Preparation method and application of Na and K co-doped g-C3N5 photocatalyst

Abstract

The present invention discloses a preparation method and application of a Na- and K-co-doped g-C3N5 photocatalyst, belonging to the technical field of composite photocatalytic materials. The invention comprises: first, preparing dicyandiamide into blocky g-C3N5 (BCN) in a muffle furnace by a thermal polycondensation method; second, using BCN, potassium chloride (KCl) and sodium chloride (NaCl) as raw materials, preparing a Na-K-co-doped few-layer thin-sheet g-C3N5 (CNAK) photo-self-Fenton catalyst by a doping and crystallinity regulation method; third, efficient photocatalytic production of H2O2 and construction of a photo-self-Fenton system to achieve efficient degradation and mineralization of new pollutants. The CNAK photo-self-Fenton catalyst prepared by the present invention can achieve Na-K doping, crystallinity regulation and morphology regulation, and the preparation process is safe, simple and efficient, solves the problem of low H2O2 production of the g-C3N5 photocatalyst, successfully constructs a photo-self-Fenton degradation system, and exhibits excellent photo-Fenton performance and good stability in the process of degrading antibiotics, does not produce secondary pollution, and has excellent environmental benefits.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a Na and K co-doped g-C3N5 photocatalyst, belonging to the technical field of composite photocatalytic materials. Background Art

[0002] With the rapid growth of global energy consumption and the intensification of environmental damage, environmental pollution is becoming increasingly serious, and green energy is becoming increasingly popular. Hydrogen peroxide (H2O2) has been widely used as a green energy source in various fields such as chemical industry, wastewater purification, and fuel cells due to the environmentally friendly, renewable, and non-toxic properties of its decomposition products. Traditional H2O2 synthesis methods mainly rely on the anthraquinone process, which is plagued by problems such as waste accumulation, increased energy consumption, and strict reaction requirements, limiting its sustainable production and production. Compared with the anthraquinone process, the photocatalytic two-electron oxygen reduction reaction is a more environmentally friendly and efficient synthetic route for the production of H2O2. Under ambient conditions, water and oxygen undergo a photocatalytic reaction on the surface of a semiconductor to produce H2O2.

[0003] In this field, graphitic carbon nitride (g-C3N5) has attracted widespread attention due to its abundant electron-rich sites and basic nitrogen. In particular, the introduction of supplementary nitrogen into the triazine unit of g-C3N5 extends its conjugated structure, resulting in higher thermodynamic stability, improved electronic properties, and a narrower energy band. However, pure g-C3N5 still faces shortcomings such as slow electron-hole pair dissociation, sluggish charge transfer kinetics, low oxygen reduction ability, and scarce active sites, which hinder its ability to photocatalytically produce H2O2. As a result, pure g-C3N5 exhibits weak photocatalytic activity for H2O2 generation. Addressing these limitations is essential for optimizing the efficiency of photocatalytic H2O2 production using g-C3N5 materials. Researchers have deployed a range of strategies, including heterojunction formation, structural engineering, element doping, and crystallinity manipulation. Among these approaches, the construction of ultrathin nanosheet structures has emerged as a particularly effective approach.

[0004] To address the above-mentioned issues and improve the photocatalytic activity of g-C3N5, the present invention designs a class of Na and K co-doped few-layer ultrathin g-C3N5 photo-Fenton catalysts. By optimizing the morphology, structure, and size of g-C3N5 through doping and crystallinity control, the catalyst becomes thinner and smaller. The synergistic effect of Na-K doping and crystallinity control not only optimizes the electronic structure and band structure of g-C3N5, giving the photocatalyst a higher carrier separation efficiency, but also increases the density of active sites on the g-C3N5 surface, introducing functional groups with higher oxygen content and polar hydroxyl groups, but also improves the selectivity of ORR and efficiently produces H2O2, thereby realizing the photo-Fenton of the catalyst. At the same time, it effectively increases electron mobility, thereby activating the n→π* electron transition, thereby effectively improving the photo-Fenton performance of g-C3N5, and efficiently degrading antibiotics in a short period of time, which is of great value in increasing the added value of related products. Summary of the Invention

[0005] In order to solve the problem of low H2O2 yield in existing g-C3N5 materials, the present invention provides a method for preparing a Na and K co-doped few-layer thin-sheet g-C3N5 photo-auto-Fenton catalyst, which specifically comprises the following steps:

[0006] (1) calcining dicyandiamide in a muffle furnace to obtain a precursor bulk carbon nitride (BCN), which is then ground for later use;

[0007] (2) grinding and mixing carbon nitride (BCN), sodium chloride (NaCl) and potassium chloride (KCl), and then calcining the mixture twice in a muffle furnace to obtain a molten salt C3N5 ultrathin nanosheet;

[0008] (3) The obtained molten salt C3N5 ultrathin nanosheets are dispersed in pure water and heated and stirred. After cooling, the ultrathin nanosheets are centrifuged and washed to remove excess molten salt and other ions. The nanosheets are dried overnight to obtain Na-K co-doped few-layer thin sheets g-C3N5 photo-Fenton catalysts.

[0009] Preferably, the mass of dicyandiamide used in step (1) is 4.95 to 5.05 g.

[0010] Preferably, the calcination temperature of the muffle furnace in step (1) is 450-550° C., the heating rate is 8-12° C. / min, and the calcination time is 2-4 h.

[0011] Preferably, the grinding time in step (1) is 10 to 20 minutes.

[0012] Preferably, the mass ratio of carbon nitride (BCN), sodium chloride and potassium chloride in step (2) is (1.5-2.5):(4.5-5.5):(4.5-5.5), and the grinding time is 30-50 min.

[0013] Preferably, the calcination temperature of the muffle furnace in step (2) is 400-500° C., the heating rate is 8-12° C. / min, and the calcination time is 3-5 h.

[0014] Preferably, the heating temperature in step (3) is 80-120° C., the rotation speed is 600-800 r / min, and the heating time is 5-12 h.

[0015] Preferably, the washing method in step (3) is to thoroughly wash and separate with hot distilled water and anhydrous alcohol respectively, and dry at 70-90° C. overnight.

[0016] Preferably, the prepared Na-K co-doped few-layer thin sheet g-C3N5 photo-Fenton catalyst is used to efficiently produce H2O2 in water.

[0017] Preferably, the prepared Na-K co-doped few-layer thin sheet g-C3N5 photo-Fenton catalyst acts in degrading tetracycline (TC) in water.

[0018] Beneficial effects of the present invention

[0019] (1) The present invention synthesizes Na-K co-doped few-layer g-C3N5 photo-auto-Fenton catalysts through doping and crystallinity regulation methods. Na-K co-doping makes g-C3N5 have more reactive sites, which can improve the utilization rate of its photogenerated electrons, and provides a new idea for the preparation and functional optimization of g-C3N5 nanosheets and metal / non-metal doped composites under the synergistic effect of doping and crystallinity regulation.

[0020] (2) The present invention adopts the g-C3N5 photo-Fenton catalyst prepared by the synergistic method of doping and crystallinity regulation. Na-K co-doping optimizes the optical properties and surface structure of g-C3N5 nanosheets and reduces the resistance of charge transfer.

[0021] (3) The Na-K co-doped few-layer g-C3N5 photo-auto-Fenton catalyst prepared by the present invention has smaller flakes and fewer layers accompanied by more delocalized electrons. Na-K co-doping can promote n→π* electron transition, which is beneficial to accelerate the separation efficiency and migration efficiency of photogenerated carriers and improve the charge density.

[0022] (4) Na-K co-doping can inhibit the recombination of photoinduced electron-hole pairs, increase the density of active sites on the g-C3N5 surface, and significantly improve the photo-Fenton performance of the g-C3N5 photo-Fenton catalyst.

[0023] (5) The Na-K co-doping of the g-C3N5 photo-Fenton catalyst in the present invention can effectively adjust the band gap of g-C3N5 to visible light and broaden its absorption range, thereby having higher visible light absorption capacity, enhanced light capture ability and excellent photocatalytic ability.

[0024] (6) The prepared Na-K co-doped CNAK photo-Fenton catalyst increased the density of active sites on the g-C3N5 surface, promoted the redox reaction, and had good photocatalytic activity, indicating that Na-K co-doping improved the photocatalytic activity of g-C3N5 to generate H2O2, and its H2O2 yield was 122.15 μmol g -1 h -1 , which is 11 times that of pure g-C3N5 (CNN) and 8-9 times that of the single-calcined molten salt g-C3N5-Na-K (BCAK) catalyst.

[0025] (7) The equipment and materials required for the preparation method of the present invention are easy to obtain, the process operation is simple, and the process conditions are concise. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 These are the XRD patterns of the catalysts prepared in Example 1 and Comparative Examples 1 to 3.

[0027] Figure 2 These are SEM images of the catalysts prepared in Example 1 and Comparative Examples 1 to 3.

[0028] Figure 3 These are the corresponding AFM height images of the catalysts prepared in Example 1 and Comparative Example 3.

[0029] Figure 4 The UV-vis spectra of the catalysts prepared in Example 1 and Comparative Examples 1 to 3 are shown.

[0030] Figure 5 PL spectra of the catalysts prepared in Example 1 and Comparative Example 3.

[0031] Figure 6 These are the EPR spectra of the catalysts prepared in Example 1 and Comparative Examples 1 to 3.

[0032] Figure 7 This is a comparison chart of the H2O2 production performance of the catalysts prepared in Example 1 and Comparative Examples 1 to 3.

[0033] Figure 8 This is the H2O2 production performance cycle diagram of the catalyst prepared in Example 1.

[0034] Figure 9 The figure is a comparison chart of the degradation performance of TC by the catalysts prepared in Example 1 and Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0035] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. However, the following embodiments are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0036] Example 1

[0037] A Na and K co-doped few-layer g-C3N5 photoauto-Fenton catalyst and a preparation method thereof, comprising the following steps:

[0038] (1) Preparation of precursor bulk BCN: 5 g of dicyandiamide was heated in a muffle furnace at 10 °C min -1 The temperature was raised to 500 °C and calcined for 3 h, and then ground in agate mortar for 15 min.

[0039] (2) 0.5 g of BCN, 1.25 g of NaCl, and 1.25 g of KCl were mixed and ground in agate mortar for 30 minutes to make them uniformly mixed, and then calcined in a muffle furnace at 10 ° C min -1 The heating rate was increased to 450℃ and calcined for 4h.

[0040] (3) After the obtained mixture was naturally cooled to room temperature, it was thoroughly washed three times with distilled water and anhydrous alcohol respectively, and then filtered and separated to remove other ions. After drying at 80°C for 12 h, the Na-K co-doped few-layer thin sheet g-C3N5 photo-auto-Fenton catalyst (CNAK) was obtained.

[0041] Comparative Example 1

[0042] For comparison, the difference between this comparative example and Example 1 is that only K is doped in this comparative example to prepare a g-C3N5-K (CNK) catalyst, comprising the following steps:

[0043] (1) Preparation of precursor bulk BCN: 5 g of dicyandiamide was heated in a muffle furnace at 10 °C min -1 The temperature was raised to 500 °C and calcined for 3 h, and then ground in agate mortar for 15 min.

[0044] (2) 0.5 g BCN and 2.5 g KCl were mixed and ground in agate mortar for 30 minutes to make them uniform, and then calcined in a muffle furnace at 10 ° C min -1 The heating rate was increased to 450℃ and calcined for 4h.

[0045] (3) After the obtained mixture was naturally cooled to room temperature, it was thoroughly washed three times with distilled water and anhydrous alcohol respectively, and then filtered and separated to remove other ions. After drying at 80°C for 12 hours, the g-C3N5-K catalyst was collected.

[0046] Comparative Example 2

[0047] For comparison, the difference between this comparative example and Example 1 is that only Na is doped in this comparative example to prepare a g-C3N5-Na (CNA) catalyst, comprising the following steps:

[0048] (1) Preparation of precursor bulk BCN: 5 g of dicyandiamide was heated in a muffle furnace at 10 °C min -1 The temperature was raised to 500 °C and calcined for 3 h, and then ground in agate mortar for 15 min.

[0049] (2) 0.5 g of BCN and 2.5 g of NaCl were mixed and ground in agate mortar for 30 minutes to make them uniformly mixed, and then calcined in a muffle furnace at 10 ° C min -1 The heating rate was increased to 450℃ and calcined for 4h.

[0050] (3) After the obtained mixture was naturally cooled to room temperature, it was thoroughly washed three times with distilled water and anhydrous alcohol respectively, and then filtered and separated to remove other ions. After drying at 80°C for 12 h, the g-C3N5-K nanosheet catalyst was collected.

[0051] Comparative Example 3

[0052] For comparison, the difference between this comparative example and Example 1 is that Na and K are not doped, and the g-C3N5 (CNN) nanosheet catalyst is prepared, comprising the following steps:

[0053] (1) Preparation of precursor bulk BCN: 5 g of dicyandiamide was heated in a muffle furnace at 10 °C min -1 The temperature was raised to 500 °C and calcined for 3 h, and then ground in agate mortar for 15 min.

[0054] (2) 0.5 g of BCN was placed in a muffle furnace for secondary calcination at 10 °C min -1 The temperature was raised to 450 °C and calcined for 4 h. After cooling to room temperature, the g-C3N5 catalyst was collected.

[0055] Comparative Example 4

[0056] For comparison, this comparative example differs from Example 1 in that only one calcination is performed to prepare a g-C3N5-Na-K (BCAK) catalyst, comprising the following steps:

[0057] 5 g of dicyandiamide, 1.25 g of NaCl and 1.25 g of KCl were heated in a muffle furnace at 10 °C min -1 The temperature was raised to 500 °C at a heating rate of 100 °C and calcined for 3 h, and then ground in agate mortar for 15 min to obtain g-C3N5-Na-K (BCAK) catalyst.

[0058] Figure 1 X-ray diffraction (XRD) experiments are shown for the precursor, the co-catalyst prepared in Example 1, and the catalysts prepared in Comparative Examples 1 to 3. The figure shows that the CNAK catalyst prepared in Example 1 not only has characteristic peaks of g-C3N5, but also no new diffraction peaks related to K and Na elements are detected. This indicates that the molten salt modification does not change the lattice structure of g-C3N5, confirming the construction of the CNAK composite material.

[0059] Figure 2 The scanning electron microscopy (SEM) of the co-doped catalyst prepared in Example 1 and the catalysts of Comparative Examples 1 to 3 is shown in the figure. It can be seen from the figure that the g-C3N5 nanosheets (CNN) prepared in Comparative Example 3 ( Figure 2 (d)), CNK prepared in Comparative Example 1 ( Figure 2 (b)), the CNA prepared in Comparative Example 2 ( Figure 2 (c) Na and K co-doped g-C3N5 nanosheets (CNAK) were further reduced in size by crystallinity control method ( Figure 2 (a)), indicating that CNAK photo-Fenton catalyst was successfully synthesized.

[0060] Figure 3 The corresponding height images of the co-doped catalyst prepared in Example 1 and the CNN catalyst prepared in Comparative Example 3 are obtained by atomic force microscopy (AFM). Figure 3 (A) and Figure 3 (B) shows that the CNN nanosheets of comparative example 3 and Figure 3 (C) and Figure 3 The relative heights of the CNAK ultrathin nanosheets of Example 1 in (D) are 16.3 nm and 3.55 nm (about 4 CN layers), respectively, indicating that they become thinner through the synergistic effect of doping and crystallinity regulation, and the morphology and size of the CNAK photo-Fenton catalyst are successfully regulated.

[0061] Figure 4The ultraviolet-visible absorption (UV-vis) spectra of the catalyst prepared in Example 1 and the catalysts prepared in Comparative Examples 1 to 3 were used to test their light-harvesting ability. The figure shows that the absorption edge of the CNN in Comparative Example 3 is located at 388 nm, while the absorption edge of the CNAK in Example 1 exhibits a significant red shift, with significantly enhanced absorption intensity in the visible light region. This indicates that Na-K doping can effectively modulate the band gap of the CNN for visible light, broadening its absorption range and enhancing its n→π* transition capability and light-harvesting ability. The combination of doping and crystallinity control can synergistically promote n→π* electron transitions and improve visible light photocatalytic activity.

[0062] Figure 5 Figure 2 shows the photoluminescence (PL) spectra of the CNAK catalyst of Example 1 and the CNN of Comparative Example 3. Compared with the CNN catalyst, the PL intensity of the CNAK light from the Fenton catalyst is the weakest and shows a significant red shift, which may be caused by the expansion of the electron conjugated system. CNAK shows only one emission peak in the PL spectrum, which originates from the →π* transition in the conjugated system, indicating that its charge pair transfer and separation effect is the best.

[0063] Figure 6 The electron paramagnetic resonance (EPR) spectra of the precursor BCN, the CNAK catalyst of Example 1, and the CNN catalyst of Comparative Example 3 can also indirectly confirm the occurrence of n→π* transition. As can be seen from the figure, the prepared material shows a clear Lorentzian line centered at a g value of 2.0052, which is related to the unpaired electrons in the conjugated aromatic ring. Relevant literature reports that n→π* electronic transitions excite more non-bonded electrons in the catalyst. Compared with CNN, CNAK exhibits a larger EPR enhancement signal span, indicating the presence of more unpaired electrons and n→π* electronic transitions.

[0064] H2O2 production experiment

[0065] The catalyst obtained in Example 1 and the catalysts obtained in Comparative Examples 1 to 3 were subjected to H2O2 production experiments, and the specific steps were as follows:

[0066] (1) Disperse 25 mg of the catalyst in a mixed aqueous solution of 30 mL of deionized water and 3 mL of ethanol.

[0067] (2) The reaction solution was placed under a simulated sunlight source using a 10W white LED light source to initiate the photoreaction test. Every 30 minutes, 3 mL of the solution was extracted and filtered through a 0.45 μm microfiltration membrane to remove the catalyst. The H2O2 concentration was then further analyzed.

[0068] (3) Iodine titration is used to test the production of H2O2. 0.05 mL of 0.01 mol L-1 was added to 1 mL of the sample solution. -1Ammonium molybdate hydrate (H 32 Mo7N6O 28 ) solution and 2 mL of 0.1 mol L -1 The potassium iodide (KI) solution was allowed to stand for 5 min and then analyzed using a 350 nm UV-visible spectrum.

[0069] Figure 7 The results show that the Na-K co-doped CNAK photo-Fenton catalyst has a higher yield than CNN, with the highest H2O2 yield of CNAK catalyst reaching 122.15 μmol g -1 h -1 , which is 11 times the H2O2 yield of CNN catalyst.

[0070] Figure 8 This is a H2O2 production cycle experiment using the CNAK photo-Fenton catalyst prepared in Example 1. The figure shows that the CNAK catalyst has good stability.

[0071] Photoauto-Fenton degradation experiment

[0072] The CNAK photo-Fenton catalyst obtained in Example 1 and the catalysts obtained in Comparative Examples 1 to 3 were used for photo-Fenton degradation of antibiotics. The specific steps are as follows:

[0073] (1) 20 mg of CNAK photo-Fenton catalyst and CNN catalyst were weighed and dispersed into 50 mL of antibiotic aqueous solution (antibiotic concentration was 10 mg / L), respectively. The mixture was stirred for 30 min in the dark and then subjected to appropriate ultrasonic dispersion to achieve adsorption-desorption equilibrium.

[0074] (2) Simulate the sunlight source by irradiating a white LED lamp with an energy intensity of 10W to start the photo-Fenton reaction.

[0075] (3) Take 5 mL of solution every 30 minutes and use UV-visible spectrophotometer (UV-1800PC) to measure the absorbance of antibiotics. Tetracycline (TC) is measured at λ = 357 nm. The concentration of antibiotics is further calculated based on the standard curve of absorbance and concentration. The results are as follows: Figure 7 shown.

[0076] from Figure 9 It can be seen that the TC removal rate of the CNN sample in comparative example 3 is only 24.43% within 10 minutes, while the TC removal rate of the Na-K co-doped CNAK photo-Fenton catalyst in Example 1 is as high as 97.45%. Na-K co-doping and crystallinity control method can improve the photo-Fenton activity of g-C3N5.

[0077] Compared with Comparative Example 3, the effect of the once-calcined BNAK prepared in Comparative Example 4 is improved to a certain extent; however, compared with the twice-calcined CNAK, the BNAK nanosheets are thicker, have fewer Na-K doping sites, and have low photocatalytic activity, resulting in worse degradation performance and lower H2O2 yield.

[0078] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present invention, and without departing from the spirit and scope of the technical solution of the present invention, which is defined by the appended claims and their equivalents.

Claims

1. Application of a Na-K co-doped g-C3N5 photocatalyst in photo-Fenton generation of hydrogen peroxide in water, characterized by: The preparation method of the Na-K co-doped g-C3N5 photocatalyst comprises the following steps: (1) calcining dicyandiamide in a muffle furnace to obtain a precursor bulk carbon nitride, which is then ground for later use; (2) After grinding and mixing carbon nitride, sodium chloride and potassium chloride, the mixture is subjected to secondary calcination in a muffle furnace to obtain a molten salt C3N5 ultrathin nanosheet; (3) The obtained molten salt C3N5 ultrathin nanosheets are dispersed in pure water, heated and stirred, cooled, centrifuged and washed, and dried overnight to obtain Na-K co-doped few-layer thin sheet g-C3N5 photo-Fenton catalyst; The calcination temperature of the muffle furnace in step (1) is 450-550°C, the heating rate is 8-12°C / min, and the calcination time is 2-4 h; The mass ratio of carbon nitride, sodium chloride and potassium chloride in step (2) is (1.5-2.5): (4.5-5.5): (4.5-5.5), and the grinding time is 30-50 min; The calcination temperature of the muffle furnace in step (2) is 400-500°C, the heating rate is 8-12°C / min, and the calcination time is 3-5 h.

2. Application of a Na-K co-doped g-C3N5 photocatalyst in photoauto-Fenton catalytic degradation of tetracycline in water, characterized by: The preparation method of the Na-K co-doped g-C3N5 photocatalyst comprises the following steps: (1) calcining dicyandiamide in a muffle furnace to obtain a precursor bulk carbon nitride, which is then ground for later use; (2) After grinding and mixing carbon nitride, sodium chloride and potassium chloride, the mixture is subjected to secondary calcination in a muffle furnace to obtain a molten salt C3N5 ultrathin nanosheet; (3) The obtained molten salt C3N5 ultrathin nanosheets are dispersed in pure water, heated and stirred, cooled, centrifuged and washed, and dried overnight to obtain Na-K co-doped few-layer thin sheet g-C3N5 photo-Fenton catalyst; The calcination temperature of the muffle furnace in step (1) is 450-550°C, the heating rate is 8-12°C / min, and the calcination time is 2-4 h; The mass ratio of carbon nitride, sodium chloride and potassium chloride in step (2) is (1.5-2.5): (4.5-5.5): (4.5-5.5), and the grinding time is 30-50 min; The calcination temperature of the muffle furnace in step (2) is 400-500°C, the heating rate is 8-12°C / min, and the calcination time is 3-5 h.

3. The use according to any one of claims 1 or 2, characterized in that: The mass of dicyandiamide used in step (1) is 4.95~5.05 g.

4. The use according to any one of claims 1 or 2, characterized in that: The grinding time in step (1) is 10 to 20 minutes.

5. The use according to any one of claims 1 or 2, characterized in that: The heating temperature in step (3) is 80-120°C, the rotation speed is 600-800 r / min, and the heating time is 5-12 h.

6. The use according to any one of claims 1 or 2, characterized in that: The washing method in step (3) is to thoroughly wash and separate with hot distilled water and anhydrous alcohol respectively, and dry at 70~90℃ overnight.

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