A method for wastewater treatment with controllable active species type

Abstract

The application provides a wastewater treatment method capable of regulating the type of active species, comprising the following steps: adding an iron-sulfur co-doped carbon nitride material and peroxyacetic acid into wastewater containing organic pollutants, treating the wastewater under the condition of stirring or the wastewater being in a flowing state, and degrading the organic pollutants in the wastewater by free radical active species and non-free radical active species generated by the iron-sulfur co-doped carbon nitride material activating the peroxyacetic acid during the wastewater treatment process; and the ratio of the free radical active species to the non-free radical active species generated by the iron-sulfur co-doped carbon nitride material activating the peroxyacetic acid can be regulated by regulating the concentration of the peroxyacetic acid in the wastewater. The method can flexibly regulate the composition of the active species generated by the catalyst activating the oxidant by regulating the concentration of the oxidant based on the water quality of the wastewater and the characteristics of the pollutants, so that the organic pollutants in the wastewater can be efficiently removed, and the convenience and efficiency of the wastewater treatment method can be improved.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment and relates to a wastewater treatment method with adjustable active species types, particularly a wastewater treatment method that adjusts the active species types by controlling the concentration of oxidant. Background Technology

[0002] Rapid industrial, agricultural, and urbanization development has led to the discharge of large amounts of industrial wastewater, agricultural wastewater, and urban sewage into lakes, reservoirs, and other water sources. In recent years, wastewater containing emerging pollutants has entered water bodies. These new pollutants in the aquatic environment possess strong biological activity, are difficult to biodegrade, and degrade slowly. Furthermore, these emerging pollutants easily enter the food chain through water bodies, accumulating in organisms and posing a significant threat to the safety and health of vertebrates, thereby having serious negative impacts on human health. Emerging pollutants are increasingly becoming a focus of attention in the field of water pollution control.

[0003] Currently, the main methods for removing emerging pollutants include physical, chemical, and biological methods. Biological methods have relatively low operating costs, but they exhibit significant selectivity and limitations in removing emerging pollutants. Physical methods primarily separate emerging pollutants from water, but the molecular structure of these pollutants remains unchanged during the treatment process; they migrate rather than be truly degraded. To convert emerging pollutants into smaller organic molecules, further treatment using other methods is required. Chemical methods have high operating costs, requiring large quantities of chemicals for treating large-scale wastewater and potentially generating substantial solid waste. Therefore, exploring an efficient and environmentally friendly water treatment technology to treat emerging pollutants has become one of the important tasks in current water environment governance.

[0004] Advanced oxidation processes (AOPs) are a high-efficiency, low-cost wastewater treatment technology. They typically utilize ultraviolet light or catalysts to activate oxidants such as hydrogen peroxide, ozone, peracetic acid, and persulfate, generating highly reactive species that degrade pollutants into low-toxicity or non-toxic small-molecule compounds. Some pollutants can even be completely mineralized into CO2 and H2O. AOPs can effectively remove emerging pollutants from wastewater. Catalysts used in AOPs are divided into homogeneous and heterogeneous categories. Homogeneous catalysis suffers from difficulties in recovery, potential for secondary pollution, and a narrow pH range. In contrast, heterogeneous catalysts offer advantages in these areas and have therefore attracted increasing attention.

[0005] Typically, heterogeneous catalysts generate multiple active species upon activating oxidants, with one species becoming dominant. The types and composition of active species generated by different heterogeneous catalysts vary, and these different types of active species exhibit different degradation characteristics for pollutants. For example, the free radical active species hydroxyl radicals have low selectivity and can oxidize and degrade most single pollutants, but their resistance to interference is poor, and they are easily quenched by coexisting water matrices (such as inorganic anions and natural organic matter) in actual wastewater, leading to a decrease in their ability to degrade target pollutants. When wastewater contains multiple organic pollutants, hydroxyl radicals will indiscriminately oxidize different types of organic pollutants, failing to selectively and preferentially degrade certain target pollutants in the wastewater. As another example, the non-free radical active species high-valence metal oxide species can efficiently transform specific pollutants (such as antibiotics in complex wastewater) and have high resistance to interference, but these species do not readily react with organic degradation products such as small molecule acids, resulting in low mineralization efficiency and difficulty in achieving effective removal of total organic carbon.

[0006] Currently, when using heterogeneous catalysts to activate oxidants and generate active species, the composition of active species produced by the same catalyst activating a particular oxidant is often fixed. Changing the dosage of the catalyst or oxidant cannot alter the composition of active species in the same catalytic oxidation system. Different heterogeneous catalysts are required to activate oxidants for pollutants with different characteristics in order to regulate the composition of active species and generate suitable active species for efficient pollutant degradation. The convenience and efficiency of this approach in practical applications still need improvement. Therefore, if it is possible to conveniently and flexibly regulate the composition of active species based on the characteristics of pollutants in wastewater without changing the heterogeneous catalyst, generating active species with high degradation capabilities for target pollutants, it will have a positive impact on maximizing pollutant treatment efficiency and optimizing economic costs. Summary of the Invention

[0007] To address the problem that existing technologies using heterogeneous catalysts to activate oxidants to generate active species have a fixed composition of active species produced by the same catalyst activating a particular oxidant, making it difficult to conveniently and flexibly control the composition of active species in the same catalytic oxidation system, this invention provides a wastewater treatment method with adjustable active species types. This allows for targeted control of the composition of active species generated by catalyst activation of oxidants based on the wastewater quality and pollutant characteristics by adjusting the oxidant concentration, thereby achieving efficient removal of organic pollutants from wastewater and increasing the convenience and efficiency of wastewater treatment methods.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0009] A wastewater treatment method with adjustable active species types includes the following steps:

[0010] Iron-sulfur co-doped carbon nitride material and peracetic acid are added to wastewater containing organic pollutants. The amount of iron-sulfur co-doped carbon nitride material added is controlled at 50-1000 mg / L, and the pH value of the wastewater is controlled at 2-7. The wastewater is treated under the conditions of stirring or the wastewater is in a flowing state. During the wastewater treatment process, the iron-sulfur co-doped carbon nitride material activates peracetic acid to generate free radical active species and non-free radical active species, which degrade the organic pollutants in the wastewater.

[0011] By adjusting the concentration of peracetic acid in wastewater, the ratio of free radical active species to non-free radical active species generated by the activation of peracetic acid by iron-sulfur co-doped carbon nitride materials can be controlled.

[0012] The preparation method of the iron-sulfur co-doped carbon nitride material is as follows:

[0013] (1) The carbon nitride precursor, sulfur donor and iron source are thoroughly mixed to obtain a precursor mixture; in the precursor mixture, the mass percentage of carbon nitride precursor is 69% to 88%, the mass percentage of sulfur donor is 7% to 28%, and the mass percentage of iron source is 0.7% to 10%.

[0014] (2) The precursor mixture is calcined at 500-600℃ for 2-4 hours to obtain iron-sulfur co-doped carbon nitride material.

[0015] In the above-mentioned wastewater treatment method with adjustable active species type, the amount of peracetic acid added is controlled so that the concentration of peracetic acid in the wastewater is 0.01 to 1 mmol / L. Preferably, the amount of peracetic acid added is controlled so that the concentration of peracetic acid in the wastewater is 0.1 to 1 mmol / L.

[0016] Furthermore, in the above-mentioned wastewater treatment method with adjustable active species types, the lower the concentration of peracetic acid in the wastewater, the higher the ratio of free radical active species to non-free radical active species generated by the activation of peracetic acid by the iron-sulfur co-doped carbon nitride material; the higher the concentration of peracetic acid in the wastewater, the lower the ratio of free radical active species to non-free radical active species generated by the activation of peracetic acid by the iron-sulfur co-doped carbon nitride material.

[0017] For example, through experiments, we found that when the dosage of iron-sulfur co-doped carbon nitride material in wastewater is 300 mg / L, when the concentration of peracetic acid in the wastewater is less than 0.5 mmol / L, the active species generated by the iron-sulfur co-doped carbon nitride material activating peracetic acid are free radical active species. When the concentration of peracetic acid in the wastewater exceeds 0.5 mmol / L, the active species generated by the iron-sulfur co-doped carbon nitride material activating the oxidant are mainly non-free radical active species.

[0018] In the above-mentioned wastewater treatment method with adjustable active species types, the free radical active species include hydroxyl radicals, acetoxy radicals and acetylperoxy radicals, with hydroxyl radicals being the main free radical active species, and the non-free radical active species being high-valence ferric oxygen species.

[0019] In the above-mentioned wastewater treatment method with adjustable active species type, in order to efficiently degrade the target organic pollutants in the wastewater, the active species with higher reactivity with the target organic pollutants in the wastewater under the conditions of wastewater quality among the free radical active species and non-free radical active species are recorded as the target active species. The concentration of peracetic acid in the wastewater is adjusted so that the main active species generated by the activation of peracetic acid by the iron-sulfur co-doped carbon nitride material is the target active species.

[0020] In practical applications, the types of active species required to degrade the target organic pollutants in the wastewater are determined based on the properties of the wastewater, such as the types and concentrations of organic pollutants and other substances coexisting in the wastewater (i.e., target active species). The concentration of peracetic acid in the wastewater is then adjusted according to the types of target active species, so that the main active species generated by the activation of peracetic acid by the iron-sulfur co-doped carbon nitride material is the target active species, thereby achieving efficient degradation of the target organic pollutants.

[0021] In the above-mentioned wastewater treatment method with adjustable active species type, when the main active species generated by the activation of peracetic acid by the iron-sulfur co-doped carbon nitride material is a free radical active species, it is preferable to control the pH value of the wastewater to 2-5; when the main active species generated by the activation of peracetic acid by the iron-sulfur co-doped carbon nitride material is a non-free radical active species, it is preferable to control the pH value of the wastewater to 2-7.

[0022] In the above-mentioned wastewater treatment method with adjustable active species type, in step (2) of preparing iron-sulfur co-doped carbon nitride material, the precursor mixture is calcined in a gas atmosphere composed of at least one of air, nitrogen and argon.

[0023] In the above-mentioned wastewater treatment method with adjustable active species, in order to improve the utilization efficiency of iron-sulfur co-doped carbon nitride material and efficiently activate peracetic acid, in step (2) of preparing iron-sulfur co-doped carbon nitride material, it is best to crush or grind the calcined product into micron-sized particles.

[0024] In the above-mentioned wastewater treatment method with adjustable active species type, in step (1) of preparing iron-sulfur co-doped carbon nitride material, the carbon nitride precursor is at least one of urea, melamine and dicyandiamine, the iron source is at least one of divalent iron salt and trivalent iron salt, and the sulfur element donor is trithiocyanic acid.

[0025] In the above-mentioned wastewater treatment method with adjustable active species types, the organic pollutant is an emerging pollutant. For example, the organic pollutant may be sulfonamide drugs, carbamazepine, ibuprofen, atrazine, etc., but is not limited to these organic pollutants.

[0026] In the above-mentioned wastewater treatment method with adjustable active species, the wastewater treatment time is related to the wastewater quality. Generally, the treatment is sufficient until the removal rate of organic pollutants in the wastewater reaches a basic equilibrium state. Typically, the wastewater treatment time can be controlled to be 15 to 60 minutes.

[0027] In the above-mentioned wastewater treatment method with adjustable active species, the dosage of iron-sulfur co-doped carbon nitride material in the wastewater is determined according to the water quality conditions of the wastewater, and the preferred catalyst dosage is 100-500 mg / L.

[0028] The principle behind the method described in this invention, which regulates the type of active species by adjusting the concentration of peracetic acid, is as follows:

[0029] The preparation of peracetic acid involves mixing sulfuric acid-treated glacial acetic acid with hydrogen peroxide. One hydrogen atom in the hydrogen peroxide is replaced by an acetyl group in the glacial acetic acid, forming peracetic acid. However, peracetic acid is unstable and degrades into glacial acetic acid and hydrogen peroxide. Therefore, peracetic acid products (e.g., commercially available peracetic acid solutions) typically contain a certain amount of hydrogen peroxide; that is, peracetic acid and hydrogen peroxide coexist in peracetic acid products. Because iron-sulfur co-doped carbon nitride is highly reactive to hydrogen peroxide coexisting in peracetic acid commercial solutions, it easily activates hydrogen peroxide to generate hydroxyl radicals. These hydroxyl radicals can also react rapidly with peracetic acid. When the peracetic acid concentration is low, it is insufficient to quench all hydroxyl radicals; in this case, the degradation of pollutants mainly relies on hydroxyl radicals. Therefore, under low-concentration peracetic acid conditions, the main active species in the iron-sulfur co-doped carbon nitride / peracetic acid system is hydroxyl radicals. As the peracetic acid concentration increases, more hydroxyl radicals are quenched by peracetic acid, and the characteristics of the high-valence ferrooxide species generated by the combination of peracetic acid and iron-sulfur co-doped carbon nitride gradually emerge. Therefore, under high-concentration peracetic acid conditions, the main active species in the iron-sulfur co-doped carbon nitride / peracetic acid system is high-valence ferrooxide species.

[0030] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0031] 1. This invention provides a wastewater treatment method with adjustable active species types. This method activates peracetic acid with an iron-sulfur co-doped carbon nitride material to generate free radical active species and non-free radical active species that degrade organic pollutants in wastewater. By adjusting the concentration of peracetic acid in the wastewater, the ratio of free radical active species to non-free radical active species generated by the activation of peracetic acid with the iron-sulfur co-doped carbon nitride material can be controlled. Based on the convenient and adjustable nature of the main active species generated by the method of this invention, in actual wastewater treatment, the composition of active species generated by the activation of peracetic acid with the iron-sulfur co-doped carbon nitride material can be flexibly adjusted according to the water quality and the characteristics of the organic pollutants contained in the wastewater. This ensures that the main active species are those with highly efficient degradation capabilities for the organic pollutants to be degraded under the wastewater quality conditions, thereby achieving efficient removal of organic pollutants from wastewater. The method of this invention can flexibly adapt to various pollution systems and meet the treatment needs of organic pollutants in complex multi-pollutant systems. Compared to existing technologies that require changing the type of heterogeneous catalyst to adjust the type of active species produced by the activating oxidant, the method of this invention increases the convenience and efficiency of wastewater treatment, which is conducive to maximizing pollutant treatment efficiency and optimizing economic costs.

[0032] 2. The method described in this invention has good controllability of the type of active species, simple control method, and relatively wide applicable pH range for wastewater. It can flexibly and conveniently control the type of active species for pollutants with different characteristics to ensure high degradation efficiency for pollutants. These features are conducive to the promotion and application of the method described in this invention in engineering practice.

[0033] 3. The method described in this invention has a simple preparation process for the sulfur-co-doped carbon nitride material on which peracetic acid is activated, the raw materials are inexpensive and readily available, and the production cost is low, which is conducive to achieving efficient wastewater treatment at low cost. Attached Figure Description

[0034] Figure 1 Figure (A) is a SEM image of the iron-sulfur co-doped carbon nitride material prepared in Example 1. Figure 1 Figures (B) to (F) are EDS diagrams of the iron-sulfur co-doped carbon nitride material prepared in Example 1.

[0035] Figure 2 This is the energy spectrum of the iron-sulfur co-doped carbon nitride material prepared in Example 1.

[0036] Figure 3 This is the X-ray photoelectron spectrum of Fe in the iron-sulfur co-doped carbon nitride material prepared in Example 1.

[0037] Figure 4 This is the result of the quenching experiment in Example 2.

[0038] Figure 5 This is the result of the quenching experiment in Example 3.

[0039] Figure 6 This is the result of the quenching experiment in Comparative Example 2.

[0040] Figure 7 This is the result of the quenching experiment in Comparative Example 3.

[0041] Figure 8 This is the result of the quenching experiment in Example 4. Detailed Implementation

[0042] The wastewater treatment method with adjustable active species types described in this invention will be further illustrated below through examples. It should be noted that the following examples are only for further illustration of this invention and should not be construed as limiting the scope of protection of this invention. Any non-essential improvements and adjustments made to this invention by those skilled in the art based on the above description are still within the scope of protection of this invention.

[0043] In the following examples, the peracetic acid (PAA) used was analytical grade PAA.

[0044] Example 1

[0045] The preparation of the iron-sulfur co-doped carbon nitride catalyst in this embodiment of the invention includes the following steps:

[0046] (1) Urea, trithiocyanate and ferric chloride hexahydrate are thoroughly ground and mixed evenly to obtain a precursor mixture; the mass percentages of urea, trithiocyanate and ferric chloride hexahydrate in the precursor mixture are 80.61%, 16.12% and 3.27% respectively.

[0047] (2) The precursor mixture was placed in a muffle furnace and calcined at 550°C for 4 hours in an air atmosphere. The calcined product was then thoroughly ground to obtain iron-sulfur co-doped carbon nitride material with a particle size in the micrometer range.

[0048] SEM images of the iron-sulfur co-doped carbon nitride material prepared in this embodiment are shown below. Figure 1 As shown in Figure (A), the EDS diagram of the iron-sulfur co-doped carbon nitride material prepared in this embodiment is as follows. Figure 1 As shown in Figures (B) to (F), by Figure 1 It can be seen that the iron-sulfur co-doped carbon nitride material is granular, and the C, Fe, N, O, and S elements are uniformly distributed within it. The energy dispersive spectroscopy (EDS) spectrum of the iron-sulfur co-doped carbon nitride material prepared in this embodiment is shown below. Figure 2 As shown. The X-ray photoelectron spectrum of Fe in the iron-sulfur co-doped carbon nitride material prepared in this embodiment is shown below. Figure 3 As shown, by Figure 3 It can be seen that the Fe element in this iron-sulfur co-doped carbon nitride material has a valence state of +3.

[0049] Comparative Example 1

[0050] In this comparative example, the iron-doped carbon nitride material was prepared using the following steps:

[0051] (1) Grind and mix urea hexahydrate ferric chloride thoroughly to obtain a precursor mixture; the mass percentages of urea and ferric chloride hexahydrate in the precursor mixture are 96.1% and 3.9% respectively.

[0052] (2) The precursor mixture was placed in a muffle furnace and calcined at 550°C for 4 hours in an air atmosphere. The calcined product was then thoroughly ground to obtain iron-doped carbon nitride material with a particle size in the micrometer range.

[0053] Example 2

[0054] In this embodiment, the iron-sulfur co-doped carbon nitride material prepared in Example 1 was used as a catalyst to activate the degradation of sulfamethoxazole (SMX) by low concentration of peracetic acid (PAA), and the main active species generated by the catalyst activating PAA during the process were tested.

[0055] (1) SMX degradation experiment

[0056] SMX was dissolved in water to form a 10 μmol / L SMX solution, which was used as the simulated wastewater. A catalyst and PAA were added to the simulated wastewater, and wastewater treatment was carried out under stirring conditions. The catalyst dosage in the simulated wastewater was 300 mg / L, and the PAA concentration was 0.4 mmol / L. Samples were taken 16 min after the addition of the catalyst and PAA, filtered through a 0.22 μm filter membrane, and the reaction was terminated with a 20 g / L sodium thiosulfate solution. The SMX concentration was detected using liquid chromatography, and the SMX removal rate was calculated. The results showed that the SMX removal rate in this embodiment was 98.5%.

[0057] (2) Quenching Experiment

[0058] tert-butanol was used as a quencher for hydroxyl radicals, methanol as a quencher for hydroxyl radicals, acetoxy radicals, and acetylperoxy radicals, and dimethyl sulfoxide (DMSO) as a quencher for hydroxyl radicals and high-valent ferrous oxide species. The portion of the SMX removal rate decreased by tert-butanol represents the contribution of hydroxyl radicals to the SMX removal rate. The portion of the SMX removal rate decreased by methanol minus the portion decreased by tert-butanol represents the contribution of acetoxy radicals and acetylperoxy radicals to the SMX removal rate. The portion of the SMX removal rate decreased by dimethyl sulfoxide minus the portion decreased by tert-butanol represents the contribution of high-valent ferrous oxide species to the SMX removal rate.

[0059] Three experimental groups and one blank control group were set up. The blank control group did not receive any quencher. Tert-butanol, methanol, and dimethyl sulfoxide were added to the simulated wastewater of each experimental group to a concentration of 10 mmol / L, respectively. Then, catalyst and PAA were added, and the wastewater was treated under stirring conditions. The catalyst dosage in the simulated wastewater was 300 mg / L, and the PAA concentration was 0.4 mmol / L. Samples were taken 16 min after the addition of catalyst and PAA, filtered through a 0.22 μm filter membrane, and the reaction was terminated with 20 g / L sodium thiosulfate solution. The concentration of SMX was detected using liquid chromatography. The results are shown below. Figure 4 As shown.

[0060] Depend on Figure 4 It can be seen that the removal rates of SMX in the experimental groups with tert-butanol, methanol, and dimethyl sulfoxide as quenchers were all low and not significantly different. Since tert-butanol is a quencher of hydroxyl radicals, this indicates that when the iron-sulfur co-doped carbon nitride material prepared in Example 1 is used as a catalyst, the main active species for SMX degradation in the activation of low-concentration PAA (0.4 mmol / L) is hydroxyl radicals, which contribute more than 85% to SMX degradation. In the experimental groups with dimethyl sulfoxide and tert-butanol as quenchers, the difference in SMX removal rates was very small. This means that when the iron-sulfur co-doped carbon nitride material prepared in Example 1 is used as a catalyst, although high-valence iron-oxygen species are generated when activating low-concentration PAA (0.4 mmol / L), their contribution to SMX degradation is very small.

[0061] Example 3

[0062] In this embodiment, the iron-sulfur co-doped carbon nitride material prepared in Example 1 was used as a catalyst to activate the degradation of SMX by high concentration of PAA, and the main active species generated by the catalyst to activate PAA during the process were tested.

[0063] (1) SMX degradation experiment

[0064] SMX was dissolved in water to form a 10 μmol / L SMX solution, which was used as simulated wastewater. A catalyst and PAA were added to the simulated wastewater, and wastewater treatment was carried out under stirring conditions. The catalyst dosage in the simulated wastewater was 300 mg / L, and the PAA concentration was 0.8 mmol / L. Samples were taken 16 min after the addition of the catalyst and PAA, filtered through a 0.22 μm filter membrane, and the reaction was terminated with a 20 g / L sodium thiosulfate solution. The SMX concentration was detected using liquid chromatography, and the SMX removal rate was calculated. The results showed that the SMX removal rate in this embodiment was 82.8%.

[0065] (2) Quenching Experiment

[0066] tert-butanol was used as a quencher for hydroxyl radicals, methanol as a quencher for hydroxyl radicals, acetoxy radicals, and acetylperoxy radicals, and dimethyl sulfoxide (DMSO) as a quencher for hydroxyl radicals and high-valent ferrous oxide species. The portion of the SMX removal rate decreased by tert-butanol represents the contribution of hydroxyl radicals to the SMX removal rate. The portion of the SMX removal rate decreased by methanol minus the portion decreased by tert-butanol represents the contribution of acetoxy radicals and acetylperoxy radicals to the SMX removal rate. The portion of the SMX removal rate decreased by dimethyl sulfoxide minus the portion decreased by tert-butanol represents the contribution of high-valent ferrous oxide species to the SMX removal rate.

[0067] Three experimental groups and one blank control group were set up. The blank control group did not receive any quencher. Tert-butanol, methanol, and dimethyl sulfoxide were added to the simulated wastewater of each experimental group to a concentration of 10 mmol / L, respectively. Then, the catalyst and PAA were added, and the wastewater was treated under stirring conditions. The catalyst dosage in the simulated wastewater was 300 mg / L, and the PAA concentration was 0.8 mmol / L. Samples were taken 16 min after the addition of catalyst and PAA, filtered through a 0.22 μm filter membrane, and the reaction was terminated with 20 g / L sodium thiosulfate solution. The concentration of SMX was detected using liquid chromatography. The results are shown below. Figure 5 As shown.

[0068] Depend on Figure 5 It can be seen that the removal rates of SMX were relatively high in the experimental groups with tert-butanol and methanol added as quenchers, indicating that hydroxyl radicals contributed the least to SMX degradation. The difference in SMX removal rates between the experimental groups with tert-butanol and methanol added was small, which means that when the iron-sulfur co-doped carbon nitride material prepared in Example 1 was used as a catalyst, although acetoxy radicals and acetylperoxy radicals were generated when activating high-concentration PAA (0.8 mmol / L), their contribution to SMX removal was small. The addition of dimethyl sulfoxide as a quencher showed the greatest inhibition of SMX degradation, indicating that when the iron-sulfur co-doped carbon nitride material prepared in Example 1 was used as a catalyst, the main active species generated when activating high-concentration PAA (0.8 mmol / L) were high-valence iron-oxygen species, which contributed more than 70% to SMX degradation.

[0069] As can be seen from Examples 2 and 3, when the iron-sulfur co-doped carbon nitride material of this invention is used to activate low-concentration (e.g., 0.4 mmol / L) PAA, the main active species generated are hydroxyl radicals. When the iron-sulfur co-doped carbon nitride material of this invention is used to activate high-concentration (e.g., 0.8 mmol / L) PAA, the main active species generated are high-valence ferrite species. That is, by adjusting the concentration of the oxidant PAA, the type of main active species generated by the iron-sulfur co-doped carbon nitride material during PAA activation can be controlled. In practical applications, depending on the characteristics of organic pollutants in wastewater, the type of main active species can be flexibly controlled by adjusting the concentration of PAA, so that the types of main active species generated are precisely those capable of efficiently degrading the target pollutants, thereby achieving efficient treatment of wastewater containing organic pollutants.

[0070] Comparative Example 2

[0071] In this embodiment, the iron-doped carbon nitride material prepared in Comparative Example 1 was used as a catalyst to activate the degradation of SMX by low concentration of PAA, and the main active species generated by the catalyst to activate PAA during the process were tested.

[0072] (1) SMX degradation experiment

[0073] SMX was dissolved in water to form a 10 μmol / L SMX solution, which was used as the simulated wastewater. A catalyst and PAA were added to the simulated wastewater, and wastewater treatment was carried out under stirring conditions. The catalyst dosage in the simulated wastewater was 300 mg / L, and the PAA concentration was 0.4 mmol / L. Samples were taken 16 min after the addition of the catalyst and PAA, filtered through a 0.22 μm filter membrane, and the reaction was terminated with a 20 g / L sodium thiosulfate solution. The SMX concentration was detected using liquid chromatography, and the SMX removal rate was calculated. The results showed that the SMX removal rate in this comparative example was 30.1%.

[0074] (2) Quenching Experiment

[0075] tert-butanol was used as a quencher for hydroxyl radicals, methanol as a quencher for hydroxyl radicals, acetoxy radicals, and acetylperoxy radicals, and dimethyl sulfoxide (DMSO) as a quencher for hydroxyl radicals and high-valent ferrous oxide species. The portion of the SMX removal rate decreased by tert-butanol represents the contribution of hydroxyl radicals to the SMX removal rate. The portion of the SMX removal rate decreased by methanol minus the portion decreased by tert-butanol represents the contribution of acetoxy radicals and acetylperoxy radicals to the SMX removal rate. The portion of the SMX removal rate decreased by dimethyl sulfoxide minus the portion decreased by tert-butanol represents the contribution of high-valent ferrous oxide species to the SMX removal rate.

[0076] Three experimental groups and one blank control group were set up. The blank control group did not receive any quencher. Tert-butanol, methanol, and dimethyl sulfoxide were added to the simulated wastewater of each experimental group to a concentration of 10 mmol / L, respectively. Then, the catalyst and PAA were added, and the wastewater was treated under stirring. The catalyst dosage in the simulated wastewater was 300 mg / L, and the PAA concentration was 0.4 mmol / L. Samples were taken 16 min after the addition of catalyst and PAA, filtered through a 0.22 μm filter membrane, and the reaction was terminated with 20 g / L sodium thiosulfate solution. The concentration of SMX was detected using liquid chromatography. The results are shown below. Figure 6 As shown.

[0077] Depend on Figure 6 It can be seen that the removal rates of SMX in the blank group and the experimental group with added tert-butanol and methanol as quenchers were both small and very similar, indicating that hydroxyl radicals, acetoxy radicals and acetylperoxy radicals have low contributions to SMX degradation. When dimethyl sulfoxide was added as a quencher, the degradation of SMX was almost completely inhibited, indicating that when the iron-doped carbon nitride material prepared in Comparative Example 1 was used as a catalyst, the main active species generated when activating low concentration PAA (0.4 mmol / L) were high-valence iron-oxygen species, which contributed more than 80% to the degradation of SMX.

[0078] Comparative Example 3

[0079] In this embodiment, the iron-doped carbon nitride material prepared in Comparative Example 1 was used as a catalyst to activate the degradation of SMX by high concentration of PAA, and the main active species generated by the catalyst activation of PAA were tested.

[0080] (1) SMX degradation experiment

[0081] SMX was dissolved in water to form a 10 μmol / L SMX solution, which was used as the simulated wastewater. A catalyst and PAA were added to the simulated wastewater, and wastewater treatment was carried out under stirring conditions. The catalyst dosage in the simulated wastewater was 300 mg / L, and the PAA concentration was 0.8 mmol / L. Samples were taken 16 min after the addition of the catalyst and PAA, filtered through a 0.22 μm filter membrane, and the reaction was terminated with a 20 g / L sodium thiosulfate solution. The SMX concentration was detected using liquid chromatography, and the SMX removal rate was calculated. The results showed that the SMX removal rate in this comparative example was 61.5%.

[0082] (2) Quenching Experiment

[0083] tert-butanol was used as a quencher for hydroxyl radicals, methanol as a quencher for hydroxyl radicals, acetoxy radicals, and acetylperoxy radicals, and dimethyl sulfoxide (DMSO) as a quencher for hydroxyl radicals and high-valent ferrous oxide species. The portion of the SMX removal rate decreased by tert-butanol represents the contribution of hydroxyl radicals to the SMX removal rate. The portion of the SMX removal rate decreased by methanol minus the portion decreased by tert-butanol represents the contribution of acetoxy radicals and acetylperoxy radicals to the SMX removal rate. The portion of the SMX removal rate decreased by dimethyl sulfoxide minus the portion decreased by tert-butanol represents the contribution of high-valent ferrous oxide species to the SMX removal rate.

[0084] Three experimental groups and one blank control group were set up. The blank control group did not receive any quencher. Tert-butanol, methanol, and dimethyl sulfoxide were added to the simulated wastewater of each experimental group to a concentration of 10 mmol / L, respectively. Then, the catalyst and PAA were added, and the wastewater was treated under stirring conditions. The catalyst dosage in the simulated wastewater was 300 mg / L, and the PAA concentration was 0.8 mmol / L. Samples were taken 16 min after the addition of catalyst and PAA, filtered through a 0.22 μm filter membrane, and the reaction was terminated with 20 g / L sodium thiosulfate solution. The concentration of SMX was detected using liquid chromatography. The results are shown below. Figure 7 As shown.

[0085] Depend on Figure 7 It can be seen that the removal rates of SMX in the blank group and the experimental group with added tert-butanol and methanol as quenchers were both small and very similar, indicating that hydroxyl radicals, acetoxy radicals and acetylperoxy radicals have low contributions to SMX degradation. When dimethyl sulfoxide was added as a quencher, the degradation of SMX was almost completely inhibited, indicating that when the iron-doped carbon nitride material prepared in Comparative Example 1 was used as a catalyst, the main active species generated when activating high concentration PAA (0.8 mmol / L) were high-valence iron-oxygen species, which contributed more than 80% to the degradation of SMX.

[0086] Based on Comparative Examples 2-3 and Examples 2-3, it is evident that, compared to Examples 2-3 where iron-sulfur co-doped carbon nitride was used as a catalyst to activate PAA for SMX degradation, Comparative Examples 2-3 using iron-doped carbon nitride as a catalyst resulted in significantly worse SMX degradation. Furthermore, in Comparative Examples 2-3, when iron-doped carbon nitride was used as a catalyst to activate low-concentration (0.4 mmol / L) and high-concentration (0.8 mmol / L) PAA, the main active species produced were high-valence ferric oxide species, and the composition of these main active species did not change with the PAA concentration.

[0087] Example 4

[0088] In this embodiment, the iron-sulfur co-doped carbon nitride material prepared in Example 1 was used as a catalyst to activate PAA to degrade SMX.

[0089] (1) SMX degradation experiment

[0090] Using actual wastewater from a farm in Shandong Province as a solvent, the target pollutant SMX was dissolved in the solvent and the pH was adjusted to 3.5 to form wastewater to be treated. The concentration of SMX in the wastewater was 10 μmol / L. Because the actual wastewater from this farm contains coexisting inorganic anions and other matrix components, which easily quench hydroxyl radicals, it adversely affects the ability of hydroxyl radicals to degrade SMX in the wastewater. In contrast, high-valence ferric oxide species are less affected by the coexisting water matrix and also have good degradation ability for SMX. Therefore, this embodiment considers controlling the concentration of PAA so that the main active species generated by the catalyst activating PAA are high-valence ferric oxide species.

[0091] The following experiment will verify this hypothesis:

[0092] ① Experiment 1: A catalyst and PAA were added to the wastewater to be treated, and the wastewater was treated under stirring conditions. The catalyst dosage in the wastewater was 300 mg / L, and the PAA concentration in the simulated wastewater was 0.2 mmol / L. Samples were taken 30 min after the addition of the catalyst and PAA, filtered through a 0.22 μm filter membrane, and the reaction was terminated with a 20 g / L sodium thiosulfate solution. The concentration of SMX was detected using liquid chromatography, and the removal rate of SMX was calculated. The results showed that the removal rate of SMX was 47.5%.

[0093] ② Experiment 2: A catalyst and PAA were added to the wastewater to be treated, and the wastewater was treated under stirring conditions. The catalyst dosage in the wastewater was 300 mg / L, and the PAA concentration in the simulated wastewater was 0.8 mmol / L. Samples were taken 30 min after the addition of the catalyst and PAA, filtered through a 0.22 μm filter membrane, and the reaction was terminated with a 20 g / L sodium thiosulfate solution. The concentration of SMX was detected using liquid chromatography, and the SMX removal rate was calculated. The results showed that the SMX removal rate was 100%.

[0094] The results of Experiments 1 and 2 show that, under the wastewater quality conditions of this embodiment, the coexisting aqueous matrix quenches hydroxyl radicals, thus adversely affecting the degradation of SMX in the wastewater. Therefore, under these conditions, controlling the main active species produced by the catalyst activation of PAA to be high-valent ferric oxide species is more advantageous. This embodiment successfully controlled the main activity by adjusting the PAA concentration, ultimately achieving efficient degradation of SMX in the wastewater.

[0095] (2) Quenching Experiment

[0096] The following examines the main active species generated under Experiment 2 and their contribution to the degradation of SMX in wastewater.

[0097] tert-butanol was used as a quencher for hydroxyl radicals, methanol as a quencher for hydroxyl radicals, acetoxy radicals, and acetylperoxy radicals, and dimethyl sulfoxide (DMSO) as a quencher for hydroxyl radicals and high-valent ferrous oxide species. The portion of the SMX removal rate decreased by tert-butanol represents the contribution of hydroxyl radicals to the SMX removal rate. The portion of the SMX removal rate decreased by methanol minus the portion decreased by tert-butanol represents the contribution of acetoxy radicals and acetylperoxy radicals to the SMX removal rate. The portion of the SMX removal rate decreased by dimethyl sulfoxide minus the portion decreased by tert-butanol represents the contribution of high-valent ferrous oxide species to the SMX removal rate.

[0098] Three experimental groups and one blank control group were set up. The blank control group did not receive any quencher. Tert-butanol was added to the simulated wastewater of each experimental group to a concentration of 20 mmol / L, methanol to a concentration of 100 mmol / L, and dimethyl sulfoxide to a concentration of 100 mmol / L, respectively. Then, catalyst and PAA were added, and wastewater treatment was carried out under stirring conditions. The catalyst dosage in the simulated wastewater was 300 mg / L, and the PAA concentration was 0.8 mmol / L. Samples were taken 30 min after the addition of catalyst and PAA, filtered through a 0.22 μm filter membrane, and the reaction was terminated with 20 g / L sodium thiosulfate solution. The concentration of SMX was detected using liquid chromatography. The results are as follows: Figure 8 As shown.

[0099] Depend on Figure 8 It can be seen that the removal rates of SMX were relatively high in the experimental groups with tert-butanol and methanol added as quenchers, indicating that hydroxyl radicals contributed the least to SMX degradation. The difference in SMX removal rates between the experimental groups with tert-butanol and methanol added was very small, indicating that when the iron-sulfur co-doped carbon nitride material prepared in Example 1 was used as a catalyst, acetoxy radicals and acetylperoxy radicals were generated when activating high-concentration PAA (0.8 mmol / L), and both contributed little to SMX removal. The addition of dimethyl sulfoxide as a quencher showed the greatest inhibition of SMX degradation, indicating that when the iron-sulfur co-doped carbon nitride material prepared in Example 1 was used as a catalyst to activate high-concentration PAA (0.8 mmol / L) to degrade SMX in actual aquaculture wastewater, the main active species generated were high-valence ferric oxide species, which contributed more than 80% to the degradation of SMX in actual wastewater.

[0100] Example 5

[0101] In this embodiment, the iron-sulfur co-doped carbon nitride material prepared in Example 1 was used as a catalyst to activate PAA to degrade ibuprofen (IBU).

[0102] IBU was dissolved in water to form an IBU concentration of 2 mg / L, which was used as simulated wastewater. A catalyst and PAA were added to the simulated wastewater, and wastewater treatment was carried out under stirring conditions. The catalyst dosage in the simulated wastewater was 200 mg / L, and the PAA concentration was 0.4 mmol / L. Samples were taken 16 min after the addition of the catalyst and PAA, filtered through a 0.22 μm filter membrane, and the reaction was terminated with a 20 g / L sodium thiosulfate solution. The IBU concentration was detected using liquid chromatography, and the IBU removal rate was calculated. The results showed that the IBU removal rate in this embodiment was 94.3%.

[0103] Example 6

[0104] In this embodiment, the iron-sulfur co-doped carbon nitride material prepared in Example 1 was used as a catalyst to activate PAA to degrade atrazine (ATZ).

[0105] ATZ was dissolved in water to form an IBU concentration of 2 mg / L, which was used as simulated wastewater. A catalyst and PAA were added to the simulated wastewater, and wastewater treatment was carried out under stirring conditions. The catalyst dosage in the simulated wastewater was 200 mg / L, and the PAA concentration was 0.4 mmol / L. Samples were taken 16 min after the addition of the catalyst and PAA, filtered through a 0.22 μm filter membrane, and the reaction was terminated with a 20 g / L sodium thiosulfate solution. The concentration of ATZ was detected using liquid chromatography, and the ATZ removal rate was calculated. The results showed that the ATZ removal rate in this embodiment was 83.9%.

[0106] Example 7

[0107] In this embodiment, the iron-sulfur co-doped carbon nitride material prepared in Example 1 was used as a catalyst to activate PAA to degrade carbamazepine (CBZ).

[0108] CBZ was dissolved in water to form a 2 mg / L CBZ solution, which was used as simulated wastewater. A catalyst and PAA were added to the simulated wastewater, and wastewater treatment was carried out under stirring conditions. The catalyst dosage in the simulated wastewater was 200 mg / L, and the PAA concentration was 0.4 mmol / L. Samples were taken 4 minutes after the addition of the catalyst and PAA, filtered through a 0.22 μm filter membrane, and the reaction was terminated with a 20 g / L sodium thiosulfate solution. The CBZ concentration was detected using liquid chromatography, and the CBZ removal rate was calculated. The results showed that the CBZ removal rate in this embodiment was 100%.

[0109] Example 8

[0110] In this embodiment, the iron-sulfur co-doped carbon nitride material prepared in Example 1 was used as a catalyst to activate PAA to degrade SMX in simulated wastewater with different pH values.

[0111] SMX was dissolved in water to form a 10 μmol / L SMX solution. The pH of the SMX solution was then adjusted to 2, 5, 7 and 9 with dilute sulfuric acid and sodium hydroxide solutions, respectively, to obtain simulated wastewater with different pH values.

[0112] Catalyst and PAA were added to simulated wastewater at various pH values, and the wastewater was treated under stirring. The catalyst dosage in the simulated wastewater was 200 mg / L, and the PAA concentration was 0.4 mmol / L. Samples were taken 16 min after catalyst and PAA addition, filtered through a 0.22 μm membrane, and the reaction was terminated with a 20 g / L sodium thiosulfate solution. The concentration of SMX was detected using liquid chromatography, and the SMX removal rate was calculated. The results showed that when the pH values ​​of the simulated wastewater were 2, 5, 7, and 9, the SMX removal rates were 94.3%, 62.2%, 34%, and 31.3%, respectively.

[0113] Catalyst and PAA were added to simulated wastewater at various pH values, and the wastewater was treated under stirring. The catalyst dosage in the simulated wastewater was 200 mg / L, and the PAA concentration was 0.8 mmol / L. Samples were taken 16 min after catalyst and PAA addition, filtered through a 0.22 μm filter membrane, and the reaction was terminated with a 20 g / L sodium thiosulfate solution. The concentration of SMX was detected using liquid chromatography, and the SMX removal rate was calculated. The results showed that when the pH values ​​of the simulated wastewater were 2, 5, 7, and 9, the SMX removal rates were 100%, 73.9%, 69%, and 58.2%, respectively.

Claims

1. A method for wastewater treatment with controllable active species type, characterized in that, Includes the following steps: Iron-sulfur co-doped carbon nitride material and peracetic acid are added to wastewater containing organic pollutants. The amount of iron-sulfur co-doped carbon nitride material added is controlled at 50~1000 mg / L, and the pH value of the wastewater is controlled at 2~7. The wastewater is treated under the conditions of stirring or the wastewater is in a flowing state. During the wastewater treatment process, the iron-sulfur co-doped carbon nitride material activates peracetic acid to generate free radical active species and non-free radical active species, which degrade the organic pollutants in the wastewater. By adjusting the concentration of peracetic acid in wastewater, the ratio of free radical active species to non-free radical active species generated by the activation of peracetic acid by iron-sulfur co-doped carbon nitride materials can be controlled. The lower the concentration of peracetic acid in the wastewater, the higher the ratio of free radical active species to non-free radical active species generated by the activation of peracetic acid by the iron-sulfur co-doped carbon nitride material; conversely, the higher the concentration of peracetic acid in the wastewater, the lower the ratio of free radical active species to non-free radical active species generated by the activation of peracetic acid by the iron-sulfur co-doped carbon nitride material. The free radical active species are mainly hydroxyl radicals, and the non-free radical active species are high-valence ferrooxide species. The active species with higher reactivity with the target organic pollutants in the wastewater under the wastewater quality conditions is designated as the target active species. The concentration of peracetic acid in the wastewater is adjusted so that the main active species generated by the activation of peracetic acid by the iron-sulfur co-doped carbon nitride material is the target active species. The preparation method of the iron-sulfur co-doped carbon nitride material is as follows: (1) The carbon nitride precursor, sulfur donor and iron source are thoroughly mixed to obtain a precursor mixture; in the precursor mixture, the mass percentage of carbon nitride precursor is 69%~88%, the mass percentage of sulfur donor is 7%~28%, and the mass percentage of iron source is 0.7%~10%. (2) The precursor mixture is calcined at 500~600 ℃ for 2~4 h to obtain iron-sulfur co-doped carbon nitride material.

2. The method for wastewater treatment according to claim 1, wherein the type of active species is controlled. The amount of peracetic acid added was controlled so that the concentration of peracetic acid in the wastewater was 0.01~1 mmol / L.

3. The method for treating wastewater by controlling the type of active species according to claim 1 or 2, characterized in that, When the main active species generated by the activation of peracetic acid by the iron-sulfur co-doped carbon nitride material are free radical active species, the pH value of the wastewater should be controlled at 2-5. When the main active species generated by the activation of peracetic acid by the iron-sulfur co-doped carbon nitride material are non-free radical active species, the pH value of the wastewater should be controlled at 2-7.

4. The method for treating wastewater by controlling the type of active species according to claim 1 or 2, characterized in that, In step (2) of preparing iron-sulfur co-doped carbon nitride material, the precursor mixture is calcined in a gas atmosphere consisting of at least one of air, nitrogen and argon.

5. The method for treating wastewater by controlling the type of active species according to claim 1 or 2, wherein, In step (1) of preparing iron-sulfur co-doped carbon nitride material, the carbon nitride precursor is at least one of urea, melamine and dicyandiamine, the iron source is at least one of divalent iron salt and trivalent iron salt, and the sulfur element donor is trithiocyanic acid.

6. The wastewater treatment method with adjustable active species type according to claim 1 or 2, characterized in that, The wastewater treatment time should be controlled to be 15-60 minutes.

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