Application of soluble alkali metal sulfide secondary activated PMS in degrading norfloxacin

Abstract

The invention relates to the technical field of catalysts, in particular to application of PMS secondarily activated by soluble alkali metal sulfide in degrading norfloxacin. The invention provides a reducing agent-soluble alkali metal sulfide for improving the reaction efficiency of a Fe (II) / PMS homogeneous catalysis system. The norfloxacin can be efficiently degraded by utilizing the reducing agent and a Fe (II) / PMS homogeneous catalysis system, iron mud is not generated in the reaction process, the method is green and environment-friendly, the pH application range is relatively wide, the dosage of Fe (II) initially required in the system is small, the pollutant treatment cost is reduced, and large-scale popularization and application are facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to application of soluble alkali metal sulfide secondary activated PMS in the degradation of norfloxacin. Background Art

[0002] Norfloxacin (NOR) has been widely used in the fields of medicine, animal husbandry and aquaculture. Like other antibiotics, norfloxacin is difficult to be completely absorbed during use. Most of it is discharged into the environment through feces or urine, and finally exists in various water bodies, causing serious harm. Therefore, it is particularly important to efficiently degrade norfloxacin in various water environments.

[0003] The ferrous ion activated peroxymonosulfate (Fe(II) / PMS) homogeneous catalytic system is simple to operate and low in cost. Compared with the heterogeneous catalytic system, its interphase mass transfer resistance is lower and the reaction rate is higher. Therefore, it is often used to degrade pollutants. There are two pathways of Fe(II) / PMS, as shown in formulas (1) and (2). During the process, Fe(II) and PMS will generate Fe(III) and sulfate radicals (SO4 ·- ), hydroxyl radical (HO · ). Generally, Fe(II) / PMS has a two-stage reaction process, which first includes a fast stage and then a slow stage. In the initial stage, due to the abundance of reactants, free radicals are generated quickly; as the reaction proceeds, due to the consumption of Fe(II), the generation of free radicals slows down.

[0004]

[0005]

[0006] In order to improve the efficiency of Fe(II) / PMS reaction, some researchers have adopted the method of adding Fe(II) in batches. For example, Ayoub et al. found that the removal rate of sulfamethoxazole after 2 hours of reaction under the condition of adding Fe(II) in batches was twice that of adding Fe(II) once. Jiang et al. found that adding Fe(II) in batches can not only improve the degradation rate of bisphenol A, but also improve the removal rate of total organic carbon in the system.

[0007] Other researchers have used organic chelating agents such as ethylenediaminetetraacetic acid and citric acid to improve the reaction efficiency. Currently, they have been widely used to accelerate the degradation of pollutants such as sulfamethoxazole, trichloroethylene and 2,4,6-trichloroanisole in Fe(II) / PMS systems. Among them, the chelating agent forms a chelate with Fe(II), which allows Fe(II) to be slowly released into the solution, effectively controlling the concentration of Fe(II) in the solution and inhibiting SO4 ·-On the other hand, the generated chelate can overcome the deficiency that Fe(II) can only exist stably under acidic conditions, thus broadening the applicable pH range of the system.

[0008] In addition, the addition of a reducing agent can effectively promote the circulation of Fe(III) and Fe(II) and thus improve the reaction efficiency of Fe(II) / PMS. Hydroxylamine is currently a widely used reducing agent. Zou et al. investigated the effect of hydroxylamine on the degradation of benzoic acid by the Fe(II) / PMS system. The results showed that the Fe(II) / PMS system could hardly degrade benzoic acid within 15 minutes, while the addition of hydroxylamine under the same conditions could degrade about 80% of benzoic acid. A decrease in the concentration of Fe(III) was detected during the process, which indirectly indicates that hydroxylamine achieves effective degradation of benzoic acid by promoting the regeneration of Fe(II).

[0009] SO5 generated by the reaction of Fe(III) generated in the Fe(II) / PMS process with PMS ·- The reactivity is much lower than SO4 ·- and HO · ; At the same time, the reaction of Fe(III) and PMS can regenerate Fe(II), but the rate constant of this reaction is extremely low, which will lead to the accumulation of Fe(III) in the solution. Fe(III) has low solubility in the medium and high pH range and is easily precipitated to form a large amount of iron sludge, which greatly inhibits the reaction activity and causes water pollution. When adding Fe(II) in batches, the utilization efficiency of Fe(II) is still low, and the added Fe(II) will eventually form Fe(III), so the problem of large amount of iron sludge cannot be overcome; the introduced chelating agent is an organic matter, which will not only increase the chemical oxygen demand of the water body, but also change the existence form of heavy metals in the water body, which has potential risks; currently, there are few types of reducing agents that have been proven to be effective, and there are also large differences in the types of reducing agents suitable for different scenarios. The most widely used reducing agent, hydroxylamine, is toxic in itself and has a high reaction rate constant with free radicals, which will compete with pollutants for free radicals.

[0010] How to provide a green, environmentally friendly and efficient method for degrading norfloxacin has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0011] In view of this, the present invention is proposed.

[0012] In a first aspect, the present invention provides the use of soluble alkali metal sulfide in a Fe(II) / PMS homogeneous catalytic system.

[0013] The present invention screened a large number of reducing agents and found that soluble alkali metal sulfide as a reducing agent can realize the conversion of Fe(III) to Fe(II) through electron transfer, and the regenerated Fe(II) secondary activation solution of the remaining PMS produces SO4 ·- and HO · , which can improve the reaction efficiency; and when soluble alkali metal sulfide is added as a reducing agent, it can promote recycling, so that the initial Fe(II) dosage required in the system is small, and the Fe(III) in the system can be "secondarily activated" without adding additional Fe(II). On the one hand, it can improve the utilization efficiency of Fe(II), and on the other hand, it can effectively limit the generation of iron sludge, so that no iron sludge is generated during the reaction process, which is green and environmentally friendly.

[0014] In addition, soluble alkali metal sulfides are inorganic substances and will not increase the chemical oxygen demand of the system, nor will they change the existence form of heavy metals in the water. The dosage of soluble alkali metal sulfides added is small and will not cause other potential risks.

[0015] Preferably, the soluble alkali metal sulfide is Na2S or K2S.

[0016] Preferably, the Fe(II) / PMS homogeneous catalytic system is used to degrade pollutants.

[0017] Preferably, the pollutants exist in natural waters, domestic wastewater or industrial wastewater.

[0018] Preferably, the pollutant is norfloxacin.

[0019] Preferably, after the Fe(II) in the Fe(II) / PMS homogeneous catalytic system is consumed, a soluble alkali metal sulfide is added to perform secondary activation of PMS.

[0020] The source of Fe(II) in the present invention includes but is not limited to FeSO4 and corresponding hydrates.

[0021] In a specific implementation process, the soluble alkali metal sulfide can be derived from other forms such as corresponding hydrates.

[0022] Furthermore, the present invention provides a method for degrading norfloxacin, comprising:

[0023] Fe(II), PMS and soluble alkali metal sulfide are simultaneously added into a solution containing norfloxacin to react;

[0024] Preferably, Fe(II) and PMS are first added to a solution containing norfloxacin for reaction, and then a soluble alkali metal sulfide is added after the Fe(II) is consumed.

[0025] The present invention finds that by adding two reagents, soluble alkali metal sulfide and Fe(II), into the system in batches, the effect of improving the NOR degradation rate under the condition of secondary activation of Fe(II) is more significant.

[0026] Preferably, the amount of the added soluble alkali metal sulfide satisfies the molar ratio of sulfide ion to Fe(II) of (1-2):1, based on the molar ratio of sulfide ion to Fe(II) in the soluble alkali metal sulfide.

[0027] The present invention further found that the higher the dosage of the added soluble alkali metal sulfide is, the better the utilization efficiency of PMS is. When the dosage is high, not all consumed PMS is used for the degradation of NOR, and the utilization efficiency of PMS is reduced. When the dosage of the soluble alkali metal sulfide is controlled within the above range, the utilization efficiency of PMS can be optimized at a lower dosage, so that the utilization efficiency of PMS and the use cost are balanced.

[0028] More preferably, the molar ratio of sulfide ion to Fe(II) is (1-1.2):1.

[0029] When the content of PMS is within the above range, better PMS utilization efficiency can be obtained with less dosage.

[0030] Preferably, the initial pH of the solution is 10 or less.

[0031] Preferably, Fe(II) is dosed only once initially.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention provides a reducing agent for improving the reaction efficiency of a Fe(II) / PMS homogeneous catalytic system. The reducing agent and the Fe(II) / PMS homogeneous catalytic system can efficiently degrade norfloxacin, and iron sludge is not generated during the reaction. The system is green and environmentally friendly, has a wide pH range of use, and reduces the initial Fe(II) dosage required in the system, thereby reducing the cost of pollutant treatment and facilitating large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the degradation process of NOR under different Na2S addition conditions.

[0035] Figure 2 This is the process of secondary activation of Fe(II) / PMS to degrade NOR with different Na2S dosages.

[0036] Figure 3 is the utilization efficiency of PMS under different Na2S dosages.

[0037] Figure 4This is the degradation process of NOR at different initial pH.

[0038] Figure 5 The graphs are the changes of pH (a) and ORP (b) of the solutions at different initial pH values ​​over time.

[0039] Figure 6 It is the species distribution in the range of pH = 1-12 when Fe(II) and Na2S coexist.

[0040] Figure 7 Statistical graphs of the degradation rate (a) and degradation contribution rate (b) of various free radicals to NOR.

[0041] Figure 8 It is the electron paramagnetic resonance spectrum of each process.

[0042] Fig. 9 is a graph showing the variation of NOR degradation rate over time.

[0043] Fig.10 PMS concentration (a) and Fe(II) concentration (b) are plotted against time.

[0044] Fig.11 This is the degradation mechanism diagram of NOR degradation promoted by Fe(II) / PMS. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] If no specific techniques or conditions are specified in the examples, all are carried out according to conventional methods or the techniques or conditions described in the literature in the field, or according to the product instructions. If no manufacturer is specified for the reagents and instruments used, all are conventional products that can be purchased through regular channels.

[0047] The following examples use Na2S as a representative to illustrate the application of soluble alkali metal sulfides in Fe(II) / PMS homogeneous catalytic system.

[0048] Example 1

[0049] This embodiment provides a method for degrading norfloxacin, comprising:

[0050] Take 20 mL of 200 mg / L NOR mother solution in a 500 mL transparent glass bottle, then take 369.2 mL of ultrapure water, 0.1 M NaOH, and 0.1 M H2SO4 solution to obtain a mixed solution with a pH of 6 ± 0.1, fix the transparent glass bottle on a shaker with a constant speed, dissolve 0.0158 g FeSO4·7H2O and 0.0137 g Na2S·9H2O in 25 mL ultrapure water, respectively, and take 5 mL of each and add them to the mixed solution, and finally add 0.8 mL of 0.1 M PMS mother solution to start the reaction.

[0051] Example 2

[0052] This embodiment provides a method for degrading norfloxacin, comprising:

[0053] Take 20 mL of 200 mg / L NOR mother solution in a 500 mL transparent glass bottle, then take 369.2 mL of ultrapure water, 0.1 M NaOH, and 0.1 M H2SO4 solution to obtain a mixed solution with a pH of 6 ± 0.1, fix the transparent glass bottle on a shaker set at a constant speed, dissolve 0.0158 g FeSO4·7H2O in 50 mL ultrapure water and take 10 mL to the mixed solution, then add 0.8 mL of 0.1 M PMS mother solution to start the reaction, dissolve 0.0126 g Na2S·9H2O in 50 mL ultrapure water, and the reaction is carried out for 16 minutes, then take 10 mL and add it to the mixed solution.

[0054] Example 3

[0055] This example provides a method for degrading norfloxacin, which is different from Example 2 in that after adding PMS mother liquor to start the reaction, 0.0189 g of Na2S·9H2O is dissolved in 50 mL of ultrapure water, and 10 mL of water is added to the mixed solution after the reaction is carried out for 16 minutes.

[0056] Example 4

[0057] This example provides a method for degrading norfloxacin, which is different from Example 2 in that after adding PMS mother liquor to start the reaction, 0.0252 g of Na2S·9H2O is dissolved in 50 mL of ultrapure water, and 10 mL of water is added to the mixed solution after the reaction is carried out for 16 minutes.

[0058] Example 5

[0059] This embodiment provides a method for degrading norfloxacin, which is different from Embodiment 2 in that the pH of the mixed solution is 3.

[0060] Example 6

[0061] This example provides a method for degrading norfloxacin, which is different from Example 2 in that the pH of the mixed solution is 9.

[0062] Example 7

[0063] This example provides a method for degrading norfloxacin, which is different from Example 2 in that the pH of the mixed solution is 12.

[0064] Test example

[0065] The degradation process of norfloxacin in the above example was monitored.

[0066] Figure 1 The degradation process of NOR under different Na2S addition conditions, wherein Fe(II) / PMS means no Na2S is added; S(II) / Fe(II) / PMS means Na2S is added at the beginning of the experiment (Example 1); Fe(II) / PMS, S(II) means Na2S is added for secondary activation when the reaction is carried out for 16 minutes (Example 2).

[0067] The results show that the NOR degradation rates after 30 minutes of reaction were 72.45% and 82.80% respectively when Na2S was added at the beginning of the experiment and when Na2S was added at 16 minutes into the reaction, which were 12.65% and 23.00% higher than those without Na2S. This indicates that the addition of Na2S can significantly increase the NOR degradation rate, and the addition of Na2S and Fe(II) in batches makes the NOR degradation rate more significantly improved under the condition of secondary activation of Fe(II).

[0068] Figure 2 This is the process of secondary activation of Fe(II) / PMS to degrade NOR with different Na2S dosages, wherein Fe(II):S(II)=1:1 corresponds to Example 2, Fe(II):S(II)=1:1.5 corresponds to Example 3, Fe(II):S(II)=1:2 corresponds to Example 4, and the control group is Fe(II):S(II)=1:0. Figure 3 It is the utilization efficiency diagram of PMS under different Na2S dosages.

[0069] The results show that with the increase of S(II) dosage, the degradation rate of NOR gradually increases after 30 minutes of reaction; but when the S(II) dosage increases, the ratio of the amount of NOR oxidized to the amount of PMS consumed within 0-30 and 15-30 minutes, that is, the utilization efficiency of PMS, decreases, which indicates that when the S(II) dosage increases, not all the consumed PMS is used for the degradation of NOR.

[0070] Figure 4 This is the degradation process of NOR at different initial pH. Figure 5The graphs are the changes of pH (a) and ORP (b) of the solutions at different initial pH values ​​over time. Figure 6 This is the species distribution diagram in the pH range of 1-12 when Fe(II) and Na2S coexist.

[0071] The results show that when the initial pH of the solution is 3, 6, 9, and 12, the NOR removal rates after 30 minutes of reaction are 70.23%, 82.80%, 66.05%, and 77.64%, respectively. This shows that the pH range of this method is relatively wide. However, it is worth noting that when the initial pH of the solution is 12, the NOR degradation rate during the reaction shows a trend of first increasing, then decreasing, and then increasing. Combined with the fact that the solution pH is greater than 10.5 during the reaction and the redox potential (ORP) is at a low value when the initial pH of the solution is 12, it can be seen that Figure 5 , it is speculated that PMS is not activated. When the solution pH is greater than 10.5, Fe(OH)2 precipitation will be generated, such as Figure 6 This indicates that when the initial pH of the solution is 12, NOR is removed by the adsorption of Fe(OH)2 rather than oxidation.

[0072] Example 8

[0073] The purpose of this example is to reveal the mechanism of action. The quenching experiment was carried out under the experimental conditions of the above Example 2, and 5.731 mL of tert-butyl alcohol (TBA) and 2.540 mL of methanol (MeOH) were added as quenching agents before adjusting the initial pH of the solution.

[0074] In the electron paramagnetic resonance experiment, 100mM 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) was used as a spin trapping agent. A certain volume of ultrapure water, DMPO reagent, PMS solution, Fe(II) solution, and S(II) solution were added in sequence. After oscillation for 15s, 30μL was sampled with a quartz standard sampling tube, and the sampling tube was placed in an EPR special sample tube for in-situ free radical generation and detection. The EPR temperature was always maintained at 20℃ by equipping a water circulation system, and the X-band frequency was 9.84GHz. The parameters of the spectrometer were set as follows: scan width was 100G, center field was 3505G, scan time was 60s, modulation amplitude was 1G, modulation frequency was 100kHz, receiver gain was 30dB, microwave attention was 25dB, normal time was 12.64ms, and time constant was 5.12ms.

[0075] In order to determine the relationship between NOR degradation rate, PMS concentration and Fe(II) concentration in the process, 120 mL of 200 mg / L NOR mother solution was taken in a 500 mL transparent glass bottle, and then 268.4 mL of ultrapure water, 0.1 M NaOH and 0.1 M H2SO4 solution were taken to obtain a mixed solution with a pH of 6±0.1. The transparent glass bottle was fixed on a shaker with a constant speed. 0.1005 g FeSO4·7H2O was dissolved in 50 mL ultrapure water and 10 mL was added to the mixed solution. Then 1.6 mL of 0.1 M PMS mother solution was added to start the reaction. 0.0795 g Na2S·9H2O was dissolved in 50 mL ultrapure water. When the reaction was carried out for 16 minutes, 10 mL was taken and added to the mixed solution.

[0076] In each experiment, 3 mL of the reaction solution was taken at a predetermined time interval (0.5, 1.5, 2.5, 5, 8, 10, 15, 16.5, 17.5, 18.5, 20, 22, 25, 30 minutes) and an equal volume of methanol was added to terminate the reaction. The mixed solution was filtered through a 0.22 μm filter membrane and the NOR concentration in the sample was determined by high performance liquid chromatography. At a predetermined time interval (0.5, 8, 15, 16.5, 19, 22, 30 minutes), 1 mL of sample was taken into a sample bottle to determine the PMS concentration and Fe (II) concentration.

[0077] By comparing the changes in NOR degradation rate over time when there is no quencher and when MeOH and TBA are used as quenchers, the degradation rate and degradation contribution rate of each free radical to NOR are obtained as follows: Figure 7 As shown, it can be seen that "secondary activation" does not change the type of free radicals generated, all of which are SO5 ·- , HO · 、SO4 ·- There are three free radicals, but the leading free radical is SO5 with a contribution rate of 42.37%. ·- Transformed into SO4 with a contribution rate of 44.96% ·- .

[0078] The electron paramagnetic resonance spectra of each process are shown in Figure 8 As shown in Figure 2, PMS alone cannot generate free radicals, while Fe(II) / PMS and S(II) / Fe(II) / PMS can generate HO · 、SO4 ·- However, compared with Fe(II) / PMS, the electron paramagnetic resonance spectrum of S(II) / Fe(II) / PMS showed that HO · 、SO4 ·- The signal is stronger, indicating that the addition of Na2S can promote HO · 、SO4 ·-In addition, SO4 ·- Signal ratio HO · Stronger, indicating that SO4 ·- Contribution rate is higher than HO · Bigger.

[0079] The changes of NOR degradation rate, PMS concentration and Fe(II) concentration over time are shown in Fig. 9 and 10 Na2S was added when the reaction was carried out for 16 minutes. It was measured that the Fe(II) concentration suddenly increased to about 6 mg / L after 30 seconds, the PMS concentration suddenly decreased to about 0 mM, and the NOR degradation rate increased by about 8%, indicating that the added Na2S achieved the "secondary activation" of PMS by reducing Fe(II) and further degrading NOR.

[0080] In summary, Na2S promotes the conversion of Fe(III) to Fe(II) and secondary activates PMS to produce SO5 ·- , HO · 、SO4 ·- Three free radicals, especially SO4 ·- , thereby increasing the oxidative degradation of NOR, such as Fig.11 shown.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. Application of soluble alkali metal sulfides in Fe(II) / PMS homogeneous catalytic system.

2. The use according to claim 1, characterized in that: The soluble alkali metal sulfide is Na2S or K2S.

3. The use according to claim 1, characterized in that: The Fe(II) / PMS homogeneous catalytic system is used to degrade pollutants.

4. The use according to claim 3, characterized in that: The pollutants are present in natural water bodies, domestic wastewater or industrial wastewater.

5. The use according to claim 4, characterized in that: The pollutant is norfloxacin.

6. The use according to any one of claims 1 to 5, characterized in that: When the PMS in the Fe(II) / PMS homogeneous catalytic system is consumed, soluble alkali metal sulfide is added to perform secondary activation of the PMS.

7. A method for degrading norfloxacin, characterized in that: include: Fe(II), PMS and soluble alkali metal sulfide are simultaneously added into a solution containing norfloxacin to react; Preferably, Fe(II) and PMS are first added to a solution containing norfloxacin for reaction, and then a soluble alkali metal sulfide is added after the Fe(II) is consumed.

8. The method according to claim 7, characterized in that The amount of the added soluble alkali metal sulfide satisfies the molar ratio of sulfide ion to Fe(II) of (1-2):1, based on the molar ratio of sulfide ion to Fe(II) in the soluble alkali metal sulfide.

9. The method according to claim 7, characterized in that: The initial pH of the solution is 10 or less.

10. The method according to any one of claims 7 to 9, characterized in that: Fe(II) was added only once initially.

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