A dom-persulfate system and its preparation method and application

Abstract

The application discloses a DOM-sulfate system, a preparation method and application thereof, and belongs to the technical field of environmental protection. The preparation method of the DOM-sulfate system comprises the following steps: mixing dry farmland soil with water, and leaching; filtering to obtain soil DOM after leaching; and mixing the obtained soil DOM with persulfate, and the system is obtained; in the system, the concentration of the soil DOM is 5-15 mg / L ‑1 ; and the concentration of the persulfate is 0.1-1 mM. The DOM-sulfate system prepared by the preparation method can improve the pH and free radical content of a photocatalytic reaction system, thereby realizing the intensification of the oxidation capacity of the persulfate system, and further improving the short-time photocatalytic degradation efficiency of organic pollutants and reducing the production and application cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environmental protection, and particularly relates to a DOM-persulfate system, a preparation method and application thereof. BACKGROUND

[0002] The photocatalytic method is an environmentally friendly pollutant degradation and conversion means, which is widely used in environmental governance in many fields. The advanced oxidation technology based on the persulfate system has attracted widespread attention due to its strong oxidation ability, and has been proved to be effective in removing organic pollutants. However, the degradation efficiency of the persulfate system alone still needs to be improved in the process of degrading organic pollutants. In order to improve the degradation efficiency, a large number of studies have focused on obtaining catalysts that can effectively improve the persulfate system. For example, Li Huanxuan synthesized two different cobalt metal organic framework materials Co-BTC(A) and Co-BTC(B) to catalyze the degradation of dibutyl phthalate by hydrothermal method; Zhang Lianke et al. prepared LaFeO3 crystals with good visible light response by ultrasonic-assisted sol-gel method, combined with persulfate (PDS) to construct a visible light (Vis) / LaFeO3 / PDS composite advanced oxidation system, which improved the degradation rate of methylene blue (MB). However, most of the catalysts used in the prior art have complex preparation process and high cost.

[0003] Studies have shown that dissolved organic matter (DOM) has multiple effects on the efficiency of advanced oxidation technology. Some studies have shown that the chromophore in DOM can absorb ultraviolet and visible light, resulting in a decrease in molar absorption coefficient, thereby inhibiting the generation of active species; in addition, DOM can quench active species or interfere with the degradation of organic pollutants. However, natural DOM is widely available and has different physicochemical properties, which provides the possibility for the rational application of DOM. Therefore, it is urgent to screen out natural DOM that is friendly to the advanced oxidation system, and to improve the degradation efficiency of pollutants in the advanced oxidation system by introducing DOM. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a preparation method of a DOM-persulfate system, which can effectively improve the oxidation ability of the persulfate system, improve the degradation efficiency of organic pollutants, and reduce the production and application cost.

[0005] Another purpose of the present application is to provide a DOM-persulfate system obtained by the preparation method.

[0006] Another purpose of the present application is to provide an application of the DOM-persulfate system in photocatalytic degradation of organic pollutants.

[0007] Another object of the present application is to provide a method for photocatalytic degradation of organic pollutants.

[0008] To achieve the above-mentioned objects, the present application provides the following technical solutions.

[0009] The present application provides a preparation method of DOM-peroxysulfate system, comprising the following steps:

[0010] The dried farmland soil is mixed with water for leaching, and the soil DOM is obtained after filtration.

[0011] In the system, the concentration of soil DOM is 5-15 mg·L -1 , and the concentration of peroxysulfate is 0.1-1 mM.

[0012] Preferably, the sampling depth of the farmland soil is 0-20 cm.

[0013] Preferably, the mass ratio of the dried farmland soil to water is 1:1-4.

[0014] Preferably, the leaching time is 1-4 h.

[0015] Preferably, the soil DOM includes aromatic protein I, aromatic protein II, fulvic acid, water-soluble microbial metabolites, and humic acid; the relative abundance of aromatic protein I is 0.5%-1.5%, the relative abundance of aromatic protein II is 0.5%-1.5%, the relative abundance of fulvic acid is 4%-8%, the relative abundance of water-soluble microbial metabolites is 10%-20%, and the relative abundance of humic acid is 70%-80%.

[0016] The present application also provides a DOM-peroxysulfate system obtained by the preparation method.

[0017] The present application also provides an application of the above DOM-peroxysulfate system in photocatalytic degradation of organic pollutants.

[0018] The present application also provides a method for photocatalytic degradation of organic pollutants, comprising the following steps: mixing a photocatalyst, the above DOM-peroxysulfate system, and an organic pollutant to be degraded to obtain a mixed system, stirring, and opening a UV light source for photocatalytic reaction.

[0019] Preferably, the concentration of the photocatalyst in the mixed system is 0.01-1 g·L -1 .

[0020] Preferably, the photocatalytic reaction time is 5-10 min.

[0021] The beneficial effects of the present application are as follows:

[0022] The DOM-persulfate system prepared by the preparation method of the DOM-persulfate system provided by the present application can improve the pH and free radical content of the photocatalytic reaction system, thereby realizing the strengthening of the oxidation capacity of the persulfate system and further improving the short-time photocatalytic degradation efficiency of organic pollutants. Compared with the use of the persulfate system alone, the degradation rate of the DOM-persulfate system is increased by 63.56% to 70.50% and the degradation rate is increased by 34.88 to 44.19% after 5 minutes of photocatalytic reaction.

[0023] Meanwhile, the soil DOM is used to strengthen the persulfate system, and the soil DOM is widely available, simple to prepare and low in price, thereby reducing the production and application cost. DETAILED DESCRIPTION

[0024] The present application provides a preparation method of a DOM-persulfate system, comprising the following steps:

[0025] The dried farmland soil is mixed with water for leaching, and the soil DOM is obtained after filtration.

[0026] In the system, the concentration of the soil DOM is 5 to 15 mg·L -1 ; and the concentration of the persulfate is 0.1 to 1 mM.

[0027] In the present application, the sampling depth of the farmland soil is 0 to 20 cm. As an implementable mode, the farmland soil is dried after removing impurities such as fallen leaves and rhizomes after sampling; the drying method can be selected according to actual needs, including natural drying and artificial drying; the artificial drying includes but is not limited to hot air drying, vacuum drying, microwave drying, etc.

[0028] In the present application, the mass ratio of the dried farmland soil to water is preferably 1:1 to 4, further preferably 1:1.5 to 3, and more preferably 1:2.5. The dried farmland soil is mixed with water for leaching, and the present application does not have special limitations on the leaching temperature, which can be carried out at room temperature. As an implementable mode, the leaching is carried out on a shaker at room temperature; the leaching time is preferably 1 to 4 hours, further preferably 1.5 to 3 hours, and more preferably 2 hours. The soil DOM is obtained after filtration, and the pore size of the filter membrane during filtration is 0.45 μm.

[0029] In the present application, the soil DOM comprises aromatic protein I, aromatic protein II, fulvic acid, water-soluble microbial metabolite and humic acid; preferably, the relative abundance of the aromatic protein I is 0.5-1.5%, the relative abundance of the aromatic protein II is 0.5-1.5%, the relative abundance of the fulvic acid is 4-8%, the relative abundance of the water-soluble microbial metabolite is 10-20%, and the relative abundance of the humic acid is 70-80%; further preferably, the relative abundance of the aromatic protein I is 0.6-1.2%, the relative abundance of the aromatic protein II is 0.6-1.2%, the relative abundance of the fulvic acid is 5-7%, the relative abundance of the water-soluble microbial metabolite is 15-18%, and the relative abundance of the humic acid is 72-77%; more preferably, the relative abundance of the aromatic protein I is 0.9%, the relative abundance of the aromatic protein II is 0.9%, the relative abundance of the fulvic acid is 6.0%, the relative abundance of the water-soluble microbial metabolite is 16.2%, and the relative abundance of the humic acid is 76.0%.

[0030] In the present application, the obtained soil DOM is mixed with persulfate; the persulfate comprises permonosulfate and / or perdisulfate; preferably, the persulfate comprises one or more of sodium persulfate, potassium persulfate and potassium hydrogen persulfate. The mixing mode is not particularly limited and can be routinely selected according to actual needs.

[0031] In the present application, as an implementable mode, in the DOM-persulfate system, the concentration of the soil DOM is preferably 7.5-15 mg·L -1 ; in the DOM-persulfate system, the concentration of the persulfate is preferably 0.2-0.8 mM, more preferably 0.5 mM.

[0032] The present application also provides a DOM-persulfate system prepared by any one of the above preparation methods. The DOM-persulfate system prepared by the DOM-persulfate system preparation method provided by the present application can improve the pH and free radical content of the photocatalytic reaction system, thereby realizing the strengthening of the oxidation capacity of the persulfate system.

[0033] The present application also provides a use of the above DOM-persulfate system in photocatalytic degradation of organic pollutants. The DOM-persulfate system provided by the present application can improve the oxidation capacity of the persulfate system and improve the short-time photocatalytic degradation efficiency of organic pollutants when used in photocatalytic degradation.

[0034] The application also provides a method for photocatalytic degradation of organic pollutants, comprising the following steps: mixing a photocatalyst, the DOM-peroxysulfate system and the organic pollutants to be degraded to obtain a mixed system, stirring, and opening a UV light source to perform photocatalytic reaction.

[0035] In the application, the photocatalyst can be selected according to actual needs, including g-C3N4, titanium dioxide or zinc dioxide, etc. As an implementable mode, the concentration of the photocatalyst in the mixed system is preferably 0.01-1 g·L -1 , further preferably 0.1-0.5 g·L -1 , and more preferably 0.2 g·L -1 . The application does not have special limitation on the source of the organic pollutants to be degraded, including organic pollutants in soil, organic pollutants in sewage, organic pollutants in kitchen waste, etc. The application does not have special limitation on the type of the organic pollutants to be degraded, including one or more of antibiotics, pesticide residues and organic dyes; the antibiotics include fluoroquinolones, tetracyclines, sulfonamides, beta-lactam antibiotics or macrolide antibiotics, etc.; the pesticide residues include glyphosate, atrazine, sulfamethoxazole or bisphenol A, etc.; the organic dyes include rhodamine B (RhB), acid orange G (AOG), methylene blue (MB), methyl orange (MO) or crystal violet (MCS), etc. As an implementable mode, the concentration of the organic pollutants to be degraded in the mixed system is preferably 1-50 mg·L -1 , further preferably 5-20 mg·L -1 , and more preferably 10 mg·L -1 . In the mixed system, the concentration of soil DOM is preferably 5-15 mg·L -1 , further preferably 7.5-15 mg·L -1 . In the mixed system, the concentration of peroxysulfate is preferably 0.1-1 mM, further preferably 0.2-0.8 mM, and more preferably 0.5 mM. After mixing, the mixed system is stirred, and a UV light source is opened to perform photocatalytic reaction. The UV wavelength of the UV light source can be selected according to the type of the photocatalyst selected. As an implementable mode, when the photocatalyst is g-C3N4, the UV wavelength is 365 nm. The photocatalytic reaction time is preferably 5-10 min.

[0036] The application applies the DOM-peroxysulfate system to photocatalytic degradation, the addition of the DOM-peroxysulfate system can improve the pH and free radical content of the photocatalytic reaction system, thereby realizing the strengthening of the oxidation ability of the peroxysulfate system, and further improving the short-time photocatalytic degradation efficiency of the organic pollutants.

[0037] The technical solutions provided by the application are described in detail below in combination with the embodiments, but they should not be understood as limiting the protection scope of the application.

[0038] In the following examples, if not specifically stated, all are conventional methods.

[0039] In the following examples, if not specifically stated, all materials, reagents, etc. can be obtained from commercial channels.

[0040] Example 1

[0041] A preparation method of a DOM-peroxysulfate system:

[0042] The soil was taken from the surface soil outside the vegetable greenhouse in Tianjin Jinnan District Hahe Education Park in September 2022, and the sampling depth was 0-20 cm.

[0043] The collected surface soil was removed from the surface fallen leaves and rhizomes, and the soil was spread on the indoor ground to dry; the dried soil was mixed with water at a weight ratio of 1:2.5 (w / w), and then extracted in a shaker at room temperature for 2 h; after the extraction was completed, the suspension was centrifuged at 8000 rpm for 5 min; then filtered through a 0.45 μm filter membrane, and the obtained filtrate was soil DOM, which was bottled, stored in the dark and refrigerated.

[0044] The three-dimensional fluorescence spectrum of soil DOM is determined by a fluorescence spectrometer. The three-dimensional fluorescence spectrum of soil DOM is generally divided into five characteristic peak regions, namely aromatic protein I, aromatic protein II, fulvic acid substances, water-soluble microbial metabolites, and humic acid substances. According to the method of reference (Chen W, Westerhoff P, Leenheer JA, et al. Fluorescence Excitation-Emission Matrix Regional Integration to Quantify Spectra for Dissolved Organic Matter [J]. Environmental Science & Technology, 2003, 37, 5701-5710), the corresponding regions of each component are divided, and the relative abundance of each component is calculated by integrating the corresponding regions of each component in the three-dimensional fluorescence spectrum. After calculation, the relative abundance of each component of soil DOM is: aromatic protein I 0.9%, aromatic protein II 0.9%, fulvic acid substances 6.0%, water-soluble microbial metabolites 16.2%, and humic acid substances 76.0%.

[0045] The soil DOM is mixed with a sodium persulfate solution, so that the concentration of soil DOM in the mixed system is 15 mg·L -1 , and the concentration of sodium persulfate is 0.5 mM, to obtain a DOM-sodium persulfate system.

[0046] Example 2

[0047] A preparation method of a DOM-sodium persulfate system:

[0048] The soil collected in Example 1 is used. The surface soil is collected by removing the fallen leaves and rhizomes on the surface, and the soil is dried on the indoor floor. The dried soil is mixed with water at a weight ratio of 1:2.5 (w / w), and then extracted on a shaker at room temperature for 2 h. After the extraction is completed, the suspension is centrifuged at 8000 rpm for 5 min. Then, the obtained filtrate is filtered through a 0.45 μm filter membrane, and the obtained filtrate is soil DOM, which is bottled, stored in the dark, and refrigerated.

[0049] The soil DOM is mixed with a sodium persulfate solution, so that the concentration of soil DOM in the mixed system is 7.5 mg·L -1 , and the concentration of sodium persulfate is 0.5 mM, to obtain a DOM-sodium persulfate system.

[0050] Example 3

[0051] A preparation method of a DOM-sodium persulfate system:

[0052] Soil collected in Example 1 was used. Surface leaves and rhizomes were removed from the collected topsoil, and the soil was spread on the indoor floor to air dry. The air-dried soil was mixed with water at a weight ratio of 1:1 (w / w) and extracted on a shaker at room temperature for 4 hours. After extraction, the suspension was centrifuged at 6000 rpm for 10 minutes. The solution was then filtered through a 0.45 μm filter membrane, and the resulting filtrate was the soil DOM, which was bottled and stored in the dark under refrigeration.

[0053] Mix soil DOM with potassium persulfate solution to make the soil DOM concentration in the mixed system 10 mg·L⁻¹ -1 The potassium persulfate concentration was 1 mM, resulting in the DOM-persulfate system.

[0054] Example 4

[0055] A method for preparing a DOM-persulfate system:

[0056] Soil collected in Example 1 was used. Surface leaves and rhizomes were removed from the collected topsoil, and the soil was spread on the indoor floor to air dry. The air-dried soil was mixed with water at a weight ratio of 1:4 (w / w) and extracted on a shaker at room temperature for 1 hour. After extraction, the suspension was centrifuged at 10,000 rpm for 3 minutes. The solution was then filtered through a 0.45 μm filter membrane, and the resulting filtrate was the soil DOM, which was bottled and stored in the dark under refrigeration.

[0057] Mix soil DOM with potassium persulfate solution to make the soil DOM concentration in the mixed system 5 mg·L⁻¹ -1 The concentration of potassium persulfate was 0.1 mM, resulting in the DOM-persulfate system.

[0058] Example 5

[0059] A method for preparing a DOM-persulfate system:

[0060] Soil collected in Example 1 was used. Surface leaves and rhizomes were removed from the collected topsoil, and the soil was spread on the indoor floor to air dry. The air-dried soil was mixed with water at a weight ratio of 1:1.5 (w / w) and extracted on a shaker at room temperature for 3 hours. After extraction, the suspension was centrifuged at 7000 rpm for 8 minutes. The solution was then filtered through a 0.45 μm filter membrane, and the resulting filtrate was the soil DOM, which was bottled and stored in the dark under refrigeration.

[0061] Soil DOM was mixed with potassium persulfate solution to achieve a soil DOM concentration of 12.5 mg·L⁻¹. -1 The potassium persulfate concentration was 0.8 mM, resulting in the DOM-persulfate system.

[0062] Example 6

[0063] A preparation method of a DOM-persulfate system:

[0064] The soil collected in Example 1 was used, and the surface soil was removed from the surface fallen leaves and rhizomes, and the soil was dried on the indoor ground. The dried soil was mixed with water at a weight ratio of 1:3 (w / w), and was extracted on a shaker at room temperature for 1.5 h. After the extraction was completed, the suspension was centrifuged at 9000 rpm for 4 min. Then, the obtained filtrate was filtered through a 0.45 μm filter membrane, and the obtained filtrate was soil DOM, which was bottled, stored in the dark, and refrigerated.

[0065] The soil DOM was mixed with the potassium hydrogen persulfate solution, so that the concentration of the soil DOM in the mixed system was 7.5 mg·L -1 , and the concentration of the potassium hydrogen persulfate was 0.12 mM, to obtain a DOM-persulfate system.

[0066] Comparative Example 1

[0067] A preparation method of a persulfate system:

[0068] The sodium persulfate solution was taken, and the concentration of the sodium persulfate was 0.5 mM, to obtain a persulfate system.

[0069] Comparative Example 2

[0070] A preparation method of a DOM-persulfate system:

[0071] A commercially available organic fertilizer was selected, and the mass fraction of organic matter in the organic fertilizer was ≥45%, and the mass fraction of total nutrients (N+P2O5+K2O) was ≥5%.

[0072] The organic fertilizer was mixed with water at a mass ratio of 1:10 (w / w), and was extracted on a shaker at room temperature for 2 h. The obtained fertilizer DOM was filtered through a 0.45 μm filter membrane.

[0073] The fertilizer DOM was mixed with the sodium persulfate solution, so that the concentration of the fertilizer DOM in the mixed system was 15 mg·L -1 , and the concentration of the sodium persulfate was 0.5 mM, to obtain a DOM-persulfate system.

[0074] Comparative Example 3

[0075] A preparation method of a DOM-persulfate system:

[0076] The same organic fertilizer as in Comparative Example 2 was mixed with water at a mass ratio of 1:10 (w / w), and was extracted on a shaker at room temperature for 2 h. The obtained fertilizer DOM was filtered through a 0.45 μm filter membrane.

[0077] The fertilizer DOM was mixed with the sodium persulfate solution, so that the concentration of the fertilizer DOM in the mixed system was 7.5 mg·L -1, the concentration of sodium persulfate was 0.5 mM, and the DOM-persulfate system was obtained.

[0078] Example 7

[0079] A photocatalytic degradation method:

[0080] The DOM-persulfate system prepared in Example 1 was used, 10 mg of g-C3N4 photocatalyst was placed in a 50 mL transparent quartz reaction tube, then tetracycline (TC), DOM-persulfate system was added, so that the concentration of g-C3N4 in the system was 0.2 g·L -1 , the concentration of sodium persulfate was 0.5 mM, and the concentration of soil DOM was 15 mg·L -1 , the concentration of TC was 10 mg·L -1 . The transparent quartz tube was placed in a multi-channel photochemical reaction device, covered with a lid, and the magnetic stirring device was turned on at a speed of 520 rpm for 30 min. After 30 min, the 365 nm ultraviolet light source was turned on, and the high-speed stirring was maintained, and the photocatalytic reaction was started. After 5 min, the photocatalytic degradation was completed.

[0081] After the solution system was prepared, the transmittance of the system was immediately detected by a UV-Vis spectrophotometer, and the pH of the system was detected by a pH meter. The transmittance of the system before photocatalytic reaction was 37.5%, and the pH was 6.89.

[0082] The residual concentration of TC (C0) at the beginning of photocatalytic reaction and the residual concentration of TC (C1) after photocatalytic reaction were detected by a UV-Vis spectrophotometer, and the degradation rate of TC was calculated by the following formula:

[0083]

[0084] Wherein, C0 is the residual concentration of TC at 0 min of photocatalytic reaction, C1 is the residual concentration of TC after photocatalytic reaction, and t is the photocatalytic reaction time.

[0085] After detection, the residual concentration of TC was 2.48 mg·L -1 after 5 min of photocatalytic reaction, and the degradation rate was 75.19%. The degradation rate of TC reached 1.16 mg·L -1 min -1 . The concentration of photo-generated hole free radicals (h + ) in the system after 5 min of illumination was 1.547e+15 spins / mm 3 , the concentration of sulfate free radicals (·SO4 - ) was 2.560e+12 spins / mm 3 , and the concentration of hydroxyl free radicals (·OH) was 1.446e+12 spins / mm 3Singlet oxygen radicals ( 1 The O2 concentration was 1.173e+11 spins / mm. 3 .

[0086] Example 8

[0087] A photocatalytic degradation method:

[0088] The DOM-persulfate system prepared by the method in Example 1 was used. 10 mg of g-C3N4 photocatalyst was placed in a 50 mL transparent quartz reaction tube, followed by the addition of tetracycline (TC) and the DOM-persulfate system, resulting in a g-C3N4 concentration of 0.2 g·L⁻¹. -1 Sodium persulfate concentration was 0.5 mM, and soil DOM concentration was 15 mg·L⁻¹. -1 TC concentration is 10 mg·L -1 Place the transparent quartz tube in a multi-channel photochemical reaction apparatus, cover it, turn on the magnetic stirrer at 520 rpm, and stir for 30 minutes. After 30 minutes, turn on the 365 nm ultraviolet light source, maintain high-speed stirring, and the photocatalytic reaction will begin. The photocatalytic degradation will be completed after 10 minutes.

[0089] Before the photocatalytic reaction, the system's transmittance was 37.5%, and the pH was 6.89. After 10 minutes of photocatalytic reaction, the residual TC concentration was 2.26 mg·L⁻¹. -1 The degradation rate was 77.39%, and the TC degradation rate reached 0.60 mg·L⁻¹. -1 min -1 .

[0090] Example 9

[0091] A photocatalytic degradation method:

[0092] The DOM-persulfate system prepared by the method in Example 2 was used. 10 mg of g-C3N4 photocatalyst was placed in a 50 mL transparent quartz reaction tube, followed by the addition of tetracycline (TC) and the DOM-persulfate system, resulting in a g-C3N4 concentration of 0.2 g·L⁻¹. -1 Sodium persulfate concentration was 0.5 mM, and soil DOM concentration was 7.5 mg·L⁻¹. -1 TC concentration is 10 mg·L -1 Place the transparent quartz tube in a multi-channel photochemical reaction apparatus, cover it, turn on the magnetic stirrer at 520 rpm, and stir for 30 minutes. After 30 minutes, turn on the 365 nm ultraviolet light source, maintain high-speed stirring, and the photocatalytic reaction will begin. The photocatalytic degradation will be completed after 5 minutes.

[0093] The detected light catalytic reaction system transmittance is 42.4%, pH is 5.47. After 5 minutes of light catalytic reaction, the residual concentration of TC is 2.79mg·L -1 , the degradation rate is 72.13%, and the TC degradation rate reaches 1.24mg·L -1 min -1 .

[0094] Example 10

[0095] A light catalytic degradation method:

[0096] The DOM-persulfate system prepared by the method of Example 2 is taken, 10mg g-C3N4 photocatalyst is placed in a 50mL transparent quartz reaction tube, then tetracycline (TC) and DOM-persulfate system are added, so that the concentration of g-C3N4 in the system is 0.2g·L -1 , the concentration of sodium persulfate is 0.5mM, the concentration of soil DOM is 7.5mg·L -1 , and the concentration of TC is 10mg·L -1 . The transparent quartz tube is placed in a multi-channel photochemical reaction device, covered with a cover, the magnetic stirring device is turned on, the speed is 520rpm, and stirring is performed for 30min. After 30min, the 365nm ultraviolet light source is turned on, high-speed stirring is maintained, the light catalytic reaction is started, and the light catalytic degradation is completed after 10min.

[0097] The detected light catalytic reaction system transmittance is 42.4%, pH is 5.47. After 10 minutes of light catalytic reaction, the residual concentration of TC is 2.43mg·L -1 , the degradation rate is 75.69%, and the TC degradation rate reaches 0.66mg·L -1 min -1 .

[0098] Comparative Example 4

[0099] A light catalytic degradation method:

[0100] The persulfate system prepared by the method of Comparative Example 1 is taken, 10mg g-C3N4 photocatalyst is placed in a 50mL transparent quartz reaction tube, then tetracycline (TC) and persulfate system are added, so that the concentration of g-C3N4 in the system is 0.2g·L -1 , the concentration of sodium persulfate is 0.5mM, and the concentration of TC is 10mg·L -1 . The transparent quartz tube is placed in a multi-channel photochemical reaction device, covered with a cover, the magnetic stirring device is turned on, the speed is 520rpm, and stirring is performed for 30min. After 30min, the 365nm ultraviolet light source is turned on, high-speed stirring is maintained, the light catalytic reaction is started, and the light catalytic degradation is completed after 5min.

[0101] The light transmittance of the system before the photocatalytic reaction was 48.2%, and the pH was 4.68.

[0102] After 5 min of photocatalytic reaction, the residual concentration of TC was 5.59 mg·L -1 , the degradation rate was 44.10%, and the TC degradation rate reached 0.86 mg·L -1 min -1 . The concentration of photo-generated hole free radicals (h + ) in the system after 5 min of illumination was 2.000e+14 spins / mm 3 , the concentration of sulfate free radicals (·SO4 - ) was 1.311e+12 spins / mm 3 , the concentration of hydroxyl free radicals (·OH) was 1.142e+12 spins / mm 3 , and the concentration of singlet oxygen free radicals ( 1 O2) was 7.699e+10 spins / mm 3 .

[0103] Comparative Example 5

[0104] A photocatalytic degradation method:

[0105] The persulfate system prepared by the method of Comparative Example 1 was taken, 10 mg of g-C3N4 photocatalyst was placed in a 50 mL transparent quartz reaction tube, and then tetracycline (TC) and persulfate system were added, so that the concentration of g-C3N4 in the system was 0.2 g·L -1 , the concentration of sodium persulfate was 0.5 mM, and the concentration of TC was 10 mg·L -1 . The transparent quartz tube was placed in a multi-channel photochemical reaction device, covered with a lid, and a magnetic stirring device was turned on at a speed of 520 rpm and stirred for 30 min. After 30 min, a 365 nm ultraviolet light source was turned on and high-speed stirring was maintained, and the photocatalytic reaction was started, and the photocatalytic degradation was completed after 10 min.

[0106] The light transmittance of the system before the photocatalytic reaction was 48.2%, and the pH was 4.68.

[0107] After 10 min of photocatalytic reaction, the residual concentration of TC was 3.41 mg·L -1 , the degradation rate was 65.94%, and the TC degradation rate reached 0.65 mg·L -1 min -1 .

[0108] Comparative Example 6

[0109] A photocatalytic degradation method:

[0110] DOM-persulfate system prepared by the method of Comparative Example 2, 10 mg of g-C3N4 photocatalyst was placed in a 50 mL transparent quartz reaction tube, and tetracycline (TC), DOM-persulfate system was added, so that the concentration of g-C3N4 in the system was 0.2 g·L -1 , the concentration of sodium persulfate was 0.5 mM, and the concentration of fertilizer DOM was 15 mg·L -1 , the concentration of TC was 10 mg·L -1 . The transparent quartz tube was placed in a multi-channel photochemical reaction device, covered with a lid, and the magnetic stirring device was turned on at a speed of 520 rpm and stirred for 30 min. After 30 min, the 365 nm ultraviolet light source was turned on, and the high-speed stirring was maintained, and the photocatalytic reaction was started, and the photocatalytic degradation was completed after 10 min.

[0111] It was detected that the light transmittance of the system before photocatalytic reaction was 29.6%, and the pH was 6.73.

[0112] After 10 min of photocatalytic reaction, the residual concentration of TC was 4.79 mg·L -1 , the degradation rate was 52.05%, and the TC degradation rate reached 0.49 mg·L -1 min -1 .

[0113] Comparative Example 7

[0114] A photocatalytic degradation method:

[0115] DOM-persulfate system prepared by the method of Comparative Example 3, 10 mg of g-C3N4 photocatalyst was placed in a 50 mL transparent quartz reaction tube, and tetracycline (TC), DOM-persulfate system was added, so that the concentration of g-C3N4 in the system was 0.2 g·L -1 , the concentration of sodium persulfate was 0.5 mM, and the concentration of fertilizer DOM was 7.5 mg·L -1 , the concentration of TC was 10 mg·L -1 . The transparent quartz tube was placed in a multi-channel photochemical reaction device, covered with a lid, and the magnetic stirring device was turned on at a speed of 520 rpm and stirred for 30 min. After 30 min, the 365 nm ultraviolet light source was turned on, and the high-speed stirring was maintained, and the photocatalytic reaction was started, and the photocatalytic degradation was completed after 10 min.

[0116] It was detected that the light transmittance of the system before photocatalytic reaction was 38.0%, and the pH was 6.53.

[0117] After 10 min of photocatalytic reaction, the residual concentration of TC was 5.11 mg·L -1 , the degradation rate was 48.92%, and the TC degradation rate reached 0.45 mg·L-1 min -1 .

[0118] From the above results, it can be seen that the DOM-peroxysulfate system of the present application can strengthen the oxidation ability of the peroxysulfate system. Compared with the use of the peroxysulfate system alone (Comparative Example 4), the use of the DOM-peroxysulfate system (Examples 7 and 9) increased the degradation rate by 63.56% to 70.50% and the degradation rate by 34.88 to 44.19% at 5 min of photocatalytic reaction. Compared with the use of the peroxysulfate system alone (Comparative Example 5), the use of the DOM-peroxysulfate system (Examples 8 and 10) increased the degradation rate by 14.79% to 17.36% at 10 min of photocatalytic reaction, and the degradation rates were not much different. According to the radical detection results of Example 7 and Comparative Example 4, it can be seen that the introduction of soil DOM in the DOM-peroxysulfate system of the present application promotes the generation of most radicals in the early stage (5 min) of the reaction, improves the oxidation ability of the peroxysulfate system, and further improves the reaction rate. It can be seen that the DOM-peroxysulfate system of the present application can strengthen the oxidation ability of the peroxysulfate system on the one hand, and improve the short-time photocatalytic degradation efficiency of organic pollutants on the other hand.

[0119] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the protection scope of the present application.

Claims

1. A method of photocatalytic degradation of organic pollutants, characterized in that, The method comprises the following steps: mixing a photocatalyst, a DOM-peroxysulfate system and an organic pollutant to be degraded to obtain a mixed system, stirring, and opening an ultraviolet light source to perform photocatalytic reaction. The preparation method of the DOM-peroxysulfate system comprises the following steps: The dried farmland soil is mixed with water to extract, and the soil DOM is obtained after filtration; and the obtained soil DOM is mixed with peroxysulfate. The soil DOM concentration in the system is 5-15 mg·L -1 ; the concentration of persulfate is 0.2-1 mM; The pore size of the filter membrane is 0.45 microns.

2. The method of claim 1, wherein, The sampling depth of the farmland soil is 0-20 cm.

3. The method of claim 1, wherein, The mass ratio of the dried farmland soil to water is 1:1-4.

4. The method of claim 1, wherein, The extraction time is 1-4 hours.

5. The method of claim 1, wherein, The soil DOM comprises aromatic protein I, aromatic protein II, fulvic acid, water-soluble microbial metabolite and humic acid; the relative abundance of the aromatic protein I is 0.5-1.5%, the relative abundance of the aromatic protein II is 0.5-1.5%, the relative abundance of the fulvic acid is 4-8%, the relative abundance of the water-soluble microbial metabolite is 10-20%, and the relative abundance of the humic acid is 70-80%.

6. The method of claim 1, wherein, The concentration of the photocatalyst in the mixed system is 0.01-1 g·L -1 .

7. The method of claim 1, wherein, The photocatalytic reaction time is 5-10 minutes.

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