Preparation method and application of g-C3N4 / PVDF composite photocatalytic membrane

Abstract

The invention belongs to the technical field of nano composite material preparation and environmental protection, and discloses a preparation method and application of a composite photocatalytic film g-C3N4 / PVDF. The photocatalyst is prepared by adopting a thermal polymerization method, and then the composite photocatalytic membrane is prepared by adopting a blending method. The preparation method comprises the following steps: firstly, preparing g-C3N4 nanoparticles by taking dicyandiamide (C2H4N4) and urea (CO (NH2) 2) as raw materials; and secondly, successfully preparing the g-C3N4 / PVDF composite photocatalytic membranes with different proportions (0.1%-0.7%) in a blending manner. The preparation method has the advantages of simple operation, easily available raw materials and low cost. The prepared photocatalytic membrane has a very good effect in the aspect of treating water pollutants, and has a good application prospect and value in the fields of membrane catalysis and membrane separation.

Description

Technical Field

[0001] The invention relates to the field of semiconductor photocatalysis and membrane separation, and relates to a preparation method of a g-C3N4 / PVDF composite photocatalytic membrane and its application in photocatalytic reduction of Cr(VI), belonging to the field of environmental protection. Background Art

[0002] In recent years, water pollution has gradually become a major issue. Reducing pollution at the source and improving pollution control measures are the most serious problems we are facing. Heavy metal chromium continues to damage aquatic systems, which has had a serious impact on human health and the ecosystem, and has restricted the sustainable development of humans and society. Compared with other hexavalent chromium reduction methods, semiconductor photocatalysis has the advantages of low cost, high efficiency, and simple operation. It is considered to be a viable alternative technology. The separation and recovery of suspended semiconductor photocatalysts from the reaction environment is still a huge challenge. Therefore, the integration of membrane filtration and photocatalysis is an ideal alternative for treating organic pollutants in wastewater.

[0003] Graphitic carbon nitride (g-C3N4) has been reported as a "reproducible" semiconductor catalyst material. g-C3N4 is a planar two-dimensional sheet structure similar to graphene, with triazine ring (C3N3) and 3-s-triazine ring (C6N7) as basic structural units, which are infinitely extended to form a network structure. The valence band and conduction band are 1.4eV and -1.3eV, respectively. The relatively narrow band gap (2.7eV) can significantly improve its utilization of sunlight. However, small-sized g-C3N4 is easy to agglomerate in aqueous solution, resulting in reduced photocatalytic efficiency. Therefore, combining small-sized photocatalysts with membrane substrates can effectively improve the photocatalytic performance, and can also change the performance of the membrane and improve the self-cleaning performance of the membrane. Summary of the invention

[0004] [Technical issues]

[0005] In view of the existing problems, a preparation scheme of a g-C3N4 / PVDF composite photocatalytic film is provided. The preparation scheme has low implementation cost and the raw materials are simple and easily available.

[0006] [Technical solution]

[0007] In order to achieve the above object, an embodiment of the present invention provides a method for preparing a g-C3N4 / PVDF composite photocatalytic film, and the preparation scheme comprises the following steps:

[0008] (1) Preparation of g-C3N4

[0009] Dicyandiamide was ultrasonically dissolved in distilled water to form a saturated solution, and then the solution was placed in a refrigerator until the dicyandiamide was recrystallized. The recrystallized dicyandiamide was dried at 50°C overnight. In the same way, recrystallized urea was obtained. Then, the recrystallized dicyandiamide and urea were mixed and thoroughly ground according to the specifications, and the mass ratio of dicyandiamide to urea was 1:4. The mixture was heated from room temperature to 550°C at a rate of 5°C / min in a tubular furnace. After keeping at 550°C for 4h, the furnace was naturally cooled to room temperature, and then the g-C3N4 sample was obtained.

[0010] (2) Preparation of g-C3N4 / PVDF casting solution

[0011] 0.1 g to 0.7 g of the photocatalyst powder was ultrasonically dispersed in 84.3 g to 84.9 g of an organic solvent DMF for 2 h, 14 g of PVDF and 1 g of PVP were added, and the mixture was mechanically stirred in a water bath at 60° C. for 8 h.

[0012] (3) Preparation of g-C3N4 / PVDF photocatalytic film

[0013] The mixture was allowed to stand overnight to defoam for 12 hours, the defoamed casting solution was poured onto a glass plate, and the film was scraped with a coating machine. The obtained film was placed in deionized water, and the excess organic solvent was discharged to obtain the final product.

[0014] In the step (1), the mass ratio of the recrystallized dicyandiamide to urea is 1:4, and the mixture is heated from room temperature to 550° C. at a rate of 5° C. / min in a tube furnace. After being kept at 550° C. for 4 hours, the furnace is naturally cooled to room temperature, and then a g-C3N4 sample is obtained.

[0015] In the step (2), the volume of DMF is 84.3 g to 84.9 g, the mass of PVP added is 1 g, the mass ratio of PVDF is 14 g, and the stirring time is 6 to 8 h.

[0016] In the step (3), the scraped membrane is immersed in deionized water to remove excess organic solvent.

[0017] According to an implementation method of the present invention, a g-C3N4 / PVDF composite photocatalytic film prepared by the above preparation method is provided, which is used to remove Cr(VI) pollutants in a water environment.

[0018] Material Source

[0019] Dicyandiamide, urea, dimethylformamide (DMF), polyvinylpyrrolidone (PVP), and polyvinylidene fluoride (PVDF) were all 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 g-C3N4 / PVDF composite photocatalytic film, so that g-C3N4 is evenly dispersed on the PVDF membrane matrix, effectively increasing the absorption area of ​​the catalyst for visible light and improving the self-cleaning ability of the membrane. The photocatalyst is excited by a xenon lamp, and a catalytic reduction reaction is achieved by contacting and interacting with pollutant molecules, so that the surrounding oxygen and water molecules are excited to become superoxide radical anions with strong oxidizing power, thereby reducing Cr (VI) in the wastewater. At the same time, the powdered photocatalyst is fixed on the membrane matrix, which solves the problem of recycling the catalyst and improves the self-cleaning ability of the membrane. The g-C3N4 / PVDF composite photocatalytic film prepared by this method has a stable structure, simple and easy-to-obtain raw materials, and a simple and easy operation process. It is an efficient green environmental protection technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 a, b, c are scanning electron micrographs of the surface, cross section, and back of the original PVDF membrane, respectively; d, e, f: scanning electron micrographs of the surface, cross section, and back of the 0.5% g-C3N4 / PVDF membrane, respectively;

[0024] Figure 2 a, b, c are the X-ray powder diffraction spectra, Fourier infrared spectra, and X-ray photoelectron spectra of g-C3N4, 0.5% g-C3N4 / PVDF, and PVDF, respectively; d is the N1s peak of the X-ray photoelectron spectrum of 0.5% g-C3N4 / PVDF;

[0025] Figure 3 The kinetic curves of Cr(VI) (10 mg / L) reduction in aqueous solution by different photocatalytic films under visible light conditions;

[0026] Figure 4 This is a graph showing the absorbance change of the solution during the photoreduction of Cr(VI) by 0.5% g-C3N4 / PVDF composite photocatalytic film under visible light conditions.

[0027] Specific implementation methods

[0028] Evaluation of the photocatalytic activity of the photocatalytic film prepared in the present invention: 6.4 g of the photocatalytic film was cut into uniform sizes of 2 cm*2 cm, added to 100 mL of Cr(VI) solution to make it evenly distributed, and then 0.02 g of citric acid was added to the solution, and irradiated with a 220 W xenon lamp as a light source for 30 minutes. During the irradiation process, the solution was sampled every 20 minutes, and the supernatant was taken and measured using a spectrophotometer at a wavelength of λ max =The absorbance intensity was measured at 433 nm.

[0029] The Cr(VI) photoreduction rate was calculated using the formula: Dr = (C0-C)*100 / C0, where: Dr is the Cr(VI) photoreduction rate, C0 is the initial concentration of Cr(VI), C is the concentration of Cr(VI) remaining in the solution at time t, and t is the reaction time.

[0030] In order to enable those skilled in the art to clearly understand the present invention, the present invention is further described in detail below in conjunction with 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.

[0031] Embodiment 1:

[0032] The following method is used to prepare the composite photocatalytic film g-C3N4 / PVDF according to the present invention:

[0033] (1) Dicyandiamide was ultrasonically dissolved in distilled water to form a saturated solution, and then the solution was placed in a refrigerator until the dicyandiamide was recrystallized. The recrystallized dicyandiamide was dried at 50°C overnight. In the same way, recrystallized urea was obtained. Then, the recrystallized dicyandiamide and urea were mixed and thoroughly ground according to the specifications, and the mass ratio of dicyandiamide to urea was 1:4. The mixture was heated from room temperature to 550°C at a rate of 5°C / min in a tube furnace. After maintaining at 550°C for 4h, the furnace was naturally cooled to room temperature, and then the g-C3N4 photocatalyst was obtained.

[0034] (2) 0.1 g of the photocatalyst was ultrasonically dispersed in 84.9 g of the organic solvent DMF for 2 h, 14 g of PVDF and 1 g of PVP were added, and the mixture was mechanically stirred in a water bath at 60° C. for 8 h to obtain a uniform casting solution.

[0035] (3) The casting solution was allowed to stand overnight to defoam for 12 hours, and the defoamed casting solution was poured onto a glass plate. The film was scraped with a coating machine, and the obtained film was placed in deionized water. The excess organic solvent was drained out, and the obtained photocatalytic film was marked as 0.1% g-C3N4 / PVDF photocatalytic film.

[0036] (4) Weigh 6.4 g of 0.1% g-C3N4 / PVDF photocatalytic film, cut it into uniform sizes of 2 cm*2 cm, and conduct a photoreduction test in a photochemical reactor. It is measured that the reduction rate of Cr(VI) by the photocatalytic film reaches 85.86% within 100 min.

[0037] Embodiment 2:

[0038] A preparation method similar to that of Example 1 was used, except that 0.3 g of the photocatalyst was weighed and ultrasonically dispersed in 84.7 g of organic solvent DMF for 2 h in (2), 14 g of PVDF and 1 g of PVP were added, and mechanical stirring was performed in a water bath at 60°C for 8 h. The obtained photocatalytic film was labeled as 0.3% g-C3N4 / PVDF photocatalytic film. 6.4 g of 0.3% g-C3N4 / PVDF photocatalytic film was weighed and cut into uniform sizes of 2 cm*2 cm. A photoreduction test was carried out in a photochemical reactor, and the reduction rate of Cr(VI) by the photocatalytic film was measured to reach 87.89% within 100 min.

[0039] Embodiment 3:

[0040] A preparation method similar to that of Example 1 was used, except that 0.5 g of the photocatalyst was weighed and ultrasonically dispersed in 84.5 g of organic solvent DMF for 2 h in (2), 14 g of PVDF and 1 g of PVP were added, and mechanical stirring was performed in a water bath at 60°C for 8 h. The obtained photocatalytic film was labeled as 0.5% g-C3N4 / PVDF photocatalytic film. 6.4 g of 0.5% g-C3N4 / PVDF photocatalytic film was weighed and cut into uniform sizes of 2 cm*2 cm. A photoreduction test was carried out in a photochemical reactor, and the reduction rate of Cr(VI) by the photocatalyst reached 95.93% within 100 min.

[0041] Embodiment 4:

[0042] A preparation method similar to that of Example 1 was used, except that 0.7 g of the photocatalyst was weighed and ultrasonically dispersed in 84.3 g of an organic solvent (DMF) for 2 h in (2), 14 g of PVDF and 1 g of PVP were added, and mechanical stirring was performed in a water bath at 60°C for 8 h. The obtained photocatalytic film was labeled as 0.7% g-C3N4 / PVDF photocatalytic film. 6.4 g of 0.7% g-C3N4 / PVDF photocatalytic film was weighed and cut into uniform sizes of 2 cm*2 cm. A photoreduction test was performed in a photochemical reactor, and the reduction rate of Cr(VI) by the photocatalyst reached 90.42% within 100 min.

[0043] Comparative Example 1:

[0044] The same steps as in Example 1 were followed, except that 50 mg of g-C3N4 photocatalyst was weighed in (1) and subjected to a photocatalytic reduction test in a photochemical reactor. The reduction rate of Cr(VI) by the photocatalyst was measured to be 64.48% within 100 min.

Claims

1. A method for preparing a g-C3N4 / PVDF composite photocatalytic film, characterized in that: The preparation method steps are as follows: (1) Recrystallized dicyandiamide and urea were mixed and placed in a tubular furnace under nitrogen insulation to prepare g-C3N4 nano-photocatalyst; (2) Preparation of g-C3N4 / PVDF casting solution: Ultrasonic dispersion of g-C3N4 nano-photocatalyst in organic solvent DMF, after ultrasonication, adding PVP and PVDF, and stirring at 60°C; (3) The stirred casting solution was allowed to stand overnight to defoam for 12 hours, and the defoamed casting solution was poured onto a glass plate. The film was scraped with a coating machine to obtain a g-C3N4 / PVDF composite photocatalytic film.

2. The method for preparing a g-C3N4 / PVDF composite photocatalytic film according to claim 1, characterized in that: In the step (1), dicyandiamide and urea are prepared into a saturated solution and low-temperature recrystallized in a refrigerator at 4°C to obtain recrystallized dicyandiamide and urea; the mass ratio of the recrystallized dicyandiamide and urea is 1:4, the mixture is placed in a tubular furnace and heated from room temperature to 550°C at a heating rate of 5°C / min and maintained for 4 hours under the condition of continuous nitrogen flow, and then naturally cooled to room temperature to obtain a g-C3N4 sample.

3. The method for preparing a g-C3N4 / PVDF composite photocatalytic film according to claim 1, characterized in that: In the step (2), the mass of g-C3N4 nanoparticles is 0.1g to 0.7g, the mass of DMF is 84.3g to 84.9g, the mass of PVP added is 1g, the mass of PVDF is 14g, and the stirring time is 6h to 8h.

4. The method for preparing a g-C3N4 / PVDF composite photocatalytic film according to claim 1, characterized in that: In the step (3), the scraped membrane is immersed in deionized water to remove excess organic solvent.

5. The method for synthesizing a g-C3N4 / PVDF composite photocatalytic film according to claim 1, characterized in that The g-C3N4 / PVDF composite photocatalytic film can be used to reduce Cr(VI) to Cr(III) in aquatic environments.

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