SA / PVA / TiO2 electrostatic spinning membrane as well as preparation method and application thereof

Abstract

The invention belongs to the field of composite membrane materials, and particularly discloses an SA / PVA / TiO2 electrostatic spinning membrane and a preparation method and application thereof, and the preparation method comprises the steps of preparation of an SA / PVA spinning solution, preparation of an SA / PVA / TiO2 spinning solution and preparation of the SA / PVA / TiO2 electrostatic spinning membrane. The prepared SA / PVA / TiO2 electrostatic spinning membrane has an excellent fiber structure and specific surface area, the removal efficiency of pollutants in the nitramine wastewater can be remarkably improved, and the greenness and harmlessness of the nitramine wastewater treatment process are realized due to the use of natural polymer components and environment-friendly photocatalytic materials of the SA / PVA / TiO2 electrostatic spinning membrane. The preparation method of the SA / PVA / TiO2 electrostatic spinning membrane is simple and controllable in preparation process and easy for large-scale production, reduces the cost and technical threshold of wastewater treatment, provides an innovative, efficient and environment-friendly solution for nitramine wastewater treatment, and has wide application prospect and social value.

Description

Technical Field

[0001] The invention relates to the field of composite membrane materials, in particular to a SA / PVA / TiO2 electrostatic spinning membrane and a preparation method and application thereof. Background Art

[0002] Explosives play an important role in military and industrial production due to their high energy density and instantaneous power. With the continuous growth of social demand, the use of explosives has brought increasing negative impacts. During their synthesis and development and the destruction of abandoned ammunition, a large amount of wastewater pollutants will be generated. These wastewater pollutants not only have a significant impact on the environment and ecology, but also seriously endanger human health. Among them, nitramine wastewater, as one of the explosive wastewaters, is difficult to effectively treat due to the large number of pollutants and rich types.

[0003] Membrane materials have received extensive attention in the field of wastewater treatment due to their large specific surface area and high porosity. Among them, electrospinning technology has become an important means of preparing high-performance membrane materials due to its advantages such as simple and controllable preparation methods and a variety of spinning raw materials. Membrane materials prepared by electrospinning technology not only have excellent physical adsorption properties, but can also be combined with materials with adsorption and photocatalytic properties to effectively remove organic pollutants in water.

[0004] Sun Fuqian et al. prepared sodium alginate (SA) and polyvinyl alcohol (PVA) composite membranes using electrospinning technology, and used calcium chloride anhydrous ethanol solution for cross-linking treatment to improve its mechanical properties. This cross-linking treatment can significantly improve the water resistance of the composite membrane because calcium chloride undergoes a cross-linking reaction with the carboxyl groups in sodium alginate to form a stable three-dimensional network structure. However, the cross-linking treatment may lead to a decrease in the heat resistance of the composite membrane because the structural integrity of some polymer chains may be destroyed during the cross-linking process. In addition, when preparing nanofibers using electrospinning technology itself, the diameter and distribution of the fibers also have an important influence on the mechanical properties.

[0005] However, the use of certain composite membrane materials alone, such as the SA / PVA composite membrane formed by combining sodium alginate (SA) and polyvinyl alcohol (PVA), has improved the adsorption performance to a certain extent, but it is still difficult to achieve efficient treatment of nitramine wastewater. Therefore, it is necessary to combine it with chemical treatment to improve the treatment efficiency of degrading organic pollutants. Among them, photocatalytic technology, as an emerging technology, has a high treatment efficiency. The main photocatalytic material currently used is TiO2, which exhibits excellent photocatalytic performance, but due to its large specific surface area and strong surface activity, TiO2 is very prone to agglomeration. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a SA / PVA / TiO2 electrospinning membrane and a preparation method and application thereof.

[0007] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0008] One of the purposes of the present invention is to provide a method for preparing a SA / PVA / TiO2 electrospinning membrane, comprising the following steps:

[0009] S1. Preparation of SA / PVA spinning solution

[0010] A polyvinyl alcohol (PVA) aqueous solution with a mass fraction of 10% and a sodium alginate (SA) aqueous solution with a mass fraction of 3% were prepared respectively, and the sodium alginate (SA) aqueous solution and the polyvinyl alcohol (PVA) aqueous solution were mixed in a volume ratio of (1-5):(5-9), mechanically stirred for 4 hours to make them uniformly mixed, and allowed to stand and precipitate to obtain a SA / PVA spinning solution;

[0011] Preparation of S2, SA / PVA / TiO2 spinning solution

[0012] Adding 2% by mass of modified nano-TiO2 particles to the SA / PVA spinning solution, ultrasonically treating for 3-6 hours, and stirring well to prepare a SA / PVA / TiO2 spinning solution;

[0013] Preparation of S3 and SA / PVA / TiO2 electrospinning membranes

[0014] Based on conventional electrospinning technology, SA / PVA / TiO2 spinning solution was prepared into SA / PVA / TiO2 electrospinning membrane; the SA / PVA / TiO2 electrospinning membrane was cross-linked with 1.5% CaCl2 ethanol solution and 3% boric acid solution for 3 hours, filtered, washed five times with distilled water, and dried in a drying oven to obtain a finished SA / PVA / TiO2 electrospinning membrane.

[0015] Furthermore, the preparation method of the modified nano-TiO2 particles is:

[0016] The nano-TiO2 particles were placed in a vacuum drying oven for drying and vacuum dried at 100°C for 12 hours; the nano-TiO2 was added to acetone and ultrasonically dispersed for 3 hours to obtain a dispersion, which was then poured into a three-necked flask and placed in a constant temperature water bath, and modified under the conditions of 8% silane coupling agent KH-550, 60°C modification temperature, and 2 hours modification time. The reaction-completed solution was placed in a centrifuge tube and centrifuged in a 15000r / min centrifuge for 50 minutes; it was then washed with deionized water for more than 5 times and vacuum dried for 4 hours to obtain modified nano-TiO2 particles.

[0017] The second object of the present invention is to provide a SA / PVA / TiO2 electrospinning membrane prepared by the above method.

[0018] The third purpose of the present invention is to provide a SA / PVA / TiO2 electrospinning membrane for use in the degradation and treatment of nitramine wastewater.

[0019] Compared with the prior art, the SA / PVA / TiO2 electrospinning membrane prepared by the present invention not only has excellent fiber structure and specific surface area, which can significantly improve the removal efficiency of pollutants in nitramine wastewater, but also realizes the greening and harmlessness of the nitramine wastewater treatment process due to its natural polymer components and the use of environmentally friendly photocatalytic materials.

[0020] The preparation method of the SA / PVA / TiO2 electrospinning membrane of the present invention has a simple and controllable preparation process, is easy to mass produce, reduces the cost and technical threshold of wastewater treatment, provides an innovative, efficient and environmentally friendly solution for nitramine wastewater treatment, and has broad application prospects and social value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the electrospinning device.

[0022] Figure 2 Morphological diagram of SA / PVA spinning solution: a-before standing; b-after standing.

[0023] Figure 3 FTIR comparison of TiO2 before and after modification: a-unmodified; b-KH550 dosage 8%, modification temperature 60℃, modification time 2h.

[0024] Figure 4 XRD comparison diagram of TiO2 before and after modification: a-unmodified; b-KH550 dosage 8%, modification temperature 60℃, modification time 2h.

[0025] Figure 5 Morphology of SA / PVA / TiO2 electrospun membrane: a-before cross-linking; b-cross-linked with 1.5% CaCl2 ethanol solution and 3% boric acid (water: ethanol = 2:8) solution for 3h.

[0026] Figure 6 This is the color change during the treatment of nitramine wastewater: a-color before the end of titration; b-color after the end of titration.

[0027] Figure 7 This is the curve of COD value variation over time in the degradation of nitramine wastewater by SA / PVA / TiO2 electrospinning membrane. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the invention.

[0029] Unless otherwise specified, the raw materials and reagents used in the following examples were commercially available.

[0030] This embodiment exemplarily demonstrates a method for preparing a SA / PVA / TiO2 electrospinning membrane. The specific preparation process is as follows:

[0031] 1) Preparation of SA / PVA spinning solution

[0032] Weigh 10g of PVA powder and add it to 90ml of deionized water. Place the beaker in a constant temperature water bath and heat it to 60°C. Place a magnetic rotor in the beaker and stir for 3 hours to prepare a uniform solution with a mass fraction of 10%. Weigh a certain amount of SA powder and add it to the beaker. Stir it with a magnetic rotor for 2 hours to prepare a 3% SA aqueous solution. Mix it with 10% PVA solution, stir it mechanically for 4 hours to make it evenly mixed, and let it stand for precipitation. The SA / PVA spinning solution is as follows before and after standing for precipitation. Figure 2 As shown by Figure 2 It can be seen that there are a lot of bubbles in the spinning solution before standing, which is caused by the solubility characteristics of polyvinyl alcohol and the introduction of gas during the stirring process. If it is not removed by precipitation treatment, it will hinder the formation of fibers during the electrospinning process, causing fiber breakage or the formation of uneven fiber structure. In order to ensure the smooth progress of the electrospinning process and the quality and performance of the fiber, it is necessary to properly precipitate the solution after stirring. After standing and settling, the solution appears as a colorless and transparent liquid.

[0033] 2) Modification of nano-TiO2 particles

[0034] Use silane coupling agent KH-550 to modify nano-TiO2 particles: Place the nano-TiO2 particles in a vacuum drying oven for drying, and vacuum dry at 100°C for 12 hours. Add nano-TiO2 to acetone and ultrasonically disperse for 3 hours to obtain a dispersion, then pour it into a three-necked flask and place it in a constant temperature water bath. Modify it under the conditions of 8% silane coupling agent KH-550, a modification temperature of 60°C, and a modification time of 2 hours. Place the reaction-completed solution in a centrifuge tube and centrifuge it in a centrifuge for 50 minutes (15000r / min). Then wash it with deionized water for more than 5 times. Finally, place the modified nano-TiO2 particles in a vacuum drying oven and dry them for 4 hours. Use FTIR and XRD to characterize the nano-TiO2 particles before and after modification. The test results are as follows: Figure 3 and Figure 4 As shown by Figure 3It can be seen that by comparing the infrared spectra before and after modification, it can be found that the absorption peak of the -OH bond in TiO2 modified by KH550 is significantly weakened, and the absorption peak at 1231cm -1 The absorption peak of -Si-C appears, which is mainly due to the -CH bond and -Si-C bond on the modifier connecting to the TiO2 surface. Figure 4 It can be seen that the position of the diffraction peak of TiO2 remains unchanged before and after modification, and its crystal phase composition does not change, indicating that the modification of KH550 is through grafting groups on the surface of TiO2 and its internal structure has not been changed.

[0035] In summary, it is shown that the KH550 modifier has successfully modified the TiO2 particles by chemical grafting without destroying their crystal structure.

[0036] 3) Preparation of SA / PVA / TiO2 electrospinning membrane

[0037] Add 2% modified nano-TiO2 particles to the SA / PVA spinning solution, ultrasonically treat for 3-6 hours, and stir thoroughly to make SA / PVA / TiO2 spinning solution. Prepare SA / PVA / TiO2 electrospinning membrane with 2wt% modified nano-TiO2 content based on electrospinning technology. The schematic diagram of the electrospinning device is shown in Figure 1 As shown, Figure 1 In the figure, the main structure of the electrospinning device can be intuitively seen. It is mainly composed of four parts: liquid propellant, metal needle, high-voltage power supply and receiving device. The high-voltage electric field is generated by the high-voltage power supply. When the spinning solution is transported to the high-voltage electric field by the propulsion device through the metal needle, the spinning solution at the needle will overcome its surface tension due to the Coulomb repulsion between charges under the action of the high-voltage electric field. With the continuous increase in the electric field strength, the interference of the droplets also increases. When the Coulomb repulsion borne by the droplets is greater than its own surface tension, the droplets will gradually elongate from a sphere to a cone until a Taylor cone is formed. The polymer jet is stretched and refined by the high-voltage electric field, and after solvent volatilization and solidification, it is finally collected by the receiving device to obtain a polymer composite film.

[0038] 4) The SA / PVA / TiO2 electrospun membrane was cross-linked with 1.5% CaCl2 ethanol solution and 3% boric acid solution (prepared by adding boric acid powder to water and ethanol solvents, where the volume ratio of water to ethanol was 2:8) for 3 hours, filtered, washed five times with distilled water, and placed in a drying oven for use. SEM characterization of the morphology is shown in Figure 5 As shown by Figure 5 It can be seen that the diameter of the SA / PVA / TiO2 electrospinning membrane is smaller before cross-linking, and the fibers are relatively independent. After 3h of cross-linking, the SA / PVATiO2 electrospinning membrane has a smaller diameter due to Ca 2+Complexation with PVA, Ca 2+ With Na in sodium alginate + Ions are exchanged, and boric acid and PVA undergo alcohol-boric acid coordination reaction to form chemical bonds. The fibers will become partially entangled, but the fibers still maintain a good shape, and their hydrophobicity and mechanical properties are also enhanced.

[0039] Application Examples

[0040] 100 ml of nitramine wastewater sample with a pH value of 8.0 and diluted 10 times was placed in a glass container, 50 mg of SA / PVA / TiO2 electrospinning membrane was added, and the reaction container was placed in a dark place and stirred until it reached adsorption equilibrium. The light source was turned on to start photocatalytic degradation, and the supernatant was taken every 5 minutes and placed in a brown glass container in a dark place for later use.

[0041] Pipette 5.0ml potassium dichromate standard solution and 10.0ml digested nitramine wastewater into a conical flask filled with zeolite, connect the condensation reflux device to the conical flask, and slowly add 15ml silver sulfate-sulfuric acid solution along the upper end of the condenser to prevent organic matter from overflowing at low boiling points, and gently shake the conical flask to mix the solution evenly. Before turning on the electric heating device, pass condensed water, and keep the solution at a slight boiling reflux for 2h to digest the water sample.

[0042] After the reflux digestion is completed, slowly add 40 ml of deionized water to the condenser tube mouth along the tube wall, let the conical flask stand and wait for it to cool to room temperature, add 3 drops of ferrous acid indicator, transfer an appropriate amount of ammonium ferrous sulfate standard solution into an acid burette for titration, record the volume of ammonium ferrous sulfate standard solution consumed to calculate the COD value, the titration end point is when the water sample color changes from yellow to blue-green to reddish brown, and the color change is as follows: Figure 6 As shown by Figure 6 It can be seen that when the standard solution of ammonium ferrous sulfate is added dropwise, the solution will appear green when the reaction approaches the end point. This is because potassium dichromate acts as an oxidant in a strong acidic solution, and +6 valent chromium will be reduced to +3 valent chromium, and the solution will appear green. When the titration approaches the end point, that is, when the remaining potassium dichromate is almost completely reduced, the ferrous ions in the solution begin to be excessive. At this time, ferrochlore forms a complex with the excess ferrous ions, making the solution appear reddish brown.

[0043] In summary, the process in which the solution color changes from green to reddish brown is the combined result of the reduction of potassium dichromate by ammonium ferrous sulfate and the titration endpoint indicated by ferrocyanide.

[0044] The degradation curve of the COD value of nitramine wastewater by SA / PVA / TiO2 electrospinning membrane was drawn based on the experimental results. Figure 7 As shown by Figure 7It can be seen that with the increase of reaction time, the COD value of nitramine wastewater shows an overall downward trend, rapidly decreasing within 60 minutes, slowly decreasing from 60 to 120 minutes, and stabilizing after 120 minutes. At this time, the COD removal rate of nitramine wastewater is 61%, indicating that most of the organic matter in the nitramine wastewater has been decomposed into water and carbon dioxide.

[0045] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. All technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a SA / PVA / TiO2 electrospinning membrane, characterized in that: The following steps are involved: S1. Preparation of SA / PVA spinning solution A polyvinyl alcohol (PVA) aqueous solution with a mass fraction of 10% and a sodium alginate (SA) aqueous solution with a mass fraction of 3% were prepared respectively, and the sodium alginate (SA) aqueous solution and the polyvinyl alcohol (PVA) aqueous solution were mixed in a volume ratio of (1-5):(5-9), mechanically stirred for 4 hours to make them uniformly mixed, and allowed to stand and precipitate to obtain a SA / PVA spinning solution; Preparation of S2, SA / PVA / TiO2 spinning solution Adding 2% by mass of modified nano-TiO2 particles to the SA / PVA spinning solution, ultrasonically treating for 3-6 hours, and stirring well to prepare a SA / PVA / TiO2 spinning solution; Preparation of S3 and SA / PVA / TiO2 electrospinning membranes Based on conventional electrospinning technology, SA / PVA / TiO2 spinning solution was prepared into SA / PVA / TiO2 electrospinning membrane; the SA / PVA / TiO2 electrospinning membrane was cross-linked with 1.5% CaCl2 ethanol solution and 3% boric acid solution for 3 hours, filtered, washed five times with distilled water, and dried in a drying oven to obtain a finished SA / PVA / TiO2 electrospinning membrane.

2. The method for preparing the SA / PVA / TiO2 electrospinning membrane according to claim 1, characterized in that: The preparation method of the modified nano-TiO2 particles is: The nano-TiO2 particles were placed in a vacuum drying oven for drying and vacuum dried at 100°C for 12 hours; the nano-TiO2 was added to acetone and ultrasonically dispersed for 3 hours to obtain a dispersion, which was then poured into a three-necked flask and placed in a constant temperature water bath, and modified under the conditions of 8% silane coupling agent KH-550, 60°C modification temperature, and 2 hours modification time. The reaction-completed solution was placed in a centrifuge tube and centrifuged in a 15000r / min centrifuge for 50 minutes; it was then washed with deionized water for more than 5 times and vacuum dried for 4 hours to obtain modified nano-TiO2 particles.

3. A SA / PVA / TiO2 electrospinning membrane prepared by the method according to claim 1 or 2.

4. Use of the SA / PVA / TiO2 electrospinning membrane as claimed in claim 3 in the degradation and treatment of nitramine wastewater.

Images