A 3D double-heterojunction catalyst hydrogel, a preparation method thereof and application thereof in photo-assisted high-iodate activation degradation of organic pollutants

Abstract

This invention relates to a 3D dual heterojunction catalyst hydrogel, its preparation method, and its application in photo-assisted periodate-activated degradation of organic pollutants. The preparation method of the 3D dual heterojunction catalyst hydrogel of this invention involves: mixing acid and LiF, adding Ti3AlC2 for heating and reaction, separating the solid phase, dispersing the obtained solid phase in an organic solvent to obtain an MXene solution; mixing a cobalt salt solution with the MXene solution and placing it in liquid nitrogen to obtain a precursor solution; mixing and stirring a dimethylimidazole aqueous solution with the precursor solution; separating the solid and liquid phases of the reaction solution to obtain the precipitate, calcining it under an inert atmosphere, mixing it with chitosan colloid, and adding an alkaline solution dropwise to obtain the 3D dual heterojunction catalyst hydrogel. This invention combines the excellent conductivity of MXene with the synergistic effect of the large specific surface area of ​​MOF and Cs, realizing an ultrafast electron transport channel and significantly improving the utilization efficiency of photogenerated carriers.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a 3D dual heterojunction catalyst hydrogel, its preparation method, and its application in photo-assisted periodate-activated degradation of organic pollutants. Background Technology

[0002] Tetracycline hydrochloride (TCH), a typical antibiotic pollutant, has become a research hotspot in water treatment due to its persistence in the environment and potential ecological risks. In recent years, periodate-based advanced oxidation technologies (PI-AOPs) have shown great potential in the deep treatment of tetracycline hydrochloride due to their unique advantages. Their technological development is mainly reflected in the following aspects: Firstly, regarding the reaction mechanism, research has shifted from single-radical oxidation to multi-component oxidation systems. Traditional processes such as Fenton primarily rely on non-selective oxidation with hydroxyl radicals (•OH), while periodate, upon activation, generates not only •OH but also superoxide radicals (•O2) through intermediates. - It can oxidize TCH and generate various reactive species such as iodine radicals (•IO3) and high-valence metal oxygen species. In particular, the photo-assisted PI activation system can efficiently and selectively generate singlet oxygen (•IO3). 1 O2), this oxidant has higher selectivity and longer effective action time for nitrogen-containing organic compounds such as TCH, thereby improving degradation efficiency.

[0003] Secondly, in catalyst development, research focuses on overcoming the inherent defects of traditional photocatalysts. Early catalysts suffered from poor stability and easy recombination of electron-hole pairs, limiting their practical applications. In recent years, by developing novel high-efficiency catalysts, such as transition metal (cobalt, manganese, etc.) based composite materials, and combining them with strategies such as surface modification and heterostructure construction, the activation efficiency of PI has been significantly improved, and the stability and recyclability of the catalytic system under complex environments have been enhanced.

[0004] Finally, in terms of application expansion, research is focused on addressing the performance degradation problem in complex aquatic matrices. Carbonates (CO32-) are commonly found in actual wastewater. 2- Components such as humic acid (HA) can severely interfere with the oxidation process. To address this challenge, researchers have effectively reduced the impact of water-based matrices on the degradation efficiency of TCH by optimizing reaction conditions (such as pH and temperature), introducing pretreatment steps, or designing interference-resistant reaction systems, thus promoting the transition of this technology from laboratory research to engineering applications.

[0005] In summary, significant progress has been made in the removal of TCH based on PI-AOPs technology through continuous optimization of reaction mechanisms, improvement of catalyst performance, and enhancement of anti-interference capabilities, providing a new technical approach for the advanced treatment of antibiotic pollutants.

[0006] Titanium dioxide (TiO2), as a classic photocatalyst, has shown great potential in environmental remediation and energy conversion due to its high chemical stability, low cost, and non-toxicity. However, its widespread application is still limited by two key bottlenecks: first, its relatively wide band gap means it can only respond to ultraviolet light, resulting in extremely low utilization of sunlight; second, the bulk recombination rate of photogenerated electrons and holes is too fast, which severely weakens quantum efficiency.

[0007] While current heterojunction engineering (such as type II and Z-type heterojunctions) offers feasible solutions to the charge separation problem, they all have inherent limitations. Traditional type II heterojunctions promote charge separation by constructing a built-in electric field, but their "sacrifice of redox potential" mechanism prevents the material from simultaneously possessing high oxidation capacity, making it unsuitable for scenarios with extremely high catalytic activity requirements, such as deep mineralization of pollutants or high-value synthesis. Z-type heterojunctions, represented by TiO2 / CdS, retain high-energy charge carriers by simulating natural photosynthesis, but their charge transfer mainly relies on random diffusion and interfacial tunneling of charge carriers, lacking direct conductive channels. This results in sluggish interfacial transport kinetics and limited overall catalytic efficiency.

[0008] In order to achieve a precise balance between efficient charge separation and strong redox capabilities, there is an urgent need to develop a highly efficient catalyst to solve the above technical problems. Summary of the Invention

[0009] To address the technical problems of insufficient catalytic performance, poor stability, slow reaction kinetics, resulting in low catalytic efficiency and difficulty in recycling of existing catalysts, thus limiting their green and sustainable applications, this invention provides a 3D dual heterojunction catalyst hydrogel, its preparation method, and its application in photo-assisted periodate-activated degradation of organic pollutants. This invention proposes a synergistic enhancement strategy based on a MOF-on-MXene flexible substrate. This strategy innovatively constructs a Schottky junction / S-type heterojunction dual heterojunction system and utilizes the 3D network structure design of the three-dimensional hydrogel to construct a highly efficient, green, and easily recyclable catalyst. Using chitosan (Cs) hydrogel as a carrier, under the S-type heterojunction mechanism, photogenerated electrons will migrate directionally through the Schottky barrier and undergo redox reactions with holes, thereby retaining strong redox capabilities while mechanistically inhibiting bulk recombination. By combining the excellent conductivity of MXene with the synergistic effect of the large specific surface area of ​​MOF and Cs, this structure not only realizes an ultrafast electron transport channel, but also significantly improves the utilization efficiency of photogenerated carriers, providing a new paradigm for the development of next-generation high-performance photocatalytic materials.

[0010] The first objective of this invention is to provide a method for preparing a 3D dual heterojunction catalyst hydrogel, comprising the following steps: (1) Mix acid and LiF, then add Ti3AlC2 and heat to react. Then separate the reaction solution into solid and liquid phases and take the solid phase. The obtained solid phase is MXene. Wash until neutral and disperse MXene in an organic solvent to obtain MXene solution. (2) Mix the cobalt salt solution and the MXene solution and freeze-cast them in liquid nitrogen in a directional manner so that ZIF-67 grows vertically on MXene to obtain the precursor solution; (3) Mix and stir the dimethylimidazole aqueous solution with the precursor solution; separate the solid and liquid phases of the resulting reaction solution to obtain the precipitate, wash and freeze dry to obtain MXene / ZIF-67 powder; calcine the obtained MXene / ZIF-67 powder under an inert atmosphere to obtain MXene / TiO2 / CoN6 dual heterostructure. (4) Mix the MXene / TiO2 / CoN6 dual heterostructure with chitosan colloid and add an alkaline solution to obtain the 3D dual heterostructure catalyst hydrogel.

[0011] In some embodiments of the present invention, in step (1), the heating reaction conditions are: rotation speed of 400~500 rpm, temperature of constant temperature sand bath of 35-55 ℃, and reaction time of 48~60 h; The acid is selected from hydrochloric acid and / or hydrofluoric acid; The concentration of the acid is 8-10 M; The organic solvent is selected from ethanol.

[0012] In some embodiments of the present invention, in step (2), the cobalt salt is selected from Co(NO3)2·6H2O and / or CoCl2·6H2O; the concentration of the cobalt salt solution is 0.025~0.075 M; The concentration of MXene solution is 7.5~15 mg / mL; The concentration ratio of cobalt salt solution to MXene solution is (1:7) to (1:9). The directional freeze casting time is 5~15 min.

[0013] In some embodiments of the present invention, in step (3), the concentration of the dimethylimidazole solution is 0.2~0.6 M; The mass ratio of the sum of the cobalt salt and dimethylimidazole to the mass of MXene is (40:1) to (50:1).

[0014] In some embodiments of the present invention, in step (3), the inert gas in the inert atmosphere includes nitrogen and / or argon, the heating and calcination temperature is 750~850 ℃, the time is 1.5~2.5 h, and the heating rate is 2~5 ℃ / min.

[0015] In some embodiments of the present invention, in step (4), the chitosan colloid further contains 1.5 to 2.5 wt% acetic acid; The mass ratio of chitosan colloid to MXene / TiO2 / CoN6 is (1:0.5) to (1:1.5).

[0016] In some embodiments of the present invention, the alkaline solution includes NaOH solution and / or KOH solution; the concentration is 2~3 wt%.

[0017] The second objective of this invention is to provide a 3D dual heterojunction catalyst chitosan hydrogel, prepared by the aforementioned method, with chitosan as the 3D network carrier, MXene / TiO2 / CoN6 contributing active sites, MXene / TiO2 and CoN6 being bonded by Co-O-Ti bonds, and CoN6 single atoms and Co nanoparticles present on the surface of MXene / TiO2 / CoN6.

[0018] A third objective of this invention is to provide the application of the 3D dual heterojunction catalyst chitosan hydrogel in the photo-assisted periodate-activated degradation of organic pollutants.

[0019] In some embodiments of the present invention, the organic pollutant includes one or more of tetracycline hydrochloride, rhodamine, and Acid Orange G.

[0020] In this invention, compared with powder materials, it is easier to recycle and has magnetic properties, making it more convenient to reuse. Based on the synthesis of double heterojunctions, Co single atoms and Co-O-Ti bonds are constructed to effectively suppress the recombination of photogenerated electrons and holes, while achieving ultrafast electron transfer and retaining a high redox potential, thereby enhancing the oxidation effect and achieving "1+1>2" high-efficiency photocatalytic activity and deep mineralization of organic pollutants.

[0021] The technical solution of the present invention has the following advantages compared with the prior art: 1) The preparation method of the present invention is simple to operate, low in cost, reproducible and universal.

[0022] 2) This invention prepares a catalyst through a one-step pyrolysis method. Compared with traditional carbon catalysts or metal oxides, this catalyst can form a stable, efficient, atomically dispersed (not easy to aggregate) catalyst, avoiding the problems of low efficiency, instability and easy agglomeration of traditional catalysts. In addition, by combining it with 3D hydrogel, this invention avoids the problem of difficult recycling of traditional powder catalysts.

[0023] 3) This invention constructs a double heterojunction and utilizes interface engineering to synergistically optimize the electronic structure, effectively suppressing the recombination of photogenerated electrons and holes, while achieving ultrafast electron transfer and retaining a high redox potential, thereby enhancing the oxidation effect and realizing highly efficient photocatalytic activity and deep mineralization of antibiotic pollutants with a "1+1>2" effect. Attached Figure Description

[0024] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 This describes the preparation process of the MXene / TiO2 / CoN6-Cs double heterojunction obtained in Example 1 of this invention.

[0025] Figure 2 The image shows the Co K-side synchrotron radiation EXAFs spectrum of the MXene / TiO2 / CoN6-Cs double heterojunction obtained in Example 1 of this invention, which demonstrates that MXene / TiO2 / CoN6 contains Co-O-Ti(Co) bonds and Co-N(O) single atoms.

[0026] Figure 3 The image shows the KPFM diagram of the MXene / TiO2 / CoN6-Cs double heterojunction obtained in Example 1 of this invention. It can be seen that the electron transfer directions between MXene / TiO2 and CoN6 are opposite under darkness / light. Among them, a is the KPFM diagram of the MXene / TiO2 / CoN6-Cs double heterojunction, and b is the surface potential change diagram of the MXene / TiO2 / CoN6-Cs double heterojunction.

[0027] Figure 4 These are the in-situ XPS spectra of the MXene / TiO2 / CoN6-Cs double heterojunction obtained in Example 1 of this invention. Similarly, it can be seen that the electron transfer directions between MXene / TiO2 and CoN6 are opposite under darkness / light. Among them, (a) is the Co 2p spectrum and (b) is the Ti 2p spectrum.

[0028] Figure 5 The diagram shows the degradation of TCH by the MXene / TiO2 / CoN6-Cs double heterojunction obtained in Example 1 of this invention and the catalyst obtained in the comparative example.

[0029] Figure 6 This is a diagram showing the degradation of TCH in different quenching agents for the MXene / TiO2 / CoN6-Cs double heterojunction obtained in Example 1 of the present invention.

[0030] Figure 7 This is the degradation of TCH under different pH conditions in Application Example 2 of the present invention. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0032] Example 1 This embodiment provides a method for preparing a 3D hydrogel photocatalyst based on a Schottky junction / S-type heterojunction: (1) Add 30 ml of 9 M HCl to the lining of the strong acid resistant reactor, and then add 2.4 g of LiF powder and stir for 5 min.

[0033] (2) Slowly add 1.5 g Ti3AlC2 into the lining of the reactor in a fume hood. After completion, cover the vent. This step takes 10 min. Finally, react the reaction solution in a sand bath at 450 rpm and 45 ℃ for 60 h to obtain the reaction solution.

[0034] (3) The obtained reaction solution was centrifuged to separate the solid phase. The obtained solid phase was washed multiple times (using ultrapure water as the detergent). After the solid powder was washed to neutral, the dispersion was centrifuged at 3500 rpm for 20 min. The upper black solution was collected and freeze-dried under vacuum overnight to obtain a few layers of MXene. The obtained 30 mg MXene was added to 1 mL of ultrapure water (30 mg / mL) and 3 mL of ethanol solvent was added. The mixture was ultrasonically dispersed for 5 min to obtain a 7.5 mg / mL MXene ethanol solution.

[0035] (4) Add 4 mL of MXene ethanol solution (7.5 mg / mL) to Co(NO3)2·6H2O (0.05 M, 40 mL) aqueous solution, mix and place in liquid nitrogen for 10 min to obtain precursor solution.

[0036] (5) Add 40 mL of aqueous solution containing dimethylimidazole (2-MeIM, 0.4 M) to the above precursor solution and stir vigorously for 90 min; centrifuge the resulting reaction solution and collect the precipitate. Wash the precipitate with ultrapure water and anhydrous ethanol (EtOH) and centrifuge to collect the solid phase. Freeze-dry the obtained solid phase under vacuum for 48 h to obtain powder, and then recover and weigh it.

[0037] (6) The obtained powder was calcined at 800 °C for 2 h under a nitrogen atmosphere with a heating rate of 2 °C / min, and finally MXene / TiO2 / CoN6 dual heterostructure was obtained.

[0038] (7) A certain amount of MXene / TiO2 / CoN6 dual heterostructure was added to chitosan colloid containing 2% acetic acid (where the mass ratio of Cs:MXene / TiO2 / CoN6 was 1:1). A 2.5wt% NaOH solution was added dropwise using a peristaltic pump to form dark-colored beads. The beads were washed until neutral and stored in anhydrous ethanol for later use, ultimately yielding a 3D hydrogel photocatalyst (MXene / TiO2 / CoN6-Cs dual heterostructure). The obtained MXene / TiO2 / CoN6-Cs dual heterostructure was structurally characterized, and the results are shown in […]. Figures 2-3 .

[0039] Depend on Figure 2 It can be seen that the MXene / TiO2 / CoN6-Cs double heterojunction achieves the expected atomic-level dispersion and contains active centers of Co-N(O) and Co-O-Ti(Co).

[0040] Depend on Figure 3 and Figure 4 It can be seen that the direction of electron transfer changes under light and darkness, indicating that there is an S-type heterojunction between MXene / TiO2 and CoN6.

[0041] Example 2 This embodiment provides a method for preparing a 3D hydrogel photocatalyst based on a Schottky junction / S-type heterojunction: (1) Add 30 ml of 9 M HCl to the lining of the strong acid resistant reactor, and then add 2.4 g of LiF powder and stir for 5 min.

[0042] (2) Slowly add 1.5 g Ti3AlC2 into the lining of the reactor in a fume hood. After completion, cover the vent. This step takes 10 min. Finally, the reaction solution is reacted in a sand bath at 450 rpm and 45 ℃ for 48 h to obtain the reaction solution.

[0043] (3) The obtained reaction solution was centrifuged to separate the solid phase. The solid phase was washed multiple times (using ultrapure water) until the solid powder was neutral. It was then redispersed in ultrapure water to obtain a dispersion. The dispersion was centrifuged at 3500 rpm for 20 min, and the upper black solution was collected and lyophilized overnight under vacuum. Finally, a few layers of MXene were obtained, which were then dispersed in ethanol to obtain an MXene ethanol solution with a concentration of 7.5 mg / mL.

[0044] (4) Add 4 mL of MXene ethanol solution (7.5 mg / mL) to Co(NO3)2·6H2O (0.05 M, 40 mL) aqueous solution, mix and place in liquid nitrogen for 10 min to obtain the precursor solution.

[0045] (5) Add 40 mL of aqueous solution containing dimethylimidazole (2-MeIM, 0.4 M) to the above precursor solution and stir vigorously for 90 min; centrifuge the resulting reaction solution and collect the precipitate. Wash the precipitate with ultrapure water and anhydrous ethanol (EtOH) and centrifuge to collect the solid phase. Freeze-dry the obtained solid phase under vacuum for 48 h to obtain powder, and then recover and weigh it.

[0046] (6) The obtained powder was calcined at 800 °C for 2 h under a nitrogen atmosphere with a heating rate of 2 °C / min, and finally MXene / TiO2 / CoN6 dual heterostructure was obtained.

[0047] (7) A certain amount of MXene / TiO2 / CoN6 dual heterostructure was added to chitosan colloid containing 2wt% acetic acid (wherein, the mass ratio of Cs:MXene / TiO2 / CoN6 was 1:1). 2.5wt% NaOH solution was added dropwise using a peristaltic pump to form dark beads. The beads were washed until neutral and stored in anhydrous ethanol for later use, finally obtaining the 3D hydrogel photocatalyst (MXene / TiO2 / CoN6-Cs dual heterostructure).

[0048] Example 3 This embodiment provides a method for preparing a 3D hydrogel photocatalyst based on a Schottky junction / S-type heterojunction: (1) Add 30 ml of 9 M HCl to the lining of the strong acid resistant reactor, and then add 2.4 g of LiF powder and stir for 5 min.

[0049] (2) Slowly add 1.5 g Ti3AlC2 into the lining of the reactor in a fume hood. After completion, cover the vent. This step takes 10 min. Finally, react the reaction solution in a sand bath at 450 rpm and 45 ℃ for 60 h to obtain the reaction solution.

[0050] (3) The obtained reaction solution was centrifuged to separate the solid phase. The solid phase was washed multiple times (using ultrapure water) until the solid powder was neutral. It was then redispersed in ultrapure water to obtain a dispersion. The dispersion was centrifuged at 3500 rpm for 20 min, and the upper black solution was collected and lyophilized overnight under vacuum. Finally, a few layers of MXene were obtained, which were then dispersed in ethanol to obtain an MXene ethanol solution with a concentration of 7.5 mg / mL.

[0051] (4) Add 4 mL of MXene ethanol solution (7.5 mg / mL) to Co(NO3)2·6H2O (0.05 M, 40 mL) aqueous solution, mix and place in liquid nitrogen for 10 min to obtain precursor solution.

[0052] (5) Add 40 mL of aqueous solution containing dimethylimidazole (2-MeIM, 0.4 M) to the above precursor solution and stir vigorously for 90 min; centrifuge the resulting reaction solution and collect the precipitate. Wash the precipitate with ultrapure water and anhydrous ethanol (EtOH) and centrifuge to collect the solid phase. Freeze-dry the obtained solid phase under vacuum for 48 h to obtain powder, and then recover and weigh it.

[0053] (6) The obtained powder was calcined at 700 °C for 2 h under a nitrogen atmosphere with a heating rate of 2 °C / min, and finally MXene / TiO2 / CoN6 dual heterostructure was obtained.

[0054] (7) A certain amount of MXene / TiO2 / CoN6 dual heterostructure was added to chitosan colloid containing 2wt% acetic acid (wherein, the mass ratio of Cs:MXene / TiO2 / CoN6 was 1:1). 2.5wt% NaOH solution was added dropwise using a peristaltic pump to form dark beads. The beads were washed until neutral and stored in anhydrous ethanol for later use, finally obtaining the 3D hydrogel photocatalyst (MXene / TiO2 / CoN6-Cs dual heterostructure).

[0055] Comparative Example 1 This comparative example provides a method for preparing a Schottky junction 3D hydrogel photocatalyst MXene / TiO2-Cs: (1) Add 30 ml of 9 M HCl to the lining of the strong acid resistant reactor, and then add 2.4 g of LiF powder and stir for 5 min.

[0056] (2) Slowly add 1.5 g Ti3AlC2 into the lining of the reactor in a fume hood. After completion, cover the vent. This step takes 10 min. Finally, react the reaction solution in a sand bath at 450 rpm and 45 ℃ for 60 h to obtain the reaction solution.

[0057] (3) The obtained reaction solution is centrifuged to separate the solid phase. The obtained solid phase is washed multiple times (the detergent is ultrapure water). After the solid powder is washed to neutral, the dispersion is centrifuged at 3500 rpm for 20 min. The upper black solution is collected and freeze-dried under vacuum overnight to finally obtain a few layers of MXene powder.

[0058] (4) The obtained MXene powder was calcined at 800 °C for 2 h under a nitrogen atmosphere with a heating rate of 2 °C / min, and finally the MXene / TiO2 heterostructure was obtained.

[0059] (5) A certain amount of MXene / TiO2 was added to chitosan colloid containing 2wt% acetic acid (wherein the mass ratio of Cs:MXene / TiO2 was 1:1). 2.5wt% NaOH solution was added dropwise by a peristaltic pump to form dark beads. The beads were washed until neutral and stored in anhydrous ethanol for later use, finally obtaining the 3D hydrogel photocatalyst (MXene / TiO2-Cs heterojunction).

[0060] Comparative Example 2 This comparative example provides a method for preparing the 3D hydrogel photocatalyst CoN6-Cs: (1) Place the aqueous solution of Co(NO3)2·6H2O (0.05 M, 40 mL) in liquid nitrogen for 10 min to obtain the precursor solution.

[0061] (2) Add 40 mL of aqueous solution containing dimethylimidazole (2-MeIM, 0.4 M) to the above precursor solution and stir vigorously for 90 min; centrifuge the resulting reaction solution and take the precipitate. The precipitate is washed with ultrapure water and anhydrous ethanol (EtOH), centrifuged to collect the solid phase, and freeze-dried under vacuum for 48 h to obtain powder, which is then recovered and weighed.

[0062] (3) The obtained powder was calcined at 800 °C for 2 h under a nitrogen atmosphere with a heating rate of 2 °C / min, and finally the CoN6 structure was obtained.

[0063] (4) A certain amount of CoN6 structure was added to chitosan colloid containing 2wt% acetic acid (where the mass ratio of Cs to CoN6 was 1:1). 2.5wt% NaOH solution was added dropwise by a peristaltic pump to form dark beads. The beads were washed until neutral and stored in anhydrous ethanol for later use, finally obtaining the 3D hydrogel photocatalyst (CoN6-Cs).

[0064] Application Example 1 This application example provides a strategy for using 3D hydrogel photocatalysts in Schottky junctions / S-type heterojunctions, including the following steps: 1) The experiment was conducted under a 35 W cold light LED lamp (wavelength range λ = 400-700 nm). In a typical photocatalysis experiment, 1-5 g / L of the 3D hydrogel photocatalyst obtained in Example 1 was mixed with TCH (10 mg / L) in water to prepare a 50 mL suspension with an initial pH of 5.3.

[0065] 2) The reaction was carried out under light irradiation at 25 °C and with stirring at 500 rpm. Before light irradiation, the mixture was stirred in the dark for 120 min to reach adsorption-desorption equilibrium. After equilibrium was established, sodium periodate (PI) (1.5 mM) was added under light irradiation to initiate the reaction. 0.9 mL samples were taken at specific time points (10, 20, 30, and 60 min) and filtered through a 0.22 μm filter membrane. 0.1 mL of Na₂S₂O₃ (1 mM) was added at the end of the reaction.

[0066] 3) TCH in the reaction solution was analyzed using a high-performance liquid chromatograph (HPLC, LC-16, Shimadzu). The test conditions were as follows: C18 column, constant temperature 30 ℃; total flow rate 1 mL / min; detection wavelength 355 nm; mobile phase was a mixture of 20% acetonitrile and 80% oxalic acid (0.01 M). The experimental results are shown below. Figure 5 ,Depend on Figure 5 It can be seen that, compared with MXene / TiO2-Cs (Comparative Example 1) and CoN6-Cs (Comparative Example 2), the degradation effect of the MXene / TiO2 / CoN6-Cs double heterojunction (Example) is greatly improved, and about 93.2% of TCH can be degraded within 60 min.

[0067] Mechanism research The reaction system of Example 1 was investigated for mechanistic effects by using different quenchers, such as tert-butanol [TBA] 0 = 1.5 M, L-histidine [LH] 0 = 2,4,6-trichlorophenol [2,4,6-TCP] 0 = 15 mM, and methyl phenyl sulfoxide [PMSO] 0 = p-benzoquinone […]. p-[BQ]0=Disodium ethylenediaminetetraacetate [EDTA-2Na]0=Silver nitrate [AgNO3]0=1.5 mM, [pH]0=5.6, when added to this system, the dominant active species are photogenerated holes (hv) and •OH, •O2. - , 1 O2, electrons (e) - ) and high-valence metal oxygen species Co(IV)=O play an auxiliary role in the degradation of TCH, such as Figure 6 As shown.

[0068] Application Example 2 A practicality test was conducted on the reaction system corresponding to Case 1. The initial solution was adjusted to different pH values ​​(3.3, 5.3, 6.5, 9.1, 11.2). The results showed that the system was more favorable for TCH degradation at pH=5.3. Figure 7 As shown.

[0069] Application Example 3 Practicality tests were conducted on the reaction system corresponding to Case 1, and different types of pollutants were used (10 mg / L). The results showed that the system could selectively degrade TCH, Rhodamine, and Acid Orange G, as shown in Table 1.

[0070] Table 1

[0071] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a 3D double-heterojunction catalyst hydrogel, characterized in that, Includes the following steps: (1) Mix acid and LiF, then add Ti3AlC2 and heat to react. Separate the solid and liquid phases to obtain the solid phase, which is MXene. Disperse MXene in an organic solvent to obtain an MXene solution. (2) Mix the cobalt salt solution with the MXene solution and freeze-cast it in liquid nitrogen to obtain the precursor solution; (3) Mix and stir the dimethylimidazole aqueous solution with the precursor solution; separate the solid and liquid phases of the resulting reaction solution to obtain the precipitate, wash and freeze dry to obtain MXene / ZIF-67 powder; calcine the obtained MXene / ZIF-67 powder under an inert atmosphere to obtain MXene / TiO2 / CoN6 dual heterostructure. (4) Mix the MXene / TiO2 / CoN6 dual heterostructure with chitosan colloid and add an alkaline solution to obtain the 3D dual heterostructure catalyst hydrogel.

2. The production method according to claim 1, characterized by, In step (1), the heating reaction conditions are: rotation speed of 400~500 rpm, constant temperature sand bath temperature of 35-55 ℃, and reaction time of 48~60 h; The acid is selected from hydrochloric acid and / or hydrofluoric acid; The concentration of the acid is 8-10 M.

3. The preparation method according to claim 1, characterized in that, In step (2), the cobalt salt is selected from Co(NO3)2·6H2O and / or CoCl2·6H2O; The concentration of the cobalt salt solution is 0.025~0.075 M; The concentration of MXene solution is 7.5~15 mg / mL; The concentration ratio of cobalt salt solution to MXene solution is (1:7) to (1:9). The directional freeze casting time is 5~15 min.

4. The method of claim 1, wherein, In step (3), the concentration of the dimethylimidazole solution is 0.2~0.6 M; The mass ratio of the sum of the cobalt salt and dimethylimidazole to the mass of MXene is (40:1) to (50:1).

5. The preparation method according to claim 1, characterized in that, In step (3), the inert atmosphere contains inactive gases including nitrogen and / or argon, and the heating and calcination temperature is 750~850 ℃, the time is 1.5~2.5 h, and the heating rate is 2~5℃ / min.

6. The preparation method according to claim 1, characterized in that, In step (4), the chitosan colloid also contains 1.5~2.5wt% acetic acid; The mass ratio of chitosan colloid to MXene / TiO2 / CoN6 is (1:0.5) to (1:1.5).

7. The preparation method according to claim 1, characterized in that, The alkaline solution includes NaOH solution and / or KOH solution, with a concentration of 2-3 wt%.

8. A 3D dual heterojunction catalyst chitosan hydrogel, characterized in that, Prepared by the preparation method according to any one of claims 1 to 7, using chitosan as a 3D network carrier, MXene / TiO2 / CoN6 as active sites, MXene / TiO2 and CoN6 are bonded by Co-O-Ti bonds, and CoN6 single atoms and Co nanoparticles exist on the surface of MXene / TiO2 / CoN6.

9. The application of the 3D dual heterojunction catalyst chitosan hydrogel according to claim 8 in the photo-assisted periodate-activated degradation of organic pollutants.

10. The application according to claim 9, characterized in that, The organic pollutants include one or more of tetracycline hydrochloride, rhodamine, and Acid Orange G.

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