https://orcid.org/0009-0009-9364-9880
ABSTRACT
Metal–organic frameworks (MOFs) have garnered significant interest in the field of photocatalysis. In this study, Z-scheme heterojunction BM-x composites consisting of bismuth bromide oxide (BiOBr) and iron-based metal–organic backbone (MIL-100(Fe)) were successfully synthesized using ethylene glycol as a solvent. The composites were characterized using various techniques. BM-x exhibit abundant functional groups, large specific surface areas, and narrow band gap energy, thus provide numerous active sites for catalytic reactions and respond well to visible light. Notably, BM-7 displays remarkable catalytic activity in a visible light-activated permonosulfate (PMS) system and achieves a degradation rate of 99.02% over 100 mg/L gold orange II (AO7) within 60 min. The effects of BM-7 and PMS addition, initial AO7 concentration, initial pH, inorganic anions, and humic acid on the degradation system were investigated. The proposed mechanism of the Z-scheme heterojunction in the BM-7 photocatalyst demonstrates effective photoelectron transfer from the BiOBr conduction band to the MIL-100(Fe) valence band, resulting in excellent catalytic activity. Radical burst experiments identified 1O2, h+, and ·O2− as the main active substances. BM-7 has high stability and reusability, with a degradation rate reduction of only 14.48% after three recycles. These findings provide valuable insights into using persulfate combined with visible light.
HIGHLIGHTS
A Z-scheme photocatalyst BiOBr/MIL-100(Fe) was prepared using a solvothermal method.
BiOBr/MIL-100(Fe) enhanced the photocatalytic-persulfate activity toward AO7.
The effects of water environmental factors on the degradation efficiency were investigated.
1O2, h+, and ·O2− radicals were the vital radicals of the photocatalytic-persulfate system.
INTRODUCTION
Water pollution has become a significant global environmental issue in recent years, leading to a scarcity of usable water resources due to water quality deterioration and water resource mismanagement (Qutub et al. 2022). The discharge of various organic pollutants, including synthetic dyes, pesticides, and antibiotics, into aquatic environments on a daily basis has resulted in continuous damage to ecosystems (Gholami et al. 2023; Tiwari et al. 2023; Xu et al. 2023). To address this problem, sulfate radical-based advanced oxidation processes (SR-AOPs) have emerged as a rapidly developing solution. Compared with the more oxidized hydroxyl radical (OH·), 
has the following advantages: (1) 
(standard redox potential (2.5 ∼ 3.1 V) is higher than OH (1.8–2.7 V)); (2) 
(longer half-life (30–40 μs), while OH· (half-life less than 1 μs); and (3) 
(adapted to the wider pH range (2–9)), while OH· (the optimal pH range is 2–4) (Gao et al. 2021; Qiu et al. 2022; Xu et al. 2022). SR-AOPs can effectively break down organic pollutants into less toxic substances (e.g., CO2 and H2O) or smaller molecular structures, and thus are effective treatment approaches for organic pollutants.
Metal–organic frameworks (MOFs) are structured materials composed of organic ligands and inorganic metal ions or clusters. These components self-assemble through coordination bonds to form ordered porous mesh structures (Wan et al. 2020; Su et al. 2023). MOFs exhibit several desirable characteristics for the application of SR-AOPs (Wang et al. 2023a, b). They possess tunable porosity, open topology, large specific surface areas, and abundant active sites. MOFs also have semiconductor-like photoinduced properties, as the internal ligand-metal charge transfer showcases high charge separation capability. MIL-100(Fe), a typical MOF, can activate permonosulfate and degrade pollutants under visible light irradiation, and thus has garnered significant interest in the field of photocatalysis. Li et al. (2022a, b) prepared MIL-100(Fe), and the photoelectrons generated by MIL-100(Fe) under visible light irradiation will drive Fe(III) on the surface to Fe(II) in situ, which effectively activated permonosulfate to degrade the pollutant. The iron-based metal–organic backbone (MIL-100(Fe)/PDI) heterojunction constructed by You et al. (2023) effectively improved the separation efficiency of photogenerated electron–hole pairs under visible light and persulfate conditions, resulting in almost 100% degradation of bisphenol A (BPA) (Lv et al. 2020). This enhanced separation led to nearly complete pollutant degradation, as the heterojunction facilitated efficient redox reactions on the photocatalyst surface and thus accelerated the production of active substances for pollutant decomposition.
Bismuth bromide oxide (BiOBr), a semiconductor material with an indirect band gap, is composed of (Bi2O2)2+ and Br− layers in a distinct layered structure. This material has been extensively studied owing to its favorable properties, such as chemical stability, non-toxicity, corrosion resistance, and excellent photocatalytic capability (Zhao et al. 2022; Ighnih et al. 2023). Despite these advantages, the practical application of BiOBr is hindered by its relatively large band gap (∼2.7 eV) and the rapid recombination of electron–hole pairs generated upon light absorption. To overcome these limitations, researchers have proposed the development of heterojunctions within BiOBr. The type II BiOBr/MoS2 heterojunctions were successfully synthesized by Zhang et al. (2021) and they greatly enhanced the transfer of charge carriers and effectively activated PMS molecules (Xu et al. 2017). Additionally, these heterojunctions improved the oxidation ability of the generated holes and enabled the efficient degradation of various organic dyes and the reduction of Cr(VI).
Inspired by the previous studies, we focus on preparing heterojunction composite photocatalysts using the solvothermal method. Specifically, MIL-100(Fe) and BiOBr were combined to form the composite photocatalysts. The main objective was to examine the degradation ability of the BiOBr/MIL-100(Fe) + PMS + Vis system toward the azodye dye gold orange II (AO7). Various factors such as photocatalyst dosage, initial AO7 concentration, permonosulfate (PMS) dosage, initial pH, common inorganic anions, and HA were systematically investigated to understand their impacts on AO7 degradation. Furthermore, an AO7 degradation mechanism by the BiOBr/MIL-100(Fe) + PMS + Vis system was proposed.
EXPERIMENTAL
Chemicals
Ferric nitrate hydrate (Fe(NO3)3·9H2O, ≥98.5%), sodium chloride (NaCl, ≥99.5%), potassium iodide (KI, ≥99.5%), and potassium bromide (KBr, ≥ 99.5%) were obtained from Sinopharm Chemical Reagents (Shanghai, China). 1,3,5-Benzenetricarboxylic acid (C6H3(CO2H)3, ≥98.0%), potassium persulfate (KHSO5, ≥99.5%), L-histidine (C6H9N3O2, ≥99.5%), and p-benzoquinone (C6H4O2, ≥99.0%) were purchased from Shanghai Maclin company. Orange II (C16H11N2NaO4S, AR), sodium nitrate (NaNO3, ≥99.5%), anhydrous ethanol (C2H6O, ≥99.7%), ethylene glycol (C2H6O2, ≥99.5%), methanol (CH3OH, ≥99.9%), sodium bicarbonate (NaHCO3, ≥99.5%), sodium carbonate (Na2CO3, ≥99.5%), tert-butanol (C4H10O, ≥99.5%), and humic acid (HA) (C9H9NO6, ≥90.0%) were obtained from Xilong Scientific Co. All the above chemicals were an analytical reagent unless otherwise specified and used without further purification.
Preparation of catalytic materials
Preparation of MIL-100(Fe)
MIL-100(Fe) is prepared by a simple one-step hydrothermal method. First, 2.020 g of Fe(NO3)3·9H2O (5.0 mmol) and 1.050 g of 1,3,5-benzenetricarboxylic acid (H3BTC) (5.0 mmol) are dispersed in a beaker containing 50 mL of deionized water. Then, the mixed solution is stirred for 60 min at room temperature to ensure uniform mixing. Subsequently, the mixed solution is transferred to a 100 mL high-pressure reaction vessel lined with polytetrafluoroethylene and subjected to a hydrothermal reaction at 160 °C in a muffle furnace for 12 h. After cooling to room temperature, it is washed three times with deionized water and anhydrous ethanol. Finally, it is dried at 60 °C for 12 h to obtain a pale yellow powder, which is MIL-100(Fe).
Preparation of BiOBr/MIL-100(Fe) composites
BM-x composite materials are prepared using a solvothermal method. First, 0.485 g of Bi(NO3)3·5H2O (1.0 mmol) is dissolved in 20 mL of EG solution, referred to as solution A. Then, 0.166 g of KBr (1.0 mmol) and a certain amount of MIL-100(Fe) are dispersed in 20 mL of EG solution, referred to as solution B. The two solutions are stirred evenly. Subsequently, solution A is slowly added dropwise into solution B to form a mixed solution. The mixed solution is transferred to a 100 mL high-pressure reaction vessel lined with polytetrafluoroethylene and reacted at 160 °C for 12 h. After naturally cooling to room temperature, it is washed three times with deionized water and anhydrous ethanol to remove residual chemicals. Finally, the composite material is dried at 60 °C for 12 h to obtain a BiOBr/MIL-100(Fe) composite photocatalytic material. Pure BiOBr is prepared without adding MIL-100(Fe). According to different mass ratios of MIL-100(Fe) to BiOBr [m(MIL-100(Fe)):m(BiOBr) = 0.3, 0.5, 0.7, 0.9], they are named as BM-3, BM-5, BM-7, and BM-9.
Catalyst characterization
The surface morphology of the photocatalysts was analyzed using a scanning electron microscope (SEM, Model X130W/TMP, The Netherlands); the surface functional groups were identified by Fourier transform infrared spectroscopy (FTIR, Thermo Scientific Nicolet iS20, USA); the surface area of the photocatalysts was determined using a fully automated specific surface and porosity analyzer; BET (Micromeritics ASAP 2460, USA) was used to determine the specific surface area, the total pore volume, and the average pore diameter of the photocatalysts; the crystal structure of the photocatalysts was analyzed by an X-ray polycrystalline diffraction analyzer (XRD, SMART APEX II, Germany); X-ray photoelectron spectroscopy (XPS, Scientific K-Alpha, USA) was used to analyze the elemental composition and valence states; and a UV–Vis spectrometer (UV–Vis DRS, UV-3600 model, Japan) was used to study the optical properties.
Photocatalytic degradation experiment
The photocatalytic degradation performance of the catalyst was evaluated by degrading the AO7 solution using a 350 W xenon lamp (λ ≥ 420 nm) as the simulated light source. First, a certain mass of photocatalyst was added to 100 mL of 100 mg/L AO7 solution and stirred for 30 min under dark reaction conditions to achieve the adsorption–desorption equilibrium. Subsequently, a certain mass of PMS was added at the same time under light conditions, 2 mL was modified to a dye wastewater sample that was added at regular intervals, and finally, the absorbance was measured by a UV–Vis spectrophotometer.
RESULTS AND DISCUSSION
Microstructure characterization
X-ray diffraction
(a) XRD and (b) FTIR images of the prepared photocatalysts.
Fourier transform infrared spectroscopy
The surface functional groups of the photocatalysts were investigated using FTIR within 400–4,000 cm−1 (Figure 1(b)). The peak at 504 cm−1 is attributed to the stretching vibration of Bi–O in BiOBr (Song et al. 2014). The prominent peak at 711 cm−1 is due to the stretching of the benzene ring (Chen et al. 2021). The characteristic peaks at 1,620, 1,574, 1,446, and 1,376 cm−1 are associated with the asymmetric/symmetric vibrations of the carboxyl group. The broad absorption band at 3,000–3,500 cm−1 is caused by the O–H vibration of the adsorbed H2O molecules or coordinated hydroxyl groups (Ahmad et al. 2020). As reported, the abundant surface functional groups of nanomaterials play a key role in the adsorption and degradation of pollutants (Zhang et al. 2023). In the BM-x composites, the corresponding characteristic peaks are enhanced with the increase of MIL-100(Fe) proportion, and no other impurity peaks are observed. FTIR confirms the formation of the BM-x composites.
Scanning electron microscopy
SEM images of (a) BiOBr, (b) BM-3, (c) BM-5, (d) BM-7, (e) BM-9, (f) MIL-100(Fe), and (g) the EDS elemental mappings of the BM-7 composite.
SEM images of (a) BiOBr, (b) BM-3, (c) BM-5, (d) BM-7, (e) BM-9, (f) MIL-100(Fe), and (g) the EDS elemental mappings of the BM-7 composite.
Nitrogen adsorption–desorption isotherms
N2 adsorption–desorption isotherms test results of different catalysts
| Catalyzer | Surface area (m2g−1) | Pore volume (cm3g−1) | Pore size (nm) |
|---|---|---|---|
| BiOBr | 6.13 | 0.033571 | 21.92 |
| MIL-100(Fe) | 501.46 | 0.323693 | 2.58 |
| BM-7 | 301.56 | 0.346934 | 4.60 |
| Catalyzer | Surface area (m2g−1) | Pore volume (cm3g−1) | Pore size (nm) |
|---|---|---|---|
| BiOBr | 6.13 | 0.033571 | 21.92 |
| MIL-100(Fe) | 501.46 | 0.323693 | 2.58 |
| BM-7 | 301.56 | 0.346934 | 4.60 |
(a, b) N2 adsorption–desorption isotherms of BiOBr, MIL-100(Fe), and BM-7.
Ultraviolet–visible diffuse reflectance spectroscopy
UV–Vis diffuse reflectance spectrum (a) and energy gap (b).
X-ray photoelectron spectroscopy
XPS spectra of BM-7: full spectrum (a), O 1s (b), Bi 4f (c), Fe 2p (d), and Br 3d (e) energy regions.
XPS spectra of BM-7: full spectrum (a), O 1s (b), Bi 4f (c), Fe 2p (d), and Br 3d (e) energy regions.
AO7 degradation performance of catalysts
Comparison of degradation performance
| Catalyst | Catalyst amount (g/L) | Pollutant | Oxidizer | Temperature (°C) | Illumination time (min) | Efficiency (%) | Ref. |
|---|---|---|---|---|---|---|---|
| MIL-53(Fe) | 0.6 | 0.05 mmol/L AO7 | 2 mmol/L PMS | 25 | 90 | 82 | Gao et al. (2017) |
| BiOBr/PBCD-B-D | 1 | 0.2 mmol/L AO7 | 1 mmol/L PMS | 30 | 60 | 98.7 | Du et al. (2021) |
| Co-MIL-101(Fe) | 0.3 | 0.1 mmol/L AO7 | 8 mmol/L PDS | 25 | 150 | 98 | |
| Cu-MIL-101(Fe) | 92 | ||||||
| Fe3O4@MIL-101 | 1.0 | 25 mg/L AO7 | 25 mmol/L PDS | 25 | 60 | 100 | |
| AgBr/LaFeO3 | 0.6 | 30 mg/L AO7 | 0.5 mmol/L PMS | 30 | 60 | 99.41 | |
| BiOBr/MIL-100(Fe) | 0.2 | 100 mg/L AO7 | 0.5 mmol/L PMS | 25 | 60 | 99.02 | This text |
| Catalyst | Catalyst amount (g/L) | Pollutant | Oxidizer | Temperature (°C) | Illumination time (min) | Efficiency (%) | Ref. |
|---|---|---|---|---|---|---|---|
| MIL-53(Fe) | 0.6 | 0.05 mmol/L AO7 | 2 mmol/L PMS | 25 | 90 | 82 | Gao et al. (2017) |
| BiOBr/PBCD-B-D | 1 | 0.2 mmol/L AO7 | 1 mmol/L PMS | 30 | 60 | 98.7 | Du et al. (2021) |
| Co-MIL-101(Fe) | 0.3 | 0.1 mmol/L AO7 | 8 mmol/L PDS | 25 | 150 | 98 | |
| Cu-MIL-101(Fe) | 92 | ||||||
| Fe3O4@MIL-101 | 1.0 | 25 mg/L AO7 | 25 mmol/L PDS | 25 | 60 | 100 | |
| AgBr/LaFeO3 | 0.6 | 30 mg/L AO7 | 0.5 mmol/L PMS | 30 | 60 | 99.41 | |
| BiOBr/MIL-100(Fe) | 0.2 | 100 mg/L AO7 | 0.5 mmol/L PMS | 25 | 60 | 99.02 | This text |
Degradation of AO7 by different photocatalysts under visible light irradiation (a) and corresponding kobs. (b) Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
Degradation of AO7 by different photocatalysts under visible light irradiation (a) and corresponding kobs. (b) Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
Effect of different systems on AO7 removal
Effectiveness of different systems in removing AO7 (a) and corresponding kobs. (b) Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
Effectiveness of different systems in removing AO7 (a) and corresponding kobs. (b) Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
Effect of reaction conditions on AO7 degradation
Effect of catalyst dosage
Effect of BM-7 dosage on AO7 degradation rate (a) and corresponding kobs. (b) Experimental conditions: PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
Effect of BM-7 dosage on AO7 degradation rate (a) and corresponding kobs. (b) Experimental conditions: PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
Effect of PMS concentration
(Equations (2) and (3)), which can interfere with AO7 degradation (Xu et al. 2013).
Effect of PMS dosage on the degradation rate of AO7 (a) and corresponding kobs. (b) Experimental conditions: catalysts dosage = 0.20 g/L, AO7 = 100 mg/L, and T = 25 °C.
Effect of PMS dosage on the degradation rate of AO7 (a) and corresponding kobs. (b) Experimental conditions: catalysts dosage = 0.20 g/L, AO7 = 100 mg/L, and T = 25 °C.
Effect of initial pollutant concentration
Effect of different AO7 concentrations on the catalytic system (a) and corresponding kobs. (b) Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, and T = 25 °C.
Effect of different AO7 concentrations on the catalytic system (a) and corresponding kobs. (b) Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, and T = 25 °C.
Effect of pH
and ·OH (Equations (4) and (5)) further inhibited AO7 degradation (Wang et al. 2021).
Effect of different initial pH on the degradation rate of AO7 (a) and corresponding kobs. (b) Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
Effect of different initial pH on the degradation rate of AO7 (a) and corresponding kobs. (b) Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
Effects of different inorganic anions
, 
, 
, or 
to investigate their effects on AO7 degradation. The results in Figure 12 show the addition of Cl−, 
, or 
minimally impacted AO7 degradation compared with the blank experiment. However, the degradation was significantly inhibited after the addition of 
or 
, as the degradation rates were only 45.52 and 18.96%, respectively. The reason for this inhibition is that 
captures 
and 
in the system, generating less oxidizable HCO3· and 
(Equations (6) and (7)) (Jia et al. 2022; Chen et al. 2023). These less reactive species consume the free radicals in the system and decelerate the reaction rate. Similarly, the addition of 
to the degradation system led to the hydrolysis of 
, which affected the degradation efficiency. Additionally, the alkaline conditions caused by 
and the effects of pH discussed above further inhibited AO7 degradation. The combined effect of these factors further inhibited AO7 degradation by 
compared with 
Effect of inorganic anions on the degradation rate of AO7 (a) and corresponding kobs. (b) Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
Effect of inorganic anions on the degradation rate of AO7 (a) and corresponding kobs. (b) Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
Effect of humic acid
and ·OH, further inhibiting AO7 degradation. However, this inhibition is only minor, indicating that non-radical substances play a crucial role in the degradation process. 
Effect of HA on the degradation rate of AO7 (a) and corresponding kobs. (b) Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
Effect of HA on the degradation rate of AO7 (a) and corresponding kobs. (b) Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
Possible mechanisms
Radical burst experiment chemistry
and ·OH at similar reaction rates, falling within 1.2–2.8 × 109 and 1.6–7.7 × 108M−1S−1, respectively. Moreover, tertiary butyl alcohol captures ·OH at a faster rate (3.8–7.6 × 108M−1S−1) compared with 
(4.0–9.1 × 108M−1S−1) (Song et al. 2017; Krishnan et al. 2022). Based on this information, we used methanol to simultaneously capture 
and ·OH, and employed tert-butanol to capture ·OH. The addition of methanol and tert-butanol reduced the AO7 degradation rate from 99.02 to 69.13% and to 94.77%, respectively. These findings indicate that both 
and ·OH are involved in the degradation process, with 
having a stronger effect. Additionally, potassium iodide and p-benzoquinone are commonly used to trap holes (h+) and superoxide radicals (
) to assess their contributions in the degradation system. The inclusion of potassium iodide and p-benzoquinone decreased the AO7 degradation rate by 52.47 and 41.01%, respectively, suggesting that h+ and 
play significant roles in the degradation process. Finally, L-histidine was introduced to capture 1O2 and evaluate the role of non-radicals in the degradation system. The addition of L-histidine significantly inhibited the degradation, which indicates the production and major role of 1O2 in the degradation process. 
Effect of different bursting agents on the catalytic system. Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
Effect of different bursting agents on the catalytic system. Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
Mechanisms for degradation
The geometric average electronegativity of the constituent atoms in the semiconductor, denoted as χ, plays a key role in the energy calculations of the system. χ is 5.10 eV for MIL-100(Fe) (Cui et al. 2024) and 6.45 eV for BiOBr (He et al. 2021). Additionally, the energy of free electrons (Ee) is around 4.5 eV vs. NHE. For MIL-100(Fe), ECB is −0.84 eV and EVB is 2.04 eV. For BiOBr, ECB is 0.62 eV and EVB is 3.28 eV. Based on experimental results and energy band calculations, it can be concluded that the composite formation of a Z-scheme heterojunction between BiOBr and MIL-100(Fe) not only effectively separates the photogenerated electron–hole pairs, but also exhibits a stronger redox capacity (Hu et al. 2023). The standard electrode potential 
is −0.33 eV vs. NHE for 
and E(·OH/OH−) is 2.40 eV vs. NHE for ·OH. The photogenerated electrons on the valence band of BiOBr cannot combine with O2 to form 
, and the holes on the conduction band of MIL-100(Fe) face difficulty in oxidizing H2O to ·OH. However, 
and ·OH are generated in the composite BM-7 system, indicating that the photogenerated electrons and holes are concentrated in the conduction band of MIL-100(Fe) and the valence band of BiOBr, respectively. These species further react with O2 and H2O to produce 
and ·OH, which are highly effective in degrading pollutants.
(1) The photoelectrons reduce the dissolved oxygen in water to
, which further reacts with H+ to produce 1O2 (Equations (10) and (11)) (Silva et al. 2023).(2) The photoelectrons transfer to BM-7, reducing Fe(III) to Fe(II). As an active center, Fe(II) effectively activates PMS to produce
and ·OH (Equations (12) and (13)), establishing the Fe(III)/Fe(II) cycle and accelerating the generation of free radicals (Chen et al. 2024).(3) The photoelectrons are directly captured by PMS to produce
(Equations (14) and (15)) (Chen et al. 2024).
Photocatalytic activation mechanism for the AO7 degradation by BM-7.
Reusable performance and stability
Cyclic test for the degradation rate of AO7 by the BM-7 + PMS + Vis system (a) and XRD plots before and after reaction. (b) Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
Cyclic test for the degradation rate of AO7 by the BM-7 + PMS + Vis system (a) and XRD plots before and after reaction. (b) Experimental conditions: catalysts dosage = 0.20 g/L, PMS = 0.5 mmol/L, AO7 = 100 mg/L, and T = 25 °C.
CONCLUSIONS
A visible-light-responsive photocatalyst BiOBr/MIL-100(Fe) was successfully prepared using a simple solvothermal method. The crystal structure, morphology, and photoelectrochemical properties of the samples were characterized using various physical and chemical characterization methods, which confirmed the successful synthesis of the nanocomposite photocatalysts. Under the optimal composite ratio (BM-7), the activated persulfate system demonstrated superior degradation performance under visible light irradiation compared with BiOBr and MIL-100(Fe). This achievement can be attributed to the construction of a Z-scheme heterojunction in BM-7 that enabled it to exhibit stronger visible light response and electron transfer ability. The BM-7 + PMS + Vis system achieved a remarkable degradation efficiency of 99.02% over AO7 (100 mg/L) within 60 min under optimal conditions. However, the degradation efficiency of the system decreased with increasing pH. The presence of 
and 
significantly inhibited the AO7 degradation, but the system exhibited strong adaptability to HA. Free radical burst experiments identified 1O2, h+, and 
as the main active substances in the BM-7 + PMS + Vis system, and the proposed mechanism for AO7 degradation involved the Z-scheme heterojunction constructed by BM-7. Furthermore, the system can equally and efficiently degrade other organic dyes. After three cycle tests, the AO7 degradation rate remained at 85.82%, indicating its potential for reuse. Therefore, the BM-7 + PMS + Vis system holds promise for advanced oxidation applications in the degradation of organic dyes.
FUNDING
This study was supported by the National Natural Science Foundation of China (No. 51808268).
CREDIT AUTHORSHIP CONTRIBUTION STATEMENT
X.L. conceptualized the study, wrote, reviewed, and edited the article. X.C. arranged the resources, wrote the review, and edited the article. J.L. investigated the work and rendered support in data curation. J.T. investigated the work and rendered support in data curation. R.W. investigated the work and edited the article.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.
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