Method for removing refractory organic pollutants by using catalytic material with surface confinement effect

Abstract

The present invention provides a method for removing refractory organic pollutants by using a catalytic material with surface confinement effect. The catalytic material with surface confinement effect is added to the wastewater containing refractory organic pollutants with a pH value of 3.0 - 9.0, adsorbed for at least 20 min, and then peroxymonosulfate is added to initiate the degradation reaction of the refractory organic pollutants in the wastewater. The wastewater treatment is completed within 5 - 30 min after adding peroxymonosulfate. The catalytic material has a pore structure and is composed of Fe, C, N, and O elements. The Fe element is in a monodispersed state in the catalytic material in the form of Fe-N4 coordination. By confining the organic pollutants near the active sites of the catalytic material, the present invention amplifies the local concentration of the pollutants, shortens the migration distance of ROS, improves the utilization rate of short-lived ROS, and uses the adsorption of the organic pollutants on the catalytic material to increase the electron transfer rate between the catalytic material and peroxymonosulfate, ultimately effectively improving the removal efficiency of the organic pollutants.

Description

Technical Field

[0001] The present invention belongs to the technical field of water treatment, and relates to a method for removing refractory organic pollutants by using a catalytic material with surface confinement effect. Background Art

[0002] With the increasing social demand for sustainable development and quality of life, water pollution has become one of the severe problems that need to be solved urgently. In particular, refractory emerging pollutants frequently detected in natural waters, such as aromatic and antibiotic pollutants, etc., have brought great challenges to the treatment of water pollution and the recycling of water resources. Therefore, the efficient and in-depth treatment of wastewater is one of the keys to solving the water pollution problem.

[0003] Among various wastewater treatment methods, advanced oxidation processes (AOPs) have attracted extensive attention because they can efficiently generate reactive oxygen species (ROS) that can effectively attack and degrade target pollutants. These ROS include sulfate radicals (SO4 ·– ), hydroxyl radicals ( · OH), singlet oxygen ( 1 O2), and superoxide radicals (O2 ·– ), etc. The catalytic processes of advanced oxidation technologies include homogeneous catalysis and heterogeneous catalysis. Homogeneous catalysis mainly uses soluble metal salts as catalysts, which has the problems that the catalysts are not easy to recover and are prone to cause secondary heavy metal pollution; heterogeneous catalysis has the characteristic that the reaction products are easy to separate, so heterogeneous catalysts have long been a popular choice for catalysts in the field of AOPs. However, the catalytic efficiency of heterogeneous catalysts is relatively low, which greatly limits sewage treatment.

[0004] To improve the catalytic efficiency, researchers have focused on modifying heterogeneous catalysts. For example, modification is carried out through doping with heteroelements such as N, S, P, B, or groups such as amino and nitro groups to change the electronic structure of the active center, thereby changing the adsorption of oxidants or accelerating the electron transfer between oxidants and active sites, and improving the catalytic activity. However, this doping process usually requires pyrolysis and is accompanied by the addition of other agents, which will greatly increase the cost of heterogeneous catalysts and does not conform to the development concept of "green chemistry". In addition, the current research on AOPs mainly focuses on modifying heterogeneous catalysts to improve the removal efficiency of pollutants, but ignores the synergistic effect between catalysis and adsorption. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for removing refractory organic pollutants by using a catalytic material with surface confinement effect, so as to improve the removal efficiency of refractory pollutants in wastewater and reduce the cost of wastewater treatment.

[0006] To achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0007] A method for removing refractory organic pollutants by using a catalytic material with surface confinement effect, comprising the following steps:

[0008] Adding the catalytic material with surface confinement effect into the wastewater containing refractory organic pollutants with a pH value of 3.0 - 9.0, adsorbing for at least 20 min, and then adding persulfate to initiate the degradation reaction of the refractory organic pollutants in the wastewater. The wastewater treatment is completed within 5 - 30 min after adding persulfate;

[0009] The catalytic material with surface confinement effect has a pore structure and is composed of Fe, C, N, and O elements. The Fe element is in a monodispersed state in the catalytic material in the form of Fe-N4 coordination, and the content of the Fe element in the catalytic material is 0.4 wt% - 1.5 wt%.

[0010] In the above technical solution, the monodispersed state refers to a state of uniform dispersion without agglomeration.

[0011] In the above technical solution, the refractory organic pollutants are organic substances containing electron-rich groups. Further, the electron-rich groups in the organic substances containing electron-rich groups include at least one of amino group and hydroxyl group. For example, sulfamethoxazole, phenol, bisphenol A, etc. are common organic substances containing electron-rich groups.

[0012] In the above technical solution, the addition amounts of the catalytic material with surface confinement effect and persulfate in the wastewater are determined according to the properties of the actual wastewater to be treated (such as the types and concentrations of pollutants in the wastewater). For specific wastewater, the addition amounts of the two can be determined by experimental screening. Generally, the addition amount of the catalytic material with surface confinement effect in the wastewater is 20 - 200 mg per liter of wastewater; the addition amount of the above persulfate in the wastewater should make the concentration of persulfate in the wastewater 0.4 - 1.0 g / L.

[0013] In the above technical solution, when adding the catalytic material with surface confinement effect into the wastewater containing refractory organic pollutants, persulfate is usually added after adsorbing for 20 - 60 min.

[0014] In the above technical solution, the particle size of the catalytic material with surface confinement effect is in the nanometer range. For example, the feasible particle size of the catalytic material can be 100 - 200 nm.

[0015] In the above technical solution, the catalytic material has good stability and recyclability. The present invention has confirmed through experiments that when the catalytic material is used to degrade sulfamethoxazole wastewater with a concentration of 20 μmol / L, and recycled 4 times, sulfamethoxazole in the wastewater can be completely removed within 10 - 15 minutes after adding persulfate. When recycled 5 times, the removal rate of sulfamethoxazole is still as high as 90% within 15 minutes after adding persulfate. Based on the experimental results, the catalytic material can be recycled, that is, after completing the treatment of a batch of wastewater, the catalytic material with surface confinement effect is recovered for the treatment of the next batch of wastewater. The number of recycling times of the catalytic material is at least 4 times, for example, it can be 4 - 5 times.

[0016] In the above technical solution, the preparation method of the catalytic material with surface confinement effect is as follows:

[0017] (1) Dissolve Zn(NO3)2·6H2O and Fe(acac)3 in methanol to obtain solution A. The concentration of Zn(NO3)2·6H2O in solution A is 0.02 - 0.03 g / mL, and the concentration of Fe(acac)3 is 0.008 - 0.01 g / mL; dissolve 2-methylimidazole in methanol to obtain solution B. The concentration of 2-methylimidazole in solution B is 0.04 - 0.06 g / mL;

[0018] Mix solution A and solution B and stir for 20 - 30 h, separate the solid product, and wash to obtain the precursor; in the mixed solution obtained by mixing solution A and solution B, the mass ratio of Zn(NO3)2·6H2O, Fe(acac)3, and 2-methylimidazole is (5 - 7.5):(2 - 2.5):(10 - 15);

[0019] (2) Disperse the precursor in methanol, then add water to obtain a precursor dispersion. Add an aqueous solution of cetyltrimethylammonium bromide, an aqueous solution of sodium hydroxide, and a methanol solution of tetraethyl orthosilicate to the precursor dispersion, stir for 2 - 3 h, separate the solid product, wash, and dry to obtain the precursor wrapped with SiO x

[0020] The volume ratio of the precursor dispersion, the aqueous solution of cetyltrimethylammonium bromide, the aqueous solution of sodium hydroxide, and the methanol solution of tetraethyl orthosilicate is (35 - 45):(0.8 - 1.2):(1.5 - 1.8):(1 - 1.5). The concentration of the precursor in the precursor dispersion is 0.01 - 0.05 g / mL, the concentration of the aqueous solution of cetyltrimethylammonium bromide is 20 - 30 mg / mL, the concentration of the aqueous solution of sodium hydroxide is 5 - 8 mg / mL, and the concentration of the methanol solution of tetraethyl orthosilicate is 0.15 - 0.3 mL / mL;

[0021] (3) For SiOx The encapsulated precursor is heated to 300 - 350 °C in an inert gas atmosphere and held at this temperature for 2 - 3 h, then heated to 900 - 950 °C and held at this temperature for 4 - 6 h, and then cooled to room temperature to obtain a calcined material;

[0022] (4) The calcined material is washed with hydrofluoric acid at a temperature of 80 - 90 °C to remove unstable metals and SiO x , and then washed with water to remove hydrofluoric acid, and dried to obtain the product.

[0023] In the above technical solution, in step (4) of preparing the catalytic material with surface confinement effect, the concentration of the hydrofluoric acid is preferably 5 wt% - 15 wt%.

[0024] The principle of the method of the present invention is mainly as follows:

[0025] In the present invention, the SiO x -encapsulated precursor is calcined and washed with hydrofluoric acid to prepare a catalytic material with surface confinement effect derived from metal-organic framework (MOF). Due to the porous structure and large specific surface area of MOF, combined with the defects created during the calcination and hydrofluoric acid washing processes, the catalytic material has abundant adsorption sites, providing the possibility for the realization of the surface confinement effect. Based on the above characteristics, the catalytic material has good adsorption capacity for organic pollutants, thereby restricting the organic pollutants near the active sites of the catalytic material, amplifying the local concentration of the pollutants, forming a surface concentration effect, greatly shortening the migration distance of ROS, being conducive to improving the utilization rate of short-lived ROS, and further improving the removal efficiency of organic pollutants. At the same time, organic pollutants usually contain electron-rich functional groups (such as amino, nitro, hydroxyl, etc.), and these organic pollutants can act as modifiers. The adsorption energy of the catalytic material modified by organic pollutants to peroxymonosulfate changes, so that the electron transfer rate between the catalytic material and peroxymonosulfate increases, and thus the removal of organic pollutants can also be accelerated. From the perspective of thermodynamics, the enrichment of reactants and the reduction of reaction products can shift the reaction equilibrium to the right, thereby increasing the reaction rate of the degradation reaction. Therefore, the method of the present invention first uses the catalytic material with surface confinement effect to have an adsorption interaction with the organic pollutants in the wastewater, and then introduces peroxymonosulfate to initiate the degradation reaction of the organic pollutants, and has high degradation ability for organic pollutants.

[0026] Compared with the prior art, the technical solution provided by the present invention has the following beneficial technical effects:

[0027] 1. The present invention provides a method for removing refractory organic pollutants by using a catalytic material with surface confinement effect. In this method, the catalytic material with surface confinement effect is added to the wastewater containing refractory organic pollutants with a pH value of 3.0 - 9.0, and after sufficient adsorption, peroxymonosulfate is added to initiate the degradation reaction of the refractory organic pollutants in the wastewater. The present invention prepares a MOF-derived catalytic material with surface confinement effect by calcining and hydrofluoric acid washing the SiO x -encapsulated precursor. This catalytic material has abundant adsorption sites. On this basis, the organic pollutants are adsorbed by the catalytic material and confined near the active sites of the catalytic material, amplifying the local concentration of the pollutants and forming a surface concentration effect. Furthermore, the migration distance of ROS is greatly shortened, which is beneficial to improving the utilization rate of short-lived ROS and the removal efficiency of organic pollutants. At the same time, the interaction between the organic pollutants and the catalytic material can change the adsorption energy of the catalytic material for peroxymonosulfate and increase the electron transfer rate between the catalytic material and peroxymonosulfate, which can also accelerate the removal of organic pollutants. The above factors enable the method of the present invention to have excellent degradation ability and high degradation efficiency for organic pollutants containing electron-rich groups.

[0028] 2. The present invention modifies the catalytic material by using organic pollutants containing electron-rich groups to improve the electron transfer rate between the catalytic material and peroxymonosulfate. Compared with the prior art method of introducing heteroelements and pyrolytic doping modification, it has the obvious advantage of lower cost, and it is also simplified, which is beneficial to reducing the wastewater treatment cost and promoting the popularization and application of the wastewater treatment method.

[0029] 3. The present invention has confirmed through experiments that by the method of the present invention, first adding the catalytic material for adsorption and then adding peroxymonosulfate to initiate the degradation reaction of organic pollutants, under the conditions of different addition amounts of the catalytic material, the first-order reaction rate constant of the degradation reaction is at least twice the degradation reaction rate constant of the method of adding the catalytic material and peroxymonosulfate simultaneously. Using the method of the present invention, when adsorbing with 60 mg / L of the catalytic material first and then adding 0.4 g / L of peroxymonosulfate to degrade 20 μmol / L of sulfamethoxazole wastewater, 99% of the sulfamethoxazole in the wastewater can be removed within 5 minutes; while when degrading 20 μmol / L of sulfamethoxazole wastewater under the condition of adding 60 mg / L of the catalytic material and 0.4 g / L of peroxymonosulfate simultaneously, it takes 15 minutes to remove 99% of the sulfamethoxazole in the wastewater. At the same time, the method of the present invention also has excellent degradation effects on phenol and bisphenol A. It shows that the method of the present invention can effectively improve the degradation efficiency of organic pollutants containing electron-rich groups, which is beneficial to promoting the application of this heterogeneous catalytic material in practical engineering.

[0030] 4. The present invention has been verified through experiments that the method of the present invention has a wide applicable range of pH values for wastewater, and can achieve good removal of pollutants in wastewater with a pH value of 3.0 - 11.0. In particular, it has higher removal ability and efficiency for pollutants in wastewater with a pH value of 3.0 - 9.0.

[0031] 5. The present invention has been verified through experiments that the catalytic material used in the method of the present invention has excellent stability and recyclability. When the catalytic material is used to degrade sulfamethoxazole wastewater with a concentration of 20 μmol / L, after 4 cycles of recycling, sulfamethoxazole in the wastewater can be completely removed within 10 - 15 minutes after adding persulfate. After 5 cycles of recycling, within 15 minutes after adding persulfate, the removal rate of sulfamethoxazole is still as high as 90%. The excellent recyclability of the catalytic material is also beneficial to reducing the cost of wastewater treatment. Brief Description of the Drawings

[0032] Figure 1 are SEM pictures of the catalytic material prepared in Example 1 at different magnifications.

[0033] Figure 2 are TEM pictures of the catalytic material prepared in Example 1 at different magnifications.

[0034] Figure 3 are high-angle annular dark-field scanning electron microscope images of the catalytic material prepared in Example 1 and the distribution of Fe, C, N, and O elements on the surface of the catalytic material.

[0035] Figure 4 are the specific surface area test results of the catalytic material prepared in Example 1.

[0036] Figure 5 Figures (A) and (B) are the synchrotron radiation test and fitting analysis results of the catalytic material prepared in Example 1.

[0037] Figure 6 are the first-order reaction rate constant test results in Examples 2, 3 and Comparative Examples 1, 2.

[0038] Figure 7 are the density functional theory calculation results of Example 2 and Comparative Example 1.

[0039] Figure 8 are the test results of the degradation performance of simulated wastewater with different initial pH values in Example 4.

[0040] Figure 9 are the test results of the cyclic stability of the catalytic material in Example 5.

[0041] Figure 10It is the test result of the degradation performance of Example 6 on different organic pollutants. Detailed implementation mode

[0042] The following further illustrates the method for removing refractory organic pollutants by using the catalytic material with surface confinement effect provided by the present invention through examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Those skilled in the art still belong to the protection scope of the present invention when making some non-essential improvements and adjustments to the present invention according to the above invention content for specific implementation.

[0043] Example 1

[0044] In this example, the catalytic material with surface confinement effect is prepared as follows:

[0045] (1) Preparation of precursor

[0046] 5.0 g of Zn(NO3)2·6H2O and 2.1 g of Fe(acac)3 are added to 240 mL of methanol and dissolved thoroughly under ultrasonic conditions, denoted as solution A; 11.1 g of 2-methylimidazole is added to 240 mL of methanol and dissolved thoroughly under ultrasonic conditions, denoted as solution B. Solution B is quickly poured into solution A, stirred vigorously for 24 h, the solid product is separated by centrifugation, and the solid product is washed several times with methanol and water successively, and dried in vacuum at 80 °C to obtain the precursor.

[0047] (2) Preparation of SiO x Wrapped precursor

[0048] The precursor obtained in step (1) is dispersed in 360 mL of methanol, and then mixed with 360 mL of deionized water. 18 mL of a cetyltrimethylammonium bromide (CTAB) solution with a concentration of 25 mg / mL, 30 mL of a NaOH solution with a concentration of 6 mg / mL, and a methanol solution of tetraethyl orthosilicate (TEOS) (obtained by dissolving 3.6 mL of TEOS in 18 mL of methanol) are added to the above solution in sequence, stirred vigorously for 2 h, the solid product is separated by centrifugation, and washed several times with methanol and deionized water successively, and dried in vacuum at 80 °C to obtain the SiO x Wrapped precursor.

[0049] (3) Calcination

[0050] The SiO x Wrapped precursor is placed in a tubular furnace, and in an N2 atmosphere, it is first heated to 300 °C at a heating rate of 5 °C / min, held at this temperature for 2 h, then heated to 900 °C at a heating rate of 5 °C / min, held at this temperature for 5 h, and then cooled to room temperature naturally to obtain the calcined material.

[0051] (4) Washing

[0052] Wash the calcined material obtained in step (3) with hydrofluoric acid at 80 °C with a concentration of 10 wt% to remove unstable metals and SiO x , and then wash with deionized water to remove hydrofluoric acid, and dry in vacuum at 80 °C to obtain a catalytic material with surface confinement effect.

[0053] The catalytic material prepared in this example was analyzed by a combined SEM and TEM-EDS analyzer, and the results are as Figures 1 - 3 shown Figure 1 are SEM pictures of the catalytic material at different magnifications, Figure 2 are TEM pictures of the catalytic material at different magnifications. It can be seen from Figures 1 - 2 that the particle size of the catalytic material is in the range of 100 - 200 nm and has a mesoporous structure. Figure 3 is the high-angle annular dark-field scanning electron micrograph of the catalytic material and the distribution of Fe, C, N, and O elements on the surface of the catalytic material. It can be seen from Figure 3 that Fe, C, N, and O elements are uniformly distributed on the surface of the catalytic material. It was found by ICP test that the content of iron element in the catalytic material prepared in this example is 0.45 wt%. Figure 4 is the specific surface area test result of the catalytic material. The specific surface area of the catalytic material is as high as 1520.90 m 2 / g. Figure 5 is the synchrotron radiation test and fitting analysis result of the catalytic material prepared in Example 1. FeSA-MNC in the figure represents the catalytic material prepared in Example 1. It can be seen from Figure 5 that the Fe element in the catalytic material is monodispersed, there is no agglomeration, and Fe exists in the form of Fe-N4 coordination.

[0054] Example 2

[0055] In this example, the method for treating refractory wastewater described in the present invention is provided. Specifically, it uses a catalytic material with surface confinement effect to cooperate with advanced oxidation technology to treat refractory wastewater. The steps are as follows:

[0056] (1) Dissolve sulfamethoxazole (SMX, SMX contains an electron-rich amino group) in water to prepare a SMX solution with a concentration of 20 μmol / L, and use this solution as simulated wastewater.

[0057] (2) Add the catalytic material prepared in Example 1 to the simulated wastewater. The concentration of the catalytic material in the simulated wastewater is 60 mg / L. Let it stand for 30 min at a temperature of 30 ± 1 °C to adsorb SMX in the simulated wastewater onto the catalytic material. Then, add persulfate (PMS) to the simulated wastewater to initiate the degradation reaction of SMX. The amount of PMS added should make the concentration of PMS in the simulated wastewater 0.4 g / L.

[0058] After adding PMS, take out 1 mL of the reaction solution at regular intervals, filter it through a 0.22 μM membrane filter, and mix the filtered solution with 20 μL of a 0.2 mol / L Na2S2O3 solution to quench the free radicals and prevent the continuous degradation of pollutants. Then, use high-performance liquid chromatography to analyze the change in the concentration of SMX over time, and calculate the removal rate of SMX and the first-order reaction rate constant. It was found that 5 min after adding PMS, the removal rate of SMX in the simulated wastewater reached 99%, and complete removal of SMX could be achieved 10 min after adding PMS. The first-order reaction rate constant is as Figure 6 shown in the data of the "pre-adsorption - oxidation" group in

[0059] Comparative Example 1

[0060] The operation of this comparative example is basically the same as that of Example 2, except that the catalytic material prepared in Example 1 and PMS are added to the simulated wastewater simultaneously to initiate the degradation of PMS.

[0061] After adding the catalytic material and PMS, take out 1 mL of the reaction solution at regular intervals, filter it through a 0.22 μM membrane filter, and mix the filtered solution with 20 μL of a 0.2 mol / L Na2S2O3 solution to quench the free radicals and prevent the continuous degradation of pollutants. Then, use high-performance liquid chromatography to analyze the change in the concentration of SMX over time, and calculate the removal rate of SMX and the first-order reaction rate constant. It was found that 15 min after adding the catalytic material and PMS, the removal rate of sulfamethoxazole in the simulated wastewater could reach 99%. The first-order reaction rate constant is as Figure 6 shown in the data of the "direct oxidation" group in

[0062] Example 3

[0063] This example conducts a total of three groups of experiments. The operations of the three groups of experiments are basically the same as those of Example 2, except that: in the first group of experiments, the concentration of the catalytic material in the simulated wastewater is controlled at 20 mg / L; in the second group of experiments, the concentration of the catalytic material in the simulated wastewater is controlled at 40 mg / L; in the third group of experiments, the concentration of the catalytic material in the simulated wastewater is controlled at 80 mg / L.

[0064] After adding PMS, 1 mL of the reaction solution was taken out at regular intervals, filtered through a 0.22 μM filter membrane, and the filtered solution was mixed with 20 μL of a 0.2 mol / L Na2S2O3 solution to quench free radicals and prevent the continuous degradation of pollutants. Then, high-performance liquid chromatography was used to analyze the change in the concentration of SMX over time, and the first-order reaction rate constant was calculated. The results Figure 6 are shown in the data of the "pre-adsorption-oxidation" group in

[0065] Comparative Example 2

[0066] A total of three groups of experiments were carried out in this comparative example. The operations of the three groups of experiments were basically the same as those in Example 2, except that in the three groups of experiments, the catalytic material and PMS were added to the simulated wastewater simultaneously. In the first group of experiments, the concentration of the catalytic material in the simulated wastewater was controlled at 20 mg / L, in the second group of experiments, the concentration of the catalytic material in the simulated wastewater was controlled at 40 mg / L, and in the third group of experiments, the concentration of the catalytic material in the simulated wastewater was controlled at 80 mg / L.

[0067] After adding the catalytic material and PMS, 1 mL of the reaction solution was taken out at regular intervals, filtered through a 0.22 μM filter membrane, and the filtered solution was mixed with 20 μL of a 0.2 mol / L Na2S2O3 solution to quench free radicals and prevent the continuous degradation of pollutants. Then, high-performance liquid chromatography was used to analyze the change in the concentration of SMX over time, and the first-order reaction rate constant was calculated. The results are as Figure 6 shown in the data of the "direct oxidation" group in

[0068] From Figure 6 the data of the "pre-adsorption-oxidation" and "direct oxidation" groups in

[0069] it can be seen that compared with the schemes of directly adding the catalytic material and PMS simultaneously in Comparative Examples 1 and 2, the schemes in Examples 2 and 3, which first add the catalytic material to adsorb with the pollutants in the simulated wastewater and then add PMS to initiate the degradation reaction, have significantly higher first-order reaction rate constants. Figure 7 shown, where Figure (A) represents the calculation results when SMX containing an electron-rich group is not introduced, and Figure (B) represents the calculation results when SMX containing an electron-rich group is introduced. From Figure 7 it can be seen that the introduction of electron-rich group organic substances can accelerate the electron transfer rate between PMS and the catalytic material.

[0070] In the present invention, the catalytic material is first added for adsorption, and then PMS is added to initiate the degradation reaction. Under the conditions of different addition amounts of the catalytic material, the first-order reaction rate constant of the degradation reaction is at least twice that of the degradation reaction rate constant when the catalytic material and PMS are added simultaneously, indicating that the method of the present invention can significantly improve the degradation efficiency of pollutants. This is mainly because: before adding PMS, the catalytic material interacts with the pollutants (such as SMX) in the simulated wastewater, adsorbing the pollutants in the pore structure of the catalytic material, and using the functional groups carried by the pollutants themselves to in-situ modify the catalytic material. On the one hand, this can confine the pollutants near the active sites of the catalytic material, greatly shortening the migration distance of ROS, which is beneficial to improving the utilization rate of short-lived ROS, thereby improving the removal efficiency of pollutants. On the other hand, the adsorption energy of PMS by the catalytic material modified by pollutants changes, increasing the electron transfer rate between the catalytic material and PMS, and thus accelerating the removal of pollutants. The present invention effectively improves the removal rate of pollutants by using the surface confinement effect of the catalytic material, and this method can save the modification cost of the catalytic material.

[0071] Example 4

[0072] In this example, the influence of the initial pH value of the wastewater on the degradation effect of the method of the present invention was investigated.

[0073] A total of six groups of experiments were carried out in this example. The operations of the six groups of experiments were basically the same as those in Example 2, except that the initial pH values of the simulated wastewater were adjusted to 3.0, 5.0, 6.4, 7.0, 9.0, and 11.0 respectively for the six groups of experiments. After adding the catalytic material, 1 mL of the reaction solution was taken out at regular intervals, filtered through a 0.22 μM filter membrane, and the filtered solution was mixed with 20 μL of a Na2S2O3 solution with a concentration of 0.2 mol / L to quench free radicals and prevent the continuous degradation of pollutants. Then, the change in the concentration of SMX with time was analyzed by high-performance liquid chromatography.

[0074] The test results of the removal rates of SMX in the six groups of experiments are as Figure 8 shown, from Figure 8It can be seen that when the initial pH value of the simulated wastewater is 3.0 - 9.0, a high removal rate and removal efficiency of SMX can be achieved during both the adsorption stage and the degradation reaction stage. Complete removal of SMX can be realized within 5 - 10 minutes after adding PMS. However, when the initial pH value of the simulated wastewater increases to 11.0, the removal rate and removal efficiency of SMX during the adsorption stage decrease significantly, and the reaction rate during the degradation reaction stage also decreases, but complete removal of SMX can still be achieved within 15 minutes. This shows that the method of the present invention has a wide applicable range of pH values for wastewater and has good removal ability and removal effect on pollutants in wastewater with a pH value of 3.0 - 11.0, especially better removal ability and effect on pollutants in wastewater with a pH value of 3.0 - 9.0.

[0075] Example 5

[0076] In this example, the recycling performance of the catalytic material was tested.

[0077] (1) SMX was dissolved in water to prepare a 20 μmol / L SMX solution, and this solution was used as the simulated wastewater.

[0078] (2) The catalytic material prepared in Example 1 was added to the simulated wastewater, and the concentration of the catalytic material in the simulated wastewater was 60 mg / L. It was left standing for 30 minutes at a temperature of 30 ± 1 °C to adsorb SMX in the simulated wastewater onto the catalytic material. Then, PMS was added to the simulated wastewater to initiate the degradation reaction of SMX, and the added amount of PMS should make the concentration of PMS in the simulated wastewater 0.4 g / L. After reacting for 15 minutes after adding PMS, the catalytic material was separated by filtration.

[0079] After adding PMS, 1 mL of the reaction solution was taken out at regular intervals, filtered through a 0.22 μM filter membrane, and the filtered solution was mixed with 20 μL of a 0.2 mol / L Na2S2O3 solution to quench free radicals and prevent continuous degradation of pollutants. Then, the change in the concentration of SMX over time was analyzed by high performance liquid chromatography, and the ratio of the concentration of SMX (C) to the initial concentration of SMX (C0) was calculated.

[0080] (3) The catalytic material separated by filtration was put into fresh simulated wastewater (the simulated wastewater prepared in step (1)) under the conditions of step (2), and the operation of step (2) was repeated.

[0081] (3) The operation of step (3) was repeated until 5 wastewater treatment cycles were completed, that is, the catalytic material was reused 5 times.

[0082] The removal rate of SMX in this example during 5 wastewater treatment cycles is as Figure 9 shown, as Figure 9It can be seen that after 5 wastewater treatment cycles, the removal efficiency of the method of the present invention for SMX did not show a significant decrease. In the 5th wastewater treatment cycle, within 15 minutes after adding PMS, the removal rate of SMX was still as high as 93%. In the previous 4 wastewater treatment cycles, within 15 minutes after adding PMS, the removal rate of SMX basically remained at 100%. The above experimental results illustrate that the catalytic material has excellent stability and recyclability.

[0083] Example 6

[0084] In this example, the method provided by the present invention was used to degrade different organic pollutants.

[0085] A total of six groups of experiments were carried out in this example. The operations of the six groups of experiments were basically the same as those in Example 2, except that different pollutants (SMX, phenol, bisphenol A, benzoic acid, nitrobenzene, atrazine) were used to prepare simulated wastewater in the six groups of experiments, and the concentration of pollutants in the simulated wastewater was 20 μmol / L. After adding the catalytic material to the simulated wastewater, it was first adsorbed for 30 minutes, and then PMS was added for a 15-minute degradation reaction. After adding the catalytic material, samples were taken at regular intervals and the concentration was measured using a high-performance liquid chromatograph to calculate the degradation amount, adsorption amount and remaining amount of the pollutants. The results are as Figure 9 shown.

[0086] It can be seen from Figure 10 that the method of the present invention has good removal effects on electron-rich pollutants (pollutants containing electron-rich groups) such as SMX, phenol and bisphenol A, but relatively poor removal effects on electron-deficient pollutants such as benzoic acid, nitrobenzene and atrazine. This is mainly because electron-rich pollutants containing amino or hydroxyl groups can change the electronic structure of the catalytic center, thereby promoting the removal of pollutants.

Claims

1. A method for removing refractory organic pollutants using a catalytic material with surface confinement effect, characterized in that, It includes the following steps: Add a catalytic material with surface confinement effect into the wastewater containing refractory organic pollutants with a pH value of 3.0 - 9.0, adsorb for at least 20 min, then add persulfate to initiate the degradation reaction of the refractory organic pollutants in the wastewater. The wastewater treatment is completed 5 - 30 min after adding persulfate; The catalytic material with surface confinement effect has a pore structure and is composed of Fe, C, N, and O elements. The Fe element is in a monodispersed state in the catalytic material in the coordination form of Fe-N4, and the content of the Fe element in the catalytic material is 0.4 wt% - 1.5 wt%. The preparation method of the catalytic material with surface confinement effect is as follows: (1) Dissolve Zn(NO3)2·6H2O and Fe(acac)3 in methanol to obtain solution A. The concentration of Zn(NO3)2·6H2O in solution A is 0.02 - 0.03 g / mL, and the concentration of Fe(acac)3 is 0.008 - 0.01 g / mL; dissolve 2-methylimidazole in methanol to obtain solution B. The concentration of 2-methylimidazole in solution B is 0.04 - 0.06 g / mL; Mix solution A and solution B and stir for 20 - 30 h, separate the solid product, and wash to obtain the precursor; in the mixed solution obtained after mixing solution A and solution B, the mass ratio of Zn(NO3)2·6H2O, Fe(acac)3, and 2-methylimidazole is (5 - 7.5):(2 - 2.5):(10 - 15); (2) Disperse the precursor in methanol, then add water to obtain a precursor dispersion. Add an aqueous solution of cetyltrimethylammonium bromide, an aqueous solution of sodium hydroxide, and a methanol solution of tetraethyl orthosilicate to the precursor dispersion, stir for 2 - 3 h, separate the solid product, wash, and dry to obtain the SiO x -coated precursor; The volume ratio of the precursor dispersion, cetyltrimethylammonium bromide aqueous solution, sodium hydroxide aqueous solution, and tetraethyl orthosilicate methanol solution is (35 - 45):(0.8 - 1.2):(1.5 - 1.8):(1 - 1.5). The concentration of the precursor in the precursor dispersion is 0.01 - 0.05 g / mL, the concentration of the cetyltrimethylammonium bromide aqueous solution is 20 - 30 mg / mL, the concentration of the sodium hydroxide aqueous solution is 5 - 8 mg / mL, and the concentration of the tetraethyl orthosilicate methanol solution is 0.15 - 0.3 mL / mL; (3)Heat the SiO x -coated precursor to 300 - 350 °C in an inert gas atmosphere and hold at this temperature for 2 - 3 h, then heat to 900 - 950 °C and hold at this temperature for 4 - 6 h, and cool to room temperature to obtain the calcined material; (4) Wash the calcined material with hydrofluoric acid at a temperature of 80 - 90 °C to remove unstable metals and SiO x , then wash with water to remove hydrofluoric acid, and dry to obtain the product.

2. The method for removing refractory organic pollutants using a catalytic material with surface confinement effect according to claim 1, characterized in that, The refractory organic pollutant is an organic substance containing an electron-rich group.

3. The method for removing refractory organic pollutants using a catalytic material with surface confinement effect according to claim 2, characterized in that, The electron-rich group in the organic substance containing an electron-rich group includes at least one of an amino group and a hydroxyl group.

4. The method for removing refractory organic pollutants using a catalytic material with surface confinement effect according to any one of claims 1 to 3, characterized in that, The addition amount of the catalytic material with surface confinement effect in the wastewater is 20 - 200 mg per liter of wastewater.

5. The method for removing refractory organic pollutants using a catalytic material with surface confinement effect according to any one of claims 1 to 3, characterized in that, The addition amount of persulfate in the wastewater should make the concentration of persulfate in the wastewater 0.4 - 1.0 g / L.

6. The method for removing refractory organic pollutants using a catalytic material with surface confinement effect according to any one of claims 1 to 3, characterized in that, Add the catalytic material with surface confinement effect into the wastewater containing refractory organic pollutants, and add persulfate after adsorbing for 20 - 60 min.

7. The method for removing refractory organic pollutants using a catalytic material with surface confinement effect according to any one of claims 1 to 3, characterized in that, The particle size of the catalytic material with surface confinement effect is in the nanometer range.

8. The method for removing refractory organic pollutants using a catalytic material with surface confinement effect according to any one of claims 1 to 3, characterized in that, After completing the treatment of a batch of wastewater, recycle the catalytic material with surface confinement effect for the treatment of the next batch of wastewater.

9. The method for removing refractory organic pollutants using a catalytic material with surface confinement effect according to claim 1, characterized in that, The concentration of hydrofluoric acid in step (4) is 5 wt% - 15 wt%.

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