Preparation method of photocatalytic material for rapidly repairing wastewater containing chromium

Abstract

The application relates to the field of nanomaterial synthesis and photocatalytic reduction of pollutants, and discloses a preparation method of a photocatalytic material for rapidly repairing chromium-containing wastewater. An amino-rich carbon dot is obtained by mixing an amino-containing carbon source material and a nitrogen source small molecule through a one-step hydrothermal method, filtering, dialysis and freeze drying; the prepared amino-rich carbon dot is subjected to water bath ultrasonic treatment with TiO2, and then hydrothermal reaction, centrifugal separation and freeze drying are carried out to obtain a composite material of the amino-loaded TiO2, which is used for reducing hexavalent chromium in photocatalysis. The TiO2 modified by the amino-rich carbon dot has a reduced forbidden band width, an expanded light absorption range and an increased positive charge amount, and the electrostatic force between the TiO2 and the negative hexavalent chromium is increased; and the modified TiO2 is loaded on a hydrogel, so that the contact between the photocatalyst and the pollutants is further improved, and the reaction is rapidly carried out. The material has high photocatalytic activity in photocatalytic treatment of the chromium-containing wastewater, and provides a valuable technical solution for the treatment of the chromium-containing wastewater.

Description

Technical Field

[0001] This invention relates to the fields of nanomaterial synthesis and photocatalytic reduction of pollutants, and particularly to a method for preparing a photocatalytic material for rapid remediation of chromium-containing wastewater. Background Technology

[0002] Hexavalent chromium pollution in water poses a serious threat to ecological security and human health. It kills aquatic organisms and inhibits the self-purification function of water bodies. Irrigating farmland with chromium-containing wastewater inhibits the digestion of soil organic matter, leading to reduced agricultural yields. Once hexavalent chromium enters the ecological cycle, it poses a significant threat to human health. Hexavalent chromium is a typical highly toxic, teratogenic, and carcinogenic heavy metal pollutant. Due to its mutagenic properties, it is classified as a Group 1 carcinogen by the International Agency for Research on Cancer. Currently, various technologies are used to reduce hexavalent chromium, such as adsorption, precipitation, ion exchange, biological methods, electrochemical methods, and photocatalysis.

[0003] With the gradual deterioration of the environment, environmentally friendly and efficient photocatalysis has gradually gained attention. Photocatalysis has advantages such as being clean, green, and simple, and has great potential in the treatment of chromium-containing wastewater. At present, there are some challenges in the photocatalytic reduction of hexavalent chromium: (1) the reduction capacity for high concentrations of hexavalent chromium is limited; (2) the reduction effect is weak under neutral and alkaline conditions, and the pH of typical industrial wastewater is generally 7-11; (3) most studies are conducted under laboratory light sources, which limits its application in real environments. Therefore, it is urgent to develop a photocatalyst that can efficiently reduce hexavalent chromium under high concentrations, a wide pH range, and natural light.

[0004] To address the aforementioned issues, it is of great importance to provide a method for preparing photocatalytic materials for the rapid remediation of chromium-containing wastewater. Summary of the Invention

[0005] To overcome the above shortcomings, this invention provides a method for preparing a photocatalytic material for the rapid remediation of chromium-containing wastewater. This method has low raw material costs, simple operation, and strong reduction effect, and has great potential application value in the field of treating chromium-containing wastewater.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a photocatalytic material for rapid remediation of chromium-containing wastewater, comprising the following steps:

[0007] S1. Preparation of carbon dot powder: Mix amino-containing carbon source material with nitrogen source small molecule solution evenly to obtain mixture a. Perform hydrothermal reaction on mixture a, cool to room temperature, dialyze the purified mixture a through a dialysis bag, and freeze dry to obtain amino-rich carbon dot powder.

[0008] S2. Preparation of carbon dot-TiO2 composite material: Amino-rich carbon dot powder and TiO2 powder are ultrasonically mixed evenly in aqueous solution to obtain mixture b. The obtained mixture b is subjected to hydrothermal reaction, cooled to room temperature, centrifuged and freeze-dried to obtain carbon dot-TiO2 composite material.

[0009] S3. Preparation of hydrogel composite material: Chitosan was dissolved in acetic acid and then added to the prepared carbon dot-TiO2 photocatalytic composite material. After mixing evenly, a mixture c was obtained. The mixture c was then frozen and dried to obtain the hydrogel composite material.

[0010] Due to their excellent modifiability and outstanding optical properties, carbon dots (CDs) offer a novel approach to improving photocatalytic efficiency. CDs are zero-dimensional carbon nanomaterials; combining them with semiconductor photocatalysts can effectively broaden the light absorption range and reduce the band gap energy, thereby enhancing photocatalytic performance. Specifically, CDs act as excellent electron donors and acceptors, improving the separation efficiency of photogenerated charges in a single photocatalyst. Furthermore, due to their surface defects, their unique upconversion photoluminescence effect converts ultraviolet light into visible light, facilitating the utilization of a wider range of solar spectra. These capabilities overcome the inherent limitations of photocatalysts and enhance their activity.

[0011] Preferably, the amino-containing carbon source material in S1 is one or more of pyridine compounds, biomass straw, and nitrogen source compounds.

[0012] Preferably, the pyridine compound includes one or more of dodecylpyridine, tetradecylpyridine, hexadecylpyridine, and octadecylpyridine, the biomass straw includes rice straw, corn straw, cotton straw, and wheat straw, and the nitrogen source compound includes one or more of methylamine, ethylamine, propylamine, ethylenediamine, and N,N-dimethylethylenediamine.

[0013] Preferably, in step S1, the amino-containing carbon source material is 1.2g, the amount of ethylenediamine solution is 20uL, and the mixed solution system is 30mL.

[0014] Preferably, the hydrothermal conditions in S1 are a temperature of 180°C and a time of 5 hours; the dialysis bag has a specification of 2000 Da; the dialysis time is 5 hours to 12 hours; and the freeze-drying time is 48 hours to 72 hours.

[0015] Preferably, the mass fraction ratio of the amino-rich carbon dot powder to the TiO2 powder in S2 is (1-3):100.

[0016] Preferably, the hydrothermal conditions in S2 are a temperature of 150°C and a time of 6 hours; the freeze-drying time is 12 hours to 24 hours.

[0017] Preferably, in S3, the chitosan is 0.5g, the acetic acid concentration is 1%, and the solution system is 50ml; the stirring condition is 4h at room temperature; and the freeze-drying time is 12h to 24h.

[0018] Preferably, the mass fraction ratio of the hydrogel to the carbon dot-TiO2 composite material in S3 is (1:9, 2:8, 3:7).

[0019] Preferably, the photocatalytic composite material is used for the reduction of hexavalent chromium.

[0020] The present invention has the following beneficial effects:

[0021] 1. The photocatalyst prepared by this invention is simple and is prepared by a one-step hydrothermal method. The raw materials used are widely available, easy to obtain, have low toxicity and low pollution. Pyridine compounds have rich multifunctionality, and their relatively high alkalinity makes them play an important role in catalysis and reaction. The comprehensive utilization of biomass straw helps to comprehensively treat agricultural waste and reduce the negative impact on farmland and the environment.

[0022] 2. The photocatalyst prepared in this invention has excellent performance in reducing hexavalent chromium. Under conditions such as high concentration of hexavalent chromium (50 mg / L), wide pH range (3, 5, 7, 9) and natural sunlight, it can almost completely reduce hexavalent chromium.

[0023] 3. In this invention, the prepared photocatalyst exhibits good stability and recyclability in both ion interference resistance experiments and cycling experiments, further demonstrating its practical applicability in real-world environments.

[0024] In summary, the band gap of TiO2 modified with amino-rich carbon dots is reduced, the light absorption range is expanded, the amount of positive charge is increased, and the electrostatic interaction between TiO2 and negatively charged hexavalent chromium is enhanced. Furthermore, loading carbon dot-TiO2 onto a hydrogel further improves the photocatalytic efficiency. This type of material exhibits highly efficient photocatalytic activity in the photocatalytic treatment of chromium-containing wastewater, demonstrating excellent hexavalent chromium reduction performance under high concentrations, a wide pH range, and natural sunlight. It provides a valuable technical solution for chromium-containing wastewater treatment applications. This invention offers a highly efficient photocatalytic material with practical application value for hexavalent chromium reduction. Attached Figure Description

[0025] Figure 1 These are high-resolution TEM images and particle size distribution maps of RN-CDs obtained in Example 1;

[0026] Figure 2 This is a high-resolution TEM image of TiO2 obtained in Example 1;

[0027] Figure 3This is a high-resolution TEM image of RN-CDs / TiO2 obtained in Example 1;

[0028] Figure 4 This is the full-scan XPS spectrum of the RN-CDs obtained in Example 1;

[0029] Figure 5 This is the C1s scan XPS spectrum of the RN-CDs obtained in Example 1;

[0030] Figure 6 This is the O1s scan XPS spectrum of the RN-CDs obtained in Example 1;

[0031] Figure 7 This is the N1s scan XPS spectrum of the RN-CDs obtained in Example 1;

[0032] Figure 8 These are the FT-IR spectra of RN-CDs, TiO2, and RN-CDs / TiO2 obtained in Example 1;

[0033] Figure 9 These are the UV / Vis diffuse reflectance spectra of TiO2 and RN-CDs / TiO2 obtained in Example 1;

[0034] Figure 10 This is the Tauc plot of TiO2 and RN-CDs / TiO2 obtained in Example 1;

[0035] Figure 11 This is the valence band XPS spectrum of RN-CDs / TiO2 obtained in Example 1;

[0036] Figure 12 This is a graph showing the reduction effect of RN-CDs / TiO2 at different initial Cr(VI) concentrations in Example 1;

[0037] Figure 13 This is a graph showing the reduction effect of RN-CDs / TiO2 at different pH values ​​in Example 1;

[0038] Figure 14 This is a graph showing the results of five cycles of RN-CDs / TiO2 in Example 1;

[0039] Figure 15 This is a graph showing the ion interference results of RN-CDs / TiO2 under real sunlight in Example 1;

[0040] Figure 16 The graph shows the photocatalytic performance of the RN-CDs / TiO2 supported hydrogel with different ratios in Example 1.

[0041] Figure 17This is a schematic diagram of the RN-CDs / TiO2 reaction principle in an embodiment of the present invention. Detailed Implementation

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Example 1:

[0044] refer to Figures 1-17 This embodiment provides a method for preparing a photocatalytic material for rapid remediation of chromium-containing wastewater, including the following steps:

[0045] S1. Preparation of amino-rich carbon dot powder: First, 1.2 g of biomass straw powder and 20 μL of ethylenediamine were sonicated in 30 mL of aqueous solution. Then, the mixture was transferred to a 50 mL Teflon-lined stainless steel autoclave and heated at 180 °C for 5 hours. After cooling to room temperature, it was centrifuged at 4000 rpm for 30 min to remove larger particles. The supernatant was then extracted, filtered through a 0.22 μm membrane filter, and purified in deionized water using a dialysis membrane with a molecular cutoff of 2000 Da for 8 hours. Finally, the carbon dot powder (RN-CDs) was collected after freeze-drying.

[0046] The ethylenediamine solution was purchased from Aladdin Reagent Company, was of analytical grade, and had a molecular weight of 60.1; the dialysis bag used an MWCO membrane; the purpose of dialysis was to remove interfering substances.

[0047] S2. Preparation of carbon dot-TiO2 photocatalyst: RN-CDs powder and TiO2 powder were mixed at a mass ratio of (1-3):100 to prepare a nanocomposite material. The resulting mixture was vigorously stirred with 20 mL of deionized water for 1 hour. Subsequently, the mixture was transferred to a 50 mL polytetrafluoroethylene-sealed autoclave and heated at 150 °C for 6 hours. After the hydrothermal reaction, the solution was centrifuged, washed twice with deionized water, and then freeze-dried for 48 hours to collect the nanocomposite material (RN-CDs / TiO2) powder.

[0048] Nano-TiO2 was purchased from Aladdin Reagent Company, analytical grade, with a molecular weight of 79.87.

[0049] S3. Preparation of hydrogel photocatalyst: Weigh 0.5g of chitosan and dissolve it in 1% acetic acid solution (50ml). After the solution becomes transparent, add carbon dot-TiO2 photocatalyst in different ratios of 9:1, 8:2, and 7:3. After stirring for 4 hours, freeze-dry the resulting mixture and collect the hydrogel photocatalyst powder.

[0050] Chitosan was purchased from Aladdin Reagent Company, with a degree of deacetylation ≥95% and a basic unit molecular weight of approximately 161.16.

[0051] The microstructures of RN-CDs, TiO2, and RN-CDs / TiO2 were analyzed using TEM. Figure 1 As shown, the amino-rich carbon dots are quasi-spherical and monodisperse, with particle sizes ranging from 3.59 to 13.8 nm among the approximately 100 particles analyzed. The average size of these particles is approximately 6.57 nm, while the lattice spacing of the RN-CDs is approximately 0.28 nm. Figure 2 The crystal structure of TiO2 is shown, with a lattice plane distance of 0.35 nm, which is characteristic of the TiO2 anatase morphology. Furthermore, Figure 3 High-resolution TEM images of the RN-CDs / TiO2 nanocomposite are presented. It can be observed that RN-CDs (0.28 nm) and TiO2 (0.35 nm) overlap in the same region, indicating that the hydrothermally synthesized RN-CDs have been successfully integrated into the surface of TiO2 nanoparticles.

[0052] To determine the structural characteristics of RN-CDs, XPS analysis was used to analyze their chemical composition and bonding arrangement. The XPS spectra of RN-CDs showed that they are mainly composed of C, O, and N elements, with C accounting for 67.92%, O for 24.64%, and N for 7.43%. Figure 4 In high-resolution C1s XPS spectra ( Figure 5 In the high-resolution O1s spectrum, three prominent peaks were observed at 286.23 eV, correlated with C=O bonds, and at 284.69 eV and 283.21 eV, correlated with CO / CN and CC / C=C bonds, respectively. Figure 6 The N1s spectrum exhibits characteristic peaks of 531.41 eV and 529.83 eV, corresponding to the OH and O lattices, respectively. Furthermore, the high-resolution N1s spectrum... Figure 7 The diagram shows two binding energy peaks at 400.01 eV and 398.01 eV, respectively, which correspond to -NH3. + It is related to the -NH2 bond.

[0053] FT-IR spectra of RN-CDs, TiO2, and RN-CDs / TiO2 are as follows: Figure 8 As shown. At 3364.33cm -1 3355.96cm -1 and 3247.59cm -1 The characteristic peak at this location corresponds to OH and NH bonds, indicating sufficient water solubility. 2929.89 cm⁻¹ -1 and 2927.15cm-1 The peak at 1637.10 cm⁻¹ belongs to the CH bond. Additionally, the peak at 1637.10 cm⁻¹... -1 1636.52cm -1 and 1574.93cm -1 The characteristic peak at this location is related to the stretching vibration of the CN / C=N bond. Notably, TiO2 modified with RN-CDs exhibits a peak at 2927.15 cm⁻¹. -1 A new CH tensile vibration peak appeared, confirming that RN-CDs were successfully loaded onto the TiO2 composite material.

[0054] The optical properties of TiO2 and RN-CDs / TiO2 composites were analyzed using ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). Figure 9 It can be seen that pure TiO2 only absorbs light with wavelengths below 361.01 nm. In contrast, the absorption edge of the RN-CDs / TiO2 composite material extends from 361.01 nm to 389.35 nm. This indicates that the incorporation of RN-CDs significantly improves the light absorption range of the photocatalyst. Further analysis can estimate the band gap energy (Eg) of the two materials. Figure 10 The Eg value of pure TiO2 is 3.24 eV, which is higher than the 2.98 eV of the RN-CDs / TiO2 composite. This difference in bandgap energy highlights the effectiveness of RN-CDs in altering the optical properties of TiO2. The bandgap energy can be derived from equations (1) and (2):

[0055] (ahv) 2 =A(hv-E) g (1)

[0056] hv=hc / λ (2)

[0057] In the formula, a is the optical absorption coefficient; A is a constant related to the transfer probability; c(3.0×10⁸ m·s²) -1 ) is the speed of light; h(6.626×10 -34 J·Hz -1 ) is Planck's constant, and v is the radiation frequency.

[0058] Figure 11 The XPS analysis results are shown, which can determine the valence band location (E) of RN-CDs / TiO2. VB The energy of the conductive band (CB) of the RN-CDs / TiO2 composite material was calculated to be 1.87 eV. The energy of the conductive band (CB) was calculated using Mulliken theory (Equation (3)). CB = -1.11eV).

[0059] E CB =E VB -Eg (3)

[0060] This demonstrates that the RN-CDs / TiO2 composite material exhibits a smaller band gap compared to pure TiO2. This characteristic of RN-CDs / TiO2 enables it to activate electrons at a lower energy threshold, highlighting its potential in solar-driven photocatalysis applications.

[0061] The reduction effect of RN-CDs / TiO2 composite material on Cr(VI) at excitation wavelengths greater than 365 nm was evaluated using a 300W xenon lamp simulating sunlight. The reduction effects of Cr at different initial concentrations were shown below. Figure 12 As shown, under the same conditions of photocatalyst dosage, reaction temperature, and solution pH, the time required to reduce Cr(VI) is directly proportional to its initial concentration. With decreasing Cr(VI) concentration, the reduction rate of Cr(VI) by RN-CDs / TiO2 increases, with the fastest reduction reaching 10 mg / L Cr(VI) within 5 minutes. Schematic diagrams of Cr(VI) solutions with different initial pH values ​​(pH = 3, 5, 7, 9) are shown below. Figure 13 As shown in the figure, the reaction rate is fastest at pH 7. Under both acidic and alkaline conditions, Cr(VI) can be completely reduced within 60 minutes, demonstrating that RN-CDs / TiO2 maintains its excellent and efficient Cr(VI) reduction capability. After five cycles, the Cr(VI) reduction rate of RN-CDs / TiO2 reaches 96.83%, showcasing its excellent recyclability. Figure 14 ).

[0062] To determine the practicality of RN-CDs / TiO2 as a photocatalyst, photocatalytic reduction experiments were conducted under real sunlight. A Cr(VI) concentration of 10 mg / L was selected as the reaction system, and 0.1 g of 2% RN-CDs / TiO2 photocatalyst was added. The results showed that under sunlight irradiation, RN-CDs / TiO2 achieved a Cr(VI) reduction rate of 97.12% within only 10 min, and complete reduction within 30 min. This highlights RN-CDs / TiO2 as an economical and efficient photocatalyst under real-world environmental conditions. Ion interference experiments were conducted by introducing common metal cations (10 mg / L). Figure 15 This indicates that Na + K + Ca 2+ Mg 2+ The presence of plasma did not hinder the efficient reduction of Cr(VI) by RN-CDs / TiO2. This indicates that RN-CDs / TiO2 is an effective photocatalyst with sufficiently good stability and anti-interference ability in the natural environment.

[0063] Further testing of the catalytic performance of the carbon dot-TiO2 photocatalyst supported on the hydrogel showed that the catalytic performance of the carbon dot-TiO2 photocatalyst supported on the hydrogel was significantly improved. Figure 16 The reduction rate of 50 mg / L Cr(VI) reached 99.75% within only 30 minutes. Furthermore, changing the ratio of hydrogel to carbon dot-TiO2 photocatalyst had no significant effect on the reduction rate. The adsorption performance of the prepared hydrogel photocatalyst in the dark reaction stage was affected by the hydrogel loading content; the higher the hydrogel loading, the stronger the adsorption performance.

[0064] The above results demonstrate that RN-CDs / TiO2 can efficiently reduce Cr(VI) under high Cr(VI) concentration, wide pH range, and natural light conditions, exhibiting superior stability, anti-interference ability, and recyclability. Furthermore, loading RN-CDs / TiO2 onto a hydrogel can further enhance the photocatalytic performance of the material.

[0065] Example 2:

[0066] This embodiment provides a method for preparing a photocatalytic material for rapid remediation of chromium-containing wastewater, including the following steps:

[0067] S1. Preparation of amino-rich carbon dot powder: First, 1.2 g of cetylpyridine and 20 μL of ethylenediamine were sonicated in 30 mL of aqueous solution. Then, the mixture was transferred to a 50 mL Teflon-lined stainless steel autoclave and heated at 180 °C for 5 hours. After cooling to room temperature, it was centrifuged at 4000 rpm for 30 min to remove larger particles. The supernatant was then extracted, filtered through a 0.22 μm membrane filter, and purified in deionized water using a dialysis membrane with a molecular cutoff of 2000 Da for 8 hours. Finally, the carbon dot powder (CPC-CDs) was collected after freeze-drying.

[0068] The cetylpyridine was purchased from Aladdin Reagent Company, analytical grade, with a molecular weight of 384.44; the ethylenediamine solution was purchased from Aladdin Reagent Company, analytical grade, with a molecular weight of 60.1; the dialysis bag used an MWCO membrane; the purpose of dialysis is to remove interfering substances.

[0069] S2. Preparation of composite photocatalyst: A nanocomposite material was prepared by mixing CPC-CDs powder and TiO2 powder at a mass fraction ratio of (1-3):100. The resulting mixture was vigorously stirred with 20 mL of deionized water for 1 hour. Subsequently, the mixed solution was transferred to a 50 mL polytetrafluoroethylene-sealed autoclave and heated at 150 °C for 6 hours. After the hydrothermal reaction, the solution was centrifuged, washed twice with deionized water, and then freeze-dried for 48 hours to collect the nanocomposite material (CPC-CDs / TiO2) powder.

[0070] Nano-TiO2 was purchased from Aladdin Reagent Company, analytical grade, with a molecular weight of 79.87.

[0071] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a photocatalytic material for rapid remediation of chromium-containing wastewater, characterized in that: Includes the following steps: S1. Preparation of carbon dot powder: Mix amino-containing carbon source material with nitrogen source small molecule solution evenly to obtain mixture a. Perform hydrothermal reaction on mixture a, cool to room temperature, dialyze the purified mixture a through a dialysis bag, and freeze dry to obtain amino-rich carbon dot powder. S2. Preparation of carbon dot-TiO2 composite material: Amino-rich carbon dot powder and TiO2 powder were ultrasonically mixed evenly in an aqueous solution to obtain mixture b. The mixture b was subjected to hydrothermal reaction, cooled to room temperature, centrifuged, and freeze-dried to obtain carbon dot-TiO2 photocatalytic composite material; S3. Preparation of hydrogel composite material: Chitosan is dissolved in acetic acid and then added to the prepared carbon dot-TiO2 photocatalytic composite material. After mixing evenly, a mixture c is obtained. The mixture c is freeze-dried to obtain the hydrogel composite material. In S1, the amino-containing carbon source material is 0.5g, the ethylenediamine solution is 250uL, and the mixed solution system is 30mL; the hydrothermal conditions in S1 are a temperature of 180℃ and a time of 5h; the dialysis bag is 2000Da, and the dialysis time is 5h to 12h; the freeze-drying time is 48h to 72h; in S2, the mass fraction ratio of the amino-rich carbon dot powder to TiO2 powder is (1~3):100; the hydrothermal conditions in S2 are a temperature of 150℃ and a time of 6h; the freeze-drying time is 12h to 24h; in S3, the chitosan is 0.5g, the acetic acid concentration is 1%, and the solution system is 50ml; the freeze-drying time is 12h to 24h; the mass fraction ratio of the hydrogel to the carbon dot-TiO2 composite material in S3 is (1:9, 2:8, 3:7).

2. The method for preparing a photocatalytic material for rapid remediation of chromium-containing wastewater as described in claim 1, characterized in that: The amino-containing carbon source material mentioned in S1 is one or more of pyridine compounds, biomass straw, and nitrogen source compounds.

3. The method for preparing a photocatalytic material for rapid remediation of chromium-containing wastewater according to claim 2, characterized in that: The pyridine compounds include one or more of dodecylpyridine, tetradecylpyridine, hexadecylpyridine, and octadecylpyridine; the biomass straw includes rice straw, corn straw, cotton straw, and wheat straw; and the nitrogen source small molecules include one or more of methylamine, ethylamine, propylamine, ethylenediamine, and N,N-dimethylethylenediamine.

4. The application of the photocatalytic composite material prepared by the method for preparing a photocatalytic material for rapid remediation of chromium-containing wastewater as described in any one of claims 1-3, characterized in that, The photocatalytic composite material is used for the reduction of hexavalent chromium.

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