A special defluorination nanofiltration membrane and a preparation method thereof

Abstract

The application provides a special nanofiltration membrane for removing fluorine and a preparation method thereof. The method comprises the following steps: preparing an aqueous phase solution containing piperazine and boronic acid functionalized carbon dots, and preparing an organic phase solution containing acyl chloride compounds; taking at least one side surface of a base film as a modification treatment surface; adding the aqueous phase solution and the organic phase solution to the modification treatment surface to perform interfacial polymerization, and obtaining a polyamide and boronic acid functionalized carbon dot modified membrane as a nanofiltration membrane. The prepared nanofiltration membrane introduces amino groups, imino groups, boronic acid groups and other hydrophilic groups through piperazine and boronic acid functionalized carbon dots, so that the hydrophilicity and acid resistance of the nanofiltration membrane are improved. The boronic acid functionalized carbon dots can generate active oxygen under irradiation of a specific wavelength, so that the bacteria on the surface of the nanofiltration membrane are inactivated, and the antibacterial function is realized. In addition, the boronic acid groups on the boronic acid functionalized carbon dots are easy to form a complex with fluorine ions under alkaline conditions, so that the effect of removing fluorine ions in water bodies is achieved.

Description

Technical Field

[0001] This invention relates to the field of nanocomposite materials, and in particular to a nanofiltration membrane specifically for fluoride removal, and a method for preparing such a membrane. Background Technology

[0002] Among existing technologies, membrane filtration is currently a highly efficient and promising water treatment method, characterized by its affordability, low energy consumption, scalability, ease of manufacturing, and eco-friendliness. Membrane filtration technologies typically include reverse osmosis (RO), forward osmosis (FO), nanofiltration (NF), and ultrafiltration (UF). Nanofiltration, a pressure-driven membrane filtration technology situated between reverse osmosis and ultrafiltration, is commonly used to separate low molecular weight substances. Compared to other filtration membranes, nanofiltration membranes offer advantages such as high permeate flux, low pressure drive, relatively high rejection rate, and lower relative cost, making their application in various scientific fields, especially water treatment, a focus of attention.

[0003] Generally, filter membranes are susceptible to fouling during use, which can be categorized into biological fouling and non-biological fouling. Non-biological fouling can usually be buffered or resolved through physical methods such as rinsing and agitation. However, biological fouling is typically irreversible, causing microorganisms to accumulate on the filter membrane surface. This not only affects water permeability but also exacerbates other types of fouling on the membrane surface due to the strong adhesion of bacteria.

[0004] Meanwhile, nanofiltration membranes are typically made of polymeric materials such as polyamide, polyethersulfone (PES), and polyetheretherketone (PEEK). While these materials possess good mechanical strength and separation performance, they may degrade or age in extreme environments such as strong acids. High hydrogen ion concentrations in acidic environments can affect the chemical stability of membrane materials, thereby reducing the membrane's antifouling ability and lifespan.

[0005] Furthermore, in the field of water treatment, excessive fluoride ion content in wastewater or environmental water bodies can easily affect human health. Excessive fluoride intake can lead to dental fluorosis, skeletal fluorosis, and even fluorosis. With the acceleration of industrialization and the influence of natural factors, fluoride pollution is becoming increasingly serious. Existing technologies include precipitation, adsorption, ion exchange, and electrochemical methods to remove fluoride ions from water. However, precipitation is prone to secondary pollution; adsorption requires large amounts of adsorbent that need to be replaced regularly; ion exchange involves high costs for resin regeneration and replacement; and electrochemical methods involve electrode materials that are prone to corrosion and are also costly. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a nanofiltration membrane for defluorination and a method for preparing a nanofiltration membrane for defluorination, which can remove fluoride ions from water and has good antibacterial and acid-resistant properties, so that the nanofiltration membrane can have a long service life.

[0007] To address the above problems, this invention discloses a method for preparing a nanofiltration membrane specifically for fluoride removal, the method comprising:

[0008] An aqueous solution containing piperazine and boric acid-functionalized carbon dots was prepared, and an organic solution containing acyl chloride compounds was also prepared.

[0009] At least one surface of the base film is used as the modified surface;

[0010] The aqueous phase solution and the organic phase solution are added to the modified surface for interfacial polymerization to obtain a polyamide and boric acid functionalized carbon dot modified membrane as a nanofiltration membrane; the nanofiltration membrane is used to remove fluoride ions from water, and has antibacterial and anti-acid properties.

[0011] Optionally, the nanofiltration membrane comprises a primary modified nanofiltration membrane;

[0012] The step of adding the aqueous phase solution and the organic phase solution to the modified surface for interfacial polymerization to obtain a polyamide and boric acid functionalized carbon dot modified membrane as a nanofiltration membrane includes:

[0013] The aqueous solution is added to the modified surface, and after soaking for a preset first treatment time, the droplets on the base film surface are removed.

[0014] The organic phase solution is added to the modified surface, and interfacial polymerization is performed. After soaking for a preset second treatment time, the surface is dried to obtain a modified nanofiltration membrane.

[0015] Optionally, the nanofiltration membrane includes a secondary modified nanofiltration membrane;

[0016] The step of adding the aqueous solution and the organic solution to the modified surface for interfacial polymerization to obtain a polyamide and boric acid functionalized carbon dot modified membrane as a nanofiltration membrane further includes:

[0017] A boric acid functionalized carbon dot solution is added to the surface of the primary modified nanofiltration membrane for secondary interfacial polymerization. After soaking for a preset third treatment time, a secondary modified nanofiltration membrane is obtained.

[0018] Optionally, the method further includes:

[0019] The nanofiltration membrane is immersed in a catechol solution, and the boric acid functionalized carbon dots on the surface of the nanofiltration membrane react with the catechol in the catechol solution to form a boric acid functionalized carbon dot-catechol probe; the boric acid functionalized carbon dot-catechol probe is used to detect fluoride ions in water.

[0020] Optionally, the boric acid functionalized carbon dots are prepared by the following method:

[0021] 3-Aminophenylboronic acid and piperazine were dissolved in water and reacted by hydrothermal method to obtain boric acid functionalized carbon dots.

[0022] Optionally, the molar ratio between the 3-aminophenylboronic acid and the piperazine is 4:1 to 1:1.

[0023] Optionally, the weight percentage of the piperazine in the aqueous solution is 1% to 5%; and the weight percentage of the boric acid functionalized carbon dots is 0.5% to 1%.

[0024] Optionally, the acyl chloride compound includes at least one of pyromellitic methyl methacrylate (PMMA), terephthaloyl chloride (TBMA), and isophthaloyl chloride (IMMA).

[0025] Optionally, the weight percentage of the acyl chloride compound in the organic phase solution is 0.1%-0.5%.

[0026] This invention also provides a nanofiltration membrane specifically for fluoride removal. The nanofiltration membrane includes a base membrane, at least one surface of which is modified with polyamide and boric acid-functionalized carbon dots. The nanofiltration membrane is used to remove fluoride ions from water and has antibacterial and anti-acid properties.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] The method for preparing a fluoride-removing nanofiltration membrane according to embodiments of the present invention involves preparing an aqueous solution containing piperazine and boric acid functionalized carbon dots, and an organic solution containing acyl chloride compounds. At least one surface of a base membrane is used as a modification surface. The aqueous solution and the organic solution are added to the modified surface for interfacial polymerization to obtain a polyamide and boric acid functionalized carbon dot modified membrane as a nanofiltration membrane. This nanofiltration membrane is used to remove fluoride ions from water, and also exhibits antibacterial and acid-resistant properties. Thus, the prepared nanofiltration membrane introduces hydrophilic groups such as amino, imino, and boric acid groups through piperazine and boric acid functionalized carbon dots, which improves the hydrophilicity and membrane flux of the nanofiltration membrane, increasing the flux by 40.98%-71.25%, while also providing good acid resistance. Simultaneously, the boric acid functionalized carbon dots can generate reactive oxygen species (ROS) under irradiation at a specific wavelength, inactivating bacteria on the nanofiltration membrane surface and achieving antibacterial function. Furthermore, the borate groups on the borate-functionalized carbon dots deprotonate under alkaline conditions, resulting in a strongly negatively charged surface. These groups readily form complexes with fluoride ions, effectively removing fluoride ions from water, achieving a fluoride ion rejection rate of over 80%. Therefore, the nanofiltration membrane provided in this invention can remove fluoride ions from water while also exhibiting good antibacterial and acid-resistant properties, resulting in a longer service life and effectively reducing the frequency of chemical cleaning. Attached Figure Description

[0029] Figure 1 These are TEM images of borate-functionalized carbon dots provided in the embodiments of the present invention.

[0030] Figure 2 This is a particle size distribution diagram of boric acid functionalized carbon dots provided in an embodiment of the present invention;

[0031] Figure 3 This is an infrared spectral characterization diagram of borate-functionalized carbon dots provided in an embodiment of the present invention;

[0032] Figure 4 This is an X-ray diffraction pattern of borate-functionalized carbon dots provided in an embodiment of the present invention;

[0033] Figure 5 This is a Zeta potential test diagram of borate-functionalized carbon dots provided in an embodiment of the present invention;

[0034] Figure 6 This is a schematic diagram of the water contact angle provided by the present invention;

[0035] Figure 7 This is a schematic diagram of water flux testing and retention rate testing of different types of salt solutions provided by the present invention;

[0036] Figure 8 This is a schematic diagram of the relationship between potential and pH provided by the present invention;

[0037] Figure 9 This is a schematic diagram illustrating the relationship between molecular weight and retention rate provided by the present invention;

[0038] Figure 10 This is a schematic diagram of the NaF retention rate at different pH levels provided by the present invention;

[0039] Figure 11 This is a schematic diagram showing the relationship between pickling time and water contact angle provided by the present invention;

[0040] Figure 12 This is a schematic diagram of the pickling time, water flux, and rejection rate provided by the present invention;

[0041] Figure 13 This is a schematic diagram illustrating the recovery of NaF retention rate provided by the present invention;

[0042] Figure 14 This is a schematic diagram illustrating the antibacterial effect against Escherichia coli provided by the present invention;

[0043] Figure 15 This is the EPR spectrum of borate-functionalized carbon dots provided in the embodiments of the present invention;

[0044] Figure 16 This is a schematic diagram of the TMB colorimetric method test provided by the present invention;

[0045] Figure 17 This is a graph showing the effect of the boric acid functionalized carbon dot-catechol probe on fluoride ion concentration monitoring provided in the embodiments of the present invention.

[0046] Figure 18 This is a graph showing the monitoring effect of fluoride ion concentration corresponding to the nanofiltration membrane prepared in Example 1 of the present invention;

[0047] Figure 19 This is a graph showing the monitoring effect of fluoride ion concentration corresponding to the nanofiltration membrane prepared in Example 2 of the present invention;

[0048] Figure 20 The fluorescence spectra of the boric acid functionalized carbon dot-catechol probe provided by this invention for different anions are shown.

[0049] Figure 21 It represents the ratio of changes in fluorescence intensity of boric acid-functionalized carbon dot-catechol probe aqueous solution for different anions. Detailed Implementation

[0050] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0051] This invention discloses a method for preparing a nanofiltration membrane specifically for fluoride removal, the method comprising:

[0052] Step 101: Prepare an aqueous solution containing piperazine and boric acid functionalized carbon dots, and prepare an organic solution containing acyl chloride compounds;

[0053] Step 102: Use at least one side surface of the base film as the modified surface;

[0054] Step 103: Add an aqueous phase solution and an organic phase solution to the modified surface for interfacial polymerization to obtain a polyamide and boric acid functionalized carbon dot modified membrane as a nanofiltration membrane; the nanofiltration membrane is used to remove fluoride ions from water, and has antibacterial and anti-acid properties.

[0055] In this embodiment of the invention, to improve the fluoride ion treatment effect of the filter membrane and extend its service life, the base membrane can be modified first. The base membrane can be, for example, a polyethersulfone (PES) membrane or a polyetheretherketone (PEEK) membrane; this invention is not limited to these types. Preferably, the base membrane is a polyethersulfone membrane.

[0056] As a specific example of the present invention, the polyethersulfone membrane can be prepared by a non-solvent phase separation method using polyethersulfone (PES), N,N-dimethylformamide (DMF) and N-methylpyrrolidone (NMP).

[0057] In practical implementation, polyamide and boric acid functionalized carbon dots can be used to modify the filter membrane, so that the modified nanofiltration membrane can remove fluoride ions from water and also has good antibacterial and acid-resistant properties.

[0058] To graft polyamide and boric acid functionalized carbon dots onto the surface of a base film, an aqueous solution containing piperazine and boric acid functionalized carbon dots, and an organic solution containing acyl chloride compounds, can be prepared, respectively. Subsequently, at least one surface of the base film can be used as a modification surface, and the aqueous and organic solutions can be added to the modified surface for interfacial polymerization.

[0059] Specifically, piperazine and acyl chloride compounds are polymerized on the modified surface to form a polyamide layer. Simultaneously, boric acid-functionalized carbon dots, containing amino groups, are polymerized with acyl chloride compounds to form a polyamide layer. These boric acid-functionalized carbon dots are then grafted onto the surface of the polyamide layer, resulting in a polyamide and boric acid-functionalized carbon dot-modified membrane used as a nanofiltration membrane.

[0060] In practical implementation, the base membrane can have one smooth side and the other rough side. The smooth side is usually flat and evenly distributed with pores. The rough side, on the other hand, is usually uneven and has a larger specific surface area and microstructure. Generally speaking, the rough side of the base membrane is more suitable for high-flux applications, low-pressure environments, and scenarios requiring strong adhesion of the active layer, such as ultrafiltration. The smooth side of the base membrane is more suitable for high-precision separation applications such as nanofiltration and reverse osmosis, water treatment with high anti-fouling requirements, and the food and pharmaceutical industries.

[0061] Therefore, the smooth surface of the base film can be used as the modified surface. At the same time, depending on actual needs, the rough surface of the base film can be used as the modified surface, or both the smooth and rough surfaces can be used as modified surfaces. This invention does not limit this.

[0062] The nanofiltration membrane prepared in the embodiments of the present invention has uniformly distributed boric acid functionalized carbon dots and polyamide grafted on its surface. Both can provide a large number of hydrophilic groups such as amino, imino, and boric acid groups for the nanofiltration membrane, which can effectively increase the hydrophilicity of the nanofiltration membrane and improve its flux.

[0063] At the same time, amino and imino groups can undergo protonation reactions in acidic environments, reacting with H+ in the environment. + Ionic reaction. Under alkaline conditions, H+... + Ions can be released. Therefore, nanofiltration membranes can possess reversible acid resistance, effectively preventing acidic environments from affecting the stability of the nanofiltration membrane and improving its service life.

[0064] The boric acid functionalized carbon dots provide the boric acid groups for the nanofiltration membrane. In an alkaline environment, these groups deprotonate, resulting in a strongly negatively charged surface that readily forms complexes with fluoride ions. This allows the nanofiltration membrane of this invention to also remove chloride ions from water. Simultaneously, in an acidic environment, the boric acid groups can protonate to form boric acid. At this point, the stability of the complex formed with fluoride ions decreases, allowing some fluoride ions to detach from the boric acid groups. Therefore, the fluoride removal function of the nanofiltration membrane can have a certain regeneration effect.

[0065] Furthermore, boric acid functionalized carbon dots can generate reactive oxygen species (ROS) under irradiation at a specific wavelength, such as 365 nm. ROS can attack the protein structures of bacterial cell membranes and cytoplasm, thereby inactivating the bacteria. As a result, the nanofiltration membrane of the present invention can have good antibacterial ability.

[0066] Nanofiltration membranes modified with polyamide and boric acid functionalized carbon dots exhibit reduced pore size due to interfacial polymerization. Simultaneously, the polar effects of polyamide and boric acid functionalized carbon dots effectively enhance the retention rates of magnesium sulfate, magnesium chloride, sodium sulfate, and sodium chloride, enabling the nanofiltration membrane to more thoroughly filter impurities from water.

[0067] In one embodiment of the present invention, the nanofiltration membrane includes a primary modified nanofiltration membrane;

[0068] The steps of adding an aqueous phase solution and an organic phase solution to the modified surface for interfacial polymerization to obtain a polyamide and boric acid functionalized carbon dot modified membrane as a nanofiltration membrane include:

[0069] S11, Add an aqueous solution to the modified surface, soak for a preset first treatment time, and then remove droplets from the base film surface;

[0070] S12, an organic phase solution is added to the modified surface to perform interfacial polymerization, and after soaking for a preset second treatment time, the surface is dried to obtain a modified nanofiltration membrane.

[0071] Specifically, the modification of the nanofiltration membrane can be achieved by first adding an aqueous solution to the surface to be modified and immersing it for a preset first treatment time, allowing the piperazine and boric acid functionalized carbon dots in the aqueous solution to be more uniformly distributed on the surface. Afterwards, excess droplets on the base membrane surface can be removed. Then, an organic phase solution is poured onto the surface, where the acyl chloride compounds can undergo interfacial polymerization with the piperazine and boric acid functionalized carbon dots to form a polyamide on the surface. The boric acid functionalized carbon dots are then grafted onto the surface via their amino groups. After drying, a primary modified nanofiltration membrane modified with polyamide and boric acid functionalized carbon dots is obtained.

[0072] The first processing time can be 2 to 5 minutes, for example, 2 minutes, 2.5 minutes, 3 minutes, 3.5 minutes, 4 minutes, 4.5 minutes, 5 minutes, etc. Preferably, the first processing time can be 3 minutes.

[0073] The second processing time can be from 1 minute to 3 minutes, for example, 1 minute, 1.5 minutes, 2 minutes, 2.5 minutes, 3 minutes, etc. Preferably, the second processing time can be 2 minutes.

[0074] In a specific implementation, the drying process can be carried out by placing the membrane after the first interfacial polymerization is completed in a drying oven and drying it at 60°C for 10 minutes.

[0075] In one embodiment of the present invention, the nanofiltration membrane includes a secondary modified nanofiltration membrane;

[0076] The step of adding an aqueous solution and an organic solution to the modified surface for interfacial polymerization to obtain a polyamide and boric acid-functionalized carbon dot modified membrane as a nanofiltration membrane also includes:

[0077] S21, add boric acid functionalized carbon dot solution to the surface of the primary modified nanofiltration membrane, perform secondary interfacial polymerization, and immerse for a preset third treatment time to obtain a secondary modified nanofiltration membrane.

[0078] In this embodiment of the invention, to further improve the permeation performance, fluoride removal performance, antibacterial function, and acid resistance of the nanofiltration membrane, the primary modified nanofiltration membrane can be further treated by adding a boric acid functionalized carbon dot solution to the modified surface of the primary modified nanofiltration membrane. This allows the boric acid functionalized carbon dots to undergo secondary interfacial polymerization with unreacted acyl chlorides on the modified surface of the primary modified nanofiltration membrane. After immersion for a preset third treatment time, the secondary interfacial polymerization reaction is completed, resulting in a secondary modified nanofiltration membrane containing more boric acid functionalized carbon dots.

[0079] The boric acid-functionalized carbon dot solution may include boric acid-functionalized carbon dots and water, with the weight percentage of the boric acid-functionalized carbon dots ranging from 0.3% to 0.7%. For example, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, etc. Preferably, the weight percentage of the boric acid-functionalized carbon dots is 0.5%.

[0080] The third processing time can be 3 to 8 minutes, for example, 3 minutes, 3.5 minutes, 4 minutes, 4.5 minutes, 5 minutes, 5.5 minutes, 6 minutes, 6.5 minutes, 7 minutes, 7.5 minutes, 8 minutes, etc. Preferably, the third processing time can be 5 minutes.

[0081] In one embodiment of the present invention, the method further includes:

[0082] S31, the nanofiltration membrane is immersed in a catechol solution. The boric acid functionalized carbon dots on the surface of the nanofiltration membrane react with the catechol in the catechol solution to form a boric acid functionalized carbon dot-catechol probe. The boric acid functionalized carbon dot-catechol probe is used to detect fluoride ions in water.

[0083] In current technologies, with the acceleration of industrialization and the influence of natural factors, fluoride pollution is becoming increasingly serious, and the fluoride ion concentration in wastewater or environmental water bodies is gradually increasing. To ensure water safety, it is usually necessary to detect the fluoride ion concentration in water. Generally, methods for monitoring fluoride ions include electrochemical monitoring methods, mass spectrometry, atomic absorption spectrometry, and chromatographic analysis. While these methods can accurately detect the concentration of fluoride ions in water, they typically require a long time and are not suitable for rapid detection of fluoride ion concentration in the field of water treatment.

[0084] In this embodiment of the invention, a nanofiltration membrane is immersed in a catechol solution. The boric acid-functionalized carbon dots on the surface of the nanofiltration membrane react with the catechol in the solution to form a boric acid-functionalized carbon dot-catechol probe with good specificity for fluoride ions. Therefore, the nanofiltration membrane prepared in this embodiment can further detect the concentration of fluoride ions in water during water treatment, effectively improving the ease of fluoride ion detection and enabling rapid detection.

[0085] Specifically, boric acid-functionalized carbon dot-modified nanofiltration membranes exhibit specificity for catechol. Under the internal filtration effect, the higher the concentration of catechol, the lower the fluorescence of the nanofiltration membrane gradually becomes, until it is quenched. Simultaneously, the boric acid-functionalized carbon dot-catechol probe formed by the reaction of boric acid-functionalized carbon dots and catechol also exhibits specificity for the nanofiltration membrane; the fluorescence intensity of the probe increases with higher fluoride ion concentration. Therefore, rapid detection of fluoride ion concentration can be achieved based on the fluorescence intensity of the probe.

[0086] In one embodiment of the present invention, boric acid functionalized carbon dots are prepared by the following method:

[0087] S41, 3-aminophenylboronic acid and piperazine are dissolved in water and reacted by hydrothermal method to obtain boric acid functionalized carbon dots.

[0088] Specifically, 3-aminophenylboronic acid and piperazine can be dissolved in water first, and then ultrasonically stirred until completely dissolved. Next, a hydrothermal method can be used to gradually raise the temperature to a preset reaction temperature and maintain this temperature for a certain period. The resulting solution is then centrifuged, the supernatant is purified by dialysis, and then rotary evaporation followed by freeze-drying to obtain dried boric acid functionalized carbon dots.

[0089] The overall reaction time of the hydrothermal method can be 500 min to 800 min, for example, 500 min, 550 min, 600 min, 650 min, 700 min, 750 min, 800 min, etc. Preferably, the overall reaction time of the hydrothermal method can be 600 min.

[0090] The reaction temperature for hydrothermal methods can be between 180℃ and 230℃, for example, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, etc. Preferably, the reaction temperature for hydrothermal methods can be 200℃.

[0091] The heating rate of the hydrothermal method can be 3–7 °C / min, for example, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, etc. Preferably, the heating rate of the hydrothermal method can be 5 °C / min.

[0092] In one embodiment of the present invention, the molar ratio between 3-aminophenylboronic acid and piperazine is 4:1 to 1:1. For example, 4:1, 3:1, 2:1, 1:1, etc. When the molar ratio between 3-aminophenylboronic acid and piperazine is appropriate, the prepared boric acid functionalized carbon dots can have a moderate number of boric acid groups and amino groups, which can better achieve the permeation performance, fluoride removal performance, antibacterial function, and acid resistance function of nanofiltration membranes.

[0093] In one embodiment of the present invention, the weight percentage of piperazine in the aqueous solution is 1% to 5%; the weight percentage of boric acid-functionalized carbon dots is 0.5% to 1%. For example, the weight percentage of piperazine can be 1%, 2%, 3%, 4%, 5%, etc. The weight percentage of boric acid-functionalized carbon dots can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc. Preferably, the weight percentage of piperazine can be 2%, and the weight percentage of boric acid-functionalized carbon dots can be 0.75%.

[0094] When the weight percentages of piperazine and boric acid functionalized carbon dots in the aqueous solution are appropriate, a suitable number of boric acid functionalized carbon dots can be uniformly dispersed on the surface of the nano-modified membrane. This can improve the permeability, fluoride removal, antibacterial, and acid resistance of the nanofiltration membrane while avoiding excessive aggregation of boric acid functionalized carbon dots, which could block the nanofiltration membrane pathways and affect its permeability.

[0095] In one embodiment of the present invention, the acyl chloride compound includes at least one of pyromellitic methyl methacrylate, terephthaloyl chloride, and isophthaloyl chloride.

[0096] Specifically, pyromellitic methyl methacrylate (PMMC), terephthaloyl chloride (TBMC), and isophthaloyl chloride (IMC) can contain a large number of acyl chloride groups, which can provide sufficient acyl chloride groups for interfacial polymerization of piperazine and boric acid functionalized carbon dots to achieve modification of nanofiltration membranes.

[0097] In one embodiment of the present invention, the weight percentage of the acyl chloride compound in the organic phase solution is 0.1%-0.5%. For example, the weight percentage of the acyl chloride compound can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, etc. Preferably, the weight percentage of the acyl chloride compound is 0.15%.

[0098] The appropriate weight percentage of acyl chloride compounds in the organic phase solution can provide sufficient acyl chloride groups for interfacial polymerization of piperazine and boric acid functionalized carbon dots, thereby modifying the nanofiltration membrane. At the same time, it can avoid excessive residue of acyl chloride compounds, which would affect the performance of the nanofiltration membrane.

[0099] In one embodiment of the present invention, the solvent in the organic phase solution may be hexane, cyclohexane, toluene, or other solvents that are immiscible with the aqueous phase and have controllable toxicity, and will not cause further adverse effects on the water body.

[0100] This invention also provides a nanofiltration membrane specifically for fluoride removal. The nanofiltration membrane includes a base membrane, at least one surface of which is modified with polyamide and boric acid-functionalized carbon dots. The nanofiltration membrane incorporates hydrophilic groups such as amino, imino, and boric acid groups through piperazine and boric acid-functionalized carbon dots, improving its hydrophilicity and membrane flux, while also exhibiting good acid resistance. Simultaneously, the boric acid-functionalized carbon dots can generate reactive oxygen species (ROS) under specific wavelength irradiation, inactivating bacteria on the nanofiltration membrane surface and achieving antibacterial function. Furthermore, the boric acid groups on the boric acid-functionalized carbon dots deprotonate under alkaline conditions, resulting in a strongly negatively charged surface that readily forms complexes with fluoride ions, effectively removing fluoride ions from water. Therefore, the nanofiltration membrane provided by this invention can remove fluoride ions from water while possessing good antibacterial and acid-resistant properties, resulting in a long service life.

[0101] To enable those skilled in the art to better understand the present invention, the following describes the preparation method of the nanofiltration membrane for fluoride removal using several specific embodiments.

[0102] Preparation of boric acid functionalized carbon dots

[0103] (1) Take 0.2g of 3-aminophenylboronic acid and 0.1g of piperazine in a beaker;

[0104] (2) Add 20 mL of deionized water to a beaker and sonicate for 15 min to completely dissolve 3-aminophenylboronic acid and piperazine in the water;

[0105] (3) Transfer the obtained solution to a polytetrafluoroethylene-lined high-pressure reactor and heat it;

[0106] (4) The heating conditions are 200℃, the heating rate is 5℃ / min, the reaction time is 600min, and the reaction is allowed to cool naturally to room temperature after the reaction is completed;

[0107] (5) Dispense the obtained solution into centrifuge tubes and centrifuge at 10000 r / min for 20 min. After centrifugation, retain the supernatant.

[0108] (6) Dialyze the obtained supernatant to remove unreacted molecules and ions from the solution;

[0109] (7) The boric acid functionalized carbon dot solution is subjected to rotary evaporation, freeze drying, vacuum drying and other treatments to obtain dry boric acid functionalized carbon dot powder.

[0110] Example 1

[0111] (1) Prepare 100g of piperazine aqueous solution, with piperazine as the solute and deionized water as the solvent. The weight percentage of piperazine is 2.00%. Add 0.75% boric acid functionalized carbon dots to the aqueous solution and sonicate for 15min to obtain the aqueous solution.

[0112] (3) Prepare 100g of organic phase solution, with solute being pyromellitic chloride and solvent being n-hexane, the weight percentage of pyromellitic chloride being 0.15%, and sonicate for 15min to obtain organic phase solution;

[0113] (4) Take an 8cm×8cm polyethersulfone membrane as the base membrane, rinse the membrane surface with deionized water, and then dry the base membrane in a 60℃ drying oven. After drying, take out the base membrane and let it cool naturally to room temperature.

[0114] (5) Fix the base film on the film-making device so that the smooth surface of the base film faces upward, and use the smooth surface of the base film as the surface for modification treatment;

[0115] (6) Pour the aqueous solution onto the membrane surface and soak for 3 minutes. Remove the membrane, remove the surface droplets at room temperature, and fix the membrane back onto the membrane fabrication device. Pour the pyromellitic acid chloride organic phase solution onto the modified surface, soak for 2 minutes, and then remove the membrane to obtain a modified nanofiltration membrane.

[0116] (7) The prepared primary modified nanofiltration membrane was placed in a drying oven and dried at 60°C for 10 min to obtain the dried primary modified nanofiltration membrane. After cooling to room temperature, it was stored in deionized water.

[0117] Example 2

[0118] (1) Dissolve boric acid functionalized carbon dots in deionized water to prepare a boric acid functionalized carbon dot solution with a weight percentage of 0.5%.

[0119] (2) Take the modified nanofiltration membrane obtained in Example 1 above, rinse the membrane surface with deionized water, and then place it in a drying oven at 60°C for 10 minutes. After drying, take out the modified nanofiltration membrane and let it cool naturally to room temperature.

[0120] (3) Fix the modified nanofiltration membrane onto the membrane fabrication device with the modified surface facing upward.

[0121] (4) Slowly drop the boric acid functionalized carbon dot solution onto the modified surface until it is completely covered, and then perform interfacial polymerization again for 5 minutes to obtain a secondary modified nanofiltration membrane.

[0122] (5) The prepared secondary modified nanofiltration membrane was placed in a drying oven and dried at 60°C for 10 min to obtain the dried secondary modified nanofiltration membrane. After cooling to room temperature, it was stored in deionized water.

[0123] Comparative Example

[0124] (1) Prepare 100g of piperazine aqueous solution, with piperazine as the solute and deionized water as the solvent. The weight percentage of piperazine is 2.00%. Sonicate for 15min to obtain the aqueous solution.

[0125] (3) Prepare 100g of organic phase solution, with solute being pyromellitic chloride and solvent being n-hexane, the weight percentage of pyromellitic chloride being 0.15%, and sonicate for 15min to obtain organic phase solution;

[0126] (4) Take an 8cm×8cm polyethersulfone membrane as the base membrane, rinse the membrane surface with deionized water, and then dry the base membrane in a 60℃ drying oven. After drying, take out the base membrane and let it cool naturally to room temperature.

[0127] (5) Fix the base film on the film-making device so that the smooth surface of the base film faces upward, and use the smooth surface of the base film as the surface for modification treatment;

[0128] (6) Pour the aqueous solution onto the membrane surface and soak for 3 minutes. Remove the membrane, remove the surface droplets at room temperature, and fix the membrane back onto the membrane fabrication device. Pour the pyromellitic acid chloride organic phase solution onto the modified surface, soak for 2 minutes, and then remove the membrane to obtain a modified nanofiltration membrane.

[0129] (7) The prepared primary modified nanofiltration membrane was placed in a drying oven and dried at 60°C for 10 min to obtain the dried primary modified nanofiltration membrane. After cooling to room temperature, it was stored in deionized water.

[0130] This invention introduces hydrophilic groups such as amino, imino, and boric acid groups into piperazine and boric acid-functionalized carbon dots, thereby improving the hydrophilicity and acid resistance of the nanofiltration membrane. Under irradiation at a specific wavelength, the boric acid-functionalized carbon dots can generate reactive oxygen species, inactivating bacteria on the nanofiltration membrane surface and achieving antibacterial function. Furthermore, the boric acid groups on the boric acid-functionalized carbon dots readily form complexes with fluoride ions under alkaline conditions, achieving the effect of removing fluoride ions from water. The following specific experimental data illustrates some of the advantages of this invention compared to existing technologies.

[0131] The boric acid functionalized carbon dots prepared in the embodiments of the present invention were characterized, and the results are as follows: Figure 1 As shown, Figure 1 This is a TEM image of boric acid functionalized carbon dots provided in an embodiment of the present invention. It can be seen that the preparation method provided in this embodiment of the present invention can be used to prepare spherical boric acid functionalized carbon dots.

[0132] The particle size distribution of the boric acid functionalized carbon dots prepared in the embodiments of the present invention was tested, and the results are as follows: Figure 2 As shown. Figure 2 This is a particle size distribution diagram of boric acid functionalized carbon dots provided in the embodiments of the present invention. It can be seen that the particle size distribution of the boric acid functionalized carbon dots prepared in the embodiments of the present invention matches that of typical carbon dots, and the average size of the boric acid functionalized carbon dots is 2.9 nm.

[0133] The boric acid functionalized carbon dots prepared in the embodiments of the present invention were characterized by Fourier transform infrared spectroscopy (FTIR), and the results are as follows: Figure 3 As shown. Figure 3 This is an infrared spectral characterization of boric acid functionalized carbon dots provided in an embodiment of the present invention. The curve at the top, indicating higher transmittance, represents boric acid functionalized carbon dots (B-CDs), while the curve at the bottom, indicating lower transmittance, represents 3-aminophenylboronic acid (3-APBA).

[0134] It can be seen that boric acid-functionalized carbon dots (B-CDs) at 3260 cm⁻¹ -1 The broad peak at 1640 cm⁻¹ is attributed to the stretching vibration of OH. Compared to 3-aminophenylboronic acid (3-APBA), the absorption peak of the boric acid-functionalized carbon dots is broadened, possibly due to the formation of numerous hydrogen bonds during the hydrothermal synthesis of boric acid-functionalized carbon dots. -1 The point is a stretching vibration of C=C. 1354cm -1 and 1057cm -1 The vibrations at 1155 cm⁻¹ are attributed to the stretching vibrations of BO and CB, respectively. -1 The unique -CN- bending vibration of boric acid functionalized carbon dots can be observed, which may be the imino group provided by the raw material piperazine to the boric acid functionalized carbon dots.

[0135] X-ray diffraction (XRD) was performed on the boric acid functionalized carbon dots prepared in the embodiments of the present invention, and the results are as follows: Figure 4 As shown. Figure 4 This is an X-ray diffraction pattern of boric acid functionalized carbon dots provided in an embodiment of the present invention. It can be seen that the boric acid functionalized carbon dots exhibit a diffraction peak and a shoulder peak at 20.5° and 41.7° respectively, corresponding to the (002) and (100) crystal planes of carbon, indicating that the boric acid functionalized carbon dots are amorphous structures.

[0136] The zeta potential of the boric acid functionalized carbon dots prepared in the embodiments of the present invention was measured, and the results are as follows: Figure 5 As shown, Figure 5This is a Zeta potential test diagram of boric acid functionalized carbon dots provided in an embodiment of the present invention. It can be seen that the potential of the boric acid functionalized carbon dots is approximately -23 mV, indicating that the surface of the boric acid functionalized carbon dots has abundant hydrophilic groups -B(OH)2, resulting in a negative charge on the surface of B-CDs.

[0137] Flux and contact angle testing

[0138] Flux tests were performed on the products prepared in Examples 1, 2, and the comparative example. The membrane flux tests were conducted in a dead-end filtration device with magnetic stirring. During the tests, the membrane pressure was set to 4 bar, and the volume of pure water passing through the membrane was measured. The pure water flux J was also measured. W The formula for calculating (in LMH) is:

[0139]

[0140] In the formula, S (unit: m) 2 ) represents the effective membrane area, ΔV (in L) represents the change in permeate volume with test time Δt (in h), and permeability A (in L·m³). -2 ·h -2 ·bar -1 ) is the water flux J w The change with pressure ΔP.

[0141] Meanwhile, the water contact angle of the products prepared in Examples 1, 2, and the comparative example was tested and photographed. The results are shown in Table 1. Figure 6 As shown.

[0142] Table 1. Flux and Contact Angle Test Results

[0143]

[0144] As shown in Table 1, the nanofiltration membranes prepared in Example 1 (IB-CDs-M) and Example 2 (II-B-CDs-M) showed flux increases of 53.37% and 66.57% respectively compared to the nanofiltration membrane in the control example (Contrast-M) at a pressure of 4 bar.

[0145] From Table 1 and Figure 6 It can be seen that the contact angle between the nanofiltration membrane of the comparative example (Contrast-M) and water is 65.1°±0.8°, the contact angle between the nanofiltration membrane of Example 1 (IB-CDs-M) and water is 42°±0.5°, and the contact angle between the nanofiltration membrane of Example 2 (II-B-CDs-M) and water is 38.9°±0.7°. It is evident that the contact angle between the nanofiltration membranes of Example 1 and Example 2 and water is lower than that of the comparative example, and the nanofiltration membranes of Example 1 and Example 2 have better hydrophilicity, with the hydrophilicity of Example 2 being superior to that of Example 1.

[0146] Combination Figures 1-5 Analysis of the reasons for the increase in water flux reveals that the nanofiltration membrane in this embodiment of the invention is modified with boric acid functionalized carbon dots. These boric acid functionalized carbon dots have a large number of hydrophilic groups, which can form hydrogen bonds with water molecules, thereby accelerating the transport of water molecules.

[0147] Furthermore, as can be seen from Examples 1 and 2, after the nanofiltration membrane undergoes primary and secondary modification with boric acid functionalized carbon dots, the water flux gradually increases while the contact angle continuously decreases. This indicates that with primary and secondary modification of the nanofiltration membrane, the number of boric acid functionalized carbon dots on the membrane surface gradually increases, the number of hydrophilic groups on the membrane surface increases, and the surface charge decreases, resulting in better hydrophilic properties.

[0148] Salt rejection rate test

[0149] The salt rejection rate of the membrane was tested in a dead-end filtration device with magnetic stirring. During the test, the permeate pressure was set to 4 bar, the solution concentration was 1000 ppm, and the pH was 8. The precise conductivity of the solution before passing through the membrane and the conductivity of the permeate after passing through the membrane were measured. The concentration of the post-permeate solution and the initial feed solution concentration were determined based on the conductivity.

[0150] Salt rejection rate R s The calculation formula (unit: %) is as follows:

[0151]

[0152] In the formula C p and C f (Unit: ppm) represent the concentration of the solution after permeation and the initial feed solution concentration, respectively.

[0153] The products prepared in Examples 1, 2, and the comparative example were subjected to NaCl, Na2SO4, MgCl2, and MgSO4 rejection rate tests, respectively. The water flux of different salt solutions was also tested using the water flux testing method described above. The results are shown in Table 2. Figure 7 As shown.

[0154] Table 2 Retention Rate Test Results

[0155]

[0156] Figure 7In (a) is a schematic diagram of water flux test results for different types of salt solutions. It can be seen that when different types of salts are added to the solution, the water flux of Example 1 (I-B-CDs-M) and Example 2 (II-B-CDs-M) is significantly better than that of the comparative example (Contrast-M). Meanwhile, since Example 2 contains more boric acid-functionalized carbon dots than Example 1, its hydrophilic performance is further superior to that of Example 1.

[0157] Figure 7 In (b) is a schematic diagram of rejection rate test results for different types of salt solutions. Reference Figure 8 In (b) and Table 2, it can be seen that the rejection rates of Example 1 (I-B-CDs-M) and Example 2 (II-B-CDs-M) for different salts are both superior to that of the comparative example (Contrast-M). This is because the nanofiltration membranes of Example 1 and Example 2 introduce polyamide and boric acid-functionalized carbon dots through interfacial polymerization, which reduces the pore size of micropores on the surface of the nanofiltration membrane to a certain extent, making it more difficult for different types of salts to pass through the nanofiltration membrane. The overall salt rejection rate order is NaCl<Na₂SO₄<MgCl₂<MgSO₄. At the same time, the boric acid-functionalized carbon dots can form slight agglomeration on the surface of the nanofiltration membrane, which further blocks different types of salts from passing through the nanofiltration membrane.

[0158] In addition, the rejection rate test environment is an alkaline environment with pH=8. In this environment, the boric acid-functionalized carbon dots on the surface of the nanofiltration membrane are deprotonated, making the surface of the nanofiltration membrane negatively charged. At this time, the surface of the nanofiltration membrane can repel anions, and has a stronger rejection effect on anions. Moreover, compared with monovalent anions with less negative charge, it can exert a stronger repulsion effect on divalent anions with more negative charge. Therefore, compared with NaCl which contains only one monovalent anion, it has a stronger rejection effect on Na₂SO₄, MgCl₂, and MgSO₄.

[0159] In summary, the embodiments of the present invention modify the nanofiltration membrane through polyamide and boric acid-functionalized carbon dots, which not only increases the permeability of the nanofiltration membrane to different salt solutions, but also improves the rejection effect on different types of salts.

[0160] Potential test

[0161] The products prepared in Example 1, Example 2, and the comparative example were subjected to potential tests at different pH values, and the results are as Figure 8 shown.

[0162] Figure 8This is a schematic diagram illustrating the potential-pH relationship provided in the embodiments of the present invention. It can be seen that Examples 1 (IB-CDs-M) and 2 (II-B-CDs-M) exhibit more significant potential changes compared to the comparative example (Contrast-M). It is evident that the nanofiltration membranes prepared in Examples 1 and 2 can carry strong positive and negative charges under different pH environments, exhibiting a stronger repulsive effect on cations or anions, thus improving the retention effect of different salts in solution, such as NaCl, Na₂SO₄, MgCl₂, and MgSO₄. Furthermore, in Example 2, due to the grafting of more boric acid functionalized carbon dots, its potential change is more pronounced than that of Example 1, and the secondary modified nanofiltration membrane of Example 2 further enhances the retention effect on different salts.

[0163] Meanwhile, it can be seen that the pH value corresponding to the 0 zeta potential of the comparative example is 5.1, the pH value corresponding to the 0 zeta potential of Example 1 is 6.8, and the pH value corresponding to the 0 zeta potential of Example 2 is 7.6. It is evident that, compared to the comparative example which carries a negative charge in most pH environments, the nanofiltration membrane of this invention can be deprotonated in an alkaline environment and protonated in an acidic environment. It can achieve dechlorination by forming a complex with fluorine in an alkaline environment and defluorination and regeneration in an acidic environment. This makes the filtration process and regeneration cycle of the nanofiltration membrane much easier to complete.

[0164] Molecular retention test

[0165] The products prepared in Examples 1, 2, and the comparative example were subjected to retention tests for molecules of different molecular weights (Da). The results are as follows: Figure 9 As shown.

[0166] Figure 9 This is a schematic diagram illustrating the relationship between molecular weight and retention rate provided in the embodiments of the present invention. It can be seen that the nanofiltration membrane prepared in the comparative example (Contrast-M) has an average PEG pore size of 1.35 nm. The nanofiltration membrane prepared in Example 1 (IB-CDs-M) has an average PEG pore size of 1.23 nm. The nanofiltration membrane prepared in Example 2 (II-B-CDs-M) has an average PEG pore size of 1.13 nm. With the increase of molecular weight (Da), the retention rates of the nanofiltration membranes in Example 1, Example 2, and the comparative example gradually increase. Example 1 and Example 2 can both have higher retention rates than the comparative example at different molecular weights, and Example 2 is further superior to Example 1.

[0167] This is because the nanofiltration membranes of Examples 1 and 2, through interfacial polymerization, introduce polyamide and boric acid functionalized carbon dots, which to some extent reduces the micropore size on the nanofiltration membrane surface. Simultaneously, the boric acid functionalized carbon dots can form slight aggregation on the nanofiltration membrane surface, further reducing the micropore size and thus improving the retention rate. Compared to Example 1, Example 2 exhibits a higher degree of interfacial polymerization and introduces more boric acid functionalized carbon dots. The aggregation of these boric acid functionalized carbon dots is more pronounced than in Example 1, resulting in a better retention rate.

[0168] NaF retention test

[0169] The salt rejection rate of the membrane was tested in a dead-end filtration device with magnetic stirring. During the test, the permeate pressure was set to 4 bar, and the NaF solution concentration was prepared at 1000 ppm. The precise conductivity of the solution before passing through the membrane and the conductivity of the permeate after passing through the membrane were measured, and the concentration of the post-permeate solution and the initial feed solution concentration were determined based on the conductivity. The NaF rejection rate at different pH values ​​was tested for the products prepared in Examples 1, 2, and the comparative example. The results are as follows: Figure 10 As shown.

[0170] As can be seen, compared with the comparative example (Contrast-M), the rejection rates of Examples 1 and 2 at different pH values ​​are superior to those of the comparative example. This is because the boric acid functionalized carbon dots on the nanofiltration membrane of the present invention can be deprotonated in an alkaline environment and protonated in an acidic environment. This allows the boric acid functionalized carbon dots to form complexes with fluorine in an alkaline environment, thereby achieving fluorine removal. In an acidic environment, the stability of the complexes formed by the boric acid functionalized carbon dots and fluorine decreases, and some fluorine is released from the complexes, resulting in a decrease in rejection rate. However, it still has a certain coordination effect with fluorine, so its rejection rate for NaF is still higher than that of the comparative example. Example 2, due to containing more boric acid functionalized carbon dots, has a higher rejection rate for NaF than Example 1.

[0171] By utilizing the difference in coordination between nanofiltration membranes and fluorine under different acidic and alkaline environments, it is also possible to achieve defluorination in an alkaline environment and defluorination regeneration in an acidic environment, thereby improving the service life of nanofiltration membranes.

[0172] Furthermore, Table 3 compares the membrane flux and rejection rate of the products prepared in Examples 1, 2, and the comparative example for NaF solution at pH=8.

[0173] Table 3 Comparison of water flux and retention rate of NaF solution.

[0174]

[0175] As shown in Table 3, the nanofiltration membrane modified with boric acid functionalized carbon dots exhibits a significantly higher NaF rejection rate than the comparative example under alkaline conditions, while maintaining good water flux. This is because the boric acid functionalized carbon dots on the nanofiltration membrane of this invention can be deprotonated in an alkaline environment, forming complexes with fluoride to achieve fluoride removal. Compared to the comparative example, the rejection effect of fluoride ions is significantly improved through coordination with fluoride ions. Simultaneously, since the boric acid functionalized carbon dots are hydrophilic groups, the water flux of the nanofiltration membrane is significantly higher than that of the comparative example. Example 2, with more boric acid functionalized carbon dots than Comparative Example 1, can better improve the water flux and rejection rate of the nano-modified membrane.

[0176] Acid resistance test

[0177] The membranes were immersed in solutions at room temperature and pH = 4 for 2-12 hours, and the changes in membrane state were observed. The results are as follows: Figure 11 , Figure 12 As shown.

[0178] Figure 11 This is a schematic diagram illustrating the relationship between pickling time and water contact angle provided in an embodiment of the present invention. Figure 14 It can be seen that as the pickling time increases, the water contact angle of Examples 1, 2, and 3 all decrease, indicating that Examples 1, 2, and the comparative example were all corroded by acid to some extent. However, compared with the comparative example, the change in contact angle of Examples 1 and 2 is smaller, indicating that Examples 1 and 2 have better acid resistance than Comparative Example 1.

[0179] Figure 12 This is a schematic diagram illustrating the pickling time, water flux, and retention rate provided in the embodiments of the present invention. The water flux is represented by a bar chart, and the retention rate is represented by a curve. It can be seen that as the pickling time increases, the water flux of the comparative example, Example 1, and Example 2 increases, while the retention rate decreases, indicating that the comparative example, Example 1, and Example 2 were all subjected to acid corrosion to some extent. However, compared to the comparative example, the changes in water flux and retention rate in Examples 1 and 2 are smaller, indicating that Examples 1 and 2 have better acid resistance than Comparative Example 1.

[0180] Renewable performance testing

[0181] Figure 13 This is a schematic diagram of the NaF rejection rate recovery provided in the embodiments of the present invention. The nanofiltration membranes of Example 1, Example 2, and the comparative example were placed in a NaF solution with a concentration of 1000 ppm and run for a period of time. Afterward, they were acid-washed with a solution of pH=4 for 5 minutes, and then the nanofiltration membranes of Example 1, Example 2, and the comparative example were placed back in the NaF solution and run.

[0182] It is evident that during the 0-60 min period, the NaF retention rates of the nanofiltration membranes in Examples 1 and 2 gradually decreased with increasing operating time. This is because the boric acid functionalized carbon dots on the membranes in Examples 1 and 2 gradually form complexes with fluoride ions. As time increases, fewer boric acid functionalized carbon dots become available, leading to a gradual decrease in fluoride ion retention rates. In contrast, the comparative example consistently maintained a lower retention rate than the examples.

[0183] Subsequently, the nanofiltration membranes of the comparative example, Example 1, and Example 2 were subjected to acid washing and then placed in NaF solution for testing again. It was observed that the NaF rejection rates of the nanofiltration membranes of Example 1 and Example 2 were 94.88% and 95.52%, respectively. This is because the stability of the complex formed between the boric acid functionalized carbon dots and fluoride ions decreased during the acid washing process, leading to the release of fluoride ions and the reduction of the boric acid functionalized carbon dots, thus regenerating the nanofiltration membranes under acidic conditions.

[0184] During the 60–120 min running period, the NaF retention rates of the nanofiltration membranes in Examples 1 and 2 gradually decreased again with increasing running time. The comparative example, however, maintained a level lower than that of the examples.

[0185] Subsequently, the nanofiltration membranes of the comparative example, Example 1, and Example 2 were subjected to a second acid washing treatment and then placed in NaF solution for testing again. It was observed that the NaF rejection rates of the nanofiltration membranes of Example 1 and Example 2 were 91.53% and 89.98%, respectively. This demonstrates that the nanofiltration membranes were regenerated through acid washing, and the rejection rate was not significantly reduced compared to the initial level. This indicates that the nanofiltration membranes provided by the embodiments of the present invention not only have a good chlorine removal effect but can also be restored through acid washing, effectively improving the service life of the nanofiltration membranes.

[0186] Antibacterial test

[0187] Antimicrobial tests were performed on the products prepared in Examples 1, 2, and the comparative example. The antimicrobial activity of the membranes was determined using a colony counting method. A membrane with an effective area of ​​2.54 cm × 7.62 cm was first sterilized with ultraviolet light for 10 min and placed on a glass slide. Then, under incandescent light, 75 μL of a 10% concentration of [unspecified substance] was used. 3 A bacterial suspension of CFU / mL was applied to the active side of the membrane, and then the membrane was covered with a glass slide at 37°C. A 40W incandescent lamp was used as the light source, 15cm from the membrane, for 3 hours. After the light exposure, the membrane was transferred to physiological saline and sonicated for 5 minutes to remove bacteria deposited on the membrane surface. Finally, the bacterial suspension was placed on a nutrient agar plate and incubated at 37°C for 12 hours, and the colony count was performed. The results are shown in Table 3. Figure 14 As shown.

[0188] Antibacterial activity E b The calculation formula is as follows:

[0189]

[0190] Table 4. Antibacterial test results

[0191] Serial Number Comparative Example Example 1 Example 2 Antibacterial rate (%) / 98.8 99.3

[0192] As shown in Table 4, compared to the comparative examples, the antibacterial rates of Examples 1 and 2 were 98.8% and 99.3%, respectively. Furthermore, from... Figure 14 As can be seen, regardless of whether it is under light or darkness, the surface of the culture dish in the comparative example is covered with tiny white bacteria, while the bacteria in Examples 1 and 2 are only a small number of white bacteria. This indicates that the nano-modified membrane provided in the embodiments of the present invention has excellent antibacterial effect against Escherichia coli.

[0193] This is because the boric acid functionalized carbon dots prepared in this invention can generate ROS, specifically O2, under irradiation at a specific wavelength. - Specifically, refer to Figure 15 , Figure 15 The EPR spectrum of the boric acid-functionalized carbon dots provided in this embodiment of the invention is shown. The EPR spectrum reveals a quartet with an intensity ratio of 1:1:1:1, indicating that the boric acid-functionalized carbon dots, acting as nanozymes, can generate reactive oxygen species (ROS) under light irradiation, exhibiting good bactericidal effects.

[0194] Further, refer to Figure 16 , Figure 16 This is a schematic diagram of the TMB colorimetric test provided in this embodiment of the invention. As can be seen, after 1 minute of illumination, the TMB (3,3',5,5'-tetramethylbenzidine) solution (sample 1) remained unchanged, while the TMB solution with boric acid functionalized carbon dots (TMB+B-CDs) (sample 2) turned blue. Further addition of superoxide dismutase (SOD) (sample 3) to the blue boric acid functionalized carbon dot and TMB mixture resulted in the disappearance of the blue color. This further demonstrates that the boric acid functionalized carbon dots possess oxidase activity. Therefore, Examples 1 and 2, modified with boric acid functionalized carbon dots, generally exhibit good antibacterial effects.

[0195] Fluoride ions (F) - Sensor testing

[0196] 1) Fluoride ions (F) of boric acid-functionalized carbon dots - Sensor testing

[0197] Adding 59 mg of catechol to 100 ml of boric acid-functionalized carbon dot solution yields a boric acid-functionalized carbon dot-catechol probe. Then, the boric acid-functionalized carbon dot-catechol probe is added to different target concentrations of fluoride ions (F...). - In the solution, fluorescence spectra at different target concentrations were tested, and the results were as follows: Figure 17 The effect of fluoride ion concentration monitoring is shown in the figure.

[0198] like Figure 17 As shown, within the fluoride ion concentration range of 0.05-4 ppm (LOD: 0.036 ppm), the fluorescence intensity of the boric acid-functionalized carbon dot-catechol probe increases with increasing fluoride ion concentration. Within this fluoride ion concentration range, the fluorescence intensity of the boric acid-functionalized carbon dot-catechol probe exhibits a linear relationship with the fluoride ion concentration: Y = 0.2259X + 0.0528, R 2 =0.9903, indicating that the fluoride ion concentration can be accurately determined by detecting the fluorescence intensity of the boric acid-functionalized carbon dot-catechol probe.

[0199] 2) Fluoride ions (F) in nano-modified membranes - Sensor testing

[0200] A nanofiltration membrane was immersed in a 10 ppm catechol solution. The boric acid-functionalized carbon dots on the nanofiltration membrane surface reacted with the catechol in the solution, forming a boric acid-functionalized carbon dot-catechol probe on the membrane surface. Different target concentrations of fluoride ions (F...) were then... - The solution was poured onto the membrane, and the fluorescence spectra of the nano-modified membrane at different target concentrations were measured to obtain the following results: Figure 18 and Figure 19 The effect of fluoride ion concentration monitoring is shown in the figure.

[0201] in, Figure 18 This is a monitoring effect diagram of the fluoride ion concentration corresponding to the nanofiltration membrane prepared in Example 1 of the present invention. It can be seen that for the primary modified nanomembrane, in the fluoride ion concentration range of 0.042-1.18 ppm (LOD: 0.018 ppm), the fluorescence intensity can form a linear relationship with the fluoride ion concentration: Y = 0.762X + 0.0115, R... 2 =0.9907. This indicates that the nanofiltration membrane prepared in Example 1 of this invention can change its fluorescence intensity with the change of fluoride ion concentration, and the two are linearly related. The fluoride ion concentration can be monitored by monitoring the fluorescence intensity of the nanofiltration membrane.

[0202] Figure 19This is a monitoring effect diagram of the fluoride ion concentration corresponding to the nanofiltration membrane prepared in Example 2 of the present invention. It can be seen that for the secondary modified nano-modified membrane, in the range of fluoride ion concentration of 0.042-1.58 ppm (LOD: 0.025 ppm), the fluorescence intensity can form a linear relationship with the fluoride ion concentration: Y = 0.5568X - 0.0018, R... 2 =0.9817. This indicates that the nanofiltration membrane prepared in Example 2 of the present invention can change its fluorescence intensity with the change of fluoride ion concentration, and the two are linearly related. The fluoride ion concentration can be monitored by monitoring the fluorescence intensity of the nanofiltration membrane.

[0203] Furthermore, 59 ppm of anions (including Cl-) can be added to the boric acid-functionalized carbon dot-catechol probe solution. - ,Br - I - HCO3 - CH3COO - HPO4 2- NO3 - and SO4 2- ) and 59ppm F - Ions. The effect of conventional anions on fluoride ion monitoring was observed, and the results are as follows: Figure 20 and Figure 21 As shown.

[0204] Figure 20 This is a fluorescence spectrum of boric acid-functionalized carbon dot-catechol probe against different anions. Figure 21 This represents the ratio of changes in fluorescence intensity of boric acid-functionalized carbon dots-catechol probe aqueous solutions for different anions. It can be seen that when the concentration of added anions is more than 9 times that of fluoride ions, the fluorescence intensity of the anions is close to that of the blank sample, indicating that the anion Cl... - ,Br - I - HCO3 - CH3COO - HPO4 2- NO3 - and SO4 2- None of the methods significantly increased fluorescence intensity. However, the addition of fluoride ions significantly increased fluorescence intensity, indicating that anions do not significantly affect the monitoring of fluoride ion concentration. The boric acid-functionalized carbon dot-catechol probe has high specificity for fluoride ions, enabling accurate monitoring of fluoride ions.

[0205] The present invention provides a detailed description of a fluoride removal nanofiltration membrane and its preparation method. Specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preparing a nanofiltration membrane specifically for fluoride removal, characterized in that, The method includes: An aqueous solution containing piperazine and boric acid-functionalized carbon dots was prepared, and an organic solution containing acyl chloride compounds was also prepared. At least one surface of the base film is used as the modified surface; The aqueous phase solution and the organic phase solution are added to the modified surface for interfacial polymerization to obtain a polyamide and boric acid functionalized carbon dot modified membrane as a nanofiltration membrane; the nanofiltration membrane is used to remove fluoride ions from water, and has antibacterial and anti-acid properties.

2. The method according to claim 1, characterized in that, The nanofiltration membrane includes a primary modified nanofiltration membrane; The step of adding the aqueous phase solution and the organic phase solution to the modified surface for interfacial polymerization to obtain a polyamide and boric acid functionalized carbon dot modified membrane as a nanofiltration membrane includes: The aqueous solution is added to the modified surface, and after soaking for a preset first treatment time, the droplets on the base film surface are removed. The organic phase solution is added to the modified surface, and interfacial polymerization is performed. After soaking for a preset second treatment time, the surface is dried to obtain a modified nanofiltration membrane.

3. The method according to claim 2, characterized in that, The nanofiltration membrane includes a secondary modified nanofiltration membrane; The step of adding the aqueous solution and the organic solution to the modified surface for interfacial polymerization to obtain a polyamide and boric acid functionalized carbon dot modified membrane as a nanofiltration membrane further includes: A boric acid functionalized carbon dot solution is added to the surface of the primary modified nanofiltration membrane for secondary interfacial polymerization. After soaking for a preset third treatment time, a secondary modified nanofiltration membrane is obtained.

4. The method according to any one of claims 1 to 3, characterized in that, The method further includes: The nanofiltration membrane is immersed in a catechol solution, and the boric acid functionalized carbon dots on the surface of the nanofiltration membrane react with the catechol in the catechol solution to form a boric acid functionalized carbon dot-catechol probe; the boric acid functionalized carbon dot-catechol probe is used to detect fluoride ions in water.

5. The method according to any one of claims 1 to 3, characterized in that, The boric acid functionalized carbon dots were prepared using the following method: 3-Aminophenylboronic acid and piperazine were dissolved in water and reacted by hydrothermal method to obtain boric acid functionalized carbon dots.

6. The method according to claim 5, characterized in that, The molar ratio between the 3-aminophenylboronic acid and the piperazine is 4:1 to 1:

1.

7. The method according to claim 1, characterized in that, The weight percentage of piperazine in the aqueous solution is 1% to 5%; the weight percentage of boric acid functionalized carbon dots is 0.5% to 1%.

8. The method according to claim 1, characterized in that, The acyl chloride compounds include at least one of pyromellitic terephthaloyl chloride, terephthaloyl chloride, and isophthaloyl chloride.

9. The method according to claim 1 or 8, characterized in that, The weight percentage of the acyl chloride compound in the organic phase solution is 0.1%-0.5%.

10. A nanofiltration membrane specifically for fluoride removal, characterized in that, The nanofiltration membrane includes a base membrane, at least one surface of which is modified with polyamide and boric acid functionalized carbon dots. The nanofiltration membrane is used to remove fluoride ions from water, and has antibacterial and anti-acid properties.

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