Zinc oxide / polydopamine heterojunction and preparation method thereof and method for adjusting n-pi conjugation interaction strength in interface

Abstract

The application relates to the technical field of semiconductor photocatalysis, in particular to a zinc oxide / polydopamine heterojunction, a preparation method thereof and a method for adjusting the n-pi conjugate interaction strength in the interface. The preparation method of the zinc oxide / polydopamine heterojunction is as follows: zinc oxide nanosheets are dispersed in a polar solvent, triethylenetetramine is added into the obtained zinc oxide dispersion liquid as an interface adjusting agent, the volume of the triethylenetetramine accounts for 2-30% of the total volume of the triethylenetetramine and the polar solvent, after stirring, the temperature of the system is adjusted to below 10 DEG C, then dopamine is added for reaction, after the reaction, the precipitate is collected and freeze-dried. The application uses triethylenetetramine as an interface adjusting agent, and by adjusting the use amount of the interface adjusting agent and the reaction temperature, the n-pi conjugate interaction strength in the ZnO / PDA heterojunction interface is adjusted.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of semiconductor photocatalysis, in particular to a zinc oxide / polydopamine heterojunction, a preparation method thereof and a method for adjusting the n-pi conjugation interaction strength in the interface. BACKGROUND

[0002] Nowadays, a large amount of fossil energy such as coal and oil is the energy guarantee for industrial development. However, the consumption of fossil energy is accompanied by huge emissions of greenhouse gases and environmental harmful substances, leading to increasingly serious greenhouse effect and energy crisis. Photocatalysis can convert carbon dioxide and water into clean chemical fuels such as methane, methanol and formic acid by using solar energy. It not only realizes the clean utilization of solar energy, but also provides a sustainable development prospect.

[0003] ZnO has the advantages of low cost, safety and environmental friendliness, and is considered as a very promising semiconductor photocatalyst. Polydopamine (PDA) as a kind of pi conjugated organic polymer has excellent light capturing ability, strong biological binding performance and good biocompatibility. Therefore, ZnO and PDA can form a heterojunction photocatalyst with n-pi interaction, which has wide application potential in many fields such as biology, medicine, energy and catalysis. However, it still faces great challenges to regulate the n-pi interaction in the ZnO / PDA heterojunction, to affect the dynamic characteristics of photo-generated carriers passing through the interface, and then to regulate the photocatalytic performance of the composite. SUMMARY

[0004] In view of the technical problem that the prior art lacks a method for adjusting the n-pi interaction strength in the ZnO / PDA heterojunction, the application provides a zinc oxide / polydopamine heterojunction, a preparation method thereof and a method for adjusting the n-pi conjugation interaction strength in the interface. Triethylenetetramine is used as an interface regulator, and by adjusting the amount of the interface regulator and the reaction temperature, the n-pi conjugation interaction strength in the interface of the ZnO / PDA heterojunction is regulated.

[0005] In the first aspect, the application provides a preparation method of a zinc oxide / polydopamine heterojunction. ZnO nanosheets are dispersed in a polar solvent, triethylenetetramine is added to the obtained ZnO dispersion as an interface regulator, the volume of the triethylenetetramine accounts for 2% to 30% of the total volume of the triethylenetetramine and the polar solvent, after stirring, the temperature of the system is adjusted to below 10 DEG C, then dopamine is added for reaction, after reaction, the precipitate is collected and freeze-dried, and the zinc oxide / polydopamine heterojunction is obtained.

[0006] Further, the polar solvent is water.

[0007] Further, the temperature of the system is adjusted to 5 to 10 DEG C.

[0008] Further, the zinc oxide nanosheet is added in an amount of 0.05-0.1 g, and the dopamine is added in an amount of 0.01-0.015 g.

[0009] Further, the triethylenetetramine is added in an amount of 2-30 mL, and the polar solvent is added in an amount of 70-98 mL.

[0010] Further, the reaction time for adding the dopamine is 2-5 min.

[0011] Further, the reaction solution and the product are separated by using a suction filtration method, the suction filtration is a kind of rapid filtration method, and the zinc oxide / polydopamine heterojunction and the reaction mother liquor can be separated in a short time, so that the dopamine cannot be excessively polycondensed, and the time effect can be avoided during the regulation.

[0012] In a second aspect, the present application provides a zinc oxide / polydopamine heterojunction prepared by using the preparation method.

[0013] In a third aspect, the present application provides a method for regulating the n-π conjugation interaction strength in the zinc oxide / polydopamine heterojunction interface, the n-π conjugation interaction strength is regulated by increasing or decreasing the amount of triethylenetetramine, the reaction temperature and the reaction time, the amount of the triethylenetetramine accounts for 2%-30% of the total volume of the reaction solvent, the reaction temperature is 5-10 ℃, and the reaction time is 2-5 min; wherein the reaction solvent refers to the triethylenetetramine and the polar solvent used in the preparation process of the zinc oxide / polydopamine heterojunction, and the polar solvent can be water.

[0014] The technical principle involved in the present application is as follows:

[0015] The dopamine can be spontaneously polycondensed in a polar solution to form polydopamine, and if not regulated, the polydopamine molecules can form a firm bound state with the surface of ZnO, or can not be attached. In the photocatalytic reaction, it is not conducive to the transmission and transfer of photo-generated electrons. The triethylenetetramine interface regulator is added in the process of the spontaneous polymerization of dopamine, and the content of the triethylenetetramine is adjusted to induce the generation of the hydrogen bond based on the amino group at the interface of zinc oxide and dopamine. The hydrogen bond based on the amino group can weaken the firm bound state between the dopamine and the zinc oxide, so that the n-π conjugation state between the zinc oxide and the dopamine interface can be regulated. Since the dopamine molecules have the characteristic of spontaneous polymerization in the solution, in order to control the reaction rate, the reaction temperature is usually lower than 10 ℃. The zinc oxide / polydopamine heterojunction and the reaction mother liquor can be separated in a few minutes by using a rapid filtration method, so as to prevent the excessive polycondensation of the dopamine. Once the dopamine is excessively polymerized in the solution, the phenomenon of accelerated polymerization will occur, and the interface interaction cannot be regulated.

[0016] The present application has the following beneficial effects:

[0017] The preparation method of the zinc oxide / polydopamine heterojunction provided by the application has a low reaction temperature (within 10 DEG C), does not use excessive stimulation, toxic chemical reagents and high-temperature and high-pressure reaction conditions, and has a mild reaction condition; the reaction is completed within several minutes, is rapid, and the method is simple and fast.

[0018] The method for adjusting the n-pi conjugation interaction strength in the zinc oxide / polydopamine heterojunction interface provided by the application can adjust the interaction between the interfaces by adjusting the content of triethylenetetramine, and has significant universality and generality. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below, and obviously, other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0020] Figure 1 Fig. 1 is an electron microscope image of the ZnO / PDA heterojunction photocatalyst samples ZP0 and ZP10 prepared in Example 1, wherein (a) is the surface morphology of sample ZP0, (b) is the surface morphology of sample ZP10, (c) is the TEM contrast morphology of sample ZP10, (d) is the high-magnification TEM contrast morphology of sample ZP10, (e) and (f) are both the high-resolution TEM contrast morphologies of sample ZP10.

[0021] Figure 2 Fig. 2 is a scanning electron microscope image of sample ZP0 prepared in Example 1.

[0022] Figure 3 Fig. 3 is an XRD pattern of the six ZnO / PDA heterojunction photocatalyst samples prepared in Example 1.

[0023] Figure 4 Fig. 4 is an ultraviolet-visible absorption spectrum of the six ZnO / PDA heterojunction photocatalyst samples prepared in Example 1.

[0024] Figure 5 Fig. 5 is an X-ray photoelectron spectroscopy comparison diagram of sample ZP10 and sample ZP0 prepared in Example 1.

[0025] Figure 6 Fig. 6 is an electron paramagnetic resonance spectrum of the six ZnO / PDA heterojunction photocatalyst samples prepared in Example 1.

[0026] Figure 7 Fig. 7 is an infrared spectrum of the six ZnO / PDA heterojunction photocatalyst samples prepared in Example 1.

[0027] Figure 8 is the photocurrent graph of the six ZnO / PDA heterojunction photocatalyst samples prepared in Example 1.

[0028] Figure 9 is the photocatalytic carbon dioxide reduction graph of the six ZnO / PDA heterojunction photocatalyst samples prepared in Example 1.

[0029] Figure 10 is the scanning electron microscope graph of sample ZP10' prepared in Example 2.

[0030] Figure 11 is the scanning electron microscope graph of sample ZP10" prepared in Comparative Example 1.

[0031] Figure 12 is the scanning electron microscope graph of sample ZP10'" prepared in Comparative Example 2. DETAILED DESCRIPTION

[0032] In order to make the person skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without creative labor should belong to the protection scope of the present application.

[0033] Example 1

[0034] Take 60 mg of ZnO nanosheet, disperse it in deionized water under ultrasonic condition, add different volumes of triethylenetetramine respectively, control the total volume of triethylenetetramine and deionized water to be 100 mL, after sufficient stirring, adjust the reaction temperature to 10℃, then add 0.012 g of dopamine raw material, after 5 min of reaction, rapidly filter by suction filtration, and vacuum freeze-dry the sample to obtain a ZnO / PDA heterojunction photocatalyst.

[0035] According to the different amounts of triethylenetetramine added, the ZnO / PDA heterojunction photocatalysts prepared when the amount of triethylenetetramine added is 0 mL, 2 mL, 5 mL, 10 mL, 20 mL and 30 mL are named as ZP0, ZP2, ZP5, ZP10, ZP20 and ZP30 respectively.

[0036] Observe the prepared samples ZP0 and ZP10 under an electron microscope, and the results are as follows Figure 1 , 2As shown, it can be seen that the optimized sample ZP10 has a PDA nanolayer on the surface with a thickness of about 2 nm; the sample ZP0 obtained without adding the interfacial regulator triethylenetetramine shows that PDA is almost unable to adhere to the surface of ZnO.

[0037] The six prepared ZnO / PDA heterojunction photocatalyst samples were characterized by X-ray diffraction, and the results are shown in Figure 3 As shown, the main peak of XRD is the peak of zinc oxide, and with the increase of the volume fraction of triethylenetetramine, the diffraction peak intensity decreases, indicating that triethylenetetramine can significantly adjust the interaction between PDA and ZnO.

[0038] The six prepared ZnO / PDA heterojunction photocatalyst samples were detected by ultraviolet-visible absorption spectrum, and the results are shown in Figure 4 As shown, with the increase of the volume fraction of triethylenetetramine, the visible light absorption intensity gradually increases, and this absorption enhancement in the visible light region is mainly caused by the interaction between PDA and ZnO, indicating that triethylenetetramine has a significant adjusting effect on the light absorption.

[0039] The prepared samples ZP10 and ZP0 were compared and analyzed by X-ray photoelectron spectrometer, and the results are shown in Figure 5 As shown, the binding energy of Zn element in sample ZP10 appears to shift to a small binding energy direction, indicating that there is n-π interaction between Zn and PDA.

[0040] The six prepared ZnO / PDA heterojunction photocatalyst samples were tested by electron paramagnetic resonance, and the results are shown in Figure 6 As shown, with the increase of the volume fraction of triethylenetetramine, the n-π interaction between Zn and PDA gradually evolves, indicating that triethylenetetramine has a significant regulating effect on the n-π conjugation interaction between Zn and PDA.

[0041] The six prepared ZnO / PDA heterojunction photocatalyst samples were tested by infrared, and the results are shown in Figure 7 As shown, with the increase of the volume fraction of triethylenetetramine, the amino groups on the surface of ZnO / PDA heterojunction increase, which is helpful to induce the formation of hydrogen bonds and successfully regulate the n-π interaction between Zn and PDA.

[0042] The six prepared ZnO / PDA heterojunction photocatalyst samples were tested by photocurrent, and the results are shown in Figure 8 As shown, after the regulation of triethylenetetramine, the photocurrent characteristics of ZnO / PDA heterojunction photocatalyst are significantly enhanced, which is very conducive to the migration and separation of photoelectrons, and thus promotes the improvement of photocatalytic performance.

[0043] The prepared six ZnO / PDA heterojunction photocatalyst samples were used to carry out a photocatalytic carbon dioxide reduction experiment, and the results are shown in Figure 9 As the triethylenetetramine volume fraction increases, the ZnO / PDA heterojunction photocatalytic performance first increases and then decreases, mainly because the appropriate triethylenetetramine adjusting agent can adjust the n-π interaction between Zn and PDA to the most suitable bound state. Under this optimal interaction condition, the photo-generated electron-hole can not only be separated efficiently, but also can quickly migrate to the surface through the interface of ZnO and PDA to participate in the photocatalytic reaction. Excessive triethylenetetramine can cause excessive polycondensation of PDA, causing serious electron and light shielding phenomenon, and reducing the photocatalytic performance.

[0044] Example 2

[0045] Take 60 mg of ZnO nanosheet, disperse it in 90 mL of deionized water under ultrasonic conditions, add 10 mL of triethylenetetramine, fully stir, adjust the reaction temperature to 5℃, then add 0.012 g of dopamine raw material, react for 5 min, then quickly filter using suction filtration, and vacuum freeze-dry the sample to obtain a ZnO / PDA heterojunction photocatalyst, named ZP10'.

[0046] Observe the prepared sample ZP10' under an electron microscope, and the results are shown in Figure 10 As shown in the figure, when the reaction temperature is adjusted to 5℃, the PDA layer on the surface of the prepared ZnO / PDA heterojunction becomes thinner, indicating that the temperature reduces the reaction rate.

[0047] Comparative Example 1

[0048] Take 60 mg of ZnO nanosheet, disperse it in 90 mL of deionized water under ultrasonic conditions, add 10 mL of triethylenetetramine, fully stir, adjust the reaction temperature to 0℃, then add 0.012 g of dopamine raw material, react for 5 min, then quickly filter using suction filtration, and vacuum freeze-dry the sample to obtain a ZnO / PDA heterojunction photocatalyst, named ZP10".

[0049] Observe the prepared sample ZP10" under an electron microscope, and the results are shown in Figure 11 As shown in the figure, when the reaction temperature is adjusted to 0℃, the low reaction temperature causes dopamine molecules to be unable to polycondense to form PDA, so PDA is almost unable to adhere to the surface of ZnO.

[0050] Comparative Example 2

[0051] Take 60 mg ZnO nanosheet, under ultrasonic condition, disperse it in 90 mL deionized water, add 10 mL triethylenetetramine, after fully stirring, adjust the reaction temperature to 10°C, then add 0.012 g dopamine raw material, after 10 min reaction, rapidly filter by using suction filtration, and vacuum freeze-dry the sample, to obtain ZnO / PDA heterojunction photocatalyst, named as "ZP10”’.

[0052] Observe the prepared sample ZP10”’ under electron microscope, the result is shown in Figure 12 As shown, when the reaction time is adjusted to 10 min, i.e. without using rapid separation of catalyst and reaction mother liquor, PDA is attached on the surface of ZnO too thick, which cannot play the effect of adjusting the interaction strength between PDA and ZnO interface.

[0053] Although the present application has been described in detail by referring to the preferred embodiments thereof, it is to be understood that the present application is not limited to them. Variations and modifications are possible in the scope of the present application as defined in the appended claims. Any skilled person in the art can make modifications and replacements without departing from the spirit and scope of the present application.

Claims

1. A method for preparing a zinc oxide / polydopamine heterojunction, characterized by, The zinc oxide nanosheet is dispersed in a polar solvent, triethylenetetramine is added to the obtained zinc oxide dispersion as an interface modifier, the volume of the triethylenetetramine accounts for 2% to 30% of the total volume of the triethylenetetramine and the polar solvent, after stirring, the temperature of the system is adjusted to 5 to 10 ℃, then dopamine is added and reacted for 2 to 5 min, after the reaction, the precipitate is collected and freeze-dried, and the zinc oxide / polydopamine heterojunction is obtained.

2. The production method according to claim 1, wherein The polar solvent is water.

3. The production method according to claim 1, wherein The added amount of the zinc oxide nanosheet is 0.05 to 0.1 g, and the added amount of the dopamine is 0.01 to 0.015 g.

4. The production method according to claim 1, wherein The reaction solution and the product are separated by suction filtration.

5. A zinc oxide / polydopamine heterojunction prepared by the preparation method according to any one of claims 1 to 4.

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