A bismuth-rich iodine bismuth oxide heterojunction photocatalyst and its preparation method and application

Abstract

The present invention discloses a bismuth-rich bismuth oxyiodide heterojunction photocatalyst, its preparation method and application. The catalyst is composed of bismuth-rich Bi4O5I2 and Bi7O9I3 nanosheets stacked layer by layer. The preparation method includes mixing bismuth nitrate pentahydrate with potassium iodide, adjusting the pH value of the solution to form a precursor, and then calcining it to obtain the bismuth-rich bismuth oxyiodide heterojunction photocatalyst. The bismuth-rich bismuth oxyiodide heterojunction photocatalyst of the present invention has the advantages of strong light absorption ability, low lattice mismatch degree, high separation efficiency of photo-generated electrons and holes, and strong photocatalytic oxidation ability. 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 is convenient for industrial utilization. The bismuth-rich bismuth oxyiodide heterojunction photocatalyst of the present invention 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:

[0008] A bismuth-rich iodine-oxidized bismuth heterojunction photocatalyst comprises the following steps:

[0009] 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;

[0010] S2. calcining the precursor obtained in step S1 to obtain a bismuth-rich iodine bismuth oxide heterojunction photocatalyst.

[0011] Furthermore, in step S1, the molar ratio of the bismuth nitrate pentahydrate to the potassium iodide is 1:1.5 to 1:2.5.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] Furthermore, in step S2, the heating rate during the calcination process is 2.3°C / min to 10°C / min.

[0016] The present invention also provides a bismuth-rich iodine bismuth oxide heterojunction photocatalyst prepared by the above-mentioned preparation method, wherein the bismuth-rich iodine bismuth oxide heterojunction photocatalyst is composed of bismuth-rich Bi 4 O 5 I 2 with Bi 7 O9 I 3 Nanosheets are stacked layer by layer.

[0017] 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.

[0018] Furthermore, the antibiotic wastewater is ciprofloxacin wastewater; the concentration of the antibiotic in the antibiotic wastewater is 10 mg / L to 30 mg / L.

[0019] 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.

[0020] Furthermore, the photocatalytic reaction time is 20 min to 40 min.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] (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 the I atoms on the complex precursor by calcination to generate bismuth-rich Bi in situ. 4 O 5 I 2 and Bi 7 O 9 I 3 , a bismuth-rich iodine-based bismuth oxide heterojunction photocatalyst was constructed. 7 O 9 I 3 Nanosheets have the advantages of wide light absorption range and high light absorption efficiency. 7 O 9 I 3 The introduction of nanosheets can serve as 4 O 5 I 2 / Bi 7 O 9 I 3 The light absorption center of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst can improve the light absorption capacity and light absorption efficiency of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst (this is because Bi 7 O 9 I 3 The absorption cutoff edge is 596nm, Bi 4 O 5 I2 The absorption cutoff edge is 504nm, Bi 7 O 9 I 3 Has a wider light absorption range, compared with Bi 4 O 5 I 2 After compounding, the drawback of narrow absorption range can be improved); on the other hand, under visible light conditions, Bi 4 O 5 I 2 with Bi 7 O 9 I 3 The two bismuth-rich iodine-based 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 Bi 4 O 5 I 2 The conduction band and Bi 7 O 9 I 3 valence band, thereby achieving the purpose of effective separation of photogenerated electrons and holes and indirectly improving the photocatalytic oxidation ability.

[0023] (2) The present invention provides a bismuth-rich iodine bismuth oxide heterojunction photocatalyst, comprising a bismuth-rich Bi 4 O 5 I 2 with Bi 7 O 9 I 3 The nanosheets are stacked layer by layer, and have 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.

[0024] (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 , with pure Bi 4 O 5 I 2 with Bi 7 O9 I 3 Compared with the original, the degradation efficiency was increased by 12.0 times and 4.6 times respectively, and the degradation efficiency still reached 93.5% after five cycles, which has the advantages of stable photocatalytic performance and high degradation efficiency.

[0025] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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:

[0027] Figure 1 This is a SEM image of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst in Example 1 of the present invention;

[0028] Figure 2 TEM image of the bismuth-rich iodine bismuth oxyiodide heterojunction photocatalyst in Example 1 of the present invention;

[0029] Figure 3 HRTEM image of the bismuth-rich iodine bismuth heterojunction photocatalyst in Example 1 of the present invention;

[0030] Figure 4 The bismuth-rich iodine bismuth oxide heterojunction photocatalyst (Bi4 / Bi7-3) in Example 1 of the present invention and the hydrothermal Bi in Comparative Example 1 4 O 5 I 2 (Bi4-S1), calcined Bi in Comparative Example 2 4 O 5 I 2 Photoluminescence spectrum of (Bi4-S2);

[0031] Figure 5 The bismuth-rich iodine bismuth oxide heterojunction photocatalyst (Bi4 / Bi7-3) in Example 1 of the present invention and the hydrothermal Bi in Comparative Example 1 4 O 5 I 2 (Bi4-S1), calcined Bi in Comparative Example 2 4 O 5 I 2 (Bi4-S2), hydrothermal Bi in comparative example 3 7 O 9 I 3 UV-Vis diffuse reflectance spectrum;

[0032] Figure 6Bi4 / Bi7-3 in Example 1 of the present invention and hydrothermal Bi in Comparative Example 1 4 O 5 I 2 (Bi4-S1), calcined Bi in Comparative Example 2 4 O 5 I 2 (Bi4-S2), hydrothermal Bi in comparative example 3 7 O 9 I 3 The relationship between time and degradation efficiency when photocatalytically degrading ciprofloxacin (CIP) wastewater;

[0033] 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;

[0034] 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

[0035] 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.

[0036] The materials and instruments used in the following examples are all commercially available.

[0037] Embodiment 1:

[0038] A method for preparing a bismuth-rich iodine-based bismuth oxide heterojunction photocatalyst comprises the following steps:

[0039] (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.

[0040] (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.

[0041] Embodiment 2:

[0042] A bismuth-rich iodine bismuth oxide heterojunction photocatalyst, the bismuth-rich iodine bismuth oxide heterojunction photocatalyst is composed of a bismuth-rich Bi 4 O 5 I 2 with Bi 7 O 9 I 3 Nanosheets are stacked layer by layer.

[0043] A method for preparing the bismuth-rich bismuth oxyiodide heterojunction photocatalyst of the present embodiment comprises the following steps:

[0044] (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.

[0045] (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.

[0046] Embodiment 3:

[0047] A bismuth-rich iodine bismuth oxide heterojunction photocatalyst, the bismuth-rich iodine bismuth oxide heterojunction photocatalyst is composed of a bismuth-rich Bi 4 O 5 I 2 with Bi 7 O 9 I 3 Nanosheets are stacked layer by layer.

[0048] A method for preparing the bismuth-rich bismuth oxyiodide heterojunction photocatalyst of the present embodiment comprises the following steps:

[0049] (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.

[0050] (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.

[0051] Comparative Example 1:

[0052] A hydrothermal Bi 4 O 5 I 2 The preparation method comprises the following steps: dissolving 2 mmol of bismuth nitrate pentahydrate in 35 mL of ethylene glycol, adding 4 mmol of potassium iodide to the solution and stirring for 30 min, adjusting the pH of the solution to 10 with 2 mol / L of sodium hydroxide, transferring the solution to a polytetrafluoroethylene-lined reactor after stirring for 30 min, sealing, reacting at 150° C. for 12 h, naturally cooling to room temperature, centrifuging, collecting the precipitate, washing and drying, and obtaining hydrothermal Bi 4 O 5 I 2 , named Bi4-S1.

[0053] Comparative Example 2:

[0054] A calcined Bi 4 O 5 I 2 The preparation method comprises the following steps:

[0055] (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.

[0056] 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.

[0057] (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 Bi 4 O 5 I 2 Precursor.

[0058] (3) placing the precursor obtained in step (2) in a crucible, covering the crucible, and placing it in a muffle furnace for calcination, specifically: controlling the heating rate of the muffle furnace to 6°C / min, heating to 410°C and maintaining for 4 hours, cooling and grinding the calcined product after the calcination is completed, and obtaining calcined Bi 4 O 5 I2 , named Bi4-S2.

[0059] Comparative Example 3:

[0060] A hydrothermal Bi 7 O 9 I 3 The preparation method comprises the following steps: adding 3 mmol of bismuth nitrate pentahydrate and 3 mmol of potassium iodide to 60 mL of ethylene glycol, stirring at room temperature for 1 hour, transferring the solution to a polytetrafluoroethylene-lined reactor, sealing, reacting at 140° C. for 12 hours, naturally cooling to room temperature, centrifuging, collecting the precipitate, washing and drying, and obtaining hydrothermal Bi 7 O 9 I 3 , named Bi7.

[0061] Comparative Example 4: (Potassium iodide dosage is too low)

[0062] 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.

[0063] Comparative Example 5: (Potassium iodide dosage is too high)

[0064] 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.

[0065] Comparative Example 6: (Calcination temperature is too high)

[0066] 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.

[0067] Comparative Example 7: (Calcination temperature is too low)

[0068] 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.

[0069] 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.

[0070] Figure 2 TEM image of the bismuth-rich iodine bismuth heterojunction photocatalyst in Example 1 of the present invention, Figure 3HRTEM image of the bismuth-rich iodine bismuth oxyiodide heterojunction photocatalyst in Example 1 of the present invention. Figure 2 It can be seen that Bi in the bismuth-rich iodine bismuth heterojunction photocatalyst 4 O 5 I 2 Nanosheets and Bi 7 O 9 I 3 Nanosheets are arranged in staggered layers. Figure 3 It can be seen that Bi 7 O 9 I 3 The exposed crystal faces are (102) and (012), Bi 4 O 5 I 2 The exposed crystal plane is the (-4-11) plane.

[0071] Figure 4 The bismuth-rich iodine bismuth oxide heterojunction photocatalyst (Bi4 / Bi7-3) in Example 1 of the present invention and the hydrothermal Bi in Comparative Example 1 4 O 5 I 2 (Bi4-S1), calcined Bi in Comparative Example 2 4 O 5 I 2 Photoluminescence spectrum of (Bi4-S2). Figure 4 It can be seen that Bi4 / Bi7-3, Bi4-S1 and Bi4-S2 have similar fluorescence peaks at an excitation wavelength of 400 nm, but Bi4 / Bi7-3 has a lower fluorescence intensity than Bi4-S1 and Bi4-S2, indicating that Bi 4 O 5 I 2 and Bi 7 O 9 I 3 The heterojunction formed by the composite effectively inhibits the electron-hole recombination, and the separation of carriers can prolong the life of photogenerated carriers, which can solve the Bi 4 O 5 I 2 Monomer and Bi 7 O 9 I 3 The problem of rapid recombination of photogenerated electrons and holes in monomers.

[0072] Figure 5 The bismuth-rich iodine bismuth oxide heterojunction photocatalyst (Bi4 / Bi7-3) in Example 1 of the present invention and the hydrothermal Bi in Comparative Example 1 4 O 5 I 2 (Bi4-S1), calcined Bi in Comparative Example 2 4O 5 I 2 (Bi4-S2), hydrothermal Bi in comparative example 3 7 O 9 I 3 UV-visible diffuse reflectance spectrum of (Bi7). 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 to visible light, with absorption band edges at 482nm, 537nm, 504nm and 596nm respectively. 4 O 5 I 2 The light absorption intensity in the range of 250nm to 380nm is significantly increased, indicating that Bi 7 O 9 I 3 with Bi 4 O 5 I 2 The composite heterojunction can improve the light absorption capacity of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst (Bi7Bi4 / Bi7-3) to a certain extent.

[0073] Test 1:

[0074] The photocatalysts prepared in Examples 1-3 and Comparative Examples 1-7 were applied to degrade antibiotic wastewater, specifically comprising the following steps:

[0075] 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.

[0076] 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.

[0077] Figure 6 Bi4 / Bi7-3 in Example 1 of the present invention and hydrothermal Bi in Comparative Example 14 O 5 I 2 (Bi4-S1), calcined Bi in Comparative Example 2 4 O 5 I 2 (Bi4-S2), hydrothermal Bi in comparative example 3 7 O 9 I 3 The relationship between time and degradation efficiency when photocatalytically degrading ciprofloxacin (CIP) wastewater; Figure 7 This 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 C 0 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:

[0078] 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.

[0079] 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.

[0080] 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.

[0081] Hydrothermal Bi in Comparative Example 1 4 O 5 I 2 The degradation efficiency of CIP by (Bi4-S1) was 58.0% after 30 min of photocatalytic reaction.

[0082] Comparative Example 2 Calcinated Bi 4 O 5 I 2 The degradation efficiency of CIP by (Bi4-S2) was 27.0% after 30 min of photocatalytic reaction.

[0083] Comparative Example 3 Hydrothermal Bi 7 O 9 I 3 The degradation efficiency of CIP by (Bi7) was 57.4% after 30 min of photocatalytic reaction.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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 hydrothermal Bi 4 O 5 I 2 The degradation efficiency and degradation rate of (Bi4-S1) were only 58.0% and 0.02831min, respectively. -1 , calcined Bi 4 O 5 I 2 The degradation efficiency and degradation rate of (Bi4-S2) were only 27.0% and 0.01066min respectively. -1 , hydrothermal Bi 7 O 9 I 3 The degradation efficiency and degradation rate of (Bi7) were only 57.4% and 0.02779min respectively. -1 By comparison, we can see that: compared with pure water thermal Bi 4 O 5 I 2 、Pure calcined Bi 4 O 5 I 2 and pure water thermal Bi 7 O 9 I 3 In comparison, the degradation rates of the bismuth-rich iodine bismuth heterojunction photocatalyst prepared by the present invention for antibiotic wastewater were increased by 4.53, 12.0 and 4.62 times, respectively. The main reason for this phenomenon is that the present invention generates Bi in situ by the solution alkalinity control method and calcination method. 4 O 5 I 2 and Bi 7 O9 I 3 , a bismuth-rich iodine-based bismuth oxide heterojunction was constructed. 4 O 5 I 2 Nanosheets and Bi 7 O 9 I 3 The synergistic effect between the nanosheets effectively improves the electron-hole separation efficiency and light absorption efficiency in the bismuth-rich iodine bismuth oxide heterojunction photocatalyst, improves the photocatalytic redox ability of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst, enhances the photocatalytic activity of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst, and ultimately achieves rapid and efficient degradation of CIP in wastewater. In addition, the material prepared in the molar ratio of bismuth nitrate pentahydrate to potassium iodide in Comparative Example 4 is 1:1. The degradation efficiency of CIP after 30 minutes of photocatalytic reaction is 27.6%, and the material prepared in the molar ratio of bismuth nitrate pentahydrate to potassium iodide in Comparative Example 5 is 1:3. The degradation efficiency of CIP after 30 minutes of photocatalytic reaction is 34.1%, which is much lower than that of Bi in Examples 1 to 3. 4 O 5 I 2 / Bi 7 O 9 I 3 The reason is that when the ratio of bismuth nitrate pentahydrate to potassium iodide is close (i.e., comparative example 4), the generated substance is a stoichiometric BiOI monomer, which has a narrow band gap and weak oxidation ability, and has a low ability to generate free radicals through photocatalysis. In addition, because the proportion of I in the raw material is small, alkalinity control and high-temperature calcination will over-etch I and generate bismuth-rich Bi 7 O 9 I 3 The photogenerated electrons and holes recombine seriously, the redox ability is relatively poor, and the number of active oxygen species generated is small, resulting in poor pollutant degradation ability. 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℃ and 200℃ respectively. The high temperature caused the material to further degrade to Bi 5 O 7 I conversion, destroying the original Bi 4 O 5 I 2 / Bi 7 O 9 I 3 The heterojunction is composed, so the degradation rate of CIP is reduced to 42.4%. However, the temperature is too low to fully etch I, and most of the generated substances are still precursors, so the degradation efficiency is only 17.9%.

[0089] Test 2:

[0090] The recyclability of bismuth-rich iodine bismuth oxyiodide heterojunction photocatalyst in the photocatalytic degradation process is investigated, including the following steps:

[0091] (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.

[0092] (2) The reaction system obtained in step (1) (ciprofloxacin wastewater with Bi4 / Bi7-3 added) was placed on a magnetic stirrer and stirred for 1 h in the dark to achieve adsorption equilibrium. 4 mL of 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 by UV-visible spectrophotometer and recorded as C 0 .

[0093] (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.

[0094] (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.

[0095] (5) Repeat steps (2) to (4) four more times.

[0096] 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.

[0097] 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 to generate bismuth-rich Bi in situ. 4 O 5 I 2 and Bi 7 O 9 I 3 , a bismuth-rich iodine-based bismuth oxide heterojunction photocatalyst was constructed. 7 O 9 I 3 Nanosheets have the advantages of wide light absorption range and high light absorption efficiency. 7 O 9 I 3 The introduction of nanosheets can serve as 4 O 5 I 2 / Bi 7 O 9 I 3 The light absorption center of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst can improve the light absorption capacity and light absorption efficiency of the bismuth-rich iodine bismuth oxide heterojunction photocatalyst (this is because Bi 7 O 9 I 3 The absorption cutoff edge is 596nm, Bi 4 O 5 I 2 The absorption cutoff edge is 504nm, Bi 7 O 9 I 3 Has a wider light absorption range, compared with Bi 4 O 5 I 2 After compounding, the drawback of narrow absorption range can be improved); on the other hand, under visible light conditions, Bi 4 O 5 I 2 with Bi 7 O 9 I 3 The two bismuth-rich iodine-based 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 Bi 4 O 5 I 2 The conduction band and Bi 7 O 9 I 3 valence band, thereby achieving the purpose of effective separation of photogenerated electrons and holes and indirectly improving the photocatalytic oxidation ability.

[0098] In addition, the present invention provides a bismuth-rich iodine bismuth oxide heterojunction photocatalyst, which is composed of bismuth-rich Bi 4 O 5 I 2 with Bi 7 O 9 I 3 The nanosheets are stacked layer by layer, and have 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. 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.

[0099] 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; the molar ratio of the bismuth nitrate pentahydrate to the potassium iodide is 1:1.5 to 1:2.5; S2. Calcinate the precursor obtained in step S1 to obtain a bismuth-rich bismuth iodide heterojunction photocatalyst; the calcination temperature of the precursor is 250° C. to 350° C., and the calcination time is 1 h to 3 h; the bismuth-rich bismuth iodide heterojunction photocatalyst is composed of bismuth-rich Bi4O5I2 and Bi7O9I3 nanosheets stacked layer by layer.

2. 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.

3. 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.

4. The preparation method according to any one of claims 1 to 3, characterized in that: In step S2, the heating rate during the calcination process is 2.3°C / min to 10°C / min.

5. An application of a bismuth-rich bismuth oxyiodide heterojunction photocatalyst prepared by the preparation method according to any one of claims 1 to 4 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.

6. The use according to claim 5, 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.

7. The use according to claim 6, 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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