Preparation of CoWO4 modified Nb2O5p-n heterojunction Nb2O5 / CoWO4 photocatalyst powder

Abstract

The invention discloses a preparation method of CoWO (cobalt tungsten oxide) modified NbOp-n heterojunction NbO5 / CoWO photocatalyst powder. The preparation method comprises the following steps: dissolving cobalt salt and tungsten salt in deionized water, stirring and mixing, carrying out hydrothermal reaction in an autoclave, washing and drying to obtain CoWO powder; the preparation method comprises the following steps: dissolving niobium oxalate and ammonium carbonate in deionized water, adding CoWO powder, carrying out a hydrothermal reaction in an autoclave, and carrying out washing and drying treatment to prepare NbO / CoWO photocatalyst powder. According to the method, the hydrothermal reaction temperature is regulated and controlled, and the mass ratio of raw materials is optimized, so that the catalyst forms a p-n heterojunction structure of NbOmicron flower loaded CoWOnano particles. The prepared catalyst has high norfloxacin wastewater degradation efficiency under visible light irradiation, has the advantages of simple preparation process, low reagent cost, high catalytic activity and good structural stability, and can be effectively applied to purification treatment of antibiotic polluted water.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic material preparation and antibiotic wastewater treatment technology, specifically involving a method for preparing CoWO4-modified Nb2O5 p-n heterojunction photocatalyst powder. This catalyst can be efficiently applied to the degradation treatment of norfloxacin antibiotic wastewater under visible light, belonging to the interdisciplinary technical field of environmental functional materials and water pollution control. Background Technology

[0002] The rapid development of industrial and pharmaceutical technologies has led to a significant increase in environmental pollution, posing a critical challenge to the sustainable development of human civilization. Aquatic ecosystems are particularly vulnerable to various organic pollutants, which pose a serious threat to human health and the integrity of ecosystems. Among these pollutants, antibiotics deserve particular attention. However, over time, the overuse and improper management of antibiotics have caused serious environmental and health problems. Faced with the severe situation of antibiotic pollution, a large number of studies have been conducted globally to reveal the environmental behavior, ecological risks, and impacts of antibiotics on human health.

[0003] Based on differences in their mechanisms of action and treatment principles, existing antibiotic removal technologies can be divided into three main categories: physical treatment technologies based on processes such as adsorption; biodegradation methods utilizing microbial metabolism; and chemical treatment processes relying on redox reactions. The advantage of adsorption is that it does not produce more toxic or recalcitrant pollutants during the treatment process, thus avoiding secondary pollution to the environment. However, the adsorbed solids themselves become a new pollutant and require proper treatment. Furthermore, adsorption methods also have disadvantages such as high cost and non-reusability. Biological treatment requires a long hydraulic retention time, which limits its treatment efficiency to some extent; for some recalcitrant organic pollutants, its removal rate often exhibits significant fluctuations, making it difficult to guarantee treatment effectiveness; the microbial communities involved in the degradation process are extremely sensitive to environmental conditions, and even small changes in parameters such as pH, temperature, and dissolved oxygen can lead to a significant decline in system performance. Chemical treatment may generate a series of byproducts, which may cause secondary pollution to the environment; chemical treatment of antibiotics usually requires the use of large amounts of chemical reagents, which themselves may be harmful to the environment. Summary of the Invention

[0004] To address the problems of low light utilization and poor carrier separation efficiency of existing photocatalysts, this invention proposes to construct Nb2O5 / CoWO4p-n heterojunctions via a hydrothermal method, utilize the narrow bandgap characteristics of CoWO4 to extend the visible light response range, and enhance carrier separation through interfacial electronic interactions, thereby improving the degradation efficiency of norfloxacin.

[0005] The preparation of a CoWO4-modified Nb2O5 p-n heterojunction Nb2O5 / CoWO4 photocatalyst powder includes the following steps: Preparation of CoWO4 powder: Cobalt salt and tungsten salt were dissolved in deionized water, stirred and mixed, and then subjected to a hydrothermal reaction. After washing and drying, CoWO4 powder was obtained. Preparation of Nb2O5 / CoWO4 composite material: Niobium oxalate and ammonium carbonate were dissolved in deionized water, and CoWO4 powder was added and subjected to hydrothermal reaction. After washing and drying, Nb2O5 / CoWO4 photocatalyst powder was obtained.

[0006] Preferably, the cobalt salt in step (1) is Co(NO3)2・6H2O; and the tungsten salt is Na2WO4・2H2O. Co(NO3)2・6H2O provides Co²⁺, whose nitrate is easily dissociated under hydrothermal conditions, and NO3⁻ does not introduce impurity ions; Na2WO4・2H2O provides WO4²⁻, and its 2:1 stoichiometric ratio matches the theoretical composition of CoWO4, ensuring that Co²⁺ and WO4²⁻ react completely.

[0007] Preferably, the surfactant cetyltrimethylammonium bromide (CTAB) is added during the stirring and mixing step (1) to regulate the dispersibility and morphology of the CoWO4 nanoparticles. Cetyltrimethylammonium bromide (CTAB) induces the growth of CoWO4 along the crystal plane through electrostatic interaction, increasing the exposure of active sites.

[0008] Preferably, the surfactant is added by the following steps: a. dissolving the cobalt salt in deionized water and stirring for 15-25 minutes; b. dissolving the tungsten salt in deionized water and stirring for 15-25 minutes; c. mixing the solutions obtained in steps a and b, adding the surfactant, and continuing to stir for 25-35 minutes until a homogeneous solution is obtained. Dissolving the cobalt and tungsten salts separately first avoids direct mixing leading to localized supersaturation, and then adding the surfactant to regulate the nucleation rate.

[0009] Preferably, in step (1), the hydrothermal reaction of the CoWO4 powder is carried out in an autoclave with a filling degree of 60%-80%. Gradient heating is used, with the temperature increased from room temperature to 130-150℃ at a rate of 5-10℃ / min, held for 6-10 hours, and then cooled to room temperature at a rate of 3-5℃ / min to optimize crystal growth orientation. After the reaction, the purple precipitate is collected. Slow heating allows Co²⁺ and WO4²⁻ to fully complex and form a uniform precursor; the holding stage promotes crystal nucleus formation and growth, and the gradient temperature avoids crystal defects caused by sudden temperature changes; slow cooling allows the crystal to grow orderly along specific crystal planes and optimizes the crystal orientation.

[0010] Preferably, in step (1), the CoWO4 powder is washed with alternating ethanol and deionized water 2-4 times, with ultrasonic oscillation at a frequency of 30-50 kHz for 5-10 min during washing to enhance impurity removal efficiency and particle dispersibility. For drying, a vacuum oven is used with a temperature setting of 60-90℃, a vacuum degree ≤0.08 MPa, and a drying time of 10-14 h. After drying the CoWO4 powder, the temperature is increased to 300-400℃ at a rate of 2-5℃ / min and held for 1-2 h to allow the surfactant to completely decompose and volatilize. Ultrasonic washing disrupts the van der Waals forces between particles, and combined with alternating ethanol and water washing, effectively removes impurities such as Na⁺ and NO⁻ adsorbed on the surface. A vacuum degree of ≤0.08 MPa lowers the boiling point of water, and a low temperature of 70-90℃ prevents particle sintering. The 300-400℃ temperature decomposes the surfactant and simultaneously repairs lattice defects during the hydrothermal process.

[0011] Preferably, the addition amount of CoWO4 powder and niobium oxalate in step (2) meets the mass ratio of 1:5-1:20, and the mass percentage of CoWO4 in the generated Nb2O5 / CoWO4 composite material is 5%-25%. When added to the niobium oxalate-ammonium carbonate mixed aqueous solution, it needs to be added slowly in 2-3 times and stirred continuously to prevent agglomeration.

[0012] Preferably, in step (2), the hydrothermal reaction of the Nb2O5 / CoWO4 composite material is carried out in a polytetrafluoroethylene-lined high-pressure reactor with a filling degree of 60%-80%, a temperature setting of 180-220℃, and a reaction time of 20-30h. During the reaction, constant temperature stirring is maintained at a speed of 50-100rpm. A magnetic field is applied during the reaction, with the magnetic field direction coaxial or perpendicular to the stirring shaft, and a magnetic field strength of 0.1-0.5T. The magnetic field is an alternating magnetic field with a frequency of 1-100Hz. The magnetic field-shear force synergy inhibits particle agglomeration and optimizes the heterojunction interface, thereby promoting uniform loading of CoWO4 nanoparticles on the Nb2O5 surface. The alternating magnetic field drives the directional migration of CoWO4 nanoparticles through magnetophoresis, while the magnetic field-shear force synergy inhibits local concentration unevenness caused by solution convection, thus improving the uniformity of the loading.

[0013] Preferably, in step (2), the Nb2O5 / CoWO4 composite material is washed 2-4 times alternately with ethanol and deionized water at a volume ratio of 1:2. For drying, a vacuum oven is used at a temperature of 50-70℃, a vacuum degree ≤0.06MPa, and a drying time of 10-14h. The resulting Nb2O5 / CoWO4 composite material is then annealed in a nitrogen atmosphere at a rate of 5-10℃ / min to 300-400℃, and held for 2-4h to remove residual organic matter and optimize the heterojunction interface. Alternating washing with ethanol and deionized water dissolves organic impurities and prevents particle aggregation due to sudden changes in solvent polarity. Low-temperature vacuum drying prevents the collapse of the hydrothermally synthesized Nb2O5 nanosheet structure. At 300-400℃, the nitrogen atmosphere prevents Nb2O5 reduction and promotes interfacial atomic diffusion to form Nb-O-Co bonds.

[0014] Preferably, the prepared Nb2O5 / CoWO4 photocatalyst powder can be used for photocatalytic degradation of norfloxacin in wastewater. When the photocatalyst powder is added to norfloxacin wastewater and reacted under visible light irradiation for 60-120 minutes, the degradation efficiency of norfloxacin can reach more than 80%.

[0015] In summary, the present invention has the following beneficial effects: The process is simple and low-cost: it is synthesized in one step by hydrothermal method, without the need for complicated equipment or high-temperature calcination. The reagents only need conventional chemicals such as cobalt salt, tungsten salt, and niobium oxalate. The synthesis conditions are mild and the process flow is short, making it suitable for large-scale production.

[0016] Process synergistic regulation and optimization: A multi-parameter synergistic process of surfactant regulation + magnetic field assistance + gradient temperature control is used to achieve uniform "core-shell" loading of CoWO4 nanoparticles on the surface of Nb2O5 micron flowers, thereby increasing the interfacial contact area.

[0017] Performance enhancement mechanism: The dual effect of the built-in electric field of the heterojunction and the interfacial chemical bonds improves the separation efficiency of photogenerated carriers and increases the reaction rate of norfloxacin degradation. Attached Figure Description

[0018] Figure 1 SEM images and EDS element-mapped images (d) of CoWO4 (a), Nb2O5 (b), and NCW-8 (c); Figure 2 XRD diffraction patterns of Nb2O5, CoWO4, NCW-8(a) and NCW-4, 8, 12, 16(b); Figure 3X-ray photoelectron spectra of Nb₂O₅, CoWO₄, and NCW-8: full spectrum (a); C 1s (b); O 1s (c); Nb 3d (d); W 4F (e); Co 2p (f); Figure 4 The instantaneous photocurrent response (a) and impedance diagram (b) of CoWO4, Nb2O5 and NCW-8 are shown. Figure 5 The diagram illustrates the effects of different catalysts on the degradation of NOR (a) and the degradation rate constant (b). Detailed Implementation

[0019] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

[0020] Example 1

[0021] 0.15 g of Co(NO3)2·6H2O and 0.16 g of Na2WO4·2H2O were added to 20 mL of deionized water and stirred for 20 min. Then, the two solutions were mixed, and 0.03 g of hexadecyltrimethylammonium bromide (CTAB) was added and stirred further for 30 min until a homogeneous solution was obtained. The mixed solution was heated to 140 °C at a rate of 5 °C / min and held for 8 h in an autoclave, then cooled to room temperature at a rate of 3 °C / min. After the reaction was complete, the formed purple precipitate was collected and washed three times alternately with ethanol and water to remove impurities, each time with ultrasonic agitation for 8 min. The washed sample was placed in a vacuum oven at 0.06 MPa and dried at 80 °C for 12 h. The dried CoWO4 powder was then further dried at 350 °C for 1 h to obtain CoWO4 powder.

[0022] Weigh out 10.5 mmol of niobium oxalate (C 10 H5NbO 20) and 7.5 mmol of ammonium carbonate ((NH4)2CO3) were added to 30 ml of deionized water and mixed. After mixing evenly, 0.04 g of CoWO4 was slowly added and the mixture was stirred for 30 min. The mixture was then transferred to a 50 ml polytetrafluoroethylene-lined high-pressure reactor. The reactor was placed in the center of an electromagnetic coil and a 2 A current was applied. The temperature was raised to 200 °C and maintained at this temperature for 24 h. During this period, the current direction was switched every 2 h. The mixture was then allowed to cool naturally to room temperature. After the reaction was completed, the precipitate was collected and washed three times with alternating ethanol and water to remove impurities. The washed sample was placed in a vacuum oven with a vacuum degree of 0.04 MPa and dried at 60 °C for 12 h. The dried sample was then heated to 350 °C in a nitrogen atmosphere and held for 2 h to obtain the Nb2O5 / CoWO4 composite material, abbreviated as NCW-4.

[0023] Example 2

[0024] 0.15 g of Co(NO3)2·6H2O and 0.16 g of Na2WO4·2H2O were added to 20 mL of deionized water and stirred for 20 min. Then, the two solutions were mixed, and 0.03 g of hexadecyltrimethylammonium bromide (CTAB) was added and stirred further for 30 min until a homogeneous solution was obtained. The mixed solution was heated to 140 °C at a rate of 5 °C / min and held for 8 h in an autoclave, then cooled to room temperature at a rate of 3 °C / min. After the reaction was complete, the formed purple precipitate was collected and washed three times alternately with ethanol and water to remove impurities, each time with ultrasonic agitation for 8 min. The washed sample was placed in a vacuum oven at 0.06 MPa and dried at 80 °C for 12 h. The dried CoWO4 powder was then further dried at 350 °C for 1 h to obtain CoWO4 powder.

[0025] Weigh out 10.5 mmol of niobium oxalate (C 10 H5NbO 20) and 7.5 mmol of ammonium carbonate ((NH4)2CO3) were added to 30 ml of deionized water and mixed. After mixing evenly, 0.08 g of CoWO4 was slowly added and the mixture was stirred for 30 min. The mixture was then transferred to a 50 ml polytetrafluoroethylene-lined high-pressure reactor. The reactor was placed in the center of an electromagnetic coil and a 2 A current was applied. The temperature was raised to 200 °C and maintained at this temperature for 24 h. During this period, the current direction was switched every 2 h. The mixture was then allowed to cool naturally to room temperature. After the reaction was completed, the precipitate was collected and washed three times with alternating ethanol and water to remove impurities. The washed sample was placed in a vacuum oven with a vacuum degree of 0.04 MPa and dried at 60 °C for 12 h. The dried sample was then heated to 350 °C in a nitrogen atmosphere and held for 2 h to obtain the Nb2O5 / CoWO4 composite material, abbreviated as NCW-8.

[0026] Example 3

[0027] 0.15 g of Co(NO3)2·6H2O and 0.16 g of Na2WO4·2H2O were added to 20 mL of deionized water and stirred for 20 min. Then, the two solutions were mixed, and 0.03 g of hexadecyltrimethylammonium bromide (CTAB) was added and stirred further for 30 min until a homogeneous solution was obtained. The mixed solution was heated to 140 °C at a rate of 5 °C / min and held for 8 h in an autoclave, then cooled to room temperature at a rate of 3 °C / min. After the reaction was complete, the formed purple precipitate was collected and washed three times alternately with ethanol and water to remove impurities, each time with ultrasonic agitation for 8 min. The washed sample was placed in a vacuum oven at 0.06 MPa and dried at 80 °C for 12 h. The dried CoWO4 powder was then further dried at 350 °C for 1 h to obtain CoWO4 powder.

[0028] Weigh out 10.5 mmol of niobium oxalate (C 10 H5NbO 20) and 7.5 mmol of ammonium carbonate ((NH4)2CO3) were added to 30 ml of deionized water and mixed. After mixing evenly, 0.012 g of CoWO4 was slowly added and the mixture was stirred for 30 min. The mixture was then transferred to a 50 ml polytetrafluoroethylene-lined high-pressure reactor. The reactor was placed in the center of an electromagnetic coil and a 2 A current was applied. The temperature was raised to 200 °C and maintained at this temperature for 24 h. During this period, the current direction was switched every 2 h. The mixture was then allowed to cool naturally to room temperature. After the reaction was completed, the precipitate was collected and washed three times with alternating ethanol and water to remove impurities. The washed sample was placed in a vacuum oven with a vacuum degree of 0.04 MPa and dried at 60 °C for 12 h. The dried sample was then heated to 350 °C in a nitrogen atmosphere and kept at this temperature for 2 h. The resulting Nb2O5 / CoWO4 composite material was abbreviated as NCW-12.

[0029] Example 4

[0030] 0.15 g of Co(NO3)2·6H2O and 0.16 g of Na2WO4·2H2O were added to 20 mL of deionized water and stirred for 20 min. Then, the two solutions were mixed, and 0.03 g of hexadecyltrimethylammonium bromide (CTAB) was added and stirred further for 30 min until a homogeneous solution was obtained. The mixed solution was heated to 140 °C at a rate of 5 °C / min and held for 8 h in an autoclave, then cooled to room temperature at a rate of 3 °C / min. After the reaction was complete, the formed purple precipitate was collected and washed three times alternately with ethanol and water to remove impurities, each time with ultrasonic agitation for 8 min. The washed sample was placed in a vacuum oven at 0.06 MPa and dried at 80 °C for 12 h. The dried CoWO4 powder was then further dried at 350 °C for 1 h to obtain CoWO4 powder.

[0031] Weigh out 10.5 mmol of niobium oxalate (C 10 H5NbO 20) and 7.5 mmol of ammonium carbonate ((NH4)2CO3) were added to 30 ml of deionized water and mixed. After mixing evenly, 0.016 g of CoWO4 was slowly added and the mixture was stirred for 30 min. The mixture was then transferred to a 50 ml polytetrafluoroethylene-lined high-pressure reactor. The reactor was placed in the center of an electromagnetic coil and a 2 A current was applied. The temperature was raised to 200 °C and maintained at this temperature for 24 h. During this period, the current direction was switched every 2 h. The mixture was then allowed to cool naturally to room temperature. After the reaction was completed, the precipitate was collected and washed three times with alternating ethanol and water to remove impurities. The washed sample was placed in a vacuum oven with a vacuum degree of 0.04 MPa and dried at 60 °C for 12 h. The dried sample was then heated to 350 °C in a nitrogen atmosphere and held for 2 h. The resulting Nb2O5 / CoWO4 composite material was abbreviated as NCW-16.

[0032] The morphology of the prepared photocatalyst samples was analyzed using scanning electron microscopy (SEM); EDS mapping analysis was performed on NCW-8.

[0033] The microstructures of Nb2O5, CoWO4, and NCW-8 are as follows: Figure 1 As shown. Figure 1 In a, pure CoWO4 consists of irregular nanoparticles and exhibits good crystallinity. Figure 1 In b, Nb2O5 can be clearly observed to have a flower-like morphology with uniform size, composed of nanosheets. Figure 1 In c, in the NCW-8 nanocomposite material, the Nb2O5 microflora structure is covered by CoWO4 nanoparticles, a phenomenon mainly caused by the in-situ growth mechanism.

[0034] In addition, EDS mapping analysis was performed to explore the elemental distribution of NCW-8. Figure 1 d. The elements W, C, Nb and Co are uniformly distributed on the NCW-8 surface, which is consistent with the results of X-ray photoelectron spectroscopy.

[0035] The phase and crystal structure of the synthesized Nb2O5, CoWO4 and NCW-4, 8, 12, 16 composite materials were analyzed by X-ray powder diffraction (XRD).

[0036] See Figure 2The diffraction peaks of the pure Nb₂O₅ sample at 2θ = 24.8°, 29.9°, 32°, 38.9°, and 52.6° correspond to the (121), (324), (314), (518), and (1119) crystal planes of Nb₂O₅ (JCPDS#19-0862), respectively. The XRD pattern of the pure CoWO₄ sample is also consistent with that of (JCPDS#15-0867). These results indicate that Nb₂O₅ and CoWO₄ without any impurities were successfully prepared. The spectra of NCW-4, 8, 12, and 16 samples are similar to those of the original Nb₂O₅, confirming that the crystal structure of Nb₂O₅ did not change during the combination of CoWO₄ and Nb₂O₅. A new characteristic peak at 35.6° was also found in the spectra, which showed a good correspondence with the (200) peak of CoWO₄. Furthermore, the absence of impurity diffraction peaks further demonstrates the good purity of the samples. These results confirm the successful synthesis of the NCW-4, 8, 12, and 16 composite materials.

[0037] The elemental composition and valence states of the NCW-8 sample were analyzed in detail using X-ray photoelectron spectroscopy (XPS).

[0038] Figure 3 The full spectrum shows that the NCW-8 sample contains five elements: C, O, Nb, W, and Co. The absence of additional impurity elements demonstrates the good purity of the NCW-8 heterostructure, which is consistent with the EDS results. The C 1s peak was corrected to 284.8 eV. Figure 3 b) Correct the XPS spectra of the sample. For the NCW-8 sample, such as... Figure 3 As shown in Figure c, the obtained O 1s spectrum exhibits two distinct peaks at 530.93 and 530.14 eV, corresponding to the characteristic binding energies of the Co-O and Nb-O bonds, respectively. From... Figure 3 As can be seen, the W4f spectrum can be fitted with a curve to obtain two peaks at 37.92 eV and 35.77 eV, corresponding to W4f respectively. 5 / 2 and W 4f 7 / 2 The Co 2p spectrum shows 780.85 eV (Co 2p 3 / 2 ) and 796.99eV (Co 2p 1 / 2 Two strong peaks. The peaks at 780.85 and 796.99 eV belong to Co. 3+ The peaks at 782.41 and 798.54 eV belong to Co. 2+ Co 2p 3 / 2 and W 4f 7 / 2 The presence of the double peaks confirms the formation of the CoWO4 phase. (Nb 3d spectrum) Figure 3 d) at 207.42 eV (Nb 3d 1 / 2) and 210.16eV (Nb3d 3 / 2 The presence of two peaks at () indicates that the niobium in the NCW-8 sample is in the +5 oxidation state. Furthermore, compared to pure CoWO4 and Nb2O5, the Nb 3d peak in NCW-8 shifts slightly towards higher binding energies, while the Co 2p peak shifts slightly towards lower binding energies, indicating an electronic interaction between Nb2O5 and CoWO4.

[0039] Photocatalysis (PC) and electrochemical impedance spectroscopy (EIS) Transient photocurrent testing is widely used to evaluate photogenerated electrons (e) in catalysts. - ) and holes (h + The separation efficiency of charge carriers is determined by AC impedance spectroscopy. AC impedance spectroscopy can reveal more deeply the migration resistance of charge carriers within the catalyst.

[0040] The magnitude of photocurrent density directly reflects the carrier separation efficiency per unit area; that is, the higher the photocurrent density, the higher the carrier separation efficiency. Figure 4 As can be seen from the results, under xenon lamp irradiation and without applied bias voltage, the order of photocurrent density of the tested catalyst samples is: NCW-8 > Nb2O5 > CoWO4. This indicates that NCW-8 has the highest carrier separation efficiency, consistent with the results of photoluminescence testing, further verifying the positive effect of composite CoWO4 on improving photocatalytic performance.

[0041] Figure 4 Figure b shows a typical Nyquist plot, which reveals the characteristics of electron transfer behavior between the electrode and the electrolyte solution. In the Nyquist plot, the length of the semicircular arc is inversely proportional to the rate of electron transfer at the interface. Therefore, based on the semicircular arc of the Nyquist plot, the order of electron transfer rates at the catalyst sample interface can be deduced as: NCW-8 > Nb2O5 > CoWO. 4。

[0042] Degradation experiment The effects of CoWO4, Nb2O5, and NCW-4, 8, 12, and 16 series catalysts on the degradation activity of norfloxacin (NOR) under visible light irradiation were compared, and the results are as follows: Figure 5 As shown.

[0043] from Figure 5As shown in Figure a, the degradation effect of light irradiation alone on NOR concentration is negligible, indicating that NOR has strong photostability. Meanwhile, CoWO4 exhibits poor degradation efficiency for NOR, while Nb2O5's degradation efficiency is only 57.7%, due to the low light utilization of CoWO4 and Nb2O5, resulting in lower NOR degradation efficiency. However, under the same conditions, the photocatalytic degradation efficiency of NOR by heterojunctions NCW-4, NCW-8, NCW-12, and NCW-16 is significantly higher than that of CoWO4 and Nb2O5 alone. Among them, NCW-8 shows the best photocatalytic performance for NOR, achieving a degradation efficiency of 83.4% after 90 minutes of irradiation. To comprehensively evaluate the catalytic activity of the materials, a pseudo-first-order kinetic model ((-ln(C)) was adopted. t The reaction rate was fitted and calculated using the formula / C0)=kt)), and the results are as follows: Figure 5 As shown in figure b, the k value of NCW-8 is the largest (0.01958 min). -1 This result is consistent with the optical property characterization of the material, indicating that the photocatalytic reaction rate is fastest at this catalyst dosage.

[0044] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for preparing a CoWO4-modified Nb2O5 p-n heterojunction (Nb2O5 / CoWO4) photocatalyst powder, characterized in that, Includes the following steps: Preparation of CoWO4 powder: Cobalt salt and tungsten salt were dissolved in deionized water, stirred and mixed, and then subjected to a hydrothermal reaction. After washing and drying, CoWO4 powder was obtained. Preparation of Nb2O5 / CoWO4 composite material: Niobium oxalate and ammonium carbonate were dissolved in deionized water, and CoWO4 powder was added and subjected to hydrothermal reaction. After washing and drying, Nb2O5 / CoWO4 photocatalyst powder was obtained.

2. The preparation of a CoWO4-modified Nb2O5 p-n heterojunction Nb2O5 / CoWO4 photocatalyst powder according to claim 1, characterized in that, The cobalt salt in step (1) is Co(NO3)2·6H2O; the tungsten salt is Na2WO4·2H2O.

3. The preparation of a CoWO4-modified Nb2O5 p-n heterojunction Nb2O5 / CoWO4 photocatalyst powder according to claim 1, characterized in that... In step (1), the surfactant cetyltrimethylammonium bromide (CTAB) is added to regulate the dispersibility and morphology of CoWO4 nanoparticles.

4. The preparation of a CoWO4-modified Nb2O5 p-n heterojunction Nb2O5 / CoWO4 photocatalyst powder according to claim 3, characterized in that... The method of adding the surfactant includes the following steps: a. Dissolving the cobalt salt in deionized water and stirring for 15-25 minutes; b. Dissolving the tungsten salt in deionized water and stirring for 15-25 minutes; c. Mixing the solutions obtained in steps a and b, adding the surfactant, and continuing to stir for 25-35 minutes until a homogeneous solution is obtained.

5. The preparation of a CoWO4-modified Nb2O5 p-n heterojunction Nb2O5 / CoWO4 photocatalyst powder according to claim 1, characterized in that... In step (1), the hydrothermal reaction of the CoWO4 powder was carried out in a high-pressure reactor with a filling degree of 60%-80%. Gradient heating was used to raise the temperature from room temperature to 130-150℃ at a rate of 5-10℃ / min. After holding at this temperature for 6-10 hours, the temperature was lowered to room temperature at a rate of 3-5℃ / min to optimize the crystal growth orientation. After the reaction was completed, the purple precipitate was collected.

6. The preparation of a CoWO4-modified Nb2O5 p-n heterojunction Nb2O5 / CoWO4 photocatalyst powder according to claim 1, characterized in that... The washing of the CoWO4 powder in step (1) involves alternating washing with ethanol and deionized water 2-4 times, followed by ultrasonic oscillation at a frequency of 30-50kHz for 5-10 minutes to enhance impurity removal efficiency and particle dispersibility. The drying process uses a vacuum oven with a temperature setting of 70-90℃, a vacuum degree of ≤0.08MPa, and a drying time of 10-14h. After the CoWO4 powder is dried, the temperature is increased to 300-400℃ at a rate of 2-5℃ / min and held for 1-2 hours to allow the surfactant to completely decompose and volatilize.

7. The preparation of a CoWO4-modified Nb2O5 p-n heterojunction Nb2O5 / CoWO4 photocatalyst powder according to claim 1, characterized in that... In step (2), the amount of CoWO4 powder added to niobium oxalate is 1:5-1:20 by mass, and the mass percentage of CoWO4 in the resulting Nb2O5 / CoWO4 composite material is 5%-25%. When added to the niobium oxalate-ammonium carbonate mixed aqueous solution, it needs to be added slowly in 2-3 times with continuous stirring to prevent agglomeration.

8. The preparation of a CoWO4-modified Nb2O5 p-n heterojunction Nb2O5 / CoWO4 photocatalyst powder according to claim 1, characterized in that... The hydrothermal reaction of the Nb2O5 / CoWO4 composite material in step (2) is carried out in a polytetrafluoroethylene-lined high-pressure reactor with a filling degree of 60%-80%, a temperature setting of 180-220℃, and a reaction time of 20-30h. During the reaction, constant temperature stirring is maintained at a speed of 50-100rpm. A magnetic field is applied during the reaction to assist the reaction. The direction of the magnetic field is coaxial or perpendicular to the stirring shaft, and the magnetic field strength is 0.1-0.5T. The magnetic field is an alternating magnetic field with a frequency of 1-100Hz. The magnetic field-shear force synergistic effect inhibits particle agglomeration and optimizes the heterojunction interface to promote the uniform loading of CoWO4 nanoparticles on the Nb2O5 surface.

9. The preparation of a CoWO4-modified Nb2O5 p-n heterojunction Nb2O5 / CoWO4 photocatalyst powder according to claim 1, characterized in that... The Nb2O5 / CoWO4 composite material in step (2) is washed with ethanol and deionized water at a volume ratio of 1:2, alternating 2-4 times. The drying is carried out in a vacuum oven at a temperature of 50-70℃ and a vacuum degree of ≤0.06MPa for 10-14h. The obtained Nb2O5 / CoWO4 composite material is then annealed in a nitrogen atmosphere at a rate of 5-10℃ / min to 300-400℃ and held for 2-4h to remove residual organic matter and optimize the heterojunction interface.

10. The preparation of a CoWO4-modified Nb2O5 p-n heterojunction (Nb2O5 / CoWO4) photocatalyst powder according to claim 1, characterized in that... The prepared Nb2O5 / CoWO4 photocatalyst powder can be used for photocatalytic degradation of norfloxacin in wastewater. When the photocatalyst powder is added to norfloxacin wastewater and reacted under visible light for 60-120 minutes, the degradation efficiency of norfloxacin can reach more than 80%.

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