterojunction interface, while Bi₅O₇I is positively charged, corresponding to the XPS tests.

  Figs. 3a and b show that Bi₅O₇I can respond efficiently to visible light and degrade 41.9% of BPAF at 90 min with a k_app of 0.00592 min^-1. After compounding MXene, the degradation rate of BPAF by MXene/Bi₅O₇I Schottky heterojunction is increased to 55.2% (k_app = 0.00891 min^-1). Moreover, in the 3-MXene/Bi₅O₇I/PMS system, about 79.0% of BPAF is degraded within 90 min (k_app = 0.01662 min^-1). The performance of the MXene/Bi₅O₇I/PMS system in degrading BPAF increases further with the increase of MXene content. Among them, 8-MXene/Bi₅O₇I/PMS displays the optimal degradation of BPAF up to 93.4% (k_app = 0.02984 min^-1), which is 5.04 and 3.35 times that of Bi₅O₇I (0.00592 min^-1) and MXene/Bi₅O₇I (0.00891 min^-1), respectively. However, the degradation rate of the 10-MXene/Bi₅O₇I/PMS system for BPAF decreases to 88.9%. This is probably because excessive MXene blocks the light and inhibits the photoexcitation of Bi₅O₇I [22]. Notably, the comparison results in Table S2 (Supporting information) demonstrate that the photocatalytic efficiency of the MXene/Bi₅O₇I/PMS system is better than that of various previously reported catalysts.

  Figure 3

  

  Figure 3.  (a) Photodegradation curves of BPAF, (b) pseudo-first-order kinetics fitted curves. Effect of catalyst dosage (c), PMS concentration (d), and pH (e) on the removal of BPAF. Conditions: Conditions: [BPAF] = 20 mg/L, [PMS] = 2.00 mmol/L, [catalyst] = 0.6 g/L, pH = 5.4, unless otherwise specified. (f) Cycle degradation experiment.

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  Fig. 3c shows the influence of the catalyst dosage on the BPAF degradation. The 8-MXene/Bi₅O₇I/PMS system with a catalyst dosage of 0.3 g/L can remove 64.9% of BPAF in 90 min. As the dosage of 8-MXene/Bi₅O₇I/PMS is increased to 0.6 g/L, the degradation rate is gradually increased to 93.4%, indicating that the additional reaction sites offered by adequate catalysts can promote the PMS activation and reactive species production. In Fig. 3d, the BPAF degradation rate rises from 79.2% to 93.4% as the PMS concentration increases from 1.00 to 2.00 mmol/L. Nevertheless, the degradation rate decreases when the PMS concentration is further increased to 2.50 mmol/L. Therefore, PMS concentration is positively correlated with the reaction efficiency within the appropriate range, whereas excessive PMS concentration reduces the efficiency because of reactant self-quenching (Eqs. 1–4) [24,25]. Herein, 0.6 g/L 8-MXene/Bi₅O₇I and 2.00 mmol/L PMS are chosen for BPAF degradation.

  $ \mathrm{HSO}_5^{-}+{ }^{\bullet} \mathrm{OH} \rightarrow \mathrm{SO}_5^{\bullet-}+\mathrm{H}_2 \mathrm{O} $

  (1)

  $ \mathrm{HSO}_5^{-}+\mathrm{SO}_4^{\bullet-} \rightarrow \mathrm{SO}_5^{\bullet-}+\mathrm{SO}_4^{2-}+\mathrm{H}^{+} $

  (2)

  $ \mathrm{SO}_4^{\bullet-}+{ }^{\bullet} \mathrm{OH} \rightarrow \mathrm{HSO}_4^{-}+1 / 2 \;\mathrm{O}_2 $

  (3)

  $ \mathrm{SO}_4^{\bullet-}+\mathrm{SO}_4^{\bullet-} \rightarrow \mathrm{S}_2 \mathrm{O}_8^{2-} $

  (4)

  The influence of pH on the catalytic activity of 8-MXene/Bi₅O₇I/PMS is explored. In Fig. 3e, 8-MXene/Bi₅O₇I/PMS exhibits excellent catalytic efficiencies over the wide pH range, with corresponding BPAF degradation rates of 88.4%, 90.4%, 94.1%, 94.2% and 94.4%, respectively. Obviously, the photodegradation efficiency increases with the increase of pH. The strong interaction between H⁺ and HSO5− under acidic conditions probably inhibits the reaction process. Moreover, excessive H⁺ can deplete ^•OH and SO₄^•‒, causing decreased reaction efficiency (Eqs. 5 and 6) [26]. In an alkaline environment, the catalytic performance is improved and even better than that in a neutral environment. This may be because excess H⁺ depletes free radicals, and therefore more free radicals are available in alkaline solutions, resulting in greater reaction efficiency.

  $ \mathrm{H}^{+}+{ }^{\bullet} \mathrm{OH}+\mathrm{e}^{-} \rightarrow \mathrm{H}_2 \mathrm{O}^{\bullet} $

  (5)

  $ \mathrm{SO}_4^{-}+\mathrm{H}^{+}+\mathrm{e}^{-} \rightarrow \mathrm{HSO}_4^{\bullet-} $

  (6)

  Photocatalytic stability is critical for the catalytic system. After five cyclic degradation experiments, 8-MXene/Bi₅O₇I/PMS still maintains high activity for degrading BPAF (Fig. 3f). Further characterization by XRD (Fig. S6a in Supporting information), scanning electron microscope (SEM) (Fig. S6b in Supporting information), and TEM (Fig. S6c in Supporting information) reveals that 8-MXene/Bi₅O₇I retains its original crystal structure and morphology, indicating the excellent stability of 8-MXene/Bi₅O₇I.

  Electron spin resonance (ESR) tests were utilized to confirm the active species. In Fig. S7a (Supporting information), the strong signal with an intensity ratio of 1:2:1:2:1:2:1 in the 8-MXene/Bi₅O₇I/PMS can be attributed to DMPO oxidation (DMPOX), while the DMPO-^•OH and DMPO- SO₄^•‒ signals are not observed. Notably, DMPOX is generated by a second-order reaction of DMPO with an oxidant, implying 8-MXene/Bi₅O₇I rapidly activates PMS and generates numerous oxidized species, indirectly disclosing the existence of ^•OH and SO₄^•‒ [27]. In Figs. S7b and c (Supporting information), peaks with intensity ratios of 1:1:1:1 and 1:1:1 correspond to O₂^•- and ¹O₂, respectively. Besides, tert–butanol (TBA) were utilizbutanol (TBA), methanol (MeOH), L-histidine, and benzoquinone (BQ) were added to perform quenching experiments to further explore the reactive species during the reaction (Fig. S7d in Supporting information). Among them, the addition of L-histidine has the most significant effect on the inhibition of the degradation reaction (23.1% degradation rate), indicating that ¹O₂ is a key species in the catalytic degradation system.

  The light absorption capacity was evaluated by UV–vis diffuse reflectance spectroscopy (DRS) (Fig. S8a in Supporting information). MXene is strongly responsive to light at wavelengths of 250–800 nm, which implies that MXene has metallic properties [28]. Bi₅O₇I has an absorption edge of about 450 nm and exhibits obvious visible light absorption. After the incorporation of MXene, the visible light absorption of MXene/Bi₅O₇I is significantly enhanced. The visible light absorption performance of MXene/Bi₅O₇I increases with the increase of MXene amount. Additionally, the band gap (E_g) of Bi₅O₇I is estimated to be about 2.85 eV based on the Kubelka-Munk equation (Fig. S9a in Supporting information) [29].

  Photoelectrochemical measurements were conducted to explore the carrier transport and separation performance of the catalytic materials [30]. Photoluminescence spectra (PL, Fig. S8b in Supporting information) show that the signal intensity of 8-MXene/Bi₅O₇I is the lowest, indicating that it has the best photogenerated carrier separation performance. In the photocurrent response experiment (Fig. S8c in Supporting information), the photocurrent intensity of 8-MXene/Bi₅O₇I is higher than that of Bi₅O₇I. Furthermore, from electrochemical impedance spectroscopy (EIS) in Fig. S8d (Supporting information), the Nyquist semicircle radius of 8-MXene/Bi₅O₇I is small, suggesting a low resistance to carrier transport. These experimental results confirm the higher photoelectron separation efficiency of 8-MXene/Bi₅O₇I, which is attributed to the presence of the Schottky junction.

  DFT was applied to analyze the adsorption abilities of PMS and catalysts. The best adsorption configuration is illustrated in Fig. 4. The adsorption energies (E_ads) of Bi₅O₇I/PMS (Fig. 4a), MXene/PMS (Fig. 4b), and MXene/Bi₅O₇I/PMS (Fig. 4c) are −0.73, −4.40, and −4.41 eV, respectively, revealing that the adsorption between PMS and catalysts is spontaneous [31]. The E_ads increases after the complexation of Bi₅O₇I with MXene, demonstrating that PMS is more easily adsorbed on the surface of MXene/Bi₅O₇I. Moreover, the bond lengths of O–O bonds in free PMS are 1.41 and 1.43 Å in Bi₅O₇I/PMS and MXene/PMS, respectively, whereas the bond length of O–O bonds in MXene/Bi₅O₇I/PMS increases significantly to 1.49 Å, indicating that the activation of PMS by MXene/Bi₅O₇I is stronger.

  Figure 4

  

  Figure 4.  Optimal adsorption configurations of (a) Bi₅O₇I/PMS, (b) MXene/PMS, and (c) MXene/Bi₅O₇I/PMS systems. (d) Possible mechanism of BPAF degradation in the MXene/Bi₅O₇I/PMS system.

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  As shown in Fig. S9b, the Mott-Schottky plot confirms that the flat band potential (E_fb) of Bi₅O₇I is −0.53 V versus Ag/AgCl, which is further converted to −0.33 V/NHE. For many n-type semiconductors, the E_fb is closely related to the conduction band (CB) and is deemed to be more positive by about 0.1 V than its conduction band potentials (E_CB). Therefore, the E_CB of Bi₅O₇I is calculated to be about −0.43 V/NHE (−4.07 eV/AVS). Since the E_g of Bi₅O₇I is 2.85 eV (Fig. S9a), the E_VB of Bi₅O₇I is 2.42 V/NHE (−6.92 eV/AVS) (Fig. 2c). Based on the above analysis, a possible mechanism for the degradation of BPAF by the MXene/Bi₅O₇I/PMS system under visible light is proposed (Fig. 4d). BPAF is efficiently degraded mainly due to the formation of Schottky heterojunction and the synergy between PMS activation and photocatalysis. First, the Schottky barrier in the Schottky heterojunction formed by MXene and Bi₅O₇I (Fig. 2c) inhibits electron-hole complexation and promotes the photocatalysis reaction to proceed. Second, Bi₅O₇I is photoexcited, generating electrons and holes in its conduction and valence bands, respectively (Eq. 7). Due to the Schottky barrier energy, the photogenerated electrons can be efficiently transported to the MXene, thus realizing the fast separation of photogenerated electrons and holes. The electrons can react with oxygen molecules to form O₂^•- (Eq. 8) and with PMS to form SO₄^•‒ and ^•OH (Eqs. 9 and 10), while h⁺ reacts with PMS to obtain SO₅^•‒ (Eq. 11) [32]. As exhibited in Eqs. 12 and 13, SO₅^•‒ further reacts with H₂O to generate a large amount of ¹O₂, in agreement with the ESR test (Fig. S7c) and the quenching experiment (Fig. S7d). Finally, under light-assisted PMS activation, a large amount of ROS is generated to react with BPAF in solution, resulting in efficient degradation of BPAF (Eq. 14).

  $ \text { Catalyst + Visible Light → } \mathrm{h}^{+}+\mathrm{e}^{-} $

  (7)

  $ \mathrm{e}^{-}+\mathrm{O}_2 \rightarrow \mathrm{O}_2 ^{\bullet^-} $

  (8)

  $ \mathrm{e}^{-}+\mathrm{HSO}_5^{-} \rightarrow \mathrm{SO}_4^{2-}+ {}^{\bullet} \mathrm{OH} $

  (9)

  $ \mathrm{e}^{-+} \mathrm{HSO}_5^{-} \rightarrow \mathrm{SO}_4^{\bullet-}+\mathrm{OH}^{-} $

  (10)

  $ \mathrm{h}^{+}+\mathrm{HSO}_5^{-} \rightarrow \mathrm{SO}_5^{\bullet-}+\mathrm{H}^{+} $

  (11)

  $ 2 \;\mathrm{SO}_5^{\bullet-}+\mathrm{H}_2 \mathrm{O} \rightarrow 1.5^1 \mathrm{O}_2+2 \;\mathrm{HSO}_4^{-} $

  (12)

  $ \mathrm{SO}_5^{\bullet-}+\mathrm{SO}_5^{\bullet-} \rightarrow{ }^1 \mathrm{O}_2+2 \;\mathrm{SO}_4^{2-} $

  (13)

  $ \mathrm{SO}_4^{\bullet-} / {}^{\bullet} \mathrm{OH} / O_2^{\bullet-} /^1 \mathrm{O}_2+\mathrm{BPAF} \rightarrow \text { degradation product } $

  (14)

  To explore the BPAF degradation in the MXene/Bi₅O₇I/PMS system, an in-depth study of the intermediates during the reaction process is required. Therefore, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), the natural population analysis (NPA), and the Fukui index of BPAF are calculated using DFT to investigate the molecular structural properties and reactive groups that may affect the degradation process of BPAF. Based on the frontier molecular orbital theory, the calculated HOMO (Fig. S10a in Supporting information) indicates that the HOMO of BPAF is mainly located on the phenolic hydroxyl group and the benzene ring, which are susceptible to electrophilic attack by electrophilic oxidizing agents (¹O₂) [33]. Meanwhile, the antibonding orbital of LUMO mainly occupies the benzene ring with moderate diffusion to the phenolic hydroxyl group and trifluoromethyl group. The electrostatic potential (ESP) map of the BPAF molecule (Fig. S10b in Supporting information) also reveals that the phenolic hydroxyl group has a partially surface negatively charged region, while the positive charge is mainly concentrated on some of the carbon atoms in the benzene ring.

  The concentrated Fukui index (Fig. S10c in Supporting information) is calculated to better characterize the oxidizing capacity of each atom of BPAF. Generally, the Fukui indices f⁰ and f^- can represent the atomic radical attack site and electrophilic attack site of BPAF, respectively. The f⁰ values of C (1), C (19), C (3), C (17), O (30), and O (32) are 0.0791, 0.0791, 0.0536, 0.0536, 0.0530, and 0.0530, respectively, which make these atoms susceptible to free radical attack. Meanwhile, the f^- values of C (1) (0.0927), C (19) (0.0927), C (4) (0.0821), C (15) (0.0821), C (3) (0.0795), and C (17) (0.0794) are relatively high, indicating that the electrophilic attack induced by ¹O₂ often occurs around the above atoms.

  Moreover, the main intermediates for the degradation of BPAF were ascertained by GC–MS (Table S3 in Supporting information). Ten intermediates are identified and a possible degradation pathway for BPAF is proposed according to product analyses and previous research (Fig. 5a) [34,35]. The pathway consists mainly of (ⅰ) an attack of the carbon atoms connecting the two aromatic rings to form P1 and P2, followed by the removal of the fluorine atom to form P3, P4, and P5, and (ⅱ) an attack of the carbon atoms on the aromatic ring leading to a series of ring-opening products (P6, P7, P8, P9, and P10).

  Figure 5

  

  Figure 5.  (a) Proposed photocatalytic degradation pathway of BPAF. (b) Acute toxicity and (c) developmental toxicity of BPAF and its degradation intermediates.

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  The acute toxicity (Daphnia magna LC₅₀, 48 h) and developmental toxicity of intermediates are predicted through the quantitative structure-activity relationship (QSAR) method employing T.E.S.T. software [36]. In Fig. 5b, the LC₅₀ of BPAF for Daphnia magna is 0.41 mg/L, which is "Toxic". The degradation intermediates are all less toxic than BPAF. Moreover, the developmental toxicity (Fig. 5c) of all intermediates is lower than that of BPAF (0.71), except for intermediates P7 (0.75) and P9 (0.78). This indicates that the catalytic system greatly reduces the BPAF toxicity.

  In conclusion, a novel 2D MXene/1D Bi₅O₇I Schottky junction was successfully synthesized for the degradation of BPAF by a PMS-assisted photocatalytic system. The 8-MXene/Bi₅O₇I/PMS system degraded 93.4% of BPAF within 90 min, which was significantly better than each single component. The introduced MXene not only raised the active sites of the system but also formed 2D/1D microstructures and Schottky structures, which facilitated the interfacial charge transport of the heterojunction and could hinder the photogenerated electron-hole complex. The catalytic mechanism was revealed through a series of DFT calculations combined with experiments. These improved properties and the synergy between photocatalysis and PMS activation enhanced the catalytic performance of the system. This study demonstrated that PMS activation synergized with Schottky heterojunction photocatalysis could efficiently degrade BPAF, which provided new insights into the treatment of organic pollutants.

  CRediT authorship contribution statement

  Feihu Mu: Investigation, Conceptualization. Benlin Dai: Software, Data curation. Chuxuan Dai: Investigation, Data curation. Xiaozhong Chu: Validation, Methodology. Jiming Xu: Validation, Software. Junyu Shen: Writing – original draft, Resources. Wei Zhao: Software, Methodology. Guohui Dong: Writing – review & editing, Visualization.

  Declaration of competing 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.

  Acknowledgments

  We greatly acknowledge the National Natural Science Foundation of China (No. 22472011), the Natural Science Major Foundation of the Jiangsu Higher Education Institutions of China (No. 22KJA610002), and the foundation of Anhui Province Key Laboratory of Pollutant Sensitive Materials and Environmental Remediation (No. PSMER2023011).

  Supplementary materials

  Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2025.111866.

  
  
• 1. [1]

     D. Azizi, A. Arif, D. Blair, et al., Environ. Res. 207 (2022) 112196. doi: 10.1016/j.envres.2021.112196

  2. [2]

     U. Rajamani, A.R. Gross, C. Ocampo, et al., Nat. Commun. 8 (2017) 219. doi: 10.1038/s41467-017-00254-8

  3. [3]

     Y. Hu, Q. Zhu, X. Yan, et al., Environ. Res. 178 (2019) 108732. doi: 10.1016/j.envres.2019.108732

  4. [4]

     J. Moreman, O. Lee, M. Trznadel, et al., Environ. Sci. Technol. 51 (2017) 12796–12805. doi: 10.1021/acs.est.7b03283

  5. [5]

     N. Liu, N. Lu, H. Yu, et al., Chem. Eng. J. 407 (2021) 127228. doi: 10.1016/j.cej.2020.127228

  6. [6]

     S. Wang, M.R. Razanajatovo, X. Du, et al., Chin. Chem. Lett. 35 (2024) 109140. doi: 10.1016/j.cclet.2023.109140

  7. [7]

     D.A. Oluwasogo, S. Varangane, Y.T. Prabhu, et al., J. Cleaner Prod. 394 (2023) 136393. doi: 10.1016/j.jclepro.2023.136393

  8. [8]

     F. Mu, B. Dai, W. Zhao, et al., Chin. Chem. Lett. 31 (2020) 1773–1781. doi: 10.1016/j.cclet.2019.12.015

  9. [9]

     Z. Weng, Y. Lin, B. Han, et al., J. Hazard. Mater. 448 (2023) 130869. doi: 10.1016/j.jhazmat.2023.130869

  10. [10]

      R. Guo, H. Zhang, C. Guo, et al., Chin. Chem. Lett. 35 (2024) 109413. doi: 10.1016/j.cclet.2023.109413

  11. [11]

      Q. Geng, H. Xie, Y. He, et al., Appl. Catal. B: Environ. 297 (2021) 120492. doi: 10.1016/j.apcatb.2021.120492

  12. [12]

      F. Mu, B. Dai, W. Zhao, et al., Chin. Chem. Lett. 32 (2021) 2539–2543. doi: 10.1016/j.cclet.2020.12.016

  13. [13]

      C. Liu, H. Huang, X. Du, et al., J. Phys. Chem. C 119 (2015) 17156–17165. doi: 10.1021/acs.jpcc.5b03707

  14. [14]

      Z. Li, H. Dong, Z. Wu, et al., Appl. Surf. Sci. 529 (2020) 147162. doi: 10.1016/j.apsusc.2020.147162

  15. [15]

      J. Wang, C. Cao, Y. Wang, et al., Chem. Eng. J. 391 (2020) 123530. doi: 10.1016/j.cej.2019.123530

  16. [16]

      M. Naguib, M. Kurtoglu, V. Presser, et al., Adv. Mater. 23 (2011) 4207-4207. doi: 10.1002/adma.201190147

  17. [17]

      J. Li, X. Chen, X. Zhu, et al., Chin. Chem. Lett. 35 (2024) 108286. doi: 10.1016/j.cclet.2023.108286

  18. [18]

      A. Sherryna, M. Tahir, ACS Appl. Energy Mater. 4 (2021) 11982–12006. doi: 10.1021/acsaem.1c02241

  19. [19]

      Z. Zhang, J.T. Yates, Chem. Rev. 112 (2012) 5520–5551. doi: 10.1021/cr3000626

  20. [20]

      H. Wu, M. Wang, F. Jing, et al., Chin. Chem. Lett. 33 (2022) 1983–1987. doi: 10.1016/j.cclet.2021.09.095

  21. [21]

      Q. Liu, Y. Lu, S. Lin, et al., Colloid. Surf. A 594 (2020) 124642. doi: 10.1016/j.colsurfa.2020.124642

  22. [22]

      S. Cao, B. Shen, T. Tong, et al., Adv. Funct. Mater. 28 (2018) 1800136. doi: 10.1002/adfm.201800136

  23. [23]

      G. Zuo, Y. Wang, W.L. Teo, et al., Chem. Eng. J. 403 (2021) 126328. doi: 10.1016/j.cej.2020.126328

  24. [24]

      Q. Hou, M. Wang, T. Li, et al., Chem. Eng. J. 464 (2023) 142566. doi: 10.1016/j.cej.2023.142566

  25. [25]

      Y. Gong, Y. Ding, Q. Tang, et al., Chin. Chem. Lett. 35 (2024) 108475. doi: 10.1016/j.cclet.2023.108475

  26. [26]

      J. Lim, D.Y. Kwak, F. Sieland, et al., Appl. Catal. B: Environ. 225 (2018) 406–414. doi: 10.1016/j.apcatb.2017.12.025

  27. [27]

      H. Li, Y. Yao, J. Zhang, et al., Chem. Eng. J. 397 (2020) 125401. doi: 10.1088/1572-9494/abb7c9

  28. [28]

      K. Zhang, D. Li, H. Cao, et al., Chem. Eng. J. 424 (2021) 130340. doi: 10.1016/j.cej.2021.130340

  29. [29]

      F. Mu, Q. Cai, H. Hu, et al., Chem. Eng. J. 384 (2020) 123352. doi: 10.1016/j.cej.2019.123352

  30. [30]

      F. Mu, B. Dai, W. Zhao, et al., J. Mater. Sci. Technol. 101 (2022) 37–48. doi: 10.1016/j.jmst.2021.05.059

  31. [31]

      J. Zhou, X. Guo, X. Zhou, et al., Chem. Eng. J. 433 (2022) 134511. doi: 10.1016/j.cej.2022.134511

  32. [32]

      Q. Wang, Z. Xu, Y. Cao, et al., Chem. Eng. J. 427 (2022) 131953. doi: 10.1016/j.cej.2021.131953

  33. [33]

      W. Li, Y. Zhang, X. Cheng, et al., Sep. Purif. Technol. 282 (2022) 119967. doi: 10.1016/j.seppur.2021.119967

  34. [34]

      J. Jia, D. Liu, Q. Wang, et al., J. Hazard. Mater. 424 (2022) 127434. doi: 10.1016/j.jhazmat.2021.127434

  35. [35]

      C. Qin, Y. Qi, Q. Zheng, et al., J. Environ. Chem. Eng. 12 (2024) 112456. doi: 10.1016/j.jece.2024.112456

  36. [36]

      J. Wang, M. Yuan, C. Li, et al., J. Colloid Interface Sci. 612 (2022) 536–549. doi: 10.1016/j.jcis.2021.12.190

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  Figure 1  FESEM images of (a) MXene nanosheets, (b) Bi₅O₇I nanorods, (c) 8-MXene/Bi₅O₇I. (d) TEM image, (e) HRTEM image, and (f, g) elemental mapping of 8-MXene/Bi₅O₇I.

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  Figure 2  Average potential profile along the Z-axis direction for (a) MXene and (b) Bi₅O₇I. (c) Schematic illustration of the Schottky junction on the interface between MXene and Bi₅O₇I. Calculated density of states (DOS) for (d) MXene and (e) Bi₅O₇I. (f) Electron density distribution in the interface between MXene and Bi₅O₇I.

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  Figure 3  (a) Photodegradation curves of BPAF, (b) pseudo-first-order kinetics fitted curves. Effect of catalyst dosage (c), PMS concentration (d), and pH (e) on the removal of BPAF. Conditions: Conditions: [BPAF] = 20 mg/L, [PMS] = 2.00 mmol/L, [catalyst] = 0.6 g/L, pH = 5.4, unless otherwise specified. (f) Cycle degradation experiment.

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  Figure 4  Optimal adsorption configurations of (a) Bi₅O₇I/PMS, (b) MXene/PMS, and (c) MXene/Bi₅O₇I/PMS systems. (d) Possible mechanism of BPAF degradation in the MXene/Bi₅O₇I/PMS system.

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  Figure 5  (a) Proposed photocatalytic degradation pathway of BPAF. (b) Acute toxicity and (c) developmental toxicity of BPAF and its degradation intermediates.

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