A Z-type heterojunction composite material, its preparation method and application

Abstract

This invention belongs to the field of photoelectric active materials and photoelectric sensing analysis technology, specifically relating to a Z-type heterojunction composite material, its preparation method, and its application. The composite material uses Ti-MOF as a precursor, annealing to obtain carboxyl-functionalized p-type 2DTiO2@C nanocakes. Chemical reduction forms AuNPs in situ on the surface of the 2DTiO2@C nanocakes, obtaining p-type 2DTiO2@C / Au nanocakes. Amino-modified p-type 3D peony-shaped BiOI is added to the p-type 2DTiO2@C / Au nanocakes, and electrostatic interaction yields the 2DTiO2@C / Au / 3DBiOI Z-type heterojunction composite material. This invention uses a metal-organic framework template-assisted calcination method, chemical reduction, and electrostatic interaction to design and prepare the Z-type heterojunction composite material, improving photoelectric activity and achieving rapid, highly sensitive, accurate, and reliable detection of hexavalent chromium ions.

Description

Technical Field

[0001] This invention belongs to the fields of photoelectric active materials and photoelectric sensing and analysis technology, specifically relating to a Z-type heterojunction composite material, its preparation method, and its application. Background Technology

[0002] Heavy metal ion pollution, as one of the most serious problems posing a threat to the natural environment and human health, has attracted widespread attention. According to the International Agency for Research on Cancer (IARC) classification (Group I), hexavalent chromium (Cr(VI)) ions can cause genetic defects, genotoxic tumors, allergies, and asthma, and harm the environment through accumulation in the surrounding environment and food chain, thus attracting researchers' attention. Therefore, the detection of Cr(VI) ions is of great significance for environmental protection, human health, and food safety. Currently, various methods have been developed for the detection of Cr(VI) ions, including electrochemical analysis, fluorescence spectroscopy, ion chromatography, atomic absorption spectrometry, high-performance liquid chromatography-inductively coupled plasma mass spectrometry, and colorimetric detection. Although the above detection methods have considerable sensitivity and accuracy, they suffer from drawbacks such as complex and laborious processes, expensive equipment, and the need for specialized operators. In contrast, photoelectrochemical (PEC) sensors, with their advantages of low cost, fast response, ease of operation, and high sensitivity, have become the focus of researchers' attention.

[0003] Since the detection performance of PEC sensors mainly depends on the photoelectric active materials, selecting and designing suitable semiconductor materials is crucial for developing high-performance PEC sensors. Currently, researchers have developed various photoelectric materials to improve the sensitivity of PEC sensors. However, individual photoelectric materials and traditional heterojunctions often suffer from problems such as small light absorption range and low electron-hole separation efficiency. Therefore, exploring novel photoelectric materials with high photoelectric conversion efficiency has become an inevitable trend. Morphology manipulation and heterostructure construction can improve the photoelectric activity of materials. With the development of nanostructure engineering in morphology manipulation, zero-dimensional (0D) quantum dots, one-dimensional (1D) nanorods, two-dimensional (2D) nanopancakes, and three-dimensional (3D) flower-like nanostructures have been developed as excellent photoelectric materials.

[0004] Heterostructure construction has been proven to be an effective method for suppressing the recombination of photogenerated electron-hole pairs. However, traditional heterostructures such as type II heterostructures, Schottky junctions, and homostructures have low electron-hole separation efficiency and insufficient photoelectric conversion efficiency. Therefore, how to construct Z-type heterostructure composite materials with excellent photoelectric properties to form photoelectrochemical (PEC) sensors for the analysis and detection of Cr(VI) ions, thus contributing to environmental monitoring and human health protection, remains a challenge. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a Z-type heterojunction composite material, its preparation method, and its application. This Z-type heterojunction material is the first to be designed and prepared using a metal-organic framework (MOF) template-assisted calcination method, chemical reduction, and electrostatic interaction, which improves photoelectric activity. Based on this, rapid, low-cost, highly sensitive, and accurate and reliable Cr(VI) ion detection is achieved.

[0006] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0007] The first objective of this application is to provide a Z-type heterojunction composite material, wherein the composite material uses Ti-MOF as a precursor, and annealing at 300-400℃ yields carboxyl-functionalized p-type 2D TiO2@C nanocakes. HAuCl4 is chemically reduced to form AuNPs in situ on the surface of the 2D TiO2@C nanocakes, resulting in p-type 2D TiO2@C / Au nanocakes. Then, amino-modified p-type 3D peony-shaped BiOI is added to the p-type 2D TiO2@C / Au nanocakes, and 2D TiO2@C / Au / 3D BiOI Z-type heterojunction composite material is obtained through electrostatic interaction.

[0008] The second objective of this application is to provide a method for preparing the aforementioned Z-type heterojunction composite material, comprising the following steps:

[0009] Preparation of S1 and 2D TiO2@C nanocakes: 1,4-phthalic acid was dissolved in a mixed solvent to form a mixed solution, and then tetrabutyl titanate was added and mixed evenly. After the reaction was completed, centrifugation, washing and drying were performed to obtain Ti-MOF precursor. The Ti-MOF precursor was annealed at 300-400℃ to obtain carboxyl-functionalized p-type 2D TiO2@C nanocakes.

[0010] Preparation of S2 and 2D TiO2@C / Au nanocakes: p-type 2D TiO2@C nanocakes were dispersed in water, HAuCl4 solution was added to form a suspension, then NaBH4 solution was added, and a reduction reaction was carried out at room temperature. After the reaction was completed, the p-type 2D TiO2@C / Au nanocakes were obtained by centrifugation, washing and drying.

[0011] S3. An amino-modified 3D peony-shaped BiOI suspension was added to a carboxyl-functionalized 2D TiO2@C / Au nanocake suspension. After stirring at room temperature, the mixture was centrifuged, washed, and dried to obtain a Z-shaped heterojunction composite material.

[0012] Preferably, in S1, the mass-to-volume ratio of 1,4-phthalic acid, the mixed solvent, and tetrabutyl titanate is 2.5–4.5 g: 49–70 mL: 2.5–4.0 mL, and the mixed solvent is N,N-dimethylformamide and anhydrous methanol mixed in a volume ratio of 44–60 mL: 5–10 mL.

[0013] Preferably, in S1, the temperature of the solvothermal reaction is 100-200°C, the time is 24-54 h, the drying is carried out overnight at 60°C, the annealing time is 4-8 h, and the heating rate is 2-15°C / min.

[0014] Preferably, in S2, the mass-to-volume ratio of the p-type 2D TiO2@C nanocake, water, HAuCl4 solution, and NaBH4 solution is 200–600 mg: 200–400 mL: 2–5 mL: 15–30 mL, the concentration of the HAuCl4 solution is 5–20 wt.%, the concentration of the NaBH4 solution is 0.05–1.2 M, the room temperature reduction reaction time is 15 min, and the drying is performed under vacuum at 60 °C to constant weight.

[0015] Preferably, in step S3, the method for preparing the amino-modified 3D peony-shaped BiOI includes the following steps:

[0016] Bi(NO3)3·5H2O was dissolved in ethanol to form solution A, and KI was dissolved in water to form solution B. The two solutions were mixed and stirred for 1 h to carry out a solvothermal reaction. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain 3D peony-shaped p-type BiOI. The 3D peony-shaped p-type BiOI was dispersed in the mixed solution by ultrasonic dispersion, and then aminopropyltriethoxysilane was added. The mixture was stirred for 12 h and reacted at 75 °C. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain amino-modified 3D peony-shaped BiOI.

[0017] Preferably, the molar volume ratio of Bi(NO3)3·5H2O to ethanol is 1.5 mmol:30 mL, the molar volume ratio of KI to water is 1.5 mmol:30 mL, the volume ratio of solution A to solution B is 1:1, the temperature of the solvothermal reaction is 180 °C, and the time is 12 h.

[0018] Preferably, the mass-to-volume ratio of the 3D peony-shaped p-type BiOI, the mixed solution, and the aminopropyltriethoxysilane is 100 mg: 100 mL: 1 mL. The mixed solution is prepared by mixing ethanol and water in a volume ratio of 19:1. The ultrasonic time is 30 min, the reaction time is 1 h, and the drying is carried out overnight at 60 °C.

[0019] Preferably, in step S3, the volume ratio of the amino-modified 3D peony-shaped BiOI suspension to the carboxyl-functionalized 2D TiO2@C / Au nanocake suspension is 9:1. The amino-modified 3D peony-shaped BiOI suspension is an aqueous solution with a concentration of 1 mg / mL; the carboxyl-functionalized 2D TiO2@C / Au nanocake suspension is an aqueous solution with a concentration of 1 mg / mL; the reaction time at room temperature is 6 h, and the drying is performed under vacuum at 60 °C to constant weight.

[0020] The third objective of this invention is to provide the application of the above-mentioned Z-type heterojunction composite material in photoelectric sensing analysis of hexavalent chromium ions. The 2D TiO2@C / Au / 3D BiOI Z-type heterojunction composite material is used to construct a photoelectrochemical sensor, and the concentration of hexavalent chromium ions is detected by utilizing the photoelectrochemical response of the photoelectrochemical sensor to hexavalent chromium ions.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) In this invention, Ti-MOF (2D MIL-125 nanocake) is used as a precursor. Carboxyl-functionalized p-type 2D TiO2@C nanocake is obtained by calcination. Then, AuNPs are formed in situ on the surface of the 2D TiO2@C nanocake by chemical reduction using HAuCl4 solution to obtain p-type 2D TiO2@C / Au nanocake. Then, amino-modified p-type 3D peony-shaped BiOI and carboxyl-functionalized p-type 2D TiO2@C / Au nanocake are electrostatically interacted to obtain 2D TiO2@C / Au / 3D BiOI Z-type heterojunction composite material.

[0023] Compared to 2D MIL-125 nanocakes, the calcined p-type 2D TiO2@C nanocakes exhibit better conductivity and visible light absorption. AuNPs possess good conductivity and, as electron shuttle media, can accelerate charge transfer, which is more conducive to the formation of Z-type electron transfer paths and effectively inhibits the recombination of photogenerated electron-hole pairs. The p-type BiOI presents a unique 3D peony flower morphology, providing a large surface area and abundant active sites, which can provide a favorable environment for the high dispersion of the modifying components (2D TiO2@C / Au nanocakes) and the diffusion of surface sacrificial agents (ascorbic acid, AA). The layered superposition of multiple petal-shaped structures allows the excitation light to be refracted and reflected multiple times within the system, improving light utilization. The multidimensional electron transport pathways on the 3D peony flower structure help accelerate electron transport. Using AA as a surface sacrificial agent can effectively eliminate photogenerated holes and hinder the recombination of photogenerated electron-hole pairs. The matching band gap and energy level between TiO2@C nanocakes and 3D peony-shaped BiOI facilitates Z-type electron transfer. Based on the excellent optoelectronic properties of the 2D TiO2@C / Au / 3D BiOI Z-type heterojunction, modifying the 2D TiO2@C / Au / 3D BiOI Z-type heterojunction onto an indium tin oxide (ITO) electrode can construct a more sensitive PEC sensor.

[0024] (2) The Z-shaped heterojunction composite material prepared in this invention has enhanced photoelectric signals. The PEC sensor constructed based on this Z-shaped heterojunction composite material has advantages such as high sensitivity, good selectivity, simple operation, rapid analysis, and ease of operation. When Cr(VI) ions are introduced into the detection system, they can compete with the 2D TiO2@C / Au / 3D BiOI Z-shaped heterojunction for the consumption of the surface sacrificial agent AA through a reduction reaction, which makes the PEC signal decrease significantly, thereby realizing the detection of Cr(VI) ions. Within a certain concentration range, the higher the concentration of the analyte, the more obvious the decrease in photocurrent signal. Experimental results show that the magnitude of the decrease in photocurrent signal and the concentration of the analyte exhibit a linear relationship within a certain range, which can achieve highly sensitive detection of the analyte. The preparation and detection methods use less reagent and have low cost. Only a small amount of materials and reagents are needed to achieve highly sensitive detection of Cr(VI) ions. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the preparation process of the Z-type heterojunction composite material of the present invention;

[0026] Figure 2 This is a scanning electron microscope image of the Z-type heterojunction composite material of the present invention;

[0027] Figure 3 The X-ray diffraction pattern of the Z-type heterojunction composite material of the present invention is shown below.

[0028] Figure 4 This is a feasibility experiment diagram of the PEC sensor of the present invention for the analysis and detection of Cr(VI) ions;

[0029] Figure 5 This is a logarithmic calibration curve of the photocurrent response of the PEC sensor of the present invention to different concentrations of Cr(VI) ions;

[0030] Figure 6 This is an experimental diagram showing the specificity of the PEC sensor of the present invention for Cr(VI) ions. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0033] Example 1

[0034] A Z-type heterojunction composite material is disclosed, wherein Ti-MOF is used as a precursor, and carboxyl-functionalized p-type 2D TiO2@C nanocakes are obtained by annealing at 380°C. AuNPs are formed in situ on the surface of the 2D TiO2@C nanocakes by chemical reduction of HAuCl4, resulting in p-type 2D TiO2@C / Au nanocakes. Then, amino-modified p-type 3D peony-shaped BiOI is added to the p-type 2D TiO2@C / Au nanocakes, and 2D TiO2@C / Au / 3D BiOI Z-type heterojunction composite material is obtained through electrostatic interaction.

[0035] The preparation method of the above-mentioned Z-type heterojunction composite material includes the following steps:

[0036] Preparation of S1 and 2D TiO2@C nanocakes: 1,4-phthalic acid (3.3 g) was dissolved in a mixed solvent (54 mL N,N-dimethylformamide and 6 mL anhydrous methanol) and magnetically stirred for 30 min to obtain a uniform and transparent mixed solution. Then, under stirring, tetrabutyl titanate (3.6 mL) was slowly injected into the above solution. After stirring for 20 min, the mixed solution was poured into a high-pressure reactor lined with polytetrafluoroethylene and kept at 150 °C for 48 h. After the reaction was completed, the mixture was naturally cooled to room temperature and the white product Ti-MOF precursor (2D MIL-125 nanocake) was collected by centrifugation, washed 5 times with anhydrous methanol, and dried at 60 °C overnight.

[0037] Preparation of carboxyl-functionalized p-type 2D TiO2@C nanocakes: The prepared 2D MIL-125 was annealed at 380℃ for 5h at a heating rate of 5℃ / min to obtain carboxyl-functionalized p-type 2D TiO2@C nanocakes.

[0038] Preparation of S2 and 2D TiO2@C / Au nanocakes: The obtained p-type 2D TiO2@C nanocakes (500 mg) were dispersed in (250 mL) of ultrapure water. Then, under magnetic stirring, HAuCl4 solution (10 wt.%, 4 mL) was injected into the 2D TiO2@C nanocakes to form a suspension. After stirring for 60 min, NaBH4 solution (0.1 M, 25 mL) was added. AuNPs were formed on the 2D TiO2@C nanocakes through a chemical reduction reaction at room temperature for 15 min. After the reaction, the nanocakes were washed 5 times with ultrapure water and then vacuum dried at 60 °C to constant weight to obtain carboxyl-functionalized 2D TiO2@C / Au nanocakes.

[0039] Preparation of S3 and 3D peony-shaped BiOI-NH2: Bi(NO3)3·5H2O (1.5 mmol) was dissolved in anhydrous ethanol (30 mL) and stirred for 60 min to form solution A; KI (1.5 mmol) was dissolved in ultrapure water (30 mL) and magnetically stirred for 60 min to form solution B; then, solution B was added to solution A under continuous stirring, and an orange-red mixture was formed. The mixture was stirred vigorously for 1 h, then transferred to a high-pressure reactor lined with polytetrafluoroethylene and subjected to a solvothermal reaction at 180 °C for 12 h; after the reaction was completed, the mixture was cooled to room temperature, centrifuged to collect the precipitate, washed 5 times with ultrapure water and ethanol, and dried under vacuum at 60 °C to obtain 3D peony-shaped p-type BiOI;

[0040] Amino modification: 100 mg of 3D peony-shaped BiOI was dispersed in an ethanol / water solution (100 mL, v / v, 19 / 1) and sonicated for 30 min. Then, aminopropyltriethoxysilane (APTES: 1 mL) was added to the suspension under magnetic stirring and stirred for 12 h. The mixture was then heated at 75 °C for 1 h. Finally, 3D peony-shaped p-type BiOI-NH2 was obtained by centrifugation, washed 5 times with ethanol, and dried overnight at 60 °C to obtain amino-modified 3D peony-shaped BiOI.

[0041] Under stirring, an amino-modified 3D peony-shaped BiOI aqueous suspension (1 mg / mL) was added to a carboxyl-functionalized 2D TiO2@C / Au nanocake aqueous suspension (1 mg / mL) (v / v, 9 / 1). The mixture was vigorously stirred for 6 h at room temperature to form a 2D TiO2@C / Au / 3D BiOI Z-shaped heterojunction. After centrifugation, washing five times with ultrapure water, and drying to constant weight in a vacuum at 60°C, the 2D TiO2@C / Au / 3D Z-shaped heterojunction composite material was obtained. The process diagram of the Z-shaped heterojunction material preparation is shown in the figure. Figure 1 As shown.

[0042] The 2D TiO2@C / Au / 3D BiOI Z-type heterocomposite material was characterized using scanning electron microscopy (SEM). Figure 2 This is a SEM image of the 2D TiO2@C / Au / 3D BiOIZ heterojunction composite material of the present invention. Figure 2 As shown, BiOI exhibits a 3D peony-like structure with uniform size, approximately 4.2 μm, assembled from numerous nanosheets. It is also evident that AuNPs adhere to the surface of the 2D TiO2@C nanocake, indicating successful deposition of Au NPs on the 2D TiO2@C nanocake. Furthermore, the 3D peony-like BiOI provides a large surface area for loading the 2D TiO2@C / Au nanocake. For the 2D TiO2@C / Au / 3D BiOI Z-type heterocomposite, its overall appearance is similar to that of pure 3D peony-like BiOI. However, the presence of finely shaped cake-like particles (TiO2@C / Au) on the larger particles (BiOI) creates a distinct interface, indicating the successful preparation of the 2D TiO2@C / Au / 3D BiOI Z-type heterocomposite.

[0043] Furthermore, X-ray diffraction (XRD) was used to characterize the prepared 2D TiO2@C / Au / 3DBiOI Z-type heterocomposite material. Figure 3 The image shows the XRD pattern of the 2D TiO2@C / Au / 3D BiOIZ heterojunction composite material of the present invention. Figure 3In the figure, curve a represents 2D MIL-125 nanoparticles, curve b represents 2D TiO2@C nanoparticles, curve c represents 2D TiO2@C / Au nanoparticles, curve d represents 3D peony-shaped BiOI, and curve e represents a 2D TiO2@C / Au / 3D BiOI Z-shaped heterocomposite material. The results are as follows: Figure 3 As shown, compared with the XRD pattern of the highly crystalline 2D MIL-125 nanopatty (curve a), the XRD pattern of the 2D TiO2@C nanopatty (curve b) indicates that the obtained 2D TiO2@C nanopatty is an amorphous phase, which may be related to the initial transformation stage of anatase TiO2 from titanium oxide clusters and the amorphous carbon groups formed by organic linkages. On the other hand, the 2D TiO2@C nanopatty has a peak at 25°, which may be caused by C in the 2D TiO2@C nanopatty. For the 2D TiO2@C / Au nanopatty (curve c), the new characteristic peaks at 38.2°, 44.3°, 64.7° and 77.8° are attributed to the diffraction of the (111), (200), (220) and (311) crystal planes of Au, respectively, further revealing the successful preparation of the 2D TiO2@C / Au nanopatty. The diffraction peaks (curve d) of the obtained 3D peony-shaped BiOI matched well with the standard card (JCPDS No. 73-2062), indicating the successful synthesis of 3D peony-shaped BiOI. After combining 3D peony-shaped BiOI with 2D TiO2@C / Au nanocakes (curve e), some weak Au diffraction peaks were observed, which were consistent with the XRD peaks of the aforementioned 2D TiO2@C / Au nanocakes. XRD analysis further confirmed that... Figure 1 A Z-type heterocomposite material of 2DTiO2@C / Au / 3D BiOI was successfully prepared.

[0044] Example 2: Construction of the PEC Sensor

[0045] Step 1: Place the ITO electrode in acetone, 1M NaOH in ethanol / water (1:1, v / v) and ultrapure water in sequence, ultrasonically clean it for 20 min with an ultrasonic cleaner, and dry it in an oven at 60℃.

[0046] Step 2: The 2D TiO2@C / Au / 3D BiOI Z-type heterojunction composite material from Example 1 was dispersed in a chitosan solution to form a uniform suspension; then, 20 μL of the suspension was used to modify a surface with an area of ​​0.25 mm². 2 The electrode was placed on a clean ITO electrode and allowed to air dry naturally, and was labeled as TiO2@C / Au / BiOI / ITO electrode.

[0047] Example 3 Feasibility Experiment

[0048] Following the Z-shaped heterojunction composite material and sensor preparation steps in Example 2 above, a TiO2@C / Au / BiOI / ITO electrode was obtained. Using the TiO2@C / Au / BiOI / ITO electrode as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum column electrode as the counter electrode, a three-electrode system was formed. The electrolyte was a 0.1M phosphate buffer solution (PBS, pH = 7.4) containing 0.1 MAA. For PEC detection, a 50 μM Cr(VI) ion sample was added to the electrolyte and reacted at room temperature for 5 min, subsequently used for the photoelectrochemical signal response of the TiO2@C / Au / BiOI / ITO electrode. The photoelectrochemical detection conditions used were: chronoamperometry, bias voltage: -0.3V; illumination time: 10 s.

[0049] By changing the concentration of Cr(VI) ions (10 nM to 200 μM) in the above detection solution, and following the same other steps, the analysis and detection of Cr(VI) ions can be achieved.

[0050] Figure 4 This is a feasibility experiment diagram for the PEC sensor of this invention to analyze and detect Cr(VI) ions. The results are as follows: Figure 4 It can be seen that the TiO2@C / Au / BiOI / ITO electrode has a significant photoelectrochemical response to Cr(VI) ions, indicating that the PEC sensor can be applied to the detection of Cr(VI) ions.

[0051] Example 4: Detection of Cr(VI) ions

[0052] A three-electrode system was formed using a TiO2@C / Au / BiOI / ITO electrode as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum column electrode as the counter electrode. Photoelectrochemical detection was initiated, and the photocurrent intensity and the photoelectric response of Cr(VI) ions in Example 3 were measured. Photocurrent response values ​​were recorded when different concentrations of Cr(VI) ions (0.01, 0.05, 0.1, 0.5, 1, 10, 50, 100, 150, 200 μM) of Cr(VI) ions were added to the electrolyte. A series of photocurrent values ​​corresponding to different concentrations of Cr(VI) ions were obtained, and a quantitative relationship between the photocurrent value and Cr(VI) ions was established. Based on this quantitative relationship, the unknown concentration of Cr(VI) ions in the sample could be determined. The photoelectrochemical detection conditions used were: chronoamperometry, bias voltage: -0.3V; illumination time: 10s.

[0053] Figure 5 This is a logarithmic calibration curve of the photocurrent response of the PEC sensor of the present invention to different concentrations of Cr(VI) ions. The results are as follows... Figure 5As shown, the photocurrent response of the sensor to Cr(VI) ions exhibits a good linear relationship with the concentration, and the linear correlation equation is I(nA) = 140.1 log C Cr(VI) -784.6(R 2 =0.9991), with a linear range of 10 nM to 200 μM and a detection limit of 6 nM, indicating that the sensor can achieve highly sensitive detection of Cr(VI) ions.

[0054] Example 5 Specificity Detection

[0055] In the experiment, the concentration of Cr(VI) ions was 50 μM, and the concentration of other ions was 1 mM. Other cations used were as follows: sodium ions (Na... + ), potassium ions (K) + ), magnesium ions (Mg 2+ ), calcium ions (Ca 2+ ), lead ions (Pb) 2+ ), cadmium ions (Cd) 2+ ), cobalt ions (Co) 2+ ), mercury ions (Hg) 2+ Nickel ions (Ni) 3+ Other anions include: chloride ion (Cl...); - ), iodide ions (I) - ), nitrates (NO3) - ), sulfate (SO4) 2- ), acetate (CH3COO) - ), carbonates (CO3) 2- Following the steps of Examples 1, 2, and 3 above, other ions were used instead of Cr(VI) for selective detection.

[0056] Figure 6 This is an experimental diagram illustrating the specificity of the PEC sensor of this invention for Cr(VI) ions. Figure 6 In the figure, Figure A shows cation specificity, and Figure B shows anion specificity. The results are as follows: Figure 6 As shown in Figure A, compared with Cr(VI) ions, other cations did not cause significant changes in the photocurrent signal; the photocurrent values ​​were almost the same as the blank. This indicates that other cations, such as Na... + K + Mg 2+ Ca 2+ Pb 2+ Cd 2+ Co 2+ Hg 2+ Ni 3+ No interference with the system; results as follows Figure 6 As shown in Figure B, other anions did not cause significant changes in the photocurrent signal, and the photocurrent values ​​were almost the same as the blank. Other anions, such as Cl...- I - NO3 - SO4 2- CH3COO - CO3 2- There is no interference with the detection system. Therefore, it can be seen that the PEC sensor constructed based on the 2D TiO2@C / Au / 3DBiOI Z-type heterojunction material of this invention shows good selectivity for the detection of Cr(VI) ions.

[0057] In summary, this invention relates to a 2D TiO2@C / Au / 3D BiOI Z-type heterojunction composite material, its preparation method, and its application in photoelectric sensing analysis of Cr(VI) ions. This Z-type heterojunction composite material exhibits enhanced photoelectric signals. The PEC sensor constructed based on this Z-type heterojunction composite material has advantages such as high sensitivity, good selectivity, simple operation, rapid analysis, and ease of use. It can achieve the detection of low concentrations of Cr(VI) ions and has good prospects for environmental monitoring applications.

[0058] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0059] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A Z-shaped heterojunction composite material, characterized in that, The composite material uses Ti-MOF as a precursor and is annealed at 300-400℃ to obtain carboxyl-functionalized p-type 2DTiO2@C nanocakes. HAuCl4 is chemically reduced to form AuNPs in situ on the surface of the 2DTiO2@C nanocakes to obtain p-type 2DTiO2@C / Au nanocakes. Then, amino-modified p-type 3D peony-shaped BiOI is added to the p-type 2DTiO2@C / Au nanocakes, and 2DTiO2@C / Au / 3DBiOI Z-type heterojunction composite material is obtained through electrostatic interaction.

2. The method for preparing the Z-type heterojunction composite material according to claim 1, characterized in that, Includes the following steps: Preparation of S1, 2DTiO2@C nanocakes: 1,4-phthalic acid was dissolved in a mixed solvent to form a mixed solution, and then tetrabutyl titanate was added and mixed evenly. After the reaction was completed, the solution was centrifuged, washed and dried to obtain Ti-MOF precursor. The Ti-MOF precursor was annealed at 300-400℃ to obtain carboxyl-functionalized p-type 2DTiO2@C nanocakes. Preparation of S2 and 2DTiO2@C / Au nanocakes: p-type 2DTiO2@C nanocakes were dispersed in water, HAuCl4 solution was added to form a suspension, then NaBH4 solution was added, and a reduction reaction was carried out at room temperature. After the reaction was completed, the nanocakes were centrifuged, washed and dried to obtain carboxyl-functionalized 2DTiO2@C / Au nanocakes. S3. An amino-modified 3D peony-shaped BiOI suspension was added to a carboxyl-functionalized 2D TiO2@C / Au nanocake suspension. After stirring at room temperature, the mixture was centrifuged, washed, and dried to obtain a Z-shaped heterojunction composite material.

3. The method for preparing the Z-type heterojunction composite material according to claim 2, characterized in that, In S1, the mass-to-volume ratio of 1,4-phthalic acid, mixed solvent, and tetrabutyl titanate is 2.5–4.5 g: 49–70 mL: 2.5–4.0 mL, and the mixed solvent is N,N-dimethylformamide and anhydrous methanol mixed in a volume ratio of 44–60 mL: 5–10 mL.

4. The method for preparing the Z-type heterojunction composite material according to claim 2, characterized in that, In S1, the temperature of the solvothermal reaction is 100–200°C, the time is 24–54 h, the drying is carried out overnight at 60°C, the annealing time is 4–8 h, and the heating rate is 2–15°C / min.

5. The method for preparing the Z-shaped heterojunction composite material according to claim 2, characterized in that, In S2, the mass-to-volume ratio of the p-type 2DTiO2@C nanocake, water, HAuCl4 solution, and NaBH4 solution is 200–600 mg: 200–400 mL: 2–5 mL: 15–30 mL. The concentration of the HAuCl4 solution is 5–20 wt.%, and the concentration of the NaBH4 solution is 0.05–1.2 M. The room temperature reduction reaction time is 15 min, and the drying is performed under vacuum at 60 °C until constant weight.

6. The method for preparing the Z-type heterojunction composite material according to claim 2, characterized in that, In S3, the preparation method of the amino-modified 3D peony-shaped BiOI includes the following steps: Bi(NO3)3·5H2O was dissolved in ethanol to form solution A, and KI was dissolved in water to form solution B. The two solutions were mixed and stirred for 1 h to carry out a solvothermal reaction. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain 3D peony-shaped p-type BiOI. The 3D peony-shaped p-type BiOI was dispersed in the mixed solution by ultrasonic dispersion, and then aminopropyltriethoxysilane was added. The mixture was stirred for 12 h and reacted at 75 °C. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain amino-modified 3D peony-shaped BiOI.

7. The method for preparing the Z-type heterojunction composite material according to claim 6, characterized in that, The molar volume ratio of Bi(NO3)3·5H2O to ethanol is 1.5 mmol:30 mL, the molar volume ratio of KI to water is 1.5 mmol:30 mL, the volume ratio of solution A to solution B is 1:1, the solvothermal reaction temperature is 180 °C, and the time is 12 h.

8. The method for preparing the Z-type heterojunction composite material according to claim 6, characterized in that, The mass-to-volume ratio of the 3D peony-shaped p-type BiOI, the mixed solution, and the aminopropyltriethoxysilane is 100 mg: 100 mL: 1 mL. The mixed solution is a mixture of ethanol and water in a volume ratio of 19:

1. The ultrasonic time is 30 min, the reaction time is 1 h, and the drying is carried out overnight at 60 °C.

9. The method for preparing the Z-type heterojunction composite material according to claim 2, characterized in that, In step S3, the volume ratio of the amino-modified 3D peony-shaped BiOI suspension to the carboxyl-functionalized 2D TiO2@C / Au nanocake suspension is 9:

1. The amino-modified 3D peony-shaped BiOI suspension is an aqueous solution with a concentration of 1 mg / mL. The carboxyl-functionalized 2D TiO2@C / Au nanocake suspension is an aqueous solution with a concentration of 1 mg / mL. The reaction time at room temperature is 6 h, and the drying is performed under vacuum at 60 °C to constant weight.

10. The application of the Z-type heterojunction composite material according to claim 1 in photoelectric sensing analysis of hexavalent chromium ions, characterized in that, The 2DTiO2@C / Au / 3DBiOIZ heterojunction composite material was used to construct a photoelectrochemical sensor, and the concentration of hexavalent chromium ions was detected by utilizing the photoelectrochemical response of the photoelectrochemical sensor to hexavalent chromium ions.

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