CN114433226A

CN114433226A - Bismuth-based photocatalytic MXene membrane material and preparation method thereof

Info

Publication number: CN114433226A
Application number: CN202210001061.4A
Authority: CN
Inventors: 程晓婕; 廖家慧; 曾广勇; 林清泉; 薛月; 赵梓俨; 李伟
Original assignee: Sichuan Normal University
Current assignee: Sichuan Normal University
Priority date: 2022-01-04
Filing date: 2022-01-04
Publication date: 2022-05-06

Abstract

The invention discloses a bismuth-based photocatalytic MXene membrane material and a preparation method thereof, wherein BiOCl is prepared by a low-temperature chemical modification method, and BiOCl nanoparticles are doped by PPy to prepare BiOCl-PPy; ti is treated by LiF + HCl mixed solution₃AlC₂(MAX phase) is stripped to obtain two-dimensional Ti with clear lamellar structure₃C₂T_xA material; the BiOCl or BiOCl-PPy dispersion solution and the MXene dispersion solution are ultrasonically mixed, and the BiOCl-PPy @ MXene/PES composite membrane is self-assembled on the PES membrane substrate by a vacuum filtration method, and is used for thoroughly purifying small molecules such as dye, antibiotics and the like in water and has good antibacterial activity. The invention researches the synergistic film forming mechanism and the separation mechanism of two materials in the composite film, organically combines the two materials through the synergistic effect between the photocatalysis technology and the film separation technology, designs and constructs the photocatalysis water treatment film with the functions of separation, purification and self-cleaning, thereby greatly reducing the cost of equipment, labor, energy consumption and the like of a water treatment scheme, and having stronger necessity and wide application prospect.

Description

Bismuth-based photocatalytic MXene membrane material and preparation method thereof

Technical Field

The invention belongs to the technical field of membrane materials and membrane preparation, and particularly relates to a preparation method of a bismuth-system photocatalytic MXene membrane material and the bismuth-system photocatalytic MXene membrane material prepared by the preparation method.

Background

In the process of city promotion and construction, the sewage resource utilization has important significance for relieving the contradiction between water resource supply and demand, reducing water pollution and guaranteeing the ecological safety of water bodies. The membrane separation technology is considered to be one of the most promising technologies in the field of wastewater treatment due to the advantages of operability at room temperature, no phase change, high separation efficiency, environmental friendliness and the like. The membrane material is the key of the membrane separation technology and also the core of the industrialization of the membrane technology. However, the traditional membrane material is easily polluted, the separation function is single, and the effect of mutual restriction between permeability and selectivity cannot be broken. Therefore, the development of a novel membrane material is an effective path for realizing comprehensive utilization of water resources, and has important theoretical value and practical significance.

MXene, a novel two-dimensional transition metal carbide or carbonitride, is considered to be a very promising water treatment material due to the unique microstructure and physicochemical properties. MXene can be represented by the chemical formula M_n+1X_nT_x(M is an early transition metal, X is carbon or nitrogen, and T is a surface active group). MXene has good propertyGood mechanical property and flexibility, two-dimensional slit-shaped channels, proper interlayer spacing and abundant hydrophilic groups (-O, -OH) on the surface, and a separation membrane with limited mass transfer can be constructed by assembling and stacking the lamellar structure. In 2015, a subject group in professor Yury gootsi reports the preparation of MXene films and the diffusion process in the films for the first time, and then a large number of scholars develop related researches on the application of MXene in the film field. Wei et al explored the performance of an MXene/PES composite membrane in oil-water separation applications, and found that improving the hydrophilicity of the MXene membrane surface accelerates the permeation of water molecules and effectively prevents oil droplets from adhering. Xu reports a double regulation strategy (interlayer insertion reduction GO) for microstructure and surface property of the MXene membrane, and the MXene membrane can effectively remove various heavy metal ions in water under the drive of no pressure. The work lays a solid theoretical foundation for accurate control of the MXene structure and realization of oriented screening of the MXene membrane, and provides a good reference meaning for constructing the MXene base membrane with high flux and selectivity.

Therefore, the two-dimensional MXene base membrane material has huge research and development and application prospects in the aspects of water body purification, comprehensive utilization of wastewater resources and the like. The preparation of the two-dimensional MXene/polyvinylidene fluoride (PVDF) composite membrane disclosed in the past comprises the following steps:

zhang Haijun has reported the preparation of two-dimensional MXene/polyvinylidene fluoride (PVDF) composite membranes. They first employed hydrofluoric acid (HF) to Ti₃AlC₂(MAX looks) carry out chemical etching, peel off the Al atomic layer in MAX looks, prepare a novel two-dimensional transition metal carbide stratiform MXene nanometer piece, after modifying MXene with sodium alginate afterwards with chemical stability high, intensity is high, polyvinylidene fluoride (PVDF) milipore filter that toughness is good is the supporting layer, adopt the mode of vacuum filtration with MXene nanometer piece self-assembling on the PVDF supporting layer, prepared novel two-dimensional MXene/PVDF complex film, it promotes and shows hydrophilic oleophobic characteristics by a wide margin to find its permeability, have good removal effect to oily water emulsion. However, the composite film also has the following problems: the lamellar structure of the separation layer is not obvious, and MXene prepared by HF etching is still in a multilayer structure and is difficult to stack on the surface of the membrane in orderThis is liable to cause poor resistance to swelling and an unclear separation mechanism. In practice, a single layer or few layers of MXene nanosheets are used to construct the separation layer of the membrane, so as to enhance the interfacial bonding force between the separation layer and the modified layer. ② the MXene separating layer has thicker thickness. This technique uses 15mg of MXene to build up a separation layer of a composite membrane, which obviously results in a large thickness (18 μm) of the separation layer and an unstable membrane separation layer. Although the stability of the composite membrane under acidic, neutral and alkaline conditions is developed, the soaking time of only 10h does not meet the practical production and use requirements. MXene/PVDF separation layer structure is simple, and although the effect of removing to the oil-water emulsion is better, difficult application in the small molecule field. Therefore, micro-regulation of MXene is required to expand its application range.

(II) preparing a PPy doped BiOCl nano sheet:

the Zhouying topic group has reported the preparation of a PPy doped BiOCl nanosheet. The BiOCl is prepared by a simple low-temperature chemical method, and an interface oxygen vacancy is successfully constructed on a (001) crystal face of the BiOCl through a hydrogen bond acting force between the high polymer PPy and the BiOCl nanosheet, so that the BiOCl-PPy nanosheet is synthesized. The research shows that BiOCl is composed of nano-sheets with the width of about 300 nm-1.5 mu m, and it is worth mentioning that the addition of PPy does not change the microscopic form of BiOCl, and BiOCl-PPy still maintains the shape structure of the two-dimensional nano-sheets, but the lamellar structure is obviously thinned. Under visible light, the photocurrent of the BiOCl-PPy is 8 times higher than that of the BiOCl due to oxygen vacancies generated at the interface of the BiOCl-PPy, which indicates that the BiOCl-PPy has higher carrier density. Therefore, a small amount of PPy significantly contributes to the above photocatalytic properties of BiOCl, and in the NO photo-oxidation reaction, the degradation rate is increased from 12% to 28%, and the byproduct yield is reduced to almost zero. However, the technique still has the following problems: the technology is only directed to the photocatalyst and is not based on the coupling of the photocatalytic technology and the membrane separation technology. BiOCl-PPy is easy to cause the change of unit cell constant during the use process, thereby influencing the stability of the photocatalyst. Secondly, the photocatalytic material is generally a nano material, and secondary problems such as load, separation and recovery, secondary pollution and the like exist in the application process, so that the effect in practical application is severely limited. The technology only aims at NO degradation, is not applied to the field of water treatment, and has yet to be researched for the treatment effect and mechanism of pollutants in the wastewater environment.

Based on the analysis, a bismuth-based photocatalytic MXene membrane material with stable structure, permeability, selectivity and the like and comprehensive performance is urgently needed in the current industry. The membrane material can thoroughly purify small molecules such as dye, antibiotics and the like in water, has good antibacterial activity, greatly reduces the cost of equipment, labor, energy consumption and the like of a water treatment scheme, and has strong necessity and wide application prospect.

Disclosure of Invention

In view of the above disadvantages, the present invention provides a membrane material which can effectively purify small molecules such as dyes and antibiotics in water and has good antibacterial activity, and the membrane material has stable structure and comprehensive properties such as permeability and selectivity.

The invention is realized by the following means:

a preparation method of a bismuth-based photocatalytic MXene membrane material comprises the following steps:

(1) preparation of MXene:

MXene(Ti₃C₂T_x) The MAX phase (Ti) is chemically etched by adopting LiF + HCl mixed reagent on the nanosheet₃AlC₂) The preparation method of the ultrasonic-assisted stripping comprises the following specific steps:

LiF (0.5g) and 12M HCl (50mL) solution were mixed slowly in a PTFE beaker and stirred for 0.5 h. Then, 0.5g of MAX powder was added to the solution and stirred at 30 ℃ for 24 hours. The resulting precipitate was washed with Deionized (DI) water and centrifuged repeatedly (3500prm, 10min) to remove the remaining acid and adjust to pH>6. After centrifugation several times, the supernatant was collected to obtain multilayered MXene nanoplatelets. Precipitation was sonicated in 100mL deionized water for 6 hours at room temperature, and this step was performed under a nitrogen atmosphere to prevent Ti₃C₂T_xThe nanoplatelets are oxidized. After centrifuging the above dispersion for 30min, the supernatant (monolayer MXene) was collected and stored by freeze-drying.

The main reaction is as follows:

Ti₃AlC₂+3LiF+3HCl＝AlF₃+3/2H₂+Ti₃C₂+3LiCl (1-1)

Ti₃C₂+2H₂O＝Ti₃C₂(OH)₂+H₂ (1-2)

Ti₃C₂+2LiF+2HCl＝Ti₃C₂F₂+H₂+2LiCl (1-3)

AlF is produced by the reaction (1-1)₃Al is stripped from the MAX phase. The subsequent reaction of (1-2) and (1-3) leads MXene surface to generate-OH, -F and ═ O groups, and neutralizes the redundant electrons on the Ti metal surface, thereby forming a stable nanosheet structure.

(2) Preparation of BiOCl-PPy:

the BiOCl-PPy nanosheet is prepared by two steps, specifically:

preparing BiOCl by a low-temperature chemical method: 19.4g of Bi (NO)₃)₃·5H₂O dissolved in 40mL of 1M HNO₃Obtaining solution A; dissolving 11.92g of KCl in 100mL of deionized water to obtain a solution B; dropwise adding the solution B into the solution A at 30 ℃ to obtain a product, and washing with ethanol and deionized water respectively; drying the product at 60 ℃ for 12h to obtain BiOCl powder;

dropping 0.5mL of pyrrole into 50mL of ethanol solution, then dropping 10mL of 160g/L Ammonium Persulfate (APS) solution into the solution at the temperature of ice bath (0 +/-0.2), continuously stirring for 24h, filtering the solution, washing with ethanol and deionized water in sequence, finally drying for 18h at the temperature of 60 ℃, and grinding and recovering; BiOCl nanoparticles (300mg) and PPy (15mg, 5%) were dispersed in deionized water; after stirring continuously for 24 hours under dark conditions, the product was washed with ethanol and deionized water, respectively, and finally dried at 60 ℃ for 18 hours to obtain 5% of BiOCl-PPy powder for later use.

(3) Construction of self-cleaning photocatalytic MXene basement membrane:

respectively dispersing 30mg of BiOCl-PPy nano-particles and 2mg of MXene nano-sheets in deionized water, and performing ultrasonic treatment for 15min to uniformly disperse the BiOCl-PPy nano-particles and the MXene nano-sheets to obtain a BiOCl-PPy nano solution and an MXene nano solution;

secondly, mixing the BiOCl-PPy nano solution and the MXene nano solution, and continuing to stir ultrasonically for 15min to mix uniformly to obtain a solution BiOCl-PPy @ MXene precursor solution;

and the BiOCl-PPy @ MXene/PES composite membrane is constructed by permeating a precursor solution onto the surface of a PES commercial membrane (with the aperture of 0.22 mu m) through a vacuum filtration device. The composition of the build membrane is shown in the table below, and a schematic of the build process is shown in FIG. 1. The BiOCl @ MXene/PES composite membrane is prepared by respectively dispersing 30mg of BiOCl and 2mg of MXene nanosheets in deionized water and repeating the process.

The invention has the beneficial effects that:

1. the photocatalytic membrane has a self-cleaning mechanism to alleviate membrane fouling problems. The invention effectively solves the technical problem that the two-dimensional membrane material is screened through the stacked nanoscale channels, and the separated pollutants are accumulated and blocked on the surface of the membrane or in the membrane holes, so that the two-dimensional membrane material is difficult to have lasting separation stability. The invention can effectively remove the pollutants accumulated between the membrane layers without chemical cleaning by introducing the photocatalytic material into the membrane separation layer structure. Under dark conditions, the dye flux of the BiOCl-PPy @ MXene/PES composite membrane is remarkably reduced after 5 cycles, and the value is 2772.7 L.m^-2·h^-1Down to 1725.9 L.m^-2·h^-1Meanwhile, the dye removal rate is respectively reduced from 88.7 percent to 16.3 percent. The above phenomena indicate that after 5 cycles, a large amount of pollutants are accumulated on the surface area of the composite membrane, and the composite membrane no longer has good separation capacity. However, under the irradiation of visible light, the flux of the BiOCl-PPy @ MXene/PES composite membrane is only 2997.4 L.m^-2·h^-1Down to 2826.5 L.m^-2·h^-1And the dye removal rate is kept above 95% after 5 cycles. The experimental results prove that the self-cleaning photocatalytic MXene composite membrane has a good self-cleaning function, can effectively degrade dye molecules attached to the surface of the membrane, and is important for prolonging the service life of the composite membrane.

2. The multifunctionality of the composite membrane is realized. The invention changes the stacking structure of MXene sheet layers by modifying BiOCl and BiOCl-PPyAnd even if the thickness of the separation layer of the original MXene membrane is close to 1 μm, and the thickness of the separation layer of the BiOCl @ MXene and BiOCl-PPy @ MXene composite membrane is close to 30 μm, the interaction between the BiOCl and BiOCl-PPy nano particles and the MXene ensures that the separation layer BiOCl @ MXene (BiOCl-PPy @ MXene) and the support layer still keep good interface bonding force and are not easy to fall off. In addition, due to the interweaving of the BiOCl or BiOCl-PPy nano particles and the MXene nano sheets, the composite membrane keeps a two-dimensional layered structure, and meanwhile, a plurality of new micron-level 'membrane pore channels' exist in the membrane structure, so that the molecular transmission is facilitated, and the permeability of the composite membrane is greatly improved. The experimental result shows that the optimal proportion of the BiOCl @ MXene composite membrane is M3 (namely the separation layer is formed by 2mg of MXene and 30mg of BiOCl), and the pure water flux of the composite membrane is 3224.5 L.m.^-2·h^-1The retention rates of Congo red, Trimeryl blue and Rodamine B are respectively 45.2%, 39.4% and 38.6%, and the removal rates of the three dyes after 8h of photodegradation reach 99.9%. Under the same proportion, the pure water flux of the BiOCl-PPy @ MXene composite membrane is 3680.2 L.m^-2·h^-1The retention rates of dye Congo red, Trimeryl blue and rhodamine B are respectively 42.5%, 32.6% and 38.6%, and the removal rate of the dye can reach 99.9% only by 6h of photodegradation, and the photocatalytic activity is obviously improved. In addition, the BiOCl-PPy @ MXene composite membrane also shows good degradation capability for antibiotics and bacteria in the water body. The degradation rate of the BiOCl-PPy @ MXene composite membrane is up to 96% for tetracycline hydrochloride, and the inhibition rates of the composite membrane are respectively 66.5% and 79.8% for escherichia coli and staphylococcus aureus. Therefore, the scheme of the invention improves the permeability of the membrane, endows the MXene-based composite membrane with the capability of responding to visible light, can purify dyes, antibiotics and bacteria in water, and provides a certain guidance for developing a novel multifunctional membrane material with selectivity and permeability.

3. The unit cell structure of the BiOCl (001) crystal face before and after PPy doping is simulated and constructed through a first linear principle (DFT). The results show that BiOCl has a long bond length

The conductive polymer (PPy) can form a strong interaction with the (001) interface of BiOCl, thereby inducing the formation of oxygen vacancies at the interface. Since oxygen molecules do not have a potential barrier for adsorption of oxygen vacancies, the adsorption of oxygen on oxygen vacancies can easily affect the activity of the photocatalytic reaction. O is₂The surface adsorption energy in BiOCl is-0.05 eV, and the surface adsorption energy on the V-BiOCl interface is-1.83 eV. Furthermore, the Δ q value of BiOCl surface was only 0.48e, increasing to 0.89e in the V-BiOCl system, indicating that the V-BiOCl surface was accompanied by more electron transfer to promote-O₂ ^-Is performed. Furthermore, O is comparable to BiOCl₂The bond angle on the V-BiOCl surface is longer, indicating that oxygen molecules are more readily adsorbed in chemisorbed form on the oxygen vacancies on the V-BiOCl surface. O is₂And BiOCl only physisorption occurs. In summary, O₂And the chemical adsorption form between the V-BiOCl activates the interface oxygen vacancy and promotes electrons and O₂Thereby promoting the formation of superoxide radical in the photocatalysis process and improving the photocatalysis activity.

Generally, the addition of BiOCl obviously improves the permeability of the composite membrane, the composite membrane is endowed with the capabilities of photocatalytic degradation of pollutants and self-cleaning, the synergistic removal of various pollutants in a complex water body by the membrane is realized, and the BiOCl-PPy with an interface oxygen vacancy is constructed by the PPy, so that the high-efficiency photocatalytic activity is shown, and the BiOCl-PPy has a good practical application prospect.

Drawings

FIG. 1 is a schematic diagram of the process of constructing a membrane according to the present invention.

Fig. 2 is a self-made photocatalytic film performance evaluation device.

FIG. 3 is a diagram of the result of DFT theoretical simulation.

Detailed Description

The present invention is described in further detail below with reference to examples, which are intended to facilitate the understanding of the present invention without limiting it in any way.

Example 1

A preparation method of a BiOCl @ MXene/PES composite membrane comprises the following steps:

(1) preparation of MXene:

LiF (0.5g) and 12M HCl (50mL) solution were mixed slowly in a PTFE beaker and stirred for 0.5 h. Then, 0.5g of MAX powder was added to the solution and stirred at 30 ℃ for 24 hours. The resulting precipitate was washed with Deionized (DI) water and centrifuged repeatedly (3500prm, 10min) to remove the remaining acid and adjust to pH>6. After centrifugation several times, the supernatant was collected to obtain multilayered MXene nanoplatelets. The precipitate was sonicated in 100mL deionized water at room temperature for 6 hours, which was performed under a nitrogen atmosphere to prevent Ti₃C₂T_xThe nanoplatelets are oxidized. After centrifuging the above dispersion for 30min, the supernatant (monolayer MXene) was collected and stored by freeze-drying.

(2) Preparation of BiOCl:

the BiOCl nanosheet is prepared by a low-temperature chemical method, and specifically comprises the following steps:

19.4g of Bi (NO)₃)₃·5H₂O dissolved in 40mL of 1M HNO₃To obtain a solution A; dissolving 11.92g of KCl in 100mL of deionized water to obtain a solution B; dropwise adding the solution B into the solution A at 30 ℃ to obtain a product, and washing with ethanol and deionized water respectively; drying the product at 60 ℃ for 12h to obtain BiOCl powder;

(3) construction of self-cleaning photocatalytic MXene base membrane:

dispersing 30mg of BiOCl and 2mg of MXene nanosheets in deionized water respectively, and performing ultrasonic treatment for 15min to uniformly disperse the BiOCl and MXene nanosheets to obtain a BiOCl nano solution and an MXene nano solution;

secondly, mixing the BiOCl nano solution and the MXene nano solution, and continuing to stir ultrasonically for 15min to mix uniformly to obtain a solution BiOCl @ MXene precursor solution;

and the BiOCl @ MXene/PES composite membrane is constructed by permeating a precursor solution onto the surface of a PES commercial membrane (with the aperture of 0.22 mu m) through a vacuum filtration device.

Example 2

A preparation method of a BiOCl-PPy @ MXene/PES composite membrane comprises the following steps:

(1) preparation of MXene:

MXene(Ti₃C₂T_x) The MAX phase (Ti) is chemically etched by adopting LiF + HCl mixed reagent on the nanosheet₃AlC₂) The ultrasonic assisted stripping method comprises the following specific steps:

LiF (0.5g) and 12M HCl (50mL) solution were mixed slowly in a PTFE beaker and stirred for 0.5 h. Then, 0.5g MAX powder was added to the solution and stirred at 30 ℃ for 24 hours. The resulting precipitate was washed with Deionized (DI) water and centrifuged repeatedly (3500prm, 10min) to remove the remaining acid and adjust to pH>6. After centrifugation several times, the supernatant was collected to obtain multilayered MXene nanoplatelets. The precipitate was sonicated in 100mL deionized water at room temperature for 6h, which was performed under a nitrogen atmosphere to prevent Ti₃C₂T_xThe nanoplatelets are oxidized. After centrifuging the above dispersion for 30min, the supernatant (monolayer MXene) was collected and stored by freeze-drying.

(2) Preparation of BiOCl-PPy:

the BiOCl-PPy nanosheet is prepared by two steps, specifically:

preparing BiOCl by a low-temperature chemical method: 19.4g of Bi (NO)₃)₃·5H₂O dissolved in 40mL of 1M HNO₃To obtain a solution A; dissolving 11.92g of KCl in 100mL of deionized water to obtain a solution B; dropwise adding the solution B into the solution A at 30 ℃ to obtain a product, and washing with ethanol and deionized water respectively; drying the product at 60 ℃ for 12h to obtain BiOCl powder;

dropping 0.5mL of pyrrole into 50mL of ethanol solution, then dropping 10mL of 160g/L Ammonium Persulfate (APS) solution into the solution at the temperature of ice bath (0 +/-0.2), continuously stirring for 24h, filtering the solution, washing with ethanol and deionized water in sequence, finally drying for 18h at the temperature of 60 ℃, and grinding and recovering; BiOCl nanoparticles (300mg) and PPy (15mg, 5%) were dispersed in deionized water; after stirring continuously for 24 hours in the dark, the product was washed with ethanol and deionized water, respectively, and finally dried at 60 ℃ for 18 hours to give BiOCl-PPy (5%) powder.

(3) Construction of self-cleaning photocatalytic MXene basement membrane:

③ the BiOCl-PPy @ MXene/PES composite membrane is constructed by permeating precursor solution to the surface of PES commercial membrane (with the aperture of 0.22 μm) through a vacuum filtration device, the composition of the constructed membrane is shown in Table 1, and the schematic diagram of the construction process is shown in figure 1.

Comparative examples 1 to 3

The process steps involved in comparative examples 1 to 3 were the same as in example 1, except for the difference in the compounding ratio of MXene content and BiOCl content, as shown in Table 1.

TABLE 1

Grouping	Film numbering	MXene content (mg)	BiOCl content (mg)
				Comparative example 1	M0	2	0
Comparative example 2	M1	2	10
				Comparative example 3	M2	2	20
Example 1	M3	2	30
				Example 2	M4	2	30(BiOCl-PPy)

Test example 1

Self-cleaning capability determination of photocatalytic film

The self-cleaning ability of the photocatalytic film was evaluated by means of a vacuum filtration apparatus (see fig. 2). The specific method comprises the following steps: under dark conditions, the dye solution was allowed to permeate through the photocatalytic membrane without washing midway through for a total of 5 cycles, and the flux and rejection rate during each cycle were recorded. Meanwhile, the operations are repeated under the illumination condition, and in the process of each cycle, after the pollutants permeate through the membrane, the composite membrane is placed under visible light for 1 hour for irradiation, and then the next cycle is carried out. Test results show that under the dark condition, the dye flux of the BiOCl-PPy @ MXene/PES composite membrane is remarkably reduced after 5 cycles and is from 2772.7 L.m^-2·h^-1Down to 1725.9L m^-2·h^-1Meanwhile, the dye removal rate is respectively reduced from 88.7 percent to 16.3 percent. The phenomenon shows that after 5 times of circulation, a large amount of pollutants are accumulated on the surface of the composite membrane, and the composite membrane does not containAnd has good separation capability. However, under the irradiation of visible light, the flux of the BiOCl-PPy @ MXene/PES composite film is only from 2997.4 L.m^-2·h^-1Down to 2826.5L m^-2·h^-1And the dye removal rate is kept above 95% after 5 cycles. The experimental results prove that the self-cleaning photocatalytic MXene composite membrane has a good self-cleaning function, can effectively degrade dye molecules attached to the surface of the membrane, and is very important for prolonging the service life of the composite membrane.

Test example 2

Determination of the multifunctional Properties of photocatalytic films

The membrane performance was tested using a home-made apparatus (see figure 2). The specific operation method comprises the following steps: the pure water flux of the membrane was calculated by permeating a certain amount of deionized water in the unit 1 by means of a vacuum filtration device and recording the time required. Wherein the effective area of the membrane surface is 12.56 cm²The operating pressure was 0.1 MPa. Meanwhile, dye solution is permeated by means of a vacuum filtration device and the rejection rate of the obtained membrane is tested; the membrane in unit 1 in unit 2 was removed from the device and subjected to a photocatalytic degradation experiment, collecting 5mL of reaction solution per hour, detecting under visible light for several hours, measuring the concentration of the dye or antibiotic solution by recording the absorbance of the different dyes or antibiotics in their characteristic peaks (CR: 664 nm; TB: 607 nm; RhB: 553 nm; TC: 356 nm).

Experimental results show that the optimal proportion of the BiOCl @ MXene composite membrane is the M3 membrane prepared in example 1 (i.e. the separation layer is composed of 2mg of MXene and 30mg of BiOCl), and the pure water flux of the composite membrane is 3224.5 L.m.^-2·h^-1The retention rates of the dyes Congo red, Trimeryl blue and rhodamine B are 45.2%, 39.4% and 38.6% respectively, and the removal rates of the three dyes after 8 hours of photodegradation reach 99.9%. The pure water flux of the BiOCl-PPy @ MXene composite membrane (M4) prepared in example 2 at the same ratio was 3680.2 L.m^-2·h^-1The retention rates of dye Congo red, Trimeryl blue and rhodamine B are respectively 42.5%, 32.6% and 38.6%, and the removal rate of the dye can reach 99.9% only by 6h of photodegradation, and the photocatalytic activity is obviously improved. In addition, aim atThe BiOCl-PPy @ MXene composite membrane also shows good degradation capability. The degradation rate of the BiOCl-PPy @ MXene composite membrane is up to 96% for tetracycline hydrochloride, and the inhibition rates of the composite membrane are respectively 66.5% and 79.8% for escherichia coli and staphylococcus aureus. Therefore, the scheme of the invention improves the permeability of the membrane, endows the MXene-based composite membrane with the capability of responding to visible light, can purify dyes, antibiotics and bacteria in water, and provides a certain guidance for developing a novel multifunctional membrane material with selectivity and permeability.

Test example 3

The unit cell structure of the BiOCl (001) crystal face before and after PPy doping is simulated and constructed through a first linear principle (DFT). All density function theoretical calculations were performed in CATSEP based on Materials Studio software version 8.0. The Perew-Burke-Emzerhof (PBE) function in Generalized Gradient Approximation (GGA) is used to exchange correlation energies and optimize the structure by using ultra-soft pseudopotentials. The plane wave cut-off energy was set to 420eV to analyze the effect of interfacial oxygen vacancies (after PPy loading) on the BiOCl state Density (DOS). The brillouin zone was sampled using a special 4 x 1Monkorst-park K point grid for geometry optimization and energy calculation. The lattice parameter used in the optimization process for constructing the superlattice structure is

α ═ β ═ γ ═ 90 °. Furthermore, the energy, maximum force, maximum stress and maximum displacement accuracy of the self-consistent iterations should be set to 2.0X 10-5eV/atom,

0.1Gpa and

the results are shown in FIG. 3, due to the long bond length of BiOCl

The conductive polymer (PPy) can form a strong interaction with the (001) interface of BiOCl, thereby inducing the formation of oxygen vacancies at the interface. Since oxygen molecules do not have a potential barrier for adsorption of oxygen vacancies, the adsorption of oxygen on oxygen vacancies can easily affect the activity of the photocatalytic reaction. O is₂The surface adsorption energy in BiOCl is-0.05 eV, and the surface adsorption energy on the V-BiOCl interface is-1.83 eV. Furthermore, the Δ q value of BiOCl surface was only 0.48e, increasing to 0.89e in the V-BiOCl system, indicating that the V-BiOCl surface was accompanied by more electron transfer to promote-O₂ ^-Is performed. Furthermore, the bond angle of O2 on the V-BiOCl surface is longer compared to that of BiOCl, indicating that oxygen molecules are more readily adsorbed in chemisorbed form on the oxygen vacancies on the V-BiOCl surface. O is₂And BiOCl only physisorption occurs.

In summary, O₂And the chemical adsorption form between the V-BiOCl activates the interface oxygen vacancy and promotes electrons and O₂Thereby promoting the formation of superoxide radical in the photocatalysis process and improving the photocatalysis activity.

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention. The method comprises the following steps:

1. except for etching MAX phase by using LiF + HCl mixed reagent, HF and NH are used by others₄HF₂Molten fluoride salt and NaOH and H₂SO₄And (3) etching by using the methods to prepare the MXene nanosheet, wherein other steps are consistent with the technical scheme of the invention, and the self-cleaning photocatalytic MXene-based composite membrane can be prepared to realize the purpose of the invention. For example, Zhang Haijun has reported the preparation of two-dimensional MXene/polyvinylidene fluoride (PVDF) composite films using hydrofluoric acid (HF) on Ti₃AlC₂Performing chemical etching to prepare a layerMXene nanosheets.

2. According to the invention, the PES membrane is used as a supporting layer of the composite membrane, if other people use organic polymer membrane materials such as Cellulose Acetate (CA) membrane, polyvinylidene fluoride (PVDF) and Polysulfone (PSF) as the supporting layer, other steps (such as preparation of BiOCl and BiOCl-PPy, preparation of MXene, suction filtration stacking method and mixing ratio) are consistent with the technical scheme of the invention, and the self-cleaning photocatalytic MXene-based composite membrane can be prepared, so that the purpose of the invention is realized. For example, Zhang Haijun adopts a polyvinylidene fluoride (PVDF) ultrafiltration membrane as a supporting layer, and MXene nanosheets are self-assembled on the PVDF supporting layer in a vacuum filtration mode, so that the novel two-dimensional MXene/PVDF composite membrane is prepared.

Claims

1. A bismuth-based photocatalytic MXene film material, comprising:

MXene nano-sheets, bismuth-based photocatalytic nano-particles and a supporting layer;

wherein: the bismuth-based photocatalytic nano particles are intercalated between MXene nano sheets to form an MXene/bismuth-based photocatalytic nano particle composite material;

the MXene/bismuth-based photocatalytic nanoparticle composite material is prepared on the supporting layer.

2. The film material of claim 1, wherein:

the MXene nano-sheet is Ti₃C₂T_x。

3. The film material of claim 1, wherein:

the bismuth-based photocatalytic nanoparticles comprise BiOCl and BiOCl-PPy.

4. The film material of claim 1, wherein:

the support layer comprises PES (polyether sulfone) membrane, cellulose acetate membrane, polyvinylidene fluoride membrane and polysulfone membrane.

5. A preparation method of a bismuth-based photocatalytic MXene membrane material comprises the following steps:

(1) obtaining MXene nanosheets by chemically etching MAX through LiF + HCl;

(2) preparing bismuth-based photocatalytic nanoparticles;

(3) respectively carrying out ultrasonic treatment on the bismuth-based photocatalytic nano particles and MXene to obtain homogeneous phase solutions, mixing the homogeneous phase solutions to obtain a precursor solution, and carrying out vacuum suction filtration on the precursor solution onto a supporting layer substrate to obtain the bismuth-based photocatalytic MXene membrane material.

6. The production method according to claim 5, wherein:

the MXene is prepared by the following method:

firstly, 0.5g of LiF and 50mL of 12M HCl solution are mixed and stirred for 0.5h to prepare etching solution for later use;

② adding 0.5g MAX into the etching solution, and stirring for 24h at 30 ℃;

thirdly, after the reaction is finished, collecting the precipitate A, washing the precipitate A with deionized water for a plurality of times, and repeatedly centrifuging the precipitate A until the pH value of the solution is more than 6.0 to obtain supernatant and a precipitate B;

fourthly, dissolving the precipitate B in 100mL of deionized water at room temperature to form a dispersion liquid, carrying out ultrasonic treatment for 6h, centrifuging the dispersion liquid for 30min, collecting supernatant, and carrying out freeze drying to obtain MXene for later use.

7. The production method according to claim 5, wherein:

the bismuth-based photocatalytic nanoparticles are prepared by the following method:

dissolving 19.4g of Bi (NO3) 3.5H 2O in 40mL of 1M HNO3 to obtain a solution A; dissolving 11.92g of KCl in 100mL of deionized water to obtain a solution B; dropwise adding the solution B into the solution A at 30 ℃ to obtain a first product, washing the first product with ethanol and deionized water respectively, and drying the first product at 60 ℃ for 12 hours to obtain BiOCl powder for later use;

dropping 0.5mL of pyrrole into 50mL of ethanol solution, then dropping 10mL of 160g/L ammonium persulfate solution into the solution under the ice bath condition, continuously stirring for 24h, filtering the solution, washing the solution by using ethanol and deionized water in sequence, finally drying the solution at 60 ℃ for 18h, and grinding and recovering;

dispersing 300mg of BiOCl nano-particles and 15mg of PPy in deionized water; continuously stirring for 24h under a dark condition, washing the product with ethanol and deionized water respectively, and finally drying at 60 ℃ for 18h to obtain 5% BiOCl-PPy powder for later use.

8. The production method according to claim 5, wherein:

the bismuth-based photocatalytic MXene membrane material is prepared by the following method:

dispersing 30mg of bismuth-based photocatalytic nano particles and 2mg of MXene nanosheets in deionized water respectively, and performing ultrasonic treatment for 15min to obtain a bismuth-based photocatalytic nano solution and an MXene nano solution for later use;

mixing the bismuth-based photocatalytic nano solution and the MXene nano solution, and continuing to stir ultrasonically for 15min to mix uniformly to obtain a precursor solution;

thirdly, penetrating the precursor solution to the surface of the support layer through a vacuum filter device to obtain the bismuth-based photocatalytic MXene membrane material.

9. The production method according to claim 8, wherein:

the bismuth-based photocatalytic nanoparticles comprise BiOCl and BiOCl-PPy.

10. A bismuth-based photocatalytic MXene membrane material prepared according to any one of the preparation methods of claims 5-9.