Non-free radical catalytic oxidation water treatment method for regulating and controlling degradation path of sulfamethoxazole by using nitrite

Abstract

The invention discloses a non-free radical catalytic oxidation water treatment method for regulating and controlling a sulfamethoxazole degradation path by using nitrite, and relates to the technical field of water treatment, and the non-free radical catalytic oxidation water treatment method comprises the following steps: adding a carbonized polydopamine coated cobalt nanoparticle material and peroxymonosulfate into a to-be-treated water body containing nitrite and sulfamethoxazole; the method comprises the following steps: firstly, carrying out adsorption of an oxidant on the surface of a catalyst, and then carrying out non-free radical catalytic oxidation, so that nitrite and sulfamethoxazole are synchronously removed within a preset reaction time; in the reaction process, nitrite serves as a removed pollutant to be subjected to oxidation-reduction conversion and also serves as a degradation path regulator to inhibit generation of nitro by-products, a non-free radical oxidation system is constructed through carbonized polydopamine coated cobalt nanoparticles and peroxymonosulfate, a degradation path is regulated and controlled by the nitrite, and the degradation of the nitro by-products is inhibited. Nitrite and sulfamethoxazole in the water body are synchronously removed, and high-toxicity nitro byproducts are inhibited.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and specifically to a non-radical catalytic oxidation water treatment method that utilizes nitrite to regulate the degradation pathway of sulfamethoxazole. Background Technology

[0002] With the rapid expansion of intensive and large-scale aquaculture globally, the complex pollution caused by aquaculture wastewater discharge has become a key bottleneck restricting the industry's sustainable development and ecological environmental safety. During the aquaculture process, the decomposition of organic matter such as animal excrement and uneaten feed drives an imbalance in the nitrogen cycle, leading to a large accumulation of nitrite (NIT) in water bodies. At the same time, antibiotics such as sulfamethoxazole (SMX) are widely used to control bacterial diseases, and the unmetabolized portion of these antibiotics is discharged with the wastewater, ultimately creating a complex pollution scenario where NIT and SMX coexist. The synergistic harm of these two pollutants far exceeds that of single pollution: NIT, as a typical toxic nitrogenous compound, can oxidize hemoglobin in the blood of aquatic organisms into methemoglobin, which has no oxygen-carrying capacity, causing tissue hypoxia and even death, and also exacerbating the proliferation and invasion of pathogenic microorganisms; SMX, on the other hand, has environmental persistence and bioaccumulation, and its ecotoxicological effects include cytotoxicity, gene expression disorder and estrogenic activity. More seriously, when NIT and SMX coexist, they will damage the metabolic activity of microorganisms and induce the spread of antibiotic resistance genes. The broad-spectrum inhibitory effect of antibiotics will hinder the activity of functional microorganisms in the biological denitrification system, further promoting the accumulation of NIT and forming a vicious cycle of "pollution-drug resistance-pollution aggravation", which poses a dual threat to the health of aquatic organisms, aquatic ecosystems and human health.

[0003] To address the aforementioned complex pollution issues, advanced oxidation processes (AOPs) based on persulfate activation (such as permonosulfate PMS and perdisulfate PDS) have been widely studied for antibiotic degradation due to their strong oxidizing properties. However, traditional AOPs mainly rely on hydroxyl radicals (·OH) and sulfate radicals (SO4). - The free radical pathways such as ·OH and SO42- have encountered insurmountable technical bottlenecks in treating NIT and SMX complex pollution: on the one hand, NIT has limited ability to react with ·OH and SO42-. - • It possesses extremely high quenching rate constants (reaching 1.2 × 10¹). 0 M -1 s -1 and 9.8×10 8 M -1 s -1The rapid consumption of free radicals and the generation of nitrogen-centered free radicals with extremely low reactivity (such as NO2・) leads to a significant decrease in SMX degradation efficiency. Simultaneously, NIT itself is difficult to remove effectively, making synergistic treatment of both types of pollutants impossible. Furthermore, NIT-mediated free radical transformation significantly alters the degradation pathway of SMX, promoting nitration of its amino groups and generating nitro byproducts such as 4-nitro-sulfamethoxazole. These derivatives exhibit persistence and ecotoxicity far exceeding that of the parent compound, creating a secondary pollution risk of "treatment equals toxicity," severely restricting the practical application of the technology. In addition, traditional free radical AOPs are extremely sensitive to water quality conditions, particularly in aquaculture wastewater with a wide pH range (3-11) and high concentrations of coexisting anions (such as Cl-). - HCO3 - HPO4 2- In such environments, free radicals are easily consumed or transformed, leading to drastic fluctuations in treatment performance and making it difficult to meet the complex operating conditions required for actual wastewater treatment.

[0004] Although some studies have attempted to optimize catalysts or adjust reaction conditions to improve performance, they have failed to fundamentally solve the problems of NIT interference and nitro byproduct formation. Summary of the Invention

[0005] The purpose of this invention is to provide a non-radical catalytic oxidation water treatment method that utilizes nitrite to regulate the degradation pathway of sulfamethoxazole, in order to solve the problems of low degradation efficiency, easy generation of toxic byproducts, and poor water quality adaptability of traditional free radical advanced oxidation processes when treating related complex pollutants.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a non-radical catalytic oxidation water treatment method utilizing nitrite to regulate the degradation pathway of sulfamethoxazole, comprising the following steps:

[0007] S1. Carbonized polydopamine-coated cobalt nanoparticles and persulfate are added to the water to be treated, which contains nitrite and sulfamethoxazole. The carbonized polydopamine-coated cobalt nanoparticles serve as a catalyst, and the persulfate serves as an oxidant. The catalyst and the oxidant constitute a heterogeneous advanced oxidation system.

[0008] S2. The heterogeneous advanced oxidation system first undergoes adsorption of the oxidant on the catalyst surface, forming a catalyst-persulfate surface composite active species, which then triggers non-radical catalytic oxidation dominated by electron transfer and with singlet oxygen as an auxiliary active species, so that nitrite and sulfamethoxazole are removed simultaneously within a preset reaction time.

[0009] S3. In the non-radical catalytic oxidation process, nitrite is both a pollutant to be removed and undergoes redox transformation, and a degradation pathway regulator, inducing the degradation pathway of sulfamethoxazole to shift towards benzene ring hydroxylation, sulfonamide bond cleavage and isoxazole epoxidation, thereby inhibiting the formation of nitro byproducts.

[0010] The nitro byproducts include 4-nitro-sulfamethoxazole and hydroxylated nitro derivatives.

[0011] Furthermore, in step S3, the nitrite is simultaneously oxidized and reduced during the non-radical catalytic oxidation reaction. The reduction products are ammonium salt and nitrogen gas, and the oxidation product is nitrate, wherein the ammonium salt is the main conversion product of nitrite.

[0012] Furthermore, the preset reaction time is 5 to 60 minutes.

[0013] Furthermore, the catalyst-persulfate surface composite active species are formed through the synergistic effect of metallic cobalt, activated carbon, and graphitic nitrogen on the catalyst surface, wherein the electron transfer pathway is as follows:

[0014] Sulfamethoxazole acts as an electron donor, transferring electrons to the active species on the surface of the catalyst-persulfate complex, thus completing the oxidative degradation. The electron transfer pathway is a non-radical process and is not affected by the free radical quenching effect of nitrite in the water to be treated.

[0015] Furthermore, the dosage of the carbonized polydopamine-coated cobalt nanoparticle material is 0.025 g / L to 0.1 g / L; the dosage concentration of the persulfate is 0.2 mM to 0.5 mM.

[0016] Furthermore, the non-radical catalytic oxidation reaction remains highly efficient and stable in water bodies with pH values ​​ranging from 3.0 to 9.0; and the simultaneous removal efficiency of sulfamethoxazole and nitrite reaches its highest at pH 9.0.

[0017] Furthermore, the generation of singlet oxygen by the auxiliary active species is regulated by nitrite. The presence of nitrite can promote the generation of singlet oxygen and synergistically enhance the degradation of sulfamethoxazole with the electron transfer pathway.

[0018] The free radical pathway is an important medium for the formation of nitro byproducts, and the enhancement of singlet oxygen and electron transfer pathways can inhibit the formation of nitro byproducts.

[0019] Furthermore, the carbonized polydopamine-coated cobalt nanoparticle material is regenerated after continuous use by heat treatment at 850°C for 10 minutes under an inert atmosphere.

[0020] Furthermore, the water to be treated contains Cl at a concentration of 1–10 mM.- HCO3 - HPO4 2- H2PO4 - or SO4 2- When one or more anions are present, the simultaneous removal of nitrite and sulfamethoxazole by the non-radical catalytic oxidation system is not significantly inhibited;

[0021] The water bodies to be treated are surface water, groundwater, and aquaculture wastewater with combined pollution characteristics of nitrite and sulfamethoxazole.

[0022] Furthermore, the carbonized polydopamine-coated cobalt nanoparticle material is used as a catalyst in combination with persulfate for the simultaneous removal of nitrite and sulfamethoxazole from water through non-radical catalytic oxidation, and the formation of nitro byproducts in the degradation products of sulfamethoxazole is inhibited in the presence of the nitrite.

[0023] Compared with existing technologies, the non-radical catalytic oxidation water treatment method provided by the present invention, which utilizes nitrite to regulate the degradation pathway of sulfamethoxazole, has the following beneficial effects:

[0024] 1. A non-radical oxidation pathway dominated by electron transfer is constructed using coexisting pollutant nitrite. This pathway does not rely on free radicals that are easily quenched by nitrite, but instead forms surface complex active species through catalysts, which directly accept electrons from sulfamethoxazole, thereby achieving innate immunity to nitrite interference. This enables the simultaneous and efficient oxidation of sulfamethoxazole and reduction / oxidation of nitrite in the same reaction network, achieving synergistic removal of pollutants.

[0025] 2. For the first time, nitrite was discovered and verified as a safety guide for the degradation pathway of sulfamethoxazole. Experiments have confirmed that the presence of nitrite can significantly inhibit the formation of highly toxic nitro byproducts during the degradation of sulfamethoxazole, directing its degradation to pathways such as hydroxylation and ring-opening to generate products with lower ecological risks. By using one pollutant to inhibit the generation of new toxicity from another pollutant, the environmental risks of the treatment process are proactively reduced from the source.

[0026] 3. The simultaneous and efficient removal of sulfamethoxazole and nitrite is achieved through catalysts and persulfate. Its non-radical dominant mechanism gives the technology strong environmental adaptability and stable performance in a wide pH range and in the presence of high concentrations of common anions, overcoming the pain point of traditional processes having strict requirements on water quality conditions. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0028] Figure 1 The catalyst characterization diagram provided in the embodiments of the present invention; wherein Figure 1 a is the X-ray diffraction (XRD) pattern of Co-N@PC. Figure 1 b represents the nitrogen adsorption-desorption isotherm and corresponding pore size distribution curve for Co-N@PC. Figure 1 c represents the Raman spectrum of Co-N@PC; Figure 1 d, 1e, and 1f are the high-resolution X-ray photoelectron spectra of the C 1s orbital, N 1s orbital, and Co 2p orbital, respectively;

[0029] Figure 2 The catalyst Co-N@PC provided in the embodiments of the present invention 850 Catalytic performance diagram; Figure 2 a represents the effect of catalyst dosage on the degradation rate of sulfamethoxazole. Figure 2 b represents the effect of persulfate on the degradation rate of sulfamethoxazole. Figure 2 c represents the effect of nitrite concentration on the degradation rate of sulfamethoxazole. Figure 2 d represents the effect of catalyst dosage on the nitrite conversion rate. Figure 2 e represents the effect of persulfate on the nitrite conversion rate. Figure 2 f represents the effect of sulfamethoxazole concentration reduction on the nitrite conversion rate;

[0030] Figure 3 The effects of different quenching agents on the degradation rate of pollutants provided in the embodiments of the present invention; Figure 3 a represents the effect of different quenchers on the removal efficiency of sulfamethoxazole. Figure 3 b shows the effect of different quenching agents on nitrite removal efficiency;

[0031] Figure 4 Electron paramagnetic resonance (EPR) spectra of the catalysts provided in the embodiments of the present invention and corresponding free radical signal intensity analysis; Figure a shows the •OH and SO4 captured by DMPO in different catalytic systems. - ·Signal, Figure 4 b represents the O2 captured by DMPO in different catalytic systems. - ·Signal, Figure 4 c represents TEMP capture in different catalytic systems. 1 O2 signal, Figure 4d represents the change in signal intensity of different free radicals over time in the catalyst + oxidant + sulfamethoxazole system. Figure 4 e represents the change in signal intensity of different free radicals over time in the catalyst + oxidant + sulfamethoxazole + nitrite system. Figure 4 f represents the change in signal intensity of different free radicals over time in the catalyst + oxidant + nitrite system;

[0032] Figure 5 In-situ Raman and electrochemical characterization for verifying electron transfer pathways provided in embodiments of the present invention; Figure 5 a is the in-situ Raman spectrum. Figure 5 b is the chronoamperometry test. Figure 5 c represents the linear sweep voltammetry test. Figure 5 d represents electrochemical impedance spectroscopy (EIS) measurement;

[0033] Figure 6 The chemical state analysis results of the catalyst after reaction provided in the embodiments of the present invention include high-resolution X-ray photoelectron spectroscopy and atomic percentage of elements; Figure 6 a represents the fine spectra of the C 1s, N 1s, O 1s, and Co 2p orbitals from 0 to 6 d and the quantitative compositional changes before and after the reaction;

[0034] Figure 7 The degradation pathway of sulfamethoxazole and the toxicity assessment data of degradation intermediates based on TEST software provided in the embodiments of the present invention; Figure 7 a represents the degradation pathway of sulfamethoxazole. Figure 7 b represents mutagenicity data. Figure 7 c represents developmental toxicity data. Figure 7 d represents the bioaccumulation coefficient data;

[0035] Figure 8 The dynamic conversion process of nitrogen at different time points in the embodiments is shown; Figure 8 'a' represents the nitrogen content detected in different systems. Figure 8 b is the kinetic curve of the conversion of nitrite to nitrate, ammonia nitrogen and nitrogen gas;

[0036] Figure 9 This is a schematic diagram illustrating the mechanism of action of the carbonized polydopamine-coated cobalt nanoparticle material / persulfate catalytic oxidation system for the simultaneous removal of sulfamethoxazole and nitrite provided in this embodiment of the invention;

[0037] Figure 10 The effects of different environmental substrates on the removal efficiency of sulfamethoxazole and nitrite provided in the embodiments of the present invention; Figure 10 a and 10b represent the effects of initial pH on the removal efficiency of sulfamethoxazole and nitrite, respectively. Figure 10c and 10d represent the effects of coexisting inorganic anions on the removal efficiency of sulfamethoxazole and nitrite, respectively. Figure 10 e and 10f represent the removal efficiencies of the catalytic oxidation system for sulfamethoxazole and nitrite in actual water bodies, respectively.

[0038] Figure 11 The catalyst cycle performance diagram is provided for an embodiment of the present invention. Figure 11 a represents the removal kinetics curves of sulfamethoxazole at different cycle numbers. Figure 11 b is the XRD pattern of the carbonized polydopamine-coated cobalt nanoparticles after the reaction. Detailed Implementation

[0039] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0040] Example 1

[0041] This embodiment uses a coordination-pyrolysis method to prepare carbonized polydopamine-coated cobalt nanoparticles (Co-N@PC). The specific steps are as follows:

[0042] Weigh 0.15 g of cobalt chloride hexahydrate (CoCl2·6H2O) and 1.0 g of dopamine hydrochloride, and dissolve them together in 500 mL of 10 mM Tris-HCl buffer solution with a pH of 8.5. Place the mixture on a magnetic stirrer and stir continuously at room temperature (25 °C) for 48 hours. After the reaction is complete, collect the resulting purplish-black solid product by vacuum filtration and wash it several times with deionized water and ethanol. Place the washed product in a vacuum drying oven at 60 °C and dry it overnight to obtain the precursor.

[0043] The dried precursor was placed in a corundum ceramic boat in a tube furnace and heated to 700℃, 850℃, and 1000℃ respectively at a heating rate of 5℃ / min under the protection of high-purity nitrogen (flow rate 50 mL / min), and held at the target temperature for 2 hours for pyrolysis carbonization. After pyrolysis, it was naturally cooled to room temperature in a nitrogen atmosphere to obtain a black powdered catalyst, named Co-N@PC. 700 Co-N@PC 850 and Co-N@PC 1000 .

[0044] Figure 1 a showcased Co-N@PC 700 Co-N@PC 850 and Co-N@PC 1000X-ray diffraction (XRD) patterns were obtained for all samples. Characteristic diffraction peaks of graphitic carbon (2θ = 27.2°) and cubic cobalt (2θ = 43.5°, 53.2°, 76.7°) were observed, confirming that the prepared Co-N@PC contained carbon and cobalt species within the experimental temperature range. The presence of elemental cobalt indicates that most of the introduced Co... 2+ During calcination, it is reduced in situ to Co by adjacent carbon atoms. 0 Rather than undergoing oxidation, the diffraction peaks of cubic cobalt show a significant increase in intensity within the temperature range of 700°C to 1000°C, indicating an increase in the crystallinity of the metallic cobalt phase.

[0045] N2 adsorption-desorption isotherm ( Figure 1 b) The results show that all samples exhibit a composite isotherm of Type I and Type IV, accompanied by an H3 hysteresis loop, indicating that the material possesses a hierarchical porous structure with micropores, mesopores, and macropores. The calculated specific surface area order is as follows:

[0046] Co-N@PC 700 (265.74m² / g)>Co-N@PC 850 (248.48m² / g)>Co-N@PC 1000 (227.02 m² / g). As the calcination temperature increases, the specific surface area gradually decreases, indicating that the carbon skeleton partially collapses at high temperatures. This phenomenon is consistent with the pore size distribution data.

[0047] Raman spectroscopy ( Figure 1 c) at 1350cm -1 and 1580cm -1 Distinct D-band (defect / disordered carbon) and G-band (graphitized carbon) characteristic peaks appear nearby. Co-N@PC 850 The calculated Id / Ig ratio was 1.09, which is higher than that of Co-N@PC. 700 (1.03) and Co-N@PC 1000 (1.05) indicates that it has the most abundant structural defects, which is generally beneficial to the improvement of catalytic performance.

[0048] like Figure 1 As shown in df, with increasing calcination temperature, the atomic percentage of carbon increases, while the contents of nitrogen and cobalt decrease. High-resolution C 1s spectrum ( Figure 1 d) It can be fitted with components such as C=C (284.0 eV), CC (284.8 eV), CN (285.6 eV), CO (286.9 eV), and C=O / C=N (289.4 eV). N 1s spectrum ( Figure 1e) can decompose into pyridine nitrogen (398.2 eV), pyrrole nitrogen (400.1 eV), and graphitic nitrogen (401.5 eV), the proportions of which vary with pyrolysis temperature. Co 2p spectrum ( Figure 1 f) indicates that cobalt is represented by Co. 0 (778.4eV), Co 2+ (781.5eV) and Co 3+ It exists in a mixed valence state of (780.0 eV) and as Co 0 Primarily. Although annealing temperature is important for low-priced cobalt (Co 0 / Co 2+ ) and high-priced cobalt (Co 3+ The relative proportion of cobalt and N has no significant effect, but medium-temperature calcination at 850℃ is more conducive to the formation of metallic cobalt. In summary, calcination temperature has a significant impact on the chemical structure of Co-N@PC, and different temperatures endow the material with unique structural advantages and limitations.

[0049] Three catalysts were preliminarily screened through pre-adsorption and direct oxidation experiments. In the Co-N@PC / persulfate oxidation system, the degradation efficiency order was: Co-N@PC 850 Co-N@PC 700 Co-N@PC 1000 This indicates that the catalyst obtained by pyrolysis at 850℃ exhibits optimal persulfate activation performance. Therefore, Co-N@PC was selected. 850 It served as a representative catalyst for all subsequent research.

[0050] Example 2

[0051] This embodiment is used to further illustrate Co-N@PC 850 The ability to simultaneously remove sulfamethoxazole and nitrite. For example... Figure 2 As shown in figure a, persulfate alone has a direct oxidation effect of approximately 20.9% on sulfamethoxazole, while Co-N@PC 850 The addition of [catalyst name] significantly accelerated the reaction kinetics, achieving a 95.3% degradation rate of sulfamethoxazole within 30 minutes. The catalyst concentration was positively correlated with the degradation efficiency of sulfamethoxazole; increasing the catalyst dosage from 0.025 g / L to 0.05 g / L increased the degradation efficiency. Since a higher dosage (0.1 g / L) did not result in a further significant improvement in kinetics, 0.05 g / L was determined to be the optimal catalyst concentration. Figure 2 b. As the persulfate concentration increased from 0.2 mM to 0.5 mM, the degradation rate of sulfamethoxazole increased from 85.4% to 100%. Figure 2c. Low concentrations of nitrite (50 μM) slightly promoted the degradation of sulfamethoxazole, possibly due to the oxidation effect of the generated NO2·; while high concentrations of nitrite (100, 200 μM) only led to a slight decrease in degradation efficiency, demonstrating the system's strong resistance to nitrite interference. Nitrite removal exhibited a similar pattern. Figure 2 d, e). Under standard conditions (catalyst 0.05 g / L, persulfate concentration 0.3 mM, pH=9), nitrite is completely removed within 30 minutes. However, as Figure 2 As shown in f, when the initial concentration of sulfamethoxazole increased from 5 to 20 mg / L, the removal of nitrite was significantly inhibited, indicating that sulfamethoxazole has an advantage in competing for active species or active sites. (Co-N@PC) 850 In the persulfate system, sulfamethoxazole is preferentially degraded, while nitrite removal is significantly affected by the coexistence of sulfamethoxazole. Nevertheless, Co-N@PC 850 The persulfate system still exhibits excellent simultaneous removal capabilities for both pollutants.

[0052] Example 3

[0053] 1. To identify the key active species in the reaction, free radical quenching experiments were conducted using specific quenching agents.

[0054] Methanol (MeOH) is used to quench OH and SO4. - • tert-butanol (TBA) is used to quench •OH, and furfuryl alcohol (FFA) is used to quench •OH. 1 O2, trichloromethane (CHCl3) is used to quench O2. - Potassium iodide (KI) is used to quench electron transfer pathways (ETPs). For example... Figure 3 As shown, in Co-N@PC 850 In the PMS / SMX / NIT system, the addition of chloroform (CHCl3) or tert-butanol (TBA), a superoxide radical quencher, has almost no effect on the degradation of sulfamethoxazole. The addition of methanol (MeOH) can simultaneously quench ·OH and SO42-. - The degradation rate decreased from 96.1% to 83.9% after adding the singlet oxygen quencher furfuryl alcohol (FFA). The degradation rate further decreased significantly to 46.3% after adding the electron transfer pathway quencher potassium iodide (KI). Most notably, the degradation of sulfamethoxazole was almost completely inhibited after adding the electron transfer pathway quencher potassium iodide (KI). This series of experiments strongly demonstrates that the electron transfer pathway (ETP) is the absolutely dominant mechanism for the degradation of sulfamethoxazole in this system, with O2 playing an important auxiliary role, while free radicals (·OH / SO4) play a more significant role. - ·) The contribution was minimal.

[0055] The active species generated in the catalytic system were further identified using electron paramagnetic resonance (EPR) testing. In Co-N@PC 850 In the PMS / SMX system, DMPO-·OH / DMPO-SO4 can be detected. - · and clear signals of TEMP-¹O2 ( Figure 4 a, c). When nitrite is added, ·OH / SO4 - • The signal was significantly weakened (consistent with the quenching effect), while ¹O2 and DMPO-O2 - • The signal strength was significantly increased ( Figure 4 b, c). Free radical signal intensity analysis ( Figure 4 df) further shows that in the coexisting system, ¹O₂ and O₂ - • The signal continued to increase with the reaction. These results indicate that the introduction of nitrite dynamically modulates the formation spectrum of active species, quenching some free radicals while promoting the formation of non-radical species (especially ¹O2).

[0056] 2. To directly confirm the existence of the electron transfer pathway (ETP), various characterization methods were employed.

[0057] Based on in-situ Raman spectroscopy ( Figure 5 a) shows that the addition of nitrite caused a blue shift in the peak, indicating that nitrite or its derivatives affected the charge environment or adsorption configuration of the catalyst surface. Electrochemical tests further clarified the electron flow direction. Chorometric amperometry ( Figure 5 b) Shows that in Co-N@PC 850 Upon addition of persulfate to the electrode, the current momentarily decreased, indicating electron transfer from the electrode to the persulfate, forming a catalyst-persulfate transition state complex. Subsequent addition of sulfamethoxazole caused the current to immediately rebound, indicating that sulfamethoxazole, acting as an electron donor, transferred electrons to this transition state complex and was thus oxidized. The addition of nitrite had little effect on the current. Linear sweep voltammetry ( Figure 5 c) The addition of PMS showed a slight increase in current density, confirming the interaction between PMS and Co-N@PC. 850 The interaction between them. The current further increased after the introduction of SMX, consistent with the conclusion that SMX provides electrons to the catalyst-persulfate transition state complex. The addition of NIT led to an increase in current, suggesting that NIT may promote electron shuttle between the electrode surface and solution contaminants. Electrochemical impedance spectroscopy (EIS) Figure 5 d) shows that with the sequential addition of persulfate and sulfamethoxazole, the charge transfer resistance continuously decreases and the interfacial electron transport efficiency increases. However, the introduction of NIT significantly increases the charge transfer resistance, indicating that characterization demonstrates the effectiveness of ETP in Co-N@PC. 850The dominant position of the / PMS system was revealed, and the key role of NIT in regulating this ETP was disclosed.

[0058] 3. Active sites play a decisive role in catalytic performance. XPS analysis of the reaction results of Co-N@PC... 850 The chemical states of the elements in the catalyst.

[0059] like Figure 6 As shown, with fresh catalyst ( Figure 2 Compared to df), the peak areas of C=O / C=N, C=C, and CC components in the C 1s spectrum of the catalyst after the reaction decreased significantly. Figure 6 a); The ratio of graphitic nitrogen to pyridine nitrogen in the N1s spectrum decreases ( Figure 6 b); The Co-O component in the O 1s spectrum is significantly reduced ( Figure 6 c) Metallic Co in the Co 2p spectrum 0 The signal weakened sharply ( Figure 6 d). These changes collectively point to: C=O / C=N groups on the catalyst surface, graphitized carbon structure (C=C / CC), graphitic nitrogen species, and metallic Co. 0 These are key active sites involved in PMS activation, surface complex formation, and electron conduction.

[0060] Example 4

[0061] This embodiment demonstrates, through product analysis and toxicity assessment, the discovery that coexisting pollutant nitrite can be used to avoid toxic byproducts, revealing the outstanding advantages of this invention in terms of environmental safety.

[0062] 1. Evolution of the degradation pathway of sulfamethoxazole and its key regulatory role in nitrite.

[0063] Non-targeted screening of the sample after 30 minutes of reaction was performed using ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS), identifying a total of 8 intermediate products (TPs). Based on this, Co-N@PC is proposed. 850 Four possible degradation pathways of sulfamethoxazole in the PMS / SMX / NIT system ( Figure 7 a), and revealed the core regulatory role of nitrite.

[0064] The four main degradation pathways proposed are as follows:

[0065] Pathway I (hydroxylation of benzene ring): ·OH or SO4 - • Attacking the benzene ring of sulfamethoxazole (e.g., the N1 position) forms a monohydroxylated product TP270a through an addition reaction. This product can be further oxidized, opening the benzene ring and successively generating TP255 and TP239.

[0066] Pathway II (Sulfanamide bond cleavage): The SN bond connecting the benzene ring and isoxazole in the sulfamethoxazole molecule is cleaved, followed by a deamination reaction to generate the small molecule product TP156.

[0067] Pathway III (Amino Oxidation and Nitration): This pathway is a key potential pathway for the generation of highly toxic nitro byproducts. The free amino group (-NH2) of the sulfamethoxazole molecule is first oxidized to a hydroxylamine derivative (TP270b), which is then further oxidized by species such as •OH and ¹O2 present in the system to generate the nitro derivative TP284 (i.e., 4-nitro-sulfamethoxazole). Subsequently, •OH attacks TP284 to undergo hydroxylation, generating TP300.

[0068] Pathway IV (isoxazole epoxidation): The active species directly attacks the isoxazole five-membered heterocycle of sulfamethoxazole, causing it to undergo ring-opening oxidation to generate the product 4-amino-N-(iminemethylene)benzenesulfonamide (TP198).

[0069] Comparative experiments were conducted to perform semi-quantitative analysis of different intermediates, providing conclusive evidence for the significant inhibitory effect of nitrite on pathway III. Under identical reaction conditions (catalyst, PMS concentration, pH, and time), product analysis was performed on two systems: one containing only SMX and the other containing both SMX and NIT. The results are shown in the table below.

[0070]

[0071] When nitrite was present in the reaction system, the peak areas of the toxic nitro products TP284 and TP300 were significantly lower than those in the control system without nitrite. For example, at pH 9, the peak area of ​​TP284 decreased by about 30%, while the peak area of ​​TP300 also decreased accordingly. This directly proves that the presence of nitrite does not merely compete with sulfamethoxazole for oxidants, but rather acts as a "chemical switch," effectively guiding the degradation of sulfamethoxazole from the formation of highly toxic nitro byproducts (pathway III) to a relatively safer degradation pathway (pathways I, II, IV) primarily involving hydroxylation and bond cleavage, thus proactively avoiding increased environmental risks at the molecular level.

[0072] 2. Based on the above quantitative assessment of the environmental safety improvement brought about by the regulation of this pathway, the toxicity assessment software (TEST) was used to predict the parent compound of sulfamethoxazole and all the identified TPs.

[0073] like Figure 7 As shown in b, all sulfamethoxazole intermediates were non-mutagenic; furthermore, although some intermediates exhibited developmental toxicity (…), Figure 7 c) and bioaccumulation factors ( Figure 7d) Similar to sulfamethoxazole, but these values ​​are significantly lower for most intermediates. Combined with the semi-quantitative analysis data of product concentrations in the table above, the addition of nitrite significantly reduced the concentrations of toxic nitro byproducts (TP284 and TP300) over a wide pH range. This effect can be attributed to the dual role of nitrite: affecting both the form and concentration of ROS and regulating ETP. This confirms that the oxidation system can effectively reduce toxicity and inhibit the formation of nitro byproducts under conditions where nitrite and antibiotics coexist.

[0074] 3. To clarify Co-N@PC 850 The conversion pathway of nitrite in the PMS / SMX / NIT system, and quantitative monitoring of NO2. - -N, NO3 - -N, NH4 + The temporal changes of key nitrogen-containing species such as -N and total nitrogen (TN) were studied. All experiments used ammonia-free aqueous solutions to avoid background interference, and the amount of N2 generated was deduced from the decrease in TN. Control experiments confirmed that the presence of sulfamethoxazole, catalyst, and persulfate did not interfere with the quantitative determination of nitrogen. Figure 8 a) Furthermore, no nitrogen from sulfamethoxazole was detected under the analytical conditions used. Figure 8 As shown in b, NO2 - -N concentration decreased rapidly, almost completely removed within 30 minutes, while NH4 concentration decreased rapidly. + -N concentration gradually increased to approximately 0.80 mg / L, and this obvious reverse trend indicates that NO2 - -N is reduced to NH4. + -N, this process may be driven by electrons (e) on the catalyst surface. - This process is mediated by [unclear - likely a specific chemical compound], consistent with previously reported reductions of dissimilar nitrite to ammonium. Furthermore, NO3 was observed throughout the entire reaction. - The accompanying increase in -N concentration confirms the involvement of the oxidation pathway. Furthermore, the TN concentration exhibits a trend of first decreasing and then increasing, attributed to two parallel processes: one is NO2... - -N is reduced to N2, and the overflow of N2 leads to a decrease in TN; secondly, the sulfamethoxazole molecule breaks down, releasing soluble amino groups that return to the aqueous phase, thus promoting the recovery of TN.

[0075] In summary, these results indicate that nitrite participates in both free radical (ROS oxidation) and non-free radical pathways (electron reduction), with NH4+ being involved in both. + -N is Co-N@PC 850 The main inorganic end product of nitrite conversion in the / PMS / SMX / NIT system is observed, which is consistent with the quenching experiment (O2). - • and •OH groups participate in the reaction, and electron transfer plays an important role.

[0076] Figure 9 Co-N@PC was showcased 850 The integrated reaction mechanism of sulfamethoxazole degradation and nitrite conversion in the PMS / SMX / NIT system: Co-N@PC 850 Firstly through Co 0 The graphite nitrogen sites adsorb and activate persulfate, forming a surface-composite active species (Co-N@PC). 850 (-persulfate); This complex primarily mediates the non-radical electron transfer pathway, playing a dominant role. Although both radical and non-radical pathways contribute, this multi-mechanism synergy ensures the efficient and simultaneous removal of both pollutants. Nitrite not only acts as a competitor inhibiting degradation kinetics but also as a regulator altering the degradation pathway of sulfamethoxazole, thereby significantly inhibiting the formation of toxic nitro byproducts; simultaneously, nitrite itself is mainly reduced to NH4 via a dissimilatory pathway. + -N.

[0077] Example 5

[0078] like Figure 10 As shown in a and b, Co-N@PC 850 The PMS system works effectively over a very wide pH range of 3-11, and especially under common weakly acidic to weakly alkaline conditions (pH 5-9), it maintains a simultaneous removal rate of over 90% for both sulfamethoxazole and nitrite. This gives the technology a strong ability to cope with pH fluctuations in real wastewater.

[0079] Commonly coexisting ions in real water bodies may interfere with the oxidation process. For example... Figure 10 As shown in c and d, even at high concentrations (10 mM) of Cl... - HCO3 - HPO4 2- In its presence, the degradation efficiency of sulfamethoxazole in the system decreases only slightly (typically ≤15%), demonstrating excellent resistance to ion interference. This is attributed to its dominant non-radical electron transfer mechanism, which is far less sensitive to free quenchers in solution than traditional free radical chain reactions. In verification experiments on actual water bodies (tap water, river water, and aquaculture pond water)... Figure 10 Despite varying background matrices, the systems maintained a sulfamethoxazole removal rate of >80% and a nitrite removal rate of nearly 100%, fully demonstrating the feasibility of their practical application.

[0080] The long-term cost of using the catalyst is critical. Cyclic experiments ( Figure 11 a) Shows that Co-N@PC 850The activity decreased after four consecutive uses, mainly due to the adsorption and blockage of organic intermediates on pores and active sites. However, its initial activity could be largely restored through a simple thermal regeneration step (heat treatment at 850°C in N2 for 10 minutes). XRD analysis ( Figure 11 (b) It was confirmed that the crystal structure of the catalyst remained unchanged before and after regeneration, demonstrating the high stability of its core structure. This easy regeneration characteristic significantly improves the economics and sustainability of the technology.

[0081] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A non-radical catalytic oxidation water treatment method for regulating sulfonamidoxazole degradation pathway using nitrite, characterized by, The method comprises the following steps: S1, adding carbonized polydopamine coated cobalt nanoparticle material and peroxymonosulfate into the water body to be treated containing nitrite and sulfamethoxazole, wherein the carbonized polydopamine coated cobalt nanoparticle material serves as a catalyst, and the peroxymonosulfate serves as an oxidant; the catalyst and the oxidant form a heterogeneous advanced oxidation system; S2, the heterogeneous advanced oxidation system first undergoes adsorption of the oxidant on the surface of the catalyst to form a catalyst-peroxymonosulfate surface complex active species, and then triggers a non-radical catalytic oxidation dominated by electron transfer and assisted by singlet oxygen, so that the nitrite and the sulfamethoxazole are simultaneously removed within a preset reaction time; S3, in the process of the non-radical catalytic oxidation reaction, the nitrite is not only subjected to redox conversion as a removed pollutant, but also serves as a degradation path regulator to induce the degradation path of the sulfamethoxazole to deviate to the direction of benzene ring hydroxylation, sulfonamide bond rupture and isoxazole ring oxidation, and inhibit the generation of nitro by-products; The nitro by-products include 4-nitro-sulfamethoxazole and hydroxylated nitro derivatives.

2. The non-radical catalytic oxidation water treatment method using nitrite to regulate sulfonamidomethoxazole degradation pathway according to claim 1, characterized in that, In the step S3, the nitrite is simultaneously oxidized and reduced in the process of the non-radical catalytic oxidation reaction, the reduction product is ammonium salt and nitrogen, and the oxidation product is nitrate, wherein the ammonium salt is the main conversion product of the nitrite.

3. The non-radical catalytic oxidation water treatment method using nitrite to regulate sulfonamidomethoxazole degradation pathway according to claim 1, characterized in that, The preset reaction time is 5 to 60 minutes.

4. The non-radical catalytic oxidation water treatment method using nitrite to regulate sulfonamidomethoxazole degradation pathway according to claim 1, characterized in that, The catalyst-peroxymonosulfate surface complex active species is formed by the synergistic effect of the metal cobalt on the surface of the catalyst, active carbon and graphite nitrogen, and the electron transfer path is as follows: The sulfamethoxazole serves as an electron donor to transfer electrons to the catalyst-peroxymonosulfate surface complex active species to complete the oxidative degradation; the electron transfer path is a non-radical process and is not affected by the radical quenching effect of the nitrite in the water body to be treated.

5. The non-radical catalytic oxidation water treatment method using nitrite to regulate sulfonamidomethoxazole degradation pathway according to claim 1, characterized in that, The addition amount of the carbonized polydopamine coated cobalt nanoparticle material is 0.025 g / L to 0.1 g / L; and the addition concentration of the peroxymonosulfate is 0.2 mM to 0.5 mM.

6. The non-radical catalytic oxidation water treatment method using nitrite to regulate sulfonamidomethoxazole degradation pathway according to claim 1, characterized in that, The non-radical catalytic oxidation reaction is highly efficient and stable in the water body with a pH value of 3.0 to 9.0; and the simultaneous removal efficiency of the sulfamethoxazole and the nitrite reaches the highest at pH 9.

0.

7. The non-radical catalytic oxidation water treatment method using nitrite to regulate sulfonamidomethoxazole degradation pathway according to claim 1, characterized in that, The generation of the auxiliary active species singlet oxygen is regulated by the nitrite, and the presence of the nitrite can promote the generation of the singlet oxygen, which cooperates with the electron transfer path to strengthen the degradation of the sulfamethoxazole; The free radical pathway is an important medium for the generation of the nitro by-products, and the enhancement of the singlet oxygen and the electron transfer path can inhibit the generation of the nitro by-products.

8. The non-radical catalytic oxidation water treatment method using nitrite to regulate sulfonamidomethoxazole degradation pathway according to claim 1, characterized in that, The carbonized polydopamine coated cobalt nanoparticle material is regenerated by heat treatment at 850℃ for 10 minutes under an inert atmosphere after continuous use.

9. The non-radical catalytic oxidation water treatment method using nitrite to regulate sulfonamidomethoxazole degradation pathway according to claim 1, characterized in that, when one or more of the anions Cl - , HCO3 - , HPO4 2- , H2PO4 - or SO4 2- is present in the water body to be treated at a concentration of 1 to 10 mM, the simultaneous removal of nitrite and sulfamethoxazole by the non-radical catalytic oxidation system is not significantly inhibited; The water body to be treated is a surface water body, underground water or aquaculture wastewater with the characteristics of composite pollution of nitrite and sulfamethoxazole.

10. The non-radical catalytic oxidation water treatment method using nitrite to regulate sulfonamidomethoxazole degradation pathway according to claim 1, characterized in that, The carbonized polydopamine coated cobalt nanoparticle material is used as a catalyst in combination with peroxymonosulfate for non-radical catalytic oxidation to simultaneously remove nitrite and sulfamethoxazole in water bodies, and to inhibit the generation of nitro byproducts in sulfamethoxazole degradation products in the presence of nitrite.

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