A method for efficiently degrading new pollutants by activating persulfate with iron-carbon nanocolloid

Abstract

The present application belongs to the technical field of water pollution treatment, and particularly relates to a method for efficiently degrading new pollutants by activating persulfate with iron-carbon nanocolloid. In order to solve the problems of short free radical lifetime and low utilization efficiency in the traditional persulfate advanced oxidation system, the present application first uses humic acid solution and iron salt solution to prepare an iron-carbon colloid solution, and then uses the solution to activate persulfate to degrade new pollutants in wastewater. Through the activation of persulfate based on the confined reaction of iron-carbon nanocolloid, the efficient removal of pollutants in wastewater is realized. When the method is applied to the treatment of new pollutants in surface water, reclaimed water and other water environments, the quenching effect of complex water matrix on free radicals can be effectively avoided, the lifetime of free radicals is prolonged, the utilization efficiency of free radicals is improved, and the purification demand of actual water environment can be better met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of water pollution treatment, and particularly relates to a method for efficiently degrading new pollutants by activating persulfate with iron-carbon nanocolloid. BACKGROUND

[0002] In recent years, with the increase in the use of industrial and agricultural production and the intensification of unreasonable disposal, a large amount of artificially synthesized organic substances, especially new pollutants, have entered water bodies. New pollutants have characteristics such as biological toxicity, environmental persistence, and biological accumulation, and even at a low concentration in the environment, they can have a high environmental and health risk, and their harm is potential and hidden. The production and use of toxic and harmful chemical substances are the main sources of new pollutants, mainly including persistent organic pollutants (POPs), pharmaceuticals and personal care products (PPCPs), endocrine disruptors (EDCs), brominated flame retardants (BFRs), and microplastics (MPs).

[0003] However, traditional water pollution treatment technologies based on physical separation and biological degradation principles are mainly used for removing nitrogen, phosphorus, COD, etc., and have very low removal efficiency for new pollutants, ultimately leading to a large amount of new pollutants entering surface and underground water environments. Although the concentration of new pollutants in the water environment is not high after dilution by water, these substances have strong environmental persistence and biological accumulation, are easily transmitted through the food chain, and are accumulated in the bodies of living organisms, ultimately affecting ecological safety and human health. Therefore, it is urgent to develop green and efficient deep water treatment technologies to improve the removal efficiency of new pollutants and reduce the harm of organic matter residues to the ecological system and human health.

[0004] Advanced oxidation technology is a technology that efficiently and rapidly degrades new pollutants by generating highly active free radicals. Among them, the advanced oxidation technology based on sulfate radicals (SO4 ·- , E 0 = 2.6V) has stronger selectivity and anti-substrate interference ability than the traditional Fenton system (HO · , E 0 = 1.9-2.7V), and has good application prospects in the treatment of new pollutants. Current advanced oxidation technologies mainly use energy radiation (such as ultraviolet light, ultrasonic waves, etc.) or catalysts (transition metal ions, metal oxides, etc.) to activate persulfate (S2O8 2- or HSO5 - ) to generate free radicals. However, free radicals have a short lifetime and low stability, and are easily quenched by non-toxic interference substrates in complex water environments, resulting in a significant decrease in the degradation efficiency of organic micro-pollutants. Therefore, in order to make the technology more suitable for the purification needs of actual water environments, it is necessary to further improve the selective degradation performance of free radicals on target pollutants. SUMMARY

[0005] In order to overcome the above-mentioned deficiencies of the prior art, the present application provides a method for efficiently degrading new pollutants based on iron-carbon nanocolloid confined activation of persulfate, which can effectively avoid the quenching effect of complex water matrix on free radicals, thereby prolonging the lifetime of free radicals and improving the utilization efficiency of free radicals, so as to promote the degradation efficiency of organic micro-pollutants and solve the problems of short lifetime and low utilization efficiency of free radicals in the traditional persulfate advanced oxidation system.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] The present application provides a method for efficiently degrading new pollutants by iron-carbon nanocolloid activation of persulfate, comprising the following steps:

[0008] S1, mixing humic acid solution and iron salt solution, adjusting pH and obtaining iron-carbon colloid solution by stirring reaction;

[0009] S2, adding the iron-carbon colloid solution obtained in S1 to wastewater containing new pollutants, and then adding persulfate solution for stirring reaction, so as to realize efficient removal of pollutants in wastewater.

[0010] Preferably, the humic acid includes natural humic acid and artificially synthesized humic acid. The natural humic acid is extracted from water bodies, soil and other environments.

[0011] Humic acid is mainly an organic substance containing aromatic rings and contains many functional groups. Because of its wide source (plant and animal organic matter after decay), its molecular structure is very complex, and there is currently no method to accurately determine its molecular structure. The solution after the reaction of humic acid solution and iron salt solution is a mixed solution containing soluble humic acid, iron ions and iron-carbon nanocolloid. The particle size of the iron-carbon nanocolloid is between 1-220 nm, which can efficiently activate persulfate; while the soluble humic acid and iron ions cannot activate persulfate and will not negatively affect the activation process. Therefore, the solution can be directly added to the reaction system, or the iron-carbon nanocolloid can be separated by ultrafiltration or reverse osmosis and then used for persulfate activation. The following is a part of the molecular structure of humic acid predicted by literature (from J.Anal.Appl.Pyrolysis 1996, 38:1-53):

[0012]

[0013] The principle of the present application for efficiently degrading new pollutants by activation of persulfate is that the ≡Fe(III) on the surface of iron-carbon nanocolloid can complex with persulfate ions to form an inner ring complex ≡Fe(III)-OOSO3 -Subsequently, the =Fe(III) sites can mediate the directional transfer of electrons from the reduced active functional groups of humic substances to the persulfate, and then generate the bound SO4 ·- Unlike the traditional free SO4 ·- , the colloidal bound SO4 ·- can react with H2O to generate HO · . On the one hand, the polydisperse structure of humic substances in the iron-carbon nanocolloid can stabilize free radicals, thereby prolonging the lifetime of free radicals. On the other hand, the iron-carbon nanocolloid can adsorb new pollutants, and the colloidal bound free radicals thereon can efficiently degrade the pollutants through surface confinement reactions, thereby avoiding the competitive consumption of free radicals by complex water matrix, improving the utilization efficiency of free radicals, and thus promoting the degradation efficiency of organic micro-pollutants.

[0014] Preferably, the iron salt includes inorganic iron salt and organic iron salt. More preferably, the iron salt includes (but is not limited to) ferric chloride, ferrous sulfate, polymeric ferric chloride, ferric nitrate.

[0015] Preferably, the molar ratio of the humic substance and the iron salt is 1-200: 1-5, calculated in terms of C / Fe molar ratio.

[0016] Preferably, the pH value of the mixed solution in S1 is 2-7, and the temperature is 20-50°C.

[0017] Preferably, the stirring speed of the reaction in S1 is 100-500 rpm, and the time is 0.5-90 min.

[0018] Preferably, the persulfate salt includes peroxymonosulfate and peroxodisulfate. More preferably, the persulfate salt includes (but is not limited to) sodium persulfate, potassium hydrogen persulfate.

[0019] Preferably, the molar ratio of the iron-carbon nanocolloid and the persulfate salt is 1-5: 1-100, calculated in terms of iron content.

[0020] Preferably, the molar ratio of the dosage of the persulfate salt to the total new pollutants in the wastewater to be treated is 1-1000: 1.

[0021] Preferably, the new pollutants include (but are not limited to) carbamazepine, atrazine, ibuprofen, sulfamethoxazole, sulfadiazine, diclofenac, dimethylphenoxyheptanoic acid, and naproxen.

[0022] Preferably, the pH of the reaction system after adding the persulfate salt solution ranges from 3 to 8.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] (1) The synthesized nanocolloid has higher activity than other iron-carbon composite materials due to the large specific surface area and high surface activity of nanomaterials;

[0025] (2) The synthesized nanocolloid can generate combined state radicals during the activation of persulfate, thereby greatly improving the lifetime of the radicals (the short lifetime of the radicals is the first problem affecting the degradation efficiency in traditional research);

[0026] (3) The synthesized nanocolloid can not only activate persulfate and stabilize radicals, but also adsorb new pollutants and efficiently degrade the pollutants through the generated combined state radicals to initiate confined reactions on the surface of the nanocolloid, which can effectively avoid the competition and consumption of radicals by complex water matrix and improve the utilization efficiency of radicals (in the traditional persulfate advanced oxidation system, the radicals are very active and exist in free state, so most of them are consumed by the water matrix, and the effect in real water is significantly lower than that in ultrapure water system);

[0027] (4) The raw materials used in the method have no toxic side effects, the material synthesis method is simple, and no secondary pollution problem is caused during use; and the reaction system involved is mild, high temperature and high pressure operation is not required, and the cost is low.

[0028] In summary, the method for efficiently degrading new pollutants based on iron-carbon nanocolloid confined activation of persulfate proposed in the application can effectively avoid the quenching effect of complex water matrix on radicals when applied to the treatment of new pollutants in surface water, reclaimed water and other water environments, thereby prolonging the lifetime of radicals and improving the utilization efficiency of radicals, solving the problems of short lifetime and low utilization efficiency of radicals in the traditional persulfate advanced oxidation system. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The high-resolution HAADF-STEM image of the iron-carbon nanocolloid synthesized in Example 1;

[0030] Figure 2 The high-resolution HAADF-STEM image and the corresponding EDS element mapping image of the iron-carbon nanocolloid synthesized in Example 1;

[0031] Figure 3 The degradation effect of different particle size iron-carbon nanocolloids synthesized in Example 2 on carbamazepine activated by potassium hydrogen persulfate;

[0032] Figure 4 The removal effect of iron colloids and iron-carbon nanocolloids synthesized in Example 3 on various organic pollutants in surface water activated by sodium persulfate;

[0033] Figure 5The nanocolloidal activated persulfate synthesized in Example 1 was used to generate HO· and SO4 ·- in the presence and absence of NaF.

[0034] Figure 6 The effect of different quenchers on the degradation of ibuprofen by the iron-carbon nanocolloidal activated potassium peroxymonosulfate synthesized in Example 2. DETAILED DESCRIPTION

[0035] The specific embodiments of the present application will be further described below. It should be noted that the description of these embodiments is used to help understand the present application, but does not constitute a limitation on the present application. In addition, the technical features involved in each of the embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0036] The experimental methods in the following examples are all conventional methods unless otherwise specified. The test materials used in the following examples are all commercially available unless otherwise specified.

[0037] Example 1:

[0038] 100 mL of 4 mgC / L humus solution (purchased from International Humic Acid Association, item number 2S101F) was added to 100 mL of 40 μΜ iron sulfate solution (the solvent of both solutions was water), the pH was adjusted to 6.0, and the reaction was stirred at 25°C water temperature at a speed of 150 rpm for 30 min. Then 10KDa ultrafiltration tube (pore size about equal to 1-3 nm) was used for separation to obtain iron-carbon nanocolloids. The synthesized iron-carbon nanocolloids were characterized by HAADF-STEM. The results are shown in Figure 1 and 2 .

[0039] Figure 1 The HAADF-STEM image of the synthesized iron-carbon nanocolloids showed that the synthesized iron-carbon nanocolloids presented irregular elliptical shape with a diameter range of 50-200 nm. Figure 2 The HAADR-STEM-EDS element mapping and EDS line scanning spectrum of the synthesized iron-carbon nanocolloids showed that the iron and carbon elements were uniformly distributed on the surface of the colloids, indicating that there were abundant ≡Fe(III) sites on the surface of the colloids.

[0040] Example 2:

[0041] Example 1: A 50 mL 10 mg C / L humic acid solution (purchased from International Humic Acid Association, item number 2S101F) was added to a 20 mL 60 μΜ iron chloride solution, the pH was adjusted to 3.6, and the reaction was stirred at 200 rpm for 60 min at a water temperature of 45 °C. The suspension after the reaction was then filtered using a 220 nM filter membrane, and the filtrate was divided into two parts: one part was separated using a 10 KDa (pore size approximately equal to 1-3 nm) ultrafiltration tube to obtain iron-carbon nanocolloid with a particle size of 1-3 nm to 220 nm (denoted as 1-3-220 nm); the other part was separated using a 100 KDa ultrafiltration tube (pore size approximately equal to 50 nm) to obtain iron-carbon nanocolloid with a particle size of 50-220 nm. The above colloids were added to two aqueous solutions containing 2 μΜ carbamazepine, respectively, and 20 μΜ potassium persulfate was added for stirring (150 rpm) reaction. The molar ratio of iron-carbon nanocolloid (calculated based on iron content) to persulfate in the reaction system (pH 3.6) was 1:10. The concentration of carbamazepine in water was determined at different reaction times. The results are shown in Figure 3 Figure 1.

[0042] Figure 3 The degradation effect of the 1-3-220 nm iron-carbon nanocolloid activated persulfate system on carbamazepine showed that the removal rate of carbamazepine was 77% after 120 min of reaction; the removal rate of carbamazepine by the system activated by the iron-carbon nanocolloid with a larger particle size (50-220 nm) was 55%. The above experimental results showed that the synthesized iron-carbon nanocolloid can efficiently activate persulfate to degrade recalcitrant emerging pollutants.

[0043] Example 3:

[0044] A 50 mL 8 mg C / L humic acid solution (purchased from International Humic Acid Association, item number 2S101F) was added to a 50 mL 50 μΜ iron chloride solution, the pH was adjusted to 5.0, and the reaction was stirred at 200 rpm for 10 min at a water temperature of 30 °C. At the same time, another treatment group was set up, which did not add humic acid, i.e., only the iron solution was stirred for reaction. Then, 50 mL of the suspension after the reaction was removed into two surface water samples containing 1 μg / L of an emerging pollutant (sulfadiazine, diclofenac, dimethylphenoxyheptanoic acid, and naproxen, respectively) [the surface water was from the Beijiang River, wherein the dissolved organic carbon (mg / L) was 1.74 ± 0.004, the pH was 7.49 ± 0.021, the Br - (mg / L) 0.034 ± 0.002, the Cl - (mg / L) 6.36 ± 0.007, the SO4 2-(mg / L) 18.29 ± 0.13, turbidity (NTU) 14.65 ± 0.07, and 1 mL of 1 mM sodium persulfate was added, and the reaction was stirred (150 rpm) for 120 min. The molar ratio of the iron-carbon nanocolloid (calculated as iron content) to persulfate in the reaction system (pH 5.0) was 1.25:1. The residual concentrations of the pollutants in each treatment group were determined by sampling. The results are shown in Figure 4 .

[0045] Figure 4 The removal effect of the four pollutants shows that the iron colloid alone cannot effectively activate sodium persulfate to degrade organic pollutants. As can be seen from the figure, the degradation efficiency of the four pollutants after the reaction is only 3-17%. In contrast, the iron-carbon nanocolloid can quickly activate sodium persulfate to degrade pollutants. The removal rates of sulfadiazine, diclofenac, dimethylphenoxyheptanoic acid, and naproxen after 120 min of reaction are 90.9%, 90.3%, 94.1%, and 87.9%, respectively. In addition, the water body is a natural surface water, and the water is rich in Cl - , Br - , and SO4 2- , etc. These substrates have little effect on the degradation efficiency of pollutants, indicating that the system can effectively avoid the interference of water body substrates.

[0046] Example 4:

[0047] The iron-carbon nanocolloid prepared in Example 1 was added to 100 mL of a 0.1 mM sodium persulfate solution (solvent: ultrapure water) (at this time, the pH was about 6.0 and no adjustment was needed), and the content of iron was 200 μM. After stirring at 100 rpm for 1 min, 1 mL of the sample was taken, 0.1 mL of 1 M 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) was added to the sample to capture the free radicals generated in the system, and the free radical signal was scanned and measured at different times using electron paramagnetic resonance spectroscopy (EPR). In order to characterize the generation of colloid-bound free radicals, 10 mM NaF (F - can promote the release of bound free radicals from the colloid into the aqueous solution by forming a fluorine-hydrogen bond on the surface of the colloid) was added to another reaction system to remove the bound free radicals from the colloid into the solution, which can be better captured by DMPO. The experimental results are shown in Figure 5 .

[0048] Figure 5 The "◆" and in the figure represent the signal parameters of HO· and SO4 ·- , respectively, indicating that there are HO· and SO4 ·-The signal strength indicates the free radical content. As can be seen from the figure, in the sample without NaF, the free radical signal significantly decreases with the reaction time, because the lifetime of free radical is very short; when NaF is added, the free radical signal significantly increases with the reaction time, which proves that the polydisperse structure of humic acid in the iron-carbon nanocolloid can stabilize the generated free radicals, thereby prolonging the lifetime of the free radicals, so as to facilitate the degradation of pollutants.

[0049] Example 5:

[0050] The 50-220 nm iron-carbon nanocolloid prepared in Example 2 was used to activate persulfate to degrade ibuprofen. In order to explore the contribution of different free radicals to the degradation of pollutants, quenching reaction was carried out on the free radicals generated in the system: 10 μM iron-carbon nanocolloid (calculated based on the iron content) and different quenching agents were added to a plurality of water bodies containing 0.5 mg / L ibuprofen, and then 200 μM potassium hydrogen persulfate was added to start the reaction, and the residual concentration of ibuprofen in water was determined at a certain time. The experimental results are shown in Figure 6 .

[0051] Figure 6 The results show that 20 mM tert-butyl alcohol (which can only quench HO·), 20 mM methanol (which can quench both HO· and SO4 ·- ), and 0.3 mM phenol (which can quench both HO· and SO4 ·- ) can completely quench the free radicals generated in the system. In addition, the dielectric constants of methanol and phenol are 33 and 12.4, respectively (the lower the dielectric constant, the stronger the affinity of the colloid surface, and the stronger the quenching effect on the bound state free radicals). Among them, tert-butyl alcohol and methanol reduce the degradation efficiency of ibuprofen by 30% and 50%, respectively, which indicates that SO4 ·- and HO· exist in the system at the same time. Compared with methanol, the inhibition of phenol with a lower dielectric constant on degradation is 100%. This indicates that phenol is more easily adsorbed on the colloid surface, thereby completely consuming the bound state free radicals. The above results again prove that the colloid-bound state free radicals are generated in the system. In addition, the adsorption capacity of methanol and phenol with different dielectric constants on the colloid is different, resulting in a significant difference in the quenching effect of the colloid-bound state free radicals, which indicates that the iron-carbon nanocolloid needs to adsorb organic matter first, and then the bound state free radicals on it can degrade the organic matter through surface confinement reaction.

[0052] In addition, the results of Example 3 show that the system is also very effective when applied to natural water bodies such as surface water (rich in Cl - , Br - and other substrates). This indicates that, compared with traditional free radicals, the free radicals generated in the system are less likely to be affected by Cl - , Br -The degradation efficiency of target pollutants is low due to the quenching of the aqueous matrix (Environ. Sci. Technol. 2020, 54, 3064-3081) according to the description of “Environ. Sci. Technol. 2014, 48, 2344-2351”, when 0.54 M Cl - When the UV / persulfate system exists, the degradation efficiency of benzoic acid is reduced by 73%; when 0.8 mM Br - is continuously added, the degradation efficiency is reduced by 98%; when HCO3 - is continuously added, the degradation efficiency is reduced by 99%). The colloidal bound radicals developed by the present application can efficiently degrade pollutants through surface confinement reaction, which can effectively avoid the influence of complex water matrix.

[0053] As can be seen from the above, the present application first uses humic acid solution and iron salt solution to prepare iron-carbon colloidal solution, and then uses it to activate persulfate to degrade new pollutants in wastewater. The method realizes efficient removal of pollutants in wastewater by activating persulfate based on the confinement reaction of iron-carbon nanocolloid. When the method is applied to the treatment of new pollutants in surface water, reclaimed water and other water environments, the quenching effect of complex water matrix on free radicals can be effectively avoided, the lifetime of free radicals is prolonged, the utilization efficiency of free radicals is improved, and the purification demand of actual water environment can be better met, so the method has a broad application prospect.

[0054] The embodiments of the present application are described in detail above, but the present application is not limited to the described embodiments. For those skilled in the art, various changes, modifications, replacements and variations of the embodiments can be made without departing from the principles and spirits of the present application, and still fall within the protection scope of the present application.

Claims

1. A method for efficiently degrading pollutants by activating persulfate with iron-carbon nanocolloids, characterized in that: The following steps are involved: S1, mixing the humus solution and the iron salt solution, adjusting the pH and stirring to obtain an iron-carbon nanocolloid solution; S2, adding the iron-carbon nanocolloid solution obtained in S1 to the wastewater containing pollutants, and then adding the persulfate solution for stirring and reacting, thereby achieving efficient removal of pollutants in the wastewater; The humus includes natural humus and artificial synthetic humus; The iron salts include inorganic iron salts and organic iron salts; Calculated based on the C / Fe molar ratio, the molar ratio of the humus to the iron salt is 1-200:1-5; The pH value of the mixed solution in S1 is 2-7, and the temperature is 20-50°C.

2. The method for efficiently degrading pollutants by activating persulfate with iron-carbon nanocolloids according to claim 1, characterized in that: The stirring reaction in S1 is carried out at a speed of 100 to 500 rpm and for a time of 0.5 to 90 min.

3. The method for efficiently degrading pollutants by activating persulfate with iron-carbon nanocolloids according to claim 1, characterized in that: The persulfates include peroxymonosulfates and peroxydisulfates.

4. The method for efficiently degrading pollutants by activating persulfate with iron-carbon nanocolloids according to claim 1, characterized in that: Calculated based on the iron content, the molar ratio of the iron-carbon nano-colloid to the persulfate is 1-5:1-100.

5. The method for efficiently degrading pollutants by activating persulfate with iron-carbon nanocolloids according to claim 1, characterized in that: The molar ratio of the persulfate dosage to the pollutants in the wastewater to be treated is 1 to 1000:

1.

6. The method for efficiently degrading pollutants by activating persulfate with iron-carbon nanocolloids according to claim 1, characterized in that: The pollutant is any one of carbamazepine, atrazine, ibuprofen, sulfamethoxazole, sulfadiazine, diclofenac, dimethylbenzylamine, and naproxen.

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