A hydroxyl-modified graphite-phase carbon nitride and a method for preparing and using the same

Abstract

The application discloses a kind of hydroxyl modified graphite phase carbon nitride and its preparation method and application, the hydroxyl modified graphite phase carbon nitride uses tartaric acid and urea as raw material, using the method of one-pot copolymerization simultaneously introduces π electron and -OH group into g-C3N4, the introduction of π electron significantly improves the photoelectric performance of CN and interface charge transfer and transport kinetics, the introduction of -OH group can effectively inhibit the decomposition of hydrogen peroxide;The preparation process of hydroxyl modified graphite phase carbon nitride proposed in the application is simple, safe, low in cost, and has excellent photocatalytic production hydrogen peroxide under visible light, and has good application prospect in green production of hydrogen peroxide.

Description

TECHNICAL FIELD

[0001] The present application relates to a modified graphite phase carbon nitride, in particular to a hydroxyl modified graphite phase carbon nitride, and also relates to the preparation method and application of the modified graphite phase carbon nitride. BACKGROUND

[0002] Hydrogen peroxide (H2O2) is widely used as a clean oxidant in various fields such as organic synthesis, disinfection and bleaching, wastewater treatment, fuel cells, etc. On the one hand, it is a clean energy, and in the reaction process, it does not produce toxic by-products, only water and oxygen; on the other hand, it has an energy density comparable to compressed hydrogen, and is more convenient to store and transport than hydrogen. At present, the industrial production of hydrogen peroxide generally uses the energy-intensive, multi-step anthraquinone method. This process involves hydrogenation and autoxidation reactions between anthraquinone and anthrahydroquinone. The reaction process involves expensive noble metal catalysts, toxic organic solvents and hydrogen gas under high pressure and high temperature conditions, which is highly polluting and dangerous. In addition, there is an electrochemical synthesis method, but this method has low selectivity and yield for producing hydrogen peroxide, and has a high risk coefficient. Therefore, there is an urgent need to develop a green and environmentally friendly method for preparing hydrogen peroxide.

[0003] Photocatalytic two-electron oxygen reduction reaction (ORR) provides a sustainable and safe method for the production of hydrogen peroxide. Photocatalytic technology has mild reaction conditions and can utilize abundant solar energy as the driving force for chemical reactions, making it a promising new technology that is universally applicable, inexpensive, safe and stable, which can replace traditional hydrogen peroxide preparation processes. Graphite phase carbon nitride (g-C3N4) is a promising photocatalyst due to its unique electronic structure, excellent chemical stability and simple preparation method.

[0004] However, the original g-C3N4 can only absorb light below 460 nm, which limits its use of visible and near-infrared light. In addition, the serious photogenerated carrier recombination affects the photocatalytic activity of g-C3N4. Conventional methods for modifying carbon nitride include doping, defect introduction, heterostructure construction, morphology control, and improving crystallinity. However, the conventional operation mode of the above methods is accompanied by high cost and complex steps, such as the use of complex and dangerous high-temperature hydrothermal method to achieve good crystallinity and strong binding force between different components for heterostructure construction and crystallization process, and the use of template method for morphology control, which is complicated. The precursors used in the doping method involve noble metals, and the hydrothermal method is used for treatment, and non-environmentally friendly sacrificial agents and pure oxygen may be added during the hydrogen peroxide test process, which greatly increases the cost of hydrogen peroxide production. SUMMARY

[0005] The application aims to provide a hydroxyl-modified graphite phase carbon nitride with simple preparation process and excellent photocatalytic performance, and a preparation method and application of the hydroxyl-modified graphite phase carbon nitride.

[0006] The hydroxyl-modified graphite phase carbon nitride is obtained by calcining a precursor solution obtained by dissolving tartaric acid and urea in water, and the mass ratio of the tartaric acid and urea is 0.01-0.05:10, and the specific surface area is 69.5m 2 .g -1 .

[0007] The preparation method of the hydroxyl-modified graphite phase carbon nitride comprises the following steps:

[0008] (1) dissolving tartaric acid and urea in water to form a precursor solution by stirring;

[0009] (2) performing calcination treatment on the precursor solution, and then cooling to room temperature to collect yellow powder to obtain the hydroxyl-modified graphite phase carbon nitride.

[0010] Preferably, in step (1), the mass ratio of the tartaric acid, urea and water is 0.01-0.05:10:0.01.

[0011] Preferably, in step (1), the stirring is magnetic stirring, the stirring rate is 300-600r / min, and the stirring time is 2-4h.

[0012] Preferably, in step (2), the calcination temperature is 540-550℃, and the temperature rising rate is 4.8-5℃ / min.

[0013] Preferably, in step (2), the holding time is 2-2.5h.

[0014] The hydroxyl-modified graphite phase carbon nitride is applied to photocatalytic production of hydrogen peroxide.

[0015] Preferably, the hydroxyl-modified graphite phase carbon nitride is added into water and mixed fully, and then light reaction is performed at room temperature to generate hydrogen peroxide.

[0016] Preferably, the concentration of the hydroxyl-modified graphite phase carbon nitride in the aqueous solution is 0.625-0.71g / L, and the irradiation time of the light reaction is 2-2.5h.

[0017] Preferably, the solution temperature is maintained at 20℃ by using a cooling circulation system, and the irradiation time of the light reaction is further preferably 2h.

[0018] Invention principle: the hydroxyl modified graphite phase carbon nitride of the application, through one-pot copolymerization reaction, takes tartaric acid and urea as raw materials to prepare the graphite phase carbon nitride (TA-CN) modified by hydroxyl groups, according to the characteristics of the reaction between water molecules and molecular oxygen, introduces strong polar hydroxyl groups on the surface of g-C3N4, promotes the effective contact and reaction of water molecules and O 2 molecules on the catalytic site, promotes the timely removal of generated H2O2 from the catalytic site, thereby reducing the decomposition of peroxide.

[0019] Due to the introduction of tartaric acid, π electrons and -OH groups are introduced at the same time, the introduction of π electrons significantly improves the photoelectric performance of the original carbon nitride, promotes the separation and transmission dynamics of charge carriers, and the -OH group has the effect of inhibiting the decomposition of hydrogen peroxide. The combination of π electrons and -OH groups makes the original CN exhibit superior hydrogen peroxide production performance under light; at the same time, the one-pot copolymerization reaction has the advantage of simple preparation method, and the above-mentioned hydroxyl modified graphite phase carbon nitride can be efficiently prepared.

[0020] Beneficial effects: compared with the prior art, the application has the following obvious advantages: (1) as a photocatalyst, the hydroxyl modified graphite phase carbon nitride has extremely high hydrogen peroxide production capacity, and the hydrogen peroxide production is up to 89.6 μmol h -1 g -1 ; (2) the preparation method of the application, one-pot copolymerization reaction can prepare hydroxyl modified graphite phase carbon nitride without complex operation, and the process is simple, safe and low in production cost. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 XRD patterns of examples and comparative examples;

[0022] Figure 2 Fourier infrared spectra of examples and comparative examples;

[0023] Figure 3 Transmission electron microscopy (TEM) of examples and comparative examples and mapping of example 2;

[0024] Figure 4 XPS patterns of examples and comparative examples;

[0025] Figure 5 Ultraviolet-visible absorption spectra of examples and comparative examples;

[0026] Figure 6 Band structure diagram of examples and comparative examples;

[0027] Figure 7 Transient fluorescence spectrum (PL) of examples and comparative examples;

[0028] Figure 8Figure showing the rate of hydrogen peroxide production over 2h for the examples and comparative examples;

[0029] Figure 9 Figure showing the TEM image for Example 2. DETAILED DESCRIPTION

[0030] The technical solutions of the present application are further described below in conjunction with the drawings.

[0031] Example 1

[0032] (1) 10 mg of tartaric acid and 10 g of urea were dissolved in 10 mL of deionized water to form a precursor solution;

[0033] (2) The precursor solution was transferred to a crucible and placed in a muffle furnace for calcination treatment. The temperature was raised to 550°C at a rate of 5°C / min and calcined for 2h. After cooling to room temperature, the yellow powder collected was TA-CN-10.

[0034] Example 2

[0035] Compared with Example 1, the amount of tartaric acid added was changed:

[0036] (1) 30 mg of tartaric acid and 10 g of urea were dissolved in 10 mL of deionized water to form a precursor solution;

[0037] (2) The precursor solution was transferred to a crucible and placed in a muffle furnace for calcination treatment. The temperature was raised to 550°C at a rate of 5°C / min and calcined for 2h. After cooling to room temperature, the yellow powder collected was TA-CN-30.

[0038] Example 3

[0039] Compared with Example 1, the amount of tartaric acid added was changed:

[0040] (1) 50 mg of tartaric acid and 10 g of urea were dissolved in 10 mL of deionized water to form a precursor solution;

[0041] (2) The precursor solution was transferred to a crucible and placed in a muffle furnace for calcination treatment. The temperature was raised to 550°C at a rate of 5°C / min and calcined for 2h. After cooling to room temperature, the yellow powder collected was TA-CN-50.

[0042] Comparative Example 1

[0043] Preparation of unmodified graphite phase carbon nitride:

[0044] 10 g of urea was transferred to a crucible and placed in a muffle furnace for calcination treatment. The temperature was raised to 550°C at a rate of 5°C / min and calcined for 2h. After cooling to room temperature, the yellow powder collected was PCN.

[0045] Comparative Example 2

[0046] Preparation of graphite phase carbon nitride after water treatment:

[0047] (1) 10 g of urea was dissolved in 10 mL of deionized water to form a solution under stirring;

[0048] (2) The precursor solution was transferred to a crucible and placed in a muffle furnace for calcination treatment, heated to 550°C at a heating rate of 5°C / min and calcined for 2 h. After cooling to room temperature, the yellow powder collected was W-CN.

[0049] Comparative Example 3

[0050] Compared with Example 1, the amount of tartaric acid added was changed:

[0051] (1) 5 mg of tartaric acid and 10 g of urea were dissolved in 10 mL of deionized water to form a precursor solution under stirring;

[0052] (2) The precursor solution was transferred to a crucible and placed in a muffle furnace for calcination treatment, heated to 550°C at a heating rate of 5°C / min and calcined for 2 h. After cooling to room temperature, the yellow powder collected was TA-CN-5.

[0053] Comparative Example 4

[0054] Compared with Example 1, the amount of tartaric acid added was changed:

[0055] (1) 70 mg of tartaric acid and 10 g of urea were dissolved in 10 mL of deionized water to form a precursor solution under stirring;

[0056] (2) The precursor solution was transferred to a crucible and placed in a muffle furnace for calcination treatment, heated to 550°C at a heating rate of 5°C / min and calcined for 2 h. After cooling to room temperature, the yellow powder collected was TA-CN-70.

[0057] For the hydroxyl-modified graphite phase carbon nitride prepared in the above examples and the materials prepared in the comparative examples, the hydroxyl-modified graphite phase carbon nitride was prepared, including the following steps:

[0058] (1) A 0.1 M potassium hydrogen phthalate solution and a 0.4 M potassium iodide solution were prepared for standby;

[0059] (2) 25 mg of TA-CN in Example 2 was added to a photocatalytic reaction bottle containing 40 mL of deionized water, stirred at a speed of 200 r / min, and subjected to a dark reaction for 30 min in the dark to exclude the interference of other factors. After 30 min, 2 mL of the reaction solution was taken for standby;

[0060] (3) After the first reaction solution was taken, the xenon lamp light source was turned on, and the photo-reaction was started. The sampling interval of the photo-reaction was 20 min / time, and a total of 6 times were sampled, for a total of 120 min.

[0061] (4) Both the photo-reaction and the dark reaction were equipped with cooling circulating water to control the temperature of the reaction solution at 20°C.

[0062] (4) 1 mL of each of the above sampling solutions, potassium hydrogen phthalate solution and potassium iodide solution was configured into a test solution, and then after standing for 30 min, it was put into an ultraviolet-visible spectrophotometer for testing. The response characteristic peak of hydrogen peroxide was near 350 nm.

[0063] Figure 1 is the XRD pattern of the examples and comparative examples; the XRD pattern of the prepared sample has two obvious characteristic peaks at 27.3° and 13.3°, corresponding to the (002) and (100) crystal faces of g-C3N4. It is preliminarily confirmed that the prepared sample is graphite phase carbon nitride.

[0064] Figure 2 is the FTIR pattern of the examples and comparative examples; the FTIR pattern of the prepared sample has similar characteristics to g-C3N4 reported in the literature. Specifically, strong stretching vibrations at 810 cm -1 and 1200-1700 cm -1 around are assigned to tri-s-triazine units and C-N / C= N heterocycles, respectively. Different is that the FTIR pattern of all TA-CN samples shows two new peaks at 990 cm -1 and 3300 cm -1 , indicating that the -OH group is successfully introduced into g-C3N4.

[0065] Figure 3 is the transmission electron microscopy (TEM) image of the examples and comparative examples and the mapping image of example 2; the TEM image shows that PCN is in the form of nanosheets without obvious pores Figure 3 a), while W-CN and TA-CN are in the form of ultra-thin porous structures, which is due to the evaporation of water during calcination, which promotes the release of endogenous gas Figure 3 b-e). The presence of element O is detected in the element mapping image and energy dispersive x-ray (EDS) spectrum of TA-CN-30.

[0066] Figure 4 is the XPS pattern of the examples and comparative examples; the surface chemical composition and state of the prepared sample were analyzed by x-ray photoelectron spectroscopy (XPS). The XPS survey spectrum confirms the presence of C Figure 4 a), N Figure 4 b) and O Figure 4c) The peak area of C-O gradually increased, and the O 1s spectrum showed a new peak at 531.2 eV for the TA-CN sample. These results indicated that the π-electron-rich domain and -OH group were simultaneously introduced into the g-C3N4 framework.

[0067] Figure 5 The UV-Vis absorption spectra of examples and comparative examples; the light absorption ability of the samples was further determined by UV-Vis-near infrared absorption spectra, and the introduction of C and -OH functional groups in the seven azine heterocycle can adjust the light absorption range of g-C3N4 to near infrared.

[0068] Figure 6 The band structure diagram of examples and comparative examples; with the increase of tartaric acid content, the band gap of TA-CN is narrowed, and the conduction band is lowered Figure 3 b).

[0069] Figure 7 The transient fluorescence spectrum (PL) of examples and comparative examples; with the increase of tartaric acid content, the intensity of PL peak gradually decreases, which indicates that the increase of π-electron can promote the separation of photo-generated carriers. At the same time, the emission peak shows obvious gradual red shift, which is consistent with the red shift of absorption edge.

[0070] Figure 8 The production rate of hydrogen peroxide of examples and comparative examples within 2h; the photocatalytic hydrogen peroxide production reaction was carried out with visible light (λ>420nm). In deionized water without sacrificial agent and additional O2 supply, the hydrogen peroxide production of PCN and WCN is very low, and after modification of hydroxyl group, the activity of TA-CN is greatly improved. Among them, the optimal solution of hydrogen peroxide production is 89.6μmol h -1 g -1 It is worth noting that with too much or too little tartaric acid, the hydrogen peroxide production of comparative example 3 and comparative example 4 gradually does not conform to the rule, because the hydroxyl group produced by the pyrolysis of tartaric acid will change its properties with the change of environment, and the concentration is too low, which may directly react with holes and be consumed in the photocatalytic process, and the concentration is too high, which may affect the desorption of products due to the too large adsorption energy, and directly affect the photocatalytic performance of the catalyst.

Claims

1. A hydroxyl-modified graphite-phase carbon nitride for photocatalytic production of hydrogen peroxide, characterized by, The hydroxyl-modified graphite-phase carbon nitride is obtained by calcining a precursor solution obtained by dissolving tartaric acid and urea in water, and the mass ratio of the tartaric acid to the urea is 0.01-0.05:10; the hydroxyl-modified graphite-phase carbon nitride is prepared by the following steps: (1) dissolving tartaric acid and urea in water to form a precursor solution by stirring; (2) calcining the precursor solution, and after heat preservation, cooling to room temperature to collect yellow powder to obtain the hydroxyl-modified graphite-phase carbon nitride.

2. The photocatalytic production of hydrogen peroxide hydroxyl modified graphite phase carbon nitride according to claim 1, characterized by, In step (1), the mass ratio of the tartaric acid, the urea and the water is 0.01-0.05:10:0.

01.

3. The photocatalytic production of hydrogen peroxide hydroxyl modified graphite phase carbon nitride according to claim 1, characterized by, In step (1), the stirring is magnetic stirring, and the stirring rate is 300-600 r / min, and the stirring time is 2-4 h.

4. The photocatalytic production of hydrogen peroxide hydroxyl modified graphite phase carbon nitride according to claim 1, characterized by, In step (2), the calcining is performed at a temperature of 540-550 ℃, and the temperature rising rate is 4.8-5 ℃ / min.

5. The photocatalytic production of hydrogen peroxide hydroxyl modified graphite phase carbon nitride according to claim 1, characterized by, In step (2), the heat preservation time is 2-2.5 h.

6. The hydroxyl-modified graphite-phase carbon nitride of claim 1 for photocatalytic production of hydrogen peroxide.

7. Use according to claim 6, characterized in that, The hydroxyl-modified graphite-phase carbon nitride is added into water and mixed thoroughly, and then the light reaction is performed at room temperature to generate hydrogen peroxide.

8. Use according to claim 7, characterized in that, The concentration of the hydroxyl-modified graphite-phase carbon nitride in the aqueous solution is 0.625-0.71 g / L.

9. Use according to claim 7, characterized in that, The light reaction is performed for 2-2.5 h.

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