Self-assembled coniferous bamboo-based carbon quantum dot modified BiOCl composite photocatalyst with inherent nitrogen and silicon as well as preparation method and application of BiOCl composite photocatalyst

Abstract

The invention discloses a self-assembled coniferous bamboo-based carbon quantum dot modified BiOCl composite photocatalyst with inherent nitrogen and silicon as well as a preparation method and application of the BiOCl composite photocatalyst. The preparation method of the composite catalyst comprises the following steps: firstly, taking bamboo pulp material preparation waste as a raw material, synthesizing bamboo-based carbon quantum dots through a hydrothermal method, and then obtaining a purified carbon quantum dot solution by adopting the steps of suction filtration and dialysis; and combining the bamboo-based carbon quantum dot solution with bismuth salt to prepare the composite catalyst. The composite catalyst shows excellent photocatalytic performance in degradation of tetracycline hydrochloride. The carbon quantum dots are prepared from bamboo pulp material preparation waste, and nitrogen (N) and silicon (Si) elements naturally contained in bamboo wood endow the carbon quantum dots with excellent electron transmission performance. The prepared composite photocatalytic material has higher catalytic activity and has a wide application prospect in the field of wastewater treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and in particular relates to a BiOCl composite photocatalyst modified by self-assembled needle-shaped bamboo-based carbon quantum dots of intrinsic nitrogen and silicon, and a preparation method and application thereof. Background Art

[0002] Tetracycline hydrochloride is a class of tetracycline antibiotics widely used in medicine and agriculture. With its long-term and widespread use in medicine and animal husbandry, a large amount of residues have been discharged into the environment, especially in water and soil. These residues are not only difficult to degrade naturally, but also bioaccumulate, posing a significant threat to ecosystems and human health. Although traditional physical, chemical and biological treatment technologies can partially remove tetracycline hydrochloride from water and soil, these methods often have problems such as low treatment efficiency, complex operation, high energy consumption and secondary pollution. Therefore, there is an urgent need to develop more efficient and sustainable treatment technologies.

[0003] Photocatalytic technology has been widely used in the field of organic pollutant wastewater treatment due to its high efficiency, green and sustainable advantages. As a potential photocatalytic material, BiOCl, although it has a unique layered structure and a moderate band gap, still faces many challenges in practical applications. First, the band gap of BiOCl is relatively wide (about 3.2 eV), which makes it mainly absorb ultraviolet light and cannot make full use of visible light, limiting the photocatalytic efficiency. Secondly, the recombination rate of photogenerated electrons and holes is high, which reduces the active carriers available for redox reactions and further weakens its catalytic performance. In addition, the specific surface area of ​​BiOCl is relatively small, which reduces the adsorption capacity of pollutants and thus affects the reaction rate. Finally, BiOCl is prone to photocorrosion under certain conditions, resulting in its structural instability and affecting its long-term performance.

[0004] Carbon quantum dots have shown significant potential in the field of pollutant treatment due to their unique optical, electrical and surface chemical properties. Carbon quantum dots can effectively utilize the visible light portion of sunlight, thereby significantly improving the photocatalytic efficiency. Its quantum confinement effect helps to significantly enhance the separation efficiency of electron-hole pairs, reduce the probability of recombination, and thus promote the efficient degradation of pollutants. In addition, the size and morphology of carbon quantum dots can be precisely controlled to optimize catalytic performance, while their surface can be chemically modified to introduce specific functional groups to further improve the selectivity and stability of the catalytic reaction. Compared with traditional treatment methods, carbon quantum dot technology not only provides higher degradation efficiency and lower energy consumption, but also can work effectively in a wider spectral range to reduce secondary pollution. Therefore, as a green treatment solution, carbon quantum dot technology has shown extremely broad application prospects.

[0005] Bamboo has shown significant advantages in the preparation and catalytic application of carbon quantum dots due to its unique porous structure and rich natural elements. Its porous structure gives bamboo great potential in material adsorption. The cell wall of bamboo is composed of multiple layers of microfibrils and microtubule bundles. These microstructures form a large number of micrometer- and nanometer-level pores, which significantly increase the specific surface area of ​​the material. In addition, the silicon element in bamboo is deposited in the cell wall in the form of silicate, giving it excellent mechanical strength. Compared with other plant materials, carbon quantum dots prepared from bamboo show better stability in physical and chemical environments, and are particularly suitable for catalytic applications in high temperature or strong acid and alkali environments. The rapid growth and high yield of bamboo make it a renewable biomass resource, thereby reducing the environmental impact of the preparation process of carbon quantum dots. In summary, bamboo-based carbon quantum dots have broad application prospects and huge development potential in the fields of photocatalysis, pollutant degradation and energy conversion. Summary of the invention

[0006] The purpose of the present invention is to provide a BiOCl composite photocatalyst modified by self-assembled needle-shaped bamboo-based carbon quantum dots of intrinsic nitrogen and silicon, and a preparation method and application thereof, so as to solve the problems of difficult degradation of tetracycline hydrochloride and unsatisfactory catalytic performance of BiOCl.

[0007] To achieve the above object, the technical solution adopted by the present invention is: A method for preparing a BiOCl composite photocatalyst modified by self-assembled needle-shaped bamboo-based carbon quantum dots of intrinsic nitrogen and silicon comprises the following steps: (1) Preparation of N, Si-CQDs: The bamboo pulp preparation waste is crushed and ground to collect bamboo powder with a particle size greater than 100 mesh; the bamboo powder is mixed with water and placed in a polytetrafluoroethylene-lined stainless steel hydrothermal autoclave to react at 180-220 °C for 8-24 hours; after the reaction is completed and cooled to room temperature, it is filtered to collect the brown-yellow liquid at the bottom layer, and further purified by dialysis to finally obtain a bamboo-based carbon quantum dot solution; preferably, a 0.22-0.45 μm filter membrane is used for filtration; a dialysis bag with a molecular weight of 500-2000 Da is used for dialysis, and the dialysis time is 24-48 hours.

[0008] (2) Preparation of N,Si-CQDs / BiOCl composite photocatalyst: Dissolve bismuth salt in ethylene glycol to obtain dispersion A; dissolve chloride salt in water to form solution B. Evenly mix an appropriate amount of bamboo-based carbon quantum dot solution and solution B to obtain a mixed solution, then add the mixed solution to dispersion A to form a uniform white suspension, and after sufficient mixing, transfer to a stainless steel hydrothermal reactor containing polytetrafluoroethylene for hydrothermal reaction; after the reaction is completed, the obtained material is cooled, separated, washed and dried to finally obtain the target product.

[0009] As a preferred technical solution, the chloride salt is potassium chloride or sodium chloride; the bismuth salt is bismuth nitrate, bismuth sulfate or bismuth chloride; and the atomic molar ratio of bismuth to chlorine in the bismuth salt and the bromide salt is 1:1.

[0010] The present invention also provides the use of the above-mentioned intrinsic nitrogen silicon self-assembled needle-shaped bamboo-based carbon quantum dots modified BiOCl composite photocatalyst in degrading pollutants in wastewater, and is particularly suitable for degrading organic pollutants such as tetracycline hydrochloride in wastewater.

[0011] The present invention has the following beneficial effects: The present invention uses the waste of bamboo pulp preparation to prepare carbon quantum dots through the technical scheme. The bamboo itself is rich in nitrogen and silicon to prepare bamboo-based carbon quantum dots rich in both N and Si, without the need to add additional nitrogen and silicon sources. The nitrogen (N) and silicon (Si) elements naturally contained in bamboo give carbon quantum dots excellent electron transport properties. Pyrrolic nitrogen has rich electron donor properties and can increase the free electron density in carbon quantum dots, thereby improving their conductivity. In addition, the presence of pyrrolic nitrogen expands the light absorption range of carbon quantum dots, so that the N, Si-CQDs / BiOCl composite photocatalytic material can significantly improve the photocatalytic efficiency. The introduction of Si elements effectively prevents the agglomeration of quantum dots and maintains their dispersibility and stability. At the same time, the rich oxygen-containing functional groups in bamboo improve the dispersibility of quantum dots in water and provide additional active sites, so that the N, Si-CQDs / BiOCl photocatalytic material has higher catalytic activity. The natural porous structure of bamboo gives carbon quantum dots a higher specific surface area and rich pore structure, thereby accelerating the adsorption of pollutants and increasing the rate of photocatalytic reactions.

[0012] The use of bamboo pulp preparation waste as raw materials realizes the high-value utilization of bamboo waste and significantly reduces the production cost. The photocatalytic material preparation method provided by the invention is simple and easy to implement, can be reused, and has a wide range of promotion and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Degradation diagram of tetracycline hydrochloride on BiOCl and N,Si-CQDs / BiOCl composite photocatalyst; Figure 2 TEM image (a) and SEM image (bc) of N,Si-CQD-200℃-16h; Figure 3 Fourier transform infrared spectrum (a) and ultraviolet spectrum (b) of N,Si-CQD-200℃-16h; Figure 4 This is the XPS spectrum of N,Si-CQD-200℃-16h; Figure 5Photocurrent response (a) and electrochemical impedance spectroscopy (ESI) (b) of N, Si-CQD-200℃-16h and 5CB-200-16. DETAILED DESCRIPTION

[0014] The present invention is further described below in conjunction with the embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0015] In addition, unless otherwise specified, the preparation processes in the following embodiments are all conventional means in the prior art in the art, and therefore, they are not described in detail.

[0016] Example 1 A method for preparing a BiOCl composite photocatalyst modified by self-assembled needle-shaped bamboo-based carbon quantum dots of intrinsic nitrogen and silicon comprises the following steps: (1) Preparation of N,Si-CQDs: Bamboo pulp preparation waste was used as raw material, which was crushed and sieved to obtain bamboo powder with a particle size greater than 100 mesh. 1.5 g of bamboo powder was mixed evenly with 60 mL of distilled water and placed in a polytetrafluoroethylene stainless steel hydrothermal autoclave. The mixture was heated at 200 °C for 8 h, cooled to room temperature, and the lower brown-yellow liquid was collected by suction filtration using a 0.22 μm filter membrane. The liquid was placed in a dialysis bag with a molecular weight of 1000 Da and dialyzed for 36 h. The resulting solution was the carbon quantum dot solution, labeled N,Si-CQDs-200 °C-8h.

[0017] (2) Preparation of N,Si-CQDs / BiOCl composite photocatalyst: 3mmol Bi(NO3)3·5H2O was dissolved in 30mL ethylene glycol (EG), first ultrasonicated for 30min, then vigorously stirred for 30min to obtain solution A; 3mmol NaCl was dissolved in 25mL deionized water to form solution B, 5mL N,Si-CQDs solution (concentration of 0.15 mg / mL, preparation conditions of hydrothermal temperature of 200℃, hydrothermal time of 8h) was added to solution B, and after thorough mixing, the mixture was added dropwise to solution A to obtain a uniform white suspension. After uniform mixing, the mixture was transferred to a stainless steel hydrothermal reactor with polytetrafluoroethylene for hydrothermal reaction at 160℃ for 10h. After the reaction was completed, the obtained product was cooled, separated, washed, and dried to obtain the N,Si-CQDs / BiOCl composite photocatalyst, which was labeled as 5CB-200-8.

[0018] Embodiment 2-4 Compared with Example 1, the difference between Examples 2-4 is that the hydrothermal temperatures for preparing N,Si-CQDs in step (1) are 180°C, 220°C and 240°C, respectively, and the other conditions are the same as those in Example 1. The prepared carbon quantum dot solutions are named N,Si-CQDs-180°C-8h, N,Si-CQDs-220°C-8h, and N,Si-CQDs-240°C-8h, respectively. Correspondingly, the composite catalysts obtained in step (2) are named 5CB-180-8, 5CB-220-8, and 5CB-240-8, respectively.

[0019] Embodiment 5-6 Compared with Example 1, the difference between Examples 5-6 is that the N,Si-CQDs prepared in step (1) are prepared under different hydrothermal times, which are 16 h and 24 h respectively. Correspondingly, the composite catalysts obtained in step (2) are named 5CB-200-16 and 5CB-200-24 respectively.

[0020] Example 7 Compared with Example 1, the difference in Example 7 is that the volumes of N,Si-CQDs added in step (2) are 1 mL, 2 mL, 10 mL and 20 mL, respectively, and the corresponding volumes of deionized water are 29 mL, 28 mL, 20 mL and 10 mL, respectively. The other conditions are the same as those in Example 1, and the prepared products are named 1CB-200-8, 2 CB-200-8, 10 CB-200-8 and 20 CB-200-8, respectively.

[0021] Comparative Example 1 Compared with Example 1, the difference of Comparative Example 1 is that no N,Si-CQDs solution is added, the volume of the corresponding deionized water is 30 mL, and the other conditions are the same as those of Example 1. The prepared product is marked as BiOCl.

[0022] Comparative Example 2 Compared with Example 1, the difference of Comparative Example 2 is that the raw material for preparing CODs is Masson pine. Other conditions are the same as those of Example 1, and the prepared products are named M-5CB-200-8.

[0023] Photocatalytic performance test - degradation of tetracycline hydrochloride The photocatalytic materials prepared in the above-mentioned embodiments and comparative examples were respectively tested for pollutant degradation performance, and the method is as follows: 100 mg of catalyst was added to 150 mL of 20 mg / L tetracycline hydrochloride solution, stirred in the dark for 30 minutes to reach adsorption equilibrium, then irradiated with a 300w Xe lamp (with a 420 nm cutoff filter), reacted for 120 minutes under visible light irradiation, and samples were taken every 20 minutes. The obtained samples were filtered through a 0.22 μm filter membrane, and the supernatant was tested for the content of tetracycline hydrochloride by a spectrophotometer, and the test wavelength was 357 nm. The results are shown in Table 1.

[0024] Table 1 Degradation rate of tetracycline hydrochloride by N,Si-CQDs / BiOCl composite photocatalyst

[0025] From Table 1 and Figure 1 It can be seen that pure BiOCl has poor adsorption and photodegradation effects on tetracycline hydrochloride. Under dark conditions, after 30 minutes of adsorption, the removal rate of tetracycline hydrochloride is only 5.6%, while after 120 minutes of illumination, the removal rate increases to 20.8%. After adding N,Si-CQDs, the adsorption and photodegradation effects of N,Si-CQDs / BiOCl composite catalyst are significantly improved, indicating that the porous structure of N,Si-CQDs is conducive to the adsorption of pollutants. In addition, the unique nitrogen (N) and silicon (Si) elements in N,Si-CQDs effectively improve the electron transport performance of N,Si-CQDs, thereby enhancing the photocatalytic activity of N,Si-CQDs / BiOCl. In particular, the degradation rate of tetracycline hydrochloride by photocatalytic material 5CB-200-16 after 120 minutes of illumination is as high as 75.1%.

[0026] The degradation effects of N,Si-CQDs prepared under different hydrothermal conditions on tetracycline hydrochloride are significantly different, because N,Si-CQDs show different physical and chemical properties at different temperatures. N,Si-CQDs have a variety of functional groups on the surface, and high temperature conditions may cause reconstruction or passivation of surface functional groups, thereby changing their surface chemical properties; while long-term hydrothermal treatment may cause the agglomeration of N,Si-CQDs particles, thus affecting the catalytic effect.

[0027] Table 2 shows the results of the analysis of the N and Si contents in bamboo and Masson pine raw materials and their carbon quantum dots. According to Table 2, the contents of nitrogen and silicon in bamboo are higher than those in Masson pine, so the contents of nitrogen and carbon in bamboo-based carbon quantum dots are also higher than those in Masson pine quantum dots. At the same time, the photocatalytic composite material M-5CB-200-8 exhibits weaker photocatalytic performance than 5CB-200-8. This shows that the inherent nitrogen (N) and silicon (Si) elements in bamboo have an important influence on the performance of N,Si-CQDs.

[0028] Table 2

[0029] Material characterization To study the microscopic morphology of N,Si-CQDs-200℃-16h, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses were performed, and the results are shown in Figure 2 As shown. The particle size of N,Si-CQDs is about 10nm and the shape is close to spherical. From the SEM image, it can be observed that these N,Si-CQDs-200℃-16h present a typical pine branch structure, indicating that single N,Si-CQDs have self-assembled. This structural feature may be closely related to the characteristics of N,Si-CQDs-200℃-16h derived from bamboo, which enables it to retain the structural characteristics of bamboo, thus presenting a pine branch arrangement.

[0030] The prepared N,Si-CQDs-200℃-16h were analyzed by infrared and ultraviolet spectra. The Fourier transform infrared spectra and ultraviolet spectra are shown in Figure 3 As shown. At 3452cm -1 , 3200 cm -1 , 2940 cm -1 , 2140 cm -1 , 1620 cm -1 , 1445 cm -1 and 1220 cm -1 The peaks at 273 cm correspond to the stretching vibrations of OH, NH, saturated carbon, C≡C, C=O, CN and COC groups, respectively, proving that N,Si-CQDs-200℃-16h contains a variety of oxygen-containing functional groups. In the UV-vis absorption spectrum, the absorption peak at 273 cm corresponds to the π-π* electronic transition in the structure, reflecting the delocalized π electron system associated with the conjugated aromatic ring in the N,Si-CQDs-200℃-16h structure, indicating that N,Si-CQDs-200℃-16h has intrinsic electronic properties.

[0031] X-ray photoelectron spectroscopy (XPS) analysis results are as follows Figure 4As shown. The characteristic peaks of C, N, O and Si are clearly observed in the full scan spectrum of N,Si-CQDs-200℃-16h. In the C1s high-resolution spectrum, the peaks at 284.57 eV, 285.33 eV, 286.40 and 288.06 eV are attributed to CC, CN, CO and C=O, respectively; while in the N1s spectrum, the peaks at 396.39 eV, 399.76 eV and 400.90 eV correspond to N-Si, NC and pyrrole-N bonds. The presence of pyrrole nitrogen can provide additional electron density for N,Si-CQDs, enhancing the electron transfer ability of N,Si-CQDs-200℃-16h. Figure 4 d shows the O1s XPS spectrum of N,Si-CQDs-200℃-16h, where the peaks at 531.20 eV, 532.04 eV, and 533.01 eV correspond to OC, O-Si, and C=O groups, respectively. In the Si 2p spectrum, the peaks at 101.63 eV, 102.65 eV, and 103.83 eV are attributed to Si-N, Si-O, and Si 4+ The presence of silicon helps to prevent the agglomeration of N,Si-CQDs-200℃-16h, which is confirmed by TEM images showing the existence of monomers of N,Si-CQDs-200℃-16h.

[0032] Figure 5 The transient photocurrent response of N,Si-CQDs-200℃-16h was demonstrated ( Figure 5 a) and electrochemical impedance spectroscopy (EIS, Figure 5 b). Figure 5 As shown in a, under visible light irradiation, N,Si-CQDs-200℃-16h exhibited significant photocurrent intensity, indicating that it can more effectively generate and separate electron-hole pairs under light conditions, thereby improving the photoelectrocatalytic performance. Figure 5 It can be seen that the photocurrent intensity of the composite catalyst 5CB-200-16 is significantly higher than that of BiOCl, which further proves that N, Si-CQDs-200℃-16h has excellent electron transport ability, which helps to effectively separate the photogenerated electrons and holes in the photocatalytic material, thereby significantly enhancing the photocatalytic activity. In order to further clarify the improvement of the photoelectron transfer rate, an electrochemical impedance spectroscopy test was carried out, and the results are as follows Figure 5b. In the EIS graph, the Nyquist arc radius is related to the charge transfer impedance in the electrochemical system. The smaller the arc radius, the lower the interfacial electron transfer resistance. The reduction in impedance helps the migration of photogenerated electrons and promotes the separation of electron-hole pairs, thereby improving the photocatalytic activity of the photocatalytic material. Compared with BiOCl, N,Si-CQDs-200℃-16h exhibits excellent electron migration ability, making the photocatalytic composite material 5CB-200-16 have the smallest Nyquist arc radius. These results further indicate that the presence of pyrrolic nitrogen and Si elements in N,Si-CQDs-200℃-16h gives it excellent electron transport properties.

[0033] Obviously, the described embodiments are only some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A method for preparing a BiOCl composite photocatalyst modified by self-assembled needle-shaped bamboo-based carbon quantum dots of intrinsic nitrogen and silicon, characterized in that: The following steps are involved: (1) After bamboo powder and water are evenly mixed, they are placed in a polytetrafluoroethylene-lined stainless steel hydrothermal autoclave and reacted at 180-220°C for 8-24 hours; after the reaction is completed and cooled to room temperature, the mixture is filtered and the brown-yellow liquid at the bottom is collected, which is further purified by dialysis to finally obtain a bamboo-based carbon quantum dot solution; (2) Dissolving bismuth salt in ethylene glycol to obtain dispersion A; dissolving chloride salt in water to form solution B; mixing an appropriate amount of bamboo-based carbon quantum dot solution and solution B to obtain a mixed solution, and then adding the mixed solution to dispersion A to form a uniform white suspension, and after sufficient mixing, transferring the suspension to a stainless steel hydrothermal autoclave containing polytetrafluoroethylene for hydrothermal reaction; after the reaction is completed, the obtained material is cooled, separated, washed and dried to finally obtain the target product.

2. The preparation method according to claim 1, characterized in that: In step (1), the bamboo powder is obtained by crushing bamboo pulp preparation waste.

3. The preparation method according to claim 1, characterized in that: In step (1), a 0.22-0.45 μm filter membrane is used for filtration; a dialysis bag with a molecular weight of 500-2000 Da is used for dialysis, and the dialysis time is 24-48 h.

4. The preparation method according to claim 1, characterized in that: In step (2), the bismuth salt is bismuth nitrate, bismuth sulfate or bismuth chloride.

5. The preparation method according to claim 1, characterized in that: In step (2), the chloride salt is sodium chloride or potassium chloride.

6. A BiOCl composite photocatalyst modified by self-assembled needle-like bamboo-based carbon quantum dots with intrinsic nitrogen and silicon, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the BiOCl composite photocatalyst modified by the self-assembled needle-shaped bamboo-based carbon quantum dots of intrinsic nitrogen silicon according to claim 6 in degrading pollutants in wastewater.

8. The use of the intrinsic nitrogen silicon self-assembled needle-shaped bamboo-based carbon quantum dots modified BiOCl composite photocatalyst in degrading pollutants in wastewater according to claim 6, characterized in that: The pollutant is tetracycline hydrochloride.

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