Preparation method of hollow amorphous n-tio2 with photocatalytic high concentration cr(vi)

Abstract

The application discloses a preparation method of hollow amorphous N-TiO2 with photocatalysis on high-concentration Cr(VI), and the hollow amorphous N-TiO2 is prepared by using three-dimensional Fe3O4 as a structural framework, mixing titanium di(2-hydroxypropanoate) dihydroxide diammonium with ultrasonic waves as a titanium source, and then hydrolyzing the titanium di(2-hydroxypropanoate) dihydroxide diammonium into Fe3O4 / amorphous TiO2 at low temperature; the hollow amorphous N-TiO2 photocatalyst is obtained by reacting in a glycol solution mixed with urea and then treating with a low-concentration acid solution. The content of the titanium di(2-hydroxypropanoate) dihydroxide diammonium is the main reason for the difference in shell thickness, and the low crystallization power is the key to obtaining and stabilizing the amorphous material. The detection result shows that the structure of the hollow amorphous N-TiO2 prepared by the application exhibits typical amorphous characteristics, such as excellent photocurrent signal, low interface resistance and strong oxygen vacancy signal, and the photocatalyst can degrade wastewater containing Cr(VI) with a concentration of 0.274 g / L under visible light irradiation.

Description

Technical Field

[0001] This invention relates to the field of photocatalyst technology, specifically a method for preparing hollow amorphous N-TiO2 with high photocatalytic concentration of Cr(VI). Background Technology

[0002] TiO2 is widely used in photocatalysts. Taking the doping of heteroatoms in photocatalysts as an example, oxygen vacancies caused by the doping of metal elements such as Mn, and the formation of TiO2 lattice by the incorporation of C atoms, are all examples of this application. 3+ Oxygen vacancies, or N atoms, are introduced into the interstitial spaces of the TiO2 lattice, creating abundant oxygen vacancies. The introduction of impurity atoms induces beneficial defects, increasing the separation rate of bulk carriers. However, in industrial-grade photocatalytic environments, single-atom-doped photocatalysts still suffer from low efficiency in treating high concentrations of pollutants.

[0003] Currently, appropriate morphology design can enhance the separation and transfer rates of intrinsic charge carriers within photocatalysts. The structure of two-dimensional nanomaterials is beneficial for shortening the diffusion path of photogenerated charge carriers, providing abundant active sites for adsorption and photocatalytic reactions. However, in practical applications, nanosheets tend to aggregate in solution, complicating recovery and increasing costs. The hollow structure of a three-dimensional microsphere matrix retains the thin-shell characteristics of sheet-like structures, with a larger internal cavity, enhancing practical light utilization.

[0004] Another method to improve carrier separation and transport efficiency is to construct amorphous components. For example, yellow amorphous TiO2 can exhibit surface adsorption and photoactivity under visible light irradiation. Due to changes in electronic properties, introducing impurity atoms such as carbon and sulfur into the bulk phase of amorphous TiO2 results in higher photocatalytic activity. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing hollow amorphous N-TiO2 with high photocatalytic concentration of Cr(VI), which constructs a uniform amorphous single-doped shell on the basis of a hollow structure to improve the treatment of high-concentration pollutants.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing hollow amorphous N-TiO2 with high Cr(VI) concentration through photocatalysis includes the following steps:

[0008] Step 1: Weigh ferric chloride hexahydrate, urea, and tetrabutylammonium bromide in a molar ratio of 1:20:4, and dissolve them in a three-necked flask containing 180 mL of ethylene glycol solution to form a red solution. Heat the solution and reflux at 195 °C for 40 min to form a green precipitate. Calcinate the green precipitate in a tube furnace under nitrogen protection for 2 h at a calcination temperature of 500 °C. After cooling, grind the calcined product to obtain three-dimensional Fe3O4 microspheres.

[0009] Step 2: Take 0.3-0.8g of the three-dimensional Fe3O4 microspheres prepared in Step 1 and add them to 35-70mL of ethanol solution to prepare solution A. Place solution A in an ice bath for 10min. Take 0.10-0.55mL of di(2-hydroxypropionic acid) diammonium hydroxide titanium and add it to 10mL of ethanol solution and mix well to prepare solution B. Add solution B dropwise to solution A. Transfer the mixture to an ultrasonic cleaner and sonicate for 30-90min at an ultrasonic power of 40kHz. Then transfer the mixture to a water bath preheated to 60-100℃ and react for 2-6h to obtain Fe3O4 / amorphous TiO2.

[0010] Step 3: Take 0.3g of Fe3O4 / amorphous TiO2 prepared in Step 2 and 0.4-2.0g of urea and add them to 35-65mL of ethanol solution and mix well. Seal the mixture in a 100mL polytetrafluoroethylene-lined high-pressure reactor and hydrothermally treat it at 140-200℃ for 10h. After the reaction is completed, centrifuge, wash and dry to obtain Fe3O4 / amorphous N-doped TiO2.

[0011] Step 4: Immerse the Fe3O4 / amorphous N-doped TiO2 prepared in Step 3 in a low-concentration acid solution for 30 min, collect the supernatant, and wash the supernatant with deionized water until neutral to obtain hollow amorphous N-TiO2 with high concentration of Cr(VI) photocatalysis.

[0012] The physicochemical properties of the prepared hollow amorphous N-TiO2 were tested as follows: particle size 1.2-1.5µm, shell thickness 8.2-23.0nm; visible light transmittance 42-70%; specific surface area 63.3-182.95m². 2 / g; photocurrent signal is 0.075-0.231µA / cm 2 The interface resistance is 374.8-943.2Ω; the oxygen vacancy signal is 0.08-0.38au.

[0013] Preferably, the ethylene glycol in step one is of analytical grade and has a mass percentage concentration of ≥98%.

[0014] Preferably, the ethanol solution in steps two and three is analytical grade and has a mass percentage concentration of 99.5%.

[0015] Preferably, in step two, the mass percentage concentration of di(2-hydroxypropionic acid)diammonium hydroxide titanium is 50%, and the CAS number is 65104-06-5.

[0016] Preferably, the low-concentration acid solution in step four is hydrochloric acid with a concentration of 2-5 mol / L.

[0017] The method described in this invention uses a three-dimensional Fe3O4 framework, ultrasonically mixed with diammonium bis(2-hydroxypropionic acid)dihydroxide as a titanium source, which can be hydrolyzed at low temperature to form Fe3O4 / amorphous TiO2. This is then reacted in an ethylene glycol solution mixed with urea, and after treatment with a low-concentration acid solution, a hollow amorphous N-TiO2 photocatalyst is obtained. The content of diammonium bis(2-hydroxypropionic acid)dihydroxide is the main reason for the difference in shell thickness, and low crystallization kinetics are key to the generation and stability of amorphous materials. Test results show that the hollow amorphous N-TiO2 prepared in this invention exhibits typical amorphous characteristics: excellent photocurrent signal, low interfacial resistance, and strong oxygen vacancy signal, enabling the photocatalyst to degrade Cr(VI)-containing wastewater with a concentration of 0.274 g / L under visible light irradiation.

[0018] The thickness of the hollow amorphous N-TiO2 prepared by this invention can be controlled by the amount of diammonium di(2-hydroxypropionic acid)dihydroxide titanium added, so that the prepared catalyst has the advantages of excellent visible light absorption rate and high carrier separation performance, and has the prospect of being applied to industrial wastewater treatment.

[0019] The hollow amorphous N-TiO2 prepared by this invention exhibits excellent reusability during use due to the stability of its composition and structure.

[0020] The raw materials used in the method described in this invention are inexpensive, effectively reducing the actual production cost of the materials. Attached Figure Description

[0021] Figure 1 This is a scanning structural diagram of the hollow amorphous material prepared in this invention;

[0022] Figure 2 This is a transmission structure diagram of the hollow amorphous material prepared in this invention;

[0023] Figure 3 The image shows the XRD pattern of the hollow amorphous material prepared according to this invention.

[0024] Figure 4 This is a specific surface area diagram of the hollow amorphous material prepared in this invention;

[0025] Figure 5 The diagram shows the photocatalytic performance of the hollow amorphous material prepared in this invention.

[0026] Figure 6 The diagram shows the photocatalytic cycle performance of the hollow amorphous material prepared in this invention.

[0027] Figure 7 The carrier separation activity of the hollow amorphous material prepared in this invention is shown. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings.

[0029] Example 1

[0030] A method for preparing hollow amorphous N-TiO2 with high Cr(VI) concentration through photocatalysis includes the following steps:

[0031] Step 1: Dissolve 4.4 mmol of ferric chloride hexahydrate, 88 mmol of urea, and 17.6 mmol of tetrabutylammonium bromide in a three-necked flask containing 180 mL of ethylene glycol solution to form a red solution. Heat the solution and reflux at 195 °C for 40 min to form a green precipitate. Calcinate the green precipitate in a tube furnace under nitrogen protection for 2 h at 500 °C. After cooling, grind the calcined product to obtain three-dimensional Fe3O4 microspheres.

[0032] Step 2: Take 0.3g of the three-dimensional Fe3O4 microspheres prepared in Step 1 and add them to 35mL of ethanol solution to prepare solution A. Place solution A in an ice bath for 10min. Take 0.25mL of di(2-hydroxypropionic acid) diammonium hydroxide titanium and add it to 10mL of ethanol solution and mix well to prepare solution B. Add solution B dropwise to solution A. Transfer the mixture to an ultrasonic cleaner and sonicate for 30min at an ultrasonic power of 40kHz. Then transfer the mixture to a water bath preheated at 80℃ and react for 2h to obtain Fe3O4 / amorphous TiO2.

[0033] Step 3: Take 0.3g of Fe3O4 / amorphous TiO2 prepared in Step 2 and 1.2g of urea and add them to 35mL of ethanol solution and mix them evenly. Seal the mixture in a 100mL polytetrafluoroethylene-lined high-pressure reactor and hydrothermally treat it at 160℃ for 10h. After the reaction is completed, centrifuge, wash and dry to obtain Fe3O4 / amorphous N-doped TiO2.

[0034] Step 4: Immerse the Fe3O4 / amorphous N-doped TiO2 prepared in Step 3 in a low-concentration acid solution for 30 min, collect the supernatant, and wash the supernatant with deionized water until neutral to obtain hollow amorphous N-TiO2 with high concentration of Cr(VI) photocatalysis.

[0035] The physicochemical properties of the prepared hollow amorphous N-TiO2 were tested as follows: particle size 1.5µm, shell thickness 10.5nm; visible light transmittance 70%; specific surface area 182.95m². 2 / g; photocurrent signal is 0.231µA / cm 2 The interface resistance is 374.8Ω; the oxygen vacancy signal is 0.38au.

[0036] Example 2

[0037] A method for preparing hollow amorphous N-TiO2 with high concentration of Cr(VI) photocatalysis is the same as in Example 1, except that in step two, 0.10 mL of di(2-hydroxypropionic acid)diammonium hydroxide titanium is added to 10 mL of ethanol solution and mixed evenly to prepare solution B.

[0038] Example 3

[0039] A method for preparing hollow amorphous N-TiO2 with high concentration of Cr(VI) photocatalysis is the same as in Example 1, except that in step two, 0.40 mL of di(2-hydroxypropionic acid)diammonium hydroxide titanium is added to 10 mL of ethanol solution and mixed evenly to prepare solution B.

[0040] Example 4

[0041] A method for preparing hollow amorphous N-TiO2 with high concentration of Cr(VI) photocatalysis is provided. The preparation method is the same as in Example 1, except that in step two, 0.55 mL of di(2-hydroxypropionic acid)diammonium hydroxide titanium is added to 10 mL of ethanol solution and mixed evenly to prepare solution B.

[0042] Example 5

[0043] A method for preparing hollow amorphous N-TiO2 with high Cr(VI) concentration through photocatalysis includes the following steps:

[0044] Step 1: Dissolve 4.4 mmol of ferric chloride hexahydrate, 88 mmol of urea, and 17.6 mmol of tetrabutylammonium bromide in a three-necked flask containing 180 mL of ethylene glycol solution to form a red solution. Heat the solution and reflux at 195 °C for 40 min to form a green precipitate. Calcinate the green precipitate in a tube furnace under nitrogen protection for 2 h at 500 °C. After cooling, grind the calcined product to obtain three-dimensional Fe3O4 microspheres.

[0045] Step 2: Take 0.8g of the three-dimensional Fe3O4 microspheres prepared in Step 1 and add them to 70mL of ethanol solution to prepare solution A. Place solution A in an ice bath for 10min. Take 0.25mL of di(2-hydroxypropionic acid)diammonium hydroxide titanium and add it to 10mL of ethanol solution and mix well to prepare solution B. Add solution B dropwise to solution A. Transfer the mixture to an ultrasonic cleaner and sonicate for 30min at an ultrasonic power of 40kHz. Then transfer the mixture to a water bath preheated at 80℃ and react for 2h to obtain Fe3O4 / amorphous TiO2.

[0046] Step 3: Take 0.3g of Fe3O4 / amorphous TiO2 prepared in Step 2 and 1.2g of urea and add them to 65mL of ethanol solution and mix them evenly. Seal the mixture in a 100mL polytetrafluoroethylene-lined high-pressure reactor and hydrothermally treat it at 160℃ for 10h. After the reaction is completed, centrifuge, wash and dry to obtain Fe3O4 / amorphous N-doped TiO2.

[0047] Step 4: Immerse the Fe3O4 / amorphous N-doped TiO2 prepared in Step 3 in a low-concentration acid solution for 30 min, collect the supernatant, and wash the supernatant with deionized water until neutral to obtain hollow amorphous N-TiO2 with high concentration of Cr(VI) photocatalysis.

[0048] The physicochemical properties of the prepared hollow amorphous N-TiO2 were tested as follows: particle size 1.2 µm, shell thickness 8.2 nm; visible light transmittance 65%; specific surface area 122.6 m². 2 / g; photocurrent signal is 0.101µA / cm 2 The interface resistance is 778.5Ω; the oxygen vacancy signal is 0.18au.

[0049] Example 6

[0050] A method for preparing hollow amorphous N-TiO2 with high Cr(VI) concentration through photocatalysis includes the following steps:

[0051] Step 1: Dissolve 4.4 mmol of ferric chloride hexahydrate, 88 mmol of urea, and 17.6 mmol of tetrabutylammonium bromide in a three-necked flask containing 180 mL of ethylene glycol solution to form a red solution. Heat the solution and reflux at 195 °C for 40 min to form a green precipitate. Calcinate the green precipitate in a tube furnace under nitrogen protection for 2 h at 500 °C. After cooling, grind the calcined product to obtain three-dimensional Fe3O4 microspheres.

[0052] Step 2: Take 0.3g of the three-dimensional Fe3O4 microspheres prepared in Step 1 and add them to 45mL of ethanol solution to prepare solution A. Place solution A in an ice bath for 10min. Take 0.55mL of di(2-hydroxypropionic acid) diammonium hydroxide titanium and add it to 10mL of ethanol solution and mix well to prepare solution B. Add solution B dropwise to solution A. Transfer the mixture to an ultrasonic cleaner and sonicate for 90min at an ultrasonic power of 40kHz. Then transfer the mixture to a water bath preheated at 60℃ and react for 6h to obtain Fe3O4 / amorphous TiO2.

[0053] Step 3: Take 0.3g of Fe3O4 / amorphous TiO2 prepared in Step 2 and 2.0g of urea and add them to 65mL of ethanol solution. Mix them evenly and seal the mixture in a 100mL polytetrafluoroethylene-lined high-pressure reactor. Perform hydrothermal treatment at 140℃ for 10h. After the reaction is completed, centrifuge, wash and dry to obtain Fe3O4 / amorphous N-doped TiO2.

[0054] Step 4: Immerse the Fe3O4 / amorphous N-doped TiO2 prepared in Step 3 in a low-concentration acid solution for 90 min, collect the supernatant, and wash the supernatant with deionized water until neutral to obtain hollow amorphous N-TiO2 with high concentration of Cr(VI) photocatalysis.

[0055] The physicochemical properties of the prepared hollow amorphous N-TiO2 were tested and are as follows: particle size of 1.2 µm, shell thickness of 23.0 nm, visible light transmittance of 42%, and specific surface area of ​​98.3 m². 2 / g; photocurrent signal is 0.129µA / cm 2 The interface resistance is 654.9Ω; the oxygen vacancy signal is 0.13au.

[0056] Example 7

[0057] A method for preparing hollow amorphous N-TiO2 with high Cr(VI) concentration through photocatalysis includes the following steps:

[0058] Step 1: Dissolve 4.4 mmol of ferric chloride hexahydrate, 88 mmol of urea, and 17.6 mmol of tetrabutylammonium bromide in a three-necked flask containing 180 mL of ethylene glycol solution to form a red solution. Heat the solution and reflux at 195 °C for 40 min to form a green precipitate. Calcinate the green precipitate in a tube furnace under nitrogen protection for 2 h at 500 °C. After cooling, grind the calcined product to obtain three-dimensional Fe3O4 microspheres.

[0059] Step 2: Take 0.3g of the three-dimensional Fe3O4 microspheres prepared in Step 1 and add them to 70mL of ethanol solution to prepare solution A. Place solution A in an ice bath for 10min. Take 0.10mL of di(2-hydroxypropionic acid) diammonium hydroxide titanium and add it to 10mL of ethanol solution and mix well to prepare solution B. Add solution B dropwise to solution A. Transfer the mixture to an ultrasonic cleaner and sonicate for 30min at an ultrasonic power of 40kHz. Then transfer the mixture to a water bath preheated to 100℃ and react for 2-6h to obtain Fe3O4 / amorphous TiO2.

[0060] Step 3: Take 0.3g of Fe3O4 / amorphous TiO2 prepared in Step 2 and 0.4g of urea and add them to 65mL of ethanol solution. Mix them evenly and seal the mixture in a 100mL polytetrafluoroethylene-lined high-pressure reactor. Perform hydrothermal treatment at 200℃ for 10h. After the reaction is completed, centrifuge, wash and dry to obtain Fe3O4 / amorphous N-doped TiO2.

[0061] Step 4: Immerse the Fe3O4 / amorphous N-doped TiO2 prepared in Step 3 in a low-concentration acid solution for 30 min, collect the supernatant, and wash the supernatant with deionized water until neutral to obtain hollow amorphous N-TiO2 with high concentration of Cr(VI) photocatalysis.

[0062] The physicochemical properties of the prepared hollow amorphous N-TiO2 were tested as follows: particle size of 1.3 µm, shell thickness of 12.8 nm, visible light transmittance of 56%, and specific surface area of ​​63.3 m². 2 / g; photocurrent signal is 0.075µA / cm 2 The interface resistance is 943.2Ω; the oxygen vacancy signal is 0.08au.

[0063] In the above embodiments, the ethylene glycol in step one is analytical grade with a mass percentage concentration ≥98%. The ethanol solutions in steps two and three are analytical grade with a mass percentage concentration of 99.5%. The di(2-hydroxypropionic acid)diammonium hydroxide titanium in step two has a mass percentage concentration of 50% and a CAS number of 65104-06-5. The low-concentration acid solution in step four is hydrochloric acid with a concentration of 2-5 mol / L.

[0064] Comparative Example 1

[0065] 0.10 mL of di(2-hydroxypropionic acid)diammonium hydroxide titanium was added to 35 mL of ethanol solution. The mixture was sealed in a 100 mL polytetrafluoroethylene-lined high-pressure reactor and hydrothermally treated at 160 °C for 10 h. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain TiO2.

[0066] 0.55 mL of di(2-hydroxypropionic acid)diammonium hydroxide titanium was added to 70 mL of ethanol solution, followed by the addition of 1.2 g of urea. The mixture was sealed in a 100 mL polytetrafluoroethylene-lined high-pressure reactor and hydrothermally treated at 160 °C for 10 h. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain AN-TiO2.

[0067] The hollow amorphous N-TiO2 prepared in Example 1 was named AH2-NTO. The hollow amorphous N-TiO2 prepared in Example 2 was named AH1-NTO. The hollow amorphous N-TiO2 prepared in Example 3 was named AH3-NTO. The hollow amorphous N-TiO2 prepared in Example 4 was named AH4-NTO.

[0068] The products prepared in Examples 1-4 and Comparative Example 1 were analyzed and described using microstructure diagrams, X-ray diffraction (XRD), specific surface area, photocatalytic performance, photocatalytic cycle performance, and carrier separation activity to illustrate the structure and performance of each batch of products.

[0069] 1. Scanning electron microscopy image analysis

[0070] Figure 1 These are the results of scanning electron microscopy of the product.

[0071] Figure 1 Magnetite Fe3O4, before modification and after low-temperature hydrothermal treatment and calcination, exhibits a distinct flower-like structure. By combining it with diammonium di(2-hydroxypropionic acid)dihydroxide titanium, and controlling the hydrothermal conditions and the amount of diammonium di(2-hydroxypropionic acid)dihydroxide titanium, hollow N-TiO2 microspheres with uniform shell thickness were synthesized. Figure 1 b、 Figure 1 The results in c show that with the increase of surface size, the thickness of hollow N-TiO2 is not uniform, but rather increases with the increase of diammonium di(2-hydroxypropionic acid)dihydroxide titanium content. Figure 1 As shown in b, the material synthesized after mechanical stirring for 30 minutes with a titanium source content of 0.25 mL even exhibited agglomeration, such as... Figure 1 As shown in c, the material was synthesized after mechanical stirring for 30 minutes with a titanium source content of 0.55 mL. Figure 1 df represents the material synthesized under ultrasonic conditions. Its shell thickness increased from 35 nm for Fe3O4 to 45 nm for AH1-NTO, 56 nm for H2-NTO, and 80 nm for AH4-NTO, respectively. In comparison, the photocatalyst synthesized under ultrasonic conditions exhibited a more uniform surface layer and a more regular thickness variation, indicating a higher dispersion between the titanium source and the substrate under ultrasonic irradiation.

[0072] 2. Transmission electron microscopy image analysis

[0073] Figure 2 The TEM images confirmed the formation of the amorphous hollow structure.

[0074] With the addition of Fe3O4 particles, the product exhibits a distinct hollow structure, such as... Figure 2 a, Figure 2 b、 Figure 2 As shown in c. For example, with the increase of diammonium di(2-hydroxypropionic acid)dihydroxide titanium content, the brightness of the product in the TEM image decreases, indicating a high TiO2 content in the material. The increase in brightness and the presence of bubble-like structures in the HR-TEM image confirm that the material has a significant hollow structure after etching. As indicated by the arrows, as... Figure 2 d、 Figure 2 e Figure 2 As shown in f. HR-TEM images of the particles reveal faint anatase lattice fringes, as... Figure 2 As shown in g, this indicates that the ultrasound-assisted low-temperature process is beneficial to the formation of amorphous TiO2. For example, when the morphology of TiO2 changes from solid to uniformly hollow, the lattice fringes of the material completely disappear, and no lattice fringes were found in the magnified local image. Therefore, it is believed that the ultrasound-assisted low-temperature process can reduce the crystallization kinetics of the material, thereby promoting the formation and stabilization of amorphous structures.

[0075] 3. XRD pattern analysis

[0076] Figure 3 The XRD spectrum in the image provides additional evidence for the amorphous properties and nitrogen doping of the material. Figure 3 The XRD characteristic peak results show that pure TiO2 particles exhibit anatase crystal structure. After N doping, the main characteristic diffraction peaks essentially disappear, indicating that the product is typically amorphous. This is because the crystallization rate is low at low temperatures, preventing the product from transforming into the corresponding crystalline structure. The diffraction peaks of the product remain consistent after the etching reaction, indicating that the template was completely removed.

[0077] 4. Specific surface area diagram analysis

[0078] Figure 4 The results showed that the specific surface areas of AH2-NTO and AN-TiO2 were 182.95 and 35.25 m², respectively. 2 / g. This result indicates that the increased specific surface area of ​​the material after hollowing provides more adsorption sites for pollutants.

[0079] 5. Photocatalytic performance analysis

[0080] In the visible light photocatalytic performance experiment, the light source used had a power of 200 mW / cm². 2A 300W xenon lamp was used for the photocatalysis. Taking 100 mg / L Cr(VI) wastewater with pH 2.01 as an example, the specific photocatalytic process is illustrated. The entire process involves two stages: dark adsorption and photocatalysis. 40 mg of photocatalyst was added to 40 mL of 100 mg / L Cr(VI) wastewater, and the real-time concentration of Cr(VI) was monitored at different illumination times using continuous sampling. After dark adsorption was complete, the light source was turned on and visible light was applied for another 2 hours, and the degradation of Cr(VI) was detected. The real-time concentration of Cr(VI) was determined using the diphenylcarbazide colorimetric method. Figure 5 The photocatalytic performance results showed that the concentration of Cr(VI) gradually decreased with increasing irradiation time, indicating that the photocatalytic activity of the material was improved. After 120 min of visible light irradiation, pure TiO2 removed 7.6 mg / L of Cr(VI). After deducting the adsorption-removed portion, the photocatalytic efficiency of pure TiO2 was close to zero. The photocatalytic activity of AN-TiO2 was 79.78% higher than that of pure TiO2, indicating that the formation of the amorphous structure significantly improved the actual catalytic efficiency of the material. Compared with AN-TiO2, the catalytic concentration of AH1-NTO increased to 63 mg / L, indicating that the formation of the hollow structure enhanced the photocatalytic activity of the material. Further increasing the content of the titanium source would further improve the catalytic activity of the material; AH2-NTO could completely photocatalyze 100 mg / L.

[0081] The optimized photocatalyst showed significant efficacy in treating high-concentration chromium-containing wastewater, especially with the assistance of triethanolamine. Figure 5 As shown in b. For example, complete removal of 0.15 g / L Cr(VI) was achieved within 120 min. Furthermore, the photocatalytic removal efficiency of Cr(VI) remained high, reaching 97.27%, 89.93%, and 54.3% at Cr(VI) concentrations of 0.2 g / L, 0.3 g / L, and 0.5 g / L, respectively. Clearly, the method synthesized in this patent has the potential to treat high-concentration chromium-containing wastewater.

[0082] 6. Analysis of photocatalytic cycle performance diagram

[0083] Figure 6 The cyclic activity of the AH2-NTO photocatalyst was investigated by performing five photocatalytic operations on Cr(VI) under the same conditions. Even after five cycles, the AH2-NTO photocatalyst still achieved a Cr(VI) reduction efficiency of nearly 100%, indicating its stable performance and promising prospects for practical applications.

[0084] 7. Carrier Separation Activity Analysis

[0085] Figure 7The results of study a indicate that the hollow structure of the product is beneficial for light absorption. For example, under 500 nm illumination, the transmittance of pure AN-TiO2 is about 8%, while after forming a hollow structure, its transmittance increases to about 70%. Under short-wavelength conditions, the transmittance of AH2-NTO is lower than that of pure AN-TiO2, indicating that the formation of a hollow structure is beneficial for the material's utilization of visible light.

[0086] Evidence for high carrier separation efficiency comes from electron spin resonance, transient photocurrent response, and electrochemical impedance spectroscopy. Figure 7 The results in b show that AN-TiO2 exhibits an electron spin resonance signal at g=2.004 compared to pure TiO2, which may be due to the generation of oxygen vacancies within the material. The ESR signal of AH2-NTO is approximately three times that of AH1-NTO, indicating its excellent carrier separation capability. Figure 7 In c, the photocurrent densities of AH2-NTO and AN-TiO2 are 0.229 uA / cm², respectively. 2 and 0.044uA / cm 2 The 5.2-fold increase indicates that the material can generate more photoelectrons per unit time under visible light irradiation. Figure 7 Figure d shows the transfer of electrons from the photocatalyst to the external circuit resistance, where the arc radius decreases sequentially from TiO2 to AN-TiO2, confirming that the amorphous structure and nitrogen doping are beneficial for electron transfer. Furthermore, the electrochemical impedance of AH2-NTO is reduced by 2.5 times compared to AN-TiO2, indicating that the hollow structure enhances electron transfer efficiency, thereby improving the photochemical quantum yield. Combined with the material's excellent photocatalytic activity, we believe that hollow amorphous N-doped TiO2 microspheres possess excellent carrier separation efficiency.

[0087] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make other equivalent modifications and improvements based on the technical teachings provided by the present invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing hollow amorphous N-TiO2 with photocatalytic high concentration of hexavalent chromium, characterized in that: Comprising the following steps: Step one, the ferric chloride hexahydrate, urea and tetrabutylammonium bromide were weighed according to the molar ratio of 1:20:4, then dissolved in a three-necked flask containing 180 mL of ethylene glycol solution to form a red solution, the solution was heated and refluxed at 195℃ for 40 min to form a green precipitate; the green precipitate was calcined in a tube furnace under nitrogen protection for 2h, and the calcination temperature was 500℃; after the calcined product was cooled, it was ground to obtain three-dimensional Fe3O4 microspheres; Step two, 0.3-0.8g of three-dimensional Fe3O4 microspheres prepared in step one was added to a solution containing 35-70mL of ethanol solution to prepare solution A, solution A was ice-bathed for 10min, 0.10-0.55mL of di (2-hydroxypropionic acid) dihydroxide titanium ammonium was added to 10mL of ethanol solution and mixed uniformly to prepare solution B, solution B was added dropwise to solution A, and the mixture was transferred to an ultrasonic cleaner and ultrasonicated for 30-90min at a power of 40kHZ, then the mixture was transferred to a preheated water bath at 60-100℃ and reacted for 2-6h to prepare Fe3O4 / amorphous TiO2; Step three, 0.3g of Fe3O4 / amorphous TiO2 prepared in step two and 0.4-2.0g of urea were added to 35-65mL of ethanol solution and mixed uniformly, then the mixture was sealed in a 100mL polytetrafluoroethylene-lined high-pressure reaction kettle and hydrothermally treated at 140-200℃ for 10h, after the reaction, centrifugation, washing and drying were carried out to obtain Fe3O4 / amorphous N-doped TiO2; Step four, the Fe3O4 / amorphous N-doped TiO2 prepared in step three was soaked in a low-concentration acid solution for 30min, the supernatant was collected, and the supernatant was washed with deionized water until neutral to obtain hollow amorphous N-TiO2 with photocatalytic high-concentration chromium (VI); The prepared hollow amorphous N-TiO2 tested has the following physicochemical properties: particle size of 1.2-1.5 µm, shell thickness of 8.2-23.0 nm; visible light transmittance of 42-70%; specific surface area of 63.3-182.95 m 2 / g; photocurrent signal of 0.075-0.231 µA / cm 2 ; interface resistance of 374.8-943.2 Ω; oxygen vacancy signal of 0.08-0.38 a.u.

2. The method of claim 1, wherein: The ethylene glycol in step one is analytical pure, with a mass percentage concentration of ≥98%.

3. The method of claim 1, wherein: The ethanol solution in step two and step three is analytical pure, with a mass percentage concentration of 99.5%.

4. The method of claim 1, wherein: The mass percentage concentration of di (2-hydroxypropionic acid) dihydroxide titanium ammonium in step two is 50%, and the CAS number is 65104-06-5.

5. The method of claim 1, wherein: The low-concentration acid solution in step four is hydrochloric acid with a concentration of 2-5mol / L.

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