A method for photocatalytic degradation of perfluorooctanoic acid by bismuth nanoparticle modified titanium dioxide

Abstract

The application belongs to the field of environmental treatment, and provides a method for photocatalytic degradation of perfluorooctanoic acid by bismuth nanoparticle modified titanium dioxide, which comprises the following steps: preparation of bismuth nanoparticle modified titanium dioxide photocatalyst and photocatalytic degradation of perfluorooctanoic acid by using the prepared catalyst. Specifically, titanium dioxide is suspended in a oxalic acid solution, bismuth salt is added, and a suspension is obtained by ultrasonic dispersion; the suspension is reacted under light, solid-liquid separation is performed, the precipitate is collected, washing, freeze-drying is performed, and a solid product is obtained; the solid product is calcined under a nitrogen atmosphere to obtain a bismuth nanoparticle modified titanium dioxide photocatalyst; and the photocatalyst is used to degrade perfluorooctanoic acid under ultraviolet light and sunlight. After modification of bismuth nanoparticles, the recombination of photo-generated electrons and holes of titanium dioxide is effectively inhibited, the absorption of light is improved, efficient degradation of perfluorooctanoic acid in water under natural sunlight can be achieved, and excellent application prospects are achieved. The problem of difficult degradation of PFOA at present is solved.

Description

Technical Field

[0001] This invention belongs to the field of environmental treatment, and specifically relates to a method for photocatalytic degradation of perfluorooctanoic acid by bismuth nanoparticles modified with titanium dioxide. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a class of synthetic organic compounds with excellent thermal stability and antioxidant capacity, widely used in industrial production and consumer goods. Perfluorooctanoic acid (PFOA) is one of the most commonly used PFAS and is widely detected in the environment. Due to its chemical stability, PFOA is difficult to degrade under natural conditions and can persist in the environment for a long time. Studies have shown that the half-life of PFOA in human serum is approximately 2.7 years, in surface seawater it is approximately 256 years, and in soil it is even longer. Toxicological studies have shown that PFOA can exert various toxic effects on organisms, such as developmental toxicity, immunotoxicity, neurotoxicity, and genotoxicity, and can accumulate in organisms through the food chain. Therefore, there is a need to develop cost-effective treatment technologies to remove PFOA from polluted water bodies and reduce its threat to the ecological environment and human health.

[0004] Due to the strong CF (~485 kJ / mol) bonds of PFOA, traditional wastewater treatment technologies struggle to remove it. Therefore, many advanced oxidation / reduction technologies have been extensively studied, including electrochemical, sonochemical, photochemical, photocatalytic, and thermochemical methods. Among these emerging technologies, heterogeneous photocatalysis shows great promise due to its mild reaction conditions, environmental friendliness, and low energy requirements. In recent years, TiO2 photocatalysts have been widely used in photocatalytic research due to their non-toxicity, low cost, excellent photocatalytic activity, and high chemical stability. However, TiO2 has significant drawbacks in degrading PFOA: its relatively wide band gap energy (approximately 3.2 eV) limits its ability to utilize sunlight; and the high recombination efficiency of photogenerated electrons and holes inhibits its photocatalytic activity in degrading PFOA. Summary of the Invention

[0005] This invention aims to address the problems existing in the prior art. Therefore, this invention provides a novel, simple, and green method for preparing a bismuth nanoparticle-modified titanium dioxide (Bi / TiO2) photocatalyst; simultaneously, the prepared Bi / TiO2 photocatalyst is used to photocatalytically degrade PFOA in the aquatic environment under ultraviolet light and sunlight, achieving the goal of simple, green, and efficient removal of PFOA from water.

[0006] The Bi / TiO2 photocatalyst prepared in this invention uses bismuth in a zero-valent nanoparticle state, unlike other techniques where bismuth is doped into the titanium dioxide structure in a trivalent ionic state. In this invention, depositing bismuth nanoparticles (Bi NPs) on the titanium dioxide surface fully utilizes the surface plasmon resonance characteristics of Bi NPs, enhancing light absorption and effectively promoting the separation of photogenerated electrons and holes in TiO2 as electron traps, thus improving photocatalytic activity, particularly for the photocatalytic degradation of perfluorooctanoic acid (PFOA), which can be achieved under sunlight. These advantages are not possessed by other ionic bismuth doping techniques.

[0007] To achieve the above objectives, the present invention employs the following technical solutions, including a method for preparing a Bi / TiO2 catalyst and a method for degrading perfluorooctanoic acid in water.

[0008] In a first aspect, the present invention provides a method for preparing a Bi / TiO2 catalyst for the degradation of PFOA in water, the method being as follows:

[0009] (1) Suspend TiO2 in oxalic acid solution, add bismuth salt, and ultrasonically disperse for 10-30 min to obtain a suspension;

[0010] (2) The suspension was reacted under light for 0.5-5 hours, the solid and liquid were separated, the precipitate was collected, washed and freeze-dried to obtain a solid product;

[0011] (3) The solid product is calcined to obtain a Bi / TiO2 photocatalyst;

[0012] The mass ratio of the active component bismuth to TiO2 in the suspension is 3:100-15:100.

[0013] Bismuth (Bi), a semi-metallic compound, boasts advantages such as low cost and environmental friendliness. Its surface plasmon resonance properties enhance the utilization of sunlight, while also acting as an electron trap to effectively separate photogenerated electrons and holes. Modifying TiO2 with bismuth nanoparticles (Bi NPs) for PFOA degradation achieves high efficiency while also being environmentally friendly and economical. Furthermore, enabling PFOA degradation under sunlight significantly reduces costs in practical applications.

[0014] In some embodiments, the concentration of TiO2 in the suspension is 0.5-1.5 g / L.

[0015] In some embodiments, the concentration of the oxalic acid solution is 0.5-2 mol / L.

[0016] In some embodiments, the bismuth salt is either bismuth nitrate or bismuth chloride.

[0017] In some embodiments, the light source used for illumination is a light source that emits light with a dominant wavelength of less than 400 nm.

[0018] In some embodiments, the freeze-drying temperature is -60 to 40°C, and the drying time is 10 to 24 hours.

[0019] In some embodiments, the calcination temperature is 250-650°C, the calcination time is 0.5-4 hours, and the calcination atmosphere is nitrogen.

[0020] In a second aspect, the present invention provides a Bi / TiO2 photocatalyst prepared by the above-described method.

[0021] A third aspect of the present invention provides a method for the photocatalytic degradation of perfluorooctanoic acid in water using Bi / TiO2, the method being as follows:

[0022] The above-mentioned Bi / TiO2 photocatalyst is added to water containing PFOA and degraded under the irradiation of a light source with a main emission wavelength of less than 400nm or sunlight to obtain the final product.

[0023] In the water, the amount of Bi / TiO2 added is 0.03-1 g / L, and the concentration of PFOA is 10-150 mg / L.

[0024] A fourth aspect of the present invention provides the application of the above-mentioned Bi / TiO2 photocatalyst in the photocatalytic degradation of PFOA in water under a light source with a dominant emission wavelength of less than 400 nm or a solar light source.

[0025] Beneficial effects of the present invention

[0026] (1) This invention uses a photochemical reduction deposition method to deposit bismuth nanoparticles (Bi NPs) onto TiO2 to prepare a Bi / TiO2 photocatalyst. The deposition of Bi NPs effectively promotes the separation of photogenerated electrons and holes in TiO2, thereby enhancing the photocatalytic activity. Compared with Bi / TiO2 prepared by the traditional hydrothermal method, the degradation efficiency of PFOA in water is significantly improved.

[0027] (2) This invention utilizes the plasmon resonance effect of Bi NPs to greatly enhance the catalyst’s ability to absorb ultraviolet and visible light, promote the generation of active free radicals, and improve the utilization of clean energy solar energy.

[0028] (3) Compared with other existing technologies, the method of the present invention degrades PFOA with mild reaction conditions, simple and easy operation, economy, greenness and high efficiency. Bi / TiO2 catalyst can achieve efficient degradation of PFOA under natural sunlight, while TiO2 has basically no degradation effect under the same conditions. Attached Figure Description

[0029] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0030] Figure 1 This is a transmission electron microscope (TEM) image of Bi / TiO2 in Example 1;

[0031] Figure 2 The X-ray diffraction (XRD) patterns of Bi / TiO2 in Example 1 and Example 2 and TiO2 in Comparative Example 1 are shown below.

[0032] Figure 3 The UV-Vis diffuse reflectance (UV-visDRS) spectra of Bi / TiO2 in Example 1 and Example 2 and TiO2 in Comparative Example 1 are shown.

[0033] Figure 4 The photoluminescence (PL) spectra of Bi / TiO2 in Example 1 and Example 2 and TiO2 in Comparative Example 1 are shown.

[0034] Figure 5 The graphs show the degradation kinetics of PFOA in Examples 1, 2, and 1 (Comparative Example 1).

[0035] Figure 6 This is a graph showing the degradation kinetics of PFOA in Example 3;

[0036] Figure 7 The graphs show the degradation kinetics of PFOA under the conditions of Example 4, Comparative Example 4, and catalyst-free conditions. Detailed Implementation

[0037] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0038] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be noted that the specific embodiments described are explanations of the present invention and not limitations thereof.

[0039] Example 1

[0040] (1) Preparation of Bi / TiO2 photocatalyst

[0041] 100 mg of TiO2 was suspended in 100 mL of 1 mol / L oxalic acid solution, and 11.6 mg of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) was added to make the mass ratio of the active component Bi to TiO2 in the suspension 5:100. The mixture was ultrasonically dispersed for 10 min. The above mixed suspension was placed in a photochemical reactor and magnetically stirred for 3 h under irradiation by a 400 W mercury lamp (main wavelength 365 nm). The gray-black precipitate was collected by centrifugation, washed several times with a small amount of ethanol and deionized water, and then dried in vacuum freeze-drying at -48 °C for 12 h. The dried material was placed in a tube furnace and heated to 450 °C at a constant rate of 15 °C / min under a nitrogen atmosphere, calcined at this temperature for 2 h, and then cooled to room temperature to obtain Bi / TiO2 (5:100).

[0042] (2) Bi / TiO2 photocatalyst for the degradation of PFOA in water

[0043] A 50 mL solution of 50 mg / L PFOA was placed in a quartz test tube, and the BT5 photocatalyst prepared in step (1) was added at a concentration of 0.12 g / L. The test tube was placed in a photocatalytic reactor, and after stirring for 30 min in the dark to reach adsorption equilibrium, a photocatalytic reaction was carried out for 30 min under irradiation with a 400 W mercury lamp (main wavelength 365 nm). Samples were taken every 5 min for testing. The removal rate of PFOA in water by this method after 30 min of photocatalytic reaction was 99.3%.

[0044] Figure 1 This is a transmission electron microscope (TEM) image of Bi / TiO2 in Example 1. It can be observed that Bi NPs were successfully loaded on TiO2, with the size of the Bi NPs around 5 nm and the size of the TiO2 particles ranging from 50 to 200 nm. The Bi NPs, deposited on TiO2 at the quantum dot size, are more conducive to light absorption and the separation of photogenerated electrons and holes, resulting in superior photocatalytic performance.

[0045] Comparative Example 1

[0046] TiO2 without Bi NPs modification was selected as the photocatalyst, and the degradation steps were the same as in Example 1 (2). The removal rate of PFOA in water by this method after 30 min of photoreaction was 3.3%.

[0047] Comparative Example 2

[0048] Commercial indium oxide (In2O3), which has a good photocatalytic degradation effect on PFOA but is expensive, was selected as the photocatalyst. The degradation steps were the same as in Example 1 (2). The removal rate of PFOA in water by this method after 30 min of photocatalytic reaction was 34.1%.

[0049] Comparative Example 3

[0050] Bi / TiO2 prepared by hydrothermal method was selected as the photocatalyst. The degradation steps were the same as in Example 1 (2). The removal rate of PFOA in water by this method after 30 min of photoreaction was 29.7%.

[0051] The specific steps for preparing Bi / TiO2 via hydrothermal method include: First, dissolving 0.121 g of Bi(NO3)3·5H2O in 10 mL of 1 M HNO3. Then, transferring the mixture to a 100 mL Teflon reactor and stirring vigorously. After dissolution, adding 55 mL of ethylene glycol and stirring for 10 min. Next, adding 0.6 g of polyvinylpyrrolidone (PVP, molecular weight 24000) and stirring for another 30 min. After complete dissolution of the solid, adding 1 g of TiO2 to the solution and ultrasonically dispersing for 30 min. Then, hydrothermally treating the suspension at 160 °C for 12 h. After the reaction, filtering to collect the solid product, washing twice each with ultrapure water and ethanol, and then drying at 60 °C for 12 h, yields the bismuth nanoparticle-modified titanium dioxide photocatalyst (Bi / TiO2). The mass ratio of Bi to TiO2 in the preparation system is 5:100.

[0052] Example 2

[0053] (1) Preparation of Bi / TiO2 photocatalyst

[0054] 100 mg TiO2 was suspended in 100 mL of 1 mol / L oxalic acid solution, and 23.2 mg Bi(NO3)3·5H2O was added to make the mass ratio of active component Bi to TiO2 in the suspension 10:100. The suspension was then ultrasonically dispersed for 10 min. Other steps were the same as in step (1) of Example 1.

[0055] (2) Bi / TiO2 photocatalyst for the degradation of PFOA in water

[0056] As in step (2) of Example 1, this method achieves a PFOA removal rate of 91.5% in water after a 30-minute photoreaction.

[0057] Figure 2 The X-ray diffraction (XRD) patterns of Examples 1, 2, and Comparative Example 1 are shown. It can be seen that the diffraction peaks corresponding to the anatase TiO2 standard card (PDF 99-0008) can be observed in the XRD patterns of Examples 1, 2, and Comparative Example 1. The diffraction peaks corresponding to the zero-valent bismuth metal standard card (PDF 85-1329) can also be observed in the patterns of Examples 1 and 2. This indicates that Bi NPs in the photocatalyst exist in a zero-valent metallic state, and no other impurity peaks were observed, indicating that the method of the present invention successfully deposited Bi NPs onto TiO2, and the obtained samples were relatively pure.

[0058] Figure 3 The images show the UV-Vis diffuse reflectance (UV-vis DRS) spectra of Examples 1, 2, and Comparative Example 1. It can be seen that the Bi / TiO2 photocatalyst exhibits significantly enhanced absorption in the UV and visible light regions compared to the original TiO2. This is mainly because the surface plasmon resonance characteristics of bismuth metal enhance the catalyst's light absorption, thereby increasing the yield of photogenerated carriers and the utilization of light energy, thus improving photocatalytic activity.

[0059] Figure 4 The photoluminescence (PL) spectra of Examples 1, 2, and Comparative Example 1 are shown. It can be observed that the PL intensity of the Bi NPs-modified catalyst is significantly weaker compared to the original TiO2. This is mainly because Bi NPs can act as electron traps, effectively promoting the separation of photogenerated electrons and holes in the catalyst, which will help degrade PFOA adsorbed on the catalyst surface.

[0060] Figure 5 The figures show the degradation kinetics curves of PFOA in Example 1, Comparative Example 1, and Comparative Example 2. It is clearly observed that Bi / TiO2 has a better degradation effect on PFOA than In2O3 and is significantly better than TiO2.

[0061] Example 3

[0062] The preparation of the Bi / TiO2 photocatalyst was the same as step (1) in Example 1. During the photocatalytic degradation of PFOA, 50 mL of a 50 mg / L PFOA solution was placed in a series of quartz test tubes, and Bi / TiO2 (5:100) prepared in step (1) of Example 1 was added at concentrations of 0.03 g / L, 0.06 g / L, 0.25 g / L, and 0.50 g / L, respectively. Other steps were the same as step (2) in Example 1. The removal rates of PFOA in water after 30 min of photocatalytic reaction were 74.8% (0.03 g / L), 91.4% (0.06 g / L), 98.4% (0.25 g / L), and 91.5% (0.5 g / L), respectively.

[0063] Figure 6 This is a degradation kinetic curve of PFOA in Example 3. It can be observed that a relatively low dosage of Bi / TiO2 still has a good effect on the removal of PFOA from water, which is beneficial for reducing wastewater treatment costs in practical applications.

[0064] Example 4

[0065] The preparation of the Bi / TiO2 photocatalyst was the same as step (1) in Example 1. During the photocatalytic degradation of PFOA, 50 mL of a 50 mg / L PFOA solution was placed in a quartz beaker, and Bi / TiO2 prepared in step (1) of Example 1 was added at a dosage of 0.12 g / L. The beaker was placed on an outdoor magnetic stirrer and exposed to sunlight (temperature 20-24℃, light intensity approximately 900 W / m²). 2 The photocatalytic reaction was carried out for 3 hours, with samples taken every 30 minutes for testing. The Bi / TiO2 photocatalyst prepared in this example achieved a 100% removal rate of PFOA in water after reacting under sunlight for 3 hours.

[0066] Comparative Example 4

[0067] TiO2 without Bi NPs modification was selected as the photocatalyst. The photocatalytic degradation process of PFOA was the same as in Example 4. However, the TiO2 in this comparative example hardly removed PFOA from the water after reacting under sunlight for 3 hours.

[0068] Figure 7 The figures show the degradation kinetics curves of PFOA under Example 4, Comparative Example 4, and catalyst-free conditions. It can be seen that Bi / TiO2 can achieve complete removal of PFOA after 2 hours of sunlight irradiation, which will greatly reduce operating costs in practical applications.

[0069] Table 1. Removal effect of different embodiments and comparative examples on PFOA

[0070]

[0071] Table 1 summarizes the PFOA removal effects in the different embodiments and comparative examples above. It can be seen that the Bi / TiO2 photocatalyst prepared by the present invention can significantly improve the removal of PFOA in water and can achieve efficient degradation under sunlight, showing excellent application prospects.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a bismuth nanoparticle-modified titanium dioxide photocatalyst for degrading perfluorooctanoic acid in water, characterized in that, include: Titanium dioxide was suspended in oxalic acid solution, bismuth salt was added, and the mixture was ultrasonically dispersed for 10-30 min to obtain a suspension. The suspension was reacted under light for 0.5-5 h, the solid and liquid were separated, the precipitate was collected, washed, and freeze-dried to obtain the solid product; The solid product was calcined to obtain a bismuth nanoparticle-modified titanium dioxide photocatalyst. The mass ratio of the active component bismuth to titanium dioxide in the suspension is 3:100-15:100; The concentration of the oxalic acid solution is 1-2 mol / L; The calcination temperature is 250-650 ℃, the calcination time is 0.5-4 h, and the calcination atmosphere is nitrogen.

2. The preparation method of the bismuth nanoparticle-modified titanium dioxide photocatalyst for degrading perfluorooctanoic acid in water as described in claim 1, characterized in that, The concentration of titanium dioxide in the suspension is 0.5-1.5 g / L.

3. The preparation method of the bismuth nanoparticle-modified titanium dioxide photocatalyst for degrading perfluorooctanoic acid in water as described in claim 1, characterized in that, The bismuth salt is either bismuth nitrate or bismuth chloride.

4. The preparation method of the bismuth nanoparticle-modified titanium dioxide photocatalyst for degrading perfluorooctanoic acid in water as described in claim 1, characterized in that, The illumination uses a light source that emits light with a main wavelength of less than 400 nm.

5. The method for preparing bismuth nanoparticle-modified titanium dioxide photocatalyst for degrading perfluorooctanoic acid in water as described in claim 1, characterized in that, The freeze-drying temperature is -60 to 40 ℃, and the drying time is 10 to 24 h.

6. The bismuth nanoparticle-modified titanium dioxide photocatalyst prepared by the method according to any one of claims 1-5.

7. A method for photocatalytic degradation of perfluorooctanoic acid in water by bismuth nanoparticles modified with titanium dioxide, characterized in that, include: The bismuth nanoparticle-modified titanium dioxide photocatalyst of claim 6 is added to water containing perfluorooctanoic acid and degraded under the irradiation of a light source with a dominant emission wavelength of less than 400 nm or by sunlight to obtain the product. In the water, the amount of Bi / TiO2 added is 0.03-1 g / L, and the concentration of PFOA is 10-150 mg / L.

8. The application of the bismuth nanoparticle-modified titanium dioxide photocatalyst according to claim 6 in the photocatalytic degradation of perfluorooctanoic acid in water under a light source with a dominant wavelength of less than 400 nm or a solar light source.

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