A catalyst, preparation method and application for solar-degradable polyurethane adhesives

Abstract

This invention claims protection for a catalyst, preparation method, and application for the solar degradation of polyurethane adhesives, belonging to the category of novel functional and structural materials. In the preparation process of this catalyst, C3N4 is first protonated, followed by partial oxidation of MXene nanosheets. Then, through mechanical mixing and electrostatic interaction, the protonated C3N4 is coupled with the partially oxidized MXene powder composited with CNTs, effectively preventing catalyst agglomeration and the recombination of photogenerated electrons, thus improving photocatalytic activity. This novel catalyst possesses a heterogeneous structure with surface-to-surface contact, optimizing catalytic performance and successfully reducing the T-peel strength of aluminum-plastic composite films to below 2N / 15mm. It enables the degradation of polyurethane adhesives in composite films at room temperature under sunlight, making the recycling of waste composite films easier and exhibiting characteristics such as high efficiency, energy saving, and environmental friendliness.

Description

Technical Field

[0001] This invention relates to a catalyst, preparation method, and application for solar-degradable polyurethane adhesives; it belongs to the field of novel functional and structural materials technology. Background Technology

[0002] Aluminum-plastic composite packaging, with its superior barrier properties, is widely used and irreplaceable in high-requirement fields such as food and pharmaceuticals. However, its efficient recycling after disposal is difficult, resulting in the waste of high-value resources and serious environmental pollution, creating a significant resource-environment conflict. In fact, this type of waste contains extremely high resource value: the plastic components (such as polyethylene, polypropylene, and polyethylene terephthalate) account for more than 12% of global petroleum-based plastic consumption, and aluminum accounts for over 20% (second only to steel). Data shows that recycling 1 ton of waste plastic can save 2.3 tons of crude oil, reduce CO2 emissions by 3.14 tons, and lower energy consumption by 70%. The green recycling and high-value reuse of aluminum-plastic composite packaging is of great significance for controlling plastic pollution and developing a low-carbon circular economy.

[0003] Currently, the main methods for separating and recycling waste aluminum-plastic composite packaging include chemical solvent separation, high-temperature pyrolysis separation, and physical-mechanical separation, but all have significant drawbacks. Chemical solvent separation requires large amounts of solvent, leading to high costs, difficulties in solvent recovery, degradation of plastic properties, and secondary pollution. High-temperature pyrolysis separation requires significant investment in equipment and has stringent requirements for exhaust gas treatment, limiting its engineering applications. Physical-mechanical separation suffers from incomplete aluminum-plastic separation and low added value of recycled materials. These methods all suffer from poor economic efficiency, incomplete separation, and secondary pollution, failing to effectively solve the problem of recycling waste aluminum-plastic composite packaging. Developing easily separable recycling technologies and theoretical systems, and developing high-performance, high-value-added products, are key directions for overcoming current limitations.

[0004] Our research team discovered that utilizing sunlight to degrade the polyurethane adhesive in aluminum-plastic composites, reducing the T-peel strength to below 2N / 15mm, makes the aluminum and plastic easier to separate and recycle. The key to this sunlight-based degradation of polyurethane adhesives lies in the preparation of a highly efficient catalyst. Currently, the reported catalysts for degrading polyurethane adhesives in composite films are mainly carbon nitride (C3N4) and its modified forms. Studies have shown that combining C3N4 with MXene catalysts is an effective way to improve their photocatalytic efficiency; however, MXene sheets are prone to self-stacking, resulting in the loss of a large number of reactive sites and a reduction in ion transport channels.

[0005] Given the above reasons, how to improve the reactivity of photocatalysts, degrade polyurethane adhesives under sunlight, facilitate the recycling and reuse of flexible packaging composite films, and achieve room temperature separation of aluminum-plastic packaging are urgent technical problems to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a highly efficient and environmentally friendly catalyst for the solar degradation of polyurethane adhesives, prepared from carbon nanotubes, MXene nanosheets, and nano-C3N4 powder, and discloses its preparation method and application to achieve room temperature separation of aluminum-plastic packaging under sunlight.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention first discloses a method for preparing a catalyst for the solar degradation of polyurethane adhesives, comprising the following steps:

[0009] S1. Preparation of protonated nano-C3N4 powder:

[0010] Nano-C3N4 powder was added to a strongly acidic aqueous solution, sonicated, and then stirred to protonate it. The protonated C3N4 was then centrifuged and washed with deionized water until neutral to remove the strong acid from the solution. Finally, the protonated nano-C3N4 powder was obtained by freeze-drying. Protonation enhances its electrostatic interaction with other components and prevents agglomeration.

[0011] S2. Preparation of CNT composite partially oxidized MXene powder:

[0012] First, CNT powder is dispersed in a deoxycholate aqueous solution to obtain a uniformly dispersed CNT dispersion.

[0013] Then, MXene nanosheets were placed in a tube furnace, heated to 200-300°C, held for 1-3 hours, and cooled to room temperature to obtain partially oxidized MXene, which was then added to the above CNT dispersion.

[0014] Next, after ultrasonic stirring, the mixture was freeze-dried to obtain CNT composite partially oxidized MXene powder.

[0015] S3. Preparation of the target catalyst:

[0016] The protonated nano-C3N4 powder obtained in step S1 above is dispersed in deionized water, and then the CNT composite partially oxidized MXene powder obtained in step S2 above is added. After magnetic stirring, the CNT composite partially oxidized MXene coupled C3N4 catalyst is obtained by freeze drying, which is the target catalyst.

[0017] Preferably, the aforementioned MXene nanosheets are Ti3C2T x -MXene or Ti2CT x -MXene.

[0018] For MXene (Ti3C2T) x-MXene or Ti2CT x While MXene itself is chemically unstable and gradually oxidizes to TiO2 when exposed to air, thus losing its role as a co-catalyst, the metal oxide formed after MXene oxidation can form heterojunctions with other semiconductors, which is more conducive to photocatalytic reactions.

[0019] This invention first involves the partial oxidation of MXene at 200-300°C to obtain Ti3C2T. x The MXene@TiO2 composite material does not disrupt the original layered structure of MXene and also constructs a Schottky junction. Therefore, the partially oxidized MXene in this invention not only possesses the excellent conductivity of MXene, making it suitable as a catalyst support, but its surface functional groups also provide active sites. Partial oxidation of the MXene surface forms an oxide film, which passivates the edges and surface of MXene to a certain extent, preventing oxidative degradation of the internal structure of MXene and improving its stability.

[0020] In the preparation process, by partially oxidizing MXene nanosheets, and then using mechanical mixing and electrostatic interaction to make C3N4 and CNT tightly adsorbed on the partially oxidized MXene nanosheets, the aggregation of catalysts can be effectively avoided and its specific surface area can be increased. The MXene nanosheets act as charge transfer interfaces to prevent the recombination of photogenerated electrons. At the same time, the nano-titanium dioxide (TiO2) generated by the partial oxidation of MXene nanosheets further improves the photocatalytic reaction activity.

[0021] Preferably, the mass ratio of the aforementioned nano-C3N4 powder to the strong acid aqueous solution is (1~3):(10~30), the concentration of the strong acid aqueous solution is 0.4~0.6M, and the strong acid is one of hydrochloric acid, sulfuric acid, and nitric acid.

[0022] More preferably, the mass ratio of the aforementioned CNT powder to the deoxycholate aqueous solution is 2~4:10~30, and the mass ratio of the CNT powder to MXene nanosheets is 2~4:1.

[0023] More preferably, the aforementioned deoxycholate is selected from one of sodium taurodeoxycholate, potassium taurodeoxycholate, sodium ursodeoxycholate, potassium ursodeoxycholate, sodium chenodeoxycholate, or potassium chenodeoxycholate, and the mass percentage concentration of the aqueous solution of the deoxycholate is 5-10%.

[0024] More preferably, in the aforementioned step S2, the method for preparing the partially oxidized MXene nanosheets is as follows: heating the MXene nanosheets to 200°C, holding at that temperature for 2 hours, and then cooling to room temperature.

[0025] More preferably, in step S3, 1-3 parts by mass of protonated nano-C3N4 powder obtained in step S1 are dispersed in deionized water, and CNT composite partially oxidized MXene powder obtained in step S2 is added at a mass ratio of nano-C3N4 powder to MXene nanosheets of 100:1-3.

[0026] The present invention also claims protection for a catalyst for solar-degradable polyurethane adhesives prepared according to the aforementioned method.

[0027] This invention further claims the application of a solar-degradable polyurethane adhesive catalyst, as described above, in the degradation of polyurethane adhesives in composite films to achieve aluminum-plastic separation and recycling. The specific method is as follows: the catalyst is added to the polyurethane adhesive, mixed evenly, coated onto a PET plastic film, dried, hot-pressed with aluminum foil, and cured at 40-60°C for 36-72 hours to obtain a PET / Al composite film; the PET / Al composite film is placed under sunlight for 60 days, and its T-peel strength is tested.

[0028] Preferably, in the aforementioned applications, the mass ratio of the catalyst to the polyurethane adhesive is 1~3:30~90.

[0029] The advantages of this invention are:

[0030] (1) This invention prepares a catalyst for the solar degradation of polyurethane adhesives using carbon nanotubes (CNTs), MXene nanosheets, and nano-carbon nitride (C3N4) powder as raw materials. CNTs are one-dimensional tubular structures with high conductivity and high aspect ratio. They are tightly composited on two-dimensional MXene nanosheets, which can inhibit MXene self-stacking, increase active sites, and help form a conductive network structure. Furthermore, the CNT composite partially oxidized MXene nanosheets coupled to bulk C3N4 have a tight interface connection that facilitates rapid electron transfer, enhances the ability of photogenerated electron transport, and reduces the photogenerated electron-hole recombination rate. At the same time, the nano-titanium dioxide (TiO2) generated by the partial oxidation of MXene nanosheets improves the photocatalytic reaction activity, thus synergistically improving the photocatalytic effect.

[0031] (2) The preparation method of the present invention is easy to implement and is efficient and environmentally friendly. By protonating C3N4 and then partially oxidizing MXene nanosheets, the protonated C3N4 and CNT composite partially oxidized MXene powder are coupled through mechanical mixing and electrostatic action. This can effectively avoid catalyst agglomeration, increase its specific surface area, and also have a relatively large pore volume and pore size. Example 1 is the best, with a specific surface area of ​​92.82 m² / g and a pore volume of 0.58 cm³ / g, providing sufficient active sites for catalytic degradation reaction.

[0032] (3) The catalyst with a novel composite structure prepared by the present invention solves the problem of reduced charge transport efficiency caused by point-to-point and point-to-surface contact of traditional catalysts. Its heterogeneous structure with surface-to-surface contact optimizes the catalytic performance and maximizes the absorption and utilization rate of sunlight. It has excellent photocatalytic outdoor implementation capability. It can degrade the polyurethane adhesive in the composite film under sunlight, reducing the T-type peel strength of the PET / Al composite film to below 2N / 15mm (the lowest is 1.63N / 15mm in Examples 1-3). It can be easily peeled at room temperature, making the waste composite film easy to recycle and realize high-value utilization. It has the characteristics of high efficiency, energy saving and environmental protection, and is of great significance for controlling plastic pollution and promoting "carbon neutrality". Attached Figure Description

[0033] Figure 1 It is Ti3C2T in Embodiment 1 of the present invention x - Comparison of infrared spectra of MXene nanosheets before and after partial oxidation;

[0034] Figure 2 This is the infrared spectrum of the catalyst prepared in Example 1 of the present invention;

[0035] Figure 3 This is the infrared spectrum of the catalyst prepared in Comparative Example 1 of the present invention;

[0036] Figure 4 It is Ti3C2T in Embodiment 1 of the present invention x XRD comparison of MXene nanosheets before and after partial oxidation;

[0037] Figure 5 This is the XRD pattern of the catalyst prepared in Example 1 of the present invention;

[0038] Figure 6 This is the XRD pattern of the catalyst prepared in Comparative Example 1 of the present invention;

[0039] Figure 7 This is the XRD pattern of the catalyst prepared in Comparative Example 3 of the present invention;

[0040] Figure 8 This is a scanning electron microscope image of the catalyst prepared in Example 1 of the present invention;

[0041] Figure 9 This is a scanning electron microscope image of the catalyst prepared in Comparative Example 1 of the present invention;

[0042] Figure 10 This is a scanning electron microscope image of the catalyst prepared in Comparative Example 2 of the present invention;

[0043] Figure 11This is a scanning electron microscope image of the catalyst prepared in Comparative Example 3 of the present invention;

[0044] Figure 12 These are XPS spectra of the O element on the surface of the aluminum film before and after catalytic degradation of the catalysts prepared in Example 1 and Comparative Example 1 of this invention.

[0045] Figure 13 This is a graph showing the T-type exfoliation strength test curve of the catalyst prepared in Example 1 of the present invention after 0 days of light irradiation;

[0046] Figure 14 This is a graph showing the T-type exfoliation strength test of the catalyst prepared in Example 1 of the present invention after 60 days of light irradiation;

[0047] Figure 15 This is a graph showing the T-type exfoliation strength test curve of the catalyst prepared in Comparative Example 1 of the present invention after 0 days of light irradiation;

[0048] Figure 16 This is a graph showing the T-type exfoliation strength test of the catalyst prepared in Comparative Example 1 of the present invention after 60 days of light irradiation.

[0049] Figure 17 This is a graph showing the T-type exfoliation strength test curve of the catalyst prepared in Comparative Example 3 of the present invention after 0 days of light irradiation.

[0050] Figure 18 This is a curve of the T-type exfoliation strength test of the catalyst prepared by Comparative Example 3 of the present invention after 60 days of light irradiation. Detailed Implementation

[0051] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0052] Unless otherwise specified, all raw materials used in this invention are commercially available. Preferred commercial procurement methods are shown in Table 1 below:

[0053]

[0054] Table 1. Preferred Commercial Procurement Methods for Each Raw Material

[0055] Example 1

[0056] This embodiment successfully prepared the target catalyst: a CNT composite partially oxidizing MXene coupled with C3N4 catalyst. The preparation process is as follows:

[0057] S1. Preparation of protonated nano-C3N4 powder:

[0058] One part by mass of nano-C3N4 powder was added to 10 parts by mass of 0.4M hydrochloric acid aqueous solution, and sonicated for 30 min, followed by stirring for 2 h to protonate it. Then, the protonated C3N4 was washed with deionized water by centrifugation until neutral to remove hydrochloric acid from the solution. Finally, the protonated nano-C3N4 powder was obtained by freeze drying.

[0059] S2. Preparation of CNT composite partially oxidized MXene powder:

[0060] First, 2 parts by weight of CNT powder were dispersed in 10 parts by weight of a 5% sodium taurine aqueous solution to obtain a CNT dispersion; then, 1 part by weight of Ti3C2T x MXene nanosheets were heated to 250°C, held for 2 hours, and then cooled to room temperature to obtain partially oxidized MXene. This partially oxidized MXene was added to the above CNT dispersion, and then subjected to freeze-drying after ultrasonic stirring to obtain CNT composite partially oxidized MXene powder.

[0061] S3. Preparation of the target catalyst:

[0062] One part by mass of the protonated nano-C3N4 powder obtained in step S1 above is dispersed in 10 parts by mass of deionized water, and then 0.03 parts by mass of the CNT composite partially oxidized MXene powder obtained in step S2 above is added. After magnetic stirring for 2 hours, the CNT composite partially oxidized MXene coupled C3N4 catalyst is obtained by freeze drying.

[0063] Example 2

[0064] The preparation process in this embodiment is basically similar to that in Example 1:

[0065] S1. Preparation of protonated nano-C3N4 powder:

[0066] Two parts by mass of nano-C3N4 powder were added to 20 parts by mass of 0.5M sulfuric acid aqueous solution, sonicated for 45 min, and then stirred for 3 h to protonate it. Then, the protonated C3N4 was washed with deionized water by centrifugation until neutral to remove hydrochloric acid from the solution. Finally, the protonated nano-C3N4 powder was obtained by freeze drying.

[0067] S2. Preparation of CNT composite partially oxidized MXene powder:

[0068] First, 3 parts by weight of CNT powder were dispersed in 20 parts by weight of a 7% potassium ursodeoxycholate aqueous solution to obtain a CNT dispersion; then, 1 part by weight of Ti3CT was added... xMXene nanosheets were heated to 300°C and held for 1 hour, then cooled to room temperature to obtain partially oxidized MXene. This partially oxidized MXene was added to the above CNT dispersion, followed by ultrasonic stirring and freeze-drying to obtain CNT composite partially oxidized MXene powder.

[0069] S3. Preparation of the target catalyst:

[0070] Two parts by mass of the protonated nano-C3N4 powder obtained in step S1 above were dispersed in 20 parts by mass of deionized water, and then 0.08 parts by mass of the CNT composite partially oxidized MXene powder obtained in step S2 above were added. After magnetic stirring for 3 hours, the CNT composite partially oxidized MXene coupled C3N4 catalyst was obtained by freeze drying.

[0071] Example 3

[0072] The preparation process in this embodiment is basically similar to that in Example 1:

[0073] S1. Preparation of protonated nano-C3N4 powder:

[0074] Three parts by weight of nano-C3N4 powder were added to 30 parts by weight of 0.6M nitric acid aqueous solution, sonicated for 60 min, and then stirred for 5 h to protonate it. Then, the protonated C3N4 was washed with deionized water by centrifugation until neutral to remove hydrochloric acid from the solution. Finally, the protonated nano-C3N4 powder was obtained by freeze drying.

[0075] S2. Preparation of CNT composite partially oxidized MXene powder:

[0076] First, 4 parts by weight of CNT powder were dispersed in 30 parts by weight of a 10% potassium ursodeoxycholate aqueous solution to obtain a CNT dispersion; then, 1 part by weight of Ti3C2T x MXene nanosheets were heated to 200°C, held for 3 hours, and then cooled to room temperature to obtain partially oxidized MXene. This partially oxidized MXene was added to the above CNT dispersion, and then subjected to freeze-drying after ultrasonic stirring to obtain CNT composite partially oxidized MXene powder.

[0077] S3. Preparation of the target catalyst:

[0078] Three parts by mass of the protonated nano-C3N4 powder obtained in step S1 above were dispersed in 30 parts by mass of deionized water, and then 0.15 parts by mass of the CNT composite partially oxidized MXene powder obtained in step S2 above were added. After magnetic stirring for 2-4 hours, the CNT composite partially oxidized MXene coupled C3N4 catalyst was obtained by freeze drying.

[0079] Comparative Example 1

[0080] The catalyst prepared in this comparative example is a CNT-composite partially oxidized MXene coupled with a conventional C3N4 catalyst. Compared with Example 1, the C3N4 was not protonated. The preparation process is as follows:

[0081] S1. Preparation of CNT composite partially oxidized MXene powder:

[0082] First, 2 parts by weight of CNT powder were dispersed in 10 parts by weight of a 5% sodium ursodeoxycholate aqueous solution to obtain a CNT dispersion; then, 1 part by weight of Ti3CT was added... x MXene nanosheets were heated to 300°C and held for 1 hour, then cooled to room temperature to obtain partially oxidized MXene. This partially oxidized MXene was added to the above CNT dispersion, followed by ultrasonic stirring and freeze-drying to obtain CNT composite partially oxidized MXene powder.

[0083] S2, Catalyst Preparation

[0084] One part by mass of nano-C3N4 powder was dispersed in 10 parts by mass of deionized water, and then 0.03 parts by mass of the CNT composite partially oxidized MXene powder obtained in S1 above was added. After magnetic stirring for 2 hours, the CNT composite partially oxidized MXene coupled with conventional C3N4 catalyst was obtained by freeze drying.

[0085] Comparative Example 2

[0086] The catalyst prepared in this comparative example is a partially oxidized MXene coupled with a conventional C3N4 catalyst. Compared with Example 1, no CNTs were added. The preparation process is as follows:

[0087] S1. Preparation of protonated nano-C3N4 powder:

[0088] One part by mass of nano-C3N4 powder was added to 10 parts by mass of 0.4M hydrochloric acid aqueous solution, and the mixture was sonicated for 30 min and then stirred for 2 h to protonate it. Then, the protonated C3N4 was centrifuged and washed with deionized water until neutral to remove the hydrochloric acid from the solution. Finally, the protonated nano-C3N4 powder was obtained by freeze-drying C3N4.

[0089] S2. Preparation of partially oxidized MXene powder:

[0090] One mass of Ti3CT x - MXene nanosheets were heated to 300°C, held at that temperature for 1 hour, and then cooled to room temperature to obtain partially oxidized MXene powder.

[0091] S3. Preparation of catalyst:

[0092] One part by mass of the protonated nano-C3N4 powder obtained in step S1 above is dispersed in 10 parts by mass of deionized water, and then 0.01 parts by mass of the partially oxidized MXene powder obtained in step S2 above is added. After magnetic stirring for 2 hours, the partially oxidized MXene coupled C3N4 catalyst is obtained by freeze drying.

[0093] Comparative Example 3

[0094] The catalyst prepared in this comparative example is a CNT@MXene coupled C3N4 catalyst. Compared with Example 1, the MXene powder was not partially oxidized. The preparation process is as follows:

[0095] S1. Preparation of protonated nano-C3N4 powder:

[0096] Three parts by weight of nano-C3N4 powder were added to 30 parts by weight of 0.6M nitric acid aqueous solution, sonicated for 60 min, and then stirred for 5 h to protonate it. Then, the protonated C3N4 was washed with deionized water by centrifugation until neutral to remove hydrochloric acid from the solution. Finally, the protonated nano-C3N4 powder was obtained by freeze drying.

[0097] S2. Preparation of CNT@MXene powder:

[0098] First, 4 parts by weight of CNT powder were dispersed in 30 parts by weight of a 10% potassium ursodeoxycholate aqueous solution to obtain a CNT dispersion; then, 1 part by weight of Ti3C2T x -MXene nanosheets were added to the above CNT dispersion, followed by ultrasonic stirring and freeze-drying to obtain CNT@MXene powder.

[0099] S3. Preparation of catalyst:

[0100] Three parts by mass of the protonated nano-C3N4 powder obtained in step S1 above were dispersed in 30 parts by mass of deionized water, and then 0.15 parts by mass of the CNT@MXene powder obtained in step S2 above were added. After magnetic stirring for 2-4 hours, the CNT@MXene coupled C3N4 catalyst was obtained by freeze drying.

[0101] Structural characterization and performance testing

[0102] (1) Infrared spectrum

[0103] The molecular structure of the catalyst product was characterized by infrared spectroscopy.

[0104] Figure 1 It is Ti3C2T in Example 1 x A comparison of the infrared spectra of MXene nanosheets before and after partial oxidation. The figure shows that: 3420 cm⁻¹ -1and 1386 cm -1 The vibrational peaks at 1627 cm⁻¹ belong to the -OH bonds adsorbed on Ti atoms and the free -OH bonds, respectively; -1 The peak at that point corresponds to the C=O bonds on the surface. After partial oxidation treatment, the Fourier transform infrared spectrum can be observed at 550 cm⁻¹. -1 The stretching vibration peak of the O-Ti-O bond in titanium dioxide was observed at [location], indicating that there is some Ti3C2T [structure]. x MXene was oxidized to form TiO2.

[0105] Figure 2 This is the infrared spectrum of the catalyst prepared in Example 1. As can be seen from the figure, the stretching vibration peaks of the C–N and C=N bonds in the aromatic CN heterocyclic compound are located at 1000 cm⁻¹. -1 Up to 1700 cm -1 3000-3500 cm -1 The broad peak at 808 cm⁻¹ represents free amino and hydroxyl groups adsorbed on the sample surface. -1 The characteristic peak at that location corresponds to the tris-s-triazine unit. This infrared detection result indicates that the partially oxidized MXene nanosheets are uniformly dispersed in the CNT matrix, and the introduction of CNT-composite partially oxidized MXene powder does not disrupt the basic bond structure of the carbon nitride framework.

[0106] Figure 3 The image shows the infrared spectrum of the catalyst prepared in Comparative Example 1. As can be seen from the image, since Comparative Example 1 does not contain amino groups, the infrared spectrum at 3500 cm⁻¹ is significantly lower. -1 Only a hydroxyl peak is observed at 1000–1300 cm⁻¹. -1 Within this range, tensile vibrations of COC and bending vibrations of CH and CC are observed, which mainly correspond to the infrared characteristic peaks of MXene.

[0107] (2) X-ray diffraction (XRD) analysis

[0108] Figure 4 It is Ti3C2T in Example 1 x A comparison of the XRD patterns of MXene nanosheets before and after partial oxidation. The figures show that: Ti3C2T x The characteristic peaks of MXene are at (002) plane at 7.5° and (110) plane at 60.5°. Meanwhile, Ti3C2T after partial oxidation treatment... x MXene not only retains the (002) and (110) characteristic peaks, but also exhibits the (101) crystal plane characteristic peak of TiO2 at 25°, which is consistent with the aforementioned infrared spectrum. This indicates that the method of the present invention enables Ti3C2T xThe surface of MXene is partially oxidized, forming an oxide film that passivates the edges and surface of MXene to a certain extent, thereby preventing the oxidative degradation of the internal structure of MXene and improving the stability of MXene.

[0109] Figure 5 , Figure 6 and Figure 7 The XRD patterns of Example 1, Comparative Example 1, and Comparative Example 3 are shown in the figures. It can be seen from the figures that compared to... Figure 6 , Figure 5 The XRD pattern shows two diffraction peaks at 13.0° and 27.3°, which are attributed to the planar arrangement (100) plane of repeating tri-s-triazine units and the stacking (002) plane of oriented aromatic structures, respectively.

[0110] in addition, Figure 5 and Figure 6 In comparison, the (002) peak shifted from 27.3° to 27.65°, indicating a decrease in interlayer spacing. This reduced interlayer spacing is beneficial for charge transfer, as it shortens the transfer distance, promoting the migration of photogenerated electrons and thus enhancing photocatalytic activity and performance. Furthermore, Figure 5 It contains the characteristic peak of the (101) crystal plane of TiO2 at 25.12°, while Figure 6 The characteristic peak (101) was not displayed, which may overlap with the broad peak (002); while Figure 7 (Comparative Example 3) and Figure 5 In comparison, it lacks Ti3C2T. x -Characteristic peak of the (101) crystal plane of TiO2 formed by partial oxidation of MXene nanosheets.

[0111] (3) Scanning electron microscope (SEM)

[0112] The surface microstructure of the prepared catalyst product was characterized by SEM.

[0113] Figure 8 This is a SEM image of the catalyst prepared in Example 1. The image shows that carbon nanotubes (CNTs) are tightly bound to partially oxidized MXene nanosheets. After protonation, they interact with negatively charged Ti3C2T nanosheets via electrostatic interactions. x The interfaces of nanosheets are more tightly connected, forming surface coupling.

[0114] Figure 9 This is a SEM image of the catalyst prepared in Comparative Example 1. The nano-C3N4 in the raw material was not protonated, but it reacted with Ti3C2T. x -MXene nanosheets can also form surface coupling, but they have certain porosity, loose structure and obvious aggregation.

[0115] Figure 10 The image shows the SEM image of the catalyst prepared in Comparative Example 2. No carbon nanotubes were added to the raw materials; protonated nano-C3N4 was loaded onto Ti3C2T solely through adsorption. x On MXene nanosheets, the interface bonding is not tight.

[0116] Figure 11 This is a SEM image of the catalyst prepared in Comparative Example 3. The raw materials did not contain Ti3C2T. x -MXene nanosheets undergo partial oxidation treatment, resulting in protonated nano-C3N4 and Ti3C2T x -MXene nanosheets have poor adhesion and large particle size, resulting in loose interfacial bonding.

[0117] (4) Specific surface area test

[0118] The test results of specific surface area, pore volume, and pore size of each embodiment and comparative example of the present invention are shown in Table 2. It can be seen that the specific surface area of ​​the six groups of samples is not significantly different. However, further analysis of the pore volume and pore size data shows that Example 1 is the optimal embodiment, with the largest pore volume and pore size, reaching 0.58 cm³ g. -1 The wavelength of 28.01 nm indicates that the composite of CNT and partially oxidized MXene expands the pore volume and pore size, which will provide more active sites for photocatalytic reactions and improve the photocatalytic performance of the material.

[0119]

[0120] Table 2. Specific surface area, pore volume, and pore size of each catalyst sample

[0121] (5) Quantitative analysis of XPS and functional groups

[0122] Furthermore, X-ray photoelectron spectroscopy (XPS) was used to investigate the oxygen state in the PET / Al composite film bonded by polyurethane adhesive. For example... Figure 12 As shown, the O 1s spectrum reveals two characteristic peaks at 531.9 eV and 533.6 eV on day 0, corresponding to the HN-C=O (carbamate) and CH2-O-C=O (ester) functional groups, respectively. After 60 days of degradation, an additional peak appears at 532.6 eV, which is attributed to the formation of the C-O-C (ether) group.

[0123] Quantitative analysis of the spectral changes in Example 1 and Comparative Example 1 is detailed in Tables 3 and 4. It can be seen that the content of urethane (HN-C=O) gradually decreases, while the content of ether (C-O-C) groups increases accordingly. The analytical results in Tables 3 and 4 indicate that when the PET / Al composite film bonded by the polyurethane adhesive ages under sunlight, chain breakage mainly occurs at the urethane (HN-C=O) groups, leading to a decrease in urethane content and the gradual formation of ether (C-O-C) groups. When the catalyst prepared in Example 1 is applied to the polyurethane adhesive, after 60 days of solar degradation, the content of HN-C=O groups decreases by 82.83%, while in Comparative Example 1 it only decreases by 17.79%. This demonstrates that the CNT composite partially oxidized MXene coupled C3N4 catalyst prepared in this invention can effectively promote the degradation of polyurethane adhesives.

[0124]

[0125] Table 3. Quantitative analysis of functional groups in the polyester / aluminum composite film of Example 1

[0126]

[0127] Table 4. Quantitative analysis of functional groups in the polyester / aluminum composite film of Comparative Example 1

[0128] (6) T-type peel strength test

[0129] The catalyst of the present invention is applied in the following specific way: the catalyst obtained in each embodiment or comparative example is added to the polyurethane adhesive, the mass ratio of catalyst to polyurethane adhesive is 1~3:30~90, mixed evenly, coated on PET plastic film, dried, hot-pressed with aluminum foil, and cured at 40~60°C for 36~72h, preferably at 45°C for 48h, to obtain PET / Al composite film. The film is placed in sunlight for 60 days, and the T peel strength of the PET / Al composite film before and after degradation is tested using a universal testing machine at room temperature.

[0130] in, Figure 13 This is a T-type peel strength test curve after 0 days of light exposure, as shown in Embodiment 1 of the present invention. Figure 14 This is a T-shaped peel strength test curve of Embodiment 1 of the present invention after 60 days of light exposure; Figure 15 This is a comparative example 1 of the present invention, showing the T-type peel strength test curve after 0 days of light exposure. Figure 16 This is a comparative example 1 of the present invention, showing the T-type peel strength test curve after 60 days of light exposure; Figure 17 This is a comparative example 3 of the present invention, showing the T-type peel strength test curve after 0 days of light exposure. Figure 18 This is a comparative example 3 of the present invention, showing the T-shaped peel strength test curve after 60 days of light exposure.

[0131] The specific test results are shown in Table 5.

[0132]

[0133] Table 5. T-peel strength of each example / comparative case after 0 / 60 days of light exposure on the composite film.

[0134] As shown in Table 5, the T-peel strength of the composite films prepared by the catalyst products of each embodiment and comparative example is not significantly different before solar photocatalytic degradation. However, after 60 days of degradation, the T-peel strength of the composite films prepared by the catalysts of Examples 1 to 3 all decreased to below 2 N / 15 mm, and were easily peeled off at room temperature. This indicates that the catalysts prepared in each embodiment of the present invention accelerated the destruction of the polyurethane adhesive crosslinking network in the composite film system under sunlight, resulting in weakened intermolecular forces and a large decrease in T-peel strength. However, after 60 days of degradation, the T-peel strength of the composite films of Comparative Examples 1, 2, and 3 was still above 3 N / 15 mm, and were not easily peeled off at room temperature. This indicates that the catalysts prepared in each comparative example have low catalytic activity and cannot effectively degrade the polyurethane adhesive in a short period of time.

[0135] In summary, this invention has produced a catalyst for the solar degradation of polyurethane adhesives. This novel catalyst composite structure solves the defects of reduced charge transport efficiency caused by point-to-point and point-to-surface contact of catalysts in traditional technologies. Its heterogeneous structure with surface-to-surface contact greatly expands the absorption and utilization rate of sunlight, and has excellent potential for outdoor photocatalysis. It can degrade composite film polyurethane adhesives under sunlight for a short period (within 60 days), and has the characteristics of high efficiency, energy saving, and environmental protection. It has good application prospects in the fields of sewage treatment, waste gas treatment, and green recycling.

[0136] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for preparing a catalyst for the solar degradation of polyurethane adhesives, characterized in that, Includes the following steps: S1. Preparation of protonated nano-C3N4 powder: Nano C3N4 powder was added to a strongly acidic aqueous solution, ultrasonicated and then stirred to protonate it. The strong acid in the solution was washed away and then freeze-dried to obtain protonated nano C3N4 powder. S2. Preparation of CNT composite partially oxidized MXene powder: CNT powder was dispersed in an aqueous solution of deoxycholate to obtain a CNT dispersion. MXene nanosheets were placed in a tube furnace, heated to 200-300℃, held for 1-3 hours, and cooled to room temperature to obtain partially oxidized MXene nanosheets. These nanosheets were then added to the above CNT dispersion, ultrasonically stirred, and freeze-dried to obtain CNT composite partially oxidized MXene powder. S3. Preparation of the target catalyst: Disperse 1-3 parts by mass of protonated nano-C3N4 powder obtained in step S1 above in deionized water, add CNT composite partially oxidized MXene powder obtained in step S2 above at a mass ratio of nano-C3N4 powder to MXene nanosheets of 100:1-3, stir magnetically, and freeze-dry to obtain C3N4 catalyst coupled with CNT composite partially oxidized MXene, which is the target catalyst. The catalyst prepared by this method forms a heterogeneous structure with surface-to-surface contact and surface coupling, thereby optimizing the catalytic performance. It can degrade the polyurethane adhesive in the composite film under sunlight, reducing the T-type peel strength of the PET / Al composite film to below 2N / 15mm.

2. The method for preparing a catalyst for solar-degradable polyurethane adhesives according to claim 1, characterized in that, The MXene nanosheets are Ti3C2T x -MXene or Ti2CT x -MXene.

3. The method for preparing a catalyst for solar-degradable polyurethane adhesives according to claim 1, characterized in that, The mass ratio of the nano-C3N4 powder to the strong acid aqueous solution is (1~3):(10~30), the concentration of the strong acid aqueous solution is 0.4~0.6M, and the strong acid is one of hydrochloric acid, sulfuric acid, and nitric acid.

4. The method for preparing a catalyst for solar-degradable polyurethane adhesives according to claim 1, characterized in that, The mass ratio of CNT powder to deoxycholate aqueous solution is 2~4:10~30, and the mass ratio of CNT powder to MXene nanosheets is 2~4:

1.

5. The method for preparing a catalyst for solar-degradable polyurethane adhesives according to claim 1, characterized in that, The deoxycholate is selected from one of sodium taurodeoxycholate, potassium taurodeoxycholate, sodium ursodeoxycholate, potassium ursodeoxycholate, sodium chenodeoxycholate, or potassium chenodeoxycholate, and the aqueous solution of the deoxycholate has a mass percentage concentration of 5% to 10%.

6. The method for preparing a catalyst for solar-degradable polyurethane adhesives according to claim 1, characterized in that, The method for preparing partially oxidized MXene nanosheets in step S2 is as follows: MXene nanosheets are placed in a tube furnace, heated to 250°C, kept at that temperature for 2 hours, and then cooled to room temperature to obtain partially oxidized MXene nanosheets.

7. A catalyst for the solar degradation of polyurethane adhesives, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 6.

8. The application of the catalyst for solar-degradable polyurethane adhesives as described in claim 7 in the degradation of composite film polyurethane adhesives to achieve aluminum-plastic separation and recycling, characterized in that, The method is as follows: the catalyst is added to the polyurethane adhesive, mixed evenly, coated onto a PET plastic film, dried, hot-pressed with aluminum foil, and cured at 40~60℃ for 36~72h to obtain a PET / Al composite film; the PET / Al composite film is placed under sunlight for 60 days and its T-peel strength is tested.

9. The application according to claim 8, characterized in that, The mass ratio of the catalyst to the polyurethane adhesive is 1~3:30~90.

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