Preparation method and application of oxygen-doped hollow tubular g-C3N4 photocatalyst

Abstract

The invention belongs to the technical field of semiconductor photocatalyst preparation and environmental protection, and discloses a preparation method and application of an oxygen-doped hollow tubular g-C3N4 photocatalyst (O-CN). The preparation method comprises the following steps: firstly, preparing a catalyst precursor by taking melamine as a raw material through a hydrothermal synthesis method, and then preparing an oxygen-doped hollow tubular g-C3N4 photocatalyst (O-CN) through a high-temperature calcination method. The preparation method is simple in equipment and convenient to operate, and materials are easy to obtain and low in cost. The prepared photocatalyst has a good effect in the aspect of treating pollutants in a water body, so that the photocatalyst has a good application prospect and value in the field of photocatalysts.

Description

Technical Field

[0001] The invention relates to the field of semiconductor catalysts, in particular to a method for preparing an oxygen-doped hollow tubular g-C3N4 photocatalyst (O-CN) and its application in photocatalytic degradation of lornoxicam (LC) and tetracycline (TC), and belongs to the field of environmental protection. Background Art

[0002] In recent years, with the rapid development of economy and the acceleration of industrialization, the discharge of wastewater has increased day by day, posing a great threat to the environment and human health. Lornoxicam and tetracycline play a positive role in human health and animal husbandry production, but if they are not completely absorbed and utilized or their metabolites enter the water body, even if their half-life in the water body is short, their large-scale and frequent use will still form "pseudo-persistent pollution", posing a threat to the ecological safety of the water environment and human health. Therefore, the development of efficient photocatalysts to degrade organic pollutants such as lornoxicam and tetracycline in water has become one of the important research directions.

[0003] Semiconductor photocatalysts can degrade organic pollutants into CO2 and H2O at room temperature. They are economical and environmentally friendly and have been widely used in the degradation of organic pollutants. Graphitic carbon nitride (g-C3N4) has been widely used in the fields of pollutant degradation, H2O2 production, disinfection, etc. due to its high stability, low cost, high response to visible light, and adjustable structure. However, the photocatalytic efficiency of g-C3N4 is severely limited by its inherent defects, such as slow carrier migration, fast recombination of photogenerated electron-hole pairs, and small specific surface area. The photocatalytic efficiency of g-C3N4 can be improved by modifying it. The modification methods include element doping, forming heterostructures with other semiconductors, and constructing micromorphology. The non-metallic elements used for doping include C, N, O, P, B, S, etc., which can further effectively improve g-C3N4 by changing the chemical properties of g-C3N4, narrowing the band gap, and adjusting the electronic structure.

[0004] The present invention is to improve the photocatalytic efficiency of g-C3N4 by using a method of doping oxygen elements. Oxygen doping can change the electronic structure, absorb more photons in the visible light region, and more effectively generate photogenerated electron-hole pairs, thereby increasing the catalytic reaction rate. In addition, oxygen doping can also adjust the band structure of g-C3N4, reduce its band gap, and make its visible light response range wider, which means that oxygen-doped g-C3N4 has higher photocatalytic activity under visible light irradiation, which helps to degrade pollutants more efficiently. At the same time, oxygen doping also increases its surface defects and active sites, thereby increasing the amount of light absorption. Therefore, the present invention uses oxygen-doped hollow tubular g-C3N4 photocatalyst to improve photocatalytic activity, which can degrade pollutants more efficiently. Summary of the invention

[0005] [Technical issues]

[0006] Aiming at the shortcomings of slow carrier migration and fast recombination of photogenerated electron-hole pairs in g-C3N4, a preparation scheme of O-CN is provided, which has low implementation cost and simple and easily available raw materials.

[0007] [Technical solution]

[0008] In order to achieve the above object, a method for preparing O-CN is provided through an embodiment of the present invention, and the preparation scheme comprises the following steps:

[0009] (1) Preparation of O-CN precursor

[0010] Melamine is dissolved in deionized water, heated and stirred at 70°C to 100°C until dissolved to obtain a melamine clear solution, which is then transferred to a polytetrafluoroethylene stainless steel autoclave and heated at 150°C to 200°C for reaction for 24 hours;

[0011] (2) Preparation of O-CN

[0012] The precursor powder is placed in a crucible, covered with a lid and placed in a tube furnace, heated in static air at 350°C to 600°C for 2 hours, kept warm for 4 hours, and then the obtained powder is ultrasonicated at 25°C for 3 hours, the obtained water suspension is washed, and dried at 50°C to 70°C to obtain O-CN powder;

[0013] In the step (1), melamine: deionized water is prepared at a ratio of 1 g: 60 mL;

[0014] In the step (1), the temperature of heating and stirring is 90°C;

[0015] In the step (1), the heating temperature in the polytetrafluoroethylene stainless steel autoclave is 180° C.;

[0016] In the step (1), the heating temperature in static air is 400° C., 450° C., 500° C., 550° C.;

[0017] In the step (2), the drying temperature of the O-CN powder is 60°C.

[0018] Material Source

[0019] Melamine and anhydrous ethanol were of analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd.

[0020] [Beneficial Effects]

[0021] In summary, the present invention has the following beneficial effects:

[0022] The present invention realizes the preparation of oxygen-doped hollow tubular g-C3N4 photocatalyst, adjusts the g-C3N4 band gap width, narrows the band gap, and expands the visible light response. The catalyst is excited by a xenon lamp. Under the irradiation of visible light, the catalyst is excited to generate a large number of holes (h + ) and electron (e - ). On the one hand, h on the valence band + Can oxidize OH - Generate ·OH, e on the conduction band - The adsorbed O2 can be reduced to generate O2 - On the other hand, the introduced oxygen-containing groups can accelerate the efficiency of carrier transfer, and under the joint action of these free radicals, pollutants are degraded. At the same time, the O-CN prepared by this method has a stable structure, simple and easy-to-obtain raw materials, and a simple operation process. It is a green and environmentally friendly technology with high efficiency and low waste. Description of the drawings:

[0023] Figure 1 This is the electron microscope image of O-CN-450.

[0024] Figure 2 The kinetic curve of LC degradation by O-CN under different illumination times.

[0025] Figure 3 The UV-visible absorption spectra of LC degradation by O-CN-550 under different illumination times.

[0026] Figure 4 The kinetic curve of TC degradation by O-CN under different illumination times.

[0027] Figure 5 The UV-visible absorption spectra of TC degradation by O-CN-450 under different illumination times. DETAILED DESCRIPTION

[0028] Evaluation of the photocatalytic activity of the photocatalyst prepared in the present invention: 50 mg and 100 mg of the catalyst were added to 100 mL of 20 mg / L lornoxicam and tetracycline solution, respectively, and irradiated with a 220 W Xe lamp for 70 minutes. Samples were taken every 10 minutes during the irradiation process, and the supernatant was taken and measured in a spectrophotometer λ max =376nm and λ max =350nm, and the degradation rate Dr was calculated by the formula: Dr = (C0-C) × 100 / C0, where C0 is the initial concentration, C is the concentration of lornoxicam and tetracycline solution measured at time t, and t is the reaction time.

[0029] In order to enable those skilled in the art to more clearly understand the present invention, the present invention is further described in detail below in conjunction with the examples. However, it should be understood that the following examples are only preferred embodiments of the present invention, and the scope of protection claimed by the present invention is not limited thereto.

[0030] Embodiment 1:

[0031] The following method is used to prepare O-CN according to the present invention:

[0032] (1) 3 g of melamine was dissolved in 180 mL of deionized water and stirred at 90° C. until completely dissolved; the melamine clear solution was transferred into a 100 mL polytetrafluoroethylene stainless steel autoclave and heated at 180° C. for 24 h; the sample was washed and dried to obtain an O-CN photocatalyst precursor.

[0033] (2) 2 g of the precursor powder was placed in a crucible, the crucible was covered with a lid and placed in a tube furnace, and heated at 400 °C in static air for 4 h at a heating rate of 5 °C / min. The obtained powder was then ultrasonicated at 25 °C for 3 h. The obtained aqueous suspension was washed and dried to obtain the O-CN-400 photocatalyst.

[0034] Embodiment 2:

[0035] The same steps as in Example 1 were followed, except that in step (2), the powder was heated at 450°C in static air for 4 h at a heating rate of 5°C / min, and then the obtained powder was ultrasonicated at 25°C for 3 h. The obtained aqueous suspension was washed and dried to obtain the O-CN-450 photocatalyst.

[0036] Embodiment 3:

[0037] The same steps as in Example 1 were followed, except that in step (2), the powder was heated at 500°C in static air for 4 h at a heating rate of 5°C / min, and then the obtained powder was ultrasonicated at 25°C for 3 h. The obtained aqueous suspension was washed and dried to obtain the O-CN-500 photocatalyst.

[0038] Embodiment 4:

[0039] The same steps as in Example 1 were followed, except that in step (2), the powder was heated at 550°C in static air for 4 h at a heating rate of 5°C / min, and then the obtained powder was ultrasonicated at 25°C for 3 h. The obtained aqueous suspension was washed and dried to obtain the O-CN-550 photocatalyst.

[0040] Table 1 Degradation effects of different embodiments on different pollutants

[0041]

Claims

1. A preparation method and application of an oxygen-doped hollow tubular g-C3N4 photocatalyst, characterized in that: The preparation method steps are as follows: (1) Preparation of oxygen-doped hollow tubular g-C3N4 photocatalyst (O-CN) precursor: Melamine was dissolved in deionized water, heated and stirred at 70°C to 100°C until dissolved to obtain a melamine clear solution, which was then transferred to a polytetrafluoroethylene stainless steel autoclave and heated at 150°C to 200°C for 24 h; (2) Preparation of O-CN photocatalyst: The precursor powder was placed in a crucible, covered with a lid and placed in a tube furnace, heated at 350°C to 600°C in static air for 2 h, kept warm for 4 h, and then the obtained powder was ultrasonicated at 25°C for 3 h. The obtained aqueous suspension was washed and dried at 50°C to 70°C to obtain an O-CN photocatalyst.

2. The preparation method and application of an oxygen-doped hollow tubular g-C3N4 photocatalyst according to claim 1, characterized in that: The step (1) is as follows: melamine: deionized water are mixed in a ratio of 1 g: 60 mL.

3. The preparation method and application of an oxygen-doped hollow tubular g-C3N4 photocatalyst according to claim 1, characterized in that: The step (1) is as follows: the temperature of heating and stirring is 90°C.

4. The method for preparing an oxygen-doped hollow tubular g-C3N4 photocatalyst according to claim 1, characterized in that: The step (1) is as follows: the heating temperature in the polytetrafluoroethylene stainless steel autoclave is 180°C.

5. The method for preparing an oxygen-doped hollow tubular g-C3N4 photocatalyst according to claim 1, characterized in that: The step (2) is as follows: the heating temperature in static air is 400°C, 450°C, 500°C, and 550°C.

6. The method for preparing an oxygen-doped hollow tubular g-C3N4 photocatalyst according to claim 1, characterized in that: In the step (2), the drying temperature of the O-CN photocatalyst is 60°C.

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