Ternary visible-light-driven photocatalyst, preparation method thereof and ultrafiltration membrane

Abstract

The invention provides a ternary visible-light-driven photocatalyst, a preparation method thereof and an ultrafiltration membrane. The ternary visible-light-driven photocatalyst comprises Ag2O, BiOI and ZnO. The molar ratio of Ag in the Ag2O to Bi in the BiOI to Zn in the ZnO is (20 to 35): (15 to 25): (75 to 85). The three components in the polyvinylidene fluoride ultrafiltration membrane achieve a good synergistic catalysis effect, the visible light catalysis performance of the polyvinylidene fluoride ultrafiltration membrane is improved, sunlight can be directly utilized, organic pollutants on the surface of the membrane can be degraded, and pollution of the membrane is effectively relieved; the film has good antibacterial, anti-pollution and self-cleaning functions, the maintenance cost of the film can be effectively reduced, and the service life of the film is prolonged. Meanwhile, under the condition that the structure of a membrane substrate is not damaged, through introduction of a proper amount of ternary visible light photocatalyst particles, the pore structure of the membrane is enriched, meanwhile, the hydrophilicity of the membrane can be improved, and the filtering performance of the membrane can be enhanced.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of membrane separation technology, and particularly relates to a ternary visible light catalyst, a preparation method thereof and an ultrafiltration membrane. BACKGROUND

[0002] Membrane separation technology has been widely applied due to its advantages such as no phase change, no chemical change, high separation efficiency, good selectivity and operation at normal temperature, especially in the field of water purification. Membrane material is the key to separation, and the performance and stability of the membrane material determine the separation effect and continuity. However, in the separation process, the membrane is easily polluted to different degrees by microorganisms, organic matter, inorganic matter and the like in the water body, resulting in membrane blockage, increased filtration resistance, and decreased filtration effect and membrane flux. This greatly increases the frequency of aeration and cleaning during treatment, increases energy consumption, reduces the service life of the membrane, and increases the use cost. Therefore, how to reduce the influence of membrane pollution on the membrane material is a difficulty in the application of membrane separation technology.

[0003] At present, the commonly used membrane material is mostly a polymer material, among which polyvinylidene fluoride is a commonly used polymer and is mostly used for preparing an ultrafiltration membrane. However, due to the hydrophobicity of the material, the membrane is easily polluted by organic matter and microorganisms in the filtration process, which greatly limits its application in water purification. Among many physical and chemical modification methods, blending modification is widely used in the modification of membrane materials due to its simple operation and easy implementation.

[0004] Photocatalysis technology is a green technology with important application prospects for effectively treating environmental pollution and water pollution. Under light conditions, the photocatalyst added in the aqueous solution system can form an electron-hole pair by migrating the electron on the valence band to the conduction band under the excitation of light, thereby inducing the generation of a group with high redox activity, effectively degrading organic pollutants and avoiding membrane blockage by organic pollutants. Traditional photocatalytic materials mostly need to be irradiated by ultraviolet light to achieve photocatalytic effect. However, ultraviolet light accounts for only 4% of the sunlight spectrum, and its use has high energy consumption and cost. In addition, the polymer membrane will be accelerated in aging under long-term irradiation of ultraviolet light, which limits the practical application of the photocatalyst. SUMMARY

[0005] The purpose of the present application is to provide a ternary visible light catalyst, a preparation method thereof and an ultrafiltration membrane. The ternary visible light catalyst in the present application can catalytically degrade organic pollutants under visible light, and has good antibacterial, anti-pollution and self-cleaning functions, which can effectively reduce the maintenance cost of the membrane and prolong the service life of the membrane.

[0006] The present application provides a ternary visible light catalyst, which comprises Ag2O, BiOI and ZnO.

[0007] The molar ratio of Ag in the Ag2O, Bi in the BiOI and Zn in the ZnO is (20-35):(15-25):(75-85).

[0008] Preferably, the Ag2O has a spherical morphology, and the particle size of the Ag2O is 20-100 nm.

[0009] Preferably, the BiOI has a flaky morphology, and the edge length of the BiOI is 150-400 nm and the thickness is 20-40 nm.

[0010] Preferably, the ZnO has a hexagonal columnar morphology, and the diameter of the ZnO is 100-200 nm and the length is 250-700 nm.

[0011] The application provides a preparation method of a ternary visible light catalyst, comprising the following steps:

[0012] A) mixing an iodine source, a Bi source and a zinc salt solution with a pH of 8-10 to obtain a mixed solution;

[0013] B) performing a hydrothermal reaction on the mixed solution to obtain a binary precursor material BiOI / ZnO;

[0014] C) mixing a silver source and the binary precursor material BiOI / ZnO in water, adjusting the pH to 8-9 and performing a photoreduction reaction to obtain a ternary visible light catalyst Ag2O / BiOI / ZnO.

[0015] Preferably, the iodine source is KI and / or NaI, and the Bi source is Bi(NO3)3·5H2O,

[0016] The molar ratio of Bi in the Bi source and iodine in the iodine source is 1:(0.9-1.1).

[0017] Preferably, the temperature of the hydrothermal reaction in the step B) is 150-190 DEG C, and the time of the hydrothermal reaction in the step B) is 6-18 hours.

[0018] Preferably, the mass of Ag in the silver source is 20-30% of the mass of the binary precursor material BiOI / ZnO.

[0019] Preferably, the photoreduction reaction is performed under irradiation of a high-pressure mercury lamp, the power of the high-pressure mercury lamp is 200-500 W, the working wavelength is 365 nm, and the irradiation time is 0.5-4 hours.

[0020] The application provides an ultrafiltration membrane comprising a polyvinylidene fluoride porous matrix and a visible light catalyst dispersed in the polyvinylidene fluoride porous matrix, wherein the visible light catalyst is the ternary visible light catalyst described above.

[0021] The application provides a ternary visible light catalyst, comprising Ag2O, BiOI and ZnO; the molar ratio of Ag in the Ag2O, Bi in the BiOI and Zn in the ZnO is (20-35):(15-25):(75-85). The application takes wide-bandgap ZnO as a main component of the photocatalyst, and through compounding with the narrow-bandgap BiOI and Ag2O, forms a certain heterojunction structure, improves the visible light photocatalytic activity of the ZnO, effectively avoids and slows down the photo-corrosion problem caused by the Ag2O and BiOI, and realizes good synergistic catalysis of the three components, improves the visible light photocatalytic performance of the polyvinylidene fluoride ultrafiltration membrane, can directly utilize sunlight, realizes degradation of organic pollutants on the membrane surface, effectively alleviates the pollution of the membrane; meanwhile, due to the antibacterial and bacteriostatic characteristics of the solid-supported ternary visible light photocatalyst Ag2O / BiOI / ZnO, the membrane has good antibacterial, anti-pollution and self-cleaning functions, can effectively reduce the maintenance cost of the membrane, and prolongs the service life of the membrane. Meanwhile, the ternary visible light photocatalyst is uniformly solid-supported in the polyvinylidene fluoride ultrafiltration membrane material, under the condition of not damaging the structure of the membrane matrix itself, through introduction of the appropriate ternary visible light photocatalyst particles, the pore structure of the membrane is enriched, and the hydrophilicity and the filtration performance of the membrane are improved. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only constitute the embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of the provided drawings.

[0023] Figure 1 It is a scanning electron microscope graph of the ternary visible light photocatalyst Ag2O / BiOI / ZnO prepared in Example 1.

[0024] Figure 2 It is a transmission electron microscope graph of the ternary visible light photocatalyst Ag2O / BiOI / ZnO prepared in Example 1.

[0025] Figure 3 It is an ultraviolet-visible diffuse reflectance spectrogram of the ternary visible light photocatalyst Ag2O / BiOI / ZnO prepared in Example 1.

[0026] Figure 4 It is an XRD spectrum of the ternary visible light photocatalyst Ag2O / BiOI / ZnO prepared in Example 1.

[0027] Figure 5The degradation performance curve of the ternary visible light photocatalyst Ag2O / BiOI / ZnO prepared in Example 1 on methyl orange;

[0028] Figure 6 The scanning electron microscope graph of the ternary visible light photocatalyst / polyvinylidene fluoride ultrafiltration membrane prepared in Example 1;

[0029] Figure 7 The curve of the water flux of the ternary visible light photocatalyst / polyvinylidene fluoride ultrafiltration membrane a prepared in Example 1 and the conventional polyvinylidene fluoride ultrafiltration membrane b prepared in Comparative Example 1 in filtering the bovine serum albumin (BSA) solution with or without visible light irradiation changing with time. DETAILED DESCRIPTION

[0030] The present application provides a ternary visible light photocatalyst, comprising Ag2O, BiOI and ZnO.

[0031] The molar ratio of Ag in Ag2O, Bi in BiOI and Zn in ZnO is (20-35):(15-25):(75-85).

[0032] In the art, the single-component Ag2O catalyst and the single-component BiOI photocatalyst have certain visible light response, but there is a problem of obvious photo-corrosion. In the present application, ZnO with a wide band gap and only under ultraviolet light irradiation has better photocatalytic activity, and is used as the main component of the visible light photocatalyst. By compounding with BiOI and Ag2O with a narrow band gap, a certain heterojunction structure is formed, which can improve the visible light photocatalytic activity of ZnO and effectively slow down the photo-corrosion problem.

[0033] In the present application, the molar ratio of Ag in Ag2O, Bi in BiOI and Zn in ZnO is preferably (20-35):(15-25):(75-85), and more preferably (25-30):(18-22):(78-82). Specifically, in the examples of the present application, the molar ratio of Bi in BiOI and Zn in ZnO is preferably (15-25):(75-85), and more preferably (16-22):(78-94), such as 15:85, 16:84, 17:83, 18:82, 19:81, 20:80, 21:79, 22:78, 23:77, 24:76, 25:75, and preferably a range value with any of the above values as the upper limit or the lower limit. The mass of Ag in Ag2O (calculated as AgNO3) is preferably 20-30% of the total mass of BiOI and ZnO, and more preferably 25-28%, such as 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, and preferably a range value with any of the above values as the upper limit or the lower limit.

[0034] In the present application, as shown in the drawings, the ternary visible light catalyst mainly comprises three kinds of granular morphologies of spherical, lamellar and hexagonal short columnar, wherein the spherical Ag2O, the lamellar BiOI and the hexagonal short columnar ZnO are interlaced with each other, and the overall distribution is relatively uniform. Figure 1

[0035] In the present application, the Ag2O has a spherical morphology, and the particle size of the Ag2O is preferably 20-100 nm, and more preferably 30-80 nm; the BiOI has a lamellar morphology, and the side length of the BiOI is 150-400 nm, and the thickness is 20-40 nm; the ZnO has a hexagonal columnar morphology, and the diameter of the ZnO is 100-200 nm, and the length is 250-700 nm.

[0036] The ternary visible light catalyst in the present application can realize the regulation of the proportion of each granular morphology, and form a granular morphology structure with interlaced compounding. The existence of multiple nanometer granular morphologies can effectively improve the active sites of the catalyst, and is beneficial to the capture and degradation of organic pollutants by the catalyst.

[0037] The present application also provides a preparation method of the ternary visible light catalyst as described above, comprising the following steps:

[0038] A) mixing an iodine source, a Bi source and a zinc salt solution with a pH of 8-10 to obtain a mixed solution;

[0039] B) performing a hydrothermal reaction on the mixed solution to obtain a binary precursor material BiOI / ZnO;

[0040] C) mixing a silver source and the binary precursor material BiOI / ZnO in water, adjusting the pH to 8-9, and performing a photoreduction reaction to obtain a ternary visible light catalyst Ag2O / BiOI / ZnO

[0041] Firstly, the zinc salt and the base are mixed in water in the present application, the pH value of the zinc salt solution is adjusted to 8-10, and the zinc salt solution is obtained by stirring at room temperature for 30-60 min.

[0042] In the present application, the zinc salt is preferably a soluble zinc salt, and more preferably Zn(NO3)2·6H2O and / or ZnCl2; the base is preferably NaOH and / or KOH; the present application does not have special limitations on the amount of the base, and the pH value of the zinc salt solution can be adjusted to 8-10.

[0043] After obtaining the zinc salt solution, the iodine source and the bismuth source are mixed with the zinc salt solution in the present application, and stirred for 20-60 min to obtain a mixed solution.

[0044] ​In the present application, the iodine source is preferably soluble iodide, more preferably KI and / or NaI; the bismuth source is preferably soluble bismuth salt, more preferably Bi(NO3)3·5H2O; the molar ratio of Bi in the Bi source to iodine in the iodine source is preferably 1:(0.9-1.1), more preferably 1:1.

[0045] In the present application, the amount of the zinc salt, the iodine source and the bismuth source is proportioned according to the ratio of BiOI to ZnO in the ternary visible light catalyst as described above, which is not described herein again.

[0046] The obtained mixed solution is transferred into a hydrothermal reaction kettle for hydrothermal reaction, and after cooling, is washed with deionized water and ethanol for multiple times, and after drying, the binary precursor material BiOI / ZnO is obtained.

[0047] In the present application, the temperature of the hydrothermal reaction is preferably 150-190℃, more preferably 160-180℃, such as 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, preferably a range value with any of the above values as the upper limit or lower limit; the time of the hydrothermal reaction is preferably 6-18 hours, more preferably 6-12 hours.

[0048] In the present application, the temperature of the drying is preferably 60-90℃, more preferably 70-80℃, and the time of the drying is preferably 6-24 hours, more preferably 12-18 hours.

[0049] After obtaining the binary precursor material BiOI / ZnO, the present application disperses the binary precursor material BiOI / ZnO, adds a silver source, stirs and mixes for 10-30 min, then adds a base to adjust the pH of the solution to 8-9, and performs photoreduction reaction.

[0050] In the present application, the mass of Ag in the silver source is preferably 20-30% of the mass of the binary precursor material BiOI / ZnO, more preferably 25-28%, such as 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, preferably a range value with any of the above values as the upper limit or lower limit.

[0051] In the present application, the base is preferably NaOH and / or KOH; the present application does not have special limitation on the amount of the base, and the pH value of the solution can be adjusted to 8-9.

[0052] The photo-reduction of the application is preferably carried out under irradiation of a high-pressure mercury lamp, the power of which is preferably 200-500 W, more preferably 300-400 W; the working wavelength of the high-pressure mercury lamp is 365 nm, and the irradiation time is preferably 0.5-4 hours, more preferably 1-3 hours.

[0053] After the photo-reduction reaction is completed, the photo-reduction reaction product is preferably washed with deionized water and ethanol, and the ternary visible light catalyst Ag2O / BiOI / ZnO is obtained after drying.

[0054] In the application, the drying temperature is preferably 60-90 DEG C, more preferably 70-80 DEG C, and the drying time is preferably 6-24 hours, more preferably 12-18 hours.

[0055] In the application, the ternary visible light photocatalyst is prepared by a simple hydrothermal method + UV reduction two-step method: in the first step, zinc salt (Zn(NO3)2.6H2O) and base (NaOH), and iodide (KI) and bismuth salt (Bi(NO3)3.5H2O) are sequentially mixed in proportion at room temperature, and then a hydrothermal reaction is carried out to obtain a binary precursor BiOI / ZnO; in the second step, the binary precursor is only dispersed in deionized water and mixed with AgNO3 for UV reduction, and finally the ternary visible light photocatalyst is obtained.

[0056] Compared with the preparation method of the photocatalyst mentioned in the prior art, the preparation method of the visible light photocatalyst in the application has the characteristics of simple preparation process, green and environmentally friendly process, and easy to realize large-scale production. The reagents involved in the application are all conventional, non-toxic or low-toxicity chemical reagents, and no unconventional, highly toxic and strongly corrosive reagents are used.

[0057] The application also provides an ultrafiltration membrane comprising a polyvinylidene fluoride porous matrix and a visible light photocatalyst dispersed in the polyvinylidene fluoride porous matrix, wherein the visible light photocatalyst is the ternary visible light photocatalyst described above.

[0058] In the application, the thickness of the ultrafiltration membrane is preferably 100-250 μm, and the application does not have special requirements for the pore size and porosity of the ultrafiltration membrane, and the pore size and porosity of the commonly used polyvinylidene fluoride ultrafiltration membrane in the art can be used, specifically, the pore size of the ultrafiltration membrane in the application is preferably 0.005-0.08 μm, more preferably 0.01-0.06 μm; and the porosity of the ultrafiltration membrane is preferably 35-85%, more preferably 40-80%.

[0059] The application also provides a preparation method of the ultrafiltration membrane described above, comprising the following steps:

[0060] (1) dispersing the ternary visible light catalyst described above in an organic solvent to obtain a catalyst dispersion liquid;

[0061] polyvinylidene fluoride and a pore-forming agent are dissolved and mixed in an organic solvent to obtain an organic mixed liquid;

[0062] (2) mixing the organic mixed liquid and the catalyst dispersion liquid, and heating and stirring to obtain a casting solution;

[0063] (3) after filtering and vacuum degassing, the casting solution is coated on the surface of a substrate, and then the coated liquid film is immersed in a coagulation bath to perform phase inversion and film formation to obtain an ultrafiltration membrane.

[0064] In the present application, the pore-forming agent is preferably one or more of polyethylene glycol, polyvinylpyrrolidone, polyethylene oxide, polyvinyl alcohol, lithium chloride and sodium chloride, wherein the molecular weight of the polyethylene glycol is preferably 200-6000, more preferably 500-5000; the polyvinylpyrrolidone preferably includes one or more of K15, K30, K60, K70, K80 and K90, the molecular weight of the polyethylene oxide is preferably 50000-500000, more preferably 100000-400000; the molecular weight of the polyvinyl alcohol is preferably 10000-120000, more preferably 50000-100000.

[0065] In the present application, in the casting solution, the mass concentration of polyvinylidene fluoride is preferably 14-20%, more preferably 15-19%, such as 14%, 15%, 16%, 17%, 18%, 19%, 20%, preferably a range value with the above-mentioned any value as the upper limit or lower limit; the mass concentration of the pore-forming agent is preferably 0.3-10%, more preferably 0.5-8%, such as 0.3%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, preferably a range value with the above-mentioned any value as the upper limit or lower limit; the mass concentration of the ternary visible light catalyst is preferably 0.2-3%, more preferably 0.5-2.5%, such as 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, preferably a range value with the above-mentioned any value as the upper limit or lower limit.

[0066] In the present application, the organic solvents in the catalyst dispersion liquid and the organic mixed liquid can be the same or different, and both are independently selected from one or more of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone and dimethyl sulfoxide.

[0067] In the present application, the filtering and vacuum degassing of the casting solution are both common methods for pretreatment of the casting solution before coating in the art, which will not be described here in detail.

[0068] In the present application, the coating thickness of the casting solution is preferably 100-250 μm, more preferably 150-200 μm.

[0069] In the present application, the coagulation bath is preferably deionized water; the temperature of the coagulation bath is preferably 20-60℃, more preferably 30-50℃, such as 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, preferably a range value with any of the above values as the upper limit or lower limit.

[0070] The present application provides a ternary visible light catalyst, comprising Ag2O, BiOI and ZnO; the molar ratio of Ag in Ag2O, Bi in BiOI and Zn in ZnO is (20-35):(15-25):(75-85). The present application takes wide band gap ZnO as the main component of the photocatalyst, and through compounding with narrow band gap BiOI and Ag2O, a certain heterojunction structure is formed, which can improve the visible light photocatalytic activity of ZnO, effectively avoid and slow down the photo-corrosion problem caused by Ag2O and BiOI, and achieve good synergistic catalysis of the three components, thereby improving the visible light photocatalytic performance of the polyvinylidene fluoride ultrafiltration membrane. The sun light can be directly used to degrade the organic pollutants on the membrane surface, effectively alleviating the pollution of the membrane. At the same time, due to the antibacterial and bacteriostatic properties of the solidified ternary visible light photocatalyst Ag2O / BiOI / ZnO, the membrane also has good antibacterial, anti-pollution and self-cleaning functions, which can effectively reduce the maintenance cost of the membrane and prolong the service life of the membrane. At the same time, the ternary visible light photocatalyst is uniformly solidified in the polyvinylidene fluoride ultrafiltration membrane material, and through the introduction of an appropriate amount of ternary visible light photocatalyst particles, the pore structure of the membrane is enriched, and the hydrophilicity and filtration performance of the membrane are also improved.

[0071] In order to further illustrate the present application, the following embodiments are used to describe the ternary visible light catalyst, the preparation method thereof and the ultrafiltration membrane provided by the present application in detail, but it should not be understood as limiting the protection scope of the present application.

[0072] Example 1

[0073] S1, Preparation of a ternary visible light photocatalyst

[0074] (1) An appropriate amount of Zn(NO3)2·6H2O was weighed, an appropriate amount of deionized water was added and stirred to dissolve, then an appropriate amount of NaOH solution was added, the pH of the solution was adjusted to 8, and the mixture was stirred at room temperature for 30 min to obtain a mixed solution A.

[0075] (2) Add appropriate amounts of KI and Bi(NO3)3·5H2O to the mixture A prepared in (1) in sequence, and stir continuously for 20 min to obtain mixture B. The molar ratio of Bi:Zn is 16:84 and the molar ratio of Bi:I is 1:1.

[0076] (3) Finally, the prepared mixture B was transferred into a hydrothermal reactor and hydrothermally reacted at 160°C for 6 hours. After cooling, it was washed several times with deionized water and ethanol and dried at 60°C to obtain the desired binary precursor material BiOI / ZnO.

[0077] (4) Weigh an appropriate amount of the binary precursor material prepared in (3) and stir and disperse it in deionized water. Add AgNO3 at a ratio of 20wt% to the binary precursor material and continue stirring and mixing for 10 min. Then add an appropriate amount of NaOH solution to adjust the pH of the solution to 8. Photoreduction is performed under the irradiation of a 500W high-pressure mercury lamp for 1 h. Finally, wash the sample with deionized water and ethanol and dry it at 60℃ to obtain a ternary visible light photocatalyst Ag2O / BiOI / ZnO.

[0078] The morphology of the ternary visible light photocatalyst Ag₂O / BiOI / ZnO prepared in Example 1 was characterized, as follows: Figures 1-2 As shown, Figure 1 This is a SEM image of the catalyst in Example 1 of the present invention. Figure 2 This is a TEM image of the catalyst in Example 1 of the present invention. Figure 1 As can be observed, the ternary visible light photocatalyst Ag2O / BiOI / ZnO in Example 1 mainly consists of three morphologies: spherical, lamellar, and hexagonal short columnar particles. The spherical Ag2O, lamellar BiOI, and hexagonal short columnar ZnO are interspersed and the overall distribution is relatively uniform. The diameter of the spherical Ag2O is about 20-100 nm, the size of the lamellar BiOI is about 150-400 nm, and the thickness is about 30 nm. The length of the columnar ZnO is about 250-700 nm, and the diameter is about 100-200 nm.

[0079] from Figure 2 As can be seen, some of the spherical Ag2O particles are dispersed on the surface of BiOI and some are attached to the surface of ZnO. The composite effect among Ag2O, BiOI and ZnO is obvious. It can be clearly seen from the figure that there are two different sets of lattice stripes intersecting each other, so it can be seen that Ag2O may have entered the interlayer of BiOI.

[0080] Figure 3 This is the UV-Vis diffuse reflectance spectrum of the catalyst in Example 1 of the present invention, obtained from... Figure 3It can be seen that although both BiOI / ZnO and Ag2O are responsive to visible light, the visible light absorption capacity of Ag2O is obviously stronger than that of BiOI / ZnO, and the compounding of Ag2O significantly improves the visible light absorption capacity of the ternary composite material Ag2O / BiOI / ZnO, and enhances the visible light photocatalytic activity thereof.

[0081] Figure 4 The XRD pattern of the catalyst in Example 1 of the present application is shown in the following figure: Figure 4 It can be seen that the main components of the catalyst prepared in Example 1 are Ag2O, BiOI and ZnO.

[0082] Figure 5 The degradation performance curve of the catalyst prepared in Example 1 of the present application to methyl orange with a concentration of 30 mg / L is shown in the following figure, and the experiment is carried out under simulated sunlight: Figure 5 It can be seen that the catalytic activity of the ternary composite photocatalyst (Ag2O / BiOI / ZnO) prepared in Example 1 is obviously superior to that of single-component Ag2O and double-component BiOI / ZnO.

[0083] S2, Preparation of a ternary visible light photocatalyst / polyvinylidene fluoride ultrafiltration membrane

[0084] (1) The prepared ternary visible light photocatalyst is ultrasonically dispersed in an appropriate amount of N,N-dimethylacetamide to obtain a mixed solution A of the modifier;

[0085] (2) Polyvinylidene fluoride and a pore-forming agent are added to N,N-dimethylacetamide, and after stirring and dissolving at 75℃ for 1h, the pre-dispersed mixed solution A of (1) is added, and heating and stirring are continued for 7h to obtain a uniformly stirred casting solution.

[0086] (3) The casting solution obtained in (2) is filtered and vacuum degassed for 6h.

[0087] (4) An automatic coating machine is used to coat the casting solution on a non-woven fabric substrate with a coating thickness of 200μm, and then the coated liquid film is immersed in a coagulation bath at a temperature of 20℃ for phase inversion film formation, and then immersed in deionized water for soaking and rinsing for 12h to obtain a ternary visible light photocatalyst / polyvinylidene fluoride ultrafiltration membrane.

[0088] In the casting solution, the addition amount of polyvinylidene fluoride is 15wt%, the addition amount of the pore-forming agent is 10wt%, the addition amount of the modifier (ternary visible light photocatalyst) is 1.9wt%, and the balance is an organic solvent; the pore-forming agent is polyethylene glycol 400 and polyvinylpyrrolidone K30.

[0089] Figure 6 The SEM image of the ultrafiltration membrane prepared in Example 1 of the present application is shown in the following figure: Figure 6It can be seen that the modified membrane pore size distribution is uniform, indicating that the introduction of Ag2O / BiOI / ZnO ternary visible light photocatalyst does not cause obvious adverse effects on the polyvinylidene fluoride ultrafiltration membrane matrix, ensuring the basic filtration function of the modified membrane.

[0090] Example 2

[0091] S1, Preparation of a ternary visible light photocatalyst

[0092] (1) An appropriate amount of Zn(NO3)2·6H2O was weighed, an appropriate amount of deionized water was added and stirred to dissolve, and then an appropriate amount of NaOH solution was added to adjust the pH of the solution to 10. The solution was stirred at room temperature for 55 min to obtain a mixed solution A.

[0093] (2) An appropriate amount of KI and Bi(NO3)3·5H2O was sequentially added to the mixed solution A prepared in (1), and the stirring was continued for 60 min to obtain a mixed solution B. The molar ratio of Bi to Zn was 25:75, and the molar ratio of Bi to I was 1:1.

[0094] (3) Finally, the prepared mixed solution B was moved into a hydrothermal reaction kettle, and hydrothermal reaction was carried out at 180℃ for 12h. After cooling, the sample was washed with deionized water and ethanol several times, and dried at 85℃ to obtain the required binary precursor material BiOI / ZnO.

[0095] (4) An appropriate amount of the binary precursor material prepared in (3) was weighed and dispersed in deionized water. According to the weight ratio of 30wt% of the binary precursor material, AgNO3 was added, and the stirring and mixing were continued for 30 min. Then, an appropriate amount of NaOH solution was added to adjust the pH of the solution to 9. Under the irradiation of a high-pressure mercury lamp with a power of 200W, the sample was photoreduced for 3h. Finally, the sample was washed with deionized water and ethanol, and dried at 90℃ to obtain a ternary visible light photocatalyst Ag2O / BiOI / ZnO.

[0096] S2, Preparation of a ternary visible light photocatalyst / polyvinylidene fluoride ultrafiltration membrane

[0097] (1) The prepared ternary visible light photocatalyst was first ultrasonically dispersed in an appropriate amount of N,N-dimethylformamide to obtain a mixed solution A of the modifier;

[0098] (2) Polyvinylidene fluoride and a pore former were added to N,N-dimethylformamide, and after stirring and dissolving at 90℃ for 2h, the pre-dispersed mixed solution A of (1) was added, and the stirring and heating were continued for 11h to obtain a uniformly stirred casting solution.

[0099] (3) The casting solution obtained in (2) was filtered and vacuum degassed for 12h.

[0100] (4) using an automatic coater, the casting solution is blade coated on a non-woven fabric substrate with a coating thickness of 120 μm, then the coated liquid film is immersed in a coagulation bath at a temperature of 60°C for phase inversion film formation, and then immersed in deionized water for 24 h of soaking and rinsing to obtain a ternary visible light photocatalyst / polyvinylidene fluoride ultrafiltration membrane.

[0101] In the casting solution, the polyvinylidene fluoride addition amount is 19 wt%, the pore former addition amount is 4 wt%, the modifier (ternary visible light photocatalyst) addition amount is 0.7 wt%, and the balance is an organic solvent; the pore former is polyvinylpyrrolidone K60.

[0102] Example 3

[0103] S1, Preparation of a ternary visible light photocatalyst

[0104] (1) An appropriate amount of Zn(NO3)2·6H2O is weighed, an appropriate amount of deionized water is added and stirred to dissolve, then an appropriate amount of NaOH solution is added, the solution pH is adjusted to 9, and the solution is stirred at room temperature for 40 min to obtain a mixed solution A;

[0105] (2) An appropriate amount of KI and Bi(NO3)3·5H2O is sequentially added to the mixed solution A prepared in (1), and stirring is continued for 40 min to obtain a mixed solution B, the molar ratio of Bi:Zn is 20:80, and the molar ratio of Bi:I is 1:1;

[0106] (3) Finally, the prepared mixed solution B is moved into a hydrothermal reaction kettle, and hydrothermal reaction is carried out at 170°C for 10 h, then the sample is washed with deionized water and ethanol several times, and dried at 75°C to obtain the required binary precursor material BiOI / ZnO.

[0107] (4) An appropriate amount of the binary precursor material prepared in (3) is weighed and dispersed in deionized water, 25 wt% of AgNO3 is added according to the ratio of the binary precursor material, stirring and mixing are continued for 20 min, then an appropriate amount of NaOH solution is added, the solution pH is adjusted to 9, and the sample is irradiated under a high-pressure mercury lamp with a power of 300 W for 2 h of photoreduction, finally, the sample is washed with deionized water and ethanol, and dried at 80°C to obtain a ternary visible light photocatalyst Ag2O / BiOI / ZnO.

[0108] S2, Preparation of a ternary visible light photocatalyst / polyvinylidene fluoride ultrafiltration membrane

[0109] (1) The prepared ternary visible light photocatalyst is first ultrasonically dispersed in an appropriate amount of dimethyl sulfoxide to obtain a mixed solution A of the modifier.

[0110] (2) Polyvinylidene fluoride, pore-forming agent were added into dimethyl sulfoxide, and stirred and dissolved at 8.0 ℃ for 1.5 h, then (1) pre-dispersed mixed solution A was added, and heated and stirred for 9 h to obtain a uniformly stirred casting solution.

[0111] (3) The casting solution obtained in (2) was filtered and vacuum degassed for 10 h.

[0112] (4) The casting solution was coated on a non-woven fabric substrate using an automatic coating machine, with a coating thickness of 150 μm, then the coated liquid film was immersed in a coagulation bath at a temperature of 50 ℃ for phase inversion film formation, and then immersed in deionized water for 18 h of soaking and rinsing to obtain a ternary visible light photocatalyst / polyvinylidene fluoride ultrafiltration membrane.

[0113] In the casting solution, the polyvinylidene fluoride addition amount was 17 wt%, the pore-forming agent addition amount was 6 wt%, the modifier (ternary visible light photocatalyst) addition amount was 1.5 wt%, and the balance was an organic solvent; the pore-forming agent was polyvinylpyrrolidone K30, polyethylene glycol 1000, and sodium chloride.

[0114] Example 4

[0115] S1, Preparation of a ternary visible light photocatalyst

[0116] (1) An appropriate amount of Zn(NO3)2·6H2O was weighed, deionized water was added and stirred to dissolve, then an appropriate amount of NaOH solution was added, the solution pH was adjusted to 9, and the solution was stirred at room temperature for 45 min to obtain mixed solution A.

[0117] (2) An appropriate amount of KI and Bi(NO3)3·5H2O was sequentially added to the mixed solution A prepared in (1), and stirred for 50 min to obtain mixed solution B, with a Bi:Zn molar ratio of 22:78 and a Bi:I molar ratio of 1:1.

[0118] (3) Finally, the prepared mixed solution B was moved into a hydrothermal reaction kettle, and hydrothermal reaction was carried out at 165 ℃ for 8 h, then the sample was washed with deionized water and ethanol several times, and dried at 65 ℃ to obtain the desired binary precursor material BiOI / ZnO.

[0119] (4) An appropriate amount of the binary precursor material prepared in (3) was weighed and dispersed in deionized water, 27 wt% of AgNO3 was added according to the ratio of the binary precursor material, and the mixture was continuously stirred for 25 min, then an appropriate amount of NaOH solution was added, the solution pH was adjusted to 8, and the sample was photoreduced under the irradiation of a high-pressure mercury lamp with a power of 400 W for 1.5 h, finally, the sample was washed with deionized water and ethanol, and dried at 75 ℃ to obtain a ternary visible light photocatalyst Ag2O / BiOI / ZnO.

[0120] S2, Preparation of ternary visible light photocatalyst / polyvinylidene fluoride ultrafiltration membrane

[0121] (1) The prepared ternary visible light photocatalyst is first ultrasonically dispersed in an appropriate amount of N,N-dimethylacetamide to obtain a mixed solution A.

[0122] (2) Polyvinylidene fluoride and a pore former are added to N,N-dimethylacetamide, and after stirring and dissolving at 85℃ for 1h, the pre-dispersed mixed solution A of (1) is added, and heating and stirring are continued for 8h to obtain a uniformly stirred casting solution.

[0123] (3) The casting solution obtained in (2) is filtered, and vacuum degassing is performed for 9h.

[0124] (4) An automatic coating machine is used to scrape coat the casting solution on a non-woven fabric substrate, and the coating thickness is 170μm. Subsequently, the coated liquid film is immersed in a coagulation bath at a temperature of 55℃ for phase inversion, and then immersed in deionized water for soaking and rinsing for 14h to obtain a ternary visible light photocatalyst / polyvinylidene fluoride ultrafiltration membrane.

[0125] In the casting solution, the polyvinylidene fluoride addition amount is 16wt%, the pore former addition amount is 7wt%, the modifier (ternary visible light photocatalyst) addition amount is 2.4wt%, and the balance is an organic solvent; the pore former is polyethylene glycol 50000, polyvinyl alcohol 1788, and lithium chloride.

[0126] Comparative Example 1

[0127] Preparation of a conventional polyvinylidene fluoride ultrafiltration membrane

[0128] (1) Polyvinylidene fluoride and a pore former are first added to a certain amount of N,N-dimethylacetamide, and after stirring and dissolving at 75℃ for 1h, the remaining N,N-dimethylacetamide is supplemented according to the ratio, and heating and stirring are continued for 7h to obtain a uniformly stirred casting solution.

[0129] (2) The casting solution obtained in (1) is filtered, and vacuum degassing is performed for 6h.

[0130] (3) An automatic coating machine is used to scrape coat the casting solution on a non-woven fabric substrate, and the coating thickness is 200μm. Subsequently, the coated liquid film is immersed in a coagulation bath at a temperature of 20℃ for phase inversion, and then immersed in deionized water for soaking and rinsing for 12h to obtain a conventional polyvinylidene fluoride ultrafiltration membrane.

[0131] In the casting solution, the polyvinylidene fluoride addition amount is 15wt%, the pore former addition amount is 10wt%, the modifier addition amount is 0wt%, and the balance is an organic solvent; the pore former is polyethylene glycol 400 and polyvinylpyrrolidone K30.

[0132] Bovine serum albumin (BSA) solution was prepared in the liquid tank of the membrane flux testing device. After membrane filtration, the solution flowed out from the outlet of the testing device and was stirred and tested under visible light irradiation. Example 1 and Comparative Example 1 show the changes in water flux of the modified polyvinylidene fluoride ultrafiltration membrane a and the conventional polyvinylidene fluoride ultrafiltration membrane b when filtering the bovine serum albumin (BSA) solution. Figure 7 As shown, by Figure 7 It can be seen that after 60 minutes of filtration under visible light irradiation, the modified membrane showed a 38.6% reduction in the water flux of bovine serum albumin (BSA) solution compared to the conventional membrane, indicating that the modified membrane prepared in Example 1 has a good antifouling effect under visible light irradiation.

[0133] The performance of the ultrafiltration membranes obtained in Examples 1-4 and Comparative Example 1 was tested, and the results are shown in Table 1. Table 1: Pure water flux and performance data of the ultrafiltration membranes in Examples and Comparative Example 1.

[0134]

[0135] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A ternary visible light catalyst, comprising Ag2O, BiOI and ZnO; The molar ratio of Ag in the Ag2O, Bi in the BiOI and Zn in the ZnO is (20-35) : (15-25) : (75-85).

2. The ternary visible light catalyst according to claim 1, characterized in that, The Ag2O has a spherical morphology, and the particle size of the Ag2O is 20-100 nm.

3. The ternary visible light catalyst according to claim 1, characterized in that, The BiOI has a sheet morphology, and the edge length of the BiOI is 150-400 nm and the thickness is 20-40 nm.

4. The ternary visible light catalyst according to claim 1, characterized in that, The ZnO has a hexagonal columnar morphology, and the diameter of the ZnO is 100-200 nm and the length is 250-700 nm. 5.A method for preparing a ternary visible light catalyst, comprising the following steps: A) mixing an iodine source, a Bi source and a zinc salt solution with a pH of 8-10 to obtain a mixed solution; B) performing a hydrothermal reaction on the mixed solution to obtain a binary precursor material BiOI / ZnO; C) mixing a silver source and the binary precursor material BiOI / ZnO in water, adjusting the pH to 8-9, and performing a photoreduction reaction to obtain a ternary visible light catalyst Ag2O / BiOI / ZnO.

6. The production method according to claim 5, wherein The iodine source is KI and / or NaI, and the Bi source is Bi (NO3) 3·5H2O. The molar ratio of Bi in the Bi source to iodine in the iodine source is 1: (0.9-1.1).

7. The preparation method according to claim 5, characterized in that, The temperature of the hydrothermal reaction in the step B) is 150-190℃, and the time of the hydrothermal reaction in the step B) is 6-18 hours.

8. The preparation method according to claim 5, characterized in that, The mass of Ag in the silver source is 20-30% of the mass of the binary precursor material BiOI / ZnO.

9. The preparation method according to claim 5, characterized in that, The photoreduction reaction is performed under irradiation of a high-pressure mercury lamp, and the power of the high-pressure mercury lamp is 200-500 W, the working wavelength is 365 nm, and the irradiation time is 0.5-4 hours. 10.An ultrafiltration membrane, comprising a polyvinylidene fluoride porous matrix and a visible light catalyst dispersed in the polyvinylidene fluoride porous matrix, wherein the visible light catalyst is the ternary visible light catalyst according to any one of claims 1-4 or the ternary visible light catalyst prepared by the method according to any one of claims 5-9.

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