A molten salt modified carbon nitride photocatalyst, its preparation method and application

Abstract

This invention belongs to the field of photocatalytic materials technology, specifically relating to a molten salt modified carbon nitride photocatalyst, its preparation method, and its application. The catalyst preparation method includes: 1) mixing graphite-phase carbon nitride, KCl, and a transition metal M... A Transition metal chloride A, containing transition metal M B 1) The transition metal chloride B is mixed and ground evenly, heated to 500-600℃ in a muffle furnace, held at that temperature, and then cooled; 2) The obtained product is washed with hot nitric acid, boiled, washed again, and vacuum dried to obtain M A M B A molten salt-modified carbon nitride photocatalyst with dual active sites. This invention effectively modulates the specific surface area and surface electronic structure of carbon nitride, introducing abundant active sites, significantly improving the migration and separation efficiency of photogenerated carriers, and promoting the generation of various active free radicals. The catalyst achieves a treatment efficiency of up to 70% for the model pollutant dimethyl sulfide under simulated sunlight, and exhibits good cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to a redox dual-site synergistic molten salt modified carbon nitride photocatalyst, its preparation method, and its application. Background Technology

[0002] Volatile organic pollutants (VOSCs) are a typical class of malodorous substances, characterized by high toxicity, strong odor, and low odor threshold. They are widely present in exhaust gases emitted from industries such as petrochemicals, livestock farming, and wastewater treatment. my country's "Odor Pollutant Emission Standard" (GB14554-1993) specifies four VOSCs among the eight malodorous pollutants: methanethiol, ethanethiol, dimethyl sulfide, and dimethyl disulfide. In existing technology, patent CN121042054A provides a highly efficient photothermal catalytic catalyst for the degradation of sulfur-containing organic gases. This scheme utilizes titanium dioxide nanotubes to construct a highly efficient catalyst for degrading sulfur-containing organic gases, with the active phase inside the tubes and a sulfur-resistant active metal outside. The drawback of this technical approach is that the photothermal catalyst operates at temperatures above 200℃, resulting in relatively harsh catalytic conditions. Summary of the Invention

[0003] In view of this, the present invention aims to provide a VOSCs degradation catalyst that can operate at room temperature under light-only conditions, thereby achieving mild reaction conditions and green and economical degradation of VOSCs.

[0004] This invention is achieved through the following technical solution:

[0005] A molten salt modified carbon nitride photocatalyst, the preparation method of which includes the following steps:

[0006] 1) Mix and grind graphitic carbon nitride g-C3N4, KCl, and a dual transition metal modifier until homogeneous. Heat the mixture in a muffle furnace to 500-600℃, hold for 3-5 hours, and then cool. The dual transition metal modifier includes a component containing transition metal M. A Transition metal chloride A and transition metal M B The transition metal chloride B, wherein the transition metal chloride A is selected from CuCl2•2H2O, FeCl2•2H2O and NiCl2•6H2O; and the transition metal chloride B is selected from MnCl2•4H2O, ZnCl2, CoCl2•6H2O and ZrCl2;

[0007] 2) The product obtained in step 1) is washed with hot nitric acid, boiled, washed again, and vacuum dried to obtain a product with M. A M B Molten salt modified carbon nitride photocatalyst with dual active sites.

[0008] Graphitic carbon nitride (g-C3N4) is a non-metallic photocatalyst with excellent visible light absorption, a unique layered porous structure, and superior chemical stability. However, pristine CN exhibits problems such as high recombination rates of photogenerated carriers and insufficient surface active sites. In existing technologies, molten salt modification (alkali metal halides, alkali metal nitrates, etc.) can regulate the crystallinity and surface electronic structure of CN, optimizing the separation efficiency of photogenerated carriers. The inventors discovered that introducing M into the photocatalyst... A M B The addition of dual active sites further enhances the catalytic performance of the modified catalyst. After modification, the charge transfer resistance of the material is significantly reduced, the photocurrent intensity is increased, and the migration and separation of photogenerated carriers are significantly promoted. The modified catalyst also exhibits increased activity of free radicals •OH and •O2. - and SO4 - The increased generation of M-doped ... A M B Subsequently, the photocatalyst exhibits a more fragmented multilayered stacked structure in its microstructure, resulting in an increased specific surface area. Simultaneously, the defect signal intensity under illumination is significantly enhanced, thus optimizing the surface adsorption properties of the photocatalyst. Further experiments by the inventors revealed that the optimization effect comprises at least two mechanisms. On the one hand, M... A and M B These are oxidation-active sites and reduction-active sites, respectively, and a synergistic catalytic mechanism exists between them during the catalytic reaction. On the other hand, it contains transition metal M... A Transition metal chloride A and transition metal M B The transition metal chloride B also exhibits a synergistic regulatory mechanism in shaping the morphology of graphitic carbon nitride. When only M... A When modified (i.e., using only transition metal chloride A to melt-treat graphitic carbon nitride), the catalyst is highly susceptible to deactivation during VOSCs degradation; when only M is used... B When modified (i.e., using only transition metal chloride B to melt-treat graphitic carbon nitride), the catalyst reaches saturation at a degradation rate of 40%. If the single component is masked after dual transition metal modification, the degradation rate of VOSCs by the catalyst is around 10% or even lower, which is weaker than that of single transition metal modification. However, when the two work synergistically, the removal rate of VOSCs jumps from 15% to 70%, and the catalyst has high cycle stability and is not easily deactivated.

[0009] Preferably, the transition metal chloride A is CuCl2•2H2O, and the transition metal chloride B is MnCl2•4H2O.

[0010] Preferably, in step 1), the mass ratio of KCl to graphite phase carbon nitride g-C3N4 is 8-15:0.5-1.5.

[0011] Preferably, in step 1), the mass ratio of the dual transition metal modifier to the graphite phase carbon nitride g-C3N4 is 10:0.5-1.5.

[0012] Preferably, the mass ratio of the transition metal chloride A to the transition metal chloride B is 3:7-5:5.

[0013] A molten salt modified carbon nitride photocatalyst, characterized in that the photocatalyst comprises a graphitic carbon nitride matrix, wherein the graphitic carbon nitride matrix is ​​doped with potassium ions, and the framework of the graphitic carbon nitride matrix contains K-NC2 groups; the graphitic carbon nitride matrix is ​​also simultaneously loaded with a transition metal M. A Active sites and transition metal M B Active site, the transition metal M A The transition metal M is selected from one of Cu, Fe, and Ni. B It is selected from one of Mn, Zn, Co, and Zr.

[0014] Preferably, the transition metal M A For Cu, the transition metal M B It is Mn.

[0015] This invention also includes a method for preparing a molten salt modified carbon nitride photocatalyst, comprising the following steps:

[0016] 1) Mix and grind graphitic carbon nitride g-C3N4, KCl, and a dual transition metal modifier until homogeneous. Heat the mixture in a muffle furnace to 500-600℃, hold for 3-5 hours, and then cool. The dual transition metal modifier includes a component containing transition metal M. A Transition metal chloride A and transition metal M B The transition metal chloride B, wherein the transition metal chloride A is selected from CuCl2•2H2O, FeCl2•2H2O and NiCl2•6H2O; and the transition metal chloride B is selected from MnCl2•4H2O, ZnCl2, CoCl2•6H2O and ZrCl2;

[0017] 2) The product obtained in step 1) is washed with hot nitric acid, boiled, washed again, and vacuum dried to obtain a product with M. A M B Molten salt modified carbon nitride photocatalyst with dual active sites.

[0018] Preferably, the transition metal chloride A is CuCl2•2H2O, and the transition metal chloride B is MnCl2•4H2O.

[0019] The present invention also includes the application of the aforementioned molten salt modified carbon nitride photocatalyst in the photocatalytic degradation of volatile sulfur-containing organic pollutants (VOSCs).

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) The molten salt modified carbon nitride photocatalyst obtained by the preparation method of the present invention not only has dual redox active sites and significantly improved specific surface area, but also contains abundant surface defects and active sites, and has high photogenerated carrier separation efficiency, which is conducive to the efficient generation of hydroxyl radicals and superoxide radicals;

[0022] 2) This invention applies molten salt-modified carbon nitride with dual redox active sites to the field of VOSCs photocatalytic purification, exhibiting excellent removal efficiency and good stability, and has high practical value. Attached Figure Description

[0023] Figure 1 The XRD and FTIR spectra of the samples obtained in Example 1 and Comparative Examples 1, 2, and 3 are shown below.

[0024] Figure 2 These are transmission electron microscopy (TEM) images of the samples obtained in Example 1 and Comparative Examples 1, 2, and 3.

[0025] Figure 3 Transmission electron microscopy (TEM) mapping images of the samples obtained in Comparative Examples 1, 2, and 3;

[0026] Figure 4 The EPR spectra of the samples obtained in Example 1 and Comparative Examples 1, 2, and 3 are shown below.

[0027] Figure 5 The graphs show the EIS and photocurrent generation of the samples obtained in Example 1 and Comparative Examples 1, 2, and 3.

[0028] Figure 6 This is a comparison chart of the photocatalytic degradation activity of the samples obtained in Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3 under simulated sunlight.

[0029] Figure 7 The activity of the samples obtained in Examples 4, 5, 6, and 7 in photocatalytic degradation of DMS under simulated sunlight;

[0030] Figure 8 This is a cyclic stability diagram of the sample obtained in Example 1 under simulated sunlight for photocatalytic degradation of DMS;

[0031] Figure 9 The graph shows the photocatalytic degradation performance of DMS by the sample obtained in Example 1 when a competitive inhibitor is added. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0033] Comparative Example 1

[0034] In this comparative example, an unmodified graphitic phase g-C3N4 (named CN) was prepared. In subsequent experiments, CN prepared by this method was used as the starting point for modification.

[0035] 20g of melamine was placed in a 100mL covered alumina crucible and placed in the center of a muffle furnace. The temperature was increased from room temperature to 550℃ at a rate of 2.3℃ / min and held for 4 hours. After the muffle furnace cooled naturally, a milky yellow solid was obtained. The solid was then ground into powder to obtain the graphite phase g-C3N4.

[0036] Example 1

[0037] 10g KCl, 6g MnCl2•4H2O, 4g CuCl2•2H2O, and 1g CN were ground evenly and placed in a 100mL covered alumina crucible. The crucible was heated from room temperature to 550℃ at a heating rate of 2℃ / min and held for 2 hours. After the muffle furnace cooled naturally, the crucible was removed, washed three times with 5wt% hot nitric acid, and boiled to remove impurity ions that affect catalytic activity. The crucible was then dried under vacuum at 70℃ overnight. The resulting powder sample was labeled as MCN-MnCu 0.4 (The 0.4 in the mark means that the mass of CuCl2•2H2O accounts for 40% of the total mass of the dual transition metal modifier when it is fed, and the same applies below).

[0038] Example 2

[0039] The preparation steps in this embodiment are the same as in Example 1, except that the masses of CuCl2•2H2O and MnCl2•4H2O are 2g and 8g, respectively, and the resulting sample is labeled as MCN-MnCu. 0.2 .

[0040] Example 3

[0041] The preparation steps in this embodiment are the same as in Example 1, except that the masses of CuCl2•2H2O and MnCl2•4H2O are 3g and 7g, respectively, and the resulting sample is labeled as MCN-MnCu. 0.3 .

[0042] Example 4

[0043] The preparation steps in this embodiment are the same as in Example 1, except that the transition metal chloride B is replaced by CoCl2•6H2O instead of MnCl2•4H2O, and the resulting sample is labeled as MCN-CoCu. 0.4 .

[0044] Example 5

[0045] The preparation steps in this embodiment are the same as in Example 1, except that transition metal chloride B is replaced by ZrCl2 instead of MnCl2•4H2O, and the resulting sample is labeled as MCN-ZrCu. 0.4 .

[0046] Example 6

[0047] The preparation steps in this embodiment are the same as in Example 1, except that transition metal chloride A is changed from CuCl2•2H2O to FeCl2•4H2O, and the resulting sample is labeled as MCN-MnFe. 0.4 .

[0048] Example 7

[0049] The preparation steps in this embodiment are the same as in Example 1, except that the transition metal chloride A is changed from CuCl2•2H2O to NiCl2•6H2O, and the resulting sample is labeled as MCN-MnNi. 0.4 .

[0050] Comparative Example 2

[0051] The preparation steps of this comparative example are the same as those of Example 1, except that the amounts of CuCl2•2H2O and MnCl2•4H2O are 10g and 0g, respectively, and the resulting sample is labeled as MCN-Cu.

[0052] Comparative Example 3

[0053] The preparation steps of this comparative example are the same as those of Example 1, except that the amounts of CuCl2•2H2O and MnCl2•4H2O are 0g and 10g, respectively, and the resulting sample is labeled as MCN-Mn.

[0054] I. Characterization of the structure of the test samples

[0055] Figure 1 The sample MCN-MnCu prepared in Example 1 0.4 XRD and FTIR spectra of CN, MCN-Mn, and MCN-Cu samples obtained in Comparative Examples 1, 2, and 3. Figure 1As can be seen from a, the XRD pattern of the sample after molten salt modification is basically similar to that of the graphite phase CN, indicating that the main structure of CN was preserved during the molten salt treatment. At the (002) crystal plane, the full width at half maximum (FWHM) of MCN-Mn and MCN-Cu is significantly wider and the peak intensity is weakened compared to CN, indicating that metal doping may introduce lattice distortion and defects, disrupting the interlayer stacking order and leading to a decrease in crystallinity. From Figure 1 b indicates that after molten salt modification, at 1125 cm⁻¹ -1 A new peak appears at this point, attributed to the asymmetric vibration of the K-NC2 group, indicating that potassium ions from the molten salt are introduced into the CN framework. Furthermore, the modified sample exhibits a similar FTIR vibrational mode to CN, suggesting that the CN synthesized by the molten salt method maintains a similar chemical structure to CN.

[0056] Figure 2 , Figure 3 The images show TEM and mapping images of the samples. CN exhibits a clear layered structure with tightly stacked layers. MCN-Cu shows a porous structure; MCN-Mn shows a layered structure at the edges, but with smaller pores; MCN-MnCu shows a more fragmented, ultrathin layered structure. The mapping images further show that C, N, O elements, as well as doped Cu and Mn elements, are uniformly dispersed in the respective samples.

[0057] Figure 4 The ESR spectra of the above samples are shown. The defect signal intensity of all samples under illumination was significantly higher than that under dark conditions, indicating that illumination promoted the formation of surface defects. The defect signal intensity of the MCN-MnCu sample was significantly higher than that of the monometallic modified samples (MCN-Mn, MCN-Cu) and the original CN sample, strongly demonstrating that the bimetallic modification of Mn and Cu synergistically increased the defect concentration in CN, providing more reaction sites. Meanwhile, after irradiation with simulated sunlight, all samples generated •OH and •O. 2- Furthermore, the generation amounts of the two free radicals showed the same trend: MCN-MnCu>MCN-Mn>MCN-Cu>CN. In addition, except for CN, significant amounts of •SO₄ were detected in the other three samples. 4- The signal strength also follows the order MCN-MnCu > MCN-Mn > MCN-Cu. The results strongly demonstrate that the synergistic effect of the Mn-Cu bimetallic combination can significantly promote the generation of various active free radicals.

[0058] II. Electrocatalytic performance characterization of test samples

[0059] Figure 5 Electrochemical impedance spectroscopy (EIS) and photocurrent curves for each sample are presented. Figure 5As can be seen from a, after CN is modified by molten salt, the charge transfer resistance is significantly reduced. Among them, the charge transfer resistance of bimetallic molten salt modified MCN-MnCu is the smallest, which is significantly lower than that of single metal modified MCN-Cu and MCN-Mn. The order of resistance is MCN-MnCu < MCN-Cu < CN < MCN-Mn. The synergistic introduction of surface Mn and Cu can effectively reduce the interfacial charge transfer resistance and optimize the carrier transport dynamics. Figure 5 The photocurrent response of sample b shows that the variation of photocurrent intensity is highly consistent with the EIS results: MCN-MnCu has the highest photocurrent intensity, followed by MCN-Cu, CN, and MCN-Mn. These results fully demonstrate that the synergistic modification of Mn and Cu bimetals by molten salt can significantly promote the migration and separation of photogenerated carriers.

[0060] III. Photocatalytic Degradation Experiment of Test Samples for VOSCs

[0061] Experiments were conducted using dimethyl sulfide (DMS) as the target compound.

[0062] The experiment was conducted under normal temperature and pressure conditions. The experimental setup used a self-designed and constructed gas-liquid-solid three-phase continuous flow reactor. A 300 W xenon lamp with an AM 1.5G sunlight simulation filter was used as the light source, with a constant operating current of 15 A. The simulated exhaust gas DMS concentration was 30 ppm, and the gas concentration was quantitatively analyzed using an online gas chromatography detection system.

[0063] The specific operating steps are as follows: 200 mg of catalyst and 200 mL of deionized water are ultrasonically dispersed evenly, loaded into the reactor, and the airtightness of the system is tested. The prepared simulated waste gas is premixed and continuously introduced into the bottom of the reactor at a constant flow rate until the DMS concentration difference between the reactor inlet and outlet stabilizes, indicating that the reaction system has reached adsorption equilibrium. The light source is turned on, and samples are taken every 10 minutes. The inlet concentration C0 and the outlet residual concentration C are calculated based on the chromatographic peak area using the external standard method. t .

[0064] The formula for pollutant degradation is as follows:

[0065]

[0066] In the formula:

[0067] —Target pollutant degradation rate, %

[0068] C0—Concentration of gaseous pollutants at the reactor inlet under steady-state conditions;

[0069] C t —Concentration of gaseous pollutants at the reactor outlet at the corresponding detection time.

[0070] Figure 6 The effects of various MCN-MnCu photocatalysts prepared from MnCl2•4H2O and CuCl2•2H2O in different mass ratios, as well as the control sample, on the treatment of DMS odor were demonstrated. The original CN catalyst showed a DMS removal rate of only 15%; after molten salt modification, the removal efficiency was improved. The DMS removal efficiencies of each MCN-MnCu catalyst were above 50%, significantly higher than the control samples MCN-Cu (36%, with gradually decreasing activity) and MCN-Mn (37%) modified with a single transition metal. Among them, MCN-MnCu… 0.4 The activity was optimal, with a DMS removal efficiency of up to 70%, indicating that Mn and Cu formed the best synergistic effect at this ratio.

[0071] Figure 7 The photocatalytic degradation effect of CN samples modified with different type A and type B metal chloride molten salts on DMS was investigated. The results showed that MCN-MnCu... 0.4 CoCu 0.4 MCN-ZrCu 0.4 MCN-MnFe 0.4 MCN-MnNi 0.4 All of them showed excellent DMS removal effects, with degradation rates between 45% and 70%.

[0072] Figure 8 Demonstration of MCN-CuMn 0.4 Cyclic stability of photocatalytic degradation of DMS. During a 200-minute illumination period, the sample maintained a stable DMS removal efficiency with almost no deactivation.

[0073] Figure 9 Demonstrates the effect of adding a competitive inhibitor on MCN-CuMn 0.4 The photocatalytic degradation performance of DMS was investigated. Thiourea was used to selectively complex Cu sites (thiourea has a much stronger coordination ability with Cu than DMS), while ethylenediaminetetraacetic acid (EDTA) was used to selectively complex Mn sites. The results showed that the addition of thiourea significantly reduced the DMS removal efficiency, while the addition of EDTA almost completely inhibited DMS degradation. This indicates that Cu and Mn sites are the key active sites in the photocatalytic degradation of DMS, playing a dominant role. Notably, the activities of MCN-Cu and MCN-Mn are similar to those of MCN-CuMn. 0.4 The effect of blocking Cu and Mn sites cannot be compared with that of Cu. The reason is that different metal modification systems have different degrees of regulation on the intrinsic structure of carbon nitride substrate, and Cu and Mn have intermetallic interactions, which change the intrinsic properties of active sites, making the blocking effect impossible to be compared equivalently. This further illustrates that Cu and Mn have significant synergistic catalytic effects.

Claims

1. A molten salt modified carbon nitride photocatalyst, characterized in that, Its preparation method includes the following steps: 1) Mix and grind graphitic carbon nitride g-C3N4, KCl, and a dual transition metal modifier until homogeneous. Heat the mixture in a muffle furnace to 500-600℃, hold for 3-5 hours, and then cool. The dual transition metal modifier includes a component containing transition metal M. A Transition metal chloride A and transition metal M B The transition metal chloride B, wherein the transition metal chloride A is selected from CuCl2•2H2O, FeCl2•2H2O and NiCl2•6H2O; and the transition metal chloride B is selected from MnCl2•4H2O, ZnCl2, CoCl2•6H2O and ZrCl2; 2) The product obtained in step 1) is washed with hot nitric acid, boiled, washed again, and vacuum dried to obtain a product with M. A M B Molten salt modified carbon nitride photocatalyst with dual active sites.

2. The molten salt modified carbon nitride photocatalyst according to claim 1, characterized in that, The transition metal chloride A is CuCl2•2H2O, and the transition metal chloride B is MnCl2•4H2O.

3. The molten salt modified carbon nitride photocatalyst according to claim 1, characterized in that, In step 1), the mass ratio of KCl to graphite phase carbon nitride g-C3N4 is 8-15:0.5-1.

5.

4. The molten salt modified carbon nitride photocatalyst according to claim 1, characterized in that, In step 1), the mass ratio of the dual transition metal modifier to the graphite phase carbon nitride g-C3N4 is 10:0.5-1.

5.

5. The molten salt modified carbon nitride photocatalyst according to claim 1, characterized in that, The mass ratio of the transition metal chloride A to the transition metal chloride B is 3:7-5:

5.

6. A molten salt modified carbon nitride photocatalyst, characterized in that, The photocatalyst comprises a graphitic carbon nitride matrix doped with potassium ions, and the framework of the graphitic carbon nitride matrix contains K-NC2 groups; the graphitic carbon nitride matrix also simultaneously supports transition metal M. A Active sites and transition metal M B Active site, the transition metal M A The transition metal M is selected from one of Cu, Fe, and Ni. B It is selected from one of Mn, Zn, Co, and Zr.

7. The molten salt modified carbon nitride photocatalyst according to claim 6, characterized in that, The transition metal M A For Cu, the transition metal M B It is Mn.

8. A method for preparing a molten salt modified carbon nitride photocatalyst, characterized in that, Includes the following steps: 1) Mix and grind graphitic carbon nitride g-C3N4, KCl, and a dual transition metal modifier until homogeneous. Heat the mixture in a muffle furnace to 500-600℃, hold for 3-5 hours, and then cool. The dual transition metal modifier includes a component containing transition metal M. A Transition metal chloride A and transition metal M B The transition metal chloride B, wherein the transition metal chloride A is selected from CuCl2•2H2O, FeCl2•2H2O and NiCl2•6H2O; and the transition metal chloride B is selected from MnCl2•4H2O, ZnCl2, CoCl2•6H2O and ZrCl2; 2) The product obtained in step 1) is washed with hot nitric acid, boiled, washed again, and vacuum dried to obtain a product with M. A M B Molten salt modified carbon nitride photocatalyst with dual active sites.

9. The preparation method according to claim 8, characterized in that, The transition metal chloride A is CuCl2•2H2O, and the transition metal chloride B is MnCl2•4H2O.

10. The application of the molten salt modified carbon nitride photocatalyst according to any one of claims 1 to 9 in the photocatalytic degradation of volatile sulfur-containing organic pollutants (VOSCs).

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