Modified carbon nitride photocatalyst, catalyst-loaded graphene-based photocatalytic membrane, and preparation method and application of modified carbon nitride photocatalyst and catalyst-loaded graphene-based photocatalytic membrane

Abstract

The invention discloses a modified carbon nitride photocatalyst, a catalyst-loaded graphene-based photocatalytic membrane and a preparation method and application thereof.The preparation method of the photocatalyst comprises the steps that urea and melamine are ground and mixed to be uniform, calcination is conducted in the nitrogen or argon atmosphere, obtained tubular carbon nitride TCN powder is added into a solvent, ultrasonic uniform treatment is conducted, and the catalyst-loaded graphene-based photocatalytic membrane is obtained; sequentially adding AgNO3 and KBr, stirring under a dark condition, then stirring under illumination for 10-30 minutes, centrifuging, washing, drying, grinding and sieving to obtain the modified carbon nitride photocatalyst. The modification of the carbon nitride photocatalyst improves the photocatalytic performance of the carbon nitride photocatalyst, a Z-type heterojunction is formed between TCN and AgBr, and photo-induced electrons in an AgBr conduction band are migrated to silver nanoparticles. The electrons are then compounded with holes in a TCN valence band, so that separation and transfer of photon-generated carriers are effectively promoted. The removal performance is enhanced through the synergistic effect of interception and photocatalytic degradation of the photocatalytic membrane, and the degradation efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic membrane preparation technology, specifically to a modified carbon nitride photocatalyst, a graphene-based photocatalytic membrane with a supported catalyst, its preparation method, and its application. Background Technology

[0002] Photocatalytic membranes are an effective method for removing antibiotic pollutants from water. While membrane separation technology can separate pollutants from water, it can only separate them, not completely remove them. Photocatalysis technology uses photocatalysts to degrade pollutants in water, but the dispersed photocatalysts in the water are difficult to recover, and the loss of catalyst materials in the water may pose environmental risks. Photocatalytic membranes combine the membrane's retention function with the photocatalytic degradation function, leveraging the membrane's retention and enrichment capabilities while simultaneously using photocatalytic degradation for complete removal.

[0003] Most existing photocatalytic membranes rely on ultraviolet light for photocatalysis, failing to fully utilize visible light. Furthermore, many photocatalytic membranes do not fulfill their separation function; they merely act as catalyst supports, or separate the membrane separation process from the photocatalytic process, trapping the catalyst before degradation. They also suffer from insufficient removal efficiency and inadequate removal rate performance.

[0004] Due to the above problems, it is necessary to propose a photocatalytic membrane that can achieve synergistic retention and photocatalytic degradation, can be carried out under visible light, balances membrane flux and degradation effect, has high removal efficiency, and is applicable to a variety of antibiotic pollutants. Summary of the Invention

[0005] To address the aforementioned technical problems in existing technologies, the present invention aims to provide a modified carbon nitride photocatalyst, a graphene-based photocatalytic membrane with a supported catalyst, its preparation method, and its application. The photocatalytic membrane of the present invention is primarily used for removing antibiotic pollutants from water.

[0006] The technical solution adopted in this invention is as follows: A method for preparing a modified carbon nitride photocatalyst includes the following steps: S1: Urea and melamine are ground and mixed evenly, and then calcined under a nitrogen or argon atmosphere to obtain tubular carbon nitride (TCN) powder. S2: Add the TCN powder obtained in step S1 to the solvent, sonicate to homogenize, add AgNO3 and KBr in sequence, stir in the dark for 1-4 hours, then stir under light for 10-30 minutes, then centrifuge, wash, dry, grind and sieve to obtain the modified carbon nitride photocatalyst.

[0007] Further, in step S1, the mass ratio of urea to melamine is 5-20:1, preferably 8-12:1.

[0008] Furthermore, in step S1, the calcination temperature conditions are as follows: the temperature is increased to 500-600℃ at a rate of 2-10℃ / min, then held at a constant temperature for 1-30min, and then naturally cooled to room temperature.

[0009] Further, in step S2, the molar ratio of KBr to AgNO3 is 5-20:1, preferably 7-10:1; the mass ratio of TCN powder to AgNO3 is 1:3-5, preferably 1:4; and the wavelength of light irradiation in step S2 is 200-300nm, preferably 240-280nm.

[0010] A graphene-based photocatalytic membrane supported on a modified carbon nitride photocatalyst comprises a base membrane, a graphene oxide (GO) base layer supported on the surface of the base membrane, and a catalyst-graphene oxide (GO) mixed layer supported on the surface of the base layer. The catalyst in the mixed layer is the modified carbon nitride photocatalyst described in this invention, and the mass ratio of the catalyst to GO in the mixed layer is 200-1000:1, preferably 500-600:1.

[0011] The method for preparing a graphene-based photocatalytic film with a supported modified carbon nitride photocatalyst includes the following steps: Step 1: The graphene oxide (GO) dispersion is filtered onto the substrate membrane surface to form a film, then dried to form a GO base layer on the substrate membrane surface; Step 2: The dispersion of catalyst and graphene oxide (GO) is further filtered on the surface of the GO base layer described in Step 1 to form a film, which is then dried to form a catalyst-graphene oxide (GO) mixed layer, thus obtaining the graphene-based photocatalytic film of the supported modified carbon nitride photocatalyst.

[0012] Further, in step 1, the base film is a PVDF film, and the loading of the GO base layer on the surface of the base film is 0.04-0.06 mg / cm³. 2 The catalyst-graphene oxide (GO) hybrid layer loading on the base layer surface is 0.3-0.5 mg / cm². 2 .

[0013] The present invention also discloses the application of the graphene-based photocatalytic membrane with the supported modified carbon nitride photocatalyst in the photocatalytic degradation and retention of organic pollutants in wastewater.

[0014] Furthermore, the organic pollutant is an antibiotic pollutant.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) The modification of the carbon nitride photocatalyst of the present invention improves its photocatalytic performance. A Z-type heterojunction is formed between TCN and AgBr, in which photogenerated electrons in the conduction band of AgBr migrate to the silver nanoparticles. These electrons then recombine with holes in the valence band of TCN, effectively promoting the separation and transfer of photogenerated charge carriers. The embedded metallic silver nanoparticles act as electronic mediators through the localized surface plasmon resonance (LSPR) effect.

[0016] (2) During the process of AgBr grafting onto the TCN surface, Ag + First, the silver ions adsorb onto the TCN surface through close coordination with amino groups. Then, through a seed growth mechanism, they react with potassium bromide to generate silver bromide. Finally, under ultraviolet light irradiation, some silver ions are reduced to elemental silver, forming Ag / AgBr. The introduction of Ag / AgBr narrows the apparent band gap of the catalyst, significantly enhancing visible light absorption. The photogenerated electrons generated in the catalyst have stronger migration capabilities; the presence of Ag / AgBr facilitates the transfer of photogenerated electrons, and the recombination of photogenerated electrons with holes is slower, resulting in a longer electron lifetime.

[0017] (2) The synergistic effect of the retention and photocatalytic degradation of the photocatalytic membrane enhances the removal performance. The retention effect of graphene as a membrane helps to enrich pollutants near the photocatalytic sites, thereby improving the degradation efficiency. When the catalyst is fixed on the GO membrane, GO effectively acts as an electron acceptor, while enhancing the LSPR effect of Ag, promoting the rapid transfer of photogenerated electrons generated after the catalyst receives light and reducing the recombination rate of photogenerated electrons and holes, thereby improving the overall light absorption efficiency. Attached Figure Description

[0018] Figure 1 These are physical images and SEM images of the tubular carbon nitride (TCN) of this invention; Figure 2 These are physical images and SEM images of the photocatalyst TCN-A-4 of this invention; Figure 3 The XRD patterns of the tubular carbon nitride (TCN) and the photocatalyst TCN-A-4 of this invention are shown. Figure 4 These are XPS images of the tubular carbon nitride (TCN) and the photocatalyst TCN-A-4 of this invention. Figure 5 These are the FTIR images of the tubular carbon nitride (TCN) and the photocatalyst TCN-A-4 of this invention; Figure 6a These are SEM images of the surface (left) and cross-section (right) of the MO membrane of this invention; Figure 6b These are SEM images of the surface (left) and cross-section (right) of the M3 membrane of this invention; Figure 7These are the XRD patterns of the M0 and M3 films of this invention; Figure 8 These are the FTIR images of the M0 and M3 films of this invention.

[0019] Figure 9 The values ​​represent the removal rate and normalized flux of sulfamethoxazole by the M3 membrane during 10 hours of continuous operation.

[0020] Figure 10 This is a comparison chart showing the photocatalytic degradation effects on SMX when TCN, TCN-A-1, TCN-A-2, TCN-A-3, TCN-A-4, and TCN-A-5 are selected as photocatalysts, respectively. Figure 11 This is a comparison of the flux of M0-M5 membranes under illumination and without illumination; Figure 12 This is a comparison of the removal rates of sulfamethoxazole by M0-M5 membranes under light and dark conditions. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0022] Example 1: Preparation of modified carbon nitride photocatalyst TCN-A, including the following steps: 1) Grind 10 g of urea and 1 g of melamine in a mortar and mix them evenly. In a tube furnace under argon atmosphere, heat the mixture from room temperature to 550 °C at a heating rate of 5 °C / min. Hold the temperature for 5 min and then allow it to cool naturally to room temperature. After grinding, obtain tubular carbon nitride (TCN) powder.

[0023] 2) TCN-A was prepared by grafting Ag / AgBr onto the TCN surface. The steps are as follows: 20 mg of TCN powder was weighed and added to 20 mL of ethanol, and sonicated for 1 h. 20 mL of a solution containing 0-100 mg AgNO3 was added to the resulting suspension, and the mixture was stirred for 30 min. Then, 0.43 g of KBr was added, and the mixture was stirred in the dark for 3 h. Afterward, it was stirred for 15 min under irradiation with a 5 W mercury lamp (λ=254 nm). The product was obtained by centrifugation, washed repeatedly with deionized water, dried overnight at 60 °C, ground, and sieved to obtain the photocatalyst.

[0024] Following the above preparation process of the photocatalyst, when the amount of AgNO3 used is 0 mg, 20 mg, 40 mg, 60 mg, 80 mg and 100 mg, the final photocatalysts are named TCN, TCN-A-1, TCN-A-2, TCN-A-3, TCN-A-4 and TCN-A-5, respectively, as shown in Table 1.

[0025] Table 1 .

[0026] Physical and SEM images of the tubular carbon nitride (TCN) prepared in Example 1 are shown below. Figure 1 As shown, the physical image and SEM image of the photocatalyst TCN-A-4 are as follows. Figure 2 As shown. From Figures 1-2 As can be seen from the physical images, the TCN catalyst powder is pale yellow, while the further modified TCN-A-4 catalyst powder is silver-gray. From... Figures 1-2 The SEM images show that TCN has a tubular structure with open ends and a hollow interior, with a diameter of approximately 100 nm to 400 nm. Ag / AgBr of TCN-A-4 is loaded on the wall of the TCN tube.

[0027] Example 1: XRD patterns of tubular carbon nitride (TCN) and photocatalyst TCN-A-4 are shown below. Figure 3 As shown, TCN exhibits two characteristic peaks of carbon nitride near 26.9° and 13.0°, corresponding to the (002) crystal plane caused by interlayer stacking of the conjugated aromatic system and the (100) crystal plane of the intralayer arrangement of the 3-S-triazine structure, respectively. After loading Ag / AgBr, the characteristic peaks of TCN weaken, possibly because the in-plane order is disrupted and the degree of stacking is reduced. Meanwhile, characteristic peaks of AgBr appear near 31.1°, 44.4°, and 55.1°, representing the (200), (220), and (222) crystal planes, respectively, indicating the presence of AgBr. However, no Ag diffraction peaks were observed, which may be because the amount of Ag reduced to Ag is small, below the detection limit, or because the crystallinity of Ag particles on the AgBr surface is poor.

[0028] XPS images of tubular carbon nitride (TCN) and photocatalyst TCN-A-4 in Example 1 are shown below. Figure 4 As shown, the full spectrum of TCN contains three significant peaks: a C 1s peak at 288.1 eV for g-C3N4, a N 1s peak at 399.1 eV, and an O 1s peak at 532.1 eV, possibly due to adsorbed hydroxyl groups, molecular oxygen, water, or other exogenous oxygen-containing substances. The full spectrum of TCN-A-4 shows additional characteristic peaks for Ag and Br compared to TCN. Characteristic Ag peaks include an Ag 4d peak at 5.1 eV, an Ag 3d peak at 368.1 eV, and Ag 3p peaks at 573.1 eV and 603.1 eV. Characteristic Br peaks include a Br 3d peak at 68.1 eV, a Br 3p peak at 181.1 eV, and a Br 3s peak at 256.1 eV.

[0029] Example 1: FTIR spectra of tubular carbon nitride (TCN) and photocatalyst TCN-A-4 are shown below. Figure 5 As shown, at 810 cm -1 1240cm -1 -1640 cm -1 and 3000 cm -1 -3500 cm -1 The above are characteristic peaks of carbon nitride, representing the typical characteristic peak of the s-triazine ring, the CN stretching vibration of the nitrogen-containing heterocycle, the NH stretching vibration of the uncondensed amino group, and the OH stretching vibration of surface-adsorbed water or hydroxyl-containing substances. These three are characteristic absorption peaks commonly found in carbon nitride, while TCN and TCN-A-4 still have peaks at 2180 cm⁻¹. -1 A characteristic absorption peak is present, which is due to the asymmetric vibration of the cyano group, indicating that some amino groups were converted to cyano groups during the synthesis process. The spectra of both TCN-A-4 and TCN show similar FTIR spectra, indicating that the loading of Ag / AgBr did not alter the chemical structure of TCN.

[0030] Example 2: Preparation of graphene-based photocatalytic film GO / TCN-A. The GO / TCN-A film was prepared by a vacuum-assisted self-assembly method, including the following steps: 1) Using a PVDF membrane with a diameter of 3 cm as the base membrane, the aqueous dispersion of 0.8 mL of 0.5 mg / mL GO was diluted to 30 mL, sonicated for 30 min, and then vacuum filtered through the PVDF membrane. The first layer of the membrane was obtained by air drying at room temperature for more than 24 h. 2) Mix 0-5 mg of the TCN-A-4 catalyst obtained in Example 1 with 5 μg of GO, dilute with 15 mL of water and mix evenly. After sonication for 30 min, vacuum filtration is performed on the first layer of the membrane obtained in step 1). After drying at room temperature for 24 h, the second layer of the membrane is obtained, which is the composite membrane.

[0031] According to the above-mentioned composite membrane preparation process, when the amount of TCN-A-4 catalyst used in step 2 is 0mg, 1mg, 2mg, 3mg, 4mg and 5mg respectively, the final composite membranes are labeled as M0 membrane, M1 membrane, M2 membrane, M3 membrane, M4 membrane and M5 membrane respectively.

[0032] The surface and cross-sectional SEM images of the M0 and M3 films in Embodiment 2 of this invention are shown below. Figure 6a and Figure 6bAs shown, the surface of M0 is generally flat with wrinkles formed by graphene nanosheets. The layered structure of graphene can be clearly seen in the cross-sectional view, and the film thickness is approximately 145 nm. On the surface of the M3 film, the catalyst can be seen to be relatively uniformly dispersed on the graphene film surface. The tubular TCN-A-4 can be clearly seen on the upper surface of the film in the cross-sectional view.

[0033] The XRD patterns of films M0 and M3 in Embodiment 2 of this invention are as follows: Figure 7 As shown, the GO film exhibits a sharp peak at 10.56°, which is the characteristic diffraction peak (002) of graphene oxide, indicating that the graphene nanosheets in the graphene oxide film are ordered and stacked, consistent with the observed morphology of the graphene film. In the spectrum of the M3 film, due to the photocatalyst layer covering the graphene surface, the (002) peak of graphene oxide is weakened, but the peak position does not change, indicating that the filtration of the photocatalyst layer does not change the interlayer spacing and ordered arrangement of the first GO layer. At the same time, characteristic peaks of TCN-A-4 appear, including (002), (200), (220), and (222), which is consistent with the XRD results of TCN-A-4.

[0034] The FTIR spectra of films M0 and M3 in Embodiment 2 of this invention are as follows: Figure 8 As shown, the M0 and M3 membranes are in the range of 3670-2900 cm⁻¹. -1 Characteristic peaks were observed in all ranges, corresponding to the stretching vibration of OH, and for M3, possibly also to the stretching vibration of NH present in TCN-A-4. The M0 film showed a peak at 1723 cm⁻¹. -1 The peak at 1619 cm⁻¹ is due to the C=O stretching vibration of the carboxyl group. -1 and 1056cm -1 The characteristic peaks at these locations correspond to the C=C stretching vibration and the epoxy ring vibration, respectively. For the M3 membrane, the typical characteristic peaks of the s-triazine ring and the characteristic peaks of the CN stretching vibration of the nitrogen-containing heterocycle are still present, proving that the chemical structure of TCN-A-4 remains unchanged after incorporation into the membrane.

[0035] Application Example 1: The prepared photocatalyst was used for the degradation of sulfamethoxazole in water.

[0036] 10 mg of catalyst was dispersed in 50 mL of 5 ppm SMX aqueous solution and magnetically stirred for 30 min under dark conditions to reach adsorption-desorption equilibrium. Samples were taken before and after the dark treatment. The solution was then irradiated with a 300 W xenon lamp (λ>420 nm) while maintaining magnetic stirring, and samples were taken every 20 min.

[0037] Following the above evaluation process for photocatalysts, when TCN, TCN-A-1, TCN-A-2, TCN-A-3, TCN-A-4, and TCN-A-5 were selected as photocatalytic degradation effects on SMX, see [see table]. Figure 10 It can be seen that the photocatalyst TCN-A-4 has the best catalytic effect on SMX. After 20 minutes of illumination, TCN-A-4 showed a degradation rate of 96%, with a first-order reaction rate constant of 0.1141 min⁻¹. -1 TCN showed a degradation rate of 51% after 2 hours of light exposure, with a first-order reaction rate constant of 0.0046 min. -1 The first-order reaction rate constant of TCN-A-4 is 24.8 times that of TCN.

[0038] Application Example 2: The prepared photocatalytic membrane was used to degrade sulfamethoxazole. The application effects of the M0-M5 membranes obtained in Example 2 were measured. The operation process was as follows: Under dark conditions, the membrane was first used to filter a 5 ppm sulfamethoxazole aqueous solution in a dead-end filtration device for more than 1 hour, maintaining an operating pressure of 1 bar to stabilize the membrane and reach adsorption-desorption equilibrium. The membrane's rejection rate was then determined based on the change in pollutant concentration before and after filtration. Subsequently, the membrane separation experiment was continued under illumination. Under a 300W xenon lamp (λ>420 nm), the pollutant concentration in the collected solution was measured, and the reduction in pollutant concentration in the collected solution was used to evaluate the membrane's pollutant removal performance under illumination. Simultaneously, the flux of filtering a 5 ppm sulfamethoxazole aqueous solution under both dark and illuminated conditions was tested at 1 bar pressure.

[0039] Following the experimental procedure described above, the flux comparison results of M0-M5 under both illuminated and unilluminated conditions are shown in the figure. Figure 11 The results comparing the removal rates of sulfamethoxazole by M0-M5 under light and dark conditions are shown in the figure. Figure 12 As shown in the figure, the GO membrane loaded with photocatalyst exhibits significantly better removal performance compared to the GO membrane without catalyst, indicating that photocatalytic degradation plays a role. Furthermore, the removal rate of SMX under illumination increases with the gradual increase of photocatalyst loading. At a catalyst loading of 3 mg (M3 membrane), the removal rate of SMX reaches over 99%. Further increasing the catalyst loading does not significantly improve the removal effect. Therefore, M3 was selected as a suitable photocatalytic membrane, and 3 mg was determined as the appropriate loading.

[0040] For the M0 membrane, under no-light conditions, with a flux of 4.6 L MH / bar, the rejection rate for sulfamethoxazole was 14.8%; under illuminated conditions, with a flux of 6.6 L MH / bar, the rejection rate for sulfamethoxazole was 28.1%. For the M3 membrane, under no-light conditions, with a flux of 4.3 L MH / bar, the rejection rate for sulfamethoxazole was 28.4%; under illuminated conditions, with a flux of 6.3 L MH / bar, the rejection rate for sulfamethoxazole was 99.3%.

[0041] The retention rate data mentioned above represents the proportion of pollutants that can be removed by the membrane alone under conditions without light; the removal rate data represents the proportion of pollutants removed under light, relying on both the membrane's retention and the catalyst's degradation under light.

[0042] Application Example 3: Following the experimental procedure of Application Example 2, the M3 membrane was continuously operated under long-term illumination for 10 hours to degrade sulfamethoxazole, with samples taken every 2 hours. The pollutant removal rate and flux during the 10-hour operation are shown in [the table below]. Figure 9 The removal rate remained above 99%, and the throughput did not decrease. Figure 9 The normalized flux in this context refers to the percentage of the flux at different times of membrane operation compared to the flux at the beginning of the first 2 hours.

[0043] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A method for preparing a modified carbon nitride photocatalyst, characterized in that, Includes the following steps: Tubular carbon nitride (TCN) powder was added to a solvent and sonicated until homogeneous. Soluble Ag salt and alkali metal bromide salt were added sequentially. The mixture was first stirred in the dark for 1-4 hours, then stirred under light for 10-30 minutes. After centrifugation, washing, drying, grinding, and sieving, the modified carbon nitride photocatalyst was obtained.

2. The method for preparing a modified carbon nitride photocatalyst as described in claim 1, characterized in that, The preparation steps of the tubular carbon nitride (TCN) powder are as follows: urea and melamine are ground and mixed evenly, and then calcined under a nitrogen or argon atmosphere to obtain tubular carbon nitride (TCN) powder. The mass ratio of urea to melamine is 5-20:1, preferably 8-12:

1.

3. The method for preparing a modified carbon nitride photocatalyst as described in claim 2, characterized in that, The calcination conditions are as follows: heat to 500-600℃ at a rate of 2-10℃ / min, then maintain the temperature for 1-30 minutes, and then cool naturally to room temperature.

4. The method for preparing a modified carbon nitride photocatalyst as described in claim 1, characterized in that, The soluble Ag salt is selected from AgNO3, the alkali metal bromide salt is selected from KBr, and the molar ratio of alkali metal bromide salt to soluble Ag salt is 5-20:1, preferably 7-10:1; the mass ratio of TCN powder to soluble Ag salt is 1:3-5, preferably 1:4; the wavelength of light irradiation in step S2 is 200-300nm, preferably 240-280nm.

5. A modified carbon nitride photocatalyst prepared by any one of claims 1-4.

6. A graphene-based photocatalytic membrane supported on a modified carbon nitride photocatalyst, characterized in that, The mixture includes a base film, a graphene oxide (GO) base layer supported on the surface of the base film, and a catalyst-graphene oxide (GO) mixed layer supported on the surface of the base layer. The catalyst in the mixed layer is the modified carbon nitride photocatalyst as described in claim 5. The mass ratio of the catalyst to GO in the mixed layer is 200-1000:1, preferably 500-600:

1.

7. The method for preparing a graphene-based photocatalytic film with a modified carbon nitride photocatalyst as described in claim 6, characterized in that, Includes the following steps: Step 1: The graphene oxide (GO) dispersion is filtered onto the substrate membrane surface to form a film, then dried to form a GO base layer on the substrate membrane surface; Step 2: The dispersion of catalyst and graphene oxide (GO) is further filtered on the surface of the GO base layer described in Step 1 to form a film, which is then dried to form a catalyst-graphene oxide (GO) mixed layer, thus obtaining the graphene-based photocatalytic film of the supported modified carbon nitride photocatalyst.

8. The preparation method according to claim 7, characterized in that, In step 1, the base film is a PVDF film, and the loading of the GO base layer on the surface of the base film is 0.04-0.06 mg / cm³. 2 The catalyst-graphene oxide (GO) hybrid layer loading on the base layer surface is 0.3-0.5 mg / cm². 2 .

9. The application of the graphene-based photocatalytic membrane with supported modified carbon nitride photocatalyst as described in claim 6 in the photocatalytic degradation and retention of organic pollutants in wastewater.

10. The application as described in claim 9, characterized in that, The organic pollutant is an antibiotic pollutant.

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