Bismuth-rich bismuth oxyiodide heterojunction photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a bismuth-rich bismuth oxyiodide heterojunction photocatalyst as well as a preparation method and application thereof. The bismuth-rich bismuth oxyiodide heterojunction photocatalyst is formed by stacking bismuth-rich Bi4O5I2 nanosheets and Bi7O9I3 nanosheets layer by layer. The preparation method comprises the following steps: mixing bismuth nitrate pentahydrate with potassium iodide, adjusting the pH value of the solution to form a precursor, and calcining the precursor to obtain the bismuth-rich bismuth oxyiodide heterojunction photocatalyst. The bismuth-rich bismuth oxyiodide heterojunction photocatalyst has the advantages of being high in light absorption capacity, low in lattice mismatch degree, high in photo-induced electron-hole separation efficiency, high in photocatalytic oxidation capacity and the like, the preparation method has the advantages of being low in raw material cost, simple and convenient in synthesis process, easy in condition control, short in consumed time and the like, the continuous batch production potential is high, and industrial utilization is facilitated. The bismuth-rich bismuth oxyiodide heterojunction photocatalyst can be used for degrading antibiotics in wastewater, has the advantages of simple application method, high degradation efficiency and good reusability, and has a good practical application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental catalysis and wastewater treatment, and in particular, relates to a bismuth-rich iodine bismuth oxide heterojunction photocatalyst and a preparation method and application thereof. Background Art

[0002] Photocatalytic technology is considered to be a promising method for removing antibiotics due to its environmental friendliness, economic feasibility, high oxidation activity, and simple operation. Designing catalysts with high visible light activity is the core of photocatalytic degradation of antibiotic wastewater.

[0003] Among monocyclic bismuth oxyhalides (BiOX, X=Br, Cl, I), since I has the largest atomic number, the band gap of BiOI is the narrowest, and the separation of photogenerated carriers becomes relatively easy, but its redox ability is also the weakest, which limits its application in the field of photocatalysis. Studies have found that by regulating the reaction conditions, the stoichiometric bismuth oxyhalide can be converted into the non-stoichiometric bismuth-rich iodine bismuth oxyiodide Bi x O y I z , the increase in the ratio of Bi to I can make Bi x O y I z It has a more dispersed conduction band and valence band, thereby increasing its redox potential. x O y I z ) has strong light absorption ability, but still has the disadvantages of poor separation efficiency of photogenerated carriers and high recombination efficiency, which seriously limits the x O y I z Widely used.

[0004] Constructing a heterojunction is an effective way to improve its photocatalytic performance. The potential difference between catalysts at the interface can accelerate the transmission of photogenerated electrons and holes, and achieve spatial separation of the two, thereby enhancing photocatalytic activity. However, the existing heterojunction based on bismuth-rich iodine bismuth oxide has the problem of high lattice mismatch.

[0005] Therefore, the industry is in urgent need of a new technology for bismuth-rich iodine-oxidized bismuth heterojunction photocatalyst. Summary of the invention

[0006] Aiming at the problems of poor light absorption capacity, fast photogenerated electron-hole recombination rate, poor photocatalytic oxidation performance, etc. existing in bismuth-rich iodine bismuth oxide materials, and the problem of high lattice mismatch of heterogeneous crystals with bismuth-rich iodine bismuth oxide as the main body, the present invention provides a bismuth-rich iodine bismuth oxide heterojunction photocatalyst and its preparation method and application, the catalyst has the advantages of strong light absorption capacity, low lattice mismatch, high photogenerated electron-hole separation efficiency, strong photocatalytic oxidation ability, etc., and its preparation method has the advantages of low raw material cost, simple synthesis process, easy control of conditions, short time consumption, high potential for continuous batch production, and convenient for industrial utilization. The bismuth-rich iodine bismuth oxide heterojunction photocatalyst of the present invention can be used to degrade antibiotics in wastewater, has the advantages of simple application method, high degradation efficiency, good reusability, and has a good practical application prospect.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: A bismuth-rich iodine-oxidized bismuth heterojunction photocatalyst comprises the following steps: S1. Add bismuth nitrate pentahydrate and potassium iodide to a solvent, mix well, and adjust the pH value of the solution to obtain a precursor; S2. calcining the precursor obtained in step S1 to obtain a bismuth-rich iodine bismuth oxide heterojunction photocatalyst.

[0008] Furthermore, in step S1, the molar ratio of the bismuth nitrate pentahydrate to the potassium iodide is 1:1.5 to 1:2.5.

[0009] Furthermore, in step S1, the solvent of the solution is ethylene glycol, the solutes are bismuth nitrate pentahydrate and potassium iodide, the volume is 50 mL to 100 mL, and the temperature is 25° C. to 50° C.

[0010] Furthermore, in step S1, the pH adjusting agent in the process of adjusting the pH value of the solution is sodium hydroxide, and the adjusted pH value is 8-11.

[0011] Furthermore, in step S2, the calcination temperature of the precursor is 250° C. to 350° C., and the calcination time is 1 h to 3 h.

[0012] Furthermore, in step S2, the heating rate during the calcination process is 2.3°C / min to 10°C / min.

[0013] The present invention also provides a bismuth-rich bismuth oxyiodide heterojunction photocatalyst prepared by the above-mentioned preparation method, wherein the bismuth-rich bismuth oxyiodide heterojunction photocatalyst is formed by stacking bismuth-rich Bi4O5I2 and Bi7O9I3 nanosheets layer by layer.

[0014] The present invention also provides an application of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst prepared by the above-mentioned preparation method in the photocatalytic degradation of antibiotic wastewater, wherein the bismuth-rich iodine bismuth oxide heterojunction photocatalyst is mixed with the antibiotic wastewater and stirred in the dark until adsorption equilibrium is reached; then a photocatalytic reaction is carried out under light conditions to complete the degradation of the antibiotic wastewater.

[0015] Furthermore, the antibiotic wastewater is ciprofloxacin wastewater; the concentration of the antibiotic in the antibiotic wastewater is 10 mg / L to 30 mg / L.

[0016] Furthermore, the added amount of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst is 0.25 g to 0.85 g of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst per liter of antibiotic wastewater.

[0017] Furthermore, the photocatalytic reaction time is 20 min to 40 min.

[0018] Compared with the prior art, the advantages of the present invention are: (1) The present invention first synthesizes a complex precursor containing three elements of Bi, O, and I in a non-stoichiometric ratio by controlling the alkalinity of the solution, and then removes part of the I atoms on the complex precursor by calcination, thereby generating bismuth-rich Bi4O5I2 and Bi7O9I3 in situ, and constructing a bismuth-rich iodine bismuth oxide heterojunction photocatalyst. On the one hand, since Bi7O9I3 nanosheets have the advantages of a wide light absorption range and high light absorption efficiency, the introduction of Bi7O9I3 nanosheets can serve as the light absorption center of the Bi4O5I2 / Bi7O9I3 bismuth-rich iodine bismuth oxide heterojunction photocatalyst, which can improve the light absorption capacity and light absorption efficiency of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst (this is because the light absorption cutoff edge of Bi7O9I3 is 596nm, the light absorption cutoff edge of Bi4O5I2 is 504nm, and Bi7O9I3 has a wider light absorption range). , after being combined with Bi4O5I2, its drawback of narrow light absorption range can be improved); on the other hand, under visible light conditions, Bi4O5I2 and Bi7O9I3 are photoexcited to generate photogenerated electrons and holes respectively. The two bismuth-rich iodine bismuth oxide materials have similar crystal structures, and the lattice mismatch at the heterojunction interface is low. Electrons and holes can quickly migrate to the conduction band of Bi4O5I2 and the valence band of Bi7O9I3 respectively, thereby achieving the purpose of effective separation of photogenerated electrons and holes and indirectly improving the photocatalytic oxidation ability.

[0019] (2) The bismuth-rich iodine bismuth oxide heterojunction photocatalyst provided by the present invention is composed of bismuth-rich Bi4O5I2 and Bi7O9I3 nanosheets stacked layer by layer, and has the advantages of strong light absorption ability, low lattice mismatch, high photogenerated electron-hole separation efficiency, strong photocatalytic oxidation ability, etc., and can efficiently degrade antibiotic wastewater. The present invention also provides a method for preparing a bismuth-rich iodine bismuth oxide heterojunction photocatalyst, which has the advantages of low raw material cost, simple synthesis process, easy control of conditions, short time consumption, high potential for continuous batch production, and convenient for industrial utilization.

[0020] (3) The present invention provides a method for treating antibiotic wastewater, and the bismuth-rich iodine bismuth oxide heterojunction photocatalyst of the present invention is used to degrade antibiotic wastewater, which has the advantages of simple application method, high degradation efficiency, and good reusability, and has a good practical application prospect. Taking ciprofloxacin as an example, when the bismuth-rich iodine bismuth oxide heterojunction photocatalyst of the present invention is used to treat ciprofloxacin wastewater with a concentration of 20 mg / L, the degradation efficiency of ciprofloxacin is as high as 100% after 30 minutes of photocatalytic reaction, and the photocatalytic degradation rate is 0.1283 min -1 Compared with pure Bi4O5I2 and Bi7O9I3, the degradation efficiency increased by 12.0 times and 4.6 times respectively, and after five cycles, the degradation efficiency still reached 93.5%, which has the advantages of stable photocatalytic performance and high degradation efficiency.

[0021] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 This is a SEM image of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst in Example 1 of the present invention; Figure 2 TEM image of the bismuth-rich iodine bismuth oxyiodide heterojunction photocatalyst in Example 1 of the present invention; Figure 3 HRTEM image of the bismuth-rich iodine bismuth heterojunction photocatalyst in Example 1 of the present invention; Figure 4 The photoluminescence spectra of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst (Bi4 / Bi7-3) in Example 1 of the present invention, the hydrothermal Bi4O5I2 (Bi4-S1) in Comparative Example 1, and the calcined Bi4O5I2 (Bi4-S2) in Comparative Example 2; Figure 5The UV-visible diffuse reflectance spectra of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst (Bi4 / Bi7-3) in Example 1 of the present invention, the hydrothermal Bi4O5I2 (Bi4-S1) in Comparative Example 1, the calcined Bi4O5I2 (Bi4-S2) in Comparative Example 2, and the hydrothermal Bi7O9I3 in Comparative Example 3; Figure 6 It is a relationship diagram of the time-degradation efficiency corresponding to the photocatalytic degradation of ciprofloxacin (CIP) wastewater by Bi4 / Bi7-3 in Example 1 of the present invention, hydrothermal Bi4O5I2 (Bi4-S1) in Comparative Example 1, calcined Bi4O5I2 (Bi4-S2) in Comparative Example 2, and hydrothermal Bi7O9I3 in Comparative Example 3; Figure 7 The relationship diagram of the time-degradation efficiency corresponding to the photocatalytic degradation of CIP by the samples obtained under different preparation conditions in Examples 1-3 of the present invention and Comparative Examples 4-7; Figure 8 This is a bar graph of the photocatalytic degradation cycle-efficiency of the bismuth-rich bismuth oxyiodide heterojunction photocatalyst in Example 1 of the present invention after five cyclic reactions. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0024] The materials and instruments used in the following examples are all commercially available.

[0025] Embodiment 1: A method for preparing a bismuth-rich iodine-based bismuth oxide heterojunction photocatalyst comprises the following steps: (1) 2.5 mmol of bismuth nitrate pentahydrate was added to 50 mL of ethylene glycol, and magnetically stirred at 40°C until the solution became transparent, then 4.5 mmol of potassium iodide was dissolved in the above solution, and the pH of the solution was adjusted to 10 with sodium hydroxide, and the precursor was obtained after continuous stirring for 30 minutes. The molar ratio of bismuth nitrate pentahydrate to potassium iodide was 1:1.8.

[0026] (2) The precursor obtained in the above step (1) is placed in a crucible, the crucible lid is covered, and the crucible is placed in a muffle furnace for calcination. Specifically, the heating rate of the muffle furnace is controlled to be 6°C / min, the temperature is raised to 300°C and maintained for 2 hours. After the calcination is completed, the calcined product is cooled and ground to obtain a bismuth-rich iodine bismuth oxide heterojunction photocatalyst, named Bi4 / Bi7-3.

[0027] Embodiment 2: A bismuth-rich bismuth iodide heterojunction photocatalyst is formed by stacking bismuth-rich Bi4O5I2 and Bi7O9I3 nanosheets layer by layer.

[0028] A method for preparing the bismuth-rich bismuth oxyiodide heterojunction photocatalyst of the present embodiment comprises the following steps: (1) 2.5 mmol of bismuth nitrate pentahydrate was added to 50 mL of ethylene glycol, and magnetically stirred at 40°C until the solution became transparent, then 3.75 mmol of potassium iodide was dissolved in the above solution, and the pH of the solution was adjusted to 10 with sodium hydroxide, and stirred continuously for 30 minutes to obtain a precursor. The molar ratio of bismuth nitrate pentahydrate to potassium iodide was 1:1.5.

[0029] (2) The precursor obtained in the above step (1) is placed in a crucible, the crucible lid is covered, and the crucible is placed in a muffle furnace for calcination. Specifically, the heating rate of the muffle furnace is controlled to be 6°C / min, the temperature is raised to 250°C and maintained for 2 hours. After the calcination is completed, the calcined product is cooled and ground to obtain a bismuth-rich iodine bismuth oxide heterojunction photocatalyst, which is named Bi4 / Bi7-1.

[0030] Embodiment 3: A bismuth-rich bismuth iodide heterojunction photocatalyst is formed by stacking bismuth-rich Bi4O5I2 and Bi7O9I3 nanosheets layer by layer.

[0031] A method for preparing the bismuth-rich bismuth oxyiodide heterojunction photocatalyst of the present embodiment comprises the following steps: (1) 2.5 mmol of bismuth nitrate pentahydrate was added to 50 mL of ethylene glycol, and magnetically stirred at 40°C until the solution became transparent, and then 6.25 mmol of potassium iodide was dissolved in the above solution, and the pH of the solution was adjusted to 10 with sodium hydroxide, and the precursor was obtained after continuous stirring for 30 minutes. The molar ratio of bismuth nitrate pentahydrate to potassium iodide was 1:2.5.

[0032] (2) The precursor obtained in the above step (1) is placed in a crucible, the crucible lid is covered, and the crucible is placed in a muffle furnace for calcination. Specifically, the heating rate of the muffle furnace is controlled to be 6°C / min, the temperature is raised to 350°C and maintained for 2 hours. After the calcination is completed, the calcined product is cooled and ground to obtain a bismuth-rich iodine bismuth oxide heterojunction photocatalyst, which is named Bi4 / Bi7-2.

[0033] Comparative Example 1: A preparation method of hydrothermal Bi4O5I2 comprises the following steps: dissolving 2mmol of bismuth nitrate pentahydrate in 35mL of ethylene glycol, adding 4mmol of potassium iodide to the solution and stirring for 30min, adjusting the pH value of the solution to 10 with 2mol / L of sodium hydroxide, transferring the solution to a polytetrafluoroethylene-lined reactor after stirring for 30min, sealing the solution, reacting at 150°C for 12h, naturally cooling to room temperature, collecting the precipitate by centrifugation, washing and drying, and obtaining hydrothermal Bi4O5I2, which is named Bi4-S1.

[0034] Comparative Example 2: A method for preparing calcined Bi4O5I2 comprises the following steps: (1) Mix 3 mmol of bismuth nitrate pentahydrate with 60 mL of ethylene glycol and stir at 30°C and 600 r / min for 15 min to obtain a transparent, colorless bismuth nitrate solution.

[0035] 8.8 mmol of potassium iodide was mixed with 60 mL of ultrapure water, and stirred at 30° C. and 600 r / min for 15 min to obtain a transparent and colorless potassium iodide solution.

[0036] (2) Add the potassium iodide solution in step (1) to the bismuth nitrate solution, stir for 60 minutes, centrifuge and wash the precipitate to obtain a Bi4O5I2 precursor.

[0037] (3) The precursor obtained in step (2) is placed in a crucible, the crucible lid is covered, and the crucible is placed in a muffle furnace for calcination. Specifically, the heating rate of the muffle furnace is controlled to be 6°C / min, the temperature is raised to 410°C and maintained for 4 hours. After the calcination is completed, the calcined product is cooled and ground to obtain calcined Bi4O5I2, which is named Bi4-S2.

[0038] Comparative Example 3: A method for preparing hydrothermal Bi7O9I3 comprises the following steps: adding 3 mmol of bismuth nitrate pentahydrate and 3 mmol of potassium iodide to 60 mL of ethylene glycol, stirring the solution at room temperature for 1 hour, transferring the solution to a polytetrafluoroethylene-lined reactor, sealing the reaction mixture, reacting the reaction mixture at 140°C for 12 hours, naturally cooling the reaction mixture to room temperature, collecting the precipitate by centrifugation, washing the precipitate, and drying the precipitate to obtain hydrothermal Bi7O9I3, which is named Bi7.

[0039] Comparative Example 4: (Potassium iodide dosage is too low) The difference between Comparative Example 4 and Example 1 is that in Comparative Example 4, 2.5 mmol bismuth nitrate pentahydrate, 2.5 mmol potassium iodide, and the molar ratio of bismuth nitrate pentahydrate to potassium iodide is 1:1, and the rest is the same as Example 1.

[0040] Comparative Example 5: (Potassium iodide dosage is too high) The difference between Comparative Example 5 and Example 1 is that in Comparative Example 5, 2.5 mmol bismuth nitrate pentahydrate, 7.5 mmol potassium iodide, and the molar ratio of bismuth nitrate pentahydrate to potassium iodide is 1:3, and the rest is the same as Example 1.

[0041] Comparative Example 6: (Calcination temperature is too high) The difference between Comparative Example 6 and Example 1 is that in Comparative Example 6, the calcination temperature is raised to 400° C., and the rest is the same as in Example 1.

[0042] Comparative Example 7: (Calcination temperature is too low) The difference between Comparative Example 7 and Example 1 is that in Comparative Example 7, the calcination temperature is raised to 200° C., and the rest is the same as in Example 1.

[0043] Figure 1 This is a SEM image of the bismuth-rich iodine bismuth oxyiodide heterojunction photocatalyst in Example 1 of the present invention. Figure 1 It can be seen that the bismuth-rich iodine bismuth oxide heterojunction photocatalyst is a porous microsphere structure composed of particles with a particle size of about 100 nm, and the diameter of the microsphere is about 5μm to 8μm.

[0044] Figure 2 TEM image of the bismuth-rich iodine bismuth heterojunction photocatalyst in Example 1 of the present invention, Figure 3 HRTEM image of the bismuth-rich iodine bismuth oxyiodide heterojunction photocatalyst in Example 1 of the present invention. Figure 2 It can be seen that the Bi4O5I2 nanosheets and Bi7O9I3 nanosheets in the bismuth-rich iodine bismuth heterojunction photocatalyst are arranged in layers. Figure 3 It can be seen that the exposed crystal planes of Bi7O9I3 are (102) and (012) planes, and the exposed crystal plane of Bi4O5I2 is (-4-11) plane.

[0045] Figure 4 The photoluminescence spectra of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst (Bi4 / Bi7-3) in Example 1 of the present invention, the hydrothermal Bi4O5I2 (Bi4-S1) in Comparative Example 1, and the calcined Bi4O5I2 (Bi4-S2) in Comparative Example 2 are shown. Figure 4 It can be seen that Bi4 / Bi7-3, Bi4-S1 and Bi4-S2 have similar fluorescence peaks at an excitation wavelength of 400nm, but Bi4 / Bi7-3 has a lower fluorescence intensity than Bi4-S1 and Bi4-S2, indicating that the heterojunction formed by the composite of Bi4O5I2 and Bi7O9I3 effectively inhibits the electron-hole recombination, and the separation of carriers can prolong the lifetime of photogenerated carriers, which can solve the problem of rapid recombination of photogenerated electrons and holes in Bi4O5I2 monomers and Bi7O9I3 monomers.

[0046] Figure 5The UV-visible diffuse reflectance spectra of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst (Bi4 / Bi7-3) in Example 1 of the present invention, the hydrothermal Bi4O5I2 (Bi4-S1) in Comparative Example 1, the calcined Bi4O5I2 (Bi4-S2) in Comparative Example 2, and the hydrothermal Bi7O9I3 (Bi7) in Comparative Example 3 are shown. Figure 5 It can be seen that Bi4 / Bi7-3, Bi4-S1, Bi4-S2 and Bi7 have strong absorption peaks in the range of 250nm to 800nm ​​and can respond under visible light, with absorption band edges of 482nm, 537nm, 504nm and 596nm respectively. Although Bi4 / Bi7-3 has the narrowest absorption range, which is similar to hydrothermal Bi4O5I2, its light absorption intensity in the range of 250nm to 380nm is significantly improved, indicating that the composite heterojunction of Bi7O9I3 and Bi4O5I2 can improve the light absorption capacity of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst (Bi7Bi4 / Bi7-3) to a certain extent.

[0047] Test 1: The photocatalysts prepared in Examples 1-3 and Comparative Examples 1-7 were applied to degrade antibiotic wastewater, specifically comprising the following steps: Weigh 0.05 g of Bi4-S1 (Comparative Example 1), Bi4-S2 (Comparative Example 2), Bi7 (Comparative Example 3), Bi4 / Bi7-1 (Example 2), Bi4 / Bi7-2 (Example 3), Bi4 / Bi7-3 (Example 1) and the photocatalysts prepared in Comparative Examples 4-7, respectively, and add them to 100 mL of ciprofloxacin (CIP) wastewater with a concentration of 20 mg / L, and stir magnetically in a dark place (i.e., under dark conditions) for 1 hour. After reaching adsorption equilibrium, turn on the light source, and carry out photocatalytic reaction under visible light (λ≥420 nm) for 30 minutes to complete the degradation of antibiotic wastewater.

[0048] Degradation efficiency: 4 mL of photocatalytic degradation solution was taken from the reaction container every 6 min, centrifuged at 7000 rpm for 5 min, and the supernatant was taken and tested on a UV-visible spectrophotometer. The experimental results are shown in Figure 6 and Figure 7 shown.

[0049] Figure 6 It is a relationship diagram of the time-degradation efficiency corresponding to the photocatalytic degradation of ciprofloxacin (CIP) wastewater by Bi4 / Bi7-3 in Example 1 of the present invention, hydrothermal Bi4O5I2 (Bi4-S1) in Comparative Example 1, calcined Bi4O5I2 (Bi4-S2) in Comparative Example 2, and hydrothermal Bi7O9I3 in Comparative Example 3; Figure 7This is a relationship diagram of the time-degradation efficiency corresponding to the photocatalytic degradation of CIP by the samples obtained under different preparation conditions in Examples 1-3 of the present invention and Comparative Examples 4-7. Figure 6 and Figure 7 In the equation, C represents the concentration of CIP after degradation, and C0 represents the initial concentration of CIP (i.e., the concentration of CIP in the solution after reaching adsorption equilibrium). Figure 6 and Figure 7 It can be seen that: The bismuth-rich bismuth iodide heterojunction photocatalyst (Bi4 / Bi7-3) in Example 1 of the present invention has a degradation efficiency of 100% for CIP after a photocatalytic reaction of 30 minutes.

[0050] The bismuth-rich bismuth iodide heterojunction photocatalyst (Bi4 / Bi7-1) in Example 2 of the present invention has a degradation efficiency of 79.9% for CIP after 30 minutes of photocatalytic reaction.

[0051] The bismuth-rich bismuth iodide heterojunction photocatalyst (Bi4 / Bi7-2) in Example 3 of the present invention has a degradation efficiency of 89.6% for CIP after 30 minutes of photocatalytic reaction.

[0052] The degradation efficiency of CIP by the hydrothermal Bi4O5I2 (Bi4-S1) in Comparative Example 1 was 58.0% after 30 minutes of photocatalytic reaction.

[0053] The degradation efficiency of calcined Bi4O5I2 (Bi4-S2) for CIP in Comparative Example 2 was 27.0% after 30 minutes of photocatalytic reaction.

[0054] The degradation efficiency of CIP by hydrothermal Bi7O9I3 (Bi7) in Comparative Example 3 was 57.4% after 30 minutes of photocatalytic reaction.

[0055] The material prepared in Comparative Example 4 with a molar ratio of bismuth nitrate pentahydrate to potassium iodide of 1:1 had a CIP degradation efficiency of 27.6% after 30 minutes of photocatalytic reaction.

[0056] The material prepared in Comparative Example 5 with a molar ratio of bismuth nitrate pentahydrate to potassium iodide of 1:3 had a CIP degradation efficiency of 34.1% after 30 minutes of photocatalytic reaction.

[0057] The material obtained by calcining at 400° C. in Comparative Example 6 has a CIP degradation efficiency of 42.4% after 30 minutes of photocatalytic reaction.

[0058] The material obtained by calcining at 200° C. in Comparative Example 7 has a CIP degradation efficiency of 17.9% after 30 minutes of photocatalytic reaction.

[0059] The results show that the bismuth-rich iodine bismuth heterojunction photocatalyst (Bi4 / Bi7-3) in Example 1 has the best degradation efficiency for CIP. After 30 minutes of photocatalytic reaction, the degradation efficiency of CIP is 100%, and the photocatalytic degradation rate is 0.12830 min -1 , while the degradation efficiency and degradation rate of hydrothermal Bi4O5I2 (Bi4-S1) were only 58.0% and 0.02831min, respectively. -1 The degradation efficiency and degradation rate of calcined Bi4O5I2 (Bi4-S2) were only 27.0% and 0.01066min, respectively. -1 The degradation efficiency and degradation rate of hydrothermal Bi7O9I3 (Bi7) were only 57.4% and 0.02779min, respectively. -1. By comparison, it can be seen that compared with pure hydrothermal Bi4O5I2, pure calcined Bi4O5I2 and pure hydrothermal Bi7O9I3, the degradation rate of antibiotic wastewater by the bismuth-rich iodine bismuth heterojunction photocatalyst prepared by the present invention is increased by 4.53, 12.0 and 4.62 times, respectively. The main reason for this phenomenon is that the present invention generates Bi4O5I2 and Bi7O9I3 in situ by solution alkalinity control method and calcination method, constructs a bismuth-rich iodine bismuth heterojunction, and effectively improves the electron-hole separation efficiency and light absorption efficiency in the bismuth-rich iodine bismuth heterojunction photocatalyst by utilizing the synergistic effect between Bi4O5I2 nanosheets and Bi7O9I3 nanosheets, improves the photocatalytic redox ability of the bismuth-rich iodine bismuth heterojunction photocatalyst, enhances the photocatalytic activity of the bismuth-rich iodine bismuth heterojunction photocatalyst, and finally achieves rapid and efficient degradation of CIP in wastewater. In addition, the degradation efficiency of CIP obtained by the material with a molar ratio of bismuth nitrate pentahydrate to potassium iodide of 1:1 in Comparative Example 4 was 27.6% after 30 minutes of photocatalytic reaction, and the degradation efficiency of CIP obtained by the material with a molar ratio of bismuth nitrate pentahydrate to potassium iodide of 1:3 in Comparative Example 5 was 34.1% after 30 minutes of photocatalytic reaction, which is much lower than the performance of the Bi4O5I2 / Bi7O9I3 heterojunction in Examples 1 to 3. The reason is that when the ratio of bismuth nitrate pentahydrate to potassium iodide is close (ie, Comparative Example 4), the generated substance is a BiOI monomer with a stoichiometric ratio, which has a narrow band gap and weak oxidation ability, and has a low ability to photocatalytically generate free radicals. Moreover, because the proportion of I in the raw material is small, the alkalinity control and high-temperature calcination will over-etch I to generate a bismuth-rich Bi7O9I3 single substance, whose photogenerated electrons and holes recombine severely, the redox ability is relatively poor, and the number of active oxygen species generated is small, resulting in its poor ability to degrade pollutants. When the proportion of potassium iodide is too large (i.e., comparative example 5), the alkalinity control and high-temperature calcination cannot fully etch the I atoms, and part of the product is still the precursor, so the catalytic efficiency is poor. In comparative examples 6 and 7, the precursors were calcined at 400°C and 200°C respectively. The high temperature caused the material to further transform into Bi5O7I, destroying the original Bi4O5I2 / Bi7O9I3 heterojunction composition, so the degradation rate of CIP dropped to 42.4%. The temperature was too low to fully etch I, and most of the generated substances were still precursors, so the degradation efficiency was only 17.9%.

[0060] Test 2: The recyclability of bismuth-rich iodine bismuth oxyiodide heterojunction photocatalyst in the photocatalytic degradation process is investigated, including the following steps: (1) Weigh 0.05 g of the bismuth-rich iodine bismuth oxyiodide heterojunction photocatalyst (Bi4 / Bi7-3) prepared in Example 1 and add it to 100 mL of ciprofloxacin wastewater with an initial concentration of 20 mg / L to obtain a reaction system.

[0061] (2) The reaction system obtained in step (1) (ciprofloxacin wastewater added with Bi4 / Bi7-3) was placed on a magnetic stirrer and stirred in the dark for 1 h to achieve adsorption equilibrium. 4 mL of the solution was taken out to represent the initial solution to be degraded, i.e., the solution at the reaction time of 0 min. Its concentration was measured using a UV-visible spectrophotometer and recorded as C0.

[0062] (3) The remaining solution from step (2) was subjected to a photocatalytic reaction under visible light. When the reaction time reached 30 min, 4 mL of the solution was taken out from the reaction system (ciprofloxacin wastewater with Bi4 / Bi7-3 added), and the solution was centrifuged at 7000 rpm for 5 min. The residual CIP concentration in the supernatant was measured using a UV-visible spectrophotometer and recorded as C.

[0063] (4) The solution after the reaction in step (3) was centrifuged and the supernatant was discarded. The Bi4 / Bi7-3 after the reaction was collected, and after desorption of CIP with ethanol, the mixture was centrifuged and dried, weighed, and re-added to 100 mL of ciprofloxacin wastewater with an initial concentration of 20 mg / L.

[0064] (5) Repeat steps (2) to (4) four more times.

[0065] Figure 8 This is a bar graph of the photocatalytic degradation cycle-efficiency of the bismuth-rich bismuth oxyiodide heterojunction photocatalyst in Example 1 of the present invention after five cyclic reactions. Figure 8 In the figure, the degradation efficiency of CIP is taken as the ordinate and the number of cycles is taken as the abscissa, where the bar graphs 1, 2, 3, 4, and 5 correspond to the photocatalytic degradation cycle-efficiency results of the first reaction, the second reaction, the third reaction, the fourth reaction, and the fifth reaction, respectively. Figure 8 It can be seen that after five cycles, Bi4 / Bi7-3 still exhibits efficient photocatalytic performance, and the degradation efficiency still reaches 93.5% after five cycles. This shows that the bismuth-rich iodine bismuth oxide heterojunction photocatalyst of the present invention has the advantages of stable photocatalytic performance and high efficiency in degradation of ciprofloxacin wastewater. It is a new type of visible light composite photocatalyst with high degradation efficiency and good reusability.

[0066] In summary, the present invention first synthesizes a complex precursor containing three elements of Bi, O, and I in a non-stoichiometric ratio by a solution alkalinity control method, and then removes part of the I atoms on the complex precursor by a calcination method, generates bismuth-rich Bi4O5I2 and Bi7O9I3 in situ, and constructs a bismuth-rich iodine bismuth oxide heterojunction photocatalyst. On the one hand, since Bi7O9I3 nanosheets have the advantages of a wide light absorption range and high light absorption efficiency, the introduction of Bi7O9I3 nanosheets can serve as the light absorption center of the Bi4O5I2 / Bi7O9I3 bismuth-rich iodine bismuth oxide heterojunction photocatalyst, which can improve the light absorption capacity and light absorption efficiency of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst (this is because the light absorption cutoff edge of Bi7O9I3 is 596nm, the light absorption cutoff edge of Bi4O5I2 is 504nm, and Bi7O9I3 has a wider light absorption range , after being combined with Bi4O5I2, its drawback of narrow light absorption range can be improved); on the other hand, under visible light conditions, Bi4O5I2 and Bi7O9I3 are photoexcited to generate photogenerated electrons and holes respectively. The two bismuth-rich iodine bismuth oxide materials have similar crystal structures, and the lattice mismatch at the heterojunction interface is low. Electrons and holes can quickly migrate to the conduction band of Bi4O5I2 and the valence band of Bi7O9I3 respectively, thereby achieving the purpose of effective separation of photogenerated electrons and holes and indirectly improving the photocatalytic oxidation ability.

[0067] In addition, the bismuth-rich iodine bismuth oxide heterojunction photocatalyst provided by the present invention is formed by stacking bismuth-rich Bi4O5I2 and Bi7O9I3 nanosheets layer by layer, and has the advantages of strong light absorption ability, low lattice mismatch, high photogenerated electron-hole separation efficiency, strong photocatalytic oxidation ability, etc., and can efficiently degrade antibiotic wastewater. The present invention also provides a method for preparing a bismuth-rich iodine bismuth oxide heterojunction photocatalyst, which has the advantages of low raw material cost, simple synthesis process, easy control of conditions, short time consumption, high potential for continuous batch production, and convenient for industrial use. At the same time, the bismuth-rich iodine bismuth oxide heterojunction photocatalyst of the present invention is used to degrade antibiotic wastewater, which has the advantages of simple application method, high degradation efficiency, and good reusability, and has a good practical application prospect.

[0068] The above embodiments are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a bismuth-rich iodine-based bismuth oxyiodide heterojunction photocatalyst, characterized in that: The following steps are involved: S1. Add bismuth nitrate pentahydrate and potassium iodide to a solvent, mix well, and adjust the pH value of the solution to obtain a precursor; S2. calcining the precursor obtained in step S1 to obtain a bismuth-rich iodine bismuth oxide heterojunction photocatalyst.

2. The preparation method according to claim 1, characterized in that: In step S1, the molar ratio of the bismuth nitrate pentahydrate to the potassium iodide is 1:1.5 to 1:2.

5.

3. The preparation method according to claim 1, characterized in that: In step S1, the solvent of the solution is ethylene glycol, the solutes are bismuth nitrate pentahydrate and potassium iodide, the volume is 50 mL to 100 mL, and the temperature is 25° C. to 50° C.

4. The preparation method according to claim 1, characterized in that: In step S1, the pH adjusting agent is sodium hydroxide during the process of adjusting the pH value of the solution, and the pH value after adjustment is 8-11.

5. The preparation method according to claim 1, characterized in that: In step S2, the precursor is calcined at a temperature of 250°C to 350°C, and the calcination time is 1h to 3h.

6. The preparation method according to claim 5, characterized in that: In step S2, the heating rate during the calcination process is 2.3°C / min to 10°C / min.

7. A bismuth-rich bismuth iodide heterojunction photocatalyst prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The bismuth-rich bismuth iodide heterojunction photocatalyst is formed by stacking bismuth-rich Bi4O5I2 and Bi7O9I3 nanosheets layer by layer.

8. Use of a bismuth-rich bismuth oxyiodide heterojunction photocatalyst prepared by the preparation method according to any one of claims 1 to 6 in photocatalytic degradation of antibiotic wastewater, characterized in that: The following steps are involved: The bismuth-rich iodine bismuth oxide heterojunction photocatalyst is mixed with antibiotic wastewater and stirred in the dark until adsorption equilibrium is reached; Then, a photocatalytic reaction is carried out under light conditions to complete the degradation of antibiotic wastewater.

9. The use according to claim 8, characterized in that: The antibiotic wastewater is ciprofloxacin wastewater; the concentration of the antibiotic in the antibiotic wastewater is 10 mg / L to 30 mg / L.

10. The use according to claim 8, characterized in that: The added amount of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst is 0.25 g to 0.85 g of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst per liter of antibiotic wastewater.

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