Semiconductor heterojunction photocatalyst for enhancing PMS activation as well as preparation method and application of semiconductor heterojunction photocatalyst
By preparing a ZnxNi1-xFe2O4@BiOBr heterojunction photocatalyst, the problem of low PMS activation efficiency in existing technologies was solved, achieving efficient degradation of organic pollutants in water. It has good stability and reusability and is suitable for the field of water treatment.
Patent Information
- Application Number
- CN202511239535.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-01
- Publication Date
- 2026-03-06
AI Technical Summary
Existing technologies are difficult to effectively activate transition metal catalysts to activate persulfate (PMS), resulting in difficulties in efficiently removing persistent pollutants from water. Furthermore, traditional methods suffer from metal ion leaching and pH dependence issues.
A ZnxNi1-xFe2O4@BiOBr heterojunction photocatalyst was prepared by a two-step hydrothermal method. By adjusting the pH and temperature conditions, nanoparticles with high catalytic activity were formed, which enhanced the PMS activation ability.
It achieves efficient degradation of organic pollutants in water in a short time, has good catalyst stability, reduces metal leaching, is suitable for large-scale production, and is applicable to the treatment of organic pollutants in the aquatic environment.
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Figure CN121607169A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of wastewater treatment catalyst material development technology, specifically to a semiconductor heterojunction photocatalyst that enhances PMS activation, its preparation method, and its application. Background Technology
[0002] In countries facing high water pressures, the solution implemented is the recycling and reuse of municipal wastewater. However, this is not without its risks, as it involves pathogenic microorganisms, micropollutants, and other pharmaceutical and personal care products (PPCPs). Notably, many PPCPs have been detected in emissions near wastewater treatment plant discharge points globally, at concentrations ranging from ng / L to mg / L, indicating that these compounds cannot be removed by conventional treatment methods. Furthermore, research on long-term exposure to aquatic ecosystems, their presence in drinking water and groundwater, and the introduction of exposed organisms into the food chain is limited.
[0003] Advanced oxidation processes (AOPs) are based on the generation of highly reactive oxidative radicals, primarily hydroxyl radicals, for the degradation of persistent pollutants. Sulfate-based PMS is highly valued for its stability and potential for further activation via UV radiation, heat, or transition metals. However, using transition metals as activators for homogeneous catalysts has significant drawbacks, such as high metal ion dosage, high pH dependence, and the need to recover the catalyst from the reaction solution. Therefore, the search for highly efficient heterogeneous catalysts capable of effectively activating PMS has been extensively reported to overcome these limitations. One of the most studied compounds is spinel ferrite, as it can be readily prepared as nanoparticles and possesses both magnetic and semiconductor properties. ZnFe₂O₄ has been extensively studied in photocatalysis due to its relatively small band gap. However, its antiferromagnetic properties hinder its practical application. Ni doping can increase ferromagnetism, enabling magnetic removal from aqueous environments. On the other hand, Bi-based photocatalysts, such as layered BiOBr semiconductors, have also been reported to exhibit high activity in decomposing PMS molecules and enhancing radical generation rates. Notably, there is a significant synergistic effect between Bi-based photocatalysts and transition metals, particularly with semiconductor magnetic nanoparticles. Summary of the Invention
[0004] The purpose of this invention is to provide a semiconductor heterojunction photocatalyst that enhances PMS activation, its preparation method, and its application.
[0005] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: A semiconductor heterojunction photocatalyst for enhancing PMS activation, the catalyst being represented by the chemical formula ZnxNi1-xFe2O4@BiOBr, is prepared via a two-step hydrothermal method.
[0006] A method for preparing a semiconductor heterojunction photocatalyst that enhances PMS activation. 2.1. ZnxNi1−xFe2O4 nanoparticles (NPs) were prepared by a hydrothermal method, where x has values of 0, 0.2, 0.5, 0.8, and 1.0, through the following steps: 2.1.1. Dissolve the corresponding transition metal nitrates in deionized water in stoichiometric amounts; 2.1.2. After mixing, the pH is adjusted to 10 by adding 1M NH4OH dropwise to form a brown gel; 2.1.3. Filter the obtained gel and seal it in a stainless steel reactor lined with polytetrafluoroethylene, and treat it at 180°C for 12 hours; 2.1.4. The obtained powder was washed with ethanol and dried at 50°C for 12 hours; 2.2. ZnxNi1-xFe2O4@BiOBr was prepared using a second hydrothermal method, through the following steps: 2.2.1. Dissolve Bi(NO3)3·5H2O and KBr in stoichiometric amounts in 30 mL of deionized water and sonicate for 5 min to form a suspension; 2.2.2. Disperse ZnxNi1−xFe2O4NPs in the above suspension and sonicate again for 30 min; 2.2.3. After continuing vigorous stirring for 60 minutes, begin the second hydrothermal treatment at 140℃ for 15 hours; 2.2.4. The obtained catalyst was filtered, washed with ethanol, and dried at 50°C for 12 h.
[0007] As an improvement, the molar ratio of ZnxNi1−xFe2O4NPs to BiOBr is 0.15.
[0008] As an improvement, the combination of Zn0.8Ni0.2Fe2O4 and BiOBr exhibits the best catalytic degradation performance during the preparation of the heterojunction photocatalyst.
[0009] A method for treating organic pollutants in actual water samples using a semiconductor heterojunction photocatalyst that enhances PMS activation. The method can effectively remove paracetamol (PAM) and other inactive substances from water.
[0010] A method for enhancing PMS activation by using a semiconductor heterojunction photocatalyst to degrade organic pollutants in water involves achieving complete removal of PAM under the conditions of 0.5 g / L Zn0.8Ni0.2Fe2O4@BiOBr, 2 mM MPMS, 10 mg / L PAM, UV-A radiation, and pH=7. The method involves adding PMS and the catalyst to a solution containing organic pollutants and maintaining the reaction for a certain time to degrade the organic pollutants.
[0011] As an improvement, the organic pollutant solution is a 50 mL PAM solution with an initial concentration of 10 mg / L; The amount of catalyst used is 0.1 to 1 g / L; The dosage of the PMS is 2 mM; The initial pH of the reaction system was 7 ± 0.2; The temperature of the reaction system is 25±0.5℃; The reaction system was stirred using a magnetic stirrer at a speed of 300 rpm.
[0012] As an improvement, the activity and structure of the catalyst remain stable after five consecutive uses through filtration, washing, and drying.
[0013] The advantages of this invention compared to the prior art are as follows: 1. The semiconductor heterojunction photocatalyst Zn0.8Ni0.2Fe2O4@BiOBr synthesized in this invention can effectively activate PMS and generate a large number of sulfate free radicals in a short time, thereby efficiently degrading PAM in water.
[0014] 2. The prepared semiconductor heterojunction photocatalyst exhibits good stability, reduces the leaching of active metals, lowers the potential pollution to the environment, and maintains long-term catalytic activity.
[0015] 3. The two-step hydrothermal synthesis method used in this invention is simple to operate, low in cost, easy to scale up for production, and beneficial for industrial applications.
[0016] 4. The catalyst of this invention can rapidly activate PMS, achieving efficient degradation of PAM in water with significant treatment effects. After five consecutive uses, the catalyst's activity and structure remain stable, demonstrating excellent reusability and providing a new and effective means for the treatment of organic pollutants in the aquatic environment. Attached Figure Description
[0017] Figure 1 TEM images of Zn0.8Ni0.2Fe2O4 NPs (a) and Zn0.8Ni0.2Fe2O4@BiOBr heterojunction (b, c, d); Figure 2 XRD patterns of BiOBr, Zn0.8Ni0.2Fe2O4 and ZnxNi1−xFe2O4@BiOBr (x=0.2, 0.5, 0.8, 1); Figure 3 The N2 adsorption-desorption isotherms are for Zn0.8Ni0.2Fe2O4 (a), BiOBr (b), and Zn0.8Ni0.2Fe2O4@BiOBr (c). Figure 4 The graphs (a) show the relationship between magnetic susceptibility and temperature for Zn0.8Ni0.2Fe2O4 NPs and Zn0.8Ni0.2Fe2O4@BiOBr heterojunctions, and the hysteresis loops (b) for the two materials at room temperature. Figure 5 XPS spectra of Zn0.8Ni0.2Fe2O4@BiOBr for Zn 2p (a), Fe 2p (b), Ni 2p (c), Bi 4f (d), Br 3d (e) and O 1s (f); Figure 6 The UV-Vis diffuse reflectance spectra (a), Tauc plot (b), Mott-Schottky plot (c), and Nyquist plot (d) of Zn0.8Ni0.2Fe2O4, BiOBr, and Zn0.8Ni0.2Fe2O4@BiOBr are shown. Figure 7 The PAM removal rates (inset shows the corresponding reaction rate constants) are shown for ZnxNi1−xFe2O4@BiOBr (a) and different Zn0.8Ni0.2Fe2O4 / BiOBr ratios (b) as catalysts, and the PAM removal rates (c) and corresponding reaction rate constants (d) are shown for Zn0.8Ni0.2Fe2O4@BiOBr as catalysts in different systems. Figure 8 The effects of different catalyst dosages (a), PMS concentrations (b), and initial pH (c) on PAM degradation efficiency were investigated. Figure 9 XRD patterns of raw and recycled Zn0.8Ni0.2Fe2O4@BiOBr (a) and the effects of different experimental periods (b), free radical scavengers (c) and coexisting anions (d) on PAM degradation efficiency (inset shows the corresponding reaction rate constants); Figure 10 This invention presents the PAM degradation mechanism. Detailed Implementation
[0018] The method for improving the activation performance and recyclability of PMS according to the present invention will be further illustrated below through examples. It should be noted that the following examples are only for further illustration of the present invention. Obviously, the described examples are merely some embodiments of the present invention, and not all embodiments.
[0019] Example 1: This embodiment provides a semiconductor heterojunction photocatalyst for enhanced PMS activation, its preparation method, and its application, comprising the following steps: Step 1. ZnxNi1-xFe2O4 NPs (x=0.2, 0.5, 0.8, 1) are prepared by hydrothermal method. The stoichiometric amounts of the corresponding transition metal nitrates are dissolved in deionized water, mixed, and the pH is adjusted to 10 by adding 1 M NH4OH to form a brown gel. The resulting gel is filtered and sealed in a stainless steel reactor lined with polytetrafluoroethylene. It is treated at 180°C for 12 h. The resulting powder is washed with ethanol and dried at 50°C for 12 h. Step 2. ZnxNi1-xFe2O4@BiOBr is prepared by a second hydrothermal method. The stoichiometric amounts of Bi(NO3)3·5H2O and KBr are dissolved in 30 mL of deionized water and ultrasonically treated for 5 min to form a suspension. ZnxNi1-xFe2O4@BiOBr is then dissolved in the suspension. The NPs were dispersed in the above suspension and ultrasonicated again for 30 min. After stirring vigorously for 60 min, a second hydrothermal treatment was started at 140℃ for 15 h. The resulting catalyst was filtered, washed with ethanol, and dried at 50℃ for 12 h.
[0020] Figure 1 TEM images of Zn0.8Ni0.2Fe2O4 NPs (a) and Zn0.8Ni0.2Fe2O4@BiOBr heterojunction (b, c, d). Figure 1 This study confirmed the efficient synthesis of Zn0.8Ni0.2Fe2O4 into NPs with an average particle size of ~7 nm. The morphology of the heterojunction catalyst has a significant impact on its performance optimization. Figure 1 Images b, c, and d depict a Zn0.8Ni0.2Fe2O4@BiOBr heterostructure, in which ferrite NPs are dispersed on the BiOBr crystal surface, resulting in a large contact interface that enhances electron-hole pair separation and exposure of reaction sites. This microstructure indicates that BiOBr and Zn0.8Ni0.2Fe2O4 combine to form numerous heterostructures.
[0021] Figure 2XRD patterns of BiOBr, Zn0.8Ni0.2Fe2O4, and ZnxNi1−xFe2O4@BiOBr (x=0.2, 0.5, 0.8, 1) are shown. The diffraction maxima of BiOBr can be represented by the quadrilateral P4 / nmm space group (JCPDS No. 78-0348). Indexing was performed. All peaks were clear, indicating good crystallinity and micron-sized grains. On the other hand, peak broadening indicated that the grain size of Zn0.8Ni0.2Fe2O4 was reduced to the nanoscale. All ferrite peaks could be indexed in the cubic Fd3m space group, crystallized within a spinel structure (JCPDS No. 08-0234). As expected, the diffraction pattern of the heterojunction catalyst was a combination of two XRD patterns. No secondary or impurity phases were detected within the resolution limit of X-ray diffraction.
[0022] Figure 3 The N2 adsorption-desorption isotherms are shown for Zn0.8Ni0.2Fe2O4 (a), BiOBr (b), and Zn0.8Ni0.2Fe2O4@BiOBr (c). Specific surface area and pore size are generally considered to determine the adsorption capacity of a catalyst and are key parameters. The isotherm morphology of Zn0.8Ni0.2Fe2O4 is type II, reflecting its non-porous or microporous nature. The isotherms of BiOBr and Zn0.8Ni0.2Fe2O4@BiOBr are type IV, with H3-type hysteresis loops. Compared to Zn0.8Ni0.2Fe2O4, BiOBr has a higher BET surface area, and the Zn0.8Ni0.2Fe2O4@BiOBr composite does not show a significant decrease in BET surface area. This may be due to the highly dispersed NPs of Zn0.8Ni0.2Fe2O4 on the surface of the BiOBr nanosheets.
[0023] Figure 4 The graphs (a) show the magnetic susceptibility versus temperature for Zn0.8Ni0.2Fe2O4 NPs and Zn0.8Ni0.2Fe2O4@BiOBr heterojunctions, and the hysteresis loops (b) for the two materials at room temperature. Figure 4 Figure 1 shows the temperature variation of the magnetic susceptibility of Zn0.8Ni0.2Fe2O4 NPs and Zn0.8Ni0.2Fe2O4@BiOBr heterojunctions. The ZFC / FC branch begins to diverge at ~25 K, indicating the presence of ferromagnetic components. The presence of net ferromagnetic components, accompanied by a relatively low particle size, makes it possible to selectively separate the heterojunction catalyst from solution by applying an external magnetic field. Figure 4b shows the magnetization and field measurements for both samples with consistent Zn0.8Ni0.2Fe2O4 particle size, exhibiting a characteristic sigmoid cycle. A nearly imperceptible coercive field (~10 Oe) characteristic of superparamagnetic behavior is present, with a magnetization of ~30 emu g⁻¹ at 298 K. As expected, due to the diamagnetism of the BiOBr catalyst, the Zn0.8Ni0.2Fe2O4@BiOBr heterojunction exhibits a relatively low magnetization but still retains good magnetic properties, allowing for magnetic removal from solution.
[0024] Figure 5 XPS spectra of Zn0.8Ni0.2Fe2O4@BiOBr for Zn 2p (a), Fe 2p (b), Ni 2p (c), Bi 4f (d), Br 3d (e), and O 1s (f). Considering the variable crystallographic sites of metal ions in ferrites, the chemical oxidation state of its surface was confirmed by XPS. Figure 5 As shown in figure a, the high-resolution Zn 2p XPS spectrum reveals the +2 oxidation state, with peaks at 1020.87 eV (2p3 / 2) and 1043.97 eV (2p1 / 2). Figure 5 b shows the Fe 2p spectrum, with four peaks located at 711.06 eV (2p³ / ²), 718.70 eV (2p³ / ² satellite peak), 724.73 eV (2p¹ / ²), and 733.10 eV (2p¹ / ² satellite peak). No double peaks were observed in the Zn 2p and Fe 2p spectra, indicating that Zn and Fe have only one valence state and lattice site: Zn²⁺ is located at a tetrahedral site, and Fe³⁺ is located at an octahedral site. Due to the extremely low Ni content in the sample (0.71 wt%), it was difficult to obtain a reliable Ni 2p spectrum for peak fitting. Nevertheless, Figure 5 Two peaks are still clearly visible in c, located at 854.2 eV (2p³ / 2) and 872.1 eV (2p¹ / 2), respectively. (Bi 4f spectrum) Figure 5 d) and Br 3d spectrum ( Figure 5 e) is decomposed into two peaks, corresponding to 164.49 eV and 159.18 eV for Bi 4f5 / 2 and 4f7 / 2, respectively, and 69.28 eV and 68.22 eV for Br 3d3 / 2 and 3d5 / 2, respectively. These can be attributed to Bi3+ and Br- in BiOBr. Figure 5 As shown in f, the O 1s spectrum can be decomposed into two peaks, located at 529.85 eV and 531.33 eV, respectively, corresponding to lattice oxygen and adsorbed oxygen.
[0025] Figure 6The UV-Vis diffuse reflectance spectra (a), Tauc (b), Mott-Schottky (c), and Nyquist (d) of Zn0.8Ni0.2Fe2O4, BiOBr, and Zn0.8Ni0.2Fe2O4@BiOBr are shown.
[0026] like Figure 6 a and Figure 6 As shown in b, the absorption edge of BiOBr is located around 430 nm, while Zn0.8Ni0.2Fe2O4 exhibits a wide absorption range from UV to visible light. It was observed that the absorption peaks of both Zn0.8Ni0.2Fe2O4 and Zn0.8Ni0.2Fe2O4@BiOBr shifted to longer wavelengths in the test range of 190-800 nm. Compared to pure Zn0.8Ni0.2Fe2O4, the spectrum of Zn0.8Ni0.2Fe2O4@BiOBr shifted to longer wavelengths in both the near-UV (300-400 nm) and visible (400-800 nm) regions, absorbing more light energy. This wider absorption wavelength range provides Zn0.8Ni0.2Fe2O4@BiOBr with a higher level of photocatalytic activity. The prepared catalyst exhibits good photoresponse ranges in both the UV and visible light regions, confirming that the photocatalytic activity of BiOBr is significantly enhanced after incorporation with Zn0.8Ni0.2Fe2O4. The band gap energies (Eg) of Zn0.8Ni0.2Fe2O4 and BiOBr are estimated to be 1.78 eV and 2.64 eV, respectively, using the tauc equation. This result also indicates that Zn0.8Ni0.2Fe2O4@BiOBr can be effectively activated under UV-A light irradiation. Figure 6 As shown in Figure c, the Mott-Schottky plot was measured to further estimate the band structure. The positive slope in the plot indicates that BiOBr and Zn0.8Ni0.2Fe2O4 are n-type semiconductors. The corresponding flat band potentials (Vfb) are -0.59 and -0.71 V vs Ag / AgCl, respectively, which can be converted to -0.39 and -0.51 V vs normal hydrogen electrode (NHE) potentials at pH 6.8. The conduction band potential (ECB) of n-type semiconductors can be considered very close to Vfb; therefore, the ECBs of Zn0.8Ni0.2Fe2O4 and BiOBr are −0.39 and −0.51 V vs NHE, respectively. Figure 6 As shown in Figure c, the valence band potentials (EVB) were calculated to be 1.27 and 2.25 eV using the formula ECB = EVB - Eg. Generally, impedance is related to the conductivity of the charge carriers; a higher impedance indicates poorer catalytic performance. For example... Figure 6 As shown in d, the Nyquist plot reflects that the formation of the heterojunction reduces the impedance, indicating better charge transfer characteristics, which effectively promotes the separation of photogenerated carriers.
[0027] Example 2: This embodiment describes the catalytic degradation of PAM under different conditions based on the above embodiment. The steps are as follows: Step 1. The experiment was conducted in a 100 mL beaker at a temperature of 25 ± 0.5 °C, with continuous stirring at 300 rpm using a magnetic stirrer. The catalyst was added to 50 mL of a 10 mg / L PAM solution. The pH of the solution was adjusted by adding 1 M NaOH, and PMS was added. Step 2. At given time intervals, 1 mL of the solution was taken out and filtered through a 0.45 µm PTFE needle-free filter. The sample was mixed with an equal volume of 2 M Na2S2O3 solution to terminate the reaction, and the sample was immediately analyzed by HPLC to determine the remaining PAM concentration. Step 3. To test the reusability of the catalyst, the reaction solution was filtered through a 0.45 µm cellulose filter, and the catalyst was washed and dried.
[0028] Figure 7 The PAM removal rates (insets show the corresponding rate constants) of ZnxNi1−xFe2O4@BiOBr (a) and different Zn0.8Ni0.2Fe2O4 / BiOBr ratios (b) as catalysts are shown in Figure 1. The PAM removal rates (c) and corresponding rate constants (d) of Zn0.8Ni0.2Fe2O4@BiOBr as catalyst in different systems are also shown. Reaction conditions: 0.5 g / L catalyst, 2 mMPMS, initial pH 7. Several heterojunction photocatalysts were tested by changing the Zn / Ni ratio of the ZnxNi1−xFe2O4@BiOBr composite material. Figure 7 Figure a shows the change in PAM degradation (C0 = 10 mg / L) over time for different heterostructures using 0.5 g / L catalyst and 2 mM PMS. ZnFe2O4@BiOBr (x = 1) exhibited the highest photocatalytic activity. However, due to the insufficient superparamagnetism of ZnFe2O4 to obtain a clear solution, rapid removal of the catalyst from the liquid medium using commercial magnets was not easily achieved. Although partial substitution of Zn with Ni reduced the PAM degradation effect, it also improved the magnetic properties of the composite material. Figure 7b shows the effect of the Zn0.8Ni0.2Fe2O4 / BiOBr ratio on PAM degradation. It can be observed that when the proportion of Zn0.8Ni0.2Fe2O4 in the composite increases to 15%, the PAM removal rate increases, then decreases significantly with further increases in the proportion. Therefore, under these conditions, 15% Zn0.8Ni0.2Fe2O4 / BiOBr exhibits the best catalytic performance. This can be attributed to the formation of more heterojunctions with increasing Zn0.8Ni0.2Fe2O4 loading, thereby improving PAM removal efficiency. However, further increasing the Zn0.8Ni0.2Fe2O4 loading may lead to the aggregation of Zn0.8Ni0.2Fe2O4 NPs, which is detrimental to the formation of thermally etched junctions. The effects of different reaction conditions on the PAM degradation process were investigated through single-condition and combined-condition experiments. Figure 7 As shown in Figure c, after a single UV-A irradiation and 100 min of PMS treatment, the degradation rates were 4.7% and 7.3%, respectively. Therefore, the photolysis and oxidation processes cannot be explained without a catalyst. Similar conclusions were found when UV-A and PMS were used in combination, with a removal rate of only 17%. Introducing the Zn0.8Ni0.2Fe2O4@BiOBr heterojunction as a catalyst improved the performance of the degradation process combined with UV-A. Based on the band gaps of ZnxNi1-xFe2O4 and BiOBr and the corresponding CB and VB positions, photoelectrons migrated from CB-ZnxNi1-xFe2O4 to CB-BiOBr, and holes diffused from VB-BiOBr to VB-ZnxNi1-xFe2O4, resulting in spatial separation of electron-hole pairs. After 100 min of treatment, the removal rate reached 38%. In the dark, the degradation trend of PAM by Zn0.8Ni0.2Fe2O4@BiOBr / PMS is as follows... Figure 7 As shown in Figure c, under 2 mM PMS conditions, ~64% of PAM was degraded within a 100-minute reaction time, achieving a remarkably high efficiency, which is evident in energy-saving water treatment. The calculated molar ratio of oxidant to PAM was 30.4, which ensured complete removal of PAM from the reactants produced by PMS decomposition. After UV-A treatment of Zn0.8Ni0.2Fe2O4@BiOBr / PMS for 100 minutes, PAM was completely removed. Figure 7As shown in Figure d, the constant for the rate of the Zn0.8Ni0.2Fe2O4@BiOBr / PMS / UV-A system is 0.03112 min⁻¹, which is 2.2 times and 5.1 times that of the system without UV-A and the system without PMS, respectively. Following the method studied previously, the synergy index was calculated to be 1.58 using the formula "synergy index = KUV / PMS / catalyst / (KUV / catalyst + KPMS / catalyst)". The enhanced catalytic activity of Zn0.8Ni0.2Fe2O4@BiOBr can be attributed to the uniform dispersion of Zn0.8Ni0.2Fe2O4 NPs on the BiOBr surface, forming an effective heterojunction with a large contact interface. This avoids the rapid recombination of these active sites, thus allowing for the separation of reduction and oxidation processes. A TOC removal rate of 66% was observed within a 100-minute reaction time, indicating that the carbon content in PAM was not completely mineralized. This demonstrates the possibility of complete mineralization of PAM using the previous degradation device, although complete mineralization, including the entire inactive species, would require a longer degradation time. It is worth noting that, under the same combined conditions, when the treated sample is pure paracetamol (p-PAM), the degradation time can be reduced to 60 minutes, and the rate constant is almost twice as long as before.
[0029] Figure 8 The effects of different catalyst dosages (a), PMS concentrations (b), and initial pH (c) on PAM degradation efficiency were investigated. Reaction conditions: 0.5 g / L catalyst, 2 mM PMS, initial pH 7. Figure 8 This study illustrates the effect of different Zn0.8Ni0.2Fe2O4@BiOBr dosages on PAM degradation after 100 min of treatment. Five different experiments were conducted using dosages ranging from 0.1 to 1 g / L, combined with 2 mM PMS and UV-A, with an initial PAM concentration of 10 mg / L. At a catalyst dosage of 0.1 g / L, the PAM concentration decreased by 60% after 100 min of reaction. The degradation rate of PAM increased with increasing catalyst dosage, reaching complete removal at 0.5 g / L, after which the removal rate decreased when the catalyst dosage exceeded 0.5 g / L. This behavior can be explained by the magnetic properties of the Zn0.8Ni0.2Fe2O4@BiOBr composite, exhibiting a clamping effect that leads to surface area loss and thus lower reactivity to PMS activation. Furthermore, light attenuation and scattering are non-negligible at high catalyst concentrations. According to our solution transmittance experiments, when using 0.5 g / L Zn0.8Ni0.2Fe2O4@BiOBr, the UV-A transmittance through the solution was 36%, while when using 0.8 g / L, the transmittance decreased by a factor of 2. Figure 8b shows the effect of different PMS concentrations on PAM degradation using 0.5 g / L Zn0.8Ni0.2Fe2O4@BiOBr and UV-A at an initial PAM concentration of 10 mg / L. Increasing the PMS concentration led to enhanced PAM degradation. For example, at 60 min, increasing the PMS concentration from 0.5 to 2 mM increased the PAM degradation rate from 60% to 93%. Further increasing the PMS concentration only increased the PAM removal rate by 6%. This soft increase is mainly due to the reaction between SO4•- and •OH radicals (Equation (1)), radical recombination (Equations (2) and (3)), or so-called scavenging. The effect of initial pH on PAM degradation is shown below. Figure 8 As shown in Figure c, the reaction rate constant is highest at pH 5, followed by acidic and neutral conditions, and lowest under alkaline conditions. The parent acid H₂SO₅ of KHSO₅ replaces HSO₅⁻ as the dominant substance at lower pH levels, thus limiting ROS formation. When the solution pH increases to alkaline, KHSO₅ gradually transforms into SO₅²⁻, which is less easily activated than HSO₅²⁻. Nevertheless, the reaction rate constant remains relatively stable at different pH values, indicating a certain degree of pH tolerance.
[0030] SO4•- + •OH → HSO4- + 1 / 2 O2 (1) SO4•- + SO4•- → S2O82- (2) •OH + •OH → H2O2 (3) Figure 9 XRD patterns of pristine and recycled Zn0.8Ni0.2Fe2O4@BiOBr (a) and the effects of different experimental periods (b), radical scavengers (c), and coexisting anions (d) on PAM degradation efficiency are shown in the inset (corresponding reaction rate constants). The reusability of the Zn0.8Ni0.2Fe2O4@BiOBr heterojunction was evaluated under the same initial conditions: 0.5 g / L regenerated Zn0.8Ni0.2Fe2O4@BiOBr, UV-A, 2 mM PMS, and 10 mg / L PAM concentration. XRD patterns of the recycled catalyst are shown below. Figure 9 As shown in figure a. No significant changes were observed compared to the original catalyst. Figure 9As shown in b, after 100 min of reaction, the PAM removal rate remained essentially unchanged from the 1st to the 5th cycle. In fact, the PAM removal rate only decreased slightly from ~100% in the first cycle to 90% in the fifth cycle. One possible explanation for the decrease in catalyst efficiency is the precipitation of ferrous ions leached from the ferrite surface, which reduces the number of active sites in consecutive cycles. Therefore, we analyzed the leaching of the catalyst from the water treatment solution. The results showed that the average ion leaching amount was less than 1 mg / L, supporting a negligible efficiency loss. All of the above results indicate that the prepared catalyst has good reusability. Previous studies have shown that SO4•- and SO5•- can be generated by chemically activating PMS in combination with cobalt and nickel iron ore (Equations (4-7)). •OH is also expected to be generated due to the reaction of sulfate radicals with the aqueous medium (Equations (8) and (9)). These radicals have effective oxidizing properties, leading to PAM degradation (Equation (10)).
[0031] M2+-OH- + HSO5- → M2+-(OH)OSO3- + OH- (4) M2+-(OH)OSO3- + OH- → M3+-OH- + SO4•- (5) M3+-OH- + HSO5- → M3+-•OOSO3- + H2O (6) M3+-•OOSO3- + H2O → M2+-OH- + SO5•- + H+ (7) SO4•- + H2O→ SO42- + •OH + H+ (8) SO4•- + OH- → SO42- + •OH (9) SO4•- / •OH + PAM → byproducts → CO2 + H2O (10) This invention establishes the pathway of PAM degradation using a chemical probe method. Therefore, MeOH, BQ, TBA, and KI were used as scavengers during the reaction to identify the types of free radicals. The results are as follows: Figure 9As shown in Figure c, both SO4•- and •OH radicals participated in the degradation process, although SO4•- activity appeared to be dominant. Two different alcohols, TBA and MeOH, were used to quench SO4•- and •OH radicals. Methanol containing α-hydrogen is commonly used to determine the total contribution of sulfate and hydroxyl radicals because the reaction rate constants have similar values. TBA without α-hydrogen showed much greater reactivity and a higher rate constant with •OH radicals. Without the addition of a quenching agent, PAM was removed by more than 90% within 100 min. The degradation rate decreased significantly after the addition of MeOH and TBA, with the decrease being more pronounced with MeOH. KI, a quencher for h+ and •OH, showed similar effectiveness to the quencher used for TBA, achieving a removal rate of nearly 80% within 100 minutes. Notably, this disabling effect can also be attributed to the reaction between KI and PMS. However, unexpected improvements were observed when p-benzoquinone (p-BQ) was added as an O2•- scavenger, even though the heterojunction's ECB was predominantly BiOBr (defined as -0.39), which reduced O2 to O2•-. p-BQ effectively decomposed PMS, with the decomposition rate increasing at pH 7–10. The reaction initially showed a high rate constant but did not reach complete degradation, indicating that PMS was consumed by the additional p-BQ. Based on these observations, it can be concluded that SO4•- is the major species involved in the degradation reaction. Figure 9 As shown in Figure d, under the same conditions, the effects of three coexisting anions (Cl-, HCO3-, and NO3-) on PAM degradation were investigated, with the inhibition effect being Cl->HCO3->NO3-. The presence of Cl- leads to the consumption of HSO5- to generate HOCl and Cl2 (Equations (11-13)). The inhibition can be attributed to the formation of weaker free radicals, such as chlorine radicals. HCO3- is generally considered a scavenger of •OH and SO4•- and generates CO3•- with a lower redox potential (E° = 1.78 V), thereby reducing the degradation rate (Equations (14) and (15)). On the other hand, NO3- has almost no effect on PAM degradation.
[0032] Cl- + HSO5- → SO42- + HClO (11) 2Cl- + HSO5- + H+ → SO42- + Cl2 + H2O (12) Cl- + SO4•- → Cl• + SO42- (13) HCO3- + SO4•- → SO42- + CO3•- + H+ (14) HCO3- + •OH → H2O + CO3•- (15) Figure 10This invention presents the proposed PAM degradation mechanism. The corresponding PAM degradation intermediates were identified by HPLC-MS at a reaction time of 30 min. At least eight intermediates were identified, and their m / z and structural formulas are included in the proposed degradation scheme. Based on the detected intermediates and intermediates published by other authors, two main degradation pathways were proposed. Detailed biotoxicity of intermediates similar to paracetamol oxidation has been investigated in previous studies. Notably, the •OH radical is more likely generated via addition or hydrogen extraction. Based on our scavenger experiments and the absence of intermediates generated by ortho, meta, or para hydroxylation of the PAM aromatic ring, we believe that SO4•- first reacts with water to oxidize PAM, generating a p-aminophenol radical and acetic acid. This radical is readily oxidized to p-aminophenol (m / z 109), resulting in two distinct degradation pathways. On one hand, SO4•- oxidizes p-aminophenol to p-nitrophenol (m / z 140), and then SO4•- reacts with H2O to generate NO2• elimination, yielding hydroquinone (m / z 110). Benzoquinone (m / z 108) is generated by SO4•- extraction of hydroxyl groups, ultimately yielding a mixture of dicarboxylic acids after ring-opening reaction. Conversely, the CN bond of the p-aminophenol benzene ring is directly attacked by SO4•-, undergoing a hydroxyl addition reaction with H2O to generate hydroxyp-aminophenol (m / z 125). SO4•- oxidizes the amino group to a nitro group (m / z 155), and the attack by SO4•- and the addition reaction with H2O lead to the elimination of NO2•, ultimately generating 1,2,4-trihydroxybenzene (m / z 126). Hydroxyl groups are extracted via SO4•- and ring-opening reactions, yielding a mixture of dicarboxylic acids.
[0033] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A semiconductor heterojunction photocatalyst enhanced for PMS activation, characterized by: The catalyst is represented by the chemical formula ZnxNi1-xFe2O4@BiOBr, and the catalyst is prepared by a two-step hydrothermal method.
2. The preparation method of the semiconductor heterojunction photocatalyst activated by PMS according to claim 1, characterized in that: 2.
1. ZnxNi1-xFe2O4 nanoparticles (NPs) are prepared by a hydrothermal method, wherein x is 0, 0.2, 0.5, 0.8 and 1.0, and the preparation is carried out by the following steps: 2.1.
1. Stoichiometric amounts of corresponding transition metal nitrates are dissolved in deionized water respectively; 2.1.
2. After mixing, the pH is adjusted to 10 by adding 1M NH4OH dropwise to form a brown gel; 2.1.
3. The obtained gel is filtered and sealed in a stainless steel reactor with a polytetrafluoroethylene liner, and treated at 180℃ for 12h; 2.1.
4. The obtained powder is washed with ethanol and dried at 50℃ for 12h; 2.
2. ZnxNi1-xFe2O4@BiOBr is prepared by a second hydrothermal method by the following steps: 2.2.
1. Stoichiometric amounts of Bi(NO3)3·5H2O and KBr are dissolved in 30mL deionized water, and ultrasonic treatment is performed for 5min to form a suspension; 2.2.
2. ZnxNi1-xFe2O4 NPs are dispersed in the above suspension and ultrasonic treatment is performed again for 30min; 2.2.
3. After continuing to stir vigorously for 60min, the second hydrothermal treatment is started, with a temperature of 140℃ for 15h; 2.2.
4. The obtained catalyst is filtered, washed with ethanol, and dried at 50℃ for 12h.
3. The method for preparing a semiconductor heterojunction photocatalyst for enhancing PMS activation according to claim 2, characterized in that: The molar ratio of ZnxNi1-xFe2O4 NPs to BiOBr is 0.
15.
4. The method for preparing a semiconductor heterojunction photocatalyst with enhanced PMS activation according to claim 2-3, characterized in that: During the preparation of the heterojunction photocatalyst, the combination of Zn0.8Ni0.2Fe2O4 and BiOBr shows the best catalytic degradation performance.
5. The method of treating organic pollutants in real water samples using a PMS-activated semiconductor heterojunction photocatalyst according to claims 1-3, characterized in that: The method can effectively remove paracetamol (PAM) and other non-active substances in water.
6. A method of activating PMS for degrading organic pollutants in water by a semiconductor heterojunction photocatalyst activated PMS according to claims 1-4, characterized in that: Under the conditions of 0.5g / L Zn0.8Ni0.2Fe2O4@BiOBr, 2mM PMS, 10mg / L PAM, UV-A radiation, and pH=7, complete removal of PAM is achieved; PMS and catalyst are added to a solution containing organic pollutants, and the reaction is maintained for a certain period of time to degrade the organic pollutants.
7. The method for activating PMS to degrade organic pollutants in water according to claim 6, characterized in that: The organic pollutant solution is a 50mL PAM solution with an initial concentration of 10mg / L; The amount of catalyst used is 0.1 to 1g / L; The amount of PMS used is 2mM; The initial pH value of the reaction system is 7±0.2; The temperature of the reaction system is 25±0.5℃; The reaction system is stirred using a magnetic stirrer at a stirring speed of 300rpm.
8. The method of Claim 1, wherein the semiconductor heterojunction photocatalyst is a PMS-activated semiconductor heterojunction photocatalyst. After being used for five times in succession, the activity and structure of the catalyst remain stable after being treated by filtration, washing and drying.