Preparation method and application of carbon-supported sulfidized nano zero-valent iron

Abstract

The application discloses a preparation method of carbon-loaded sulfidized nano zero-valent iron, and specifically relates to the following steps: preparing a biochar carrier: drying and grinding Enteromorpha powder, and then placing the powder in a tube furnace to burn the biochar under nitrogen; preparing a NaBH4 and Na2S2O4 mixed solution: dissolving NaBH4 and Na2S2O4 in water to obtain the mixed solution; mixing a FeSO4.7H2O solution and the biochar, stirring under the condition of nitrogen, adding the NaBH4 and Na2S2O4 mixed solution drop by drop after stirring, continuously stirring to fully sulfidize, cleaning and collecting black solid precipitates in the suspension, and then vacuum drying and grinding to obtain the carbon-loaded sulfidized nano zero-valent iron. The application further discloses application of the carbon-loaded sulfidized nano zero-valent iron in degrading ciprofloxacin.

Description

Technical Field

[0001] This invention relates to a method for preparing carbon-supported sulfide nano-zero valent iron, and also to the application of activated persulfate obtained by the above method in the degradation of ciprofloxacin. Background Technology

[0002] Ciprofloxacin (CIP) is a third-generation fluoroquinolone antibiotic widely used to treat various bacterial infections. However, CIP is not completely metabolized in organisms, leading to the excretion of large amounts of residual CIP into the ecosystem. Reports indicate that CIP has been detected in surface water, groundwater, and even drinking water. The residue and accumulation of CIP in water can trigger the proliferation of drug-resistant bacteria, leading to outbreaks of "superbugs." Therefore, how to efficiently remove CIP has become a widely concerned issue. In the past decade, efficient degradation based on the generation of free radicals from activated persulfate has emerged as a novel advanced oxidation technology and has been applied to the treatment of various recalcitrant organic pollutants. 2+ It is one of the commonly used persulfate activators, however, Fe 2+ When used as an activator, the reaction rate is relatively fast, resulting in low persulfate degradation efficiency. However, if Fe is used directly... 2+ Activation will make the catalyst difficult to separate, causing secondary pollution, and sulfate free radicals are prone to self-quenching due to excess.

[0003] Nano-zero-valent iron (nZVI) possesses some traditional properties of nanomaterials (high specific surface area, high surface energy, high surface activity) and also exhibits the magnetic properties of iron nanomaterials, making it a preferred activator for persulfates. However, nZVI is prone to aggregation and passivation (Fe... 2+ The rapid release and poor electron selectivity of Fe10 ... 0 The sulfur-iron protective shell, formed by combining with sulfur, adheres to the surface of the nano-zero-valent iron. This shell not only effectively prevents the oxidation of the nano-zero-valent iron but also provides Fe for a long time. 2+ Furthermore, the sulfides they contain can alter the hydrophobicity, conductivity, and adsorption selectivity of the shell, greatly promoting the transfer of electrons from Fe. 0Electron transfer from the core to the surface of nano-zero-valent iron effectively improves the removal efficiency of recalcitrant pollutants. However, due to its magnetic properties and nanoscale characteristics, S-nZVI particles still exhibit agglomeration. How to effectively inhibit S-nZVI particle agglomeration and further improve its dispersibility in the environment and its pollutant removal efficiency is currently a hot research topic, with solid-support technology considered one of the most effective methods. Currently, carbonaceous materials are often used as supporting materials for nZVI. Biochar (BC), prepared by pyrolysis of biomass under low-oxygen conditions, is a multifunctional carbonaceous material with great application potential. BC possesses properties such as porosity, strong adsorption, alkalinity, high specific surface area, high cation exchange capacity, and abundant oxygen-containing functional groups. Loading S-nZVI particles onto a BC solid support to construct a sulfide nano-zero-valent iron / biochar (S-nZVI / BC) composite material not only effectively disperses S-nZVI and provides more stable loading sites, offering diffusion and transport channels for ferrous iron and electrons, but also allows the oxygen-containing functional groups in its structure to act as intermediates for electron transfer, activating persulfate and improving the composite material's antibiotic degradation performance. However, existing carbon-supported sulfide nano-zero-valent iron preparation methods are cumbersome, time-consuming, and the sulfide shell layer is located in the Fe... 0 Problems include uneven surface distribution, low content of reducing sulfur, and low amount of oxygen-containing functional groups in biochar. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a method for preparing carbon-supported sulfide nano-zero valent iron. This method uses *Ulva prolifera* to prepare a biochar carrier. The obtained biochar carrier has abundant active functional groups and a rich pore structure, which can effectively improve the loading capacity and reactivity of sulfide nano-zero valent iron. After biochar loading, the degree of aggregation between sulfide nano-zero valent iron particles is greatly reduced. This not only increases the specific surface area of ​​sulfide nano-zero valent iron, but also increases the effective active sites of sulfide nano-zero valent iron.

[0005] Another objective of this invention is to provide the application of carbon-supported sulfide nano-zero-valent iron prepared by the above method in the degradation of ciprofloxacin. Based on the biochar carrier prepared from Ulva prolifera, it can significantly increase the types of free radicals (singlet oxygen, sulfate radicals, hydroxyl radicals, and superoxide radicals) generated after persulfate activation in the persulfate system, thereby achieving efficient removal of ciprofloxacin in a short time under the premise of low persulfate addition, and even in alkaline environment, efficient removal of ciprofloxacin can be achieved in a short time.

[0006] Technical solution: The preparation method of carbon-supported sulfide nano-zero valent iron according to the present invention includes the following steps:

[0007] (1) Preparation of biochar carrier: After drying, grinding and sieving the seaweed powder, it is placed in a tube furnace and nitrogen gas is introduced to burn biochar. The carbonization temperature is 600℃, the heating rate is 5℃ / min, and the carbonization time is 2-3h.

[0008] (2) Preparation of NaBH4 and Na2S2O4 mixed solution: Dissolve NaBH4 and Na2S2O4 in water to obtain a mixed solution of NaBH4 and Na2S2O4. The concentration of NaBH4 in the mixed solution is 0.26-0.27 mol / L and the concentration of Na2S2O4 is 0.001575-0.0126 mol / L.

[0009] (3) Mix FeSO4·7H2O solution and biochar, stir under nitrogen gas, add NaBH4 and Na2S2O4 mixture dropwise after stirring, continue stirring after the addition is complete to make it fully sulfided, wash and collect the black solid precipitate in the suspension, and then vacuum dry and grind it to obtain carbon-supported sulfided nano-zero valent iron.

[0010] In step (1), the raw material is ground through a 100-mesh sieve. The smaller the particle size of the raw material, the greater the pyrolysis yield.

[0011] In step (3), the molar ratio of NaBH4 to FeSO4·7H2O is 2.89–3:1, and the molar ratio of Na2S2O4 to FeSO4·7H2O is 0.0175–0.14:1.

[0012] In step (3), the mass ratio of biochar to FeSO4·7H2O is 0.1047 to 0.6283:1.

[0013] In step (3), the mixture is stirred for 10 to 15 minutes under nitrogen purging, and stirred for another 10 to 15 minutes after the addition is complete.

[0014] In step (3), the product is dried under vacuum at 60°C for 8–10 hours.

[0015] In step (3), the carbon-supported sulfidated nano-zero-valent iron is loaded on the surface and pores of biochar, the mass ratio of biochar to sulfidated nano-zero-valent iron is 0.5 to 3:1, and the molar ratio of sulfur to nano-zero-valent iron is 0.035 to 0.28:1.

[0016] The above-mentioned application of carbon-supported sulfide nano-zero-valent iron in the degradation of ciprofloxacin involves adding persulfate and carbon-supported sulfide nano-zero-valent iron to water containing ciprofloxacin to carry out a degradation reaction; wherein, the concentration of persulfate in the water is 0.5 mmol / L to 3 mmol / L, and the concentration of carbon-supported sulfide nano-zero-valent iron is 0.4 g / L to 1 g / L.

[0017] The initial concentration of ciprofloxacin in the water was 10 mg / L to 40 mg / L; the pH of the water was 3 to 9, and the pH was adjusted by hydrochloric acid and sulfuric acid.

[0018] The degradation time ranges from 0 to 90 minutes.

[0019] The biochar-supported sulfide nano-zero-valent iron prepared by this invention can effectively reduce the agglomeration of sulfide nano-zero-valent iron and improve its dispersibility. Furthermore, the sulfide shell of the biochar-supported sulfide nano-zero-valent iron material prepared by this invention exhibits good Fe... 0 The surface is uniformly distributed with a high content of reducing sulfur, thus significantly improving the reactivity of sulfide nano-zero-valent iron in water. This is because the present invention uses a specific sulfur precursor and a pre-sulfidation method to achieve the sulfide iron shell layer in Fe... 0 The technology achieves uniform surface distribution and a high reducing sulfur content (pre-sulfurization refers to the synthesis of S-nZVI by adding sulfur precursors and sodium borohydride together to an iron precursor solution). The FeS content of the S-nZVI shell... x It has good electrical conductivity and can accelerate electrons from Fe. 0 The release of the core to the material surface increases the electronegativity of the material, thereby facilitating the adsorption and removal of target pollutants. S-nZVI is hydrophobic and can inhibit Fe... 0 Side reactions with water increase the selectivity of electrons for target pollutants and prolong the reaction time. Simultaneously, sulfidation modification prevents rapid oxidation and deactivation of nZVI during use, and S-nZVI can stably release Fe. 2+ To compensate for Fe 2+The rapid consumption drawback of the biochar material enhances its reactivity in the reaction system. Furthermore, compared to other biomass, *Ulva prolifera* biochar possesses abundant oxygen-containing functional groups, a large specific surface area, high cation exchange capacity, and strong adsorption capacity. These abundant oxygen-containing functional groups act as intermediates for electron transfer, activating persulfate and further improving the composite material's antibiotic degradation performance. Its pore structure increases both the material's loading capacity and its antibiotic adsorption. After the material is added, the biochar carrier derived from *Ulva prolifera* significantly increases the types of free radicals generated after persulfate activation in the persulfate system. Firstly, electrons transfer from the oxygen functional groups on the S-nZVI and BC surfaces of the S-nZVI / BC composite material to the persulfate to generate free radicals. Simultaneously, the Fe released from the sulfurized nano-zero-valent iron on the biochar-supported surface... 2+ The reaction with persulfate further activates the persulfate to generate sulfate radicals. The sulfate radicals react with water or hydroxide to generate hydroxyl radicals. Two hydroxyl radicals react to generate hydrogen peroxide. The sulfate radicals react with hydrogen peroxide to generate superoxide radicals. As an intermediate, superoxide radicals can mediate the generation of highly reactive, high-energy excited-state oxygen molecules—singlet oxygen. Under the action of these four types of free radicals, the material can achieve rapid and efficient removal of antibiotics.

[0020] Beneficial effects: Compared with the existing technology, the present invention has the following significant advantages: (1) The method of the present invention uses seaweed to prepare biochar carrier. The biochar carrier obtained has rich active functional groups and rich pore structure, which can effectively improve the loading of sulfide nano-zero valent iron and the reactivity of sulfide nano-zero valent iron; (2) The biochar carrier prepared by the present invention based on seaweed can significantly increase the types of free radicals (singlet oxygen, sulfate free radical, hydroxyl free radical, superoxide free radical) generated after persulfate activation when degrading ciprofloxacin in the persulfate system, thereby achieving efficient removal of ciprofloxacin in a short time under the premise of low persulfate addition, and even in alkaline environment, efficient removal of ciprofloxacin can be achieved in a short time. Attached Figure Description

[0021] Figure 1 SEM images of *Ulva prolifera* biochar, S-nZVI, and S-nZVI / BC in Example 6;

[0022] Figure 2 TEM images of S-nZVI and S-nZVI / BC in Example 6;

[0023] Figure 3 The X-ray photoelectron spectrum of carbon-supported sulfide nano-zero valent iron (S-nZVI / BC) in Example 6 is shown below.

[0024] Figure 4The degradation of ciprofloxacin in water by carbon-supported sulfide nano-zero-valent iron activated persulfate under different persulfate addition amounts;

[0025] Figure 5 The degradation effect of activated persulfate on ciprofloxacin in water under different amounts of carbon-supported sulfide nano-zero valent iron added;

[0026] Figure 6 The degradation effect of carbon-supported sulfide nanoparticles activated by zero-valent iron on persulfate in water on the basis of different initial concentrations of pollutants is shown in the figure.

[0027] Figure 7 The degradation effect of carbon-supported sulfide nanoparticles activated by zero-valent iron on persulfate in water on different pH values ​​is shown in the figure.

[0028] Figure 8 The zeta potential of carbon-supported sulfide nano-zero valent iron (S-nZVI / BC) in Example 6 at different pH values;

[0029] Figure 9 Graphs showing the degradation effects of ciprofloxacin in water using different systems;

[0030] Figure 10 This is an experiment in Example 6 on the free radical quenching of ciprofloxacin in water by activated persulfate degradation using carbon-supported sulfide nano-zero valent iron (S-nZVI / BC).

[0031] Figure 11 The image shows the EPR spectrum of free radicals generated by carbon-supported sulfide nano-zero valent iron (S-nZVI / BC) activating persulfate to degrade ciprofloxacin in water in Example 6. Detailed Implementation

[0032] Example 1

[0033] The present invention provides a method for preparing carbon-supported sulfide nano-zero-valent iron, comprising the following steps:

[0034] (1) Preparation of biochar carrier (BC): Dry and grind the seaweed powder through a 100-mesh sieve, put it into a quartz boat (compact it), and burn the biochar in a tube furnace with nitrogen gas. After the temperature of the tube furnace drops to about 50°C, take out the quartz boat and grind the biochar in the boat into powder for later use. Specifically: put the quartz boat into the tube furnace, install the furnace plugs and pipes on both sides, first purge with nitrogen gas for 5 minutes, set the furnace initial temperature to 50°C, the heating rate to 5°C / min, the heating temperature to 600°C, and the holding time to 120 minutes.

[0035] (2) Preparation of FeSO4·7H2O solution: Weigh 2.502g of FeSO4·7H2O and place it in a beaker. Add pure water to dissolve it and transfer it to a 100mL volumetric flask. Dilute it with water to the mark and shake well to obtain a FeSO4·7H2O solution with a concentration of 0.09mol / L.

[0036] (3) Preparation of NaBH4 and Na2S2O4 mixed solution: Weigh 1.0214g NaBH4 and 0.0274g Na2S2O4 into a beaker, add pure water to dissolve them, transfer to a 100mL volumetric flask, dilute with water to the mark, shake well to obtain NaBH4 and Na2S2O4 mixed solution. In the mixed solution, the concentration of NaBH4 is 0.27mol / L and the concentration of Na2S2O4 is 0.001575mol / L.

[0037] (4) Preparation of carbon-supported sulfide nano-zero valent iron (S-nZVI / BC): 100 mL of 0.09 mol / L FeSO4·7H2O solution and 1.048 g of biochar were added to a 1 L three-necked flask. The temperature was maintained at 25 °C and stirred for 15 min under nitrogen purging. Then, 100 mL of a mixture of NaBH4 and Na2S2O4 was added dropwise. After the addition was completed, the mixture was stirred at the same speed for 15 min to allow it to fully sulfide. The resulting black solid was carbon-supported sulfide nano-zero valent iron. The carbon-supported sulfide nano-zero valent iron was washed three times with anhydrous ethanol and then dried under vacuum at 60 °C for 8 h. It was then taken out, ground into powder, and labeled as S1.

[0038] In the carbon-supported sulfide nano-zero valent iron obtained in Example 1, the molar ratio of sulfur to nano-zero valent iron was 0.035:1, and the mass ratio of biochar to sulfide nano-zero valent iron was 2:1.

[0039] Example 2

[0040] The preparation methods of Example 2 and Example 1 are basically the same, the only difference being that the mass of Na2S2O4 added in step (3) is 0.0548g, and carbon-supported sulfide nano-zero valent iron (S-nZVI / BC) is obtained, which is numbered S2.

[0041] In the carbon-supported sulfide nano-zero valent iron obtained in Example 2, the molar ratio of sulfur to nano-zero valent iron was 0.07:1, and the mass ratio of biochar to sulfide nano-zero valent iron was 2:1.

[0042] Example 3

[0043] The preparation methods of Example 3 and Example 1 are basically the same, the only difference being that the mass of Na2S2O4 added in step (3) is 0.1096g, and carbon-supported sulfide nano-zero valent iron (S-nZVI / BC) is obtained, which is numbered S3.

[0044] In the carbon-supported sulfide nano-zero valent iron obtained in Example 3, the molar ratio of sulfur to nano-zero valent iron was 0.14:1, and the mass ratio of biochar to sulfide nano-zero valent iron was 2:1.

[0045] Example 4

[0046] The preparation methods of Example 4 and Example 1 are basically the same, except that the mass of Na2S2O4 added in step (3) is 0.2192g, and carbon-supported sulfide nano-zero valent iron (S-nZVI / BC) is obtained, which is numbered S4.

[0047] In the carbon-supported sulfide nano-zero valent iron obtained in Example 4, the molar ratio of sulfur to nano-zero valent iron was 0.28:1, and the mass ratio of biochar to sulfide nano-zero valent iron was 2:1.

[0048] Example 5

[0049] The preparation methods of Example 5 and Example 1 are basically the same, the only difference being that the biochar added in step (4) is 0.262g, and carbon-supported sulfide nano-zero valent iron (S-nZVI / BC) is obtained, which is numbered S5.

[0050] In the carbon-supported sulfide nano-zero valent iron obtained in Example 5, the molar ratio of sulfur to nano-zero valent iron was 0.07:1, and the mass ratio of biochar to sulfide nano-zero valent iron was 0.5:1.

[0051] Example 6

[0052] The preparation methods of Example 6 and Example 1 are basically the same, except that the biochar added in step (4) is 0.524g, and carbon-supported sulfide nano-zero valent iron (S-nZVI / BC) is obtained, which is numbered S6.

[0053] In the carbon-supported sulfide nano-zero valent iron obtained in Example 6, the molar ratio of sulfur to nano-zero valent iron was 0.07:1, and the mass ratio of biochar to sulfide nano-zero valent iron was 1:1.

[0054] Example 7

[0055] The preparation methods of Example 7 and Example 1 are basically the same, except that the biochar added in step (4) is 1.572g, and carbon-supported sulfide nano-zero valent iron (S-nZVI / BC) is prepared and numbered S7.

[0056] In the carbon-supported sulfide nano-zero valent iron obtained in Example 7, the molar ratio of sulfur to nano-zero valent iron was 0.07:1, and the mass ratio of biochar to sulfide nano-zero valent iron was 3:1.

[0057] Antibiotic degradation in water: In 50 mL of water with an initial ciprofloxacin concentration of 10 mg / L, 30 mg of the products prepared in Examples 1-7 (numbered S1-S7) and 0.0270 g of persulfate were added respectively. The pH value was 5, and the pure water used in the experiment was neutral. The solution was quickly transferred to a constant temperature shaker and shaken at 25°C and 180 r / min for 90 min. After that, 4.2 mL of the supernatant was collected, filtered through a 0.45 μm filter membrane, and then analyzed.

[0058] The effects of S1 to S7 prepared in Examples 1 to 7 on the degradation of ciprofloxacin in water are shown in Table 1.

[0059] Table 1

[0060] S1 (sulfur-iron molar ratio is 0.035:1, carbon-iron mass ratio is 2:1) 92.42 S2 (sulfur-iron molar ratio of 0.07:1, carbon-iron mass ratio of 2:1) 95.16 S3 (sulfur-iron molar ratio of 0.14:1, carbon-iron mass ratio of 2:1) 90.92 S4 (sulfur-iron molar ratio of 0.28:1, carbon-iron mass ratio of 2:1) 88.94 S5 (sulfur-iron molar ratio of 0.07:1, carbon-iron mass ratio of 0.5:1) 94.73 S6 (sulfur-iron molar ratio of 0.07:1, carbon-iron mass ratio of 1:1) 97.45 S7 (sulfur-iron molar ratio of 0.07:1, carbon-iron mass ratio of 3:1) 92.90

[0061] As shown in Table 1, the degradation effect of carbon-supported sulfide nano-zero-valent iron on ciprofloxacin increases with the increase of the sulfur-iron molar ratio from 0.035:1 to 0.07:1. This is because the formation of sulfides can reduce the oxidation degree of nano-zero-valent iron to some extent, thereby reducing the formation of iron oxides. Furthermore, the low band gap of the generated sulfide-iron compounds facilitates the transfer of electrons from Fe. 0 The iron is transferred to the surface of carbon-supported sulfurized nanoparticles with zero valent iron, and then reaches the target pollutant. However, when the sulfur-iron molar ratio increases from 0.07:1 to 0.28:1, the degradation rate of ciprofloxacin decreases. Under conditions of excess sulfur, the modification process consumes a large amount of Fe. 0 More ferric sulfides are generated on the surface of carbon-supported sulfide nano-zero-valent iron, which may lead to the formation of high-bandgap FeS2, thus slowing down the electron transfer rate and blocking the active sites on the surface of carbon-supported sulfide nano-zero-valent iron. Increasing the carbon-iron mass ratio from 0.5:1 to 1:1 improves the degradation effect because the increased biochar content increases the specific surface area of ​​the biochar, and the abundant carbon pores increase the adsorption of ciprofloxacin. Secondly, the biochar loading slows down the oxidation of sulfide nano-zero-valent iron to some extent and also increases the contact area between pollutants and reaction sites on the sulfide nano-zero-valent iron. However, when the carbon-iron mass ratio increases to 3:1, the excessive biochar content blocks the exposed active reaction sites of the sulfide nano-zero-valent iron, resulting in poor reaction performance.

[0062] Figure 1 (a) is a scanning electron microscope image of the biochar of *Ulva prolifera* from this invention. Figure 1 (b) is a scanning electron microscope image of zero-valent biochar nanoparticles without loading in Comparative Example 1. Figure 1 (c) is a scanning electron microscope image of the carbon-supported sulfide nanoparticles with zero valence in Example 6. Figure 1 (a) It can be seen that the surface of the *Ulva prolifera* biochar is smooth and has a rich porous structure. Figure 1(b) It can be seen that the sulfide nano-zero valent iron has a spherical appearance and uniform shape and size. At the same time, it is evident that the sulfide nano-zero valent iron particles have undergone severe agglomeration, tightly clustered together in a chain-like structure. This is due to the high surface energy and magnetic attraction of the sulfide nano-zero valent iron. Figure 1 (c) After being loaded with Ulva prolifera biochar, the sulfide nano-zero valent iron particles are uniformly dispersed on the surface and in the pores of the biochar, and the degree of aggregation between particles is greatly reduced. This not only increases the specific surface area of ​​nano-zero valent iron, but also increases the effective active sites of nano-zero valent iron.

[0063] Figure 2 (a) is a transmission electron microscope image of sulfide nanoparticles with zero valent iron. Figure 2 (b) is a transmission electron microscope image of the carbon-supported sulfide nanoparticles with zero valence in Example 6. Figure 2 In (a), the sulfide nano-zero-valent iron is relatively clustered, exhibiting a chain-like distribution. However, it can also be observed that there are no other excess impurities around the sulfide nano-zero-valent iron, indicating that the sulfide shell layer is located within the Fe... 0 The surface is uniformly distributed. Figure 2 (b) After loading, it can be seen that the aggregation degree of sulfide nano-zero valent iron is greatly reduced. The larger specific surface area of ​​biochar provides an ideal support for nano-zero valent iron, maximizing its specific surface area, exposing more active sites, and enhancing its reactivity.

[0064] Figure 3 This indicates that X-ray photoelectron spectroscopy was used to analyze the elemental composition of carbon-supported sulfide nanoparticles (S-nZVI / BC) in Example 6 and to determine their chemical states on the particles. The total electron spectra of each element were obtained within the X-ray scanning range of 0–1000 eV for S-nZVI / BC. Figure 3 In (e), a Fe 2p peak around 709 eV, an O 1s peak around 529 eV, a C 1s peak around 282 eV, and a relatively weak S 2p peak around 166 eV are clearly observed, confirming the presence of C, O, S, and Fe elements on the S-nZVI / BC surface. To further determine the chemical states of C, O, S, and Fe, peak fitting was performed on each of these four elements. Figure 3 As shown in (a), six peaks are obtained by dividing the total Fe2p peak of the S-nZVI / BC material. The binding energies at 724.8 eV, 712.7 eV, and 710.0 eV correspond to Fe3O4, Fe3O4 and FeO(OH), Fe(II)-O, respectively; 723.2 eV and 709.9 eV correspond to Fe(II); and 707.4 eV corresponds to Fe 0This indicates that the prepared S-nZVI / BC material contains nano-zero-valent iron and iron oxides. The formation of iron oxides may be due to the material surface coming into contact with air during the subsequent cleaning process after the S-nZVI / BC material is prepared. The highly reactive nature of the nano-zero-valent iron leads to the oxidation of some of the zero-valent iron. Alternatively, it may be due to contact with a small amount of air during the drying process, resulting in oxidation of the S-nZVI / BC surface. Figure 3 (b) Peak separation was performed on the XPS spectrum of S2p, yielding three peaks. The binding energies at 168.0 eV, 163.7 eV, and 162.5 eV correspond to SO42-, respectively. 2- , FeS and S n 2- S2 2- The peaks and analysis results show that sulfur in S-nZVI / BC exists in the form of ferrous sulfide, polysulfides and sulfate ions, with a high content of reducing sulfur. The sulfur-iron compounds not only have a low band gap but also have hydrophobicity, which can significantly improve the reactivity of sulfur-containing nano-zero ferric iron in water. In addition, the presence of sulfur-iron compounds can protect the sulfur-containing nano-zero ferric iron particles, improve the dispersibility of nanoparticles to a certain extent, and prevent them from being oxidized. Figure 3 (c) shows the C1s peak in the XPS spectrum of S-nZVI / BC. The peak at 287.4 eV can be attributed to the C=O functional group, and the peak at 284.3 eV represents the CC and C=C functional groups. Biochar exhibits a relatively stable carbonaceous structure after high-temperature pyrolysis. Furthermore, the CH functional group may correspond to the carbon fraction peak at 283.3 eV. The presence of numerous carbon-containing groups and the high carbon intensity in the overall spectrum are due to the uniform dispersion of S-nZVI on BC, while biochar itself has a rich carbon content and a wide variety of carbon-containing groups. Figure 3 (d) The original O1s peak was fractionated, resulting in approximately three peaks. The peak at 531.3 eV represents the presence of the -OH group, due to the abundance of hydroxyl and carboxyl functional groups on the surface of biochar. The peak at 530.5 eV represents the presence of the O1s group. 2- The peak at 529.3 eV indicates the presence of CO groups, which is due to the presence of carbon oxides on S-nZVI / BC. These results demonstrate the successful preparation of S-nZVI / BC. Compared to other carriers, biochar synthesized from *Ulva prolifera* biomass possesses a better pore structure and a larger specific surface area, which is more conducive to the distribution of S-nZVI on its surface. Therefore, *Ulva prolifera* biochar can effectively improve the dispersion stability and reactivity of zero-valent sulfur nanoparticles. Furthermore, the abundant active functional groups on *Ulva prolifera* biochar can effectively activate persulfate, promote the generation of four free radicals, and thus improve the degradation effect.

[0065] Comparative Example 1

[0066] The preparation methods of Comparative Example 1 and Example 6 are basically the same, the only difference being that the carbonization temperature in step (1) during the preparation of biochar is 500℃, and carbon-supported sulfide nano-zero valent iron (S-nZVI / BC) is obtained.

[0067] Comparative Example 2

[0068] The preparation methods of Comparative Example 2 and Example 6 are basically the same, the only difference being that the carbonization temperature in step (1) during the preparation of biochar is 700℃, and carbon-supported sulfide nano-zero valent iron (S-nZVI / BC) is obtained.

[0069] Comparative Example 3

[0070] The preparation methods of Comparative Example 3 and Example 6 are basically the same, the only difference being that the biochar prepared in step (1) is alkali washed before calcination to obtain carbon-supported sulfide nano-zero valent iron (S-nZVI / BC).

[0071] Comparative Example 4

[0072] The preparation methods of Comparative Example 4 and Example 6 are basically the same, except that the Na2S2O4 solution in step (3) is replaced with Na2S solution to obtain carbon-supported sulfide nano-zero valent iron (S-nZVI / BC).

[0073] Comparative Example 5

[0074] The preparation methods of Comparative Example 5 and Example 6 are basically the same, except that the Na2S2O4 solution in step (3) is replaced with Na2S2O3 solution to obtain carbon-supported sulfide nano-zero valent iron (S-nZVI / BC).

[0075] Antibiotic degradation in water: In 50 mL of water with an initial ciprofloxacin concentration of 10 mg / L, 30 mg of the products prepared in Example 6 and Comparative Examples 1-5, and 0.0270 g of persulfate were added respectively. The pH value was 5. The mixture was quickly transferred to a constant temperature shaker and shaken at 25°C and 180 r / min for 90 min. After that, 4.2 mL of the supernatant was taken and filtered through a 0.45 μm filter membrane for analysis (see Table 2).

[0076] Table 2

[0077] S6 (sulfur-iron molar ratio of 0.07:1, carbon-iron mass ratio of 1:1) 97.45 Comparative Example 1 80.24 Comparative Example 2 83.41 Comparative Example 3 84.55 Comparative Example 4 90.21 Comparative Example 5 91.34 .

[0078] Carbon-supported sulfide nano-zero-valent iron was prepared based on biochar carriers formed from different raw materials. The carbon-supported sulfide nano-zero-valent iron obtained from kelp biochar was numbered M2, the carbon-supported sulfide nano-zero-valent iron obtained from corn biochar was numbered M3, the carbon-supported sulfide nano-zero-valent iron obtained from pine biochar was numbered M4, the carbon-supported sulfide nano-zero-valent iron obtained from sludge biochar was numbered M5, and the carbon-supported sulfide nano-zero-valent iron obtained from wheat biochar was numbered M6.

[0079] Application of carbon-supported sulfide nano-zero-valent iron prepared based on different biochar supports in the degradation of antibiotics in water:

[0080] In 50 mL of water with an initial ciprofloxacin concentration of 10 mg / L, 30 mg of S6 and products numbered M2 to M6, 0.0270 g of persulfate were added respectively. The pH value was 5. The mixture was quickly transferred to a constant temperature shaker and shaken at 25 °C and 180 r / min for 90 min. After that, 4.2 mL of the supernatant was collected, filtered through a 0.45 μm filter membrane, and then tested.

[0081] Table 3 shows the effect of carbon-supported sulfide nano-zero-valent iron prepared based on different biochar carriers on the degradation of ciprofloxacin in water.

[0082] Table 3

[0083] S6 97.45 M2 36.41 M3 26.21 M4 8.63 M5 46.30 M6 39.06

[0084] The product S6 prepared in Example 6 was used to conduct a water degradation test of ciprofloxacin. The amount of persulfate added to the system was 0.5, 1, 2, and 3 mmol / L, the amount of carbon-supported sulfide nano-zero valent iron added was 0.6 g / L, the initial concentration of pollutants was 10 mg / L, the pH value was 5, and the system was quickly transferred to a constant temperature shaker and shaken at 25°C and 180 r / min for 0–90 min. After that, 4.2 mL of the supernatant was collected, filtered through a 0.45 μm filter membrane, and then tested.

[0085] Figure 4 This study investigated the degradation of ciprofloxacin in water using carbon-supported sulfide nanoparticles activated with zero-valent iron under different persulfate concentrations. The degradation rate of ciprofloxacin gradually increased with increasing persulfate concentration. Specifically, when the persulfate concentration increased from 0.5 mmol / L to 2 mmol / L, the degradation rates were 95.06%, 94.93%, and 97.45%, respectively. However, when the persulfate concentration was further increased to 3 mmol / L, the degradation rate began to decrease. This is because the increased persulfate concentration proportionally increased the generation of sulfate free radicals, thus improving the degradation efficiency. Furthermore, the dissolution of more persulfate in water also released a large amount of H₂. + This promotes material corrosion and generates more SO4. ·-However, excessive sulfate free radicals can lead to self-elimination reactions, resulting in a decrease in the reaction efficiency.

[0086] The product S6 prepared in Example 6 was used to conduct a water degradation test of ciprofloxacin. The amount of persulfate added to the system was 2 mmol / L, and the amount of carbon-supported sulfide nano-zero valent iron added was 0.4, 0.6, 0.8, and 1.0 g / L, respectively. The initial concentration of pollutants was 10 mg / L; the pH value was 5. The system was quickly transferred to a constant temperature shaker and shaken at 25°C for 0–90 min at a speed of 180 r / min. After that, 4.2 mL of the supernatant was collected, filtered through a 0.45 μm filter membrane, and then tested.

[0087] Figure 5 This study investigated the degradation of ciprofloxacin in water by activated persulfate under different dosages of carbon-supported sulfide nano-zero-valent iron. When the dosages of carbon-supported sulfide nano-zero-valent iron were 0.4 g / L, 0.6 g / L, 0.8 g / L, and 1 g / L, the corresponding ciprofloxacin degradation efficiencies were 95.34%, 97.45%, 96.82%, and 97.26%, respectively. Within the first 15 minutes of the reaction, the degradation rate was rapid at all four dosages, with a rapid increase in ciprofloxacin degradation efficiency. After 30 minutes, the degradation rate stabilized, and the ciprofloxacin degradation efficiency reached its maximum at 90 minutes. The degradation efficiency is related to the number of active sites on the surface of the carbon-supported sulfide nano-zero-valent iron; increasing the number of active sites accelerates the adsorption and degradation of ciprofloxacin. Increasing the dosage of carbon-supported sulfide nano-zero-valent iron effectively increases the number of active sites in the reaction system, allowing more ciprofloxacin to be adsorbed onto the outer surface of the carbon-supported sulfide nano-zero-valent iron. However, if the volume and concentration of the pollutant solution remain unchanged, further increasing the dosage of carbon-supported sulfide nano-zero-valent iron may increase the agglomeration of iron nanomaterial particles.

[0088] The product S6 prepared in Example 6 was used to conduct a water degradation test of ciprofloxacin. The amount of persulfate added to the system was 2 mmol / L, the amount of carbon-supported sulfide nano-zero valent iron added was 0.6 g / L, and the initial concentrations of pollutants were 10, 20, 30, and 40 mg / L, respectively; the pH value was 5. The system was quickly transferred to a constant temperature shaker and shaken at 25°C for 0–90 min at a speed of 180 r / min. After that, 4.2 mL of the supernatant was collected, filtered through a 0.45 μm filter membrane, and then tested.

[0089] Figure 6This study investigated the degradation of antibiotics in water by persulfate activated by carbon-supported sulfide nanoparticles with zero-valent iron (ZFI) at different initial pollutant concentrations. With the same amount of ZFI, for a low-concentration (10 mg / L) ciprofloxacin solution, the system contained a sufficient number of ZFI, resulting in ample active sites on the surface for sufficient contact with ciprofloxacin molecules, leading to the fastest degradation rate. However, for a high-concentration (40 mg / L) ciprofloxacin solution, the number of ciprofloxacin molecules increased significantly, limiting the number of active sites on the ZFI and thus slowing the degradation rate. Another possible reason is that the amount of persulfate added to the system was constant, therefore the SO4 generated during the reaction... ·- The amount is limited; for low-concentration (10 mg / L) ciprofloxacin solutions, SO42-... ·- The amount is excessive, so the contact between carbon-supported sulfide nano-zero valent iron and ciprofloxacin is sufficient, resulting in a faster degradation rate of the system.

[0090] The product S6 prepared in Example 6 was used to conduct a water degradation test of ciprofloxacin. The amount of persulfate added to the system was 2 mmol / L, the amount of carbon-supported sulfide nano-zero valent iron added was 0.6 g / L, the initial concentration of pollutants was 10 mg / L, and the pH values ​​were 3, 5, 7, and 9, respectively. The mixture was quickly transferred to a constant temperature shaker and shaken at 25°C for 0–90 min at a speed of 180 r / min. After that, 4.2 mL of the supernatant was collected, filtered through a 0.45 μm filter membrane, and then tested.

[0091] Figure 7 This study investigated the activation of persulfate by carbon-supported sulfide nano-zero-valent iron at different pH values ​​to degrade ciprofloxacin in water. Under alkaline conditions, the passivation layer on the surface of the carbon-supported sulfide nano-zero-valent iron resulted in lower reactivity, while under acidic conditions, the passivation layer was corroded, leading to higher activity. The highest degradation rate (97.94%) was observed at pH 3, while the degradation efficiency remained at 89.04% at pH 9. This demonstrates that the carbon-supported sulfide nano-zero-valent iron prepared in Example 6 can effectively activate persulfate over a wide pH range, thus maintaining good removal capacity for ciprofloxacin.

[0092] Figure 8 The zeta potentials of carbon-supported sulfide nano-zero-valent iron (S-nZVI / BC) in Example 6 at different pH values ​​are shown, with an isoelectric point of pH = 3.35. At pH values ​​below 3.35, the positive charge on the material surface attracts persulfate anions, and ciprofloxacin is largely degraded. When the pH value increases from 3.35 to 12, the material surface carries a large number of negative charges, causing the material to repel persulfate anions and reducing its persulfate activation performance. Figure 7 The characteristics of the reaction and Figure 6 Mutual verification is formed.

[0093] Figure 9 The graph shows the degradation effect of ciprofloxacin in water by different systems. The degradation effect is PS < BC < BC+PS < S-nZVI < S-nZVI / BC < S-nZVI+PS < S-nZVI / BC+PS. Persulfate alone has no degradation effect. The degradation efficiency of BC+PS is 68.62%, because in addition to the strong adsorption performance of biochar due to its carbon porous structure, the oxygen-containing groups carried on biochar can also activate persulfate to a certain extent, promoting the degradation of pollutants.

[0094] The degradation efficiency of S-nZVI+PS is 95.86%, which is due to the sustainable release of Fe. 2+ It promotes the generation of sulfate free radicals and has a significantly better effect on CIP degradation. S-nZVI / BC+PS has the best degradation effect, reaching 97.45%. It not only takes into account the rich pore structure of biochar, but also improves the stability and dispersibility of nZVI. Furthermore, the iron sulfide coating slows down the oxidative corrosion of nano-zero valent iron, providing a continuous iron source for PS activation and promoting the continuous progress of the reaction.

[0095] Figure 10 This study describes the free radical quenching experiment in Example 6, which involved the activation of carbon-supported sulfide nano-zero-valent iron (S-nZVI / BC) to degrade ciprofloxacin in water by persulfate. Methanol was selected to quench SO4. ·- and HO · tert-butanol quenching HO · L-histidine quenching 1 O2, quenching of p-benzoquinone · O2 - The quenching results from methanol and tert-butanol show that the reaction was inhibited after the addition of the quencher, indicating that the SO4 in the system was not significantly reduced. ·- and HO · It played a role. The degradation efficiency of the system after adding L-histidine was 84.44% at 90 min, indicating the presence of [the substance] in the solution. 1 O2 was added, and the degradation efficiency of the system with p-benzoquinone was 19.21% after 90 minutes, indicating that the free radicals that played a major role were O2. · O2 - ,and 1 O2, SO4 ·- and HO · It also plays a role in CIP degradation.

[0096] To further determine the types of dominant free radicals in the CIP degradation process of the S-nZVI / BC+PS system, electron paramagnetic resonance (EPR) spectrometry was used as the testing instrument. Figure 11The image shows the EPR spectrum of free radicals generated by carbon-supported sulfide nano-zero valent iron (S-nZVI / BC) activating persulfate to degrade ciprofloxacin in water in Example 6. Figure 11 (a) is SO4 ·- and HO · The EPR spectra showed no obvious signal in PS and S-nZVI / BC alone, but significant SO42- was observed in the mixed solution of S-nZVI / BC+PS with added DMPO. ·- and HO · The peak of free radicals. Similarly, in Figure 11 (b) 1 In the EPR spectrum of O2, TEMP- was detected only when S-nZVI / BC and PS were present together. 1 The characteristic peak of O2 (intensity ratio 1:1:1). Figure 11 (c) is · O2 - The EPR spectrum also confirmed the presence of [the substance] in the solution. · O2 - , 1 O2, SO4 ·- and HO · Free radicals.

Claims

1. The application of carbon-supported sulfide nano-zero-valent iron as a catalyst in the degradation of ciprofloxacin, characterized in that, The specific application process is as follows: In 50 mL of water with an initial concentration of 10 mg / L of ciprofloxacin, 30 mg of carbon-supported sulfide nano-zero valent iron and 0.0270 g of persulfate were added, the pH value was set to 5, and the mixture was quickly transferred to a constant temperature shaker and shaken at 25°C for 90 min at a speed of 180 r / min. The degradation rate of ciprofloxacin was 97.45%. The above-mentioned carbon-supported sulfide nano-zero-valent iron was prepared by the following method, the specific steps of which are as follows: (1) Preparation of biochar carrier: Dry and grind the seaweed powder through a 100-mesh sieve and put it into a quartz boat. Place the quartz boat into a tube furnace, install the furnace plugs and pipes on both sides, purge with nitrogen for 5 minutes, set the furnace initial temperature to 50℃, the heating rate to 5℃ / min, the heating temperature to 600℃, and the holding time to 120 minutes. After the temperature of the tube furnace drops to 50℃, take out the quartz boat and grind the biochar in the boat into powder for later use. (2) Preparation of FeSO4·7H2O solution: Weigh 2.502g of FeSO4·7H2O and place it in a beaker. Add pure water to dissolve it and transfer it to a 100mL volumetric flask. Dilute it with water to the mark and shake well to obtain a FeSO4·7H2O solution with a concentration of 0.09mol / L. (3) Preparation of NaBH4 and Na2S2O4 mixture: Weigh 1.0214g NaBH4 and 0.0548g Na2S2O4 into a beaker, add pure water to dissolve, transfer to a 100mL volumetric flask, dilute with water to the mark, shake well to obtain NaBH4 and Na2S2O4 mixture. In the mixture, the concentration of NaBH4 is 0.27mol / L and the concentration of Na2S2O4 is 0.001575mol / L. (4) Preparation of carbon-supported sulfide nano-zero valent iron: 100 mL of 0.09 mol / L FeSO4·7H2O solution and 0.524 g of biochar were added to a 1 L three-necked flask. The temperature was kept at 25 °C and stirred for 15 min under nitrogen purging. Then, 100 mL of NaBH4 and Na2S2O4 mixture was added dropwise. After the addition was completed, the mixture was stirred at the same speed for 15 min to allow it to fully sulfide. The resulting black solid was carbon-supported sulfide nano-zero valent iron. The carbon-supported sulfide nano-zero valent iron was washed three times with anhydrous ethanol and then dried under vacuum at 60 °C for 8 h. It was then taken out and ground into powder. In the obtained carbon-supported sulfide nano-zero valent iron, the molar ratio of sulfur to nano-zero valent iron was 0.07:1, and the mass ratio of biochar to sulfide nano-zero valent iron was 1:1.

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