Preparation method and application of a Z-type heterojunction upconversion photocatalyst

Abstract

The present invention discloses a preparation method and application of a Z-type heterojunction upconversion photocatalyst, which can be synthesized by a solid phase method and a hydrothermal method or a solvothermal method. The solid phase method uses Bi2O3 and NH4F, and obtains a precursor BiOF by high temperature sintering, and then adds TiO2, an activator, a sensitizer and a zinc source for secondary sintering. The hydrothermal method or the solvothermal method is to dissolve a bismuth source and a fluorine source in water or a mannitol solution, add a titanium source and other reactants, and then stir and bake. Due to its strong built-in electric field, this photocatalyst can accelerate the separation and transfer of carriers, improve the luminescence intensity and upconversion efficiency, and thus show efficient photocatalytic degradation performance. In addition, the preparation method of this material is simple, low-cost, suitable for large-scale production, and has good industrial and market application potential.

Description

Technical Field

[0001] The invention belongs to the technical field of up-conversion photocatalysts, and in particular relates to a preparation method and application of a Z-type heterojunction up-conversion photocatalyst. Background Art

[0002] For a long time, the low near-infrared response of semiconductor photocatalysts has become a key factor limiting their practical applications. In response to this, researchers have designed upconversion (UC) photocatalysts to achieve efficient utilization of near-infrared light. UC emission can indirectly utilize near-infrared light by converting low-energy near-infrared light into high-energy ultraviolet and visible light emissions through a multi-photon absorption process. Since the theory was proposed, a series of studies on the UC function to improve photocatalytic efficiency have been reported. However, UC photocatalysts still face the problem of low UC utilization, and the resulting photocatalysts are difficult to meet people's requirements for high photocatalytic efficiency. Therefore, it is urgent to find an effective strategy to solve the problem of low UC utilization of UC photocatalysts.

[0003] Generally speaking, efficient UC utilization of UC photocatalysts requires high UC emission intensity of the luminescence center and strong absorption response of the photocatalyst. For rare earth-doped UC luminescence, the linear spectrum of rare earth ions comes from the electric dipole transition between the 4f-4f energy levels, which is forbidden according to the parity selection rule, resulting in low luminescence efficiency of most rare earth ions. However, studies have shown that the built-in electric field (IEF) may break the original electric dipole forbidden transition between the 4f-4f energy levels of rare earth ions, increase the probability of radiative transition, and enhance fluorescence emission. Therefore, constructing an IEF in the UC photocatalyst system is expected to enhance the UC emission intensity and thus improve the UC utilization rate. In addition, for the photocatalytic process, the construction of IEF can also provide a strong driving force for photogenerated carriers and accelerate their separation and transportation efficiency. Therefore, constructing an IEF in the UC photocatalyst system is expected to achieve efficient photogenerated carrier separation efficiency and strong UC luminescence efficiency, ultimately improving the photocatalytic efficiency.

[0004] Constructing a Z-type heterojunction is an effective strategy to achieve IEF regulation. In a Z-type heterojunction, the difference in the Fermi levels of the two-phase semiconductors causes the charge redistribution at the heterojunction interface to form an IEF. Generally, a Z-type heterojunction consists of a reduced semiconductor with a high conduction band (CB) position and an oxidized semiconductor with a low valence band (VB) position, which is staggered in band gap. Bi3Ti2O8F is a reduced semiconductor with a higher CB in the bismuth-based photocatalytic family. In our previous work, we evaluated the good application potential of upconversion rare earth-doped Bi3Ti2O8F photocatalyst. However, the UC utilization rate of the upconversion rare earth-doped Bi3Ti2O8F photocatalyst is low, resulting in its unsatisfactory photocatalytic efficiency. Therefore, we need to find a semiconductor with a suitable band gap to construct a Z-type heterojunction with upconversion rare earth-doped Bi3Ti2O8F to effectively improve its photocatalytic efficiency.

[0005] ZnO is an oxide semiconductor with a wide direct band gap and large exciton binding energy. In addition, ZnO has the advantages of low cost, non-toxicity, and easy formation of photogenerated holes with high oxidation ability, and can be used to degrade environmental pollutants. Based on the band gap characteristics of ZnO and Bi3Ti2O8F, it is speculated that ZnO can perfectly match the band gap structure of upconversion rare earth-doped Bi3Ti2O8F photocatalysts, and construct IEF-regulated Z-type heterojunction upconversion photocatalysts to improve photocatalytic activity.

[0006] Therefore, this paper proposes a preparation method and application of a Z-type heterojunction upconversion photocatalyst Summary of the invention

[0007] In order to solve the above technical problems, the present invention designs a preparation method and application of a Z-type heterojunction upconversion photocatalyst. The photocatalyst obtained by the preparation method provided by the present invention has high carrier separation efficiency and high upconversion utilization rate, which can significantly improve the photocatalytic efficiency.

[0008] In order to achieve the above technical effects, the present invention is implemented through the following technical solutions:

[0009] A Z-type heterojunction upconversion photocatalyst, characterized in that its composition is: ZnO / Bi 3-0.03(x+y) Ti2O8F:x%M 3+ ,y%N + , wherein 2≤x≤20; 1≤y≤4; said M includes Yb 3+ or Nd 3+ , N includes Er 3+ , Tm 3+ Or Ho 3+ .

[0010] A method for preparing a Z-type heterojunction upconversion photocatalyst, characterized in that it is synthesized by a solid phase method and comprises the following steps:

[0011] S1: Bi2O3 and NH4F are placed in an agate mortar at a molar ratio of 0.5 to 1:1, and an appropriate amount of alcohol is added to fully grind until dry; the obtained powder is loaded into a corundum crucible and placed in a muffle furnace, and sintered at a high temperature of 200 to 500°C for 4 to 24 hours to obtain the precursor BiOF;

[0012] S2: Place the precursor BiOF in an agate mortar, add TiO2, activator, sensitizer and zinc source at the same time, add appropriate amount of alcohol and grind thoroughly until dry; wherein, the molar ratio of BiOF to TiO2 is 0.5-1:1; the molar ratio of activator to BiOF is 0.5-2:100; the molar ratio of sensitizer to BiOF is 1-10:100; the molar ratio of zinc source to BiOF is 1-100:100; the obtained powder is loaded into a corundum crucible and placed in a muffle furnace, and sintered at a high temperature of 400-800°C for 4-24h.

[0013] A method for preparing a Z-type heterojunction upconversion photocatalyst, characterized in that it is synthesized by a hydrothermal or solvothermal method, comprising the following steps:

[0014] (1) dissolving a bismuth source and a fluorine source in a molar ratio of 1 to 5:1 in water or a mannitol solution and stirring to obtain a first solution, and adding a titanium source to the water or mannitol solution and stirring to obtain a second solution; adding the first solution to the second solution and stirring to obtain an initial solution, and adjusting the solution pH to a range of 8 to 12; wherein the molar ratio of the bismuth source to the titanium source is 0.5 to 1:1;

[0015] (2) adding an activator, a sensitizer and a zinc source to the initial solution obtained in step (1); wherein the molar ratio of the activator to the bismuth source is 0.5 to 2:100, the molar ratio of the sensitizer to the bismuth source is 1 to 10:100, and the molar ratio of the zinc source to the bismuth source is 1 to 100:100; after stirring evenly, transferring the solution to a polytetrafluoroethylene liner, and placing it in an oven at a temperature of 160 to 250° C. for reaction for 4 to 24 hours, washing and drying after the reaction is completed.

[0016] Furthermore, the activator in S2 is Er 3+ , Tm 3+ Or Ho 3+ , the sensitizer is Yb 3+ or Nd 3+ , the zinc source is ZnO or ZnCO3.

[0017] Furthermore, the bismuth source in step (1) is at least one of bismuth nitrate pentahydrate, bismuth carbonate, bismuth phosphate or bismuth sulfate; the fluorine source is at least one of potassium fluoride, sodium fluoride or ammonium fluoride; and the titanium source is at least one of titanium dioxide, titanium tetrachloride or tetrabutyl titanate.

[0018] Another object of the present invention is to provide an application of a Z-type heterojunction upconversion photocatalyst, characterized in that it is used as a photocatalyst in the degradation of organic dyes, endocrines, antibiotics and heavy metal pollutants.

[0019] The beneficial effects of the present invention are:

[0020] The strong built-in electric field of the Z-type heterojunction prepared by the present invention accelerates carrier separation while retaining the high redox ability of the catalyst. In addition, the built-in electric field enhances the upconversion luminescence efficiency of rare earth ions and improves the upconversion utilization rate, thereby significantly improving the photocatalytic activity. The preparation method of the material of the present invention is simple, low-cost, suitable for large-scale production, and has industrial and market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0022] Figure 1 It is the XRD spectrum of the Z-type heterojunction upconversion photocatalyst of the present invention;

[0023] Figure 2 is the absorption spectrum of the Z-type heterojunction upconversion photocatalyst of the present invention;

[0024] Figure 3 It is the upconversion emission spectrum of the Z-type heterojunction upconversion photocatalyst of the present invention;

[0025] Figure 4 It is a full-spectrum catalytic degradation diagram of the Z-type heterojunction upconversion photocatalyst of the present invention; DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Example 1

[0028] See also Figures 1 to 4 As shown, the chemical formula of the Z-type heterojunction upconversion photocatalyst material is ZnO / Bi 2.67 Ti2O8F:10%Yb 3+ , 1%Er3+ , using solid phase synthesis, the preparation method of the material is as follows:

[0029] S1: Place Bi2O3 and NH4F in an agate mortar at a molar ratio of 0.5 to 1:1, add an appropriate amount of alcohol and grind thoroughly until dry. Put the obtained powder into a corundum crucible and place it in a muffle furnace, and sinter at 200 to 500℃ for 4 to 24h to obtain the precursor BiOF.

[0030] S2: According to Bi 3+ 、Ti 4+ , Er 3+ , Yb 3+ 、Zn 2+ The precursors BiOF, TiO2, Er2O3, Yb2O3 and ZnO obtained in S1 were weighed in a molar ratio of 2.67:2:0.03:0.3:0.12, and an appropriate amount of alcohol was added to fully grind until dry. The obtained powder was placed in a corundum crucible and placed in a muffle furnace, and sintered at 400-800℃ for 4-24h to obtain a ZnO / Bi 2.67 Ti2O8F:10%Yb 3+ , 1%Er 3+ Z-type heterojunction upconversion photocatalyst.

[0031] Example 2

[0032] The chemical formula of the Z-type heterojunction upconversion photocatalyst material is ZnO / Bi 2.67 Ti2O8F:10%Yb 3+ , 1%Er 3+ , using solid phase synthesis, the preparation method of the material is as follows:

[0033] S1: Place Bi2O3 and NH4F in an agate mortar at a molar ratio of 0.5 to 1:1, add an appropriate amount of alcohol and grind thoroughly until dry. Put the obtained powder into a corundum crucible and place it in a muffle furnace, and sinter at 200 to 500℃ for 4 to 24h to obtain the precursor BiOF.

[0034] S2: According to Bi 3+ 、Ti 4+ , Er 3+ , Yb 3+ 、Zn 2+ The precursors BiOF, TiO2, Er2O3, Yb2O3 and ZnCO3 obtained in S1 were weighed in a molar ratio of 2.67:2:0.03:0.3:0.12, and an appropriate amount of alcohol was added to fully grind until dry. The obtained powder was placed in a corundum crucible and placed in a muffle furnace, and sintered at 400-800℃ for 4-24h to obtain a ZnO / Bi 2.67 Ti2O8F:10%Yb3+ , 1%Er 3+ Z-type heterojunction upconversion photocatalyst.

[0035] Example 3

[0036] The chemical formula of the Z-type heterojunction upconversion photocatalyst material is ZnO / Bi 2.67 Ti2O8F:10%Yb 3+ , 1%Er 3+ , synthesized by hydrothermal or solvothermal method, the preparation method of the material is as follows:

[0037] (1) dissolving a bismuth source and a fluorine source in a molar ratio of 1 to 5:1 in water or a mannitol solution and stirring to obtain a first solution, adding a titanium source to the water or mannitol solution and stirring to obtain a second solution; adding the first solution to the second solution and stirring to obtain an initial solution, and adjusting the pH value of the solution to 8 to 12;

[0038] (2) Weigh Er(NO3)3, Yb(NO3)3 and ZnO in a molar ratio of 0.1:1:0.4 and add them to the above solution. After stirring evenly, put the solution into a polytetrafluoroethylene liner and place it in an oven at 160-250°C for 4-24 hours to obtain a ZnO / Bi 2.67 Ti2O8F:10%Yb 3+ , 1%Er 3+ Z-type heterojunction upconversion photocatalyst.

[0039] Example 4

[0040] The chemical formula of the Z-type heterojunction upconversion photocatalyst material is ZnO / Bi 2.67 Ti2O8F:10%Yb 3+ , 1%Er 3+ , using solid phase synthesis, the preparation method of the material is as follows:

[0041] S1: Place Bi2O3 and NH4F in an agate mortar at a molar ratio of 0.5 to 1:1, add an appropriate amount of alcohol and grind thoroughly until dry. Put the obtained powder into a corundum crucible and place it in a muffle furnace, and sinter at 200 to 500℃ for 4 to 24h to obtain the precursor BiOF.

[0042] S2: According to Bi 3+ 、Ti 4+ , Er 3+ , Yb 3+ 、Zn 2+The precursors BiOF, TiO2, Er2O3, Yb2O3 and ZnO obtained in S1 were weighed in a molar ratio of 2.67:2:0.03:0.3:0.3, and an appropriate amount of alcohol was added to fully grind until dry. The obtained powder was placed in a corundum crucible and placed in a muffle furnace, and sintered at a high temperature of 400-800℃ for 4-24h to obtain a ZnO / Bi 2.67 Ti2O8F:10%Yb 3+ , 1%Er 3+ Z-type heterojunction upconversion photocatalyst.

[0043] Embodiment 5:

[0044] The chemical formula of the Z-type heterojunction upconversion photocatalyst material is ZnO / Bi 2.67 Ti2O8F:10%Yb 3+ , 1%Er 3+ , using solid phase synthesis, the preparation method of the material is as follows:

[0045] S1: Place Bi2O3 and NH4F in an agate mortar at a molar ratio of 0.5 to 1:1, add an appropriate amount of alcohol and grind thoroughly until dry. Put the obtained powder into a corundum crucible and place it in a muffle furnace, and sinter at 200 to 500℃ for 4 to 24h to obtain the precursor BiOF.

[0046] S2: According to Bi 3+ 、Ti 4+ , Er 3+ , Yb 3+ 、Zn 2+ The precursors BiOF, TiO2, Er2O3, Yb2O3 and ZnCO3 obtained in S1 were weighed in a molar ratio of 2.67:2:0.03:0.3:0.3, and an appropriate amount of alcohol was added to fully grind until dry. The obtained powder was placed in a corundum crucible and placed in a muffle furnace, and sintered at 400-800℃ for 4-24h to obtain a ZnO / Bi 2.67 Ti2O8F:10%Yb 3+ , 1%Er 3+ Z-type heterojunction upconversion photocatalyst.

[0047] Embodiment 6:

[0048] The chemical formula of the Z-type heterojunction upconversion photocatalyst material is ZnO / Bi 2.67 Ti2O8F:10%Yb 3+ , 1%Er 3+ , synthesized by hydrothermal or solvothermal method, the preparation method of the material is as follows:

[0049] (1) dissolving a bismuth source and a fluorine source in a molar ratio of 1 to 5:1 in water or a mannitol solution and stirring to obtain a first solution, adding a titanium source to the water or mannitol solution and stirring to obtain a second solution; adding the first solution to the second solution and stirring to obtain an initial solution, and adjusting the pH value of the solution to 8 to 12;

[0050] (2) Weigh Er(NO3)3, Yb(NO3)3 and ZnO in a molar ratio of 0.1:1:1 and add them to the above solution. After stirring evenly, put the solution into a polytetrafluoroethylene liner and place it in an oven at 160-250°C for 4-24 hours to obtain a ZnO / Bi 2.67 Ti2O8F:10%Yb 3+ , 1%Er 3+ Z-type heterojunction upconversion photocatalyst.

[0051] Embodiment 7:

[0052] Photocatalytic activity test:

[0053] The photocatalytic activity of the samples for the degradation of organic dyes, antibiotics and heavy metal ions was evaluated under a 300W xenon lamp (CEL-LAX500). The reactor used was a customized quartz reactor with a volume of 100ml. 10mg of the sample was added to the pollutant solution (40mL, 10mg / L) and stirred in the dark for 0.5h to ensure adsorption-desorption equilibrium. 4mL of the reaction solution was taken out regularly. The supernatant was analyzed with a UV-1800 spectrophotometer.

[0054] Depend on Figure 1 It can be seen that the ZnO / Bi3Ti2O8F:Yb prepared in the embodiment 3+ , Er 3+ Z-scheme heterojunction photocatalyst and pristine Bi3Ti2O8F:Yb 3+ , Er 3+ All of them correspond to the characteristic peaks of standard Bi3Ti2O8F, and no ZnO diffraction peaks are observed, which is attributed to its low loading amount. Figure 2 It can be seen that the ZnO / Bi3Ti2O8F:Yb prepared in the embodiment 3+ , Er 3+ Compared with the original Bi3Ti2O8F:Yb 3+ , Er 3+ and ZnO have stronger absorption response. Figure 3 It can be seen that the ZnO / Bi3Ti2O8F:Yb prepared in the embodiment 3+ , Er 3+ Compared with the original Bi3Ti2O8F:Yb 3+ , Er 3+The photocatalyst has a stronger upconversion luminescence intensity. Figure 4 It can be seen that the ZnO / Bi3Ti2O8F:Yb prepared in the embodiment 3+ , Er 3+ Compared with the original Bi3Ti2O8F:Yb 3+ , Er 3+ Photocatalysts significantly improve the efficiency of photocatalytic degradation of pollutants.

Claims

1. A Z-type heterojunction upconversion photocatalyst, characterized in that: Its composition is: ZnO / Bi 3-0.03(x+y) Ti2O8F:x%M 3+ , y%N 3+ , where 2≤x≤20; 1≤y≤4; the M 3+ Yb 3+ or Nd 3+ , N 3+ For Er 3+ 、Tm 3+ Or Ho 3+ .

2. The method for preparing a Z-type heterojunction upconversion photocatalyst according to claim 1, characterized in that: The solid phase synthesis method includes the following steps: S1: Bi2O3 and NH4F are placed in an agate mortar at a molar ratio of 0.5 to 1:1, and an appropriate amount of alcohol is added to fully grind until dry; the obtained powder is loaded into a corundum crucible and placed in a muffle furnace, and sintered at a high temperature of 200 to 500°C for 4 to 24 h to obtain the precursor BiOF; S2: Place the precursor BiOF in an agate mortar, add TiO2, activator, sensitizer and zinc source at the same time, add appropriate amount of alcohol and grind thoroughly until dry; the molar ratio of activator to BiOF is 0.5-2:100; the molar ratio of sensitizer to BiOF is 1-10:100; the molar ratio of zinc source to BiOF is 1-100:100; the obtained powder is loaded into a corundum crucible and placed in a muffle furnace, and sintered at a high temperature of 400-800°C for 4-24 h.

3. The method for preparing a Z-type heterojunction upconversion photocatalyst according to claim 1, characterized in that: The synthesis is carried out by hydrothermal or solvothermal method, comprising the following steps: (1) dissolving a bismuth source and a fluorine source in a molar ratio of 1 to 5:1 in water or a mannitol solution and stirring the solution to obtain a first solution, and adding a titanium source to the water or mannitol solution and stirring the solution to obtain a second solution; adding the first solution to the second solution and stirring the solution to obtain an initial solution, and adjusting the pH value of the solution to 8 to 12; (2) Adding an activator, a sensitizer and a zinc source to the initial solution obtained in step (1); wherein the molar ratio of the activator to the bismuth source is 0.5-2:100, the molar ratio of the sensitizer to the bismuth source is 1-10:100, and the molar ratio of the zinc source to the bismuth source is 1-100:100; after stirring evenly, transferring the solution to a polytetrafluoroethylene liner, and placing it in an oven at a temperature of 160-250°C for reaction for 4-24 hours, washing and drying after the reaction is completed.

4. A method for preparing a Z-type heterojunction upconversion photocatalyst according to claim 2 or 3, characterized in that: The activator is Er 3+ , Tm 3+ Or Ho 3+ , the sensitizer is Yb 3+ or Nd 3+ , the zinc source is ZnO or ZnCO3.

5. The method for preparing a Z-type heterojunction upconversion photocatalyst according to claim 3, characterized in that: The bismuth source in step (1) is at least one of bismuth nitrate pentahydrate, bismuth carbonate, bismuth phosphate or bismuth sulfate; the fluorine source is at least one of potassium fluoride, sodium fluoride or ammonium fluoride; and the titanium source is at least one of titanium dioxide, titanium tetrachloride or tetrabutyl titanate.

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