Preparation method and application of ti3c2 / ag2o / la (oh)3 nanocomposite

Abstract

The application relates to the technical field of photocatalytic new materials, and discloses a preparation method and application of a Ti3C2 / Ag2O / La(OH)3 nano composite material, and the specific preparation method is as follows: La(NO3)3.6H2O is dissolved in a mixture of deionized water and a NaOH solution, and the mixture is stirred intensively to obtain a suspension; Ag2O and Ti3C2 MXene are added to the suspension, and stirring and heating in a high-pressure kettle are carried out; the precipitate is obtained after cooling; the precipitate is washed with ethanol and deionized water for multiple times, centrifuged, and dried to obtain the Ti3C2 / Ag2O / La(OH)3 nano composite material. The Ti3C2 / Ag2O / La(OH)3 nano composite material prepared by the application has excellent photocatalytic activity, and provides a new physical basis for the development of a heterostructure photocatalyst.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photocatalysis new materials, and particularly relates to a preparation method and application of Ti3C2 / Ag2O / La(OH)3 nano composite material. BACKGROUND

[0002] Wastewater contains heavy metal ions and organic pollutants, which affect human health and the environment, and has become a serious global problem faced by modern society. Various wastewater treatment liquids have been applied to remove organic pollutants in water. Photocatalysis is generally considered to be a potential candidate for wastewater degradation. Since the discovery of TiO2, many semiconductors have been studied for the decomposition of organic pollutants, such as g-C3N4, Zn2SnO4, BiOX, PbBiO2X. Among these semiconductors, La(OH)3 has attracted extensive attention as a promising photocatalyst due to its unique physical and chemical properties. In addition, one-dimensional La(OH)3 nanostructures can be easily obtained, with unique morphology, large specific surface area and novel electrical properties. The large band gap of La(OH)3 nanowires or nanorods limits their practical application in photocatalytic wastewater treatment. Only ultraviolet light in sunlight can be absorbed. Therefore, it is crucial to extend the response to the visible light region of La(OH)3-based photocatalysts. Xiao et al. effectively extended the visible light response by introducing Ag / AgCl into La(OH)3 nanorods. Sun et al. prolonged the visible light absorption and separated the charge carriers by coupling BiOI with La(OH)3 nanorods, thereby improving the photocatalytic performance. Therefore, it is expected that La(OH)3-based nanorods will exhibit excellent photocatalytic performance when combined with other semiconductors

[0003] Ti3C2-MXene, as a new type of two-dimensional nanostructure, shows great potential in high-efficiency photocatalytic performance. In addition, the large number of -O and -OH groups on the surface make it easy to establish strong connections with other semiconductors. Compared with graphene-based two-dimensional nanomaterials, the surface Ti atoms may have stronger redox capacity than C atoms. Excellent metal conductivity also ensures the transfer of charge carriers. Due to these excellent properties, Ti3C2 MXene has been widely applied to improve photocatalytic performance by compounding with other semiconductors (such as TiO2 / Ti3C2, g-C3N4 / Ti3C2, SnS / Ti3C2, BiOI / Ti3C2, PbBiO2X / Ti3C2, ZnGa2O4 / Ti3C2). Therefore, it is expected that the composite of La(OH)3 nanorods and Ti3C2-MXene will enhance the visible light response and promote the separation and transfer of charge carriers, thereby improving the photocatalytic activity. SUMMARY

[0004] Invention purposes: In view of the problems in the prior art, the application provides a preparation method and application of Ti3C2 / Ag2O / La(OH)3 nanocomposite, a new heterostructure Ti3C2 / Ag2O / La(OH)3 nanorod is prepared by a hydrothermal method, wherein the addition of Ti3C2-MXene and other components can effectively expand the response to the visible light region, and the introduction of Ag2O nanoparticles promotes the separation and transfer of carriers. The Ti3C2 / Ag2O / La(OH)3 nanocomposite prepared by the application has excellent photocatalytic activity.

[0005] Technical scheme: The application provides a preparation method of Ti3C2 / Ag2O / La(OH)3 nanocomposite, comprising the following steps:

[0006] S1. Dissolve La(NO3)3·6H2O in a mixture of deionized water and NaOH solution, and stir vigorously to obtain a suspension;

[0007] S2. Add Ag2O and Ti3C2 MXene to the suspension, stir, heat in an autoclave, cool, and take the precipitate;

[0008] S3. Wash the precipitate with ethanol and deionized water for multiple times, centrifuge, dry, and obtain Ti3C2 / Ag2O / La(OH)3 nanocomposite.

[0009] Further, the mass ratio of La(NO3)3·6H2O, Ag2O and Ti3C2 MXene is 10.8g:0.4g:20-100mg.

[0010] Further, in S1, the concentration of the NaOH solution is 1mol / L.

[0011] Further, in S1, the volume ratio of the NaOH solution and deionized water is 1:4.

[0012] Further, in S2, the specific conditions of heating are as follows: the heating temperature is 150-180℃, and the heating time is 24-26h.

[0013] Preferably, in S3, the number of washing times is 5-6 times.

[0014] Further, in S3, the specific conditions of drying are as follows: the drying temperature is 55-65℃, and the drying time is 10-14h.

[0015] Preferably, in S1, the time of vigorous stirring is 20-30min.

[0016] The application further provides application of the Ti3C2 / Ag2O / La(OH)3 nanocomposite prepared by the method according to any one of the above in photocatalytic decomposition of methylene blue.

[0017] Theoretical explanation: Ti3C2 MXene, as a new 2D material, shows great potential in the field of photocatalysis. (i) Ti3C2 MXene has many hydrophilic functional groups (-OH and -O) on its surface, which enables it to easily build strong connections with various semiconductors; (ii) the excellent metal conductivity of Ti3C2 MXene ensures efficient carrier transfer; (iii) the Ti sites exposed on Ti3C2 MXene have stronger redox capacity than carbon materials; (iv) there are many hydrophilic functional groups on Ti3C2 MXene, which promote its strong interaction with water molecules; (v) Ti3C2 MXene can stably function in aqueous solution. Considering the above outstanding characteristics of Ti3C2 MXene, it is expected to become a promising material in the field of photocatalysis. In the application, La(OH)3 can build strong links with the surface functional groups of Ti3C2 MXene, and be closely connected together. At the same time, the electrons on Ti3C2 can be transferred to the conduction band of La(OH)3, and the electrons on the conduction band of La(OH)3 can be further transferred to Ag2O, realizing efficient separation of carriers.

[0018] Beneficial effects: Compared with the prior art, the application adopts one-pot hydrothermal method to prepare a new heterostructure Ti3C2 / Ag2O / La(OH)3 nanocomposite. In the nanocomposite prepared by the application, the addition of Ti3C2-MXene and other components can effectively expand the response to the visible light region, and the introduction of Ag2O nanoparticles promotes the separation and transfer of carriers. The Ti3C2 / Ag2O / La(OH)3 nanocomposite exhibits obvious photocatalytic activity under visible light due to the synergistic effect of Ti3C2-MXene and Ag2O. The application provides a new physical basis for the development of heterostructure photocatalysts. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A schematic diagram for preparation of the Ti3C2 / Ag2O / La(OH)3 nanocomposite of the application;

[0020] Figure 2 XRD pattern (A) and FT-IR spectrum (B) of the Ti3C2 / Ag2O / La(OH)3 nanocomposite prepared by the application and pure La(OH)3 material, Ag2O / La(OH)3 material and Ti3C2 / La(OH)3 material; Figure 2 A) and FT-IR spectrum (B) of the Ti3C2 / Ag2O / La(OH)3 nanocomposite prepared by the application and pure La(OH)3 material, Ag2O / La(OH)3 material and Ti3C2 / La(OH)3 material; Figure 2 B);

[0021] Figure 3 X-ray photoelectron spectra of the Ti3C2 / Ag2O / La(OH)3 nanocomposite material, pure La(OH)3 material, Ag2O / La(OH)3 material, and Ti3C2 / La(OH)3 material prepared in this invention;

[0022] Figure 4 The Ti3C2 / Ag2O / La(OH)3 nanocomposite material prepared in this invention ( Figure 4 B) and pure La(OH)3 materials ( Figure 4 A) SEM image;

[0023] Figure 5 These are TEM and HR-TEM images of the Ti3C2 / Ag2O / La(OH)3 nanocomposite material and pure La(OH)3 material prepared in this invention, wherein... Figure 5 A is a TEM image of pure La(OH)3 material. Figure 5 B is the HR-TEM image of pure La(OH)3 material. Figure 5 C is a TEM image of the Ti3C2 / Ag2O / La(OH)3 nanocomposite material. Figure 5 D is the HR-TEM image of the Ti3C2 / Ag2O / La(OH)3 nanocomposite material;

[0024] Figure 6 The BET surface area of ​​the Ti3C2 / Ag2O / La(OH)3 nanocomposite material, pure La(OH)3 material, Ag2O / La(OH)3 material, and Ti3C2 / La(OH)3 material prepared in this invention is ( ) Figure 6 A) and pore size distribution curve ( Figure 6 B);

[0025] Figure 7 The diffuse reflectance ultraviolet-visible absorption spectra of Ti3C2 / Ag2O / La(OH)3 nanocomposite materials, pure La(OH)3 materials, Ag2O / La(OH)3 materials, and Ti3C2 / La(OH)3 materials prepared in this invention are shown in the following figures. Figure 7 The curves of (A) and (αhv)¹ / ² versus photon energy ( Figure 7 B);

[0026] Figure 8 The photocatalytic activity of the Ti3C2 / Ag2O / La(OH)3 nanocomposite material, pure La(OH)3 material, Ag2O / La(OH)3 material, and Ti3C2 / La(OH)3 material prepared in this invention is shown to be ( Figure 8 A) Absorption spectrum of residual MB ( Figure 8B), the first-order kinetics curve of MB degradation Figure 8 C) and the cyclic performance of Ti3C2 / Ag2O / La(OH)3 nanocomposite MB degradation Figure 8 D);

[0027] Figure 9 The detection diagram of oxide species in the process of photocatalytic degradation of MB by the Ti3C2 / Ag2O / La(OH)3 nanocomposite prepared in the application, wherein, Figure 9 A represents the signal of hydroxyl radicals (·OH), Figure 9 B represents the signal of superoxide radicals (·O 2- );

[0028] Figure 10 The mechanism diagram of photocatalytic degradation of MB by the Ti3C2 / Ag2O / La(OH)3 nanocomposite prepared in the application. DETAILED DESCRIPTION

[0029] The application will be described in detail below in conjunction with the embodiments.

[0030] Embodiment 1:

[0031] At room temperature (25℃), 10.8 g of La(NO3)3·6H2O was dissolved in a mixture of 32 mL of deionized water and 8 mL of NaOH solution (1 mol / L) and stirred vigorously for 30 min. Then, 0.4 mg of Ag2O and 40 mg of Ti3C2 MXene were added to the suspension. After stirring for 1 hour, the entire suspension was transferred to a 50 mL polytetrafluoroethylene-lined autoclave and heated at 150℃ for 24 hours. After natural cooling to room temperature, the obtained precipitate was washed with ethanol and deionized water six times. The obtained precipitate was centrifuged and dried in an oven at 60℃ for 12 hours. The Ti3C2 / Ag2O / La(OH)3 nanocomposite was obtained and denoted as Ti3C2 / Ag2O / La(OH)3-1.

[0032] Embodiment 2:

[0033] In this embodiment, the mass of Ti3C2 MXene is 20 mg, and the Ti3C2 / Ag2O / La(OH)3 nanocomposite prepared in this embodiment is denoted as Ti3C2 / Ag2O / La(OH)3-2.

[0034] In addition, this embodiment is completely the same as embodiment 1, which will not be described here.

[0035] Embodiment 3:

[0036] The present embodiment is substantially the same as embodiment 1, except that the mass of Ti3C2 MXene in the present embodiment is 100 mg. The Ti3C2 / Ag2O / La(OH)3 nanocomposite prepared in the present embodiment is denoted as Ti3C2 / Ag2O / La(OH)3-3.

[0037] In addition, the present embodiment is completely the same as embodiment 1, and will not be described here.

[0038] Comparative Example 1:

[0039] At room temperature (25 °C), 10.8 g of La(N03)3-6H20 was dissolved in a mixture of 32 mL of deionized water and 8 mL of NaOH solution (1 mol / L) with vigorous stirring for 30 min. The entire suspension was transferred to a 50 mL polytetrafluoroethylene-lined autoclave and heated at 150 °C for 24 hours. After natural cooling to room temperature, the obtained precipitate was washed with ethanol and deionized water six times. The obtained precipitate was centrifuged and dried in an oven at 60 °C for 12 hours to obtain pure La(OH)3material.

[0040] Comparative Example 2:

[0041] At room temperature (25 °C), 10.8 g of La(N03)3-6H20 was dissolved in a mixture of 32 mL of deionized water and 8 mL of NaOH solution (1 mol / L) with vigorous stirring for 30 min. Then, 0.4 mg of Ag20 was added to the suspension. After stirring for 1 hour, the entire suspension was transferred to a 50 mL polytetrafluoroethylene-lined autoclave and heated at 150 °C for 24 hours. After natural cooling to room temperature, the obtained precipitate was washed with ethanol and deionized water six times. The obtained precipitate was centrifuged and dried in an oven at 60 °C for 12 hours to obtain Ag20 / La(OH)3material.

[0042] Comparative Example 3:

[0043] At room temperature (25 °C), 10.8 g of La(N03)3-6H20 was dissolved in a mixture of 32 mL of deionized water and 8 mL of NaOH solution (1 mol / L) with vigorous stirring for 30 min. Then, 40 mg of Ti3C2 MXene was added to the suspension. After stirring for 1 hour, the entire suspension was transferred to a 50 mL polytetrafluoroethylene-lined autoclave and heated at 150 °C for 24 hours. After natural cooling to room temperature, the obtained precipitate was washed with ethanol and deionized water six times. The obtained precipitate was centrifuged and dried in an oven at 60 °C for 12 hours to obtain Ti3C2 / La(OH)3material.

[0044] The Ti3C2 / Ag2O / La(OH)3nanocomposites prepared in the embodiments and the pure La(OH)3, Ag2O / La(OH)3, Ti3C2 / La(OH)3prepared in the comparative examples were characterized and analyzed for performance, and the results were as follows:

[0045] I. Material characterization:

[0046] 1. The XRD patterns of the pure La(OH)3, Ag2O / La(OH)3, Ti3C2 / La(OH)3prepared in the comparative examples and the Ti3C2 / Ag2O / La(OH)3material prepared in the embodiments are shown in FIG. 1A, to check the phase composition and crystal structure of the prepared photocatalysts. The results showed that the diffraction peaks of the pure La(OH)3sample at 15.6 Figure 2 A, 27.3 o , 28.0 o , 31.6 o , 39.5 o , 48.2 o , and 48.6 o were consistent with the standard XRD card (JCPDS. No. 36-1481) of La(OH)3, which could be attributed to the (100), (110), (101), (200), (201), (300), and (211) crystal planes of La(OH)3. o Figure 2 No other impurity diffraction peaks related to La species were detected in FIG. 1A, indicating that only La(OH)3crystals existed in this work. The XRD peaks of the Ag2O / La(OH)3, Ti3C2 / La(OH)3, and Ti3C2 / Ag2O / La(OH)3samples were basically consistent with those of the pure La(OH)3sample. This indicated that the addition of Ag2O and / or Ti3C2-MXene did not change the crystal structure of La(OH)3. It should be noted that in this work, almost no XRD peaks related to Ag2O and Ti3C2 MXene were detected. This could be due to the relatively low content of Ag2O (nominal 0.4 mg) and Ti3C2 MXene (nominal 40 mg) compared with La(OH)3(nominal 475 mg). XPS and SEM characterization could effectively confirm the presence of Ag2O (nominal 0.4 mg) and Ti3C2 MXene.

[0047] 2. FT-IR spectroscopy is an effective characterization means for determining the presence of La(OH)3, especially OH- groups. The FT-IR spectra of the pure La(OH)3, Ag2O / La(OH)3, Ti3C2 / La(OH)3prepared in the comparative examples and the Ti3C2 / Ag2O / La(OH)3material prepared in the embodiments are shown in FIG. 2A. Figure 2 ​B. For all La(OH)3-based samples, a strong and sharp peak was observed at 3609 cm -1 -1, which is attributed to the stretching vibration of O-H bond in La(OH)3. The latter two weak peaks at 3414 cm -1 -1 and 1640 cm -1 -1 are attributed to the hydroxyl groups from the surface-adsorbed H2O molecules. In addition, the three strong peaks around 1492 cm -1 -1, 1384 cm -1 -1 and 850 cm -1 -1 are caused by the surface carbonate groups. The CO2 molecules in air react with H2O molecules to form carbonate, which is usually detected on the surface of La(OH)3. The last strong peak at around 647 cm -1 -1 is attributed to the stretching vibration of La-O-H bond. Therefore, the FT-IR spectra confirm the successful synthesis of La(OH)3. In addition, the peaks related to Ag2O and Ti3C2 MXene are still not detected due to the low content of Ag2O and Ti3C2 MXene.

[0048] 3. X-ray photoelectron spectroscopy (XPS) measurements were performed on the Ti3C2 / Ag2O / La(OH)3 samples to investigate the chemical states of the corresponding elements, confirming the coexistence of Ag2O and Ti3C2-MXene. Figure 3 A shows the typical La3d5 / 2 and La3d3 / 2 XPS spectra. The doublet structure is shown in Figure 3 A. The main peaks of La3d5 / 2 and La3d3 / 2 for La(OH)3 are at 835.0 eV and 851.8 eV, respectively. The other two peaks at 838.6 eV and 855.6 eV can be attributed to the La3d5 / 2 and La3d3 / 2 peaks, respectively, with higher binding energies than the main peaks, due to the O2p participation in the oscillation process → La4f charge transfer. Figure 3 B shows the O1s spectra of the Ti3C2 / Ag2O / La(OH)3 samples. The O1s peak can be fitted into two peaks at 530.8 eV and 532.0 eV, respectively. The strong peak at about 530.8 eV can be attributed to the lattice oxygen ions, and the weak peak at about 532.0 eV can be attributed to the surface-adsorbed hydroxyl species. Figure 3 C shows the XPS Ag 3d spectra of the Ti3C2 / Ag2O / La(OH)3 samples. A pair of weak peaks at 367.5 eV and 373.6 eV is observed, which is due to the Ag 3d5 / 2 and Ag 3d3 / 2 of Ag2O. Figure 3D shows the Ti 2p spectra of the Ti3C2 / Ag2O / La(OH)3 sample. Two weak peaks are observed at 455.4 eV and 458.1 eV, the former (455.4 eV) can be attributed to Ti-C bond, the latter (458.1 eV) can be attributed to Ti-O bond. The XPS results show that both Ag2O and Ti3C2 MXene exist in the Ti3C2 / Ag2O / La(OH)3 sample.

[0049] 4. To investigate the morphology of the prepared La(OH)3-based sample, the SEM images of pure La(OH)3 and Ti3C2 / Ag2O / La(OH)3 sample are shown in Figure 4 A and B. Figure 4 A shows the SEM image of the La(OH)3 sample, which is composed of many one-dimensional nanorods. The average length of these nanorods is about 200 nm-500 nm. Figure 4 B shows the SEM image of the Ti3C2 / Ag2O / La(OH)3 sample. Ti3C2-MXene has a unique layered structure. La(OH)3 nanorods are randomly dispersed on the surface of Ti3C2-MXene layered structure. The results show that the photo-induced electrons and holes between La(OH)3 nanorods and Ti3C2 MXene are easily transferred. To further investigate the morphology of the La(OH)3-based sample, TEM images will be shown in the following section.

[0050] 5. To investigate the morphology and surface microstructure of the La(OH)3-based sample, the TEM and HR-TEM images of (A and B) La(OH)3 and (C and D) Ti3C2 / Ag2O / La(OH)3 sample are shown in Figure 5 . Figure 5 A shows a typical TEM image of La(OH)3 nanorods. The pure La(OH)3 sample is composed of many one-dimensional nanorods. The length of the nanorods varies from 100 nm to 500 nm, and the diameter is about 12 nm. Figure 5 B is the HR-TEM image of La(OH)3 nanorods. The lattice spacing is 0.319 nm, corresponding to the (101) plane of La(OH)3. As shown in Figure 5 C, the layered structure of Ti3C2 MXene, the nanoparticle structure of Ag2O and the rod-like nanostructure of La(OH)3 are observed. As shown in Figure 5 D, it is found that the lattice spacing is 0.337 nm, corresponding to the (110) plane of Ag2O. In addition, another clear lattice spacing of 0.282 nm is observed on the (200) plane of La(OH)3. The TEM results confirm the coexistence of Ti3C2-MXene, Ag2O nanoparticles and La(OH)3 nanorods. La(OH)3 nanorods and Ag2O nanoparticles are dispersed on the surface of Ti3C2-MXene.2 - The MXene surface forms a close interfacial contact, which is beneficial for the transfer and separation of carriers.

[0051] 6、N2 adsorption-desorption characterization was used to study the BET surface area (SBET) of pure La(OH)3, Ag2O / La(OH)3, Ti3C2 / La(OH)3 and Ti3C2 / Ag2O / La(OH)3 nanocomposite photocatalysts prepared in the comparative examples, as shown in Figure 6 A. All samples showed typical type IV isotherms, indicating that the La(OH)3-based nanorod photocatalysts had mesoporous structures. The hysteresis curve of H3 showed high adsorption at relatively high pressure (0.9-1.0), indicating the presence of mesopores and macropores. The pore size distribution curves of pure La(OH)3, Ag2O / La(OH)3, Ti3C2 / La(OH)3 and Ti3C2 / Ag2O / La(OH)3 nanorod photocatalysts are shown in Figure 6 B. All La(OH)3 nanorod photocatalysts included mesopores and macropores in the range of 20-100 nm. The main peak of the pore size distribution was concentrated in the range of 40-50 nm. These results further demonstrated the presence of hierarchical mesoporous and macroporous structures in this study. SEM and TEM analysis showed that the aggregation of La(OH)3 nanorods formed an ordered structure of mesopores and macropores. The specific surface area, pore volume and pore size of pure La(OH)3, Ag2O / La(OH)3, Ti3C2 / La(OH)3 and Ti3C2 / Ag2O / La(OH)3 nanorod photocatalysts. The specific surface area of La(OH)3 nanorods increased with the addition of Ti3C2 MXene and decreased with the addition of Ag2O.

[0052] II. Performance analysis:

[0053] 1. The band structure of semiconductor photocatalysts is a key factor affecting their photocatalytic performance. In order to better understand the band structure of these La(OH)3-based photocatalysts, the diffuse reflectance ultraviolet-visible absorption spectra of pure La(OH)3, Ag2O / La(OH)3, Ti3C2 / La(OH)3 and Ti3C2 / Ag2O / La(OH)3 samples are shown in Figure 7As shown in Figure A, pure La(OH)3 nanorods exhibit strong absorption in the deep ultraviolet band of 200–300 nm. This strong absorption is attributed to interband transitions of electrons. After Ag2O is combined with La(OH)3, the Ag2O / La(OH)3 sample shows a weak absorption peak near 400 nm, which is due to electronic transitions induced by Ag2O. This indicates that the introduction of Ag2O can effectively extend the response to the visible light region. In addition to strong absorption in the ultraviolet region, Ti3C2 / La(OH)3 and Ti3C2 / Ag2O / La(OH)3 samples also exhibit strong broad absorption in the 300–800 nm range. This is due to the continuous band structure of Ti3C2-MXene. Furthermore, compared with Ti3C2 / Ag2O / La(OH)3, the absorption spectrum of the Ti3C2 / Ag2O / La(OH)3 sample is further enhanced due to the contribution of Ag2O. Therefore, introducing Ag₂O and Ti₃C₂-MXene into La(OH)₃ nanorods can effectively improve the optical response of the nanorods. The enhanced light response, especially the visible light response, can induce more charge carriers to participate in the photocatalytic reaction, ultimately improving the photocatalytic activity.

[0054] The band gap of La(OH)3-based photocatalysts is calculated using the formula: (αhv)n = k(hv - Eg). Since La(OH)3 is an indirect semiconductor, this work estimates n to be 1 / 2. Therefore, the band gap of these La(OH)3-based photocatalysts can be determined by plotting (αhv)1 / 2 against photon energy, as shown below. Figure 7 As shown in Figure B, the band gap of La(OH)3 is 3.82 eV, indicating that the introduction of Ag2O and Ti3C2-MXene did not change the band structure of the La(OH)3 nanorods. The band gap of the Ti3C2 / La(OH)3 sample is 1.33 eV, which is related to the band gap of Ag2O. It is well known that the potentials of the conduction band and valence band are closely related to the generation of reactive free radicals. The valence band potential was determined using EVB = X - EC + 0.5Eg, where X is the electronegativity of the semiconductor, EC is the energy of the free electron on the hydrogen scale (4.5 eV), and Eg is the band gap of the semiconductor. The X values ​​for Ag2O and La(OH)3 are 5.29 eV and 5.67 eV, respectively. The band gaps for Ag2O and La(OH)3 are 1.33 eV and 3.82 eV, respectively. The calculated valence band potentials for Ag2O and La(OH)3 are +1.46 V and +3.08 V, respectively. Furthermore, the conduction band potential can be determined by the following equation: ECB = EVB – Eg. Therefore, the conduction band potentials of La(OH)3 and Ag2O are estimated to be -0.74 V and +0.13 V, respectively.

[0055] 2. The photocatalytic performance of the pure La(OH)3, Ag2O / La(OH)3, Ti3C2 / La(OH)3 prepared in the comparative example and the Ti3C2 / Ag2O / La(OH)3 material prepared in the embodiment was evaluated by degradation under visible light irradiation by MB (λ>420 nm). Figure 8 (A) Photocatalytic activity of pure La(OH)3, Ag2O / La(OH)3, Ti3C2 / La(OH)3, and Ti3C2 / Ag2O / La(OH)3 samples; (B) Absorption spectra of residual MB in Ti3C2 / Ag2O / La(OH)3 samples under different irradiation times; (C) First-order kinetic curves of MB degradation in pure La(OH)3, Ag2O / La(OH)3, Ti3C2 / La(OH)3, and Ti3C2 / Ag2O / La(OH)3 samples; (D) Cyclic performance of MB degradation in Ti3C2 / Ag2O / La(OH)3 samples. The photocatalytic performance of pure La(OH)3, Ag2O / La(OH)3, Ti3C2 / La(OH)3, and Ti3C2 / Ag2O / La(OH)3 samples was evaluated by MB degradation under visible light irradiation (λ>420 nm). Figure 8 As shown in Figure A. In the blank experiment, without the addition of any photocatalyst, MB was difficult to decompose. Pure Ti3C2 samples also failed to decompose MB under irradiation. Pure La(OH)3 samples showed poor photocatalytic performance after 80 minutes of irradiation; the MB degradation rate was less than 20% after 80 minutes of irradiation. After Ag2O composite, the photocatalytic activity of Ag2O / La(OH)3 was slightly improved. The MB decomposition rate was approximately 29%, and the reaction coefficient (k value) was 4.05 × 10⁻³ min⁻¹ (see Figure A). Figure 3 C). The introduction of Ti3C2-MXene can effectively improve photocatalytic performance. After irradiation for 80 min, 70% of the methylene blue was degraded. Figure 8The k value of the Ti3C2 / La(OH)3 sample in C was estimated to be 1.41 x 10-2min-1, which was almost 5.7 times that of the pure La(OH)3 sample (2.48 x 10-3min-1). The Ti3C2 / Ag2O / La(OH)3 sample exhibited the best photocatalytic performance due to the coexistence of Ag2O and Ti3C2-MXene. After 80 min of irradiation, about 93% of methylene blue was degraded. The reaction coefficient (k value) was 3.29 x 10-2min-1, which was 2 times, 8 times and 13 times that of the Ti3C2 / La(OH)3 sample (1.41 x 10-2min-1), the Ag2O / La(OH)3 sample (4.05 x 10-3min-1) and the pure La(OH)3 sample (2.48 x 10-3min-1), respectively. The absorption spectra of the residual MB at different times in the presence of the Ti3C2 / Ag2O / La(OH)3 sample are shown in Figure 8 B. With the extension of irradiation time, the main absorption peak centered at 660 nm gradually weakened, indicating that the MB molecules were decomposed into CO2 and H2O. In addition, the stability and reusability of the Ti3C2 / Ag2O / La(OH)3 sample are shown in Figure 8 D. After 5 cycles of experiments, the Ti3C2 / Ag2O / La(OH)3 sample still had good photocatalytic performance and there was no obvious loss of photocatalytic activity.

[0056] 3. The generation of oxidizing species is one of the key factors in the photocatalytic degradation process. ESR (electron spin resonance) is generally considered to be a powerful characterization technique for detecting oxidizing species. DMPO (5,5-dimethyl-1-pyrroline-N-oxide) is commonly used to capture hydroxyl radicals (·OH) and superoxide radicals (·O 2- ). In a mixture of 10 mg photocatalyst and 0.5 mL methanol, 45 μL DMPO was added. After 5 min of ultrasonic treatment, the signals of hydroxyl radicals (·OH) and superoxide radicals (·O 2- ) were recorded after 5 min and 10 min of irradiation in the dark, as shown in Figure 9 . After 5 min of irradiation, the hydroxyl radical signal was clearly visible, and after 10 min of irradiation, the signal peak intensity was further enhanced. At the same time, with the extension of irradiation time, the superoxide radical signal was enhanced. In addition, it should be noted that the signal intensity of superoxide radicals was quite weak, indicating that only a small amount of superoxide radicals (·O 2- ) were generated under irradiation. Therefore, it can be reasonably concluded that the hydroxyl radicals (·OH) are the main oxidizing species of the Ti3C2 / Ag2O / La(OH)3 sample. These generated hydroxyl radicals (·OH) will react with MB molecules to generate final products H2O and CO2.

[0057] 4、Based on the experimental data and analysis, the mechanism of the prepared Ti3C2 / Ag2O / La(OH)3 material for photocatalytic degradation of MB is as shown in Figure 10 For pure La(OH)3nanorods, due to the larger band gap of La(OH)3(3.82 eV), it is difficult to excite electrons and holes under visible light irradiation (λ>420 nm). For the Ag2O / La(OH)3sample, due to the introduction of Ag2O, the visible light response is extended in the visible light region. Under visible light irradiation (λ>420 nm), electrons are excited from the valence band of Ag2O to the conduction band of Ag2O. Since the bottom of the conduction band of La(OH)3is more negative than that of Ag2O, the photoexcited electrons in the conduction band of Ag2O cannot transfer to the conduction band of La(OH)3, but recombine with the holes in the valence band. The photo-generated electrons and holes cannot be effectively separated. Therefore, compared with pure La(OH)3, the photocatalytic activity of the Ag2O / La(OH)3sample is only slightly improved. For the Ti3C2 / La(OH)3sample, due to the continuous energy band structure of Ti3C2-MXene, the visible light response is effectively enhanced. The electrons on the Fermi level of Ti3C2-MXene can be excited to the conduction band of La(OH)3nanorods, and further participate in the photocatalytic reaction. Therefore, the photocatalytic activity of the Ti3C2 / La(OH)3sample is significantly higher than that of pure La(OH)3and the Ag2O / La(OH)3sample.

[0058] Compared with the Ti3C2 / La(OH)3sample, the visible light response of the Ti3C2 / Ag2O / La(OH)3sample is slightly improved. The photocatalytic performance of the Ti3C2 / Ag2O / La(OH)3sample is significantly better than that of the Ti3C2 / La(OH)3sample. Under visible light irradiation, electrons can be excited from the Fermi level of Ti3C2 MXene to the conduction band of La(OH)3. In addition, the excited electrons in the conduction band of La(OH)3will further transfer to the conduction band of Ag2O, effectively separating the charge carriers. These charge carriers can react with the O2 molecules adsorbed on the surface to produce redox active species, degrading the MB molecules.

[0059] In addition, it is noted in Figure 10 that the conduction band bottom of Ag2O is more negative than the oxidation-reduction potential of O 2 / 2 2- (-0.33 eV, vs-NHE). The electrons in the conduction band of Ag2O cannot reduce O 2 to O 2- species. These electrons will recombine with O 2 and H +The reaction generates H2O2, which will further react with electrons to generate hydroxyl radicals (•OH). This is probably the reason why hydroxyl radicals (•OH) are the main oxidizing species in this work. Hydroxyl radicals (•OH) have strong redox ability and can degrade organic pollutants into CO2 and H2O. In addition, the holes on the valence band of La(OH)3 and Ag2O can also directly oxidize MB molecules into CO2 and H2O. The results show that the Ti3C2 / Ag2O / La(OH)3 sample has the best photocatalytic activity for methylene blue under visible light.

[0060] In summary, the present application uses one-pot hydrothermal method to prepare a new type of heterojunction Ti3C2 / Ag2O / La(OH)3 nanocomposite. In this material, the addition of Ti3C2-MXene and other components can effectively extend the response to the visible light region, and the introduction of Ag2O nanoparticles promotes the separation and transfer of carriers. The Ti3C2 / Ag2O / La(OH)3 nanocomposite prepared by the present application exhibits obvious photocatalytic activity under visible light due to the synergistic effect of Ti3C2-MXene and Ag2O. In addition, the present application proposes a possible mechanism for the catalytic decomposition of MB by Ti3C2 / Ag2O / La(OH)3 nanocomposite. The present application provides a new physical basis for the development of heterojunction photocatalysts.

[0061] The above-mentioned embodiments are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent transformation or modification made according to the spirit and essence of the present application should be covered within the protection scope of the present application.

Claims

1. A method for preparing a Ti3C2 / Ag2O / La(OH)3 nanocomposite material, characterized in that, Includes the following steps: S1. Dissolve La(NO3)3·6H2O in a mixture of deionized water and NaOH solution, and stir vigorously to obtain a suspension; S2. Add Ag2O and Ti3C2 MXene to the suspension, stir, place in an autoclave for heating, cool, and collect the precipitate; S3. The precipitate was washed multiple times with ethanol and deionized water, centrifuged, and dried to obtain Ti3C2 / Ag2O / La(OH)3 nanocomposite material.

2. The method for preparing the Ti3C2 / Ag2O / La(OH)3 nanocomposite material according to claim 1, characterized in that: The mass ratio of La(NO3)3·6H2O, Ag2O and Ti3C2 MXene is 10.8g:0.4g:20~100 mg.

3. The method for preparing the Ti3C2 / Ag2O / La(OH)3 nanocomposite material according to claim 1, characterized in that: In S1, the concentration of the NaOH solution is 1 mol / L.

4. The method for preparing the Ti3C2 / Ag2O / La(OH)3 nanocomposite material according to claim 1, characterized in that: In S1, the volume ratio of the NaOH solution to the deionized water is 1:

4.

5. The method for preparing the Ti3C2 / Ag2O / La(OH)3 nanocomposite material according to claim 1, characterized in that: In S2, the specific heating conditions are: heating temperature of 150-180℃ and heating time of 24-26h.

6. The method for preparing the Ti3C2 / Ag2O / La(OH)3 nanocomposite material according to claim 1, characterized in that: In S3, the washing is performed 5-6 times.

7. The method for preparing the Ti3C2 / Ag2O / La(OH)3 nanocomposite material according to claim 1, characterized in that: In S3, the specific drying conditions are: drying temperature 55-65℃, drying time 10-14h.

8. The method for preparing the Ti3C2 / Ag2O / La(OH)3 nanocomposite material according to claim 1, characterized in that: In S1, the vigorous stirring time is 20-30 min.

9. The application of a Ti3C2 / Ag2O / La(OH)3 nanocomposite material prepared by any one of claims 1-8 in the photocatalytic decomposition of methylene blue.

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