Method for degrading wastewater pollutants by adsorption coupling advanced oxidation method

Abstract

The invention provides a method for degrading wastewater pollutants by an adsorption coupling advanced oxidation method, and the prepared composite membrane can adsorb dye in dye liquor, so that the dye in the dye liquor is enriched, and part of dye molecules are removed; meanwhile, metal ions in the composite membrane serve as catalytic active sites, free radicals with extremely high oxidability are generated on a reaction interface by catalyzing an oxidizing agent, dye molecules adsorbed by the composite membrane are subjected to oxidative degradation, and pollutants are removed. Compared with other powder type adsorbents, the fiber membrane is used as the carrier, the carrier can solve the problems that the powder type adsorbents are agglomerated and difficult to recycle, and the carrier can conduct strong interaction with a catalyst through surface functional groups to guide the transfer path of electrons, so that the catalytic oxidation activity is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of pollutant treatment, and in particular to a method for degrading wastewater pollutants by adsorption coupling with advanced oxidation method. Background Art

[0002] The printing and dyeing industry has become a key and difficult area for industrial wastewater treatment due to its complex processes such as fabric pretreatment, dyeing and printing, and post-finishing. Printing and dyeing wastewater has a deep color and a high organic matter content, and cannot be naturally degraded by the self-repair ability of the environment.

[0003] At present, the main methods for treating wastewater pollutants are physical methods and chemical methods, etc. The adsorption method removes pollutants by fixing them in the hollow structure of the adsorbent. Physical adsorption only aggregates pollutants by transferring them to other stages, and the pollutants are not completely eliminated and destroyed. General chemical methods have poor adaptability to sewage and it is difficult to achieve ideal treatment effects. Summary of the Invention

[0004] In view of the above problems, a method for degrading wastewater pollutants by adsorption coupling with advanced oxidation method is proposed to overcome or at least partially solve the above problems, including: Modifying an ultrafiltration membrane with sodium hydroxide to form a modified membrane; Immersing the modified membrane in a methanol solution containing cobalt nitrate hexahydrate and stirring to form a first solution, and then pouring a methanol solution containing 2-methylimidazole into the first solution and stirring to form a second solution; Transferring the second solution to an ultrasonic cleaner, treating it for a preset time, then taking out the modified membrane, cleaning the modified membrane with anhydrous methanol and deionized water, and drying to obtain a composite membrane; Putting the composite membrane into a dye solution and adding an oxidant to react for a certain period of time.

[0005] Optionally, the ultrafiltration membrane is any one of a polyester membrane, a polypropylene membrane, and a polyacrylonitrile membrane.

[0006] Optionally, modifying the ultrafiltration membrane with sodium hydroxide to form a modified membrane includes: Adding deionized water and sodium hydroxide into a conical flask in sequence, stirring evenly at room temperature for 20 minutes, then adding a 3×3 cm polyacrylonitrile membrane that has been cut into the conical flask; then transferring the conical flask to a shaking sample dyeing machine, continuously shaking for 1 hour under the condition that the target temperature is 65 °C, taking out the sample membrane after the reaction, washing the sample membrane several times with deionized water to remove impurities and unreacted solvents on the surface, and drying at 40 °C for 6 hours to obtain a modified membrane; wherein, the molar ratio of deionized water to sodium hydroxide is 50:1.

[0007] Optionally, immerse the modified membrane in a methanol solution containing cobalt nitrate hexahydrate and stir to form a first solution. Then pour a methanol solution containing dimethylimidazole into the first solution and stir to form a second solution, including: Dissolve cobalt nitrate hexahydrate in anhydrous methanol and stir for 30 minutes to form a base solution. Then add the modified membrane to the base solution and stir for 30 minutes to form a first solution; Dissolve dimethylimidazole in anhydrous methanol and stir for 30 minutes, then pour it into the first solution to form a mixed solution. Stir the mixed solution for 30 minutes to form a second solution; Wherein, the molar mass ratio of cobalt nitrate hexahydrate to anhydrous methanol is 1:364; the molar mass ratio of dimethylimidazole to anhydrous methanol is 1:87.

[0008] Optionally, transfer the second solution to an ultrasonic cleaner and process it for a preset time, then take out the modified membrane, wash the modified membrane with anhydrous methanol and deionized water, and dry it to obtain a composite membrane, including: Transfer the second solution to an ultrasonic cleaner and process it for 30 minutes, then take out the modified membrane. Wash the surface of the modified membrane several times with anhydrous methanol solution and deionized water respectively, and dry it at 40 °C for 6 hours to obtain a composite membrane.

[0009] Optionally, the oxidant is any one of hydrogen peroxide, persulfate and persulfate.

[0010] Optionally, the mass ratio of the oxidant to the dye solution is 1:12500.

[0011] Optionally, the reaction time for putting the composite membrane into the dye solution and adding the oxidant is 5 to 40 minutes.

[0012] Optionally, before reacting for a certain time after adding the oxidant, it also includes: adjusting the pH value of the dye solution to 3.

[0013] Optionally, the method further includes: after reacting for a certain time after adding the oxidant, take out the composite membrane from the dye solution, transfer it to deionized water, and at the same time clean the composite membrane with ultrasonic waves, and then separate and dry the composite membrane. The embodiments of the present invention have the following advantages: The composite membrane prepared by the present invention can adsorb the dye in the dye solution, realize the enrichment of the dye in the dye solution, and remove some dye molecules; at the same time, use the metal ions in the composite membrane as catalytic active sites to catalyze the oxidant to generate extremely strong oxidizing free radicals at the reaction interface, and oxidize and degrade the dye molecules adsorbed by the composite membrane to realize the removal of pollutants. Compared with other powder-type adsorbents, the present invention uses a fiber membrane as a carrier, which can not only solve the problems of agglomeration and difficult recovery of powder-type adsorbents, but also can have a strong interaction with the catalyst through surface functional groups, guide the electron transfer path, and thus improve the catalytic oxidation activity. Brief Description of the Drawings

[0014] In order to more clearly illustrate the technical solutions of the present invention, the drawings required for the description of the present invention will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0015] Figure 1 is a flowchart of a method for degrading wastewater pollutants by an adsorption-coupled advanced oxidation process provided by an embodiment of the present invention; Figure 2 is a flowchart for preparing a composite membrane provided by an embodiment of the present invention. Detailed Embodiments

[0016] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the drawings and specific embodiments. Obviously, the described embodiments are some embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0017] Referring to Figure 1 , a flowchart of a method for degrading wastewater pollutants by an adsorption-coupled advanced oxidation process provided by an embodiment of the present invention is shown, which may specifically include the following steps: Step 101, modifying the ultrafiltration membrane with sodium hydroxide to form a modified membrane.

[0018] In an embodiment of the present invention, the ultrafiltration membrane can be modified with sodium hydroxide, and a high-density active functional group can be constructed on the membrane surface through a controllable alkali etching reaction. The ultrafiltration membrane can be selected from any one of polyester membranes, polypropylene membranes, and polyacrylonitrile membranes. It can be understood that carboxyl or hydroxyl groups can be generated directionally on polyester membranes, polypropylene membranes, and polyacrylonitrile membranes after treatment with sodium hydroxide. For example, the cyano group of the polyacrylonitrile membrane is hydrolyzed to a carboxyl group, providing strong coordination sites for metal ions and realizing the in-situ stable growth of metal-organic framework particles. These directionally generated oxygen-containing polar groups (such as carboxyl, hydroxyl, etc.) have strong metal chelating ability and can firmly anchor transition metal ions such as cobalt and iron. When the modified membrane is immersed in a metal salt solution, the metal ions are fixed at the membrane surface sites, and then the organic ligands (such as dimethylimidazole) of the metal-organic framework crystal and the pre-fixed metal ions are orderly coordinated at the solid-liquid interface to form a dense and porous catalytic layer with a thickness of about 500 microns. This structure not only provides a large specific surface area for pollutant adsorption, but also significantly improves the utilization rate of catalytic active sites due to its stable metal-support electronic interaction.

[0019] In practical applications, deionized water and sodium hydroxide can be added to a conical flask in sequence. After stirring evenly at room temperature for 20 minutes, a pre-cut polyacrylonitrile membrane of 3×3 cm is added to the conical flask. Then, the conical flask is transferred to a shaking small-sample dyeing machine and continuously shaken for 1 hour under the condition that the target temperature is 65 degrees Celsius. After the reaction ends, the sample membrane is taken out, and the sample membrane is washed several times with deionized water to remove surface impurities and unreacted solvents, and dried for 6 hours under the condition of 40 degrees Celsius to obtain a modified membrane. Among them, the molar ratio of deionized water to sodium hydroxide is 50:1.

[0020] As an example, deionized water and sodium hydroxide solution (molar ratio 50:1) can be measured and placed in a 250 mL conical flask, and stirred at room temperature of 25°C for 20 minutes to ensure that sodium hydroxide is completely dissolved to form a homogeneous modification solution. The pre-cut 3×3 cm polyacrylonitrile ultrafiltration membrane is immersed in the modification solution and left standing for 5 minutes to fully wet the membrane. Subsequently, the conical flask is transferred to a shaking small-sample dyeing machine and continuously reacted for 1 hour in a constant temperature environment of 65 degrees Celsius in a bidirectional reciprocating shaking mode. It can be understood that this temperature is precisely controlled below the glass transition temperature of polyacrylonitrile, which can not only activate the cyano hydrolysis reaction but also avoid thermal deformation of the membrane structure. Immediately after the reaction terminates, the membrane sample is taken out and washed in three stages with pre-cooled deionized water under a nitrogen protection flow to thoroughly remove the residual alkali solution and hydrolysis by-products on the surface. Finally, the membrane is dried in a constant temperature blast drying oven at 40°C for 6 hours to obtain a light yellow modified membrane.

[0021] Step 102: Immerse the modified membrane into a methanol solution containing cobalt nitrate hexahydrate and stir to form a first solution, and then pour a methanol solution containing 2-methylimidazole into the first solution and stir to form a second solution.

[0022] Step 103: Transfer the second solution to an ultrasonic cleaner, process it for a preset time, then take out the modified membrane, wash the modified membrane with anhydrous methanol and deionized water, and dry it to obtain a composite membrane.

[0023] In the embodiment of the present invention, cobalt nitrate hexahydrate can be dissolved in anhydrous methanol and stirred for 30 minutes to form a base solution, and then the modified membrane is added to the base solution and stirred for 30 minutes to form a first solution; 2-methylimidazole is dissolved in anhydrous methanol and stirred for 30 minutes and then poured into the first solution to form a mixed solution, and the mixed solution is stirred for 30 minutes to form a second solution; the second solution is transferred to an ultrasonic cleaner and processed for 30 minutes, then the modified membrane is taken out, and the surface of the modified membrane is washed several times with anhydrous methanol solution and deionized water respectively, and dried for 6 hours under the condition of 40 degrees Celsius to obtain a composite membrane. Among them, the molar mass ratio of cobalt nitrate hexahydrate to anhydrous methanol is 1:364; the molar mass ratio of 2-methylimidazole to anhydrous methanol is 1:87.

[0024] In practical applications, cobalt nitrate hexahydrate can be mixed with anhydrous methanol in a molar mass ratio of 1:364 and stirred for 30 minutes to form a uniform cobalt ion-based solution. Subsequently, it is immersed in a modified ultrafiltration membrane rich in carboxyl or hydroxyl groups on the surface, and slowly stirred for 30 minutes to achieve bidentate chelation and anchoring of cobalt ions on the membrane surface. Separately, dimethylimidazole is dissolved in anhydrous methanol in a molar mass ratio of 1:87 to prepare a solution, which is slowly added to the above system and stirred for 10 minutes to trigger interfacial coordination self-assembly, forming a primary metal-organic framework structure. It is transferred to a 40 kHz ultrasonic reactor and treated for 30 minutes to regulate the uniformity of crystal growth using the cavitation effect. Finally, it is successively washed with anhydrous methanol gradient, ultrasonically cleaned with deionized water, and vacuum dried at 40 °C for 6 hours to obtain a dense and porous catalytic layer. This process realizes the in-situ confined growth of metal-organic framework particles on the carrier surface through concentration gradient control and precise energy input.

[0025] As Figure 2 shown, in another embodiment of the present invention, cobalt nitrate hexahydrate can also be dissolved in anhydrous methanol (molar mass ratio of 1:364), and stirred for 30 min to obtain solution A. Secondly, dimethylimidazole is dissolved in anhydrous methanol (molar mass ratio of 1:87), and stirred for 30 min to obtain solution B. The prepared modified membrane is added to solution A and slowly stirred for 30 min, and then solution B is added to solution A and stirred for 10 min. After the reaction system is treated under ultrasonic conditions for 30 min, the sample is taken out, and the impurities on the surface of the fiber membrane are repeatedly washed clean with anhydrous methanol solution and deionized water respectively, and dried at 40 °C for 6 h to obtain a composite membrane with metal-organic framework particles on the surface.

[0026] The thickness of the microparticles on the surface of the composite membrane prepared in the embodiment of the present invention can be controlled at about 500 microns. The membrane surface is covered by a layer of dense microparticles, which have a large specific surface area and a porous structure, can quickly adsorb dyes in the dye solution, and have a strong adsorption effect.

[0027] Step 104, putting the composite membrane into the dye solution and adding an oxidant to react for a certain period of time.

[0028] In the embodiment of the present invention, the composite membrane can be first put into the dye wastewater for adsorption of dye molecules. Then an oxidant is added to cause a catalytic oxidation reaction with the metal ions on the fiber membrane to generate strongly oxidizing free radicals, realizing the removal of dye molecules in the dye solution. In practical applications, the oxidant can be any one of hydrogen peroxide, peroxymonosulfate, and persulfate. The mass ratio of the oxidant to the mass of the dye solution can be 1:12500. The reaction time for putting the composite membrane into the dye solution and adding the oxidant can be 5 to 40 minutes.

[0029] The main reaction equations involved can include: (1)HSO5 -→SO4 •- +OH • (2)S2O8 2- →2SO4 •- (3)M n+ +HSO5 - →M (n+1)+ +SO4 •- +OH - (4)M n+ S2O8 2- →M (n+1)+ SO4 •- +SO4 2- (5)SO4 •- +≡Organic → CO2 + H2O + ≡ Among them, ≡Organic represents pollutants, and ≡ represents adsorption sites.

[0030] In practical applications, the prepared composite membrane can be immersed in 0.02 mmol / L dye wastewater at a mass ratio of 1:1000 for adsorption. Subsequently, an oxidant is added to the system at a ratio of 1:12500. During the reaction cycle of 5 - 40 min, samples are taken at intervals of Δt, and the absorbance of the dye solution is measured at a wavelength of 551 nm using an ultraviolet-visible spectrophotometer to monitor the degradation efficiency in real time.

[0031] It can be understood that after reacting with the oxidant for a certain period of time, the composite membrane can be taken out of the dye solution and transferred to deionized water. Meanwhile, the composite membrane is cleaned using ultrasonic waves, and then separated and dried to achieve the recycling of the composite membrane and reduce costs.

[0032] As an example, the prepared composite membrane can be cut into a rectangle with a mass of 0.03 g and placed in 3 mL of rhodamine B dye solution with a concentration of 0.02 mmol / L. An adsorption test is carried out under dark conditions. After 1 h of adsorption, the absorbance of the dye solution is measured, and the adsorption rate of the dye is 17.6%. The composite membrane is immersed in the dye solution again, and then 50 mg / L of peroxymonosulfate is added to trigger the Co 2+ / SO4 •- -dominated Fenton-like reaction. After 10 min of reaction, the removal rate of the dye in the solution can reach over 95%. The composite membrane is taken out of the dye solution and transferred to 20 mL of deionized water. After ultrasonic cleaning for 10 min, the composite membrane is separated and dried. Using the composite membrane to repeat the above steps, the removal rate of the dye can still reach over 90%.

[0033] As an example, the prepared composite membrane can also be cut into a rectangle weighing 0.03 g and placed in 3 mL of a rhodamine B dye solution with a concentration of 0.02 mmol / L. An adsorption test is carried out under dark conditions. After 1 h of adsorption, the absorbance of the dye solution is measured, and the adsorption rate of the dye is 17.6%. The composite membrane is immersed in the dye solution again, and 80 mg / L of persulfate is added to trigger a high-density free radical chain reaction. After 10 min of reaction, the removal rate of the dye in the solution can reach over 99%. The composite membrane is taken out of the dye solution, transferred to 20 mL of deionized water, ultrasonically cleaned for 10 min, and then the composite membrane is separated and dried. After repeating the above steps twice with this composite membrane, the removal rate of the dye can still reach over 95%.

[0034] In the embodiment of the present invention, the pH value of the dye solution can also be adjusted to 3 before adding the oxidant and reacting for a certain period of time.

[0035] Exemplarily, the prepared composite membrane can be cut into a rectangle weighing 0.03 g and placed in 3 mL of a rhodamine B dye solution with a concentration of 0.02 mmol / L. An adsorption test is carried out under dark conditions. After 1 h of adsorption, the absorbance of the dye solution is measured, and the adsorption rate of the dye is 17.6%. The composite membrane is immersed in the dye solution again and the pH of the system is adjusted to 3. 80 mg / L of an oxidant is added, and after 5 min of reaction, the removal rate of the dye in the solution can reach over 98%. The composite membrane is taken out of the dye solution, transferred to 20 mL of deionized water, ultrasonically cleaned for 10 min, and then the composite membrane is separated and dried. After repeating the above steps twice with this composite membrane, the removal rate of the dye can still reach over 95%.

[0036] As another embodiment of the present invention, the prepared composite membrane can be cut into a rectangle weighing 0.03 g and placed in 3 mL of different dye solutions with a concentration of 0.02 mmol / L, including methyl orange, reactive red, and methylene blue dyes. An adsorption test is carried out under dark conditions. After 1 h of adsorption, the absorbance of the dye solution is measured. The composite membrane is immersed in the dye solutions containing different dyes again, 80 mg / L of an oxidant is added, and after 5 min of reaction, the removal rate of the dye in the solution can reach over 80% for all. The composite membrane is taken out of the dye solution, transferred to 20 mL of deionized water, ultrasonically cleaned for 10 min, and then the composite membrane is separated and dried. After repeating the above steps twice with this composite membrane, the removal rate of the dye can still reach over 70%.

[0037] In the present invention, through the adsorption-coupled oxidation technology, the fine particles on the composite membrane can serve as the adsorption sites for dyes, adsorb the dyes in the dye solution, realize the enrichment of the dyes in the dye solution, and remove part of the dye molecules. The metal ions in the composite membrane are used as catalytic active sites to catalyze hydrogen peroxide, peroxymonosulfate and persulfate at the reaction interface to generate highly oxidizing free radicals such as hydroxyl radicals, superoxide radicals, sulfate radicals, etc., and oxidize and degrade the dye molecules adsorbed in the fine particles, thereby realizing the removal of pollutants. This process can complete the removal of pollutants in the waste liquid without adding other catalysts, and is mainly achieved by the heterogeneous Fenton and Fenton-like reactions of the metal ions on the composite membrane and the oxidant to generate highly oxidizing free radicals. The adsorption of dye molecules is realized through the porous structure of the substances on the composite membrane, and then the dye molecules on its surface are degraded through oxidation, realizing a virtuous cycle process of adsorption, degradation, re-adsorption and re-degradation, which has high practicability in the actual degradation process. Compared with other powdered adsorbents, the present invention uses a fiber membrane as the carrier. The carrier can not only solve the problems of agglomeration and difficult recovery of the powdered adsorbent, but also have a strong interaction with the catalyst through the surface functional groups, guide the electron transfer path, and thus improve the catalytic oxidation activity.

[0038] The above provides a detailed introduction to a method for degrading wastewater pollutants by adsorption-coupled advanced oxidation. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A method for degrading wastewater pollutants by adsorption-coupled advanced oxidation process, characterized in that, The method includes: Modifying an ultrafiltration membrane with sodium hydroxide to form a modified membrane; Immersing the modified membrane in a methanol solution containing cobalt nitrate hexahydrate and stirring to form a first solution, and then pouring a methanol solution containing dimethylimidazole into the first solution and stirring to form a second solution; Transferring the second solution to an ultrasonic cleaner, processing for a preset time, taking out the modified membrane, cleaning the modified membrane with anhydrous methanol and deionized water, and drying to obtain a composite membrane; Placing the composite membrane in a dye solution and adding an oxidant to react for a certain period of time.

2. The method according to claim 1, wherein The ultrafiltration membrane is any one of a polyester membrane, a polypropylene membrane, and a polyacrylonitrile membrane.

3. The method according to claim 2, wherein The modifying the ultrafiltration membrane with sodium hydroxide to form a modified membrane includes: Sequentially adding deionized water and sodium hydroxide into a conical flask, uniformly stirring at room temperature for 20 minutes, and then adding a 3×3 cm polyacrylonitrile membrane that has been cut into the conical flask; then transferring the conical flask to a shaking sample dyeing machine, continuously shaking at a target temperature of 65 °C for 1 hour, taking out the sample membrane after the reaction, washing the sample membrane several times with deionized water to remove impurities and unreacted solvents on the surface, and drying at 40 °C for 6 hours to obtain a modified membrane; wherein, the molar ratio of the deionized water to the sodium hydroxide is 50:

1.

4. The method according to claim 3, characterized in that The immersing the modified membrane in a methanol solution containing cobalt nitrate hexahydrate and stirring to form a first solution, and then pouring a methanol solution containing dimethylimidazole into the first solution and stirring to form a second solution includes: Dissolving cobalt nitrate hexahydrate in anhydrous methanol and stirring for 30 minutes to form a base solution, and then adding the modified membrane into the base solution and stirring for 30 minutes to form a first solution; Dissolving dimethylimidazole in anhydrous methanol, stirring for 30 minutes, and then pouring it into the first solution to form a mixed solution, and stirring the mixed solution for 30 minutes to form a second solution; Wherein, the molar mass ratio of the cobalt nitrate hexahydrate to the anhydrous methanol is 1:364; the molar mass ratio of the dimethylimidazole to the anhydrous methanol is 1:

87.

5. The method according to claim 4, characterized in that, The transferring the second solution to an ultrasonic cleaner, processing for a preset time, taking out the modified membrane, cleaning the modified membrane with anhydrous methanol and deionized water, and drying to obtain a composite membrane includes: Transferring the second solution to an ultrasonic cleaner, processing for 30 minutes, taking out the modified membrane, cleaning the surface of the modified membrane several times with an anhydrous methanol solution and deionized water respectively, and drying at 40 °C for 6 hours to obtain a composite membrane.

6. The method according to claim 1 or 5, characterized in that The oxidant is any one of hydrogen peroxide, monopersulfate, and dipersulfate.

7. The method according to claim 6, wherein The mass ratio of the oxidant to the dye solution is 1:12500.

8. The method according to claim 7, wherein The reaction time for placing the composite membrane in the dye solution and adding the oxidant is 5 to 40 minutes.

9. The method according to claim 8, characterized in that, Before adding the oxidant and reacting for a certain period of time, it further includes: adjusting the pH value of the dye solution to 3.

10. The method according to claim 9, characterized in that The method further includes: after adding the oxidant and reacting for a certain period of time, taking out the composite membrane from the dye solution, transferring it to deionized water, simultaneously cleaning the composite membrane with ultrasonic waves, and then separating and drying the composite membrane.

Images