Method for removing trace or trace N-nitrosodimethylamine in water by metal coordination polymer catalytic membrane

Abstract

The invention discloses a method for removing trace or trace N-nitrosodimethylamine in water by using a self-assembled metal coordination polymer catalytic membrane. The self-assembled metal coordination polymer catalytic membrane material is added into a reaction flask of an N-nitrosodimethylamine solution subjected to nitrogen deoxidation treatment, the amount of loaded zero-valent iron is 25.7 mg / g to 171.4 mg / g, and the initial concentration of N-nitrosodimethylamine is 47.4 mu g / L to 196.5 mu g / L. The reaction bottle is sealed and then placed on a multi-point intelligent magnetic stirrer for magnetic stirring reaction, the rotating speed is 200 rpm, the temperature is 25 DEG C, the pH is 2.5-9.5, and stirring is conducted for 1.5 h. A carboxylated high-molecular polyacrylonitrile membrane is used as a base material, poly (diallyldimethylammonium chloride) polycation and polyacrylic acid polyanion electrolyte are assembled on the surface of the base membrane by adopting an electrostatic self-assembly technology, and the high-molecular self-assembled composite membrane with a large number of carboxyl groups is prepared. And preparing the self-assembled metal coordination polymer catalytic membrane through a metal-polycation electrolyte coordination technology and a classical liquid phase reduction method. The content of iron in the self-assembly metal coordination polymer catalytic membrane and the thickness of a surface functional layer are conveniently and effectively regulated and controlled by controlling the number of assembly layers, the concentration of iron ions in coordination reaction, the pH value of the solution and the like, high activity and stability are kept, and the method has the advantages of being simple in preparation process, low in cost, high in removal rate and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for removing trace or trace N-nitrosodimethylamine in water, belonging to water purification treatment process. BACKGROUND

[0002] N-nitrosodimethylamine is a disinfection by-product produced after chlorination disinfection treatment. N-nitrosodimethylamine is one of the typical N-nitrosamines with potential strong carcinogenicity. The USEPA determines N-nitrosodimethylamine as a B2 carcinogen, and the unit carcinogenic risk concentration is 0.7 ng·L -1 , and the carcinogenic risk coefficient reaches 10 -6 . EPA has listed it as a priority control pollutant, and the IRIS recommends that the concentration of N-nitrosodimethylamine should be lower than 7 ng·L -1 . However, the existing water treatment process cannot meet the standard of N-nitrosodimethylamine, so it is urgent to treat N-nitrosodimethylamine in drinking water.

[0003] N-nitrosodimethylamine is a semi-volatile yellow oily liquid, which is not easy to be bio-enriched and particle-adsorbed, and can enter groundwater through soil and sediment. At present, the methods for reducing N-nitrosodimethylamine in drinking water mainly include physical methods such as activated carbon adsorption, silicon dioxide adsorption, resin adsorption, and zeolite adsorption, reverse osmosis method, photolysis technology such as ultraviolet irradiation method, application of advanced oxidation technology such as ozone, hydrogen peroxide, and Fenton reagent, biological degradation method, and metal reduction method such as zinc and iron. However, these methods for removing N-nitrosodimethylamine have some shortcomings. N-nitrosodimethylamine has high water solubility and low Henry's law constant, and the treatment effect of conventional physical adsorption method and reverse osmosis method is poor; the ultraviolet irradiation method has high energy consumption and high cost; although the advanced oxidation technology can efficiently degrade most organic matters, the removal efficiency of N-nitrosodimethylamine is limited by hydroxyl radicals; the reaction time of the biological degradation method is relatively long, which is much higher than the time required by photolysis and advanced oxidation.

[0004] Zero-valent iron is the most inexpensive iron-based source in environmental materials. As a new type of catalyst material, it has superior adsorption performance due to its large specific surface area and surface energy, and its unique surface effect and small size effect can improve its reaction activity and degradation efficiency. Years of research has shown that zero-valent iron has different degrees of removal effect on various organic, inorganic and heavy metal pollutants. Compared with the above several methods for removing N-nitrosodimethylamine, zero-valent iron has the advantages of high efficiency, low energy consumption, and easy control, and is a drinking water purification process technology with broad development prospects.

[0005] In order to overcome the limitations of zero-valent iron in environmental water remediation, such as easy passivation, easy aggregation and difficult recovery, the application loads active metal zero-valent iron particles on a polyacrylonitrile film carrier with a large specific surface area through static layer-by-layer self-assembly and metal-poly-cation electrolyte coordination technology, so as to remove trace and trace N-nitrosodimethylamine in water. SUMMARY

[0006] The application is directed to the drawbacks of the above various methods, and proposes a novel method for removing trace and trace N-nitrosodimethylamine in water by using self-assembled metal coordination polymer catalytic membrane materials. The method has the advantages of inexpensive materials, simple preparation, no secondary pollution, fast removal rate and the like. A carboxylated high molecular polyacrylonitrile film is used as a base material, and poly-diallyl dimethyl ammonium chloride polycation and poly-acrylic acid polyanion electrolyte are assembled on the surface of the base film by using electrostatic self-assembly technology, so as to prepare a high molecular self-assembled composite film with a large number of carboxyl groups. Then, the self-assembled metal coordination polymer catalytic membrane is prepared through metal-poly-cation electrolyte coordination technology and classical liquid phase reduction method.

[0007] The content of iron in the self-assembled metal coordination polymer catalytic membrane and the thickness of the surface functional layer can be conveniently and effectively controlled by controlling the number of assembled layers, the concentration of iron ions in the coordination reaction and the solution pH. In an aqueous solution, the self-assembled metal coordination polymer catalytic membrane has strong reduction performance, and can rapidly undergo an oxidation-reduction reaction with N-nitrosodimethylamine, so as to reduce N-nitrosodimethylamine to dimethylamine, thereby achieving the purpose of removing N-nitrosodimethylamine from water.

[0008] The self-assembled metal coordination polymer catalytic membrane is placed in an aqueous solution containing a certain amount of N-nitrosodimethylamine and treated by nitrogen deoxidation. The zero-valent iron fixed on the surface of the composite membrane rapidly undergoes an oxidation-reduction reaction with N-nitrosodimethylamine, and N-nitrosodimethylamine is reduced to dimethylamine, so that N-nitrosodimethylamine in drinking water is removed.

[0009] In the reaction bottle of N-nitrosodimethylamine solution treated by nitrogen deoxidation, the self-assembled metal coordination polymer catalytic membrane material is added, wherein the amount of loaded zero-valent iron is 25.7 mg / g to 171.4 mg / g, and the initial concentration of N-nitrosodimethylamine is 47.4 μg / L to 196.5 μg / L. After the reaction bottle is sealed, it is placed on a multi-point intelligent magnetic stirrer for magnetic stirring reaction, the stirring speed is 200 rpm, the temperature is 25°C, the pH is in the range of 2.5 to 9.5, and the stirring time is 1.5 h.

[0010] The beneficial effects of the application are shown in the following aspects:

[0011] 1.Using electrostatic self-assembly technology, polydiallyldimethylammonium chloride (PDADMAC) polycation and polyacrylic acid (PAA) polyanion electrolyte are assembled on the surface of the base film to prepare a high-molecular self-assembled composite film with a large number of carboxyl groups. Then, through metal-polycation electrolyte coordination technology and classical liquid-phase reduction method, a (Fe0-PDADMAC / PAA)n composite catalytic film is prepared. The obtained film material can not only use coordination complexation to fix the precursor (Fe2+) of Fe0 on the surface of the film carrier to prepare a self-assembled metal coordination polymer catalytic film, but also can fix the Fe ion generated after Fe0 releases electrons in the reduction of N-nitrosodi-methylamine on the film surface, slow down or prevent the generation of iron oxide, avoid the generation of secondary pollution, and improve the utilization efficiency of Fe0.

[0012] 2.N-nitrosodi-methylamine reacts with zero-valent iron on the surface of the film carrier, and the reaction kinetics is excellent in the removal of N-nitrosodi-methylamine.

[0013] 3.In the process of reducing N-nitrosodi-methylamine, the amount of residual Fe ion in water is extremely low, most of the Fe ion is fixed on the composite film by coordination with the carboxyl group on the film surface. The content of iron ion in the solution is <0.1 mg / L, which meets the "Drinking Water Health Standards (GB5749-2006)".

[0014] 4.When the temperature of the reaction solution is in the range of 25-45℃, the removal effect does not change significantly with the temperature, and this material can be effectively used for the removal of N-nitrosodi-methylamine in water under various climate temperature conditions.

[0015] 5.When several common inorganic anions such as NO3 - , HCO3 - , Cl - , SO4 2- exist in the reaction solution, the removal of N-nitrosodi-methylamine is not affected, and this material can be effectively used for the removal of N-nitrosodi-methylamine in water containing impurities.

[0016] 6.The self-assembled metal coordination polymer catalytic film has a significant effect on the removal of N-nitrosodi-methylamine, high removal rate, fast speed, technical feasibility, simple operation, easy-to-obtain material, good economic and environmental benefits, so it can be applied to actual water treatment. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Correspondence between the number of layers of the self-assembled metal coordination polymer catalytic film and the concentration of N-nitrosodi-methylamine

[0018] Figure 2Correspondence between different N-nitrosodimethylamine initial concentrations and N-nitrosodimethylamine concentrations

[0019] Figure 3 Correspondence between different solution initial pH values and N-nitrosodimethylamine DETAILED DESCRIPTION

[0020] Example 1

[0021] This example verifies the effect of Fe loading on self-assembled metal coordination polymer catalytic membranes on N-nitrosodimethylamine reduction reactions. 0

[0022] A 50ml ground conical flask equipped with a rubber stopper was used to add the N-nitrosodimethylamine reaction solution with a concentration of 150μg / L, which had been prepared. The reaction was performed on a multi-point intelligent magnetic stirrer at a reaction temperature of 25℃ and a rotation speed of 200r / min. The reaction solution was subjected to N2deoxidation treatment.

[0023] The initial pH value of the reaction solution was adjusted to 6.5, and 0.42g of self-assembled metal coordination polymer catalytic membranes with assembly layers of 1, 3, 5, 7, and 9 were added, respectively. The iron loading on the membrane surface was 25.7mg / g, 77.6mg / g, 114mg / g, 151.7mg / g, and 171.4mg / g, respectively, as determined by the o-phenanthroline method. The reaction time was 1.5h. The concentration of N-nitrosodimethylamine was detected using a Waters e2695 type high performance liquid chromatograph, and the removal efficiency was calculated to be 11.4%, 27.45%, 46%, 59.2%, and 65.8%, respectively. The total soluble iron in the final reaction solution was determined to be 0.043mg / L, 0.032mg / L, 0.08mg / L, 0.084mg / L, and 0.07mg / L, respectively, by inductively coupled plasma atomic emission spectrometry (ICP-AES), which is less than 0.1mg / L. The content of the detected total soluble iron in the final reaction solution meets the requirements of the Standards for Drinking Water Health (GB5749-2006). Therefore, the present application can effectively prevent the generation of secondary iron ion pollution.

[0024] Therefore, the removal rate of N-nitrosodimethylamine increases with the increase of the assembly layer number of the self-assembled metal coordination polymer catalytic membrane, and the reaction tends to be stable within 1.5h, indicating that the self-assembled metal coordination polymer catalytic membrane is fast and efficient in removing N-nitrosodimethylamine, as shown in the accompanying Figure 1

[0025] Example 2

[0026] This example verifies the effect of different N-nitrosodimethylamine initial concentrations on N-nitrosodimethylamine reduction reactions. ​​

[0027] The N-nitrosodimethylamine reaction solution with the concentration of 47.3 μg / L, 97.7 μg / L, 150.2 μg / L and 196.5 μg / L was prepared. The N-nitrosodimethylamine reaction solution with the four concentrations was added into four 50 ml conical flasks with rubber stoppers, respectively. The reaction solution was treated by N2 deoxidation. The magnetic stirring reaction was carried out on a multi-point intelligent magnetic stirrer, and the reaction temperature was 25°C and the rotation speed was 200 r / min.

[0028] The initial pH value of the reaction solution was adjusted to 6.5. The self-assembled metal coordination polymer catalytic membrane with the assembly layer number of 5 was added into the reaction flask at 0.42 g, and the zero-valent iron content on the surface of the composite membrane was 114 mg / g. The reaction time was 1.5 h. The concentration of N-nitrosodimethylamine was detected by using a Waterse2695 type high performance liquid chromatograph, and the removal efficiency was calculated to be 45.89%, 45.33%, 46% and 46.7%, respectively. The total soluble iron in the final reaction solution was determined by using inductively coupled plasma emission spectrometry (ICP-AES), and the content was 0.021 mg / L, 0.032 mg / L, 0.071 mg / L and 0.084 mg / L < 0.1 mg / L. The content of the total soluble iron detected in the final reaction solution can meet the requirements of the Standards for Drinking Water Health (GB5749-2006).

[0029] Therefore, the removal rate of the self-assembled metal coordination polymer catalytic membrane for N-nitrosodimethylamine has little relationship with the initial concentration of N-nitrosodimethylamine. As shown in the following table. Figure 2

[0030] Example 3:

[0031] This example is to verify the influence of different solution initial pH values on the reduction reaction of N-nitrosodimethylamine.

[0032] The 50 ml conical flask with rubber stopper was used to add the N-nitrosodimethylamine reaction solution with the concentration of 150 μg / L, and the magnetic stirring reaction was carried out on a multi-point intelligent magnetic stirrer, and the reaction temperature was 25°C and the rotation speed was 200 r / min. The reaction solution was treated by N2 deoxidation.

[0033] ​The initial pH of the reaction solution was adjusted to 2.52, 3.51, 5.1, 6.5, 8.51, and 9.49, respectively. The self-assembled metal coordination polymer catalytic membrane with 5 layers was added to the reaction bottle at a dosage of 0.42 g, and the content of zero-valent iron on the surface of the composite membrane was 114 mg / g. The reaction time was 1.5 h. The concentration of N-nitrosodimethylamine was detected by Waters e2695 high-performance liquid chromatograph, and the removal efficiency was calculated to be 40.1%, 41.2%, 42.5%, 46%, and 38.7%, respectively. The total dissolved iron in the final reaction solution was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) to be 0.098 mg / L, 0.084 mg / L, 0.09 mg / L, 0.072 mg / L, and 0.07 mg / L, which was less than 0.1 mg / L. The content of total dissolved iron detected in the final reaction solution met the requirements of the Standards for Drinking Water Health (GB 5749-2006). Therefore, the investigation of the effect of different pH values on the removal of N-nitrosodimethylamine showed that the removal rate under neutral conditions was significantly higher than that under acidic and alkaline conditions. It was shown in FIG. 1 that the pH value had a great influence on the removal of N-nitrosodimethylamine by the self-assembled metal coordination polymer catalytic membrane. Figure 3

[0034] Example 4

[0035] This example is to verify the influence of different reaction temperatures on the reduction reaction of N-nitrosodimethylamine.

[0036] A 50 ml ground conical flask equipped with a rubber stopper was used to add the N-nitrosodimethylamine reaction solution with a concentration of 150 μg / L. The reaction temperature of the multi-point intelligent magnetic stirrer was set to 25°C, 35°C, and 45°C, respectively, and the magnetic stirring reaction was carried out at a speed of 200 r / min. The reaction solution was treated by passing N2 to remove oxygen.

[0037] ​The initial pH of the reaction solution was adjusted to 6.5. 0.42 g of a self-assembled metal coordination polymer catalytic membrane with 5 assembled layers was added to the reaction flask. The concentration of zero-valent iron on the surface of the composite membrane was 114 mg / g. The reaction time was 1.5 h. The concentration of N-nitrosodimethylamine was detected using a Waterse2695 high-performance liquid chromatograph, and the removal efficiencies were calculated to be 46%, 45.6%, and 44%, respectively. Inductively coupled plasma atomic emission spectrometry (ICP-AES) determined the total dissolved iron in the final reaction solution to be 0.084 mg / L, 0.075 mg / L, and 0.087 mg / L (<0.1 mg / L). The total dissolved iron content detected in the final reaction solution met the requirements of the "Standards for Drinking Water Quality" (GB5749-2006). Therefore, the study of the effect of different reaction temperatures on the removal of N-nitrosodimethylamine showed that temperature had no effect on the removal of N-nitrosodimethylamine by the self-assembled metal coordination polymer catalytic membrane.

[0038] Example 5:

[0039] This example verifies the presence of inorganic NO3 in the solution. - HCO3 - Cl - SO4 2- The effect of ions on the reduction of N-nitrosodimethylamine by a self-assembled metal coordination polymer catalytic membrane.

[0040] The prepared N-nitrosodimethylamine reaction solution with a concentration of 150 μg / L was added to a 50 ml ground glass conical flask equipped with a rubber stopper. The reaction was carried out by magnetic stirring on a multi-point intelligent magnetic stirrer at a temperature of 25°C and a speed of 200 r / min. The reaction solution was then treated with N2 for deoxygenation.

[0041] 0.42 g of a self-assembled metal coordination polymer catalytic membrane with 5 assembled layers was added to the reaction flask. The concentration of zero-valent iron on the surface of the composite membrane was 114 mg / g, and the reaction time was 1.5 h. The concentration of N-nitrosodimethylamine was detected using a Waters e2695 high-performance liquid chromatograph, and the removal efficiency was calculated. Compared with the reaction system without the addition of inorganic ions, the final removal efficiency of N-nitrosodimethylamine was >40%. Several inorganic ions present in the solution, Cl... - SO4 2- It has virtually no impact on the final removal rate of N-nitrosodimethylamine, NO3. - HCO3 - It slightly reduced the removal rate of N-nitrosodimethylamine, but did not affect the final removal rate.

[0042] Analysis of Results in the Attached Figures

[0043] 1. Appendix Figure 1Results analysis

[0044] In the attached Figure 1 , when the self-assembly metal coordination polymer catalytic membrane 0.42 g is added, the assembly layer number is 1, 3, 5, 7, 9, the reaction speed of the assembly layer number 9 with N-nitrosodiethylamine is the fastest, the reaction speed of the assembly layer number 7, 5 is the second, and the reaction of the least assembly layer number with N-nitrosodiethylamine is the slowest. The results show that the increase of the assembly layer number can enhance the removal effect of N-nitrosodiethylamine. It is known by using o-phenanthroline to measure iron that the loadings of iron on the surfaces of the membranes with the assembly layer number of 1, 3, 5, 7, 9 are 25.7 mg / g, 77.6 mg / g, 114 mg / g, 151.7 mg / g and 171.4 mg / g respectively. Further analysis shows that the larger the assembly layer number is, the finer the distribution of zero-valent iron on the membrane is, and the more active sites for reaction will be. It is the increase of the active sites of zero-valent iron that leads to the increase of the removal rate.

[0045] 2、attached Figure 2 Results analysis

[0046] In the attached Figure 2 , when the initial concentration of N-nitrosodiethylamine is 47.3 μg·L -1 , 97.7 μg·L -1 , 150.2 μg·L -1 and 196.5 μg·L -1 , the maximum removal rates of N-nitrosodiethylamine by the self-assembly metal coordination polymer catalytic membrane with the assembly layer number of 5 are 45.89%, 45.35%, 46% and 46.7% respectively. It can be seen that the removal rate of N-nitrosodiethylamine by the self-assembly metal coordination polymer catalytic membrane has little relationship with the initial concentration of N-nitrosodiethylamine. With the progress of the reaction, the active sites of zero-valent iron gradually decrease, so the reduction capacity of the self-assembly metal coordination polymer catalytic membrane for N-nitrosodiethylamine is limited.

[0047] 3、attached Figure 3 Results analysis

[0048] In the attached Figure 3In the experiment, with the initial pH of N-nitrosodimethylamine increasing from 2.52 to 6.5, the removal rate of N-nitrosodimethylamine by the self-assembled metal coordination polymer catalytic membrane reached the peak. Continue to increase the pH value, the removal rate decreased, and when the pH increased to 9.49, the removal rate of N-nitrosodimethylamine was the smallest. It showed that the redox reaction between the self-assembled metal coordination polymer catalytic membrane and N-nitrosodimethylamine was greatly affected by pH, and both acid and alkali had certain inhibitory effect on the reaction. Further proved that the reduction reaction of N-nitrosodimethylamine was better under neutral conditions, and the reaction condition was mild. Therefore, in the actual water treatment, the solution pH should be 6.5 when applying this method to remove N-nitrosodimethylamine, so as to achieve good removal effect.

Claims

1. A method for removing trace or ultratrace amounts of N-nitrosodimethylamine from water using a self-assembled metal-coordination polymer catalytic membrane, characterized in that: The self-assembled metal coordination polymer catalytic membrane (Fe 0 -PDADMAC / PAA) n When added to water and reacted with N-nitrosodimethylamine, the material cleaves the N-N bond of N-nitrosodimethylamine, reducing it to dimethylamine, thereby effecting removal of N-nitrosodimethylamine.

2. The self-assembled metallo-coordination polymer catalytic membrane (Fe 0 -PDADMAC / PAA) n Process for the removal of N-nitrosodimethylamine from water, characterized in that The iron loading in the material is 25.7mg / g-171.4mg / g.

3. The self-assembled metallo-coordination polymer catalytic membrane (Fe 0 -PDADMAC / PAA) n Process for the removal of N-nitrosodimethylamine from water, characterized in that The pH value of the N-nitrosodi-methylamine aqueous solution is adjusted to the range of 2.5-9.

5.

4. The self-assembled metallo-coordination polymer catalytic membrane (Fe 0 -PDADMAC / PAA) n Process for the removal of N-nitrosodimethylamine from water, characterized in that The initial concentration of N-nitrosodi-methylamine is 47.4μg / L-196.5μg / L.

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