A method for catalytic degradation of pollutants

Abstract

The present invention discloses a method for catalytically degrading pollutants, comprising adding a trivalent bismuth salt aqueous solution to a buffered salt solution and a water mixture containing phenolic pollutants, generating bismuth hydroxide in situ in the mixture, and then utilizing the bismuth hydroxide to catalyze ferrate to degrade the water pollutants. The present invention solves the problem of how to efficiently catalyze Fe(VI) and organic pollutants in water after generating bismuth hydroxide in situ. Due to the characteristic that Bi(III) itself is extremely easy to hydrolyze to generate hydroxide precipitates, the bismuth hydroxide precipitates generated in situ in water are easy to recycle and process, will not cause secondary pollution, and can be recycled multiple times. In combination with ferrate, it can effectively achieve efficient removal of multiple phenols in water. Its application in Fe(VI) catalytic reaction efficiency enhancement has excellent application prospects.

Description

Technical Field

[0001] The invention relates to a method for degrading phenolic pollutants, in particular to a method for degrading phenolic pollutants by in-situ generating bismuth hydroxide and catalyzing ferrate. Background Art

[0002] Ferrate (Fe(VI)), a strong oxidant, boasts strong selectivity, high efficiency, and the absence of toxic byproducts. In water treatment, it can be used for efficient oxidation, sterilization, adsorption, and flocculation, particularly in the removal of pharmaceuticals and personal care products from water. However, Fe(VI) is unstable in water and rapidly self-decomposes. Furthermore, its high production cost and complex processing conditions limit its application.

[0003] To solve the above problems, researchers improved the oxidation capacity of the oxidation system by generating catalysts in situ in the oxidation system. Journal literature (Synergistic effect of aqueous removal offluoroquinolones by acombined use of peroxymonosulfate and ferrate(VI), Chemosphere2017,177,144-148. Accelerated Oxidation of Organic Contaminants byFerrate(VI): The Overlooked Role of Reducing Additives,Environ.Sci.Technol.2018,52(19).Oxidation of manganese(II)with ferrate:Stoichiometry,kinetics,products and impact of organic carbon,Chemosphere2016,159,457-464.Insights into the role of in-situ and ex-situ hydrogen peroxidefor enhanced ferrate(VI)towards oxidation of organic contaminants,WaterRes.2021,203,117548.Efficient activation of ferrate(VI)by colloid In the prior art described in

[15] , the synergistic methods for Fe(VI) are mainly focused on the synergistic effects of persulfate (PMS), thiosulfate (S2O3 2- ), sulfite (SO3 2- ), Cu(II), Fe(III), and other reducing anions. However, these methods have drawbacks such as introducing secondary water pollution and difficulty in recycling. Therefore, the search for other efficient and recyclable catalysts is necessary to expand the application of Fe(VI).

[0004] Bismuth-based catalysts (such as bismuth oxyhalides, bismuth-based oxygen-containing salts, etc.) are widely used in the field of photocatalysis, but there has been no relevant research on the application of trivalent bismuth ions (Bi(III)) to the removal of organic pollutants in water. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a method for catalytic degradation of pollutants, by enhancing the ferrate oxidation degradation system through the in-situ generation of bismuth hydroxide in the polluted water body, thereby solving the problems of secondary pollution and recovery difficulties existing in the existing ferrate enhancement means.

[0006] The problem of in situ generation of bismuth hydroxide in water as a pollutant degradation catalyst is solved, and the in situ generated bismuth hydroxide efficiently catalyzes Fe(VI) to degrade organic pollutants in water.

[0007] Technical solution: The method of catalytically degrading pollutants described in the present invention includes in-situ generation of bismuth hydroxide in a water body containing pollutants, and then using the bismuth hydroxide to catalyze ferrate to degrade the water pollutants.

[0008] Taking advantage of the fact that Bi(III) itself is very easy to hydrolyze to form hydroxide precipitate, the in-situ generated bismuth hydroxide precipitate is used to catalyze the Fe(VI) degradation of pollutants by ferrate.

[0009] Preferably, the method for in-situ generation of bismuth hydroxide is: adding a trivalent bismuth salt aqueous solution to a water body containing pollutants to generate a bismuth hydroxide precipitate in situ.

[0010] Preferably, the trivalent bismuth salt comprises at least one of bismuth nitrate, bismuth sulfate, and bismuth chloride; and the pH of the pollutant-containing water ranges from 3 to 10. The trivalent bismuth salt can be a pure substance or a bismuth salt hydrate. An appropriate pH value facilitates the rapid and uniform formation of a flocculent bismuth hydroxide precipitate in water. The flocculent bismuth hydroxide particles are finer and more uniform, with a larger surface area in contact with the water, making it more suitable for use as a catalyst.

[0011] Preferably, the trivalent bismuth salt aqueous solution is prepared by dissolving a trivalent bismuth salt in an aqueous nitric acid solution; and the pH of the pollutant-containing water is adjusted by adding a buffered salt solution. The buffered salt solution ensures that the pH of the water remains within the optimal reaction pH range, preventing large pH fluctuations during the reaction that could affect the formation of bismuth hydroxide precipitation.

[0012] Preferably, the buffered salt solution is one of borate buffer, citrate buffer or phosphate buffer; the concentration of the nitric acid aqueous solution is 0.5-1.5 M. The trivalent bismuth salt aqueous solution is prepared by dissolving the trivalent bismuth salt in water using dilute nitric acid.

[0013] Preferably, a trivalent bismuth salt aqueous solution is added to the pollutant-containing water until Bi 3+ The final concentration is 0.1-10 mM.

[0014] Preferably, the water pollutants are phenolic pollutants, and the phenolic pollutants include at least one of 2-hydroxybenzophenone, benzophenone-1, benzophenone-3, benzophenone-4, benzophenone-7, benzophenone-8, bisphenol S, bisphenol A, 2,4-difluorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, 4-chlorophenol, and phenol. The present invention can be used to degrade phenolic pollutants, but for other types of micropollutants in water except phenolic substances, Fe(VI)-Bi 3+ Oxidative systems may have similar reactivities.

[0015] Preferably, the in-situ generation of bismuth hydroxide to catalyze ferrate to degrade water pollutants specifically includes the following steps:

[0016] (1) Mixing a buffered salt solution with water containing pollutants and adjusting the pH to 3-10;

[0017] (2) adding a trivalent bismuth salt aqueous solution to the mixed solution in step (1) to generate a bismuth hydroxide precipitate in situ;

[0018] (3) After bismuth hydroxide precipitate is formed, ferrate stock solution is added to react to degrade water pollutants.

[0019] The concentration of ferrate in the ferrate stock solution in the above-mentioned catalytic degradation step is 10-120 mM, the final concentration of ferrate is 10-300 μM, and the molar ratio of ferrate to pollutant is 2.5-30:1; the solvent of the ferrate stock solution is a potassium boron aqueous solution, which is prepared by dissolving sodium tetraborate and dipotassium hydrogen phosphate in water.

[0020] Beneficial Effects: Compared with existing technologies, the present invention offers the following significant advantages: the bismuth hydroxide catalyst employed in the present invention is generated in situ, resulting in a simple preparation method, a short catalyst generation time, and high catalytic degradation efficiency, achieving efficient degradation of various phenolic pollutants in just 5 minutes. The in-situ bismuth hydroxide precipitate generated in water is easily recovered and can be recycled multiple times. After five cycles, the degradation rate remains above 95%, demonstrating excellent catalytic performance. Combined with ferrate, it can effectively and efficiently remove various phenolic pollutants from water. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a scanning electron micrograph of in-situ generated bismuth hydroxide;

[0022] Figure 2Schematic diagram of 2-HBP degradation kinetics;

[0023] Figure 3 is Fe(VI)-Bi 3+ Schematic diagram of the degradation kinetics of various phenols by the system;

[0024] Figure 4 This is a statistical diagram showing the effect of recycling bismuth hydroxide as a catalyst;

[0025] Figure 5 is Fe(VI)-Bi 3+ Schematic diagram of the catalytic mechanism of the system;

[0026] Figure 6 XRD spectra of the catalyst before and after catalytic degradation reaction;

[0027] Figure 7 XPS spectra of the catalyst before and after catalytic degradation reaction;

[0028] Figure 8 Comparison of open circuit potentials of different reaction systems;

[0029] Figure 9 Comparison of instantaneous current changes in different reaction systems. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0031] Example 1: Fe(VI)-Bi 3+ The method for the system to degrade 2-hydroxybenzophenone (2-HBP) is as follows:

[0032] (1) Weigh an appropriate amount of 2-HBP solid and dissolve it in a 100 mL volumetric flask. Prepare a 2.0 mM 2-HBP stock solution with ultrasound-assisted dissolution and store it at 4°C in the dark. Use the 2-HBP stock solution to simulate water samples containing phenolic pollutants.

[0033] (2) Weigh 0.2312 g of potassium ferrate solid and dissolve it in 4.0 mL of potassium boron solution to prepare a 40 mM ferrate stock solution; the potassium boron aqueous solution is prepared by dissolving sodium tetraborate and dipotassium hydrogen phosphate in water, and the concentration of sodium tetraborate in the potassium boron aqueous solution is 1 mM, and the concentration of dipotassium hydrogen phosphate is 5 mM.

[0034] (3) 6.0634 g of bismuth nitrate pentahydrate (Bi(NO₃)₃·9H₂O) was weighed and dissolved in 12.5 mL of 1 M nitric acid aqueous solution. The volume was then adjusted to 25 mL with 0.1 M dilute nitric acid aqueous solution to prepare a 0.5 M bismuth nitrate aqueous solution. 100 μL of 8 M NaOH solution was pre-added to 30 mL of 20 mM borax / boric acid buffer solution (pH 8.0) so that the pH of the reaction system after the addition of the bismuth nitrate aqueous solution reached the desired optimal reaction pH, i.e., pH 8.0.

[0035] (4) Add 150 μL of 2-HBP stock solution to 30 mL of borate buffer system (pH 8.0), and add 300 μL of 0.5 M Bi(NO3)3 aqueous solution under magnetic stirring to make Bi in the mixed solution 3+ The final concentration is 5 mM;

[0036] (5) After the formation of a white flocculent precipitate was observed (the precipitation process took about 10 seconds), 75 μL of 20 mM ferrate stock solution was added to start the reaction and time the reaction. The molar ratio of ferrate to 2-HBP was 5:1, and the final concentration of ferrate was 50 μM. The concentration of 2-HBP in the system was determined by high performance liquid chromatography and its degradation rate was calculated. The morphology of the bismuth hydroxide precipitate is as follows: Figure 1 shown.

[0037] result Figure 2 As shown, Figure 2 Figure 2 is a schematic diagram of the degradation kinetics of 2-HBP by ferrate under in situ bismuth hydroxide catalysis conditions. It can be seen that the in situ generated Bi(OH)3 precipitate has little adsorption to the reaction substrate (such as 5mM Bi 3+ group), when Bi(NO3)3 was added at a final concentration of 5 mM, the removal rate of 2-HBP increased by 36% (from 35% to 71%).

[0038] Example 2: The rest are the same as Example 1, except that:

[0039] The concentration of ferrate stock solution was 10 mM, the molar ratio of ferrate to 2-HBP was 2.5:1, and the final concentration of ferrate was 25 μM. Bismuth nitrate was replaced by bismuth sulfate, which was dissolved in 0.5 M nitric acid aqueous solution. Borax / boric acid buffer solution was replaced by citric acid buffer solution, and the optimal reaction pH was maintained at 3.0. Bi in the mixed solution was 0.5 M nitric acid aqueous solution. 3+ The final concentration is 10 mM.

[0040] Example 3: The rest are the same as Example 1, except that:

[0041] The concentration of ferrate stock solution was 120 mM, the molar ratio of ferrate to 2-HBP was 30:1, and the final concentration of ferrate was 300 μM. Bismuth nitrate was replaced by bismuth chloride, which was dissolved in 1.5 M nitric acid aqueous solution. Borax / boric acid buffer solution was replaced by phosphate buffer solution, and the optimal reaction pH was maintained at pH 7.4. Bi in the mixed solution was 100 μM. 3+ The final concentration is 0.1 mM.

[0042] Example 4: According to the same method as in Example 1, 2-HBP was replaced by other phenolic pollutants for degradation experiments. The results are as follows: Figure 3 As shown in the figure, under similar reaction conditions, the present invention has good removal performance for benzophenone-1, benzophenone-3, benzophenone-4, benzophenone-7, benzophenone-8, bisphenol S, bisphenol A, 2,4-difluorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, 4-chlorophenol, and phenol, and has high universality for phenol pollutants in water bodies. Figure 3 In the figure, (a) is a schematic diagram of the degradation kinetics of benzophenone-1; (b) is a schematic diagram of the degradation kinetics of benzophenone-3; (c) is a schematic diagram of the degradation kinetics of benzophenone-4; (d) is a schematic diagram of the degradation kinetics of benzophenone-7; (e) is a schematic diagram of the degradation kinetics of benzophenone-8; (f) is a schematic diagram of the degradation kinetics of bisphenol A; (g) is a schematic diagram of the degradation kinetics of bisphenol S; (h) is a schematic diagram of the degradation kinetics of 2,4-difluorophenol; (i) is a schematic diagram of the degradation kinetics of 2,3,4,6-tetrachlorophenol; (j) is a schematic diagram of the degradation kinetics of 2,4,6-trichlorophenol; (k) is a schematic diagram of the degradation kinetics of 4-chlorophenol; (l) is a schematic diagram of the degradation kinetics of 2-hydroxybenzophenone.

[0043] Example 5: Experiment on the recycling of bismuth hydroxide as a catalyst:

[0044] The catalyst precipitate after the first reaction in Example 1 was centrifuged and washed once with methanol solution and then with deionized water. The washed catalyst precipitate was transferred to a borate buffer solution, and then the 2-HBP stock solution and the ferrate stock solution were added. The second reaction was then repeated. Multiple cycles of reaction steps were repeated in this manner.

[0045] The results are as follows Figure 4 As shown, from left to right are the degradation rates of the catalyst after 6 cycles. The recycling experiment of bismuth hydroxide as a catalyst proves that it still has excellent catalytic performance after 5 cycles, and the degradation rate of phenol pollutants can still reach more than 95%.

[0046] In the above Fe(VI)-Bi 3+In the degradation reaction system, the catalytic mechanism of bismuth hydroxide is that ferrate can oxidize bismuth hydroxide containing trivalent bismuth ions to sodium bismuthate containing pentavalent bismuth ions, and then the sodium bismuthate containing pentavalent bismuth ions undergoes an oxidation-reduction reaction with phenolic pollutants and is reduced to bismuth hydroxide containing trivalent bismuth ions (such as Figure 5 shown).

[0047] In order to confirm the catalytic mechanism of degradation of phenolic pollutants in the above examples, the applicant conducted the following experiments:

[0048] According to the XRD spectrum (X-ray diffraction, XRD) of the material after catalytic degradation reaction, the characteristic peak of sodium bismuthate can be found and corresponds to the JCPD standard spectrum (No.85-1130) (such as Figure 6 shown);

[0049] XPS (X-ray photoelectron spectroscopy, XPS) characterization results show that the binding energy peak of the material shifted by 0.14 eV after the reaction (such as Figure 7 This is consistent with the literature report that the binding energy of Bi ions increases with increasing valence [S. Hofmann, Auger-and X-Ray Photoelectron Spectroscopy in Materials Science, Springer, New York 2013, p. 487.], further proving the formation of high-valent bismuth.

[0050] According to the electrochemical experimental results, Figure 8 As shown in the figure, the open circuit potential in the catalytic system is significantly enhanced, indicating that the oxidation ability in the catalytic system is enhanced; in addition, a GOP experimental system was constructed to compare the instantaneous current in the catalytic system and the non-catalytic system. Figure 9 The results showed that the instantaneous current intensity in the catalytic system increased, indicating that the single electron transfer process was enhanced in the catalyst experimental group.

Claims

1. A method for catalytic degradation of pollutants, characterized in that: The method comprises generating bismuth hydroxide in situ in a water body containing pollutants, and then utilizing the bismuth hydroxide to catalyze ferrate to degrade the water pollutants; the method for generating bismuth hydroxide in situ comprises: adding a trivalent bismuth salt aqueous solution to the water body containing pollutants to generate bismuth hydroxide precipitation in situ; adding the trivalent bismuth salt aqueous solution to the water body containing pollutants until Bi 3+ The final concentration is 0.1-10 mM; the trivalent bismuth salt includes at least one of bismuth nitrate, bismuth sulfate, and bismuth chloride; the pH value of the water body containing pollutants ranges from 3 to 10; the trivalent bismuth salt aqueous solution is prepared by dissolving a trivalent bismuth salt in a nitric acid aqueous solution; the pH value of the water body containing pollutants is stabilized by adding a buffered salt solution; the water pollutants are phenolic pollutants; the method of using bismuth hydroxide to catalyze ferrate to degrade water pollutants is as follows: after the bismuth hydroxide precipitate is generated in situ, a ferrate stock solution is added to the water body containing pollutants to react and degrade the water pollutants; the concentration of ferrate in the ferrate stock solution is 10-120 mM, the final concentration of ferrate is 10-300 μM, and the molar ratio of ferrate to pollutants is 2.5-30:1; the solvent of the ferrate stock solution is a potassium boron aqueous solution, which is prepared by dissolving sodium tetraborate and dipotassium hydrogen phosphate in water.

2. The method for catalytic degradation of pollutants according to claim 1, characterized in that: The buffered salt solution is one of borate buffer, citrate buffer or phosphate buffer; the concentration of the nitric acid aqueous solution is 0.5-1.5 M.

3. The method for catalytic degradation of pollutants according to claim 1, characterized in that: The phenolic pollutants include at least one of 2-hydroxybenzophenone, benzophenone-1, benzophenone-3, benzophenone-4, benzophenone-7, benzophenone-8, bisphenol S, bisphenol A, 2,4-difluorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, 4-chlorophenol, and phenol.

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