Biquaternary phosphonium salts, fiber film materials, their preparation methods and applications in heavy metal adsorption

Abstract

This invention belongs to the field of nanofiber thin film technology, specifically disclosing a bis-quaternary phosphonium salt, 1,4-p-diphenylbis(triphenylphosphonium chloride), with chloride as the anion and the bis-quaternary phosphonium salt as the cation. The bis-quaternary phosphonium salt can be electrospun into a fiber thin film material. This bis-quaternary phosphonium salt thin film material exhibits good thermal stability, excellent adsorption effect on heavy metal Cr(VI) in acidic industrial wastewater, and is easy to recover, reducing secondary pollution. Furthermore, the preparation method of this invention is simple to operate, requires only simple equipment, is easy to operate, consumes little solvent, saves costs, and is conducive to industrial promotion.

Description

Technical Field

[0001] This invention belongs to the field of nanofiber thin film technology, specifically relating to a bis-quaternary phosphonium salt, thin film material, its preparation method and adsorption application. Background Technology

[0002] The heavy metal chromium (Cr) is toxic and non-biodegradable, posing a destructive threat to sustainable ecosystems and human health. Chromium (Cr) has high solubility and mobility in the environment, typically existing as chromates (CrO4). 2- HCrO4 - ) and dichromate (Cr2O7) 2- Heavy metals (Cr(VI)) exist in aqueous solutions in the form of oxygen-containing anions. Currently, methods for removing heavy metals from water include ion exchange, membrane separation adsorption, solvent extraction, and electrochemical precipitation. Among these, membrane separation adsorption is considered an effective wastewater treatment process that is simple to prepare, low in cost, highly efficient, easy to recover, and produces no secondary pollution. However, preparing a good adsorbent is essential for achieving better adsorption results. Quaternary phosphonium salts have a positively charged phosphorus content (P), a large ionic radius, and strong polarization, making them suitable for adsorbing negatively charged heavy metal pollutants. However, directly using quaternary phosphonium salts to adsorb heavy metals is difficult to recover and can easily cause secondary pollution. Summary of the Invention

[0003] The purpose of this invention is to provide a quaternary phosphonium salt that has the characteristics of rapid adsorption of heavy metal Cr(VI) in acidic industrial wastewater and no secondary pollution, and a fiber film material prepared therefrom.

[0004] To achieve the above objectives, the present invention provides a bis-quaternary phosphonium salt, 1,4-p-diphenylbis(triphenylphosphonium chloride), with chloride as the anion and the bis-quaternary phosphonium salt as the cation, and its chemical structure is shown in formula (I):

[0005]

[0006] The present invention also provides a method for preparing the above-mentioned bis-quaternary phosphonium salt, comprising the following steps:

[0007] A certain proportion of 1,4-dichlorobenzyl and tri-tolylphosphine are mixed, dissolved in an appropriate amount of organic solvent (preferably acetone), and heated to react (stirred and refluxed at 65-70°C for 18-24 hours). After the reaction is completed, the solid and liquid phases are separated, and the solid product is washed (preferably with acetone) and dried to obtain a bisquaternary phosphonium salt. The molar ratio of 1,4-dichlorobenzyl and tri-tolylphosphine is 1:(1-1.5).

[0008] The bis-quaternary phosphonium salt of the present invention can be used to prepare fiber film materials, comprising the following steps:

[0009] A certain amount of polyacrylonitrile (PAN) is added to a mixed solution of DMSO and DMF (preferably, the mass ratio of DMSO to DMF is 1:0.8-1.2), and dissolved at 70-90℃ (with constant temperature stirring) to obtain a spinning solution. A certain amount of the aforementioned bis-quaternary phosphonium salt is added to the obtained spinning solution, and dissolved at 55-65℃ (with constant temperature stirring). After standing to remove bubbles, spinning is performed to obtain a bis-quaternary phosphonium salt fiber film material. The preferred spinning conditions are: voltage 15.8 kV, receiving distance 15 cm, and liquid supply rate 0.8 mL·h. -1 The slide speed is 15.0 mm·s -1 The ambient temperature was 32℃ and the relative humidity was 52.1%.

[0010] Preferably, the mass concentration of the spinning solution is 10-20%.

[0011] Preferably, the amount of bisquaternary phosphonium salt added to the above spinning solution is 1-3 wt%.

[0012] Beneficial effects: The bis-quaternary phosphonium salt thin film material of the present invention has good thermal stability and excellent adsorption effect on heavy metal Cr(VI) in acidic industrial wastewater. It is easy to recover and reduces secondary pollution. Moreover, the preparation method of the present invention is simple to operate, requires simple instruments and equipment, is easy to operate, requires less solvent, saves costs, and is conducive to industrial promotion. Attached Figure Description

[0013] Figure 1 This is the electrospray mass spectrum of 1,4-p-diphenylbis(triphenylphosphonium chloride) of the present invention.

[0014] Figure 2 The preparation process of the bis-quaternary phosphonium salt fiber film of the present invention is described.

[0015] Figure 3 Microscopic images of the 1,4-p-diphenylenebis(triphenylphosphonium chloride) fiber film material of the present invention (left: blank PAN film; right: bisquaternary phosphonium salt fiber film).

[0016] Figure 4 The biquaternary phosphonium salt fiber film of the present invention was tested at different pH values ​​for 100 mg·L⁻¹. -1 Adsorption effect of Cr(VI) (Left: blank PAN; Right: bisquaternary phosphonium salt fiber film).

[0017] Figure 5 Standard curve of Cr(IV) concentration (mg·L) -1 ).

[0018] Figure 6 The present invention describes the removal of 100 mg·L⁻¹ of bis-quaternary phosphonium salt fiber membrane at different pH values. -1Data graph for Cr(VI) (left: blank PAN; right: bis-quaternary phosphonium salt fiber film).

[0019] Figure 7 The biquaternary phosphonium salt fiber film of the present invention is effective against 500 mg·L⁻¹ -1 The pseudo-first-order and pseudo-second-order dynamic fitting curves are shown.

[0020] Figure 8 The Langmuir and Freundlich isotherms of the bis-quaternary phosphonium salt fiber membrane adsorbing Cr(VI) according to the present invention are shown.

[0021] Figure 9 This is the infrared spectrum of the bis-quaternary phosphonium salt of the present invention.

[0022] Figure 10 This is the infrared spectrum of the bis-quaternary phosphonium salt fiber film of the present invention.

[0023] Figure 11 This is a thermogravimetric curve of the bis-quaternary phosphonium salt fiber film of the present invention.

[0024] Figure 12 The infrared spectrum of the bis-quaternary phosphonium salt after adsorption of Cr(VI) is shown in the present invention.

[0025] Figure 13 This is an EDS image of the bis-quaternary phosphonium salt thin film after adsorbing Cr(VI) according to the present invention. Specific implementation methods

[0026] To better understand the present invention, the technical solution of the present invention will be described below through specific embodiments. Example

[0027] A method for preparing 1,4-diphenylenebis(triphenylphosphonium chloride) fiber thin film material includes the following steps:

[0028] (1) Preparation of Bi[TPP]Cl2: Weigh 3 mmol of 1,4-dichlorobenzyl and 4 mmol of triphenylphosphine into a 100 mL ground glass conical flask, add 30 mL of acetone to dissolve, stir and reflux at 65~70℃ for 20 hours, a white precipitate is formed, filter under reduced pressure, wash 3 times with a small amount of acetone, and dry under vacuum to obtain a white solid powder as the target product, biquaternary phosphonium salt.

[0029] (2) Preparation of Bi[TPP]Cl2 fiber film material: Weigh 1.5 g of polyacrylonitrile and add it to a solution with a mass ratio of DMSO:DMF of 1:1. Stir at 80℃ until completely dissolved to prepare a spinning solution with a concentration of 15wt%. Add 0.2 g of bis-quaternary phosphonium salt to the spinning solution and stir at 60℃ until completely dissolved. After standing to remove bubbles, load the solution into a dry syringe and spin under the following conditions: voltage 15.8 kV, receiving distance 15 cm, and liquid supply rate 0.8 mL·h. -1 The slide speed is 15.0 mm·s -1 The ambient temperature was 32℃ and the relative humidity was 52%. A white fiber film was finally obtained. The spinning process is detailed below. Figure 2 The structures of PAN and the drug-loaded membrane are clear, the fibers are evenly distributed, and there is no obvious clumping, indicating that the electrospinning was successful. Microscopic images are shown below. Figure 3 . Example

[0030] A method for preparing 1,4-diphenylenebis(triphenylphosphonium chloride) fiber thin film material includes the following steps:

[0031] (1) Preparation of Bi[TPP]Cl2: Weigh 3 mmol of 1,4-dichlorobenzyl and 4.5 mmol of triphenylphosphine into a 100 mL ground glass conical flask, add 30 mL of acetone to dissolve, stir and reflux at 65~70℃ for 18 hours, a white precipitate is formed, filter under reduced pressure, wash 3 times with a small amount of acetone, dry under vacuum to obtain a white solid powder as the target product bisquaternary phosphonium salt.

[0032] (2) Preparation of Bi[TPP]Cl2 fiber film material: Weigh 1.0 g of polyacrylonitrile and add it to a solution with a mass ratio of DMSO:DMF of 1:0.8. Stir at 80℃ until completely dissolved to prepare a spinning solution with a concentration of 15wt%. Add 0.2 g of bis-quaternary phosphonium salt to the spinning solution and stir at 60℃ until completely dissolved. After standing to remove bubbles, load the solution into a dry syringe and spin under the following conditions: voltage 15.8 kV, receiving distance 15 cm, and liquid supply rate 0.8 mL·h. -1 The slide speed is 15.0 mm·s -1 The ambient temperature was 32℃ and the relative humidity was 52%, resulting in a white fiber film. Example

[0033] A method for preparing 1,4-diphenylenebis(triphenylphosphonium chloride) fiber thin film material includes the following steps:

[0034] (1) Preparation of Bi[TPP]Cl2: Weigh 3 mmol of 1,4-dichlorobenzyl and 3 mmol of triphenylphosphine into a 100 mL ground glass conical flask, add 30 mL of acetone to dissolve, stir and reflux at 65~70℃ for 24 hours, a white precipitate is formed, filter under reduced pressure, wash 3 times with a small amount of acetone, and dry under vacuum to obtain a white solid powder as the target product, biquaternary phosphonium salt.

[0035] (2) Preparation of Bi[TPP]Cl2 fiber film material: Weigh 2.0 g of polyacrylonitrile and add it to a solution with a mass ratio of DMSO:DMF of 1:1.2. Stir at 80℃ until completely dissolved to prepare a spinning solution with a concentration of 15wt%. Add 0.2 g of bis-quaternary phosphonium salt to the spinning solution and stir at 60℃ until completely dissolved. After standing to remove bubbles, load the solution into a dry syringe and spin under the following conditions: voltage 15.8 kV, receiving distance 15 cm, and liquid supply rate 0.8 mL·h. -1 The slide speed is 15.0 mm·s -1 The ambient temperature was 32℃ and the relative humidity was 52%, resulting in a white fiber film.

[0036] The adsorption performance of the bis-quaternary phosphonium salt thin film material from Example 1 was tested. Specific implementation method: Five 40 mg portions of PAN fiber film and bis-quaternary phosphonium salt fiber film were weighed and added to the solutions with V=20 mL and C=100 mg·L⁻¹, respectively. -1 Dynamic adsorption was simulated by placing the Cr(VI) solution in a shaker at pH 1–5. After 6 h of adsorption, an appropriate amount of Cr(VI) solution was diluted, and 1 mL of colorimetric reagent was added for color development. The absorbance was measured at 540 nm. The adsorption effect is shown in the figure below. Figure 4 The relationship between Cr(VI) concentration and absorbance value was measured using the same method, and its standard curve is shown in [reference needed]. Figure 5 The results showed that PAN fiber films had an effect on 100 mg·L⁻¹ pH at pH 1–5. -1 The adsorption effect of Cr(VI) was the worst, with removal rates all below 6%. Within the pH range of 1–5, the removal rate of Cr(VI) by the bis-quaternary phosphonium salt fiber membrane decreased with increasing pH. At pH 1, the adsorption effect of Cr(VI) was the best, with a removal rate exceeding 70%; at pH 5, the adsorption effect of Cr(VI) was the worst, with a removal rate of around 40%. This indicates that the fiber membrane loaded with bis-quaternary phosphonium salt has a good adsorption effect on Cr(VI). Figure 6 Chromium ion concentration (mg·L) in the adsorption experiment -1 The removal rate R% is calculated by equation (1), the adsorption capacity is calculated by equation (2), and the adsorption capacity is calculated by equation (3), where A is the absorbance value, C0, C t The concentrations before and after adsorption are given by qt, where qt is the equilibrium concentration at C.t Adsorption capacity at time (mg·g) -1 ), m is the amount of adsorbent added, and V is the volume of the Cr(VI) solution.

[0037]

[0038] To investigate the adsorption mechanism of Cr(VI) on the bis-quaternary phosphonium salt thin film, adsorption kinetics and isothermal adsorption curve fitting were performed (Equations 4-7). 500 mg·L⁻¹ -1 A solution of hexavalent chromium (CrVI) was prepared by adding a quaternary phosphonium salt fiber membrane. The adsorption time (5-180 min) was varied to determine the time required for the membrane to reach saturation for Cr(VI) adsorption and the concentration of hexavalent chromium in the supernatant. The adsorption capacity of the quaternary phosphonium salt fiber membrane for hexavalent chromium ions was calculated according to formula (3), and the experimental results were fitted using pseudo-first-order and pseudo-second-order adsorption kinetic models. The results showed that the adsorption of the quaternary phosphonium salt fiber membrane material mainly occurred in the first 30 min. The adsorption capacity of Cr(VI) was high and the adsorption efficiency was fast in the early stage, which was attributed to the high diffusion distance and active site density within the particles. The adsorption rate of Cr(VI) was slow in the later stage and tended to reach equilibrium at 3 h. Within 5-180 min, the adsorption capacity of Cr(VI) increased from 75.4 mg·g⁻¹ to 82.33 mg·g⁻¹. -1 R of the two adsorption kinetic models 2 All values ​​are greater than 0.9, indicating that the adsorption of Cr(VI) by the bis-quaternary phosphonium salt fiber membrane involves both physical and chemical adsorption. (See...) Figure 7 qe and qt (mg·g) -1 The values ​​) represent the adsorption amounts of Cr(VI) at equilibrium and at time t (min), respectively. k1 and k2 represent the rate constants of PFO and PSO, respectively.

[0039]

[0040] Table 1. Relevant parameters of pseudo-first-order and pseudo-second-order dynamic fitting curves

[0041]

[0042] Take 100~500 mg·L -1 A solution of hexavalent chromium (CrVI) was prepared by adding a bis-quaternary phosphonium salt fiber membrane and incubating at room temperature with constant shaking until adsorption equilibrium was reached. The concentration of hexavalent chromium in the supernatant was measured, and the equilibrium adsorption capacity was calculated. The experimental results were fitted using the Langmuir and Freundlich isotherm adsorption models. The results showed that the regression coefficient Ri of the bis-quaternary phosphonium salt fiber membrane for Cr(VI) was consistent with that of the hexavalent chromium (CrVI) in the Langmuir and Freundlich models. 2The R values ​​for the two models are 0.9800 and 0.9961, respectively, and the fitting values ​​are... 2 A value > 0.9 indicates that this type of fiber film exhibits both monolayer and multilayer adsorption. At 28℃, q is obtained using the Langmuir isotherm equation. max The value was 280.45 mg.g -1 ,See Figure 8 The theoretical saturated adsorption capacity of the bis-quaternary phosphonium salt fiber membrane for Cr(VI) is higher than the maximum adsorption capacity measured in actual experiments. Compared with other modified polyacrylonitrile fiber membranes for Cr(VI), the bis-quaternary phosphonium salt fiber membrane exhibits superior adsorption performance for Cr(VI), as shown in Table 3. Furthermore, the n value obtained from fitting the Freundlich equation is between 0 and 1, further verifying that the bis-quaternary phosphonium salt fiber membrane is an excellent adsorbent material. max K represents the maximum adsorption capacity. L K is the Langmuir constant; F This is Freundlich's constant.

[0043] Table 2. Relevant parameters of Freundlich and Langmuir isotherm adsorption curves.

[0044]

[0045] Table 3 Comparison of Cr(VI) adsorption performance of different substances loaded on PAN fibers

[0046]

[0047] Table 4 Comparison of Cr(VI) adsorption performance of different substances loaded on PAN fibers

[0048]

[0049] The infrared spectrum of the detection of bis-quaternary phosphonium salts is shown in Figure 9. The 3007 cm⁻¹ in the infrared spectrum... -1 The peak at 2945 cm⁻¹ is attributed to the stretching vibration of the C–H bond on the benzene ring; -1 2864 cm -1 The peak at 1589 cm⁻¹ is considered to be the C−H stretching vibration of the benzyl CH₂ group; -1 1416 cm -1 The peak at 1111 cm⁻¹ is considered to be the C=C stretching vibration of the benzene ring; -1 The characteristic peak at 856 cm⁻¹ is for C−P bonds; the characteristic peaks for monosubstituted benzene derivatives appear at 856 cm⁻¹. -1 781 cm -1 738 cm -1 Place.

[0050] The infrared spectrum of the bis-quaternary phosphonium salt fiber film is shown in the figure. Figure 10 In PAN films, 2939 cm -1 For sp 3 Hybrid C−C skeleton mode, 2240 cm -1 The vibrational characteristic peak belonging to the −CN functional group is 1734 cm⁻¹. -1 Stretching vibrations attributable to the carbonyl group, 1450 cm⁻¹ -1 It is the C-H deformation vibration in the fiber structure (Sun) et al (2020). After the addition of the bis-quaternary phosphonium salt, characteristic peaks of the quaternary phosphonium salt appeared on the fiber film, indicating that the quaternary phosphonium salt was successfully loaded onto the film. (Figure 3008 cm⁻¹) -1 The peak at 2934 cm⁻¹ is attributed to the stretching vibration of the C–H bond on the benzene ring; -1 2868 cm -1 The peak at 1588 cm⁻¹ is considered to be the C−H stretching vibration of the benzyl CH₂ group; -1 1448 cm -1 The peak at 1110 cm⁻¹ is considered to be the C=C stretching vibration of the benzene ring; -1 The characteristic peak at 855 cm⁻¹ is for C−P bonds; the characteristic peaks of monosubstituted benzene derivatives appear at 855 cm⁻¹. -1 785 cm -1 At the point of observation, PAN fiber film and bisquaternary phosphonium salt fiber film were found that the new peak was assigned to the quaternary phosphonium salt, and no obvious peak shift was observed, indicating that no chemical reaction occurred during electrospinning.

[0051] The thermal stability of the biquaternary phosphonium salt fiber film material was tested, see [reference needed]. Figure 11 10 mg of bis-quaternary phosphonium salt fiber film was weighed and tested under nitrogen protection at a temperature range of 35-900℃. (See attached image.) Figure 6 The process involved two mass losses. In the first stage, decomposition began at 198℃, at which point the material's structure began to break down, resulting in a weight loss of 43%. In the second stage, starting at 299℃, a loss of 31% occurred. This indicates that the bis-quaternary phosphonium salt fiber membrane is stable below 198℃ and can be applied to water treatment.

[0052] The infrared spectrum of the bis-quaternary phosphonium salt fiber film for detecting Cr(VI) adsorption is shown in the figure. Figure 12 It was found that the characteristic peaks of the functional groups changed after the adsorption of Cr(VI). (2246 cm⁻¹) -1 and 1197 cm -1 These are the characteristic peaks of the C≡N triple bond and the −CN bond on the alkyl chain of PAN, respectively. The blue line is at 3028 cm⁻¹. -1 1111 cm -1The wavelengths at which the C−H and C−P stretching vibrations on the benzene ring are located are 804 cm⁻¹. -1 and 648 cm -1 The peaks are characteristic of monosubstituted benzene derivatives, indicating the presence of quaternary phosphonium salts in the film. A new characteristic peak appears on the red line at 942 cm⁻¹. -1 The area at which the chromium absorption band is located indicates the electrostatic interaction between the Cr(VI) anion and the adsorbent during the adsorption process.

[0053] EDS of bisquaternary phosphonium salt fiber membranes adsorbing Cr(VI) is shown in [reference needed]. Figure 13 As can be seen, C, N, P, Cl, and Cr elements are distributed on the material. P, Cl, and Cr elements are distributed in the fiber mesh, and Cr is always found around P. Therefore, its adsorption mechanism is that the bis-quaternary phosphonium salt is released from the fiber film and chemically adsorbed with hexavalent chromium, and then adsorbed onto the fiber film through physical adsorption.

Claims

1. A fiber film material, characterized in that, Made by a method including the following steps: A certain amount of polyacrylonitrile is added to a mixed solution of DMSO and DMF and dissolved at 70-90℃ to obtain a spinning solution; a certain amount of bis-quaternary phosphonium salt is added to the obtained spinning solution and dissolved at 55-65℃. After standing to defoam, electrospinning is performed to obtain a bis-quaternary phosphonium salt fiber film material. The chemical structure of the bis-quaternary phosphonium salt is shown in formula (I): 。 2. The fiber film material according to claim 1, characterized in that: The electrospinning conditions were: voltage 15.8 kV, receiving distance 15 cm, and liquid supply rate 0.8 mL·h. -1 The slide speed is 15.0 mm·s -1 The ambient temperature was 32℃ and the relative humidity was 52.1%.

3. The fiber film material according to claim 1, characterized in that: The mass ratio of DMSO to DMF in the mixed solution is 1:0.8-1.

2.

4. The fiber film material according to claim 1, characterized in that: The mass concentration of the spinning solution is 10-20%; the amount of bis-quaternary phosphonium salt added to the spinning solution is 1-3 wt%.

5. The application of the fiber film material according to claim 1 in the adsorption of heavy metal Cr(VI) in acidic industrial wastewater.

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