Preparation and application of carbon-nitrogen co-doped zinc oxide nanocomposite

Abstract

This invention discloses a method for preparing carbon-nitrogen co-doped zinc oxide nanocomposite materials. Low-cost zinc nitrate hexahydrate is used as the zinc source, polyethyleneimine as the carbon and nitrogen sources, and ethanol as the solvent. The photocatalyst is prepared in one step using a solvothermal method. The photocatalyst is prepared by dissolving zinc nitrate hexahydrate in anhydrous ethanol, then adding an equal volume of polyethyleneimine ethanol solution dropwise to the zinc nitrate ethanol solution while continuously stirring. The mixture is then transferred to a polytetrafluoroethylene (PTFE) reactor and reacted at 120–200 °C for 4–25 h. After the reaction, the mixture is centrifuged, washed, and dried to obtain the carbon-nitrogen co-doped zinc oxide (CN-ZnO) photocatalyst. In this composite material, ZnO is a zinc oxide nanocrystal with a lead-zinc oxide structure. The doped elements improve the structure and morphology of the zinc oxide photocatalyst, resulting in superior adsorption and photocatalytic performance compared to undoped nanomaterials. This invention achieves C and N co-doped ZnO nanocomposite materials in one step without the addition of any precipitants, catalysts, or oxygen donors. Its preparation conditions are relatively mild, and the equipment and processes are simple, with a short process flow, low cost, and other green and environmentally friendly advantages, making it suitable for industrialization.

Description

Technical Field

[0001] This invention relates to the preparation and application of a carbon-nitrogen co-doped zinc oxide nanocomposite material, belonging to the field of nanocomposite material technology. Background Technology

[0002] In recent years, with industrial development, the demand for water resources has gradually increased, while global water pollution has become increasingly prominent. Human industrial activities have resulted in the massive discharge of wastewater, leading to a gradual increase in the concentration of organic pollutants in the Earth's surface waters, seriously threatening human survival and the living environment. In particular, many recalcitrant organic dyes, such as azo dyes with complex aromatic compounds, are the most abundant type of synthetic dye, accounting for approximately 60-70% of total synthetic dye usage. Most azo dyes are difficult to biodegrade under aerobic conditions and are easily converted into aromatic carcinogens under anaerobic conditions, with a very long natural degradation time. Therefore, how to rationally and efficiently treat organic dyes in wastewater has attracted much attention.

[0003] Photocatalytic degradation of organic dyes in water is an environmentally friendly technology that protects human health. Compared with traditional methods for treating organic dye wastewater, photocatalysis can use sunlight directly as an energy source, converting light energy into chemical energy through a photocatalyst to degrade pollutants in wastewater. ZnO is a promising photocatalyst with advantages such as high catalytic activity, strong oxidizing power, diverse morphologies, safety and non-toxicity, readily available raw materials, low preparation cost, good biocompatibility, and excellent chemical and thermal stability. However, the low quantum efficiency of ZnO leads to a high probability of photogenerated electron-hole recombination, reducing its photocatalytic activity. Simultaneously, its narrow spectral response range, typically exhibiting higher photocatalytic activity under ultraviolet light, limits its photocatalytic activity. To overcome these problems and improve the photodegradation performance of ZnO for organic pollutants, the preparation of composite materials of ZnO with carbon and nitrogen compounds has attracted increasing attention. Current research on inorganic and organic modification of ZnO to enhance its adsorption and photocatalytic performance for specific pollutants is extensive. However, there is limited research on the preparation of CN-doped zinc oxide composites via a one-step solvothermal method for the adsorption and photocatalytic degradation of organic dyes in wastewater. Therefore, applying CN-doped zinc oxide composites to the treatment of organic dye wastewater, thereby improving its adsorption and photocatalytic performance, could play a significant role in the treatment of such wastewater. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing carbon-nitrogen co-doped zinc oxide nanocomposite materials to overcome the shortcomings of existing technologies.

[0005] I. Preparation of carbon-nitrogen co-doped zinc oxide nanocomposites 1. Preparation of nanocomposite materials The carbon-nitrogen co-doped zinc oxide nanocomposite material of the present invention is prepared in one step by using ferric nitrate hexahydrate (Zn(NO3)2·6H2O) and polyethyleneimine (PEI) as raw materials and ethanol (EtOH) as solvent, via a solvothermal method (STM).

[0006] The specific preparation process is as follows: Zinc nitrate hexahydrate was dissolved in anhydrous ethanol, and then polyethyleneimine was added and dispersed evenly. The mixture was then transferred to a polytetrafluoroethylene reactor and reacted at 120-200 °C for 5-25 h. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain CN-ZnO nanocomposite material.

[0007] The molar ratio of zinc nitrate hexahydrate to polyethyleneimine is 81.5:1 to 2.7:1.

[0008] The washing process is carried out using anhydrous ethanol and deionized water.

[0009] The drying process involves drying at 50-80°C for 9-11 hours.

[0010] 2. Effects of solvothermal reaction conditions on the properties of composite materials (1) Effect of solvothermal temperature on the properties of composite materials To investigate the effect of solvothermal temperature on the material composition and properties, we conducted the following experiment: 2.14 g of Zn(NO3)2·6H2O was dissolved in 30 mL of EtOH and stirred until dissolved. 1.0 mL of polyethyleneimine was added to 30 mL of EtOH and stirred until dissolved. Then, the polyethyleneimine ethanol solution was added dropwise to the zinc nitrate ethanol solution while continuously stirring. The mixed solution was then transferred to a polytetrafluoroethylene reactor and reacted at different solvothermal temperatures (100, 140, and 180 °C) for 10 h each. After centrifugation, washing, and drying, the composite material CN-ZnO-100~180 was obtained. Figure 1 The composite material CN-ZnO-100~180 obtained at different solvothermal temperatures was treated with 40.0 mL of 10 mg·L⁻¹ solution. -1 Adsorption and photocatalytic degradation performance of methyl orange solution. (Charts are provided.) Figure 1 It can be seen that the adsorption and photocatalytic properties of the product are improved with increasing solvothermal reaction temperature. In other words, low temperatures are unfavorable for the formation of carbon-nitrogen co-doped zinc oxide nanocomposites. Experimental results show that when the solvothermal temperature is controlled between 160 and 200 °C, the resulting composite material exhibits good adsorption and photocatalytic properties. Subsequent experiments selected a solvothermal temperature of 180 °C.

[0011] (2) Effect of polyethyleneimine addition on the properties of composite materials To investigate the effects of different amounts of polyethyleneimine on the material composition and properties, the amount of polyethyleneimine added was selected to be 0.01~1.5 mL, and the reaction was carried out at a solvothermal temperature of 180℃ for 10 h. Other experimental conditions were the same as above, and the prepared material was labeled as CN-ZnO-0.01~1.5. Figure 2 This is a graph showing the effect of polyethyleneimine addition on the adsorption and photocatalytic degradation performance of methyl orange. Figure 2 It can be seen that when the amount of polyethyleneimine added is 1.5 mL, the adsorption performance and photodegradation rate of the prepared composite material are approximately 15.0% and 20%, respectively. However, when the amount of polyethyleneimine is 0.05 mL, these figures reach over 55% and 90%, respectively. This indicates that a large amount of polyethyleneimine is not conducive to the preparation of composite materials with excellent performance.

[0012] (3) Effect of solvothermal reaction time on the properties of composite materials To investigate the effects of different solvothermal reaction times on the material composition and properties, 0.05 mL of polyethyleneimine was added, and the reaction was carried out at a solvothermal temperature of 180 °C for 5–25 h, with other reaction conditions as described above. The prepared material was labeled CN-ZnO-5–25. Figure 3 This diagram shows the adsorption and photocatalytic degradation performance of the products obtained at different reaction times for methyl orange. Figure 3 It is evident that the adsorption performance of the composite material improves with increasing solvothermal reaction time. When the solvothermal reaction time is 25 hours, the adsorption performance reaches 85.3%, but the photocatalytic performance improvement is not significant. After 30 minutes of illumination, the photocatalytic performance reaches a maximum of 90.1%, with virtually no further improvement thereafter. When the solvothermal reaction time is 20 hours, the photocatalytic performance of the composite material reaches 96.7% after 180 minutes of UV irradiation, while the adsorption performance also reaches 64.5%. Considering the economic efficiency of material preparation and photocatalytic performance, a solvothermal time of 20 hours was chosen.

[0013] II. Structure and Properties of Carbon-Nitrogen Co-doped Zinc Oxide Nanocomposites The structure and properties of the prepared CN-ZnO sample were characterized and analyzed using XRD, FTIR, SEM, and elemental analysis techniques.

[0014] 1. XRD Analysis Figure 4 The image shows the XRD pattern of the CN-ZnO-0.05~1.5 samples prepared in this invention. Figure 4 It can be seen that when the amount of polyethyleneimine added reaches 1.5 mL, the material at 2 θTwo strong diffraction peaks appeared at angles of 13.2° and 27.7°, corresponding to the (002) and (100) crystal planes of graphitic carbon nitride. Simultaneously, characteristic diffraction peaks of hexagonal wurtzite zinc oxide were observed, indicating that when the amount of polyethyleneimine added to the material reached 1.5 mL, the material was mainly composed of carbon and nitrogen compounds and zinc oxide. As the amount of polyethyleneimine added decreased, at 2... θ The two diffraction peaks appearing at angles of 13.2° and 27.7° showed significantly reduced in intensity or even disappeared, while at 2... θ The diffraction peak intensities at angles of 31.8°, 34.6°, 36.5°, 47.8°, and 56.8° were significantly enhanced, corresponding to increased diffraction peak intensities of ZnO and zinc oxide, indicating improved crystallinity of the sample. Therefore, the addition of an appropriate amount of polyethyleneimine facilitates the formation of hexagonal wurtzite-structured zinc oxide and improves its crystallinity.

[0015] 2. FTIR analysis Figure 5 FTIR spectra of polyethyleneimine (PEI) and the samples CN-ZnO-0.05~1.5 prepared in this invention. Comparison with PEI revealed that samples CN-ZnO-0.5 and CN-ZnO-1.5 exhibited a 1767 cm⁻¹ pattern. -1 and 1620 cm -1 Polyethyleneimine polymer v C=N Stretching vibration absorption peaks and graphitic carbon v C=C Stretching vibration absorption peak, 808 cm⁻¹ -1 The absorption peak is a characteristic absorption peak of the carbon nitride triazine ring structure; this indicates that in Zn 2+ Under the influence of [unspecified agent], polyethyleneimine underwent a polymerization reaction, forming graphitic carbon nitride. The sample CN-ZnO-0.05 was [dissolved] at 432 cm⁻¹. -1 There was an obvious v Zn-O Stretching vibration absorption peak and 1620 cm⁻¹ -1 Graphitized carbon at the location v C=C The stretching vibration absorption peak indicates that a small amount of polyethyleneimine can promote the absorption of Zn. 2+ It is converted to ZnO, and at the same time, 1038 cm⁻¹ in the sample -1 Nearby v C-N The stretching vibration absorption peaks confirm the presence of C and N in the sample, further demonstrating that the CN co-doped ZnO composite material was prepared using a one-step solvothermal method.

[0016] 3. Elemental Analysis To understand the content of C and N elements in the composite material, the nitrogen, carbon, and hydrogen elements in the composite materials prepared with different amounts of polyethyleneimine were analyzed, and the corresponding N / C ratios were determined. The results are shown in Table 1. Table 1 shows the elemental analysis results of ZnO and CN-ZnO-0.05 samples prepared in this invention.

[0017] Table 1. Elemental analysis of C, N, and H in ZnO and CN-ZnO composite materials. 4. SEM Analysis Figure 6 The images show SEM images of ZnO (a, b) and CN-ZnO-0.05 (c, d) samples prepared in this invention at different magnifications. Observations reveal that ZnO forms irregularly shaped, rugby ball-like materials, while CN-ZnO forms rugby balls composed of relatively uniformly sized nanoparticles, confirming that the prepared materials are nanomaterials. Figures a and b clearly show that ZnO nanoparticles exhibit significant agglomeration, while CN-ZnO-0.05 (c, d) nanoparticles demonstrate good dispersion properties, with a particle size of approximately 20 nm. This indicates that polyethyleneimine (PEI) effectively prevents the agglomeration of ZnO nanoparticles, resulting in uniformly sized rugby ball-shaped materials.

[0018] III. Application Exploration of Carbon-Nitrogen Co-doped Zinc Oxide Nanocomposites 1. Effects of different methyl orange concentrations on the adsorption and photocatalytic performance of the composite material Considering the influence of the initial concentration of methyl orange on the adsorption and photocatalytic properties of the composite material, an experiment on the concentration of methyl orange was conducted using CN-ZnO-20 nanocomposite material. The results are as follows: Figure 7 As shown.

[0019] Depend on Figure 7 It can be seen that when the concentration of methyl orange is 5 mg·L⁻¹ -1 At a concentration of 25 mg·L⁻¹, the adsorption performance reached a maximum of 72.3%. With increasing methyl orange concentration, the adsorption performance of the composite material for methyl orange showed a decreasing trend. -1 At a concentration of 10 mg / L, the adsorption performance reached a minimum of 30.6%. This indicates that when the concentration of methyl orange is low, the composite material mainly relies on adsorption. When a large number of methyl orange molecules are adsorbed onto the surface of the composite material, it affects the subsequent photocatalytic performance. This is because the large number of methyl orange molecules adsorbed on the surface of the composite material blocks the generation of photogenerated carriers, thereby reducing its photocatalytic performance. After 180 min of illumination, its photocatalytic degradation rate only reached 82.3%. -1At that time, its adsorption rate was 53.0%. After 60 minutes of illumination, its degradation rate reached 92.4%. This indicates that the appropriate concentration of methyl orange has a significant impact on the adsorption and photocatalytic performance of the material. Therefore, a methyl orange concentration of 10 mg·L⁻¹ was selected. -1 As a condition for subsequent experiments.

[0020] 2. Effects of different composite material dosages on the adsorption and photocatalytic performance of the composite material Based on the above experiments, the composite material dosages were selected as 0.5, 1.0, 1.5, 2.0, and 2.5 g·L⁻¹. -1 The experimental results are as follows Figure 8 As shown. By Figure 8 It can be seen that when the catalyst dosage is 2.5 g·L -1 The optimal adsorption efficiency for methyl orange was 73.5% at a catalyst dosage of 1.0 g·L⁻¹. -1 The best photocatalytic degradation effect of methyl orange was achieved when the light was applied for 60 minutes, with a rate of 92.4%.

[0021] In summary, this invention employs a solvothermal method to synthesize CN-doped ZnO composite materials in one step without the addition of any precipitants or catalysts, preparing a uniformly distributed CN-ZnO nanoparticle-based composite material. During the CN-ZnO nanocomposite material composite process, Zn... 2+ Polyethyleneimine promotes or catalyzes the polymerization of ZnO nanoparticles, while effectively inhibiting their directional growth and aggregation, thus improving the adsorption and photocatalytic properties of ZnO nanomaterials. In the composite material, ZnO is a zinc oxide nanocrystal with a lead-zinc oxide structure. The synergistic effect between ZnO and the composite material and nitrogen and carbon compounds results in superior crystallinity, adsorption, and photocatalytic properties compared to nano-ZnO materials, making it widely applicable in adsorption materials, electrocatalysis, photocatalysis, and gas-sensitive materials. Furthermore, this invention offers significant advantages such as simple process, short flow, low cost, and environmental friendliness, making it suitable for industrialization. Attached Figure Description

[0022] Figure 1 Adsorption and photocatalytic properties of composite materials prepared at different solvothermal temperatures.

[0023] Figure 2 Adsorption and photocatalytic properties of composite materials prepared with different amounts of polyethyleneimine.

[0024] Figure 3 Adsorption and photocatalytic properties of products obtained under different solvothermal times.

[0025] Figure 4 XRD patterns of the composite material CN-ZnO-0.05~1.5.

[0026] Figure 5 FTIR spectra of polyethyleneimine and composite material CN-ZnO-0.05~1.5.

[0027] Figure 6 SEM images of samples ZnO and CN-ZnO-0.05.

[0028] Figure 7 The effect of different methyl orange concentrations on the adsorption and photocatalytic performance of composite materials.

[0029] Figure 8 The effect of different amounts of composite materials on the adsorption and photocatalytic performance of the composite materials. Detailed Implementation

[0030] The present invention will be further explained and described below with reference to specific embodiments. Example

[0031] 2.14 g of Zn(NO3)2·6H2O was dissolved in 30 mL of EtOH and stirred until dissolved. 0.05 mL of polyethyleneimine was added to 30 mL of EtOH and stirred until dissolved. Then, the polyethyleneimine ethanol solution was added dropwise to the zinc nitrate ethanol solution while continuously stirring. The mixed solution was then transferred to a polytetrafluoroethylene (PTFE) reactor and reacted at a solvothermal temperature of 180 °C for 20 h. After centrifugation, washing, and drying, the composite material CN-ZnO-20 was obtained. 1.0 g of photocatalyst was added to 40 mL of a 10 mg·L⁻¹ solution. -1 In an aqueous solution of methyl orange, magnetic stirring was turned on in the dark and timing was started. After 30 minutes, a 4 mL sample was taken, centrifuged, and then a 15W UV lamp with a main wavelength of 365 nm was turned on for photocatalytic experiment. A 4 mL sample was taken every 60 minutes, centrifuged, and the absorbance of the supernatant at 464 nm was measured using a U2001 UV spectrophotometer. The removal rate of methyl orange by the material was calculated based on the concentration of methyl orange in the supernatant and the initial concentration. The adsorption performance of the material was calculated based on the removal rate of methyl orange after 30 minutes of dark adsorption. The experimental results showed that the adsorption performance and photocatalytic degradation performance of the composite material CN-ZnO-20 for methyl orange were 53.0% and 92.4%, respectively.

Claims

1. A method for preparing carbon and nitrogen co-doped zinc oxide nanocomposite, characterized in that: First, zinc nitrate hexahydrate and polyethyleneimine were dissolved in anhydrous ethanol. Then, the polyethyleneimine ethanol solution was added dropwise to the zinc nitrate ethanol solution while stirring continuously. The mixture was then transferred to a polytetrafluoroethylene reactor and reacted at 120-200 °C for 4-25 h. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain CN-ZnO nanocomposite material. The ratio of zinc nitrate hexahydrate to polyethyleneimine is 0.01 mL to 0.5 mL of polyethyleneimine for every 2.14 g of zinc nitrate hexahydrate.

2. The method for preparing a carbon-nitrogen co-doped zinc oxide nanocomposite material as described in claim 1, characterized in that: The washing process is carried out using anhydrous ethanol and deionized water.

3. The method for preparing a carbon-nitrogen co-doped zinc oxide nanocomposite material as described in claim 1, characterized in that: The drying process involves drying at 50-80°C for 9-11 hours.

4. A carbon-nitrogen co-doped zinc oxide nanocomposite material prepared by the method described in claim 1.

5. An application of a carbon-nitrogen co-doped zinc oxide nanocomposite material prepared by the method described in claim 1 in the adsorption and photocatalytic degradation of organic dyes in wastewater.

6. The application of the carbon-nitrogen co-doped zinc oxide nanocomposite material as described in claim 5 in the adsorption and photocatalytic degradation of organic dyes in wastewater, characterized in that: The organic dye is methyl orange.

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