A method for photocatalytic degradation of perfluorooctanoic acid in water by using boron hydroxide

Abstract

The application discloses a method for photocatalytic degradation of perfluorooctanoic acid in water by using boron hydroxide, and belongs to the field of wastewater treatment. The method comprises the following steps: adding boron hydroxide as a photocatalyst into water containing perfluorooctanoic acid, mixing thoroughly, and then performing a photocatalytic degradation reaction under a light source; the light source is ultraviolet light, yellow light or red light; and the pH of the water containing perfluorooctanoic acid ranges from 3 to 7. The method uses boron hydroxide (Al(OH)3, Ga(OH)3 and In(OH)3) which is low in cost and simple in preparation process to perform photocatalytic degradation of perfluorooctanoic acid, can improve the degradation efficiency of perfluorooctanoic acid in water, and can perform photocatalytic degradation under different light sources and in a wide pH range, so that the application range of photocatalysis is expanded, and the method is conducive to the treatment of PFOA contaminated water in actual production.

Description

TECHNICAL FIELD

[0001] The application relates to the sewage degradation field, in particular to a method for photocatalytic degradation of perfluorooctanoic acid in water by using boron hydroxide. BACKGROUND

[0002] Perfluorooctanoic acid (PFOA) is defined as a “persistent organic pollutant” due to its strong persistence, bioaccumulation and toxicity, and has been classified as a Class 1 carcinogen. Its transformation and removal in the environment have attracted much attention. Therefore, it is necessary to explore efficient and low-cost degradation methods to improve the degradation efficiency of PFOA.

[0003] At present, various types of photocatalysts have been used in the degradation process of PFOA, mainly focusing on semiconductor photocatalysts such as titanium dioxide, gallium oxide and indium oxide. Among them, the photocatalytic reaction system using boron metal oxide (indium oxide and gallium oxide) as the catalyst can effectively degrade PFOA under relatively mild conditions. However, the photocatalysts at present still have defects such as complex catalyst preparation process, high synthesis cost and harsh reaction conditions, which limit their practical application in environmental technology. Therefore, it is necessary to explore other efficient and low-cost catalysts. SUMMARY

[0004] The purpose of the present application is to provide a method for photocatalytic degradation of perfluorooctanoic acid in water by using boron hydroxide, which has a simple synthesis process and high degradation efficiency.

[0005] Technical solution: The method for photocatalytic degradation of perfluorooctanoic acid in water by using boron hydroxide comprises the following steps: adding boron hydroxide as a photocatalyst to water containing perfluorooctanoic acid, mixing thoroughly, and then performing photocatalytic degradation reaction under light source.

[0006] Further, the boron hydroxide is aluminum hydroxide, gallium hydroxide or indium hydroxide, preferably aluminum hydroxide.

[0007] Further, the mass ratio of perfluorooctanoic acid to aluminum hydroxide is 1:8-12, preferably 1:10.6.

[0008] Further, the mass ratio of perfluorooctanoic acid to gallium hydroxide is 1:300-600, preferably 1:400.

[0009] Further, the mass ratio of perfluorooctanoic acid to indium hydroxide is 1:40-60, preferably 1:56.

[0010] Further, the preparation method of the boron group hydroxide adopts an alkali precipitation method, and the steps are as follows: a first concentration sodium hydroxide solution is added dropwise into a solution containing an aluminum salt, a gallium salt or an indium salt, a white flocculent precipitate is generated, then a second concentration sodium hydroxide solution is added dropwise, after the generation of the precipitate is completed, the precipitate is washed with a solvent and dried, the obtained solid is cooled and ground, and the obtained solid powder is the boron group hydroxide.

[0011] Further, the concentration of the first concentration sodium hydroxide solution is 8-10 M, which is used to generate a certain amount of flocculent precipitate, and the concentration of the second concentration sodium hydroxide solution is 1-2 M, which is used to control the particle size of the generated Al(OH)3 or Ga(OH)3 or In(OH)3 and prevent pH jump.

[0012] Further, the aluminum salt, the gallium salt or the indium salt is aluminum nitrate nine hydrate (Al(NO3)3·9H2O) or gallium nitrate X hydrate (Ga(NO3)3·xH2O) or indium nitrate X hydrate (In(NO3)3·xH2O).

[0013] Further, before the photocatalytic degradation reaction, pre-mixing is required, that is, the boron group hydroxide solid powder is mixed with the water body containing perfluorooctanoic acid and stirred in the dark for 2.0-4.0 h, and the purpose is to make PFOA fully adsorbed to the surface of the solid powder of the boron group hydroxide.

[0014] Further, the pH of the water body containing perfluorooctanoic acid is 3-7, and preferably 7.

[0015] Further, the acid used for pH adjustment of the water body containing perfluorooctanoic acid is hydrochloric acid, and the base is sodium hydroxide.

[0016] Further, the light source is ultraviolet light, yellow light or red light.

[0017] Further, the degradation reaction conditions are as follows: the reaction is carried out at 24-26℃ for 24-50 h.

[0018] Further, the concentration of PFOA in the water body is 1.0 mg / L-100.0 mg / L.

[0019] Beneficial effects: Compared with the prior art, the present application has the following remarkable advantages: (1) The series of boron hydroxides (Al(OH)3, Ga(OH)3 and In(OH)3) adopted by the present application have high photocatalytic degradation efficiency on perfluorooctanoic acid, can perform photodegradation under different light sources and also can perform photocatalysis in a wider pH range, greatly widening the application range of perfluorooctanoic acid degradation, and being conducive to the treatment of PFOA contaminated water bodies in actual production; (2) The boron hydroxide is prepared based on the alkali precipitation method, and the synthesis process is simple and time-saving; (3) It is verified through experiments that after UV light irradiation for 48h, the degradation efficiency of PFOA can be increased by 33.6% at most, and after yellow light or red light (LED lamp) irradiation, the reaction efficiency of the Al(OH)3 or Ga(OH)3 or In(OH)3 photocatalytic PFOA system can be increased by 23.5% at most compared with the PFOA photolysis system alone. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The transmission electron microscope images and X-ray diffraction images of the Al(OH)3, Ga(OH)3 or In(OH)3 prepared in Example 1 are shown in (a)-(c) and (d)-(e), respectively;

[0021] Figure 2 The light reaction equipment self-made in Example 4 is shown in (a)-(c) and (d)-(e), respectively;

[0022] Figure 3 The degradation performance of the boron hydroxide on PFOA under the 300W mercury lamp in Examples 1-3 is shown in (a)-(c) and (d)-(e), respectively;

[0023] Figure 4 The degradation performance of the boron hydroxide on PFOA under yellow light in Examples 4-6 and under red light in Examples 7-9 is shown in (a)-(c) and (d)-(e), respectively;

[0024] Figure 5 The utilization efficiency of the boron hydroxide is shown in (a)-(c) and (d)-(e), respectively;

[0025] Figure 6 The degradation of PFOA and the photocatalytic mechanism of the boron hydroxide are shown in (a)-(c) and (d)-(e), respectively;

[0026] Figure 7 The Zeta potential of the three boron hydroxides under different pH is shown in (a)-(c) and (d)-(e), respectively;

[0027] Figure 8 The FT-IR spectra of the boron hydroxide, PFOA and the corresponding adsorption sample are shown in (a)-(c) and (d)-(e), respectively;

[0028] Figure 9 The 19 F nuclear magnetic resonance light diagram;

[0029] Figure 10The UV-Vis diffuse reflectance absorption spectra of three boron group hydroxides;

[0030] Figure 11 In the middle, (a)-(c) are the emission spectra of the three boron group hydroxides under 650 nm variable power excitation, and (d)-(f) are the fitting graphs of luminescence intensity and excitation power. Detailed Implementation

[0031] The present invention will now be further described in conjunction with specific embodiments and accompanying drawings.

[0032] Example 1: The method for photocatalytic degradation of perfluorooctanoic acid in water using boron group hydroxides provided in this example includes the following steps:

[0033] (1) Preparation of photocatalysts – boron group hydroxides Al(OH)3, Ga(OH)3 and In(OH)3:

[0034] Place 375.1g Al(NO3)3·9H2O (or 255.7g Ga(NO3)3·xH2O or 300.8g In(NO3)3·xH2O) in a beaker, add water to completely dissolve it. First, add 8M NaOH dropwise to the solution. After a white flocculent precipitate begins to form, replace the 8M NaOH with 1M NaOH, while monitoring the pH of the solution. Add NaOH until the pH of the solution reaches 7, so that the Al in the solution... 3+ or Ga 3+ or In 3+ Complete precipitation yields Al(OH)3, Ga(OH)3, or In(OH)3. At this point, stop adding NaOH, allow the precipitate to stand, then pour off the supernatant and wash the precipitate 2-3 times with methanol and purified water to remove soluble impurities. Dry the precipitate at 120°C, collect the solid, cool, and grind to obtain 78.0g Al(OH)3, 120.7g Ga(OH)3, or 165.8g In(OH)3.

[0035] The prepared boron hydroxides were characterized by tests, such as... Figure 1 As shown. Figure 1 (a) is a transmission electron microscope image of the Al(OH)3 catalyst. As can be seen from the image, the synthesized Al(OH)3 has a regular or incompletely regular sheet-like structure. The incompletely regular sheet-like Al(OH)3 has a length of 1.40 μm and a width of 1.52 μm. The regular sheet-like structure is approximately square, with a length and width of about 1.68 μm. Figure 1 Image (b) shows a transmission electron microscope (TEM) image of the Ga(OH)3 catalyst. As can be seen from the image, the synthesized Ga(OH)3 has a regular rod-shaped structure with a length of about 1.04–2.27 μm. Figure 1(c) is a transmission electron microscopy image of the In(OH)3catalyst, from which it can be seen that the synthesized In(OH)3has a spherical structure with a diameter of about 16 nm.

[0036] Figure 1 (d) is an X-ray diffraction pattern (XRD) of the Al(OH)3catalyst, the Al(OH)3synthesized by the alkali precipitation method has sharp characteristic peaks at 29.4°, 31.4°, 38.6°, 47.8° and 48.5°, which belong to (0-11), (-111), (-1-21), (-2 11) and (0-12) crystal faces, respectively. Figure 1 (e) is an XRD pattern of the Ga(OH)3catalyst, the synthesized Ga(OH)3has crystal faces of (220), (310), (222), (321) and the like. Figure 1 (f) is an XRD pattern of the synthesized In(OH)3catalyst, which has obvious (200) and (400) crystal faces.

[0037] The above characterization results show that the boron hydroxides Al(OH)3, Ga(OH)3and In(OH)3are successfully synthesized.

[0038] (2) 100 mg of PFOA solid was weighed into a 1.0 L volumetric flask, stirred to dissolve and diluted to volume to obtain a 100 mg / L PFOA stock solution;

[0039] (3) A 300 W mercury lamp was placed in an XPA-7 type light reaction instrument and preheated for 30 min to stabilize the light intensity output;

[0040] (4) 7.5 mL of the 100 mg / L PFOA stock solution and 142.5 mL of deionized water were mixed uniformly to obtain a mixed solution, the pH of the mixed solution was adjusted to 7, 8 mg of boron hydroxide Al(OH)3was added to the mixed solution, the concentration of Al(OH)3in the mixed solution was 53.3 mg / L, and the concentration of PFOA in the mixed solution was 5 mg / L; then the mixed solution was stirred in the dark for 2 h to reach adsorption equilibrium, 30.0 mL of the solution was taken into a quartz tube for light reaction, the lamp cover of the light reaction instrument was pulled down at the preset reaction time point, 1.0 mL of the reaction solution was taken from the light reaction tube into a 10 mL plastic centrifugal tube, 4 mL of methanol was added, stirred and extracted for 40 min, the change in the concentration of PFOA was monitored using high performance liquid chromatography-mass spectrometry, and the degradation rate of PFOA was calculated.

[0041] Example 2: The difference from Example 1 is that in step (3), 300 mg of boron hydroxide Ga(OH)3was added to the mixed solution, and the concentration of Ga(OH)3in the mixed solution was 2000.0 mg / L.

[0042] Example 3: The difference from Example 1 is that in step (3), 42 mg of boron hydroxide In(OH)3 is added to the mixed solution, and the concentration of In(OH)3 in the mixed solution is 280.0 mg / L.

[0043] Example 4: The difference from Example 1 is that in step (3), the 300 W mercury lamp light source is replaced by a yellow or red LED lamp, and the XPA-7 type light reaction instrument is replaced by a self-made light reaction device, as shown in Figure 2

[0044] Example 5: The difference from Example 4 is that in step (3), 300 mg of boron hydroxide Ga(OH)3 is added to the mixed solution, and the concentration of Ga(OH)3 in the mixed solution is 2000.0 mg / L.

[0045] Example 6: The difference from Example 4 is that in step (3), 42 mg of boron hydroxide In(OH)3 is added to the mixed solution, and the concentration of In(OH)3 in the mixed solution is 280.0 mg / L.

[0046] Example 7: The difference from Example 4 is that in step (3), the yellow light is replaced by a red LED lamp.

[0047] Example 8: The difference from Example 7 is that in step (3), 300 mg of boron hydroxide Ga(OH)3 is added to the mixed solution, and the concentration of Ga(OH)3 in the mixed solution is 2000.0 mg / L.

[0048] Example 9: The difference from Example 7 is that in step (3), 42 mg of boron hydroxide In(OH)3 is added to the mixed solution, and the concentration of In(OH)3 in the mixed solution is 280.0 mg / L.

[0049] Comparative Example 1: PFOA is subjected to single light degradation

[0050] (1) 100 mg of PFOA solid is weighed into a 1 L volumetric flask, stirred and dissolved to obtain a 100 mg / L PFOA stock solution;

[0051] ​(2) Put the 300W mercury lamp in the XPA-7 type light reaction instrument, preheat for 30 min, and make the output stable light intensity;

[0052] (3) 7.5 mL of 100 mg / L PFOA stock solution and 142.5 mL of deionized water were mixed uniformly to obtain a mixed solution, the pH of the mixed solution was adjusted to 7, the concentration of PFOA in the mixed solution was 5 mg / L, and then the light reaction was carried out, at the preset reaction time point, the lamp cover of the light reaction instrument was pulled down, 1.0 mL of reaction solution was taken out from the light reaction tube into a 10 mL plastic centrifugal tube, 4 mL of methanol was added, stirring extraction was carried out for 40 min, the change of PFOA concentration was monitored by high performance liquid chromatography-mass spectrometry, and the degradation rate was calculated.

[0053] Comparative Example 2: The difference from Comparative Example 1 is that in step (2), the 300W mercury lamp light source is replaced by yellow light, and the XPA-7 type light reaction instrument is replaced by a self-made light reaction device, and the light degradation experiment is repeated.

[0054] Comparative Example 3: The difference from Comparative Example 2 is that in step (2), the yellow light is replaced by red light, and the light degradation experiment is repeated.

[0055] The degradation performance of PFOA in Examples 1-9 and Comparative Examples 1-3 is shown in the graphs of Figure 3 and Figure 4 .

[0056] As can be seen from Figure 3 , under the optimal reaction conditions, compared with the single light degradation system, the degradation of PFOA is promoted by 18.5%, 33.6% and 7.1% respectively after 48h UV light irradiation after the addition of Al(OH)3, Ga(OH)3 and In(OH)3. There is no obvious degradation of PFOA after yellow light or red light LED irradiation, and the photocatalytic efficiency of Al(OH)3, Ga(OH)3 and In(OH)3 under the optimal dose can reach 23.5%( Figure 4 ).

[0057] In order to determine the catalytic performance of Al(OH)3, Ga(OH)3 and In(OH)3, the degradation concentration of PFOA was evaluated at 1 mmol of hydroxide (formula: degradation concentration (L·mmol -1 ) = degradation concentration of PFOA / amount of substance of hydroxide). The size relationship of efficiency is Al(OH)3 > In(OH)3 > Ga(OH)3 (as shown in Figure 5 ).

[0058] In the above photocatalytic reaction system, the catalytic mechanism of the boron hydroxide is as follows: on the one hand, the synthesized boron hydroxide has a positive charge on the surface under the condition of pH 7, and there is an electrostatic interaction between the negative PFOA and the surface of the hydroxide. PFOA is adsorbed to the surface of the hydroxide in a monodentate complex manner, and there is a weak hydrogen bond interaction between the CF2 group of PFOA and the hydroxyl group on the surface of the hydroxide. The complexing mode reduces the bond energy of the α-C-C bond in PFOA. Under the action of UV light, the α-C-C bond in PFOA is easily dissociated to form C7H 15 and CO2·; on the other hand, the holes in the hydroxide can oxidize PFOA ions; in addition, under the irradiation of yellow light and red light, the hydroxide has a two-photon absorption effect, which reduces the dissociation energy of the α-C-C bond and makes the C-C bond more easily broken to form C7H 15 and CO2· Figure 6 ).

[0059] In order to verify the mechanism of the photocatalytic degradation of PFOA by the hydroxide in the above examples, the applicants conducted the following experiments: the zero potential point of the hydroxide was measured, and the results showed that the zero potential points of the three hydroxides were 8.40, 7.09 and 7.56, respectively. Under the condition of pH = 7, the surface of the hydroxide is positively charged Figure 7 ).

[0060] The original and PFOA-adsorbed hydroxides were characterized by infrared spectroscopy. According to the calculation formula Δν = ν as (COO - )-ν s (COO - ), the wave number difference in the PFOA-Al(OH)3, PFOA-Ga(OH)3 and PFOA-In(OH)3 systems was 261 cm -1 , 271 cm -1 and 277 cm -1 , respectively. Figure 8 , it is determined that the hydroxide and PFOA are monodentate complexation.

[0061] 19F NMR spectroscopy results show that the peaks at -84.12, -121.26, -123.88, -124.34, -124.80, 125.14 and -128.82 ppm in the PFOA sample are attributed to the end C(8)F3 and C(2-7)F2 groups, respectively. After PFOA is adsorbed on the surface of hydroxide, the end C(8)F3 groups in PFOA-Al(OH)3, PFOA-Ga(OH)3 and PFOA-In(OH)3 show a shift of 0.42, 0.40 and 0.32 ppm, respectively. In addition, the peaks of C(3-6)F2 groups overlap into one large peak, indicating that the CF2 groups of PFOA can interact with the surface hydroxyl groups of hydroxide through hydrogen bonding. Figure 9

[0062] The results of EPR tests, quenching experiments and aeration experiments show that the holes in the hydroxide can oxidize PFOA ions. The results of UV-Vis diffuse reflectance tests show that Al(OH)3 has a significant absorption peak at 300.0 nm. Similarly, Ga(OH)3 and In(OH)3 have significant absorption peaks at 268.0 nm and 312.0 nm, respectively, so the band gap energies E g of Al(OH)3, Ga(OH)3 and In(OH)3 are 4.1 eV, 4.6 eV and 4.0 eV, respectively. Figure 10 The range of hv from yellow light to red light (496.0 nm-775.0 nm) is about 1.6 eV-2.5 eV, so the range of hv to 2hv is 3.2 eV-5.0 eV. The E g of hydroxide is in this range, so there may be a two-photon absorption effect. The hydroxide shows upconversion luminescence effect (emission peaks appear at 510.0 nm and 460.0 nm) under 650 nm laser excitation. The results of variable power tests show that the luminescence intensity is proportional to the square of the power when the excitation power increases, thereby proving that the hydroxide has a two-photon absorption effect. Figure 11

[0063] Example 10: Analysis of influencing factors of PFOA degradation under photocatalytic system

[0064] From the above examples, it can be seen that Al(OH)3 has the most excellent photocatalytic properties for PFOA degradation. In this example, the pH of the water body is adjusted to 3-7 or a certain amount of common anions (Cl - , SO4 2- and HCO3 - , NO3 - ) is added to the water body for photocatalytic experiments to determine the influence of water quality factors on the performance of Al(OH)3 photocatalytic degradation of PFOA.

[0065] ​​After 48h UV irradiation, Al(OH)3 has good photocatalytic effect on PFOA under non-extreme conditions (pH = 3.0-7.0); Cl - 、SO4 2- and HCO3 - have obvious inhibitory effect on the degradation of PFOA, and the degradation rate of PFOA decreases by 4.2%, 15.1% and 17.5% respectively during 48h light irradiation, while NO3 - has no obvious inhibitory effect on the degradation of PFOA, and only decreases from 53.0% to 52.8%.

[0066] The above results show that boron hydroxide, especially Al(OH)3 solid, has certain application potential and can be considered for the degradation of PFOA in water.

[0067] Comparative Example 4: The difference from Example 2 is that Ga2O3 is used instead of boron hydroxide Ga(OH)3, and the concentration used here is 0.5g / L.

[0068] Comparative Example 5: The difference from Example 3 is that In2O3 is used instead of boron hydroxide In(OH)3, and the concentration used here is 0.5g / L.

[0069] It is found from the degradation efficiency of PFOA in Comparative Example 2-Example 3 and Comparative Example 4-Comparative Example 5 that Ga(OH)3 has about 18% higher catalytic performance on PFOA than Ga2O3 at the same concentration, and In(OH)3 has about 12% higher catalytic performance on PFOA than In2O3, indicating that boron hydroxide has better degradation effect on PFOA than oxide and has broader application prospect.

Claims

1. A method for photocatalytic degradation of perfluorooctanoic acid in water using boron-based hydroxide, characterized by, The steps are: adding boron hydroxide as a photocatalyst into a water body containing perfluorooctanoic acid, mixing thoroughly, and then performing photocatalytic degradation reaction under a light source; the boron hydroxide is aluminum hydroxide, gallium hydroxide or indium hydroxide.

2. The method of claim 1, wherein, The mass ratio of the perfluorooctanoic acid to the aluminum hydroxide is 1:8-12.

3. The method of claim 1, wherein, The mass ratio of the perfluorooctanoic acid to the gallium hydroxide is 1:300-600.

4. The method of claim 1, wherein, The mass ratio of the perfluorooctanoic acid to the indium hydroxide is 1:40-60.

5. The method of claim 1, wherein, The preparation method of the boron hydroxide adopts an alkali precipitation method, and the steps are: adding a first concentration sodium hydroxide solution drop by drop into a solution containing aluminum salt, gallium salt or indium salt, generating white flocculent precipitate, then adding a second concentration sodium hydroxide solution drop by drop, waiting for the precipitate to be generated completely, washing the precipitate with a solvent, drying, cooling the obtained solid, grinding, and the obtained solid powder is the boron hydroxide.

6. The method of claim 5, wherein, The concentration of the first concentration sodium hydroxide solution is 8-10M, and the concentration of the second concentration sodium hydroxide solution is 1-2M.

7. The method of claim 6, wherein, The pH of the water body containing perfluorooctanoic acid is 3-7.

8. The method of claim 1, wherein, The light source is ultraviolet light, yellow light or red light.

9. The method of claim 1, wherein, The conditions of the degradation reaction are: reacting at 24-26℃ for 24-50h.

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